A High Cell-Bearing Capacity Multibore Hollow Fiber Device for Macroencapsulation of Islets of Langerhans

Hydrogel-Encapsulated Pancreatic Islet Cells as a Promising Strategy for Diabetic Cell Therapy

Islet transplantation has now become a promising treatment for insulin-deficient diabetes mellitus. Compared to traditional diabetes treatments, cell therapy can restore endogenous insulin supplementation, but its large-scale clinical application is impeded by donor shortages, immune rejection, and unsuitable transplantation sites. To overcome these challenges, an increasing number of studies have attempted to transplant hydrogel-encapsulated islet cells to treat diabetes. This review mainly focuses on the strategy of hydrogel-encapsulated pancreatic islet cells for diabetic cell therapy, including different cell sources encapsulated in hydrogels, encapsulation methods, hydrogel types, and a series of accessorial manners to improve transplantation outcomes. In addition, the formation and application challenges as well as prospects are also presented.

Hypoxia within subcutaneously implanted macroencapsulation devices limits the viability and functionality of densely loaded islets

Introduction

Subcutaneous macroencapsulation devices circumvent disadvantages of intraportal islet therapy. However, a curative dose of islets within reasonably sized devices requires dense cell packing. We measured internal PO2 of implanted devices, mathematically modeled oxygen availability within devices and tested the predictions with implanted devices containing densely packed human islets.

Methods

Partial pressure of oxygen (PO2) within implanted empty devices was measured by noninvasive 19F-MRS. A mathematical model was constructed, predicting internal PO2, viability and functionality of densely packed islets as a function of external PO2. Finally, viability was measured by oxygen consumption rate (OCR) in day 7 explants loaded at various islet densities.

Results

In empty devices, PO2 was 12 mmHg or lower, despite successful external vascularization. Devices loaded with human islets implanted for 7 days, then explanted and assessed by OCR confirmed trends proffered by the model but viability was substantially lower than predicted. Co-localization of insulin and caspase-3 immunostaining suggested that apoptosis contributed to loss of beta cells.

Discussion

Measured PO2 within empty devices declined during the first few days post-transplant then modestly increased with neovascularization around the device. Viability of islets is inversely related to islet density within devices.

Immune-Protective Formulations and Process Strategies for Improved Survival and Function of Transplanted Islets

Type 1 diabetes (T1D) is an autoimmune disease caused by the immune system attacking and destroying insulin-producing β cells in the pancreas. Islet transplantation is becoming one of the most promising therapies for T1D patients. However, its clinical use is limited by substantial cell loss after islet infusion, closely related to immune reactions, including instant blood-mediated inflammatory responses, oxidative stress, and direct autoimmune attack. Especially the grafted islets are not only exposed to allogeneic immune rejection after transplantation but are also subjected to an autoimmune process that caused the original disease. Due to the development and convergence of expertise in biomaterials, nanotechnology, and immunology, protective strategies are being investigated to address this issue, including exploring novel immune protective agents, encapsulating islets with biomaterials, and searching for alternative implantation sites, or co-transplantation with functional cells. These methods have significantly increased the survival rate and function of the transplanted islets. However, most studies are still limited to animal experiments and need further studies. In this review, we introduced the immunological challenges for islet graft and summarized the recent developments in immune-protective strategies to improve the outcomes of islet transplantation.

Hollow fibers: from fabrication to applications

Hollow fibers have attracted more and more attention due to their broad range of applications in numerous fields. We review the latest advance and summarize the fabrication methods, types and applications of hollow fibers. We mainly introduce the fabrication methods of hollow fibers, including co-extrusion/co-axial spinning methods, template methods, 3D printing methods, electrospinning methods, self-crimping methods and gas foaming process. Meanwhile, we summarize four types of hollow fibers: one-layered hollow fibers, multi-layered hollow fibers, multi-hollow fibers and branched hollow fibers. Next, we focus on the main applications of hollow fibers, such as gas separation, cell culture, microfluidic channels, artificial tubular tissues, etc. Finally, we present the prospects of the future trend of development. The review would promote the further development of hollow fibers and benefit their advance in sensing, bioreactors, electrochemical catalysis, energy conversion, microfluidics, gas separation, air purification, drug delivery, functional materials, cell culture and tissue engineering. This review has great significance for the design of new functional materials and development of devices and systems in the related fields.