Testing of Brushite (CaHPO_4-2H_2O) in Synthetic Biomineralization Solutions and In Situ Crystallization of Brushite Micro-Granules

摘要

Conventional flat plate-shaped brushite, dicalcium phosphate dihydrate, CaHPO_4-2H_2O), produced by reacting Ca-chloride and alkali phosphate salt solutions, were found to undergo a maturation process (changing their Ca/P molar ratio from 0.8 to the theoretical value of 1) similar to those seen in biological apatites. Water lily (WL)-shaped brushite crystals were produced in nonstirred aqueous solutions at room temperature in 24 h, by using precipitated calcite and NH_4H_2PO_4 as the starting chemicals. The hydrothermal transformation of WLtype brushite into octacalcium phosphate (OCP) or Ca-deflcient hydroxyapatite (CDHA) was tested at 37℃ by using four different biomineralization solutions, including Tris-buffered SBF (synthetic body fluid) and sodium lactate-buffered SBF solutions. All four solutions used in this study consumed the starting brushite in 1 week and caused transformation into a biphasic mixture of nanocrystalline OCP and CDHA of high surface area. WL-type brushite crystals when synthesized in the presence of small amounts of Zn~(2+) ions resulted in the formation of, for the first time, spherical micro-granules of brushite. Synthesis of brushite in spherical form was difficult prior to this study.