Category: Prosthetics

Johns Hopkins researchers have developed a proof-of-concept for a prosthetic arm with fingers that, for the first time, can be controlled with a wearer’s thoughts.

The technology was tested on an epileptic patient who was not missing any limbs.  The researchers used brain mapping technology to bypass control of his arms and hands.  (The patient was already scheduled for a brain mapping procedure.) Brain electrical activity was measured for each finger.

This was an invasive procedure, which required implanting an array of 128 electrode sensors, on sheet of film, in the part of the brain that  controls hand and arm movement. Each sensor measured a circle of brain tissue 1 millimeter in diameter.

After compiling the motor and sensory data, the arm was programmed to allow the patient to move individual fingers based on which part of his brain was active.

The team said said that the prosthetic was initially 76 percent accurate, and when they combined the signals for the ring and pinkie fingers, accuracy increased to 88 percent.

Click to view Johns Hopkins video.

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Spinal injury patients, and those with lost limbs, sometimes have neural prosthetic devices implanted in an attempt to regain independence.  They are used for deep brain stimulation and brain controlled external prosthetics.  However, neural prosthetics are often rejected by the immune system, and can  fail because of a mismatch between soft brain tissue and rigid devices.

University of Pennsylvania‘s Mark Allen and colleagues have created an implantable neural prosthetic device that is biocompatible and replaces silicon and noble metal. The goal is to avoid immune-system rejection, failures due to tissue strain, neurodegeneration, and decreased fidelity of recorded neural signals.

Caltech and Keck researchers implanted neuroprosthetics in a part of the brain that controls the intent to move, with the goal of producing more natural and fluid motions.   The study, published in Science, was led by Richard Andersen.  A quadriplegic implanted with the device was able to perform a fluid handshaking gesture and  play “rock, paper, scissors” using a separate robotic arm.

Andersen  and colleagues improved the versatility of movement that a neuroprosthetic can offer by recording signals from  the PPC brain region.  He said: “The PPC is earlier in the pathway (than the motor-cortex, a target of earlier neuroprosthetics,) so signals there are more related to movement planning—what you actually intend to do—rather than the details of the movement execution.  We hoped that the signals from the PPC would be easier for the patients to use, ultimately making the movement process more intuitive. Our future studies will investigate ways to combine the detailed motor cortex signals with more cognitive PPC signals to take advantage of each area’s specializations.”

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Ossur‘s sensor implant allows amputees to control  bionic prosthetic limbs with their minds.  Myoelectric sensors are surgically placed in residual muscle tissue.  Prosthetic movement is triggered via a receiver.

Ossur’s existing “smart limbs”  are capable of real-time learning and automatically adjust to a user’s gait, speed and terrain.   However,  conscious thought is still required.

According to Thorvaldur Ingvarsson, the company’s R&D lead, “the (implant) technology allows the user’s experience with their prosthesis to become more intuitive and integrative. The result is the instantaneous physical movement of the prosthesis however the amputee intended. They no longer need to think about their movements because their unconscious reflexes are automatically converted into myoelectric impulses that control their Bionic prosthesis.”

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Washington University‘s Daniel Moran has received a DARPA grant to test a device that would stimulate nerves in the upper arm and forearm of prosthetic users.  The goal is for the wearer to be able to feel hot, cold, and a sense of touch.  In a related development last year, MC10‘s Roozbeh Ghaffari developed artificial skin for prosthetics that mimics the sensitivity of real skin.  Its silicon and gold sensors detect pressure, moisture, heat and cold (see ApplySci, 12/30/14).

Moran’s electrode is designed to stimulate sensory nerve cells in the ulnar and median nerves in the arms. The ulnar nerve is the largest  in the body unprotected by muscle or bone and is connected to the ring finger and pinkie finger on the hand. The median nerve in the upper arm and shoulder is connected to the other fingers on the hand. Together, the two nerves control movement and sensations including touch, pressure, vibration, heat, cold and pain in all of the fingers.

This novel  macro-sieve peripheral nerve interface is designed to stimulate regeneration of the ulnar and median nerves to transmit information back into the central nervous system.

The device is in an early stage, and will only be implanted in non-human primates at this time.

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