BIOMEDICAL APPLICATIONS VI: CARBON NANOTUBES AS BIOSENSING AND BIO-INTERFACIAL MATERIALS - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 204

Another special aspect of CNTs is their novel physical properties. Some
materials with novel and extensively strong properties have been produced
using CNTs. It was even believed that CNTs might be suitable for building
space elevators and other robust constructions. 77
Vigolo et al. 78 found CNTs' high lexibility and resistance to torsion. They
designed a method to prepare carbon ibres using CNTs. By injecting CNTs'
suspension to polyvinylalcohol (PVA) solution low, the CNTs underwent
alignment followed by aggregation and resulted in long CNT ibres. Those
CNT ibres were excellent in lexibility and resistance to torsion and could
be curved through 360° in a few micrometres without breaking. Dalton and
coworkers 79 produced super-tough CNT composite ibres of 100 m length by
a coagulation-based spinning method. The ibres were many times stronger
than steel wires. Walters and collaborators 80 reported that the SWNTs'
strength is very high (37 GPa) and that the CNT ropes could be extended
elastically by 5.8% before breaking.
Furthermore, the density-normalised strength of SWNTs is more
impressive and excellent for applications in which light structural materials
are needed. Wong et al. 81 indicated that the density-normalised strength
of SWNTs were 56 times that of steel wires. Such outstanding mechanical
characteristics suggest CNTs to be good candidates for applications as
biomaterials, such as artiicial bone scaffold materials.
At last, CNTs are known to orient under the inluence of an alternating
current (AC) electric ield and form aligned patterns on a lat surface. 82 Chung
et al. 83 demonstrated a scalable and highly parallel process of electric-ield-
induced CNT positioning and alignment that can lead to mass assembly of
nanostructures and nanoscale devices. Chen and Zhang 84 were recently able
to align SWNTs avoiding CNT entanglement between 2D co-planar parallel
electrodes for potential applications in high-performance nano-devices.
Chen and coworkers 85 aligned CNTs between electrode gaps with a high
degree of alignment and the appearance of uniform coverage. In addition,
the application of dielectrophoretically aligned CNTs as an ordered substrate
for tissue engineering was explored. 86 These studies made it convenient to
manipulate CNTs for bio-engineering materials.
In addition, CNTs possess some novel advantages which make them
suitable for next-generation scaffolds. For instance, CNTs may carry a neutral
electric charge, which sustains the highest cell growth and production of
plate-shaped crystals. 87-88 Meanwhile, CNTs may be metallic and show good
conductivity. An electric ield may stimulate the healing of various tissues.
A mechanical bone injury is often accompanied by an electrical signal, and
therefore a conductive scaffold is very promising for stimulating cell growth
and tissue regeneration by facilitating physioelectrical signal transfer. 89,90