Research Bits: April 13

Washable battery
Researchers from the University of British Columbia developed a washable, flexible, and stretchable battery.

“Wearable electronics are a big market and stretchable batteries are essential to their development,” said Dr. Ngoc Tan Nguyen, a postdoctoral fellow at UBC’s faculty of applied science. “However, up until now, stretchable batteries have not been washable. This is an essential addition if they are to withstand the demands of everyday use.”

The battery’s key components are zinc and manganese dioxide, which are ground into particles and embedded in the stretchable and biocompatible polymer poly(styrene – isobutylene – styrene) (SIBS).

“We went with zinc-manganese because for devices worn next to the skin, it’s a safer chemistry than lithium-ion batteries, which can produce toxic compounds when they break,” said Nguyen.

Several layers of these polymers are wrapped inside a casing of the same polymer, creating an airtight and waterproof seal.

“We put our prototypes through an actual laundry cycle in both home and commercial-grade washing machines. They came out intact and functional and that’s how we know this battery is truly resilient,” said Bahar Iranpour, a PhD student at UBC. The battery was able to withstand 39 wash cycles and retained 75% of its capacity following 500 charge and discharge cycles.

The team is working to increase the battery’s power output and cycle life. They also expect the cost to be reasonable. “The materials used are incredibly low-cost, so if this is made in large numbers, it will be cheap,” said Dr. John Madden, electrical and computer engineering professor and director of UBC’s Advanced Materials and Process Engineering Lab. “Wearable devices need power. By creating a cell that is soft, stretchable and washable, we are making wearable power comfortable and convenient.”

Flexible photodetectors
Engineers from the Georgia Institute of Technology developed soft, flexible photodetectors that can act like a second skin and stretch up to 200% more than its original dimension without significantly losing its electric current. Made from a synthetic polymer and an elastomer, it absorbs light to produce an electrical current.

“Think of a rubber band or something that’s soft and stretchable like human skin yet has similar electrical semiconducting properties of solid or rigid semiconductors,” said Canek Fuentes-Hernandez, formerly in the School of Electrical and Computer Engineering of Georgia Tech and now an associate professor in Electrical and Computer Engineering at Northeastern University in Boston. “We’ve shown that you can build stretchability into semiconductors that retains the electrical performance needed to detect light levels that are around hundred million times fainter than produced by a light bulb used for indoor illumination.”

“Electronic devices are very brittle typically, which is okay with conventional devices fabricated on rigid substrates. But as soon as you use soft substrates that becomes an issue,” said Olivier Pierron, professor in the School of Mechanical Engineering at Georgia Tech.

The researchers tested the material’s reliability, gradually increasing it until a sample with a thickness of 500 nanometers worked.

“It was still super thin. Under dry conditions, it would just crumble. We had to use a water reservoir to keep its shape,” said Kyungjin Kim, then a Georgia Tech Ph.D. mechanical engineering student and now an assistant professor in the University of Connecticut’s Department of Mechanical Engineering.

The water acted like plastic wrap keeping the thin films in place without crumbling or losing shape, enabling the researchers to stretch the material and measure its mechanical properties.

To test for electrical signals coming out of the device under illumination, electronic terminals had to be embedded on it, which also had to be deformable. “Fabricating stretchable electronic terminals was a major challenge in and of itself,” said Felipe Andres Larrain, at the time an ECE PhD graduate at Georgia Tech and now an assistant professor at Adolfo Ibáñez University in Chile.

One application would be medical wearables, where a flexible and conformable sensor could reduce the motion artifacts caused by movement. “Moving around can drastically affect the usability of collected data but being able to reposition devices on the body to minimize or eliminate motion artifact is a big deal,” noted Gabriel Cahn, a project manager for Huxley Medical, a biosensor startup in Atlanta, who recently graduated from Georgia Tech with a doctorate in flexible electronics. “Having electronics that can flex, twist, bend and conform to non-flat surfaces and move with your body will allow you to place these sensors in more advantageous places to collect biometric data. It will be infinitely more useful in helping diagnose or monitor existing medical illnesses.”

The team also thinks it could have applications beyond wearables for health monitoring, such as robotics and implants. “The soft device also could be attractive for implantable electronics for bio-electronic applications since the interfaces comply with the dynamic motion of the soft biological tissues, reducing the foreign body reaction,” said Kim.

Equine wearables
Biomedical engineers and veterinarians from Purdue University developed a horse slicker that can enable remote monitoring of a horse’s cardiac, respiratory, and muscular systems via Bluetooth.

Slickers are lightweight, close-fitting garments often used to protect a horse’s coat before shows and to prevent blanket rubs. The team adapted an off-the-shelf version for the experiment.

Chi Hwan Lee, associate professor of biomedical engineering in Purdue’s Weldon School of Biomedical Engineering, said the team developed a dual regime spray and technique to directly embed a pre-programmed pattern of functional nanomaterials into the slicker’s fabrics to add the e-textile capabilities to the slicker. By using existing garments, the e-textiles can take advantage of existing ergonomic designs for a commercial grade of wearability, comfortability, air permeability, and machine washability.

Researchers observe a cardiac, respiratory, and muscular test on a horse and capture the horse’s vital signs on a laptop via Bluetooth technology from a specially designed horse slicker. (Credit: Purdue University photo/Rebecca McElhoe)

“These specially designed e-textiles can comfortably fit to the body of humans or large animals under ambulatory conditions to collect bio-signals from the skin such as heart activity from the chest, muscle activity from the limbs, respiration rate from the abdomen or other vital signs in an extremely slight manner,” Lee said. “Our technology will significantly extend the utility of e-textiles into many applications in clinical settings.”

The team is working to develop continuous 24-hour monitoring of horses with chronic disease or those receiving care in a veterinary ICU.

“We believe that our technology will be helpful in diagnosis or management of chronic diseases,” Lee said. “Remote health monitoring under ambulatory conditions would be useful for farm and household animals, as it could potentially minimize clinic visits, especially in rural areas. It would also increase the efficiency in managing a large number of farm/household animals at once from a distance, even overnight.”

One application would be monitoring monitor severe equine asthma, which the researchers said affects 14% of adult horses. “Continuous monitoring would allow early detection of disease flair-up before it gets serious, offering an opportunity to nip it in the bud,” said Laurent Couëtil, a professor of large animal internal medicine in Purdue’s College of Veterinary Medicine. “Remote monitoring opens the possibility of sending vital information to the veterinarian to help make timely and informed treatment decisions.”

The researchers have field for a patent on the technology. Along with versions for other large animals, they plan to develop a version for human use.