Thermally Responsive Polymers for Wearable Calorimeters

Citation

Costanza, Vincenzo (2022) Thermally Responsive Polymers for Wearable Calorimeters. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/0hf9-8m62. https://resolver.caltech.edu/CaltechTHESIS:05272022-085102678

Abstract

The measurement of the body core temperature (BCT) can provide insightful health information spanning from hypothermia and heat stroke to inflammations and infections. In addition, the continuous monitoring of the BCT can unlock new possibilities for people’s well-being such counting of burnt calories, prediction of the ovulation period in the female population, and for the assessment of mental health issues. However, the integration of a BCT sensor in wearable devices is extremely challenging, since standard methods cannot combine minimal invasiveness with high measurement accuracy. Dual heat flux (DHF) thermometry is a novel technique that allows the precise estimation of BCT from the measurement of skin temperature. Nevertheless, the limited precision of currently available temperature sensors has not favored the wide spread of devices based on this architecture. In this thesis, we present the fabrication of a fully wearable DHF thermometer realized by integrating new polymers with a remarkable temperature sensitivity. In these particular polymers, an increase in temperature results in a change of the ionic conductivity. In the first part of this work, we focus on the understanding of the ion transport mechanism in these polymers and, in particular, on the nature of the interaction between the functional groups present on the polymer backbone and the conducting species (i.e. metal cations and water molecules). We show that the ion’s coordinating environment is the key to make these materials highly sensitive to temperature. The second part of the thesis tackles the fabrication of a BCT sensor, integrating these temperature responsive polymers in an ultrathin DHF thermometer. Building on the understanding of the nature of the temperature response, we optimize the polymer’s composition to obtain a thermal sensitivity that allows a good precision when measuring the BCT. Finally, we characterize the performance of the fabricated DHF thermometer in different conditions, assessing the sensor’s accuracy and response time.

Thesis Files