Biomedical Engineering Reference
In-Depth Information
Powers et al. (2006) have summarized five basic rules for physicochemical characterization:
1. The sample used for characterization assessments should be representative of the material.
2. The size and shape should be measured as dispersed a state as possible.
3. The most appropriate method for measurement should be applied.
4. The particles should be measured in desired amounts to ensure precision and accuracy.
5. As far as possible, the characteristics of the particles should be measured under the same
conditions as its application.
1.7.2
I
n
V
Itro
a
ssessMeNt
In vitro
toxicity studies are valuable in the optimization of NP design.
In vitro
methods to assess
NP toxicities can be classified as mechanistic or viability assays. The mechanistic assays are those
that seek to assess the effects of NPs on various cellular processes, whereas viability assays are
concerned solely with whether a given NP results in cell death.
Owing to their lower costs and efficacy,
in vitro
studies are the most preferred studies for the
assessment of toxicity.
In vitro
assays consist of subcellular systems, such as macromolecules;
organelles; cellular systems, such as individual cells, culture, barrier systems; and whole tissues,
such as organs, slices, and explants. Before the administration into biological systems (mice or
rabbits), it is very important to ascertain the right dosage or a safe concentration of the drug.
That is where
in vivo
studies play a pivotal role. The toxicity of the drug is first tested in cell
culture to assess the suitability and dosage for
in vitro
studies (Geldenhuys et al. 2011).
Although
in vitro
tests are quick and straightforward, there are some limitations, such as the
correlations of the
in vitro
to the
in vivo
environments. The process of immortalization alters the
cells' properties and sensitivities. Also, some cells are more sensitive than others to a certain kind
to toxin as compared to other cells in a different culture. Because the cells are isolated from their
natural environment, they may not be an appropriate model. For example, Lee et al. (2009) reported
that 2D cell cultures that are commonly used in
in vitro
studies may not correctly reflect the actual
toxicity of NPs, as they do not represent functions of 3D tissues that have complex cell-to-cell and
cell-to-matrix interactions with different diffusion or transport conditions.
There may also be interferences with specific toxicology assays based on the properties of the
NM. These are a result of the following unique physical and chemical properties: high surface areas
that may lead to increased adsorption capacities, optical properties that may interfere with fluores-
cence or visible light absorption detection systems, increased catalytic activities due to enhanced
surface energies, and magnetic properties that make them redox active and thus interfere with meth-
ods based on redox reactions (Kroll et al. 2009). Interferences with colorimetric assays, such as
the MTT 3-(4,5 dimethylthiazol-2-yl)-2-5-diphenyl tetrazolium bromide (MTT) assay, have been
reported (Doak et al. 2009, Kroll et al. 2009, Monteiro-Riviere and Inman 2006, Monteiro-Riviere
et al. 2009, Pulskamp et al. 2007, Scalf and West 2006, Song et al. 2010). For example, CNTs inter-
act with formazan crystals and make them insoluble (Wörle-Knirsch et al. 2006). Consequently,
such variables can lead to conflicting results (Doak et al. 2009, Monteiro-Riviere et al. 2009, Wörle-
Knirsch et al. 2006). Thus, if such interferences are suspected, additional tests would be required
to confirm the findings.
1.7.2.1 DNA Synthesis and Damage
DNA synthesis assays are commonly used to assess cell proliferation or to quantify the number
of cells in each stage of the cell cycle (which can subsequently reveal cell cycle arrest at a given
point). The incorporation of 5-bromo-2-deoxyuridine (BrdU) into newly synthesized DNA has been
frequently employed to quantify DNA synthesis in nanotoxicity assays. The genotoxicities of sil-
ver (Ag) NPs and PEG-coated cadmium selenide/zinc sulfide (CdSe/ZnS) QDs on lung epithelial
cancer (A549) and skin epithelial (HSF-42) cells were assessed by utilizing the aforementioned
