The body regulates its metabolism precisely and continuously, with specialised cells in the pancreas constantly monitoring the amount of sugar in the blood, for example. When this blood sugar level increases after a meal, the body sets a signal cascade in motion in order to bring it back down.In people suffering from diabetes, this regulatory mechanism no longer works exactly as it should. Those affected therefore have too much sugar in their blood and need to measure their blood sugar level and inject themselves with insulin in order to regulate it. This is a relatively imprecise approach compared to the body’s own mechanism.<h2>Equipping cells with special functions</h2>Martin Fussenegger is Professor of Biotechnology and Bioengineering at the Department of Biosystems Science and Engineering of ETH Zurich in Basel. With the above situation in mind, he and his team have been working on cell therapies for some time. One day, the hope is that these therapies will allow metabolic diseases such as diabetes to be treated individually and precisely – or even cured.But how do these cell therapies work? First, the researchers modify human cells by incorporating a network of genes that give the cells special abilities. These cells are <a>implanted</a> under the skin, for example, and the network is activated by a specific external stimulus.<h2>A suitable switch is key</h2>To that end, the researchers have developed various types of switches over recent years. Some can be controlled electrically, others with light, and one even using music by the British rock band Queen (see <a href="https://ethz.ch/en/news-and-events/eth-news/news/2023/08/cells-with-an-ear-for-music-release-insulin.html">ETH News</a>).The researchers in Basel have now developed another variant, which they have presented in the journal <a href="https://doi.org/10.1038/s41551-025-01350-7">Nature Biomedical Engineering.</a>“For me, this solution is the best gene switch that my group and I have built so far,” says Fussenegger. The reason is that the switch can be triggered using the long-established active ingredient nitroglycerine, and that the means of application – sticking a patch to the skin – is very simple. Corresponding patches are already available to buy in various sizes in any pharmacy.Nitroglycerine quickly diffuses out of the patch and into the skin, where it encounters an implant that contains modified human kidney cells.<h2>Network activated by nitric oxide</h2>These cells specifically intercept the nitroglycerine and have a built-in enzyme that converts it into nitric oxide (NO), a natural signalling molecule. In the body, NO normally causes blood vessels to dilate, leading to increased blood flow. It is broken down within a few seconds and therefore only affects a very localised area.The implanted cells are modified so that NO triggers the production and release of the chemical messenger GLP-1, which in turn boosts insulin release by the beta cells of the pancreas and thus regulates blood sugar level. GLP-1 also triggers a feeling of satiety, thereby reducing food intake.The new switch is made exclusively of human constituents – that is, it contains no components from other species. “That’s a new and groundbreaking feature,” says Fussenegger. With components from other species, there is always a risk of false triggering, interference with the body’s own processes, or immune reactions. “Here, we’re able to rule that out.”<h2>A whole arsenal of switches</h2>In the last 20 years, the ETH professor has developed various different gene switches, some of which respond to physical triggers such as current, sound waves or light. Which type has the best chance of being implemented one day?“Physical triggers are interesting because we don’t need to use molecules that interfere with the body’s own processes,” the biotechnologist says. He explains that electrical signals are ideal for controlling switches and gene networks using portable electronics such as smartphones or smartwatches – and AI can then be incorporated, too. “I therefore think electrogenetic cell therapies have the best chances of implementation. In terms of chemical switches, I see the new solution as being in pole position,” says Fussenegger.However, the further development of these cell therapies based on gene switches is a complex and lengthy process. “Developing a cell therapy to market maturity not only takes decades but also requires lots of staff and sufficient resources,” says the researcher. “There’s no shortcut.”Until now, Fussenegger’s work has focused mainly on cell therapies for diabetes, which is one of the world’s most prevalent metabolic diseases, affecting one in ten people. “That’s the model disease we work with. Fundamentally, however, it’s also possible to develop cell therapies for other metabolic, autoimmune or even neurodegenerative diseases – in principle, for everything that requires dynamic regulation.” According to Fussenegger, many drugs are like a hammer that is used to strike at a problem blindly. “Cell therapies, on the other hand, solve the problem in a similar way to the body,” he says.<h2>Reference</h2>Mahameed M, Xue S, Danuser B, Charpin-El Hamri G, Xie M, Fussenegger M: Nitroglycerin-responsive gene switch for the on-demand production of therapeutic proteins, Nature Biomedical Engineering, 14 February 2025, doi: <a href="https://doi.org/10.1038/s41551-025-01350-7">external page10.1038/s41551-025-01350-7</a>

A skin patch with nitroglycerine is the switch that controls an implant underneath (symbolic image). (Image: Josef Kuster / ETH Zurich)

ETH researchers have developed a new gene switch that can be activated using a commercially available nitroglycerine patch applied to the skin. One day, researchers want to use switches of this kind to trigger cell therapies for various metabolic diseases.

A new switch for the cell therapies of the future

In this episode, we explore how traditional Chinese medicine has inspired the development of innovative pulse sensor technology and discover how ancient wisdom and modern tech are coming together to revolutionize health monitoring and diagnostics.

Podcast: How Traditional Chinese Medicine Is Shaping Modern Wearables

This article was discussed in our <a href="https://www.wevolver.com/profile/the.next.byte" rel="noopener noreferrer">Next Byte podcast</a>.&nbsp;<iframe height="200px" width="100%" frameborder="no" scrolling="no" seamless="" src="https://player.simplecast.com/e790fa6b-0c91-48f4-a264-655a8b3aea07?dark=false" class="fr-draggable" data-lf-form-tracking-inspected-kn9eq4roawkarlvp="true" data-lf-yt-playback-inspected-kn9eq4roawkarlvp="true" data-lf-vimeo-playback-inspected-kn9eq4roawkarlvp="true"></iframe> The full article will continue below.<hr>Continuously monitoring a person’s pulse can provide meaningful medical information, such as heart rate and, indirectly, blood pressure. However, pulse waves can vary dramatically from person to person and even within the same person at different times of day and during different activities. These variations make it difficult for current wearable pulse sensors to accurately record useful data, which is especially problematic for those with cardiovascular disease or high-risk factors for those diseases.&nbsp;To solve this problem, a team led by Penn State researchers looked first not to the future, but back — to principles of pulse monitoring in traditional Chinese medicine, first described more than 3,000 years ago. Using these principles, the researchers designed a pressure-sensing platform to identify the optimal pulse signal, which they combined with a machine learning model to also predict blood pressure. &nbsp;They published their results in <a href="https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.202410312" target="_blank">Advanced Materials</a>. &nbsp;<img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNzM0NDgxOTQ4OTYzLTI0MDU2MC1wc24tbGFycnktY2hlbmcuanBnIiwiZWRpdHMiOnsicmVzaXplIjp7IndpZHRoIjo5NTAsImZpdCI6ImNvdmVyIn19fQ==" style="width: 100%px;" class="fr-fic fr-dib">“In traditional Chinese medicine, doctors would take the pulse at three positions on the wrist: cun, guan and chi,” said co-corresponding author <a href="https://www.esm.psu.edu/department/directory-detail-g.aspx?q=HUC24" target="_blank">Huanyu “Larry” Cheng</a>, the James L. Henderson, Jr. Memorial Associate Professor of Engineering Science and Mechanics at Penn State. “As they probed the wrist with three fingers at three locations, they would increase the pressure to measure the pulse from shallow to a bit deeper. This would give a more accurate reading of the pulse signals, regardless of if the person was having an active or sedentary day, for example.”&nbsp;Cheng said that they incorporated these two concepts, adaptive pressure and multiple locations on the wrist, into the design of a wearable health monitor. The researchers used 3D-printing to print a sensor array — one device with several sensors. This approach allows them to address the issue of data derived from a single point on the wrist and to better collect data from multiple places on the wrist and at several depths. &nbsp;“The sensor array is fully printed, both because that is less expensive than more traditional methods of assembling a sensor, and because then the sensor array is easier to manipulate, which makes it a better wearable device,” Cheng said, explaining that by fully printing the device, the researchers can rapidly prototype the individualized pressure sensor array. “The pressure sensor array also creates a 3D map of the pulse information across time.” &nbsp;The team then integrated the sensor array with a machine-learning model to accurately predict other health monitoring information, such as blood pressure, the researchers said.&nbsp;“With a machine learning algorithm, we can predict the blood pressure in terms of different values from systolic, diastolic and medium artery blood pressure, all from the 3D-pulse mapping,” said co-author Libo Gao, associate professor at Xiamen University.&nbsp;The researchers said they plan to continue developing their device, and its integration with machine learning, with the hope that the approach will help improve health care monitoring in the future.&nbsp;The other authors on the paper are Guirong Wu, Zengxing Zhang and Chenyang Xue, Xiamen University; Xikuan Zhang and Zekun Yang, the North University of China; Fei Lu and Xueli Nan, Shanxi University; and Xin Wang, of both Xiamen University and Shanxi University. &nbsp;This research was supported by the National Key Research and Development Program of China, the National Natural Science Foundation of China, the Science and Technology on Vacuum Technology and Physics Laboratory Fund, the Fundamental Research Funds for the Central Universities and the Xiaomi Young Talents Program/Xiaomi Foundation, Shenzhen Science and Technology Program.

A team led by Penn State researchers used principles of pulse monitoring in traditional Chinese medicine to design a pressure-sensing platform to identify the optimal pulse signal, which they combined with a machine learning model to also predict blood pressure.     Credit: Provided by Huanyu "Larry" Cheng. All Rights Reserved.

A team led by Penn State researchers looked first not to the future, but back — to principles of pulse monitoring in traditional Chinese medicine, first described more than 3,000 years ago.

Old wisdom meets new tech: Traditional Chinese medicine inspires pulse sensors

Two new kinds of on-skin electronics allow users to build and customize them directly on the body – with potential applications in biometric sensing, medical monitoring, interactive prosthetic makeup and more.<a href="https://www.hybridbody.human.cornell.edu/#/skinlink/">SkinLink</a>, developed by the&nbsp;<a href="https://www.hybridbody.human.cornell.edu/">Hybrid Body Lab</a> led by&nbsp;<a href="https://www.human.cornell.edu/people/hk932">Cindy Hsin-Liu Kao</a>, assistant professor of human centered design in the College of Human Ecology, is an on-skin electronic interface that can be fabricated right on the body, providing flexibility in design depending on the intended use. And&nbsp;<a href="https://www.hybridbody.human.cornell.edu/#/ecskin/">ECSkin</a> is an electrochromic display interface that also can be fabricated in situ, and features modular design through tiles that can be arranged as desired.Some of the potential applications for SkinLink include vital-sign and posture monitoring, proximity sensing and body art.“Both of these projects are modular prototyping toolkits, to enable much more intricate on-skin circuitry prototyping,” Kao said. “And users are able to build the circuitry directly on the skin surface.”Doctoral student and lab member Pin-Sung Ku is lead author of “<a href="https://dl.acm.org/doi/10.1145/3596241">SkinLink:&nbsp;On-body Construction and Prototyping of Reconfigurable Epidermal Interfaces</a>,” which was presented in early October at UbiComp/ISWC ’24, the Association for Computing Machinery’s international joint conference on pervasive and ubiquitous computing.The work earned a Distinguished Paper Award from the journal, Proceedings of the ACM on Interactive, Mobile, Wearable and Ubiquitous Technologies, where it was originally published in June 2023.<a href="https://dl.acm.org/doi/10.1145/3659613">ECSkin: Tessellating Electrochromic Films for Reconfigurable On-skin Displays</a>, which published May 15, 2024, in the same journal and for which Ku is also lead author, was also presented at the conference. Kao is senior author for both papers.SkinLink represents a step forward from&nbsp;<a href="https://news.cornell.edu/stories/2022/11/skinkit-offers-versatile-wearable-skin-computing">SkinKit, which the lab developed</a> and presented at UbiComp in 2021. The earlier iteration featured slim and flexible printed circuit boards in temporary tattoo form, but the boards had predefined behaviors and larger surface areas, making customizability a challenge.“There were several issues we didn’t address in SkinKit, such as how to allow users to program the modules the way they want to,” Ku said. “For SkinKit, everything was pre-programmed; users had to attach things in a certain order. With SkinLink, there is more customizability of the functions they like.”With SkinKit, for example, the circuitry had to be built before applying it to the body; with SkinLink, users can put one module on the body, then another, for more customizability.&nbsp;The SkinLink toolkit consists of functional circuit modules, made of flexible printed circuit boards, and flexible, custom-designed wiring (called trace modules, or traces) that connect the sensor and actuator modules to the microcontroller board.That’s a key difference from SkinKit: Smaller circuit boards are connect via flexible wiring, allowing for greater freedom of motion without sacrificing connectivity.&nbsp; “The circuit boards are somewhat rigid,” Ku said, “but we created the traces to be elastic, stretchable and flexible, so as not to hinder body movement.”The on-body fabrication process starts with selecting and programming the circuit board and trace modules. The microcontroller board can be repeatedly programmed during this step, to fine-tune the circuit functions. The boards can be temporarily placed on the body and customized, before final placement.The researchers conducted A/B testing of SkinLink, comparing its usability with SkinKit in a 14-person study, and found that SkinLink enables a more flexible wiring process than SkinKit, along with unrestricted circuit arrangement and superior wearability. Compared to the SkinKit, the SkinLink interface has a much smaller footprint, better stretchability, easier fabricating and more seamless wear.SkinKit, Kao said, offered a “low floor” – a term coined by computer scientist Ben Shneiderman, meaning that people with little or no experience can quickly get started designing and prototyping wearable tech. SkinLink takes it a couple of steps further, she said.“Another goal is what we call ‘high ceilings and wide walls,’” she said. “High ceilings means increasing the complexity of the prototypes; wide walls refers to the vast array of things that could be designed. That’s what I think SkinLink really does.”Kao said she sees both SkinLink and ECSkin as “enabling technologies,” with a variety of potential uses. Some of the studies with SkinLink involved artists, wearable tech researchers, and psychology researchers for physiology sensing; she also envisions applications beyond humans.&nbsp;“Being able to use this as a functional technology for physiological sensing or artistic practice is one application,” she said. “Our work has focused on skin interfaces for humans, but I think there could also be potential for designing ‘skin’ interfaces for other living beings, such as animals, and sensing for agricultural purposes, even on plants. We are interested in bringing SkinLink to broader disciplines to support on-skin prototyping.”

An ECSkin on-body display, composed of modular electrochromic films, is flexible and soft, and easily conforms to complex body parts such as the wrist. Hybrid Body Lab/Provided

Two new kinds of on-skin electronics allow users to build and customize them directly on the body – with potential applications in biometric sensing, medical monitoring, interactive prosthetic makeup and more.

On-body electronics can monitor health, support creative expression

To advance soft robotics, skin-integrated electronics and biomedical devices, researchers at Penn State have developed a 3D-printed material that is soft and stretchable — traits needed for matching the properties of tissues and organs — and that self-assembles. Their approach employs a process that eliminates many drawbacks of previous fabrication methods, such as less conductivity or device failure, the team said. &nbsp;They published their results in <a href="https://onlinelibrary.wiley.com/doi/10.1002/adma.202400082" target="_blank">Advanced Materials</a>. &nbsp;&nbsp;“People have been developing soft and stretchable conductors for almost a decade, but the conductivity is not usually very high,” said corresponding author Tao Zhou, Penn State assistant professor of engineering science and mechanics and of biomedical engineering in the College of Engineering and of materials science and engineering in the College of Earth and Mineral Sciences. “Researchers realized they could reach high conductivity with liquid metal-based conductors, but the significant limitation of that is that it requires a secondary method to activate the material before it can reach a high conductivity.”&nbsp;Liquid metal-based stretchable conductors suffer from inherent complexity and challenges posed by the post-fabrication activation process, the researchers said. The secondary activation methods include stretching, compressing, shear friction, mechanical sintering and laser activation, all of which can lead to challenges in fabrication and can cause the liquid metal to leak, resulting in device failure. &nbsp;&nbsp;“Our method does not require any secondary activation to make the material conductive,” said Zhou, who also has affiliations with the Huck Institutes of the Life Sciences and the Materials Research Institute. “The material can self-assemble to make its bottom surface be very conductive and its top surface self-insulated.”&nbsp;In the new method, the researchers combine liquid metal, a conductive polymer mixture called PEDOT:PSS and hydrophilic polyurethane that enables the liquid metal to transform into particles. When the composite soft material is printed and heated, the liquid metal particles on its bottom surface self-assemble into a conductive pathway. The particles in the top layer are exposed to an oxygen-rich environment and oxidize, forming an insulated top layer. The conductive layer is critical for conveying information to the sensor — such as muscle activity recordings and strain sensing on the body — while the insulated layer helps prevent signal leakage that could lead to less accurate data collection.&nbsp;<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1719495196118-240205-psnbody1-tao.jpg" style="width: 100%px;" class="fr-fic fr-dib">The new material, shown here, can self-assemble to make its bottom surface conductive and its top surface self-insulated. Credit: Marzia Momin. All Rights Reserved.“Our innovation here is a materials one,” Zhou said. “Normally, when liquid metal mixes with polymers, they are not conductive and require secondary activation to achieve conductivity. But these three components allow for the self-assembly that produces the high conductivity of soft and stretchable material without a secondary activation method.” &nbsp;The material can also be 3D-printed, Zhou said, making it easier to fabricate wearable devices. The researchers are continuing to explore potential applications, with a focus on assistive technology for people with disabilities.&nbsp;The papers other authors are Salahuddin Ahmed, Marzia Momin and Jiashu Ren, all doctoral students in the Penn State engineering science and mechanics department, and Hyunjin Lee, a doctoral student in the biomedical engineering department at Penn State. This work was supported by the National Taipei University of Technology-Penn State Collaborative Seed Grant Program and by the Department of Engineering Science and Mechanics, the Materials Research Institute and the Huck Institutes of the Life Sciences at Penn State.&nbsp;<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1719495222063-240205-psnbody2-tao.jpg" style="width: 100%px;" class="fr-fic fr-dib">The researchers 3D print the novel material.&nbsp;Credit: Marzia Momin. All Rights Reserved.

Penn State researchers developed a new soft and stretchable material that can be 3D-printed. The material can be used to fabricate wearable devices, such a sensor that can be worn on a finger, as shown here. Credit: Marzia Momin. All Rights Reserved.

To advance soft robotics, skin-integrated electronics and biomedical devices, researchers at Penn State have developed a 3D-printed material that is soft and stretchable — traits needed for matching the properties of tissues and organs — and that self-assembles.

Self-assembling, highly conductive sensors could improve wearable devices

In this episode, we discuss a novel sticker capable of monitoring the health of organs in real time allowing for more successful organ transplants and catching signs of diseases earlier than ever!

Podcast: Sticker to Monitor Your Internal Organs

In this episode, we discuss the shortcomings of previous attempts at making flexible wearable sensors and how researchers at CalTech have addressed them to create high performance stress sensor stickers.

Podcast: Stress Sensing Stickers

This article was discussed in our <a href="https://www.wevolver.com/profile/the.next.byte" rel="noopener noreferrer" target="_blank">Next Byte podcast</a>.&nbsp;<iframe height="200px" width="100%" frameborder="no" scrolling="no" seamless="" src="https://player.simplecast.com/1e9bb08c-384a-4d12-983e-8af2e63c741b?dark=false" class="fr-draggable" data-lf-form-tracking-inspected-kn9eq4roawkarlvp="true" data-lf-yt-playback-inspected-kn9eq4roawkarlvp="true" data-lf-vimeo-playback-inspected-kn9eq4roawkarlvp="true"></iframe> The full article will continue below.<hr>MIT engineers have developed a small ultrasound sticker that can monitor the stiffness of organs deep inside the body. The sticker, about the size of a postage stamp, can be worn on the skin and is designed to pick up on signs of disease, such as liver and kidney failure and the progression of solid tumors.<img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNzA3NzI0MzU5MjkzLU1JVC1TZWVpbmdTdGlmZm5lc3MtMDEtcHJlc3NfMC5qcGciLCJlZGl0cyI6eyJyZXNpemUiOnsid2lkdGgiOjk1MCwiZml0IjoiY292ZXIifX19" style="width: 766px;" class="fr-fic fr-dib">A small ultrasound sticker, worn on the skin, can monitor the stiffness of organs deep inside the body. The MIT-developed sensor could detect signs of disease such as liver and kidney failure, and the progression of solid tumors. Image: Courtesy of the researchersIn an <a href="https://science.org/doi/10.1126/sciadv.adk8426" target="_blank">open-access study appearing today</a> in Science Advances, the team reports that the sensor can send sound waves through the skin and into the body, where the waves reflect off internal organs and back out to the sticker. The pattern of the reflected waves can be read as a signature of organ rigidity, which the sticker can measure and track.“When some organs undergo disease, they can stiffen over time,” says the senior author of the paper, Xuanhe Zhao, professor of mechanical engineering at MIT. “With this wearable sticker, we can continuously monitor changes in rigidity over long periods of time, which is crucially important for early diagnosis of internal organ failure.”The team has demonstrated that the sticker can continuously monitor the stiffness of organs over 48 hours and detect subtle changes that could signal the progression of disease. In preliminary experiments, the researchers found that the sticky sensor can detect early signs of acute liver failure in rats.The engineers are working to adapt the design for use in humans. They envision that the sticker could be used in intensive care units (ICUs), where the low-profile sensors could continuously monitor patients who are recovering from organ transplants.“We imagine that, just after a liver or kidney transplant, we could adhere this sticker to a patient and observe how the rigidity of the organ changes over days,” lead author Hsiao-Chuan Liu says. “If there is any early diagnosis of acute liver failure, doctors can immediately take action instead of waiting until the condition becomes severe.” Liu was a visiting scientist at MIT at the time of the study and is currently an assistant professor at the University of Southern California.The study’s MIT co-authors include Xiaoyu Chen and Chonghe Wang, along with collaborators at USC.Sensing wobblesLike our muscles, the tissues and organs in our body stiffen as we age. With certain diseases, stiffening organs can become more pronounced, signaling a potentially precipitous health decline. Clinicians currently have ways to measure the stiffness of organs such as the kidneys and liver using ultrasound elastography — a technique similar to ultrasound imaging, in which a technician manipulates a handheld probe or wand over the skin. The probe sends sound waves through the body, which cause internal organs to vibrate slightly and send waves out in return. The probe senses an organ’s induced vibrations, and the pattern of the vibrations can be translated into how wobbly or stiff the organ must be.Ultrasound elastography is typically used in the ICU to monitor patients who have recently undergone an organ transplant. Technicians periodically check in on a patient shortly after surgery to quickly probe the new organ and look for signs of stiffening and potential acute failure or rejection.“After organ transplantation, the first 72 hours is most crucial in the ICU,” says another senior author, Qifa Zhou, a professor at USC. “With traditional ultrasound, you need to hold a probe to the body. But you can’t do this continuously over the long term. Doctors might miss a crucial moment and realize too late that the organ is failing.”The team realized that they might be able to provide a more continuous, wearable alternative. Their solution expands on an <a href="https://news.mit.edu/2022/ultrasound-stickers-0728" target="_blank">ultrasound sticker</a> they previously developed to image deep tissues and organs.“Our imaging sticker picked up on longitudinal waves, whereas this time we wanted to pick up shear waves, which will tell you the rigidity of the organ,” Zhao explains.Existing ultrasound elastrography probes measure shear waves, or an organ’s vibration in response to sonic impulses. The faster a shear wave travels in the organ, the stiffer the organ is interpreted to be. (Think of the bounce-back of a water balloon compared to a soccer ball.)The team looked to miniaturize ultrasound elastography to fit on a stamp-sized sticker. They also aimed to retain the same sensitivity of commercial hand-held probes, which typically incorporate about 128 piezoelectric transducers, each of which transforms an incoming electric field into outgoing sound waves.“We used advanced fabrication techniques to cut small transducers from high-quality piezoelectric materials that allowed us to design miniaturized ultrasound stickers,” Zhou says.The researchers precisely fabricated 128 miniature transducers that they incorporated onto a 25-millimeter-square chip. They lined the chip’s underside with an adhesive made from hydrogel — a sticky and stretchy material that is a mixture of water and polymer, which allows sound waves to travel into and out of the device almost without loss.In preliminary experiments, the team tested the stiffness-sensing sticker in rats. They found that the stickers were able to take continuous measurements of liver stiffness over 48 hours. From the sticker’s collected data, the researchers observed clear and early signs of acute liver failure, which they later confirmed with tissue samples.“Once liver goes into failure, the organ will increase in rigidity by multiple times,” Liu notes.“You can go from a healthy liver as wobbly as a soft-boiled egg, to a diseased liver that is more like a hard-boiled egg,” Zhao adds. “And this sticker can pick up on those differences deep inside the body and provide an alert when organ failure occurs.”The team is working with clinicians to adapt the sticker for use in patients recovering from organ transplants in the ICU. In that scenario, they don’t anticipate much change to the sticker’s current design, as it can be stuck to a patient’s skin, and any sound waves that it sends and receives can be delivered and collected by electronics that connect to the sticker, similar to electrodes and EKG machines in a doctor’s office.“The real beauty of this system is that since it is now wearable, it would allow low-weight, conformable, and sustained monitoring over time,” says Shrike Zhang,&nbsp;an associate professor of medicine at Harvard Medical School and associate bioengineer at Brigham and Women’s Hospital, who was not involved with the study. “This would likely not only allow patients to suffer less while achieving prolonged, almost real-time monitoring of their disease progression, but also free trained hospital personnel to other important tasks.”The researchers are also hoping to work the sticker into a more portable, self-enclosed version, where all its accompanying electronics and processing is miniaturized to fit into a slightly larger patch. Then, they envision that the sticker could be worn by patients at home, to continuously monitor conditions over longer periods, such as the progression of solid tumors, which are known to harden with severity.“We believe this is a life-saving technology platform,” Zhao says. “In the future, we think that people can adhere a few stickers to their body to measure many vital signals, and image and track the health of major organs in the body.”

“We used advanced fabrication techniques to cut small transducers from high-quality piezoelectric materials that allowed us to design miniaturized ultrasound stickers,” Xuanhe Zhao, professor of mechanical engineering at MIT, says. Image: Courtesy of the researchers

The sticky, wearable sensor could help identify early signs of acute liver failure.

This ultrasound sticker senses changing stiffness of deep internal organs

The adoption of healthcare monitoring devices that are both flexible and conform to the wearer have gained traction1. Spurred on by the need for remote care during the COVID-19 pandemic and technological advances in sensor accuracy, wearable health monitoring devices have become more ubiquitous in many areas of healthcare. In particular, there has been a rise in the development of wearable sensing and monitoring devices for telemedicine operations. Telemedicine has grown significantly in the last few years—and even more so during the COVID-19 pandemic when doctor-patient contact was limited—to remotely monitor patients in their own homes so hospitals could free up much-needed beds. While wearable technologies can be used in clinical environments to provide an analysis, much of their potential is in remote health monitoring.These wearable sensing devices typically make use of flexible materials, such as polymers, thin films, 2D materials and other nanomaterials. Health monitoring devices often consist of a flexible material that conforms to the wearer and is integrated with electronic components, including sensors, a power source—be it a battery, solar cell, or some other type of energy harvester like a nanogenerator—communication technologies if it transmits data to a central processing system, and any relevant circuitry.Building electronic components that are small and flexible enough to be used in wearable technologies is not that straightforward, and is why different nanomaterials—especially 2D materials—are often used to create the components because they fit the bill and can be easily integrated. But another approach is gathering interest: printing sensors—the most crucial aspects of a monitoring system—directly onto the wearable device.These printed sensors are sometimes made of 2D materials and other nanomaterials, but other materials can also be used as well. The ability to print sensors onto wearable health monitoring devices could pave a way to a much simpler and easier route to commercializing more wearable monitoring devices—especially if conventional, inexpensive, or easy-to-use printing technologies are used to print the sensor.<h2>Why Printed Sensors?</h2>While a range of advanced deposition and nanodeposition methods exist that can fabricate thin-film sensors on the substrate for wearable devices—often a soft polymer due to their flexibility and conformability—a number of biomedical sensors can be printed using screen printing techniques. Other techniques, such as inkjet and transfer printing, can be used as well, but screen printing is seen as the best option for printing sensors.Screen printing equipment is widely available, has a relatively low cost, and is easier to use than more advanced deposition methods, so it offers a much more scalable and commercially feasible route for using printed sensors in healthcare monitoring devices. Screen printing can also be used with many materials—from polymer solutions to conductive nanomaterial inks—so it is a versatile platform for printing a number of sensors.So, why print sensors instead of creating them through other manufacturing routes? Screen printing is a simple, fast, and efficient printing technique that can produce a large number of identical patterns in a single print. For large-scale operations and commercialization potential, screen printing can easily be adapted for mass production at a lower cost than other methods.From a performance perspective, screen printing provides high-resolution patterning and can print over large areas. The ability of screen printing to deposit material on demand in a given location also helps to reduce waste—especially on large scales—compared to traditional manufacturing methods because it is all done in a single step.There are, therefore, a number of manufacturing benefits with using printing methods. Beyond that, a greater design capability exists for health wearables because printing methods enable the production of sensors that are not only very thin but also provide the ability to print on the surface of the device. This approach is much simpler than trying to integrate devices into the material matrix of the wearable. You can also create a more customized sensor because you can print on demand, and the printing process can be changed to make a different sensor much easier than a typical manufacturing line.In terms of the materials compatible with screen printing, the scope is vast. Depending on the type of sensor being created, a whole host of materials can be used. On the one hand, a range of metals can be made into printable conductive inks to build the sensor. Common metals for wearable health sensors include gold, copper, platinum, nickel, aluminum, and silver. Beyond metals, a range of nanomaterial composites (graphene, carbon nanotubes composites), functional nanomaterial inks, and silver composites have all been used as the active sensing surface in printed health wearable sensors.The sensors also need a platform to be printed on. This often takes the form of a conductive polymer so that the sensor can better interact with the skin and the other components to provide higher sensitivity and reliability. PEDOT:PSS is the polymer platform that is most widely used for printed sensors, but other polymer materials include polyacetylene, polypyrrol, polyphenylene, poly (p-phenylene vinylene), and polythiophene polyaniline.<h2>The Printed Sensors of Interest in Healthcare Monitoring Applications</h2>Just as many materials can be used to create printed health sensors, many different types of printable sensors are used in health monitoring devices. Take, for example, strain-based sensors. Strain-based sensors measure a form of movement, and these wearable sensors are used in human-physiological signal monitoring and human-joint motion monitoring approaches.Another healthcare specialty measures different biomolecules and human signals. Non-strain-based sensors detect the biomolecule of interest directly or by directly measuring a physiological parameter that the patient exhibits. From a molecule-sensing perspective, a number of biomolecules in the blood can be detected, with glucose levels being a common one as well as the presence of sweat on a person’s skin. From a signal detection perspective, printed sensors can now detect respiration and heartbeat levels in a patient and provide remote electrocardiogram (ECG) monitoring.Another class of printed sensors for wearables is sensor arrays. In sensor arrays, multiple sensors work together to detect more complex issues or issues that require analysis from several stimuli angles. Sensor arrays are helpful in monitoring gait during walking, monitoring the sitting posture of wheelchair users, and monitoring the skin.Finally, there’s been advances in the development of printed temperature sensors for wearable health devices. Thermal sensing is a key area in disease detection because the body suffers thermal stresses when there is a disease present, and the rise in both skin and deep body temperature can be a primary indicator of a serious disease. Using printed temperature sensors, health wearables can detect a range of chronic diseases, such as cardiovascular, diabetic, and pulmonological diseases, as well as cancer.<h2>Conclusion</h2>Health monitoring wearables are gaining acceptance as an effective way to remotely measure many health factors of a patient. The most important aspect of these wearables is the sensing system that provides the analysis on the patient. For patients to be willing to wear the health monitoring device over an extended amount of time, the sensors and other components need to flex with the wearable component. While integrating flexible sensors is possible—for example, by using thin nanomaterials—printing sensors on the device’s surface is much easier, requires less material, and is much more scalable.A variety of printed health wearables are already in existence (commercially and academically. The printing methods discussed offer a route to achieve widespread distribution of health wearables. While many options are available, screen printing is the leading printing technology because it is highly versatile and can be used with many materials to create sensors that monitor different aspects of a person’s health—from heart rate to detecting a chance of a disease, to the different biomolecules in their blood, and many more in between.

The COVID-19 pandemic and advancements in sensor technology have led to the widespread adoption of wearable health monitoring devices, particularly for telemedicine, to facilitate remote patient monitoring.

Printable Sensors: A Key Technology for Health Wearables?

This article was discussed in our <a href="https://www.wevolver.com/profile/the.next.byte" rel="noopener noreferrer" target="_blank">Next Byte podcast</a>.&nbsp;<iframe height="200px" width="100%" frameborder="no" scrolling="no" seamless="" src="https://player.simplecast.com/437b67d4-99c8-455a-9ae6-e487b81825a1?dark=false" class="fr-draggable" data-lf-form-tracking-inspected-kn9eq4roawkarlvp="true" data-lf-yt-playback-inspected-kn9eq4roawkarlvp="true" data-lf-vimeo-playback-inspected-kn9eq4roawkarlvp="true"></iframe> The full article will continue below.<hr>In the latest of a series of innovative designs for wearable sensors that use sweat to identify and measure physiological conditions, Caltech's Wei Gao, assistant professor of medical engineering, has devised an "electronic skin" that continuously monitors nine different markers that characterize a stress response. Those wearing this electronic skin—a small, thin adhesive worn on the wrist, called CARES (consolidated artificial-intelligence-reinforced electronic skin)—are free to engage in all their normal daily activities with minimal interference during testing, which allows for the measurement of both baseline and acute levels of stress.<img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNzA2NTEyNDkyMDc2LUdhb19XZWktU3RyZXNzLVN3ZWF0LVNlbnNvci01LVdFQi53aWR0aC00NTAgKDEpLmpwZyIsImVkaXRzIjp7InJlc2l6ZSI6eyJ3aWR0aCI6OTUwLCJmaXQiOiJjb3ZlciJ9fX0=" style="width: 300px;" class="fr-fic fr-dib">Stress is a slippery concept. We talk about "feeling stressed" or a situation "being stressful," and we may attach stress to physical symptoms: "I have a stress headache" or "I'm grinding my teeth at night. It must be stress." The term stress can apply to all sorts of feelings, symptoms, behaviors, and experiences.Hans Selye, a physician and chemist born in Vienna in 1907, was the first to define stress as a medical condition. Struck by the similar complaints—such as tiredness, low appetite, and lack of motivation—that he heard from patients suffering from very different illnesses, Selye speculated that all of the patients were responding to what they had in common: being sick. He defined stress as a "nonspecific response of the body to any demand."Stress may be experienced positively as excitement or energy, or negatively as shock or anxiety. But however stress may be experienced emotionally, it is now widely agreed that depending on its severity and duration, both acute and chronic stress can damage our physical and mental health, and reduce our ability to function as we would like.Because stress is, as Selye described it, "nonspecific," there is no single biomarker available to tell us definitively whether or how much a person is stressed. However, stress generates a constellation of bodily reactions that, taken together, can provide a measure of stress independent of self-reports. Gao is monitoring this constellation with CARES.<img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNzA2NTEyNDI2MzM3LUdhb19XZWktU3RyZXNzLVN3ZWF0LVNlbnNvci00LVdFQl8zSW1tM1pKLndlYnAiLCJlZGl0cyI6eyJyZXNpemUiOnsid2lkdGgiOjk1MCwiZml0IjoiY292ZXIifX19" style="width: 766px;" class="fr-fic fr-dib">A sweat sensor worn on the wrist, lifted to show the thinness of the device. Credit: Wei Gao and Changhao Xu"When a person is under stress, hormones like epinephrine, norepinephrine, and cortisol are released into the bloodstream," explains Gao, who is also an investigator with the Heritage Medical Research Institute and a Ronald and JoAnne Willens Scholar. "Sweat becomes rich with metabolites like glucose, lactate, and uric acid, and electrolytes like sodium, potassium, and ammonium. These are substances we have measured before using <a href="https://www.caltech.edu/about/news/new-wearable-sensor-detects-even-more-compounds-in-human-sweat" target="_blank">microfluidic sampling on a wearable sweat sensor</a>. What is new in CARES is that sweat sensors are integrated with sensors that record pulse waveforms, skin temperature, and galvanic skin response: physiological signals that also indicate stress in predictable ways."New materials further boost the performance of CARES. Though previously used materials for sweat sensors could be produced efficiently via inkjet printing and were capable of accurate measurement of even very scarce compounds, the materials gradually broke down in the presence of bodily fluids. The introduction of a nickel-based compound helps to stabilize the enzymatic-based sensors, such as those that detect lactate or glucose, as does a new polymer added to the ion-based sensors, which detect biomarkers like sodium or potassium. "Adding these new materials greatly enhances the sensor stability during long-term operation," Gao reports. Like previous sweat sensors, CARES can be battery powered and can wirelessly communicate with a phone or computer via Bluetooth.Another important innovation with CARES is the addition of machine learning. Because stress comes in many different forms and stimulates a complex response affecting many different bodily systems, interpreting a wealth of data accurately is key to the usefulness of CARES and other sensors. Experiments inducing stress in subjects wearing the CARES device demonstrated that the sensor accurately measures the interrelatedness of physiological (such as pulse) and chemical (such as glucose) biomarkers. Subjects also answered questionnaires to self-report their feelings of anxiety and psychological stress before and after exposure to stressful situations like vigorous exercise or intense video gameplay. Data showed clear correlations between self-reports of stress and its physicochemical correlates as measured by CARES."High levels of stress and anxiety caused by demanding work environments, such as those experienced by soldiers or astronauts, can significantly affect performance," Gao notes. "Early detection of the severity of stress allows for timely intervention. Our wearable sensor, combined with machine learning, has the potential to provide real-time stress-level insights."The paper describing the CARES device, titled "A physicochemical sensing electronic skin for stress response monitoring," appears in the January 19 issue of Nature Electronics. Co-authors are Changhao Xu (MS '20), Yu Song, Juliane R. Sempionatto, Samuel R. Solomon (MS '23), You Yu, Roland Yingjie Tay, Jiahong Li, Wenzheng Heng (MS '23), Jihong Min (MS '19), and Alison Lao of Caltech; Hnin Y. Y. Nyein of Hong Kong University of Science and Technology; and Tzung K. Hsiai and Jennifer A. Sumner of UCLA.

In the latest of a series of innovative designs for wearable sensors that use sweat to identify and measure physiological conditions, Caltech's Wei Gao has devised an "electronic skin" that continuously monitors nine different markers that characterize a stress response.

Measuring Stress

In this episode, we discuss the accidental discovery of how amputees can sense temperature in their phantom limbs and how EPFL researchers have exploited this to develop the first generation of prosthetics that can feel.

Podcast: Amputees Feel Warmth In Their Missing Hand

 Innovations such as biomimicry, software inspired by insect brains, smart skin, neuromorphic computing, and other emerging technologies further expand robots' capabilities and push the boundaries of robotics hardware.

The 2023 Manufacturing Robotics Report: Hardware

If you&rsquo;ve ever tried giftwrapping an odd-shaped present like a teddy bear, you can appreciate the challenge that surgeons face when grafting artificial skin onto an injured body part. Like wrapping paper, engineered skin comes in flat pieces, which can be difficult and time-consuming to stitch together around an irregularly shaped body part.Bioengineers at Columbia University appear to have solved this problem by devising a way to grow engineered skin in complex, three-dimensional shapes, making it possible to construct, for example, a seamless &ldquo;glove&rdquo; of skin cells that can be easily slipped onto a severely burned hand.The researchers reported their findings in a paper published Jan. 27 in&nbsp;<a data-extlink="" href="https://www.science.org/doi/10.1126/sciadv.ade2514" rel="noopener noreferrer" target="_blank">Science Advances(link is external and opens in a new window)</a>.&ldquo;Three-dimensional skin constructs that can be transplanted as &lsquo;biological clothing&rsquo; would have many advantages,&rdquo; says lead developer&nbsp;<a href="https://www.dermatology.columbia.edu/profile/hasan-e-abaci-phd" target="_blank">Hasan Erbil Abaci, PhD</a>, assistant professor of dermatology at Columbia University Vagelos College of Physicians and Surgeons. &ldquo;They would dramatically minimize the need for suturing, reduce the length of surgeries, and improve aesthetic outcomes.&rdquo;The current study also revealed that the continuous 3D grafts have better mechanical and functional properties than conventional, pieced-together grafts.<h2>3D scaffolding</h2>The process of creating the new skin grafts begins with a 3D laser scan of the target structure, such as a human hand. Next, a hollow, permeable model of the hand is crafted using computer-aided design and 3D printing. The exterior of the model is then seeded with skin fibroblasts, which generate the skin&rsquo;s connective tissue, and collagen (a structural protein). Finally, the outside of the mold is coated with a mixture of keratinocytes (cells that comprise most of the outer skin layer, or epidermis) and the inside is perfused with growth media, which support and nourish the developing graft.Except for the 3D scaffold, the researchers employed the same procedures used to make flat engineered skin and the entire process took the same time, about three weeks.In a first test of the 3D engineered skin, constructs composed of human skin cells were successfully grafted onto the hind limbs of mice. &ldquo;It was like putting a pair of shorts on the mice,&rdquo; Abaci says, &ldquo;The entire surgery took about 10 minutes.&rdquo; Four weeks later, the grafts had completely integrated with the surrounding mouse skin, and the mice reacquired full functions of the limb.Mouse skin heals differently than human skin, so the researchers next plan to test the grafts on larger animals with skin biology that more closely matches that of humans. Clinical trials on humans are likely years away.<h2>Redesigning engineered skin</h2>The 3D grafts are the first major re-design of engineered skin grafts since they were first introduced in the early 1980s. &ldquo;Engineered skin started with only two cell types, but human skin has around 50 types of cells. Most research had focused on mimicking the cellular components of human skin,&rdquo; Abaci says. &ldquo;As a bioengineer, it&rsquo;s always bothered me that the skin&rsquo;s geometry was overlooked and grafts have been made with open boundaries, or edges. We know from bioengineering other organs that geometry is an important factor that affects function.&rdquo;Abaci and his team realized they could make more lifelike grafts when 3D printers became available and could create three-dimensional scaffolds necessary for making the engineered skin.&ldquo;We hypothesized that a 3D fully enclosed shape would more closely mimic our natural skin and be stronger mechanically, and that&rsquo;s what we found,&rdquo; Abaci says. &ldquo;Simply remaining faithful to the continuous geometry of human skin significantly improves the composition, structure, and strength of the graft.&rdquo;In the future, Abaci envisions grafts could be custom-made from a patient&rsquo;s own cells. With only a 4X4 mm skin sample, enough cells can be cultured and multiplied to create enough skin to cover a human hand.&ldquo;Another compelling use would be face transplants, where our wearable skin would be integrated with underlying tissues like cartilage, muscle, and bone, offering patients a personalized alternative to cadaver transplants,&rdquo; Abaci says.<hr>The study is titled &ldquo;<a href="https://epicure.cumc.columbia.edu/content/about-epicure-center" target="_blank">Engineering Edgeless Human Skin with Enhanced Biomechanical Properties</a>.&rdquo;The other contributors (all at Columbia University): Alberto Pappalardo, David Alvarez Cespedes, Shuyang Fang, Abigail R. Herschman, Eun Young Jeon, Kristin M. Myers, and Jeffrey W. Kysar.

Creating a "glove" of engineered skin begins with a 3D-printed scaffold and ends three weeks later with a construct ready for grafting. Images: Alberto Pappalardo and Hasan Erbil Abaci / Columbia University Vagelos College of Physicians and Surgeons.

Columbia University devising a way to grow engineered skin in complex, three-dimensional shapes, making it possible to construct, for example, a seamless “glove” of skin cells that can be easily slipped onto a severely burned hand.

Bioengineered Skin Grafts that Fit Like a Glove

In general, silicone based conductive pastes are rare and the versions with AgCl fillers- needed for many medical wearable applications- are even rarer! <a data-attribute-index="0" data-entity-hovercard-id="urn:li:fs_miniProfile:ACoAACBPPG0BiuMqPPP9xTDFydt590kiUA2t-Us" data-entity-type="MINI_PROFILE" href="https://www.linkedin.com/in/ACoAACBPPG0BiuMqPPP9xTDFydt590kiUA2t-Us" id="isPasted" target="_blank">David Dewey</a> from <a data-attribute-index="2" data-entity-hovercard-id="urn:li:fs_miniCompany:27073286" data-entity-type="MINI_COMPANY" href="https://www.linkedin.com/company/fujikura-kasei-co-ltd/" target="_blank">FUJIKURA KASEI Co Ltd</a> unveiled this paste for the first time in June at <a data-attribute-index="4" data-entity-hovercard-id="urn:li:fs_miniCompany:71510477" data-entity-type="MINI_COMPANY" href="https://www.linkedin.com/company/techblick/" target="_blank">TechBlick</a>. The pastes can offer 1-10 E-4 ohm/sqr when cured at 150C for 30min or so on substrates such as PET or silicone sheet.&nbsp;These inks are compatible with other silicone-based (insulator, adhesive, etc) out of Fujikura&#39;s portfolio, enabling one to print complex multi-layer medical wearable devices on stretchable substrates like silicone!The short video below offers further information<iframe src="https://player.vimeo.com/video/739956599" frameborder="0" allowfullscreen="" class="fr-draggable" data-lf-yt-playback-inspected-kn9eq4roawkarlvp="true" style="width: 774px; height: 476px;"></iframe>

In general, silicone based conductive pastes are rare and the versions with AgCl fillers- needed for many medical wearable applications- are even rarer! 

Stretchable silicone-based medical devices with AgCl fillers?

This article was first published on <a href="https://news.mit.edu/2022/sensor-electronic-chipless-0818" id="isPasted" rel="noopener noreferrer" target="_blank">MIT News</a>. &nbsp;<hr>Wearable sensors are ubiquitous thanks to wireless technology that enables a person&rsquo;s glucose concentrations, blood pressure, heart rate, and activity levels to be transmitted seamlessly from sensor to smartphone for further analysis.Most wireless sensors today communicate via embedded Bluetooth chips that are themselves powered by small batteries. But these conventional chips and power sources will likely be too bulky for next-generation sensors, which are taking on smaller, thinner, more flexible forms.Now MIT engineers have devised a new kind of wearable sensor that communicates wirelessly without requiring onboard chips or batteries. Their design, detailed today in the journal&nbsp;Science, opens a path toward chip-free wireless sensors.The team&rsquo;s sensor design is a form of electronic skin, or &ldquo;e-skin&rdquo; &mdash; a flexible, semiconducting film that conforms to the skin like electronic Scotch tape. The heart of the sensor is an ultrathin, high-quality film of gallium nitride, a material that is known for its piezoelectric properties, meaning that it can both produce an electrical signal in response to mechanical strain and mechanically vibrate in response to an electrical impulse.The researchers found they could harness gallium nitride&rsquo;s two-way piezoelectric properties and use the material simultaneously for both sensing and wireless communication.In their new study, the team produced pure, single-crystalline samples of gallium nitride, which they paired with a conducting layer of gold to boost any incoming or outgoing electrical signal. They showed that the device was sensitive enough to vibrate in response to a person&rsquo;s heartbeat, as well as the salt in their sweat, and that the material&rsquo;s vibrations generated an electrical signal that could be read by a nearby receiver. In this way, the device was able to wirelessly transmit sensing information, without the need for a chip or battery.&ldquo;Chips require a lot of power, but our device could make a system very light without having any chips that are power-hungry,&rdquo; says the study&rsquo;s corresponding author, Jeehwan Kim, an associate professor of mechanical engineering and of materials science and engineering, and a principal investigator in the Research Laboratory of Electronics. &ldquo;You could put it on your body like a bandage, and paired with a wireless reader on your cellphone, you could wirelessly monitor your pulse, sweat, and other biological signals.&rdquo;Kim&rsquo;s co-authors include first author and former MIT postdoc Yeongin Kim, who is now an assistant professor at the University of Cincinnati; co-corresponding author Jiyeon Han of the Korean cosmetics company AMOREPACIFIC, which helped motivate the current work; members of the Kim Research Group at MIT; and other collaborators at the University of Virginia, Washington University in St. Louis, and multiple institutions across South Korea.<h2>Pure resonance</h2>Jeehwan Kim&rsquo;s group previously developed a technique, called&nbsp;<a href="https://news.mit.edu/2018/study-flexible-electronics-made-exotic-materials-1008" target="_blank">remote epitaxy</a>, that they have employed to quickly grow and peel away ultrathin, high-quality semiconductors from wafers coated with graphene. Using this technique, they have fabricated and explored various flexible, multifunctional electronic films.In their new study, the engineers used the same technique to peel away ultrathin single-crystalline films of gallium nitride, which in its pure, defect-free form is a highly sensitive piezoelectric material.The team looked to use a pure film of gallium nitride as both a sensor and a wireless communicator of surface acoustic waves, which are essentially vibrations across the films. The patterns of these waves can indicate a person&rsquo;s heart rate, or even more subtly, the presence of certain compounds on the skin, such as salt in sweat.The researchers hypothesized that a gallium nitride-based sensor, adhered to the skin, would have its own inherent, &ldquo;resonant&rdquo; vibration or frequency that the piezoelectric material would simultaneously convert into an electrical signal, the frequency of which a wireless receiver could register. Any change to the skin&rsquo;s conditions, such as from an accelerated heart rate, would affect the sensor&rsquo;s mechanical vibrations, and the electrical signal that it automatically transmits to the recever.&nbsp;&ldquo;If there is any change in the pulse, or chemicals in sweat, or even ultraviolet exposure to skin, all of this activity can change the pattern of surface acoustic waves on the gallium nitride film,&rdquo; notes Yeongin Kim. &ldquo;And the sensitivity of our film is so high that it can detect these changes.&rdquo;<h2>Wave transmission</h2>To test their idea, the researchers produced a thin film of pure, high-quality gallium nitride and paired it with a layer of gold to boost the electrical signal. They deposited the gold in the pattern of repeating dumbbells &mdash; a lattice-like configuration that imparted some flexibility to the normally rigid metal. The gallium nitride and gold, which they consider to be a sample of electronic skin, measures just 250 nanometers thick &mdash; about 100 times thinner than the width of a human hair.They placed the new e-skin on volunteers&rsquo; wrists and necks, and used a simple antenna, held nearby, to wirelessly register the device&rsquo;s frequency without physically contacting the sensor itself. The device was able to sense and wirelessly transmit changes in the surface acoustic waves of the gallium nitride on volunteers&rsquo; skin related to their heart rate.The team also paired the device with a thin ion-sensing membrane &mdash; a material that selectively attracts a target ion, and in this case, sodium. With this enhancement, the device could sense and wireless transmit changing sodium levels as a volunteer held onto a heat pad and began to sweat.The researchers see their results as a first step toward chip-free wireless sensors, and they envision that the current device could be paired with other selective membranes to monitor other vital biomarkers.&ldquo;We showed sodium sensing, but if you change the sensing membrane, you could detect any target biomarker, such as glucose, or cortisol related to stress levels,&rdquo; says co-author and MIT postdoc Jun Min Suh. &ldquo;It&rsquo;s quite a versatile platform.&rdquo;<hr>&quot;Reprinted with permission of&nbsp;<a href="https://news.mit.edu/2022/sensor-electronic-chipless-0818" id="isPasted" rel="noopener noreferrer" target="_blank">MIT News</a>&quot;&nbsp;

The device senses and wirelessly transmits signals without bulky chips or batteries. Courtesy of the researchers

artificial skin sensors

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