| One of the critical factors influencing the cell/tissue survival in cryopreservation is the warming process. Currently, most cryopreserved cells/tissues are warmed by the conventional, heat-convection method. Due to the low thermal conductivity and high specific heat of biological materials, this convective warming regime can only make a slow and non-uniform warming process, which causes lethal intracellular ice-recrystallization, devitrification, and thermal stress/fracture in the samples/tissues. Electromagnetic thawing could be an ideal approach to reach rapid and uniform heating. During EM warming, heat is generated volumetrically, which means materials can absorb energy internally. This characteristic leads to the advantages of EM thawing, such as rapid and uniform heating.; The main objective of this research is to investigate (theoretically and experimentally) the possibility of using a single-mode microwave cavity to achieve rapid and uniform warming of cryopreserved biomaterials. A numerical model is developed to simulate the electric field distribution in the test materials placed inside a rectangular single mode resonant cavity. The model employs Method of Moment to solve Maxwell's equations. The effect of material dimension and temperature on the electric field inside the material is investigated. Dielectric properties of materials are important for EM warming results. To study the temperature dependent dielectric properties of biomaterials, resonant cavity perturbation method is developed to allow measurement of dielectric properties at different temperatures. Dielectric properties of various cryoprotective agents (CPA) solutions are measured using this method. Thermal stabilities of these solutions for EM warming are also investigated. Finally, an EM rewarming system is designed. The system includes a rectangular resonant cavity, which is excited in TE101 mode at frequency near 434 MHz. The source frequency can be adjusted dynamically during the warming process to track the resonant frequency of the cavity. The sample to be thawed can be placed at the center of the cavity. Experiments are conducted on cryopreserved CPA solutions using this system. Results show that EM warming can produce higher warming rate than conventional warming methods. |
