Self-Powered Load Sensors for Total Knee Replacement Health Monitoring - The goal of this research is to make a prototype of a self-powered load sensing system for Total Knee Replacement (TKR) and show its effectiveness via pre-clinical testing on cadaver knees under simulated activities of daily living. TKR is the most common surgery, and it is growing in numbers because of the osteoarthritis epidemic in older people and sports accidents in younger people. During joint replacement surgeries, prosthesis are aligned to provide appropriate kinematics and stability. Unfortunately, aberrant loading patterns resulting from implant misalignment or ligament imbalance after surgery can result in early failure. Tracking the long-term health of the implant is difficult without quantitative joint load data. This is especially true for telehealth, which have become increasingly common due to restrictions on in-person clinic visits as a result of the COVID-19 pandemic. The ability to noninvasively measure loads using embedded autonomous sensors would enable earlier identification of aberrant loading and the development of treatment strategies. State-of-the-art technologies use electromagnetic or piezoelectric transducers. Electromagnetic devices require incorporation of a coil and magnets within the prosthesis, which may weaken the structure. Piezoelectric transducers, on the other hand, are most commonly made of ceramics that contain lead posing obvious health risks. Lead-free Piezoelectric materials have been made, but they have lower power density, especially compared to newer energy harvesting technology. Triboelectric energy harvesting is a newly discovered energy harvesting technique based on contact electrification and electrostatic induction. Triboelectric energy harvesters convert cyclic motion to electricity by generating charges at micro-patterned textured contacting surfaces. The wide range of materials that exhibit triboelectric properties allows flexibility in the design of harvesters for low cost, high sensitivity, high power density and biocompatibility, making them ideal for implant applications. To take advantage of this promising new technology, we propose a self-powered load monitoring system for TKR that can be customized and installed between the ultra-high molecular weight polyethylene (UHMWPE) bearing and the tibial tray, allowing the device to be incorporated into any TKR system. The load monitoring system comprises four harvesters, one in each quadrant of the tibial tray, and a frontend electronics system. The system can monitor the force distribution across four quadrants over time. This information is essential in health monitoring of the implant because aberrant load transmission is a leading cause of implant revision surgeries. The amount of energy harvested is small (~20 microwatts), but is adequate for extracting important features of the load throughout the day. The data will be gathered on a computer and normal versus abnormal loading patterns will be classified using artificial neural networks. This creative approach enables the sensor to continuously operate using solely the power produced by the harvester. The proposed project can revolutionize the biomedical implant field by providing quantitative data that can guide health care decision making.
