ADSORPTION OF ALBUMIN ON CALCIUM HYDROXYLAPATITE

Adsorption of bovine serum albumin (BSA) on calcium hydroxylapatite (HAP) with different Ca/P molar ratios ranging from 1.55 to 1.70 and on HAP surface-modified by silicate and fluoride ions has been studied at pH 6.0 and 288 K. The adsorption isotherms of BSA on HAP particles are of the Langmuir type and adsorption of BSA generated a negative charge on HAP. Unmodified HAP particles which have a larger Ca/P molar ratio tended to yield a larger electrically positive zeta potential, which in turn gave a larger saturated amount of adsorbed BSA (n(s)) as a result of their electrostatic attractive force. The surface modification by silicate ions increased the surface acidity and made the HAP surface more electrically negative so as to yield smaller n(s) values. On the contrary, surface modification by fluoride ions increased n(s) two-fold over that on the unmodified surface. This fact could be explained by the formation of highly basic CaF2 on the HAP surface.