Atomic scale insight into the adsorption mechanism of aspartic acid on Ti-6Al-4V dental implants: a combination of DFT and AIMD.

Aspartic acid (Asp) serves as a critical component in surface modification strategies for Ti-6Al-4V dental implants, although the adsorption mechanisms of Asp on Ti-6Al-4V oxide layers remain unclear. Herein, the adsorption mechanisms of Asp on pristine and V or Al doped rutile TiO(2) (110) surfaces are systematically investigated using density functional theory (DFT) and ab initio molecular dynamics (AIMD). Pristine TiO(2) exhibits fifteen distinct Asp adsorption configurations, with the more stable configurations primarily governed by synergistic dual-functional group coordination and proton transfer mechanisms, which collectively enhance binding strength. AIMD simulations reveal the dynamic adsorption evolution of the Asp functional group at room temperature, involving molecular reorientation and facile hydroxyl proton migration. Electronic structure analyses demonstrate that localized electron-deficient regions at 5-fold coordinated Ti sites and d-orbital-driven covalent bonding dominate the robust Asp anchoring. The doping of Al or V reduces electron transfer at surface active sites compared to pristine TiO(2) following Asp adsorption, thereby weakening the adsorption strength between the substrate and Asp. Al doping at 5-fold coordinated Ti sites directly weakens the adsorption strength because of its reduced electron-donating capacity and diminishing orbital overlap with non-localized sp(3)-hybridized orbitals of Al (E(ads) is decreased by ~ 20%). In contrast, V doping at 6-fold coordinated Ti sites induces long-range electronic perturbations, indirectly lowering the adsorption strength of 5-fold coordinated Ti sites (E(ads) is reduced by ~ 6%). The obtained results indicate that the doped Al and V atoms in TiO(2) formed on the Ti-6Al-4V surface detrimentally impacts bioactive molecular coatings, necessitating mitigation strategies. This work provides atomic-scale insights for engineering TiO(2)-based biointerfaces, balancing dopant effects and adsorption performance in implant design through tailored surface oxidation protocols.