Knee replacement surgery is one of the world’s most common orthopedic procedures, but those implants don’t last forever. Even the latest smart implants wear out, loosen or just fail to meet patient expectations and require revision surgery.
An international research team, including Western Engineering professor Ryan Willing, has solved one problem with these cutting-edged devices by developing a novel technique that harnesses friction from an individual’s own movements to charge the implant.
The concept of using smart implants is growing ever-more popular, with the promise they could provide essential analytics to surgeons, therapists and physical trainers related to the behavior of their knee during recovery, while ensuring enriched, lifelong mobility moving forward. This is especially important as knee replacement surgeries are being offered to younger, more active individuals.
Currently, load-sensing implants are used in a research setting, or as a temporary aid during surgery, but there is a major problem. Most smart implants need either a battery or an external power source to charge them, so continuous and long-term monitoring is not possible.
Willing and his collaborators from Binghamton University (NY) and Stony Brook University (NY) have discovered a way to collect triboelectric energy, a type of energy that is collected from friction.
“We’re basically harvesting electricity though the same mechanism that causes the static charge to occur when you rub a balloon on your hair,” said Willing, a member of Western’s Bone and Joint Institute. “It’s friction, which creates a small charge, and if you can harness that charge you can use it to do something useful. In our case, it would power the telemetry circuitry in the implant to actually beam out knee loading information from the individual.”
The research team determined the new smart, self-powered implant needs 4.6 microwatts to function and preliminary testing showed the average person’s walk produces six microwatts of power, more than enough to power the sensors.
The new implant features two ridge-shaped surfaces within it, which rub against one another when a person walks. The frictional sliding that occurs as a result transfers electrons from one surface to another, which provides the self-powered charge to the implant.
“Since the voltage created is proportional to the amount these surfaces slide with respect to one another, and that depends on the amount of load being applied, we’re also able to measure forces. It’s really a two-in-one, energy harvesting and load-sensing device within a single mechanism,” Willing said.
The study, supported by the National Institute for Health Research, was published by the journal Smart Materials and Structures.