Master of Engineering Science
Mechanical and Materials Engineering
Willing, Ryan T.
Instrumented implants provide the potential to measure the in vivo tibiofemoral forces that are transmitted through total knee replacements (TKR). The continuous feedback from instrumented implants can be used to objectively justify actions to reduce the risk of implant failure. The main obstacle in developing “smart implants” is reliably powering such devices. Energy harvesting mechanisms, such as the triboelectric effect, can be leveraged to produce usable electricity and measure the transmitted loads in TKRs. A compliant package that interlocks with commercially available TKR components was designed to house triboelectric generators (TEG). Prototypes were more compliant than what was expected from the computational models. During fatigue testing, the prototype failed prematurely due to inherent issues with additive manufacturing. However, these issues can be mitigated with improved post-processing techniques. This package serves as a novel approach to integrating self-powering load sensors in currently available knee implants.
Summary for Lay Audience
Osteoarthritis (OA), or the cartilage degradation in joints, can lead to pain and joint dysfunction. In severe cases of OA, the diseased joint may need to be reconstructed. Knee implants, consisting of metal components resurfacing the shin bone and thigh bone with a plastic insert in-between, replace the diseased bone, relieve pain and restore function. Over time, knee implants can fail for several reasons, such as implant loosening from the surrounding bone and abnormal motion between the thigh bone and the shinbone. Devices that measure forces transmitted through knee implants can improve our understanding of what a knee implant undergoes daily, thus providing information on how to prevent implant failure.
Currently, devices that monitor a patient’s knee loads are unavailable. The main reason for this is because of the difficulty of powering these devices. Sensors that can generate power from human motion can be used to measure the loads acting on knee implants. Load sensors have been developed to generate power from static electricity. These sensors require a compliant package to cushion the forces acting on them when placed within a knee implant.
This thesis outlines the design of such a package. The package was designed using computer simulations and then its performance was measured through lab experiments. Prototypes of the package design were made with 3D printed titanium. In one lab experiment where the applied load was intentionally shifted from one side of the package to the other, the prototype predictably deformed more in the location where forces were concentrated. However, the 3D printed package was softer than what was predicted in the computer simulations. During durability testing, the package prototype underwent loading that simulates walking. Implant components should last for millions of cycles, but the current prototype failed prematurely. 3D printed titanium parts may have internal holes and defects that reduce the longevity of the parts. The fatigue strength of the package could be improved with heat treatment and removal of surface defects. The use of this package with embedded load sensors is a novel perspective on measuring the forces that act on knee implants.
Yamomo, Geofrey, "Design and Analysis of a Compliant 3D Printed Energy Harvester Package for Knee Implants" (2019). Electronic Thesis and Dissertation Repository. 6728.