Sterilization, toxicity, biocompatibility and clinical applications of polylactic acid/ polyglycolic acid copolymers

A novel processing technique is reported to construct three-dimensional biodegradable polymer foams with precise anatomical shapes. The technique involved the lamination of highly-porous membranes of porosities up to 90%. Implants with specific shapes were prepared made of poly(L-lactic acid) and copolymers of poly(DL-lactic-co-glycolic acid) to evaluate feasibility. The biomaterials produced have pore morphologies similar to those of the constituent membranes. The pores of adjacent layers of laminated devices are interconnected, resulting in continuous pore structures. The compressive creep behaviour of multilayered devices is also similar to that of the individual layers. Recent discoveries from our group and others that organs and tissues can be regenerated and reconstructed, using cells cultured on synthetic biodegradable polymers, renders this method useful in creating polymer-cell graft for use in cell transplantation.

This study determined the difference in rate of degradation between pure polymers of lactic acid (pla), glycolic acid (PGA), and various ratios of copolymers of these two substances. Fast-cured and slow-cured polyglycolide was compared with copolymers of glycolide/lactide intermixed in ratios of 75:25, 50:50, and 25:75, as well as pure polylactide. A total of 420 rats were implanted with carbon-14 and tritium-labeled polymers in bone and soft tissue. At intervals of 1, 2, 3, 5, 7, 9, and 11 months, groups of five animals with the implants in bone and five with the implants in the abdominal wall were sacrificed. The implant area as well as tissue from the liver, spleen, kidney, lung and some muscle tissue was analyzed for radioactivity along with the urine and feces collected throughout the experiment. Half-lives of the different polymers and copolymers were calculated from the radioactivity present in the implant area for each time interval. Half-life of the polymers and copolymers decreased from 5 months for 100% PGA to 1 week with 50:50 PGA:PLA copolymer and rapidly increased to 6.1 months for 100% PLA. Fast-cured PGA had a half-life in tissue of 0.85 months. No difference in rate of degradation was seen in soft tissue or bone. No significant radioactivity was detected in urine, feces, or tissue samples. From this study, it is concluded that control of degradation rate of the implant could best be attained by varying the composition of PLA and PGA between 75% and 100% PLA along with a corresponding 25% to 0% PGA. This would provide a half-life range of the implant of from 2 weeks to 6 months.