Algae Powered Robot Arm
Researchers at Delft University of Technology have built a soft robot arm that bends, grasps and lifts without a motor or a battery. The arm runs on living microalgae and light. The work is published in Nature Communications.
The device is a green strip roughly two centimetres long and one millimetre thick, made from two hydrogel layers with the microalgae growing on its surface. Marie-Eve Aubin-Tam, who led the research, says the shape of the strip can be changed easily to produce different movements and functions.
And the motion comes from the algae's metabolism. Under light they photosynthesise, using carbon dioxide and light energy to make sugars while also drawing on nitrogen to build cell components. Those processes raise the pH inside the hydrogel, and because the two layers respond to acidity differently they swell by unequal amounts, which forces the strip to curl.
Switch the light off and the reaction runs the other way. The algae burn their stored fuel and release carbon dioxide, pushing the pH back down. Fan Jiang, a doctoral candidate and the first author, says the actuator starts bending in the opposite direction within 10 seconds.
To show the bending is useful, the team built grippers from the same material. A hook shaped device lifted a rubber ring out of the water. A small gripper closed around a metal ball and then let it go when the light went off.
But the movement is slow. The paper reports that the full bending stroke takes up to 18 hours, and that the device held its performance across 10 cycles of continuous operation. The films released by the university are sped up 1800 times.
The organism doing the work is a single celled green alga, Chlamydomonas reinhardtii, living in a hydrogel bilayer that swells and shrinks as the acidity shifts. The material is a proof of concept, and keeping the algae alive is part of the engineering problem. The arm does not feed itself.
Aubin-Tam puts the starting point plainly. "We didn't start with a specific application," she says. "Our goal has always been to bring the research of living materials to new levels." Her paper points to wider uses, including blinds and farm equipment that change shape or orientation as the light changes.
So the near term application is small scale work underwater, where a cable or a battery is the awkward part of the design. Nothing here is close to a product, and the bending is far too slow for handling anything that moves. What the Delft team has shown is that living cells can be built into a material and made to do mechanical work with light as their only input.
A strip of two hydrogel layers coated with microalgae, about 2 cm long and 1 mm thick
Photosynthesis raises the pH, the layers swell unevenly and the strip curls, while darkness reverses it
The full bending stroke takes up to 18 hours, though the first response arrives in 10 to 20 seconds
The team lifted a rubber ring and gripped a metal ball underwater to demonstrate it
Proposed uses include blinds and agricultural devices that react to changing light
Source: TU Delft, Nature Communications
