Smart skin for real time health monitoring

Skin can send health-related signals, but what if skin could be smarter, capable of monitoring and sharing specific health information? That question drove a team led by Penn State researchers to develop an adhesive sensing device that attaches to human skin to detect and monitor the wearer’s health.

“Despite significant efforts on wearable sensors for health monitoring, there haven’t been multifunctional skin-interfaced electronics with intrinsic adhesion on a single material platform prepared by low-cost, efficient fabrication methods,” says co-corresponding author Huanyu “Larry” Cheng, the James L. Henderson, Jr. Memorial associate professor of engineering science and mechanics in the Penn State College of Engineering. “This work, however, introduces a skin-attachable, reprogrammable, multifunctional, adhesive device patch fabricated by simple and low-cost laser scribing.”

Cheng explains that conventional fabrication techniques for flexible electronics are complicated and costly. Sensors built on flexible substrates aren’t necessarily flexible themselves, limiting the flexibility of the entire device. Cheng’s team previously developed biomarker sensors using laser-induced graphene (LIG), which involves using a laser to pattern 3D networks on a porous, flexible substrate.

“However, the LIG-based sensors and devices on flexible substrates aren’t intrinsically stretchable and can’t conform to interface with human skin for bio-sensing,” Cheng says, noting human skin can change in shape, temperature, and moisture levels, especially during physical exertion when monitoring might be necessary. “Although LIG can be transferred to stretchable elastomers, the process can greatly reduce its quality.”

As a result, Cheng says, it’s more difficult to program a sensor device to monitor specific biological or electrophysical signals. Even when the device can be appropriately programmed, its sensing performance is often degraded.

“To address these challenges, it’s highly desirable to prepare porous 3D LIG directly on the stretchable substrate,” says co-author Jia Zhu, an associate professor at the University of Electronic Science and Technology of China.

The researchers achieved this goal by making an adhesive composite with molecules called polyimide powders and amine-based ethoxylated polyethylenimine – a type of polymer that can modify conductive materials – dispersed in a silicone elastomer. The stretchable composite accommodates direct 3D LIG preparation and conforms and adheres to non-uniform, changeable shapes such as humans.

The researchers experimentally confirmed the device can monitor the pH value, glucose and lactate concentrations in sweat, heart rate, and nerve performance in real time. To reprogram the device they simply apply clear tape over the LIG networks and peel them off. The substrate can then be re-lasered to new specifications. Once it becomes too thin, the entire device can be recycled.

According to Cheng, the device remains adhesive and capable of monitoring even when the skin is slick. Currently powered by batteries or near-field communication nodules, the device could potentially harvest energy and communicate over radio frequencies, resulting in a standalone, stretchable adhesive platform capable of sensing biomarkers and monitoring electrophysical signals. The team plans to work toward this goal in collaboration with physicians to eventually apply the platform to manage various health challenges.

“We would like to create the next generation of smart skin with integrated sensors for health monitoring – along with evaluating how various treatments impact health – and drug delivery modules for in-time treatment,” Cheng says.

This research was published in Advanced Materials and funded by the U.S. National Institutes of Health, the U.S. National Science Foundation, Penn State, the University of Electronics Science and Technology China, and the National Natural Science Foundation of China. Contributing to this work were researchers from Penn State, University of Electronic Science and Technology of China, and the Suzhou Institute of Biomedical Engineering and Technology of the Chinese Academy of Sciences.