Artificial ‘skin’ system transmits the pressure of touch

Might someday be applied to prosthetics to mimic human skin’s ability to feel sensation
October 16, 2015

“Gimmie five”: Model robotic hand with artificial mechanoreceptors (credit: Bao Research Group, Stanford University)

Researchers have created a sensory system that mimics the ability of human skin to feel pressure and have transmitted the digital signals from the system’s sensors to the brain cells of mice. These new developments, reported in the October 16 issue of Science, could one day allow people living with prosthetics to feel sensation in their artificial limbs.

Artificial mechanoreceptors mounted on the fingers of a model robotic hand (credit: Bao Research Group, Stanford University)

The system consists of printed plastic circuits, designed to be placed on robotic fingertips. Digital signals transmitted by the system would increase as the fingertips came closer to an object, with the signal strength growing as the fingertips gripped the object tighter.

How to simulate human fingertip sensations

To simulate this human sensation of pressure, Zhenan Bao of Stanford University and her colleagues developed a number of key components that collectively allow the system to function.

As our fingers first touch an object, how we physically “feel” it depends partially on the mechanical strain that the object exerts on our skin. So the research team used a sensor with a specialized circuit that translates pressure into digital signals.

To allow the sensory system to feel the same range of pressure that human fingertips can, the team needed a highly sensitive sensor. They used carbon nanotubes in formations that are highly effective at detecting the electrical fields of inanimate objects.

Stretchable skin with flexible artificial mechanoreceptors (credit: Bao Research Group, Stanford University)

Bao noted that the printed circuits of the new sensory system would make it easy to produce in large quantities. “We would like to make the circuits with stretchable materials in the future, to truly mimic skin,” Bao said. “Other sensations, like temperature sensing, would be very interesting to combine with touch sensing.”


Abstract of A skin-inspired organic digital mechanoreceptor

Human skin relies on cutaneous receptors that output digital signals for tactile sensing in which the intensity of stimulation is converted to a series of voltage pulses. We present a power-efficient skin-inspired mechanoreceptor with a flexible organic transistor circuit that transduces pressure into digital frequency signals directly. The output frequency ranges between 0 and 200 hertz, with a sublinear response to increasing force stimuli that mimics slow-adapting skin mechanoreceptors. The output of the sensors was further used to stimulate optogenetically engineered mouse somatosensory neurons of mouse cortex in vitro, achieving stimulated pulses in accordance with pressure levels. This work represents a step toward the design and use of large-area organic electronic skins with neural-integrated touch feedback for replacement limbs.