Comparison of In Vivo Properties of Hydroxyapatite-Polyhydroxybutyrate Composites Assessed for Bone Substitution

This study compared 3 composites made of hydroxyapatite and polyhydroxybutymte to determine their biocompatibility, osteointegration, and osteoconduction in rabbits bone defects. Hydroxyapatite-polyhydroxybutyrate was tested in a 10:90 vol/vol ratio for composite 1, 25:75 for composite 2, and 50:50 for composite 3, whereas defects in the control group remained unfilled. Limbs were clinically and radiographically evaluated, and samples were taken 8, 45, and 90 days after surgery for histologic and histomorphometrical analysis. No significant difference was found in the clinical parameters: pain, lameness, dehiscence, infection, and edema among the 4 groups. No signs of osteolysis or periosteal reaction were observed. Bone regeneration in groups 1, 2, and 3 occurred histomorphologically similar to the control group. No inflammatory infiltrate was present on any date of observation. More bone than connective tissue was significantly found in the defects of the 3 groups on all observation dates, and the percentage of bone tissue in the interface was similar for composites 2 and 3. Bone and connective tissue were observed in pores of composites 2 and 3. Osteoclasts were found in the bone-composite interface, and multinucleated giant cells were seen on the surface of composite fragments, found among mesenchymal tissue on the 45th and 90th days. No significant difference was observed in osteoclast number among the 4 groups. In summary, composites were considered biocompatible and able to integrate to bone. They also showed signs of biodegradability, and composites 2 and 3 were osteoconductive, the first displaying best characteristics for bone substitution.