Internal vs. External Thread Cryotubes: How Do You Choose the Right One?
When storing cells, microorganisms, or other biological samples for extended periods, what type of tube should you use?
Laboratories use a variety of sample containers, including microcentrifuge tubes and screw-cap tubes. However, not every tube designed for routine laboratory work is suitable for low-temperature sample storage.
Cryotubes, also known as cryogenic storage tubes or cryogenic vials, are specifically designed for sample preservation under designated low-temperature conditions.
One important difference between cryotubes is their cap design: internal thread and external thread.
In this article, we explain the differences between these two designs and discuss the factors researchers should consider when choosing cryotubes for sample storage.
1. What Is a Cryotube, and How Is It Different from a Microcentrifuge Tube?
A cryotube is a container designed to store biological samples, such as cells and microorganisms, under low-temperature conditions.
Conventional microcentrifuge tubes are widely used for routine laboratory procedures, including sample dispensing, mixing, centrifugation, and short-term handling. Cryotubes, on the other hand, are designed with low-temperature storage and subsequent sample retrieval in mind.
One of the most important differences is the design of the tube and its cap.
Many conventional microcentrifuge tubes use snap caps that close by applying pressure. Cryotubes commonly feature screw caps that are secured by twisting the cap onto the tube.
However, a screw-cap design alone does not mean a tube is suitable for all cryogenic storage conditions.
Storage temperature limits and intended applications vary between products. Researchers should always review the manufacturer's specifications before use.
2. What Is the Difference Between Internal and External Thread Cryotubes?
Cryotubes are generally available in two common cap configurations: internal thread and external thread.
An internal thread cryotube has threads located inside the tube opening. Part of the cap extends into the tube as it is screwed into place.
An external thread cryotube has threads located on the outside of the tube opening, with the cap fitting over the exterior of the tube.
These differences involve more than appearance.
With an internal thread design, part of the cap enters the tube opening. Care should therefore be taken when handling cap surfaces that may come into contact with the sample or the interior of the tube.
With an external thread design, the threaded closure is positioned around the outside of the tube opening, resulting in a different arrangement of the cap and the tube's inner surfaces.
However, it is important not to assume that either thread design automatically provides better contamination prevention or sealing performance.
These characteristics depend on the overall product design, including the sealing mechanism, materials, manufacturing quality, and intended operating conditions.
The appropriate choice depends on the requirements of the laboratory application.
3. What Should You Consider When Selecting Cryotubes for Sample Storage?
Choosing a cryotube involves more than selecting its thread configuration.
One of the first considerations is the intended storage temperature and storage equipment.
Conventional laboratory freezers, ultra-low-temperature freezers, and liquid nitrogen vapor-phase storage systems operate under different conditions.
In particular, researchers should distinguish between the vapor phase and liquid phase of liquid nitrogen.
If liquid nitrogen enters a tube, it can rapidly expand into gas when the tube warms, potentially causing a dangerous increase in internal pressure.
For this reason, direct immersion in liquid nitrogen should be avoided unless the manufacturer explicitly approves the product for that application.
Another important consideration is sample volume.
Depending on the sample composition, freezing may cause volume expansion. Appropriate filling volumes should therefore be determined according to the sample characteristics and the manufacturer's recommendations.
Researchers should also consider compatibility with storage racks and cryogenic boxes, available labeling space, and the ease of opening and closing the caps.
These practical factors can have a significant impact on efficiency, particularly in laboratories that manage large numbers of samples.
4. How Does Cryotube Cap Design Affect Handling and Usability?
In addition to meeting the required storage conditions, cryotubes should be convenient to handle during routine laboratory workflows.
Laboratories managing numerous samples frequently perform operations such as opening and closing caps, identifying specimens, and organizing tubes in storage boxes.
For example, WATSON BIO LAB offers the 2.0 mL Internal Thread Cryotube (1396-201S), featuring a screw-cap closure and a self-standing tube design.
The product also incorporates a cap-locking mechanism using corresponding projections on the tube and cap, designed to assist with secure closure.
A labeling area on the top of the cap supports sample identification and organization.
Explore the product: 2.0 mL Internal Thread Cryotube – 1396-201S
Internal thread caps may sometimes become difficult to open by hand when overtightened. For workflows requiring frequent sample retrieval, ease of opening and closing should also be considered.
It is important to remember that secure closure does not necessarily guarantee suitability for every storage condition. Always follow the product's specified operating requirements.
5. Should You Choose an Internal or External Thread Cryotube?
The most suitable thread configuration depends on the type of sample being stored and the laboratory's handling procedures.
Internal thread cryotubes have a cap structure that extends into the tube opening, so researchers should take this into account when establishing procedures for cap handling and sample retrieval.
External thread cryotubes use threads on the outside of the tube opening, providing an alternative closure arrangement.
WATSON BIO LAB also offers the 2.0 mL External Thread Cryotube (1396-200S).
Its external thread configuration provides another option for laboratories selecting tubes based on their preferred cap-handling procedures and storage equipment.
Explore the product: 2.0 mL External Thread Cryotube – 1396-200S
Neither internal nor external thread designs should be considered universally superior.
Even cryotubes with the same nominal capacity can differ in dimensions, cap construction, compatible storage conditions, and handling characteristics.
Selecting a tube based on the intended application and laboratory workflow is more important than choosing a particular thread configuration by default.
Conclusion: Choose Cryotubes Based on Storage Conditions and Cap Design
Cryotubes are essential consumables designed for storing biological samples under specified low-temperature conditions.
Internal and external thread cryotubes differ in their cap structures, which can influence handling procedures, contact between cap surfaces and the tube interior, and everyday usability.
However, thread configuration alone cannot determine sealing performance or storage suitability.
Researchers should consider storage temperature, equipment, sample volume, tube dimensions, and cap operation when selecting an appropriate cryotube.
WATSON BIO LAB offers 1.0 mL and 2.0 mL cryotubes in both internal and external thread configurations, providing options for different laboratory workflows.
Selecting the right cryotube for your application helps support safer sample handling and more efficient sample management.