Origami-Inspired Stretchable Strain Sensors to Find Application in Wearables and Implantables

Existing stretchable strain sensors often rely on soft materials like rubber. However, these materials can undergo irreversible changes in their properties with repeated use, leading to unreliable deformation measurements. The challenge is to develop sensors that can stretch significantly, respond rapidly, and provide accurate readings even when dealing with substantial and dynamic deformations. In response, researchers have turned to an origami-inspired solution to create novel sensors that could potentially find applications in detecting organ deformations, wearables, and soft robotics.

Researchers at the University of Southern California (USC, Los Angeles, CA, USA) have introduced a new structure for the sensors after drawing inspiration from origami. Their innovative design allows the folding of more rigid materials with electrodes on both sides of the panel (imagine the sensor as an open book with electrodes on the front and back covers). As the electrodes unfold, they measure the strength of the electrical field between them. The team has developed a model that translates this measurement into a value that captures the extent of the deformation. These sensors can be attached to moving soft structures—ranging from the mechanical tendons of prosthetic limbs to the pulsating tissues of human internal organs—to monitor shape changes and proper function without the need for cameras.

The newly devised sensors can stretch up to three times their original size while maintaining high sensing accuracy even after repeated usage. Moreover, these sensors exhibit rapid responsiveness, detecting deformations in less than 22 milliseconds within very small areas (about 5 square millimeters). Furthermore, they can identify strains from various directions. Due to their capacity to precisely measure extensive, intricate, and fast deformations, these sensors offer numerous possibilities for practical implementation in wearable electronics, prosthetics, and robotics. They can find applications in tracking the movements of soft robots, monitoring human joint motions, or even observing organs such as the bladder to identify abnormalities indicative of disease. While initially designed for controlling soft robotics—ranging from delicate robotic grippers to snake-like surveillance devices—these sensors are also suitable for innovations in biomedicine.

“We can apply these sensors as wearable or implantable biomedical devices for healthcare monitoring,” explained Hangbo Zhao who led the research group. “For example, tracking the movement and flexibility of our skin or our joints. There’s also high demand for developing implantable sensors that can continuously monitor the functional status of internal organs that undergo cyclic expansion and contraction.”

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