Abstract
The adsorption behavior of albumin (BSA) and lysozyme (LSZ) on rod-shaped and plate-shaped hydroxyapatite (HA) was investigated to evaluate the influence of crystal orientation and morphology on the selective protein adsorption of HA. The rod-shaped HA was prepared by hydrothermal treatment from β-tricalcium phosphate (β-TCP) in H3PO4 solution (pH 2.0 and 4.0 for HA-pH 2.0 and HA-pH 4.0). The plate-shaped HA was synthesized by hydrolysis of CaHPO4–2H2O (DCPD) in NaOH solution at 40°C and 80°C (HA-40°C and HA-80°C). The synthesized HA was characterized using scanning electron microscopy (SEM) and X-ray diffractometry (XRD). HA-pH 2.0 and HA-pH 4.0 produced rod-shaped crystals that were highly oriented to the a-face plane, whereas HA-40°C and HA-80°C showed a plate-like shape and a c-face preferred orientation. The peak intensity ratio I(300)/I(002) (a/c intensity ratio) from the XRD patterns increased in the following order: HA-80°C, HA-40°C, HA-pH 2.0 and HA-pH 4.0. It also increased as the Ca/P ratio decreased. The amount of adsorbed BSA increased in the following order: HA-pH 4.0, HA-pH 2.0, HA-40°C and HA-80°C. The amount of adsorbed LSZ on HA increased in the following order – HA-pH 2.0, HA-pH 4.0, HA-40°C and HA-80°C – with a corresponding decrease in the a/c intensity ratio. The BSA/LSA adsorption ratio increased with the a/c intensity ratio in the range of 3.3–8.9, and the BSA and LSZ were selectively adsorbed on HA, depending on the crystal shape.