Abstract
Stem cells have the capacity to self-renew and differentiate to specialized cells, which are usually sensitive to cryopreservation. Therefore, the cell survival rate of stem cells using common cryopreservation protocol is generally not ideal. High cooling rates are crucial for decreasing the usage of cryoprotectants (CPAs) and promoting the successful vitrification of stem cells. In this study, we adopted liquid helium (LHe) instead of liquid nitrogen (LN2) as the cryogen to achieve high cooling rates for vitrifying stem cells with high viability and complete functions. A numerical model was established to simulate the cooling processes of vitrifying specimens by immersing them in LHe and LN2. The calculated results revealed higher cooling rates when plunging specimens into LHe than into LN2. The high viability of human bone-derived mesenchymal stem cells (hBMSCs) and human embryonic stem cells (hESCs) after vitrifying into LHe also shows the superiority of LHe as the cryogen. Furthermore, considerable cell viability was achieved by vitrification in LHe, even when decreasing the concentrations of CPAs. Additionally, post-vitrification, the cells still maintained high attachment and proliferation efficiency, normal stemness, and multipotential differentiation both for hBMSCs and hESCs. LHe is prospective to be employed as a universal cryogen for vitrification which has a great potential for widespread applications, including bioengineering and clinical medicine.
Highlights
Stem cell-based therapy which restores tissue structures and functions is a floushiring area in modern medicine [1]
There was no significant difference in proliferation between fresh and vitrified human bone-derived mesenchymal stem cells (hBMSCs) (Figure 5b). Human embryonic stem cells (hESCs) retained undifferentiated colony morphology after vitrification in
The results indicated that vitrified hESCs showed no significant difference in the expression of the three genes (Figure 7c)
Summary
Stem cell-based therapy which restores tissue structures and functions is a floushiring area in modern medicine [1]. Mesenchymal stem cells with immunomodulatory and immunosuppressive properties are ideal for allogeneic transplantation [2]. Human embryonic stem cells (hESCs) show excellent advantages in tissue regeneration and transplantation [3]. To follow the therapy schedule, large quantities of stem cells need to be preserved with high cellular viability and excellent functions to achieve with time. The continuous culture is expensive and time-consuming, and stem cells may lose the stemness and functions during the processes. Cryopreservation ensures the suspension of chemical, biological, and physical processes of cells at ultra-low temperatures for the long term [4], which is an important supporting technology for stem cell-based therapy [5]
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