A Plant-Inspired Extrusion Technique for Soft Robots

Existing soft-growing robots typically drag solid material, which converts into a permanent structure by the robot via heat and pressure. It gets increasingly difficult to pull that solid material around turns and bends, so the robots cannot easily move around obstacles or winding paths. Researchers at the University of Minnesota Twin Cities developed a new plant-inspired extrusion process for synthetic material growth via liquid rather than a solid. This discovery provides opportunities to create better soft robots for navigating rough terrain, inaccessible areas, and the human body.

"This is the first time these concepts have been fundamentally demonstrated," said Chris Ellison, a lead author of the paper. "Developing new ways of manufacturing are paramount for the competitiveness of our country and for bringing new products to people. On the robotic side, robots are being used more and more in dangerous, remote environments, and these are the kinds of areas where this work could have an impact."

Plants rely on water to move the building blocks, which turn into solid roots during the plant's outward growth. The team replicated this ability with synthetic material via photopolymerization, converting liquid monomers into a solid. This process allows a robot to move around obstacles and winding paths without dragging solid material behind.

"We were really inspired by how plants and fungi grow," said Matthew Hausladen, first author of the paper and a Ph.D. student in the University of Minnesota Twin Cities Department of Chemical Engineering and Materials Science. "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."

The team's technology can be used for manufacturing applications as well. Ultimately, this technique depends on light and liquid to work, so it doesn't require processes relying on heat, pressure, and costly machinery to develop and shape materials.

"A very important part of this project is that we have material scientists, chemical engineers, and robotic engineers all involved," Ellison explains. "By putting all of our different expertise together, we really brought something unique to this project, and I'm confident that not one of us could have done this alone. This is a great example of how collaboration enables scientists to address really hard fundamental problems while also having a technological impact."