Energy Harvesting and Sensing with Embedded Piezoelectric Ceramics in Knee Implants

The knee replacement is one of the most common orthopedic surgical interventions in the United States; however, recent studies have shown up to 20% of patients are dissatisfied with the outcome. One of the key issues to improving these operations is a better understanding of the ligamentous balance during and after surgery. The goal of this work is to investigate the feasibility of embedding piezoelectric transducers in the polyethylene bearing of a total knee replacement to act as self-powered sensors to aid in the alignment and balance of the knee replacement by providing intra- and postoperative feedback to the surgeon. A model consisting of a polyethylene disc with a single embedded piezoelectric ceramic transducer is investigated as a basis for future work. A modeling framework is developed including a biomechanical model of the knee joint, a finite element model of the knee bearing with encapsulated transducer, and an electromechanical model of the piezoelectric transducer. Model predictions show that a peak voltage of 2.3 V with a load resistance of 1.01 MΩ can be obtained from a single embedded piezoelectric stack, and an average power of 12 μW can be obtained from a knee bearing with four embedded piezoelectric transducers. Uniaxial compression testing is also performed on a fabricated sample for model validation. The results found in this work show promising potential of embedded piezoelectric transducers to be utilized for autonomous, self-powered in vivo knee implant force sensors.