The effect of surface roughness of microporous membranes on the kinetics of oxygen consumption and ammonia elimination by adherent hepatocytes

In membrane hybrid liver support devices (HLSDs) using isolated hepatocytes where oxygen is transported only by diffusion to the cells, about 15-40% o f the cell mass is likely to be in direct contact with the semipermeable me mbranes used as immunoselective barriers: quantitative effects of membrane surface properties on the kinetics of hepatocyte metabolic reactions may al so affect HLSD performance. In this paper, we report our investigation of the effects of surface morpho logy of two microporous commercial membranes on the kinetics of oxygen cons umption and ammonia elimination by primary hepatocytes in adhesion culture. Isolated rat hepatocytes were cultured on polypropylene microporous membra nes with different surface roughness and pore size in a continuous-flow bio reactor whose fluid dynamics was optimized for the kinetic characterization of liver cell metabolic reactions. Collagen-coated membranes were used as the reference substratum. Hepatocyte adhesion was not significantly affecte d by membrane surface morphology. The rates of the investigated reactions i ncreased with ammonia concentration according to saturation kinetics: the v alues of kinetic parameters V-max and K-M increased as cells were cultured on the membrane with the greatest membrane surface roughness and pore size. For the reaction of oxygen consumption, V-max increased from 0.066 to 0.1 pmol h(-1) per cell as surface roughness increased from 70 to 370 nm. For t he kinetics of ammonia elimination. KM increased from 0.23 to 0.32 mM and V -max increased from 1.49 to 1.79 pmol h(-1) per cell with membrane surface roughness increasing from 70 to 370 nm. Cells cultured on collagen-coated m embranes consistently yielded the highest reaction rates. The V-max values of 0.18 and 2.84 pmol h(-1) per cell for oxygen consumption and ammonia eli mination, respectively, suggest that cell functions are also affected by th e chemical nature of the substratum.