Organ-on-a-Chip Systems: Microengineering to Biomimic Living Systems

"Organ-on-a-chip" systems integrate microengineering, microfluidic technologies, and biomimetic principles to create key aspects of living organs faithfully, including critical microarchitecture, spatiotemporal cell-cell interactions, and extracellular microenvironments. This creative platform and its multiorgan integration recapitulating organ-level structures and functions can bring unprecedented benefits to a diversity of applications, such as developing human in vitro models for healthy or diseased organs, enabling the investigation of fundamental mechanisms in disease etiology and organogenesis, benefiting drug development in toxicity screening and target discovery, and potentially serving as replacements for animal testing. Recent advances in novel designs and examples for developing organ-on-a-chip platforms are reviewed. The potential for using this emerging technology in understanding human physiology including mechanical, chemical, and electrical signals with precise spatiotemporal controls are discussed. The current challenges and future directions that need to be pursued for these proof-of-concept studies are also be highlighted.

The Effect of Nitric Oxide on Ammonia Decomposition in Co-cultures of Hepatocytes and Hepatic Stellate Cells

Hepatic functions, such as albumin secretion and ammonia metabolism, are upregulated in response to hepatocyte growth factor (HGF) produced by hepatic stellate cells (HSC), as well as nitric oxide (NO) produced by endothelial cells under shear stress. However, the simultaneous effect of HSC and NO has not been previously investigated in a tri-co-culture model containing hepatocytes with HSC and endothelial cells under shear stress. We hypothesized that NO inhibits HGF production from HSC. To test this idea, we constructed a mono-culture model of hepatocytes and a co-culture model of hepatocytes and HSC and measured ammonia decomposition and HGF production in each model under NO load. Ammonia decomposition was significantly higher in the co-culture model under 0 ppm NO load, but no significant increase was observed under NO load. In the co-culture model, HGF was produced at 1.0 ng/mL under 0 ppm NO load and 0.3 ng/mL under NO load. Ammonia decomposition was increased by 1.0 ng/mL HGF, but not by 0.3 ng/mL HGF. These results indicated that NO inhibits HGF production from HSC; consequently, the effects of NO and co-culture with HSC cannot improve hepatic function simultaneously. Instead, the simultaneous effect of 1.0 ng/mL HGF and NO may further enhance hepatic function in vitro.