Video Inspired by plants and fungi, scientists have devised a method to help so-called soft robots travel along tricky pathways by growing as they move.

Unlike their more traditional metallic counterparts, soft robots have flexible bodies and their motion is controlled by manipulating materials to shuffle them along on their journey. Soft robots are expected to be able to navigate through difficult environments, such as the human body, a lot better than hard, metallic machines, though they may still struggle when faced with awkward twists or sharp turns.

A team of researchers led by academics at the University of Minnesota have built a soft robot that can move through this kind of difficult terrain by growing in length, nudging it around corners and other turns. The robot squeezes out a long rope of resin out from behind it to push it along its path.

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"We were really inspired by how plants and fungi grow," Matthew Hausladen, first author of the paper [2]published in the Proceedings of the National Academy of Sciences of the United States of America and a PhD student at the University of Minnesota, [3]said .

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"We took the idea that plants and fungi add material at the end of their bodies, either at their root tips or at their new shoots, and we translated that to an engineering system."

You can watch a video demonstration of the robot below.

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[7]Youtube Video

The resin is pumped out at one end to produce a growing hollow tube, like squeezing toothpaste, and the process is controlled using photopolymerisation, a technique often used in 3D printers. UV light initiates a chemical reaction that causes the liquid-based resin to harden as it grows at a rate of 12 cm per minute, and this tube can reach as much as 1.5 m in length. We're told it's still flexible enough to be bendy around corners.

These robots essentially each emit a long cord of material that molds to their environment, all while pushing the devices along, much like how fungi can push through soil and grow along the roots of a tree.

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THe robot cannot retract its tail and move backwards, we note. The team believes its method, once suitably miniaturized, may prove useful one day in developing soft robots to complete medical tasks within the body.

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"We think a compelling possible use case is in accessing parts of vasculature inaccessible by current catheter technology," Hausladen told The Register .

"Many blood vessels in parts of the body, like the brain, are very tortuous paths, and navigation with traditional catheter technology becomes difficult.

"This is because catheters are controlled from the base and pushed through the blood vessels. Eventually, the force of friction on these catheters becomes quite high and it becomes difficult to push the catheter any further into a blood vessel. On the other hand, by growing a catheter from a liquid resin, only the tip is moving and experiences friction, allowing you to grow inside of a very tortuous blood vessel."

The material uses monomers that have been FDA approved and is safe for biomedical applications. But the technology is still far off from being used in the human body. All the components have to be miniaturized to fit inside blood vessels.

"I would say more near term applications for this technology would be focused at larger scales, such as infrastructure deployment and exploration, as miniaturization presents some challenges," Hausladen concluded. ®

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[2] https://www.pnas.org/doi/10.1073/pnas.2201776119

[3] https://cse.umn.edu/college/news/engineers-discover-process-synthetic-material-growth-enabling-soft-robots-grow-plants

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[9] https://www.theregister.com/2021/07/06/roachbots/

[10] https://www.theregister.com/2021/03/05/floppy_robot_take_snail_fish/

[11] https://www.theregister.com/2015/07/10/boffins_3d_print_a_soft_jumping_robot/

[12] https://www.theregister.com/2021/01/21/programmable_metamaterial_nature/

[13] https://whitepapers.theregister.com/