Hierarchical structures of functionalized Detonation NanoDiamonds (DNDs) for biomedical applications

Titanium and its alloys are among the most used materials for medical implants as they fulfil most of the requirements for a truly biocompatible material. However, there is always room for improvement, as infections and low wear resistance are the most frequent causes of implant rejection. In order to improve their biological, chemical and mechanical properties, different surface modifications have been proposed, each with its advantages and setbacks. In this thesis, a new surface coating based on Detonation NanoDiamonds (DNDs) is introduced. DNDs are small carbon nanocrystals or nanoparticles with sizes within the range of 5-10 nm, although they tend to form bigger aggregates and agglomerates in suspensions. Their high surface-to-bulk ratio and the excellent biocompatibility make DNDs a prime choice for innovative biomaterials. After a first structural characterisation of the DND particles, three main aspects of the proposed coating were investigated. Dynamic light scattering, Zeta potential measurements and UV-VIS absorption spectroscopy were employed to identify a stable, water based suspension with the smallest achievable agglomerate size, between 40 and 50 nm, which was observed in a bead-milled colloid with pH 12. Based on the surface analysis using scanning electron microscopy, atomic force microscopy and nano indentation analysis, covalent bonding of detonation nanodiamonds to the implant surface appeared to be more suitable as a coating strategy than dip coating or electrophoretic deposition. The biochemical modification of the surface of DND agglomerates was carried out by binding fluorescently labelled single-stranded DNA molecules to the nanoparticles and assessing the successful covalent functionalisation with fluorescent microscopy, dynamic light scattering and Zeta potential measurements. Based on the results obtained in this thesis, different strategies towards designing the optimal DND-based surface coating and towards the introduction of wear and infection resistant medical implants are finally presented.