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  • Articles  (227)
  • Wiley-Blackwell  (227)
  • International Union of Crystallography
  • 1985-1989  (227)
  • 1955-1959
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  • Technology  (227)
  • 1
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 21 (1987), S. 683-700 
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: This study examines the interaction of human low density lipoprotein (LDL) with a select group of biomedical polymers. The adsorption characteristics of LDL on cured filler-free poly(dimethyl Siloxane) (C-PDMS), Biomer, Cardiomat 610, Kraton 1650, poly(hydroxyethyl methacrylate) (PHEMA) and glass are presented. Adsorption of LDL to charged hydrophilic glass control surfaces occurred rapidly, reaching plateau concentrations within one minute (0.19 ± 0.01 ug/cm2). Adsorption of LDL to polymer surfaces appeared to be dependent upon both the polymer hydrophobicity (or apolar nature), and flexibility (or dynamic nature) at the interface. Increased surface concentrations were observed for Biomer (0.32 ± 0.01 ug/cm2) as well as other polymers which exhibited both hydrophobic and elastomeric próperties. Temperature changes between 25°C and 37°C were found to significantly influence the surface concentration of LDL on Biomer (0.16 ± 0.01 ug/cm2 at 25°C versus 0.32 ± 0.01 ug/cm2 at 37°C). A lipid core phase transition at 36°C was believed to be responsible for the temperature influence. Preliminary competitive adsorption studies of LDL with albumin (HSA) and serum on silicone surfaces suggests that LDL adsorption occurred rapidly and preferentially (0.25 ± 0.01 ug/cm2 for LDL alone; 0.33 ± 0.01 ug/cm2 for LDL + HSA; 0.15 ± 0.01 ug/cm2 LDL + serum). Preliminary studies on the role of LDL in calcification were not conclusive. It can be concluded that LDL adsorption is dependent upon polymer hydrophobicity, flexibility and temperature. Competitive adsorption experiments suggests that LDL may have substantial influence on protein adsorption.
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 24 (1987), S. 1921-1939 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A theory is described which guarantees an upper and lower bound estimate of the discretization error in numerical solutions of elliptic boundary value problems. This method gives bounded global estimates of the error in the energy norm. Pointwise estimates of the error in the solution variable or its derivatives can then be obtained if the numerical solution is exhibiting pointwise monotonic convergence.The versatility of this method is illustrated by its application to numerical solutions from finite element, finite difference and boundary element methods.
    Additional Material: 8 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 21 (1985), S. 409-420 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Presented in this paper is a finite element method for the analysis of nonlinear oscillations which exhibit periodic response. The basic idea of the method is to recast the initial value problem as a boundary value problem in which the domain (that is, period) may be unknown. We apply the method to study the free response of the conservative oscillator ü + mu + ∊f(u)=0, where m is either - 1, 0 or 1, f(u) is an odd nonlinear function, and ∊ need not be small. The harmonically forced case, ü + mu + ∊f(u) = Psin Ωt, is also considered, and it is shown that the superharmonic response can be efficiently calculated using this technique.
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  • 4
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 28 (1989), S. 331-358 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The finite strip method is applied to the non-linear analysis of plate structures. Large deflection effects are included via first order non-linearities in the strain-displacement relations, and material non-linearities are included via the von Mises yield criterion and associated flow rule. The virtual work equations are integrated numerically using Gauss quadrature, and the resulting non-linear equations are solved by Newton-Raphson iteration. Numerical results are presented for many applications including uniformly loaded rectangular and I beams, and square plates with either simply supported or clamped ends (or edges). The results are compared with known results from analytical and/or finite element analyses. Finally, a uniformly loaded stiffened panel is analysed and the results are compared with finite element results. In all cases, the results indicate that a single bending mode in the strip direction is sufficient to yield engineering accuracy for design purposes.
    Additional Material: 23 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 21 (1987), S. 1039-1055 
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: An exact discrete numerical solution to the Grabowski model for predicting cell adhesion to polymer surfaces is discussed. The solution technique allows the possibility of taking into account cell-cell interactions within the flow situation and the multistep process involved in thrombus formation. The proposed solution also allows modification of the wall reaction rate model into a two specie reaction rate which distinguishes between the kinetics of contact adhesion and irreversible adhesion. The solution allows determination of effective diffusivity (De) and surface reaction rate (k) constants. Use of the model to examine available experimental data results in the following conclusions: (1) static or dynamic cell adhesion cannot be considered to be diffusion limited; (2) for flow conditions De is a monotonically increasing function of shear rate; (3) under static, i. e., zero flow conditions, De appears to be markedly larger than for flow conditions.
    Additional Material: 5 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 20 (1986), S. 1347-1357 
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Ultra low temperature isotropic (ULTI) carbon-coated polyester suture material was evaluated histologically and mechanically in dogs. These results were compared to those obtainedfor uncoated polyester and polybutylate coated polyester. The suture materials were used in therepair of the surgically incised medical collateral ligament and subcutaneous tissues to evaluate the potential of the carbon-coated system for ligamentous repairs. Following surgery, the dogs were sacrificed at periods of 1-48 weeks postoperatively for evaluation of tissue biocompatibility and mechanical strength of the materials. The polybutylate-coated polyester suture broke at lower force levels than did comparable sizes of uncoated or carbon-coated polyester. All three types showed a high retention (〉98%) of mechanical strength at 48weeks, often exhibiting an increase in tensile strength due to tissue ingrowth. The histologic response to carbon-coated polyester was equal to or better than the response to either the uncoated polyester or polybutylate-coated polyester. A greater degree of tissue growth into the carbon-coated material was evident at most time periods following an initial acute inflammatory response which was also present in the other materials.
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  • 7
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 22 (1988), S. 541-553 
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Densely sintered synthetic hydroxyapatite (HA) is used as an implant material because of its excellent tissue biocompatibility. In order to maximize the biological potential of this calcium phosphate, we have investigated the incorporation of carbonate into HA to make a material which more closely resembles the mineral found in bones and teeth. The aim of the present study was to determine the conditions under which sintered carbonated apatites of specific carbonate content could be produced. The apatites were prepared by heating compressed pellets of precipitated carbonated apatite under a carbon dioxide/steam or nitrogen/steam atmosphere between 825 and 1050°C. The products were analyzed chemically and the surfaces examined by x-ray diffraction, infrared spectroscopy, reflected light microscopy, and scanning electron microscopy. The results showed that carbonate loss during sintering could be reliably predicted, making it possible to produce materials with specific carbonate content, and with specific physical and chemical composition.
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  • 8
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 22 (1988), S. 887-903 
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: A knee simulator was used to study the wear of carbon fiber reinforced UHMWPE(Poly Two) (Poly Two is a registered trademark of Zimmer, USA) tibial and patellar components against Ti-6Al-4V, titanium nitride (TiN)-coated Ti-6Al-4V, and cobaltchromium-molybdenum femoral components. The prostheses tested were regular sized Miller-Galante total knees mounted on 316L stainless steel fixtures using bone cement. An environmental chamber surrounded the knee and maintained bovine serum lubricant at 37°C. The specimens were tested using consecutive blocks of 464 level walking steps, 8 ascending stairs and 8 descending stairs for a total of 100,000 steps. The wear mechanisms found on the tibial components were scratching, carbon fiber associated damage, surface deformation, pitting, minor abrasion, and delamination. Three forms of carbon fiber associated damage were identified; fibers pulled from the surface, broken fibers, and UHMWPE removed from the surface fibers. The SEM evaluation revealed a pit forming mechanism. No correlation was found between femoral component material and tibial surface damage. Visual examination of the femoral components revealed no signs of wear or scratching on the cobalt-chromium-molybdenum or TiN-coated Ti-6Al-4V components. There were, however, many light surface scratches on the uncoated Ti-6Al-4V components, which were also observed in a supplementary test of an uncoated Ti-6Al-4V component tested with a conventional polyethylene tibial component.
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  • 9
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 21 (1987), S. 43-57 
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: A new method has been developed to evaluate the relative thrombogenicity of vascular catheters. The technique provides a means to quantitatively differentiate between catheters made from different polymeric materials. Autologous In-111 labeled platelets were infused into a dog model and catheters were then inserted into the external jugular vein of the dog. The neck region was scanned using gamma camera imaging. Comparisons between catheter materials were made using computer generated uptake slopes during the first 40 min of the scan. In addition to scintigraphy, visual assessment of thrombus deposition, thrombus weight, platelet deposition, and scanning electron microscopy were used to validate the technique. Poly(vinyl chloride), polyurethane, heparinized polyurethane, and silicone catheter materials were tested. It was found that heparinized polyurethane was the least thrombogenic of all materials evaluated.
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  • 10
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 22 (1988), S. 497-508 
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: We compared two assays for estimating the amount of active heparin bound to a catheter surface: (1) a kinetic assay based on the inactivation of thrombin by antithrombin III, and (2) thrombin uptake. Both assays were used to estimate the amount of heparin activity on a series of catheters coated with no heparin, covalently bound heparin, and ionically bound heparin. The kinetic assay produced estimates of surface-bound heparin activity and showed that some binding methods resulted in destruction of most of the heparin's biologic activity. In contrast, the thrombin uptake assay did not correlate with the amount of heparin activity on the catheter surface. Substantial thrombin uptake was found on surfaces coated with no heparin or inactive heparin, while low thrombin uptake was found on surfaces with high levels of heparin activity in the kinetic assay. We conclude that: (1) a kinetic assay based on the heparin accelerated inactivation of thrombin by antithrombin III can be used to estimate the amount of active heparin bound to a catheter surface, and (2) thrombin uptake studies do not correlate with heparin activity and do not predict which heparin binding method will result in the highest concentration of active heparin on the catheter surface.
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