Preservation of biological samples such as tissues, plasma and forensic and pathology specimens relies on maintaining proper storage temperatures and on the type of sample and analysis to be done. Sample temperatures must be monitored and facilities supported by backup systems and tracking.1 As per the FDA, frozen samples should be kept at –28 to –18 °C and refrigerated samples between –2 and –8 °C; ambient samples should be protected from heat and moisture.2
Biosample preservation monitoring and record-keeping
The importance of record-keeping is stressed in FDA Office of Regulatory Affairs publications. Dr. F. John Mills, chairman of the board of BioStorage Technologies (Indianapolis, Ind.), notes that “Many current systems are not able to comprehensively record the process of handling of samples and provide a complete historical record of the temperature at which the sample has been stored, emphasizing any deviation in temperature, particularly freeze–thaw cycles.”3
Monitoring and record-keeping are addressed by the Centers for Disease Control (CDC) in its recommendations for vaccine storage and handling4 covering what is known as the “cold chain,” from manufacturing to administering vaccines. Losses due to poor vaccine-storage practices run into thousands of dollars annually and include not only vaccine replacement but also the inconvenience of calling back for revaccination those who received compromised vaccine.
This article provides criteria to consider when purchasing equipment for biosample preservation: refrigeration systems including defrosting options, temperature capability/temperature control, alarming and record-keeping.
Refrigeration systems for biosample preservation
Advances in laboratory refrigerators and freezers along with temperature monitoring, alarm and record-keeping devices provide researchers with a wide range of equipment from which to choose. Storage capacity and storage temperature decisions are guided by lab needs and appropriate regulations and recommendations for short- or long-term biosample preservation.
Household and commercial-scale refrigerators and freezers are not recommended for use in laboratories because they lack the ability to maintain strict temperature control, which can include rapid temperature recovery when doors are opened to place or retrieve samples. While scientific refrigerators and freezers are more expensive, the cost of sample degradation due to incorrect temperature storage is far greater. Points to consider when selecting refrigeration equipment include:
Temperature capability
Scientific refrigerators typically operate from 2 °C to 10 °C and freezers from –25 °C to –10 °C. Low-temperature freezers are available for temperatures of –25°, –30° and –40 °C. Ultralow-temperature freezers can be set from –50° to –86 °C (note: lower-temperature units require more power).
Ultralow-temperature upright and chest freezers maintain internal temperatures for long-term sample storage due to efficient insulation and cabinet- and door-mounted gaskets. Equipment with separate internal compartments with individual insulated magnetic catch doors confine ambient air to the compartment being accessed. Labs that work with a large number of samples should look for ultralow-temperature freezers with compartments fitted with individual specimen racks (see Figure 1). These can hold fiberboard containers that accommodate cell dividers. Labeling compartment doors, specimen racks and fiberboard containers makes content removal and return faster and enhances operating efficiency.
Temperature monitoring and control
Key to CDC vaccine storage compliance is temperature monitoring and control. Recommendations can apply to storage of biological samples. Some scientific refrigerators and freezers have built-in capability; others can be brought into compliance with optional equipment.
Internal temperatures for biostorage and biobanking refrigeration units are best monitored with product temperature sensors. These are inserted into a bottle of glycerin or glycol to mimic the temperature of the samples because internal air temperature changes faster than sample temperature when storage unit doors are opened. Since the variation in content temperature is the important factor, product sensors avoid unnecessary temperature alarms triggered by routine door openings. Sensors may be used to record product temperature in two areas of the unit as well as air temperature.
Temperature control options range from simple dial-type thermostats with letters or numbers (cold, colder, coldest) to sophisticated digital LED display microprocessor temperature controllers. The internal temperature display may be located at the bottom or near the top of smaller units. Premium scientific refrigeration systems use programmable logic controls, the best choice to maintain the absolute minimum temperature drift. High-end models also allow setting temperatures to one decimal place.
Temperature excursion alarming
This is an important feature when storing temperature-sensitive biological specimens. Alarming functions take the form of built-in digital audio and visual high/low temperature alarms, some with contacts that alert personnel elsewhere in the laboratory. Otherwise compliant equipment can be fitted with optional digital temperature alarms. These consist of internal sensors placed in bottles as described above. They are connected by wire passing over the hinge-side door gasket or through optional sensor access ports to an external control and display module.
Extremely critical temperature monitoring systems are available to provide local and remote alarming, including contacting offsite personnel by e-mail, text, phone or pager, and can be fitted to any scientific refrigerator or freezer. On-door sample storage is not recommended because opening doors causes immediate exposure to ambient conditions.
Article Source:https://www.labcompare.com/10-Featured-Articles/334037-Refrigeration-Practices-for-Biological-Sample-Preservation/
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