Antioxidant inhibition of poly(carbonate urethane) in vivo biodegradation

This study compared the effect of an antioxidant on the in vivo biodegradation of a poly(carbonate urethane) (PCU) and a poly(ether urethane) (PEU). Unstrained PEU and PCU films with and without Santowhite were implanted subcutaneously into 3-month-old Sprague-Dawley rats for 3, 6, and 12 months. Characterization of unstabilized PEU and PCU with ATR-FTIR and SEM showed soft-segment and hard-segment degradation consistent with previous studies. In particular, evidence of chain scission and crosslinking of the surface was present in the ATR-FTIR spectra of explanted specimens. Addition of 2.2 wt % antioxidant inhibited the in vivo degradation of both PCU and PEU. Although the antioxidant probably improved polyurethane biostability by decreasing the susceptibility of the polymer to degradation, modulation of the cellular response to prevent the release of degradative agents was also possible. To differentiate the effects, the foreign-body response was investigated with the use of a standard cage implant protocol. Polyurethane films were implanted in wire mesh cages subcutaneously in rats for 4, 7, and 21 days. There were no statistical differences among materials in the inflammatory exudate cell counts, adherent cell densities, or percent fusion of macrophages into foreign-body giant cells (FBGCs). Therefore, it was concluded that the antioxidant inhibited degradation by capturing oxygen radicals that would otherwise cause polyurethane chain scission and crosslinking.