A study was performed to assess the effects of tri-calcium phosphate filler on the tissue response, mechanical properties and degradation characteristics of injection moulded poly L-lactide (PLLA) and poly-hydroxybutyrate co valerate (7 mole % valerate) (PHB7V).

Test pieces for mechanical evaluation were prepared according to ASTM and British Standards. These were aged both in vitro, using a phosphate buffered saline solution (PBS) at pH 7.4 and 37°C and in vivo, subcutaneously using Dutch rabbits. Tensile strength of the materials was monitored, together with molecular weight (Mw) of the polymer as determined by gel permeation chromatography (GPC). The host response to intraosseous implants placed transcortically in the femurs of New Zealand rabbits, was assessed using an undecalcified, unstained, polarised light technique on resin embedded and polished sections.

The materials had good biocompatibility. The bone response to the polymers and composites was very similar. Histology showed that new bone was formed at the defect site, which grew up to the material surface and remodelled into new physiological bone tissue. The rate of degradation of the poly-L-lactide and it's composite with tri-calcium phosphate as assessed by tensile strength and Mw was found to be consistent with the rate for bone healing. Poly-hydroxybutyrate co valerate and its composite with tri-calcium phosphate degraded more slowly.