**4. Conclusion**

Recent studies on the *in vitro* cytotoxicity of nonmagnetic and magnetic structures in biomedical applications were reviewed, taking into account nanoparticles and nanowires/nanorods. A summary of the results of representative studies is provided in **Table 1**.

Comparisons between the cytotoxicities of those different nanomaterials are generally difficult to make, due to the vast range of methods, concentrations, dimensions, cell lines, etc. For instance, the concentrations reported in the different studies were typically evaluated using either ICP or cryogenic TEM. However, the concentration or dose of the nanomaterial plays a significant role in the cytotoxic response as well as the biomedical applications.

In addition, the particle size plays a major role in the cytotoxic properties of the nanostructure, whereby both the cellular uptake efficiency and pathway are affected, with smaller particles

**Table 1.** Summary of *in vitro* cytotoxicity studies with different kinds of nanoparticles (NPs) and nanowires (NWs), NWs with aspect ratio < 10 are often called nanorods (NR), SPION referred to superparamagnetic iron oxide NPs.

The induction of ROS after dissolving the nanostructures in the lysosomes was shown to be the primary underlying cause of the toxicity in several cases, leading to cell death through the apoptotic pathway, due to ROS generation and mitochondrial damage. The acidic condition inside the lysosome increases the digestion of the particles, enhancing the release of ions that

being internalized faster than larger ones.

**Nanostructure** 

**Surface coating**

Au NPs – 1 and 10 ppm 2–4,

Au NRs PEG 0.5 mM 65 nm

Ag NWs – 4 μg/cm2 100 nm

40–50 nm NPs, 250 μg/mL for 10–15 nm NPs

SPIONs – 100–250 μg/mL 47 nm BRL 3A rat

per cell

Ni NWs – 5 μg/mL 5.4 μm

SPIONs PEG 1 mg/mL for

Fe NWs – 10,000 NWs

**Nanostructure concentration**

**Average size**

5–7 and 20–40 nm diameter

length and 11 nm width

diameter and 28 μm length

40–50 nm diameter, 10–15 nm diameter

10 μm length and 50 nm diameter

length and 33 nm diameter

Au NPs BSA – 20 nm HepG2 95% LDH assay [31]

J774 A1 macrophages

**Cell line Cell viability Viability test References**

Review of *In vitro* Toxicity of Nanoparticles and Nanorods: Part 1

HeLa cells >90% MTT assay [45]

decrease in cell proliferation and increase of membrane instability

40–50 nm NPs, 70% for 10–15 nm NPs

HCT 116 cells <80% MTT, LDH

70% MTT, LDH

assay

assay

Multisizer quantification

http://dx.doi.org/10.5772/intechopen.76365

Alamar Blue, LDH assay

MTT assay [75]

MTT assay [98]

[40]

221

[64]

[53]

[107]

Cell proliferation decreased to 30–40% for all three sizes at 10 ppm

THP-1 cells Significant

hTERT-BJ1 100% for

HeLa cells No significant effect

liver cells

**type**

While the concentrations and exposure times are critical factors, the toxicity of these nanostructures is also material dependent. These relations can be seen in **Figure 5**, which presents the average values reported for the cell viabilities (ignoring differences in concentrations, incubation times, etc.), when exposed to the nanomaterials in the studies covered in **Table 1**. Fe nanomaterials showed higher cell viabilities than Au ones.


and membrane permeability, they found Ni NWs to be nontoxic for low incubation times (<10 hours) and concentrations (<100 NWs per cell). Hossain and Kleve then investigated the effects of Ni NWs on human pancreatic adenocarcinoma Panc-1 cells [104]. Using NWs of around 6.5 μm in length and 215 nm in diameter, a dose-dependent cytotoxic response was shown, including ROS generation and the induction of apoptosis and cell cycle arrest in the

phase. A similar response was then reported for HeLa cells, along with mitochondrial

We reported the cytotoxicity of Ni NWs in human fibroblast WI-38 cells [106] and human colorectal carcinoma HCT 116 cells [107]. Whereas WI-38 cells showed no significant decrease of cell viability up to doses of 120 μg/mL for 24 hours of incubation and the viability of HCT 116 cells decreased significantly at the same incubation time for doses as low as 5 μg/mL. For both cell lines, NWs were internalized and appeared in the cytosol inside membrane-bound compartments, possibly lysosomes, as shown previously [102], with the internalization in HCT 116 cells taking place through the phagocytosis pathway. Apoptosis was also confirmed to be the cell death pathway, which would later progress into secondary necrosis and induce cell membrane instability and LDH leakage. Lastly, it was also confirmed that Ni2+ is released intracellularly following NW uptake, due to the acidic pH inside the lysosomes. Although the percentage of this intracellular dissolution is low compared to the total dose, it is plausible that the leeched Ni2+ contributes to the cytotoxic effects observed. It should be mentioned that Au-coated Ni NWs showed an improved biocompatibility, possibly due to the Au reducing the degree of dissolution, while also providing a functionalization layer [108, 109]. Similarly, we have reported the stabilization of Fe NWs by coating with a poly(MPC) homopolymer in order to increase dispersion and

Recent studies on the *in vitro* cytotoxicity of nonmagnetic and magnetic structures in biomedical applications were reviewed, taking into account nanoparticles and nanowires/nanorods.

Comparisons between the cytotoxicities of those different nanomaterials are generally difficult to make, due to the vast range of methods, concentrations, dimensions, cell lines, etc. For instance, the concentrations reported in the different studies were typically evaluated using either ICP or cryogenic TEM. However, the concentration or dose of the nanomaterial plays a

While the concentrations and exposure times are critical factors, the toxicity of these nanostructures is also material dependent. These relations can be seen in **Figure 5**, which presents the average values reported for the cell viabilities (ignoring differences in concentrations, incubation times, etc.), when exposed to the nanomaterials in the studies covered in **Table 1**.

A summary of the results of representative studies is provided in **Table 1**.

significant role in the cytotoxic response as well as the biomedical applications.

Fe nanomaterials showed higher cell viabilities than Au ones.

G0 /G<sup>1</sup>

220 Cytotoxicity

membrane depolarization [105].

biocompatibility [110].

**4. Conclusion**

**Table 1.** Summary of *in vitro* cytotoxicity studies with different kinds of nanoparticles (NPs) and nanowires (NWs), NWs with aspect ratio < 10 are often called nanorods (NR), SPION referred to superparamagnetic iron oxide NPs.

In addition, the particle size plays a major role in the cytotoxic properties of the nanostructure, whereby both the cellular uptake efficiency and pathway are affected, with smaller particles being internalized faster than larger ones.

The induction of ROS after dissolving the nanostructures in the lysosomes was shown to be the primary underlying cause of the toxicity in several cases, leading to cell death through the apoptotic pathway, due to ROS generation and mitochondrial damage. The acidic condition inside the lysosome increases the digestion of the particles, enhancing the release of ions that

**Author details**

Jasmeen Merzaban<sup>1</sup>

**References**

2018]

c2cs15260f

10.1016/j.tibtech.2008.04.005

1825. DOI: 10.1002/adma.200902557

2012;**8**:147-166. DOI: 10.1016/j.nano.2011.05.016

10.1016/j.biomaterials.2010.09.024

Theranostics. 2013;**3**:595-615. DOI: 10.7150/thno.5366

Jose Efrain Perez1,2, Nouf Alsharif1,2, Aldo Isaac Martínez Banderas1,2, Basmah Othman<sup>1</sup>

1 Division of Biological and Environmental Sciences and Engineering, King Abdullah

2 Division of Computer, Electrical and Mathematical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal, Kingdom of Saudi Arabia

University of Science and Technology, Thuwal, Kingdom of Saudi Arabia

and Jürgen Kosel2

[1] ASTM International. Standard Terminology Relating to Nanotechnology [Internet]. 2012. Available from: https://www.astm.org/Standards/E2456.htm [Accessed: March 15,

[2] Sanvicens N, Marco MP. Mint: Multifunctional nanoparticles – properties and prospects for their use in human medicine. Trends in Biotechnology. 2008;**26**:425-433. DOI:

[3] Sau TK, Rogach AL, Jäckel F, Klar TA, Feldmann J. Mint: Properties and applications of colloidal nonspherical noble metal nanoparticles. Advanced Materials. 2010;**22**:1805-

[4] Brigger I, Dubernet C, Couvreur P. Mint: Nanoparticles in cancer therapy and diagnosis. Advanced Drug Delivery Reviews. 2002;**54**:631-651. DOI: 10.1016/S0169-409X(02)00044-3

[5] Doane TL, Burda C. Mint: The unique role of nanoparticles in nanomedicine: Imaging, drug delivery and therapy. Chemical Society Reviews. 2012;**41**:2885. DOI: 10.1039/

[6] Parveen S, Misra R, Sahoo SK. Mint: Anoparticles: A boon to drug delivery, therapeutics, diagnostics and imaging. Nanomedicine: Nanotechnology, Biology, and Medicine.

[7] Li L, Jiang W, Luo K, Song H, Lan F, Wu Y, Gu Z. Mint: Superparamagnetic iron oxide nanoparticles as MRI contrast agents for non-invasive stem cell labeling and tracking.

[8] Xie H, Zhu Y, Jiang W, Zhou Q, Yang H, Gu N, Zhang Y, Xu H, Xu H, Yang X. Mint: Lactoferrin-conjugated superparamagnetic iron oxide nanoparticles as a specific MRI contrast agent for detection of brain glioma *in vivo*. Biomaterials. 2011;**32**:495-502. DOI:

[9] Kuo S-W, Lin H-I, Ho JH-C, Shih Y-RV, Chen H-F, Yen T-J, Lee OK. Mint: Regulation of the fate of human mesenchymal stem cells by mechanical and stereo-topographical

\*

Review of *In vitro* Toxicity of Nanoparticles and Nanorods: Part 1

http://dx.doi.org/10.5772/intechopen.76365

, Timothy Ravasi<sup>1</sup>

\*Address all correspondence to: jurgen.kosel@kaust.edu.sa

,

223

**Figure 5.** Average cell viability when exposed to nanomaterials reported in **Table 1**, considering nanoparticles (NP), nanorods (NR), and nanowires (NW).

affect the viability of the cells. However, the oxidation of Fe nanostructures did not decrease the cell viability.

Adding a coating to the nanostructure typically affected both the toxicity and the surface charge of the nanostructure, where cationic surfaces are more toxic than anionic. For instance, coating Au with TA coating led to the decrease of the cell viability to around 70%, whereas with a PEG coating, the viability was maintained above 90%.

The cytotoxicity of the nanomaterial depends also on the nanostructure's shape. In this regard, several advantages have been reported for NWs over NPs. For instance, they enhance the drug-loading capacity, due to their large surface area. Moreover, magnetic NWs, due to their higher magnetization, can be better manipulated by the use of the magnetic field than NPs. An interesting observation from **Figure 5** is that NWs/NRs are, on average, less cytotoxic than NPs. This was attributed to the increased interaction of the nanomaterial with the cells, due to the large surface area.

While all these studies contributed to obtain a better picture of the cytotoxicity of nanomaterials and the underlying mechanisms, it is a persisting issue that a consistent measurement and reporting system will be needed for future studies. This will not only enable performing more accurate comparisons of the toxicological characteristics of nanostructures but also to better evaluate the potential of using them for biomedical applications.
