Morphology regulation of Sr-substituted hydroxyapatite by L-glutamic acid in a solvent- and initial temperature-dependent manner

Abstract A bi-solvent system (ethanol and water) with the presence of L-glutamic acid (L-glu) was developed to achieve the controlled synthesis of whisker-like or urchin-like Sr-substituted HA (SrHA) through hydrothermal treatment. The effects of initial temperature of aqueous solution (ASIT), the presence of Sr, and ethanol proportion on HA morphology were investigated and the underlying mechanisms were illustrated. The results indicate that Sr and ethanol have antagonistic effects on the size of HA whisker, the introduction of Sr tends to reduce the whisker size, while the addition of ethanol tends to increase the nucleation efficiency. Finally, the whisker size and uniformity of SrHA can be regulated via ethanol proportion in the bi-solvent system. ASIT mainly affects the uniformity of solution by affecting Brownian motion in solution, which couples with the different solubility of L-glu and reactant ions in water and ethanol, ultimately determines whether the morphology of HA is whisker-like or urchin-like. Our bi-solvent system simplifies the complex process of template agent screening compared with the ways that introducing several templates agents to achieve the morphology regulation, and enriches the methods of controlled synthesis of different morphological Sr-HA. This feasible method may provide new strategy for simplifying the synthesis of other ions-doping HA with a certain morphology.