Strategies to improve islet survival and function in macroencapsulation devices for the treatment of patients with type I diabetes

Introduction: Insulin-deficient diabetes mellitus (type I diabetes, T1D) is a chronic disease that requires lifelong treatment. Pancreatic islet transplantation is a promising therapy for patients with T1D. However, the survival and function of transplanted islets are limited by the immune response and lack of oxygen supply. To meet these challenges, there is a need for advanced encapsulation systems that can protect and support the transplanted islets. This study proposes strategies to improve the microenvironment, distribution and oxygen provision of islet in a modular macroencapsulation device. Methods: Pseudoislets with defined size were prepared in microwells from native neonatal porcine islet-like cell clusters (NICCs) and embedded in alginate and multi-armed poly(ethylene glycol) (starPEG)-glycosaminoglycan (GAG) hydrogels. The viability and function of the pseudoislets were assessed using glucose-stimulated insulin secretion (GSIS) assay, and fluorescence microscopy after antibody as well as fluorescein diacetate (FDA) and propidium iodide (PI) staining. An intrinsic disk-shaped oxygen generating module was designed and fabricated by embedding calcium peroxide (CaO2) in poly(dimethylsiloxane) (PDMS) utilizing 3D-printing and PDMS molding techniques. Moreover, finite element analysis was used to simulate the oxygen distribution inside and around single islets with different diameter immobilized in a hydrogel in the absence and presence of an additional oxygen supply (COMSOL Multiphysics®). Results: Pseudoislets embedded in starPEG-heparin hydrogels showed a higher viability compared to those in an alginate hydrogel and naked pseudoislets. The PDMS-CaO2 oxygen-generating disks were characterized with regards to their oxygen release profile, and were shown to produce sufficient amounts of oxygen over a period of 28 days. However, computational simulation confirmed the oxygen deficiency in larger islets and their tendency to form a hypoxic core even in the presence of an additional oxygen source. Further studies are required to optimize the oxygen supply to the transplanted islets in the early post-transplantation period. Conclusion: The proposed strategies of embedding pseudoislets of defined size in an advanced artificial matrix and of a sustained oxygen release via a customized oxygen generating module address challenges of currently existing macroencapsulation systems for the treatment of T1D. They have the potential to improve the survival and function of the islet graft. This will be further investigated in ongoing studies. This work was supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) (Project ID 213602983 – TRR 127). The authors thank Dr. med. vet. Elisabeth Kemter, Martin Kraetzl and Sarah Grimus (LMU, Munich) for providing the isolated neonatal porcine islets. References: 1. Ludwig, B. et al., Proc. Natl. Acad. Sci. USA, 114, 11745-11750, 2017 2. Freudenberg, U., et al., Adv. Mater., 28: 8861-8891, 2016 3. Pedraza, E. et al., Proc. Natl. Acad. Sci. USA, 109- 4245, 2012