Fig. 1.

Typical cooling curves for PCDs. PCDs were operated according to the manufacturer's instructions. Thin wire thermocouples (TWTc) were inserted through adapted PCD lids into the centre of spe­cially adapted cryovials containing 1 mL of CPA (10% DMSO in FBS). These were then placed in the PCD. The remaining spaces were filled with cryovials containing 1 mL of CPA. All cryovials were equilibrated at 20°C for between 20 and 30 min before transfer of the PCD to a monitored, controlled-access −80°C freezer. The temperature was recorded every 6 s for 5 h using a multi-channel datalogger. The illustrations show position of the TWTc. Mean cooling rate (MCR) between −10 and −40°C was based on the number of technical replicates per experiment shown on the graph. A minimum of 3 experiments were performed in each group. A PCDs Mr Frosty and CoolCell 12. B CoolCell FTS30 (note reduced cooling rate compared to the CoolCell 12). C Stacked PCDs. Two Mr Frostys were treated as above but stacked on top of each other and placed within the same compartment of the −80°C freezer. Of the 4 TWTc shown, two were housed in the upper and two in the lower PCD. Note the significantly reduced cooling rate for cryovials in the upper PCD.