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  • 1
    ISSN: 1057-9257
    Keywords: conductive polymers ; polyaniline ; palladium dopants ; platinum dopants ; catalytic hydrogenation ; active centres ; catalyst aging ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The chemical and structural surface-aging effects brought about by the presence of water in emeraldine base (EB) polyaniline (PANI) doped with Pd or Pt protonic acids were studied. IR spectroscopy, XRD, XPS and heterogeneous catalytic hydrogenation (alkyne→alkene→alkane) were applied to characterise the PANI-Pd and PANI-Pt. Interpretation of the results gave the surface characteristics, structure, chemical catalytic activity and stability mainly of PANI-Pd specimens. The unique form of catalytically active centres therein was the surface complex [PdCl4]2- with Pd 3d5/2 BE=337·7 eV. The most promising among the PANI-Pd catalysts studied were those dried in a slow, long procedure (3 months, zeolite 5A). Copyright © 1998 John Wiley & Sons, Ltd.
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  • 2
    ISSN: 1057-9257
    Keywords: remote PECVD ; silane ; nitrogen ; silicon nitride ; argon dilution ; hydrogen content ; stoichiometry ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: In Part I we reported the results of an emission spectroscopic study of the plasma obtained in an SiH4-N2-Ar mixture. It was shown that argon in metastable electronic excited states provides a high concentration of atomic nitrogen. In this part we report the results of a study of the influence of argon dilution on the growth rate, composition and properties of silicon nitride films. The exact influence of nitrogen dilution with argon depends on the process parameters and on the method of coupling of the RF power, but it is found in general that a high concentration of atomic nitrogen leads to changes in the relative amounts of Si-Hj and N-Hi bonds and in the Si/N ratio of deposited films. In particular, it is shown that hydrogen incorporation can be reduced and improved stoichiometry can be obtained. © 1998 John Wiley & Sons, Ltd.
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  • 3
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    Advanced Materials for Optics and Electronics 8 (1998), S. 61-76 
    ISSN: 1057-9257
    Keywords: magnetic molecular materials ; conducting molecular materials ; polyoxometalates ; TTF ; ET ; conducting polymers ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The different approaches used by the authors for the synthesis of new molecular materials exhibiting simultaneously magnetic and conducting properties are presented here. The aim is to prepare materials where a magnetic and a conducting sublattice coexist and/or interact in order to obtain either coexistence of properties or coupling between them. The strategy described is a hybrid one that combines various types of inorganic metal complexes with planar organic π-electron donors of the TTF family or with organic matrices made of conducting polymers. There are four main combinations: (i) magnetic polyoxometalates with organic donors - this strategy has already produced more than 10 radical salts where a magnetic character coexists with a conducting or semiconducting one; (ii) small magnetic anions with organic donors - in this case one of the most promising results has been the synthesis of one of the very few known examples of magnetic molecular metals; (iii) ferro- and ferrimagnetic oxalate-bridged bimetallic layers with organic donors; (iv) magnetic polyoxometalates incorporated into electrodeposited films of conducting polymers. © 1998 John Wiley & Sons, Ltd.
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  • 4
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    Advanced Materials for Optics and Electronics 8 (1998), S. 87-91 
    ISSN: 1057-9257
    Keywords: friction coefficient ; wear coefficient ; tribology ; conducting polymers ; 2,6-naphthalenedisulphonate (2,6-NDS) ; 1,5-naphthalenedisulphonate (1,5-NDS) and 2-naphthalenesulphonate (NS) polypyrroles ; sliding test ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: It is known that, with careful control of conditions, polypyrrole films with counter-ions of toluene sulphonic acid sodium salt and methane phosphonic acid sodium salt can be produced with friction coefficients comparable with or even better than PTFE. Here we now report a systematic study of polypyrrole with various planar anions for tribological bearing applications. Thus naphthalene disulphonate-doped polypyrrole has a kind of laminar structure with very good adhesion to the surface. Polymer films were electrodeposited on glass lenses and tested in a friction apparatus for friction and wear measurements. The film orientation was measured by low-angle X-ray diffraction and the surface structure was evaluated by both AFM and SEM for different film thicknesses. The friction coefficient and wear rate of such bearings were measured under loads up to 5 N and at speeds up to 30 mm s-1 and were found to be 0·06 and 0·04 nm mm-1 respectively. © 1998 John Wiley & Sons, Ltd.
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  • 5
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    Advanced Materials for Optics and Electronics 8 (1998), S. 121-128 
    ISSN: 1057-9257
    Keywords: self-assembly ; charge transfer ; electron-conducting monolayers ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Suitably modified mono- and bimolecular films, including bilayer lipid membranes (BLMs), offer exceptionally good opportunities for probing electric field effects on charge transfer and redox reactions in biosensor and molecular electronics research and development.This work presents the redox reactions of tetracyano-p-quinodimethane (TCNQ) molecules incorporated in a self-assembled octadecanethiol monolayer (SAM) on polycrystalline gold electrodes, depending upon the type of supporting electrolyte cations and their concentration. Our results show that TCNQ-modified Au-SAM electrodes exhibit selectivity versus alkali metal cations in aqueous supporting electrolyte (∽10 kJ mol-1 difference between K+ and Li+ and between Cs+ and K+). The slope of the ‘calibration curves’ for Li+ and K+ is about 59 mV per decade of concentration of the analyte. The explanation of this behaviour is based on the Donnan potential model; however, an ion-pairing effect can also be involved. Our preliminary results show also that the TCNQ molecules within the octadecanethiol monolayer may act as a molecular redox device. © 1998 John Wiley & Sons, Ltd.
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  • 6
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    Advanced Materials for Optics and Electronics 8 (1998), S. 147-155 
    ISSN: 1057-9257
    Keywords: synthesization ; chalcopyrite ; CuGaSE2 single phase ; X-ray diffraction ; stoichiometric deviations ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The dependence of the structural parameters on compositional deviations of CuGaSe2 has been studied. These deviations have been induced along an ingot by a single fusion of the components at 1150 °C and subsequent slow cooling in a stationary ampoule in a vertical furnace. All along the sample a single chalcopyrite phase is present and a compositional gradient along the ingot was found by energy-dispersive analysis of X-rays (EDAX) measurements, the upper part being rich in Ga (series B) and the lower part in Cu (series A), with Cu/Ga ratios of 0·95 and 1·1 respectively. A hypothesis of the existence of two phases in the melt is proposed to explain these facts. The unit cell parameters, anion displacement and Cu and Ga occupation numbers in their sublattices were analysed by X-ray powder diffraction and Rietveld refinement methods. In series A the occupation numbers are near stoichiometry, while in series B a Cu defect appears. In both series, changes in unit cell parameter are related to changes in Cu content, suggesting the presence of a fraction of Cu ions either as interstitials or at Ga sites when Cu is in excess, or of Cu vacancies in its sublattice when there is a Cu deficiency. © 1998 John Wiley & Sons, Ltd.
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  • 7
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    Advanced Materials for Optics and Electronics 8 (1998), S. 195-199 
    ISSN: 1057-9257
    Keywords: chiral waveguides ; preparation of modified ATR method ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Chiral properties of planar waveguide structures with a core layer formed by a poly(methyl methacrylate) (PMMA) host matrix doped with chiral santonin were investigated by means of a modified attenuated total reflection (ATR) method. Distinct modification of the observed ATR spectra was revealed for right and left circularly polarised incident beams. From comparison of the experimental spectra with theoretical curves, the following specific rotation was obtained: [α]20633=11,200 deg cm2 g-1 (santonin/ PMMA mass ratio 2:1). The origin of the observed optical activity and its influence on the waveguide dispersion characteristics are briefly discussed. © 1998 John Wiley & Sons, Ltd.
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  • 8
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    Advanced Materials for Optics and Electronics 8 (1998), S. 213-213 
    ISSN: 1057-9257
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: No abstract
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  • 9
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    Advanced Materials for Optics and Electronics 8 (1998), S. 263-267 
    ISSN: 1057-9257
    Keywords: semiconductors ; low-dimensional systems ; crystal structure ; optical properties ; photoluminescence ; Raman spectra ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The structural, optical and related properties (i.e. photoluminescence and resonance Raman spectra) of some synthetic (i.e. unconventional) low-dimensional semiconductor systems such as K2Cd3S4, [CH3SC(NH2)=NH2]3PbI5 and [H3N(CH2)6NH3]BiI5 are reported. They are compared with the properties of the corresponding higher-dimensionality systems. A blue shift of the excitonic bands and an enhancement of their binding energy and intensity were observed by decreasing the dimensionality or the size of the materials active part. The results are similar to those obtained from conventional semiconductors by decreasing the dimensionality or the size and are attributed to quantum confinement of excitons. © 1998 John Wiley & Sons, Ltd.
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  • 10
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    Advanced Materials for Optics and Electronics 8 (1998), S. 309-316 
    ISSN: 1057-9257
    Keywords: optical gas sensing ; polysiloxane ; azobenzene ; NO2 ; molecular modelling ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Siloxane copolymers having as side-chains azobenzene derivatives bearing different electron-withdrawing and donating substituents were deposited as thin films by dip coating, and their behaviour upon exposure to 100 pm NO2 was studied by UV/visible spectroscopy. Electron-donating substituents at the ortho positions on the aromatic rings in the azo unit have significant influence on the absorbance changes produced by exposure to NO2, and this is explained by modelling, which suggests that interaction between the electrophilic nitrogen atom in NO2 and the electron clouds of the azobenzene skeleton is responsible for the sensing process, rather than the formation of a Wheland intermediate or other product of chemical reaction. Especially effective substituents are methoxy groups in either aromatic ring ortho or the azo linkage, which also produce a significant increase in intensity of the long-wavelength n-π* transition. This moves the optical interrogation signal to a wavelength range of particular benefit for potential applications. Copyright © 1998 John Wiley & Sons, Ltd.
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  • 11
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    Advanced Materials for Optics and Electronics 8 (1998), S. 303-308 
    ISSN: 1057-9257
    Keywords: polyaniline ; emeraldine base ; carbon fluoride ; lithium cells ; aprotic solvent ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Polyaniline (PANI) has been used for modification of the electrochemical behaviour of a carbon fluoride ((CFx)n) cathode in a lithium cell. PANI and (CFx)n powders were carefully mixed and the electrochemical properties and kinetic parameters of the composite (CFx)n-PANI cathode were evaluated by galvanostatic and potentiodynamic techniques. An increase in exchange current has been found for electrodes with addition of polyaniline in the form of emeraldine base (EB). During the reduction process of carbon fluoride using 1 M lithium perchlorate solution in organic solvent, the ternary intercalation compound CLixF is formed and then irreversibly decomposed into carbon and lithium fluoride. The insertion of lithium cations into the (CFx)n layered structure is diffusionally controlled, hence improvement in electronic properties of this fluoride material by the presence of conducting PANI chains and enhancement of discharge performance were found for 25% addition of PANI. Copyright © 1998 John Wiley & Sons, Ltd.
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  • 12
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    Advanced Materials for Optics and Electronics 8 (1998), S. 229-245 
    ISSN: 1057-9257
    Keywords: unimolecular rectifier ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Asymmetries in the macroscopic and the nanoscopic DC electrical conductivity through Langmuir-Blodgett multilayers and monolayers of γ-(n-hexadecyl)quinolinium tricyanoquinodimethanide (HDQ-3CNQ, 1) are due to a transition from the ground-state zwitterion to a probably neutral excited-state conformer, thus confirming without a shadow of a doubt the rectification of electrical current by a single molecule. © 1998 John Wiley & Sons, Ltd.
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  • 13
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    Advanced Materials for Optics and Electronics 8 (1998), S. 285-294 
    ISSN: 1057-9257
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Field effect transistors with an organic material as active layer are at present essentially used to determine the mobilities in these materials. Until now, in analysing the measured current characteristics, only the simplest (Shockley) model has been used which accounts neither for this type of thin film transistor (TFT), which operates in depletion and accumulation, nor for the nature of the carriers. Starting from two-dimensional simulations for the analogous silicon TFT, we have developed an analytical model for the TFT that accounts for several peculiarities of the current characteristics of this type of transistor. In addition, a first modification has been developed which describes the situation when the charged states are polarons and bipolarons, as is the case in organic materials. Applications to published experimental current characteristics show that a general reanalysis is needed. Copyright © 1998 John Wiley & Sons, Ltd.
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  • 14
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    Advanced Materials for Optics and Electronics 8 (1998), S. 31-37 
    ISSN: 1057-9257
    Keywords: self-assembled monomolecular layers ; chemical modification ; ATR/FTIR' electrical conductivity ; fluorescence ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Self-assembled monomolecular layers have been formed on a glass substrate with 3-aminopropyltriethoxysilane. The amino groups were chemically modified with either salicylaldehyde or 4-formylpyridine, then a TCNQ-pyridine CT complex was formed on a limited area of the surface, making a molecular conductive channel. This area is electrically conducting and we have observed it with the aid of SEM and direct measurements. ATR/FTIR and fluorescence spectroscopy were also used to monitor the monomolecular layer formation and modification processes. © 1998 John Wiley & Sons, Ltd.
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  • 15
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    Advanced Materials for Optics and Electronics 8 (1998), S. 53-60 
    ISSN: 1057-9257
    Keywords: organic conductors ; electron correlations ; dielectric-metal transition ; superconductivity ; Fermi surface ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The electronic structure and superconductivity of layered organic materials based on the bis(ethylenedithio)tetrathiafulvalene molecule (BEDT-TTF, hereafter ET) with essential intra-ET correlations of electrons are analysed. Taking into account the Fermi surface topology, the superconducting electronic density of states (DOS) is calculated for a realistic model of κ-ET2X salts. A d-symmetry of the superconducting order parameter is obtained and a relation is found between its nodes on the Fermi surface and the superconducting phase characteristics. The results are in agreement with the measured non-activated temperature dependences of the superconducting specific heat and NMR relaxation rate of central 13C atoms in ET. © 1998 John Wiley & Sons, Ltd.
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  • 16
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    Advanced Materials for Optics and Electronics 8 (1998), S. 81-85 
    ISSN: 1057-9257
    Keywords: conducting polymers ; polypyrrole ; optical absorption ; pressure ; piezochromism ; conformation ; infrared spectra ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: A pressure dependence of the optical absorption spectra of BF-4-doped polypyrrole has been observed at pressures below atmospheric pressure. The two absorption bands at photon energies of 1·2 and 3·0 eV depend on the pressure: a decrease in the high-energy absorption is accompanied by an increase in the low-energy absorption and its shift towards lower energies. The Fourier transformation infrared reflection spectra also depend on the pressure in this region of pressures. The results are interpreted as a pressure-induced conformational transition of the polypyrrole chain. © 1998 John Wiley & Sons, Ltd.
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  • 17
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    Advanced Materials for Optics and Electronics 8 (1998), S. 101-105 
    ISSN: 1057-9257
    Keywords: biosensor ; protein immobilisation ; protein modification ; electrochemistry ; nitrotyrosine ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Use of electrosynthetic methodology allows the production of hen egg-white lysozyme (HEWL) either mononitrated at tyrosine 23 or bisnitrated at tyrosines 20 and 23, but never nitrated at tyrosine 53. This is a different sequence from that obtained by the chemical nitrating agent tetranitromethane, and when reduced by dithionite, the selectively modified enzyme can be anchored at pH 5 via the unique aromatic amino group to magnetic beads or other suitable matrices. HEWL so immobilised loses less than 10% of cell-wall lytic activity compared with the approximately 50% loss of activity when immobilised by conventional methodology at pH 9 via essentially random reaction at lysine residues and other functionalities which are nucleophilic at this pH. This result offers promise as a general method for selective protein immobilisation in biosensors and similar applications. © 1998 John Wiley & Sons, Ltd.
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  • 18
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    Advanced Materials for Optics and Electronics 8 (1998), S. 157-160 
    ISSN: 1057-9257
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 19
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    Advanced Materials for Optics and Electronics 8 (1998), S. 187-193 
    ISSN: 1057-9257
    Keywords: antifouling ; biofouling ; hydrogel ; benzalkonium chloride ; ultraviolet-visible spectroscopy ; underwater optics ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: A hydrogel based on poly(2-hydroxyethyl methacrylate) (PHEMA) containing benzalkonium chloride (BAK) can be used as an environmentally acceptable, fouling-resistant material in the marine environment. The loaded hydrogel system is transparent and has the potential to be used in the protection of optical ports in underwater instruments. Ultraviolet-visible (UV-vis) spectroscopy was used to study the optical properties of the material after a marine exposure period. The optical transmittance of PHEMA/ BAK was higher for 10 weeks than that detected for poly(methyl methacrylate) (PMMA), a material currently used in commercial instruments, which confirmed the superior fouling resistance of the PHEMA/ BAK combination. The UV-vis spectroscopic method was quick, relatively cheap and accurate enough to allow the effects of the development of marine fouling on transparent surfaces for use in marine underwater optical applications to be monitored. © 1998 John Wiley & Sons, Ltd.
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  • 20
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    Advanced Materials for Optics and Electronics 8 (1998), S. 9-12 
    ISSN: 1057-9257
    Keywords: LPE growth ; Ga-Bi solution ; ‘purification effect’ ; photoluminescence ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Thick, intentionally undoped GaAs epitaxial layers grown by LPE from Ga-Bi solution with different contents of Bi in liquid solvent (from 0 to 82 at.%Bi) were studied by photoluminescence (PL) at temperature &helvbi;T&helvbd;=2 K. The dependence of the photoluminescence spectrum on the content of Bi in solution was analysed. © 1998 John Wiley & Sons, Ltd.
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  • 21
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    Advanced Materials for Optics and Electronics 8 (1998), S. 47-52 
    ISSN: 1057-9257
    Keywords: ligand gated ; channel protein ; biomembrane ; biosensor ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: We demonstrate a novel protective configuration for a gated channel biosensor. The bilayer membrane containing the channel proteins is formed by a simple self-assembly technique ensuring continuous coverage of the interface between two slabs of agarose gel by a biomimetic lamella in a fluid state. The gel protects both membrane surfaces from mechanical shock and contact with low-energy media while allowing diffusion of biomolecules up to 10 MDa in weight. The technique has been demonstrated using both dioleoyl-phosphatidylcholine (DOPC) and a phosphatidylcholine lipid cross-linked with a short polysiloxane chain (PSPC). The conductance per unit area of the channel-free membrane produced by this method was less than 25 S m-2 for DOPC and 2 S m-2 for PSPC, and the bilayer nature of the barrier in both cases has been demonstrated by measurement of the capacitance. The applicability to sensors has been confirmed using gramicidin-D, a 1·1 kDa unilamellar lipid bilayer pore former, and partially confirmed using valinomycin, a selective ion transporter. On incorporation of gramicidin the membrane conductance increased by over an order of magnitude. © 1998 John Wiley & Sons, Ltd.
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  • 22
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    Advanced Materials for Optics and Electronics 8 (1998), S. 93-96 
    ISSN: 1057-9257
    Keywords: ithiolene ; tetrathiafulvalene ; molecular conductor ; molecular magnetism ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The salt [TTF]2[Fe(tdas)2] has been prepared by electocrystallisation and its conductivity and magnetic properties are reported. The X-ray structure has been determined. © 1998 John Wiley & Sons, Ltd.
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  • 23
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    Advanced Materials for Optics and Electronics 8 (1998), S. 45-45 
    ISSN: 1057-9257
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: No Abstract
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  • 24
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    Advanced Materials for Optics and Electronics 8 (1998), S. 1-8 
    ISSN: 1057-9257
    Keywords: electrodeposition ; copper-indium-selenide ; thin films ; layer-by-layer deposition ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The electrochemical bath used for growing device-quality CIS (CuInSe2) thin films by co-deposition as well as layer-by-layer (LBL) deposition was characterised and optimised with respect to the film properties. The bath composition was varied by changing the Cu, In and Se ion concentrations in specific ratios in both co-deposition and LBL deposition. The film properties were analysed using techniques such as SEM (scanning electron microscopy), EPMA (electron probe microanalysis), AES (Auger electron spectroscopy) and XRD (X-ray diffraction). The structural, morphological and compositional properties of the films were characterised and their variation is attributed to the bath composition and growth conditions. © 1998 John Wiley & Sons, Ltd.
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  • 25
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    Advanced Materials for Optics and Electronics 8 (1998), S. 13-22 
    ISSN: 1057-9257
    Keywords: remote PECVD ; silane ; nitrogen ; silicon nitride ; argon dilution ; emission spectroscopy ; metastable states ; atomic nitrogen ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: In a series of two papers we describe the effect of argon dilution of the nitrogen passed through the RF discharge region on the plasma composition, growth rate and some characteristics of silicon nitride films deposited by remove PECVD. In this part we report the results of an emission spectroscopic study of the plasma obtained in an SiH4-N2-Ar mixture. It is shown that argon in metastable electronic excited states plays an important role during the RPECVD of silicon nitride films by providing a high concentration of atomic nitrogen which is necessary for the promotion of film growth. In Part II the influence of argon dilution on the growth rate, composition and some properties of silicon nitride films deposited by capacitively and inductively coupled remote PECVD is discussed. © 1998 John Wiley & Sons, Ltd.
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  • 26
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    Advanced Materials for Optics and Electronics 8 (1998), S. 77-80 
    ISSN: 1057-9257
    Keywords: conducting polymers ; polypyrrole ; electrical conductivity ; pressure ; conformation ; glass transition ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: We describe the observation of a pressure-induced variation in the electrical conductivity of BF-4-doped polypyrrole at pressures below atmospheric pressure. We also show that there are anomalies in the temperature dependence of the electrical conductivity in cyclic measurements at temperatures of 240 and 310 K. The pressure effect is interpreted as a pressure-induced order-disorder conformational transition. The anomalies in the temperature dependence are attributed to the glass transition and melting of the polymer. © 1998 John Wiley & Sons, Ltd.
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  • 27
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    Advanced Materials for Optics and Electronics 8 (1998), S. 97-99 
    ISSN: 1057-9257
    Keywords: TCNQ salts ; IR spectra ; melting ; charge transfer, electron-phonon coupling ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The infrared spectra (400-7000 cm-1) of three composites based on salts of tetracyano-p-quinodimethane (TCNQ) and methyl-TCNQ with N-alkyl-isoquinolinium cations are measured as a function of temperature (up to about 450 K). The influence of composite melting on the charge transfer and vibrational bands is studied. It is found that melting causes an irreversible transition into a new phase. © 1998 John Wiley & Sons, Ltd.
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  • 28
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    Advanced Materials for Optics and Electronics 8 (1998), S. 111-119 
    ISSN: 1057-9257
    Keywords: PPV ; conjugated polymers ; quasi-particles ; ab initio calculation ; infrared spectra ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: We investigate the quasi-particle conformational defects (excitons, polarons and bipolarons) in phenylene vinylene oligomers (PVOs) consisting of up to 12 repeat units. The conformations are determined by minimisation of the total Hartree-Fock energy calculated at 3-21G level. The Hartree-Fock calculations of the excited states are followed by the CI-Singles calculation. The bond length alternation along the oligomer chain is discussed. On the basis of these results the vibrational transitions are calculated. To correct the basis set truncation error, the vibrational frequencies are multiplied by a uniform scaling factor. The types of vibrations are assigned. The theoretical spectra are in good agreement with the experimental infrared vibrational spectrum of poly(p-phenylene vinylene) (PPV). © 1998 John Wiley & Sons, Ltd.
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  • 29
    ISSN: 1057-9257
    Keywords: gallium nitride ; nanocrystallites ; detonation ; gallium azide ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: High quality nanoscale, phase-pure hexagonal gallium nitride (GaN) crystallites have been synthesized by the thermal induced detonation of molecular precursors of the type (R3N)Ga(N3)3 (R=CH3, C2H5, etc.). The method allows the control of the particle size regime from 2 to about 1000 nm. X-ray diffraction and Rietveld simulations revealed an anisotropic platelet-like shape of the particles. The obtained GaN material was as well characterized by transmission electron microscopy and electron diffraction, photoluminescence spectroscopy, SEM, IR, RAMAN, thermal gas effusion/mass spectrometry, thermal analysis, elemental analysis. Gas absorption measurements (BET method) showed a specific surface area of about 90 m2 · g-1. © 1998 John Wiley & Sons, Ltd.
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  • 30
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    Advanced Materials for Optics and Electronics 8 (1998), S. 181-186 
    ISSN: 1057-9257
    Keywords: poly(4,7-benzothiophene vinylene) ; polymer interfaces ; conjugated polymers ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: In this paper we determine the LUMO level position of poly(4,7-benzothiophene vinylene) (PBTV), a heterocyclic poly(phenylene vinylene) (PPV) analogue, using tunnelling current measurements. We compare the energy level positions with those measured for PPV and determine their shifts. The experimental results are compared with theoretical predictions and good agreement is observed. © 1998 John Wiley & Sons, Ltd.
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  • 31
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    Advanced Materials for Optics and Electronics 8 (1998), S. 201-209 
    ISSN: 1057-9257
    Keywords: amorphous molecular semiconductors ; electron-hole pairs ; excitons ; photoconductivity ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Processes of charge carrier photogeneration and recombination are investigated in films of poly-N-epoxypropylcarbazole doped with polymethine dye. Films with blocking contacts were illuminated with light from either the region of dye absorption or beyond this region. The kinetics of accumulation and relaxation of electron-hole pairs with lifetimes greater than tens or hundreds of seconds was studied. It is presumed that the reason for the growth of recombination luminescence intensity in an external electric field is connected with the increase in efficiency of radiative recombination stimulated by electrons captured from photogenerated excitons. © 1998 John Wiley & Sons, Ltd.
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  • 32
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    Advanced Materials for Optics and Electronics 8 (1998), S. 247-262 
    ISSN: 1057-9257
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The synthesis of a number of side chain liquid crystalline polymers for quadratic non-linear optical (NLO) applications is reported. The active chromophore is a charge transfer (CT) biphenyl derivative which possesses mesogenic properties itself. The liquid crystalline behaviour of these polymers was established by differential scanning calorimetry (DSC), optical microscopy and X-ray diffraction. The active chromophores were oriented by the standard corona poling technique and the degree of axial ordering was determined as a function of poling conditions by linear optical absorption. Growth of the second-harmonic generation (SHG) signal was used to probe the induction of polar order. These experiments clearly indicated that liquid crystallinity results in an enhancement of the polar order over that of isotropic materials. The second-order NLO susceptibility tensor components d31 and d33 were measured by the SHG technique. The ratio d33/ d31 was found to be much larger than 3, in agreement with molecular statistical models. Values of d33 up to 30-35 pm V-1 were obtained at 1064 nm fundamental wavelength. These values are essentially not resonance-enhanced, since the chromophore absorption occurs below 350 nm. © 1998 John Wiley & Sons, Ltd.
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  • 33
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    Advanced Materials for Optics and Electronics 8 (1998), S. 317-324 
    ISSN: 1057-9257
    Keywords: gas sensing ; nitrogen dioxide ; stilbene ; biphenyl ; UV-visible spectroscopy ; thin films ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Thin films of a selection of stilbene and biphenyl side-chain substituted liquid crystal polymers based on polysiloxanes were deposited using an automated dip-coating technique and exposed to either 100 ppm NO2 gas and/or concentrated nitric acid vapour, the consequent effect being monitored by changes in the UV-visible spectra of the material. No effective response to NO2 was observed from the biphenylene analogue, but the stilbene derivatives showed spectral changes to suggest that an interaction occurs between the vapour and the bridge position of the stilbene side-chain. The stilbenes also show a marked pre-conditioning phenomenon upon exposure to nitric acid vapour prior to exposure to nitrogen dioxide. This procedure gives a material that has a more reversible response on exposure to NO2 gas than an anagolous film that has not been pre-treated. Copyright © 1998 John Wiley & Sons, Ltd.
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  • 34
    ISSN: 1057-9257
    Keywords: As-S wafers ; X-ray exposure ; microstructuring ; bulk optic element ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The possibilities of ‘resistless’ microstructuring of As36·1S63·9 wafers by soft X-ray irradiation and wet alkaline etching have been investigated. Scanning electron microscopy is used to study the influence of the exposure and processing parameters on the depth and acuity of the patterned structures. Structures 1 μm wide are obtained by irradiation with an energy flux of 2000 mJ cm-2, followed by etching in a solution of pH 10·8 at a temperature of 23°C for a processing time of 18 min. It is established that by X-ray irradiation and suitable processing of As36·1S63·9 wafers, microstructures of a depth up to 0·65 μm could be patterned. The structured wafers could be used as diffraction elements for IR optics. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 163-171 
    ISSN: 1057-9257
    Keywords: chemical-based computing ; reaction-diffusion systems ; polymer materials for chemical computing ; Belousov-Zhabotinsky media ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Promising potentialities are opened up by the use of polymer materials for the elaboration of information-processing devices based on reaction-diffusion media. In this work, features of image processing by Belousov-Zhabotinsky media formed on the basis of hydrogel matrices and using catalyst immobilisation on the surface of solid supports have been investigated. Such active media structures have been found to improve significantly the quality of images in the course of their processing by the media. The spatial resolution of the media increases considerably in going from liquid Belousov-Zhabotinsky media and media functioning in polymer matrices to media based on catalyst immobilisation on the surface of solid supports. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 173-180 
    ISSN: 1057-9257
    Keywords: coated hybrid particles ; nanoparticle composites ; surface plasmon resonance ; optical properties ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Semiconductor/metal hybrid nanoparticle composites have been prepared in a glass host by a modified melt/quench process and examined with respect to their optical properties. The coated hybrid nanoparticles exhibit surface plasmon resonance absorption spectra which are red-shifted compared with that of a dispersion of homogeneous Ag nanoparticles in the same host. The position of the plasmon resonance was a sensitive function of the heat treatment schedule. A theoretical model based on effective medium theory for the coated hybrid particles was used to describe the shift of the plasmon position in the optical spectra as a function of the coating thickness. The calculated absorption spectra of the coated hybrid particles agree well with the experimental results. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 215-228 
    ISSN: 1057-9257
    Keywords: fullerene ; fullerides ; charge transfer complexes ; spectroscopy ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Some possible uses of vibrational and electronic spectroscopies in characterising the basic interactions in C60 and C70 complexes are pointed out. We report on the wealth of infrared spectra of (usually) single crystals of C60 and C70 clathrates and complexes with organic donors. The changes in the spectral parameters of the complexes in comparison with those of the neutral fullerene molecules are attributed to redistribution of the charge on the spherical C60 or elongated C70 molecules in their compounds. Some general considerations on the origin of the IR, NIR, VIS and UV spectral variations are also given. © 1998 John Wiley & Sons, Ltd.
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  • 38
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    Advanced Materials for Optics and Electronics 8 (1998), S. 269-276 
    ISSN: 1057-9257
    Keywords: organic charge transfer salts ; conducting polymers ; electronic properties ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: We are exploring the electronic properties of novel materials such as conducting polymer-coated polyester fibres and charge transfer complexes configured in resistive, gated (FET) and diode configurations. In this paper we will consider several areas where we are attempting to make sensors and/ or primitive devices from molecular materials. Our most successful result so far is the temperature-dependent resistivity of polypyrrole-coated polyester fibres. Here we find that the conductivity is thermally activated and produces a reliable, highly sensitive indicator of temperature in a cryogenic environment. Using parallel configurations of fibres, sensors with different limiting resistances can be fabricated. We have also placed insulated electrical gates on single crystals of various metallic and insulating charge transfer salts and have attempted to alter the charge transfer character by the application of high electric fields. With polymethylmethacrylate (PMMA) insulating layers, gate voltages up to 150 V have been acquired with no leakage or heating. Similar measurements on diode devices fabricated from charge transfer complexes with different electronic structures are also in progress, and our preliminary results will be presented. Prospects and plans for developing these materials into viable sensors and devices are discussed. © 1998 John Wiley & Sons, Ltd.
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    Advanced Materials for Optics and Electronics 8 (1998), S. 277-284 
    ISSN: 1057-9257
    Keywords: calix[4]resorcinarenes ; charge transfer (CT) complexes ; tetracyanoquinodimethane (TCNQ) ; tetracyanoethylene (TCNE) ; non-linear optical (NLO) materials ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Lipophilic calix[4]resorcinarenes - condensation products of resorcinol and lauryl aldehyde comprising four resorcinol units - form electron donor-acceptor complexes with electron acceptors tetracyanoquinodimethane (TCNQ) and tetracyanoethylene (TCNE) in organic solvents. Their formation was confirmed by EPR and UV-vis spectroscopy, except for compounds c1 and c3 which did not form charge transfer (CT) complexes with TCNE. Titration experiments involving calixarenes and electron acceptors indicated the presence of species of different stoichiometries. Complexes with ligands c1-c4 were characterised spectroscopically. CT bands appeared in most cases. © 1998 John Wiley & Sons, Ltd.
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  • 40
    ISSN: 0021-9304
    Keywords: implant ; titanium ; osteoblasts ; surface roughness ; 1α,25- (OH)2D3 ; differentiation ; local factor ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Surface roughness has been shown to affect differentiation and local factor production of MG63 osteoblast-like cells. This study examined whether surface roughness alters cellular response to circulating hormones such as 1α,25-(OH)2D3. Unalloyed titanium (Ti) disks were pretreated with HF/HNO3 (PT) and then were machined and acid-etched (MA). Ti disks also were sandblasted (SB), sandblasted and acid etched (CA), or plasma sprayed with Ti particles (PS). The surfaces, from smoothest to roughest, were: PT, MA, CA, SB, and PS. MG63 cells were cultured to confluence on standard tissue culture polystyrene (plastic) or the Ti surfaces and then treated for 24 h with either 10-8M or 10-7M 1α,25-(OH)2D3 or vehicle (control). Cellular response was measured by assaying cell number, cell layer alkaline phosphatase specific-activity, and the production of osteocalcin, latent (L) TGFβ, and PGE2. Alkaline phosphatase activity was affected by surface roughness; as the surface became rougher, the cells showed a significant increase in alkaline phosphatase activity. Addition of 1α,25-(OH)2D3 to the cultures caused a dose-dependent stimulation of alkaline phosphatase activity that was synergistic with the effect caused by surface roughness alone. 1α,25-(OH)2D3 also caused a synergistic increase in osteocalcin production as well as local factor (LTGFβ and PGE2) production on the rougher CA, SB, and PS surfaces, but it had no effect on the production on smooth surfaces. The inhibitory effect of surface roughness on cell number was not affected by 1α,25-(OH)2D3 except on the SB surface. 1α,25-(OH)2D3 decreased cell number, increased alkaline phosphatase activity and osteocalcin production, and had no effect on LTGFβ or PGE2 production by MG63 cells grown on tissue culture polystyrene. These data suggest that bone cell response to systemic hormones is modified by surface roughness and that surface roughness increases the responsiveness of MG63 cells to 1α,25-(OH)2D3. They also suggest that the endocrine system is actively involved in normal bone healing around implants. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 77-85, 1998.
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  • 41
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    Journal of Biomedical Materials Research 39 (1998), S. 102-119 
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: An investigation was performed to study the mechanical performance of fiber-reinforced composite hip prostheses. In Part I of the study, a three-dimensional finite element code was developed for analyzing a composite hip prosthesis in a femur. The material properties of the composite were treated as anisotropic and inhomogeneous while the properties of the femoral bone were treated as anisotropic and homogeneous. All the materials were assumed to behave linear-elastically. Thermoplastic graphite/PEEK material was selected for the study. No slippage was assumed at the interface between the implant and the surrounding femoral bone. In Part II, numerical simulations were performed using the code to study the performance of a composite prosthesis in the femur. The stress/strain distributions, micromotions, and strain energy density of the surrounding femoral bone were evaluated and found to be related to initial fixation and long-term stability of the prosthesis in the femur. Numerous fiber orientations were studied, and the results of the calculations were compared with those generated from a prosthesis made of cobalt chrome and Ti-6Al-4V titanium alloys. Based on the analysis, it was shown that compared to conventional metallic implants more favorable stresses and deformations could be generated in the femur using composite implants. In addition, by changing fiber orientations according to femoral loads, a composite implant could be designed specifically for the left or the right femur. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 102-119, 1998.
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  • 42
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    Journal of Biomedical Materials Research 39 (1998), S. 153-160 
    ISSN: 0021-9304
    Keywords: low-contact stress prosthesis ; polyethylene failure ; total knee arthroplasty ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: From January 1985 to December 1990, 598 consecutive New Jersey low-contact stress (LCS) total knee arthroplasties (TKAs) were performed for gonarthrosis. Among these 598 operations, 322 were with rotating platform elements and 276 were with meniscal bearing elements. During 5 to 8 years of follow-up, eight knees had severe symptomatic polyethylene failure that required revision surgery; all eight cases were meniscal bearing types. The failed polyethylene inserts were retrieved and studied. It was observed that there were four probable failure mechanisms associated with the catastrophic polyethylene wear. First, insufficient thickness of the meniscal bearing was the major reason for wear. Second, the malpositioning of the metal tibial tray in the transverse plane resulted in the breaking of the meniscal bearing. Third, the inability of the patellar to rotate due to tissue ingrowth made the polyethylene break. Last, yellowing of the subsurface of the meniscal bearing was a sign of polyethylene failure. These four possible failure mechanisms are all associated with the design of the meniscal bearing type of LCS knee prostheses. Therefore, it is suggested that the design of the LCS knee prosthesis should be modified. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 153-160, 1998.
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  • 43
    ISSN: 0021-9304
    Keywords: femoral neck ; fracture ; osteosynthesis ; stability ; polylactide ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The initial stability of femoral neck osteosynthesis provided by three self-reinforced poly-L-lactide (SR-PLLA) or three metallic cannulated screws was compared. A standard transverse subcapital osteotomy was created with a hand saw in 19 pairs of human cadaver femora. Two fixation methods were randomly used in each pair. Fixations were exposed to a progressive cyclic loading test to determine the deflection curves, the ultimate load-carrying capacity, and the total amount of load absorbed. One pair served as a pilot and two nonoperated pairs served as controls. The positioning of the three fixation screws, whether one screw proximally and two screws distally or vice versa, provided equal stability. Metallic fixation proved to be more stable than SR-PLLA fixation as the average maximum load-carrying capacity was 3400N for the metallic and 2600N for the SR-PLLA fixation. However, SR-PLLA screws showed sufficient fixation properties for considering clinical trials in Garden I-II femoral neck fractures in well cooperative patients. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 171-175, 1998.
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  • 44
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    Journal of Biomedical Materials Research 39 (1998), S. 200-206 
    ISSN: 0021-9304
    Keywords: cell culture ; flow cytometry ; cytoxicity assay ; scanning electron microscopy ; titanium-tantalum ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: To evaluate the biocompatibility of a new titanium-tantalum alloy, with qualities superior to titanium alone, for use in oral implantology, fibroblast and epithelial cell lines were grown on plastic, titanium, copper, and titanium-tantalum supports. Studies using scanning electron microscopy, flow cytometry, and cytotoxicity assays were conducted to compare the different supports. Scanning electron microscopic observations showed high densities of fibroblasts and epithelial cells with well-developed attachment systems in the form of cytoplasmic projections. Cell densities were lower on titanium and titanium-tantalum surfaces than on plastic. Cell numbers, as determined by cytotoxicity assays, were significantly higher on plastic than on titanium or titanium-tantalum surfaces while fibroblasts proliferated better than epithelial cells on both metal surfaces. Flow cytometric analyses of cell cycles did not reveal any significant variations in the distribution of cells among the cycle phases on the three materials. We found no differences with regard to the parameters studied between titanium and the titanium-tantalum alloy. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 200-206, 1998.
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  • 45
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    Journal of Biomedical Materials Research 39 (1998), S. 215-221 
    ISSN: 0021-9304
    Keywords: bovine pericardium ; collagen fibers ; light scattering ; bioprostheses ; heart valves ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: In Part I of this work we used small-angle light scattering (SALS) to quantify the fiber architecture of 20 bovine pericardial sacs, along with corresponding tissue-thickness measurements, to determine optimal material selection sites. In order to determine the anatomic consistency of these sites, the fiber architecture and thickness data from all 20 sacs were averaged together using a cartographic analysis method that took advantage of the geometry of the prolate spheroid mold used to process the sacs. Optimal selection sites were determined based on a local criteria where all fiber preferred directions within a 2.54-cm circular area were within ±10°. The largest contiguous area (LCA) for the entire BP sac was 20.54 cm,2 located in the vicinity of the left ventricle of the heart. The LCA tissue thicknesses were also relatively uniform, further supporting the use of these areas. However, even within these optimal areas there was a ±20° standard deviation in local fiber preferred directions, resulting in at best a 40° spread in local preferred directions. The observed structural variability may be due to regionally heterogeneous physiologic loadings induced by the ligamentous attachments. These attachments may alter the regional fiber preferred orientation to support local mechanical loadings. Overall, given the inherent structural variability of the BP sac, we conclude that use of anatomic location alone will not consistently guarantee the selection of tissue specimens with a highly homogeneous and predictable fibrous structure. It is thus suggested that a direct fiber measurement presorting method be employed when selecting BP specimens for bioprosthetic applications where tissue structural homogeneity and uniformity is critical. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 215-221, 1998.
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  • 46
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    Journal of Biomedical Materials Research 39 (1998), S. 9-15 
    ISSN: 0021-9304
    Keywords: fiber-optic pH sensor ; pH sensing membrane ; fluorescent probe ; SNAFL ; photo-crosslinking ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: A fiber-optic pH sensor was prepared using the self-referencing fluorescent pH probe carboxy seminaphthofluorescein (SNAFL-2). The ratio of the emission from the base form of this dye and the emission near the isoemissive point is insensitive to variations in the excitation intensity and photobleaching. The carboxy SNAFL-2 and a photoaffinity crosslinker, 4-azido-2,3,5,6-tetrafluorobenzoic acid, succinimidyl ester, were attached onto poly(acrylamide-co-vinylamine) to form a hydrophilic functional membrane for the fiber-optic sensor. Photo crosslinking was used to create a crosslinked pH-sensing membrane and covalently bind the membrane onto the surface of the PMMA optical fiber. The fluorescent properties of the membrane-fiber conjugate have been determined. The membrane is stable, and the pH sensor shows a fast response time and excellent resolution in a wide pH range of 3 to 11. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 9-15, 1998.
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  • 47
    ISSN: 0021-9304
    Keywords: endothelial cells ; mesothelial cells ; cell seeding ; PTFE ; blood flow ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: An investigation was made into the effect of blood flow on endothelial cells (EC) and mesothelial cells (MC) seeded on a vascular expanded polytetrafluoroethylene (ePTFE) prosthesis coated with a fibroblastic matrix. Endothelial cells were obtained from the external jugular vein and MC from the omentum. To test the performance of prostheses, a custom designed, femoral “ex vivo” circuit was developed in mongrel dogs. Four study groups were established: a control group, A1, where prostheses were uncoated and seeded with EC; a second control group, A2, where prostheses were uncoated and seeded with MC; group B1 where prostheses were coated with a fibroblastic matrix and seeded with EC; and group B2 where coated prostheses were seeded with MC. All cells were labeled with 111Indium oxine (10 μCi/mL) before seeding. After the seeded cells had formed a monolayer on the ePTFE prostheses (which took approximately 24 h) the prostheses were placed in the “ex vivo” circuit. The rates of blood flow to which prostheses were exposed were measured at the point of inflow (117.5 ± 12.50 mL/min, mean ± SD) and outflow (72.6 ± 14.3 mL/min). MC showed a greater baseline radionuclide uptake than did EC. The cells of groups B1 and B2 adhered sufficiently to the fibroblastic matrix and covered enough of the prosthetic surface to be positioned in the “ex vivo” circuit (76.90 ± 8.24% surface covered in EC-seeded prostheses and 71.65 ± 6.23% in MC-seeded prostheses). After exposure to blood flow the quantity of radionuclide-labeled cells and the prosthetic surface covered by them were greatly reduced though the fibroblast-coated prostheses showed greater cell retention. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 32-39, 1998.
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  • 48
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    Journal of Biomedical Materials Research 39 (1998), S. 61-70 
    ISSN: 0021-9304
    Keywords: immunoisolation of pancreatic islets by encapsulation ; polyelectrolyte complexation ; control of capsule permeability ; size exclusion chromatography ; protein A sepharose-antibody complex ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Transplantation of immunoisolated islets of Langerhans has been proposed as a promising approach to treating insulin-dependent diabetes mellitus. Recently, a cell delivery system based on a multicomponent microcapsule has been designed for the immunoisolation of insulin-secreting pancreatic islets. The capsule, formed by polyelectrolyte complexation of sodium alginate and cellulose sulfate with poly(methylene-co-guanidine), markedly has improved mechanical strength compared with the widely used alginate/poly(L-lysine) capsules. It also provides a flexibility for readily adjusting membrane thickness and capsule size, and, more important, the membrane permeability can be altered over a wide range of molecular sizes. To rigorously test the capsule diffusion properties, we have improved capsule permeability measurement by using two complementary methods: (1) size exclusion chromatography with dextran standards; and (2) newly developed methodology for assessing permeability to a series of biologically relevant proteins. Viability and function of rat pancreatic islets enclosed in the capsules with different permeability were tested in vitro. The insulin secretion of encapsulated islets was well preserved even though slightly delayed in comparison with a control group of free islets. We believe that the unique features of this encapsulation system together with the precise characterization of its physical parameters will enable us to find the optimal range of capsule permeability for in vitro and in vivo survival and function of encapsulated pancreatic islets. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 61-70, 1998.
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  • 49
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    Journal of Biomedical Materials Research 39 (1998), S. 86-91 
    ISSN: 0021-9304
    Keywords: styrene-butadiene-styrene triblock copolymer ; dimethyl amino ethyl methacrylate ; graft copolymer ; heparin ; biomaterial ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The grafting of dimethyl amino ethyl methacrylate (DMAEMA) onto styrene-butadiene-styrene triblock copolymer (SBS) membrane was subsequently conducted by UV-radiation induced graft copolymerization without degassing to obtain the SBS-g-DMAEMA copolymer membrane. The substituted amino groups on the SBS-g-DMAEMA graft copolymer membrane were quaternized with iodomethane, and then the membrane was treated with heparin to prepare the heparin-containing SBS-g-DMAEMA copolymer membrane (SBS-g-DMAEMA-HEP). The graft copolymer membrane (SBS-g-DMAEMA) and the heparin-containing SBS-g-DMAEMA copolymer membrane (SBS-g-DMAEMA-HEP) were characterized by FTIR spectroscopy. The heparin content was determined by toluidine blue heparin assay. Contact angle, water content, and protein adsorption of fibrinogen and albumin experiments were also performed to evaluate the effect of graft amount and heparin content on the biocompatibility of SBS-g-DMAEMA and SBS-g-DMAEMA-HEP graft copolymer membranes. By using Kaelble's equation, the surface tension of SBS-g-DMAEMA and SBS-g-DMAEMA-HEP were determined. It was found that with increasing grafting amount and the heparin content, the surface tension and water content of SBS-g-DMAEMA membrane increased, whereas the contact angle decreased. The amount of the adsorption of albumin and fibrinogen decreased with increasing graft amount and heparin content. However, there was a minimum for adsorption of proteins in the SBS-g-DMAEMA and SBS-g-DMAEMA-HEP membranes. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 86-91, 1998.
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  • 50
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    Journal of Biomedical Materials Research 39 (1998), S. 120-129 
    ISSN: 0021-9304
    Keywords: polyethylene (UHMWPE) ; implant retrieval ; total hip arthroplasty ; wear ; ultrasound ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: A new, in vitro ultrasound-based method to measure the thickness of acetabular polyethylene components was developed and applied to 26 uncomplicated autopsy-retrieved components and 40 unused components. The average age at total hip arthroplasty was 62 years and the average time in service of the retrieved components was 49 months. The clinical notes indicated that each of the arthroplasties was functioning well at the time of the patients death. Thickness distributions in the retrieved components had two distinct patterns. Eighteen of the retrieved components (69%) had their thinnest areas self-contained and located near the polar point. In the other 8 retrieved components (31%) the areas of minimum thickness were adjacent to the rim. Thickness distribution in the unused cups was predominately concentric with the thinnest area located near the polar point (85% of the cups). Detection limits for dimensional change were established based on the variability found in the unused liners. Fifteen of the 26 retrieved components (58%) had areas of reduced thickness which exceeded the detection limits; the average thickness reduction rate for these components was 0.076 mm per year. The other 11 retrieved components (42%) lacked such areas. The 15 cups with areas of reduced thickness had a longer time in service (63 ± 18 months) than the 11 cups without areas of reduced thickness (32 ± 25 months) (p = 0.003), but no other clinical factor (age, gender, Harris hip score, size and inclination of the cup, type of femoral fixation) was associated with these 15 cups. Cylindrical models to estimate volumetric change tended to underestimate the actual changes, suggesting that the actual particulate burden may be greater than previously appreciated.Finding that the pattern of thickness reduction can vary suggests that distinctive hip loading modes may be present postoperatively in patients with total hip arthroplasty. The wear rates of these components are consistent with wear rates calculated from radiographic data for well-functioning implants and are considerably lower than wear rates calculated for surgically-retrieved implants, indicating that autopsy-derived retrievals may be more representative of the majority of components currently in service than surgically-derived retrievals. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 120-129, 1998.
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  • 51
    ISSN: 0021-9304
    Keywords: fluorapatite ; hydroxyapatite ; implant ; resorption ; stereology ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Resorption (defined as loss of ceramic coating because of cellular activity or dissolution) of ceramic coatings is a matter of concern for the long-term performance of ceramic-coated implants. A new fluorine-containing coating, fluorapatite (FA), has been shown to be more stable than hydroxyapatite (HA) in unloaded models. In a weight-bearing model in trabecular bone, we evaluated loss (defined as reduction of coating irrespective of type of mechanism) of HA and FA coatings during 25 weeks of implantation. Eight mature dogs had HA- or FA-coated implants inserted bilaterally into the weight-bearing region of the medial femoral condyle. Quantified loss of ceramic coating was estimated at the light microscopic level using stereological methods. The experiment showed significant loss of both types of coatings. However, no statistical difference in loss of ceramic coating was found regarding surface area, implant coverage, volume, and thickness (p = 0.77, p = 0.13, p = 0.56, p = 0.23, respectively). Completely resorbed HA coating was replaced by 36 ± 6.0% (range: 26-42) bone in direct contact with the implant surface compared with 29 ± 16.0% (range: 12-59) for FA (p = 0.40), suggesting that the implant was firmly fixed despite loss of the ceramic coating. Transmission electron microscopy in combination with electron energy spectroscopy and electron spectroscopic imaging showed that osteclast-like cells, osteocytes, macrophage-like cells, and fibroblasts had phagocytosed calcium-containing fragments, indicating cell-mediated resorption of the ceramic coating. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 141-152, 1998.
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  • 52
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    Journal of Biomedical Materials Research 39 (1998), S. 40-51 
    ISSN: 0021-9304
    Keywords: polyethylene particles ; macrophages ; phagocytosis ; cytokines ; histology ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: In this study, an in vitro model has been developed to examine the interactions of macrophages with ultrahigh molecular-weight polyethylene (UHMWPE) and high-density polyethylene (HDPE) particles. Polyethylene particles are the major constituent of the material debris formed as a result of orthopedic implant wear. However, the study of polyethylene particle interactions with cells has been limited. UHMWPE (18-20 μm) and HDPE (4-10 μm) were suspended in soluble collagen type I and subsequently solidified on glass coverslips. The particle chemistry was characterized by Fourier transform infra-red spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). Mouse cell line macrophages (IC-21) were established on the collagen-particle substrata and maintained for up to 24 h. The response of the cells to the particles was examined by light and transmission electron microscopy (LM and TEM), as well as by scanning electron microscopy (SEM), and compared to cells on control collagen surfaces without particles. Histological analysis of the samples revealed that the macrophages surrounded larger particles (18-20 μm) and the cells appeared to be attached to the surface of the particles, and the smaller particles (4-10 μm) had been phagocytosed within 2 h. Inflammatory cytokines (TNF-α, IL-1α, IL-1β, and IL-6), lysosomal enzymes (β-galactosidase and hexosaminidase), and prostaglandin E2 were released into the medium, and IL-1α, IL-1β, PGE2, β-galactosidase, and hexosaminidase levels were significantly increased over collagen control values. The results demonstrate active phagochemotaxis by macrophages for wear particulates and validate this model as a means of studying the specific in vitro interactions of polyethylene with cells. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 40-51, 1998.
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  • 53
    ISSN: 0021-9304
    Keywords: PVDF ; differential scanning calorimetry ; X-ray scattering ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The outstanding biocompatibility of the polyvinylidene fluoride (PVDF) monofilament suture together with other desirable characteristics, such as ease of handling and resistance to biodegradation, makes it an attractive alternative monofilament suture material for cardiovascular surgery. However, to achieve a high performance suture, the polymeric raw material must be exposed to different treatments, which lead to different degrees and types of crystallization. Since these crystalline modifications deeply influence the mechanical characteristics and the biostability of the sutures, the authors hereby propose a method of quantifying the different structures of PVDF using wide angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). The commercial devices are achieved by coloring and processing the polymeric raw material. The white and unprocessed 4-0 unswaged suture presents 19% of the α phase, 38% of the β structure, and no γ form. Coloration increases the amount of the β phase by 5-9% at the expense of the α phase. On the other hand, processing the fibers lead to the conversion of some of the amorphous phase to the γ structure, the importance of which is 6-7%. Finally, tensile measurements performed on the different PVDF fibers clearly proves that their mechanical characteristics depend on the presence of these crystalline forms in the polymeric structure of PVDF. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 184-189, 1998.
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  • 54
    ISSN: 0021-9304
    Keywords: occlusive effects ; lactic acid-glycolic acid copolymer membrane ; expanded polytetrafluoroethylene membrane ; environmental scanning electron microscope ; gingival fibroblasts ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The cell occlusive effects on human gingival fibroblasts of degradable lactic acid-glycolic acid copolymer membranes (noncoated membranes) and membranes coated with a sucrose ester of fatty acid (coated membranes) were studied and compared with those of expanded polytetrafluoroethylene (e-PTFE) membranes. The membranes were immersed in a culture medium periodically for 21 days and interposed into a chemotaxis chamber, and the fibroblasts then were cultured in the chamber for another 7 days. The passage rate of cells through the membranes was calculated and the change in surface structure of each membrane after immersion for 28 days was observed by an environmental scanning electron microscope. The passage rate of coated membranes (3.4 ± 2.2%) was significantly lower than that of noncoated (25.7 ± 5.1%) at the 28th day whereas the passage rate of e-PTFE membranes was 0.8-1.5%. Many pores were observed on the noncoated membranes before immersion while the coating material covered most of the pores on the coated membranes. The average pore size of the noncoated membranes was larger than that of the coated membranes at day 28. The structure of the e-PTFE membranes underwent no change. The passage rate of the coated membranes was not different from the e-PTFE membranes, suggesting an effect that might be useful for a guided tissue regeneration procedure. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 554-559, 1998.
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  • 55
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    Journal of Biomedical Materials Research 39 (1998), S. 580-587 
    ISSN: 0021-9304
    Keywords: plasma spraying ; hydroxyapatite ; decomposition ; vaporization ; amorphous ; X-ray diffraction ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Thermally processed hydroxyapatite coatings used on dental implants and hip prostheses for enhanced fixation may typically consist of a number of chemical and structural phases. These phases affect coating performance and tissue attachment. Hydroxyapatite was plasma sprayed to examine the phase evolution during processing. Coatings were examined with X-ray diffraction and elemental analysis. Results indicate that phase transformations are produced by (a) preferential removal of hydroxyl and phosphate leading to a change in melt composition, and (b) the high cooling rate due to the thermal spray process. Hydroxyl group removal promotes the amorphous phase and oxyapatite. Further heating produces a less viscous melt facilitating decomposition of hydroxyapatite to tricalcium and tetracalcium phosphate. Phosphate removal during flight produces a more calcium-rich melt preferring tetracalcium phosphate and calcium oxide formation. A proposed model shows the phase location within the lamellae of these coatings. Coating processes must thus prevent removal of hydroxide and phosphate during processing to maximize the hydroxyapatite content. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 580-587, 1998.
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  • 56
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    Journal of Biomedical Materials Research 39 (1998), S. 244-251 
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Glass-reinforced HA composites were produced using phosphate-based glasses, and a structure refinement was carried out to determine the effect of the glass on the structure of the residual HA. Quantitative phase analysis showed that the glass causes some of the HA to decompose to β-TCP and, at higher temperatures, to α-TCP. It also was indicated that when three phases were present, the formation of the α-TCP arose from decomposition of the β-TCP and not from further decomposition of HA to α-TCP. The unit cell dimensions showed a decrease in the a axis and an increase in the c axis, giving an overall unit cell decrease in volume. There also was a significant effect based on the amount of glass added. The changes found in the composite containing the 4 wt % glass were attributed to the loss of carbonate and loss of hydroxyl. This was expected to cause shrinkage in the unit cell; however this was not seen, and therefore the major changes in the unit cell were attributed to the ions from the glass taking an interstitial role in the HA structure, thus not allowing the unit cell to shrink as much as expected. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 244-251, 1998.
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  • 57
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    Journal of Biomedical Materials Research 39 (1998), S. 266-276 
    ISSN: 0021-9304
    Keywords: polyethylene glycol ; diacrylate ; peptide ; photopolymerization ; RGD ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Photopolymerized crosslinked networks of poly(ethylene glycol; PEG) diacrylate (MW 8000) were derivitized throughout their bulk with Arg-Gly-Asp (RGD)-containing peptide sequences. Incorporation was achieved by functionalizing the amine terminus of the peptide with an acrylate moiety, thereby enabling the adhesion peptide to copolymerize rapidly with the PEG diacrylate upon photoinitiation. PEG diacrylate hydrogels derivitized with RGD peptide at surface concentrations ranging from 0.001 to 1 pmol/cm were studied in vitro for their ability to promote spreading of human foreskin fibroblasts over 24 h. Hydrogels not derivitized with peptides were poor substrates for adhesion, permitting spreading of only 5% of the seeded cells. When immobilized with no spacer arm, both RGD and RDG (inactive control) supported spreading of ∼50% and ∼15% of cells at 1 and 0.1 pmol/cm2 surface concentrations, respectively; lower concentrations did not promote spreading. When a MW 3400 PEG spacer arm was incorporated between the hydrogel and the peptide linkage, incorporation of 1 pmol/cm RGD promoted 70% spreading whereas RDG at the same concentration did not promote spreading. In addition, when cells were seeded in serum-free medium, only RGD peptides incorporated with a spacer arm were able to promote spreading. Thus peptide incorporated into PEG 8000 diacrylate hydrogels without a spacer arm nonspecifically mediated cell spreading whereas incorporation via a MW 3400 PEG spacer arm was required to permit cell spreading to be specifically mediated. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 266-276, 1998.
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  • 58
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    Journal of Biomedical Materials Research 40 (1998), S. 12-23 
    ISSN: 0021-9304
    Keywords: resin composite ; silane treatment ; mechanical properties ; water sorption ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: A series of microfilled resin composites were formulated by incrementally mixing either agglomerated 20 nm or unagglomerated 50 nm silica microfillers into monomers composed of diphenyloxymethacrylate and TEGDMA. The microfiller particles were prepared with and without a γ-methacryloxypropyl-trimethoxy silane coupling agent. Following polymerization, five material properties were tested: uniaxial tensile strength, Young's modulus in slow compression, Knoop hardness, water sorption, and toothbrush abrasion resistance. Results from these tests indicated that microfiller content clearly was the most influential parameter affecting material property performance. Composites containing 20 nm particles demonstrated greater water sorption, higher Knoop hardness, and better resistance to toothbrush wear. Surprisingly, the application of silane to microfiller surfaces did not greatly improve composite performance for most of the material properties tested in this study. However, water sorption behavior over a 3-year period was observed to be more stable for materials possessing silane-treated particles. Future evaluation of coupling agents should include long-term water storage prior to conducting mechanical tests. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40,12-23, 1998.
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  • 59
    ISSN: 0021-9304
    Keywords: red cell substitute ; microcirculation ; hemoglobin ; liposome ; polyethyleneglycol ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Phospholipid vesicles encapsulating purified hemoglobin [Hb vesicles (HbV); diameter 259 ± 82 mm; oxygen affinity 31 mm Hg; [Hb] 5 and 10 g/dL] were developed to provide oxygen-carrying capacity to plasma expanders. Their function as a blood replacement was tested in the subcutaneous microvasculature of awake hamsters during severe hemodilution in which 80% of the red blood cell mass was substituted with suspensions of the vesicles in 5% human serum albumin (HSA) solution. Vesicles were tested with membranes that were unmodified (HbV/HSA) or conjugated with polyethyleneglycol (PEG) on the vesicular surface (PEG-HbV/HSA). The viscosity of 10 g/dL HbV/HSA was 8 cP at 358 s-1 owing to the intervesicular aggregation, while that of 10 g/dL PEG-HbV/HSA was 3.5 cP, since PEG chains inhibit aggregation. Both materials yielded normal mean arterial pressure, heart rate, and blood gas parameters at all levels of exchange, which could not be achieved with HSA alone. Subcutaneous microvascular studies showed that PEG-HbV/HSA significantly improved microhemodynamic conditions (flow rate, functional capillary density, vessel diameter, and oxygen tension) relative to unmodified HbV/HSA. Even though the enhancement of PEG modification did not achieve the functional characteristics of the blood-perfused microcirculation, PEG reduced vesicular aggregation and viscosity, improving microvascular perfusion relative to the unmodified type. These results highlight the significance of microvascular analysis in the design of red cell substitutes and the necessity of surface modification of HbV to prevent aggregation. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 66-78, 1998.
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  • 60
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    Journal of Biomedical Materials Research 40 (1998), S. 104-114 
    ISSN: 0021-9304
    Keywords: HA ; particles ; dissolution ; macrophage ; osteolysis ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: It is controversial as to whether debris from hydroxyapatite (HA)-coated implants jeopardizes the long-term success of total joint replacements. It has been hypothesized that liberated HA particles are engulfed by macrophages and through normal cellular digestion prevent osteolysis and third-body wear. HA particulates, however, have been observed at the interface and on polyethylene articulating surfaces. There is limited data demonstrating the ability of HA to dissolve at the acidity levels associated with macrophage organelle digestion. The objective of this study was to determine if particulate HA could dissolve at the pH levels found in macrophage organelles. Characterized HA particles were placed into buffered solutions corresponding to phagosomal organelle pH levels: cytoplasmic (pH 7), phagosomal (pH 6), and lysosomal (pH 5). Flasks were under continuous agitation in a shaker chamber at 37°C. Calcium and phosphate ions were measured beyond the maximum life span of an activated macrophage. The data showed that calcium ions rose within the first 24 h and then remained constant throughout the experiment for all pH groups. Phosphate ion concentration showed a similar pattern at the lysosomal pH but remained undetected at the other organelle pH levels. The saturation point was highest at the lysosomal pH level and lowest at the cytoplasmic pH level. The results of this experiment leave the potential for HA particles to dissolve following macrophage digestion. However, caution must be exercised when interpreting the macrophage organelle digestion hypothesis; the size of the HA particle, the length of time required to completely dissolve the particle, and potential cellular toxicity all are factors that have yet to be determined before this hypothesis can be validated. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 104-114, 1998.
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  • 61
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    Journal of Biomedical Materials Research 40 (1998), S. 145-152 
    ISSN: 0021-9304
    Keywords: bioactive bone cement ; Bis-GMA resin ; AW glass-ceramic ; mechanical properties ; bioactivity ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: We examined the influence of the proportion of glass-ceramic powder in a bioactive bone cement of our formula on the bone-bonding ability of cement. Changes in cement bonding with time also were examined. The bioactive bone cement consisted of MgO-CaO-SiO2-P2O5-CaF2 glass-ceramic powder (AW-GC powder) and bisphenol-α-glycidyl methacrylate (Bis-GMA)-based resin. AW-GC powder was added to the cement as 0%, 30%, 50%, 70%, and 80% w/w. Rectangular plates (2 × 10 × 15 mm) of each cement with polished surfaces were implanted into the proximal metaphysis of the tibiae of male rabbits, and the failure load was measured by detaching tests 10 and 25 weeks after implantation. The failure loads of each cement were 0% = 0.03, 30% = 1.52, 50% = 2.67, 70% = 3.56, and 80% = 5.59 kg at 10 weeks, and 0% = 0.05, 30% = 1.68, 50% = 2.77, 70% = 3.80, and 80% = 6.37 kg at 25 weeks. Observation of the cement-bone interface revealed that all bioactive bone cements (30%-80%) formed direct contact with bone whereas intervening fibrous tissue was observed in all specimens of the 0% group. By scanning electron microscopy, all bioactive bone cements (30%-80% groups) showed direct contact with bone at the cement-bone interface. In the 0% group, direct contact with bone at the cement-bone interface was not observed. By electron-probe microanalysis, a Ca-P-rich layer was not detected at the cement-bone interfaces of the 30%-70% bioactive bone cements, but in some samples of the 80% cement specimens a thin Ca-P-rich layer (3 μm thick) was observed at the interface at 10 and 25 weeks after implantation. These results show that all of the bioactive bone cements tested had the ability to bond to bone and to function as bioactive composites of ceramics and polymers. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 145-152, 1998.
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  • 62
    ISSN: 0021-9304
    Keywords: basophils ; mast cells ; metal ions ; toxic histamine release ; apoptosis ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Recent data suggest that distinct metal ions can be released from dental alloys or other biomaterials, and may cause toxic effects on various cells. In this study, the effects of 14 metal ions on histamine release from human blood basophils (n = 4), isolated tissue mast cells (lung n = 8, uterus n = 2, skin n = 1, gingiva n = 1), the basophil cell line KU-812, and the mast cell line HMC-1 were analyzed. Of the 14 metal ions, Ag+ (0.33 mM) and Hg2+ (0.33 mM) were found to induce release of histamine in blood basophils, KU-812, mast cells, and HMC-1. The effects of Ag+ and Hg2+ were dose dependent and were observed within 60 min of incubation. In primary mast cells and basophils, Au3+ (0.33 mM) also induced histamine release, whereas no effects of Au3+ on HMC-1 or KU-812 cells were seen. The other metal ions showed no effects on primary or immortal cells within 60 min. However, Pt4+ (0.33 mM) induced histamine liberation in HMC-1 and lung mast cells after 12 h. The Ag+- and Hg2+-induced rapid release of histamine from HMC-1 was associated with ultrastructural signs of necrosis, but not apoptosis. In contrast, prolonged exposure to Pt4+ (0.33 mM, 14 h) induced apoptotic cell death in HMC-1 cells, as assessed by electron microscopy and DNA analysis. Together, certain metal ions induce distinct cytopathogenic effects in mast cells and basophils. Whereas Ag+, Hg2+, and Au3+ cause direct toxicity, Pt4+ causes cell death through induction of apoptosis. Whether such effects contribute to local adverse reactions to metal-containing biomaterials in vivo remains to be determined. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 560-567, 1998.
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  • 63
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    Journal of Biomedical Materials Research 39 (1998), S. 588-593 
    ISSN: 0021-9304
    Keywords: polyepsiloncaprolactone nanocapsules ; indium oxine ; in vitro release kinetics ; esterases ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The main purpose of this study was to determine the influence of factors (pH, enzymes, etc.) chosen partially to mimic in vivo conditions on the release of a model drug, indium oxine, from polyepsiloncaprolactone (PCL) nanocapsules in vitro. A nanocapsule suspension, an emulsion (O/W), and a solution in olive oil were prepared in order to compare the release of a radioactive tracer, indium oxine, as a function of time by an in vitro dialysis method. Nanocapsules were prepared by interfacial deposition of PCL and characterized by particle size distribution (laser light scattering) and determination of the polymer molecular weight by gel permeation chromatography (GPC). The results of this study suggest that the partition coefficient between the acceptor medium and the olive oil is the major parameter governing the release of the isotope, at least in the absence of significant enzyme activity. The PCL wall of nanocapsules is a barrier that does not seem to retard the release of indium. The addition of porcine liver esterases accelerated the degradation of PCL. This study confirms that the release of a drug from nanocapsules may be very different depending on the in vivo location, that is, the administration site. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 588-593, 1998.
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  • 64
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    Journal of Biomedical Materials Research 39 (1998), S. 611-620 
    ISSN: 0021-9304
    Keywords: transmission electron microscopy ; high voltage electron microscopy ; osteogenesis ; bone remodeling ; bone-implant interface ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: This report presents transmission electron and high voltage transmission electron microscopic observations of bone and associated remodeling tissues directly interfacing with endosteal dental implants. Undecalcified interfacial tissues were serially sectioned from mandibular samples encasing 60 implants placed into 30 dogs. Two-dimensional ultrastructural analyses and three-dimensional stereology showed that osteogenesis adjacent to dental implants is a dynamic interaction of osseous cells and a collagenous fiber matrix. This study showed that the interfacial bone consists of a mineralized collagen fiber matrix associated with an inorganic (hydroxylapatite) matrix. This study suggested that an unmineralized collagen fiber matrix initially is laid down directly at the implant surface, and that this matrix then is mineralized. Osteoblasts interacted with this matrix, eventually becoming encased within developing lacunae during the remodeling process. This process formed the cellular (osteocyte) aspects of the developed bone. Osteocyte processes extended through canaliculi directly to the implant surface. Apparently, these processes also were entrapped within canaliculi during the mineralization events. At times, these processes paralleled the implant surface. The bone-implant interfacial zone was primarily fibrillar (both mineralized and unmineralized) in morphology, with an electron-dense, ruthenium positive deposition. This electron-dense material was approximately 20 to 50 nanometers in thickness, and only this thin layer separated the remodeled mineralized bone from the implant. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 611-620, 1998.
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  • 65
    ISSN: 0021-9304
    Keywords: ureteral stent ; encrustation ; hydrogel ; Aquavene® ; silicone ; polyurethane ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The effective long-term use of indwelling ureteral stents is often hindered by the formation of encrusting deposits which may cause obstruction and blockage of the stent. Development of improved ureteral stent biomaterials capable of preventing or reducing encrustation is therefore particularly desirable. In this study, the suitability as a ureteral stent biomaterial of Aquavene®, a novel poly(ethylene oxide)/polyurethane composite hydrogel was compared with that of silicone and polyurethane, two materials widely employed in ureteral stent manufacture. Examination of Aquavene® in dry and hydrated states by confocal laser scanning microscopy, scanning electron microscopy, and atomic force microscopy showed the presence of numerous channels within a cellular matrix structure. The channel size increased considerably to as much as 10 μm in diameter in the hydrated state. Aquavene® provided superior resistance to encrustation and intraluminal blockage over a 24-week period in a simulated urine flow model. Unobstructed urine flow continued with Aquavene® at 24 weeks, whereas silicone and polyurethane stents became blocked with encrustation at 8 and 10 weeks, respectively. Weight loss within Aquavene® on the order of 9% (w/w) over the 24-week flow period indicates that extraction of the noncrosslinked poly(ethylene oxide) hydrogel may be responsible for the prevention of encrustation blockage of this biomaterial. In the dry state, Aquavene® was significantly harder than either silicone or polyurethane, as shown by Young's modulus, and rapidly became soft on hydration. These additional properties of Aquavene® would facilitate ease of stent insertion in the dry state past obstructions in the ureter and provide improved patient comfort on subsequent biomaterial hydration in situ. Aquavene® is a promising candidate for use in the urinary tract, as it is probable that effective long-term urine drainage would be maintained in vivo. Further evaluation of this novel biomaterial is therefore warranted. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 642-649, 1998.
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  • 66
    ISSN: 0021-9304
    Keywords: surface characteristics ; titanium implants ; osseointegration ; bone response ; loaded implants ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Many dental clinical implant studies have focused on the success of endosseous implants with a variety of surface characteristics. Most of the surface alterations have been aimed at achieving greater bone-to-implant contact as determined histometrically at the light microscopic level. A previous investigation in non-oral bone under short-term healing periods (3 and 6 weeks) indicated that a sandblasted and acid-etched titanium (SLA) implant had a greater bone-to-implant contact than did a comparably-shaped implant with a titanium plasma-sprayed (TPS) surface. In this canine mandible study, nonsubmerged implants with a SLA surface were compared to TPS-coated implants under loaded and nonloaded conditions for up to 15 months. Six foxhound dogs had 69 implants placed in an alternating pattern with six implants placed bilaterally in each dog. Gold crowns that mimicked the natural occlusion were fabricated for four dogs. Histometric analysis of bone contact with the implants was made for two dogs after 3 months of healing (unloaded group), 6 months of healing (3 months loaded), and after 15 months of healing (12 months loaded). The SLA implants had a significantly higher (p 〈 0.001) percentage of bone-to-implant contact than did the TPS implants after 3 months of healing (72.33 ± 7.16 versus 52.15 ± 9.19; mean ± SD). After 3 months of loading (6 months of healing) no significant difference was found between the SLA and TPS surfaced implants (68.21 ± 10.44 and 78.18 ± 6.81, respectively). After 12 months of loading (15 months of healing) the SLA implants had a significantly greater percentage (p 〈 0.001) of bone-to-implant contact than did the TPS implants (71.68 ± 6.64 and 58.88 ± 4.62, respectively). No qualitative differences in bone tissue were observed between the two groups of implants nor was there any difference between the implants at the clinical level. These results are consistent with earlier studies on SLA implants and suggest that this surface promotes greater osseous contact at earlier time points compared to TPS-coated implants. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 1-11, 1998.
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  • 67
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    Journal of Biomedical Materials Research 40 (1998), S. 48-56 
    ISSN: 0021-9304
    Keywords: bioactive glass ; hydroxyapatite ; cell adhesion ; fibronectin ; protein conformation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Bioactive glasses and ceramics enhance bone formation and bond directly to bone, and have emerged as promising substrates for bone tissue engineering applications. Bone bioactivity involves physicochemical surface reactions and cellular events, including cell attachment to adsorbed extracellular matrix proteins. The effects of fibronectin (Fn) adsorption and glass surface reaction stage on the attachment of osteoblast-like cells (ROS 17/2.8) to bioactive glass were analyzed. Bioactive glass disks were pretreated in a simulated physiologic solution to produce three reaction layers: unreacted glass (BG0), amorphous calcium phosphate (BG1d), and carbonated hydroxyapatite (BG7d). Synthetic hydroxyapatite (sHA) and nonreactive borosilicate glass (CG) were used as controls. A spinning disk device which applied a linear range of forces to attached cells while maintaining uniform chemical conditions at the interface was used to quantify cell adhesion. The number of adherent cells decreased in a sigmoidal fashion with applied force, and the resulting detachment profile provided measurements of adhesion strength. For the same amount of adsorbed Fn, cell adhesion was higher on surface-reacted bioactive glasses (BG1d and BG7d) than on BG0, CG, and sHA. For all substrates, cell attachment was primarily mediated by the RGD binding site of Fn, as demonstrated by blocking experiments with antibodies and RGD peptides. Cell adhesion strength increased linearly with adsorbed Fn surface density. Analysis of this fundamental relationship revealed that improved adhesion to reacted bioactive glasses resulted from enhanced cell receptor-Fn interactions, suggesting substrate-dependent conformational changes in the adsorbed Fn. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 48-56, 1998.
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  • 68
    ISSN: 0021-9304
    Keywords: X-ray diffraction ; ceramic ; external fixation ; coating ; biocompatibility ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The in vivo compatibility and degradation aspects of an innovative coating to be sprayed onto titanium implants were investigated. The surface of fluorinated apatite (fHA), consisting of fluorhydroxyapatite plasma sprayed in a vacuum atmosphere, was treated with carbonate to improve its biological compatibility. fHA coating was compared with titanium implants coated (a) with hydroxyapatite (HA) by the traditional plasma spraying, and (b) with titanium oxide (TiOx). Screw-shaped implants were inserted in the cortical bone of sheep tibiae. X-ray diffraction (XRD) analysis of bone tissue and coatings was carried out at 2, 4, 12 and 36 weeks after surgery. The crystallographic habit of the implant-facing bone, as well as the structural stability of the coating, were evaluated. For each time period and type of ceramic bone apatite lattice at the interface, no significantly different reference apatite lattice and no foreign peak were recorded. Two weeks after implantation, the bone at the interface was strongly unmineralized in all samples; after 4 weeks, poorly mineralized bone microareas decreased. At 12 weeks, the newly formed bone tissue at the interface with both the new coating and HA coating was shown to be fully mineralized; this crystallographic habit was retained at 36 weeks, when particle release from the tested material was lower compared to the controls. The XRD pattern of bone apatite surrounding the coating particles was unmodified. The innovative coating did not alter the mineralization process at the interface. It improved implant osteointegration, mainly due to a limited release of particles. Consequently, clinical performance of external fixation treatment could be improved by modifying the chemical composition of the implant surface. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 86-91, 1998.
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  • 69
    ISSN: 0021-9304
    Keywords: methylmethacrylate ; polymethylmethacrylate ; free radicals ; polymerization ; redox polymerization ; bone cements ; in vitro study ; osteoblasts ; cytotoxicity ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Polymerization of orthopedic cements makes use of a peroxide initiator which is decomposed by an accelerator to provide free radicals. Free radicals which act on the monomer molecules are also known to induce cell lesions and cell death. We used an in vitro model of cement polymerization to study the effects of free radicals release on osteoblast-like cells. Initiation of methylmethacrylate was done with benzoyl peroxide and acceleration by N,N-dimethylaniline. Bulk polymerization was done in calibrated test tubes which were left aging until use. Polymers (aged from J1 to J31 days after completion of the polymerization process) were sawed to produce slices. Slices were rinsed in distilled water and free radical release was measured by spectrophotometric titration with p-iodonitrotetrazolium. Saos-2 osteoblast-like cells were cultured in parallel on the slices. Cells appeared to be round and were altered when grown on slices prepared freshly after polymerization. Cytomorphometric analysis of the cell shape surface area and form-factor polyethylene confirmed that they spread and flatten on slices prepared a long time after polymerization. Free radical release from polymethylmethacrylate cements is a long-lasting event that can induce bone cells alterations in their neighborhood. Two cytotoxic mechanisms were evidenced: (a) polymer slices released a stable toxic component which could be removed by extensive washing; (b) they released free radicals which were still detectable several days after the end of polymerization. The titration curve was a negative exponential. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 124-131, 1998.
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  • 70
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    Journal of Biomedical Materials Research 40 (1998), S. 164-169 
    ISSN: 0021-9304
    Keywords: gingiva ; collagen ; polysaccharides ; heparin ; dextran ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Gingival fibroblasts are particularly involved in the physiologic maintenance and repair of periodontium. During these processes, cell proliferation and synthesis of a collagen-rich gingival matrix should be controlled. A dextran derivative, namely, carboxy methyl dextran benzylamide sulfonate (CMDBS), considered to be a functional analog of heparin, was previously described to regulate proliferation of different types of cells and independently to modulate the expression of collagen biosynthesis. In this report, we demonstrate that CMDBS and heparin inhibited gingival fibroblast proliferation. We then analyzed collagen biosynthesis by measuring the incorporation of the radiolabeled [3H]proline precursor into collagen by postconfluent gingival fibroblasts. Our results showed CMDBS did not alter total collagen synthesis; it induced the preferential accumulation of newly synthesized collagen into the pericellular matrix; and it decreased the expression of type III collagen, particularly in the cell layer. Taken together, our results suggest that by inhibiting cell proliferation, CMDBS could induce the synthesis of an extracellular collagenous matrix which forms a network between gingival fibroblasts. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 164-169, 1998.
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  • 71
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    Journal of Biomedical Materials Research 40 (1998), S. 195-203 
    ISSN: 0021-9304
    Keywords: polyurethane ; phosphorylcholine ; protein adsorption ; phospholipid adsorption ; ellipsometry ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: In a previous report we demonstrated that the blood compatibility of poly(ether urethane) (PEU) was improved by grafting phosphorylcholine (PC) groups on the surface. The improved blood compatibility was indicated by decreased platelet adsorption/activation and reduced thrombin formation at the polymer surface in experiments in which the surfaces were contacted with platelet-rich plasma in vitro. In the present study, we investigated the effect of grafted PC groups at a PEU surface on protein and phospholipid adsorption. Adsorption of human fibrinogen (Fg), human serum albumin (Alb), human high-molecular-weight kininogen (HMWK), and dioleoyl phosphatidylcholine (DOPC) vesicles was measured by ellipsometry. For this purpose, thin PEU films were cast on silicon wafers. The polymer film was photochemically modified with a PC-containing aryl azide. The presence of PC groups on the polymer surface was demonstrated by ESCA (Electron Spectroscopy for Chemical Analysis). The hydrophilicity of the polymer surface increased by the surface modification, as indicated by a decrease of the contact angle from 59° before to 43° after modification. Our data show that the presence of PC groups has little effect on the adsorption of proteins to a PEU surface. The highest adsorption was observed for Fg (0.49 μg/cm2 on PC-modified PEU and 0.50 μg/cm2 on PEU), followed by HMWK (0.28 μg/cm2 on both PC-modified PEU and PEU), and Alb (0.16 μg/cm2 on PC-modified PEU and 0.18 μg/cm2 on PEU). Protein adsorption was further studied on a “biomembrane-like” DOPC bilayer formed on hydrophilic silicon. We found no protein adsorption on this DOPC bilayer. The adsorption of small unilamellar DOPC vesicles on the polymer surfaces amounted to about 0.06 μg/cm2 (corresponding to circa 30% of monolayer coverage) and was similar for PC-modified PEU and PEU. Despite this partial surface coverage, preadsorbed DOPC on the polymer surface diminished the subsequent adsorption of proteins considerably. These results show that the mere presence of phosphorylcholine groups on a PEU surface is insufficient to suppress protein adsorption. The highly ordered structure of natural phospholipid bilayers seems to be required to suppress protein adsorption effectively. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 195-203, 1998
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  • 72
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    Journal of Biomedical Materials Research 40 (1998), S. 115-123 
    ISSN: 0021-9304
    Keywords: entrapment ; islet ; reversible gel ; disulfide bond ; bioartificial pancreas ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Currently, there are three types of devices for a bioartificial pancreas; microencapsulation, an extravascular diffusion chamber, and an intravascular diffusion chamber. The purpose of the present study was to provide a new extracellular matrix hydrogel for the devices of extra- and intravascular diffusion chamber types. As the sol-gel transition of this hydrogel is reversible, refilling of islets in vivo will be possible without a severe traumatic procedure. The hydrogel was produced from a polyacrylamide derivative carrying thiol groups synthesized by radical copolymerization of acrylamide and N,N′-bis-acrylcystamine, followed by reduction of the disulfide bonds in the copolymer. This water-soluble copolymer was used to entrap hamster islets by re-formation of disulfide bonds on the copolymer to produce a hydrogel. The formed hydrogel was easily reliquefied by reduction of the disulfide crosslinks to thiols. Insulin release from the islet-entrapped hydrogel continued for more than 1 month when examined in vitro. A static glucose stimulation test for the entrapped islets exhibited an increased insulin release. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 115-123, 1998.
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  • 73
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    Journal of Biomedical Materials Research 40 (1998), S. 180-186 
    ISSN: 0021-9304
    Keywords: chargeable functional groups ; gradient surfaces ; corona discharge ; surface grafting ; platelet adhesion ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Functional group gradients were prepared on low-density polyethylene (PE) sheets. The surface density of grafted functional groups was gradually changed along the sample length by way of corona discharge treatment with gradually increasing power following graft copolymerization of acrylic acid (AA), sodium p-styrene sulfonate (NaSS), or N,N-dimethyl aminopropyl acrylamide (DMAPAA). AA and NaSS are negatively chargeable and DMAPAA is positively chargeable in phosphate-buffered saline or plasma solution at pH 7.3-7.4. The prepared functional group gradient surfaces were characterized by measurement of the water contact angle, by electron spectroscopy for chemical analysis, and by Fourier transform infrared spectroscopy in the attenuated total reflectance mode. All these measurements indicated that the functional groups were grafted onto the PE surfaces with gradually increasing density. The platelets adhered to the functional group gradient surfaces along the sample length were counted and observed by scanning electron microscopy. It was observed that the platelet adhesion to the gradient surfaces decreased gradually with the increasing surface density of functional groups. This may be related to the hydrophilicity of the surfaces. The DMAPAA-grafted surface showed a large amount of platelet adhesion, probably due to its positive charge character, while the AA-grafted surface, which is charged negatively, showed poor platelet adhesion. However, the NaSS-grafted surface, which is also charged negatively, showed a relatively large amount of platelet adhesion. This may be associated with the existence of an aromatic ring close to the ionizable group in NaSS. It seems that surface functional groups and their charge character, as well as wettability, play important roles for platelet adhesion. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 180-186, 1998
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  • 74
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    Journal of Biomedical Materials Research 40 (1998), S. 204-213 
    ISSN: 0021-9304
    Keywords: growth hormone delivery ; bioactivity ; poly(∊-caprolactone); solvent casting; particulate leaching ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: We have characterized the biodegradable material poly(∊-caprolactone) (PCL) as a delivery system for recombinant human growth hormone (hGH). Two contrasting methods for the manufacture of the biomaterial were investigated: namely, solvent casting and solvent casting particulate leaching; the latter yielded porous PCL discs. The degree of porosity, which was assessed by scanning electron microscopy, could be controlled by incorporating selected concentrations of particulate sodium chloride during the manufacturing process. Bioactive hGH released from the PCL preparations was quantified with a highly sensitive and precise bioassay which was based upon hGH activation of rat lymphoma Nb2 cells. Eluates obtained from control discs of PCL which had not been loaded with hGH proved to be nontoxic when tested on these cells. The release of bioactive hGH from hormone-loaded nonporous discs of PCL was found to be a direct function of the initial hormone loading dose. Increased porosity of the discs manufactured by solvent casting particulate leaching increased the delivery of hGH from discs which had been immersion loaded. However, hGH release after surface loading was independent of porosity. Hormone concentrations were also assessed by immunoassay so that the ratios of bio- to immunoactivity (B:I ratio) of the hormone release could be determined. We found that the B:I ratio of the hormone after release from unstored discs was identical to that of the hormone prior to its incorporation into the PCL, demonstrating that the mild incorporation procedures utilized had not adversely affected the structural integrity of the hormone. However, if the hormone-loaded discs were stored at 37°C prior to elution, the B:I ratios of the hGH released decreased indicating that this compromised the bioactive site. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 204-213, 1998
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  • 75
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    Journal of Biomedical Materials Research 40 (1998), S. 314-323 
    ISSN: 0021-9304
    Keywords: polyethylene oxide (PEO) ; sulfonated PEO ; surface modification ; segmented polyurethane ; platelet adhesion ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Polyethylene oxide (PEO) surfaces were prepared by the addition of PEO- and sulfonated PEO-containing amphiphilic block copolymers as surface-modifying additives in a segmented polyurethane (PU). PEO-PPO-PEO triblock copolymers (Pluronics) with different PEO chain lengths (from 2 to 80) were used as additives. The prepared film surfaces were characterized by the measurement of dynamic water contact angles and electron spectroscopy for chemical analysis. It was observed that the PU films containing 10 wt % of PEO additives were surface-saturated with the additives regardless of their PEO chain length, but the PEO chains were more projected from the film surfaces containing the additives with longer PEO chains. The water absorption of the films increased largely with the increasing PEO chain length of the additives. The addition of PEO additives produced film surfaces that were in a gel-like state. The films demonstrated some extraction of the PEO additives. However, the additives with higher molecular weights were entrapped more stably into the PU matrix. The mechanical properties (tensile strength and elongation) of the films were changed by the addition of PEO additives, but the differences were not significant compared to the control PU. The platelet adhesion on the film surfaces decreased with increasing PEO chain length of the additives. The film surface containing additives with long PEO chains (chain length of 80) was particularly effective in preventing platelet adhesion. The effect of negatively charged sulfonate groups on the prevention of platelet adhesion appeared only on the film surfaces containing additives with short PEO chains. For longer PEO chains, the chain mobility effect was more dominant than the negative charge effect on the prevention of platelet adhesion. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 314-323, 1998.
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    Journal of Biomedical Materials Research 40 (1998), S. 358-364 
    ISSN: 0021-9304
    Keywords: hydroxyapatite ; hydroxyl groups ; hexamethylene diisocyanate ; isocyanatoethyl methacrylate ; coupling agents ; surface modification ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The surface grafting reactions of a series of isocyanates with hydroxyapatite particles at different temperatures were studied by Infrared spectrophotometry (IR) and thermal gravimetric analysis (TGA). The study results show that both hexamethylene diisocyanate (HMDI) and isocyanatoethyl methacrylate (ICEM) react readily with HA while ethyl isocyanate acetate (EIA) and butyl isocyanate (BIC) have lower reactivity towards HA particles. It also has been found that the reaction of ICEM with HA follows a second-order reaction mechanism, despite the heterogeneous nature of the reaction, while the reaction of HMDI with HA does not due to the complexity of the reaction. Based on this study, it is concluded that ICEM and HMDI are suitable agents for the coupling of polymers due to their reactivity towards HA. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 358-364, 1998.
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  • 77
    ISSN: 0021-9304
    Keywords: UHMWPE ; plasma sterilization ; gamma sterilization ; structure ; fatigue ; wear ; gas sterilization ; low temperature sterilization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The effects of gamma radiation and low temperature hydrogen peroxide gas plasma (HPGP) sterilization on structure and cyclic mechanical properties were examined for orthopedic grade ultra-high-molecular-weight polyethylene (UHMWPE) and compared to each other as well as to no sterilization (control). Density was monitored with a density gradient column and was found to be directly influenced by the sterilization method employed: Gamma radiation led to an increase, while plasma did not. Oxidation of the polymer was studied by observing changes in the carbonyl peak with Fourier transform infrared spectrometry and was found to be strongly affected by both gamma radiation and subsequent aging, while plasma sterilization had little effect. Gamma radiation resulted in embrittlement of the polymer and a decreased resistance to fatigue crack propagation. This mechanical degradation was a direct consequence of postradiation oxidation and molecular evolution of the polymer and was not observed in the plasma-sterilized polymer. Both gamma radiation and plasma sterilization led to improved wear performance of the UHMWPE compared to the nonsterile control material. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 378-384, 1998.
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  • 78
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    Journal of Biomedical Materials Research 40 (1998), S. 414-418 
    ISSN: 0021-9304
    Keywords: lubrication ; cartilage ; lubricin ; wear ; hyaluronate ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Purified human umbilical hyaluronate and a commercial preparation of rooster comb hyaluronate (Healon®) intended for intra-articular viscosupplementation did not demonstrate the same degree of boundary-lubricating ability as bovine synovial fluid or its purified lubricating mucin, lubricin (p 〈 0.01). Boundary lubrication was measured in vitro in an arthrotripsometer oscillating natural latex against polished glass under a load of 0.35 MPa with an entraining velocity of 0.37 mm/s. The two hyaluronate solutions possessed the same hyaluronate concentration as synovial fluid, but Healon was 4.5 times more viscous. Present practice of viscosupplementation therapy for degenerative joint disease is limited and fails to implicate the important role of synovial mucin. Boundary lubrication provided by synovial mucin, independent of its viscosity, is not replicated by hyaluronate hydrogels. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 414-418, 1998.
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    Journal of Biomedical Materials Research 40 (1998), S. 434-441 
    ISSN: 0021-9304
    Keywords: collagen ; bioprostheses ; glutaraldehyde ; calcification inhibitors ; serum conditioning ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The purpose of this study was to evaluate the effects of the calcification inhibitors FeCl3 and sodium dodecyl sulfate (SDS) on the morphology of glutaraldehyde-crosslinked type I collagen sponges and on their serum conditioning. Scanning electron microscopy (SEM) showed that the morphology of the sponges, already modified by glutaraldehyde crosslinking, underwent further changes after treatment of the hydrogels with inhibitors. Coral-like structures were found to branch from the bulk of the material especially in the case of SDS-treated samples. The composition and morphology of the conditioning layers was characterized after 48 h incubation in serum by SDS-polyacrylamide gel electrophoresis-immunoblot of the adsorbed proteins, by energy-dispersive X-ray analysis of the elements (EDX), and by SEM of the conditioned surfaces. All the samples showed the adsorption of proteins with molecular weights ranging from 10 to 203 kD. However, the peculiar adsorption of an approximately 10-kD band (complement C3 fragment) and of fibronectin were detected in the case of glutaraldehyde-crosslinked collagen. On the other hand, glutaraldehyde-crosslinked collagen treated with 0.1M FeCl3 showed the remarkable adsorption of a 29-kD band. The glutaraldehyde-crosslinked hydrogels showed the massive precipitation of crystals on their exposed surfaces, whereas a disordered network structure surrounding the collagen fibrils was found in the case of the samples pretreated with inhibitors. A predominant precipitation of sodium and chloride was detected in all the sponges, although the ratio between the peaks changed from from one hydrogel to another. The results reported in this article clearly indicate that the treatments with SDS and FeCl3 change the surface conditioning of collagen sponges, suggesting a possible role of deposited serum solutes in affecting mineralization processes on bioprosthesis. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 434-441, 1998.
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    Journal of Biomedical Materials Research 40 (1998), S. 464-474 
    ISSN: 0021-9304
    Keywords: calcium phosphate coatings ; magnetron sputtering ; osteoblast ; in vitro ; bone ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: In previous studies we developed a RF magnetron sputter technique for the production of thin Ca-P coatings. With this technique coatings can be produced that vary in Ca/P ratio as well as in structural appearance. The aim of this investigation was to obtain more understanding of the biological behavior of these coatings by way of in vitro experiments. The effect of noncoated titanium (Ti) and three different Ca-P-sputtered surfaces on the proliferation and differentiation (morphology and matrix production) of osteoblast-like cells was studied. Proliferation was determined using counting procedures; morphology was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Fluorescent markers and energy-dispersive X-ray microanalysis (EDX) were used to obtain quantitative and compositional information about the resultant calcified extracellular matrix (ECM). Results demonstrated that proliferation of the osteoblast-like cells was significantly (p 〈 0.05) higher on noncoated than on Ca-P-coated samples. On the other hand, more mineralized ECM was formed on the coated surfaces. In addition, TEM confirmed that the cells on the coated substrates were surrounded by ECM with collagen fibers embedded in crystallized, needle-shaped structures. On the basis of these findings, we concluded that: (1) the investigated Ca-P sputter coatings possess the capacity to activate the differentiation and expression of osteogenic cells, and (2) bone formation proceeds faster on Ca-P surfaces than on Ti substrates. Further, this bone-inductive effect appeared to be dependent on the Ca-P ratio of the deposited coatings. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 464-474, 1998.
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    Journal of Biomedical Materials Research 40 (1998), S. 475-489 
    ISSN: 0021-9304
    Keywords: human femur ; chimpanzee femur ; greyhound femur ; femur morphology ; total hip replacement ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The canine model remains an animal of choice for determining the efficacy and safety of various materials and designs used in human total hip replacement (THR). The primate also is used in orthopedic-related research for studying limb anatomy, gait, and age-related bone loss. In order to better understand the appropriateness of these animal models for human THR, external morphologies of thirty-three adult Caucasian human, sixteen adult chimpanzee, and forty-two adult greyhound femora were compared using osteometric methods. Measured parameters included anteversion angle, cervico-diaphyseal angle, femoral head offset in the frontal plane, and anterior bow profiles along the femoral diaphysis. Although some of the measured parameters were approximately similar between species (e.g., mean cervico-diaphyseal angle of humans and chimpanzees), the majority demonstrated morphologic differences that may be biomechanically significant for interpreting stress transfer across the hip (e.g., mean anteversion angle and mean normalized femoral head offset between species). Additionally, age-related changes in proximal femoral morphology and gait pattern, as well as species-related differences in local muscle and inertial forces, may result in notably different loading conditions across the hip joint of each species. Therefore, discretion must be exercised when evaluating canine or primate THR materials and designs for potential use in the human hip. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 475-489, 1998.
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  • 82
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    Journal of Biomedical Materials Research 40 (1998), S. 520-529 
    ISSN: 0021-9304
    Keywords: 3D carbon/carbon composite ; collagen/apatite composite ; coating ; grafting ; phosphorylation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: A three-dimensional carbon/carbon composite (3D C/C) was studied as potential bone-repairing material; its major mechanical properties were found to be closer to those of human bone than other common bone-repairing materials available. In vitro calcification tests revealed that as-received 3D C/C is almost bioinert in simulated body fluid (SBF) over an immersion period of 4 weeks. To improve the bioactivity of 3D C/C, surface modification was accomplished through two practical routes: (1) grafting with polyethylene glycol (PEG) and (2) phosphorylation and precalcification. After grafting with α, ω di(aminopropyl) polyethylene glycol 800 (NH2-PEG-NH2), a continuous layer of calcium phosphate was formed on the surface of 3D C/C in SBF after 4 weeks. Phosphorylated 3D C/C samples have the ability to induce apatite precipitation after precalcification in a saturated Ca(OH)2 solution for 1 week. To speed up the coating process, a calcification solution with collagen was developed in which a collagen/apatite coating layer can be formed on 3D C/C in 9 h in ambient conditions. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 520-529, 1998.
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  • 83
    ISSN: 0021-9304
    Keywords: biphasic calcium phosphate ceramic ; monocyte ; lipopolysaccharides ; polymyxin B ; cell degradation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Numerous cell types, such as monocytes and osteoclasts, are involved in calcified matrix degradation. In this context, calcium-phosphate ceramics present similar degradation processes in vivo and in vitro to those found in a natural calcified substrate. As the monocyte/macrophage lineage is among the first cells to appear in ceramic implantation sites, it is a key protagonist in inflammatory reaction and biodegradation mechanisms. This study investigated the ability of human monocytes/macrophages activated by various agents [lipopolysaccharides (LPS), polymyxin B (PMB)] to degrade biphasic calcium-phosphate ceramics. PMB sulfate is a bacteriostatic antibiotic that modulates LPS-induced cell activities in vivo and in vitro. Degradation pits (about 10 μm) produced on the pellet surface by these monocytes were discrete, with well defined margins. LPS increased the degradation of calcium-phosphate ceramic (number of lacunae, mean pellet surface area degraded) in a dose-dependent manner whereas polymyxin B downmodulated it significantly. The addition of 2 μg/mL of polymyxin B reduced the number of degradation lacunae and the extent of degraded surface area induced by 0.1 μg/mL LPS by 87% and 64%, respectively. Thus this cell culture system can be very useful in the study of cellular degradation of biomaterials and of the influence of therapeutic agents that may modulate these cell activities. © 1998 John Wiley & Sons, Inc. J. Biomed Mater Res, 40, 336-340, 1998
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  • 84
    ISSN: 0021-9304
    Keywords: bone morphogenetic protein-2 ; hydroxyapatite ; osseointegration ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: To determine if recombinant human bone morphogenetic protein-2 (rhBMP-2) can be adsorbed onto porous ceramic hydroxyapatite (HA) and promote the integration of HA to host bone, 54 subperiosteal pockets were created on the skulls of 19 adult Pasteurella-free white rabbits. Fourteen HA implants were saturated with saline and placed in subperiosteal pockets (control), 22 HA implants were saturated with saline and placed into subperiosteal pockets after burring 1-2 mm of calvarium to expose bleeding cancellous bone, and 18 HA implants were saturated with rhBMP-2 and placed into subperiosteal pockets. The animals were sacrificed at 1 month with examination to determine implant mobility. Histology was used to determine the amount of bone growth into the implant. Of the 14 control sites, 10 implants were found to be freely mobile, five demonstrated host bone resorption, and only one exhibited bone growth into the implant. Of the 22 burred sites, eight were freely mobile and 10 demonstrated bone growth into the implant (p = 0.04). Of the 18 rhBMP-2 sites, only two were freely mobile, none demonstrated host bone resorption, and 16 exhibited bone growth into the implant (p = 0.00002). This study supports the use of porous ceramic HA as a biocompatible, osteoconductive implant material for use in craniomaxillofacial augmentation and reconstruction. It also provides evidence that rhBMP-2 enhances osseointegration, thereby fixing the implant in position against the host-bone interface. In the clinical setting, osseous fixation of the implant should aid in preventing displacement, minimizing host bone resorption, and decreasing the incidence of extrusion. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 359-363, 1998.
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  • 85
    ISSN: 0021-9304
    Keywords: cartilage ; growth factors ; tissue engineering ; osteogenic protein-1 ; cartilage repair ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The objective of this study was to examine in vitro the influence of recombinant human osteogenic protein-1 [rhOP-1, or bone morphogenetic protein-7 (BMP-7)] on cartilage formation by human and goat perichondrium tissue containing progenitor cells with chondrogenic potential. Fragments of outer ear perichondrium tissue were embedded in clotting autologous blood to which rhOP-1 had been added or not added (controls), and the resulting explant was cultured for 3 weeks without further addition of rhOP-1. Cartilage formation was monitored biochemically by measuring [35S]-sulphate incorporation into proteoglycans and histologically by monitoring the presence of metachromatic matrix with cells in nests. The presence of rhOP-1 in the explant at the beginning of culture stimulated [35S]-sulphate incorporation into proteoglycans in a dose-dependent manner after 3 weeks of culture. Maximal stimulation was reached at 40 μg/mL (human explants: +148%; goat explants: +116%). Histology revealed that explants treated with 20-200 μg/mL of rhOP-1, but not untreated control explants, contained areas of metachromatic-staining matrix with chondrocytes in cell nests. It was concluded that rhOP-1 stimulates differentiation of cartilage from perichondrium tissue. The direct actions of rhOP-1 on perichondrium cells in the stimulation of chondrocytic differentiation and production of cartilage matrix in vitro provides a cellular mechanism for the induction of cartilage formation by rhOP-1 in vivo. Thus rhOP-1 may promote early steps in the cascade of events leading to cartilage formation and could prove to be an interesting factor in the regeneration of cartilage in articular cartilage defects. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 614-620, 1998.
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  • 86
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    Journal of Biomedical Materials Research 40 (1998), S. 646-659 
    ISSN: 0021-9304
    Keywords: titanium ; surface treatment ; surface roughness ; surface composition ; surface energy ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Surgical implant finishing and sterilization procedures were investigated to determine surface characteristics of unalloyed titanium (Ti). All specimens initially were cleaned with phosphoric acid and divided into five groups for comparisons of different surface treatments (C = cleaned as above, no further treatment; CP = C and passivated in nitric acid; CPS = CP and dry-heat sterilized; CPSS = CPS and resterilized; CS = C and dry-heat sterilized). Auger (AES), X-ray photoelectron (XPS), and Raman spectroscopic methods were used to examine surface compositions. The surface oxides formed by all treatments primarily were TiO2, with some Ti2O3 and possibly TiO. Significant concentrations of carbonaceous substances also were observed. The cleaning procedure alone resulted in residual phosphorus, primarily as phosphate groups along with some hydrogen phosphates. A higher percentage of physisorbed water appeared to be associated with the phosphorus. Passivation (with HNO3) alone removed phosphorus from the surface; specimens sterilized without prior passivation showed the thickest oxide and phosphorus profiles, suggesting that passivation alters the oxide characteristics either directly by altering the oxide structure or indirectly by removing moieties that alter the oxide. Raman spectroscopy showed no crystalline order in the oxide. Carbon, oxygen, phosphorus, and nitrogen presence were found to correlate with previously determined surface energy. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 646-659, 1998.
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  • 87
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    Journal of Biomedical Materials Research 41 (1998), S. 30-40 
    ISSN: 0021-9304
    Keywords: laminin-5 ; titanium alloy ; passivation ; epithelial cells ; attachment ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Enhancement of epithelial cell attachment to laminin-5-coated titanium alloy (Ti-6Al-4V) implant material was evaluated in vitro. Protein analysis showed that Ti-6Al-4V has a high affinity for laminin-5 and adsorbed significantly more laminin-5 than laminin-1. DNA analysis showed that laminin-5 enhanced attachment of normal human epidermal keratinocytes (NHEK) to Ti-6Al-4V significantly more than did laminin-1 or uncoated controls. The effect of passivation on laminin-5 adsorption and activity on Ti-6Al-4V also was evaluated. Passivation had no significant effect on the amount of protein adsorbed; however, AFM, ESCA, and ToF-SIMS analyses suggested that passivation affects the conformation of adsorbed laminin-5. Although laminin-5 coating significantly enhanced rapid attachment of epithelial cells to both passivated and unpassivated Ti-6Al-4V, surface area measurements showed that cells spread on laminin-5-coated passivated Ti-6Al-4V covered a significantly larger surface area than cells spread on laminin-5-coated unpassivated samples. TEM analysis showed that cells formed significantly more hemidesmosomes on the surface of laminin-5 coated passivated than on the surface of laminin-5 coated unpassivated titanium alloy. The enhancement of rapid cell attachment, spreading, and hemidesmosome assembly on laminin-5-coated passivated samples may reflect better integration between epithelial cells and titanium alloy and thus may be predictive of long-term implant stability. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 30-40, 1998.
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  • 88
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    Journal of Biomedical Materials Research 41 (1998), S. 49-57 
    ISSN: 0021-9304
    Keywords: dextran derivatives ; CMDBS ; thrombin ; heparin cofactor II ; anticoagulant ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Carboxymethyl dextran benzylamide sulfonate/sulfates (CMDBS) are synthetic polysaccharides with anticoagulant activity. We synthesized eight different highly substituted CMDBS and one CMDSu. We studied both their anticoagulant activity and the catalysis of thrombin (T) inhibition by heparin cofactor II (HCII) and antithrombin (AT) in the presence of these dextran derivatives relative to heparin and dextran sulfate (DXSu). The anticoagulant activity of CMDBS was due both to direct thrombin inhibition and to catalysis of thrombin inhibition by HCII. The anticoagulant and catalytic activities of CMDBS were related mainly to their molecular weight and sulfate content. The interaction of the dextran derivatives with thrombin does not involve the active site of the enzyme. A kinetic study showed that all the CMDBS exhibited higher affinity for thrombin than heparin did but lower affinity than DXSu did, suggesting that the benzylamide and sulfate groups potentiate the interaction between the dextran derivatives and thrombin. This study shows that the mechanism by which the dextran derivatives inhibit thrombin is original and is related to preferential interaction with thrombin; this both inhibits the clotting activity of the enzyme and increases the reaction rate of thrombin inhibition by HCII. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 49-57, 1998.
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  • 89
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    Journal of Biomedical Materials Research 41 (1998), S. 95-103 
    ISSN: 0021-9304
    Keywords: ToF SIMS ; XPS ; radiolabeling ; polystyrene and tissue culture polystyrene ; fibronectin ; protein adsorption, orientation, and conformation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Protein adsorption is widely studied by a variety of techniques, but there still is little known about protein orientation and conformation after adsorption. This probably is due to the large number of parameters involved, such as the characteristics of the surface and the structure of the protein. In this study, the adsorption of fibronectin was investigated with three different techniques: radiolabeling, X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (ToF SIMS) on polystyrene and oxidized polystyrene. The first two techniques have been widely used to study protein adsorption, allowing us to determine the amount of protein adsorbed on each surface. The ToF SIMS, however, is a technique just emerging for the study of protein adsorption. This study confirms its utility since ToF SIMS is found to be sensitive to the protein orientation and/or conformation at the surface. Indeed, the ToF SIMS peaks characteristic of the protein show differences in their reduced intensity between the two substrates. These differences, which are not detected by XPS, are attributed to different orientations and/or conformations of the protein. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 95-103, 1998.
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  • 90
    ISSN: 0021-9304
    Keywords: polypyrrole ; polyester ; conductivity ; in vitro ; cell culture ; cell activation ; interleukin expression ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Electrically conducting polypyrrole-treated films have recently been shown to influence the morphology and function of mammalian cells in vitro. This type of polymer represents a possible alternative biomaterial for use in vascular implantation. The present study compared the in vitro biocompatibility of five different polyester woven fabrics having increasing levels of electrical conductivity ranging from 4.5 × 104 to 123 Ω/square with that of low density polyethylene and polydimethylsiloxane primary reference materials. Biocompatibility was measured in terms of four different types of in vitro cellular response, including (a) an indirect and (b) a direct control organotypic culture assay using endothelial cells, (c) a polymorphonuclear (PMN) cell activation study using flow-cytometric measurements of CD11/CD18 integrin molecule expression, and (d) a semiquantification of interleukin (IL)-6 mRNA expression on monocytes/macrophages using reverse-transcriptase polymerase chain reaction. The organotypic culture study revealed that the fabrics with high levels of conductivity exhibited lower cell migration, proliferation, and viability. The PMN activation study of blood from 10 healthy adult donors demonstrated that the two most conductive fabrics were able to identify the more reactive donors. The levels of IL-6 mRNA expression by monocytes/macrophages decreased as the conductivity level of the fabrics increased. The results of the present study therefore indicate that high levels of conductivity (〈200 Ω/square) on polyester fabrics are detrimental to the growth, migration, and viability of endothelial cells; induce elevated PMN activation; and affect the intracellular metabolism of monocytes. They also point to a specific range of conductivity (103 〈 104 Ω/square) which is associated with an optimum in vitro cellular response. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 519-526, 1998.
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  • 91
    ISSN: 0021-9304
    Keywords: transforming growth factor-beta1 (TGF-β1) ; wax-like polymer ; biodegradation ; biocompatibility ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The study reported describes an experimental biodegradable polymer ceramic composite with wax-like handling properties that was combined with 2.0 μg of recombinant human transforming growth factor beta (rhTGF-β1). The polymer/rhTGF-β1 combination was introduced into standard-sized calvarial defects in rabbits to evaluate biodegradability, biocompatibility, hemostasis control, and bone promotion. The experimental wound model was a standard-sized circular calvarial defect 8 mm in diameter. The experimental design included 24 skeletally mature New Zealand white rabbits divided evenly between two time periods (6 and 12 weeks) and among three experimental treatments (untreated defects and defects treated with polymer with or without rhTGF-β1). Evaluations consisted of clinical examinations, standardized radiography, radiomorphometry, as well as histology and histomorphometry. Data were analyzed by an Analysis of Variance (ANOVA) and Fisher's Protected Least Significant Difference test at each time period (level of significance p≤ 0.05). Radiomorphometry data indicated that standard-sized defects treated with the wax-like polymer alone and the polymer plus 2.0 μg of TGF-β1 were significantly more radiopaque than control sites at both 6 and 12 weeks. Histomorphometric data revealed the amount of new bone was significantly greater at 6 weeks in the polymer plus 2.0 μg of TGF-β1 and in the control group than in the polymer alone. Moreover, at 12 weeks, there was significantly more new bone in the control than in either the polymer alone or the polymer plus 2.0 μg of TGF-β1. We speculate the incomplete biodegradation of the polymer ceramic composite contributed to the radiopacity and may have retarded osseous regeneration. It is important that the bone wax-like polymer material was biocompatible and acted as a hemostatic agent. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 584-592, 1998.
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  • 92
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    Journal of Biomedical Materials Research 41 (1998), S. 624-632 
    ISSN: 0021-9304
    Keywords: calcium phosphate coatings ; interface strength ; RF magnetron sputter deposition ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: In previous studies, an RF magnetron sputter technique was developed for the production of thin calcium phosphate coatings. Several deposition parameters were found to influence the growth rate and the stoichiometry of the coatings. For instance, deposition with additional oxygen pressure decreased the Ca to P ratio of the coatings to 1.67. For application of these coatings on actual Ti implants, it is important to know their adhesive tensile strength with the implant surface and how it varies with the deposition parameters. Motivated by these goals, the aim of this study was to measure the adhesive tensile strength of these coatings with Ti substrates and to study its variation with the deposition parameters. Since most mechanical characterization methods are incapable of providing a direct measure of the interface's fundamental strength, a novel laser spallation experiment was used to accomplish this task. In this experiment, a compressive stress pulse is generated on the back side of a substrate by impinging a 3-ns long Nd:YAG laser pulse. The stress pulse propagates through the substrate and is reflected into a tensile stress wave from the free surface of the coating deposited on its front surface. The returning tensile pulse pries off the coating if its amplitude is high enough. The peak interface tensile stress is computed by using the optically recorded free surface displacement of the coating. Because interface decohesion is accomplished at a strain rate of almost 107 s-1, all inelastic processes essentially are suppressed and the measured value essentially is the intrinsic tensile strength of the interface. Tensile strength values in the range of 500-900 MPa were recorded for the interfaces between sputter-deposited calcium-phosphate coatings and Ti substrates. To confirm the locus of failure, the spalled spots were examined using SEM and EDS. The variation in the measured values was related to the changes in the deposition conditions. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 624-632, 1998.
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  • 93
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    Journal of Biomedical Materials Research 41 (1998), S. 657-670 
    ISSN: 0021-9304
    Keywords: platelets ; prothrombinase ; adherent ; biomaterials ; thrombin ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Platelet adhesion to biomaterials is often used as an index of blood compatibility, but a more clinically relevant issue is whether the adherent platelets are able to promote clot formation (i.e., if they are in the procoagulant state). Platelets rapidly generate thrombin when they are in the procoagulant state and the Va/Xa complex is present. We found that adherent platelets are procoagulant by three different methods: binding of FITC-Annexin V, acceleration of thrombin generation in the presence of Xa, Va, and prothrombin; and clotting of recalcified plasma. In the clotting time studies, the effect of adherent platelets on TCPS was completely eliminated by the addition of Annexin V, which is known to bind tightly to procoagulant platelets. The degree of procoagulant activity of adherent platelets was determined by measuring thrombin generation rates in the presence of the clotting factors Va, Xa, and prothrombin and normalizing to the number of adherent platelets. Two key observations were made in these studies. First, the procoagulant activity of platelets adherent to untreated and to several types of treated polystyrenes, as well as to glass and PET, was much greater than the procoagulant activity of unstimulated bulk phase platelets. Little difference in the procoagulant activity of adherent platelets was observed among the materials tested, however. Second, the procoagulant activity of platelets prestimulated with ionophore and subsequently allowed to adhere to Plastek® M was much greater than when adherent platelets were stimulated by the adhesion event only. Measured values for platelet adhesion, platelet activation, and contact activation of blood plasma are discussed in the context of their potential combined impact on blood clotting. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 657-670, 1998.
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  • 94
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    Journal of Biomedical Materials Research 41 (1998), S. 104-110 
    ISSN: 0021-9304
    Keywords: bone morphogenetic protein ; osteoblasts ; microspheres ; poly(d,l lactide-co-glycolide) ; cellular responses ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Porous 50:50 poly(d,l lactide-co-glycolide) microspheres containing varying amounts of “free” recombinant human bone morphogenetic protein-2 (rhBMP-2) were evaluated for their ability to induce/enhance expression of osteoblastic characteristics by pluripotent mesenchymal cells in vitro. “Free” protein (Fp) is defined as protein present on the surface and within the porous matrix of the microspheres. Four preparations of bioerodible particles (BEP) were used: blank - without rhBMP-2; low Fp - 24 μg of free rhBMP-2 per g of particles; medium Fp - 403 μg/g; and high Fp - 884 μg/g. C3H10T1/2 cells (C3H) and bone marrow stromal cells (BMC) were cultured with 1 mg of BEP for up to 4 weeks, and cell growth and expression of osteogenic responses were determined weekly. For both cell types, control cultures (neither BEP nor rhBMP-2) and cultures with blank BEP exhibited no or minimal osteoblastic characteristics. Compared to control and blank BEP cultures, C3H cells responded to particles having medium and high amounts of free rhBMP-2 with increased cell growth and alkaline phosphatase activity, but osteocalcin secretion and mineralization were not markedly influenced. Low Fp BEP enhanced only the alkaline phosphatase activity of C3H cells. In contrast, although growth was not affected, rhBMP-2-loaded BEP increased alkaline phosphatase activity, osteocalcin secretion, and mineralization in BMC cultures in a dose-dependent manner (i.e., blank 〈 low 〈 medium 〈 high Fp). © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 104-110, 1998.
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  • 95
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    Journal of Biomedical Materials Research 41 (1998), S. 398-404 
    ISSN: 0021-9304
    Keywords: feldspar glass ; crystallization ; cubic leucite, microstructure ; X-ray diffraction ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Previous studies have shown that the crystallization of glasses in the system K2O-Al2O3-SiO2, in the primary field of leucite, is not possible without modification of the composition. Leucite (KAlSi2O6) is used as a reinforcing phase in some compositions for all-ceramic dental restorations. However, because of their higher coefficient of thermal expansion, these materials cannot be veneered with conventional metal-ceramic porcelains. The purposes of this study were to investigate the crystallization behavior of a glass in the system K2O-Al2O3-SiO2 and to evaluate the effect of heat treatment on the crystal size, percent crystallinity, and coefficient of thermal expansion of the material. Ion-exchanged glass powder was prepared by mixing the glass with rubidium nitrate and heat-treating at 450°C for 4, 8, 24, or 48 h. Bars were made from these powders and baked under vacuum at 1038°C for 2 min. The bars made from the powder ion-exchanged for 48 h were further heat-treated for 4 h at either 800°C, 850°C, 900°C, 950°C, or 1038°C. X-ray diffraction analyses showed cubic leucite was the only crystalline phase in the specimens made from the powders ion-exchanged for 4, 8, 24, or 48 h and baked at 1038°C for 2 min. Further heat treatment for 4 h at either 800°C, 850°C, 900°C, 950°C, or 1038°C promoted the growth of cubic leucite. In addition, a second phase identified as tetragonal rubidium-leucite was present in the specimens heat-treated for 4 h at 1038°C. SEM observations showed that all specimens made from the powders ion-exchanged for 48 h exhibited small spherical crystals dispersed in a glassy matrix. The percent crystallinity ranged from 18.9% to 42.9% and the average particle size was between 0.64 to 1.18 μm. The coefficients of thermal expansion ranged between 8.076 and 8.788 × 10-6/°C. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 398-404, 1998.
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  • 96
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    Journal of Biomedical Materials Research 41 (1998), S. 167-170 
    ISSN: 0021-9304
    Keywords: FT-IR ; microspectroscopy ; infrared ; injectable biomaterial ; calcium phosphate ; bone substitute ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Hydroxypropylmethylcellulose (HPMC) of high-viscosity grade is used as a ligand for a bioactive calcium phosphate ceramic (the filler) in a ready-to-use injectable sterilized biomaterial for bone and dental surgery. Application of physico-chemical methods such as XPS, NMR, or Raman spectroscopy encounters difficulties when used to study such a multiphased material. This paper reports on the application of FT-IR microspectroscopy (FT-IRM) for the investigation of inorganic and organic phases of the rough composite and separated phases obtained by mechanical or chemical extraction methods. A comparison of FT-IRM with the conventional KBr pellet method was made and indicates that the macro and micro FT-IR methods are complementary: the former revealed new chemical groups not visualized with the KBr method whereas the latter detected the major compound of the blend. FT-IR microspectroscopy was revealed to be a powerful method of analysis that is complementary to other existing spectroscopic methods. Moreover, it is expected to be a useful tool in the study of biomaterials in biological samples. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 167-170, 1998.
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  • 97
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    Journal of Biomedical Materials Research 41 (1998), S. 468-473 
    ISSN: 0021-9304
    Keywords: macrophages ; cobalt chromium ; bone resorption ; cytokines ; aseptic loosening ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The purpose of this study was to elucidate the mechanisms by which cobalt chromium particulate wear debris contribute to the aseptic loosening of total joint prostheses. Incubation of macrophages with cobalt chromium led to release of tumor necrosis factor-α (TNF-α) and prostaglandin E2 (PGE2), but did not lead to release of interleukin-1β (IL-1β) or interleukin 6 (IL-6). Exposure of macrophages cocultured with osteoblasts to cobalt chromium also led to significant release of TNF-α and PGE2, but did not lead to significant IL-6 or IL-1β production. The release of PGE2 in the coculture system was greater than that detected when macrophages were exposed to cobalt chromium without the osteoblast contribution. Exposure of radiolabeled calvaria to media from macrophages incubated with cobalt chromium in coculture with osteoblasts led to release of 45Ca. In contrast, exposure of radiolabeled calvaria to media from isolated macrophages incubated with these particles did not result in release of 45Ca. Exposure of macrophages to cobalt chromium was toxic, as reflected by release of the intracellular enzyme lactate dehydrogenase. Macrophages play a role in the initiation of bone resorption at the interface through the phagocytosis of cobalt chromium particles and subsequent release of TNF-α and PGE2. The presence of osteoblasts at the interface may be required for amplification of the inflammatory response and ultimately for bone resorption. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 468-473, 1998.
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    Journal of Biomedical Materials Research 41 (1998) 
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
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  • 99
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    Journal of Biomedical Materials Research 41 (1998), S. 541-548 
    ISSN: 0021-9304
    Keywords: apatite ; chitin ; in situ precipitation ; hydroxyapatite ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Composites of chitin with calcium phosphate were obtained by in situ precipitation of the mineral from a supersaturated solution onto chitin scaffolds. The chitin scaffolds were obtained by freeze drying to give a highly porous structure possessing a polar surface favorable for apatite nucleation and growth. The extent and arrangement of calcium phosphate deposits on the chitin and substituted chitin scaffolds were explored. Up to 55% by mass of calcium phosphate could be incorporated into chitin scaffolds. Deposits on the chitin surface were of a continuous apatite carpet nature while deposits on carboxymethylated chitin surfaces displayed a spherical morphology. Carboxymethylation of chitin exerts an overall inhibitory effect towards calcium phosphate deposition, but it provides for site-specific nucleation of the mineral phase. In situ precipitation can be an important route in the future production of various polymer-calcium phosphate composites. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 541-548, 1998.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 100
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 41 (1998), S. 549-559 
    ISSN: 0021-9304
    Keywords: photopultrusion ; composites ; fiber-reinforced polymers ; photopolymerization ; methacrylates ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: To develop a dual-curing monomer system for the photopultrusion of reformable (soft) composites, a microhardness assay showed that in a blend with 2,2-Bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl] propane (Bis-GMA), the substitution of methyl methacrylate (MMA) for triethylene glycol dimethacrylate (TEGDMA) delayed the onset of gelation during photopolymerization. Adding lauroyl peroxide permitted the completion of polymerization thermally. This system was used to form silicate-glass-fiber-reinforced composites, with varying degrees of conversion, by photopultruding over a range of pulling speeds. Sol-gel extractions demonstrated both fully soluble and insoluble matrices. For the soluble material, gel permeation chromatography elucidated a trimodal distribution of molecular weights that corresponded to MMA, Bis-GMA, and polymeric molecules with molecular weights in the tens of thousands. Composites with matrix solubilities above about 10% wt could be swaged after photopultrusion to change the cross section from circular to rectangular before thermal processing. The effect on the final elastic modulus was small (∼44GPa, as measured in flexure for 57% vol-reinforced composites); but the final flexure strength was reduced by approximately 25% to a constant of about 1.2 GPa. Morphological characteristics that were seen in the circular-sectioned precursors were observed in the swaged rectangular products as well, including flaws when swaging was conducted at matrix solubilities above about 75%. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 549-559, 1998.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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