Nonwoven fibrous membranes were formed from electrospinning lecithin solutions in a single processing step. As the concentration of lecithin increased, the micellar morphology evolved from spherical to cylindrical, and at higher concentrations the cylindrical micelles overlapped and entangled in a fashion similar to polymers in semi-dilute or concentrated solutions. At concentrations above the onset of entanglements of the wormlike micelles, electrospun fibers were fabricated with diameters on the order of 1 to 5 micrometers. The electrospun phospholipid fibers offer the potential for direct fabrication of biologically based, high-surface-area membranes without the use of multiple synthetic steps, complicated electrospinning designs, or postprocessing surface treatments.

Our research demonstrates electrospun nonwoven fibrous scaffolds from a low molar mass gemini ammonium surfactant, N,N'-didodecyl-N,N,N',N'-tetramethyl-N,N'-ethanediyldiammonium dibromide (12-2-12). Cryogenic transmission electron microscopy (cryo-TEM) and solution rheological experiments revealed micellar morphological transitions of 12-2-12 in water and water:methanol (1:1 vol). The microstructure of 12-2-12 in water transitioned from entangled, cylindrical, threadlike micelles to branched threadlike micelles, and a viscoelastic, entangled, highly branched network of threadlike micelles with increasing concentration finally formed. In sharp contrast, the solution behavior of 12-2-12 in water:methanol produced a drastically different micellar microstructure compared to that in water, and the morphology transitioned from partitioned, globular micelles to overlapped micelles at an overlap concentration (C*) of 11 wt %. Electrospinning 12-2-12 from water did not produce fibers at any concentration; however, electrospinning 12-2-12 in water:methanol at concentrations greater than 2C* produced hydrophilic continuous fibers with diameters ranging from 0.9 to 7 microm. High surface area scaffolds with hydrophilic surfaces offer potential as charged controlled-release membranes, tissue engineering scaffolds, and coatings for biologically compatible devices.

Bilayer lipid membranes (BLMs) have received significant attention over the past several decades because of their applications in biological and material sciences. BLMs consist of two amphiphilic lipid layers arranged with their hydrophilic head region exposed to the surrounding aqueous environment and hydrophobic domains in the core. In biology, lipid membranes confine and support the cell structure while selectively controlling the diffusion of ions and proteins between the intra- and extracellular matrix (ECM). Naturally derived lipid monomers spontaneously self-assemble to develop smart gateways that recognize and incorporate desired protein transporters or ion channels. BLMs are useful research models of lamellar lipid assemblies and associated protein receptors in cell membranes. The transport properties of lipid membranes can be tuned through careful consideration of the solution medium, transporter functionality, and pH, as well as other environmental conditions. BLMs are of particular interest in the design of biofunctional coatings, controlled release technologies, and biosensors; however, high-performance applications require lipid membranes to remain stable under harsh denaturing conditions. Accordingly, synthetic strategies are often proposed to increase the chemical and mechanical stability of lipid assemblies. The polymerization of self-assembled lipid structures is a strategy that results in robust biocompatible architectures, and diverse reactive functional groups are available for the synthesis of monomeric lipids. The selection of the polymerizable functionality and its precise location within the lipid assembly influences the ultimate supramolecular microstructure and polymerization efficiency. The biomimetic potential of polymerized lipids depends on the stability and robustness of the self-assembled membranes, and it is essential that the polymerizable functionality not disturb the amphiphilic nature of the lipid to maintain biocompatibility. Innovative applications are the motivational force for the development of durable polylipid compositions. Surface modification with biocompatible polylipids provides the opportunity for specific binding of biological molecules for applications as sensors or controlled release delivery vehicles. The ability to create stable lipid assemblies requires a comprehensive understanding of the mechanism of lipid polymerization in confined supramolecular geometries. The future is exciting as researchers begin to fully understand the morphology of polylipids in an effort to successfully produce naturally derived sustainable materials. In this Account, we highlight recent efforts to covalently stabilize lipid membranes and discuss emerging applications of mechanically robust self-assembled lipid architectures.

The high shear forces generated during the pulsed ultrasound of dilute polymer solutions lead to large tensile forces that are focused near the center of the polymer chain, but quantitative experimental evidence regarding the force distribution is rare. Here, pulsed ultrasound of quantitatively geminal-dihalocyclopropanated (gDHC) polybutadiene provides insights into the distribution. Pulsed ultrasound leads to the mechanochemical ring-opening of the gDHC mechanophore to a 2,3-dihaloalkene. The alkene product is then degraded through ozonolysis to leave behind only those stretches of the polymer that have not experienced large enough forces to be activated. Microstructural and molecular weight analysis reveals that the activated and unactivated regions of the polymer are continuous, indicating a smooth and monotonic force distribution from the midchain peak toward the polymer ends. When coupled to chain scission, the net process constitutes the rapid, specific, and reagentless conversion of a single homopolymer into block copolymers. Despite their compositional polydispersity, the sonicated polymers assemble into ordered lamellar phases that are characterized by small-angle X-ray scattering.