Optimization of Hepatocyte Spheroid Formation for Hepatic Tissue Engineering on Three-Dimensional Biodegradable Polymer within a Flow Bioreactor prior to Implantation

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Abstract
We hypothesize that in vitro conditioning of hepatocytes within biodegradable poly-L-lactic acid (PLLA) polymer matrices prior to implantation may increase hepatocyte survival and function after transplantation. The purpose of this study was to optimize the culture conditions of hepatocytes in a pulsatile flow bioreactor. PLLA discs were seeded with rat hepatocytes in a concentration of 2.5, 5, 10, 20 and 40 × 106 cells/ml. Seeded discs were exposed to recirculated perpendicular flow of 0, 7, 15, 24, 32, 52 ml/min of supplemented Williams’ Medium E and harvested after 6 days in flow culture. Only under flow conditions the hepatocytes formed spheroidal aggregates (SphA) of 50–260 µm in diameter with a liver-like morphology and active metabolic function. The number of SphA was examined by phase contrast microscopy and the reductive enzyme function of the hepatocytes was tested using MTT. Hematoxylin and eosin histology showed vital hepatocytes within the SphA less than 200 µm in diameter but central necrosis in the SphA exceeding this size. Immunohistochemical staining confirmed albumin production of hepatocytes within the SphA. The optimal cell seeding concentration was 10 × 106 cells/ml with a flow speed of 24 ml/min. SphA of hepatocytes cultured with this flow bioreactor method may prove useful as a functional unit for tissue engineering of an in vivo liver substitute.