A Flexible Temperature Sensing Insole for Diabetic Foot Ulcer Monitoring with an Investigation into the Self Powering of Wearables via Energy Harvesting

Abstract

Wearable devices promise to improve quality of life and reduce strain on healthcare systems, but real-world usage remains uncommon due to multiple limitations. This thesis describes enhancements to current generation wearables to increase both effectiveness and utilisation. Firstly, this is achieved through improved social acceptability by concealing devices in footwear. Although the foot is not a typical location for physiological sensing, the research herein demonstrates the benefit of temperature sensing at the foot. Secondly, the benefits of foot sensing alongside the increased potential for energy harvesting, reducing the need for battery maintenance, are refined and demonstrated. Monitoring foot temperature has been demonstrated as an evidence-based method for preventing diabetic foot ulcer (DFU) formation, a life-changing complication of diabetes that can lead to amputation. However, there are no devices that can continuously monitor temperature at the foot, are suitable for use in diabetic participants, or that can be personalised to the anatomy of an individual. Here, a new device for foot temperature monitoring, enabling new physiological measurements that were not previously possible, is presented. This thesis also presents an exploratory study using this device in participants with diabetes. The results show that the temperature rise at the foot is faster in participants with diabetes, which has not previously been observed or reported. This new data suggests that rise time may be suitable as a biomarker, indicating the development of a DFU. Placing devices at the foot can reduce the need for battery recharging, as lower body locations have been demonstrated as energy-dense for kinetic energy harvesting. Previous investigations have focused on energy harvesting at the ankle rather than the foot, due to ease of device placement. An investigation into the amount of power that can be harvested from the foot itself compared to other locations, including a detailed analysis into the frequency content at multiple body locations and how this affects harvester tuning, is presented. This concludes that the foot not only offers the largest amount of power while walking compared to any other location of the body but is also the least sensitive to changes in cadence. Finally, this thesis builds on this energy harvesting work to investigate how much energy can be harvested across a very large group of participants. Data from the UK Biobank is used to assess the energy harvesting potential from >60,000 participants over a week. This gives the largest ever study into energy harvesting potential and allows stratification of the available energy by age, sex, presence of diabetes, and other factors. The work in this thesis enables personalised design to advance the next generation of wearables as they become a key part in healthcare.

Date of Award	31 Dec 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Peter Green (Supervisor) & Alex Casson (Supervisor)