Rice researchers advance the manufacturing of sophisticated shape-shifting soft robots

Researchers at universities around the world have been working on soft robots and medical implants that can reconfigure themselves on demand. This sort of shape-shifting material is closer to reality thanks to researchers from Rice University's Brown School of Engineering. The scientists developed a method to print objects that can be manipulated to take on alternative forms when exposed to temperature changes, and electric current, or stress.Researchers consider this reactive 4D printing. Scientists have been able to make structures that can change shape in molds since 2018, but the same chemistry used in 3D printing limited the structures to shapes that sat in the same plane. That meant the shape-shifting materials couldn't be designed with bumps or other complex curvatures as their alternate shape.

Overcoming that limitation led the researchers to decouple the printing process from the shaping. Researchers say the materials they designed, once fabricated, can change shape autonomously. The team's idea was to use multiple reactions in sequence to print the material and then dictate how it would change shape. Rather than trying to accomplish all the shape-changing in one step, the new approach gives more flexibility in controlling the initial and final shapes.

The big challenge was to create a liquid crystal polymer ink that incorporates a set of mutually exclusive chemical links between molecules. Once the two programmed forms reset the material could morph back-and-forth when it's heated or cooled, as an example. One challenge was to find a polymer mix that could be printed in the catalyst bath and still hold its original programmed shape.

One remaining limitation of the new process is the ability to print unsupported structures, such as columns. Accomplishing this requires a solution that gels just enough to support itself during printing. Researchers are working towards that goal, and once achieved, it will allow researchers to print a far more complex combinations of shapes.