Search will be available as the English edition grows.
Microalgae embedded with a hydrogel make a soft actuator bend as light switches on and off. Researchers used the principle to build a simple gripper that lifts small objects without a conventional motor or battery.
Soft robots can grasp delicate objects and adapt to their surroundings in ways that are difficult for rigid machines. But their motion still requires energy and a system that converts that energy into mechanical force. Researchers at Delft University of Technology have now demonstrated a different approach: letting living microalgae do part of the work.
In a study published in Nature Communications, the researchers combine the microalga *Chlamydomonas reinhardtii* with a hydrogel that changes shape as the acidity around it changes. The result is a soft green strip that can bend back and forth as light is switched on and off.
The demonstrated actuator is about two centimetres long and one millimetre thick. It does not use a conventional electric motor to drive the movement. Instead, the algae's metabolism creates the chemical change to which the hydrogel responds.
When illuminated, the algae use light and carbon dioxide in photosynthesis. Together with nitrogen assimilation, these processes raise the pH inside the material. That changes the pH-responsive polymer in the hydrogel, causing its two layers to swell by different amounts and making the strip bend.
When the light is switched off, the cells continue to respire and release carbon dioxide. The pH then falls again and the deformation reverses.
Light therefore acts as a control signal, while the living cells convert energy and environmental chemistry into the local pH shift that drives the actuator.
The researchers report that the movement begins to reverse within roughly 10–20 seconds after the lighting conditions change. Large bending amplitudes develop over longer timescales. The system maintained its reversible response through ten continuous light and dark cycles in the experiments.
The researchers also shaped the actuator so that it could perform simple gripping tasks. In demonstrations, it hooked and lifted a small rubber ring, while another configuration could grasp and release a small metal ball through light-controlled bending.
That does not make the system a finished autonomous robot. The demonstrations primarily show that the biologically driven deformation can be converted into a useful mechanical action rather than remaining only a measurable material response in the laboratory.
The principle is particularly interesting for soft systems because such robots often rely on pumps, compressed air, electrical wiring or other external components to move. Here, the photosynthetic cells perform part of the energy conversion inside the material itself.
Biohybrid materials combine living cells with engineered materials. One advantage is that cells already contain sophisticated mechanisms for sensing and responding to their environment, harvesting energy and carrying out chemical processes that would be complicated to engineer from scratch.
Microalgae are especially interesting because they use light as an energy source. The researchers therefore point to the possibility of future soft devices that operate with little external energy input and respond directly to environmental conditions.
That could eventually be relevant to soft grippers, adaptive materials or systems that change shape with light. The study does not, however, show that such products are ready for deployment.
Living components also introduce new constraints. The cells must remain in an environment where they can survive and continue functioning. Response speed, lifetime, robustness, control of larger structures and performance outside laboratory conditions all require further investigation.
The main point is therefore not the practical capacity of the small gripper. It is the coupling of photosynthetic metabolism to programmable mechanical motion within one material.
Instead of biology merely inspiring the robot, biology becomes an active part of the machinery. Light provides the signal, the algae change the chemistry, and the material turns that change into motion.
KEEP EXPLORING
Researchers have developed an artificial skin with more than 10,000 touch sensors that organizes signals more like the human nervous system. In experiments, it let robots detect very fine surface structures and react automatically to potentially harmful contact.
Humanoid robots need enormous amounts of experience before they can work reliably in the real world. DexForce wants to move much more of that training into simulation.
Compostable polyesters carrying degrading enzymes inside the material broke down strongly from coastal water to depths of 5,503 metres. The approach could make some plastics less persistent at sea, but it is not yet a solution for conventional plastic waste.