Read/Search this Article
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.