Theoretical investigations of a novel microfluidic cooling/warming system for cell vitrification cryopreservation

Ultra-fast cooling and rewarming are essential to vitrification cryopreservation. In this work the existing cooling/warming approaches are reviewed and then a novel microfluidic system is proposed. The main concerns of the design includes: (a) enhancing the external heat transfer coefficients by utilizing micro-channel array on the chip surface; (b) increasing the sample surface versus its volume by holding the sample inside the system as an ultra-thin film. By alternatively using liquid nitrogen or warm water as its working fluid, the system can be used for both cooling and warming. To assess its application for achieving ultra-fast cooling/warming rates, the magnitudes of external heat transfer coefficients (h) during cooling and warming are theoretically investigated, and then the transient temperature distribution, the cooling/warming rates and the vitrification/devitrification tendencies of sample solution are numerically studied. It is concluded that an ultra-high h (>104 W/m2 K) can be obtained by the microfluidic system in both cooling and warming processes, which efficiently improves the cooling/warming rates and then decreases the degree of ice formation. Moreover, the system demonstrates good feasibility in the capacity of sample volume. Therefore, the microfluidic method should be a promising approach for improving vitrification cryopreservation.