Material properties of absorbable self-reinforced fibrillated poly-96L/4D-lactide (SR-PLA96) rods; a study in vitro and in vivo

A study was carried out to investigate changes in mechanical properties and degradation of self-reinforced fibrillated poly-96L/4D-lactide (SR-PLA96) rods in vitro and in vivo. The viscosity-average molecular weight, M-v, of the intact sterile (gamma irradiated) rods was around 50 000 g mol(-1). The SR-PLA96 rods of diameter 1.1 mm by 30 mm and diameter 4.5 mm by 50 mm wer e immersed in phosphate-buffered saline or implanted in the dorsal subcutis of rabbits. Bending, shear and torsion strength and bending modulus, toget her with the changes of viscosity and crystallinity, were measured up to 24 wk. The strength values showed only a slight decrease during the follow-up period with the exception of torsion strength, that decreased to 52% of th e initial value during 24 wk. There were no statistically significant diffe rences in the strength retention between in vitro and in vivo groups. Cryst allinity increased over time, being 46-49% at 24 wk. The M-v of the rods de creased over 50% by 24 wk. These promising results motivated us to continue the studies with the fixation of experimental cortical bone osteotomies wi th SR-PLA96 intramedullary rods. (C) 1999 Kluwer Academic Publishers.