A novel multi-coaxial bioreactor for three-dimensional cultures of adherent cell types, such as liver, is described. It is composed of four tubes of increasing diameter placed one inside the other, creating four spatially isolated compartments. Liver acinar structure and physiological parameters are mimicked by sandwiching cells in the space between the two innermost semi-permeable tubes, or hollows fibers, and creating a radial flow of media from an outer compartment (ECC), through the cell mass compartment, and to an inner compartment (ICC). The outermost compartment is created by gas-permeable tubing, and the housing is used to oxygenate the perfusion media to periportal levels in the ECC. Experiments were performed using distilled water to correlate the radial flow rate (Q(r)) with (1) the pressure drop (DeltaP) between the media compartments that sandwich the cell compartment and (2) the pressure in the cell compartment (P(c)). These results were compared with the theoretical profile calculated based on the hydraulic permeability of the two innermost fibers. Phase-contrast velocity-encoded magnetic resonance imaging was used to visualize directly the axial velocities inside the bioreactor and confirm the assumptions of laminar flow and zero axial velocity at the boundaries of each compartment in the bioreactor. Axial flow rates were calculated from the magnetic resonance imaging results and were similar to the measured axial flow rates for the previously described experiments.

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A novel “multicoaxial hollow fiber bioreactor” has been developed consisting of four concentric tubes, the two innermost tubes are called hollow fibers. Bioartificial livers are created by culturing liver progenitors in the space between the two innermost hollow fibers and with culture media contained in the two compartments (intracapillary and extracapillary) sandwiching the cell compartment. The outermost compartment is used for gas exchange. A hydrodynamic model has recently been established to predict the optimum hydraulic permeability and bioreactor operational parameters to create the physicochemical environment found in the liver acinus.1 However, perfusion with serum‐free hormonally‐defined media and inoculation of cells introduces membrane fouling into the equation, and this parameter must be incorporated into the model. Using commercially available semipermeable hollow fibers (1 mm [0.65 μm pores] and 3 mm [0.1 μm pores] outer diameters [o.d]), the primary cause of resistance is the middle hollow fiber. Preliminary studies using bioreactors inoculated with isolated rat hepatocytes and perfused with serum‐containing culture media demonstrated that the middle hollow fiber is the primary site of fouling, and this fouling ultimately causes cell mortality by blocking the transfer of nutrients. Experiments were performed to determine the best commercially available middle hollow fiber for construction of bioreactors and two 3‐mm outer‐diameter middle hollow fibers were compared: polypropylene and polysulfone, with 0.2 μm and 0.1 μm pore sizes, respectively. Dead‐ended and cross flow configurations were compared for their effectiveness at reducing membrane fouling in the middle hollow fiber by determining the change in resistance with time. The results demonstrate that the 0.2‐μm pore size polypropylene hollow fiber is the best choice for construction of the multicoaxial hollow‐fiber bioreactor, and that cross flow results in two orders of magnitude lower resistance than dead‐ended flow after 36 h.