In vivo and in vitro degradation of glycine/DL-lactic acid copolymers

Abstract

A series of copolymers of glycine and DL-lactic acid with various compositions was synthesized and their in vivo and in vitro degradation behavior was studied. For the in vivo examination, discs of the copolymer films were subcutaneously implanted in rats. The in vitro studies were carried out in phosphate buffer at pH = 7.4 and 37 degrees C. The decrease in molecular weight, the loss of weight, and the tissue reactions of the different copolymers were determined after 2, 5, and 10 weeks. Poly(DL-lactic acid) was used as reference material. The in vivo and in vitro degradation behavior of the polymers was comparable. The decrease of molecular weight of the copolymers and poly(DL-lactic acid) in time was similar. The weight loss for copolymers with a higher mole fraction of glycine units started earlier. The copolymer with the highest content of glycine units disappeared completely within 10 weeks both in vivo and in vitro. The poly(DL-lactic acid) implant lost only 25% weight over the same period. Tissue reactions against all materials started with an acute inflammatory reaction caused by the trauma of implantation, followed by wound-healing processes, ending in a very mild foreign body reaction for the poly(DL-lactic acid) and a more excessive macrophage mediated foreign body reaction for the glycine/DL-lactic acid copolymers. The tissue reaction was more severe for polymers having a higher rate of degradation.