Biomedical Engineering Reference
In-Depth Information
ratio, while SWNT-Lys-NH 3 + appeared most eficient at a 1:1 charge ratio.
Conversely, in the case of MWCNT-NH 3 + , being highly condensed (95%) DNA,
the tubes maintained similar levels of transfection eficiency across all charge
ratios. Finally, it was noticed that a degree of strong electrostatic interaction
was necessary to avoid dissociation on dilution or competition with other
molecular species (e.g., blood components) interacting with the CNT-DNA
complex.
In addition, Cai et al. developed an eficient delivery technique, called
nanotube spearing, by which plasmid DNA immobilised onto nickel-
embedded nanotubes was speared into targeted cells through the application
of an external magnetic ield. 88 The authors observed that in order to respond
to the applied magnetic ield, CNTs needed to be less than 2 μm long. The
mechanism behind this technique is nano-penetration of the cell membrane,
which determines an eficient molecular delivery of plasmid DNA into splenic
B cells, lymphocytes and neurons. Although the investigation was speciic
for plasmid DNA, the technique showed high versatility, since it could be
exploited for the delivery of proteins and RNA segments as well. Moreover, in
contrast with previously reported studies, nanotube spearing required very
low concentrations of CNTs for an ideal transduction, mainly in the range of
100 fm of tubes. Similarly, it is envisaged that the amount of DNA, which was
kept 10 3 times higher than CNTs, could be minimised in future experiments.
On the whole, a successful transduction of plasmid DNA into non-dividing (B
cells and neurons) and dividing cells was achieved with values comparable
to viral vectors, but with the additional advantage of lack of immunogenicity
due to this promising nanotube spearing.
The latest paper using plasmid DNA for gene delivery was published by
Richard et al. , 89 who obtained an enhanced cell transfection in vitro when
plasmid DNA was conjugated to CNTs previously functionalised with cationic
amphiphilic molecules (Fig. 5.27). In fact the amphiphile adsorbed on the
CNTs created positive charges on their surface, thus preventing aggregation
in biological media.
Although it could be argued that the addition of DNA to cationic amphiphiles
onto the CNTs could possibly detach the cationic molecules from the surface,
light scattering of the supernatant did not detect any suspended particle, thus
indicating that the complexes formed were stable. Moreover, it was observed
that the eficiency of transfection of functionalised MWCNTs was higher than
that of naked DNA, but much lower than that of functionalised SWCNTs. It is
highly possible that the larger-size complexes could be responsible for better
internalisation into the cells and thus improved transfection. More precisely,
the eficiency of transfection was 100 times higher when using SWCNTs
functionalised by the lipid instead of pyrenyl polyamine, because the addition
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