Synchronized Microfluidic System to Dynamically Assess Pancreatic Islet Function beyond Glucose-Stimulated Insulin Secretion

The endocrine function of pancreatic islets goes beyond glucose stimulated insulin secretion (GSIS). Besides glucose, dynamic regulation through a variety of incretin hormones, drugs, and metabolites have been shown to modulate insulin secretion. The most commonly applied ex vivo and in vitro methodologies to study islet function are static in nature; carried out in standard well formats for extended incubation times. This approach ignores the dynamic nature of secretion and regulation thereof, and limits the complexity of scientific questions that may be posed. In the last decade several groups have begun using microfluidic devices to assess islet function in a dynamic environment, which aims to mimic a physiological bolus of glucose followed by imaging and secretory analysis. Thus far no commercial research device has been made available to the scientific community, requiring the in-house development of microfluidic islet analysis systems by groups aiming to take a more in-depth view of pancreatic islet function. We have developed a fabrication processes for poly-methyl methacrylate (PMMA) microfluidic chips, with micromilled channels and pockets into which islets will be hydrostatically trapped. These optically clear chips allow for direct fluorescent imaging of the trapped islets, with real-time calcium flux (Fura-2-AM) and mitochondrial potential (Rhodamine 123) assays. Using the I²C (Inter-Integrated Circuit, NXP Semiconductors) protocol, we are able to synchronize several microcontrolled syringe pumps (and a fraction collector) to produce precise concentrations of glucose, hormones, metabolites, and factors of interest in a time-dependent manner. This system has applications in our study of the effects of bariatric surgery (in rodents) on pancreatic islet function, as well as the mechanisms by which myokines may directly regulate pancreatic endocrine function.