Exploiting Spontaneous and Self-Assembly to Design Biomimetic Functionalized Nanotube-Lipid Hybrid Structures
Via Dissipative Particle Dynamics (DPD) approach, we study the design and creation of lipid-functionalized amphiphilic nanotube 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 (M. Dutt et al., Nanoscale 2011) 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., ACS Nano 2011). (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., Current Nanoscience 2011). 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. Finally, we will demonstrate the guided motion of these hybrid vesicles using a suitably functionalized pipette. Ultimately, these nanotube-lipid systems can be used for making hybrid controlled release vesicles.