摘要:

AbstractThe use of porous metallic coatings for fixation of total joint prostheses by bone ingrowth has become a widespread alternative to fixation with PMMA bone cement. However, concerns about such coatings include long‐term effects of metal ion release, potential coating loss, and decreased substrate fatigue strength. The biological fixation capability of a nonporous, high‐integrity plasmasprayed CoCr coating with low surface area was compared to a conventional sintered bead coating in goat cortical and cancellous bone sites after 8 and 16 weeks of implantation. Histological evaluation showed substantial variations in fixation quality between individual animals and between surgical sites with no consistent difference between implant types. Shear testing of bonelimplant interfaces showed that although conventional porous coating exhibited higher overall average shear strengths in cortical bone sites at both time periods, the differences were not statistically significant. In cancellous sites, the average shear strengths achieved with conventional porous and plasmasprayed coatings were essentially equal. Analysis using average paired differences, however, revealed that when porous and plasma‐coated implants are placed in identical sites of contralateral limbs, the plasma coatings consistently yielded higher shear strengths in cancellous bone sites at the later time period. Since current design theory for biological fixation favors metaphysical fixation, this surface may offer potential advantages over conventional porous coa

ISSN:0021-9304    

DOI:10.1002/jbm.820260502

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractA polyvinyl alcohol hydrogel (PVA) was reacted with a CI8 isocyanate at 80°C in dimethyl formamide (DMF) in order to improve the platelet reactivity of the hydrogel through an inf hence on albumin adsorption or retention. A C, isocyanate was used as a control. Surface coverage by XPS appeared to be ∼100% for both C4and C18modified surfaces, although the limited solubility of C18isocyanate in DMF may have resulted in a nonuniform surface. Relative to PVA or the solvent treated control, octadecylation resulted in increased albumin adsorption (from a single protein solution) and increased retention when the adsorbed albumin was exposed to a fibrinogen solution. However, octadecylation did not obviate the platelet reactivity problem in preliminary studies: systemic platelet counts were reduced by about half over 4 days in a canine AV shunt experiment and the initial rate of platelet destruction for C IR‐PVA was greater (36%/ day) even than for the solvent‐treated PVA. Surprisingly in preliminary studies butylation of PVA resulted in little or no thrombocytopenia and did not appear to increase significantly the fractional rate of platelet destruction relative to the shunt only blank. It is presumed that the nonspecific effect of alkylation (independent of chain length) was the dominant contribution to the reduced platelet reactivity. A similar effect of C18‐PVA presumably would have been observed had the limited solubility of C18isocyanate not precluded a uniform surface

ISSN:0021-9304    

DOI:10.1002/jbm.820260503

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractFiber reinforced polymer (FRP) composites are being developed as alternatives to metals for structural orthopedic implant applications. FRP composite fracture behavior and environmental interactions are distinctly different from those which occur in metals. These differences must be accounted for in the design and evaluation of implant performance. Fiber/ matrix interfacial bond strength in a FRP composite is known to strongly influence fracture behavior. The interfacial bond strength of four candidate fiber/matrix combinations (carbon fiber/polycarbonate, carbon fiber/polysulfone, polyaramid fiber/polycarbonate, polyaramid fiber/ polysulfone) were investigated at 37°C in dry andin vivosimulated (saline, exudate) environments. Ultimate bond strength was measured by a single fiber‐microdroplet pull‐out test. Dry bond strengths were significantly decreased following exposure to either saline or exudate with bond strength loss being approximately equal in both the saline and exudate. Bond strength loss is attributed to the diffusion of water and/or salt ions into the sample and their interaction with interfacial bonding. Because bond degradation is dependent upon diffusion, diffusional equilibrium must be obtained in composite test samples before the full effect of the test environment upon composite mechanical behavior can be determ

ISSN:0021-9304    

DOI:10.1002/jbm.820260504

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractA transparent poly (ether urethane) (PEU) was considered for use as a foldable intraocular lens material. The PEU was found to possess excellent mechanical, optical, and surface characteristics for this application. In uitro hydrolytic and ultraviolet aging studies suggested the PEU to be tolerant to conditions simulating 3–10 years of normal intraocular exposure. Different behavior was obtained, however, from intraocular and subcutaneous implantation of the PEU. After 6 months of intraocular exposure in the feline model, prototype PEU lenses had lost most or all of their optical resolving power. SEM analysis demonstrated scattered pitting and cracking on the lens surfaces. Degradation was found to be more extreme after as little as 30 days of subcutaneous exposure in rabbits. Severe pitting over the entire surface of implanted flat PEU specimens was observed by SEM. Macroscopic examination showed the samples to be frosty in appearance. It was postulated that the subcutaneous implant environment provides an accelerated in uivo model for materials intended for intraocular use. A minimum acceleration of 6–10X was estimated on a preliminary basis. The PEU studied here was found to be unsuitable for use as a foldable intraocular lens mater

ISSN:0021-9304    

DOI:10.1002/jbm.820260505

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe long‐term (1‐ and 2‐year) adverse tissue responses including tumor formation by subcutaneous implanation of polyurethanes (PUS) and silicone (Sil) films intorats were compared. The weight‐averaged molecular weights (Mw) of the PUS prepared from 4,4′‐diphenylmethanediisocyanate, poly (tetramethyleneglycol) of M, = 1000 and 1,4‐butanediol are 220,000 (U‐4), 124,000 (U‐6), and 55,600 (U‐8). The 50:50 mixed film of U‐6 and silicone (U‐b/sil) was prepared by rollmixing of the noncured silicone and the U‐6 solution followed by evaporation of the solvent and heat‐curing at 70°C. The tissue responses around implants were classified into four groups as follows: (A) tumor, (B) atypical cell proliferation accompanied by preneoplastic changes, (C) cell proliferation without preneoplastic changes, (D) no obvious responses. In both implantation periods, the PUS gave higher incidents of the adverse responses including tumor formation in comparison to Sil. No significant molecular weightdependent trend was found in a 1‐year study using U‐4, 6, and 8. Significant PU‐dose‐dependent trends were found in a 2‐year study: the total active incidence (A + B + C), U‐6(22/29)>U‐6/si1(11/29)>sil(7/28); tumor incidence (A), U‐6(11/29)>U‐6/si1(2/29) = si1(2/28). No detectable amounts of 4,4′‐methylenedianiline (MDA) were found in the PUS. The methanol extracts from the PUS were negative in the mutagenicity tests. These indicate no relationship between the tumor formation by the PU films and the mutagenicities of the

ISSN:0021-9304    

DOI:10.1002/jbm.820260506

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractFracture surfaces of both monotonic and fatigue loaded bone cement samples were examined to investigate the fractographic characteristics of PMMA. Classic cleavage step river patterns were observed on all monotonically loaded samples, running downstream in the direction of crack propagation. AH fatigue cracks initiated at internal pores and the direction of crack propagation of many cracks was discernible. Porosity, pore size, and pore size distribution were found to affect the crack initiation and fatigue behavior of bone cement. Statistical analysis revealed a strong negative correlation between twodimensional porosity present on the fracture surfaces and the cycles to failure. The fractographic observations of these fatigue samples elucidate one reason why porosity reduction by centrifugation or vacuum mixing increases the fatigue life of PMMA bone cement.

ISSN:0021-9304    

DOI:10.1002/jbm.820260507

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe effect of time at 600°C and of small additions of Al2O3and B2O3on the sintering of two composite materials of (1) hydroxylapatite (C ∼I O (P O ∼)∼(O H )∼) and bioactive glass (SiO2‐CaO‐P2O5‐Na2O) or (2) rhenanite (CaNaPO,) and bioactive glass were studied. Scanning microscopy, quantitative EDX, x‐ray diffraction, helium gas density measurements, and diametral measurements were performed on the resulting composites. No reactions were observed with the SEM or XRD between the hydroxylapatite particles and the glass matrix within sufficient sintering times to achieve maximum density. (∼) The rhenanitecontaining composites were observed to form Na2O2CaO3SiO2crystals by x‐ray diffraction, probably as a result of dissolution of the rhenanite particle surfaces into the glass phase, the crystals formed in the glass or at the interface of the glass, and the ceramic particles. However, within the short sintering times needed to achieve maximum density the rhenanite particles remained mostly intact. The rhenanitecontaining materials gave better results than the hydroxylapatite‐containing materials. The glass composition had a great effect on the

ISSN:0021-9304    

DOI:10.1002/jbm.820260508

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThrombin production in plasma in contact with various materials was consistent with a first‐order autocatalytic model (d[T]/dt = k,[T]; [TI] = thrombin concentration, t = time, k, = thrombin production rate constant) since the initial portion of a semilogarithmic plot of thrombin concentration against time was linear. Thrombin concentration was measured in clotting plasma (phospholipid enhanced or plateletrich plasma) using fluorogenic substrate (BMCA) by aliquot sampling at various intervals or more conveniently by monitoring cumulative fluorescence. The latter was generated by the action, on BMCA incubated in the clotting plasma, of the thrombin as it was generated. The thrombin concentration was determined from the first derivative of the S‐shaped cumulative fluorescence curve. kp, was greater for glass (7.92 × 10−3cm/than) for the other materials (polypropylene, polystyrene, polyethylene and PVA; kp, ∼3.1 × 10−3cm/s) in plasma with cephalin without flow. A kp, for heparin PVA could not be determined since the thrombin concentration was too low to be quantified. A larger difference between polyethylene and PVA was noted with platelet‐rich plasma without flow while lower values (1.0 × cm/s) were noted in a flow system but at a higher surface to volume ratio. The first‐order rate constant can be used in simple models relating production of thrombin at a wall of a tube to its mass transfer away from the wall in flowing blood. One such model predicts that the concentration of thrombin at the wall should become infinite at the point in the tube when the mass transfer coefficient equals kp. According to this model, kpon the order of cm/s would be a useful target for a nonthrom

ISSN:0021-9304    

DOI:10.1002/jbm.820260509

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

ISSN:0021-9304    

DOI:10.1002/jbm.820260501

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY