The first generation of blood oxygenators based on porous membranes was developed only after the appearance in the 1980s of hydrophobic polypropylene (PP) membranes with submicron pores for ultrafiltration. These membranes have excellent gas permeance, a porosity of up to 55% with a pore diameter of up to 0.03 μm 171 , and a hydrophobic surface energy that prevents the penetration of plasma into the pores. However, porous PP membranes have a short lifetime of only several hours after which the gas permeance is reduced by membrane wetting (Figure ). Indeed, the adsorption of plasma proteins onto the pore's surface increases the surface energy of the material, eventually allowing the plasma to break through 154 .