摘要:

AbstractAnex vivoshunt, established in dogs between both femoral arteries and right atrium, has been used to quantify the platelet deposition on six prosthetic materials used in the construction of cardiovascular prostheses: highly porous knitted Dacron (intervascular HP 800, 1400 mL/cm2/min/120 mm Hg), low‐porosity woven Dacron (intervascular LP 200, 200 mL/cm2/min/120 mm Hg), double velour knitted Dacron, Avcothane 51 elastomere, and the mesothelial and epipericardial surfaces of bovine pericardium. In the search for a method to prevent platelet thrombi formation on these materials, we studied four groups of dogs: group 1 (control), group 2 (5 mg/kg body weight (BW)/day acetylsalicylic acid), group 3 (20 mg/kg BW/day acetylsalicylic acid), and group 4 (5 mg/kg BW/day acetylsalicylic acid plus 5 mg/kg BW/day dipyridamole). Platelets were labeled with111In‐oxine. The least thrombogenic material was Avcothane 51 elastomere. The only effective treatment for reduction of platelet deposition on the six materials was 5 mg/kg BW/day of acetylsalicylic acid. The dose used in group 3 only decreased the deposition of platelets on three of the six materials studied. The treatment employed in group 4 did not significantly reduce the deposition of platelets on any of the materials when compared with the control group. © 1994 John Wiley&Sons,

ISSN:0021-9304    

DOI:10.1002/jbm.820280102

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractPure soluble silica prepared by a sol‐gel method induced bone‐like hydroxyapatite formation onto its surface when the silica was immersed in a simulated body fluid (SBF), whereas silica glass and quartz did not. This finding directly supports the hypothesis that hydrated silica plays an important role in biologically active hydroxyapatite formation on the surfaces of bioactive glasses and glass‐ceramics, which leads to bone‐bonding. Gel‐derived titania is also a hydroxyapatite inducer because of its abundant TiOH groups. These results provide further insight into the unique osseointegration of titanium and its alloys. It is suspected that gel‐derived titania develops an apatite layer by taking calcium and phosphate from the body fluid, thus producing bonebonding. Although sufficient AlOH groups may remain in the alumina gel, they do not serve to initiate apatite generation when immersed in SBF. This phenomenon explains the fact that an intermediate fibrous tissue is usually found to separate the alumina implant from bone. One may infer that both abundant OH groups and negatively charged surfaces of gel‐derived silica and titania are important for hydroxyapatite induction. Material which possesses and / or develops both a negatively charged surface and abundant OH groups in a physiologically‐related fluid is most likely to be an efficient apatite inducer. Such materials are suitable candidates to serve as bone‐bonding biomaterials. © 1994 Jo

ISSN:0021-9304    

DOI:10.1002/jbm.820280103

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractPoly‐L‐lactide (PLLA) plates, 20 × 10 × 1 mm in size, with flat surfaces, were implanted into 50 young male Wistar rats subcutaneously, and the incidence of tumors for 2 years under specific pathogen‐free (SPF) conditions was evaluated. Tumors arose in 22 rats (at the implant sites in 20, and distant from the implantation site in 2). As a control, plates of medical‐grade polyethylene of the same shape were implanted into 50 rats. Tumors appeared in 23 of these rats (21 at the sites of the plates, and 2 ectopically). In 30 rats given sham operations, no tumors appeared in the 2 year observation period. Histologically, all the tumors were mesenchymal malignant tumors resembling fibrosarcoma or malignant fibrous histocytoma (MFH) in humans. In 6 of the PLLA tumors and 3 of the PE tumors, bone formation was observed. There was no significant difference between the incidence of tumors caused by PLLA plates and that of tumors caused by medical‐grade polyethylene plates. Macroscopically, PLLA plates retained their initial shape for 2 years. Scanning electron microscopy revealed small holes on the surfaces of the plates, and their molecular weight was reduced to 8% of the initial value. © 1994 John Wil

ISSN:0021-9304    

DOI:10.1002/jbm.820280104

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractComposites comprised of calcium deficient hydroxyapatite (CA/P = 1.5) and gelatin form in about 4 h at 38°C. The solid reactants used are CaHPO4and Ca4(PO4)2O and the liquid reactant is gelatin solution. The reaction forming hydroxyapatite occurs in several steps. Based on the measurement of heat liberation, there is an initial period where the reaction rate is low. This is followed by a period of constant reaction until the reaction is complete. Analysis of the variation in pH shows that hydroxyapatite formation occurs at a steady state pH near 8.2. Analyses of the evolution of crystalline phases indicates that Ca4(PO4)2O is consumed prior to complete reaction resulting in a phase assemblage of hydroxyapatite (CA/P>1.5) and CaHPO4. Further reaction results in compositional adjustments in hydroxyapatite as CaHPO4is consumed. Microstructurally, the composites which form consist of clusters of hydroxyapatite embedded in a gelatin network. The presence of gelatin does not influence the morphology of the hydroxyapatite which forms nor does it retard its rate of formation. © 1994 John Wiley&Sons, In

ISSN:0021-9304    

DOI:10.1002/jbm.820280105

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe purpose of this study was to characterize the physicochemical properties of calcific deposits that cause the failure of tissue‐derived heart valve bioprostheses. This was done in an effort to understand the mechanism of pathologic biomineralization in the cardiovascular system and potentially prevent deterioration of bioprostheses. Calcific deposits taken from 10 failed bioprosthetic valves that had been implanted in patients for 2–13 years were characterized by chemical analysis, x‐ray diffraction, FTIR spectroscopy, scanning electron microscopy, polarized light microscopy, and solubility measurements. The combined results identified the biomineral as an apatitic calcium phosphate salt with substantial incorporation of sodium, magnesium and carbonate. The average Ca/PO4ratio for this “young” pathologic biomineral was ∼1.3, considerably lower than ∼1.7 found in mature atherosclerotic plaque biomineral and mature skeletal biomineral, both of which approximate hydroxyapatite in composition. Deproteinated calcific deposits from bioprostheses had thermodynamic solubilities comparable to those of both atherosclerotic plaque, typical pathologic biomineral and hydrolyzed octacalcium phosphate (OCP, Ca4H(PO4)3· 2.5 H2O), a proposed precursor phase to biomineral apatite. This later finding, together with chemical composition and structrual details of the bioprostetic deposits themselves, supports a mechanism of cardiovascular calcification in which OCP plays a crucial role in the formation of the final apatitic phase. This suggests an approach toward prevention of bioprosthetic tissue calcification through control of the formation of the kinetically favored OCP precursor and/or its transformation into bioapatite. © 1994 John Wiley&Sons, Inc.This article is a U.S. Government work and, as such, is in the public domain in the United St

ISSN:0021-9304    

DOI:10.1002/jbm.820280106

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractUniaxial tensile tests were performed on glutaraldehyde fixed bovine pericardial strips prepared from chemically modified pericardial samples. These samples originated from an area which demonstrated anisotropic mechanical properties in the native material and which is suitable for the construction of leaflets for pericardial bioprostheses. After glutaraldehyde fixation the tissue had retained its anisotropicity in stiffness and strength in two orthogonal directions. In the range of the functional stresses for a heart valve leaflet (>1 MPa) the unconstrained fixation regime had modified the initial anisotropic elastic behavior into a more isotropic one. The implications of these findings are that leaflets manufactured from bovine pericardium can be made to resemble, to a degree, the well known anisotropy found in two orthogonal direction in natural human heart valve leaflets, or porcine bioprosthetic heart valve leaflets. © 1994 John Wiley&Sons, Inc

ISSN:0021-9304    

DOI:10.1002/jbm.820280107

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractCurrentin vitrobiocompatibility methods do not evaluate the degradation of biomaterials after contact with enzymes that might be present in the oral or systemic environment. In this study, two methods ofin vitroenzyme degradation and a method for the separation of the degradative products by high performance thinlayer chromatography (HPTLC) are reported. In the first method two dental adhesives, Scotchbond and Scotchbond II, and two dental composites, Helimolar and P‐50, were evaluated. These materials were incubated with four different enzymatic preparations for periods of up to 72 h. The enzymes were lipase, esterase, and liver enzyme extracts from both mouse and rat. Chloroform soluble products extracted from the aqueous phase were examined by HPTLC for decomposition products resulting from enzyme activity. The second method was similar, but analyzed the aqueous fraction directly without chloroform extraction. In this method five dental restorative materials, P‐50, P‐30, Scotochbond II, Silux, and Silux Plus, were incubated with a nonspecific porcine liver esterase. In addition to the polymerized biomaterials. Monomers containing methacrylic acid units were also hydrolyzed with esterase and analyzed by ion chromatography to establish the sensitivity of the enzyme simulator. Each biomaterial presented thin‐layer zones not present before enzymatic action. These experiments provide support that aqueous enzymatic action may facilitate the hydrolytic weakening of polymeric biomaterials. © 1994 John Wiley&S

ISSN:0021-9304    

DOI:10.1002/jbm.820280108

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractHydroxyapatite‐glass‐titanium (HA‐G‐Ti) functionally gradient composite plates bound face‐to‐face by nylon wire were soaked in a simulated body fluid. The gap between the plates was filled with the precipitates after soaking for 6 months, and a tight chemical bond was formed between them. Field emission‐type (FE) scanning electron microscopy (SEM) and transmission electron microscopy observations revealed that the growth rate and morphology of the precipitates differed widely from the outside portion to the inside one on the surface region of the composite plates. In the portion relatively near the outside, the mutually bonded portion, needle‐like precipitates with preferred orientation to the c‐axis were markedly observed. From the results of Fourier transform infrared spectroscopy and energy dispersive x‐ray microanalysis, it was found that the precipitates were Ca‐deficient carbonate apatite with low crystallinity. On the other hand, HA‐G‐Ti composite rods were implanted in the femur of beagle dogs for 3 months. FE‐SEM observations demonstrated that needle‐like precipitates were deposited on both the surfaces of the composite and bone at the portion having a narrow gap, about 0.1–0.2 mm between them prepared deliberately before implantation. It was found that both the morphologies and the composition of the precipitatesin vivowere similar to thosein vitro.It is concluded that the HA particles on the surface of the composite act as nucleation sites for precipitation in physiologic environments, whereas the glass matrix is independent to

ISSN:0021-9304    

DOI:10.1002/jbm.820280109

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractQuantitative description of foreign body giant cell (FBGC) formation on implanted polymer surfaces as a function of time can conceivably correlate cell adhesion with polymer properties and possibly predict the behavior of the polymerin vivo.In the present study, the formation of FBGCs on various biomedical polymers was quantified by two parameters: the density of adherent macrophages present initially that participate in FBGC formation (d0) and the rate constant for cell fusion (k); both kinetic parameters were used to calculate the time‐dependent FBGC density (dfc).The materials used were: three Pellethane poly(etherurethanes) (PEUs) varying in weight percent of hard segment, one poly(etherurethane urea) (PEUU), and NHLBI‐DTB primary reference materials: low density polyethylene (LDPE), silica‐free polydimethylsiloxane (PDMS). The results indicated that up to 5 weeks of implantation, FBGCs were formed from the fusion of one population of adherent macrophages present by 3 days post‐implantation. Furthermore, only a small fraction (<8%) of this initial adherent macrophage population participated in FBGC formation. Based on the results of previous studies and the current study, it was concluded that increase in PEU hard segment weight percent, surface hardness and hydrophobicity increased total protein adsorption and effectively increased d0and dfc. No further correlations between the material properties of all polymers and the cell kinetics can be made at this time. However, this study demonstrated that macrophage adhesion and FBGC formation can be quantified with the cell fusion model, and are modulated by various polymer properties. © 1994 John Wiley&S

ISSN:0021-9304    

DOI:10.1002/jbm.820280110

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractParticulate wear‐debris are detected in histiocytes/macrophages of granulomatous tissues adjacent to loose joint prostheses. Such cell‐particle interactions have been simulatedin vitroby challenging macrophages with particles dosed according to weight percent, volume percent, and number of particles. Each of these dosage methods has inherent shortcomings due to varying size and density of challenging particles of different compositions. In this study we challenged P388D1macrophages with titania and polystyrene particles (>2 μm), with dosage based on the ratio of the surface area of the particles to the surface area of the cells. The effect of size and composition on (1) the bone resorbing activity, (2) fibroblast proliferation, and (3) secretion of IL‐1 and PGE2was determined.Macrophage response to particulate debris appears to be dependent on particle size, composition, and dose as given by surface area ratio. P388D1macrophages challenged with titania particles released IL‐1, but did not stimulate fibroblasts. Inhibition of macrophage DNA synthesis at higher surface area ratios suggests cell damage or death. Particle‐stimulated cells increased bone resorption up to 125% of controls but released only basal levels of PGE2.Macrophages stimulated by wear particles are expected to synthesize numerous factors affecting events in the bone‐implant interface. Using the concept of surface area ratio allows us to study and compare such cellular responses to wear particles in a standardized manner. © 1994 John Wi

ISSN:0021-9304    

DOI:10.1002/jbm.820280111

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY