In recent years cerium oxide has been used prolifically in various engineering and biological applications.1–10
Ceria nanoparticles (nanoceria), as opposed to their coarser counterparts, have a large number of surface defects. These defects, which are primarily surface oxygen vacancies, cause a change in the local electronic and valence arrangement that stabilizes the trivalent oxidation state (III).11–13
Ceria and nanoceria can be found in several high-end research technologies, such as solid-oxide fuel cells,14
high-temperature oxidation protection materials,15
and more recently, solar cells.18
Recently, ceria nanoparticles have emerged as a fascinating and lucrative material in biomedical science due to their unique ability to switch oxidation states between III and IV based on environmental conditions.19
The ability of nanoceria to switch between oxidation states is comparable to that of biological antioxidants.2
This capability imparts nanoceria with the very important biological property of radical scavenging. A sustained and collaborative effort has demonstrated the capability of nanoceria to protect against cellular damage caused by various radicals in different tissues and organ systems as well as biomedical applications. Nanoceria has been shown to impart protection against the reactive oxygen species (ROS)1
and against radiation damage.3
Lung cancer, colon cancer, breast cancer, pancreatic cancer, and prostate cancer are common causes of morbidity and mortality in the United States, with approximately 100 new cases diagnosed each day. Recently, ROS have been implicated in the development of cancer, including the initiation, promotion, and progression phases.20
For example, ROS may interfere with cytoplasmic and nuclear signal transduction pathways, cause structural alterations in DNA, and modulate genes related to cell proliferation, apoptosis, and differentiation processes.21
McGinnis et al. have shown ceria nanoparticles can prevent retinal degeneration induced by intracellular peroxide molecules.1
The application of ceria nanoparticles in the treatment of spinal cord injury and other central nervous system-based neuron degenerative diseases4
has proven the biological importance of nanoceria beyond doubt. A molecular mechanism to explain the antioxidant properties of nanoceria has been established using a superoxide dismutase mimetic activity-based model.2
In the wake of several reports that describe the potential toxicity of certain nanophase materials, the unique biomedical properties of nanoceria suggest that it may be an ideal nanophase material.22,23
In order to develop medical applications for nanoceria, it is important to synthesize nanoceria in biologically relevant media so that it is compatible with organism physiology. Synthesis of stable aqueous media of nanoceria requires the understanding of colloidal chemistry (zeta potential, particle size, dispersant, pH of solution, etc.)24
as well as reduction/oxidation behavior. It must be noted that the synthesis of nanoceria in biocompatible media is a challenging task as the synthesis should not interfere with the redox ability of nanoceria and the nanoparticles so formed should not be toxic to cells. A host of biologically relevant media, including ethylene glycol (EG), polyethylene glycol (PEG), glucose, or dextran, can serve as media for synthesizing and/or dispersing the nanoceria particles. 25,26
While nanoceria particles can be synthesized and then re-dispersed in biological media, our experience with precipitation and redispersion has been limited with respect to biological efficacy. Thus this paper will discuss the direct synthesis of nanoceria in various aqueous biocompatible media and the cell viability of these materials. A brief overview of biological importance of nanoceria and its relation to the unique chemistry of nanoceria is paramount to this discussion.
How would you…
…describe the overall significance of this paper?
Due to its unique redox properties, cerium oxide (ceria) is finding widespread use in the treatment of medical disorders caused by reactive oxygen intermediates. The synthesis of nanoceria in biocompatible media has also been reported along with cell viability.
…describe this work to a materials science and engineering professional with no experience in your technical specialty?
Reactive oxygen species have been recently implicated in the initiation, promotion, and progression phases of tumor development. The unique valence and oxygen defect structure of cerium oxide nanoparticles can be optimized to promote scavenging of reactive oxygen species.
…describe this work to a layperson?
Cerium oxide nanoparticles exhibit unique capabilities for quenching free radicals. In this paper, the synthesis and biological properties of these materials were examined. These materials could find widespread use in the treatment of free radical-mediated medical disorders.