1. Introduction
Nanoparticles (NPs) are materials that are less than 100 nm in size [
1,
2] and are widely used in various biomedical applications such as biosensors [
3,
4], transfection agents [
5], and cancer treatment [
6,
7] due to their modifiable material properties. Magnetic NPs (MNPs) coated with biocompatible materials are used in biomedical applications as contrast agents in magnetic resonance imaging (MRI)-based cell labeling, cell tracking, cell separation, and drug delivery vehicles [
8,
9,
10,
11,
12]. For example, silica-coated magnetic nanoparticles MNPs@SiO
2(RITC) are synthesized MNPs consisting of a cobalt ferrite core, CoFe
2O
3, and a silica shell surrounded by rhodamine B isothiocyanate (RITC) and are used for cell labeling and tracking in vivo [
13].
Despite their benefits in biomedical applications, NPs pose potential risks to human health when accidentally entering the human body. These risks include [
14], respiratory and cardiovascular problems [
15], and neurodegenerative diseases [
16,
17] due to their nanoscale physicochemical properties, such as a large surface-to-volume ratio, Fenton reaction, and integration of organic compounds [
18,
19,
20]. One of the main reasons that contribute to the toxicity of NPs is their reactive surface area [
21], which induces free radical reactive oxygen species (ROS) [
22,
23] that cause inflammation, endoplasmic reticulum stress, decreased proteasome activity, and disruption of cellular metabolism [
24,
25]. In particular, NPs induce ROS production, which in turn leads to lipid peroxidation and abnormalities in the cellular mechanisms and cytoskeleton [
26].
NPs also cause toxicity in the cellular cytoskeleton by altering its organization, decreasing cell membrane fluidity, and damaging cytoskeletal proteins [
27]. When NPs enter the cell
via endocytosis, they disrupt the actin structure and damage cellular tight junctions of the cells [
28]. After internalization of NPs into the cell, ROS production increases by more than 50%, inducing lipid peroxidation and resulting in decreased cell membrane fluidity [
28]. Furthermore, NPs alter cytoskeletal components such as fascin (FSCN1) and paxillin (PXN) [
28]. These toxic effects of NPs on the cell cytoskeleton can change biochemical signals that affect the cell's mechanobiological responses, such as traction force (TF) production and rigidity sensing. These responses determine essential cellular functions such as cell migration, division, and proliferation [
29,
30].
Various methods have been developed to assess the toxicity of NPs, as shown in
Figure 1. Biochemical methods such as ATP, ROS, and lipid production levels have been used to demonstrate the toxicity of MNPs@SiO
2(RITC) in multiple cells at higher concentrations of 1 µg/µl. Migration and invasion assays have also been used to investigate NP toxicity [
25,
31]. However, these methods may not be sensitive enough to detect the toxic effects of MNPs@SiO
2(RITC) even at concentrations of 1 µg/µl. On the contrary, mechanobiological analyses, such as cell surface area, cell aspect ratio, length of filopodia, focal adhesion area, TF production, and stiffness detection measurements, are more sensitive to detecting the toxicity of NPs below 1 µg/µl [
31,
32]. Biochemical assays that are used to study the effects of NPs have typically been applied to collective cells and may not be sensitive enough to detect NP concentrations below 1 µg/µl. In contrast, mechanobiological methods that are used to study the behavior of individual cells are more sensitive in detecting NP toxicity but require advanced equipment and skilled personnel. As a result, there have been relatively few studies on nanotoxicity that have utilized mechanobiology methods.
Figure 1.
Schematic diagram illustrating the various biochemical and mechanobiological methods used to study nanotoxicity.
Figure 1.
Schematic diagram illustrating the various biochemical and mechanobiological methods used to study nanotoxicity.
A variety of technology platforms and assessment systems have been developed to analyze the mechanical and physical changes that occur at the cellular level, allowing for the analysis of biophysical phenotypes. These changes can provide insights into how mechanical signals affect the biological and functional responses of cells to NP treatment [
31,
33,
34]. Methods used to study cell biophysical responses include atomic force microscopy, micropipette aspiration, uniaxial stretcher, optical and magnetic tweezers [
31,
35,
36]. Advanced techniques, such as tensile force microscopy, have been developed to analyze the mechanical forces between cells and their surrounding matrix using soft elastic gel substrates [
37,
38]. Recently, submicron elastomeric pillars made of polydimethylsiloxane (PDMS) have been developed to detect nanometer-levels of cellular traction forces [
31,
39,
40] and rigidity sensing [
32,
41]. These techniques incorporate microscopy to study cells treated with NPs [
32,
42].
The mechanobiological response elicited by biomechanical signals from the external environment is essential for regulating normal cell functions. Altered mechanobiological responses can lead to diseases such as cancer, asthma, and heart disease [
43], highlighting the importance of studying the mechanobiological effects of NPs on cells. To investigate these effects, various methods have been employed, including the use of polydimethylsiloxane (PDMS) pillars to study cell motility, TF production, and rigidity sensing contractions of a cell. Soft and rigid PDMS surfaces have also been utilized in conjunction with cell morphological analysis to study a cell's rigidity sensing ability. Mechanobiological methods focus on early events of cell attachment, spreading, and motility, making them a fast and sensitive approach for studying the toxicity of NPs.
This review provides an overview of the toxicity of various nanoparticles (NPs) on the components of the cell cytoskeleton, including their corresponding toxic concentrations. Additionally, we examine the effects of MNPs@SiO2(RITC) on cell mechanobiology, specifically in terms of cell motility, TF production, and rigidity sensing. Given the limited research on the toxic effects of NPs in the field of mechanobiology, this review focuses exclusively on MNPs@SiO2(RITC) and its potential implications. By exploring the toxic effects of NPs on cell mechanobiology, this review aims to shed light on the broader impacts of NPs on cell function and to provide insights into new ways of analyzing NP toxicity to make them safer for biomedical applications.