The In Vitro and In Vivo Biodegradable Behavior of Hydroxyapatite Granules in the Presence of Different Crystals

The in vitro and in vivo degradation behavior and osteogenic ability of new hydrothermal hydroxyapatites (HAs) were investigated. Two different HA granules with short and long-rod HA crystals (SRHA and LRHA, respectively) were hydrothermally synthesized. A low pH immersion test was performed to observe morphological degradation features. At 2 days, HA in a low pH immersion fluid revealed pitfall-like degradations on the surface. Both HA granules were implanted in rat calvaria bone defects. The biodegradable behavior and effects of new bone formation were histologically and radiographically investigated. At 4 and 24 weeks after surgery, defect areas were filled with implanted HAs and newly formed bone. No differences in boundary area shapes between SRHA and LRHA were found. The area of LRHA degradation was greater compared with SRHA (p < 0.05). At 24 weeks, implanted HA granules showed inward incursion of fibrous tissue and tissue fluid. Accordingly, in vivo hydrothermal HA indicated good osteogenesis and progress.