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  • 1
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The in-vivo response to a composite material obtained with polyetherimide (PEI) reinforced with carbon/glass fibers was investigated by histological methods by implanting cylinders in muscle and in bone of the New Zealand White rabbit. A common metallic alloy, widely used in orthopaedic surgery, was used as control (Stellite). The aim of the study was to analyze the biological response towards the surface of the material. Composite implants and metallic implants did not induce adverse or inflammatory reactions. The morphological picture produced was similar, in muscle and in bone, for both materials. In muscle, cylinders were confined by an extremely thin fibrous layer and the overall appearance of the muscular tissue was normal. In bone, cylinders were confined by a nearly annular rim of newly formed bone. From these data it is possible to derive that the response to PEI-based composite material is comparable with the response to metallic substrate and, then, the material can be suitable for clinical application. ©1999 Kluwer Academic Publishers
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 7 (1996), S. 695-698 
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Autocrosslinked polysaccharide (ACP) polymers are inter- and intra-molecular esters of hyaluronan (HA) in which part of the carboxyl group is esterified with hydroxyl groups of the same and/or different molecules of the polysaccharides. Suspensions of ACPs in bidistilied water, with relative levels of crosslinking varying from 5% to 20% and different weight concentrations, were obtained to analyse their viscoelastic properties. The steady shear tests showed the pseudoplastic behaviour of ACP, viscosity having a higher value at higher concentrations and degrees of crosslinking. The viscoelastic properties showed an essentially elastic behaviour in the examined frequency range, and they can be modulated by varying both the degree of crosslinking and the weight concentration.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 6 (1995), S. 161-166 
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: In this paper, the non-isothermal cure behaviour of a dental composite, activated by visible light, is described using a heat transfer model that, coupled with a reaction kinetic expression, is able to predict the temperature and the degree of reaction in the composite. The temperature and the degree of reaction profiles inside the composite are calculated, as a function of the cure time, taking into account the system geometry, the thermal diffusivity of the composite, and the resin reaction rate. Material properties, boundary and initial conditions and the kinetic behaviour are the input data of the heat transfer model. Once the degree of reaction is known, the glass transition temperature profiles across the thickness of the composite are calculated. Experimentally measured glass transition temperatures are used for the evaluation of an extinction coefficient capable of accounting for the effects of the light absorption through the thickness on the polymerization kinetics. Finally, the effects of the non-isothermal cure conditions on the application of these materials in dental restorations are discussed.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 8 (1997), S. 75-83 
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The polymerization behaviour of bone cements during total hipreplacements is characterized by a fast and highly non-isothermal bulk reaction.In the first part of this paper the reaction kinetics are analysed bycalorimetric analysis in order to determine the rates of polymerization inisothermal and non-isothermal conditions. A phenomenological kinetic model,accounting for the effects of autoacceleration and vitrification, is presented.This model, integrated with an energy balance, is capable of predicting thetemperature across the prosthesis, the cement and the bone and the degree ofreaction in the cement, during in situ polymerization. The temperatureand the degree of reaction profiles are calculated, as a function of the settingtime, taking into account the system geometry, the thermal diffusivity of bone,prosthesis and cement, and the heat rate generated by the reaction according tothe kinetic model. Material properties, boundary and initial cond!itions are the input data of the heat transfer model. Kinetic and heat transfermodels are coupled and a numerical solution method is used. The model is appliedin order to study the effects of different application procedures on temperatureand degree of reaction profiles across the bone–cement–prosthesissystem.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 9 (1998), S. 317-324 
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract A new bone cement based on poly(ethylmethacrylate) (PEMA), hydroxyapatite powder (HA) and n-butylmethacrylate monomer (n-BMA) has been studied using isothermal and non-isothermal polymerization. Methacrylate monomers are highly reactive and release a considerable amount of heat during polymerization. A quantitative understanding of the methacrylate polymerization is necessary because the thermal history of the polymerization has considerable influence on the final properties of a bone cement. In the first part, polymerization kinetics are analysed by means of differential scanning calorimetry (DSC). DSC data are used to evaluate a phenomenological model describing the cure kinetics of this new bone cement. In the second part, a kinetic model coupled with the energy balance is used to obtain temperature and degree of conversion profiles in the bone–cement–prosthesis system, under non-isothermal conditions, as function of initial temperature and thickness of the cement. Material properties, boundary and initial conditions and the kinetic behaviour are the input data for the numerically solved heat-transfer model. The temperature at the bone/cement interface, can be considered as a weak point, often responsible for total joint replacement failure. For this particular bone cement exhibiting a low exotherm and low glass transition temperature, the interfacial temperature is lower than the threshold level for thermal tissue damage (50 °C). The conversion occurs almost completely, avoiding problems with unreacted monomers that can be released by the cement, giving rise to tissue damage. © 1998 Chapman & Hall
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Applied composite materials 4 (1997), S. 69-81 
    ISSN: 1573-4897
    Keywords: nanocomposites ; roughness ; fractal dimension
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract An analytical model is presented for the determination of the fractal dimensions of particles which are widely used as reinforcement in nanocomposites. The model is used to characterize the surface irregularity or roughness. It was found that fractal dimensions of both the contour and surface of particles depend only on the relative particles size ratio between secondary particles and subunits. It is proposed that, in practical applications, the fractal dimension of a certain reinforcement particle can be obtained by a combination of this model and a state-of-the-art instrument that can determine the sizes of primary and secondary particles by image analysis. It is possible to relate the fractal dimension with the adhesion and other physical and chemical properties at the interface between particles and matrix.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Applied composite materials 2 (1996), S. 385-393 
    ISSN: 1573-4897
    Keywords: nanocomposites ; poly(methyl methacrylate) ; silica
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract It is possible to optimize the performance of the inorganic-organic composites dispersing the inorganic component in the organic matrix on a nanomiter length scale. If dry the inorganic phase cannot be intimately dispersed during the incorporation in the matrix. When the particle surface is organically modified, and the incorporation is made starting from a liquid dispersion (particles in polymer solution), the resulting composites exhibit an excellent homogeneity. Here, monolithic [poly(methyl methacrylate)/monodisperse silica particles] nanocomposites have been prepared and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic light scattering (DLS), micro-hardness, and differential scanning calorimetry (DSC).
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  • 8
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The understanding of substrate dependence of cellular differentiation is important in the surface design of biocompatible artificial devices as well as cell-incorporated tissue engineered devices. In an attempt to understand some of the genetic and epigenetic aspects of the control of cell differentiation in the presence of two different materials, Chronoflex (CH) and plasma treated Chronoflex coated with Hyaluronan (CH-HA), we used primary cultures of human myogenic cells, a model that encompasses cell proliferation, migration, fusion, and differentiation dependent gene activation. By testing both the material samples on the growth of human myoblasts in primary cultures, we demonstrated that both CH and CH-HA substrates were able to support the cell growth since they did not affect cell count and DNA synthesis. On the contrary, the degree of myoblast differentiation, assessed as a function of creatine phosphokinase (CPK) activity on living cells, was completely different on the two biomaterials. Indeed, the amount of CPK increased on CH-HA cultured cells as a result of myotube formation, while CH grown myoblasts remained unfused and displayed no increase on the CPK activity even after 12 days culture. Moreover, the expression level of MyoD and myogenin mRNA, both related to myogenic cell differentiation, appeared extremely low in CH-grown cells, while they were rapidly induced in CH-HA cultured myoblasts. © 1999 Kluwer Academic Publishers
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 10 (1999), S. 671-676 
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract In the dentistry field, synthetic hydroxyapatite can be conveniently used as semiabsorbable alloplastic material to solve a number of clinical problems. The hydroxyapatite structure influences bone ingrowth as well as its resorption. In particular, pore size must exceed 100 μm to allow new bone ingrowth. Because of its brittleness, highly porous hydroxyapatite is difficult to handle without causing damage, and, therefore, its mechanical performance has to be improved placing the material on a dense hydroxyapatite substrate. Dense/porous hydroxyapatite laminates can be obtained by slip casting technology. The method starts with the preparation of a ceramic powder–binder–solvent system. This slurry produces, after solvent evaporation, a soft green tape, that is successively baked at 300 °C to remove all organic component, and finally sintered at high temperature (1200 °C). The material porosity cannot be significantly modified by changes in the slurry composition and sintering temperature; therefore, the macroporous hydroxyapatite layer must be obtained using a porous hydroxyapatite powder. The powder is prepared by grinding of green tape pieces and the resulting coarse material is successively baked at 300 °C. Such material is mixed with a polymer solution and cast on a green tape substrate. Layer fractures are not observed in both film bulks and interface, because during sintering the consolidation of two layers happens simultaneously. In the resulting material, the first layer consisted of macroporous hydroxyapatite with high osteoconductive properties, and the second layer was a dense hydroxyapatite substrate able to improve the laminate mechanical properties. © 1999 Kluwer Academic Publishers
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 10 (1999), S. 65-68 
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract A new generation of electrocardiogram (ECG) electrodes have been fabricated and superficially modified by a special controlled precorrosion process. The electrodes have been characterized by scanning electron microscopy (SEM), resistance–capacitance measurements (RCM) and simulated defibrillation recovery (SDR). The resulting surface of the Sn alloys was rough, and, consequently, a large active surface area was available. As a result, a higher electrocardiogram electrode performance, including low alternating current (a.c.) impedance, excellent time stability and improved SDR, was achieved. Such new design can surely find important future applications in clinical diagnosis. © 1999 Kluwer Academic Publishers
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