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The M-135 Cryoguard™ Thermal Exposure Indicator

Product Descriptionindicator-picture-with-buy-now-new-cropped.jpg

The M-135 Cryoguard Thermal Exposure Indicator signals thermal exposure at or above -135°C by irreversibly changing color from green to red. Upon transfer from an initial environment at or below -160⁰C to an environment at -135⁰C, the indicator exhibits a noticeable color change within two hours. The time to affect a color change dramatically decreases with increasing temperature, as illustrated in the below figure. At ~18⁰C, the time required to affect a color change is 1.9 minutes. The distinct real-time signal allows recipients and users of perishable cryopreserved materials to verify the maintenance of cryo-environments quickly and reliably.


*****The Cryoguard Activation Tool is required for proper activation of the Cryoguard M-135 Thermal Exposure Indicator. *****


Product Applications

1. Continuous monitoring of frozen materials during shipping.

2. Continuous monitoring of frozen materials while being inspected by customs agents.

3. Continuous monitoring of frozen materials during storage.

4. Continuous monitoring of frozen materials during power outages when freezer control systems are not working.

5. Continuous monitoring of frozen materials during their transient removal from freezers for handling by personnel.

6. Continuous monitoring of materials in dry shippers.

7. Indicators fit inside freezer box partitions and on cryovials and freezer canes.


M-135 indicators are used at or below -160⁰C to monitor cryopreserved materials such as heat sensitive laboratory specimens, vitrified oocytes, sperm, embryos, cord blood, and bone marrow.


Technical Specifications

What Does a Green M-135 Indicator Signify?

A completely green indicator (with no red or colorless regions) means that the material in the vicinity of the indicator was never at -135⁰C for more than two hours or at -120°C for more than 12 minutes or at -100°C for more than 6 minutes.

The graph below shows the time required at various test temperatures to affect a 10-100% color change, upon transfer of the M-135 indicator from an environment at or below -160°C to an environment at the plotted test temperature.






Activation of the M-135 Indicator



Click Here for a video of the activation procedure of the M-135 Indicator.

The activation process involves freezing the indicator in liquid nitrogen, removing it from the cryo-environment, slowly depressing its activation pin, and immediately re-freezing the indicator in liquid nitrogen. Indicators should be activated and re-frozen one at a time in order to minimize time between these two steps. After re-freezing, the indicator is ready to monitor the desired environment. When using our Activation Tool, the entire process can take place on a freezer cane.

***For more detailed activation information, please visit the Activation Guide page. 

Note: When handling frozen indicators, one should avoid contact with bare hands to prevent heat transfer and freeze burn. Warning: Protective shielding including safety glasses and gloves should be used when handling indicators that have been submersed in liquid nitrogen to prevent injury in the unlikely event that the indicator shatters upon removal from the liquid nitrogen.

Recommended Procedure:


1. Place the indicator in the bottom vial of a freezer cane with its label end up.

2. Completely freeze the indicator by immersing it in liquid nitrogen for ~10 minutes.

3. Remove the freezer cane from the liquid nitrogen canister.

NOTE: Exposure times longer than 35 seconds in steps 4 and 5 may result in a thermal exposure signal upon activation.

4. Immediately situate the indicator, still on the freezer cane, between the two panels of the activation tool. The pin should be in line with the depression on the mobile panel of the compression tool.

5. Allow the indicator to thaw slightly for about 15-25 seconds while applying gentle pressure until the pin begins to depress and can be easily compressed with the activation tool. Slowly push the pin in so that it is flush with the indicator housing. Indicators frozen for longer than the minimum freezing time in step 2 may require longer thawing times to activate the indicator without applying excessive pressure which may bend the pin or damage the activation mechanism.

6. Rapidly refreeze the indicator by immersing the freezer cane in liquid nitrogen again for ~10 minutes. This prevents a premature thermal exposure signal and readies the indicator for monitoring.

7. Place the indicator in the environment to be monitored, in any freezer can vial, with its label end up. 


Coolant Compatibility

The indicator can be used in contact with liquid nitrogen, liquid nitrogen vapor phase, and with frozen materials in dry shippers and mechanical freezers.

Shelf-life and Storage

Indicators are shipped ~8 months prior to their expiration date, which appears on the indicator label. Whether activated or not, indicators should not be used after the expiration date. Unactivated M-135 indicators should be stored at or below -18°C (e.g. in freezer). When storing M-135 Indicators in the freezer, it is best to avoid bringing unactivated indicators back to room temperature prior to activation, since this fluctuation of temperature may prematurely activate the indicators. 

Size and Packaging

Indicators are sealed in a plastic housing approximately 1" long and 0.5" in diameter. The indicator housing contains eyelets for wiring it to the monitored material. An alert label for affixing to containers monitored by the indicator is supplied with each indicator. The alert label is a 1" x 4.25" peel and stick adhesive label. 

Chemical Composition

Indicator solutions have an approximate volume of 1 mL per unit and are comprised of buffered mixtures of aqueous dyes, alcohols, glycols and water. Indicators may be safely discarded as standard waste.

Quality Assurance

Several indicators in each batch are tested in a Model 7450 CryoMed Controlled Rate Freezer using NIST calibrated thermocouple thermometers to verify that the indicators in each batch perform as specified in the above figure. 

Procedure for Disposing Used/Damaged/Expired Indicators

Indicators at room temperature may be discarded as standard toxic waste. To discard indicators that were stored in a cold environment, place them in a covered container at room temperature until completely thawed before disposal. 

X-ray Irradiation Notice

Although Cryoguard indicators can be safely exposed to x-rays from diagnostic and security scanners, the indicators should not be exposed to ionizing x-ray radiation. Exposure to ionizing x-rays will permanently deactivate the indicator, causing it to lose its ability to signal thermal exposure. Indicators may still be used with irradiated products, after the products have been irradiated.