Red blood cells as oxygen carrier during normothermic machine perfusion of kidney grafts: Friend or foe?

Renal ex vivo normothermic machine perfusion (NMP) is under development as an assessment tool for high-risk kidney grafts and as a means of achieving more physiologically accurate organ preservation. On-going hemolysis has been reported during NMP, as this technique relies on red blood cells for oxygen delivery. In this study, we confirm the occurrence of progressive hemolysis during 6-hour kidney NMP. NMP-associated erythrostasis in the glomeruli and in peri-glomerular vascular networks points to an interaction between the red blood cells and the graft. Continuous hemolysis resulted in prooxidative changes in the perfusate, which could be quenched by addition of fresh frozen plasma. In a cell-based system, this hemolysis induced redox stress and exhibited toxic effects at high concentrations. These findings highlight the need for a more refined oxygen carrier in the context of renal NMP.

Endothelial to mesenchymal transition in kidney fibrosis.

Fibrotic disease are characterized by the uncontrolled accumulation of extracellular matrix (ECM) components leading to disruption of tissue homeostasis. Myofibroblasts as main ECM-producing cells can originate from various differentiated cell types after injury. Particularly, the process of endothelial-to-mesenchymal transition (endMT), describing phenotypic shifts of endothelial cells (ECs) to adopt a fully mesenchymal identity, may contribute to the pool of myofibroblasts in fibrosis, while leading to capillary rarefaction and exacerbation of tissue hypoxia. In renal disease, incomplete recovery from acute kidney injury (AKI) and the ensuing fibrotic reaction stand out as major contributors to chronic kidney disease (CKD) development. While the focus has largely been on impaired tubular epithelial repair as a potential fibrosis-driving mechanism, alterations in the renal microcirculation post-AKI, and in particular endMT as a maladaptive response, could hold equal significance. Dysfunctional interplays among various cell types in the kidney microenvironment can instigate endMT. Transforming growth factor beta (TGF-ß) signaling, with its downstream activation of canonical/Smad-mediated and non-canonical pathways, has been identified as primary driver of this process. However, non-TGF-ß-mediated pathways involving inflammatory agents and metabolic shifts in intercellular communication within the tissue microenvironment can also trigger endMT. These harmful, maladaptive cell-cell interactions and signaling pathways offer potential targets for therapeutic intervention to impede endMT and decelerate fibrogenesis such as in AKI-CKD progression. Presently, partial reduction of TGF-ß signaling using anti-diabetic drugs or statins may hold therapeutic potential in renal context. Nevertheless, further investigation is warranted to validate underlying mechanisms and assess positive effects within a clinical framework.

The Relevance of Advanced Therapy Medicinal Products in the Field of Transplantation and the Need for Academic Research Access: Overcoming Bottlenecks and Claiming a New Time.

The field of transplantation has witnessed the emergence of Advanced Therapy Medicinal Products (ATMPs) as highly promising solutions to address the challenges associated with organ and tissue transplantation. ATMPs encompass gene therapy, cell therapy, and tissue-engineered products, hold immense potential for breakthroughs in overcoming the obstacles of rejection and the limited availability of donor organs. However, the development and academic research access to ATMPs face significant bottlenecks that hinder progress. This opinion paper emphasizes the importance of addressing bottlenecks in the development and academic research access to ATMPs by implementing several key strategies. These include the establishment of streamlined regulatory processes, securing increased funding for ATMP research, fostering collaborations and partnerships, setting up centralized ATMP facilities, and actively engaging with patient groups. Advocacy at the policy level is essential to provide support for the development and accessibility of ATMPs, thereby driving advancements in transplantation and enhancing patient outcomes. By adopting these strategies, the field of transplantation can pave the way for the introduction of innovative and efficacious ATMP therapies, while simultaneously fostering a nurturing environment for academic research.

Chronic Pancreas Allograft Rejection Followed by Successful HLA-Incompatible Islet Alloautotransplantation: A Novel Strategy?

The purpose of pancreas or islet transplantation is to restore glycemic control in order to mitigate diabetes-related complications and prevent severe hypoglycemia. Complications from chronic pancreas allograft rejection may lead to transplantectomy, even when the endocrine function remains preserved. We present first evidence of a successful HLA incompatible islet re-transplantation with islets isolated from a rejecting pancreas allograft after simultaneous kidney pancreas transplantation. The pancreas allograft was removed because of progressively painful pancreatic panniculitis from clinically uncontrolled chronic rejection. The endocrine function was preserved. Induction treatment for this "islet alloautotransplantation" consisted of plasmapheresis, IVIg and alemtuzumab. At 1 year, the patient retained islet graft function with good glycemic control and absence of severe hypoglycemia, despite persistent low-grade HLA donor-specific antibodies. His panniculitis had resolved completely. In our point of view, islet alloautotransplantation derived from a chronically rejecting pancreas allograft is a potential option to salvage (partial) islet function, despite preformed donor-specific antibodies, in order to maintain stable glycemic control. Thereby it protects against severe hypoglycemia, and it potentially mitigates kidney graft dysfunction and other diabetes-related complications in patients with continued need for immunosuppression and who are otherwise difficult to retransplant.

European Society for Organ Transplantation (ESOT) Consensus Statement on the Role of Pancreas Machine Perfusion to Increase the Donor Pool for Beta Cell Replacement Therapy.

The advent of Machine Perfusion (MP) as a superior form of preservation and assessment for cold storage of both high-risk kidney's and the liver presents opportunities in the field of beta-cell replacement. It is yet unknown whether such techniques, when applied to the pancreas, can increase the pool of suitable donor organs as well as ameliorating the effects of ischemia incurred during the retrieval process. Recent experimental models of pancreatic MP appear promising. Applications of MP to the pancreas, needs refinement regarding perfusion protocols and organ viability assessment criteria. To address the "Role of pancreas machine perfusion to increase the donor pool for beta cell replacement," the European Society for Organ Transplantation (ESOT) assembled a dedicated working group comprising of experts to review literature pertaining to the role of MP as a method of improving donor pancreas quality as well as quantity available for transplant, and to develop guidelines founded on evidence-based reviews in experimental and clinical settings. These were subsequently refined during the Consensus Conference when this took place in Prague.

Quantification of Unmethylated Insulin DNA Using Methylation Sensitive Restriction Enzyme Digital Polymerase Chain Reaction.

Assessment of specific ß-cell death can be used to determine the quality and viability of pancreatic islets prior to transplantation and hence predict the suitability of the pancreas for isolation. Recently, several groups have demonstrated that unmethylated insulin (INS)-DNA is correlated to ß-cell death in type 1 diabetes patients and during clinical islet isolation and subsequent transplantation. Here, we present a step-by-step protocol of our novel developed method for quantification of the relative amount of unmethylated INS-DNA using methylation sensitive restriction enzyme digital polymerase chain reaction This method provides a novel and sensitive way to quantify the relative amount of ß-cell derived unmethylated INS-DNA in cellular lysate. We therefore suggest that this technique can be of value to reliably determine the purity of an islet preparation and may also serve as a measure of the quality of islets prior to transplantation measuring unmethylated INS-DNA as a reflection of the relative amount of lysed ß-cells.

Metabolic needs of the kidney graft undergoing normothermic machine perfusion.

Normothermic machine perfusion (NMP) is emerging as a novel preservation strategy. During NMP, the organ is maintained in a metabolically active state that may not only provide superior organ preservation, but that also facilitates viability testing before transplantation, and ex situ resuscitation of marginal kidney grafts. Although the prevailing perfusion protocols for renal NMP are refined from initial pioneering studies concerning short periods of NMP, it could be argued that these protocols are not optimally tailored to address the putatively compromised metabolic plasticity of marginal donor grafts (i.e., in the context of viability testing and/or preservation), or to meet the metabolic prerequisites associated with prolonged perfusions and the required anabolic state in the context of organ regeneration. Herein, we provide a theoretical framework for the metabolic requirements for renal NMP. Aspects are discussed along the lines of carbohydrates, fatty acids, amino acids, and micronutrients required for optimal NMP of an isolated kidney. In addition, considerations for monitoring aspects of metabolic status during NMP are discussed.

Clinical use of donation after circulatory death pancreas for islet transplantation.

Due to a shortage of donation after brain death (DBD) organs, donation after circulatory death (DCD) is increasingly performed. In the field of islet transplantation, there is uncertainty regarding the suitability of DCD pancreas in terms of islet yield and function after islet isolation. The aim of this study was to investigate the potential use of DCD pancreas for islet transplantation. Islet isolation procedures from 126 category 3 DCD and 258 DBD pancreas were performed in a 9-year period. Islet yield after isolation was significantly lower for DCD compared to DBD pancreas (395 515 islet equivalents [IEQ] and 480 017 IEQ, respectively; p = .003). The decrease in IEQ during 2 days of culture was not different between the two groups. Warm ischemia time was not related to DCD islet yield. In vitro insulin secretion after a glucose challenge was similar between DCD and DBD islets. After islet transplantation, DCD islet graft recipients had similar graft function (AUC C-peptide) during mixed meal tolerance tests and Igls score compared to DBD graft recipients. In conclusion, DCD islets can be considered for clinical islet transplantation.

Hypothermic oxygenated machine perfusion of the human pancreas for clinical islet isolation: a prospective feasibility study.

Due to an increasing scarcity of pancreases with optimal donor characteristics, islet isolation centers utilize pancreases from extended criteria donors, such as from donation after circulatory death (DCD) donors, which are particularly susceptible to prolonged cold ischemia time (CIT). We hypothesized that hypothermic machine perfusion (HMP) can safely increase CIT. Five human DCD pancreases were subjected to 6 h of oxygenated HMP. Perfusion parameters, apoptosis, and edema were measured prior to islet isolation. Five human DBD pancreases were evaluated after static cold storage (SCS). Islet viability, and in vitro and in vivo functionality in diabetic mice were analyzed. Islets were isolated from HMP pancreases after 13.4 h [12.9-14.5] CIT and after 9.2 h [6.5-12.5] CIT from SCS pancreases. Histological analysis of the pancreatic tissue showed that HMP did not induce edema nor apoptosis. Islets maintained >90% viable during culture, and an appropriate in vitro and in vivo function in mice was demonstrated after HMP. The current study design does not permit to demonstrate that oxygenated HMP allows for cold ischemia extension; however, the successful isolation of functional islets from discarded human DCD pancreases after performing 6 h of oxygenated HMP indicates that oxygenated HMP may be a useful technology for better preservation of pancreases.

Vascular bioengineering of scaffolds derived from human discarded transplant kidneys using human pluripotent stem cell-derived endothelium.

The bioengineering of a replacement kidney has been proposed as an approach to address the growing shortage of donor kidneys for the treatment of chronic kidney disease. One approach being investigated is the recellularization of kidney scaffolds. In this study, we present several key advances toward successful re-endothelialization of whole kidney matrix scaffolds from both rodents and humans. Based on the presence of preserved glycosoaminoglycans within the decelullarized kidney scaffold, we show improved localization of delivered endothelial cells after preloading of the vascular matrix with vascular endothelial growth factor and angiopoietin 1. Using a novel simultaneous arteriovenous delivery system, we report the complete re-endothelialization of the kidney vasculature, including the glomerular and peritubular capillaries, using human inducible pluripotent stem cell -derived endothelial cells. Using this source of endothelial cells, it was possible to generate sufficient endothelial cells to recellularize an entire human kidney scaffold, achieving efficient cell delivery, adherence, and endothelial cell proliferation and survival. Moreover, human re-endothelialized scaffold could, in contrast to the non-re-endothelialized human scaffold, be fully perfused with whole blood. These major advances move the field closer to a human bioengineered kidney.

Metabolic imaging of fatty kidney in diabesity: validation and dietary intervention.

Background: Obesity and type 2 diabetes have not only been linked to fatty liver, but also to fatty kidney and chronic kidney disease. Since non-invasive tools are lacking to study fatty kidney in clinical studies, we explored agreement between proton magnetic resonance spectroscopy (1H-MRS) and enzymatic assessment of renal triglyceride content (without and with dietary intervention). We further studied the correlation between fatty kidney and fatty liver. Methods: Triglyceride content in the renal cortex was measured by 1H-MRS on a 7-Tesla scanner in 27 pigs, among which 15 minipigs had been randomized to a 7-month control diet, cafeteria diet (CAF) or CAF with low-dose streptozocin (CAF-S) to induce insulin-independent diabetes. Renal biopsies were taken from corresponding MRS-voxel locations. Additionally, liver biopsies were taken and triglyceride content in all biopsies was measured by enzymatic assay. Results: Renal triglyceride content measured by 1H-MRS and enzymatic assay correlated positively (r = 0.86, P < 0.0001). Compared with control diet-fed minipigs, renal triglyceride content was higher in CAF-S-fed minipigs (137 ± 51 nmol/mg protein, mean ± standard error of the mean, P < 0.05), but not in CAF-fed minipigs (60 ± 10 nmol/mg protein) compared with controls (40 ± 6 nmol/mg protein). Triglyceride contents in liver and kidney biopsies were strongly correlated (r = 0.97, P < 0.001). Conclusions: Non-invasive measurement of renal triglyceride content by 1H-MRS closely predicts triglyceride content as measured enzymatically in biopsies, and fatty kidney appears to develop parallel to fatty liver. 1H-MRS may be a valuable tool to explore the role of fatty kidney in obesity and type 2 diabetic nephropathy in humans in vivo.

Pancreatic α-cell mass in obesity.

While it is well recognized that obesity is associated with an increased ß-cell mass, the association with α-cell mass is less clear. Type 2 diabetes (T2DM) associated with obesity is a bihormonal disease characterized by inadequate insulin secretion and hyperglucagonaemia. We examined ß- and α-cell mass throughout the pancreas in obese and lean subjects. Pancreatic tissue of the head, body and tail region of the pancreas was examined from 15 obese subjects (body mass index [BMI] ≥ 27 kg/m2 ) and 15 age-matched lean subjects (BMI ≤ 25 kg/m2 ) without diabetes. In obese subjects both ß- and α-cell mass were proportionally higher compared with lean subjects, thereby maintaining the α- to ß-cell ratio. The adaptation to obesity occurred preferentially in the head of the pancreas. As data so far have been derived from histological studies of ß- and α-cell adaptation, in which the head region of the human pancreas was not included, the adaptive capacity of humans to obesity has previously been underestimated. Obesity is associated with an increased α-cell mass, which could contribute to the hyperglucagonaemia observed in people with T2DM.

Genetically engineered human islets protected from CD8-mediated autoimmune destruction in vivo.

Islet transplantation is a promising therapy for type 1 diabetes, but graft function and survival are compromised by recurrent islet autoimmunity. Immunoprotection of islets will be required to improve clinical outcome. We engineered human ß cells to express herpesvirus-encoded immune-evasion proteins, "immunevasins." The capacity of immunevasins to protect ß cells from autoreactive T-cell killing was evaluated in vitro and in vivo in humanized mice. Lentiviral vectors were used for efficient genetic modification of primary human ß cells without impairing their function. Using a novel ß-cell-specific reporter gene assay, we show that autoreactive cytotoxic CD8(+) T-cell clones isolated from patients with recent onset diabetes selectively destroyed human ß cells, and that coexpression of the human cytomegalovirus-encoded US2 protein and serine proteinase inhibitor 9 offers highly efficient protection in vitro. Moreover, coimplantation of these genetically modified pseudoislets with ß-cell-specific cytotoxic T cells into immunodeficient mice achieves preserved human insulin production and C-peptide secretion. Collectively, our data provide proof of concept that human ß cells can be efficiently genetically modified to provide protection from killing mediated by autoreactive T cells and retain their function in vitro and in vivo.

A cell-free nutrient-supplemented perfusate allows four-day ex vivo metabolic preservation of human kidneys.

The growing disparity between the demand for transplants and the available donor supply, coupled with an aging donor population and increasing prevalence of chronic diseases, highlights the urgent need for the development of platforms enabling reconditioning, repair, and regeneration of deceased donor organs. This necessitates the ability to preserve metabolically active kidneys ex vivo for days. However, current kidney normothermic machine perfusion (NMP) approaches allow metabolic preservation only for hours. Here we show that human kidneys discarded for transplantation can be preserved in a metabolically active state up to 4 days when perfused with a cell-free perfusate supplemented with TCA cycle intermediates at subnormothermia (25 °C). Using spatially resolved isotope tracing we demonstrate preserved metabolic fluxes in the kidney microenvironment up to Day 4 of perfusion. Beyond Day 4, significant changes were observed in renal cell populations through spatial lipidomics, and increases in injury markers such as LDH, NGAL and oxidized lipids. Finally, we demonstrate that perfused kidneys maintain functional parameters up to Day 4. Collectively, these findings provide evidence that this approach enables metabolic and functional preservation of human kidneys over multiple days, establishing a solid foundation for future clinical investigations.

Alternative splicing and differential expression of the islet autoantigen IGRP between pancreas and thymus contributes to immunogenicity of pancreatic islets but not diabetogenicity in humans.

AIMS/HYPOTHESIS: Thymic expression of self-antigens during T-lymphocyte development is believed to be crucial for preventing autoimmunity. It has been suggested that G6PC2, the gene encoding islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP), is differentially spliced between pancreatic beta cells and the thymus. This may contribute to incomplete elimination of IGRP-specific T lymphocytes in the thymus, predisposing individuals to type 1 diabetes. We tested whether specific splice variation in islets vs thymus correlates with loss of tolerance to IGRP in type 1 diabetes. METHODS: Expression of G6PC2 splice variants was compared among thymus, purified medullary thymic epithelial cells and pancreatic islets by RT-PCR. Differential immunogenicity of IGRP splice variants was tested in patients and healthy individuals for autoantibodies and specific cytotoxic T lymphocytes using radiobinding assays and HLA class I multimers, respectively. RESULTS: Previously reported G6PC2 splice variants, including full-length G6PC2, were confirmed, albeit that they occurred in both pancreas and thymus, rather than islets alone. Yet, their expression levels were profoundly greater in islets than in thymus. Moreover, three novel G6PC2 variants were discovered that occur in islets only, leading to protein truncations, frame shifts and neo-sequences prone to immunogenicity. However, autoantibodies to novel or known IGRP splice variants did not differ between patients and healthy individuals, and similar frequencies of IGRP-specific cytotoxic T lymphocytes could be detected in both patients with type 1 diabetes and healthy individuals. CONCLUSIONS/INTERPRETATION: We propose that post-transcriptional variation of tissue-specific self-proteins may affect negative thymic selection, although this need not necessarily lead to disease.

Monitoring ß-Cell Survival After Intrahepatic Islet Transplantation Using Dynamic Exendin PET Imaging: A Proof-of-Concept Study in Individuals With Type 1 Diabetes.

Intrahepatic transplantation of islets of Langerhans (ITx) is a treatment option for individuals with complicated type 1 diabetes and profoundly unstable glycemic control, but its therapeutic success is hampered by deterioration of graft function over time. To improve ITx strategies, technologies to noninvasively monitor the fate and survival of transplanted islets over time are of great potential value. We used [68Ga]Ga-NODAGA-exendin-4 (68Ga-exendin) positron emission tomography (PET)/computed tomography (CT) imaging to demonstrate the feasibility of quantifying ß-cell mass in intrahepatic islet grafts in 13 individuals with type 1 diabetes, nine after ITx with functional islet grafts and four control patients not treated with ITx. ß-Cell function was measured by mixed-meal tolerance test. With dynamic 68Ga-exendin PET/CT images, we determined tracer accumulation in hepatic hotspots, and intrahepatic fat was assessed using MRI and spectroscopy. Quantification of hepatic hotspots showed a significantly higher uptake of 68Ga-exendin in the ITx group compared with the control group (median 0.55 [interquartile range 0.51-0.63] vs. 0.43 [0.42-0.45]). GLP-1 receptor expression was found in transplanted islets by immunohistochemistry. Intrahepatic fat was not detected in a majority of the individuals. Our study provides the first clinical evidence that radiolabeled exendin imaging can be used to monitor viable transplanted islets after intraportal ITx. ARTICLE HIGHLIGHTS: This clinical study researched the potential of radiolabeled exendin to follow the fate and survival of intrahepatic islet grafts. Is it feasible to quantitatively detect intrahepatic islet transplants with [68Ga]Ga-NODAGA-exendin-4 (68Ga-exendin) positron emission tomography (PET) imaging? Our study findings indicate that the imaging technique 68Ga-exendin PET can be used to monitor viable islet mass after intrahepatic islet transplantation in humans. Alongside functional measures, 68Ga-exendin PET imaging could significantly aid in the evaluation of strategies designed to improve islet engraftment, survival, and function.

Activin A induces a non-fibrotic phenotype in smooth muscle cells in contrast to TGF-ß.

AIMS: Activin A and transforming growth factor-ß1 (TGF-ß1) belong to the same family of growth and differentiation factors that modulate vascular lesion formation in distinct ways, which we wish to understand mechanistically. METHODS AND RESULTS: We investigated the expression of cell-surface receptors and activation of Smads in human vascular smooth muscle cells (SMCs) and demonstrated that activin receptor-like kinase-1 (ALK-1), ALK-4, ALK-5 and endoglin are expressed in human SMCs. As expected, TGF-ß1 activates Smad1 and Smad2 in these cells. Interestingly, activin A also induces phosphorylation of both Smads, which has not been reported for Smad1 before. Transcriptome analyses of activin A and TGF-ß1 treated SMCs with subsequent Gene-Set Enrichment Analyses revealed that many downstream gene networks are induced by both factors. However, the effect of activin A on expression kinetics of individual genes is less pronounced than for TGF-ß1, which is explained by a more rapid dephosphorylation of Smads and p38-MAPK in response to activin A. Substantial differences in expression of fibronectin, alpha-V integrin and total extracellular collagen synthesis were observed. CONCLUSIONS: Genome-wide mRNA expression analyses clarify the distinct modulation of vascular lesion formation by activin A and TGF-ß1, most significantly because activin A is non-fibrotic.

PRISM: A Novel Human Islet Isolation Technique.

BACKGROUND: Successful pancreatic islet isolations are a key requirement for islet transplantation in selected patients with type 1 diabetes. However, islet isolation is a technically complex, time-consuming, and manual process. Optimization and simplification of the islet isolation procedure could increase islet yield and quality, require fewer operators, and thus reduce cost. METHODS: We developed a new, closed system of tissue collection, washing, buffer change, and islet purification termed PancReatic Islet Separation Method (PRISM). In the developmental phase, pump and centrifuge speed was tested using microspheres with a similar size, shape, and density as digested pancreatic tissue. After optimization, PRISM was used to isolate islets from 10 human pancreases. RESULTS: Islet equivalents viability (fluorescein diacetate/propidium iodide), morphology, and dynamic glucose-stimulated insulin secretion were evaluated. PRISM could be performed by 1 operator in 1 flow cabinet. A similar islet yield was obtained using PRISM compared to the traditional islet isolation method (431 234 ± 292 833 versus 285 276 ± 197 392 islet equivalents, P = 0.105). PRISM islets had similar morphology and functionality. CONCLUSIONS: PRISM is a novel islet isolation technique that can significantly improve islet isolation efficiency using fewer operators.

Oxidative Stress Leads to ß-Cell Dysfunction Through Loss of ß-Cell Identity.

Pancreatic ß-cell failure is a critical event in the onset of both main types of diabetes mellitus but underlying mechanisms are not fully understood. ß-cells have low anti-oxidant capacity, making them more susceptible to oxidative stress. In type 1 diabetes (T1D), reactive oxygen species (ROS) are associated with pro-inflammatory conditions at the onset of the disease. Here, we investigated the effects of hydrogen peroxide-induced oxidative stress on human ß-cells. We show that primary human ß-cell function is decreased. This reduced function is associated with an ER stress response and the shuttling of FOXO1 to the nucleus. Furthermore, oxidative stress leads to loss of ß-cell maturity genes MAFA and PDX1, and to a concomitant increase in progenitor marker expression of SOX9 and HES1. Overall, we propose that oxidative stress-induced ß-cell failure may result from partial dedifferentiation. Targeting antioxidant mechanisms may preserve functional ß-cell mass in early stages of development of T1D.

Oxidative stress in pancreatic alpha and beta cells as a selection criterion for biocompatible biomaterials.

The clinical success rate of islet transplantation, namely independence from insulin injections, is limited by factors that lead to graft failure, including inflammation, acute ischemia, acute phase response, and insufficient vascularization. The ischemia and insufficient vascularization both lead to high levels of oxidative stress, which are further aggravated by islet encapsulation, inflammation, and undesirable cell-biomaterial interactions. To identify biomaterials that would not further increase damaging oxidative stress levels and that are also suitable for manufacturing a beta cell encapsulation device, we studied five clinically approved polymers for their effect on oxidative stress and islet (alpha and beta cell) function. We found that 300 poly(ethylene oxide terephthalate) 55/poly(butylene terephthalate) 45 (PEOT/PBT300) was more resistant to breakage and more elastic than other biomaterials, which is important for its immunoprotective function. In addition, it did not induce oxidative stress or reduce viability in the MIN6 beta cell line, and even promoted protective endogenous antioxidant expression over 7 days. Importantly, PEOT/PBT300 is one of the biomaterials we studied that did not interfere with insulin secretion in human islets.