In recent years, prosthetics have improved by leaps and bounds, allowing amputees and people with paralysis to literally leap and bound—plus drink beer with their minds. But one feature of functional limbs has been out of robotic reach: the sense of touch.

Now, researchers have edged closer to providing that sense, revealing today an artificial material that can mimic the pressure sensing capabilities of skin. The flexible material, reported in Science, could one day blanket fake limbs or paralyzed body parts to restore a person’s ability to feel.

The sense of touch is critical to the human experience, said coauthor Benjamin Tee, an electrical and biomedical engineer at the Agency for Science Technology and Research in Singapore. Restoring feeling in amputees and people with paralysis could help them carry out normal activities, such as cooking, playing contact sports, and, you know, fighting the empire. Tee, a Star Wars fan, told Ars that he has wanted to make artificial skin ever since watching The Empire Strikes Back, in which Luke Skywalker gets a prosthetic arm after being injured in a fight with Darth Vader.

Tee wasn’t the first to come up with the idea of artificial skin. Earlier versions of artificial skin exist, but none has been able to mimic how human skin senses mechanical force, Tee said.

When real skin is pressed, biological sensors embedded in the tissue send out a pulsed signal to neurons in the brain. The frequency of the pulses varies, indicating to the brain how much force is being applied. For instance, 50 pulses per second could tell the brain that there’s a force from 50 grams, Tee said.

But past versions of faux skin didn’t generate pulsed signals. Instead, they generated direct current with changing amplitude based on the amount of force. That electrical signal then had to be calibrated and converted before it could directly activate neurons—an energy intensive method that could easily drift out of calibration.

To make a more realistic, energy-efficient artificial skin, Tee and colleagues created a multi-layered, battery-powered material, tricked out with pressure sensors and circuitry that produces pulsed signals. They call the flexible material the Digital Tactile System, or DiTact.

The top layer of the DiTact contains the sensors, which are tiny upside-down pyramids, about 50 microns wide at the base, made of rubber and conductive carbon nanotubes. When a pyramid is squished, its carbon nanotubes come into contact with each other. This allows current from an 11-volt battery to flow through the pyramid and into the DiTact’s inner layer. The more a pyramid is squeezed, the more current gushes through.

In the inner layer, that current flows through a ring oscillator circuit—a circuit that generates voltage spikes. The more current into the circuit, the higher the frequency of spikes. The output frequencies of the DiTact range from 0 to 200 hertz, which is in line with the biological range of signal frequencies.

Those pressure-specific, pulsed signals can then directly activate neurons. So far, Tee and colleagues have hooked up the DiTact to mouse neurons grown in petri dishes, proving that the material can charge up those cells to varying degrees depending on pressure.

The researchers also took an optogenetic approach, which uses light to stimulate neurons. To do this, the researchers converted the electrical pulses from the DiTact into light pulses by hooking the material up to an LED. When connected to a mouse neuron that was genetically engineered to respond to light, the DiTact again stimulated the cell based on pressure.

“It’s a big step” for artificial skin, said Northeastern University bioengineer Ryan Koppes, who was not involved with the study. The DiTact hits all the marks, he said. It’s flexible, low-energy, and produces a biologically relevant signal for neurons.

Next, Tee said, is to add additional sensors into the skin to measure things like temperature.

Science, 2015. DOI: 10.1126/science.aaa9306 (About DOIs).