Adsorption of Glycerol on Hydroxyapatite Enhanced Colloidal Stability in Phosphate Buffered Saline Solution

The biocompatibility of hydroxyapatite (HAP) has led to its application in various fields. To accomplish practical biological applications, such as drug/gene delivery, the colloidal stability of HAP in phosphate-buffered saline (PBS) is particularly important. In this study, we prepared a glycerol incorporated-HAP (Gly-HAP) by heating HAP in a glycerol environment at 200 degree celsius. To compare morphology and colloidal stability, HAP prepared at room temperature (RT-HAP) was thermally treated in water at 200 degree celsius (H2O-HAP). The heat treatment of HAP in both water and glycerol solutions results in an increase in the crystallinity of HAPs. Due to the low solubility of HAP in glycerol and the adsorption of glycerol on the HAP surface, crystal growth is limited. However, the heat-treated HAP under water increased in size by approximately four times compared to the initial crystallites. Compared to RT-HAP and H2O-HAP, Gly-HAP shows improved colloidal stability in PBS, which originates from the adsorption of glycerol on the HAP surface that inhibits the agglomeration of individual HAP precipitates.