Gao, DayongWang, Ziyuan2026-02-052026-02-052025Wang_washington_0250E_29050.pdfhttps://hdl.handle.net/1773/55266Thesis (Ph.D.)--University of Washington, 2025Cryopreservation is the primary method for long-term storage of biological materials, ranging from small cellular samples to larger tissues and whole organs. Its key advantage is enabling biobanking, which is vital for advancing biomedical research in areas such as cell therapy, tissue engineering, and organ transplantation, and ultimately improving the quality of life for millions of people worldwide. However, cryopreservation has not been widely adopted in large-scale industrial applications or routine clinical practice, especially for large samples such as tissues and organs. This limitation arises because there is currently no commercially available or widely accepted heating technology capable of reliably rewarming large cryopreserved samples while maintaining their viability and functionality. Evaluating the performance of heating in cryopreservation hinges on two key factors: heating rate and uniformity. A higher heating rate can reduce the required cryoprotective agent (CPA) concentration, thereby decreasing the toxicity associated with CPA solutions. However, this increased rate often leads to greater thermal stress due to larger temperature gradients, which is a significant concern with traditional conductive or convective heating methods. This issue becomes more pronounced as the sample size increases. Consequently, conventional heating technologies can only achieve limited heating rates for small samples and are not suitable for larger ones due to these constraints. Multiple rewarming modalities are under active development, including nanowarming, Joule heating, laser heating, and dielectric heating, each with distinct advantages and trade-offs. This dissertation focuses on dielectric heating and, specifically, the design, improvement, and validation of a single-mode electromagnetic resonance (SMER) system. This work comprises four innovations: (i) design of a SMER rewarming system; (ii) a control strategy to improve SMER rewarming performance; (iii) optimization of the vitrification solution for SMER rewarming; and (iv) design of a high-power SMER rewarming system aimed at future human organ cryopreservation. This work first developed a single-mode electromagnetic resonance (SMER) rewarming platform for large-volume cryopreservation. The system integrates five subsystems: RF generation (signal generator plus high-power amplifier), control module, real-time monitoring (fiber-optic thermometry and reflected-power sensing), safety module (circulator, dummy load, directional coupler), and the SMER cavity applicator. The dimensions of the SMER cavity applicator was derived from Maxwell’s equations and tuned to the TE101 mode at 434 MHz to place an electric-field antinode at the cavity center for controllable dielectric heating. Finite-element electromagnetic-thermal modeling (COMSOL) predicted resonance at 434.8 MHz and quantified absorbed power density, confirming strong, center-focused fields. Bench validation used a 25 mL cryoprotectant sample (10% DMSO + 0.25 M trehalose) rewarmed from −80 °C to 0 °C. Measured and simulated temperature histories agreed closely. These results validated the design of the SMER rewarming system, demonstrating its viability as a path toward tissue- and organ-scale rewarming. The work then addressed one of the significant challenges in SMER systems, resonance tracking, because efficient conversion of electromagnetic energy to heat occurs only at resonance. Even slight detuning yields very low heating rates (approaching those achieved by air convection) and high reflected power, posing risks to operators and sensitive devices. Previous resonance-tracking approaches relied on experienced operators or trade-off methods (e.g., intermittent feedback control). To address this challenge, extremum seeking control (ESC), an adaptive control approach, was implemented. Compared with manual control, ESC increased the heating rate by 16.8% and significantly reduced risks associated with manual operation, including potential equipment damage during operator training or from occasional procedural errors. ESC also delivered adequate heating rate and uniformity at a 25 mL scale, surpassing the capabilities of conventional water-bath rewarming. To further improve SMER rewarming performance, I built a dielectric measurement system to characterize and optimize vitrification solutions. Temperature-dependent permittivity and loss (−150 to 0 °C) were measured by the cavity perturbation method, with broadband (100–1,500 MHz) profiling via an open-ended coaxial probe to guide vitrification solution choice and frequency-specific optimization at 434 MHz. DPVP exhibited a high dielectric constant and a loss peak near −40 °C that helped limit thermal runaway, but VS55 was selected for 50 mL scaling. To enhance absorption, multi-walled carbon nanotubes (MWCNTs) were dispersed, their concentration verified by TGA, and 0.5 wt% was identified as optimal for VS55 based on the loss tangent at 434 MHz. Jurkat cell tests indicate increased toxicity during prolonged ice exposure but acceptable post-thaw recovery under standard protocols. In 50 mL experiments, VS55 under the 400 W ESC-SMER system failed to exceed the CWR (center/edge 47.59/45.53 °C min⁻¹), whereas 0.5 % MWCNT + VS55 achieved 84.52/99.67 °C min⁻¹, surpassing the CWR and enabling successful, uniform rewarming. Together, the dielectric-property mapping and nanoparticle augmentation provide a practical route to scaling SMER rewarming capability to 50 mL volume samples. To overcome the 400 W ceiling of a signal-generator-plus-amplifier setup, this work adopted a 3-kW solid-state RF source operating at 900 - 930 MHz and engineer a TE101 rectangular cavity (915 MHz), with ESC-based resonance tracking, monitoring, and safety modules. At 1 kW, 25 mL VS55 achieves center/edge rewarming rates of 308.25/340.10 °C·min⁻¹, 49.5%/75.0% higher than the prior 400 W, 434 MHz SMER system with acceptable uniformity. Biological tests on 12 mL Jurkat suspensions show post-thaw recovery of 71.4 ± 5.59% (1 kW SMER rewarming) vs 48.5 ± 13.5% (water-bath rewarming), indicating that better rewarming performance improves the viability of cryopreserved samples. Current limits on sample volume (< 25 mL) stem from operating frequency (the 900–930 MHz band reduces penetration depth and shifts with loading), generator tuning range (volume-dependent detuning below 900 MHz), and elevated reflections that constrain the delivered power. Future work targets lower-frequency solid-state sources, cavity retuning to keep loaded resonance within the band, and improved matching to unlock the full 3 kW and scale beyond 100 mL. This dissertation also outlines plans for future improvements, focusing on optimization of the high-power SMER rewarming system, including resonant cavity design, power delivery, and customization of a solid-state generator. In addition, cryopreservation studies on animal organs will be conducted to further evaluate the system’s capabilities.application/pdfen-USnoneCarbon nanotubeCryopreservationDielectric heatingExtremum seeking controlSingle-mode electromagnetic resonant cavitySolid-state generatorMechanical engineeringBioengineeringElectromagneticsMechanical engineeringThesis