(599a) Harnessing Self-Assembly to Design Functionalized Nanotube-Lipid Hybrid Structures

Via Dissipative Particle Dynamics (DPD) approach, we study the design
and creation of functionalized amphiphilic nanotube-lipid hybrid
structures. Individual lipids are composed of a hydrophilic head group
and two hydrophobic tails. Each bare nanotube encompasses an ABA
architecture, with a hydrophobic shaft (B) and two hydrophilic ends
(A). To allow controlled transport through the nanotube, we also
introduce hydrophilic hairs at one or both ends of the tube.Our
earlier investigations on nanotube-lipid bilayer interactions
(Nanoscale, 2011, 3, 240) demonstrated that bare and single-end hairy
nanotubes spontaneously penetrate and assume a trans-membrane position
in the bilayer; this process is found to critically depend upon the
membrane tension. On the other hand, the double-end hairy nanotubes
are not unable spontaneously self-organize into the bilayer, and
require the formation of a stable pore for its insertion. Based upon
our earlier findings, we use two different approaches to generate the
hybrid structures. (1) For the double-end hairy nanotube, we use the
self-assembly of the amphiphilic lipids and the nanotubes in a
hydrophilic solvent to create equilibrium hybrid structures such as a
vesicle or a bicelle. The formation of a specific structure depends
upon the concentrations of each component (M. Dutt et
al. submitted). (2) For the bare and single-end hairy nanotubes, we
add a nanotube into a solvent bath containing a pre-assembled vesicle
and observe its spontaneous insertion into the vesicle bilayer to
assume a transmembrane position. We sequentially add the nanotubes one
at a time after the previous nanotube has been inserted (M. Dutt et
al. submitted). In both these approaches, the nanotubes in the hybrid
vesicles are found to self-organize in the bilayer into smectic-,
tripod- or tetrapod-like structures.  We also show that the nanotubes
insertion and clustering within the vesicle strongly affects the
vesicle shape in cases of a sufficiently large number of
tubes. Ultimately, these nanotube-lipid systems can be used for making
hybrid controlled release vesicles.