Oxygen-Releasing Coaxial Fiber Membranes for Sustained Viability of Transplanted Islet Cells

About 1.5 million Americans suffer from type 1 diabetes (T1D), which requires continuous exogenous insulin injection or islet transplantation due to the loss of pancreatic beta cells. Current treatments are effective but lead to various complications, such as hypoglycemia, insulin pump failures, ulcers, etc. Although insulin-producing islet transplantation can be a potential cure replacing current diabetic treatments, maintaining sufficient initial oxygen level and promoting blood vessel formation are major challenges for the survival of newly transplanted islets. To be viable cells require oxygen since newly transplanted cells and tissues are not yet attached to the body’s vascular system. Therefore, oxygen must be delivered via diffusion, which may be insufficient in many cases.¹ In order to provide the appropriate oxygen level after transplantation and to accelerate vascularization for transplanted cells, a two-fold approach is investigated that combines providing an initial source of oxygen using calcium peroxide (CPO) and promoting vascularization through the release of proteins in the transplant area. CPO reacts with water to produce oxygen, as well as hydrogen peroxide. Due to the possible cytotoxicity of hydrogen peroxide in islets, the enzyme catalase is added to decompose hydrogen peroxide into water and oxygen, further increasing oxygen generation with lower cytotoxicity to islets.

Coaxial electrospinning is a versatile tool to produce the drug delivery system not only providing the controlled release kinetics of encapsulated molecules, but also having an enhanced biocompatibility for seeded cells.² The delivery vehicle is based on a membrane formed from core/sheath polymer fibers, which incorporated CPO and the protein lysozyme in the PCL/PVP fiber core and the catalase in the PEO fiber sheath, and was successfully fabricated using coaxial electrospinning. SEM observation showed uniform fiber formation in a diameter of ~2.3 µm. The core-sheath structure and the presence of COP in coaxially electrospun membrane samples were confirmed using TEM and EDS analysis, respectively.

For oxygen release kinetics, the CPO/catalase membrane showed the highest oxygen release amount of ~ 23 mg/L accumulated after 8 days of incubation, compared to ~13 mg/L CPO-only membrane over the same period. The higher level of released oxygen amount from the CPO/catalase membrane confirms that the catalase enzyme was effectively incorporated into the fibers during coaxial electrospinning and maintained its functionality for converting hydrogen peroxide into oxygen molecules. The PEO-PCL/PVP membrane containing CPO with or without the enzyme catalase produced oxygen for 8 days while simultaneously releasing proteins from sheath. To investigate the effectiveness of the coaxial fiber delivery system for oxygen delivery, we have evaluated its in-vitro efficacy using a spheroid model with rat insulinoma cells, INS-1 832/2. Studying oxygen availability in 3-dimensional spheroids is crucial because it more closely replicates oxygen consumption by pancreatic islets. In hypoxic conditions, oxygen gradients within the islets cause core necrosis, with oxygen being significantly lower in the core compared to the surface. For groups without oxygen release, immediate necrosis formation was observed after only 1 day of incubation in hypoxic environment. However, all fiber membranes containing CPO significantly improved beta cell spheroid viability for 5 days or more with ~ 90% cell viability. The oxygen releasing coaxial fiber membrane has promise for sub-cutaneous islet transplantation to achieve insulin independence for individuals with Type-1 diabetes.

1. Banerjee, I., Strategies for Vascularizing Pancreatic Islets and Stem Cell–Derived Islet Organoids, Current Transplantation Reports 2021, 8 (3), 220-227.
2. Han, D.; Steckl, A. J., Coaxial Electrospinning Formation of Complex Polymer Fibers and their Applications, ChemPlusChem 2019, 84 (10), 1453-1497.