Microwave-Water Bath Hybrid Warming for Frozen Cryoprotectant Solution Using a Helical Antenna

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.

To explore a hybrid warming process using two heat sources (microwave and water bath) simultaneously to achieve faster and more uniform heating.

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.

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.

The study indicated that warming rate and temperature uniformity increased with the microwave-water bath hybrid heating process.