Adsorption of bovine serum albumin onto hydroxyapatite

The adsorption of bovine serum albumin (BSA) onto hydroxyapatite (HA) has been studied as a function of protein concentration, pH and ionic strength. Isotherm data (adsorption being a reversible process) have been analysed using the Langmuir model, the adsorption parameters AT (maximum amount of protein adsorbed, mg m−2) and K (affinity constant, L g−1) being calculated for each solution condition (except NaF). For the pH dependence of adsorption, both AT and K increase with decreasing pH, indicating that both electrostatic and hydration effects are important. For the ionic strength dependence, increasing NaCl concentrations result in a slight increase in AT, but K decreases. With increasing CaCI2 concentrations the AT and K values increase, the opposite being true for increasing concentrations of Na2HPO4. NaF both enhances and inhibits adsorption depending on the concentration. Possible reasons for these results are discussed.