Prosthetic limbs are becoming increasingly high-tech and realistic, but they're not there just yet. A group of researchers from Stanford University, however, are working to take things a step further.

The study, published in Science, details the fact that engineers have been able to successfully create a stretchable circuit that is able to sense pressure and turn that data into nerve impulses. In other words, they made artificial skin that can be used to feel things.

When it comes to prosthetic limbs, the ability to touch can mean the difference between being able to interact with things in the world and being able to sense that physical interaction. A big part of that puzzle was the development of flexible circuits that have sensors and can detect things like pressure, heat, stretching and so on. The real issue, however, isn't detecting touch, but turning touch into a nerve impulse that the brain can sense.

According to the study, transmitting pressure data to the brain involves being able to gather the signals and then using a microcontroller, or very small computer, to turn those signals into something that the body is able to process. This, however, can translate into "noise" to the data that is being gathered by the brain, so the signal needs more energy to be properly processed. The team at Stanford hoped that instead of adding an extra step, they could change how the sensor works.

"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 research lead Zhenan Bao of Stanford. 

The new sensors use a layer of carbon nanotubes, which are able to conduct more electricity if they are compressed. This basically creates a number of electrical pulses that can be sent to the brain.

The team tested the new method by using a different system called optogenetics, in which cells are modified to respond to light. The sensor itself was connected to an LED that flashed with pulses, which in turn activated mouse neurons. While this doesn't say exactly what the skin feels, it does indicate that the interface is able to successfully interact with brain cells.

The next step is to shrink the individual sensors so that they can fit into small areas, which would better mimic real skin. Once that happens, the team's goal is to test the system with a live animal rather than just cells, after which the team wants to create robotic limbs and wearable devices.

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