Enhanced bone formation onto the bone surface using a hydroxyapatite/collagen bone-like nanocomposite

The process of bone formation onto the bone surface using a hydroxyapatite/collagen bone-like nanocomposite (HAp/Col) was investigated. Immersion tests were performed to evaluate the impact of pH on the degradation of the specimens in an aqueous environment. The specimens were soaked in aqueous solutions of pH 4.0, 5.0, and 7.0. Using standardized images, the top-view areas of the specimens were measured. Animal experiments were performed to investigate the bone formation process onto the bone surface. The specimens were placed under the rat calvarial periosteum, and mu CT image analysis and histological observation were performed on samples harvested on postoperative Days 3, 5, and 7. In all experiments, beta-tricalciumphosphate (beta-TCP) was adopted as the control. HAp/Col turned to gel in acidic environments below pH 5.0. In contrast to the beta-TCP, the HAp/Col specimens placed under the periosteum expanded and attained a hollow structure with a gel-filled center, accompanied by larger volume of new bone and appearance of TRAP-positive multinucleated cells on postoperative Day 5. Therefore, HAp/Col can enhance bone formation onto the bone surface via induction of TRAP-positive multinucleated cells, and may have clinical applications.