Long term in vivo degradation and tissue response to photo-cross-linked elastomers prepared from star-shaped prepolymers of poly(ε-caprolactone-co- D,L-lactide)

Abstract

Long term in vivo degradation, and tissue response to, cylindrical elastomers made of photo-cross-linked star-poly(e-caprolactone-co-D,L-lactide) triacrylate were investigated through subcutaneous implantation in rats. The elastomers were prepared via UV initiated cross-linking of prepolymers of equimolar amounts of monomers; a high crosslink density elastomer (ELAST 1250) was prepared from a prepolymer of 1250 Da and a low cross-link density elastomer (ELAST 7800) was prepared from a prepolymer of 7800 Da. The elastomers were characterized using cross-polarization magic angle spinning solid state 13C NMR and attenuated total reflectance fourier transform infrared spectroscopy. The progress of the in vivo degradation process was followed by employing SEM, uniaxial tensile, mass loss, water uptake, and sol content measurements. The rate of in vivo degradation was faster than the rate of in vitro degradation for both ELAST 1250 and ELAST 7800. Long term in vivo degradation studies indicated that both elastomers undergo bulk hydrolysis along with surface erosion occurring due to the physiological environment. In the case of low cross-link density elastomers, the onset of mass loss was accompanied with an increase in both water uptake and sol content, whereas, in the case of high crosslink density elastomers, only the water uptake increased. This degradation pattern was due to crazing of the high crosslink density elastomers. ELAST 7800 cylinders were totally degraded, and ELAST 1250 cylinders had lost 80% of their mass, within 30 weeks. A minor host reaction with minimal vascularity and inflammation was invoked, with a milder tissue response observed with more highly crosslinked cylinders. © 2009 Wiley Periodicals, Inc.