Put very simply, the skin is comprised of two layers of rubbery plastic skin with a flexible circuit printed on, courtesy of the folks at Xerox Parc. Sandwiched between the two is a run of carbon nanotubes, which conduct electricity when they're pushed closer together. The harder the compression, the more current passes between them, which is how the skin can understand differences in pressure.
That, however, isn't enough, since that data would still have to be transmitted somehow into the user's brain. In the end, the team opted to harness a field of science called optogenetics, which involves genetically-engineering cells so that they react to specific frequencies of light. By creating optogenetic neurons that are capable of sensing light patterns, the team proved that it's possible to make this technology work in a person.
Admittedly, we're still years away from an initial human test, and project leader Professor Zhenan Bao doesn't believe that optogenetics is a suitable solution. There are also more things that just pressure that human skin can sense, like temperature and friction, all of which would still need to be replicated. Even so, this breakthrough could prove to be enormous in the hopefully not-too-distant future.
[Image Credit: Stanford University Bao Lab]