Biomedical Engineering Reference
In-Depth Information
at very low aqueous concentrations.
43
As an example, the use of CdSe QDs in
humans may be limited because these contain the heavy metals cadmium which
are reportedly toxic to cells at concentrations as low as 10
u
g/mL.
44
The vari-
ous properties of the QD such as its size, charge, concentration, capping mate-
rial, functional groups, and mechanical stability have been studied as possible
determining factors in toxicity.
45
Although toxicology is an area that is critical
in medicine, there is currently a wide gap between research on NMs medical
applications and nanotoxicology.
46
Today, nanotechnology has begun to show its worth and possible contribu-
tions to the future of medicine and health care. In drug delivery, gene delivery,
and immunotherapy, the ideal NMs can achieve high payload, biocompatibil-
ity, selective targeting, long circulation time, low immunogenicity, and efficient
penetration of barriers to achieve timely arrival at the tissues of interest without
clinical side effects.
47
The penetration of NMs into cells and eventually into the
diseased tissues can open various applications as delivery vehicles in various
disease therapies. But, different NMs of different compositions, sizes, surface
topography, and other properties need to be scrutinized meticulously to estab-
lish the efficacy and safety for their use in humans.
Toxicity studies can begin with in vitro tests using various cell lines that play
a vital role in predicting the response of animal and humans to a broad range of
compounds.
48-51
In vitro studies are used as the first line for screening the toxic
biological consequences of potential therapeutic compounds before in vivo test-
ing.
52
Common conventional in vitro toxicity assays use colorimetric or fluores-
cent dyes as markers to determine cell viability assessing membrane integrity
(i.e. neutral red, calcein AM) or cell metabolism (i.e. MTT, alamar Blue) (same
source). However, although these assays provide reliable data for classic small
molecule cytotoxicity studies, they have to be adapted for the assessment of
NMs
51
to avoid inaccurate results. Existing technique need to be calibrated and/
or new techniques need to be developed for accurate toxicity screening and
evaluation of the toxicity and health risk potentials of NMs. The prediction that
nanotechnology-based products will reach nearly 4T dollars by 2015 and will
continue to grow
53
needs to be coupled with the growth on nanotoxicological
research.
54
This chapter on nanotoxicology and remediation will focus on finished and
on-going various toxicity evaluations of various NMs that are used and currently
being developed for medical applications. A few of commercially available
NMs that are currently being developed for imaging, drug delivery, biosensors,
and other medical applications will be featured in this chapter.
8.2 NM
s
EXHIBITING TOXICITY
Many of the NMs that have emerged to be useful in medicine have shown mild
to no evidences of toxicity to date. However, both long- and short-term effects
need to be evaluated in order to establish immediate and future damage from
