People who have lost a hand not only suffer from the increased difficulty of performing routine tasks, they also lose the sensation required to manipulate objects gracefully. We have reported on several researches aiming to restore sense of touch and now, as part of DARPA’s Hand Proprioception and Touch Interfaces (HAPTIX) program, Ripple, a medical device company in Salt Lake City, is also building a myoelectric implant with an implantable neural stimulator that activates peripheral nerves to restore sensation.Every day we use our hands as tools to complete the tasks of daily living, and we also use our hands as sensors to learn about the world around us. Sensory nerves in our fingers tell us about the texture and temperature of objects as well as allow reflexes to prevent items from slipping from our grasp.
New prosthetic hands increasingly look more like sophisticated marvels from sci-fi movies, but people have difficulty using these artificial hands because the devices do not have access to the subtle signals the body sends to produce coordinated motions. Also, the absence of sensory information from the robotic hand makes the prosthesis seem more like a foreign object than an extension of the body. “A hand that cannot feel does not feel like a hand,” explains Dr. Daniel McDonnall, Director of Research at Ripple.
Similarly to other bionic hands, Ripple’s myoelectric implant solution also includes multiple electrodes to be implanted in the forearm to detect signals from the remaining muscles that formerly were used to move the hand and wrist. These electrodes connect to an electronics package implanted under the skin that wirelessly sends signals from the forearm muscles to a receiver built into the prosthetic arm.
The sense of touch is created by the implantable neural stimulator that selectively activates nerve fibers that carry sensory information from the limb to the brain. Mechanical sensors built into the prosthetic hand can detect when the hand touches an object as well as proprioceptive information, such as whether the prosthetic hand is open or closed. Ripple’s neural stimulator will use information from these mechanical sensors to activate specific nerves to restore natural sensation from the missing hand.
Ripple’s device has been under development for five years with ongoing support from the National Institutes of Health. The company plans to coordinate with researchers at the University of Pittsburgh and the University of Utah to conduct clinical trials evaluating performance of these systems in human subjects.
For more information about Ripple, visit rppl.com.