Automatic Planar Asymmetric Lipid Bilayer Membrane Formation toward Biological High-Throughput Assay

This paper describes automation of planar lipid bilayer formation by introducing a stepping motor to a microfluidic device. Planar lipid bilayers or lipid vesicles are useful to understand biological reactions and to investigate the interaction between lipids and proteins. Therefore, to acquire large amount of the information, high-throughput production of planar lipid bilayers or giant vesicles (GVs) is necessary. The droplet split-and-contact method, which enhances the efficiencies of both planar lipid bilayer formation and GV generation, needs to be automated for increasing the throughput. Previous droplet split-and-contact devices were manipulated manually; hence, the influence of manipulation on planar lipid bilayer formation was not evaluated quantitatively. First, to develop an automated system for generating asymmetric planar lipid bilayers, a stepping motor, which allows to control the angular speed of the rotor, is integrated into the droplet split- and-contact device (Fig. $1(\mathrm{b)$). Next, we assessed planar lipid bilayer generation at various angular speeds and found the speed limit for bilayer formation. Finally, we generated asymmetric planar lipid bilayers that have different lipid composition on outer and inner leaflets using this automated device and confirmed the asymmetry of the planar lipid bilayers by generating GVs.