2012|13 Annual Report Fraunhofer IGB

76 50 μm 50 μm BIOARTIFICIAL PROXIMAL TUBULE DEVICE Anke Hoppensack M.Sc., Dr.-Ing. Jan Hansmann Background and challenge The kidney has several vitally important functions such as blood homeostasis, blood pressure regulation and the remov- al of endogenous and exogenous toxic waste products from the blood. Therefore, kidney failure can rapidly lead to severe, life-threatening clinical outcomes. Current standard therapies are dialysis and donor organ transplantation. However, a con- stant shortage of donor organs exists and dialysis still has sev- eral drawbacks [1]. For instance, the body loses valuable sub- stances such as amino acids or glucose with the ﬁltrate that is generated and subsequently withdrawn during dialysis. In the body, a structure which is called the renal proximal tubule recovers the majority of these molecules after endogenous ﬁl- tration. The complexity of this functional unit cannot be mim- icked by a technical device at the moment. Therefore, one strategy to improve dialysis is to include cellular components into an extracorporeal ﬁlter system [2]. Our project partner, Advanced Technologies and Regenera- tive Medicine (ATRM), LLC, a Johnson & Johnson company, established a source of highly proliferative and functional cells from human kidney tissue [3]. Our part of the project was to develop techniques for the kidney-speciﬁc culture of these hu- man kidney-derived cells (hKDCs) and to enable their usage in a bioartiﬁcial proximal tubule device. Inﬂuence of culture substrate In a ﬁrst approach, hKDCs were cultured on commercially available synthetic membranes under standard cell culture conditions. However, cells are exposed to a variety of biologi- cal and physical cues in vivo. These cell-speciﬁc conditions guide cell differentiation and maintain cellular functionality. For the imitation of a natural microenvironment, biologically- derived scaffolds with a complex composition were used. Cell culture experiments under static conditions revealed a strong inﬂuence of the used substrate on the cells. Human KDCs that were cultured on a synthetic membrane grew in an unphysiological multilayered formation and exhibited a ﬂat morphology. In contrast, the biological matrix promoted the formation of a monolayered epithelium, which is characteristic for the proximal tubule (Fig. 1). Derivative of culture conditions and model for glucose transport Culture conditions were derived from a ﬁnite element model of the proximal tubule. In a tailor-made compartmental bio- reactor system (Fig. 2), the cell-scaffold-constructs were cul- tured dynamically. A mathematical model for the concentra- tion of glucose was developed to investigate the glucose mass transport activity of the hKDCs. The model incorporates pas- sive and active transport (Figs. 3 and 4). Transport through a cell was differentiated into inﬂux and efﬂux and the barrier of the substrate was considered. Furthermore, the glucose con- sumption by the cells was implemented. The model param- eters for glucose diffusion, consumption and transport could be calculated on the basis of experimental data. Therefore, hKDCs were cultured at the interface between a donor and acceptor compartment and the glucose concentration was measured over time in both compartments. Finally, model vali- dation was performed. PHARMACY 2 31 e

2012|13 Annual Report Fraunhofer IGB

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