Master of Engineering Science
Musculoskeletal Health Research
Holdsworth, David W.
Due to sensor size and supporting circuitry, in vivo load and deformation measurements are currently restricted to applications within larger orthopaedic implants. The objective of this thesis is to repurpose a commercially available low-power, miniature, wireless, telemetric, tire-pressure sensor (FXTH87) to measure load and deformation for future use in biomechanical applications. The capacitive transducer membrane of the FXTH87 was modified, and a relationship was reported between applied compressive deformation and sensor signal value. The sensor package was embedded within a deformable enclosure to illustrate potential applications of the sensor for monitoring load. Finite element analysis was an effective tool to predict the fatigue life and failure location of 3D-printed Ti-6Al-4V and PLA load cells. Finite element models of fracture fixation loading scenarios were developed to evaluate the feasibility of internal sensing components. The proposed device presents a sensitive and precise means to monitor high-capacity loads within small-scale, deformable enclosures.
Summary for Lay Audience
Each year, there are hundreds of thousands of lower limb long bone fractures. The bone fractures are predominantly caused during trauma, such as motor vehicle accidents, or falls in the aging population. With most fractures, the affected area is stabilized using either internal or external fracture fixation devices. Internal fixation components include fracture fixation plates and intramedullary nails. These implants ensure that the broken bone segments are properly aligned and stable, so that the natural bone healing process is fast and successful. Unfortunately, in some cases, union between the broken bone segments does not occur or takes longer than normal. Prolonged bone nonunion can lead to fatigue failure of the fixation implant, which further damages the tissue surrounding the fracture location. Monitoring of the bone healing process is very subjective and highly dependent on the experience of clinicians to evaluate the affected region. There is a clear need for a sensorized implant that is capable of providing an objective measure of bone healing. The challenge is most currently available sensor packages are too big or do not have the necessary functionalities to be embedded within an orthopaedic implant. In this thesis, a miniature wireless sensor was developed using a commercially available tire pressure sensor. This novel sensor package is capable of monitoring load, small-scale displacement, acceleration, and temperature all within a miniature package. To demonstrate that this sensor was capable of being embedded within an orthopaedic implant, the sensor was instrumented within a custom 3D-printed deformable structure. The combination of the novel sensor and deformable enclosure generated a functional load cell that is capable of measuring physiological loads. To evaluate the performance of the load cells, the structures were subjected to theoretical and experimental mechanical testing. To determine if the novel miniature sensor package could be feasible for instrumentation within a fracture fixation implant, finite element models of long bone fracture fixation using a custom orthopaedic implant were generated. The miniature wireless sensor package described in this thesis is well suited to monitor load and displacement in many biomedical, commercial, and industrial small-scale and remote measurement applications.
Anderson, William, "Development of a Wireless Telemetry Load and Displacement Sensor for Orthopaedic Applications" (2021). Electronic Thesis and Dissertation Repository. 7971.
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