Printing soft silicone robots

A picture of John Morrow presenting his research to a small audience.

By changing the consistency of silicone rubber, John Morrow, a graduate student in robotics, enabled a 3D printer to assemble silicone into complex shapes. The breakthrough could hold the key to 3D printing of silicone soft-bodied robots. 

Morrow and his colleague, Osman Dogan Yirmibesoglu, a Ph.D. student in robotics, presented their findings at the 2017 Graduate Research Showcase. 

“The robotics field is looking closely at 3D printing as another way to build soft robots,” said Morrow, who is a joint M.S./Ph.D. student in robotics. He added that current techniques for building soft-bodied robots out of silicone, such as molding, are messy, fraught with human error, and limit design options. Silicone is well-suited for making soft robots because the material is so pliable (able to stretch to 900% of its initial dimensions). But before it’s cured, silicone is a runny liquid that doesn’t hold its shape when extruded through a 3D printer head. “It just forms puddles, so we needed a way to make the silicone firmer,” Morrow explained. 

Morrow and his team mixed an additive into the silicone supply that causes it to thicken. They also custom built a 3D printer head that mixes and extrudes the two component parts of silicone liquid. Once the silicone is deposited in the desired shape, heaters speed along the curing process to solidify it. The result is a solid but pliable silicone rubber. The technique has allowed the group to create complex geometries with seamless internal voids, which are crucial for soft-robot mobility. 

Soft robots are made to move by pumping air or liquid into their internal chambers. Exact movements, such as bending or twisting, can be controlled by how those hollow areas are shaped and constricted, so the ability to assemble robots with great precision is vital to assuring they move as intended. 

“Our focus is to make hollow objects without any internal support or seam, because seams can break easily when under pressure,” said Morrow. “Forming silicone soft robots using a 3D printer could release us from all limitations to future soft-robot design. We believe our technique imposes the fewest limits on whatever type of soft robots you want to make.” 

Morrow’s faculty advisor, Assistant Professor Yiğit Mengüç, added that the potential impact of 3D silicone printing reaches far beyond robotics and could lead to breakthroughs in other fields, such as medicine. “What’s really exciting is that this technique is not just for building soft robots,” he said. “Medical device manufacturers, for example, could use it to make highly flexible endoscopes, custom prosthetics, or devices we can’t even imagine yet. It opens up endless possibilities.”

— Steve Frandzel

Jan. 5, 2022