Characterization of albumin- and lysozyme–adsorption evaluated on two differently prepared apatites

Abstract

Ca2+-deficient hydroxyapatite (r-HAp) originated from cattle bones and stoichiometric hydroxyapatite (s-HAp) derived from reagents were prepared by wet syntheses. The adsorption characteristics of albumin (BSA) and lysozyme (LSZ) on the two HAp surfaces were compared by changing the heating temperature of the powders at 273–1073 K in a stream of water vapour. The saturated amount of adsorption (ASA(B) for BSA and ASA(L) for LSZ) on these HAp powders changed little at 273–673 K (Region I), but at 673–1073 K (Region II), clearly increased with crystallite size growth and transformation of crystal morphology. As far as the surface proportions of HAp for P- and C-adsorption sites (the ratios ASA(L)/ASA(B)) are concerned, r-HAp gave no change in Region I and decreased in Region II, whereas those for s-HAp were kept constant through all regions. The heats of LSZ adsorption, QL, for r-HAp and s-HAp, respectively, increased and decreased in Region II. These differences could be a result of the Ca2+-deficient structure of r-HAp with the OH−-vacancy and loosening surface structure due to segregation of impurities in Region II. r-HAp exhibited a 157% higher heat of BSA adsorption, QB, and a 60% lower QL in Region I than s-HAp. Conclusively, r-HAp can be used as an excellent adsorbent, rather than s-HAp, because of its chromatographic characteristics for the separation of acidic and basic proteins. © 1998 Chapman & Hall