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New Adhesive Smart Skin for Health Monitoring

A team of researchers from Penn State has developed an adhesive sensing device that seamlessly attaches to human skin to detect and monitor the wearer's health. The study was published in the journal Advanced Materials.

Wearable Health Monitors with the Development of a Novel Adhesive Sensing Device
Penn State researchers recently developed an adhesive sensing device that seamlessly attaches to human skin to detect and monitor the wearer’s health. The writable sensors can be removed with tape, allowing new sensors to be patterned onto the device. Image Credit: Jia Zhu

Skin can send health-related signals, such as tightness indicating dryness and the need for moisture. But what if skin could be even smarter, capable of monitoring and sharing specific health information like glucose concentration in sweat or heart rate? This question inspired a team led by Penn State researchers to develop an adhesive sensing device that seamlessly attaches to the skin, enabling the detection and monitoring of the wearer’s health.

The details of the smart skin, including its efficient reprogramming capability to detect various signals and its recyclability, were detailed in the paper.

The paper was included in the prestigious "Rising Stars" series, a collaboration among multiple journals aimed at showcasing the contributions of early career researchers globally. Additionally, the researchers filed a provisional patent application for their innovative work.

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. This work, however, introduces a skin-attachable, reprogrammable, multifunctional, adhesive device patch fabricated by simple and low-cost laser scribing.

Huanyu Cheng, the James L. Henderson, Study Co-corresponding Author and Jr. Memorial Associate Professor, Department of Engineering Science and Mechanics, Pennsylvania State University

According to Cheng, traditional methods of fabricating flexible electronics can be difficult and expensive, particularly when sensors constructed on flexible substrates or fundamental layers are not always flexible themselves. The device’s overall flexibility could thus be restricted by the stiffness of the sensor.

Previously, Cheng's team pioneered biomarker sensors utilizing laser-induced graphene (LIG). This technique entails employing a laser to create intricate 3D networks on a porous and flexible substrate. The interplay between the laser and the substrate's materials results in the formation of conductive graphene

Cheng added, “However, the LIG-based sensors and devices on flexible substrates are not intrinsically stretchable and can’t conform to interface with human skin for bio-sensing, noting that human skin is changeable in shape, temperature and moisture levels, especially during physical exertion when monitoring heart rate, nerve performance or sweat glucose levels might be necessary. Although LIG can be transferred to stretchable elastomers, the process can greatly reduce its quality.”

Therefore, Cheng highlighted the challenge of programming a sensor device to reliably monitor specific biological or electrophysical signals due to the dynamic nature of human skin. Even when programming is successful, the sensing performance of such devices is often compromised.

To address these challenges, it is highly desirable to prepare porous 3D LIG directly on the stretchable substrate.

Jia Zhu, Ph.D., Study Co-author, Department of Engineering Science and Mechanics, Penn State

Zhu is also an Associate Professor at the University of Electronic Science and Technology of China.

To achieve this goal, the researchers devised an adhesive composite comprising polyimide powders, which enhance strength and heat resistance, along with amine-based ethoxylated polyethylenimine—a polymer capable of modifying conductive materials—dispersed within a silicone elastomer or rubber.

This stretchable composite not only facilitates direct 3D LIG preparation but also possesses adhesive properties, enabling it to conform to and adhere to non-uniform, variable shapes, such as those found on human skin.

Experimental validation demonstrated the device's capability to monitor pH levels, glucose, and lactate concentrations in sweat, comparable to measurements obtained via finger prick blood draws.

Moreover, it can be reprogrammed to track real-time metrics like heart rate, nerve performance, and sweat glucose concentrations.

Reprogramming is simplified by applying clear tape over the LIG networks and then peeling them off. The substrate can subsequently be re-lasered to meet new specifications, allowing up to four iterations before becoming too thin. Ultimately, when the device reaches the end of its lifespan, it can be recycled in its entirety.

According to Cheng, the device remains adhesive and capable of monitoring even when the skin is slippery from perspiration or water.

Currently powered by batteries or near-field communication nodules, similar to a wireless charger, the device has the potential to harvest energy and communicate via radio frequencies, resulting in a standalone, stretchable adhesive platform capable of sensing desired biomarkers and monitoring electrophysical signals, according to researchers.

The team plans on working toward this goal, in collaboration with physicians, to eventually apply the platform to manage various diseases such as diabetes and monitor acute issues like infections or wounds.

Cheng added, “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 also works with the Departments of Biomedical Engineering, Mechanical Engineering, Architectural Engineering, and Industrial and Manufacturing Engineering, as well as the Materials Research Institute and the Institute for Computational and Data Sciences.

Other collaborators affiliated with the Department of Engineering Science and Mechanics at Penn State include Xianzhe Zhang, Chenghao Xing, and Shangbin Liu, all graduate students, and Farnaz Lorestani, associate research fellow.

Co-authors from outside of Penn State include Yang Xiao, Jiaying Li, Ke Meng, Min Gao, Taisong Pan and Yuan Lin, all from the University of Electronic Science and Technology of China; and Yao Tong, Yingying Zhang, Senhao Zhang, Benkun Bao and Hongbo Yang from the Suzhou Institute of Biomedical Engineering and Technology, Chinese Academy of Sciences. Li is also affiliated with the institute.

This research was supported by the National Science Foundation of the United States, Penn State, the University of Electronics Science and Technology China, the National Institutes of Health of the United States, and the National Natural Science Foundation of China.

Journal Reference:

Zhu, J., et al. (2024) Direct Laser Processing and Functionalizing PI/PDMS Composites for an On-Demand, Programmable, Recyclable Device Platform. Advanced Materials.

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