Loss-Free Fluids Gripper

What it does

The loss-free fluids gripper is a liquid handling tool that can manipulate tiny amounts of fluids without substantial residues. Such new fluid interacting method can potentially reduce the consumption of medical or experimental disposables.

Your inspiration

To ensure the accuracy and obviate the cross-contaminations, liquid transfer disposables such as micropipette tips and microtubes are omnipresent in fields such as healthcare and pharmaceutical industries, increasing the cost of diagnosis and therapy. Once used, the disposables are contaminated with body fluids or hazardous chemicals, threatening the environmental safety and complicating the waste management. We get inspirations from some semiaquatic insects’ tarsi which consists of retractable hydrophilic ungues and hydrophobic hairs. We design the fluid gripper that can reversibly switch its adhesion to liquid.

How it works

The fluid gripper consists of microfibre array and mesh of micropores. The microfibres’ size is commensurate with the mesh pores, thereby, the fibre array can either protrude out of or retract behind the mesh through mechanical reconfiguration. The microfibres possess high liquid affinity whereas the mesh is treated to be liquid repellent. The non-wettings mesh makes touching liquid droplets remain their spherical shapes without spreading. Because of the high liquid affinity of microfibres, as the fibre array presents, the surface is highly-adhesive towards fluids, otherwise, the surface maintains its non-stickiness. The surface can capture fluids when it is adhesive and release fluids as it turns nonsticky. The surface can even precisely aliquot nano-litre liquid droplets through trapping and repelling of liquid among the fibre array space. In this way, droplets with volume of one thousandth of the mosquito-sucked blood volume can be precisely prepared.

Design process

The three key steps to create the fluids gripper are the fabrication of non-wetting meshes and microfibre array followed by the assembly of the two components. A piece of polyester mesh was used as the background mesh. To prevent wicking of contacting liquid droplets, we covered the mesh with a superhydrophobic coating. The surface of the mesh became rough because of the micro- and nanoscale hydrophobic structures, endowing the treated mesh with a water contact angle of 151°. A small bundle of peeled optical fibres was used as the movable microfibres. The tips of the fibres were smooth with exposed fused quartz that was inherently hydrophilic. Protective jackets were used to maintain the spacing between the centres of neighbouring fibres such that each fibre could protrude out of a pore in the mesh. The superhydrophobic mesh was attached to the top of a syringe while the hydrophilic fibre array was fixed to the plunger of the syringe using commercial adhesives. As the plunger advanced or retreated, the array of quartz fibres either protruded into or retracted from the non-wetting mesh. The on/off switching of the surface’s adhesion to water droplets is controlled by moving the array of microfibres.

How it is different

Many tools and devices such as micropipettes and microsyringes are offered to transfer tiny amounts of fluids. Generally, they all exploit small tube geometries and control fluids through pressure differences. The inaccuracy of pressure controls, partial wetting properties of tube sidewalls and large liquid/solid contact areas jointly diminish the manipulation precision and dexterousness. Unlike such conventional counterparts, the fluid grippers are controlled through linear mechanical translations. No pressure modulation is required. The liquid/solid contacts are minimized, thereby making the manipulation process nearly loss-free. The fluids gripper is the only compact and minimized tool that can manipulate liquids in nanolitre range. The fluids gripper resembles a non-wetting hand that may be integrated into intelligent robotic arms to perform skillful handling of liquids.

Future plans

The fluids gripper has been a degree project and published in a well-known scientific journal. In the next step, we will further polish and refine the designs and fabrications to improve the prototypes. We plan to start a startup business on the basis of our design. In the future, we hope that our methods can be widely employed in vast fields such as healthcare and drug discovery, reducing their cost and minimizing the environmental impacts.

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