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  • 1
    ISSN: 1573-9686
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Finite element stress analysis has been applied to examine the stress patterns in a prosthesis requiring fixation in the medullary shaft of a long bone. No specific prosthesis is considered but rather a generally applicable geometry has been chosen. This consists of a cylindrical section of cortical bone within which is implanted a prosthesis composed of a solid central rod surrounded by a porous coating. The finite element analysis utilized an axisymmetric model to determine the distribution of stresses throughout the system. The effect of changes in length of prosthesis, thickness of porous coating, depth and type of tissue ingrowth, and type of porous coating material were studied under conditions of axisymmetric loading. The results indicate that with complete bone ingrowth, the maximum shear stress and the distance necessary for load transfer are both independent of implant length. However, with incomplete ingrowth, increasing implant length reduces shear. Incomplete growth also produces lower shear stresses but higher shear strains in areas without ingrowth. In addition, a porous polyethylene coating gives a more even load transfer and lower shear than a porous coating of a high modulus material.
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  • 2
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Determination of potential cytotoxicity is a central issue in current biocompatibility testing standards such as ISO and ASTM. Most of these tests do not assess biocompatibility of a biomaterial with regard to cell function. This study was aimed at screening a number of potential parameters that could be included in assessment of cell functional aspects of biocompatibility. Human umbilical vein endothelial cells (HUVEC) were seeded directly on titanium, NiCr alloy, CoCr alloy, PMMA, PE, PU, PVC, and silicone, or were exposed to the material extracts. Cytotoxicity was assessed for these materials through MTT conversion, crystal violet protein determination and Ki67 expression. In addition, expression of the cell adhesion molecules E-selectin, cadherin-5 and PECAM, as well as of the adhesion-associated proteins fibronectin and vinculin (focal adhesions), was determined by immunocytochemistry and western blotting. Cytotoxicity was not detected with the material extracts. Cells were able to adhere to bare metals, but not polymers. Fibronectin preadsorption resulted in adhesion and spreading also on the polymers. Cells were able to establish cell–cell contacts and focal adhesions. Western blotting, in combination with differential detergent extraction, indicated that linkage of cell–cell adhesion markers to the cytoskeleton may be used as an additional parameter relevant to cell function.
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  • 3
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Since many fibres are very strong, they are considered to have useful potential for fibre reinforcement of orthopaedic and dental implant materials. Fibres exposed on the surface of composites may significantly influence the cellular response not only due to the chemistry but also due to the fibre size and shape. This study has concentrated on investigation of cellular responses to fibre-specific aspects of fibre-reinforced composites. Four multifilament materials with diameter less than 20 μm were used: Kevlar 29(K), silicon carbide(SiC), nylon 66(N), and polyethylene terephthalate(PET). Established cell line L929 fibroblasts were used as the cell model. Cell behaviour on the surfaces of fibres was examined using direct cell counting (after 3, 5, 8 h and 1, 2, 3 days), scanning electron microscopy (SEM) (after 2 h and 2 days), and fluorescent staining of F-actin, which was analysed by confocal laser scanning microscopy (CLSM) (after 2 h and 2 days). The results showed that fibroblasts adhered and grew very well on all fibre surfaces, although less cells were observed on PET from direct cell counting. Significant orientational behaviour of cells was found on all fibre surfaces from the SEM and CLSM analysis, independent of the bulk chemistry of the fibres.
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  • 4
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Aseptic loosening is one of the major reasons for failure of joint prostheses. The periprosthetic tissue has previously been described microscopically; however, little work has been devoted towards quantitating genes expressed by cells at the materials/tissue interface. This study aims to characterize the phenotypic expression of osteoblasts and test the feasibility of quantifying the level of gene expression in periprosthetic tissue sections by combining in situ hybridization and image analysis techniques. There are many factors to consider when quantifying mRNA, in that comparing labeling between different cDNA probes, these should have comparable length and base comparison. The probes should be labeled with the same specific activity, that is the amount of probe to label added is the same, both between different probes and between batches of the same probe. Chromagen color reactions are variable in that the color development is not always linear and more likely follows a sigmoidal curve. Samples should only be compared when it is known that the reaction has been in the linear range. The image analysis of such staining introduces further factors which should be considered and controlled. Color analysis is a very complex problem with respect to reproducibly analyzing histological sections. The brightness component of the image should be independent of the colors within the image, in conventional RGB (red, green and blue) signalling mode this is not possible, while when using HSI (hue saturation and intensity) mode this becomes possible, and factors like staining intensity and brightness of the image become much more accountable and controllable. With these factors identified, we consider that the quantitative image analysis approach does allow comparison of patterns of bone-related mRNAs and demonstrates differences in expression in these osteogenic factors depending on distance from the prosthesis, tissue type, patient and device. © 1998 Kluwer Academic Publishers
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  • 5
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The possibility that three different types of metal ions, Cr(III), Co(II) and Ni(II), all relevant to metallic biomaterials, might influence chemotaxis has been investigated. Two new techniques, not previously used in biomaterials research involving the study of locomotor morphology of neutrophils and cell movement through agarose gels, were used in this study. Chromium ion concentrations from 0.05 to 10 p.p.m. and cobalt ion concentrations from 0.5 to 30 p.p.m. were not chemotactic for neutrophils under agarose and did not induce neutrophils to polarize. As neutrophils must take up a locomotor morphology before migrating, it is clear that cobalt and chromium ions in a protein-free environment are not chemotactic for human neutrophils. Concentrations of 〉 2.5 p.p.m. nickel ions did induce neutrophils to polarize, probably a result of the nickel ions causing depolarization of the neutrophil plasma membrane.
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  • 6
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Cellular responses to silicone and latex were investigated using flow cytometry, to determine the cells involved in the inflammatory responses and to characterize the differences in the response between these materials, if any. A panel of 11 monoclonal antibodies were selected to cover the range of cells that could be involved in the response, each antibody being directly conjugated with fluorescein isothiocyanate (FITC). The materials were implanted subcutaneously into rats in tubular form; the tubes were sealed at one end with Silastic adhesive. Two tubes per animal were implanted, using four animals per time period for 1, 2, 5 and 7 day implantation periods. After these times the animals were sacrificed and the tubes retrieved and then spun to harvest the exudate from the lumen. This exudate was analysed using flow cytometry. Significant and reproducible differences in cell number and antibody positivity were observed between these two materials. Latex had a much larger cellular response and showed significant increases in antibody positivity that involved macrophages or granulocytes of unusual size and granularity. Overlap between antibody positivity made specific characterization difficult and led to many questions about the effect of exposure to a material and its effect on cell morphology and phenotype, particularly in the case of macrophages.
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  • 7
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: A series of medical grade polymers and one non-medical grade polymer, in the form of tubes closed at one end, were implanted subcutaneously into the dorso-lumbar region of rats. The samples were retrieved after 1, 2, 5, 7 and 14 days and the exudate which formed within the lumen of the tubes analysed by flow cytometry. Positivity for each of six antibodies: CD45RO (pan leucocyte), OX42 (macrophage/monocyte), CD5 (T-lymphocyte), CD45RA (B-lymphocyte), Interleukin-2 (IL-2) receptor and Major Histocompatibility class II (MHC-II) antigen were tested. The volumes of exudates and their total cellularities varied greatly from material to material, but there was no relationship between the two. Silicone, for example, had the greatest exudate volume at all time periods, but the lowest cellularities after day 5. Large numbers of granulocytes and macrophages were observed in all materials, with smaller populations of T-lymphocytes, which also demonstrated high IL-2 receptor expression. High levels of MHC-II expression were observed and attributed mainly to the macrophage population. All materials demonstrated the very reactive nature of this type of model: a massive inflammatory reaction continuing right up to 14 days in all cases, seemingly acute in cellular composition with high immunological activity. It is concluded that flow cytometry is an extremely useful tool in probing the interaction of cells with artificial materials.
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  • 8
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The role of temperature and shear rate in the activation status of aggregating platelets and platelet microparticles (MPs) was investigated in a modified concentric-cylinder rotational viscometer. Whole blood anticoagulated with citrate was exposed to a range of shear rates typical of cardiopulmonary bypass circuits (0, 1000, 2000 and 4000 s-1) over four temperatures spanning hypothermic to mildly hyperthermic conditions (24, 30, 37 and 42°C) for short durations (100 s). Aliquots of blood were double-stained for CD41 (platelet GPIIb/IIIa) and CD62 (P-selectin). Platelets, platelet aggregates, MPs and red blood cell-platelet and -MP aggregates were identified by flow cytometry by acquiring only CD41-positive particles and differentiating on a plot of CD41 versus forward light scatter. The activation status of each particle was quantified by measuring CD62 expression (α-granule release). A degree of correlation between the shedding of MPs and the formation of platelet–platelet aggregates was observed for the data as a whole (r=0.85 for p〈0.01), although this trend was not observed for a shear rate of 4000 s-1. The mean expression of CD62 on both platelets and MPs was maintained at a very low level for all temperature and shear rate combinations. There was, however, a number of very highly activated MPs associated with red blood cells at high shear rates.
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  • 9
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The soft tissue response of adult rats to a drug-loaded copolymer hydrogel was studied histologically by using monoclonal antibodies specific for certain inflammatory cell types. A hydrogel was loaded with Diclofenac sodium, a non-steroidal anti-inflammatory drug, and designed to release the drug at a constant rate after implantation into muscle tissue. The sites of antibody binding were analysed automatically, by using an image analysis system, providing information on the number of inflammatory cells and their distribution relative to the hydrogel implant. The ability to measure these and other parameters is considered to be of major importance in the assessment of biocompatibility. The experiments demonstrate that Diclofenac sodium (25–30 µg ml−1) reduced the number of macrophages and neutrophils found at the implant site compared with a PBS control. Diclofenac sodium did not have any effect on the T cell response.
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  • 10
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: The MTT test has been widely used as a rapid and sensitive method for screening anticancer drugs. In this paper, we used this method to assess the cytocompatibility of three materials: Keviar 29, silicon carbide and polyvinyl chloride (PVC) in both a quantitative and a qualitative manner. The materials were prepared by cleaning in 70% ethanol, autoclaved or gamma-sterilized. Extracts were prepared at four time periods (1, 2, 3 and 4 weeks) and two temperatures (37°C and 80°C). The extracts were used in the MTT assay and the data were collected and analysed with ONEWAY and DUNCAN procedures using the statistical computer package SPSSx. The MTT staining procedure was also used in direct contact with the materials. The result from the MTT assay demonstrated that Kevlar, SiC and PVC extracted at 37°C were not cytotoxic while PVC extracted at 80°C did show some cytotoxicity, especially the material that had been gamma-sterilized. In the direct contact test the Kevlar showed no cytotoxicity. The SiC did show some localized toxicity when the material had been autoclaved, however, SiC subject to prior cleaning with ethanol showed no cytotoxicity. The PVC that had been autoclaved caused a cytotoxic response whereas the material that had been gamma-sterilized or cleaned in ethanol showed good cytocompatibility. This paper demonstrates that the MTT staining procedure is a useful technique to study the cytocompatibility of materials in both a quantitative and a qualitative manner. It is also shown that the cellular response to the materials tested is dependent on the method of preparation.
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