4D-Printed Soft Robots Can Self-Assemble

A new 4D-printed soft robot developed by researchers at Cell Press is able to self-assemble when heated. It can carry out tasks like rolling uphill and navigating unpredictable landscapes. 

The tube-shaped prototype was presented in the journal Matter on September 22.

Wei Feng is a materials scientist at Tianjin University in China and senior author of the paper.

“Like an insect with antennae, the robot can surmount a small obstacle. But when the obstacle is too high, it will turn back,” says Feng. “The whole process is spontaneous without human interference or control.”

4D-Printed With Fourth Dimension

The robot is first a flat and rectangular sheet of a 3D-printed liquid crystal elastomer, which is a type of plastic material that is stretchy. Once the surface beneath this sheet is heated, the robot then twists up to form a tubule that resembles a spring. The reason this robot is 4D-printed rather than 3D-printed is that the change in shape under external stimulation adds time as a fourth dimension.

The contact from the hot surface causes a strain in the material after the robot forms a tubule. This in turn causes the robot to roll in one direction, with the driving force behind the motion being extremely strong. In fact, it is so strong that the robot is capable of climbing up a 20 degree incline or carrying weights that are up to 40 times of its own. The velocity of the robot depends on its length, with the longer length robots rolling faster than the shorter ones. 

Testing the Robots

The researchers set these robots to perform tasks and demonstrate their skills while being recorded. One of these included a race between the different sized robots and another one that was carrying a cart. In these videos, the robots also demonstrated how they could change their behaviors based on the surroundings. If the robot encountered a challenging obstacle, it could do things like climb up a step or change directions. 

Senior author Feng was surprised by the robot’s behavior.

“We processed the liquid crystal elastomers into samples of various shapes through 4D printing and stimulated these samples with light, heat, and electricity to observe their response,” he says. “We found many interesting driving phenomena besides deformation.”

According to the researchers, these robots could be used in the future to carry out tasks in small and confined places, such as in a pipe. They could also operate in extreme conditions, such as intensely hot surfaces.

“We hope that soft robots will no longer be limited to simple actuators, which can only change shape in a fixed position,” says Feng.