Tag Archives: Houbing Huang

Printing wearable circuits onto skin

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.

Getting too hot? Strap on your personal cooling unit

Individual cooling units for firefighters, foundry workers, and others working in hot conditions are still in the future but if Pennsylvania State University (Penn State) researchers have their way that future is a lot closer than it was. From an April 29, 2016 news item on Nanotechnology Now,

Firefighters entering burning buildings, athletes competing in the broiling sun and workers in foundries may eventually be able to carry their own, lightweight cooling units with them, thanks to a nanowire array that cools, according to Penn State materials researchers.

An April 28, 2016 Penn State news release by A’ndrea Elyse Messer, which originated the news item, describes some of the concepts and details some of the technology,

“Most electrocaloric ceramic materials contain lead,” said Qing Wang, professor of materials science and engineering. “We try not to use lead. Conventional cooling systems use coolants that can be environmentally problematic as well. Our nanowire array can cool without these problems.”

Electrocaloric materials are nanostructured materials that show a reversible temperature change under an applied electric field. Previously available electrocaloric materials were single crystals, bulk ceramics or ceramic thin films that could cool, but are limited because they are rigid, fragile and have poor processability. Ferroelectric polymers also can cool, but the electric field needed to induce cooling is above the safety limit for humans.

Wang and his team looked at creating a nanowire material that was flexible, easily manufactured and environmentally friendly and could cool with an electric field safe for human use. Such a material might one day be incorporated into firefighting gear, athletic uniforms or other wearables. …

Their vertically aligned ferroelectric barium strontium titanate nanowire array can cool about 5.5 degrees Fahrenheit using 36 volts, an electric field level safe for humans. A 500 gram battery pack about the size of an IPad could power the material for about two hours.

The researchers grow the material in two stages. First, titanium dioxide nanowires are grown on fluorine doped tin oxide coated glass. The researchers use a template so all the nanowires grow perpendicular to the glass’ surface and to the same height. Then the researchers infuse barium and strontium ions into the titanium dioxide nanowires.

The researchers apply a nanosheet of silver to the array to serve as an electrode.

They can move this nanowire forest from the glass substrate to any substrate they want — including clothing fabric — using a sticky tape.

“This low voltage is good enough for modest exercise and the material is flexible,” said Wang. “Now we need to design a system that can cool a person and remove the heat generated in cooling from the immediate area.”

This solid state personal cooling system may one day become the norm because it does not require regeneration of coolants with ozone depletion and global warming potentials and could be lightweight and flexible.

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

Toward Wearable Cooling Devices: Highly Flexible Electrocaloric Ba0.67Sr0.33TiO3 Nanowire Arrays by Guangzu Zhang, Xiaoshan Zhang, Houbing Huang, Jianjun Wang, Qi Li, Long-Qing Chen, and Qing Wang. Advanced Materials DOI: 10.1002/adma.201506118 Article first published online: 27 APR 2016

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.

One final comment, I’m trying to imagine a sport where an athlete would willingly wear any material that adds weight. Isn’t an athlete’s objective is to have lightweight clothing and footwear so nothing impedes performance?