Algae-Powered Soft Robot Arms Bend and Grip When Light Hits

The pH-responsive layer changes a lot. According to the researchers, between pH 3 and 7 it was about 37 percent of its original weight, while at pH 11 it reached four times that weight.

Local effect, slow motion

Other pH-responsive soft robots exist, but they typically require changing the chemistry of all the surrounding liquid. The algal version acts much more locally, which makes it better suited to uses where environmental impact must stay minimal.

Speed is the drawback. The chemical shift starts about 20 seconds after light is applied and about 10 seconds after it goes dark, but significant bending takes several hours.

After the first proof of concept, the team built a four-fingered gripper that closes in light. It lifted a hollow metal sphere and released it when the light went off. A hook-shaped gripper picked up and set down a rubber ring. Both objects weighed far less than a small paperclip.

What comes next

The devices need no external energy besides light and no complex mechanical parts. "Microalgae are plantlike organisms that are largely self-sustaining," said Marie-Eve Aubin-Tam, who led the research, adding that this gives the actuator potential for long-term operation with minimal external input.

The team hopes the approach will lead to more autonomous, environment-responsive soft robots for automated agriculture, fluid control in lab-on-a-chip devices or underwater robotics. Because the algae are not genetically modified, the biosafety concerns often tied to microbe-based technologies do not apply.