Bioabsorption of polylactides with different molecular properties.

In order to study the effects of factors governing the bioabsorption rate of polylactides, implantation tests were carried out in rabbits using various samples (20 x 10 x 2 mm3) differing in their chemical composition, residual monomer content, and molecular orientation. Copolymer samples with a higher lactic acid content showed a lower rate of absorption, whereas those with a higher unreacted monomer content were absorbed faster and showed a more drastic decrease in molecular weight. In contrast, degradation of the purified polymers was slow; the purified poly-L-lactide showed no weight change and a 50% reduction in molecular weight after 6 months of implantation. Scanning electron microscopy of the samples containing monomers showed a microporous structure extending from the surface to the inner region a few days after implantation, whereas the purified poly-L-lactide did not exhibit a microporous structural change even after 10 months of implantation.