HIGH-STRENGTH HYDROXYAPATITE/POLY(L-LACTIDE) COMPOSITE FOR INTERNAL FIXATION OF BONE FRACTURES: EVALUATION OF ITS BONDING ABILITY TO BONE

High-strength hydroxyapatite (HA)/poly (L-lactide) (PLLA) composites for use as biodegradable fracture-fixation devices have been produced using a new compression molding method. The purpose of this study was to investigate the bone-bonding ability of these HA/PLLA composites. The composites contained 30% by weight of HA particles with a mean diameter of 3 μm. The initial bending strength and flexural elastic modulus of this composite were 280 MP a and 7.8 GP a, respectively. Rectangular plates made of this composite and of unfilled PLLA were implanted into the proximal tibiae of mature rabbits. Detaching tests and histological examinations were performed at 8 and 25 weeks after implantation. The tensile failure loads of the composite and unfilled PLLA were 1.39 kgf and 0.05 kgf at 8 weeks, and 2.60 kgf and 0.25 kgf at 25 weeks, respectively. There were significant differences between the composite and unfilled PLLA during the experiment (p< 0.05 at each point: two-way ANOVA). Histological examination showed that HA/PLLA bonded directly to bone throughout the experimental period, while unfilled PLLA exhibited intervening fibrous tissue between bone and plate. No inflammatory cells were found in the vicinity of either composite or unfilled PLLA plates, even at 25 weeks. These results indicate that the bone-bonding ability of the HA/PLLA composite could enhance fixation stability in the treatment of fractured bones.