ISSN:0021-9304    

DOI:10.1002/jbm.820260102

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractTensile strength of the interface between hydroxyapatite (HA) and bone was tested. Scanning electron microscopy was used to observe the tensile failure mode and the morphological change of hydroxyapatite ceramic surface in bone. The porosity of hydroxyapatite is 14% and pore size less than 2 μm. After 2 weeks of implantation, the tensile strength of the interface is 0.72 MPa. After 4, 8, and 16 weeks, the average tensile strength stayed at 1.5 MPa. SEM showed that tensile failure occurred at the HA–bone interface at the second week, but after 4 weeks, the failure occurred between HA particles within the bulk, and not at the HA–bone interface. Calcified tissue was directly deposited on the HA ceramic surface and exits also in the micropores. Near the interface, sintered necks among HA ceramic particles were subjected to biodegrada

ISSN:0021-9304    

DOI:10.1002/jbm.820260103

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractAcoustic emission (AE) events and event intensities (e.g., event amplitude, counts, duration, and energy counts) were recorded and analyzed during fatigue loading of uncoated and porous‐coated Ti‐6A1‐4V AE source location, spatial filtering, event, and event intensity distributions were used to detect, monitor, analyze, and predict failures. AE provides the ability to spatially and temporally locate multiple fatigue cracks, in real time. Fatigue of porous‐coated Ti‐6A1‐4V is governed by a sequential, multimode fracture process of: transverse fracture in the porous coating; sphere/sphere and sphere/substrate debonding; substrate fatigue crack initiation; slow and rapid substrate fatigue crack propagation. Because of the porosity of the coating, the different stages of fracture within the coating occur in a discontinuous fashion, There‐fore, the AE events generated are intermittent and the onset of each mode of fracture in the porous coating can be detected by increases in AE event rate. Changes in AE event rate also correspond to changes in crack extension rate, and may therefore be used to predict failure. AE offers two distinct advantages over conventional optical and microscopic methods of analyzing fatigue cracks–it is more sensitive and it can determine the time history of damage progression. The magnitude of the AE event intensities increased with increasing stress. Failure mechanisms are best differentiated by analyzing AE event amplitudes. Intergranular fracture and microvoid coalescence generated the highest AE event amplitudes (100 dB), whereas, plastic flow and friction generated the lowest AE event amplitudes (55–65 dB). Fractures in the porous coating were characterized by AE event amplitudes o

ISSN:0021-9304    

DOI:10.1002/jbm.820260104

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe influence of polyurethane sulfonation on fibrinogen adsorption from plasma and on plasma coagulation has been investigated. Sulfonated polyurethanes were synthesized using a two‐step solution polymerization in which a diamino disulfonic acid was used as chain extender, thus incorporating sulfonate groups into the hard segments. Polymer molecular weights were determined by size exclusion chromatography and weight average values were in the range of 50,000 to 200,000. Equilibrium water uptake of solid polymer specimens was substantial and was found to increase with increasing sulfonate content. Titration of sulfonate groups allowed an estimate of the retention of free sulfonate in the polymers which ranged from 50 to 85%. Loss of free sulfonate is attributed to reaction of isocyanate with sulfonate groups during chain extension. Both surface chemistry and hydrophilicity were assessed using a combination of ESCA and water contact angle measurements. The ESCA data indicate enrichment of soft segment in the surface. Contact angles show increasing hydrophilicity with increasing sulfur content. Fibrinogen adsorption from plasma to the sulfonated polyurethane surfaces was studied using radioiodine labeling. Fibrinogen surface concentration was found to increase strongly as sulfonate content increased. Fibrinogen adsorption behavior is quite different from that of conventional unsulfonated polyurethanes in the sense that the adsorption levels are much higher and there is little displacement of initially adsorbed fibrinogen (Vroman effect). The data are interpreted i n terms of two mechanisms: fibrinogen uptake (i.e., absorption) into a polymer–plasma “gel” hypothesized to exist at the surface of these materials, and adsorption in the usual sense. Thrombin times of human plasma in which polymer particles were suspended were prolonged and were found to increase with increasing sulfonate content of the polymers, suggesting that sulfonate groups confer a measure of anti‐coagulant activity on these

ISSN:0021-9304    

DOI:10.1002/jbm.820260105

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractA nonionic, high‐water‐content, highstrength hydrogel based on N‐vinyl pyrrolidinone (NVP) and a novel hydrophilic‐bulky monomer, 4‐t‐butyl‐2‐ hydroxycyclohexylmethacrylate (TBCM), was developed. The TBCM was prepared in three relatively simple, high‐yield steps. The copolymerization of NVP with varying concentrations of TBCM resulted in transparent hydrogel films possessing a wide range in mechanical and physical properties. A copolymer composition of 91.7 parts NVP, 8.0 parts TBCM, and 0.3 parts ethylene glycol dimethacrylate (EGDMA) gave a transparent, flexible film possessing a water content of 86%, a modulus of 130 g/mm2, and a tear strength of 3.4 g/mm. In contrast, a copolymer composition of 49.7 parts NVP, 50 parts TBCM, and 0.3 parts EGDMA gave a transparent, hard hydrogel film possessing a water content of 26% and a modulus of 86,000 g/mm2. All of the high‐water co‐polymer compositions developed resulted in lysozyme uptake typical of nonionic high‐water‐content hydrogels and oxygen permeability levels greater than 50 (cm3O2(STP) · cm)

ISSN:0021-9304    

DOI:10.1002/jbm.820260106

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractA scanning electron microscopy study is reported of the nature and morphology of fracture surfaces in pyrocarbons commonly used for the manufacture of mechanical heart‐valve prostheses. Specifically, silicon‐alloyed low‐temperature‐isotropic (LT1)‐pyrolytic carbon is examined, both as a coating on graphite and as a monolithic material, following overload, stress corrosion (static fatigue), and cyclic fatigue failures in a simulated physiological environment of 37°C Ringer's solution. It is found that, in contrast to most metallic materials yet in keeping with many ceramics, there are no distinct fracture morphologies in pyrocarbons which are characteristic of a specific mode of loading; fracture surfaces appear to be identical for both catastrophic and subcritical crack growth under either sustained or cyclic loading. We conclude that caution should be used in assigning the likely cause of failure of pyrolytic carbon heart‐valve components using fractographic

ISSN:0021-9304    

DOI:10.1002/jbm.820260107

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractAdsorption of fibrinogen onto hydrophobic and hydrophilic quartz surfaces was studied by ellipsometry and transmission electron microscopy (TEM) of negatively stained proteins. The initial adsorption at the hydrophobic surface, measured by ellipsometry, can be described by an apparent forward rate constant klof 2 × 104M−1s−1. This constant was time‐dependent and is therefore considered as a rate coefficient. The apparent forward rate coefficient of adsorption to a hydrophilic surface was both time‐dependent and concentration‐dependent, indicating a history‐dependent process of adsorption. Plateau levels of adsorption were concentration‐dependent and lower at the hydrophilic quartzsur face (1.2 pmol/cm2) than at the hydrophobic surface (1.8 pmol/cm2). These surface concentrations correspond to rather tight‐packed monolayers of molecules adsorbed end‐on. The initial desorption can be described by a first order rate constant (k−1≈10−4s−1), down to 80‐90% of the initial surface concentration. The dissociation rate then decreased (k−1≈10−6s−1) resulting in an apparently stable level of adsorbed protein. Slow changes of the binding strength of adsorbed proteins was seen during 24–72 h adsorption time. Deviations from an ideal equilibrium isotherm were seen both in the time dependence and as concavities in a Scatchard plot, suggesting intermolecular cooperativity. At low bulk concentrations a heterogeneous distribution of fibrinogen molecules was found at the surface below monolayer coverage. The supramolecular structure was characterized by the formation of end‐to‐end dimers and trimers laying down at the surface. At higher surface concentration adsorbed molecules showed polycrystalline structure with repeated nearest neighbordistances at 16 nm. The distribution of adsorbed fibrinogen molecules indicates that surface‐adsorbed fibrinogen may form a two‐phase system, containing significant amounts of water. The atypical kinetics and concentration dependence of fibrinogen adsorption may thus be due to properties of a two‐dimensional phase

ISSN:0021-9304    

DOI:10.1002/jbm.820260108

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractTricalcium phosphate (TCP) is an osteoconductive bioceramic which, when applied to a porous‐coated prosthesis, may enhance osseous ingrowth and mechanical stability. TCP plasma‐sprayed and unsprayed porous‐coated tibial intramedullary rods were bilaterally implanted in seven adult rabbits. All rabbits were killed at 12 weeks. Pull‐out tests were performed on 4 rabbits while all were evaluated histologically for osseous response and adverse tissue reaction. TCP‐sprayed implants showed significantly greater osseous ingrowth in comparison to unsprayed implants. Neither implant type exhibited adverse tissue reactions. Average pull‐out strengths were 69 lb for treated rods and 72 lb for controls (p>0.05); quality of fit for all pull‐out specimens except one was deemed poor. We conclude that plasmasprayed TCP enhances osseous ingrowth into porous‐coated devices. However, our data further suggest that enhanced ingrowth may not always lead to en

ISSN:0021-9304    

DOI:10.1002/jbm.820260109

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractSmall‐diameter (<6 mm) clinically available vascular grafts often fail due in part to the inherent thrombogenicity of artificial polymers. Transplantation of endothelial cells onto the lumen of these vascular grafts has been suggested as one method to overcome this thrombogenicity. We have developed a compliant polyurethaneurea (PEUU) 4‐mm graft with a luminal surface modified by a glow discharge gas plasma. Autologous microvessel endothelial cells were isolated from canine falciform ligament fat, were transplanted onto the luminal surface of the grafts using an intraoperative isolation and sodding technique, and both endothelial‐cell‐treated and non‐cell‐treated grafts were placed as bilateral carotid interposition grafts in a canine model. After 5 weeks of implantation, explanted control (non‐cell‐treated) grafts exhibited a deposition of platelets, white cells and fibrin characteristic of a thrombogenic surface. MVEC sodded grafts exhibited a multicellular lining within but distinct from the lumen of the PEUU graft. The blood‐contacting surface of this lining exhibited an antithrombogenic endothelial cell monolayer. We suggest that the PEUU graft supported the initial deposition of MVEC and development of an endothelial cell lining. During the 5 weeks of implantation this lining continued to proliferate and detached from the PEUU graft substratum. The final neocellular lining exhibited a luminal diameter and histological features similar t

ISSN:0021-9304    

DOI:10.1002/jbm.820260110

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe commonly used method for quantitative evaluation of the strength of a bone‐implant interface is the push‐out test. In order to give an impulse to standardization and to gain more insight in the biomechanics of the push‐out test, a finite element analysis of this test was performed. This study focused on the influence of test conditions on the push‐out results. The influence of the following four parameters on the interface stress distribution was tested: (a) clearance of the hole in the support jig, (b) Young's modulus of the implant; (c) cortical thickness; and (d) implant diameter. The distance between the implant and the support jig turned out to be very critical for the occurrence of peak stresses in the interface. Variations of the Young's modulus of the implants resulted in a wide range of interface shear stresses. Variation of the cortical thickness showed a reciprocal relationship between cortical thickness and interface shear stress. However, the interface stress distribution remained uniform under the specific test circumstances. These findings also hold for variations in implant diameter. The present investigation shows that the clearance of the hole in the support jig, and the Young's modulus of the implant are parameters which most strongly influence the interface stress distribution. The clearance of the hole in the support jig is the most critical parameter, but also the parameter that can be controlled most easily. Lack of standardization with regard to these parameters can lead to uninterpretable test results. It is recommended that the clearance of the hole in the support jig is at least 0.7 mm and that push‐out results are only compared with each other when materials with similar Young's modulus are

ISSN:0021-9304    

DOI:10.1002/jbm.820260111

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY