In blood oxygenators, membranes are responsible for physically separating the blood side from the gas side while still allowing gas exchange. The requirements to be respected by membranes for ECMO systems are, firstly, to meet the desired gas permeability as well as a suitable selectivity for O2/CO2, and to maintain them over time. The ideal membrane should allow oxygen exchange rates comparable to the human lung, thus between 210-3200 ml/min 166 . Secondly, mechanical, and chemical characteristics of the membrane should be stable and minimize or ideally avoid plasma leakage. Last but foremost, membrane materials should be hemocompatible, hence prevent protein adsorption, platelets activation, and inflammation. Hemocompatibility is so far the biggest challenge faced by membrane technology in AO.