Mammalian cells cultured in simulated weightlessness take advantage of a favorable environment, experiencing low shear stress and reduced turbulence. NMR spectroscopy allows the on-line noninvasive monitoring of cell growth and metabolism. With this in mind, we developed a novel bioreactor that fits into a NMR instrument and in which the simulated weightlessness conditions are obtained by a suitable medium and a flow-lift suspension. In detail, the gravitational vector acting on cells is counterbalanced by the hydrodynamic thrusts created by a bottom-up spiral flow of a fluid having increased density. We validate its efficiency (a) by calculating the main physical parameters as relative velocity, shear stress, and oxygen transport, and (b) by comparing the experimental results of growing a cell culture in the proposed bioreactor with those obtained using an established simulated weightlessness system (rotating wall vessel, NASA). As a test study we focused on the proliferation of human umbilical vein endothelial cells (HUVEC) in terms of cell viability and organization of their cytoskeleton.