摘要:

AbstractThe principal cause of the clinical failure of bioprosthetic heart valves fabricated from glutaraldehyde‐pretreated porcine aortic valves is calcification. Other prostheses composed of tissue‐derived and polymeric biomaterials also are complicated by deposition of mineral. We have previously demonstrated that: (a) Failure due to calcification of clinical bioprosthetic valves can be simulated by either a large animal circulatory model or subdermal implants in rodents. (b) Calcification of bioprosthetic tissue has complex host, implant, and mechanical determinants. (c) The initial calcification event in the rat subdermal model is the mineral deposition in devitalized cells intrinsic to the bioprosthetic tissue within 48 to 72 h, followed later by collagen mineralization. (d) Initiation of bioprosthetic tissue mineralization, like that of physiological bone formation, has “matrix vesicles” as early nucleation sites. (e) Alkaline phosphatase (AP), an enzyme also associated with matrix vesicles involved in bone mineral nucleation, is present in both fresh and fixed bioprosthetic tissue at sites of initial mineralization. (f) Certain inhibitors of bioprosthetic tissue calcification (e.g., Al3+, Fe3+) are localized to the sites at which alkaline phosphatase is present. On the basis of these results, we hypothesize that alkaline phosphatase is a key element in the pathogenesis of mineralization of bioprosthetic tissue. In the present studies, we focused on the relationship of AP to early events in calcification, and the inhibition of both calcification and AP activity by FeCl3and AlCl3preincubations. Subdermal implants of glutaraldehyde pretreated bovine pericardium (GPBP) were done in 3‐week‐old rats. AP was characterized by enzymatic hydrolysis of paranitrophenyl phosphate (pnpp), and by histochemical studies. Calcification was evaluated chemically (by atomic adsorption spectroscopy) and morphologically (by light microscopy). The results of these studies are as follows: (a) Extractable AP activity is present in fresh but not glutaraldehyde‐pretreated bovine pericardial tissue. However, histochemical studies reveal active AP within the intrinsic devitalized cells of GPBP, despite extended glutaraldehyde incubation. (b) Extrinsic AP is rapidly adsorbed following implantation, with peak activity at 72 h (424 ± 67.2 nm pnpp/mg protein/min enzyme activity [units]), but markedly lesser amounts at 21 days (96.8 ± 3.9 units). (c) Simultaneously to the AP activity maximum, bulk calcification is initiated, with GPBP calcium levels rising from 1.2 ± 0.1 (unimplanted) to 2.4 ± 0.2 μg/mg at 72 h, to 55.6 ± 3.1 μg/mg at 21 days, despite a marked decline in AP activity at this later time. (d) Preincubation of GPBP in either FeCl3or AlCl3, at concentrations (0.1 M) which inhibited GPBP calcification, significantly reduce AP activity. We conclude that endogenous AP activity is present but not extractable in unimplanted GPBP fixed for extended periods. However, concurrent with the time of the onset of GPBP calcification in the rat subdermal model, AP adsorbed following implantation rises sharply to a maximum, thereby augmenting intrinsic enzyme. Preincubations of GPBP in either AlCl3or FeCl3not only prevent calcification, but also result in reduction in AP activity. These results strongly suggest that AP is an important cofactor in the mechanism of bioprosthetic valve mineralization and may be a fruitful target for anticalc

ISSN:0021-9304    

DOI:10.1002/jbm.820250802

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe presence of implanted biomaterials increases host susceptibility to infections. Once established, biomaterial‐mediated infections are resistant to treatment and persist until the device is removed. The objective of this work was to study the prevention of bacterial‐biofilm formation on polymeric implant (polyurethane) by controlled release of incorporated antibacterial agents (parabens). By embedding parabens in PU by the solvent‐cast method, matrices with amorphous dispersions (or solid solutions) were obtained. Release rate modulation was achieved by using different MW parabens and by a rate‐limiting membrane. Preliminaryin vitroantibacterial studies of both methyl and propyl paraben matrices exhibited significant inhibition ofStaphylococcus epidermidisbiofilm formation. Propyl paraben matrices (15 and 20% w/w drug load) decreased the number of colony‐forming units on PU surface to 2 × 104/mL, in comparison to 6 × 105on control polymers. This significant reduction was obtained without any effect on the number of viable bacteria in the suspension culture. This type of delivery system provides regional prophylactiv activity by creating a high local concentration of antibact

ISSN:0021-9304    

DOI:10.1002/jbm.820250803

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractVitronectin (VN) was competitively adsorbed with human serum albumin (HSA), fibrinogen (FGN), and fibronectin (FN) from binary component mixtures in order to compare the relative affinities of these proteins for various polymer materials. Competitive adsorption was monitored by incubating radiolabeled protein solutions inside 0.125‐in. i.d. tubing of the polymers, flushing with buffer, and measuring the adherent radioactiviy. Adsorption experiments at equal mass concentrations of the competing proteins revealed that VN comprises at least 75% by weight of the adsorbed protein when competitively adsorbed with HSA and approximately 50% by weight when competitively adsorbed with FGN and FN on all surfaces except a poly(ethylene oxide)‐based polyurethane where it comprised closer to 80 wt%. When VN was competitively adsorbed in the presence of increasing amounts of HSA, FGN, and FN, the amount of VN adsorbed on a weight basis was diminished the most by FGN. HSA had the least inhibitory effect at low bulk concentrations and FN had the weakest effect at higher bulk concentration levels. When HSA, FGN, and FN were competitively adsorbed in the presence of increasing amounts of VN, VN diminished their adsorption on a weight basis in the order: HSA>FN>

ISSN:0021-9304    

DOI:10.1002/jbm.820250804

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe aim of this study was to obtain more information about the bone reaction to titanium and hydroxypatite (HA)‐coated titanium implants during the first 3 months after implantation. Therefore, uncoated and coated implants were inserted into the tibia of rabbits for various implantation periods. The histological results demonstrated that although there were no marked differences in bony reaction at the cortical level to the different implant materials, HA‐coating appeared to induce more bone formation in the medullary cavity. It was also noted, that 3 months after insertion loss of coating thickness had occur

ISSN:0021-9304    

DOI:10.1002/jbm.820250805

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractPlates of calcite (CaCO3) were implanted in rabbit tibiae, and their biocompatibility and bonding ability to bone were studied. The plates were also implanted subfascially in rabbit muscle for 8 weeks, and changes on their surfaces in the body were examined. Contact microradiography and Giemsa surface stain demostrated direct bonding between calcite and bone without interpositions. The average failure load of the interface between calcite and bone was 4.11 kg, indicating an adequate strength of bonding. However, a Ca‐P‐rich layer, which formed on the surfaces of other bioactive ceramicsin vivo, was not detected by a scanning electron microscope‐electron probe x‐ray microanalyzer. Scanning electron micrographs of the surface of calcite implanted subfascially for 8 weeks showed marked degradation and a rough surface. However, the surface apatite layer was not detected by thin‐film x‐ray diffraction analysis and Fourier transform infrared reflection spectroscopy. Calcite is a biodegradable material that bonds to bone without a surface apatite layer. The mechanical bonding provided by the anchoring effect of the newly formed bone into the surface roughness of calcite is considered to be a major factor in calcite

ISSN:0021-9304    

DOI:10.1002/jbm.820250806

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractAn electron spin resonance (ESR) technique is employed to determine the free radical distribution in the articulating surfaces of retrieved acetabular cups and knee‐joint plateaus (retrieved after more than 6 years of implantation). Similar measurements made on samples prepared from cyclically stressed and unstressed cups, and on samples following oxidations in nitric acid and intralipid solutions provided sufficient data to gain more knowledge about the combined chemical and mechanical effects on PE free radicals during implantation. In UHMWPE free radicals are primarily initiated by gamma‐ray sterilization; however, during implantation, peroxy (scission type) free radicals are formed and reach a maximum concentration level (equilibrium state) due to oxidation by chemical (hemoglobin and/or synovial fluids) environment of the joints. Subsequently, due to frictional heating and stress in the loading zones, free radical reaction is accelerated and their number is reduced only in those areas. This is consistent with the observations of a temperature rise in acetabular cups duringin vitrofrictional wear stress tests andin vivotelemetry observations, as reported by others. Compared with the previously reported SEM micrographs the low‐free‐radical regions are correlated with high‐wear areas and the high‐free‐radical regions with the l

ISSN:0021-9304    

DOI:10.1002/jbm.820250807

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe calcium phosphate formation at the surface of bioactive glass was studiedin vitro. Glass rods and grains were immersed in different aqueous solutions and studied by means of scanning electron microscopy and energy dispersive x‐ray analysis. Surface morphological changes and weight loss of corroded grains were monitored. In‐depth compositional profiles were determined for rods immersed in the different solutions. The solutions used were tris‐buffer (trishydroxy‐methylaminomethane + HCl), tris‐buffer prepared using citric acid (trishydroxy‐methylaminomethane + C6H8O7·H2O), and a simulated body fluid, SBF, containing inorganic ions close in concentration to those in human blood plasma. It was found that the calcium phosphate formation at the surface of bioactive glassin vitroproceeds in two stages. When immersing the glass in tris or in SBF a Ca,P‐rich surface layer forms. This accumulation takes place within the silica structure. Later, apatite crystals forming spherulites appear on the surface. The Ca/P‐ratio of initially formed calcium phosphate was found to be about unity. It is proposed that this is due to bonding of phosphate to a silica gel. The surface is stabilized, i.e., leaching is retarded, by the rapid Ca,P‐accumulation within the silica structure before apatite crystals are observed on the surface. It is proposed that the initially formed calcium phosphate is amorphous and that the crystallization is initiated within the silica gel. The crystallizing surface provides nucleation sites for extensive apatite formation on the glass surface. In the presence of citrate no Ca,P‐accumulation occur at the glass surface, but soluble Ca‐citrate complexes form. By comparing the weight loss during corrosion in tris with that in the calcium and phosphate containing SBF, it is possible to establish whether the glass can induce apatite formation

ISSN:0021-9304    

DOI:10.1002/jbm.820250808

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractVarious models have been proposed to examine blood‐prosthetic materials interactions in terms of the effect of the prosthetic material on platelet structure and function, blood coagulation and fibrinolysis, and tissue infiltrates (cellular or acellular). In addition, these modeles have been used to examine the change in the graft surface over time. Particular difficulties in examining graft‐materials interactions include species differences, short residence time for blood‐materials interactions with commonly employed short grafts, and length of study limitations withex vivoshunts. In this paper we report a canine, carotid‐aorta subcutaneous prosthetic graft model. The specific advantages of this model are the length of the graft, which allows prolonged contact of blood with the prosthetic surface; the subcutaneous location of the graft, which allows repeated sampling of blood along the graft; and the healing characteristics of canine grafts. We selected the canine model because the healing characteristics are morphologically similar to those in humans in that endothelialization of the prosthetic surface is limited. Other models, such as the pig, are favored for use when examining blood coagulation, platelet, or fibrinolytic studies; however, these models can fully endothelialize prosthetic s

ISSN:0021-9304    

DOI:10.1002/jbm.820250809

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

ISSN:0021-9304    

DOI:10.1002/jbm.820250810

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

ISSN:0021-9304    

DOI:10.1002/jbm.820250801

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY