Living microalgae powered reversible bending in a soft hydrogel strip in a peer-reviewed laboratory study. Light changed the cells’ metabolism and the surrounding acidity, making the strip’s two layers swell differently. Demonstrations included grasping small objects. The first response was rapid, but large bends took hours, limiting the speed of this proof of principle.
A single peer-reviewed laboratory study demonstrated a soft actuator powered by living Chlamydomonas reinhardtii, a freshwater microalga. The cells sit on a two-layer hydrogel strip, a water-rich polymer material. Light-dependent photosynthesis and nitrogen metabolism change local acidity. One layer swells more strongly than the other, bending the strip; respiration-associated changes in darkness reverse the movement.[1]
The system requires no genetically modified algae. Comparable movement was absent from a hydrogel without cells under changing light. Inhibiting photosynthesis or heat-inactivating the cells stopped the response. Local acidity changes within the material were larger than those in the surrounding liquid. These controls support a close interaction between cell metabolism and the polymer rather than simple heating by light or the passive presence of cells.[1]
Initial responses began quickly, but large bends developed over hours. The structure maintained about 300 degrees of movement over 10 cycles. Each cycle included illumination lasting 3 hours followed by darkness lasting 15 hours. It retained light-responsive bending after 60 days. Smaller reversible movements also appeared in shorter cycles, with darkness lasting 30 minutes after illumination for 10 minutes. Under controlled laboratory conditions, the actuator grasped a ball weighing 18.4 mg and manipulated a ring weighing 52.5 mg.[1]
