A Microfluidic Hanging-Drop-Based Islet Perifusion System for Studying Glucose-Stimulated Insulin Secretion From Multiple Individual Pancreatic Islets

Abstract

Islet perifusion systems can be used to monitor the highly dynamic insulin release of pancreatic islets in glucose-stimulated insulin secretion (GSIS) assays. Here, we present a new generation of the microfluidic hanging-drop-based islet perifusion platform that was developed to study the alterations in insulin secretion dynamics from single pancreatic islet microtissues at high temporal resolution. The platform was completely redesigned to increase experimental throughput and to reduce operational complexity. The experimental throughput was increased fourfold by implementing a network of interconnected hanging drops, which allows for performing GSIS assays with four individual islet microtissues in parallel with a sampling interval of 30 s. We introduced a self-regulating drop-height mechanism that enables continuous flow and maintains a constant liquid volume in the chip, which enables simple and robust operation. Upon glucose stimulation, reproducible biphasic insulin release was simultaneously observed from all islets in the system. The measured insulin concentrations showed low sample-to-sample variation as a consequence of precise liquid handling with stable drop volumes, equal flow rates in the channels, and accurately controlled sampling volumes in all four drops. The presented device will be a valuable tool in islet and diabetes research for studying dynamic insulin secretion from individual pancreatic islets.

Circuit-Based Design of Microfluidic Drop Networks

“…Microfluidic channels typically have a constant resistance given by Equations (2), (3), or (4), depending on their cross section and channel length. However, reservoirs [ 9 ], drops [ 10 , 11 , 12 , 13 ], and other elements that can fill or empty over time will lead to varying channel lengths and, therefore, are modeled as continuously variable hydraulic resistances. The filling and emptying dynamics of such reservoirs is discussed in Supplementary Materials section “Filling or emptying reservoirs” .…”

“…Mechanical fluidic sources ( Table 1 ) are the only sources able to supply a steady flow rate. The flow rate can be constant when a continuous flow through the microfluidic network is defined, e.g., for continuous sampling [ 10 , 15 ], substance dosing [ 16 ], or medium replenishment [ 11 ]. The prescribed flow rate can also vary, e.g., for applying varying shear stresses [ 17 ] or periodically increasing liquid turnover [ 11 ].…”

“…Numerically solving this set of differential equations resulted in various useful values: The flow rate through each element was computed and could be used to estimate shear stresses within a channel [ 12 , 13 ]. In turn, by modifying the channel design of a microfluidic chip, shear stresses could be tuned to ensure that physiological shear stress levels are achieved in adherent cell cultures; The flow rates at nodes and their ratios could be used to estimate molecule mixing within a microfluidic network [ 18 ]; Reservoir volumes were computed and could be used to optimize the tilting scheme to ensure that flow rates remained relatively constant during the operation of a microfluidic chip [ 12 , 13 ]; Inlet pressure for flow-rate-driven chips could be evaluated and minimized to avoid excessive pressure on fluidic sources; Drop volumes were computed as a function of time and could be used to optimize the operation of self-controlled hanging-drop setups [ 10 ]; Drop volumes were computed as a function of time and could be minimized to obviate catastrophic drop failures [ 10 , 11 , 12 ]. …”

Modeling and measuring glucose diffusion and consumption by colorectal cancer spheroids in hanging drops using integrated biosensors

“…The fluidic network consisted of four parallel channels with two hanging drops each, supplied via one or two inlets. We used continuous imaging of a free-floating 10 μm-thick SU-8 ring that sedimented to the bottom of the hanging drop to control the height of a single hanging drop 29 . This continuous imaging was performed with an inverted microscope using a 10x objective.…”

Integrated experimental-computational analysis of a liver-islet microphysiological system for human-centric diabetes research

“…We have previously presented a two-organ MPS integrating liver and pancreas, which offers an advantage over single-organ MPS for studying glucose homeostasis (Bauer et al, 2017). Recent advances in MPS technology have led to the development of single organ-MPS for both liver (Lee et al, 2007;Materne et al, 2013;Banaeiyan et al, 2017;Du et al, 2017;Ortega-Prieto et al, 2018) and pancreas (Wu Jin et al, 2021), which are two major organs involved in the maintenance of glucose homeostasis. However, single organ-MPS have limited relevance for studying metabolic diseases like T2DM, as the underlying pathophysiology involves disruption in the homeostatic cross-talk between several organs.…”