Soft Robots Use Temperature Sensitive Material to Swim Through Water

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Engineers from California Institute of Technology and ETH Zurich have created soft robots capable of self-propulsion without using any motors, servos or even power supply.

They are constructed from a material which deforms with temperature changes and this is how they paddle through the water.

Principle behind soft robots

The propulsion system relies on strips of a flexible polymer that is curled when cold and stretched out when warm. The polymer is positioned to activate a switch inside the robot’s body that is further attached to a paddle. The paddle rows the robot forward like a rowboat.

The switch used in the robot is made from a bistable element – a material that can be stable in two distinct geometries. Here it is built from straps of an elastic material that, when pushed on by the polymer, snaps from one position to another.

When the cold robot is placed in the warm water, the polymer stretches out activating the switch and results in sudden release of energy that paddles the robot forward. These polymer strips can be tuned to give specific responses at different times as thicker strip takes longer time than thinner strip to warm up, stretch out and ultimately activate its paddle. This feature of tunability allows the team to design robots capable of turning and moving at different speeds.

They used chains of bistable elements to transmit signals and build computer-like logic gates. Also, they linked up the polymer elements and switches in a way that allows the four-paddled robot to propel itself forward, drop off a small payload and then paddle backward.

Now, scientists look forward to adding more functionalities and responsivities like using polymers to get activated by pH or salinity. A challenge that the team is facing at present is that when the bistable elements snap and release their energy, they have to be manually reset in order to work again. The team is exploring ways to redesign the bistable elements so that they can self-reset when water temperature shifts again, making them potentially capable of swimming on indefinitely, so long as water temperature keeps fluctuating.