Synthetic lipid membranes are self-assembled biomolecular double layers designed to approximate the properties of living cell membranes. These membranes are employed as model systems for studying the interactions of cellular envelopes with the surrounding environment in a controlled platform. They are constructed by dispersing amphiphilic lipids into a combination of immiscible fluids enabling the biomolecules to self-assemble into ordered sheets, or monolayers at the oil-water interface. The adhesion of two opposing monolayer sheets forms the membrane, or the double layer. The mechanical properties of these synthetic membranes often differ from biological ones mainly due to the presence of residual solvent in between the leaflets. In fact, the double layer compresses in response to externally applied electrical field with an intensity that varies depending on the solvent present. While typically viewed as a drawback associated with their assembly, in this work the elasticity of the double layer is utilized to further quantify complex biophysical phenomena. The adsorption of charged molecules on the surface of a lipid bilayer is a key property to decipher biomolecule interactions at the interface of the cell membrane, as well as to develop effective antimicrobial peptides and similar membrane-active molecules. This adsorption generates a difference in the boundary potentials on either side of the membrane which may be tracked through electrophysiology. The soft synthetic membranes produced in the laboratory compress when exposed to an electric field. Tracking the minimum membrane capacitance allows for quantifying when the intrinsic electric field produced by the asymmetry is properly compensated by the supplied transmembrane voltage. The technique adopted in this work is the intramembrane field compensation (IFC). This technique focuses on the current generated by the bilayer in response to a sinusoidal voltage with a DC component, V DC . Briefly, the output sinusoidal current is divided into its harmonics and the second harmonic equals zero when V DC compensates the internal electric field. In this work, we apply the IFC technique to droplet interface bilayers (DIB) enabling the development of a biological sensor. A certain membrane elasticity is needed for accurate measurements and is tuned through the solvent selection. The asymmetric DIBs are formed, and an automated PID-controlled IFC design is implemented to rapidly track and compensate the membrane asymmetry. The closed loop system continuously reads the current and generates the corresponding voltage until the second harmonic is abated. This research describes the development and optimization of a biological sensor and examines how varying the structure of the synthetic membrane influences its capabilities for detecting membrane-environment interactions. This platform may be applied towards studying the interactions of membrane-active molecules and developing models for the associated phenomena to enhance their design.

Controlled diffusive transport between regions within a compartmentalized structure is an essential feature of cellular-inspired materials. Using the droplet interface bilayer (DIB) technique, biomolecular soft materials can be constructed in an oil medium by connecting multiple lipid-coated microdroplets together through interfacial bilayers. While traditionally achieved through the incorporation of pore forming toxins (PFTs), signal propagation within DIB assemblies can be remotely controlled through the integration of photopolymerizable phospholipids (23:2 DiynePC) into the aqueous phase. Since such strategy allows for the formation of UV-C triggered pathways only between droplets both containing DiynePC, polymerizable phospholipids have shown an advantage of reducing undesired diffusion and forming conductive pathways. The partial polymerization of lipid bilayers formed through the DIB platform is still to this date underexplored in the literature. In a previous work, we have shown that the incorporation of 23:2 DiynePC into lipid bilayers allows for the creation of patterned conductive pathways in a 2D DIB structure. The properties of photosensitive bilayers were also investigated but not their channel activity. The functionalization of bilayers-based photosensitive structures through transmembrane channels remains an under-investigated mean of achieving further differentiated conductive channels. This work explores the reconstitution of several transmembrane channels such as alpha-hemolysin ( αHL ) and alamethicin (ALM) into partially polymerized lipid bilayers. We believe that the ability to incorporate transmembrane channels into photosensitive DIB soft structures allows for further differentiation of signal propagation pathways by including both edge-defect induced pores as well as more traditional and bio-derived transporters.

A recent achievement in the droplet interface bilayer (DIB) technique is the ability to link multiple lipid-encased aqueous droplets in an oil medium to construct a membrane-based network. Highly flexible, efficient and durable compared to other lipid bilayer modeling techniques, these systems establish a framework for the creation of biocompatible and stimuli-responsive smart materials with applications ranging from biosensing to reliable micro-actuation. Incorporating ferrofluids droplets into this platform has proven to accelerate the networks’ building mechanism through remote magnetic-control of the droplets movement and has reduced the likelihood of failure during the pre-network-completion phase. Additionally, ferrofluid drops may be placed in the final network structure as they are macroscopically homogenous and behave as single phased liquids. Due to their paramagnetic characteristics, no residual magnetization is observed in the ferrofluid upon removal of the external magnetic field, allowing for simple control of the magnetically responsive droplets. Aside from the ferrofluids reliability in contact-free manipulation of bilayer networks, this work shows a different feature of having such hybrid ferrofluid-water DIB networks: magnetic-sensibility and actuation. Once pre-structured mixed networks are formed, a magnetic source is used to generate various magnetic fields in the vicinity of the DIB webs; changes in structural responses are then observed and used to induce protein channel gating in DIB networks channeling the functionality of a switch. Tailored architectures are accordingly evaluated and their suitability for the creation of microfluidic-magneto sensors and actuators is assessed.

Multiple lipid encased water droplets may be linked together in oil to form large networks of droplet interface bilayers thus creating a new class of stimuli-responsive materials for applications in sensing, actuation, drug delivery, and tissue engineering. While single droplet interface bilayers have been extensively studied, comparatively little is known about their interaction in large networks. One particular problem of interest is understanding the impact of the coalescence of two neighboring droplets on the overall structural integrity of the network. Here, we propose a computational modeling scheme that predicts and characterizes the mechanical properties of the multiple lipid bilayer interfaces within the droplet network upon intentional coalescence of adjacent droplets. Droplet networks with tailored architectures are synthesized with the aid of magnetic motor droplets containing a biocompatible ferrofluid. The equilibrium configuration of the droplet networks is compared to computational prediction which defines the overall stability by summing the interfacial energies. Once the networks are completed, failure in selected membranes is induced. As the targeted droplets coalesce together, the equilibrium structure of the network is altered and the remaining droplets may shift to new configurations dictated by their minimized mechanical energies.

Model cellular membranes respond to chemical and electrical stimuli, regulating transport and exchange between two neighboring aqueous droplets. This regulated exchange may prove useful for controlling aqueous micro-environments for studying stimuli-responsive encapsulated bacteria. This concept is explored in this work, focusing on characterizing the bacterial response within a synthetic cellular environment. In the droplet interface bilayer (DIB) approach, aqueous micro-droplets deposited in an oil reservoir with dissolved lipids are coated with lipid monolayers and arranged into artificial cellular networks. This approach has been explored for potential use as a biologically-inspired smart material, but new material transduction pathways are necessary. This may be accomplished by combining this bottom-up approach to synthetic biology with living organisms such as stimuli-responsive bacteria. Bacteria encapsulation within the microfluidic droplets begins with a strain of Escherichia coli ( E. coli ), XL1-Blue. These flagellated bacteria naturally respond and move towards chemoattractants such as casamino acids, and their motion may be tracked through differential interference contrast (DIC) and fluorescent microscopy. Chemotaxis of XL1-Blue was assessed through low-flow perfusion of the chemoattractant (casamino acids) into a buffer solution containing the bacteria through a tailored capillary tube. Next, the response of bacteria within asymmetric DIB networks separating the bacteria and the chemoattractant were studied.

Networks of biomolecular unit cells are proposed as a new type of biologically inspired intelligent materials. These materials are derived from natural cellular mechanics and aim to improve current biologically-inspired technologies by recreating the desired systems from the basic building block of the natural world; the cell. The individual biomolecular unit cell is able to replicate natural cellular abilities through a combination of lipid bilayer membranes containing embedded proteins and peptides. While individual unit cells offer an ideal testing environment for demonstrating proofs of concept, more advanced abilities require larger networks, utilizing cell-to-cell interactions. The cell-to-cell interactions often involve multiple modes of communication, which have been identified for this paper as primarily electrical, chemical, and mechanical phenomenon. Previous modeling efforts have incorporated the electrical portion through equivalent circuit models, but these lack the ability to fully explain some of the network characteristics. A new formulation is presented here to illustrate how these three classes of phenomenon may be coupled to achieve various engineering design goals.

The bilayer lipid membrane (BLM) is a naturally occurring thin layer of phospholipid molecules that surrounds cellular systems. The membrane operates as a near-impermeable barrier allowing for the generation of membrane potentials across the layer through changes in ionic concentrations. This membrane is required for regular cell function ranging from storing energy to passing signals. Engineering advancements have allowed for the rapid creation of artificial bilayer membranes, and these membranes are currently considered for many biomimetic applications. The application of interest for this paper is the further development of these cellular systems for sensing applications. This will be accomplished through a combined fluid-bilayer model, allowing for study of the bilayer transduction properties at both high and low frequencies. Several approaches are discussed and applied to multiple cell systems with or without embedded voltage-dependent ion pores. Finally the results are studied and evidence is presented for the development of a new molecular model for cellular systems combining chemical, electrical, and mechanical stimuli.