Molecular investigations of tripeptide adsorption onto TiO₂ surfaces: Synergetic effects of surface nanostructure, hydroxylation and bioactive ions

Micro-/nano-topographies on the surface of titanium-based biomaterials are critical features responsible for protein adsorptions, and investigations into the underlying molecular mechanisms are essential to improving the biocompatibility of titanium-based biomaterials. In the present work, classical molecular dynamics simulations were conducted to study the synergetic influences of surface nanostructures, hydroxylation states and bioactive ions on the adsorption of collagen tripeptides onto the TiO₂ surfaces. The nanostructures on the non-hydroxylated surface, i.e., grooves or ridges, favor the formation of highly ordered layers of water molecules at the surface, which create strong barriers for stable adsorptions of tripeptides. Surface hydroxylation, however, makes the water distribution less ordered and more dispersive on hydroxylated surfaces. Thus, tripeptides are able to adsorb stably on the hydroxylated grooves, by passing through the loosely packed water layers and forming hydrogen bonds with the surface hydroxyls. Moreover, the hydroxylation on the grooved surfaces also facilitates the aggregation of calcium/phosphate ions. Consequently, the intermediate calcium/phosphate ions reduce the energy barriers of compact water layers and provide active sites for tripeptide adsorption. The present computational study provides insights into the intrinsic mechanisms of peptide adsorptions on the nanostructured Ti-based biomaterial surface.