Programmable freeze-substitution and cryo-embedding device.

The construction and performance of a modular and fully controllable freeze-substitution device are described. The core of the device consists of a heavy brass block providing a large, stable thermal mass. The block is composed of two perforated plates and a base plate forming nine deep wells, which enable the concomitant substitution of several samples in various substitution fluids, and in large volumes. The wells are surrounded by an isometric network of tunnels through which either liquid nitrogen or hot air can flow. The isometric network enables heat transfer across short uniform distances throughout the entire block's volume, thus minimizing temperature gradients and differences. The temperature of the substitution fluid, rather than that of the metal block, is monitored by a programmable controller, enabling the presetting of any freeze-substitution regime.