Xin Tang Announces that A Fluid gripper is adhesive and loss-free: Gripper surface is inspired by tarsi of aquatic insects that can handle a wide range of fluids just like soft solids.

Manipulation techniques are the key for the material process, parts assembly, spanning a wide range of industries. Intelligent robots armed with either rigid or soft hands are developed to handle various types of solid objects, such as heavy cargos or delicate electronics. However, convenient handling of fluids is still a cumbersome task despite their omnipresence.

By integrating a microfibre array of high liquid affinity with liquid-repellent mesh, HKU researchers design “mechano-regulated surfaces”. The surface appears non-wetting to fluids. Liquid droplets on the surface remain their spherical shapes without spreading or substantial retention. By controlling the presence of the microfibre array, the surface switches its adhesion, thereby, the surface can capture fluids when it is adhesive and release fluids as it turns nonsticky.

The research was published in the Nature Communications (Mechano-Regulated Surface for Manipulating Liquid Droplets. Nat. Commun. 2017, 8, 14831.).

“We consider this work as a first step towards the development of loss-free manipulation tools for multiscale liquids,” said Liqiu Wang, the professor of mechanical engineering at HKU and the corresponding author of the paper. “Our dexterous hands enable us to perform the finest craftsmanship. When the handling target is a tiny amount of liquids rather than solids, our hands are tied, thereby instruments such as micropipettes/pumps are utilized in the healthcare industry to transfer and transport liquids such as precious medicines or blood samples. Such liquid manipulation methods consume numerous disposable medical products, including pipette tips and microtubes, leading to high testing costs and hazardous wastes. Our surface can freely handle fluids in a nearly lossless manner, enabling multi-step liquid processing without consumables. The surface is a gripper that can manipulate fluids in a way similar to the handling of solids.”

The mechano-regulated surfaces consist of microfiber array and mesh of micropores. The microfibres’ size is commensurate with the mesh pores, thereby, the fiber array can either protrude out of or retract behind the mesh through ready mechanical reconfiguration. Because of the contrastive wettability of the binary components, as the fiber array presents, the surface is highly-adhesive towards fluids, otherwise, the surface maintains its non-stickiness. Apart from picking up micro-liter liquid droplets, the surface can even precisely aliquot nano-liter liquid droplets through trapping and repelling of liquid among the fiber array space. In this way, droplets with a volume of one-thousandth of the mosquito-sucked blood volume can be precisely prepared. The surface shows precise and rapid manipulating capability towards multiscale liquids.

“In addition to manipulating capability towards the tiny amount of liquid, the non-wetting gripper can handle multiple droplets in parallel and be adapted for different types of fluids,” said Xin Tang, the first author of the paper. “The surface may change the way we interact with fluids and opens the doors for precise aliquot and control of liquids through ready mechanical reconfiguration. The new liquid processing technique may benefit numerous fields, such as drug discovery, microassay, and chemical synthesis.”

Next, the researchers aim to extend the handling liquid volume range and develop surface with spatially addressable adhesion switch, thus, a single surface can enable rich and patch-independent liquid control.

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