Real-time In-situ Lactate Monitoring in 3D Multi-cellular Spheroid Cultures by Using Enzyme-based Biosensors in Hanging Drop Networks

Recent advances in microfluidic technologies for cell-to-cell interaction studies

Microfluidic cell cultures are ideally positioned to become the next generation of in vitro diagnostic tools for biomedical research, where key biological processes such as cell signalling and dynamic cell-to-cell interactions can be reliably analysed under reproducible physiological cell culture conditions. In the last decade, a large number of microfluidic cell analysis systems have been developed for a variety of applications including drug target optimization, drug screening and toxicological testing. More recently, advanced in vitro microfluidic cell culture systems have emerged that are capable of replicating the complex three-dimensional architectures of tissues and organs and thus represent valid biological models for investigating the mechanism and function of human tissue structures, as well as studying the onset and progression of diseases such as cancer. In this review, we present the most important developments in single-cell, 2D and 3D microfluidic cell culture systems for studying cell-to-cell interactions published over the last 6 years, with a focus on cancer research and immunotherapy, vascular models and neuroscience. In addition, the current technological development of microdevices with more advanced physiological cell microenvironments that integrate multiple organ models, namely, the so-called body-, human- and multi-organ-on-a-chip, is reviewed.

A549 and MRC-5 cell aggregation in a microfluidic Lab-on-a-chip system

In this paper, we present a culture of A549 and MRC-5 spheroids in a microfluidic system. The aim of our work was to develop a good lung cancer model for the evaluation of drug cytotoxicity. Our research was focused on determining the progress of cell aggregation depending on such factors as the depth of culture microwells in the microdevices, a different flow rate of the introduced cell suspensions, and the addition of collagen to cell suspensions. We showed that these factors had a significant influence on spheroid formation. It was found that both MRC-5 and A549 cells exhibited higher aggregation in 500 μm microwells. We also noticed that collagen needs to be added to A549 cells to form the spheroids. Optimizing the mentioned parameters allowed us to form 3D lung tissue models in the microfluidic system during the 10-day culture. This study indicates how important an appropriate selection of the specified parameters is (e.g., geometry of the microwells in the microsystem) to obtain the spheroids characterized by high viability in the microfluidic system.

Accessing 3D microtissue metabolism: Lactate and oxygen monitoring in hepatocyte spheroids

3D hepatic microtissues, unlike 2D cell cultures, retain many of the in-vivo-like functionalities even after long-term cultivation. Such 3D cultures are increasingly applied to investigate liver damage due to drug exposure in toxicology. However, there is a need for thorough metabolic characterization of these microtissues for mechanistic understanding of effects on culture behaviour. We measured metabolic parameters from single human HepaRG hepatocyte spheroids online and continuously with electrochemical microsensors. A microsensor platform for lactate and oxygen was integrated in a standard 96-well plate. Electrochemical microsensors for lactate and oxygen allow fast, precise and continuous long-term measurement of metabolic parameters directly in the microwell. The demonstrated capability to precisely detect small concentration changes by single spheroids is the key to access their metabolism. Lactate levels in the culture medium starting from 50µM with production rates of 5µMh^-1 were monitored and precisely quantified over three days. Parallel long-term oxygen measurements showed no oxygen depletion or hypoxic conditions in the microwell. Increased lactate production by spheroids upon suppression of the aerobic metabolism was observed. The dose-dependent decrease in lactate production caused by the addition of the hepatotoxic drug Bosentan was determined. We showed that in a toxicological application, metabolic monitoring yields quantitative, online information on cell viability, which complements and supports other methods such as microscopy. The demonstrated continuous access to 3D cell culture metabolism within a standard setup improves in vitro toxicology models in replacement strategies of animal experiments. Controlling the microenvironment of such organotypic cultures has impact in tissue engineering, cancer therapy and personalized medicine.