Development of an oscillating magnetic field-assisted supercooling system for bovine embryo preservation

In-vitro-produced embryos have become an important biomaterial for accelerating genetic improvements in livestock, increasing the need for reliable short- and mid-term preservation strategies. This study was conducted to investigate the effects of oscillating-magnetic-field-assisted supercooling on the survival of bovine in vitro fertilization embryos. A supercooling preservation system combining Helmholtz-type coils with a precise circulating cooling chamber was designed and fabricated to maintain the embryos in a uniform supercooled state. Blastocyst-stage embryos were preserved at -4°C in a hypothermic preservation medium under exposure to an oscillating magnetic field of 10 Hz with flux densities ranging from 0 to 20 mT. The preservation medium remained stably supercooled at -4°C without freezing under all magnetic field conditions, and the magnetic flux density did not alter the cooling behavior. The embryos were preserved for 24 h and subsequently cultured for an additional 24 h to assess their post-preservation viability. Survival rates were higher in all magnetic field groups than in the control group (0 mT), with values of 48.66% (0 mT), 60.07% (5 mT), 62.85% (10 mT), 75.69% (15 mT), and 68.96% (20 mT). Notably, the 15 mT group exhibited the highest survival rate, showing a significant improvement over the control. Although the magnetic field did not affect the supercooling characteristics of the preservation solution, it markedly enhanced embryo survival at -4°C. The results demonstrated that the application of an oscillating magnetic field did not disrupt the stability of the supercooled state while also improving cellular tolerance to low-temperature stress. These findings provide a promising foundation on which to develop magnetic-field-based non-freezing preservation technologies for biological specimens.