‘Smart’ prosthetics monitor for infection, stress

Technology News | October 6, 2017

By Rich Pell

Called the Monitoring OsseoIntegrated Prostheses (MOIP), the artificial limb is equipped with specially designed sensors to monitor walking gait, alert wearers of prosthetic wear, and warn of potential infection risk. The prosthesis was specifically designed to address issues frequently encountered with traditional leg prosthetics, which can be painful to wear and prone to causing infection.

“This new class of intelligent prostheses could potentially have a profound impact on warfighters with limb loss,” says Dr. Liming Salvino, a program officer in ONR’s Warfighter Performance Department. “MOIP not only can improve quality of life, but also usher in the next generation of prosthetic limbs.”

Traditional leg prosthetics typically fit amputees via a socket that encloses the residual limb, exerting pressure on the limb’s soft tissue and causing pain and chafing, sores and blisters, and possible infection. Such prosthetics often require frequent adjustment – which is both time consuming and costly – and amputees often choose a wheelchair as a preferable alternative.

The MOIP limb alternative instead features a titanium fixture that is surgically implanted into the thigh bone (or femur) of the amputee. The bone grows – or “osseointegrates” – at the connection point, leaving only a small metallic connector protruding from the remaining leg, from which an artificial limb can be attached or detached at will.

While this approach addresses many of the pain and motion issues associated with traditional artificial limbs, infection risk remains from the metal connector that protrudes from the residual limb. To address the issue, say the researchers, they are developing both electrochemical sense-and-respond approaches and “smart” skin technologies.

These include a bio-compatible sensor array embedded within an amputee’s residual limb, as well as additional sensors on the MOIP prosthetic itself. According to the ONR scientists, the biocompatible sensor array is the first technology of its kind, and tracks changes in body temperature and pH balance – both indicators of possible infection.

The array also monitors how well the bone and prosthetic limb are fusing together and healing, allowing doctors to speed the recuperation process. Over time, say the researchers, the sensors can evaluate the prosthetic’s strength, how much stress is being placed on it, and any changes to movement and walking gait.

“One game-changing application of this technology would be as a tool to inform doctors when prosthetics can be safely loaded after surgery, leading to more accurate determination of when patients are ready for physical therapy after receiving a new prosthetic,” says Dr. Jerome Lynch, a University of Michigan engineering professor who is overseeing the sensor array’s development. “Right now, doctors study X-ray images of a limb when making that determination.”

“Because the sensors transmit information wirelessly, doctors also could potentially study patient data via a handheld reader,” he says. “Think of it as an extremely specialized Fitbit. This could dramatically improve the recovery and long-term quality of life for patients.”

The researchers have successfully created a MOIP sensor array prototype using synthetic bone models. They hope to have a new, improved model ready for clinical trials early next year.

Office of Naval Research