摘要:

A bioresorbable aliphatic polyester was synthesized by bulk copolymerization of a 1/1 M/M L,L-lactide/ε-caprolactone mixture using zinc metal as initiator. The actual composition of the copolymer was found to be 1.5/1 as deduced from1H NMR spectra obtained in DMSO-d6 solutions where higher resolution was obtained as compared with chlorinated solvents. Resonances due to L-lactyl units (L) exhibited triads stereosensitivity, ε-oxycaproyl units (C) being sensitive to dyads. Average lengths of both poly(lactic acid) and polycaprolactone sequences were evaluated and showed the presence of rather long PLA blocks. Furthermore, no CLC triad signal was found, suggesting the absence of transesterification rearrangements. 10 x 10 x 2 mm specimens made of the copolymer were allowed to age in isoosmolar pH = 7.4 phosphate buffer at 37°C. Degradation was monitored by various analytical techniques such as SEC, X-ray diffractometry, DSC, and1H NMR. Data were compared with the behaviour of PCL and PLA homopolymers allowed to age under similar conditions. Crystallinity and composition changes arc discussed in terms of preferential degradation in L- and C-containing amorphous domains, crystallized long PLA blocks being much more resistant.

ISSN:0920-5063    

DOI:10.1163/156856296X00237

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Previously, we found that when fibrinogen-coated polyurethanes resided in a buffer for a period of time (the 'residence time') platelet adhesion to these materials decreased. Other changes in adsorbed fibrinogen such as decreases in polyclonal antibody binding and SDS elutability supported the conclusion that fibrinogen undergoes postadsorptive conformational changes. Subsequently we measured the binding of monoclonal antibodies to the three putative platelet binding sites on fibrinogen, using a single mid-range concentration of antibody. We found that binding of a monoclonal antibody to the platelet binding site at the C-terminus of the gamma chain of fibrinogen changed little with residence time, while binding of monoclonal antibodies to the other two putative binding sites on fibrinogen either increased with residence time (RGDF at Aα 95-98), or first increased and then decreased with residence time (RGDS at Aα 572-575). In the current study, we measured antibody binding affinity, Ka, by measuring antibody binding at a series of antibody concentrations. This is a more sensitive method for detecting changes in adsorbed fibrinogen than measuring antibody binding from a single antibody concentration. The Kawas determined for two antibodies, M 1 (4A5), which binds to a platelet binding domain of fibrinogen (y 402-411) and R 1 (155 B1616), which binds to residues 87-100 of the Aα chain (containing an RGDF site). A summary of the results for the M1 antibody are as follows. The Ka was higher for M1 binding to fibrinogen adsorbed to Immulon I® than to Biomer®, Biospan® or poly(ethylene terephthalate), suggesting that fibrinogen adsorbed to Immulon I® is more platelet adhesive than fibrinogen adsorbed to the other polymers. On Biospan®, the Kadecreased from 2.8 x 109to 1.0 x 109M-1after a 24 h 37°C residence time, which correlated with the decrease in platelet adhesiveness of adsorbed fibrinogen observed previously under these conditions. The change in Kawas greater when adsorbed fibrinogen was kept under denaturing conditions. For example, the Kadecreased from 2.8 x 109to 0.8 x 109M-1after a 1 h 70°C residence time whereas it remained approximately the same, 2.9 x 109M-1, after a 24 h 0°C residence time.

ISSN:0920-5063    

DOI:10.1163/156856296X00246

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A series of aliphatic polyamide (nylon) sheets with different draw ratios were prepared and their blood-contacting properties examined in relation to the bulk and surface characteristics. Increases in both the molecular orientation and crystallinity were observed with increasing draw ratio. Their surface wettability slightly decreased with draw ratio, indicating less amide linkages at their surfaces by the drawing process. An increase in contact angle hysteresis by the drawing process is thought to be due to the existence of more amorphous chains at the surfaces. The adsorption of albumin and fibrinogen onto nylon sheets was significantly reduced with draw ratio, suggesting the formation of well-established crystalline-amorphous microdomain structures at the surfaces. Blood compatibility of these surfaces was greatly improved with draw ratio in terms of a change in cytoplasmic calcium levels in platelets contacting these surfaces. Thus, it is suggested that the control of crystalline-amorphous microdomain structures by the drawing process is a feasible approach to improve blood compatibility of commercially available semicrystalline polyamides.

ISSN:0920-5063    

DOI:10.1163/156856296X00255

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In an earlier article we demonstrated that xenogeneic islets of Langerhans in an agarose/poly(styrenesulfonic acid) (PSSa) microcapsule were protected from the host's immune rejection and that diabetic animals maintained a normal glucose level for a long period of time after their transplantation. In this study, we attempted to make clear the immuno-isolative mechanism of the agarose-PSSa microcapsule from the standpoint of permeability of antibodies and complement proteins through this microcapsule membrane. It was found that the microcapsule was unable to prevent the permeation of IgG for longer than a few days, but protect the encapsulated cells from cytolytic complement attack. This strongly suggests that the cytolytic complement activity was lost during permeation through the micorcapsule, probably because of the strong interaction of PSSa in the membrane with complement proteins. Based on these findings we proposed the minimum requirement for the immuno-isolative memebrane to be applicable to xenotransplantation.

ISSN:0920-5063    

DOI:10.1163/156856296X00264

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor