Ultra-thin tattoo developed to give tactile sensation

Touch is a fundamental sense, and touching the surrounding environment and perceiving tactile sensations from external stimuli is an almost fully automatic skill, fundamental to perform several daily tasks.

IIT researchers recognised that replicating tactile sensations in artificial wearable devices could find multiple important uses, such as reproducing sensory feedback in amputees using a robotic limb, controlling teleoperated robots with a higher precision, providing information to blind people through ‘Braille displays’, or as interfaces in virtual environments and gaming, enhancing user’s immersive experience.

Developed by IIT researchers Arianna Mazzotta and Virgilio Mattoli, the prototype technology is an electronic temporary tattoo a few micrometres thick that is designed to arouse a tactile sensation on skin in contact with the device through thermal, electrical and mechanical stimulation.

Consisting of a silver electrode printed on tattoo paper, researchers said the device can be easily transferred directly on human skin by simply wetting it with some water.

The temporary transfer tattoo paper was coated with a 1-micrometre-thick parylene layer for mechanical strength, with the silver electrodes printed on top. Wiring was then added, followed by polystyrene microparticles to create tiny spaces designed to trap air, with another layer of parylene on top.

The device is based on an electro-thermo-pneumatic actuation strategy, which consists of electrically heating a small volume of air enclosed between two very thin films, in a ‘fast and very localised manner.’ As it expands, the air generates forces that can be felt by the skin contacting the device.

In a statement, ITT said: “Preliminary usage test results showed great promise in terms of functionality, suggesting the use of this technology as a possible new standard in the manufacturing of lightweight, portable, and energy-efficient tactile displays.”

After initial testing on a glass slide, the researchers tested the electronic tattoo protype on a human fingertip to measure its capability of eliciting tactile sensations. The subject reported nine out of 10 tactile simulations.

Powered by a very small battery at low voltages (less then 300mW), researchers said safety for the device user was of utmost priority; the participant reported feeling no pain or temperature increase during the tests.

The testing demonstrated the functioning of a single ‘tactile’ dot, and researchers said they are working on the implementation of displays that will include several tactile pixels, called taxels, which can be activated independently, and allow for the reproduction of letters, numbers, and directional and dynamic patterns on the skin.

The research paper was published as part of an issue dedicated to ultra-thin electronics in Advanced Electronic Materials, and can be read in full here.