Imagine a future where prosthetics wearers could tell the difference between a limp or firm handshake. That might soon be possible, as after eight years of work, researchers have created a small patch of artificial skin that sends pressure sensations to brain cells.
"The aim of our research was to make a synthetic skin that communicates information about pressure in the same way that real skin does," Alex Chortos, a researcher at Bao's Research Group at Stanford University, told me. "We're creating electronic devices that communicate information about the surrounding directly into the body in a way that the brain can understand."
The artificial skin is made of flexible, organic materials, and in a paper published Thursday in the journal Science, researchers describe its two-layered composition. While the upper layer contains pressure sensors, the lower layer contains an electronic circuit that converts pressure sensing signals into electrical pulses that can be communicated with mice brain cells.
The researchers tested their sensor by stimulating the mice brain cells in vitro using optogenetics (when nerves are engineered to respond to light).
"We showed that the signal from our sensor can be inputted into these cells in a petri dish, and that the cells responded in the expected way based on the pressure information that we provided," explained Chortos.
Chortos said that one of the main challenges was getting the circuit and sensor layer to work together effectively. "There are a lot of issues related to matching the electrical resistance of the two components, so a lot of optimization went into making the idea pressure sensor for this circuit," he said.
Another challenge was creating sensors that can sense the same degrees of pressure that a human can. The team moulded carbon nanotubes into pyramidal microstructures for their sensors as this allowed them to channel signals from the electrical field of objects exerting pressure onto the electrodes in the sensor, more effectively. The sensors can detect anything from a light finger tap to a strong handshake.
Currently, the researchers only have a small patch of plastic skin to experiment with. However, in the future, they want to create a larger surface area that can cover, for example, a prosthetic hand or arm. They also want to create more advanced bio-integrated electronics.
"Real skin has a very high density of different sensor types, so what we're working on next is making the sensors smaller and integrating more of them with different functionalities into a single sensor skin," said Chortos.
Inroads are slowly being made in prosthetic touch technology. Last year, a group of researchers from South Korea published a study in Nature Communications for a similar artificial skin capable of sensing temperature and humidity. According to Chortos, further advancements could be made in the next three to six years.
The applications of these artificial skins aren't just limited to prosthetics either. They could potentially be used on disaster robots so that they can get better tactile feedback from their environment, as well as in healthcare devices.
"In the short term, we hope to use the sensitive skin-like sensors for wearable health monitoring applications," Zhenan Bao, lead study author, told me. "Our devices could be mounted on skin like a piece of bandage and used to measure vital signs such as heart rate and blood pressure."