Abstract
The application of nanoscience in medicine has undoubtedly led to dramatic improvements in the healthcare sector. Yet, the use of nanomaterials in oral health and preventive dentistry remains underdeveloped. In particular, the prevention of tooth decay (the most common disease worldwide) and the subsequent treatment of carious lesions, which are ongoing challenges in dentistry, could significantly benefit from new research advances. Here, the development of two distinct nanomaterials innovations is presented with the aim of preventing dental caries.
First, C=C–modified silver nanoparticles were synthesised with a final aim of bestowing antimicrobial properties to resin-based dental materials. The use of the microemulsion synthetic method allowed the formation of small (< 5 nm) uniformly dispersed spherical silver nanoparticles (AgNPs) with a methacrylate (MMA)-based capping agent covalently bound to the AgNP surface through a strong sulfur-silver bond. It was found that these C=C–modified silver nanoparticles, referred to as MMA-AgNPs throughout this thesis, would be able to partake in photopolymerisation reactions, such as those used for the setting of resin-modified glass ionomer cements. It is theorised that this would result in AgNPs uniformly dispersed through and covalently bound to the resin material. The yield of silver was however too low for practical applications so before this avenue could be explored, it was found necessary to improve the yield of the microemulsion synthesis.
A combination of nuclear magnetic resonance and dynamic light scattering experimental techniques was therefore used in an attempt to understand the interactions of the MMA-derivative secondary capping agent and the reverse micelle system, thought to be responsible for the low yield of the MMA-AgNPs synthesis. The behaviour of the capping agent was found to be strongly dependent on the presence of silver nanoparticles within the reverse micelle, the latter being seen as a driving force for irreversible aggregation upon addition of the capping agent to the system. Whilst insightful, this specific study proved unsuccessful for the optimisation of the microemulsion synthesis of C=C–modified silver nanoparticles, though it is believed that further research is warranted.
The second innovation discussed herein is the fabrication of new porous, nanoscale metal-organic frameworks (nMOFs) containing Ca2+ and/or Sr2+, and Na+ ions using the microemulsion due to the growing evidence of the osteogenic properties of calcium and strontium. The tunability of the microemulsion method allowed the formation of nMOFs of morphologies and compositions that are not easily achieved on the macroscale. Indeed, the surfactant used in this microemulsion method (sodium bis(2-ethylhexyl)sulfosuccinate, NaAOT) was found to act as an unexpected source of Na+ ions, allowing the synthesis of unique di- or tri-metallic nMOFs. A preliminary study looking at using AOT as a source of alternative metal ion involved the synthesis of Mg(AOT)2 is also discussed herein.
The nMOFs are designed to be employed in a dental cement to restore the damaged tooth through slow continuous release of Ca2+ and/or Sr2+ for remineralisation purposes. The feasibility of incorporating the nMOFs to a glass ionomer cement was evidenced in a proof-of-concept study. The mechanical properties of dental cements used in this study were not found to be significantly impacted by the addition of nMOF whilst the bioactivity of nMOF-modified cements seemed enhanced. This study therefore provides an excellent platform for future investigations of the biomedical use of nMOFs.