Hello! The transfer of samples to a lower temperature should not be a problem. It will be good if the time taken to transport can be reduced, it's possible to use cooled racks.

Hello Giulia Lencioni

The correct procedure to cryopreserve human tissue samples would be as follows:

You may collect fresh tissue in sterile condition. You may cut small fragments (about 1-3 mm^3) and place them in cryopreservation medium in cryovials. The cryovials should be placed in isopropanol freezing container (cooling at the rate of -1 degree C /min) in -80 degree C freezer for 4 to 24 hours. Then transfer the cryovials in vapor phase liquid nitrogen for long-term storage.

You understood correctly that storing samples at -80°C is not recommended for long term storage. It is recommended only for a few months. As Georgy Leonov mentioned, transfer of human tissue samples from -80 degree C to -140 degree C should be done in less time to avoid thawing of the tissue samples. Try to keep the temperature as low as possible.

You could make use of dry ice. Depending on environmental conditions, you could use a cool box with crushed dry ice that will maintain the samples at -80 degree C. To extend the cooling duration, simply replenish the dry ice. Use of dry ice to transfer samples would help to avoid temperature rise and sample damage.

Best.