The influence of surface energy on competitive protein adsorption on oxidized NiTi surfaces

NiTi shape memory alloy surfaces, untreated, and oxidized by a new oxidation treatment (OT) in order to obtain a Ni-free surface, have been compared in terms of surface energy and protein adsorption behavior. The polar and dispersive components of the surface energy have been determined. A competitive adsorption process between fibronectin and albumin has been carried out by 125I-radiolabeling. Moreover, the adhesion strength between both proteins and NiTi surfaces has been evaluated by performing an elution test. The results show that the OT treatment enhances the hydrophilic character of NiTi surfaces by significantly increasing the polar component of their surface energy. Moreover, the OT treatment increases the amount of fibronectin and albumin adsorbed. It also increases the fibronectin affinity for NiTi surfaces. The elution test results could suggest a conformational change of fibronectin as a function of chemical composition of NiTi material and of surface treatment. Finally, a linear correlation between the amount of adsorbed albumin and the polar component of the surface energy of NiTi surfaces has been demonstrated. This work indicates that the OT treatment has an influence on the surface energy value of NiTi materials, which in turn influences the protein adsorption process.