Big Developments Bring Us Closer to Fully Untethered Soft Robots

Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and Caltech have developed new soft robotic systems that are inspired by origami. These new systems are able to move and change shape in response to external stimuli. The new developments bring us closer to having fully untethered soft robots. The soft robots that we possess today use external power and control. Because of this, they have to be tethered to off-board systems with hard components. 

The research was published in Science Robotics. Jennifer A. Lewis, a Hansjorg Wyss Professor of Biologically Inspired Engineering at SEAS and co-lead author of the study, spoke about the new developments. 

“The ability to integrate active materials within 3D-printed objects enables the design and fabrication of entirely new classes of soft robotic matter,” she said. 

The researchers used origami as a model to create multifunctional soft robots. Origami, through sequential folds, is able to change into multiple shapes and functionalities while staying in a single structure. The research team used liquid crystal elastomers that are able to change their shape when exposed to heat. The team utilized 3D-printing to get two types of soft hinges. Those hinges fold depending on the temperature, and they can be programmed to fold into a specific order. 

Arda Kotikan is a graduate student at SEAS and the Graduate School of Arts and Sciences and the co-first author of the paper. 

“With our method of 3D printing active hinges, we have full programmability over temperature response, the amount of torque the hinges can exert, their bending angle, and fold orientation. Our fabrication method facilitates integrating these active components with other materials,” she said. 

Connor McMahan is a graduate student at Caltech and co-first author of the paper as well. 

“Using hinges makes it easier to program robotic functions and control how a robot will change shape. Instead of having the entire body of a soft robot deform in ways that can be difficult to predict, you only need to program how a few small regions of your structure will respond to changes in temperature,” he said.

The team of researchers built multiple soft devices. One of these devices was an untethered soft robot called “Rollbot.” It starts as an 8 centimeters long and 4 centimeters wide flat sheet. When it is in contact with a hot surface of around 200°C, one set of the hinges folds and shapes the robot into a pentagonal wheel. 

On each of the five sides of the wheel, there are more sets of hinges that fold when in contact with a hot surface. 

“Many existing soft robots require a tether to external power and control systems or are limited by the amount of force they can exert. These active hinges are useful because they allow soft robots to operate in environments where tethers are impractical and to lift objects many times heavier than the hinges,” said McMahan.

This research that was conducted focused solely on temperature responses. In the future, the liquid crystal elastomers will be studied further as they are also able to respond to light, pH, humidity, and other external stimuli. 

“This work demonstrates how the combination of responsive polymers in an architected composite can lead to materials with self-actuation in response to different stimuli. In the future, such materials can be programmed to perform ever more complex tasks, blurring the boundaries between materials and robots,” said Chiara Daraio, Professor of Mechanical Engineering and Applied Physics at Caltech and co-lead author of the study.

The research included co-authors Emily C. Davidson, Jalilah M. Muhammad, and Robert D. Weeks. The work was supported by the Army Research Office, Harvard Materials Research Science and Engineering Center through the National Science Foundation, and the NASA Space Technology Research Fellowship.