Tag Archives: Huanyu Cheng

Printing wearable circuits onto skin

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It seems that this new technique for creating wearable electronics will be more like getting a permanent tattoo where the circuits are applied directly to your skin as opposed to being like a temporary tattoo where the circuits are printed onto a substrate and then applied to then, worn on your skin.

Caption: On-body sensors, such as electrodes and temperature sensors, were directly printed and sintered on the skin surface. Credit: Adapted from ACS Applied Materials & Interfaces 2020, DOI: 10.1021/acsami.0c11479

An Oct. 14, 2020 American Chemical Society (ACS) news release (also on EurekAlert) announced this latest development in wearable electronics,

Wearable electronics are getting smaller, more comfortable and increasingly capable of interfacing with the human body. To achieve a truly seamless integration, electronics could someday be printed directly on people’s skin. As a step toward this goal, researchers reporting in ACS Applied Materials & Interfaces have safely placed wearable circuits directly onto the surface of human skin to monitor health indicators, such as temperature, blood oxygen, heart rate and blood pressure.

The latest generation of wearable electronics for health monitoring combines soft on-body sensors with flexible printed circuit boards (FPCBs) for signal readout and wireless transmission to health care workers. However, before the sensor is attached to the body, it must be printed or lithographed onto a carrier material, which can involve sophisticated fabrication approaches. To simplify the process and improve the performance of the devices, Peng He, Weiwei Zhao, Huanyu Cheng and colleagues wanted to develop a room-temperature method to sinter metal nanoparticles onto paper or fabric for FPCBs and directly onto human skin for on-body sensors. Sintering — the process of fusing metal or other particles together — usually requires heat, which wouldn’t be suitable for attaching circuits directly to skin.

The researchers designed an electronic health monitoring system that consisted of sensor circuits printed directly on the back of a human hand, as well as a paper-based FPCB attached to the inside of a shirt sleeve. To make the FPCB part of the system, the researchers coated a piece of paper with a novel sintering aid and used an inkjet printer with silver nanoparticle ink to print circuits onto the coating. As solvent evaporated from the ink, the silver nanoparticles sintered at room temperature to form circuits. A commercially available chip was added to wirelessly transmit the data, and the resulting FPCB was attached to a volunteer’s sleeve. The team used the same process to sinter circuits on the volunteer’s hand, except printing was done with a polymer stamp. As a proof of concept, the researchers made a full electronic health monitoring system that sensed temperature, humidity, blood oxygen, heart rate, blood pressure and electrophysiological signals and analyzed its performance. The signals obtained by these sensors were comparable to or better than those measured by conventional commercial devices. 

Here’s a link to and a citation for the paper,

Wearable Circuits Sintered at Room Temperature Directly on the Skin Surface for Health Monitoring by Ling Zhang, Hongjun Ji, Houbing Huang, Ning Yi, Xiaoming Shi, Senpei Xie, Yaoyin Li, Ziheng Ye, Pengdong Feng, Tiesong Lin, Xiangli Liu, Xuesong Leng, Mingyu Li, Jiaheng Zhang, Xing Ma, Peng He, Weiwei Zhao, and Huanyu Cheng. ACS Appl. Mater. Interfaces 2020, 12, 40, 45504–45515 Publication Date:September 11, 2020 DOI: https://doi.org/10.1021/acsami.0c11479 Copyright © 2020 American Chemical Society

This paper is behind a paywall.

Bend it, twist it, any way you want to—a foldable lithium-ion battery

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A Feb. 26, 2013 news item on ScienceDaily features an extraordinary lithium-ion battery,

Northwestern University’s Yonggang Huang and the University of Illinois’ John A. Rogers are the first to demonstrate a stretchable lithium-ion battery — a flexible device capable of powering their innovative stretchable electronics.

No longer needing to be connected by a cord to an electrical outlet, the stretchable electronic devices now could be used anywhere, including inside the human body. The implantable electronics could monitor anything from brain waves to heart activity, succeeding where flat, rigid batteries would fail.

Huang and Rogers have demonstrated a battery that continues to work — powering a commercial light-emitting diode (LED) — even when stretched, folded, twisted and mounted on a human elbow. The battery can work for eight to nine hours before it needs recharging, which can be done wirelessly.

The researchers at Northwestern have produced a video where they demonstrate the battery’s ‘stretchability’,

The Northwestern University Feb. 26, 2013 news release by Megan Fellman, which originated the news item, offers this detail,

“We start with a lot of battery components side by side in a very small space, and we connect them with tightly packed, long wavy lines,” said Huang, a corresponding author of the paper. “These wires provide the flexibility. When we stretch the battery, the wavy interconnecting lines unfurl, much like yarn unspooling. And we can stretch the device a great deal and still have a working battery.”

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The power and voltage of the stretchable battery are similar to a conventional lithium-ion battery of the same size, but the flexible battery can stretch up to 300 percent of its original size and still function.

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Huang and Rogers have been working together for the last six years on stretchable electronics, and designing a cordless power supply has been a major challenge. Now they have solved the problem with their clever “space filling technique,” which delivers a small, high-powered battery.

For their stretchable electronic circuits, the two developed “pop-up” technology that allows circuits to bend, stretch and twist. They created an array of tiny circuit elements connected by metal wire “pop-up bridges.” When the array is stretched, the wires — not the rigid circuits — pop up.

This approach works for circuits but not for a stretchable battery. A lot of space is needed in between components for the “pop-up” interconnect to work. Circuits can be spaced out enough in an array, but battery components must be packed tightly to produce a powerful but small battery. There is not enough space between battery components for the “pop-up” technology to work.

Huang’s design solution is to use metal wire interconnects that are long, wavy lines, filling the small space between battery components. (The power travels through the interconnects.)

The unique mechanism is a “spring within a spring”: The line connecting the components is a large “S” shape and within that “S” are many smaller “S’s.” When the battery is stretched, the large “S” first stretches out and disappears, leaving a line of small squiggles. The stretching continues, with the small squiggles disappearing as the interconnect between electrodes becomes taut.

“We call this ordered unraveling,” Huang said. “And this is how we can produce a battery that stretches up to 300 percent of its original size.”

The stretching process is reversible, and the battery can be recharged wirelessly. The battery’s design allows for the integration of stretchable, inductive coils to enable charging through an external source but without the need for a physical connection.

Huang, Rogers and their teams found the battery capable of 20 cycles of recharging with little loss in capacity. The system they report in the paper consists of a square array of 100 electrode disks, electrically connected in parallel.

I’d like to see this battery actually powering a device even though the stretching is quite alluring in its way. For those who are interested here’s a citation and a link to the research paper,

Stretchable batteries with self-similar serpentine interconnects and integrated wireless recharging systems by Sheng Xu, Yihui Zhang, Jiung Cho, Juhwan Lee, Xian Huang, Lin Jia, Jonathan A. Fan, Yewang Su, Jessica Su, Huigang Zhang, Huanyu Cheng, Bingwei Lu,           Cunjiang Yu, Chi Chuang, Tae-il Kim, Taeseup Song, Kazuyo Shigeta, Sen Kang, Canan Dagdeviren, Ivan Petrov  et al.   Nature Communications 4, Article number: 1543 doi: 10.1038/ncomms2553  Published 26 February 2013

The article is behind a paywall.

Surgery with fingertip control

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In the future, ‘surgery at your fingertips’ could be literally true. Researchers at the University of Illinois at Urbana-Champaign have created a silicon nanomembrane that can be fitted onto the fingertips and could, one day, be used in surgical procedures. From the Aug. 9, 2012 news item on ScienceDaily,

The intricate properties of the fingertips have been mimicked and recreated using semiconductor devices in what researchers hope will lead to the development of advanced surgical gloves.

The devices, shown to be capable of responding with high precision to the stresses and strains associated with touch and finger movement, are a step towards the creation of surgical gloves for use in medical procedures such as local ablations [excising or removing tissue] and ultrasound scans.

Researchers from the University of Illinois at Urbana-Champaign, Northwestern University and Dalian University of Technology have published their study August 10, in IOP [Institute of Physics] Publishing’s journal Nanotechnology.

The Aug. 10,2012 posting on the IOP website  offers this detail about the research,

The electronic circuit on the ‘skin’ is made of patterns of gold conductive lines and ultrathin sheets of silicon, integrated onto a flexible polymer called polyimide. The sheet is then etched into an open mesh geometry and transferred to a thin sheet of silicone rubber moulded into the precise shape of a finger.

This electronic ‘skin’, or finger cuff, was designed to measure the stresses and strains at the fingertip by measuring the change in capacitance – the ability to store electrical charge – of pairs of microelectrodes in the circuit.  Applied forces decreased the spacing in the skin which, in turn, increased the capacitance.

The fingertip device could also be fitted with sensors for measuring motion and temperature, with small-scale heaters as actuators for ablation and other related operations

The researchers experimented with having the electronics on the inside of the device, in contact with wearer’s skin, and also on the outside. They believe that because the device exploits materials and fabrication techniques adopted from the established semiconductor industry, the processes can be scaled for realistic use at reasonable cost.

“Perhaps the most important result is that we are able to incorporate multifunctional, silicon semiconductor device technologies into the form of soft, three-dimensional, form-fitting skins, suitable for integration not only with the fingertips but also other parts of the body,” continued Professor Rogers [John Rogers, co-author of the study].

Here’s what an image of these e-fingertips,

Virtual touch. Electronic fingertips could one day allow us to feel virtual sensations. Credit: John Rogers/University of Illinois at Urbana-Champaign

Krystnell A offers a more detailed description of the e-fingetips in an Aug. 9, 2012 story for Science NOW,

Hoping to create circuits with the flexibility of skin, materials scientist John Rogers of the University of Illinois, Urbana-Champaign, and colleagues cut up nanometer-sized strips of silicon; implanted thin, wavy strips of gold to conduct electricity; and mounted the entire circuit in a stretchable, spider web-type mesh of polymer as a support. They then embedded the circuit-polyimide structure onto a hollow tube of silicone that had been fashioned in the shape of a finger. Just like turning a sock inside out, the researchers flipped the structure so that the circuit, which was once on the outside of the tube, was on the inside where it could touch a finger placed against it.

To test the electronic fingers, the researchers put them on and pressed flat objects, such as the top of their desks. The pressure created electric currents that were transferred to the skin, which the researchers felt as mild tingling. That’s a first step in creating electrical signals that could be sent to the fingers, which could virtually recreate sensations such as heat, pressure, and texture, the team reports online today in Nanotechnology.

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Rogers says another application of the technology is to custom fit the “electronic skin” around entire organs, allowing doctors to remotely monitor changes in temperature and blood flow. Electronic skin could also restore sensation to people who have lost their natural skin, he says, such as burn victims or amputees.

Here’s a link to the article which is freely accessible for 30 days after publication, from the Aug. 9, 2012 news item on ScienceDaily,

Ming Ying, Andrew P Bonifas, Nanshu Lu, Yewang Su, Rui Li, Huanyu Cheng, Abid Ameen, Yonggang Huang, John A Rogers. Silicon nanomembranes for fingertip electronics. Nanotechnology, 2012; 23 (34): 344004 DOI: 10.1088/0957-4484/23/34/344004

My best guess is that free access will no longer be available by Sept. 7 (or so) , 2012. I last wrote about John Rogers’ work in an Aug. 12, 2011 posting about electronic tattoos.