Breathable’ Electronics Pave the Way for More Functional Wearable Tech

This sleeve incorporates the new electronic material, allowing it to function as a video game controller.

Engineering researchers have created ultrathin, stretchable electronic material that is gas permeable, allowing the material to “breathe.” The material was designed specifically for use in biomedical or wearable technologies, since the gas permeability allows sweat and volatile organic compounds to evaporate away from the skin, making it more comfortable for users – especially for long-term wear.

“The gas permeability is the big advance over earlier stretchable electronics,” says Yong Zhu, co-corresponding author of a paper on the work and a professor of mechanical and aerospace engineering at North Carolina State University. “But the method we used for creating the material is also important because it’s a simple process that would be easy to scale up.”

Specifically, the researchers used a technique called the breath figure method to create a stretchable polymer film featuring an even distribution of holes. The film is coated by dipping it in a solution that contains silver nanowires. The researchers then heat-press the material to seal the nanowires in place.

“The resulting film shows an excellent combination of electric conductivity, optical transmittance and water-vapor permeability,” Zhu says. “And because the silver nanowires are embedded just below the surface of the polymer, the material also exhibits excellent stability in the presence of sweat and after long-term wear.”

“The end result is extremely thin – only a few micrometers thick,” says Shanshan Yao, co-author of the paper and a former postdoctoral researcher at NC State who is now on faculty at Stony Brook University. “This allows for better contact with the skin, giving the electronics a better signal-to-noise ratio.

“And gas permeability of wearable electronics is important for more than just comfort,” Yao says. “If a wearable device is not gas permeable, it can also cause skin irritation.”

To demonstrate the material’s potential for use in wearable electronics, the researchers developed and tested prototypes for two representative applications.

The first prototype consisted of skin-mountable, dry electrodes for use as electrophysiologic sensors. These have multiple potential applications, such as measuring electrocardiography (ECG) and electromyography (EMG) signals.

“These sensors were able to record signals with excellent quality, on par with commercially available electrodes,” Zhu says.

The second prototype demonstrated textile-integrated touch sensing for human-machine interfaces. The authors used a wearable textile sleeve integrated with the porous electrodes to play computer games such as Tetris. Related video can be seen at https://youtu.be/7AO_cq8A_BE.

“If we want to develop wearable sensors or user interfaces that can be worn for a significant period of time, we need gas-permeable electronic materials,” Zhu says. “So this is a significant step forward.”

The paper, “Gas-Permeable, Ultrathin, Stretchable Epidermal Electronics with Porous Electrodes,” is published in the journal ACS Nano. First author of the paper is Weixin Zhou, a Ph.D. student at Nanjing University of Posts and Telecommunications (NUPT) who worked on the project while a visiting scholar at NC State.

The paper was co-authored by Hongyu Wang, a Ph.D. student at NC State, and by Qingchuan Du of NUPT. Co-corresponding author of the paper is Yanwen Ma, a professor at NUPT.

The work was done with support from the National Science Foundation, under grant number CMMI-1728370.

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Note to Editors: The study abstract follows.

“Gas-Permeable, Ultrathin, Stretchable Epidermal Electronics with Porous Electrodes”

Authors: Weixin Zhou, Qingchuan Du and Yanwen Ma, Nanjing University of Posts and Telecommunications; Shanshan Yao, North Carolina State University and Stony Brook University; and Hongyu Wang and Yong Zhu, North Carolina State University

Published: April 29, ACS Nano

DOI: 10.1021/acsnano.0c00906

Abstract: We present gas-permeable, ultrathin, and stretchable electrodes enabled by self-assembled porous substrates and conductive nanostructures. Efficient and scalable breath figure method is employed to introduce the porous skeleton and then silver nanowires (AgNWs) are dip-coated and heat-pressed to offer electric conductivity.

The resulting film has a transmittance of 61%, sheet resistance of 7.3 Ω/sq, and water vapor permeability of 23 mg cm^-2 h^-1. With AgNWs embedded below the surface of the polymer, the electrode exhibits excellent stability with the presence of sweat and after long-term wear.

We demonstrate the promising potential of the electrode for wearable electronics in two representative applications – skin-mountable biopotential sensing for healthcare and textile-integrated touch sensing for human-machine interfaces.

The electrode can form conformal contact with human skin, leading to low skin-electrode impedance and high quality biopotential signals. In addition, the textile electrode can be used in a self-capacitance wireless touch sensing system.

An Ultra-Thin – Wearable Health Monitor made possible by a ‘Graphene Ink Tattoo’ designed and developed at the University of Texas at Austin

University of Texas at Austin. This is the world’s thinnest wearable Health Monitor, designed and developed by the researchers at the University of Texas at Austin, in the form of a “Graphene-Ink Tattoo”.

Most health monitors in use today are bulky and tend to restrict patients movements. This graphene tattoo will eliminate these restrictions. It picks up electric signal given off by the body and transmits it to a smartphone app.

Watch the Video:

Abstract: Tattoo-like epidermal sensors are an emerging class of truly wearable electronics, owing to their thinness and softness. While most of them are based on thin metal films, a silicon membrane, or nanoparticle-based printable inks, we report sub-micrometer thick, multimodal electronic tattoo sensors that are made of graphene.

The graphene electronic tattoo (GET) is designed as filamentary serpentines and fabricated by a cost- and time-effective “wet transfer, dry patterning” method. It has a total thickness of 463 ± 30 nm, an optical transparency of ∼85%, and a stretchability of more than 40%.

The GET can be directly laminated on human skin just like a temporary tattoo and can fully conform to the microscopic morphology of the surface of skin viajust van der Waals forces. The open-mesh structure of the GET makes it breathable and its stiffness negligible. A bare GET is able to stay attached to skin for several hours without fracture or delamination.

With liquid bandage coverage, a GET may stay functional on the skin for up to several days. As a dry electrode, GET–skin interface impedance is on par with medically used silver/silver-chloride (Ag/AgCl) gel electrodes, while offering superior comfort, mobility, and reliability. GET has been successfully applied to measure electrocardiogram (ECG), electromyogram (EMG), electroencephalogram (EEG), skin temperature, and skin hydration.

Read More Here

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Scientists Create Customizable, Fabric-Like Power Source for Wearable Electronics

Scientists at Nanyang Technological University, Singapore (NTU Singapore) have created a customizable, fabric-like power source that can be cut, folded or stretched without losing its function.

Led by Professor Chen Xiaodong, Associate Chair (Faculty) at the School of Materials Science & Engineering, the team reported in the journal Advanced Materials (print edition 8 January) how they have created the wearable power source, a supercapacitor, which works like a fast-charging battery and can be recharged many times.

Crucially, they have made their supercapacitor customizable or “editable”, meaning its structure and shape can be changed after it is manufactured, while retaining its function as a power source. Existing stretchable supercapacitors are made into predetermined designs and structures, but the new invention can be stretched multi-directionally, and is less likely to be mismatched when it is joined up to other electrical components.

The new supercapacitor, when edited into a honeycomb-like structure, has the ability to store an electrical charge four times higher than most existing stretchable supercapacitors. In addition, when stretched to four times its original length, it maintains nearly 98 per cent of the initial ability to store electrical energy, even after 10,000 stretch-and-release cycles.

Experiments done by Prof Chen and his team also showed that when the editable supercapacitor was paired with a sensor and placed on the human elbow, it performed better than existing stretchable supercapacitors. The editable supercapacitor was able to provide a stable stream of signals even when the arm was swinging, which are then transmitted wirelessly to external devices, such as one that captures a patient’s heart rate.

The authors believe that the editable supercapacitor could be easily mass-produced as it would rely on existing manufacturing technologies. Production cost will thus be low, estimated at about SGD$0.13 (USD$0.10) to produce 1 cm2 of the material.

The team has filed a patent for the technology.

Professor Chen said, “A reliable and editable supercapacitor is important for development of the wearable electronics industry. It also opens up all sorts of possibilities in the realm of the ‘Internet-of-Things’ when wearable electronics can reliably power themselves and connect and communicate with appliances in the home and other environments.

“My own dream is to one day combine our flexible supercapacitors with wearable sensors for health and sports performance diagnostics. With the ability for wearable electronics to power themselves, you could imagine the day when we create a device that could be used to monitor a marathon runner during a race with great sensitivity, detecting signals from both under and over-exertion.”

The editable supercapacitor is made of strengthened manganese dioxide nanowire composite material. While manganese dioxide is a common material for supercapacitors, the ultralong nanowire structure, strengthened with a network of carbon nanotubes and nanocellulose fibres, allows the electrodes to withstand the associated strains during the customisation process.

The NTU team also collaborated with Dr. Loh Xian Jun, Senior Scientist and Head of the Soft Materials Department at the Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR).

Dr. Loh said, “Customisable and versatile, these interconnected, fabric-like power sources are able to offer a plug-and-play functionality while maintaining good performance. Being highly stretchable, these flexible power sources are promising next-generation ‘fabric’ energy storage devices that could be integrated into wearable electronics.”

Flexible Batteries Power the Future of Wearable Technology: U of Manchester

Credit: University of Manchester

The rapid development of wearable technology has received another boost from a new development using graphene for printed electronic devices.

New research from The University of Manchester has demonstrated flexible battery-like devices printed directly on to textiles using a simple screen-printing technique.

The current hurdle with wearable technology is how to power devices without the need for cumbersome battery packs. Devices known as supercapacitors are one way to achieve this. A supercapacitor acts similarly to a battery but allows for rapid charging which can fully charge devices in seconds.

Now a solid-state flexible supercapacitor device has been demonstrated by using conductive graphene-oxide ink to print onto cotton fabric. As reported in the journal 2-D Materials the printed electrodes exhibited excellent mechanical stability due to the strong interaction between the ink and textile substrate. 

Further development of graphene-oxide printed supercapacitors could turn the vast potential of wearable technology into the norm. High-performance sportswear that monitors performance, embedded health-monitoring devices, lightweight military gear, new classes of mobile communication devices and even wearable computers are just some of the applications that could become available following further research and development.

To power these new wearable devices, the energy storage system must have reasonable mechanical flexibility in addition to high energy and power density, good operational safety, long cycling life and be low cost.

 Credit: University of Manchester

Dr Nazmul Karim, Knowledge Exchange Fellow, the National Graphene Institute and co-author of the paper said: “The development of graphene-based flexible textile supercapacitor using a simple and scalable printing technique is a significant step towards realising multifunctional next generation wearable e-textiles.”

“It will open up possibilities of making an environmental friendly and cost-effective smart e-textile that can store energy and monitor human activity and physiological condition at the same time”.

Graphene-oxide is a form of graphene which can be produced relatively cheaply in an ink-like solution. This solution can be applied to textiles to create supercapacitors which become part of the fabric itself.

Dr Amor Abdelkader, also co-author of the paper said: “Textiles are some of the most flexible substrates, and for the first time, we printed a stable device that can store energy and be as flexible as cotton.

“The device is also washable, which makes it practically possible to use it for the future smart clothes. We believe this work will open the door for printing other types of devices on textile using 2-D-materials inks.”

The University of Manchester is currently completing the construction of its second major graphene facility to complement the National Graphene Institute (NGI). Set to be completed 2018, the £60m Graphene Engineering Innovation Centre (GEIC) will be an international research and technology facility.

The GEIC will offer the UK the unique opportunity to establish a leading role in graphene and related two-dimensional materials. The GEIC will be primarily industry-led and focus on pilot production and characterisation.

 Explore further: Researchers develop simple way to fabricate micro-supercapacitors with high energy density

Provided by: University of Manchester

 

 

Long-Term Health Monitoring Possible through Breathable, Wearable Electronics on Our Skin

The diagram at top illustrates the structure of gold nanomesh conductors laminated onto the skin surface. The nanomesh, constructed from polyvinyl alcohol (PVA) nanofibers and a gold (Au) layer, adheres to the skin when sprayed with water, …more

A hypoallergenic electronic sensor can be worn on the skin continuously for a week without discomfort, and is so light and thin that users forget they even have it on, says a Japanese group of scientists. The elastic electrode constructed of breathable nanoscale meshes holds promise for the development of noninvasive e-skin devices that can monitor a person’s health continuously over a long period.

Wearable electronics that monitor heart rate and other vital health signals have made headway in recent years, with next-generation gadgets employing lightweight, highly elastic materials attached directly onto the skin for more sensitive, precise measurements. However, although the ultrathin films and rubber sheets used in these devices adhere and conform well to the skin, their lack of breathability is deemed unsafe for long-term use: dermatological tests show the fine, stretchable materials prevent sweating and block airflow around the skin, causing irritation and inflammation, which ultimately could lead to lasting physiological and psychological effects.

“We learned that devices that can be worn for a week or longer for continuous monitoring were needed for practical use in medical and sports applications,” says Professor Takao Someya at the University of Tokyo’s Graduate School of Engineering whose research group had previously developed an on-skin patch that measured oxygen in blood.

In the current research, the group developed an electrode constructed from nanoscale meshes containing a water-soluble polymer, polyvinyl alcohol (PVA), and a gold layer—materials considered safe and biologically compatible with the body. The device can be applied by spraying a tiny amount of water, which dissolves the PVA nanofibers and allows it to stick easily to the skin—it conformed seamlessly to curvilinear surfaces of human skin, such as sweat pores and the ridges of an index finger’s fingerprint pattern.

An array of nanomesh conductors attached to a fingertip, top, and a scanning electron microscope (SEM) image of a nanomesh conductor on a skin replica, bottom. Credit: 2017 Someya Laboratory.

The researchers next conducted a skin patch test on 20 subjects and detected no inflammation on the participants’ skin after they had worn the device for a week. The group also evaluated the permeability, with water vapor, of the nanomesh conductor—along with those of other substrates like ultrathin plastic foil and a thin rubber sheet—and found that its porous mesh structure exhibited superior gas permeability compared to that of the other materials.

Furthermore, the scientists proved the device’s mechanical durability through repeated bending and stretching, exceeding 10,000 times, of a conductor attached on the forefinger; they also established its reliability as an electrode for electromyogram recordings when its readings of the electrical activity of muscles were comparable to those obtained through conventional gel electrodes.

The electric current from a flexible battery placed near the knuckle flows through the conductor and powers the LED just below the fingernail. Credit: 2017 Someya Laboratory.

“It will become possible to monitor patients’ vital signs without causing any stress or discomfort,” says Someya about the future implications of the team’s research. In addition to nursing care and medical applications, the new device promises to enable continuous, precise monitoring of athletes’ physiological signals and bodily motion without impeding their training or performance.

 Explore further: Novel e-skin may monitor health, vital signs

More information: Akihito Miyamoto et al, Inflammation-free, gas-permeable, lightweight, stretchable on-skin electronics with nanomeshes, Nature Nanotechnology (2017). DOI: 10.1038/nnano.2017.125

Journal reference: Nature Nanotechnology  

Provided by: University of Tokyo

 

Breakthrough in thin electrically conducting sheets paves way for smaller electronic devices

Through nanotechnology, physicists Dr Raymond McQuaid, Dr Amit Kumar and Professor Marty Gregg from Queen’s University’s School of Mathematics and Physics, have created unique 2-D sheets, called domain walls, which exist within crystalline materials.

The sheets are almost as thin as the wonder-material graphene, at just a few atomic layers. However, they can do something that graphene can’t – they can appear, disappear or move around within the crystal, without permanently altering the crystal itself.

This means that in future, even smaller electronic devices could be created, as electronic circuits could constantly reconfigure themselves to perform a number of tasks, rather than just having a sole function.
Professor Marty Gregg explains: “Almost all aspects of modern life such as communication, healthcare, finance and entertainment rely on microelectronic devices. 

The demand for more powerful, smaller technology keeps growing, meaning that the tiniest devices are now composed of just a few atoms – a tiny fraction of the width of human hair.”

Breakthrough in thin electrically conducting sheets paves way for smaller electronic devices Credit: Queen’s University Belfast

“As things currently stand, it will become impossible to make these devices any smaller – we will simply run out of space. This is a huge problem for the computing industry and new, radical, disruptive technologies are needed. One solution is to make electronic circuits more ‘flexible’ so that they can exist at one moment for one purpose, but can be completely reconfigured the next moment for another purpose.”

The team’s findings, which have been published in Nature Communications, pave the way for a completely new way of data processing.

Professor Gregg says: “Our research suggests the possibility to “etch-a-sketch” nanoscale electrical connections, where patterns of electrically conducting wires can be drawn and then wiped away again as often as required.

“In this way, complete electronic circuits could be created and then dynamically reconfigured when needed to carry out a different role, overturning the paradigm that electronic circuits need be fixed components of hardware, typically designed with a dedicated purpose in mind.”

Breakthrough in thin electrically conducting sheets paves way for smaller electronic devices Credit: Queen’s University Belfast

There are two key hurdles to overcome when creating these 2-D sheets, long straight walls need to be created. These need to effectively conduct electricity and mimic the behavior of real metallic wires. It is also essential to be able to choose exactly where and when the domain walls appear and to reposition or delete them.

 Through the research, the Queen’s researchers have discovered some solutions to the hurdles. Their research proves that long conducting sheets can be created by squeezing the crystal at precisely the location they are required, using a targeted acupuncture-like approach with a sharp needle. The sheets can then be moved around within the crystal using applied electric fields to position them.

Dr Raymond McQuaid, a recently appointed lecturer in the School of Mathematics and Physics at Queen’s University, added: “Our team has demonstrated for the first time that copper-chlorine boracite crystals can have straight conducting walls that are hundreds of microns in length and yet only nanometres thick. 

The key is that, when a needle is pressed into the crystal surface, a jigsaw puzzle-like pattern of structural variants, called “domains”, develops around the contact point. The different pieces of the pattern fit together in a unique way with the result that the conducting walls are found along certain boundaries where they meet.

“We have also shown that these walls can then be moved using applied electric fields, therefore suggesting compatibility with more conventional voltage operated devices. Taken together, these two results are a promising sign for the potential use of conducting walls in reconfigurable nano-electronics.”

 

More information: Raymond G.P. McQuaid et al. Injection and controlled motion of conducting domain walls in improper ferroelectric Cu-Cl boracite, Nature Communications (2017). DOI: 10.1038/ncomms15105

Provided by: Queen’s University Belfast

A New “Skin-Like” triboelectric Nanogenerator for Multifunction Power Sources and Wearable Electronics

A transparent electronic skin for tactile sensing. Credit: Xiong Pu

A team of researchers with the National Center for Nanoscience and Technology in China has developed what it is calling a skin-like triboelectric nanogenerator (STENG). In their paper published in the journal Science Advances, the group describes the nanogenerator they built and offer suggestions for its use.

 

Prior research led to the construction of TENG devices that generate electricity by pressing materials together and taking them apart, creating an electrostatic charge. In this new effort, the researchers put an S in front of the name of their TENG device to highlight its similarity to human skin.

To make the new device, the group mixed an elastomer with an ionic hydrogel to create a material that is both flexible and nearly transparent. Unlike other TENG devices, the elastomer can be used as the layer that is electrified while the hydrogel can work as the electrode. This allowed for much better stretching abilities—the team reports a 1000 percent improvement over other TENGs.

The researchers report that the material is also nearly clear, allowing 96.2 percent of light to pass through it—this, they suggest, makes it useful for devices that require transmission of optical data. The nanogenerator was able to continue functioning properly in temperatures up to 30° C, and with humidity as high as 30 percent. Testing showed that the material was capable of producing up to 145 volts and had a power density of 35 milliwatts per square meter when configured as an open circuit. The team notes also that all of the materials used to make the device are inexpensive, light and readily available

 

More information: Ultrastretchable, transparent triboelectric nanogenerator as electronic skin for biomechanical energy harvesting and tactile sensing, Science Advances  31 May 2017: Vol. 3, no. 5, e1700015, DOI: 10.1126/sciadv.1700015

Abstract
Rapid advancements in stretchable and multifunctional electronics impose the challenge on corresponding power devices that they should have comparable stretchability and functionality. We report a soft skin-like triboelectric nanogenerator (STENG) that enables both biomechanical energy harvesting and tactile sensing by hybridizing elastomer and ionic hydrogel as the electrification layer and electrode, respectively.

A circular soft and transparent triboelectric nanogenerator. Credit: Xiong Pu

For the first time, ultrahigh stretchability (uniaxial strain, 1160%) and transparency (average transmittance, 96.2% for visible light) are achieved simultaneously for an energy-harvesting device. The soft TENG is capable of outputting alternative electricity with an instantaneous peak power density of 35 mW m−2 and driving wearable electronics (for example, an electronic watch) with energy converted from human motions, whereas the STENG is pressure-sensitive, enabling its application as artificial electronic skin for touch/pressure perception.

Our work provides new opportunities for multifunctional power sources and potential applications in soft/wearable electronics.

Journal reference: Science Advances

 

UC San Diego: Printed, flexible and rechargeable battery can power Wearable Sensors, Solar Cells, Electronics

Stretchable printed batteries

 

Nanoengineers at the University of California San Diego have developed the first printed battery that is flexible, stretchable and rechargeable. The zinc batteries could be used to power everything from wearable sensors to solar cells and other kinds of electronics.

The work appears in the April 19, 2017 issue of Advanced Energy Materials.

The researchers made the printed batteries flexible and stretchable by incorporating a hyper-elastic polymer material made from isoprene, one of the main ingredients in rubber, and polystyrene, a resin-like component. The substance, known as SIS, allows the batteries to stretch to twice their size, in any direction, without suffering damage.

The ink used to print the batteries is made of zinc silver oxide mixed with SIS. While zinc batteries have been in use for a long time, they are typically non-rechargeable. The researchers added bismuth oxide to the batteries to make them rechargeable.

“This is a significant step toward self-powered stretchable electronics,” said Joseph Wang, one of the paper’s senior authors and a nanoengineering professor at the Jacobs School of Engineering at UC San Diego, where he directs the school’s Center for Wearable Sensors. “We expect this technology to pave the way to enhance other forms of energy storage and printable, stretchable electronics, not just for zinc-based batteries but also for Lithium-ion batteries, as well as supercapacitors and photovoltaic cells.”

The prototype battery the researchers developed has about 1/5 the capacity of a rechargeable hearing aid battery. But it is 1/10 as thick, cheaper and uses commercially available materials. It takes two of these batteries to power a 3 Volt LED. The researchers are still working to improve the battery’s performance. Next steps include expanding the use of the technology to different applications, such as solar and fuel cells; and using the battery to power different kinds of electronic devices.

Researchers used standard screen printing techniques to make the batteries–a method that dramatically drives down the costs of the technology. Typical materials for one battery cost only $0.50. A comparable commercially available rechargeable battery costs $5.00 Batteries can be printed directly on fabric or on materials that allow wearables to adhere to the skin. They also can be printed as a strip, to power a device that needs more energy. They are stable and can be worn for a long period of time.

Making the batteries rechargeable

The key ingredient that makes the batteries rechargeable is a molecule called bismuth oxide which, when mixed into the batteries’ zinc electrodes, prolongs the life of devices and allows them to recharge. Adding bismuth oxide to zinc batteries is standard practice in industry to improve performance, but until recently, there hasn’t been a thorough scientific explanation for why.

Last year, UC San Diego nanoengineers led by Professor Y. Shirley Meng published a detailed molecular study addressing this question (download PDF here). When zinc batteries discharge, their electrodes react with the liquid electrolyte inside the battery, producing zinc salts that dissolve into a solution. This eventually short circuits the battery. Adding bismuth oxide keeps the electrode from losing zinc to the electrolyte. This ensures that the batteries continue to work and can be recharged.

The work shows that it is possible to use small amounts of additives, such as bismuth oxide, to change the properties of materials. “Understanding the scientific mechanism to do this will allow us to turn non-rechargeable batteries into rechargeable batteries—not just zinc batteries but also for other electro-chemistries, such as Lithium-oxygen,” said Meng, who directs the Sustainable Power and Energy Center at the UC San Diego Jacobs School of Engineering

From Innovation to Market

Rajan Kumar, a co-first author on this Advanced Energy Materials paper, is a nanoengineering Ph.D. student at the Jacobs School of Engineering. He and nanoengineering professor Wang are leading a team focused on commercializing aspects of this work. The team is one of five to be selected to join a new technology accelerator at UC San Diego. The technology accelerator is run by the UC San Diego Institute for the Global Entrepreneur, which is a collaboration between the Jacobs School of Engineering and Rady School of Management.

Kumar is excited at the prospect of taking advantage of all that the IGE Technology Accelerator has to offer.

“For us, it’s strategically perfect,” said Kumar, referring to the $50,000 funding for prototype improvements, the focus on prototype testing with a strategic partner, and the entrepreneurship mentoring.

Kumar is confident in the team’s innovations, which includes the ability to replace coin batteries with thin, stretchable batteries. Making the right strategic moves now is critical for commercialization success.

“It’s now about making sure our energies are focused in the right direction,” said Kumar.

In addition to the IGE Technology Accelerator, the team was also recently selected to participate in the NSF Innovation-Corps (I-Corps) program at UC San Diego, also administered by the Institute for the Global Entrepreneur. One of the key tenets of the I-Corps program is helping startup teams validate their target markets and business models early in the commercialization process. Through NSF I-Corps, for example, Kumar has already started interviewing potential customers which has helped the team better focus their commercialization strategy.

Through these programs, Kumar is focused on leading the team through a series of milestones in order to best position their innovations to refine “both what to build and who to build it for,” he said.

Paper Citation

“All-Printed, Stretchable Zn-Ag₂O Rechargeable Battery via Hyperelastic Binder for Self-Powering Wearable Electronics” in the journal Advanced Energy Materials.http://onlinelibrary.wiley.com/doi/10.1002/aenm.201602096/full

Authors: Rajan Kumar, Jaewook Shin, Lu Yin, Jung-Min You, Prof. Shirley Meng and Prof. Joseph Wang, Department of Nanoengineering, Jacobs School of Engineering, University of California San Diego.

Joseph Wang is a distinguished professor, holds the SAIC endowed chair, and serves as chair of the Department of NanoEngineering at the UC San Diego Jacobs School of Engineering where he directs the Center for Wearable Sensors.

Shirley Meng is a professor in the Department of NanoEngineering and Director of the Sustainable Power and Energy Center at the UC San Diego Jacobs School of Engineering.

Research funders include: Advanced Research Projects Agency-Energy (DE-AR0000535); Rajan Kumar acknowledges the U.S. National Science Foundation (NSF) Graduate Research Fellowship under Grant No (DGE-1144086).

This work was performed in part at the San Diego Nanotechnology Infrastructure (SDNI), a member of the National Nanotechnology Coordinated Infrastructure, which is supported by the U.S. National Science Foundation (NSF).

Gold foil discovery could lead to wearable technology – Flexibility is the Key

An example of a gold foil peeled from single crystal silicon. Credit: Reprinted with permission from Naveen Mahenderkar et al., Science [355]:[1203] (2017).

Some day, your smartphone might completely conform to your wrist, and when it does, it might be covered in pure gold, thanks to researchers at Missouri University of Science and Technology.

Writing in the March 17 issue of the journal Science, the Missouri S&T researchers say they have developed a way to “grow” thin layers of gold on single crystal wafers of silicon, remove the gold foils, and use them as substrates on which to grow other electronic materials.

The research team’s discovery could revolutionize wearable or “flexible” technology research, greatly improving the versatility of such electronics in the future.

According to lead researcher Dr. Jay A. Switzer, the majority of research into wearable technology has been done using polymer substrates, or substrates made up of multiple crystals. “And then they put some typically organic semiconductor on there that ends up being flexible, but you lose the order that (silicon) has,” says Switzer, Donald L. Castleman/FCR Endowed Professor of Discovery in Chemistry at S&T.

Because the polymer substrates are made up of multiple crystals, they have what are called grain boundaries, says Switzer. These grain boundaries can greatly limit the performance of an electronic device.

“Say you’re making a solar cell or an LED,” he says. “In a semiconductor, you have electrons and you have holes, which are the opposite of electrons. They can combine at grain boundaries and give off heat. And then you end up losing the light that you get out of an LED, or the current or voltage that you might get out of a solar cell.”

Most electronics on the market are made of silicon because it’s “relatively cheap, but also highly ordered,” Switzer says.

“99.99 percent of electronics are made out of silicon, and there’s a reason – it works great,” he says. “It’s a single crystal, and the atoms are perfectly aligned. But, when you have a single crystal like that, typically, it’s not flexible.”

By starting with single crystal silicon and growing gold foils on it, Switzer is able to keep the high order of silicon on the foil. But because the foil is gold, it’s also highly durable and flexible.

“We bent it 4,000 times, and basically the resistance didn’t change,” he says.

The gold foils are also essentially transparent because they are so thin. According to Switzer, his team has peeled foils as thin as seven nanometers.

Switzer says the challenge his research team faced was not in growing gold on the single crystal silicon, but getting it to peel off as such a thin layer of foil. Gold typically bonds very well to silicon.

“So we came up with this trick where we could photo-electrochemically oxidize the silicon,” Switzer says. “And the gold just slides off.”

Photoelectrochemical oxidation is the process by which light enables a semiconductor material, in this case silicon, to promote a catalytic oxidation reaction.

Switzer says thousands of gold foils—or foils of any number of other metals—can be made from a single crystal wafer of silicon.

The research team’s discovery can be considered a “happy accident.” Switzer says they were looking for a cheap way to make single crystals when they discovered this process.

“This is something that I think a lot of people who are interested in working with highly ordered materials like single crystals would appreciate making really easily,” he says. “Besides making flexible devices, it’s just going to open up a field for anybody who wants to work with single crystals.”

Explore further: ‘Nanospears’ could lead to better solar cells, lasers, lighting

More information: Naveen K. Mahenderkar et al. Epitaxial lift-off of electrodeposited single-crystal gold foils for flexible electronics, Science (2017). DOI: 10.1126/science.aam5830

Journal reference: Science

Provided by: Missouri University of Science and Technology

Read more at: https://phys.org/news/2017-03-gold-foil-discovery-wearable-technology.html#jCp

Read more at: https://phys.org/news/2017-03-gold-foil-discovery-wearable-technology.html#jCp

Environmentally-friendly graphene textiles could enable wearable electronics

Credit: Jiesheng Ren

A new method for producing conductive cotton fabrics using graphene-based inks opens up new possibilities for flexible and wearable electronics, without the use of expensive and toxic processing steps.

Wearable, textiles-based electronics present new possibilities for flexible circuits, healthcare and environment monitoring, energy conversion, and many others. Now, researchers at the Cambridge Graphene Centre (CGC) at the University of Cambridge, working in collaboration with scientists at Jiangnan University, China, have devised a method for depositing graphene-based inks onto cotton to produce a conductive textile. The work, published in the journal Carbon, demonstrates a wearable motion sensor based on the conductive cotton.

Cotton fabric is among the most widespread for use in clothing and textiles, as it is breathable and comfortable to wear, as well as being durable to washing. These properties also make it an excellent choice for textile electronics. A new process, developed by Dr Felice Torrisi at the CGC, and his collaborators, is a low-cost, sustainable and environmentally-friendly method for making conductive cotton textiles by impregnating them with a graphene-based conductive ink.

Based on Dr Torrisi’s work on the formulation of printable graphene inks for flexible electronics, the team created inks of chemically modified graphene flakes that are more adhesive to cotton fibres than unmodified graphene. Heat treatment after depositing the ink on the fabric improves the conductivity of the modified graphene. The adhesion of the modified graphene to the cotton fibre is similar to the way cotton holds coloured dyes, and allows the fabric to remain conductive after several washes.

Although numerous researchers around the world have developed wearable sensors, most of the current wearable technologies rely on rigid electronic components mounted on flexible materials such as plastic films or textiles. These offer limited compatibility with the skin in many circumstances, are damaged when washed and are uncomfortable to wear because they are not breathable. 

“Other conductive inks are made from precious metals such as silver, which makes them very expensive to produce and not sustainable, whereas graphene is both cheap, environmentally-friendly, and chemically compatible with cotton,” explains Dr Torrisi.

 

Co-author Professor Chaoxia Wang of Jiangnan University adds: “This method will allow us to put electronic systems directly into clothes. It’s an incredible enabling technology for smart textiles.”

The work done by Dr Torrisi and Prof Wang, together with students Tian Carey and Jiesheng Ren, opens a number of commercial opportunities for graphene-based inks, ranging from personal health technology, high-performance sportswear, military garments, wearable technology/computing and fashion.

Electron microscopy image of a conductive graphene/cotton fabric. Credit: Jiesheng Ren

 

“Turning cotton fibres into functional electronic components can open to an entirely new set of applications from healthcare and wellbeing to the Internet of Things,” says Dr Torrisi “Thanks to nanotechnology, in the future our clothes could incorporate these textile-based electronics and become interactive.”

Graphene is carbon in the form of single-atom-thick membranes, and is highly conductive. The group’s work is based on the dispersion of tiny graphene sheets, each less than one nanometre thick, in a water-based dispersion. The individual graphene sheets in suspension are chemically modified to adhere well to the cotton fibres during printing and deposition on the fabric, leading to a thin and uniform conducting network of many graphene sheets. This network of nanometre flakes is the secret to the high sensitivity to strain induced by motion. A simple graphene-coated smart cotton textile used as a wearable strain sensor has been shown to reliably detect up to 500 motion cycles, even after more than 10 washing cycles in normal washing machine.

The use of graphene and other related 2D materials (GRMs) inks to create electronic components and devices integrated into fabrics and innovative textiles is at the centre of new technical advances in the smart textiles industry. Dr Torrisi and colleagues at the CGC are also involved in the Graphene Flagship, an EC-funded, pan-European project dedicated to bringing graphene and GRM technologies to commercial applications.

Graphene and GRMs are changing the science and technology landscape with attractive physical properties for electronics, photonics, sensing, catalysis and energy storage. Graphene’s atomic thickness and excellent electrical and mechanical properties give excellent advantages, allowing deposition of extremely thin, flexible and conductive films on surfaces and – with this new method – also on textiles. This combined with the environmental compatibility of graphene and its strong adhesion to cotton make the graphene-cotton strain sensor ideal for wearable applications.

The research was supported by grants from the European Research Council’s Synergy Grant, the International Research Fellowship of the National Natural Science Foundation of China and the Ministry of Science and Technology of China. The technology is being commercialised by Cambridge Enterprise, the University’s commercialisation arm.

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More information: Jiesheng Ren et al. Environmentally-friendly conductive cotton fabric as flexible strain sensor based on hot press reduced graphene oxide, Carbon (2017). DOI: 10.1016/j.carbon.2016.10.045

Journal reference: Carbon

Provided by: University of Cambridge