Application of Microfluidics in the Field of Diabetes and Islets

Type I Diabetes Mellitus (TIDM) is an autoimmune disease, which involves the destruction of beta-cells leading to insulin deficiency and an increase in blood glucose levels. Microencapsulation of human islets is a promising therapy for treatment of TIDM without the need for immunosuppressants. However, one disadvantage associated with microencapsulation is the possible induction of islet hypoxia due to the prevention of revascularization and an increase in the oxygen diffusion distance. In order to investigate the effects of hypoxia on encapsulated islets, a microfluidic array was developed and integrated with oxygenation control to provide and mimic various hypoxic conditions. We were able to demonstrate that hypoxia impairs the function of microencapsulated islets at the single islet level, showing a heterogeneous pattern reflected in intracellular calcium signaling, mitochondrial energetic, and redox activity. Our approach demonstrated an improvement over conventional hypoxia chambers. This work demonstrates the feasibility of array-based cellular analysis and opens up new modality to conduct informative analysis and cell-based screening for microencapsulated pancreatic islets. One of the major challenges of current in vivo tools to study islets and diabetes is the limited number of islets that can be assessed in a single device. Another challenge is the inability to satisfactorily assess the heterogeneous property of individual islets, especially when testing a large quantity of islets simultaneously. Examination of heterogeneous properties at the individual islet level often provides more detailed physiological or pathophysiological information than averaging-based population methodologies. For example, it will enable better understanding of human islet functionality from a reasonable sample size and will provide a better predictive value for islet transplant outcomes if many individual islets can be individually assessed instead of averaging a bulk response. In this report, the aim is to develop a novel microfluidic islet array, based on the hydrodynamic trapping principle, for investigating the complexity of physiological or pathophysiological behavior of individual pancreatic islets in a larger islet population. Furthermore, we aim to explore the feasibility of array-based cellular analysis to provide more informative data on pancreatic islets and to act as a platform to evaluate antidiabetic drugs. Our Lab collaboration with MIT determined that fibrosis of materials is largely dependent on the size and shape. It has been proven that islets prepared in 1.5-mm alginate capsules were able to restore blood-glucose control for up to 180 days, a period more than five times longer than for conventionally sized 0.5-mm alginate encapsuleted islet. These new findings propose that the in vivo biocompatibility of biomedical devices can be significantly enhanced simply by tuning their spherical dimensions. In third project, a new platform has been designed, verified and successfully tested that can be successfully applied to investigate and study the properties of 1.5 mm macrocapsules and also to evaluate the functionality of islets inside these microcapsules. The device is capable of immobilizing macrocapsules for short-term and long-term dynamic and static stimulation and live cell imaging. Using this new platform, we are continuing the study on macrocapsules to investigate how the size/volume of the immune-isolation material affects islet functionality. Lastly, in order to achieve insulin independence, a minimum of 5000 IEq/ kilogram patient body weight is needed per islet cell transplantation. Currently, islet quantification prior to transplantation is conducted manually, which can result in increased variability in total counts as well as being time-consuming. To overcome this challenge a microfluidic based islet quantification platform integrated with a smartphone has been proposed for accurate, cost-effective and rapid islet cell counting and quantification. In these four projects, we were able to demonstrate an array of applications for microfluidic technology in the study of both naked and encapsulated islet cells that can help to better understand diabetes

Alginate encapsulation as long-term immune protection of allogeneic pancreatic islet cells transplanted into the omental bursa of macaques

The transplantation of pancreatic islet cells could restore glycaemic control in patients with type 1 diabetes. Microspheres for islet encapsulation have enabled long-term glycaemic control in rodent models of diabetes; however, humans transplanted with equivalent microsphere formulations have experienced only transient islet graft function owing to a vigorous foreign-body response (FBR), to pericapsular fibrotic overgrowth (PFO) and, in upright bipedal species, to the sedimentation of the microspheres within the peritoneal cavity. Here, we report the results of the testing in non-human primate (NHP) models of seven alginate formulations that were efficacious in rodents, including three that led to transient islet graft function in clinical trials. All formulations elicited significant FBR and PFO 1 month post implantation; however, three chemically modified, immune-modulating alginate formulations elicited a reduced FBR. In conjunction with a minimally invasive transplantation technique into the bursa omentalis of NHPs, the most promising chemically modified alginate derivative (Z1-Y15) protected viable and glucose-responsive allogeneic islets for 4 months without the need for immunosuppression. Chemically modified alginate formulations may enable the long-term transplantation of islets for the correction of insulin deficiency.National Institutes of Health (U.S.) (Grant EB000244)National Institutes of Health (U.S.) (Grant EB000351)National Institutes of Health (U.S.) (Grant DE013023)National Institutes of Health (U.S.) (Grant CA151884