Protein adsorption on needle-shaped hydroxyapatite prepared by hydrothermal treatment of mixture composed of CaHPO₄·2H₂O and β-Ca₃(PO₄)₂

Abstract

The behavior of protein adsorption on needle-shaped hydroxyapatite (HAp) crystals was investigated and compared with that on irregularly shaped HAp crystals in phosphate buffer solutions. The proteins used were bovine serum albumin (BSA) and lysozyme chloride (LSZ). The effect of phosphate ions in the buffered solutions was evaluated at concentrations in the range 2-200 mol·m^-3. In 50 mol·m^-3 or lower buffer concentrations, the saturated amount of BSA adsorbed on needle-shaped HAp was greater than that on irregularly shaped HAp. The saturated amount of BSA adsorbed on needle-shaped HAp decreased with increasing phosphate buffer concentration. This resulted in little difference in BSA adsorption between the needle-shaped HAp and the irregularly shaped HAp at phosphate concentrations of 100 mol·m^-3 or higher. In contrast, the saturated amount of adsorbed LSZ increased with increasing phosphate buffer concentrations up to 10 mol·m^-3 and subsequently decreased with increasing phosphate concentrations between 10 and 200 mol·m^-3. There were no differences in the protein adsorption behaviors between the needle-shaped HAp and irregularly shaped HAp at a phosphate concentration of 200 mol·m^-3. A specific adsorption, useful for the separation of BSA and LSZ proteins was observed for the needle-shaped HAp at a low phosphate buffer concentration. This separation was caused by the large a-face surface area of the needle-shaped HAp by comparison with that of the irregularly shaped HAp.