Engineering lipid tubules using nano-sized building blocks: the combinatorial self-assembly of vesicles

Abstract

Nano-sized lipid vesicles with tailored properties have been used as building blocks to generate lipid tubules between two glass surfaces. The tubules formed not only have defined orientation, width, and length, but they can also grow to be as long as 13 mm under ambient conditions, without externally supplied flow, temperature control, or catalyzing agents. Tubule membrane and its internal aqueous content can be manipulated by controlling the combination of different vesicle's lipid composition and aqueous entrapment. This self-assembly process opens up new pathways for generating complicated and flexible architectures for use in biocompatible molecular and supramolecular engineering. We demonstrated these possibilities by generating tubules encapsulated with siRNA, tubules with multiple branches, and polymerized fluorescent tubules in a single-throughput self-assembly process.

Directed Self-Assembly of Lipid Nanotubes from Inverted Hexagonal Structures

“…17 Microfluidic systems have been also used to fabricate similar structures by extruding lipid membranes through a microaperture, 24 or by controlling the lipid hydration, 25 shear force, 26 and the aqueous entrapment within flow cells. 27 In such works, the lipid-tubule formation is fundamentally based on the shape transformation of lamellar structures by applying a point load. 1,2-Dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) is a zwitterionic conicalshaped lipid.…”

The freedom of confinement in complex fluid

“…Selfassembly of phospholipids in an aqueous solution can generate lipid vesicles-spherical, bilayered lipid membranes that enclose an aqueous core. 16 By encapsulating functional molecules in the core and tailoring the properties of the membrane, one can make vesicles that act as biomimetic devices. Under certain conditions, lipid vesicles can further organize into structures such as tubular networks.…”

“…Our group recently used a simple confinement-enhanced self-assembly method to form long, oriented lipid tubules in a thin film (see figure 5). 16 Lipid tubules with a variety of properties and functionalities can be constructed by combining appropriate vesi- cle building blocks. Most important, the method is inexpensive, is simple, and does not rely on external flow, temperature control, or catalyzing agents-highly desirable traits for a composite biomaterials fabrication technique.…”

Lipid tubule growth by osmotic pressure

“…Two methods have been routinely used to prepare lipid solutions: ethanol injection and film hydration [34,36,37]. In ethanol injection, the lipid (Soy-95%) is dissolved in ethanol to make a bulk solution and this solution is subsequently injected into water to make solutions of different concentrations.…”

“…Recently, the authors' group has synthesized lipid tubules with defined orientation, length and width [34]. When confined between two glass surfaces, lipid vesicles rapidly assemble into oriented tubules that can grow to a few millimetres in length without externally supplied flow, temperature control or catalysing agents.…”