Calcium phosphate crystal growth under controlled environment through urea hydrolysis

In this study, octacalcium phosphate (OCP, Ca₈ (HPO₄)₂(PO₄)₄ 5H₂O) micro-fibers were successfully synthesized and isolated purely from the aqueous solution in the environment controlled by urea hydrolysis. During the process, the OCP micro-fibers were suspended in the middle of the reaction solution and weaved a thin film after isolation from the solution. The as-synthesized OCP fibers had the length larger than ∼200 μm, the width equal to ∼2 μm and the aspect ratio as high as 100. Various characterizations proved that the OCP fibers were well crystallized and contained no other impurities that were critical for the materials used in biomedical applications. This study revealed that using urea hydrolysis to control the reaction ambient was an effective way to produce pure OCP without any impurities. This study also demonstrated that dicalcium phosphate anhydrous (DCPA, CaHPO₄) pre-precipitation was the necessary step for OCP fiber growth, yet itself was another useful bioceramics. OCP fibers could be potentially used as the woven porous bioceramics or form fiber-reinforced composite biomaterials.