Wearable Sensors Could Make Health Monitoring and Treatment More Timely and Affordable

03/01/2021

Huanyu “Larry” Cheng in the Penn State classroom; Dr. Cheng has conducted his research at Penn State since 2015.

A new wearable health device could deliver real-time medical data for individuals with eye or mouth diseases, according to Huanyu  “Larry” Cheng, Dorothy Quiggle Career Development Professor in the Penn State Department of Engineering Science and Mechanics. The wearable sensor—currently being prototyped—could collect biofluids (like tears or saliva) for analysis, sending data to smartphones and/or doctors, and could even deliver medicine.

HappyValley Industry recently spoke to Dr. Cheng about his work and its potential to change impact the future of healthcare.

The developed wearable tattoo electronics and dissolvable sensors will help transform healthcare monitoring from hospital-centered to people-centered.  

HappyValley Industry: What is your research topic and why is it important on a global scale?

Dr. Cheng: In a nutshell, my group focuses on the design, fabrication and application of skin-like wearable devices and degradable electronics. My research contributes to bio-integrated devices that address the mismatch between soft tissues and stiff electronics, enabling applications from diagnostic and/or therapeutic platforms to human-machine interfaces. The developed wearable tattoo electronics and dissolvable sensors will help transform healthcare monitoring from hospital-centered to people-centered.  

For example, we sought to create a device that collects both small and large substances of biofluids (e.g., sweat, interstitial fluids, tears and saliva), which can be analyzed for certain conditions on a rapid, continuous basis, rather than waiting on test results from samples in a lab. 

In another recent work, we have demonstrated a simple yet universal fabrication technique. With the use of a novel sintering aid layer, our method allows metal nanoparticles to be sintered at low or even room temperatures, as compared to several hundreds of degree C in alternative approaches. Our new fabrication scheme has been applied to enable skin-printed sensors for physiological signal monitoring, as well as paper-/fabric-based printed circuit boards (FPCBs) for signal conditioning/readout and wireless transmission. We are very excited to see the possibility of applying this technique for the soft body area sensor network, as a promising direction toward the future class of skin-interfaced, wearable electronics. The demonstrated high-performance skin-printed sensors could precisely and continuously capture temperature, humidity or local moisture change, blood oxygen saturation, electrophysiological signals (e.g., electrocardiogram, electromyography), among others. With enhanced signal quality and improved performance over their commercial counterparts, these skin-printed sensors with other expanded modules provide a repertoire of wearable electronics for health monitoring. Additionally, the system with demonstrated modules of on-body sensors for physiological signal monitoring and FPCBs for wireless transmission can be applied to signal the progression and severity in COVID-19 patients.

HappyValley Industry: How do you envision your research impacting/changing your industry?

Dr. Cheng: The ultimate application of these bio-integrated devices for practical and convenient applications hinges on the seamless integration of on-body sensors with wireless transmission modules. Multifunctional on-body sensors can precisely and continuously monitor the health conditions of the human body, whereas the wireless transmission modules can wirelessly power up the sensors and transmit the data generated from them to the cloud for the healthcare professionals. As a promising direction toward this class of integrated systems, the soft body area sensor network includes on-body sensors for physiological signal monitoring and flexible printed circuit boards (FPCBs) for signal conditioning/readout and wireless transmission. Realization of the soft body area sensor network currently relies on various sophisticated fabrication approaches from lithography and transfer printing to direct printing, especially when stretchable sensors are separated from readout circuits (e.g., FPCBs). In particular, extensive efforts have been devoted to exploring the integration of wearable electronics on paper/fabric or human skin. However, there lacks a simple yet universal approach to fabricate all of the modules relevant to the soft body area sensor network, due to the challenging requirements of low-temperature processing on textured surfaces with easy removal capabilities. 

We are interested in applying this multifunctional, wearable sensing technology for diagnostic confirmation and timely treatments for cardiopulmonary diseases, including COVID-19, pneumonia and fibrotic lung diseases. With excellent electromechanical and underwater performance, this sensing technology can also be used to track and monitor marine mammals.

We report a simple yet universally applicable fabrication technique with the use of a novel sintering aid layer to enable direct printing and room-temperature sintering of various metal inks for constructing paper-/fabric-based FPCBs and on-body sensors. The fabrication scheme relies on a sintering aid layer consisting of an adhesive polyvinyl alcohol (PVA) paste and nanoadditives (e.g., TiO2 or CaCO3, among others). By using the sintering aid layer on various paper/fabric substrates or the human skin, the sintering temperature of metal nanoparticles (NPs) is significantly reduced even to room temperature. The reduced sintering temperature of Ag NPs with the use of the sintering aid layer can be attributed to the increased grain boundary diffusion coefficient from charge neutralization, which is revealed by the experiment and phase-field simulations. The sintering aid layer also reduces the surface roughness of various substrates to allow the printing of an ultrathin layer of metal patterns with improved electromechanical performance against various mechanical deformations such as bending or folding.

We are interested in applying this multifunctional, wearable sensing technology for diagnostic confirmation and timely treatments for cardiopulmonary diseases, including COVID-19, pneumonia and fibrotic lung diseases. With excellent electromechanical and underwater performance, this sensing technology can also be used to track and monitor marine mammals. We also plan to explore the extended capabilities of our existing platform in both sensors and FPCBs.

HappyValley Industry: What inspired you to follow this line of research?

Dr. Cheng: As with many other researchers in the field, I start to work in this area by exploring photolithographic processes for sensor/device fabrication in the cleanroom. Though of high quality, this type of approach is costly and involves the use of sophisticated equipment, which is challenging to use in prototyping or small-scale production. To address these challenges, we start[ed] to explore more rapid and low-cost fabrication techniques, so that the resulting sensors and devices can be easily transitioned to the marketplace for the consumers to use. 

Now, working on biodegradable sensors, I wish that we could have devices available for patients like him. 

We are also highly motivated and excited to work on this line of research not only for the diseased but also for healthy aging. As one example, my father fell … and broke his rib cage almost 10 years ago, when I was still a Ph.D. student. Though it [required] a small surgery, the implanted supporting structures for improved bone healing would have to be removed in a second surgical operation after. Now, working on biodegradable sensors, I wish that we could have devices available for patients like him. As a result, I determined to continue my efforts to work on tattoo-like wearable and degradable sensors for biomedicine. 

As a small step to address the grand challenge in health monitoring, the central focus of our group now is on self-powered, wireless, multifunctional systems from low-cost fabrication approaches, which also presents many interesting future directions in our field. For the self-powered devices, one project in our group focuses on stretchable rectennas for harvesting ambient RF energies for charging batteries or powering electronics. The multifunctional aspect also leads us to work on stretchable gas sensors for detecting gaseous biomarkers from the human body and exposed environment. One alternative low-cost fabrication approach in our group enables direct fabrication of biodegradable and long-lasting sensors on 3D curvilinear freeform surfaces.

Furthermore, we are also interested in combining wearable devices and big data analysis for health informatics in the new era. The interdisciplinary nature of these diverse future directions calls for the joint efforts between clinicians and engineers with diverse backgrounds to help facilitate the fast development in this burgeoning field.

Without the help from my colleagues here, I cannot imagine how long it would take for us to build up a research program in this multidisciplinary area. 

HappyValley Industry: Why did you choose to conduct this research at Penn State specifically?

Dr. Cheng: I came to Penn State in 2015. It has been fascinating to learn the various types of research activities (and the names of departments) on campus over the past few years, which provides excellent collaboration opportunities. This aspect is especially important and attractive to me, as my research area is interdisciplinary and calls for joint efforts from diverse backgrounds. Without the help from my colleagues here, I cannot imagine how long it would take for us to build up a research program in this multidisciplinary area. 

HappyValley Industry: Would you encourage other researchers to make their home in Happy Valley, and why?

Dr. Cheng: During my Ph.D. study at Northwestern, I spent a year and a half in Champaign, Illinois, without a car. Even with car rentals, my wife and I used to drive three hours to get to and from Chicago. Therefore, the landscape in Pennsylvania immediately got our attention. Though I was warned about the weather, we find it is certainly not as extreme as that in Chicago. Happy Valley is also a nice place to raise kids. Our family has been fishing and hiking a lot and I hope we will have more opportunities to go skiing and hunting as my daughter grows up.

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