The multi-organ-chip (MOC) - a universal microfluidic platform for long-term tissue maintenance and substance testing

Introduction: The ever growing amount of new substances released to the market and the limited predictability of current in vitro test systems has led to a great need for new solutions for substance testing. Many drugs like troglitazone, that had to be removed from the market due to drug induced liver injury, show their toxic potential only after chronic long term exposure. But for long-term multiple dosing experiments, a controlled microenvironment is pivotal, as even minor alterations in extracellular conditions may greatly influence the cell physiology. Materials and methods: We present a micro-engineered, bioreactor based human in vitro tissue culture test system aiming to support predictive substance testing at relevant throughput. A microcirculation system interconnecting several tissue culture spaces within a PDMS-embedded microfluidic channel circuit is reproducibly perfused by a peristaltic on-chip micro-pump, providing a near physiologic fluid flow and volume to liquid ratio (Fig. 1). Results: It could be shown, that this micro-bioreactor system is capable of supporting various tissues of human origin (cell lines, primary cells and biopsies) over a culture period of up to 28 days. Single-tissue cultures as well as co-cultures of liver equivalents, generated from HepaRG and primary human hepatic stellate cells, and human skin punch biopsies were performed on the multi-organ-chip platform. Viability of the cells was assessed by TUNEL / Ki67 staining and was markedly increased compared to static controls. Furthermore, cell polarity of hepatocytes inside the liver equivalents was restored as shown by the expression of specific transporters, tight junctions and the formation of rudimentary bile canalicular like structures. Assessing the metabolic activity showed that a stable steady state with only minor fluctuations was obtained after 5-7 days of single and co-cultures. Experimental results also including the vascularization of the microcirculation channel system with human endothelial cells will be presented. Furthermore, the liver toxic effect of troglitazone could be successfully modeled in this system. An increase in the release of LDH to the culture medium could be observed during the experiment, as well as a markedly increase in dead liver cell count at troglitazone treated cultures.