Physicochemical and Antibacterial Properties of Bivalent Freeze and Furnace Dried Nanoscale Cerium Oxide

Bone healing is a complex process, and if not managed, can lead to bacterial infections, non-union and compromised healing of bone. The broad overuse of antibiotics has led to the emergence of antibiotic-resistant bacteria. Due to the growing urgency to minimise the dependency on antibiotic drugs, alternative treatment strategies, including the use of nanoparticles, have attracted significant attention. Bivalent cerium oxide nanoparticles (Ce4+ and Ce3+) synthesised via a hydroxide mediated approach were calcined at 280, 385 and 815 ˚C identified using the Simultaneous Thermal Analysis technique. The resulting nanoparticles were characterised using X-ray Powder Diffraction, Fourier Transform Infrared Spectroscopy, Ultraviolet-Visible Spectroscopy, Transmission Electron Microscopy, and Electron Energy Loss Spectroscopy. The antibacterial potential of cerium oxide nanoparticles corresponds to the particle size and the presence of oxygen vacancies in the fluorite crystal structure. The antibacterial efficacy of nanoparticles was characterised at concentrations of 50, 100 and 200 µg/ml and tested against the following strains, Escherichia coli, Staphylococcus epidermis and Pseudomonas aeruginosa by determining the half-maximal inhibitory concentration (IC50). The calcination temperature was found to affect the agglomeration tendency, particle size distribution and the ratio of Ce3+:Ce4+ oxidation states. The hydroxide mediated approach yielded spherical nanoparticles of ceria with particles size ranging from 4 nm to 53 nm. The freeze-dried bivalent nanoparticles exhibited 18.5 ± 1.2%, 10.5 ± 4.4%, and 13.8 ± 5.8% increased antibacterial efficacy against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus epidermis, respectively compared to nanoparticles consisting solely of Ce4+ ions, i.e. nanoparticles calcined at 815 ˚C.