In vivo degradation behavior of photo-cross-linked star-poly(epsilon-caprolactone-co-D,L-lactide) elastomers.

We have recently reported on the preparation of biodegradable elastomers through photo-cross-linking acrylated star-poly(epsilon-caprolactone-co-D,L-lactide). In this paper we assess the change in their physical properties during in vivo degradation in rats after subcutaneous implantation over a 12 week period. These parameter changes were compared to those observed in vitro. Two different cross-link densities were examined, representing the range from a high Young's modulus to a low Young modulus. Elastomers having a high cross-link density exhibited degradation behavior consistent with a surface erosion mechanism, and degraded at the same rate in vivo as observed in vitro. Young's modulus and the stress at break of these elastomers decreased linearly with the degradation time, while the strain at break decreased slowly. Elastomers having a low cross-link density exhibited a degradation mechanism consistent with bulk erosion. Young's modulus and the stress at break of these elastomers decreased slowly initially, followed by a marked increase in mechanical strength loss after 4 weeks. The elastomers were well tolerated by the rats over the 12 week period in vivo.