A team of researchers led by the University of California, San Diego, has developed a soft, stretchable electronic device that can simulate the feeling of pressure or vibration when worn against the skin. The device, reported in a paper published in Science Roboticsrepresents a step toward creating haptic technologies that can reproduce a more diverse and realistic range of touch sensations.
The device consists of a soft, stretchable electrode attached to a silicone patch. It can be worn as a sticker on the fingertip or forearm. The electrode, which is in direct contact with the skin, is connected via wires to an external power source. By sending a mild electrical current through the skin, the device can produce sensations of pressure or vibration, depending on the frequency of the signal.
“Our goal is to create a wearable system that can deliver a wide range of tactile sensations using electrical signals, without causing the wearer pain,” said Rachel Blau, co-first author of the study and a postdoctoral researcher in nanoengineering at the UC San Diego Jacobs School of Engineering.
Existing technologies that mimic a sense of touch through electrical stimulation often cause pain due to the use of stiff metal electrodes, which do not conform well to the skin. The air gaps between these electrodes and the skin can cause painful electrical currents.
To address these issues, Blau and a team of researchers led by Darren Lipomi, professor in the Aiiso Yufeng Li Family Department of Chemical and Nano Engineering at UC San Diego, developed a soft, stretchable electrode that seamlessly conforms to the skin.
The electrode is made of a new polymer material constructed from the building blocks of two existing polymers: a conductive, stiff polymer known as PEDOT:PSS, and a soft, stretchy polymer known as PPEGMEA. “By the ratio of this one [polymer building blocks]“We have molecularly developed a material that is both conductive and stretchable,” says Blau.
The polymer electrode is laser cut into a spring-shaped, concentric design and attached to a silicone substrate. “This design improves the stretchability of the electrode and ensures that the electrical current is focused on a specific location on the skin, providing localized stimulation to prevent pain,” says Abdulhameed Abdal, a Ph.D. student in the Department of Mechanical and Aerospace Engineering at UC San Diego and the other co-first author of the study. Abdal and Blau worked on the synthesis and fabrication of the electrode with UC San Diego nanoengineering students Yi Qie, Anthony Navarro and Jason Chin.
In tests, the electrode device was worn on the forearm of 10 participants. Working with behavioral scientists and psychologists from the University of Amsterdam, the researchers first identified the lowest perceptible level of electrical current. They then adjusted the frequency of the electrical stimulation, allowing participants to experience sensations categorized as pressure or vibration.
“We found that by increasing the frequency, participants felt more vibrations instead of pressure,” Abdal said. “This is interesting because biophysically it was never known exactly how current is sensed through the skin.”
The new insights could pave the way for the development of advanced haptic devices for applications such as virtual reality, medical prosthetics and wearable technology.
This work was supported by the National Science Foundation Disability and Rehabilitation Engineering program (CBET-2223566). This work was performed in part at the San Diego Nanotechnology Infrastructure (SDNI) at UC San Diego, a member of the National Nanotechnology Coulated Infrastructure, which is supported by the National Science Foundation (grant ECCS-1542148).
