Page 341 - Praxair - Specialty Gases and Equipment Reference Guide

Cryogenic Products

Cryopreservation Overview

Cryopreservation refers to frozen storage of biological the planned or potential use of the sample. In general, once
materials at ultra-low temperatures to maintain their critical a substance is in the solid phase (i.e., frozen), there is no
quality attributes. Cryopreservation is crucial for many types such thing as too cold. Most degenerative processes are
of cells, tissues, and cellular components in a wide variety significantly slowed in cryogenic storage due to both the
of industries and academic disciplines. Praxair offers a lower temperatures and the reduced molecular mobility.
world-class portfolio of cryogenic gases, equipment, and The glass transition temperature of water near -137 °C is
services to enable cryopreservation applications. typically identified as the critical temperature below which
molecular mobility is dramatically reduced and degradation
Risk mitigation efforts are important to avoid deterioration processes are effectively arrested. Cryogenic freezers
of precious samples stored in this manner. Key factors to generally operate at temperatures below the critical glass
consider include: type of refrigeration system, critical storage transition temperature. At warmer temperatures, such as
temperature, and cryogenic storage phase. -80 °C, degradation processes still operate, albeit slowly,
Ultra-low temperature freezers can be categorized as and can have undesirable impact over timeframes of
either mechanical, compressor-based systems or cryo- months or years.
genic systems. Mechanical systems remove heat by Cryogenic freezers can be operated in a liquid-phase or
cycling a refrigerant through low and high pressures; they vapor-phase mode. In the liquid-phase mode, the biological
are generally operated between -70 and -86 °C. Cryogenic material is immersed in the liquid nitrogen. For vapor-phase
freezers exploit the refrigeration power of liquid nitrogen, operation, most freezers hold a reservoir of liquid nitrogen
which has a normal boiling point near -196 °C. Cryogenic in the base of the freezer while the biological materials are
freezers offer access to colder storage temperatures than positioned above the reservoir in the cold nitrogen vapor
mechanical freezers. Cryogenic freezers also fundamentally created by the continuous boiling of the liquid nitrogen.
provide superior reliability and sample security. Cryogenic Today’s high efficiency vapor-phase freezers are sufficiently
freezers do not rely on compressor systems that can fail insulated to maintain operating temperatures as low as
due to electrical power disruption or mechanical breakdown. -190 °C at the top of the freezer away from the liquid nitro-
If for some reason liquid nitrogen could not be added to a gen reservoir. Storing in liquid phase provides the longest
cryogenic freezer, the highly insulated freezer will typically possible hold times and coldest possible temperature.
keep the samples below the target critical temperature for Vapor-phase freezers are preferred for many applications,
several days to weeks, depending on the quantity of liquid because they mitigate concerns over cross contamination
nitrogen in the freezer when the disruption occurred. and exposure of samples to liquid nitrogen.
The optimal temperature for which biological samples With its deep experience and extensive capabilities,
should be stored will vary depending on a number of Praxair stands ready to support its customers in selecting
factors, including type of material, surrounding matrix, and and implementing the right cryopreservation systems for
their needs.
Section E – Gas Handling Equipment

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