Hydroxylapatite/poly(L-lactide) composites: an animal study on push-out strengths and interface histology.

In the development of new materials for resorbable systems for bone fixation and replacement, composites of hydroxylapatite and poly (L-lactide) (HA/PLLA) were tested. In a transcortical implantation model in goats the interactions at the bone-implant interface were studied with post-operative intervals up to 1 year. Push-out testing of the implants indicated that PLLA reinforced with 50 wt% hydroxylapatite or PLLA plasma-sprayed with a hydroxylapatite coating of 50 microns thickness increases interfacial shear strength at 3 months of implantation when compared to unfilled poly(L-lactide) (P < .01). Scanning electron microscopy showed that the failure mode was predominantly at the coating-implant interface. Implantation periods longer than 3 months did not result in a significant increase in push-out strength because of the resorbing PLLA matrix. In support of the above findings there was histological evidence, on a light microscopical level, of increased bone contact at the interface for the composites, HA incorporated in or coated on PLLA, compared to unfilled poly(L-lactide).