Knee replacement surgery is one of the world’s most common orthopedic procedures, but the implants don’t last forever. They can wear out, loosen or just fail to meet patient expectations and require revision surgery. A new self-powered, load-sensing smart implant could help reduce the required number of ‘revision’ operations significantly.
An international research team, including Ryan Willing from Western University, has developed a novel technique that harnesses friction from an individual’s own movements to charge smart knee implants.
The concept of using smart implants is growing ever-more popular, with the promise that 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. Currently, 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 harvest 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,” explains 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,” says Willing, an Assistant Professor in Western’s Departments of Mechanical and Materials Engineering and Biomedical Engineering.