Stanford researchers working on elastic skin devices

The SPIE optical science conference Aug. 28 through Sept. 1 at the San Diego Convention Center included an Aug. 30 plenary presentation by Stanford University professor of chemical engineering Zhenan Bao on applications for stretchable electronics, including skin placement.

"Stretchable Electronic Materials for Skin-Inspired Devices" addressed the molecular design concepts for stretchable semiconductors, dielectrics, and conductors used to fabricate stretchable transistors and simple circuits.

"We're going to start to wear our electronics," Bao said.

The elastonics must have stretchable properties and must be able to accommodate strain on skin.

"Our approach is to take soft materials which are already compatible with soft tissue and skin but turn them into higher-performance electronic materials," said Bao.

Stanford's materials science program is working with the design school on applications which would include monitoring devices and artificial skin. Wearable elastonics would be in one of four regions: enhanced wearables, smart clothing and peripherals (such as glasses), dermal (on-skin) sensors, and subdermal (implanted) sensors.

"Our goal is to be able to mimic biological systems," Bao said. "We want to build electronic materials that can mimic all the functions of skin."

The components as well as the device itself must have the stretchable properties.

"A very important component is the printed circuit," Bao said. "For the stretchable electronic material it's still relatively new."

One of the issues to be addressed is the change in electrical characteristics with strain. The research also covers the comparison between a double-layer capacitor and a convention capacitor.

"If we go to much lower frequencies we can see there's dramatic increase in the capacitance," said Bao. "There are some ions that can migrate to the surface of the electrode."

In a double-layer capacitor the capacitance is independent of thickness while an inverse relationship between capacitance and thickness exists for a conventional capacitor.

"Using this as the guideline then we can now start looking how to incorporate new functionalities," Bao said. "We want to have chemical bonds that can readily break more easily."

The dynamic bonds can strengthen the energy dissipation, and research has shown a level with no visible crack function even at 100 percent strain.

"We're able to now actually reach a state for this kind of material comparable to state of art," Bao said.

Integration of the material is an additional area of work.

"These materials are going to be encapsulated when we actually use them," Bao said. "Stretchable encapsulation material will be a big challenge."