IN-VIVO TESTING OF CROSS-LINKED POLYETHERS .2. WEIGHT-LOSS, IR ANALYSIS, AND SWELLING BEHAVIOR AFTER IMPLANTATION

As reported in Part I (''In vivo testing of crosslinked polyethers. I. Tissue reactions and biodegradation,'' I. Biomed. Mater. Xes., this i ssue, pp. 307-320), microscopical evaluation after implantation of cro sslinked (co)polyethers in rats showed differences in the rate of biod egradation, depending on the presence of tertiary hydrogen atoms in th e main chain and the hydrophilicity of the polyether system. Ln this a rticle (Part II) the biostability will be discussed in terms of weight loss, the swelling behavior, and changes in the chemical structure of the crosslinked polyethers after implantation. The biostability incre ased in the order poly(POx) < poly(THF-co-OX) < poly(THF) for the rela tively hydrophobic polyethers. This confirmed our hypothesis that the absence of tertiary hydrogen atoms would improve the biostability. On the other hand, signs of biodegradation were observed for all polyethe r system studied. Infrared surface analysis showed that biodegradation was triggered by oxidative attack on the polymeric chain, leading to the formation of carboxylic ester and acid groups. It also was found t hat in the THF-based (co)polyethers, alpha-methylene groups were more sensitive than beta-methylene groups. For a hydrophilic poly(THF)/PEO blend, an increase in surface PEO content was found, which might be du e to preferential degradation of the PEO domains. (C) 1996 John Wiley & Sons, Inc.