In situ time-resolved X-ray diffraction study of evolution of nanohydroxyapatite particles in physiological solution

Nanosized hydroxyapatite (nano-HA) is known to be of enhanced biological efficacy, being used in medical events as a mix with physiological solution, saline or patient's blood before the application. This study is aimed at the investigation of the time evolution of both phase composition and particle size of nano-HA in aqueous (isotonic 0.9% NaCl) solution. An energy-dispersive X-ray diffraction method, allowing the real time rapid data collection was employed. The X-ray amorphous component of initial powder was shown to convert fully into the crystalline hydroxyapatite (HA), the characteristic crystallization time being of approximately 25 min. The initial crystallite average size (approximately 35 nm) was enlarged by a factor of about 4 within the first 100 min after mixing the powder with the physiological solution and no more structural changes were detected during the following period. The sigmoidal kinetics of the HA crystal growth was evidenced.