Binghamton University research moves closer to ’smart’ sensors in knee replacements

If you have a knee replacement, imagine pointing your phone at your knee and pulling up an app that tells you how much stress the artificial joint is experiencing. Knowing the activities that cause the biggest problems — which can lead to a second replacement surgery — would be invaluable.

Research led by Binghamton University is closer to making this technology a reality.

Professor Shahrzad “Sherry” Towfighian — a faculty member from the Thomas J. Watson College of Engineering and Applied Science’s Department of Mechanical Engineering — has worked toward “smart-knee” tech over the past decade. In 2022, she received a $2.3 million grant from the National Institutes of Health to fund her research.

According to the American College of Rheumatology, nearly 800,000 total knee replacements are done every year in the U.S., and that number is expected to rise sharply by 2030 as the population ages and sports injuries become more common.

“These implants should last for the rest of their lives. They don’t want revision surgery, but one in five patients has loosening or imbalance in the joint,” Towfighian said. “We need to solve this issue, because right now there are no sensors inside the implant to show any indication of problems, and then it becomes too late to fix it. The ability to noninvasively measure loads using embedded sensors would enable earlier identification of aberrant loading and the development of treatment strategies.”

Powering these sensors would be piezoelectric and triboelectric transducers, which convert the knee’s movements into small amounts of power.

Recently published papers from Towfighian and PhD candidates Mahmood Chahari, Osama Abdalla, and Elham Mahmoudi in the journals Nano Energy, Sensors, and IEEE/ASME Transactions on Mechatronics focus on the best transduction materials and designs for energy harvesting-based load sensors.

For the best results, the answer to “smart knee” implants seems to be a combination of triboelectric generation (when two objects contact or slide against each other) and piezoelectric generation (which relies on vibrations and pressure). Different materials offer a range of sensor sensitivities as well.

“Because the output of the harvester is proportional to the load that it receives, it serves both as a sensor and an energy harvester,” Towfighian said. “As state-of-the-art power management and wireless communication circuits can operate in the microwatt range that the harvester produces, it is possible to create a self-powered load sensor.”

Contributors to this research include colleagues at Stony Brook University and Western University in London, Canada.

“We compared our results with a joint simulator from Associate Professor Ryan Willing, our collaborator at Western University. It simulates the six degrees of freedom in the knee joint,” Towfighian said. “In terms of the performance, we think we have characterized it well. The part that remains is to seal the device and test it on cadaveric legs to ensure biocompatibility and accurate sensor performance.”