Written By Kevin Kerfoot / Reviewed By Ray Spotts
Electronic skin - known as e-skin - is a thin, translucent material that can mimic the function and mechanical properties of human skin. A number of different types and sizes of wearable e-skins are now being developed in labs around the world as researchers recognize their value in diverse medical, scientific and engineering fields.
Researchers at Binghamton University, State University of New York, have developed skin-inspired electronics to conform to the skin, allowing for long-term, high-performance, real-time wound monitoring in users. Conventional biosensor technology, while a great advancement in the medical field, still has limitations to overcome and improvements to be made to enhance their functionality.
Researchers at Binghamton University’s Intimately Bio-Integrated Biosensors lab have developed a skin-inspired, open-mesh electromechanical sensor that is capable of monitoring lactate and oxygen on the skin.
“We eventually hope that these sensors and engineering accomplishments can help advance healthcare applications and provide a better quantitative understanding in disease progression, wound care, general health, fitness monitoring and more,” says Matthew Brown, a Ph.D. student at Binghamton University.
“We are focused on developing next-generation platforms that can integrate with biological tissue - skin, neural and cardiac tissue. This topic was interesting to us because we were very interested in real-time, on-site evaluation of wound healing progress in a near future. Both lactate and oxygen are critical biomarkers to access wound-healing progression.”
The researchers designed a sensor that is structured similarly to that of the skin’s micro architecture. The paper, “Skin-inspired, Open Mesh Electrochemical Sensors for Lactate and Oxygen Monitoring,” was published in Biosensors and Bioelectronics.
This wearable sensor is equipped with gold sensor cables capable of exhibiting similar mechanics to that of skin elasticity. The researchers hope to create a new mode of sensor that will meld seamlessly with the wearer’s body to maximize body analysis to help understand chemical and physiological information.
They hope that future research will use this skin-inspired sensor design to incorporate more biomarkers and create even more multifunctional sensors to help with wound healing. They also hope to see these sensors incorporated into internal organs to gain an increased understanding about the diseases that affect these organs and the human body.
Self-Healable Electronic Skin
University of Colorado Boulder researchers have developed a new type of malleable, self-healing and fully recyclable "electronic skin" that has applications ranging from robotics and prosthetic development to better biomedical devices.
The new CU Boulder e-skin has sensors embedded to measure pressure, temperature, humidity and air flow, says Assistant Professor Jianliang Xiao, who lead the research effort with CU Boulder chemistry and biochemistry Associate Professor Wei Zhang. The results were published in the journal Science Advances.
This electronic skin has several distinctive properties to provide better mechanical strength, chemical stability and electrical conductivity. "What is unique here is that the chemical bonding of polyimine we use allows the e-skin to be both self-healing and fully recyclable at room temperature," Xiao said.
"Given the millions of tons of electronic waste generated worldwide every year, the recyclability of our e-skin makes good economic and environmental sense.”
Another benefit of the e-skin is that it can be easily conformed to curved surfaces like human arms and robotic hands by applying moderate heat and pressure to it without introducing excessive stresses. "Let's say you wanted a robot to take care of a baby," Zhang added.
"In that case you would integrate e-skin on the robot fingers that can feel the pressure of the baby. The idea is to try and mimic biological skin with e-skin that has desired functions. To recycle the skin, the device is soaked into recycling solution, making the polymers degrade into oligomers - polymers with polymerization degree usually below 10 - and monomers - small molecules that can be joined together into polymers - that are soluble in ethanol.
The silver nanoparticles sink to the bottom of the solution. The recycled solution and nanoparticles can then be used to make new, functional e-skin."
An Elastic Skin Sensor For Home Healthcare Applications?
Another new ultrathin, elastic display that fits snugly on the skin can show the moving waveform of an electrocardiogram recorded by a breathable, on-skin electrode sensor. Combined with a wireless communication module, this integrated biomedical sensor system - called "skin electronics" - can transmit biometric data to the cloud.
With advances in semiconductor technology, wearable devices can now monitor health by first measuring vital signs or taking an electrocardiogram, and then transmitting the data wirelessly to a smartphone. The readings or electrocardiogram waveforms can be displayed on the screen in real time, or sent to either the cloud or a memory device where the information is stored.
The newly-developed skin electronics system aims to go a step further by enhancing information accessibility for people such as the elderly or the infirm, who tend to have difficulty operating and obtaining data from existing devices and interfaces.
It promises to help ease the strain on home healthcare systems in aging societies through continuous, non-invasive health monitoring and self-care at home. The integrated system combines a flexible, deformable display with a lightweight sensor composed of a breathable nanomesh electrode and wireless communication module.
The skin display is stretchable by as much as 45 percent of its original length. Led by Professor Takao Someya - and developed by a collaboration between researchers at the University of Tokyo's Graduate School of Engineering and Dai Nippon Printing – the skin display consists of an array of micro LEDs and stretchable wiring mounted on a rubber sheet.
"Our skin display exhibits simple graphics with motion," says Someya. "Because it is made from thin and soft materials, it can be deformed freely."
Improving Quality Of Life
The skin display is far more resistant to the wear and tear of stretching than previous wearable displays. It is built on a structure that minimizes the stress resulting from stretching on the juncture of hard materials, such as the micro LEDs, and soft materials, like the elastic wiring, a leading cause of damage for other models. It is the first stretchable display to achieve superior durability and stability in air.
The nanomesh skin sensor can be worn on the skin continuously for a week without causing any inflammation. Although this sensor was capable of measuring temperature, pressure and myoelectricity - the electrical properties of muscle - it successfully recorded an electrocardiogram for the first time in the latest research.
The researchers applied tried-and-true methods used in the mass production of electronics, specifically, screen printing the silver wiring and mounting the micro LEDs on the rubber sheet with a chip mounter and solder paste commonly used in manufacturing printed circuit boards. Applying these methods will likely accelerate the commercialization of the display and help keep down future production costs.
DNP is looking to bring the integrated skin display to market within the next few years by improving the reliability of the stretchable devices through optimizing its structure, enhancing the production process for high integration, and overcoming technical challenges such as large-area coverage.
"The current aging society requires user-friendly wearable sensors for monitoring patient vitals in order to reduce the burden on patients and family members providing nursing care," Someya added. "Our system could serve as one of the long-awaited solutions to fulfill this need, which will ultimately lead to improving the quality of life for many."
Flexible Skin Helping Prosthetics For Robots
Engineers from the University of Washington and UCLA have developed a flexible sensor "skin" that can be stretched over any part of a robot's body or prosthetic to accurately convey information about shear forces and vibration that are critical to successfully grasping and manipulating objects.
The research team from the UW College of Engineering and the UCLA Henry Samueli School of Engineering and Applied Science has demonstrated that the physically robust and chemically resistant sensor skin has a high level of precision and sensitivity for light touch applications - opening a door, interacting with a phone, shaking hands, picking up packages, handling objects, among others.
The bio-inspired robot sensor skin, described in Sensors and Actuators A: Physical, mimics the way a human finger experiences tension and compression as it slides along a surface or distinguishes among different textures. It measures this information with similar precision and sensitivity as human skin, and could vastly improve the ability of robots to perform everything from surgical and industrial procedures to cleaning a kitchen.
"Robotic and prosthetic hands are really based on visual cues right now such as, 'Can I see my hand wrapped around this object?' or 'Is it touching this wire?' But that's obviously incomplete information," says senior author Jonathan Posner, a UW professor of mechanical engineering and of chemical engineering.
"If a robot is going to dismantle an improvised explosive device, it needs to know whether its hand is sliding along a wire or pulling on it. To hold on to a medical instrument, it needs to know if the object is slipping. This all requires the ability to sense shear force, which no other sensor skin has been able to do well."
Some robots today use fully instrumented fingers, but that sense of "touch" is limited to that appendage and you can't change its shape or size to accommodate different tasks. The other approach is to wrap a robot appendage in a sensor skin, which provides better design flexibility.
But such skins have not yet provided a full range of tactile information. "Traditionally, tactile sensor designs have focused on sensing individual modalities: normal forces, shear forces or vibration exclusively,” added co-author and robotics collaborator Veronica Santos, a UCLA associate professor of mechanical and aerospace engineering.
“However, dexterous manipulation is a dynamic process that requires a multimodal approach. The fact that our latest skin prototype incorporates all three modalities creates many new possibilities for machine learning-based approaches for advancing robot capabilities."
An Important Breakthrough
The new stretchable electronic skin, which was manufactured at the UW's Washington Nanofabrication Facility, is made from the same silicone rubber used in swimming goggles. The rubber is embedded with tiny serpentine channels roughly half the width of a human hair that are filled with electrically conductive liquid metal that won't crack or fatigue when the skin is stretched, as solid wires would do.
When the skin is placed around a robot finger or end effector, these microfluidic channels are strategically placed on either side of where a human fingernail would be.
As you slide your finger across a surface, one side of your nailbed bulges out while the other side becomes taut under tension. The same thing happens with the robot or prosthetic finger. The microfluidic channels on one side of the nailbed compress while the ones on the other side stretch out.
When the channel geometry changes, so does the amount of electricity that can flow through them. The research team can measure these differences in electrical resistance and correlate them with the shear forces and vibrations that the robot finger is experiencing.
"It's really following the cues of human biology," says lead author Jianzhu Yin. "Our electronic skin bulges to one side just like the human finger does and the sensors that measure the shear forces are physically located where the nailbed would be, which results in a sensor that performs with similar performance to human fingers."
Placing the sensors away from the part of the finger that's most likely to make contact makes it easier to distinguish shear forces from the normal "push" forces that also occur when interacting with an object, which has been difficult to do with other sensor skin solutions.
Recent experiments have shown that the skin can detect tiny vibrations at 800 times per second, better than human fingers. "By mimicking human physiology in a flexible electronic skin, we have achieved a level of sensitivity and precision that's consistent with human hands, which is an important breakthrough," Posner added. "The sense of touch is critical for both prosthetic and robotic applications, and that's what we're ultimately creating."
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With over 30 years of writing and editing experience for newspapers, magazines and corporate communications, Kevin Kerfoot writes about natural health, nutrition, skincare and oral hygiene for Trusted Health Products’ natural health blog and newsletters.
Founder Ray Spotts has a passion for all things natural and has made a life study of nature as it relates to health and well-being. Ray became a forerunner bringing products to market that are extraordinarily effective and free from potentially harmful chemicals and additives. For this reason Ray formed Trusted Health Products, a company you can trust for clean, effective, and healthy products. Ray is an organic gardener, likes fishing, hiking, and teaching and mentoring people to start new businesses. You can get his book for free, “How To Succeed In Business Based On God’s Word,” at www.rayspotts.com.