Per(i)fusion culture works on the one side with gas saturated media and on the other side the arise of gas bubbles in tubes and culture containers has to be prevented. It leads to uncontrollable changes of liquid pressure and hinders a continuous supply of medium in the developing tissue. Especially in gradient culture experiments gas bubbles have to be eliminated, since liquid pressure differences in the luminal and basal compartment will damage the tissue and lead to an unphysiological leakness.

To minimize the arise of gas bubbles in per(i)fusion culture a gas expander module was developed. The module is a bicameral system in which gas bubbles are eliminated so that they do not reach the culture container. Furtheron, when the module is placed before a gradient culture container a constant pressure of liquid in both compartments is obtained. In the lid of the module 2 ports are present to connect the basal and luminal per(i)fusion line. By this method both liquid streams can be paralled to obtain identical pressures of liquid in the basal and luminal compartment.