Foot Prosethics Controlled With Subconscious Commands

An Iceland-based company is now developing the second generation of a system that allows amputees to control foot prosthetics naturally, with subconscious commands.

Prosthetic limbs are becoming more flexible and easier for amputees to use, with some even beginning to offer tactile feedback, but in general, they still lack the natural ebb and flow that comes from commands from the brain. Brain-controlled artificial limbs are still largely confined to the laboratory and may require complex surgery. But an Iceland-based company is now developing the second generation of a system that allows amputees to control foot prosthetics naturally, with subconscious commands.

Össur already produces smart, bionic limbs capable of real-time learning and adjusting to a person’s gait, speed, and terrain. But the new development expands that, using implanted sensors to send intuitive brain commands to an artificial foot, allowing the person to walk more naturally. Users in Iceland and the UK have been testing the technology successfully for almost two years but Össur executives believe it can be improved as sensor technology—a key to the system—improves.

“We had been working on biomedical products for over a decade,” said Magnus Oddson, vice president of R&D prosthetics for Össur. He said the mechanical sensors they used at the time worked, “But it was difficult to predict what one would do.” They were not successful with lower-limb users, he said.

Össur turned to the California-based Alfred Mann Foundation, which already was working with sensors implanted in human bodies. Össur used AMF’s tiny implanted myoelectric sensors in muscle tissue of the lower limbs of two users. The IMES, through a receiver within a prosthetic foot, instantaneously triggers the desired movement subconsciously, without a lapse and in real time.

While tests on the initial users are successful, Oddson said Össur is backing off original plans to bring the device to market, preferring to wait until the next generation of sensors is developed. “It will have the ability to send out more information and use less energy,” he said.

Össur claims its device is the first to use an implanted sensor within a patient’s body. Other mind-controlling prosthetics incorporated transplanted muscle tissue from another part of the body. That requires brain retraining to use it.

In the initial tests, the procedure to implant the tiny sensors—3x80mm—took only fifteen to twenty minutes and was done through a one-centimeter incision. They are placed at the front and back of the muscle, but are not attached to specific nerves and are powered by tiny magnetic coils placed in the socket, a hollow and cushioned element that fits over the limb and connects to the prosthesis. The prosthesis moves based on which sensor picks up the impulse from the muscle.

Össur’s Proprio model

The prosthesis was Össur’s Proprio model, which incorporates a battery-powered motor with sensors that adjust the angle of the foot based on the user’s stride. It works automatically. Using the IMES technology, the command from the brain reaches the foot before muscles can contract, reducing or eliminating the lag time between command and action.

Oddson said the sensor-controlled system redistributes the weight of the user. That has been an issue for users of lower-limb prosthetics. They often favor the ‘good’ leg, placing more weight or balance on it. That can cause back or joint problems after extended use.

One of the biggest benefits to the user is regaining the strength in the muscles above the amputated portion of the leg. “The muscles are not connected to any joint, so they do not serve a purpose for motion,” noted Oddson. “But when you send a signal to the prosthetic device, that is a great incentive to rehab the muscles. Muscles actually gain strength and get large. The ability to stabilize the limb within the socket is a secondary function of these actions.”

Oddson noted that users of the first generation prosthetics now are not using them on a daily basis, but mostly for demonstrations. Durability is a problem. “An issue with one person is that he is a mechanic and works in a harsh environment,” he said. “So there is some damage with the wires that come with the system.”

Developing prosthetics with grant funding

The Reykjavik-based firm is not the only developer of brain-controlled prosthetics. Researchers at Johns Hopkins University, working under $120m in grants from the Defense Advanced Research Projects Agency, are developing modular prosthetic limbs.

A prosthetic arm developed by the team is controlled by a person’s mind and has 26 joints that can curl up to 45 pounds. It requires surgery to remap the affected nerves and relocate them to an appropriate location where the limb is attached to a sensory cap. Because it is modular, it also can be customized for people who have varying needs, such as a hand or partial limb. Researchers are working to reduce the cost.

In 2015, Össur had hoped to bring the brain-controlled prosthetic system to market within three to five years. Those plans are delayed while new sensor development plays out. Oddson said the new system will be a new product that will require the firm to go back square one in testing and obtaining approval from the Federal Food and Drug Administration.