As useful as they are for amputees, prosthetic legs aren't the most comfortable things to wear. With the whole body pressing down on the point of contact, they can be painful, awkward to walk with and cause infections. Now scientists from the Office of Naval Research (ONR) have developed a more comfortable and "smart" prosthetic that can be attached and detached at will, and monitored for infection and stress with an array of sensors.

One of the most common types of artificial leg is a socket prosthesis, which supports the body by fitting around the end of the remaining limb. But these can put too much pressure on the soft tissue there, leading many amputees to opt for a wheelchair instead.

The ONR device is called the Monitoring OsseoIntegrated Prosthesis (MOIP). To improve comfort, the prosthesis has a titanium fixture that is surgically implanted into the patient's thigh bone, which in time grows around – or "osseointegrates" – the metal. A small connector is left poking out of the patient's leg, and an artificial limb can then be attached to that. With the point of contact moved away from the soft tissue, this kind of prosthetic is more comfortable to wear and allows for a more natural walking motion.

Infection can still be a problem though, and dealing with that is where the M in MOIP comes in. Bio-compatible sensors are embedded within the patient's remaining limb, and attached to other sensors in the prosthetic. Together, these sensors monitor a range of factors that can help doctors track the patient's progress, and prevent and treat infection.

The sensor array tracks the patient's body temperature and pH balance as symptoms of infection, and keeps an eye on how well the bone is fusing with the prosthetic. That can help doctors figure out when it's safe for the patient to put weight on their new limb, and data can be gathered over time to track eventual wear and tear.

"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 Jerome Lynch, lead researcher on the project. "Because the sensors transmit information wirelessly, doctors also could potentially study patient data via a handheld reader. 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 so far developed and tested a prototype of the MOIP, with an array of sensors embedded in a synthetic bone model. With that proving successful, the team is planning to improve the model for clinical trials by next year. In the long run, the technology should be able to work with upper limbs as well.