Adsorption characteristics of albumin and lysozyme on heat-treated hydroxyapatite

Adsorption characteristics of bovine serum albumin (BSA) and lysozyme prepared from egg white (LSZ) were investigated on hydroxyapatite (HAp) powders which were prepared in a stream of water vapor and in air at the heating temperatures of 673-1473 K, The BSA or LSZ adsorption isotherm obtained on these HAp's in phosphate buffer solutions satisfied Langmuir's equation, regardless of the kind of gas atmosphere for the HAp heat treatment. The saturated amount of adsorption per surface area (designated by A(SA) (B) for BSA and A(SA) (L) for LSZ) and the heat of adsorption (Q(B) for BSA and Q(L) for LSZ) increased and decreased, respectively, with gradual increase in the crystallite size of HAp at 673-1073 K (region I). At 1073-1473 K (region II), A(SA) (B) and A(SA) (L) appreciably increased, whereas Q(B) and Q(L) were gradually reduced due to the transforming morphology of HAp particles as well as grain growth. A(SA) (L) became about fourfold larger than A(SA) (B), and Q(L) became 10-30% higher than Q(B) in the two regions, indicating that the adsorption ability of LSZ on the P-sites of HAp is stronger than that of BSA on the C-sites of HAp. The increase of HAp heating temperature can effectively enhance the growth of crystallite size and the transformation of microstructure, so that the total numbers of C- and P-sites increase and both the basic strength of the C-sites and acid strength of the P-sites are reduced, The ratios of the numbers of the two sites (P/C) were kept almost constant at 4.34 +/- 0.01 in region I and gradually increased from 4.34 to 4.75 in region II.