Synthesis and hydrolytic degradation of graft copolymers containing poly(lactic acid) side chains: in vitro release studies of bioactive molecules

Graft copolymers were synthetized by radical copolymerization of poly(DL lactic acid) (PLA) methacrylate, a hydrolyzable macromonomer, and tert-butyl acrylate, a hydrophobic monomer in order to obtain degradable polymers. Cast films have been immersed in artificial sea water. The influence of different parameters on the kinetics of hydrolytic degradation have been examined, including the tert-butyl acrylate/macromonomer molar ratio, the nature of the PLA end group (acid or ester functionality), the average length of the PLA side chain (Pn = 7 or 10) and the temperature (20 and 37 degreesC). Immediately after immersion, clear changes in the film surface topography have been observed by atomic force microscopy observations, due to water diffusion. The uptake of water is concentrated in microdomains. The degradation of the copolymers was monitored by the appearance of lactic acid, pH variations and SEC measurements. Their suitabilities for the release of bioactive agent (cuprous oxide) were studied by Inductively Coupled Plasma. The results showed that increasing the proportion of lactic acid units leads to faster degradation and the release of cuprous oxide is correlated with the degradation of PLA. (C) 2002 Elsevier Science Ltd. All rights reserved.