Today, our most advanced prostheses can do pretty much everything we use our hands or feet for. But to make them as good as or better than a natural limb, they've got to feel natural themselves.
Controlling an artificial arm just by thinking is an important step, and we're getting good at it. But getting feedback from it — feeling where it is and what it's touching — is more difficult.
Researchers are just figuring out how to use brain implants to transmit the sense of touch in paralyzed patients. They found the same tech can give prosthetic limbs their own senses. Their tester reported sensations of warmth and pressure on the prosthetic fingers that felt "natural," even when he was blindfolded.
Artificial limbs won't be as responsive as our natural ones until we solve these challenges. Once we do, though, there's nothing stopping them from being stronger and faster than stock.