We report on a microfluidic technique for fabricating monodisperse asymmetric giant unilamellar vesicles (GUVs) possessing the Gram-negative bacterial outer membrane lipid composition.

We present a microfluidic technique that generates asymmetric giant unilamellar vesicles (GUVs) in the size range of 2–14 μm. In our method, we (i) create water-in-oil emulsions as the precursors to build synthetic vesicles, (ii) deflect the emulsions across two oil streams containing different phospholipids at high throughput to establish an asymmetric architecture in the lipid bilayer membranes, and (iii) direct the water-in-oil emulsions across the oil–water interface of an oscillating oil jet in a co-flowing confined geometry to encapsulate the inner aqueous phase inside a lipid bilayer and complete the fabrication of GUVs. In the first step, we utilize a flow-focusing geometry with precisely controlled pneumatic pressures to form monodisperse water-in-oil emulsions. We observed different regimes in forming water-in-oil multiphase flows by changing the applied pressures and discovered a hysteretic behavior in jet breakup and droplet generation. In the second step of GUV fabrication, an oil stream containing phospholipids carries the emulsions into a separation region where we steer the emulsions across two parallel oil streams using active dielectrophoretic and pinched-flow fractionation separations. We explore the effect of applied DC voltage magnitude and carrier oil stream flow rate on the separation efficiency. We develop an image processing code that measures the degree of mixing between the two oil streams as the water-in-oil emulsions travel across them under dielectrophoretic steering to find the ideal operational conditions. Finally, we utilize an oscillating co-flowing jet to complete the formation of asymmetric giant unilamellar vesicles and transfer them to an aqueous phase. We investigate the effect of flow rates on properties of the co-flowing jet oscillating in the whipping mode (i.e., wavelength and amplitude) and define the phase diagram for the oil-in-water jet. Assays used to probe the lipid bilayer membrane of fabricated GUVs showed that membranes were unilamellar, minimal residual oil remained trapped between the two lipid leaflets, and 83% asymmetry was achieved across the lipid bilayers of GUVs.

In materials printing applications, the ability to generate fine droplets is critical for achieving high-resolution features. Other desirable characteristics are high print speeds, large stand-off distances, and minimal instrumentation requirements. In this work, a tunable electrohydrodynamic (EHD) printing technique capable of generating micron-sized droplets is reported. This method was used to print organic resistors on flat and uneven substrates. These ubiquitous electronic components were built using the commercial polymer-based conductive ink poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), which has been widely used in the manufacturing of organic electronic devices. Resistors with widths from 50 to 500 μm and resistances from 1 to 70 Ω/μm were created. An array of emission modes for EHD printing was identified. Among these, the most promising is the microdripping mode, where droplets 10 times smaller than the nozzle's inner diameter were created at frequencies in excess of 5 kHz. It was found that the ink flow rate, applied voltage, and stand-off distance all significantly influence the droplet generation frequency. In particular, the experimental results reveal that the frequency increases nonlinearly with the applied voltage. The non-Newtonian shear thinning behavior of PEDOT:PSS strongly influenced the droplet frequency. Finally, the topology of a 3-dimensional target substrate had a significant effect on the structure and function of a printed resistor.

bilayers from SiOx control films shows no variation with pH. The difference can be attributed to the strong and weak variations, respectively, of the TiOx and SiOx surface charge over the pH range studied. A free energy model is developed to predict bilayer stability based on electrostatic contributions derived from double layer theory, van der Waals forces, steric repulsion, and short-range hydration forces. The model accurately predicts the observed bilayer-substrate separations and accounts for the increased bilayer fluctuations when the bilayer is far from the substrate. Implications for new measurement platforms and devices involving tunable floating bilayers are discussed.

To probe the complexity of biological systems, large numbers of independent experiments are needed to gather statistically reliable information. A platform that performs these experiments at high-throughput demands precise control over the formation and delivery of microcapsules. Microfluidics enables passive and active modes of droplet formation, manipulation, and mixing. Aqueous- and organic-based emulsions serve as well-defined compartments that encapsulate target materials (e.g., cells, reagents, nucleic acid, and nanoparticles) in femto- to picoliter volumes surrounded by an immiscible fluid. In this work, we demonstrate a high-throughput PDMS-based microfluidic device for fabrication and control of uniform micron-size water-in-oil and oil-in-water emulsions. Passive and active modes of droplet generation (i.e., hydrodynamic flow focusing and electrospray, respectively) are utilized to form droplets in the size range of 1 to 100 μm. We also leverage dielectrophoretic forces to steer the microemulsions across flows of organic or inorganic phases. The dielectrophoretic force provides high-speed separation with no moving elements and does not require droplet charging. Two electrode designs of AC- and DC-based circuits incorporated into the PDMS block are proposed. We investigate the effect of frequency and voltage on the degree of deflection and separation efficiency of the emulsions. We show that the fabricated microcapsules can be used as templates to build synthetic lipid bilayer model membranes that more accurately mimic physiological conditions. In addition, our microfluidic-based device integrated with on-board electronics can be used as an essential component in high-speed screening bioassays.