Protecting Tg during retrieval, picking and storage workflow
October 21, 2015
We have talked about the rate of warming of samples, the danger of crossing Tg and best practices to avoid and control warming, but we have not performed any complete workflow experiments while monitoring sample temperature.
At the ESBB Conference in London last month I presented a poster that did just
this. We stored a sample in the BioStore™ III Cryo storage system (B3Cryo), retrieved it, moved it to a CryoPod Carrier, moved the vial to simulate a picking/identifying operation, and finally stored the vial back into the B3Cryo system. We monitored and logged the sample temperature throughout all the operations.
The good news is that at all times the sample stayed below -135°C (Tg). The cautionary news is that timing is critical during all transient exposures.
Let’s dive into the findings a bit more…
The purpose of the experiments and poster was to ensure samples did not cross Tg during a typical workflow when using new cryo technology products.
When it comes to cryogenic cold chain management, there are continued learnings and best practices we can take from these experiments that also apply to manual use.
- Timing is critical during any and all exposures outside of the initial cryogenic environment.
- When the vial was lifted out of the CryoPod (from -183°C) it warmed at 1.2°C/second. We’ve seen this warming rate before and it is encouraging to see it is repeatable.
- Conduction heat transfer improves the rate of cooling
- The vial in a cryobox cooled quicker (re-equilibrated) when placed back into the CryoPod than when put into an LN2 freezer. This is interesting, because the LN2 freezer is actually colder (-190°C vs -183°C). The reason for this is the addition of conductive heat transfer. The vial sat in a cryobox on the metal bottom of the CryoPod basket which has liquid nitrogen in an absorber underneath it. Therefore, rather than primarily cooling from convection (like in an LN2 vapour freezer), the vial experienced conductive cooling in addition to convective cooling. This resulted in much faster sample temperature recovery, as you can see in Figure 3 in the poster.
- Innocent samples offer insulation (both good and bad)
- When the vial was placed back into the LN2 freezer we placed one vial by itself and another in the middle of surrounding vials (that were already in the LN2 freezer). The surrounded vial warmed less, but cooled slower, whereas the alone vial warmed more, but cooled faster (interesting!). This is another example of a variable that effects warming/cooling and should be considered in an SOP. [Figure 4]