Researchers at the Indian Institute of Technology have developed an ultra-thin electronic tattoo that can reproduce the wearer's localized touch. Such devices have potential for use in making lightweight, portable tactile displays as well as healthcare and robotics devices.
The sense of touch is essential for grasping and manipulating objects, experiencing the world, and enabling communication between machines and humans. Replicating the sense of touch through wearable devices has a variety of important uses, such as providing feedback to robotic arms for amputees or providing information to the visually impaired, as well as use in virtual reality and gaming.
Researchers at the Italian Institute of Technology (IIT) have developed an ultra-thin wearable electronic tattoo that provides localized tactile sensation through thermal, electrical and mechanical stimulation. They chose temporary transfer tattoo paper as the base for the device because the paper can effectively transfer to non-planar surfaces and create electrodes and electrical pathways that adhere well to human skin.
A 1-micron-thick layer of paraxylene is applied to the tattoo paper to enhance mechanical strength, and then an ultra-thin conductive silver ink film is printed directly on it. Then the wiring is added, followed by polystyrene particles, which create tiny voids that trap air, and then a layer of parylene on top.
The device, whose entire thickness is only a few microns, works via electrothermal and pneumatic stimulation. Rapid, localized electrical heating creates a small amount of air between the two layers of parylene. As the air expands, the force of the air can be felt on the skin touching the device.
After testing the completed device on a glass slide, the researchers placed the electronic tattoo on a person's fingertip to demonstrate its ability to induce a sense of touch. Subjects felt 9 out of 10 stimulations, and there was no pain or temperature increase during testing. Additionally, the device is powered by a tiny battery with very low voltage (less than 300 milliwatts), making it safe for the wearer.
This work demonstrates the capabilities of a single taxel or TActile pixel, a sensor that recognizes the pressure of contact with a physical object. Researchers are working on developing larger tactile displays containing multiple taxels that can be activated independently of each other, allowing letters, numbers and patterns to be reproduced on the skin.
"In this work, our focus was on developing and characterizing single taxa," the researchers said. "However, this approach, materials and fabrication techniques can be extended to implement more complex devices, such as larger tattooable tactile displays."
They believe their method has potential for developing lightweight, portable tactile displays and devices.
The research was published in the journal Advanced Electronic Materials.