Simplified formation of ultrasmall lipid bilayer between parallel micrometer channels using Laplace pressure for assessing membrane instability under shear flow

Abstract

Microfluidic devices containing artificial cellular membranes have been developed for biology, biosensors, and bioengineering. Although forming a lipid bilayer between two microchannels has advantages for integrating cellular membrane functions into continuous chemical processing and evaluating cellular membrane responses under fluid-flow-induced shear stress, it typically suffers from complex operation of external pumps and contamination of the lipid bilayer by residual organic solvent. This study presents a simplified formation process of an ultrasmall lipid bilayer between parallel micrometer channels leveraging dominant surface tension effects. Utilizing 4 μm channels with partial hydrophobic modification, the simple operation of a parallel two-phase flow involving an aqueous phase and a lipid-containing organic phase (chloroform) was achieved under a controlled 101 kPa Laplace pressure. After parallel two-phase flow was formed to create a lipid monolayer at the aqueous/organic interface, the organic phase was replaced with the aqueous phase, maintaining the interface position via Laplace pressure. A 2.2 × 3.7 μm2 lipid bilayer with a thickness of 4.2–6.4 nm and reduced contamination was successfully formed, as verified by fluorescence and capacitance measurements. To demonstrate the functionality of this parallel-channel platform, the stability of the lipid bilayer was evaluated under shear stress induced by pressure-driven flows. The results indicated that the bilayer partially ruptured at a shear rate higher than 0.27 μs−1, suggesting a critical shear rate that induces membrane instability. This work demonstrates the feasibility of the developed in vitro platform for studying cellular membranes at the subcellular level and conducting fL-chemical operations using cellular membrane functions.