A common challenge in microfluidic cell cultures has to do with analysis of cell function without replacing a significant fraction of the culture volume and disturbing local concentration gradients of signals. To address this challenge, we developed a microfluidic cell culture device with an integrated bioanalysis unit to enable on-chip analysis of picoliter volumes of cell-conditioned media. The culture module consisted of an array of 140 microwells with a diameter of 300 m which were made low-binding to promote organization of cells into 3D spheroids. The bioanalysis module contained a droplet generator unit, 15 micromechanical valves and reservoirs loaded with reagents. Each 0.8 nL droplet contained an aliquot of conditioned media mixed with assay reagents. The use of microvalves allowed us to load enzymatic assay and immunoassay into sequentially generated droplets for detection of glucose and albumin, respectively. As a biological application of the microfluidic device, we evaluated hormonal stimulation and glucose consumption of hepatic spheroids. To mimic physiological processes occurring during feeding and fasting, hepatic spheroids were exposed to pancreatic hormones, insulin or glucagon. The droplet-based bioanalysis module was used to measure uptake or release of glucose upon hormonal stimulation. In the future, we intend to use this microfluidic device to mimic and measure pathophysiological processes associated with hepatic insulin resistance and diabetes in the context of metabolic syndrome.
Keywords: Automated microfluidics; Glucose metabolism; Hepatic spheroids; In-droplet assay; On-chip bioanalysis.
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