Static magnetic field increases survival rate of dental pulp stem cells during DMSO-free cryopreservation

Abstract

Successful and efficient cryopreservation of living cells and organs is a key clinical application of regenerative medicine. Recently, magnetic cryopreservation has been reported for intact tooth banking and cryopreservation of dental tissue. The aim of this study was to assess the cryoprotective effects of static magnetic fields (SMFs) on human dental pulp stem cells (DPSCs) during cryopreservation. Human DPSCs isolated from extracted teeth were frozen with a 0.4-T or 0.8-T SMF and then stored at -196 °C for 24 h. During freezing, the cells were suspended in freezing media containing with 0, 3 or 10% DMSO. After thawing, the changes in survival rate of the DPSCs were determined by flow cytometry. To understand the possible cryoprotective mechanisms of the SMF, the membrane fluidity of SMF-exposed DPSCs was tested. The results showed that when the freezing medium was DMSO-free, the survival rates of the thawed DPSCs increased 2- or 2.5-fold when the cells were exposed to 0.4-T or 0.8-T SMFs, respectively (p < 0.01). In addition, after exposure to the 0.4-T SMF, the fluorescence anisotropy of the DPSCs increased significantly (p < 0.01) in the hydrophilic region. These results show that SMF exposure improved DMSO-free cryopreservation. This phenomenon may be due to the improvement of membrane stability for resisting damage caused by ice crystals during the freezing procedure.

Effects of Magnetic Fields on Freezing: Application to Biological Products

“…They suggested that the cryoprotective effect of static MFs is not because of MF effects on water molecules, but to enhanced biophysical stability of the cell membrane that reduces dehydration damage during freezing. Similar results and conclusions were found by Lin and others () after freezing dental pulp stem cells in static MFs of 400 and 800 mT.…”

“…To do so, it is necessary to evaluate magnetic effects not only in water but also in other molecules that could be affected by MFs. Thus, as mentioned before, Lin and others (,b, ) have already pointed out the role that phospholipids could play in the cryoprotective effect of static MFs. Moreover, Kobayashi and Kirschvink () suggested that the presence of ferromagnetic materials in biological tissues, principally biologically precipitated magnetite (Fe 2 O 4 ), could be relevant to inhibit ice nucleation.…”

“…For this reason, the interest of the scientific community on magnetic freezing is increasing. Several authors, from different universities and research centers, have performed experiments to assess the effect of MFs on freezing of a wide variety of products: water (Semikhina and Kiselev ; Aleksandrov and others ), aqueous solutions (Rohatgi and others ; Iwasaka and others ; Mok and others ), nanofluids (Jia and others ), foods (Watanabe and others ; James and others ), cells (Kaku and others ; Lin and others ), tissues (Lee and others ), organs (Samanpachin and others ; Niino and others ), and even organisms (Naito and others ; Morono and others ). The experiments have been carried out in both commercial equipment (Yamamoto and others ; Kaku and others ; Lee and others ; James and others ) and lab prototypes specially designed for the trials (Rohatgi and others ; Suzuki and others ; Lou and others ).…”

Static magnetic field regulates proliferation, migration, differentiation and YAP/TAZ activation of human dental pulp stem cells

“…However, the optimum SMF magnitude to promote cell proliferation is yet to be determined. Lew et al () demonstrated that 0.4‐T SMF significantly enhanced the proliferation of DPSCs (Lin et al, ). It was also reported that 60 and 120 μT of SMF could promote the proliferation of endothelial cells (Martino, Perea, Hopfner, Ferguson, & Wintermantel, ).…”

“…Bondemark et al () indicated that there are no changes in human dental pulp or gingival tissue adjacent to the magnet implants. Lew et al () and Lin et al () reported that 0.4‐Tesla (T) SMF promotes DPSCs proliferation. A 0.29‐T SMF does not influence the cell cycle and proliferation but accelerate the osteogenic differentiation and mineralization of dental pulp cells (Hsu & Chang, ).…”