Engineering oxygen vacancies through construction of morphology maps for bio-responsive nanoceria for osteosarcoma therapy

Abstract

The present work provides guidelines for the engineering of oxygen vacancy concentrations using morphology-maps based on the characteristics of nanoceria (CeO_2−x) nanocubes, nanorods, and truncated nanooctahedra. These were characterised by XRD, TEM, BET, DLS, and XPS. The morphology maps reveal that the redox performance, particle size, and surface roughness (apparent porosity) can be optimised by engineering the oxygen vacancy concentrations, but the morphology is dominated by the reaction temperature. However, the oxygen vacancy concentration is controlled by the concentration of the NaOH precipitant/oxidant. These vacancies can be potentially located at the surface, subsurface, and bulk regions, but the subsurface vacancies provide the principal redox activity. The biological effects of nanoceria in terms of oxygen vacancies were analysed in normal and cancer cells. Nanoceria particles exhibit antioxidant and cytoprotective effects at physiological pH 7.4 but prooxidant and cytotoxic effects at tumour microenvironment pH 6.4. The relative redox performances and cytotoxicities are in the order nanocubes < nanorods < truncated nanooctahedra, which is a direct reflection of the relative oxygen vacancy concentrations. The redox performance of nanoceria has been contextualised by cellular uptake and its quantification in osteosarcoma cells.