Petal-like apatite formed on the surface of tricalcium phosphate ceramic after soaking in distilled water

In the present study six types of tricalcium phosphate ceramic were prepared and soaked in distilled water for different periods to investigate whether a surface apatite layer was formed on TCP ceramics or not. X-ray diffractometry (XRD) and Fourier-transformed infrared (FTIR) spectrometer were used to examine the changes in crystalline phases and functional groups of TCP ceramics for different soaking periods. Calcium and phosphate ions released from TCP ceramics during soaking were recorded by atomic absorption analysis and ion-coupled plasma. Results revealed that αTCP, αTCP/βTCP mixture (αβTCP) and βTCP ceramic were gradually dissolved. There was no apatite layer formed on their surface after being immersed in distilled water for different durations of time. Mg-TCP ceramic, tricalcium phosphate doped with Mg ions, exhibited a lower dissolution rate than the other types of TCP ceramics. Apatite crystals were also not formed on the surface of Mg-TCP ceramic when immersed in distilled water. Tribasic calcium phosphate, prepared from wet precipitation method, was converted to βTCP/HAP (HβTCP) or αTCP/βTCP/HAP (HαβTCP) crystalline composition at different sintering temperatures (1150°C and 1300°C). The surface apatite layer did not appear on HβTCP ceramic after soaking. We observed that petal-like apatite was formed on the HαβTCP ceramic surface after being immersed for 2 weeks. αTCP phase of HαβTCP ceramic was not directly converted to apatite during soaking. The surface apatite layer formed on the HαβTCP ceramic surface was due to the precipitation of the calcium and phosphate ions released from αTCP dissolution. HAP, which existed in the structure of HαβTCP ceramic, plays a role as apatite-precipitating seed to uptake calcium and phosphate ions. TCP ceramics which lacked αTCP and HAP content neither converted to apatite nor formed surface apatite on their surfaces during immersion.