Toward Self-Powered Load Imbalance Detection for Instrumented Knee Implants Using Quadrant Triboelectric Energy Harvesters

In this study, we proposed a triboelectric nanogenerator (TENG) as a pressure sensor to measure the load imbalance on the tibial tray. To detect the load imbalance, we proposed a segmented quadrant design. The TENG pressure sensors with various micro-patterns, including pyramid, cylindrical, and bar patterns, are utilized to measure the axial forces with different sensitivity in different quadrants of the tibial tray. The functionality of the instrumented implant is examined through experimental testing on the package, evaluating its sensing capabilities and power harvesting. The relationship between each quadrant output and the axial force is determined, which enables characterizing the self-powered sensor performance. This relationship is then used to find the center of pressure, which is an important parameter for implant design. The detection of a shift in the center of pressure can be an early indication of loosening, which is one of the major causes of knee implant failure. In addition, we investigated the apparent power captured in resistance loads by applying a sinusoidal cyclic loading to the package harvester. Under an average walking load of 2200 N, each quadrant of the harvester-package prototype produces an apparent power of approximately <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mn>5</mml:mn> <mml:mi>μ</mml:mi> <mml:mspace></mml:mspace> <mml:mtext>W</mml:mtext></mml:math> at 1 Hz and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mn>10</mml:mn> <mml:mi>μ</mml:mi> <mml:mspace></mml:mspace> <mml:mtext>W</mml:mtext></mml:math> at 2 Hz.