Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have designed a liquid that behaves as both a solid and a fluid owing to the presence of tiny gas-filled capsules. An unusual relationship between pressure and volume enables this material to grasp fragile objects.

The first-of-its-kind metafluid uses a suspension of small, elastomer spheres – between 50 to 500 microns – that buckle under pressure, radically changing the characteristics of the fluid. The metafluid could be used in everything from hydraulic actuators to program robots, to intelligent shock absorbers that can dissipate energy depending on the intensity of the impact, to optical devices that can transition from clear to opaque.

Metamaterials – artificially engineered materials whose properties are determined by their structure rather than composition – have been widely used in a range of applications for years. But most of the materials – such as the metalenses pioneered in the lab of Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS – are solid. 

Using a highly scalable fabrication technique, the research team produced hundreds of thousands of these highly-deformable spherical capsules filled with air and suspended them in silicon oil. When the pressure inside the liquid increases, the capsules collapse, forming a lens-like half sphere. When that pressure is removed, the capsules pop back into their spherical shape. 

That transition changes many of the liquid’s properties, including its viscosity and opacity. Those properties can be tuned by changing the number, thickness and size of the capsules in the liquid.  

The researchers demonstrated the programmability of the liquid by loading the metafluid into a hydraulic robotic gripper and having the gripper pick up a glass bottle, an egg and a blueberry. In a traditional hydraulic system powered by simple air or water, the robot would need some kind of sensing or external control to be able to adjust its grip and pick up all three objects without crushing them. 

Source: Nature

Image: Mia Stendal/azorobotics.com