Variations between Biomer lots. 2: The effect of differences between lots on in vitro enzymatic and oxidative...

In vitro degradation of two lots of Biomer, a commercial poly(ether urethane urea), has been investigated in order to understand possible mechanisms for in vivo degradation. Two lots of Biomer, BSUA001 and BSP067, were used in the study. Lot BSUA001 contained a poly(diisopropylaminoethyl-methacrylate), an ultraviolet-stabilizing additive. This additive was absent in lot BSP067. Samples of each lot were exposed to two hydrolytic enzymes, papain and leucine aminopeptidase, and to hydrogen peroxide for 24 h. The extent of degradation was assessed using high-pressure gel permeation chromatography and x-ray photoelectron spectroscopy (XPS). Statistically significant changes in the molecular-weight distribution occurred in lot BSP067 for all three treatments. Only the hydrogen peroxide treatment resulted in statistically significant changes in the molecular weight of lot BSUA001. XPS data for samples of lot BSUA001 that had been treated with hydrogen peroxide revealed the formation of nitroso groups and protonated amines at the surface. The data suggest that surface chemistry is important for enzyme catalyzed degradation, while permeability is important for degradation by hydrogen peroxide.