Just over 15 years ago, Johnny Matheny was diagnosed with fibrosarcoma, a rare form of cancer that attacked the connective tissue around the bones of his left hand. His doctors gave him a choice: Amputate the hand or die. He could still feel his hand after it was gone, a so-called phantom limb caused by signals firing through the nerves that once connected his hand to his brain. Now fully in remission from the cancer, Matheny has spent years volunteering for experiments, test-driving the fanciest, most advanced prosthetics available. But while these devices offered high-tech motor control and vibration feedback, some things were still missing, including the ability to feel temperature.