Uptake and toxicity of cerium dioxide nanoparticles with different aspect ratio
Graphical Abstract
Introduction
Nanoparticles are commonly defined as particulate matter with one or more dimensions at the nanoscale, and the application of engineered nanoparticles has been explosively extended with the development of nanotechnology and the nano-industry. In addition, owing to relatively excellent chemical, electrical, magnetic, and luminescent properties, rare earth elements have been used as raw materials for the development of oxide nanoparticles as well as metals. The term ‘rare earth’ originated from a typical dispersion due to geochemical characteristics and rarity in mineral form but is relatively plentiful in Earth’s crust. Especially cerium is the 25th most abundant element, and cerium dioxide nanoparticles (CeONPs) can function as significant electrical conductors and catalysts due to two common oxidation states (Ce3+ and Ce4+) on the surface. Thus, they have been extensively applied in research for future energy development, such as solid fuel cells, fuel additives, solar cells, and batteries (Eriksson et al., 2018; Xu and Qu, 2014; Chen et al., 2018; Das et al., 2013). As well, the radical scavenging capacity and low toxicity of CeONPs are promising for application as antioxidants and UV protectants in pharmaceutical fields and the cosmetic industry. Moreover, CeONPs have been developed for chemical-mechanical polishing, which is essential in the fabrication process of semiconductor devices in combination with silica nanoparticles (Chen and Stephen Inbaraj, 2018).
Meanwhile, accumulated evidence suggested that the smaller size and larger surface area of nano-sized particles can make it easier to interact with cellular components than micro-sized particles, causing more severe cellular damage (Braakhuis et al., 2014). The surface charge can also significantly influence the cellular uptake and interaction between nanoparticles and organelles (or biomolecules), followed by cell death (Asati et al., 2010). Additionally, the shape has been demonstrated as a critical factor that affects the toxicity and inflammatory response of nanoparticles in vivo and in vitro (Dong et al., 2019, Huang et al., 2019; Danielsen et al., 2020). Therefore, the potential adverse effects of engineered nanoparticles, especially with high volume production and high economic importance, on human health and the environment should be evaluated in detail with a thorough validation of the characterization of nanomaterials (Gorka et al., 2015). In our previous study, we developed CeO2 nanorods with various crystalline structures (single and polycrystalline), revealing a one-dimensional morphology with a smooth surface and an uneven surface, respectively (Sung et al., 2018). In addition, we found no significant differences between cytotoxicity induced by four sizes of CeONPs with different surface properties (15, 25, 35, and 40 nm) (Park et al., 2008).
Macrophages are phagocytes that serve in the front line of the specific and non-specific immune responses against foreign bodies, and alveolar macrophages, a type of macrophage found in the alveoli of the lungs, play a central role in the clearance of foreign bodies which pass the mechanical defense lines of the respiratory tract. Therefore, healthy alveolar macrophages are essential for the uptake and clearance of inhaled nanoparticles, ultimately maintaining normal lung function. In this study, we aimed to identify the effects of shape in CeONPs-induced toxicity by comparing the pulmonary inflammatory response of hexagonal- and rod-shaped CeONPs (hereafter, H-CeONPs and R-CeONPs, respectively) in mice. In addition, we tried to identify indicators that can predict responses what will happen in animals using alveolar macrophages.
Section snippets
Manufacturing and characterization of CeONPs
H-CeONPs (Sung et al., 2019) and R-CeONPs (Sung et al., 2018) were synthesized through a time-dependent hydrothermal method, respectively. Firstly, Ce(NO3)3∙6 H2O (2.5 g, ACROS, purity 99.5%) and NH4OH (8 mL, SAMCHUN, purity 28–30%) were dissolved in distilled water (DW, 62.5 mL) with stirring. The as-prepared solution was reacted in a 100-mL Teflon-lined stainless-steel autoclave at 90 °C for 6 h or 1 h (for H-CeONPs or R-CeONPs, respectively). The as-obtained particles were washed using DW
Characterization
As shown in Fig. 1A and B, R-CeONPs were comprised of straight nanorods with approximately 13 nm, and the driving force of the growth of R-CeONPs exhibited oriented attachment, which minimizes the surface energy of the facet to create anisotropy (Sung et al., 2018). The lattice fringe of the nanowire of R-CeONPs was consistent with the (100) interplanar spacing of the cubic CeO2 (Fmm, PDF No.81–0792), revealing the growth direction of [211] (Fig. 1B). The detailed morphology between the
Discussion
The development of a reliable model to predict the toxicity of nanomaterials is possible through the accumulation of scientific data obtained from in vitro and in vivo tests performed with nanoparticles that show different properties. Proteins bound on the surface of nanoparticles (known as ‘protein corona’) can significantly affect the interaction between nanoparticles and the biological system by altering the surface properties of nanoparticles used in tests, resulting in inconsistent results
Declaration of Competing Interest
The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Eun-Jung Park reports was provided by The Ministry of Science and ICT.
Acknowledgement
This research was supported by a grant from the Ministry of Science and ICT (2021M3A7B6031389 and 2021R1F1A1054211).
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These authors contributed equally to this work as first authors.