Characterization of bioactive glass nanoparticles for composites in biomedical applications

Bioactive glasses have been known for their osteogenic and antibacterial properties for many years. Their versatility of applications in regenerative medicine plays a significant part in the vast amount of related scientific studies currently taking place. In the last few decades, using various metals as dopants in bioactive glasses has considerably enhanced their biological properties, making them excellent candidates for therapeutic treatments. This thesis focuses on the study of the structural and biological properties of silica-based bioactive glass nanoparticles, co-doped with silver and cerium. More specifically, the synthesis protocol for Ag-doped bioactive glass nanoparticles, previously characterized elsewhere, was modified to incorporate cerium into the glass network, replacing aluminum. The nanomaterial was developed using a modified Stöber method, one-step catalysis process. The characterization is centered on three main areas of properties: structure and composition, degradation and bioactivity, as well as biocompatibility and antibacterial activity. Firstly, the structure of the modified silica network was evaluated through X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), Thermogravimetric analysis (TGA), Differential Thermal Analysis (DTA), Transmission electron microscopy (TEM) and Dynamic Light Scattering (DLS). The synthesised nanoparticles (~7 nm) were found to have low network connectivity and great thermal stability for temperatures up to 1300 oC, as well as having a tendency to form agglomerates (50-70 nm) due to their surface charge of -25.5 mV. The successfull incorporation of the targeted elements, in a uniformly distributed manner, not accounting for the lack of an exact quantification of phosphorus, was verified. Additionally, the partial reduction of silver to metallic and cerium oxide within the samples was identified. Notably, the existence of silver ions in the glass matrix was also indirectly confirmed. The degradation of the particles was evaluated in terms of size distribution and pH level in TRIS buffer suspension, while the in vitro bioactivity was assessed in simulated body fluid (SBF). The measurements indicated a faster degradation rate in the first week of suspension, compared to the following 2 weeks of immersion. Additionally, the formation of hydroxyapatite bone-like layer was found to start after 5 days of suspension and was further investigated with XRD, FTIR, TEM and SEM-EDS. Moreover, to avoid the risk of toxic levels of pH (~8) in the first days of degradation, a 4-day pre-conditioning of the nanoparticles to maintain neutral pH values in the medium, was deemed necessary before the biological characterization. Various concentrations of the glass nanoparticles were tested for hemolysis, cell proliferation and antibacterial behaviour, using human red blood cells, periodontal ligament fibroblast cells (PDLFs) and St. aureus, respectively. The results found all the concentrations to be non-hemolytic. Increased cell proliferation was facilitated in low concentrations, while higher concentrations exhibited promising antimicrobial activity over 48 hours.