ULT or Cryogenic Temperatures?
What Are the Best Biosample Freezer Storage Options?
Ultra-Low Temperature (ULT) storage at -80°C, which is above true cryogenic conditions, is employed at virtually every research facility. The standard method to achieve these temperatures is a mechanical compressor-driven storage system. These freezers were originally designed as an alternative to dry ice since for many years that was the only low-temperature refrigeration option available to research scientists. Thankfully, we’ve evolved, and there are new solutions for biosample storage.
What’s the Best Storage Temperature for Biosamples?
The temperature requirement for material storage requires several important factors to be considered:
- Type of material being stored
- Reason for storage
- Expected duration of the storage / potential future use after the initial research is completed
ULT (-80°C) is a good storage temperature for many types of biosamples because it slows down the rate of molecular degradation. If managed correctly, the samples can be stored at -80°C for several years without significant loss of quality. However, some samples, such as certain proteins and antibodies, need to be stored at much lower temperatures.
Material with Inherent Viability
For biologics which have inherent viability, storage at any temperature above -135°C effectively delays loss of viability but does not prevent it. If you are storing material for a long-term study, planning a follow-up study in the future or are required to maintain material viability for future research, storage above -135°C is not a good option. You need a true cryogenic option of -190°C.
Having decided on the correct storage temperature, the next issue is how to create this environment for the long term. Key points to consider include:
- Safety
- Stability
- Temperature variation
- Ability of the environment to react to stress
- Operating costs
When providing cold space for any reason, the defining factor for the above criteria is based on insulation quality. The removal of energy from the freezer space to create the optimal temperature environment can be achieved in two ways:
- Mechanical compressor
- Sacrificial refrigerant
The effectiveness of each method is primarily determined by the inherent heat leak of the environment employed.
Mechanical Compressor-Based Freezers
A typical mechanical compressor-based freezer, when operated at -80°C, has a heat leak of between 1 and 3KW depending on the age of the unit. Other factors negatively influencing the compressor system include insulation degradation and breakdown of heat removal efficiency due to aging. Heat is constantly being removed by the cooling system and released to the surrounding space, which then must be removed by external cooling (facility A/C) since the rise in temperature around the storage unit reduces the cooling efficiency of the system. This additional mechanical stress on the compressor unit causes a drop in efficiency, higher power consumption and mechanical failure if not corrected. In addition to these effects, the ability of the system to recover from any additional stress placed on the cold space, such as opening the door or adding warm material, is significantly reduced since the effective cooling cycle time of the unit is often already at maximum.
Sacrificial Refrigerant-Based Freezers (SRBF)
Basing a cold space provision on a sacrificial refrigerant system, such as liquid nitrogen, has multiple benefits.
- The cold space container has, at -80°C, a significantly lower heat leak (approximately 0.008KW) and is 3 orders of magnitude lower than the mechanical system due to the vacuum construction of the vessel.
- As the sacrificial refrigerant based system is actively cooled, any stress placed on the system by opening the lid to access material or placing warm material into the storage area is actively compensated for by “boiling off” more refrigerant.
Typically, a 5° temperature rise in the SRBF storage area can be compensated for in less than a minute, delivering a significantly more stable temperature environment. A compressor-based system in this situation can take several hours to fully compensate and stabilize the temperature.
The main benefit of the SRBF system is demonstrated when a major stress point is encountered. If, for example, power is completely cut to the cold space and no backup generation is available, a mechanical based cold space (due to the relatively poor insulation) will experience a temperature rise of 20° an hour. In the same scenario, the SRBF system will sustain the interior environment for 72 to 96 hours before gaining the same temperature rise when operated at a specific temperature. Equilibrated by an LN2 reservoir, the temperature can be maintained for several weeks.
Finally, because power consumption of the more efficient SRBF vacuum vessel is much lower and there is no net warming effect on the surroundings, heat is absorbed by the sacrificial refrigerant rather than being expelled into the room. The net power savings compared to the mechanical compressor, plus facility air conditioning, can be 5KW/Hr. Since the only net emission from the liquid nitrogen-cooled system is N2 gas, there is no associated carbon footprint which provides an obvious benefit for operations focused on sustainability goals.
IC Biomedical Radiance Cooling Freezer Technology (RCFT)
For the past 18 months, IC Biomedical has worked on the design and build of the world’s first radiance-cooled liquid nitrogen-based storage system – the new Revolution high-capacity freezer series. Revolution offers a capacity equivalent to three large compressor-based systems, unmatched sample storage density and provides significant floor space savings at any repository facility. Similarly, the 96-hour temperature hold without power reduces the requirement for backup power generation and massively reduces the load and cost of AC systems.
Cooled with a patent-pending liquid nitrogen atomization system, temperatures can be set at any point between -20° and -190°C with a control band as narrow as +/- 2°C and a maximum temperature variation within the sample space of +/- 3°C. Maintenance costs are very low with no consumable parts and running costs demonstrate considerable savings over electrically powered systems.
Greater Peace of Mind
The major benefit to the user is the quality of the storage environment and the safety that the very extended hold time can provide. The risk of an overnight failure unnoticed by staff, a unit accidentally unplugged or turned off by a cleaning crew or an ignored alarm is almost eliminated, ensuring that samples always have the maximum protection in a uniform, stable environment.
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The Revolution Series from IC Biomedical
IC Biomedical’s Radiance Freezer Technology (RFT) is now available in the new Revolution Series of high-capacity freezers, which include a feature package designed for the 21st century repository. Managed by its new PLC control system with a full connectivity suite, Revolution freezers offer:
- Individual password access with full audit trail capability
- Auto lid locking with password or RFID card access
- Patented drilled-aluminum manifold plumbing
- Five onboard RTD temperature sensors for full temperature mapping plus the capability to accept independent monitoring sensors.
- Internal LED lighting
- Built-in fog extraction systems to support full visibility to the sample area
- Motorized tray system, which can drive the tray to the desired position from the control panel before the lid of the unit is opened. This reduces the time requirement for the operator to place their hands into the system to locate material. It can also segment access to the freezer since individual users can be granted permission to access only certain sections of the shared freezer’s storage area. This helps prevent valuable materials being accessed by unauthorized users.
- Connection to external monitoring systems such as alarms, temperature monitoring systems, and building management applications that are supported via an available gateway. External notifications of events, including alarms or alerts via SMS or text message, is also available.
For more information on the new Revolution Series, click here.