Acute respiratory distress syndrome (ARDS) is currently seen in huge numbers of patients worldwide due to the COVID-19 pandemic, but also before that, respiratory diseases were the third largest cause of death in the EU. Current therapy for respiratory failure includes mechanical ventilation and extracorporeal membrane oxygenation (ECMO) both associated with high morbidity and mortality. In ECMO devices the functionality of the lungs tissue membranes that are responsible for gas exchange during breathing is usually taken over by bundles of synthetic cylindrical hollow fiber membranes. Geometries and transport characteristics of standard hollow fiber membranes are not suitable for re-building the structurally complex and dynamic contracting microstructure of the mammalian lung and consequently, artificial devices to assist/replace respiration still face major limitations in size, flow characteristics and hemocompatibility that impede the development of efficient intracorporeal devices. In BioMembrOS, we want to follow a groundbreaking new biomimetic approach, and replicate main characteristics of the most effective respiration found in vertebrates, mainly birds and fish, in order to develop membrane structures that will serve as key elements for a novel generation of artificial respiration devices. To reach this goal, we will a) optimize geometry of the membrane structure by mimicking microstructure of the gills of fish to increase outer surface per membrane area, mimicking globular shape of the gas transporting inner lumen and interconnected arrangement of membrane fibers of avian respiration; b) design and control flow characteristics and boundary layer applying μPIV experimental flow investigations and structural design optimization; c) design and synthesize bi-soft segment polyurethane membranes with increased hemocompatibility and gas permeability with phase inversion; and d) verify and benchmark the boosted mass transfer capabilities by in-vitro blood tests