WASHINGTON, Aug. 21 (Xinhua) -- U.S. engineers have developed a fully untethered soft robotic system that can move or change shape in response to external stimuli.

The study published on Wednesday in the journal Science Robotics showed the origami-inspired device using materials known as liquid crystal elastomers change shape when exposed to heat.

Researchers from Harvard University and Caltech 3D-printed two types of soft hinges that fold at different temperatures and can be programmed to fold in a specific order.

The untethered soft robot nicknamed the "Rollbot" begins as a flat sheet, about eight centimeters long and four centimeters wide. When placed on a hot surface about 200 degrees Celsius, one set of hinges folds the robot into a pentagonal wheel.

Then, another set of hinges embedded on each of the five sides of the wheel folds when in contact with the hot surface, alternately propelling the wheel to turn to the next side, according to the study.

"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," said Connor McMahan, a graduate student at Caltech and co-first author of the paper.

Another device, when placed in a hot environment, can fold into a compact folded shape resembling a paper clip and unfold itself when cooled, according to the study.

The researchers said the liquid crystal elastomers can be programmed to respond to light, acidity, humidity and other external stimuli.

The study showed that the responsive polymers in an architected composite can be programmed to perform ever more complex tasks, blurring the boundaries between materials and robots, according to the researchers.