Effective cellular cryopreservation while maintaining high cell viability is achieved by preventing intracellular and extracellular ice crystal formation using the Cells Alive System (CAS), a programmed freezer that applies a magnetic field. Here, the optimal temperature settings of the CAS were determined using rat sciatic nerves as a model tissue. Firstly, it was found that Schwann cell survival was increased by pre-cooling the samples in the ice crystal formation zone, increasing the freeze-thaw speed, and freezing-thawing in a magnetic field. Secondly, the setting (intensity and frequency) of the magnetic field at freezing-thawing was changed, and the optimum magnetic field strength was determined by evaluating cell viability. At the set temperature excluding previous studies, the minimum temperature was set to - 50 °C and kept frozen for 15 min, and then thawed immediately. The highest cell viability (27%) was achieved at 0.67 mT (intensity 3 [29.6 V] and frequency setting 10 [60 Hz]). The effects of the freeze-thaw program were assessed using transplanted sciatic nerve tissues removed after 2, 4, and 8 weeks. Anterior tibial muscle wet weight increased at 8 weeks in the control (without freezing) and after freezing-thawing in a magnetic field, compared to that without a magnetic field. Fluorescence staining of the sciatic nerve with anti-S100 antibodies revealed that Schwann cell counts increased at the transplanted site (at 8 weeks) of nerves that were freeze-thawed in a magnetic field. Overall, the CAS prevented ice crystal formation in rat sciatic nerves and could be used to maintain cell viability during cryopreservation.
Keywords: Cell Alive System; Freeze–thaw; Magnetic field frequency; Magnetic field intensity; Tissue cryopreservation.