BIOMEDICAL AND BIOMEDICINE APPLICATIONS OF CNTs - Bio-Inspired and Nanoscale Integrated Computing - page 493

Therefore, excitation and emission wavelengths should be selected carefully based
on the particular application [28].
18.3.2. Biopharmaceutics
18.3.2.1. Drug Delivery. Like other device industries, increasing concerns
over rising health care costs have led to the development of novel drug delivery
techniques that are cost effective. The important characteristic of an efficient drug
delivery system is the ability to perform controlled and targeted drug delivery. For
this purpose, drugs should be released at an appropriate rate, as rapid release of
drugs may lead to incomplete absorption, gastrointestinal disorders, and other
side effects. In addition, care needs to be taken so that the drugs will not
decompose during delivery, as some drugs are toxic in nature. To this end, drugs
should be encapsulated in a carrier during transit in the body while maintaining
their biological and chemical properties. Also, the drug delivery material must be
compatible with the drug; the delivery material should bind easily with the drug.
The material should decompose at the completion of its use either by solubilizing
or by elimination via excretory roots of the body. CNTs can be used as a carrier
for drug delivery, as they are adept at entering the nuclei of cells. Researchers have
found that functionalized CNTs can cross the cell membrane. In addition, they are
of a size where cells do not recognize them as harmful intruders. Martin and Kohli
[29] reported that CNTs can be used as drug delivery materials because they have
larger inner volumes, as compared to the dimensions of the tube, that can be filled
with the desired chemical and biological species. In addition, CNTs have distinct
inner and outer surfaces that can be differentially modified for functionalization.
As a result, the outer surface of CNTs can be immobilized with biocompatible
materials and the inside can be filled with the desired biochemical payload. CNTs
have open mouths, which make the inner surface accessible for insertion of species
inside the tube. Molecular dynamics simulations show that van der Waals and
hydrophobic forces are important for the insertion process. The van der Waals
forces have a dominant role in the CNT species. Gao et al. [30] found that in a
water-solute environment, a DNA molecule could be inserted into CNTs via an
extremely rapid dynamic interaction process. Based on their studies, they
suggested that the encapsulated CNT-DNA molecular complex can be applied
in DNA-modulated molecular electronics, molecular sensors, electronic DNA
sequencing, and gene delivery systems. Kong et al. [31] found that the encapsula-
tion of biological molecules in CNTs can be accelerated at high temperatures.
Finally, CNTs can be organically functionalized to make them soluble in organic
solvents and aqueous solutions. Soluble CNTs can be coupled with amino acids
and bioactive peptides for further derivatization. These drug delivery systems may
form the basis for anticancer treatments, gene therapies, and vaccines in future, as
the carrier can enter damaged cells and release enzymes either to initiate an
autodestruct sequence of cells or to repair the cell for normal functioning. In the
future, the application of CNTs as drug encapsulators for treatment of brain