POLY(L-LACTIDE) - A LONG-TERM DEGRADATION STUDY IN-VIVO .1. BIOLOGICAL RESULTS

Three poly(L-lactides) with different molecular weights were synthesized. Small blocks (3 X 3 X 2 mm) and rods (25 X 3 X 2 mm) were produced either by injection moulding (amorphous parts, M(vis) 200 000 and 120 000, respectively) or machined out of a solid as-polymerized polylactide block (crystalline parts, M(vis) 429 000) and implanted into the dorsal muscle of rats. After 1 to 116 wk the rats were killed and the implants were recovered. Histological preparation was carried out using the cutting-grinding technique. All three polylactides had incorporated well, forming a collagenous fibrous layer. Crystalline block polylactide remained stable in form and structure over the whole observation period. Amorphous injection-moulded specimens developed a rough surface within weeks, then deep resorptive lacunae after ca. 1 yr and became totally degraded (M(vis) 120 000) or nearly totally degraded (M(vis) 200 000) after 2 yr. This velocity of biodegradation seems to meet the requirements for an absorbable material for osteosynthesis. Long-term implantation into rodents brings the problem of foreign-body tumorigenesis independent of the chemical nature of implants (the Oppenheimer effect). Observations in this study and in the literature are discussed.