Understanding the Adsorption of Small Biomolecules on Model Implant Surfaces

Abstract

The adsorption of biomolecules on metal oxides is believed to be a critical early step in the osseointegration of titanium biomedical devices. Surface science experiments and simulations have been done to study the adsorption mechanism. However, the results are significantly influenced by the following such as the experimental conditions, the deposition methods, and the degradation of the biomolecules during the characterisation process. In this thesis, the adsorption behaviours, including chemical states, adsorption geometries and surface orientations of the biomolecules on TiO2(110) single crystal surface, are studied to provide a fundamental understanding. The reference spectra of 15 biomolecules are obtained by X-ray photoelectron spectroscopy (XPS), carefully minimising the beam damage and providing support for peak assignments for the later biomolecule on the TiO2(110) surface. Secondly, the deposition methods, including evaporation, electrospray and liquid droplet methods, are tested. Among these methods, the liquid droplet method was first invented, where the solution pH can be easily altered, and the molecules can be easily deposited on the substrate surface without bringing more adventitious carbon from the atmosphere. Then, synchrotron-based XPS and near-edge X-ray absorption fine structure (NEXAFS) are employed to study the orientation of aspartic acid (Asp), arginine (Arg), lysine (Lys), tryptophan (Try), tyrosine-ala (Tyr-Ala) and glutathione (GSH) on TiO2(110) single crystal. Results showed that the biomolecules prefer to anchor to the substrate by the deprotonated carboxylate groups, which are perpendicular to the surface. For biomolecules with ring structures, the ring is almost parallel to the substrate for Trp. Lastly, the adsorption of GSH is studied by in situ XPS and NEXAFS with 0-5 mbar water vapour pressure, showing the thin water layer on top of the GSH layer may accelerate the decomposition process with the help of the incident X-ray.

Date of Award	31 Dec 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Andrew Thomas (Supervisor), Rob Lindsay (Supervisor) & Alex Walton (Supervisor)