STABILISATION OF CARBON NANOTUBE SUSPENSIONS - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 3

(a) (b)

(c)

Figure 1.2 CNTs acting as nanoneedles. (a) A schematic of a CNT crossing the plasma
membrane; (b) a TEM image of MWNT-NH 3 + interacting with the plasma membrane
of A549 cells; (c) a TEM image of MWNT-NH 3 + crossing the plasma membrane of HeLa
cells. Reproduced from Lacerda et al. 7 with permission . See also Colour Insert.

Administration of free drugs has numerous limitations: limited solubility,
poor biodistribution, lack of selectivity, unfavourable pharmacokinetics, as
well as the propensity to cause collateral damage to healthy tissue. A drug
delivery system allows for the enhancement of the pharmacological and
therapeutic proiles of free drugs.
Advances in nanotechnology have resulted in CNTs being used as
pharmaceutical excipients and as building blocks for delivery systems. CNTs
have been shown to exhibit properties that are desirable for eficient drug
delivery systems, such as the ability to achieve controlled and targeted delivery.
The interaction between CNTs and pharmaceutically active compounds can
occur in three ways. First, the CNT can act as a porous matrix which entraps
active compounds within the CNT mesh or bundle (Fig. 1.3a). Second, the
compound can attach itself to the exterior surface of the CNT (Fig. 1.3b). The
inal mechanism of interaction involves the interior channel of CNTs acting as
a “nanocatheter” or “nanocontainer” (Fig. 1.3c). 10
The purpose of targeted drug delivery is to enhance the eficiency, while
diminishing the noxious effects, of the therapeutic agent. CNTs can chemically
undergo surface modiication to achieve targeted delivery by attachment of
ligands to the functional groups on the CNT surface. These ligands, which
are speciic to certain receptors, can carry CNTs directly to the speciic site
without affecting non-target sites. On the other hand, diagnostic moieties like