Adsorption of glycosaminoglycans to commercially pure titanium

Aqueous solutions of the glycosaminoglycans (GAG), chondroitin-4-sulphate (C4S), chondroitin-6-sulphate (C6S), heparan sulphate (HS) and hyaluronan (HY) were reacted with 5 g samples of both native and calcium-treated titanium powder (99.5% pure) for 0-48 h in 10 ml volume at 37 degrees C. Residual GAG was detected in the supernatant following recovery of the TiO2-GAG complex by centrifugation (5000 g for 1 min) as hexuronic acid using the carbazole tetraborate method of Bitter and Muir. No adsorption on to native TiO2 was evident. In contrast, prior treatment of TiO2 with calcium produced a significant adsorption of C4S to a maximum of 60 micrograms of GAG per gram Ti. Only trace amounts of C6S, HS and hyaluronan interacted in the same way. Further evidence of interaction was obtained following the liberation of bound GAG from the TiO2-Ca-GAG complex with EDTA and identification using cellulose acetate electrophoresis. These findings suggest that calcium ions are required for adsorption of GAG to TiO2 which is mediated through the anionic determinants of the GAG surface and that the special configuration of C4S, the predominant chondroitin sulphate isomer found in alveolar bone, is important in the adsorption process. The implication of these findings in relation to the interaction between bone and titanium implants is discussed.