Biomedical Engineering Reference
In-Depth Information
CNTs are emerging as innovative tools in nano- and biotechnology. Since 1998,
CNTs have been widely used for producing transistors and other electronics (Freitag
2006 ) and sensors (Sinha et al. 2006 ; Gruner 2006 ) and also as substrates for cel-
lular growth (Mattson et al. 2000 ; Correa-Duarte et al. 2004 ; Zanello et al. 2006 ;
Sirivisoot et al. 2007 ; Razal et al. 2008 ) .
For applications of CNTs in biology, a prerequisite is they being biocompatible
and nontoxic. The toxic effects of CNTs on environment and health have become an
issue of strong concern (Wörle-Knirsch et al. 2006 ) . Increasing evidence indicates
that many nanomaterials currently employed may not be completely safe and may
affect biological behavior. As a consequence, the prolonged exposure to CNT-based
devices might trigger potential immune-defense responses or other dangerous
effects. Moreover, different functionalizations play a role in increasing or decreas-
ing CNTs' toxicity and some studies pointed out that CNTs are variably toxic for
cells (Sato et al. 2005 ; Kagan et al. 2006 ; Sayes et al. 2006 ; Magrez et al. 2006 )
while others reported the absence of a particular toxicity (Dumortier et al. 2006 ) .
The interfacing of CNTs with biological systems has been also focused on the inter-
actions between CNTs and relevant molecules, such as peptides (Dieckmann et al.
2003 ; Katz and Willner 2004 ), proteins (Katz and Willner 2004 ; Balavoine et al.
1999 ; Chen et al. 2001 ; Patolsky et al. 2004 ), and DNA (Katz and Willner 2004 ;
Balavoine et al. 1999 ; Chen et al. 2001 ; Patolsky et al. 2004 ; Tsang et al. 1997 ) . It
has been shown that protein-nanotube conjugates preserve protein properties and
activities; thus, from this point of view, CNTs can be regarded as biocompatible. On
the issue of toxicity, there is also a general agreement on the fact that CNTs can be
harmful for health in the sense of similarly to other micro- or nanoparticles, CNTs
are nanometer-scale materials, and their size allows them to enter deeply in the lung
tissues (Poland et al. 2008 ). Pristine CNTs are neither water soluble nor wettable,
and so they are extremely diffi cult to eliminate from the body. Recently, Lam et al.
demonstrated that CNTs were responsible for infl ammation, epithelioid granulomas
(microscopic nodules), fi brosis, and biochemical and toxicological changes in the
lungs (Lam et al. 2004 ). This study also revealed that SWNTs were more toxic than
quartz particles. It should be noted, however, that this material appears to be bio-
compatible, since systemic administration of CNTs does not cause any detectable
toxic effects (Liu et al. 2008 ) .
In 2000, a study realized by Mattson and coworkers suggested that CNTs could
be used as substrates for neuronal growth. After this fi rst report, several groups
developed single neurons or cultured neuronal circuits using as substrate a CNT
thin fi lm (Hu et al. 2004 ; Hu et al. 2005 ; Lovat et al. 2005 ; Mazzatenta et al. 2007 ;
Gheith et al. 2006 ; Pappas et al. 2007 ; Wang et al. 2006 ; Matsumoto et al. 2007 ;
Gabay et al. 2007 ). The electrical properties of CNTs as well as their biocompat-
ibility (at least when immobilized on surface) make these materials the perfect
candidates for neuronal growth and also for development of implantable devices
displaying peculiar properties in interfacing with neuronal electrical activity, and
thus CNTs could serve as an extracellular scaffold, sustaining and interacting with
neurite growth and signaling, with a wide range of applications in neurology
health care.
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