Why Should Mammalian Cells Be Frozen Slowly?
Mammalian cells are crucial for various biological and medical research applications, including drug discovery, gene therapy, and cell-based therapies. To preserve these valuable cells for future use, they are often frozen and stored in liquid nitrogen. However, the rate at which mammalian cells are frozen plays a critical role in their survival and viability upon thawing. This article delves into the reasons why mammalian cells should be frozen slowly.
Firstly, freezing mammalian cells slowly helps to minimize the formation of ice crystals within the cells. When cells are rapidly frozen, the water inside them turns into ice crystals almost instantaneously. These ice crystals can cause mechanical damage to the cell membrane, organelles, and DNA, leading to cell death or reduced viability upon thawing. By freezing cells slowly, the ice crystals have more time to form in a controlled manner, reducing the likelihood of cell damage.
Secondly, slow freezing allows for the controlled release of solutes from the cells. During the freezing process, the concentration of solutes inside the cells increases as water molecules freeze and leave behind solutes. If the cells are frozen too quickly, the solute concentration can become too high, leading to osmotic stress and cell damage. Slow freezing enables the gradual release of solutes, helping to maintain a more physiological environment within the cells and improve their survival upon thawing.
Thirdly, slow freezing helps to reduce the formation of ice-induced reactive oxygen species (ROS). ROS are highly reactive molecules that can cause oxidative stress and damage to cellular components. Rapid freezing can generate a large amount of ROS, leading to cell damage and reduced viability. By freezing cells slowly, the production of ROS is minimized, thus protecting the cells from oxidative stress.
Furthermore, slow freezing allows for the maintenance of cell shape and structure. When cells are rapidly frozen, the rapid expansion of ice crystals can cause cells to swell and burst. This phenomenon, known as ice crystal-induced cell lysis, can result in significant loss of cellular material and reduced viability. Slow freezing helps to preserve the cell shape and structure, minimizing cell lysis and improving cell recovery upon thawing.
Lastly, slow freezing can improve the recovery of cell function after thawing. Cells frozen slowly tend to have higher viability and functionality upon thawing compared to those frozen rapidly. This is because slow freezing helps to minimize the damage to cellular components and maintain the integrity of the cell membrane and organelles. As a result, cells frozen slowly are more likely to retain their biological functions and be suitable for downstream applications.
In conclusion, mammalian cells should be frozen slowly to minimize ice crystal-induced damage, reduce osmotic stress, minimize ROS production, maintain cell shape and structure, and improve cell recovery and functionality upon thawing. By following proper freezing protocols, researchers can ensure the long-term preservation and viability of mammalian cells for various biological and medical applications.
