Ding Guifu's team from Shanghai Jiaotong University published a cover paper on high-performance directional transport of droplets in Small Methods

Recently, the team of Ding Guifu of the MEMS Multivariate Compatible Integrated Manufacturing Technology Laboratory of the Department of Micro-Nano Electronics, School of Electronic Information and Electrical Engineering made progress in the field of droplet directional transport, and the relevant results were "High-performance directional water transport using a two-dimensional periodic Janus gradient structure" (Two-dimensional periodic Janus gradient structure to achieve high-performance directional transport of droplets) was published
in the form of a cover paper in the international authoritative journal Small Methods (IF=15.
367).

Introduction to the paper

This paper proposes a periodic Janus gradient structure with terminal potential wells, which realizes rapid and long-distance directional transport of droplets with extremely low volume loss along the way, which provides a strategy for comprehensively improving the directional transport performance of droplets, which is expected to promote the development of
microfluidics, on-chip chemical synthesis, water collection, heat and mass transfer and drug delivery.

Research background

Droplet directional transport has a wide range of applications
in many fields such as physics, chemistry and biomedicine.
Organisms in nature provide many inspirations for the controlled manipulation of droplets, such as Janus wettability on the back of desert beetles that effectively promotes water collection, the asymmetric topology of the cactus spine driving the rapid transport of droplets from the tip to the root, and the periodic microcavity structure on the surface of the mouth margin of Nepenthes to achieve continuous directional transport
of droplets.
Inspired by this, researchers have designed a series of biomimetic surfaces with wettable gradients and/or structural gradients, and many advances
have been made in the directional transport of droplets.
However, existing transportation strategies often have mutual constraints of speed and distance, and the innovative structure with both fast and long-distance directional transportation capabilities is worth exploring
.

Highlight results

Inspired by the Janus wetted surface on the back of desert beetles, the geometric gradient structure of the cactus thorn and the periodic microcavity structure on the surface of the oral margin of Nepenthes insect, the research team proposed a 2D periodic Janus gradient structure (PJGS) with terminal potential wells to overcome the shortcomings of high along resistance and high loss in many 3D droplet transport systems, and to make up for the shortcomings
of 2D structures in long-distance transportation 。 The droplets have achieved long-distance transport at an average speed of more than 400 mm/s in PJGS, the normalized transport distance (transport distance/droplet diameter) of 3 μL droplets can reach 23.
4, and the volume loss along the high-throughput droplet transport is as low as 6.
02%, which has outstanding
comprehensive advantages.

Design of bionic surfaces

The directed delivery run of droplets on PJGS is

Based on the flexible application of the confined domain effect, PJGS can effectively regulate the kinetic mechanics
of droplet transport in its confined structure.
The ultra-contrast wettability promotes the rapid release and conversion of the surface energy of the droplet into kinetic energy, giving the droplet itself a high initial momentum, combined with the driving force generated by the multi-site region of the periodic flow channel, the liquid film of the PJGS flow channel is formed very quickly
.
The formation of liquid film transforms the solid-liquid interaction into liquid-liquid interaction, which greatly reduces the resistance of fluid transport and enables subsequent droplets to be transported
quickly and long distances along the liquid film layer of the periodic flow channel.
In addition, the terminal potential well can continuously guide the droplets in the flow channel to spontaneously flow to the place to reduce its own surface energy, combined with the pinning effect of the well boundary on the liquid bulge, PJGS exhibits ultra-low volume loss
along the high-throughput droplet transport.

Droplet directional transport mechanism

Based on PJGS's high-performance droplet directional transport, a prototype system integrating droplet metering, merging, splitting and rapid transport has been developed, which can complete complex microfluidic tasks
on open surfaces.

Complete complex microfluidic tasks on open surfaces

This research work was supported
by Shanghai Micro-Nano Integrated Manufacturing Technology Platform (20DZ2291300).
Xie Dongdong, a doctoral student at the Institute of Electrical Engineering, is the first author of the paper, Dr.
Zhang Baoyue of RMIT University is the co-first author, and Professor Ding Guifu is the corresponding author
of the paper.

Ding Guifu Team Homepage: https://gpmems.
sjtu.
edu.
cn/

Link to the paper: https://onlinelibrary.
wiley.
com/doi/10.
1002/smtd.
202200812