The purpose is to help guide you in selecting the appropriate cryogenic product for your long-term storage needs.
This includes why you need cryogenic temperatures, various applications for cryogenic storage, different methods of cryogenic storage, differences between LN2 storage vessels, differences between mechanical and LN2 storage, and sample preparation.
Why choose cryogenic temperatures for storage?
Maintain sample viability! Cryogenic temperatures are necessary for long term or indefinite storage and critical sample preservation. The temperature of –130C is the point of “Glass Transition” and where all metabolic activity ceases to exist. Therefore, at temperatures of –130C or colder, the aging process stops and cells can be store indefinitely.
What applications would you need cryogenic storage for?
The following are some examples of specimens stored in cryogenic temperatures:
· Bone marrow
· Stem Cells
· Heart valves
Samples for long term research where patients may be deceased such as HIV Aids virus or any similar situation
What methods are available for cryogenic storage?
Basically there are two types of equipment for storing samples in cryogenic temperatures. One is a mechanical cryogenic freezer, which cools with means of a refrigeration system consisting of an insulated foamed-in-place cabinet, compressor, evaporator and refrigerants. The other type of equipment is an LN2 storage tank, which maintains temperature by means of a vacuum insulated tank and liquid nitrogen. There are several varieties of LN2 storage tanks, which consist of auto-fill or manual fill and vapor phase or liquid phase. All of which are really a customer’s preference. We can discuss the advantages and disadvantages of each and help the customer select the one that is best suited for their application.
What are some of the basic differences between LN2 Storage?
The manual fill tanks are usually used for quantities of samples ranging from a couple hundred to approximately 6,000 vials. These tanks have to be manually filled with liquid nitrogen, but have much longer holding times due to a smaller neck opening, which reduces the static evaporation rate. The auto-fill tanks are much more convenient and provide much larger storage capacities, ranging approximately from 6,000 to 39,000 vials. The auto-fill tanks do provide larger storage capacities, but also use more liquid nitrogen due to larger neck openings and pre-cooling of lines during an auto-fill.
What type of sample storage systems is available?
We are capable of providing solutions for storing vials, straws, and bags by means of boxes, canes, or canisters. See Rack and Canister Guide or accessory section of each brochure for more details.
What is the difference between vapor phase and liquid phase?
Again, this is a customer preference. Many customers choose to store in liquid phase particularly in liquid phase for several reasons. One, it helps provide more uniform temperatures when everything is submerged in liquid at a temperature of –196C. And the other reason is for safety margin. Meaning that in the event of a natural disaster (such as hurricanes, floods, earthquakes, snow or ice storms, ect.) the LN2 supplier couldn’t make delivery for some reason; you have several days of safe storage due to
the fact that the average static evaporation rate of the auto-fill tank is approximately one inch per day. Therefore, if you had 25” of liquid in your auto-fill storage tank, you would have approximately 20 days of safety margin (with no lid openings or heat loads inserted) before you have to start being concerned.
However, storing in liquid phase will use more LN2 due to the fact that when you remove a rack, their will be more LN2 evaporation.
A paper written several years ago about the possibility of cross contamination (if liquid would enter one vial and transport a sample into another vial) in liquid phase. Due to this article, several customers are now choosing vapor phase, whereas the samples are not submerged under liquid. In this case, you eliminate any remote possibility of cross contamination, but don’t have as much safety margin in terms storage time in the event the LN2 supplier can’t make delivery due to natural disasters such as hurricanes, earthquakes, ice or snowstorms, etc.
What is the difference between LN2 cryogenic storage and mechanical cryogenic storage and why should I choose one method over the other?
Some manufacturers will try to lead you specifically in one direction or another. This is generally due to the fact they do not have both types of equipment (mechanical cryogenic freezers as well as manual and auto-fill LN2 tanks) to offer.
There are advantages and disadvantages to both types of systems. Thermo Scientific is the only manufacturer that makes both the mechanical cryogenic freezers and liquid nitrogen storage vessels. This allows the customer to make a choice depending on what their needs are, instead of someone trying to sell one or the other because that is all they have to offer.
Below is a list of advantages and disadvantages of both systems. This will provide a better understanding of both systems and allow you to make a choice based on your specific needs.
The mechanical cryogenic freezer – Advantages
· Provides a nice uniform temperature of –140C or –150C depending on the size of cabinet selected. The –150C chamber is of the smaller size, but does provide a little more margin of safety it terms of holding time (in the event of a power failure).
In these cabinets there is no gradient temperature differences
throughout the top and bottom of the chamber, therefore, providing more temperature stability.
· If by chance you do not have to budget or personally pay for electricity, this can be a savings for you due to the fact you don’t have to constantly purchase LN2.
· Not having to use LN2 may be better due to concerns about safety. Whether it would be in regards to handling it or affixation from it.
The mechanical cryogenic freezer – Disadvantages
· A mechanical cryogenic freezer doesn’t have as much margin of safety in terms of time. Meaning if you had a power failure or mechanical failure the cabinet will start to warm up and you do not want to get above –130C, which is the critical point of temperature not to exceed.
· Due to the fact you are storing precious samples in a cryogenic freezer, you should consider an LN2 back-up system. In which case you will be using LN2 anyhow. Liquid nitrogen will be boiling off whether you are using it or not. Therefore, still having to budget for LN2.
· A mechanical cryogenic freezer is noisier and generates heat into the room, which may require larger HVAC systems to handle it.
The auto-fill LN2 storage tank – Advantages
· Provides good safety margin in terms of time. Meaning in the event of a power failure or mechanical failure, the time of static evaporation rate is fairly slow. Therefore providing two to three days of holding time without having to do anything.
· In the event of a power fail or mechanical fail, you can still manually fill the storage tank.
· Due to the fact there is no compressor, there is no noise (other than a liquid fill) or heat generated into the room. Making it more energy efficient.
The auto-fill LN2 storage tank – Disadvantages
· Although temperatures stay well below the critical temperature of –130C, there is a gradient temperature difference in the auto-fill vessels when storing in vapor phase.
· Due to the fact these are an auto-fill system, you will have to budget for and purchase LN2 on a consistent basis.
· There may be safety concerns in regards to handling LN2 or affixation from it.
Whether you need a mechanical cryogenic freezer or an LN2 storage tank is strictly up to you. Both systems provide cryogenic temperatures for long-term, indefinite, or critical sample storage. The purpose of this document is to provide the necessary information so that you can make the best selection based on your particular needs or preferences.
What about sample preparation for cryogenic storage?
In many cases, sample storage is not only important, but so is the method of freezing the sample. In these cases, one should consider a controlled rate freezer.
Not all samples require a controlled rate freeze however, many do and in some cases customers (GMP/GLP labs) want a controlled rate freeze.
The advantages of controlled rate freezing are to improve viability when the sample is thawed. This is due to a precise controlled slow rate of freeze through the critical phase change whereas the samples are triggered to freeze at a precise time while at the same time, absorbing the release of latent heat.
Some customers (GMP/GLP labs) choose a controlled rate freezer to “control the process”. Controlled rate freezing eliminates variation in the process, which provides reliable repeatability.
For more information, please contact us at +45 4362 4647