State-of-the-art lung support systems are limited to short time application because of a lack of long term hemocompatibility and protein absorption on the membrane surfaces. In a highly interdisciplinary project at RWTH Aachen University a biohybrid lung assist system with endothelialised gas exchange flat membranes is developed to improve long term compatibility of oxygenators. To increase the gas exchange performance of flat membranes hollows are imprinted in the membrane surfaces. This approach is based on the research of B. J. Bell-house et al. [1], who discovered this effect, now known as Bellhouse-effect, around 1960. In this paper a processes to manufacture membrane assemblies for oxygenation with imprinted hollows on the flat membrane surfaces is reviewed.