JOURNALOF MATERIALS SCIENCE: MATERIALS IN MEDICINE 12 (2001) 959±963 The in¯uence of polymeric membrane surface free energy on cell metabolic functions L. DE BARTOLO 1 * , S. MORELLI 1 , A. BADER 2,3 , E. DRIOLI 1 1 Research Institute on Membranes and Modelling of Chemical Reactors, IRMERC-CNR, c/o University of Calabria, via P. Bucci, cubo 17/C, I-87030 Rende (CS), Italy 2 Leibniz Institute for Biotechnology and Arti®cial Organs (LEBAO), Medizinische Hochschule Hannover, Podbielskistrasse 380, D-30659 Hannover, Germany 3 Gesellschaft fu Èr Biotechnologische Forschung Braunschweig (GBF), Organ und Gewebekulturen, Mascheroder Weg 1, D-38124 Braunschweig, Germany E-mail: debartol@irmerc.cs.cnr.it In membrane bioarti®cial organs using isolated cells, polymeric semipermeable membranes are used as immunoselective barriers, means for cell oxygenation and also as substrata for adhesion of anchorage-dependent cells. The selection of cytocompatible membranes that promote in vitro celladhesionandfunctioncouldbedependentonitsmembraneproperties. In this study we investigated the physicochemical aspects of the interaction between the membrane and mammalian cells in order to provide guidelines to the selection of cytocompatible membranes. We evaluated the metabolic behavior of isolated liver cells cultured on various polymeric membranes such as the ones modi®ed by protein adsorption. The physico-chemical properties of the membranes were characterized by contact angle measurements. The surface free energy of membranes and their different parameters acid (g  ),base(g  )andLifshitz-vanderWaals(g LW )werecalculatedaccordingtoGood-vanOss's model. The adsorption of protein modi®ed markedly both contact angle and membrane surface tension. In particular, membrane surface free energy decreased drastically with increased water contact angle. For each investigated membrane we observed that liver speci®c functions of cells improve on hydrophilic membrane surfaces. For all investigated membranestherateofammoniaeliminationincreasedwithincreasingofmembranesurface free energy. # 2001 Kluwer Academic Publishers 1. Introduction In bioarti®cial organs using isolated cells, polymeric semipermeable membranes are used as immunoselective barriers between patient's blood and the xenocytes to prevent rejection [1]. Membranes also provide a large exchange area to supply cells with amounts of nutrients and oxygen necessary for their metabolism [2]. In some devices as in the case of bioarti®cial liver, membranes also act as the substrata for cell adhesion, the hepatocytes being anchorage-dependent cells [3]. Most mammalian cells must be supported by a tissue speci®c extracellular matrix, which plays an essential role in the cell proliferation and the maintenance of tissue functions of a large number of organs and tissues. In vitro the same mechanical and chemical support must be provided to cell culture microenvironment. The capacity of a membrane to perform a support function for cell culture depends on its surface properties. Surface free energy, electric charge and morphology might all affect cell attachment and its behavior either indirectly, e.g. by controlling adsorption of the proteins present in the culture medium (or secreted by the cells), or directly, e.g. by guiding cell spreading with suitable surface topo- graphy [4, 5]. As a result, such properties play a critical role in cell-substratum interaction and have to be considered in the selection of membranes suitable for biomedical devices. Previously we showed that the morphology of hepatocytes adherent to a substratum changes with its properties and that liver cells interact better with rougher and wettable membranes in comparison to non-wettable and smooth membranes [6±7]. The basis for this difference is still poorly understood but may be explained in part by variation of the amounts and conformation of adhesion proteins, which adsorb on native substratum contacting cells. Measurements of the wettability of membrane, expressed by the contact angle in the presence of different liquids permit to evaluate and to compare surface free energy of membranes with different physico-chemical properties. Such measure- ments before and after modi®cation of native membranes in culture medium might be predictive indices of their * Address to whom correspondence should be addressed. 0957±4530 # 2001 Kluwer Academic Publishers 959