Development of Optimal Electromagnetic Resonance Rewarming Technology for Cryopreservation
The development of successful cryopreservation technology has been restricted to small biological materials due to the limited effective rewarming techniques. Either for conventional cryopreservation techniques which remain a certain fraction of ice crystals or vitrification which aims to exclude ice crystal in the subzero temperature range completely, the rewarming rapidity plays a significant role in the recovery of the biological materials after cryopreservation. Additionally, for larger materials such as tissues and organs, the uniformity of the temperature profile is indispensable to maintain the integrity of the cryopreserved biological matrix. The major challenges for traditional convective rewarming method, i.e., water bath, lie in that the high specific heat of cryopreserved materials likely result in a slow warming by the unsatisfactory heat source; and a large temperature gradient is induced by conductive heat transfer within the sample. The cryopreserved cells are exposed to cryoinjuries for a longer time if rewarming is insufficiently rapid in the case of conventional cryopreservation. For tissue or organ preservation, even if a vitrified state has been achieved by the addition of high concentration cryoprotective agent (CPA) solutions and/or designed cooling process, the slow rewarming can lead to devitrification and recrystallization, introducing considerable ice crystals that should be avoided. On the other hand, the non-uniform temperature profile brought by the convective heating method leads to the thermal stress induced fractures, which can tear apart the vitrified tissues. Hence, an effective rewarming should be both rapid and uniform, to guarantee the successful cryopreservation or vitrification of biological materials. Potentially it may be the most promising to achieve the goal by utilizing the electromagnetic waves, but several issues remain to inhibit the further practical applications. This dissertation reports on research in which an electromagnetic resonance rewarming technique is developed and optimized aiming for the organ and tissue preservation. An optimization procedure is established as the following steps: (1) determination of the essential physical properties of the CPA/vitrification solutions; (2) analysis and estimation of the combined electromagnetic and heat transfer phenomenon; (3) theoretical simulation and investigation of the rewarming process based on the measured properties; and (4) practical setup of an electromagnetic resonance system and enhancement by adding superparamagnetic nanoparticles. First, the effectiveness of vitrification of bulk biological material is mainly dominated by the composition and concentration of the vitrification solutions. To avoid devitrification or fractures which relies upon the absorption of electromagnetic energy and heat diffusion, the fundamental electric properties, thermal properties of vitrification solutions are indispensable for the following estimation of the electromagnetic rewarming efficacy. The dielectric properties were determined by a designed measurement system adopting the cavity perturbation method. The thermal conductivities were measured, and differential scanning calorimeter was used to determine the specific heat. The analysis of these preliminary measurement results was conducted for a selection of CPA/vitrification solutions. Due to the nonlinearity of the coupled electromagnetic and heat transfer equations, an accurate analytic prediction is hardly achieved to the electromagnetic rewarming outcomes. Hence, a numerical simulation model was established to estimate the warming procedure and select CPA solutions, optimal geometry of the cryopreserved materials and several other parameters before conducting experiments. In particular, a hybrid electromagnetic-conduction rewarming concept was raised and tested to maintain the higher warming rate and reduce the temperature non-uniformity of the cylindrical cryopreserved materials. The numerical model can simulate the field and optimize the parameters of the electromagnetic rewarming system, to achieve a higher power utilization efficiency. With the assistance of a numerical model, the electromagnetic resonance rewarming system was designed, assembled, and optimized, particularly the coupling between the system source and resonance chamber. In addition, a frequency tracking component was added to ensure the resonant state during the rewarming process, when the cryopreserved materials shift the resonance as temperature increases. Finally, to fully utilize the electromagnetic field energy provided by the dynamic controlled electromagnetic resonance rewarming system, we took advantage of magnetic nanoparticles (MNPs) to absorb magnetic field energy to further enhance the energy conversion efficiency, which overcame the low electromagnetic energy absorption ability problem that previous attempts suffer from. An ultra-high power utilization efficiency was obtained and we achieved over 200 C min−1 rewarming rate for tens of mL cryopreserved samples. In addition, we also investigated the effect of nanoparticle size and concentration on the rewarming results and thermal properties. The closed system preventing electromagnetic radiation outwards reduced the possible concomitant side effects when increasing nanoparticles or raising the electromagnetic power. With the remarkably low dosage of nanoparticles (0.1 mg mL−1 Fe) compared to other MNPs based rewarming applications (over 1 mg mL−1 Fe), this study opens a door for new approaches to explore novel rewarming techniques for the tissue and organ preservation.
- Mechanical engineering