Polymeric membranes used in bioreactors for bioartificial livers are generally chosen for their transport and separation properties to provide liver cells with adequate nutrients supply and avoid rejection. Possible effects of membrane surface properties on cell metabolism are generally given little consideration. The reported effects of membrane surface wettability on adherent liver cells are qualitative and inconsistent, possibly due to the variation of other surface properties and the culture in Petri dishes, often at confluence, under uncontrolled time-and space-varying metabolite concentrations. In this investigation, rat liver cells were cultured in sub-confluent adhesion on model membranes hydrophilized by physical treatment featuring varying surface wettability in a continuous-flow recycle bioreactor. Bioreactor optimization permitted to culture cells at uniform and measurable pericellular concentrations of metabolic substrates, and to challenge them with controlled increasing ammonia concentrations. Membrane surface wettability was characterized in terms of water sorption, dynamic contact angle, and oxygen content by XPS. The kinetics of oxygen consumption, ammonia elimination and urea synthesis of cells adherent on membranes with increasing wettability was characterized at increasing ammonia concentrations. Cells exhibited increasingly better metabolic functions on membranes with increasing surface wettability. Metabolic reaction rate differences were increasingly more evident at increasing ammonia concentrations. Membrane surface wettability appeared to mainly affect cell capacity to respond to the ammonia challenge. (C) 2014 Elsevier B.V. All rights reserved.