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Pneumatic soft robot mimics self rotating action of fruit fly larvae

Soft-bodied robots are unlocking a new era of adaptive machines that can safely interact with the human body, squeeze through tight spaces, and propel themselves autonomously.

Designing soft robots that can move around by themselves has been challenging. Luckily, nature has already done the hard work.

Drosophila or fruit fly larvae have a remarkable escape strategy—they roll away from danger. A study by researchers from China found that the larvae bend their bodies into a "C-shape" and roll sideways, rotating around their body's cross-section.

Inspired by this mechanism, they designed a pneumatic soft robot that successfully mimicked the larval rolling behavior, even in the presence of faulty actuators driving the motion. The findings are in Â鶹ÒùÔºical Review Letters.

The invention of the wheel is uniquely human, as nature lacks perfect wheels and generally views rolling as an inefficient form of locomotion.

In rare instances, some animals resort to moving as a last-ditch escape strategy during high-stakes situations, such as fleeing predators or escaping dangerous environments. These rolling motions are passive, imprecise and lack direction, often relying on external forces like wind, gravity or ground direction. For example, web-toed salamanders tumble down slopes, effectively surrendering control as they roll to safety.

Some animals, however, have evolved to develop active rolling strategies, and Drosophila larvae are one of them. To escape danger, these worm-like larvae curl into a C-shape and spin along their long axis, rolling away from threats.

Scientists believe that the larvae are not reliant on external factors because the force generated while rolling is much greater than gravity or ground reaction forces, and the larvae can successfully roll even when placed upside down.

Thus, the following question is raised: What exactly is the driving torque for larval rolling?

To uncover how they roll, researchers genetically modified the larvae to express a muscle-activity marker, then observed them in a water-filled microfluidic chamber using light-sheet microscopy. Since larvae roll in response to potentially harmful stimuli, the researchers heated the water in the bath to 40°C to induce the rolling behavior.

The researchers conducted ablation experiments, where a laser was used to remove or destroy certain sections of muscles to determine which of the larva's 11 segments was essential for continuous rolling in larvae.

The findings reveal that rolling depends on the coordinated activation of axial muscles within a specific range of angles. The mechanical model developed by the team explains how sequential muscle contractions deform the hydrostatic skeleton and interact with the environment to produce the rolling motion.

Building on these findings, the researchers developed a soft robot made of silicone rubber and fiber constraints, capable of generating and sustaining rotation through the actuation of four pneumatically controlled internal chambers.

Pressurizing one chamber made the robot stretch, but the fiber constraints caused it to bend in the opposite direction. They found that pressurizing the four chambers one after another could make the robot roll forward. This worked even with damaged actuators.

Drawing from nature's principles, this work pushes the boundaries of soft robotics, which, when done right, is poised to transform search-and-rescue operations, health care and exploration in complex environments.