Artificial Skin Made With Carbon Nanotubes Sends Sensation To Brain Cell

Posted: Oct 16 2015, 2:43am CDT | by , in News | Latest Science News


Artificial Skin made with Carbon Nanotubes Sends Sensation to Brain Cell
Photo Credit: Bao Lab

Stanford engineers develop an artificial skin sensor.

Stanford engineers take Apple's 3D Touch to the next level. The Stanford team has developed a plastic skin that can detect how hard it is being pressed and generate an electric signal to deliver this sensory input directly to a living brain cell.

Zhenan Bao, a professor of chemical engineering at Stanford, has worked a decade to develop a material that mimics skin's ability to flex and heal, while also serving as the sensor net that sends touch, temperature and pain signals to the brain. 

The goal of Bao is to create a flexible electronic fabric embedded with sensors that could cover a prosthetic limb and replicate some of skin's sensory functions.

Bao's work, reported today in Science, takes another step toward her goal by replicating one aspect of touch, the sensory mechanism that enables us to distinguish the pressure difference between a limp handshake and a firm grip.

"This is the first time a flexible, skin-like material has been able to detect pressure and also transmit a signal to a component of the nervous system," said Bao, who led the 17-person research team responsible for the achievement.

The heart of the technique is a two-ply plastic construct: the top layer creates a sensing mechanism and the bottom layer acts as the circuit to transport electrical signals and translate them into biochemical stimuli compatible with nerve cells. 

The top layer in the new work featured a sensor that can detect pressure over the same range as human skin, from a light finger tap to a firm handshake.

To digitize this pressure-sensing capability, the Stanford engineers scattered billions of carbon nanotubes through the waffled plastic. Putting pressure on the plastic squeezes the nanotubes closer together and enables them to conduct electricity.

This allowed the plastic sensor to mimic human skin, which transmits pressure information as short pulses of electricity, similar to Morse code, to the brain. 

Increasing pressure on the waffled nanotubes squeezes them even closer together, allowing more electricity to flow through the sensor, and those varied impulses are sent as short pulses to the sensing mechanism. Remove pressure, and the flow of pulses relaxes, indicating light touch. Remove all pressure and the pulses cease entirely.

The team then hooked this pressure-sensing mechanism to the second ply of their artificial skin, a flexible electronic circuit that could carry pulses of electricity to nerve cells.

Bao's team has been developing flexible electronics that can bend without breaking. 

For this project, team members worked with researchers from PARC, a Xerox company, which has a technology that uses an inkjet printer to deposit flexible circuits onto plastic. Covering a large surface is important to making artificial skin practical, and the PARC collaboration offered that prospect.

To show the connectivity of the artificial skin to a biological neuron, the team used a technique developed by Karl Deisseroth, a fellow professor of bioengineering at Stanford who pioneered a field that combines genetics and optics, called optogenetics. 

Researchers bioengineer cells to make them sensitive to specific frequencies of light, then use light pulses to switch cells, or the processes being carried on inside them, on and off.

Optogenetics was only used as an experimental proof of concept, Bao said, and other methods of stimulating nerves are likely to be used in real prosthetic devices. Bao's team has already worked with Bianxiao Cui, an associate professor of chemistry at Stanford, to show that direct stimulation of neurons with electrical pulses is possible.

Bao's team envisions developing different sensors to replicate, for instance, the ability to distinguish corduroy versus silk, or a cold glass of water from a hot cup of coffee. This will take time. There are six types of biological sensing mechanisms in the human hand, and the experiment described in Science reports success in just one of them.

But the current two-ply approach means the team can add sensations as it develops new mechanisms. And the inkjet printing fabrication process suggests how a network of sensors could be deposited over a flexible layer and folded over a prosthetic hand.

"We have a lot of work to take this from experimental to practical applications," Bao said. "But after spending many years in this work, I now see a clear path where we can take our artificial skin."

The details of this research have been published in a paper titled "A skin-inspired organic digital mechanoreceptor" the journal Science.


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.

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The Author

<a href="/latest_stories/all/all/2" rel="author">Luigi Lugmayr</a>
Luigi Lugmayr () is the founding chief Editor of I4U News and brings over 15 years experience in the technology field to the ever evolving and exciting world of gadgets. He started I4U News back in 2000 and evolved it into vibrant technology magazine.
Luigi can be contacted directly at




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