Taking cues from nature, medical soft robots get smart

Newswise — Physical human feats, whether it is nailing a guitar solo or sinking a half-court shot in basketball, require a high level of coordination between the sensory functions of our skin and motor functions of our muscles. What kind of achievements could robots perform with the same cohesion between sensing and action? 

In the medical space, researchers at the University of North Carolina (UNC) at Chapel Hill have begun to explore the possibilities. 

The team developed soft robots primarily made of two layers — one simulating skin and the other muscle — that can autonomously detect and respond to different physiological stimuli. In a proof-of-concept study published in Nature Communications, the authors tested their robots’ diagnostic and therapeutic potential across several model organs, including a mouse model of heart disease. The data suggest that this implantable technology could have wide applicability. 

“Complications associated with traditional medical implants often stem from a mechanical, chemical, or functional mismatch between device and tissue. Our biomimetic soft robot addresses these challenges with its long-lasting, biocompatible materials and ability to adapt to the dynamic conditions of the body,” said senior study author Wubin Bai, Ph.D., a professor of applied physical sciences at UNC-Chapel Hill. 

The base layer of the robot is composed of a thermally responsive hydrogel that can contract and relax like muscle, allowing the implant to bend and softly grip organs inside the body. Bound to this muscle layer is the robot’s electronic skin, or e-skin, which is made of a soft polymer that can contain a wide variety of components—both sensors and stimulators—that can affect the robot and surrounding tissue. 

The researchers designed the robot to turn sensory information into physical responses, letting physiological changes in the body dictate the robot’s actions. For example, sensors on the e-skin can detect local changes in the body’s temperature, acidity, electrical activity, and mechanical strain, while mini electrodes can stimulate tissue, and electrical heaters can trigger the robot’s muscle layer to contract. 

They fabricated several dual-layered robots of different shapes, some taking the form of a simple ribbon, while other multi-armed robots emulated starfish. With on-board circuits allowing for wireless power and data transmission, these devices maintained a slim profile across configurations. 

The researchers assessed the robots through several benchtop tests they developed based on conversations with physicians about various clinical challenges.

In one test, a four-armed robot gently gripped a balloon that the researchers filled and emptied with water, simulating changes in bladder volume. The device measured the strain of the ‘bladder’ as it filled, automatically responding with electrical stimulation to trigger emptying after it reached a certain threshold, hinting at potential utility for bladder dysfunction. 

For another experiment, they demonstrated that a robot could twist itself into a helical shape around a plastic model artery to gauge simulated blood pressure. This capability could alleviate surgeons of performing the difficult task of manually wrapping vascular cuffs around arteries, which is done to detect blockages during certain procedures, Bai said. 

The team also explored their technology’s potential for long-term drug delivery in the gastrointestinal tract. The researchers showed that the robot that could easily travel through a rubber model esophagus but expand in a model stomach, which could prevent its passage and lengthen the window in which drugs could be released from the device. In separate benchtop experiments they showed the robot could both measure acidity and release a model drug. 

Another set of tests brought the technology into a more realistic proving ground — a beating heart. 

Some critical heart surgeries require attaching a device to the cardiac surface that supplies electrical stimulation to create a normal heart rhythm while the organ recovers. But when these traditional flat devices are attached to curved and beating heart tissue, the interface generates stress that can disturb normal cardiac function, Bai explained. 

The researchers placed four-armed robots onto the surface of hearts in living mice, where the wet hydrogel of the artificial muscle both adhered to and gently gripped the heart tissue. 

The authors found that the technology could both measure heart muscle activity and modulate it through electrical stimulation. They did not detect any indications of inflammation or injury two weeks after implantation. 

Bai and his colleagues hope that their robots will eventually help human patients, but before that, they plan to add functionality to the technology and evaluate it in animal models that more closely match our physiology. 

“By taking inspiration from our own versatile tissues, these researchers are developing a robotic tool that exhibits a similar versatility in addressing many challenges in the biomedical space,” said Tiffani Lash, Ph.D., program director in the Division of Health Informatics Technologies at the National Institute of Biomedical Imaging and Bioengineering (NIBIB). 

This research was supported in part by a grant from NIBIB (R01EB034332). 

This science highlight describes a basic research finding. Basic research increases our understanding of human behavior and biology, which is foundational to advancing new and better ways to prevent, diagnose, and treat disease. Science is an unpredictable and incremental process—each research advance builds on past discoveries, often in unexpected ways. Most clinical advances would not be possible without the knowledge of fundamental basic research. 

Study reference: Lin Zhang et al. Skin-inspired, sensory robots for electronic implants. Nature Communications. DOI: 10.1038/s41467-024-48903-z