BIOMEDICAL AND BIOMEDICINE APPLICATIONS OF CNTs - Bio-Inspired and Nanoscale Integrated Computing - page 498

variations in differentiation due to functionalization and show promise for bone
graft materials [2, 4, 45].
18.4. COMMERCIAL BIOMEDICAL APPLICATIONS
OF CARBON NANOTUBES
The unique and diverse properties of CNTs, in addition to the wide range of
functionality afforded by chemical modification, allows for many exciting applica-
tions. Due to their nanometer dimensions, CNTs have the potential to interact at
the cellular and molecular level. This characteristic is just beginning to be exploited
and has already shown great promise in biological and medical applications. At the
time of this writing, only a few companies have begun to invest in commercializing
carbon nanotubes for different medical applications [1-5].
18.4.1. Drug and Gene Delivery
The global drug delivery market is expected to grow substantially in the coming
years. Developments in nanotechnology-based drug delivery are expected to have
significant impacts, enhancing the capabilities of current drugs and creating whole
new therapeutics. It is estimated that the global market share for nanoparticle-
based therapeutics is expected to grow to from 0.9% to 5.2% by 2012, comprising
a $4.8 billion industry. Carbon nanotubes are among the promising new
nanoparticles that can be used for drug and gene delivery.
Since the first demonstration of the functionalized SWCNT translocation of
the cell membrane and the ability to penetrate the cell nucleus to deliver a
bioactive peptide, [46] several CNT-based drug and gene delivery applications
have been developed. In the initial study, cycloaddition techniques were used to
covalently modify the sidewalls of CNTs. Cationically modified SWCNTs and
MWCNTs have been used for electrostatic association with plasmid DNA that
was subsequently delivered into cells. Double functionalization of SWCNTs for
delivery of multiple therapeutics has shown promise, as well as similar applica-
tions achieving dual functionality through sidewall cyclo-adition and simulta-
neous end oxidation routes to introduce drug delivery and fluorescent probing
functionalities [47].
During an in vivo study, covalently functionalized SWCNTs with a neutraliz-
ing B cell epitope from the foot-and-mouth disease virus were administered into
mice. Immunization of the mice with the SWCNT complexes induced a strong
immune response from the functionalized peptide while immunogenicity was not
observed from the nanotubes themselves.
A more recent in vivo study covalently functionalized SWCNTs with carbor-
ane (a cluster compound of boron and carbon atoms) and administered the
complex intravenously into mice with implanted EMT6 tumor cells for the
purpose of boron neutron capture therapy [48]. Analysis of the distribution of
the SWCNT complex in tumor, blood, lung, liver, and spleen samples found that