Viscous property and osteogenesis induction of hydroxyapatite thermal decomposition product mixed with gelatin implanted into rabbit femurs

The viscosity of hydroxyapatite thermal decomposition product mixed with gelatin (HATDP-G) and the osteogenesis induced by this mixture were investigated. To determine the viscosity of HATDP-G, we measured the average diameter of a slumped mass of HATDP-G (0.5 ml) according to the American Dental Association Specification No. 8 [1], with some modifications, and compared it with that of an equal mass of HATDP and of polymethylmethacrylate (PMMA) bone cement. The mean diameter of 10 samples each of HATDP-G, HATDP, and PMMA bone cement was 26.8±0.9 mm, 19.6±0.2 mm and 29.2±0.3 mm, respectively, 2 min after the mixing procedure. HATDP-G was injected into the bone marrow of the right femurs of 25 rabbits. As the control, gelatin with saline solution was injected into the left femurs. New bone formation was observed in all 20 femurs from three weeks after injection. No new bone formation was observed in the control femurs. The affinity index [2–4], a parameter of osteogenesis, was 19.8±6.1%, 27.5±2.6%, 52.9±9.5%, and 76.3±1.9% at 3, 6, 12 and 24 weeks after the injection, respectively. Significant increases in the affinity index were found between weeks 6 and 12, and weeks 12 and 24 (p<0.05). Our findings indicated that HATDP-G might be successfully used as a bioactive bone cement.