LONG-TERM IN-VIVO DEGRADATION AND BONE REACTION TO VARIOUS POLYLACTIDES .1. ONE-YEAR RESULTS

Injection-moulded pins from poly(L-lactide), poly(L/DL-lactide) (95/5% ) were implanted in the cortex of the tibiae of sheep. The bone-implan t interface was evaluated to observe whether there is any bone resorpt ion caused by the implants. The molecular weight and crystallinity cha nges upon implantation were also measured. There was no net bone loss around the implants or sterile cyst formation in any of the animals im planted with polylactides up to 1 year. The new bone formed around the poly(L-lactide) and poly(L/D-lactide) pins was separated from the imp lants with a thin layer of connective tissue. For the implants from po ly(L/DL-lactide), there was direct apposition of bone on the polymeric material. At 1 year of implantation, the implants were not completely resorbed, although the molecular weight of polylactides was reduced f rom 40 000-50 000 to 500-3000. The crystallinity at 1 year was about 4 5% for poly(L/D-lactide) and poly(L/DL-lactide) and 65% for poly(L-lac tide), respectively, indicating the presence in the degraded material of thermodynamically stable crystals. (C) 1997 Elsevier Science Limite d.