MATERIAL PROPERTIES AND TISSUE REACTION DURING DEGRADATION OF POLY(96L/4D-LACTIDE) - A STUDY IN-VITRO AND IN RATS

To investigate the mechanical and physical properties of, and the histological reaction to, as-polymerized poly(96L/4D-lactide) (PLA96), a degradation study was performed in vitro and in rats. The PLA96 studied had a molecular weight (($) over bar M(w)) of 1.5 x 10(6) g/mole. Test samples were implanted subcutaneously in the back of rats or put in phosphate-buffer. The mechanical and physical properties of PLA96 showed major changes during the fi rst 3 weeks of degradation. Tensile strength (sigma(b)), impact strength and ($) over bar M(w) decreased rapidly. The heat of fusion (Delta H-m), a measure for crystallinity, increased whereas the melting temperature (T-m) remained almost constant. The mechanical properties were lost completely after 7 weeks of degradation. After 55 weeks, both water absorption and mass loss had reached approximately 30%, and ($) over bar M(w) had decreased to 15 x 10(3) g/mole. Delta H-m had slightly increased further but T, remained unchanged. The measurements during degradation in vitro did not show significant (p > 0.05) differences from the measurements during degradation in vivo. The histological reaction to PLA96 could be characterized as a mild foreign body reaction without signs of inflammation.