Expansion properties of alginate beads as cell carrier in the fluidized bed bioartificial liver

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Liquid fluidization offers the advantage of homogeneous and controllable expansion of suspended particles with limited pressure drop and favorable heat and mass transfer conditions. Bioreactors can exploit such potential and fluidized-bed-based biomedical devices acting as bioartificial liver have proved an effective alternative to other solutions. In such a systems, alginate beads hosting individual or agglomerated hepatic cells are fluidized by a perfusion medium, with the bioreactor performance significantly affected by the hydrodynamics and mass transfer. In the present work, the intrinsic and fluidization properties of alginate beads are carefully analyzed using two rigs at different scales. Appropriate alginate beads were prepared by the technique of alginate drop gelation in calcium chloride. The beads were characterized in terms of size distribution and density, obtaining a Sauter mean diameter D=813μm and density ρ=1020kg/m3. The latter value is very close to usual perfusion fluids, requiring careful evaluation also of the liquid properties. Expansion properties were evaluated for free alginate beads (i.e. without hepatic cells) using appropriate saline solutions as fluidization medium. Bed expansion tests over a wide range of voidage values have been conducted in a 1-cm diameter column used for perfusion during in vitro experiments as well as in a 10-cm diameter column close to human size bioreactor at ambient (20°C) conditions. Expansion data, terminal velocity measurements and velocity-voidage plots are reported and elaborated on in terms of Richardson-Zaki parameters.