Impedance Spectroscopy for Surface and Fracture Wounds: Sensor Development and Clinical Application

Wearable sensors and instrumented implants have wide-ranging clinical applications, and their continued development in recent years has led to advances inpersonalized healthcare. Innovations in electronics and trends in mobile health are extending the capabilities of traditional medical practice. For a number of clinical conditions, there remains a lack of standardized methods for assessing patients, with physicians often relying on subjective physical examinations that can differ depending on medical training and experience. The work in this thesis focuses on developing objective tools using electrical impedance spectroscopy (EIS) to monitor surface and fracture woundsEIS measures the frequency-dependent opposition to the flow of electrical current, and has been used to quantitatively characterize cellular changes. This work begins by examining pressure ulcers, tissue damage caused by prolonged pressure on the skin, which are commonly analyzed using photographs and ruler measurements. Prevention efforts involve nursing staff repositioning patients every few hours to relieve pressure on a particular area, which is highly time and labor intensive. A “smart bandage” was designed to non-invasively detect and monitor pressure ulcers by identifying changes in tissue health. By utilizing EIS over a flexible electrode array, visually intuitive maps were produced to determine areas with tissue damage and areas at risk for further injury. To extend this technology to deep tissue injuries, this work also details development of an instrumented implant to monitor bone fracture healing. X-ray radiographs arethe most common method of assessing fracture repair, but are only useful at later stages because they rely on mineralization of tissue. Microscale sensors were designed and built to locally measure healing fractures in rodent models, and EIS was employed to robustly track longitudinal differences in healing trends. Advancements in miniaturized and flexible electronics haveenabled these kinds of physiological monitoring devices, which can guide clinical decision-making and facilitate early intervention. By instrumenting items like bandages and fracture fixation implants already widely used in hospital settings, this work demonstrates that EIS technology can be integrated into current health management strategies with minimal disruption to clinical workflows.