Dutch engineers build a soft robot arm powered by living algae and light

Engineers at Delft University of Technology in the Netherlands have built a soft robotic arm that needs no battery, motor or circuit board to move. Instead, it is driven by a living skin of microscopic algae that bend the arm as they photosynthesize, a design the researchers describe in a paper published this week in Nature Communications.

The device, reported in a university announcement on Thursday, is a proof-of-concept rather than a finished tool. But it points to a growing effort in robotics to replace batteries and motors with living cells that generate their own motion from light and simple nutrients.

Most soft robots today still rely on conventional power sources in disguise: pumps that push air through rubber chambers, small electric motors buried inside flexible skins, or batteries that need periodic recharging or replacement. Each of those solutions adds weight, complexity and a finite operating time, a particular problem for robots meant to work somewhere hard to reach, such as underwater or inside a sealed greenhouse. The appeal of an actuator powered by living algae is that, as long as light and water are available, the "fuel system" largely maintains itself.

A strip that bends toward, then away from, the light

The actuator itself is unglamorous: a green, rubbery strip about 2 centimeters long and 1 millimeter thick, made of two layers of hydrogel with a living film of microalgae grown across its surface. When a lamp is switched on, the algae begin photosynthesizing, a process that raises the pH inside the gel. Because the two hydrogel layers respond differently to that chemical shift, one swells more than the other and the strip curls.

Turn the light off, and the effect reverses. The algae switch to consuming their stored food, releasing carbon dioxide and lowering the gel's pH again. "Within 10 seconds the actuator already starts bending in the opposite direction," said Fan Jiang, a PhD candidate in the lab of professor Marie-Eve Aubin-Tam and the paper's first author, in the university's release. In demonstrations shared by the team, versions of the strip curled into a hook to lift a small rubber ring and closed around a metal ball underwater, where the algae's aquatic lifestyle gives the design a natural advantage.

"Our proof-of-concept actuator is a green and soft strip made of two different hydrogel layers," said Marie-Eve Aubin-Tam, the professor who led the work at TU Delft's bionanoscience department.

Living cells as the power source

Robots that incorporate living tissue are not new. Earlier this year, engineers at MIT described a paper-thin swimming robot whose fins were lined with light-responsive muscle cells grown from mice, which contracted to propel it through water. That approach, like most muscle-powered robots before it, required growing animal muscle tissue in bulk and feeding it externally.

The Delft team's algae are different in one respect the researchers consider important: the organisms largely feed themselves. "Microalgae are plantlike organisms that are largely self-sustaining," Aubin-Tam said, needing only light and water rather than a nutrient-rich growth medium that has to be regularly replenished. That could make algae-driven actuators simpler and cheaper to maintain than ones built from animal muscle, though the Delft device is far slower and less powerful than either muscle-based robots or conventional motorized grippers.

The Delft team also built variations beyond the single grasping arm, including strips that curl into spirals and flower-shaped actuators whose "petals" open and close as light conditions change, according to footage included with the university's release. Because the motion itself is slow, the team recorded much of it on video sped up as much as 36 times to make the bending visible on a human timescale.

No application yet, but several in mind

The researchers have not built the device for a specific job. "We didn't start with a specific application," Aubin-Tam said, describing the work as basic research into how living organisms can be wired into mechanical systems. Still, the team points to a few directions worth exploring: light-sensitive window blinds or agricultural shading devices that adjust themselves without wiring, soft grippers gentle enough to handle fragile aquatic specimens, and, more broadly, a step toward soft robots that draw their energy directly from ambient light rather than a battery that needs recharging or replacing.

Soft, biohybrid robotics of this kind remains a small corner of engineering research, well short of practical deployment. The Delft actuator is a single component, not a complete robot, and the published demonstrations involve lifting a rubber ring and grasping a metal ball rather than any task with obvious commercial value. The algae also depend on a steady light source and an aquatic or humid environment to survive, limiting where such a device could operate.

What comes next

The team, which also includes postdoctoral researcher Friedrich Kleiner, says future work will focus on more complex shapes and on understanding how factors such as light intensity, nutrient levels and algae species affect the speed and strength of the bending motion. The university's announcement frames the current arm as a starting point for a broader class of "living" actuators rather than a finished component, and the full methods and data behind the demonstration appear in the peer-reviewed paper, which other labs can now use to test the approach with different algae species or hydrogel formulations.

Independent researchers outside the Aubin-Tam lab have not yet published a response to the findings, which were distributed Thursday through EurekAlert!, the science-press clearinghouse run by the American Association for the Advancement of Science, alongside the university's own release. For now, the arm exists only in the Delft lab, one of several small signs that engineers are looking past batteries and motors toward organisms that already know how to turn light into movement.