A self-healing medical sensor that can sense skin temperature and adjust to it is currently in development.

PALO ALTO, Calif. — In order to fulfill their potential as healthcare monitoring tools, wearable electronics will need to undergo two fundamental changes: I they will need to be able to morph from rigid to soft to meet evolving structural requirements, and (ii) they will need to be able to repair their own normal wear and tear. Researchers have created multifunctional sensors using liquid metal and specific polymers.

Penn State’s James L. Henderson, Jr. Memorial Associate Professor of Engineering Science and Mechanics Hyanyu “Larry” Cheng and his team of researchers published their findings in the journal Advanced Materials.

Since the layers of a rigid sensor can stack on top of one another without deforming, Cheng argues that producing sensors in a rigid state is preferable to manufacture them in a soft state. The crucial information provided by sensors is best viewed on a hard screen, thus sensors benefit from this rigidity as well. When worn by a patient, a soft sensor can better adhere to the topography of the skin, providing more accurate readings of temperature, heart rate, and other vital signs that can be used to track the progression of a disease or increase general health awareness.

In the past, “we have to truly employ two sorts of gadgets because we didn’t have the means to get these two wedded together,” Cheng added. But now we show that a change in temperature can be used to regulate the transition from hard to soft in a sensor. The sensor is flexible when at body temperature but hardens again when chilled.

According to their findings, this also aids in removing the sensor from the skin after use.

“When the sensor is soft, the adhesion property is stronger,” said Li Yang, first author and co-corresponding author and currently a professor in the School of Health Sciences and Biomedical Engineering at Hebei University of Technology in Tianjin, China. “For instance, you can use an ice pack on the skin to get the sensor material to harden and peel off the skin on its own. The adhesion changes from strong to weak, making it easier to remove without causing any harm to the skin. Babies and the elderly, whose skin is more likely to be fragile, benefit greatly from this.

The self-healing capabilities of a sensor were demonstrated

Using thermal switching, in which the material’s state is changed by applying or removing heat, isn’t completely novel, having previously been attempted at extremely high temperatures. According to Cheng, it is novel to perform this at a temperature appropriate for the human body. The use of a liquid metal, which offers performance similar to a solid metal but allows for flexibility in the design shape, was crucial to their successful demonstration of this technology with medical electronic sensors. The self-healing capabilities of a sensor were demonstrated thanks in part to the use of liquid metal.

Even if the sensor develops cracks or other mechanical damage over time, it may repair itself so that crucial monitoring can go as usual. As a bonus, it can make the gadget last longer.

Researchers utilized a polymer that forms hydrogen bonds with a liquid metal to speed up the device’s recovery time. Previous work has utilized the hydrogen bond for self-healing, but Cheng claims that this has been done in a more restricted fashion, which lengthens the time necessary for the device to mend.

According to Cheng, “Even though people have been working on different self-healing materials in the past, the results can only be obtained after 24 hours or more,” but in this case, “we can do that in a much faster manner, potentially as quickly as five minutes or so.” In cases where the sickness being examined could be fatal, waiting 30 hours without collecting data from the human body is unacceptable. Our method has the potential to bring back the function in a matter of seconds.

Thermal switching and self-healing properties into large-scale sensors

The team’s next step is to include thermal switching and self-healing properties into large-scale sensors that may be put to use everywhere from hospitals to nursing homes to keep tabs on the development of a disease.

Hao Wang, Biqiang Jin, and Jinrong Wu of Sichuan University in Chengdu, China; and Zihan Wang, Chuizhou Meng, Xue Chen, Runze Li, He Wang, Mingyang Xin, Zeshang Zhao, and Shijie Guo of Hebei University of Technology in Tianjin, China; are the other authors of the work.

Cheng has ties to numerous Penn State departments and centers, including the Mechanical Engineering Department, the Biomedical Engineering Department, the Architectural Engineering Department, the Industrial and Manufacturing Engineering Department, the Institute for Computational and Data Sciences, the Engineering, Energy, and Environmental Institute, and the Sustainability Institute.

The investigation was funded by the China Postdoctoral Science Fund, the National Institutes of Health, the National Science Foundation, Penn State, and the National Natural Science Foundation of China.