BIODEGRADATION AND TISSUE-REACTION IN A LONG-TERM IMPLANTATION STUDY OF POLY(L-LACTIDE)

Three poly(L-lactides) with different molecular weights were synthesiz ed as solid blocks from the melt. Two of those were ground and samples were produced by injection moulding. Specimens, cubes (2 x 3 x 3 mm) and rods (2 x 3 x 25 mm), were machined out of the samples, yielding t he amorphous parts. Specimens of the crystalline parts were directly m achined out of the third block. All were implanted into the paraverteb ral muscle of 70 rats to explore the biodegradation of poly(L-lactide) in vivo and the tissue changes at the implantation site. The rats wer e sacrificed after 1 to 116 weeks and the implants recovered. Histolog ical sections of the cubes including the surrounding tissue were prepa red by the cutting-grinding technique according to Donath. The three d ifferent materials were incorporated well, forming a collagenous layer . The crystalline poly(L-lactide) (M(vis) 429 000) remained almost sta ble in form and structure over the whole observation period. No signs of inflammation or foreign-body reaction were observed. The amorphous poly(L-lactide) of higher molecular weight (M(vis) 203 000) degraded n early completely, whereas the amorphous poly(L-lactide) of lower molec ular weight (M(vis) 120 000) was totally resorbed. After about 8 weeks both injection-moulded materials degraded progressively, subsequently accompanied by a mild to moderate foreign-body reaction. The degradat ion in the inner part of the implants proceeded faster than in the cor tex. The final biodegradation appeared accompanied by a resorptive his tiocytic inflammation. The degradation rate and velocity of the amorph ous poly(L-lactides) did not overtax the absorption capacity of the su rrounding tissue. These properties of biodegradation seem to meet the requirements for a biodegradable material in osteosynthesis.