摘要:

AbstractThe diffusivities of thrombin and antithrombin III in a heparin–polyvinyl alcohol hydrogel were estimated and used to demonstrate that diffusion limits the effectiveness of the immobilized heparin in the interior of such hydrogels. Diffusivities were calculated from permeabilities and partition coefficients measured with films in a diffusion chamber apparatus. The diffusion coefficients were estimated to be 6 ± 4 × 10−8cm2/s for thrombin and 4 ± 2 × 10−8cm2/s for antithormbin III in 10% gel membranes with or without immobilized heparin. Using the diffusivity of thrombin and a Thiele‐type modulus, the effectiveness factor of a spherical heparin–PVA bead used to accelerate the inactivation of thrombin by antithrombin III was found to be 4–9% (diameter range 250–105 μm). While indicating that diffusion of thrombin limited the full utilization of the immobilized heparin, these values for the effectiveness factor could not completely account for the low apparent heparin activity (0.2%) in a thrombin time test of heparin–PVA “beads” (J. Biomed. Mater. Res.,17, 359 (1983)). Other factors such as the immobilization chemistry or the diffusion of thrombin–antithrombin III complex must be considered for a full explanation of

ISSN:0021-9304    

DOI:10.1002/jbm.820220802

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe hydrolytic stability of microporous Mitrathane polyetherurethane urea vascular prostheses has been evaluated at pH 7 and pH 9, at 37°, 60°, and 80°C for time periods of up to 968 days. Mechanical strength was evaluated using a hydrodynamic burst test and surface chemical changes by x‐ray photoelectron spectroscopy. The samples held at 80°C showed the greatest mechanical strength loss which corresponded to the hydrolysis of the urethane groups. It was concluded that the gross in vivo surface degradation of Mitrathane prostheses, observed after six months, could not have been caused by simple chemical hydrolysis alone, as the polymer was found to be stable at 37°C for at least 11

ISSN:0021-9304    

DOI:10.1002/jbm.820220803

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe objective of this study is to alter the fiber morphology of a linear aliphatic polyester, polyglycolic acid, by annealing treatment and to examine the changes of its degradation properties. The annealing was done at 150°C, 170°C, and 190°C, and the specimens were annealed in four different strained conditions, freely hung, 0, 1, and 10%. After annealing treatments, the specimens were subject toin vitrohydrolytic degradation by immersing them in phosphate‐buffer solution of pH 7.4 at 37°C for up to 28 days. The thermal properties and gross morphology of the specimens were obtained. It was found that annealing treatments resulted in initial higher levels of crystallinity, which, in turn, influenced the hydrolytic degradation of the fiber. Among all the annealing conditions, the freely hung specimens annealed at 190°C exhibited the most pronounced annealing effect on hydrolytic degradation, and was consistent with the observed gross morphologic changes. The change in the characteristics of fiber structure (i.e., the return to the stage of less oriented conformation upon freely hung annealing) was thought to be the

ISSN:0021-9304    

DOI:10.1002/jbm.820220804

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractIn vitrocell culture techniques were used to evaluate the effect of several clinically significant biomedical polymers on monocyte activation and Interleukin 1 (IL1) production. Isolated human peripheral blood monocytes were cultured in the presence of a panel of five biomedical polymers routinely used in a variety of clinical applications: Polyethylene (PE), silica‐free polydimethylsiloxane (PDMS), woven Dacron fabric, expanded polytetrafluoroethylene (ePTFE) and the segmented polyurethane, Biomer. Monocytes generated IL1 in the presence of all five materials. Maximal levels of IL1 were generated at 24 h in monocyte‐polymer cultures supplemented with serum and additionally stimulated with lipopolysaccharide (LPS). No difference was observed due to serum source. Results from cultures supplemented with fetal bovine serum were not significantly different from those obtained with human serum supplemented cultures. The thymocyte proliferative activity generated by monocytes in the presence of these biomedical polymers was neutralized by a specific polyclonal anti‐IL1 antiserum. Statistically significant differences in IL1 production were observed between polymers, allowing their classification according to reactivity into high (Dacron, PE), intermediate (ePTFE) and low (Biomer, PDMS) reactive g

ISSN:0021-9304    

DOI:10.1002/jbm.820220805

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThree different sieve size fractions of ergotcontaining biodegradable microcapsules were examined bothin vitroandin vivo. The sieve sizes and average particle diameter, (μm), were: less than 45–75 (X̄ = 30); 75–106 (X̄ = 79), 106–177 (X̄ = 130). These microcapsules contained ca. 9% drug and were produced from 50:50 poly(DL‐lactide‐co‐glycolide). The objective was to determine the effect of particle size onin vivoandin vitrodegradation rates. The microcapsules were injected into rat gastrocnemius muscle and excised and examined at various time points up to 70 days. Initially a minimal tissue response was noted which was characterized by a sharply localized acute inflammatory reaction. Following this, connective tissue and foreign body giant cells engulfed the microcapsules at 20–30 days. Only vestiges of the microcapsules were found surrounded by minimal connective tissue and foreign body giant cells after 60–70 days. The tissue reaction was a minimal, sharply localized foreign body giant cell and connective tissue process for all three size groups of microcapsules. The largest microcapsules (X̄ = 130 μm) exhibited a slightly greater tendency to undergoin vivoandin vitrodegradation relative to the other groups. However, it can be concluded that over the microcapsule size ranges examined minimal differences in the degradation properties of the polymeric matrices and consequently those of the mic

ISSN:0021-9304    

DOI:10.1002/jbm.820220806

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

ISSN:0021-9304    

DOI:10.1002/jbm.820220807

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

ISSN:0021-9304    

DOI:10.1002/jbm.820220801

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY