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  • 1
    ISSN: 1573-4838
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Abstract The preparation of films from blends of collagen and poly(vinyl alcohol) is described and the transport properties of these films are evaluated. Different crosslinking procedures, dehydrothermal crosslinking and crosslinking by glutaraldehyde, have been used. The transport properties of these films have been studied using model solutes such as sodium chloride, vitamin B12 and bovine albumin. The results are compared with those obtained using commercial products such as Cuprophan® and poly(acrylonitrile) dialysis membranes. The aim of our study was to analyse the effects of different crosslinking methods and the effects of blending with poly(vinyl alcohol) upon the permeation characteristics of collagen-based membranes.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials science 5 (1994), S. 33-39 
    ISSN: 1573-4838
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Poly(ester-ether-ester) block copolymers, belonging to a class of biodegradable materials, were synthesized from poly(ethylene glycol) and ε-caprolactone by a simple ring-opening mechanism, which avoids the use of potentially toxic inorganic or organometallic initiators. The morphological and mechanical properties of such materials were investigated by gelpermeation chromatography, vapour pressure osmometry, proton magnetic resonance, infrared spectroscopy, differential scanning calorimetry, X-ray diffractometry and stress-strain tensile tests. The biocompatibility was investigated by cytotoxicity and hemocompatibility tests; the cytotoxicity was tested by the Neutral Red uptake assay, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay, the Kenacid Blue R-binding method, and by the cell proliferation test on polymer films; the hemocompatibility was tested by the contact activation both of the coagulation cascade (intrinsic pathway), by the plasma prekallikrein activation test, and of the thrombocytes, by measuring the release of platelet factor 4 and β-thromboglobulin. The experimental results show that such a polymerization process permits high-molecular mass block copolymers with relatively good tensile and mechanical properties to be obtained. Their cyto- and hemo-compatibility makes them suitable for employment as biomaterials.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials science 10 (1999), S. 431-435 
    ISSN: 1573-4838
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Abstract Hydrogels are three-dimensional polymeric networks very similar to biological tissues and potentially useful as drug delivery systems. Poly(vinyl alcohol)-based hydrogels containing different amounts of dextran or chitosan were prepared using the freezing–thawing method. Repeated freezing–thawing cycles of a poly(vinyl alcohol) (PVA) aqueous solution lead to the formation of crystallites which act as cross-linking sites, and a hydrogel with a high capacity to swell is obtained. The effects of the two different polysaccharides on the properties of the obtained materials were investigated by differential scanning calorimetry, dynamic mechanical analysis and scanning electron microscopy. In addition the release with time of poly(vinyl alcohol) in aqueous medium, was monitored and evaluated. On the basis of the obtained results it seems that the presence of dextran favors the crystallization process of PVA, allowing the formation of a more ordered and homogeneous structure. Instead, chitosan seems to perturb the formation of PVA crystallites leading to a material with a less regular structure. © 1999 Kluwer Academic Publishers
    Materialart: Digitale Medien
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  • 4
    ISSN: 1573-4838
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Two synthetic polymers, poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA) were blended, in different ratios, with two biological polymers, collagen (C) and hyaluronic acid (HA). These blends were used to prepare two different materials, sponges and hydrogels, which were loaded with growth hormone (GH). The GH released, was monitored in vitro using a specific enzyme-linked immunoadsorbent (ELISA) assay. The results show that GH is released in a dose-dependent manner, from HA/PAA sponges and from HA/PVA and C/PVA hydrogels. The amount of GH released was proportional to the percentage of the natural polymer (HA and C). The release of GH from HA/PAA sponges was constant with time, whereas in HA/PVA hydrogels it was linear for the first 3 days followed by a slower release. The GH release pattern in C/PVA hydrogels was different, with a slow release for the first 3 days followed by a more rapid release. The concentrations of GH released from the materials were within a physiological range and sufficient to have a local effect on cellular proliferation. The effects of GH were tested in vitro using primary human osteoblast-like cells (HOBS) and measuring cell proliferation and alkaline phosphatase (ALP), a biochemical marker of HOB cell differentiation.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials science 6 (1995), S. 71-75 
    ISSN: 1573-4838
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Hydrogels are three-dimensional polymeric networks very similar to biological tissues. Many synthetic polymers can be used in preparing hydrogels. Among them poly(vinyl alcohol) (PVA), physically crosslinked by repeated freeze-thawing cycles of polymer aqueous solutions, is widely employed to make hydrogels for biomedical applications. To increase the similarity between hydrogels and natural tissues and to obtain “polymeric hybrid tissues”, we attempted to incorporate 3T3 cells, from a mouse fibroblast cell line, into PVA hydrogels obtained by one freeze-thawing cycle using as a solvent complete culture medium. Hydrogels were also made using eight freeze-thawing cycles from PVA solutions prepared using as a solvent either complete culture medium or water. Cell adhesion experiments were performed by seeding 3T3 and human umbilical vein endothelial cells (HUVEC) on to the hydrogel surface. The effect of the solvent and of the different number of freeze-thawing cycles on the mechanical characteristics of the PVA hydrogels were investigated by dynamic-mechanical techniques. A scanning force microscope analysis of the hydrogel surface viscoelastic properties was also carried out. Our results show that PVA is not cytotoxic. Although PVA hydrogel surface characteristics do not seem to favour the adhesion of substrate-dependent cells, encouraging results were obtained with the 3T3 cells incorporation. DMA analysis indicates that the networks prepared by eight freeze-thawing cycles possess a mechanical consistency comparable, even slightly better, than the ones prepared by only one freeze-thawing cycle and used for the cell incorporation studies.
    Materialart: Digitale Medien
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  • 6
    ISSN: 1573-4838
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: To better understand and optimize the fine interactions that occur during adhesion events between human cells and synthetic materials, we seeded human umbilical vein endothelial cells (HUVEC) onto ethylene-vinyl alcohol (EVOH) copolymer films prepared by casting. Different adhesive proteins, e.g. fibronectin and gelatin, and the monoclonal antibody (MoAb) CLB-HEC19 specific for the endothelial cell membrane were used to coat the materials. We used atomic force microscopy (AFM) to analyse the EVOH film structure, to test its planarity and homogeneity, before seeding it with endothelial cells. The metabolic changes induced in the endothelial cells by interactions with the copolymer functional groups and the adhesive proteins were monitored by a micro-electronic pH sensor, positioned close to the HUVEC monolayer. We found that the adhesion of HUVEC onto various substrates was finely modulated by the MoAb CLB-HEC19 and that the endothelial cell metabolic rate was enhanced when cultured onto a CLB-HEC19 coating. Surface roughness seems also to play a role in the interaction with HUVEC. The AFM measurement analysis demonstrated that L6 surface is rougher than R20. These surface characteristics could favour cell adhesion; in fact HUVEC adhesion results on R20 were significantly lower than on L6.
    Materialart: Digitale Medien
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  • 7
    ISSN: 1573-4838
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: The mechanical, biological and surface properties of films, based on blends of soluble collagen and poly(vinyl alcohol), were investigated. Films prepared by casting were cross-linked by a dehydro-thermal treatment. The mechanical behaviour of the materials was studied by dynamic-mechanical thermal analysis. The biological properties of the films were evaluated by performing cytotoxicity and cytocompatibility in vitro tests. Surface characterization was carried out by X-ray electron spectroscopy. The results obtained indicate that these materials behave as two-phase systems and a remarkable enrichment of collagen in the surface with respect to the bulk was observed. Cytocompatibility tests show that the blending of the two polymers creates a better substrate for cell growth in comparison with pure components.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials science 10 (1999), S. 301-307 
    ISSN: 1573-4838
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Abstract The release of human growth hormone (GH) from bioartificial polymeric materials in the form of hydrogels, was measured in vitro for up to 3 weeks. Poly(vinyl-alcohol) (PVA) was blended, in different ratios, with two biological polymers, dextran and chitosan respectively. These blends were used to prepare hydrogels, using a freeze–thawing method. The hydrogels were loaded with GH, and their potential use as delivery systems was investigated. The release with time of PVA, in aqueous medium, was also monitored and evaluated. Scanning electron microscopy was used to investigate the structure of the hydrogels. The results obtained indicated that GH can be released from both dextran/PVA and chitosan/PVA hydrogels. The initial GH concentration used for sample loading affected the total quantity of GH released but not the pattern of release. The amount of GH released was affected by the content of the biological component. The percentage of PVA released was low but it was, however, related to the content of chitosan and dextran in the blends. ©1999 Kluwer Academic Publishers
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials science 5 (1994), S. 613-616 
    ISSN: 1573-4838
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Hydrogels of hyaluronic acid (HA) and poly(vinyl alcohol) (PVA) were prepared using eight freezing-thawing cycles from HA/PVA blends (10/90, 20/80, 30/70, 40/60, 50/50, and 0/100 (w/w) ratios). The biocompatibility of the hydrogels was tested by means of in vitro cytotoxicity and cytocompatibility tests using cell culture techniques. The release with time of HA and PVA, the two hydrogel components, ion aqueous medium was also monitored and evaluated. The results indicate that all the hydrogels are not cytotoxic, while cell adhesion was very scarce in PVA and was not improved by the addition of HA. The release kinetics of HA and PVA from the hydrogels were different. After 2 h, HA percentages from about 80 (10/90 blend) to 100% (20/80, 40/60 blends) were released from the hydrogels into the aqueous medium. In contrast, the percentages of released PVA remain lower in time compared with HA, reaching a plateau after 24 h and ranging from a maximum of about 13% (0/100 blend) to a minimum of about 6% (10/90, and 20/80 blends).
    Materialart: Digitale Medien
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  • 10
    ISSN: 1573-4838
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Abstract Hydrogels are three-dimensional polymeric networks very similar to biological tissues and potentially useful as soft tissue substitutes and drug delivery systems. Many synthetic polymers can be used to make hydrogels: poly (vinyl alcohol) is widely employed to make hydrogels for biomedical applications. Improvements in the biocompatibility characteristics of synthetic materials could be achieved by the addition of biological macromolecules. The resulting materials named “bioartificial polymeric materials” could possess the good mechanical properties of the synthetic component and adequate biocompatibility due to the biological component. We have used poly (vinyl alcohol) to make hydrogels containing various amounts of hyaluronic acid. These bioartificial materials were studied to investigate the effect of the presence of the hyaluronic acid on the structural properties of the hydrogels. Thermal, mechanical, morphological and X-ray analyses were performed. A close correspondence between the network consistency and the degree of crystallinity developed in the matrix suggested that the hyaluronic acid, when its content is about 20%, could provide heterogeneous crystallization nuclei for poly (vinyl alcohol) thus increasing the crystallization degree, and consequently, the storage modulus.
    Materialart: Digitale Medien
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