The discovery of the excellent gas transfer capacity of silicone rubber by Kammermeyer in 1957 lead the way toward a new type of non-porous membrane for gas exchange processes In microfluidic blood oxygenators, PDMS is the material of choice to fabricate flat nonporous membranes due to its excellent permeability to oxygen and carbon dioxide (PO2: 800 Barrer, PCO2: 3800 Barrer at 35°C 179 ) and its ease of microfabrication by spin coating or casting. Even though the gas permeability is an intrinsic property of the material, in the case of PDMS membranes the fabrication method, as well as surface treatments, can influence the arrangement of polymer chains, increasing or reducing the free volumes that allow gas diffusion inside the network, thus impacting the final gas permeability of the membrane.