Synthesis and characterization of hydroxyapatite with different crystallinity: effects on protein adsorption and...

Increasing demand exists for the development of a tissue-engineered alternative in the repair of nonunion and critical-sized bone defects. The delivery of osteoinductive proteins, such as bone morphogenetic proteins (BMPs), to replicate physiological bone-healing process appears a logical and promising option, but is currently limited in its clinical application due to lack of a suitable drug carrier. The study aimed to investigate the effects of the crystallinity of hydroxyapatite (HA) drug carrier on adsorption of proteins onto and their release from the carrier. HA samples with different crystallinities were synthesized under controlled conditions, that is, pH, temperature, and maturation time, and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and surface area analyzer. Results demonstrated that both bovine serum albumin (BSA) and cytochrome C had a greater tendency to bind onto amorphous calcium phosphate (ACP) than crystalline HA, and the adsorption rate was correlated oppositely with the HA crystallinity. For both BSA and cytochrome C, the release kinetics of protein from HA depended on the crystallinity of HA, in which ACP had the highest release rate at 74%, whereas only 15% of proteins were released from the highly crystalline HA over a 14-day period. Burst release within 12 h of incubation was observed for all groups.