Effects of AC electric fields on the cryopreservation of SD rat liver tissues

The cryopreservation, which refers to preserve the cells or tissues at the subzero temperatures, will inevitably face the problem of cryoinjury caused by the ice crystallization. The application of external field during the freezing process of specimen provides a promising approach to avoid the injury and thus promote the efficiency of the preservation. In the present work, we froze the SD rat liver tissues accompanied with the AC electric field (with field strength E=0.125kV/m~1.0kV/m, frequency f=100kHz~10MHz). The cryopreservation efficiency of the approach has been evaluated by the dielectric properties and the microstructure studies of tissues after frozen for 5h and thawed. We compared the dielectric frequency spectra and the transmission electron microscopic (TEM) images of the following three groups: a) fresh tissues; b) thawed tissues after normally freezing; c) thawed tissues after freezing with AC field. The dielectric frequency spectra results suggest that some curves in group c) to group a). Furthermore, TEM images indicate that the cellular structures in group c) are less severely injured than group b). The phenomena may result from the fact that the AC electric fields affect the formation and growth of the ice crystal during the liquid-solid phase transition, and thus inhibit the cryo-injury.