Effects of gallic acid on the morphology and growth of hydroxyapatite crystals

Objective: This study was designed to explore the effect of gallic acid (GA, one of the ingredients of chemical compounds from galla chinensis) on the morphology and growth of hydroxyapatite crystals. Methods: The crystals was produced by mixing CaCl2 and KH2PO4 with or without GA (4 g/L) at room temperature for 3, 12, 24 h and 3, 7, 14 days. Subsequently, the micro-structure, morphology and composition of the crystals were investigated via SEM, XRD, ATR-FTIR and fluorescence microscopy. Results: The mineral phase was hydroxyapatite in both groups after 14 days, but their processes and the morphology were completely different. The crystals from groups utilizing GA for 14 days were urchin-like, while loose needle-like crystals were observed in groups without GA. XRD results indicated that GA might limit the growth of the crystals, mainly on the 0 0 2 direction. The results of ATR-FTIR and fluorescence microscopy revealed that the unique structures might caused by the participation of GA during crystals formation. Conclusion: GA might affect and participate into the formation of the hydroxyapatite, and regulate the morphology and structure of the crystals, to enhance the remineralization process. (C) 2014 Elsevier Ltd. All rights reserved.