Biomedical Engineering Reference
In-Depth Information
2012). The increased mechanical properties and enhanced biomineralization
make PLLA/ND-ODA nanocomposites promising materials for bone
surgical fixation devices and regenerative medicine.
Despite research into potential biomedical applications of carbon-based
nanocomposites, there have been many published studies on the cytotoxicity
of carbon nanostructures (Smart et al., 2006). Some research groups
detected high toxicity in both cells (Chen et al., 2006; Margrez et al., 2006;
Nimmagadda et al., 2006; Sayes et al., 2006; Cui et al., 2005; Jia et al., 2005;
Monterio-Riviere et al., 2005; Shvedora et al., 2003;) and animals (Huczko
et al., 2005; Muller et al., 2005; Warheit et al., 2004), and explained
mechanisms to cell damage at molecular and gene expression levels (Ding
et al., 2005).
Exposure to single-walled carbon nanotubes (SWNTs) resulted in
accelerated oxidative stress (increased free radical and peroxide generation
and depletion of total antioxidant reserves), loss in cell viability and
morphological alterations to cellular structure. It was concluded that these
effects were a result of high levels of iron catalyst present in the unrefined
SWNT. Possible dermal toxicity in handling unrefined CNT was noted.
Similar dermal toxicity warnings were echoed in 2005, in a study that
found MWNTs initiated an irritation response in human epidermal
keratinocyte (HEK) cells (Monterio-Riviere et al., 2005). Purified MWNT
incubated (at doses of 0.1-0.4 mg/ml) with HEK cells for up to 48 h were
observed to localize within cells (Fig. 17.4), elicit the production of the pro-
inflammatory cytokine release, and decrease cell viability in a time- and
dose-dependent manner.
These controversial results reported by different researchers reflect the
complex material properties of SWNTs and MWNTs. In addition, different
synthesis methods may produce CNTs with different diameters, lengths and
impurities. The results urge caution when handling CNTs and the
introduction of safety measures in laboratories should be seriously
considered. Most importantly, the success of CNT technology is dependent
upon the continuation of research into the toxicology of CNT and CNT-
based nanocomposites. At the same time, pharmacological development
must continue in parallel before providing guidelines for safe use in
biomedical applications.
17.4 Three-dimensional porous scaffolds
The development of composite scaffolds is advantageous as the properties of
two or more types of materials can be combined to better suit the
mechanical and physiological demands of the host tissue. The tissues in the
body are organized into 3D structures as a function of organs. Scaffolds
with a designed microstructures provide structural support and adequate
