Conformational changes of fibrinogen adsorption onto hydroxyapatite and titanium oxide nanoparticles

The effect of surface adsorption on protein structure is of increasing inte rest in the biological, medical, and industrial fields. The structure of fi brinogen, a major plasma protein, adsorbed onto TiO2 and HA was examined by employing differential scanning calorimetry (DSC), circular dichroism (CD) , and fluorescence spectroscopy. It was found that the TiO2 surface slightl y decreased the ordered secondary structure of the protein; the fibrinogen conformation further changed upo washing and desorption. The alpha-helix co ntent decreased gradually during the adsorption, washing, and desorption pr ocesses. The results were also used to estimate the overall structure of th e protein in the adsorbed and desorbed states. It is significant that the f ibrinogen transition enthalpy increased in each case upon adsorption onto H A. The transition enthalpy increased upon adsorption onto TiO2 in two out o f three cases tested. These results, combined with the DSC thermograms of f ibrinogen at different ionic strengths, suggest that electrostatic interact ions are the main mechanism controlling the adsorption of fibrinogen to TiO 2 and HA. (C) 1999 Academic Press.