Biomedical Microdevices

, Volume 12, Issue 3, pp 409–417

Microfluidic perifusion and imaging device for multi-parametric islet function assessment

Authors

  • Adeola F. Adewola
    • Department of Transplant/SurgeryUniversity of Illinois
  • Dongyoung Lee
    • Department of Transplant/SurgeryUniversity of Illinois
  • Tricia Harvat
    • Department of Transplant/SurgeryUniversity of Illinois
  • Javeed Mohammed
    • Department of Biomedical TechnologyKing Saud University
  • David T. Eddington
    • Department of BioengineeringUniversity of Illinois
    • Department of Transplant/SurgeryUniversity of Illinois
    • Department of BioengineeringUniversity of Illinois
    • Department of Transplant/SurgeryUniversity of Illinois
Article

DOI: 10.1007/s10544-010-9398-1

Cite this article as:
Adewola, A.F., Lee, D., Harvat, T. et al. Biomed Microdevices (2010) 12: 409. doi:10.1007/s10544-010-9398-1

Abstract

A microfluidic islet perifusion device was developed for the assessment of dynamic insulin secretion of multiple pancreatic islets and simultaneous fluorescence imaging of calcium influx and mitochondrial potential changes. The fanned out design of the second generation device optimized the efficient mixing and uniform distribution of rapid alternating solutions in the perifusion chamber and allowed for the generation of reproducible glucose gradients. Simultaneous imaging of calcium influx and mitochondrial potential changes in response to glucose stimulation showed high signal-noise ratio and spatial-temporal resolution. These results suggest that this system can be used for detailed study of the endocrine function of pancreatic islets with simultaneous imaging of intracellular ion fluxes and mitochondrial membrane potential changes. This tool can be used for quality assessment of islets preparation before transplantation and for in vitro studies of islet function.

Keywords

Islets physiologyImagingGlucose gradientMicrofluidics

1 Introduction

Microfluidic devices have emerged as valuable tools for biomedical research (Hansen and Quake 2003) and in clinical settings (Maheswaran et al. 2008). The advantage of microfluidic devices over conventional perfusion devices is that they use relatively small amounts of reagents and analytes, significantly decreasing costs. The small scale also allows leveraging of microscale phenomena such as laminar flow (Taylor et al. 2006; Mosadegh et al. 2007; Liu et al. 2008) and fast diffusion (Higgins et al. 2007) for new experimental modalities not possible with macroscale tools. Additionally, multiple tasks or assays can be integrated onto a single device for improved experimental throughput.

Condensing multiple assays into one microfluidic device has the potential to distinguish good islet preparations from poor preparations which could potentially solve one of the limitations of islet transplantations. By directly measuring metabolic viability including calcium influx and mitochondrial potential changes in response to insulin secretagogues this could provide improved predictors of islet viability function and transplant outcomes. One of the standard methods to analyze islet function is through perifusion of pancreatic islets (Cabrera et al. 2008). This well established technique is used to study the kinetics of insulin secretion. The fundamental physiological role of pancreatic beta-cells is to monitor and respond to moment-to-moment changes of blood glucose levels through insulin secretion. Under physiological conditions, insulin secretion is tightly regulated and depends on intracellular dynamic calcium changes and mitochondrial membrane potential changes. The monitoring of dynamic insulin secretion versus static insulin secretion provides a distinct advantage for understanding islet physiology and Pathophysiology. It is also of great interest for the evaluation of isolated human islets prior to transplantation to avoid transplanting dysfunctional islets that would work poorly in the recipient. Since microfluidic devices have been demonstrated to provide an ideal and even superior extracellular environment for cells including islets, several attempts have been made to apply microfluidic devices to islet studies. These studies looked at continuous perifusion with online electrophoresis immunoassay of single and multiple mouse islets. Other studies looked at calcium communication and oscillation in single islets, and a droplet-based microfluidic device using a microelectrode for manipulating and observing molecular signals was also developed (Roper et al. 2003; Rocheleau et al. 2004; Chen et al. 2008). These specialized methods exemplify the challenges and difficulties involved in the islet field; however, the technical complexity of these devices such as the fabrication and hardware requirements made them less suitable for routine laboratory and clinical use.

We have previously described the development of a simple microfluidic chip to characterize the kinetics of insulin secretion capable of single-channel fluorescence imaging, which is similar to the currently described device illustrated in Fig. 1 (Mohammed et al. 2009). There are several unique features associated with this three-layer chip. First, the bottom-most layer consists of an array of tiny circular wells (500 μm diameter and 150 μm depth) that help to immobilize the islets while exposed to flow and maximize the exposed surface area. We previously demonstrated that this design can successfully immobilize islets ranging in size from 50–500 μm at a flow rate up to 1 ml/min without islets rolling from well to well and without islet damage. Second, the device can be used simultaneously for dynamic insulin secretion and fluorescence imaging for single and multiple islets. Third, a 6-parallel channel system was developed on one chip which allowed several independent experiments to be conducted at the same time. While this microfluidic device was employed successfully, the chamber design was not optimized as Flouorescein isothiocyanate (FITC) simulations demonstrated that even at a speed of 1 ml/min, there was significant differences of fluorescence intensity between upper and lower parts of the perifusion chamber as shown in Fig. 2. There was less perifusion in the lower part of the chamber where the islets were located as compared to the upper chamber. In addition, the distribution of FITC solution in various regions of the chamber bottom was not uniform. These weaknesses could potentially limit the device application, especially when multiple islets at different regions are being studied simultaneously.
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Fig. 1

Design of the microfluidic device and experimental setup. The schematic depicts the cross-section view and experiment setup (left part) and the isometric view of a single-chamber of PDMS microfluidic device is shown in the image insert (right part). The device contains two layers. The bottom layer consists of an array of small circular (150 μm deep, 500 μm diameter) wells that help immobilize the islets exposed to flow. The top is a large circular well (perifusion chamber, 3 mm deep, and 7 mm diameter) that encompasses the array of the tiny wells. Inlet and outlet rectangular microchannels (500 mm deep, 2 mm wide) with fanned out-ends designs were connected to perifusion chamber

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Fig. 2

Software simulation of fluorescence mixing. (a) Molar concentration of dye on device surface area, (b) Molar concentration superimposed with vector profile of flow, (c) Y-cross section of velocity of flow, and (d) Velocity superimposed with vector profile of flow. Top panel images were obtained from original device and lower panel images were obtained from modified device. Left side bar represents molar concentration and right side bar represent velocity/magnitude. Both side bars increase from bottom to top

In this work, our goal was to address these limitations and develop a chip that would become a practical research tool for quantitative monitoring of dynamic insulin secretion. To do this we further characterized the capability of the system through generating and maintaining a complex chemical gradient in the device. In addition, we also developed the device to be a multiplexed system capable of simultaneous monitoring of dynamic insulin secretion in combination with multiple fluorescence probes. We also demonstrated the ability of this device to generate various stimulation profiles such as constant ramps, ramping up and down, and steps in a completely automated setup.

2 Methods and materials

2.1 Software simulation

The microfluidic devices were designed using CFD-GEOM software. For the original device, a 3-D computational grid was designed with inlet and outlet as straight channels with dimension of 2 mm in width, 19 mm in length, and 500 µm in height. With a large circular well (perifusion chamber, 7 mm wide and 3 mm deep) located in the middle. The bottom-layer consists of an array of tiny circular wells (500 μm diameter and 150 μm depth). Fluorescence simulation experiments indicated that in the original perifusion chamber there was uneven distribution with a time-delay between different regions, especially during the wash out period. We speculated that this was caused by the straight inlet design of the microchannel. To improve reagent mixing in the perifusion chamber, we applied the simulation of a computational grid using CFD-GEOM so that the inlet mixing channel tapered to the circular well was radically fanned out (inwardly) to a final width of 5 mm. Similarly, the outlet channel was designed to be radically fanned out (outwardly). Another modification was to place the inlet and outlet microchannel at the same level as the large circular well instead of being on top of the wells, intending to reduce liquid vibration and sudden hydrodynamic pressure changes. The modeled grids were used for simulating exchange of solution in the circular well and velocity of flow at an inlet flow rate of 1 ml/min in CFD-ACE software. Simulation of mixing in the device was done by setting the initial condition of the channel to have a fluid with 0 molar concentration of water and then we flowed in a fluid with 1 molar concentration of dye. The simulation results were processed using CFD-View software. These simulations were done at steady state.

2.2 Device fabrication

The device fabrication has been described previously (Mohammed et al. 2009). In brief, a 3-inch silicon wafer was first cleaned with acetone, methanol and isopropanol and dried with nitrogen gas. The silicon wafer was further treated with an oxygen plasma at 100 W for 30 s (Plasma Preen) to oxidize any residual organics. SU-8 photoresist was then spin coated on the wafer, patterned and developed using standard protocols. These steps were repeated for the second layer. PDMS was poured over each photoresist mold and cured at 80° for 1 h and 45 min. The inlet, outlet and large circular wells were formed on the appropriately cured PDMS using syringe needles or a cork borer. All of the layers were then bonded together using oxygen plasma to form the final perifusion device.

2.3 Mixing experiments

The efficiency of solution mixing in the perifusion chamber of the modified device was first characterized experimentally by using a fluorescence dye. In brief, DI water was perfused through the device for 30 s, followed by the dye (2 mM FITC, Sigma, MO) for 60 s. The dye was then flushed out with DI water. Time-lapse images were collected for different positions in the device with a high-speed, high-resolution charge-couple device (CCD, Retiga,SRV, Fast 1394 QImaging) and analyzed using image processing software (Slidebook,4.2, Olympus).

Complex glucose gradient profiles were characterized by mixing two different concentrations of glucose solutions delivered by two syringe pumps (Harvard Apparatus 22, Harvard Apparatus). One pump supplied a low glucose solution and another pump supplied a high glucose solution. The glucose solutions were mixed using a Y-shape connector (En-30726-41, Cole Palmer, Size 1/16 in. of ID) plus 10 cm tubing attached to it to ensure proper mixing before entering the inlet mixing microchannel. The flow rate and injection volume of both pumps were controlled by custom-made software developed through LabView system (Supporting Information, SI). The profiles of linear, bell-shape, and square-shape glucose gradients were assessed and compared to expected values. Glucose concentration was measured using a glucometer (Ascensia, Elites XL).

2.4 Isolation and culturing of islets of langerhans

The pancreatic islets of 8–12 weeks old C57/B 6 mice (Jackson Laboratory, Main) were isolated and cultured as previously described (Avila et al. 2006). Briefly, the pancreas was injected in a retrograde manner through the pancreatic duct with 0.375 mg/dl Collagenase P. The distended pancreas was incubated at 37°C for 15 min and shaken vigorously for 5 s to dissociate the pancreatic acinar tissue and then washed twice with HBSS. Discontinuous Ficoll (Mediatech, VA) gradients were used for islet purification. The islets were then cultured in RPMI-1640 medium supplemented with 10% fetal bovine serum (Hyclone Inc, MA) and antibiotics at 37°C.

2.5 Simultaneous islet perifusion and fluorescence imaging

For all perifusion and imaging experiments, 25–30 mice islets were incubated with 5 µM Fura-2/AM (a calcium indicator, Molecular probes, CA) and/or 2.5 µM Rhodamin 123 (Rh123, a mitochondrial potentials indicator, Sigma, MO) for 30 min at 37°C in Krebs-Ringer buffer (KRB) containing 2 mM glucose. Then islets were introduced into the temperature-controlled microfluidic device through the inlet microchannel and mounted on an inverted epifluorescence microscope (Leica DMI 4000B). The loaded islets were then perifused by a continuous flow of KRB2 at 37°C (pH 7.4) for 10 min. KRB containing different concentrations of glucose and other stimulators were administered to the islets using a peristaltic pump or syringe pumps. Multiple islets could be simultaneously observed with 10–20× objectives. Dual-wavelength Fura-2 was excited ratiometrically at 340 and 380 nm, and changes in [Ca2+]c are expressed as F340/F380 (%). Rh123 is a lipophilic cation that partitions selectively into the negatively-charged mitochondrial membrane. Hyperpolarization of the mitochondrial membrane causes uptake of Rh123 into the mitochondria and a decrease in fluorescence is observed due to intermolecular crowding and quenching. Rh123 is excited at 495 nm; Excitation wavelengths were controlled by means of suitable excitation filters (Chroma Technology) mounted in a Lambda DG-4 wavelength switcher. Emission of Fura-2/AM and Rh123 fluorescence was filtered using a Fura2/FITC polychroic beamsplitter and double band emission filter (Chroma Technology. Part number: 73,100bs). SimplePCI software (Hamamatsu Corp) was used for imaging acquisition and analysis. These images were collected with a high-speed, high-resolution charge-coupled device (Retiga-SRV, Fast 1394, QImaging). In addition, aliquots were collected by a fraction collector from the device every minute to measure insulin secretion.

2.6 Insulin ELISA method

The perfusate samples were frozen at -80°C until quantification with the ELISA kit. Insulin was measured using a Mammalian or Mice Insulin ELISA (Mercodia AB, Uppsala, Sweden) kit, according to the protocol provided by the manufacturer.

3 Results

3.1 Microfluidic device design and modification

The modified microfluidic device and experimental setup is shown in Fig. 1. The schematic depicts the cross-section view and experimental setup (left part) and an isometric view of the perifusion chamber is shown in the insert image (right part). The bottom layer of the device consists of an array of small circular (150 μm deep, 500 μm diameter) wells that help immobilize the islets exposed to flow. The next layer is a large circular well also called the perifusion chamber (3 mm deep, 7 mm diameter) that encompasses the array of the tiny wells. The modified mixing microchannel and outlet channel were placed at the same level as the perifusion chamber. A radically inward design (fanned out shape) tapered to the perifusion chamber was fabricated so that vortex fluid flowed downward into the perifusion chamber was accelerated and the flow of the liquid from the mixing chamber was unrestricted. The work energy of the liquid introduced into the perifusion chamber was substantially spent when the liquid reached the lower end of the perifusion chamber. An off-chip Y-shape mixer was also used to further help reagent mixing for the creation of a chemical gradient.

3.2 Software simulation and experimental simulation

In order to achieve a more uniform distribution of the solution in the perifusion chamber, the channel width leading to the perifusion chamber was fanned out. Simulation of the modified device was carried out to determine if there was any improvement compared to the original device. The exchange from water to dye showed that the fluorescence dye was more uniformly distributed in the modified perifusion chamber as shown in Fig. 2 bottom panel in comparison to original device shown in Fig. 2 top panel. This improvement could be due to the increase in downward flow and decrease in velocity flow of the new device showed in Fig. 2(c) and (d) bottom panel. It is imperative to have adequate flow exchanges in the perifusion chamber without disturbing the cells in the bottom wells for the imaging experiments. Our results show there was more fluid shunting in the original device as seen in Fig. 2(c) and (d) top panel which in turn leads to decreased fluid exchange times. On the other hand, the flow pattern of the fanned out channel is more evenly distributed and most of the solution flows into the perifusion chamber before exiting the device. To confirm these preliminary simulations, experiments were carried out using FITC dye as shown in Fig. 3(a) and (b). These experiments demonstrated that the fanned out channel improved the uniform distribution of the solution and reduced delay times that were observed in the original device.
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Fig. 3

Experimental mixing using Flouorescein Isothiocyanate (FITC): Plots of fluorescence intensity vs. time across different regions in the perifusion chamber during the perifusion (flow rate of 1 ml/min of DI water for 30 s followed by FITC 2 mM for 60 s and then the FITC was flushed out with DI water (intensity values are area average of n = 3 scans at a region of intensity. (a) original device, (b) modified device

Next, we tested the behavior of flow dynamics in the perifusion chamber at varying flow rates (0.25, 0.5, and 1.0 ml/ml) as shown in Fig. 4. The simulation results demonstrated that at all three flow rates, the flow dynamic profiles were almost identical. Minor expected time differences for reaching maximum fluorescence intensity and washing periods were identified but these minor discrepancies will not affect the application of this system.
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Fig. 4

Experimental mixing using Flouorescein isothiocyanate at varying flow rates. Plots of fluorescence intensity vs. time across different regions in the perifusion chamber during the perifusion at flow rate of (a) 0.25 ml/min, (b) 0.5 ml/min , and (c) 1 ml/min. DI water was flushed for 30 s followed by 2 mM FITC for 60 s and then the FITC was washed out with DI water (intensity values are area average of n = 3 scans at a region of intensity)

3.3 The creation of glucose gradients in the microfluidic network

There are several means to create a desired concentration gradient in microfluidic networks (Atencia et al. 2009; Du et al. 2009). Yet, most methods generate gradients with respect to position and not with respect to time. For these experiments, we implemented a method to expose the islets to a temporal concentration gradient. We tested the creation of various glucose gradients including profiles of linear, bell-shape, and square-shape and compared them with the expected values as shown in Fig. 5. Figure 5(a) shows a linear glucose gradient from 5 mM to 25 mM glucose (1 mM/min interval). Figure 5(b) shows a symmetric bell shape of glucose profile from 2 mM to 14 mM glucose (0.8 mM/min interval). Figure 5(c) shows a square shape glucose gradient from 5 mM to 14 mM glucose. All three of these glucose gradients created in our microfluidic network were consistent with the expected values. Experimentally we observed a controlled glucose gradient profile with this microfluidic network, indicating that the reagents were well-mixed in the Y-type mixer and inlet channel in spite of the simplicity of the geometry. Minimal deviations of the experimental profile from the theoretical profiles were observed, and these deviations would not affect the practical application of this device.
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Fig. 5

The creation of glucose gradients in the microfluidic network. Various glucose gradients were created through two syringe pumps controlled by self-developed software. (a) Linear 5–25 mM glucose vs. expected value, (b) Symmetric bell shape glucose profile at range of 2–14 mM vs. expected value, and (c) Square shape of 5–14 mM glucose vs. expected value. (n = 3 for each glucose profile)

3.4 Spatial-temporal resolution of the islet perifusion system

A sensitive analytical technique with high signal-to-noise ratios and high spatial-temporal resolution is required to achieve an accurate and fundamental understanding of the cellular mechanism involved in islets insulin secretion. In order to test spatial-temporal resolution of the system, we studied Fura-2 calcium signaling of islets in response to glucose stimulation with varying flow rate (0.25, 0.5, and 1 ml/min). Our results showed that the signal-to-noise ratio of Fura-2 fluorescence was very high (Fig. 6). The F/F0 (amplitude of signal) stimulated by 14 mM glucose in the mouse islets was also comparable to other published systems (Zhou et al. 2000; Gimi et al. 2006). With varying flow rates, there were no time-delays of the fluorescence signal, another indication of an efficient mixing in the perifusion chamber. At all three different flow rates, the system could accurately detected the typical biphasic calcium signals in response to 14 mM glucose stimulation with good spatial-temporal resolution.
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Fig. 6

Temporal resolution of calcium signaling response to glucose at varying flow speed. Rodent islets were loaded with 5 µM of Fura-2/AM and stimulated with 14 mM glucose. The representive records of calcium influx at varying flow speed setup. (a) 0.25 ml/min, (b) 0.5 ml/min, and (c) 1.0 ml/min expressed as F340/380. A representative trace from three independent experiments is shown

3.5 Simultaneous islet perifusion and multiple-channel fluorescence imaging

Simultaneous monitoring of multiple parameters in response to insulin secretion secretagogues is very important for islet studies. To date, there has been no published technique that can simultaneously conduct islet perifusion with multiple-channel fluorescence imaging, especially for the observation of multiple islets simultaneously. Building on our previous work (Mohammed et al. 2009), the present study expanded its application for multiple channel fluorescence monitoring of islets physiology. Figure 7(a) shows a representative trace of dynamic insulin secretion, calcium influx, and mitochondrial potential in response to 14 mM glucose stimulation. This figure clearly demonstrates a physiological response sequence of glucose-stimulation, with very low fluorescence noise and high spatial resolution. This system can also detect the typical biphasic pattern of secreted insulin and calcium influx. Figure 7(b) shows a record of Tolbutamide-stimulated insulin secretion, calcium influx, and mitochondrial potentials changes. Since Tolbutamide is a KATP channel closer, it had no effect on mitochondrial potentials and its effects on the calcium changes could be blocked by Diazoxide, a KATP channel opener.
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Fig. 7

Simultaneous islet perifusion and multiple-channel fluorescence imaging. (a) A representive record of temporal insulin secretion, calcium influx (Fura-2 ratio of fluorescence), and mitochondrial potentials changes (Rh123) of mouse islets stimulated with 14 mM glucose, (b) A representive record of temporal insulin secretion, calcium influx (Fura-2 ratio of fluorescence), and mitochondrial potentials changes (Rh123) of mouse islets stimulated with 250 µM Tolbultamide and followed by inhibition by 150 µM Diazoxide. These results are representive records from three independent experiments

Application of a glucose ramp on islet studies provides useful information about the islet functionality and defects, especially for studying insulin secretagogues and inhibitors. Figure 8 demonstrates the typical insulin secretion, calcium influx, and mitochondrial potential changes observed from mouse islets in response to 2–25 mM glucose stimulation.
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Fig. 8

Dynamic insulin secretion and multiple fluorescence imaging of rodent islets in the glucose ramp. A representive record of dynamic insulin secretion, calcium influx (Fura-2 ratio of fluorescence), and mitochondrial potentials changes (Rh123) of mouse islets in a glucose ramp setup (2–25 mM). The results showed a representative record from three independent experiments

With our modified design we also found that immediately after perifusion begins, a stable baseline release of insulin is established in a much shorter time (less than 10 min) when compared to the original design which took 20 min (data not shown) and no initial spike of insulin was recorded. The dramatic initial response of islets to a sudden increase of the glucose concentration has been previously described as a result of very sharp and rapid transient insulin peak followed by a return to or below baseline (Sweet et al. 2002). The modified design consisting of the fanned out inlet and outlet microchannel in addition to relocation of position could potentially be involved in dramatically reducing the hydrodynamic pressure changes experienced during the medium changes and mixing.

4 Discussion

Previously, we presented a microfluidic perifusion system capable of simultaneously imaging multiple islets with a single fluorescence probe. This manuscript details a second generation of this device along with the added capability of a controlled glucose ramping with networked syringe pumps. Our results demonstrate the inlet channels have a significant influence on the flow dynamics and reagent mixing in our microfluidic system. Simultaneous and uniform distribution of the glucose solution in the perifusion chamber to all islets is very important for the application of islet perifusion technique. An important factor when studying the islet metabolism during transition between steady states is the time required for equilibration of the tested substance in the extracellular space of tissue. Our results indicate that the modified microfluidic system has a very quick and uniform mixing and reagent exchange in the perifusion chamber with no delay in the different regions inside the chamber. This was also confirmed in software simulation and experimental setup incorporating the fanned out channel design.

The second generation microfluidic perfusion system is capable of generating a complex concentration profile with simple control of syringe pumps. The underlying principle is to combine the simple geometry of design to construct composite stimulation profiles with a higher level of complexity and consistency. Our approach was to create a practically relevant system that is able to generate user-prescribed chemical gradients and profiles. The results indicate that this system can produce a linear glucose concentration profile, symmetric bell, and step profiles with a simple Y-connector in combination with our modified fanned out channel in agreement with expected values.

The system can also impose these profiles on islets while assessing multiple metabolic parameters simultaneously. The high spatial-temporal resolution of these parameters in response to glucose is well resolved by this system. This modified device uses a relatively small chamber volume (100μL) capable of measuring a characteristic biphasic insulin secretory pattern or other hormones using different flow rates without losing spatial-temporal resolution. Although, we observed minimal deviations of the experimental profile from the theoretical profiles in the creation of our chemical gradient and also in the flow dynamics at different flow rates. Attempts to optimize the spatial-temporal resolution of one parameter often interfered with the other parameters that we are simultaneously measuring; therefore, the current geometry of our device is a compromise for all three of our measured parameters. Thus, these small deviations were acceptable for our proposed semi-quantitative evaluation of human islet function. However, future applications of this device requiring a more precise and specific application may need to address these deviations. It is also worth noting that islet recovered from the chamber after experiments were morphologically intact, confirming that this device does not generate any physical stress to the islets.

Human islet transplantation has emerged as a promising alternative for Type I diabetes treatment with varying success rates. Currently, there is a lack of a comprehensive, quantitative, and robust method to assess human islets prior to transplantation, limiting the success rate. This perifusion system presented here could facilitate the development of a systematic, non-invasive approach to assessing islet metabolic and functional integrity in a real time manner prior to transplantation. In addition, this new device outlined here has other useful applications. The functional and anatomic integrity of islets maintained with continuous flow in the perifusion chamber suggests that this modified system could be used also for other tissues and cell types.

5 Conclusion

The flow characteristics of this microfluidic perifusion system allow for high spatial-temporal resolution experiments to assess islet endocrine function and metabolic parameters in whole islets. The present perifusion system is intended to provide a controlled experimental condition to correlate the dynamics of insulin release to metabolic events such as calcium influx and mitochondrial potential changes. These studies have demonstrated that our microfluidic device is an ideal tool for studying islet physiology in real time, allowing us to evaluate multiple islets in a very small volume with a rapid response. Future studies will focus this device to evaluate human islet potency prior to transplantation which could potentially lead to predicting islet transplantation outcomes.

Acknowledgements

Work was supported by American Association of University Women International fellowship to Adeola Adewola, NIH/NCRR (U42RR023245) to Jose Oberholzer and The Chicago Diabetes Project.

Copyright information

© Springer Science+Business Media, LLC 2010