Cells should also be protected against “frostbite” MXene, the “dark horse” of the material industry, helps cell freezing and resurrection

Icing in cold conditions can be inconvenient and extremely risky for humans. Similarly, in the field of cryobiology, the formation and growth of ice can cause fatal damage to cells, tissues, organs, and other life resources during cryopreservation. Ice injuries, in particular, have become a limiting bottleneck in the field of organ transplantation.

Recently, Professor Zhao Gang of the School of Information Science and Technology of the University of Science and Technology of China cooperated with Liu Huilan, director of the First Affiliated Hospital of the University of Science and Technology of China, to achieve efficient cryogenic cryopreservation of living cells based on the synergistic ice inhibition effect of two-dimensional titanium carbide MXene nanosheets. The research results were published in The American Chemical Society- Nano.

Schematic diagram of synergistic ice inhibition effect of two-dimensional titanium carbide (Ti3C2Tx) MXene nanosheets.png

Synergistic ice inhibition effect of two-dimensional titanium carbide MXene nanosheets Provided by the research group

Cryopreservation “learned”

The so-called cryopreservation technology refers to the cells, tissues, organs and other living materials placed under a deep low temperature environment (usually -80 °C, -196 °C), under which various biochemical reactions in the organism are delayed or even suspended, and the cells are in a state of “suspended animation” or “dormancy”.

Why is it necessary to cryopreserve live cells? “This is because there is often a time lag between the acquisition of living cells and their final use, ranging from a few days to months or even years. To ensure that cells are ‘alive’ when they are used and that their biological function is still intact, they need to be refrigerated and frozen when they are at their best. Zhao Gang introduced to China Science News.

Therefore, cryopreservation, as an indispensable storage method for many life resources, plays an irreplaceable role in cell therapy, biobank establishment, regenerative medicine and other fields. For example, cryopreservated immune cells can be used to treat diseases; Freezing egg cells allows a woman’s fertility to be preserved.

At present, the internationally accepted deep and low temperature cryopreservation methods are mainly divided into two categories: slow cryopreservation method and vitrification preservation method. However, both methods face a common challenge – the re-temperature melting process before sample use requires a faster rewarming rate. If the rewarming rate is not fast enough, recrystallization or transvitalization may occur inside the sample.

“To put it simply, during the rewarming process, the Xiaoice crystals will change in shape and orientation, becoming large ice crystals, and glassy water will form ice cores again, and eventually become large ice crystals.” This process can cause fatal damage to cells, even more severely than the damage caused by ice crystal formation during the cooling process. Zhao Gang further explained that this is currently an internationally recognized challenge.

Therefore, it is crucial to achieve the synergistic suppression of ice crystals during the rewarming process. Among them, the most important thing is to find a suitable ice suppression material.


The members of the research group are doing cryomic microscopy experiments, and the research group provides pictures

Increased cell viability to 81%

Functional nanomaterials are the research hotspots of ice-suppressing materials, but most of the existing research focuses on the molecular ice inhibition effect of nanomaterials, and the research on its synergistic ice inhibition effect (such as molecular ice inhibition effect combined with photothermal or magnetothermal effects) is still rare.

In this study, the team set its sights on the “dark horse” of the materials world , the two-dimensional titanium carbide MXene nanosheet. In recent years, this material has demonstrated excellent physical and chemical properties and is widely used in energy storage and collection, electromagnetic shielding, sensors and biomedical fields.

Surprisingly, the team found that this material has a synergistic ice suppression effect, that is, passive ice suppression is combined with the active ice suppression effect of light and heat.

Therefore, the team innovatively introduced a suitable concentration of two-dimensional titanium carbide MXene nanosheets in the cryoprotectant solution to prepare a nano-cryoprotectant suspension. The suspension was then mixed and balanced with the living cell-hydrogel construct to be preserved to complete the addition of permeable cryoprotectant, and then the sample was collected into a plastic straw tube, and the tube was placed directly in liquid nitrogen to quickly complete the cooling and freezing process.

Studies have shown that during the cooling and freezing process, the two-dimensional titanium carbide MXene nanoparticles have a significant inhibitory effect on the formation and growth of ice crystals, allowing living cells to safely “suspend death”.

In the rewarming process, the two-dimensional titanium carbide MXene nanosheet gives full play to its own photothermal effect, that is, the energy absorbed by the near-infrared laser is converted into heat, which acts as an efficient space heat source, greatly improving the uniformity of the internal rewarming of the sample, and also improving the average rewarming rate of the entire sample.

Zhao Gang said, “Experimental results show that as long as the rewarming process reaches a sufficiently high rewarming rate and rewarming uniformity, the risk factors that occur in the cooling process and the hazards that may occur in the rewarming stage can be reduced or even eliminated to a certain extent, so that living cells can survive smoothly.” ”

The data show that during the cooling and melting of living cell-hydrogel constructs, the two-dimensional titanium carbide MXene nanosheets can reduce the ice damage induced by stem cell freezing, and ultimately increase the cell viability from 38.4% to 80.9%.

Develop new preservation strategies from a biomimicry perspective

In fact, cryopreservation technology is a strategy for long-term preservation, usually under normal temperature conditions, it is impossible to achieve long-term preservation of some samples and forced to take a method of reducing the temperature.

The ideal long-term preservation method is actually to introduce as few exogenous substances as possible into the biological sample system at room temperature to achieve preservation. However, at present, this cannot be done at room temperature, so it is necessary to make some efforts to reduce the temperature, which is the reason for low temperature preservation.

Zhao Gang believes that the most ideal low-temperature preservation method is actually to integrate the advantages of slow cryopreservation and vitrification preservation, and eliminate all its shortcomings of the preservation method, that is, the use of ultra-low concentration, ultra-low toxicity of low temperature protection agent, to achieve ultra-rapid cooling glass preservation.

However, this ideal cryopreservation method also faces many challenges, including finding or synthesizing, low toxicity/non-toxic, and highly effective cryoprotectants; Effectively improve the sample rewarming rate and the temperature uniformity of the deregulation process.

Zhao Gang said that in the next step, the team will explore some natural antifreeze life phenomena in nature, learn from the physical mechanism behind them, and develop new preservation strategies from the perspective of biomimicry, which is also an important research direction in the future. At the same time, it is also an important direction to use physical and engineering methods to break through the limitations of temperature change rate and temperature uniformity in the existing cryopreservation system and further improve the efficiency of glass transformation. (Source: China Science Daily Wang Min)

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