OXIDATIVE BIODEGRADATION MECHANISMS OF BIAXIALLY STRAINED POLY(ETHERURETHANE UREA) ELASTOMERS

As part of ongoing studies in polyurethane biostability and biodegrada tion, we have investigated an in vitro system to test strained poly(et herurethane urea) (PEUU). Recently, we utilized this system to reprodu ce in vivo stress cracking in strained Pellethane(R). In this study, s trained PEUU was tested to determine whether it degrades through a com mon mechanism with Pellethane(R) and to further examine the steps invo lved in this degradation. Biaxially strained PEUU elastomers were trea ted with an alpha(2)-macroglobulin (alpha(2)-Mac) protein solution fol lowed by an oxidative H2O2/CoCl2 treatment. Characterization of the st rained PEUU specimens was performed with attenuated total reflectance- Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), electron spectroscopy for chemical analysis, and contact angle analysis. The results from these characterization techniques provide c onclusive evidence that biodegradation of PEUU and Pellethane(R) occur s through a common mechanism. Chemical changes to the PEUU include cle avage of the polyether soft segments and urethane linkages, leaving th e hard segment domains unaffected. SEM analysis shows that this chain cleavage leads to the development of severe pitting and cracking of th e PEUU surface. In addition, the in vitro degradation accurately repro duces the in vivo degradation chemically and physically. This result v erifies that the primary species responsible for biodegradation of PEU Us, in vivo, are hydroxyl and/or hydroperoxide radicals. alpha(2)-Mac pretreatment increases the rate of degradation compared to direct trea tment in H2O2/CoCl2. As the PEUU soft segment chains are cleaved, the degradation products are extracted into the treatment solution or envi ronment. Finally, a new biodegradation mechanism of PEUUs is presented that involves crosslinking of the polyether soft segments. (C) 1995 J ohn Wiley & Sons, Inc.