Conformal heating on biomedical applications and the corresponding heat transfer model

Abstract

Flexible electronics have led to many important research applications in physiological measurements, medical therapy and Human-machine interface (HMI). The research mainly focuses on modifying the device geometry, structures, selecting the suitable material and exploring novel applications. Among these research, conformal heating and the corresponding applications are still underexplored. This thesis aims to investigate the conformal heating applications of these flexible devices as well as the respective heat transfer physics. Here, we introduce an ultrathin heater that can attach conformally onto liver organ and perform thermal ablation. Square serpentine and Archimedean spiral are designed to be the heater pattern. The material design and the fabrication techniques are described in this thesis. The heater can rise to temperature more than 50 oC which is high enough to cause denaturation of cell’s protein. The devices demonstrate promising capability to serve as ablative tool for surface cancer treatment. In additional to heating (heater mode), the Archimedean spiral pattern can operate as a temperature sensor (sensor mode). The temperature of the conformal spiral device is linearly (R2 > 0.999) related to the resistance by the temperature coefficient of resistance (TCR) which allows extracting thermal information by measuring the device’s resistance. Besides, calculation and investigation are conducted to examine the conformality of device on bio-tissues. Furthermore, ex vivo ablation on the porcine liver is performed by the conformal heater. Thermal properties of liver were extracted by comparing one-dimensional heat conduction experiment and calculations. The extracted thermal conductivity k was found to be 0.504 Wm-1K-1 while the thermal diffusivity α was found to be 1.51 × 10-7 m2s-1. These thermal properties were input into finite element analysis (FEA) simulation model to validate the temperature profile and the ablation effect of the conformal heaters. Both the experiment and simulation model show consistent results in the temperature profile. Apart from thermal ablation, Archimedean spiral devices can integrate with robotic gripper system to perform heat-and-sense interactions (thermal interaction) because of its sensing/heating feature. The details of the interaction are described in this thesis. The fast response time (around 10 second) have demonstrated the device as a HMI apparatus. The apparatus can be potentially applied in surgical robots or other stimulation systems.