ADSORPTION OF CHONDROITIN-4-SULFATE AND HEPARIN ONTO HYDROXYAPATITE -EFFECT OF BOVINE SERUM-ALBUMIN

The adsorption of chondroitin-4-sulphate (C4S) and heparin onto hydrox yapatite (HA) has been studied in the absence and presence of bovine s erum albumin (BSA). Isotherm data at pH 6.8 have shown that BSA in sol ution has no effect on C4S adsorption, whereas heparin affinity and ad sorption decrease. These data suggest that C4S and BSA bind to differe nt calcium sites on the HA surface. Heparin and BSA may compete for th e same calcium sites, or alternatively form heparin-BSA complexes lead ing to less binding due to steric effects. Evidence of an interaction between heparin and BSA in solution has been shown in this study, ther e being negligible interaction for C4S. BSA adsorption-from solution o nto HA decreases with increasing C4S/heparin solution concentration, w hich may be due to glycosaminoglycan-induced conformational change of BSA from a compact to an extended structure. For the HA precoated with BSA, both C4S and heparin adsorption decrease above a certain solutio n concentration. A possible explanation is that precoated BSA masks bi nding sites for the C4S/heparin. The percentage of BSA desorbed from t he precoated HA in the presence of C4S and heparin is < 10% and < 30% respectively, indicating that BSA is strongly bound to the HA surface. (C) 1997 Elsevier Science Limited. All rights reserved.