摘要:

AbstractThe purpose of this research was to evaluate the torsional strength and ductility of CP titanium in the as received condition, heat treated below the α → β transition temperature, and glass bead blasted. Results were compared to as‐received samples of implant quality 316L stainless steel. Little or no effect of any of the treatments was noted. The torsional strength of all titanium samples was comparable to 316L stainless and the torsional ductility of the titanium was significantly greater than 316L stainless (p<.01). These results are significantly different than those obtained when torsion testing bone screws of the same material. A hypothesis is proposed for the differences in these re

ISSN:0021-9304    

DOI:10.1002/jbm.820250302

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractRecent reports have shown that despite extensive preclinical testing, vascular grafts of biological origin undergo severe biodegradation and aneurysm formation after two or more years of implantation in man. The purpose of this study was to develop a laboratory model to quantitate and correlate the stability of crosslinked collagen graftsin vitroandin vivo. This resistance to biodegradation was assessed by measuring changes in suture pullout force and sample weight in response to controlled digestion with bacterial collagenase, in 0.5‐cm‐long cylindrical graft segments (chemically processed bovine carotid artery and human umbilical cord vein) that were implanted in the rat subcutis for 2 to 12 weeks. Scar tissue was removed from the explants by brief enzymatic digestion, a process that was inhibited when graft segments had become infected. Changes in dry weight were more consistent than were changes in wet weight; drying the graft segments had no effect on their degradationin vivoorin vitro. Intact cylindrical rings suffered somewhat less damage than did opened, flattened cylinders. Graft degradation increased markedly with implantation time, and was detected after only 3 weeks. We conclude that the rat subcutis model, when combined with controlled enzymatic digestion, first to remove scar tissue and then to challenge structural integrity, provides an accelerated assay by which to predict the stability of collagen vascular gra

ISSN:0021-9304    

DOI:10.1002/jbm.820250303

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractRelatively low‐molecular‐weight copolyesters of glycolic acid (GA) with lactones such as γ‐butyrolactone (BL), δ‐valerolactone (VL), and ϵ‐caprolactone (CL) were synthesized by copolycondensation without catalysts. The resulting copolyesters are intended as carriers for drug delivery systems. Copolyesters with approximately 85 mol% GA (number‐average molecular weight (Mn): 2900 ± 100) are crystalline and solid and show a parabolic‐typein vivodegradation pattern. Thein vivodegradation of amorphous‐pasty poly (GA/CL) (approximately 50/50 mol%) changed from parabolic‐type to lineartype to S‐type pattern as their molecular weight increased. A luteinizing hormonereleasing hormone agonist, D‐Leu,6desGly10‐LHRH ethylamide monoacetate (LHRH agonist), was incorporated into small cylinders with these copolyesters. An initial burst of LHRH agonist was observed for cylinders prepared with parabolic‐type degrading copolyesters, in contrast to a marked delay in LHRH agonist release for cylinders prepared with S‐type degrading copolyesters. The resulting daily dose of drug was maintained an approximately constant, though decreasing stepwise with time. For example, the daily amount of LHRH agonist releasedin vivofrom a cylinder prepared with poly(GA/CL) (50/50 mol%;Mn= 4500) was 61 ± 39 μg/day throughout an experimental period of 10 weeks with a corresponding pharmacol

ISSN:0021-9304    

DOI:10.1002/jbm.820250304

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractIn order to find a material that would improve cartilage repair, we investigated the use of porous polylactic acid matrix (PLA) with and without periosteal grafts in large articular defects in the medial femoral condyles of 18 New Zealand white rabbit knees. The right knee defect was filled with PLA, the left defect was filled with PLA and a periosteal graft. All animals were killed at 12 weeks. PLA allowed for thede novogrowth of neocartilage at the articular surface in all specimens and appeared to serve as a scaffolding for cell migration and matrix formation. Histologically, small amounts of PLA remained under the neocartilage with the majority being replaced by bone. PLA was a suitable carrier for periosteal grafts with a high graft survival rate (89%) and proliferation of a neocartilage which was thicker and more closely resembled articular cartilage than PLA alone knees. Biochemically, there was more type II collagen in the grafted knees (83%) than in the PLA alone knees (65%). Biomechanical tests of the neocartilage included equilibrium displacement, aggregate modulus, and apparent permeability. These tests were not statistically different between PLA alone and grafted knees. Comparison to normal cartilage indicated that the neocartilage was less stiff but had similar permeability. A consistent repair of the articular defects was achieved with and without periosteal grafts resulting in a tissue that closely resembled hyaline articular cartilage.

ISSN:0021-9304    

DOI:10.1002/jbm.820250305

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractA series of segmented polyurethanes (SPUs) containing various polyol soft segments was prepared and their resistance to oxidative degradation was investigated after aging in AgNO3solution. The SPU with the polyether soft segment showed a large reduction in mechanical strength after exposure to the oxidative environment. Surface cracking was often observed for these specimens. XPS measurements revealed that scission of the ether linkage occurs upon oxidation. The oxidative resistance of SPUs containing aliphatic hydrocarbon soft segments was significantly improved over the poly(tetramethylene oxide) (PTMO) based polyurethane.

ISSN:0021-9304    

DOI:10.1002/jbm.820250306

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractAn apatite‐ and wollastonite‐containing glass‐ceramic (A · W‐GC) has been reported to form a tight bond with living bone through an apatite layer formed on its surface. This layer is considered to be formed by dissolution of Ca2+and HSiO3−ions from the glass‐ceramic into the surrounding body fluids. In order to confirm this proposed mechanism for the surface reaction of A · W‐GC, three kinds of glass in the systems CaOSiO2, CaOSiO2CaF2, and CaOSiO2P2O5were implanted into the tibiae of rabbits for 3 or 8 weeks. Contact microradiography and SEM‐EPMA showed that all three kinds of glass formed a Ca, P‐rich layer in combination with a Si‐rich layer on their surfaces within 3 weeks and formed a direct bond with bone via these layers. The detaching test, performed 8 weeks after implantation, showed that the loads required to detach the implants from the bone were almost equal for the phosphorus‐free and the phosphorus‐containing glasses. It was concluded that even P2O5‐free CaO · SiO2glass formed a Ca,P‐rich layer on its surface and bonded tightly with living bone. If glasses and glass‐ceramics release at least Ca2+and HSiO3−ions, this would be sufficient for them to form the Ca,P‐rich layer on their surfacesin

ISSN:0021-9304    

DOI:10.1002/jbm.820250307

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper deals with the kinetics of tint transfer in soft contact lenses. A mathematical model taking into account both diffusion and chemical reactions is proposed and physicochemical parameters are determined. It is shown that bulk tinting is more effective in practice than surface tinting.

ISSN:0021-9304    

DOI:10.1002/jbm.820250308

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractIn vitromethods were developed to measure the air content of vascular graft walls and the thrombogenicity of this air. Gas content (volume %) of expanded polytetrafluoroethylene (ePTFE) grafts from different sources ranged from 75.5 ± 0.4% to 61.8 ± 0.3%. Exposure of Vitagraft ePTFE to a vacuum prior to saline immersion replaced 87.5% of the gas nuclei with saline (denucleation). Acetone and ethanol immersion produced 98.9% and 94.3% denucleation, respectively. Denucleation was essentially complete when vacuum exposure was followed by hydrostatic pressure treatment at 500 psig or greater. The influence of gas content on thrombogenicity was determined by immersing graft samples in whole canine blood and weighing the adherent thrombus. Denucleation significantly reduced adherent thrombus weight compared with control grafts (p<0.001). Air in Vitagraft walls was responsible for 84% of the adherent thrombus weight at four minutes. The described methods could be employed to assess the hemocompatibility of various biomaterial

ISSN:0021-9304    

DOI:10.1002/jbm.820250309

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractPrevious studies using light microscopy have demonstrated that micromachined grooved surfaces inhibit epithelial (E) downgrowth and affect cell orientation at the tissue/implant interface. This study investigates the ultrastructure of the epithelial and connective‐tissue attachment to titanium‐coated micromachined grooved, as well as smooth control, implant surfaces. V‐shaped grooves, 3, 10, or 22 μm deep, were produced in silicon wafers by micromachining, replicated in epoxy resin, and coated with 50‐nm titanium. These grooved, as well as smooth, titanium‐coated surfaces were implanted percutaneously in the parietal area of rats and after 7 days processed for electron microscopy. The tissue preparation technique used in this study enabled us to obtain ultrathin sections with few artifacts from the area of epithelial and connective‐tissue attachment. The histological observations demonstrated that E cells closely attached to, and interdigitated with, the 3‐μm and 10‐μm grooves. In contrast, E cells were not found inside the 22‐μm‐deep grooves and made contact only with the flat ridges between the grooves. As a general rule, fibroblasts (F) were oriented parallel to the long axis of the implants and produced a connective tissue capsule with 3‐μm and 10‐μm‐deep grooved surfaces as well as smooth surfaces. On the 22‐μm‐deep grooved surfaces, however, F inserted obliquely into the implant. The attachment of F to the titanium surface was mediated by two zones; a thin (≈︁20 nm), amorphous, electron dense zone immediately contacting the titanium surface, and a fine fibrillar zone extending from the amorphous zone to the cell membrane. As oblique orientation of F has been associated with the inhibition of epithelial downgrowth, micromachined grooved surfaces of appropriate dimensions have the potential to improve

ISSN:0021-9304    

DOI:10.1002/jbm.820250310

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractAlbumin and fibrinogen were competitively adsorbed onto dimethyldichlorosilane‐coated glass (DDS‐glass) and platelet activation was examined as a function of the surface fibrinogen concentration. The weight ratio of albumin to fibrinogen in the adsorption solution was varied from 10 to 700. Platelet activation was quantitated by the area and circularity of spread platelets. When the DDS‐glass was coated with albumin alone, platelets were only contact adherent and could not spread at all. After competitive adsorption of fibrinogen and albumin, however, platelets were able to spread on the surface. Platelet activation increased linearly as the surface fibrinogen concentration increased up to 0.02 μg/cm2. Platelets were able to activate fully if the surface fibrinogen concentration was 0.02 μg/cm2or higher, even though the surface was dominated by albumin. It appears that platelets can activate fully as long as only a small fraction (2–15%) of the surface is covered with tightly bound f

ISSN:0021-9304    

DOI:10.1002/jbm.820250311

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY