Electrochemically and Mechanically Regulated Liquid Metal Gate via Giant Surface Tension Alteration

Liquid gates can provide an effective method to control the release of substances. However, the size of liquid gates and the control methods limit their broad applications. The controllable large deformation of liquid metals (LMs) makes it possible to be used in liquid gate design with simple actuation methods. Here an LM gate that can be easily driven under moderate conditions is proposed, on demand opening at mild electrical voltage (2–5 V) and closing at an oscillating mechanical force (≈0.05 N) in a wide range of pH (2–12). The gating mechanism relies on the large surface tension alteration at these conditions, which directly changes the shape of the LM from a flat film to a contracted meniscus to one side of the copper gate-frame. As demonstrated, this gate can be applied to release substances such as liquid (ink), biomolecule (insulin) by free diffusion. Moreover, single-channel and multichannel gates can be realized for high throughput control. The biocompatibility of the whole gate is also proved by cytotoxicity assays. Above all, a novel LM gate is offered with simple structure and easy control, which may bring inspiration to applications in controlled substance release and separation.