AbstractAs the majority of the polymers used as cardiovascular grafts so far do not match the elasticity of human arteries (100–1000 kPa) and the required endothelialization, a multifunctional material approach is needed to allow the adjustment of the mechanical properties while at the same time exhibiting a haemocompatible surface. Recently soft poly(n-butyl acrylate) networks (cPnBA) with adjustable mechanical properties were introduced as candidate materials with a surface that can be endothelialized. In this study, angiogenically stimulated intermediate CD163+ monocytes/macrophages (aMO2) were utilized as a cellular cytokine release system to realize the functional endothelialization of the hydrophobic cPnBA surface. We investigated the influence of co-cultured aMO2 on the morphology, density and cytokine secretion of human umbilical venous endothelial cells (HUVEC) seeded on cPnBA with an elastic modulus of around 250 kPa (cPnBA0250). A functional confluent HUVEC monolayer could be developed in the co-culture within 3 days. In contrast, the HUVEC in the monoculture exhibited stress fibres, broadened marginal filament bands and significantly more and larger cell-free areas in the monolayer, indicating incomplete cell–substrate binding. Remarkably, a functional confluent monolayer formation could only be achieved in co-cultures; it did not develop with the sole supplementation of recombinant VEGF-A165 to the HUVEC monocultures (unpublished data). The study demonstrated the multifunctional potential of cPnBA in combination with aMO2 as a cellular cytokine release system, adapting their secretion to the demand of HUVEC. In this way, a functional confluent monolayer could be generated within 3 days.