Biomolecules – biomaterials interactions: IR study of the adsorption, in model conditions, of glycine on Hydroxyapatite and TiO2

This thesis has been devoted to the study of the adsorption of an amino acid, glycine (Gly), on the surface of different nanomaterials representative of inorganic biomaterials. In particular, a kind of calcium phosphate, hydroxyapatite, that is considered as a synthetic model of the main mineral constituent of human bones, and a commercial kind of titanium dioxide (P25 produced by Degussa), considered in its pristine and fluorinated forms; actually titanium oxide layers, often with a nanostructured texture, are found at the surface of Ti-alloy orthopaedic/dental implants. The knowledge of the behaviour of the surface of these materials toward biomolecules, is of interest for optimizing their performances when used in prosthetics implants. In particular, the considered materials were of interest mainly due to their nanostructure, because such dimensional features are known to increase the biomimetic/bioactive character, leading to more favourable interactions with the biological environment. Moreover, the investigation at a molecular level of the interaction of materials and biomolecules, usually dissolved in aqueous medium with a rich chemical composition, is a really difficult task. Furthermore, the role, nature and structure, at an atomic level, of the sites exposed at the surface of biomaterials entered only quite recently in the pool of factors to be known to rationalize/optimize the behaviour of such materials towards biomolecules. In this respect, also the achievement of new insights with a fundamental character about materials-biomolecules interactions, even actually in model conditions, is of interest. Thus, the experimental work carried out in this thesis started from a model condition: the glycine adsorption from the vapour phase, and then moved to a more realistic system, where the absorption of glycine was carried out from aqueous solutions, where the interaction with the materials surface is mediated by the solvent.
This dissertation is structured in a first chapter to introduce the subject of the “Biomaterials”, which represent the “applicative scenario” of the subject of the results obtained in the present work, with a particular attention to the “biological surface science” the scientific sector dealing with the processes that occur at the interface between a solid and a biological environment. On the basis of this considerations the target of this thesis was defined, the next two chapters are devoted to the presentation of the studied materials and the employed techniques. Due to the central role of glycine in this research, in the fourth chapter, literature and experimental data dealing with the physical-chemical features of this aminoacid, have been reported. Special attention was devoted to the IR spectra of glycine in different forms, as IR spectroscopy was the method used to investigate the Gly/materials interactions. The experimental results obtained for glycine adsorption from the vapour phase are reported in chapter five, considering separately, in different section, the investigation dealing with each specific material. In particular, for hydroxyapatite, also a supporting comparison with computational data is reported as landmark for the interpretation of experimental data. Finally, in the last chapter (the sixth) preliminary results of the study of glycine interaction, with hydroxyapatite and TiO2 P25, in an aqueous environment, are reported.