“The design and construction of prostheses that can emulate a natural sense of touch is of growing research interest,” reads the paper’s introduction. “However, many of the exciting innovations in this field will likely remain out of reach for most people… Our vision is to introduce a low-cost sensing wearable that can be applied retroactively to prosthetics to address this gap.”

Their solution lies in the fact that many users of prostheses put socks on them just like any ordinary foot. Why not make this sock out of smart fabric? So that’s just what they did. Layers of conductive fabric sandwich a piezoresistive layer, creating a pressure-sensitive grid covering the entire foot and ankle.

This was in turn connected to a ring of vibrating motors that can be worn wherever the user finds convenient. Pressure on a certain part of the foot would cause certain motors to vibrate at different frequencies. The researchers also tested a version that transmitted the angle at which a prosthetic knee is bent.

The earliest reference to the idea of a pressure-sensitive limb covering in science fiction, as far as I know, is the Chemelectric Afferent Nerve-Analogues from This Immortal, a terrific 1966 novel by Roger Zelazny:

A worthy opponent was the golem. Hasan had it programmed at twice the statistically-averaged strength of a man and had its reflex-time upped by fifty percent. Its memory contained hundreds of wrestling holds and its governor theoretically prevented it from killing or maiming its opponent - all through a series of chemelectric afferent nerve-analogues, which permitted it to gauge to an ounce the amount of pressure necessary to snap a bone or tear a tendon. Rolem was about five feet, six inches in height and weighed around two hundred fifty pounds...

An earlier example of this idea may be found in the sensitive robot fingers from The Exile of Time (1931) by Ray Cummings.

"He recently passed," said Migul. We stopped, I close beside the stooping metal figure. The Robot's voice was a furtive sepulchral whisper that filled me with awe.

"How long ago?" I asked.

"He passed here an hour or two ago, perhaps. The vibrations are fading out. But it was Tugh. Well do I know him. Put your hand down. Feel the vibrations?"

"I cannot. My fingers are not that sensitive, Migul."

A faint contempt was in the Robot's tone. "I forgot that you are a man."