Effect of Titanium Oxide Functionalized Surface on Adsorption and Dynamic Behaviour of the Amino Acids in an Aqueous Environment Using an All Atomic Molecular Dynamics Simulation

Abstract

Amino acids play vital roles in various events that take place at the interface, such as the adsorption of constituents of tissue fluids onto the material surface, protein behaviour on the implant surface that can affect blood coagulation, bacterial and cell adhesion also change the implant surface properties. Pure titanium and its alloys are widely used for implant fabrication, coating, and drug delivery systems. Titanium dioxide (TiO2) is the passivating layer on top of the titanium surface in corrosive environments such as implant–tissue fluid interface. Understanding the adsorption behaviour of small biomolecules, such as amino acids on TiO2 surfaces, is essential for designing and optimizing biomaterials for biomedical applications. In this study, we investigate the effects of TiO2 functionalized surfaces on amino acid adsorption through all atomic molecular dynamic’s simulations. Using the BIOVIA Materials Studio 2020 software package and the COMPASS force field, which accurately models atomistic interactions in condensed-phase systems, a realistic model of the TiO2 surface functionalized with hydroxyl (-OH), carboxylate (-COOH), amine (-NH2), and thiol (-SH) groups was constructed. Five representative amino acids, including alanine (Ala), glutamine (Gln), lysine (Lys), cysteine (Cys), and aspartic acid (Asp), were selected to provide a diverse range of properties of the biomolecules for studying the adsorption process on TiO2 functionalized surfaces. The molecular simulations to study the process of adsorption were performed using the Forcite Module in Materials Studio at a temperature of 298 K in the canonical (NVT) ensemble. The results revealed that the TiO2 functionalized surface exhibits preferential adsorption of amino acids through a combination of electrostatic, hydrogen bonding, and hydrophobic interactions. The binding energy of amino acids depends on their properties and the characteristics of the TiO2 surface. During the adsorption of alanine on the TiO2 surface, hydrophobic interactions play a significant role, while charged amino acids such as lysine and aspartic acid depend on strong electrostatic interactions with the surface for adsorption. This study also delves into the dynamic behaviour of amino acids on top of various TiO2 surfaces in an aqueous environment as well as their interaction with both water molecules and the surface through hydrogen bonding. The concentration profile of water molecules on top of various TiO2 surfaces was studied. These findings provide valuable insights into the adsorption behaviour of amino acids on TiO2 functionalized surfaces at the atomic level. The results contribute to a fundamental understanding of molecular interactions at implant tissue fluid interfaces and help devise novel TiO2-based nanostructures with improved performance and functionality.