In Delft, a living algae arm bends toward the light and picks up a metal ball — no battery needed

It looks like a tiny green ribbon, about 2 centimetres long. Shine a light on it, and it curls; switch the light off, and within ten seconds it begins to unbend. Researchers at Delft University of Technology in the Netherlands grew microalgae on a two-layer gel strip: as the algae photosynthesise, they change the water's acidity, one layer swells more than the other, and the strip bends — enough to hook a rubber ring and grasp a small metal ball, they show in Nature Communications. Because the algae feed themselves on light, the little arm could run for a long time with almost no outside energy. Lead researcher Marie-Eve Aubin-Tam calls it a step toward soft robots that are 'more autonomous and environmentally responsive.'

SDG 9 · Industry, innovation and infrastructure — Mechanism: tech innovation