Designing Tunable Bio-nanostructured Materials via Self-Assembly of Amphiphilic Lipids and Functionalized Nanotubes
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Designing Tunable Bio-nanostructured Materials via Self-Assembly of Amphiphilic Lipids and Functionalized Nanotubes Meenakshi Dutt1, Olga Kuksenok2 and Anna C. Balazs2 1 Chemical and Biochemical Engineering, Rutgers- The State University of New Jersey, Piscataway, New Jersey 08854, USA 2 Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA ABSTRACT Via the Dissipative Particle Dynamics (DPD) approach, we study the self-assembly of hybrid structures comprising lipids and end-functionalized nanotubes. 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 for regulated transport through the nanotube, we also introduce hydrophilic hairs at one end of the tube. The amphiphilic lipids are composed of a hydrophilic head group (A) and two hydrophobic tails (B). We select the dimensions of the nanotube architecture to minimize its hydrophobic mismatch with the lipid bilayer. We find the amphiphilic lipids and functionalized nanotubes to self-assemble into a stable hybrid vesicle or a bicelle in the presence of a hydrophilic solvent. We demonstrate that the morphology of the self-assembled functionalized nanotube-lipid hybrid structures is controlled by the rigidity of the lipid molecules and concentration of the nanotubes. INTRODUCTION Lipid-based nanomaterials are used in a broad range of industrial applications, such as pharmaceuticals, personal products or food 1,2,3. An effective approach to the design and utilization of these lipid-based nanomaterials requires understanding their equilibrium morphologies. The equilibrium morphology of these nanomaterials is dependent upon its nanoscopic building blocks, their functional integration and external conditions, such as temperature and properties of the solvent. We are interested in designing nanostructured materials using amphiphilic lipid molecules and functionalized nanotubes via self-assembly. We find the equilibrium morphology to be determined via the properties of the building blocks (such as the molecular rigidity, concentration of the nanotubes) and the temperature. Our results provide general guidelines for tuning the morphology of hybrid systems comprised of, or analogous to lipids and functionalized nanotubes. THEORY Similar to Molecular Dynamics (MD) simulations, Dissipative Particle Dynamics 4 (DPD) captures the temporal evolution of a many-body system through the numerical integration of Newton’s equation of motion. Unlike MD simulations, DPD involves the use of soft, repulsive interactions and a momentum-conserving thermostat. Because all the forces conserve momentum locally, hydrodynamic behavior emerges even in systems containing only a few
hundred particles 4. The equations of motion are integrated in time with a modified velocityVerlet algorithm. The basic structural units in our system are the twin-tailed lipids 6,7 (see Fig. 1a) and amphiphilic, bare (see Fig.
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