Runner using heart rate monitor training running, smartwatch checking performance or GPS. Man athlete looking at stopwatch. Healthy runner closeup on trail running workout. Wearable technology for tracking activity.

Stretchable stopwatch, ideal for runners, lights up human skin

Image credit: Dreamstime

Researchers from the American Chemical Society (ACS) have developed a stretchable light-emitting device that operates at low voltages and is safe for human skin – ideal for runners in need of an instant stopwatch.

Over the years, scientists have developed stretchable light-emitting devices called alternating-current electroluminescent (ACEL) displays that can be stuck on the skin or other surfaces, similar to a temporary tattoo. However, these displays have typically required relatively high voltages to achieve sufficient brightness, which could create safety concerns.

To overcome this issue, Desheng Kong of Nanjing University, China and his colleagues aimed to develop an ACEL that could operate at lower voltages, making it safer to apply to human skin.

Adapted from ACS Materials Letters 2019, DOI: 10.1021/acsmaterialslett.9b00376

Image credit: A stretchable light-emitting device becomes an epidermal stopwatch

To make the device, the researchers sandwiched an electroluminescent layer, made of light-emitting microparticles dispersed in a stretchable dielectric material, between two flexible silver nanowire electrodes.

The device contained a new type of dielectric material in the form of ceramic nanoparticles embedded in a rubbery polymer, which increased the brightness compared with existing ACEL displays.

Using this material, the team created a four-digit stopwatch display, which they mounted onto the back of a volunteer’s hand. At low voltages, the stretchable display was sufficiently bright to be viewed under indoor lighting.

“The practical feasibility is demonstrated by an epidermal stopwatch that allows intimate integration with the human body,” the team said in the study.

According to the researchers, this bright stretchable display could find a broad range of applications in smart wearables, soft robotics and human-machine interfaces.

The device may also be applicable to runners, who would not need to carry a stopwatch or check their phone in order to check the length of time they have been running.

The researchers added: “The high-permittivity nanocomposites reported here represent an attractive building block for stretchable electronic systems, which may find a broad range of applications in intrinsically stretchable transistors, sensors, light-emitting devices and energy-harvesting devices.”

The study was published in ACS Materials Letters.

In July this year, researchers at the Georgia Institute of Technology designed a wireless stretchable health monitor, stating that it avoids many of the skin injuries and allergic reactions associated with conventional adhesive sensors with conductive gels.

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