Rapid Electromagnetic Rewarming of Cryopreserved Tissues Using Nano-Magnetoparticles: Feasibility Study

Cryopreservation and banking of biological cells and tissues have been widely utilized in scientific research and clinical applications. All practical cryopreservation protocols require biomaterials to survive two processes: cooling down to cryogenic storage temperature and the subsequent rewarming. Many investigations have shown that both cooling and rewarming rates are critical to the survival of cryopreserved cells, tissues, and organs [1]. Experimental evidence from a range of cell and organ model systems has suggested that better results may sometimes be obtained by rapid rewarming, particularly if the biomaterials have been cryopreserved via vitrification [2]. Unfortunately, the vitrification also introduces a new hazard — the formation of ice crystals during thawing the samples. By rewarming the vitrified biomaterials rapidly, it is possible to avoid recrystallization of the numerous micro ice nuclei formed during the cooling process [2]. For tissue samples with dimensions more than a few millimeters, the need for rapid rewarming precludes the use of the traditional approaches such as heat convection and conduction because the low thermal diffusivity of biomaterials prevents energy from conducting into the centre sufficiently quickly. Electromagnetic heating may be the only feasible method, which offers a significant advantage (i.e., heat is generated volumetrically) over conventional heating methods. However, for bulk tissue sample, the warming rate of tissue at the center of sample will inevitably be much less than that close to the surface. Such undesired results will lead to non-uniform heating, and may further result in thermal runaway, which is localized as exponential increase in temperature due to the temperature dependence of water’s dielectric properties [3]. In addition, for some cases, the warming rate of cryopreserved tissue by electromagnetic heating may still be not large enough. To solve the above problems, this study proposed an effective approach to perform rapid and uniform electromagnetic rewarming for cryopreserved bulk tissues through adjuvant use of nano-magnetoparticles. The principle of the present method is similar to that of electromagnetic induced nano-hyperthermia.