Amputees are getting new mind-control powers over their prosthetic limbs to gently pick up soft objects without crushing them, as well as the ability to lock-and-load their prosthesis directly into their bones and muscles.
Two research groups — at Case Western Reserve University in Cleveland and the Chalmers University in Sweden — published papers in Science Translational Medicine today on their successful studies with prosthetic patients, both of whom lost their arms in accidents.
“They are both exciting technologies and I look forward to using themselves with my patients,” said Todd Kuiken, professor of physical medicine and rehabilitation at Northwestern University’s Feinberg School of Medicine, who although was not associated with either project is an expert in the field of developing prosthetic devices.
The Cleveland group, led by associate professor of biomedical engineering Dustin Tyler, built a cuff-like device designed to fit around major nerve bundles in the arm. This is different from other techniques that connect electrodes to nerves by inserting them through the protective membranes.
Researchers from Tyler’s team implanted three electrode cuffs in one patient’s arm, enabling him to feel 19 distinct points. Two were put in the upper arm of a second patient, enabling him to feel 16 distinct locations.
The researchers developed computer algorithms that converted the sensory input from objects taped to a patient’s artificial hand into varying patterns of electrical signals. The sensors can’t tell the difference between cotton and sandpaper, but can detect degrees of pressure. The different signal patterns passed through the cuffs, where the nerves picked them up and delivered them to the brain.
One object produced a sensation that the patient immediately recognized as a cotton ball. He was correct.
By having better sense of pressure, patients can more precisely control the movements of a prosthetic hand; they’re able to gently pick up a cherry tomato without smashing it or squeeze toothpaste onto a toothbrush.
After the electrical stimulation, the patients said they felt like they were grabbing things with their own hand rather than using an artificial one, Tyler explained.