Characterization of differently prepared apatites by adsorption behavior of albumin

Two kinds of hydroxyapatite powder (HAp) were prepared by wet syntheses using cattle bones (r-HAp) and reagents (s-HAp). The physicochemical natures of the two HAp's during heating in air or a stream of water vapor were compared within the temperature range of 273-1073 K. The white powders obtained commonly gave a single phase of HAp and were commonly characterized within the two temperature regions of 273-673 K (Region I) and 673-1073 K (Region II), regardless of the gas atmosphere. The crystallite size (CS), the specific surface area (SA) and the total pore volume (VT) changed little in Region I, whereas they varied considerably in Region II. The adsorption of bovine serum albumin (BSA) on these HAp's in phosphoric acid buffer solutions was satisfied with the Langmuir isotherm equation. The saturated amount (ASA) of the adsorption and the heat of adsorption (Q) for BSA linearly increased and decreased, respectively, with increasing CS, with the slope of the lines differing between the r-HAp and s-HAp cases. Based on these results, it was concluded that the adsorption behavior of BSA on the C-site of HAp is strongly controlled by the crystallite size rather than the pore structure. r-HAp had a 157% higher Q in Region I and 22-44% larger ASA in Region II than s-HAp, indicating an advantage as an adsorbent for biopolymers.