How do you freeze something for a long period of time without it being damaged by ice crystals? You must use an ultra-low freezer fort a constant temperature below minus thirty degrees Celsius to do this. Freezing items in this manner is called vitrification.
What Ultra-Low Freezers Do
Ultra-low freezers protect biological samples by keeping them at temperatures below –30ºC. Laboratories need to keep samples at a vitrified state to keep ice crystals from forming, thus damaging the samples. Stopping ice crystals from forming is done by rapidly freezing items. This is absolutely essential for long-term storage of frozen items. Ultra-low freezers run much cooler than a normal freezer. Standard ultra-low freezers run between -45°C and -90°C. Like normal freezers they come in both vertical or horizontal unit types. Vertical units are usually used to save space.
How Ultra-Low Freezers Work
Ultra-low freezers have shelves that hold samples, and each shelf has another door that helps maintain a uniform temperature. This ensures that samples can be placed and removed without disturbing the temperature of the other samples. Ultra-low freezers are extremely insulated, and heavily sealed using a multiple sealing system.
Ultra-low Freezer use air-cooled condensers to maintain ultra-low temperatures. The condenser circulates the ultra-cooled air and forces it by fan by the refrigerant tubes. The refrigerant fluids in these tubes gaseous compounds that can easily be liquefied and have high critical temperatures and low critical pressures while limiting hazard and toxicity. Chemical refrigerants are assigned an R number which is determined systematically according to molecular structure. The best refrigerant fluids used in ultra-low freezers are R170, R23, and R290.
The only way to ensure long-term frozen storage without worrying about your samples being damaged by ice crystals and to keep the constant temperature below –30ºC is to use ultra-low freezers. It is also important to use a temperature monitoring system to ensure your ultra low freezers maintain a temperature below –30ºC.