Background: Successful cryopreservation of organs and/or tissues of large dimension is challenging due to damages by solute concentration and thermal stress caused by crystallization during cooling and devitrification/recrystallization during rewarming. The key to reduce thermal stresses in cryopreserved biomaterials during rewarming is fast and uniform heating.
Objective: To explore a hybrid warming process using two heat sources (microwave and water bath) simultaneously to achieve faster and more uniform heating.
Materials and methods: Rewarming of frozen cryoprotectants (CPA) using microwave and 37ºC water bath at the same time was experimentally studied. A helical antenna was installed at the center of a 1.8 mL cryovial. Microwave (2.4 GHz) was generated, amplified and transported to the helical antenna through the matched coaxial cables. Frozen CPA solution in the cryovial at an initial temperature of -196ºC was rewarmed by microwave and water bath. The temperature of two selected points in the sample with the maximum temperature difference was measured by thermocouples during rewarming.
Results: During rewarming of the frozen sample in 37ºC water bath without microwave, the warming rate was 70.2ºC min-1 with the maximum temperature gradient of 1.07ºC mm-1 in the sample. With microwave added to form a hybrid warming process, the warming rate was increased to be 100.5ºC min-1 with a smaller temperature gradient of 0.68ºC mm-1.
Conclusion: The study indicated that warming rate and temperature uniformity increased with the microwave-water bath hybrid heating process.