Title: Reproducible reformation of a bilayer lipid membrane using microair bubbles
Authors: Izumi Hashimoto1,2, Toshihisa Osaki1, Hirotaka Sugiura1, Hisatoshi Mimura1, Sho Takamori1, Norihisa Miki1,2, Shoji Takeuchi1,3,4
Planar bilayer lipid membranes (BLMs) are widely used as models for cell membranes in various applications, including drug discovery and biosensors. However, the nanometer-thick bilayer structure, assembled through hydrophobic interactions of amphiphilic lipid molecules, makes such BLM systems mechanically and electrically unstable. In this study, we developed a device to reform BLMs using a microair bubble. The device consists of a double well divided by a separator with a microaperture, where a BLM was formed by infusing a lipid-dispersed solvent and an aqueous droplet into each well in series. When the BLM ruptured, a microair bubble was injected from the bottom of the well to split the merged aqueous droplet at the microaperture, which resulted in the reformation of two lipid monolayers on the split droplets. By bringing the two droplets into contact, a new BLM was formed. An angled step design was introduced in the BLM device to guide the bubble and ensure the splitting of the merged droplet. We also elucidated the optimal bubble inflow rate for the reproducible BLM reformation. Using a 4-channel parallel device, we demonstrated the individual and repeatable reformation of BLMs. Our approach will aid the development of automated and arrayed BLM systems.
Fig.1 Schematic diagrams of the bubble-assisted reformation of a BLM. (a) A microchannel is integrated at the bottom of the BLM device for inflow of a microair bubble using an external pump. (b) A cross-sectional view of the device, illustrating the reformation process of a ruptured BLM by introducing a microbubble. BLM, bilayer lipid membrane.
Fig.2 Three types of fabricated devices. (a) A device for observation of the trajectory of air bubbles using a microscope from the top. A bubble is infused from the bottom inlet. A step design is located aside from the inlet. (b) A magnified image of the step design in (a) and a cross section of the step, inlet, and channel along the line A–A′. The depth of the step is 0.5 mm and the angle θ is changed from 30° to 180°. (c) A single-channel BLM device with a double well. (d) A magnified image of the double well. A separator with a microaperture divides the wells, and a pair of electrodes are embedded at the bottom. (e) A magnified image of the step design. A bubble inlet with a 90° step is designed at a distance of 0.7 mm from the separator for BLM reformation. (f) A 4-channel BLM device with the bubble inlet for BLM reformation. The device is mounted on an in-house developed 4ch amplifier for electrical recording. Details of the device designs are described in Supporting Information: Figure S1. 4ch, 4-channel; BLM, bilayer lipid membrane.
Fig.3 Guide of an air bubble by an angled step. (a) Time-lapse images capturing the formation of a bubble on a surface with a 90° step angle, at an inflow rate of 30 μL/min (top view). The bubble moved along the center of the step. (b) Center positions of microair bubbles detached from the bottom surface at an inflow rate of 30 μL/min and various step angles: From the right, the step angle is 30°, 60°, 90°, 120°, 150°, and 180°, respectively. Ten bubbles were observed for each angle (N = 10), and dashed lines indicate the bubble inlet and step border. The positive y-direction represents the bubble's advancement along the step.
Droplet（《液滴》）是由吉林大学主办，与国际著名出版公司Wiley合作出版的英文国际性学术期刊，是国际上第一本全面报道液滴／气泡交叉领域科研成果的学术期刊。目前为季刊，主要发表液滴／气泡相关领域的原创性研究论文、综述及评论性文章，重点报道与液滴／气泡相关的结构、材料和系统设计、制备和调控等方面的基础研究及工程应用。现任主编为中国科学院院士任露泉教授、美国加利福尼亚大学洛杉矶分校C.J.Kim教授。执行主编由香港理工大学王钻开教授担任。
目前，Droplet（《液滴》）已通过全球最具影响力的开放存取期刊目录（Directory of Open Access Journals, DOAJ）评估，正式被DOAJ数据库收录。本刊旨在成为跨学科的高水平学术交流平台，展示液滴和气泡相关领域的前沿研究成果，推进国际科研传播与合作。
编辑部总编：张成春教授，副总编：王丹编审。
