New wearable device capable of recording the electrical activity of the heart and muscles, as well as delivering therapeutic electrical and thermal stimulations. It is suitable for flexible joints, like the wrist, and allows reliable heat transfer even when the wrist is flexed or extended. Credit: Institute for Basic Science (IBS)

A new, soft and stretchable bioelectronics mesh is able to record the electrical activity of human heart and muscles, a discovery that could be implemented for pain relief, rehabilitation and prosthetic motor control.

Researchers from the Center for Nanoparticle Research, within the Institute for Basic Science, have created the wearable, implantable device that measures electrophysiological signals and applies electrical and thermal stimulations.

The researchers used gold-coated silver nanowires mixed with polystyrene-butadiene-styrene (SBS)—a conductive rubber—to develop the stretchable patch.

“We took advantage of silver's high conductivity, SBS' stretchability, and gold's high biocompatibility,” Hyeon Taeghwan, director of the Center for Nanoparticle Research and corresponding co-author, said in a statement. “Finding the right proportion of each material was the key to success.”

In the study, the researchers explained the benefits of using the silver–gold (Ag–Au) nanowires.

“Because oxidation and/or corrosion can increase the contact resistance between nanowires, and Ag nanowires are vulnerable to these processes when exposed to biofluids such as sweat, interstitial fluid and blood, we examined the oxidation resistance of our Ag–Au nanowire using hydrogen peroxide as the oxidant,” the study states. “[Transmission electron microscopy] images show that the Ag nanowire is heavily oxidized and corroded, while the Ag–Au nanowire with the protective Au shell remains intact.

“Resistance against oxidation was further confirmed by UV–vis spectra, which show a significantly diminished extinction spectrum for Ag nanowires that have undergone oxidation and an unchanged spectrum for Ag–Au nanowires.”

To improve the stretchability of the material, the researchers increased the toughness of the Ag-Au nanocomposite using a heat rolling-press process.

Because the device is soft, elastic and stretchable, it can follow the contours of flexible joints like the human wrist. When it is worn on the forearm, the device can monitor electromyogram signals and deliver both electrical and thermal stimulations in therapeutic applications.

 “The conformal contact minimizes the gap between the electrode and skin, so high-quality signals can be obtained,” the study states. “Furthermore, the low resistance of the Ag–Au nanocomposite electrodes is helpful in reducing the impedance of the device on the skin, thus providing the capability to obtain an ECG and EMG from the human skin with a high signal-to-noise ratio.” 

The team also developed a customizable mesh that they fit over the lower part of a pig’s heart that can read signals from the entire heart to identify possible lesions and ultimately help with recovery.

The mesh was able to register the change of electrocardiogram signals caused by an acute heart attack. The mesh is also stable during repetitive heart movement and does not interfere with the heart’s natural pumping activity.

“Although various soft cardiac devices have been reported for the rat heart,” Choi Suji, first co-author of the study said in a statement. “This study on pigs can approximate human physiology more accurately. We aim to study heart diseases, and stimulate the heart more effectively by synchronizing cardiac pumping activity.”

The researchers plan to maximize the conductivity and stretchability even further in the future by designing novel, non-toxic materials and studying the therapeutic effect of the mesh in cardiac diseases.

The study was published in Nature Nanotechnology.