Islet transplantation and encapsulation: an update on recent developments

Immunoprotection Strategies in β-Cell Replacement Therapy: A Closer Look at Porcine Islet Xenotransplantation

Type 1 diabetes mellitus (T1DM) is characterized by absolute insulin deficiency primarily due to autoimmune destruction of pancreatic β-cells. The prevailing treatment for T1DM involves daily subcutaneous insulin injections, but a substantial proportion of patients face challenges such as severe hypoglycemic episodes and poorly controlled hyperglycemia. For T1DM patients, a more effective therapeutic option involves the replacement of β-cells through allogeneic transplantation of either the entire pancreas or isolated pancreatic islets. Unfortunately, the scarcity of transplantable human organs has led to a growing list of patients waiting for an islet transplant. One potential alternative is xenotransplantation of porcine pancreatic islets. However, due to inter-species molecular incompatibilities, porcine tissues trigger a robust immune response in humans, leading to xenograft rejection. Several promising strategies aim to overcome this challenge and enhance the long-term survival and functionality of xenogeneic islet grafts. These strategies include the use of islets derived from genetically modified pigs, immunoisolation of islets by encapsulation in biocompatible materials, and the creation of an immunomodulatory microenvironment by co-transplanting islets with accessory cells or utilizing immunomodulatory biomaterials. This review concentrates on delineating the primary obstacles in islet xenotransplantation and elucidates the fundamental principles and recent breakthroughs aimed at addressing these challenges.

Pancreas after kidney transplantation, is it the time to overcome the stigma?

BACKGROUND

Pancreas transplantation is the most effective treatment to improve quality of life and overcome complications in patients with end-stage renal disease and diabetes mellitus. One of the main approaches for concurrent renal disease and diabetes mellitus which has been underutilized during the past decade is a pancreas transplant after kidney transplantation. Our study aimed to quantify outcomes following pancreas after kidney transplants (PAKs) in the United States from 2001 to 2020 with an emphasis on graft and patient survival.

METHODS AND MATERIALS

A retrospective registry analysis was performed by accessing the OPTN/UNOS database for PAKs that were performed in the United States from January 2001 to April 2020. The study population was divided into two subgroups: patients receiving a pancreas transplant between 2001 and 2010 and those receiving a pancreas transplant between 2011 and 2020.

RESULTS

The study examined a total number of 3706 PAK recipients; patients who received a PAK from January 2001 through December 2010 (n = 2892) and those who received a PAK from January 2011 to April 2020 (n = 814). The selection process of transplant recipients did not drastically change throughout the 2001-2010 and 2011-2020 periods. Length of stay at the hospital after the transplantation improved significantly in the 2011-2020 group relative to the 2001-2010 group (8.48 vs. 10.08 days, mean, p < 0.01). Additionally, more transplantation with 4-6 human leukocyte antigen mismatch occurred in the 2011-2020 group than in the 2001-2010 group (80.6% vs. 71.4%, p < 0.01). The pancreas preservation time of 13.35 h in the 2001-2010 group decreased significantly to 11.17 h in the 2011-2020 group (p < 0.001). The mean donor's amylase and lipase also decreased significantly in the 2011-2020 cohort. Significant graft survival improvement was observed in the 2011-2020 group compared to the 2001-2010 group after a long-term follow-up (p < 0.001). The mean Calculated Pancreas Donor Risk Index was 1.08 for the 2001-2010 group and 0.99 for the 2011-2020 group with a significant difference (p < 0.001).

CONCLUSION

The beneficial results and improved outcomes observed in PAK patients demonstrate the effectiveness of the operation for individuals in need of a pancreas transplant. PAKs can prove to be a meaningful solution to overcome long waiting times, decrease the donor-recipient imbalance, expand the donor pool, and overcome the current underutilization in order to improve the short- and long-term quality of life in the groups of interest.

Short-term function and immune-protection of microencapsulated adult porcine islets with alginate incorporating CXCL12 in healthy and diabetic non-human primates without systemic immune suppression: A pilot study

Replacement of insulin-producing pancreatic beta-cells by islet transplantation offers a functional cure for type-1 diabetes (T1D). We recently demonstrated that a clinical grade alginate micro-encapsulant incorporating the immune-repellent chemokine and pro-survival factor CXCL12 could protect and sustain the integrity and function of autologous islets in healthy non-human primates (NHPs) without systemic immune suppression. In this pilot study, we examined the impact of the CXCL12 micro encapsulant on the function and inflammatory and immune responses of xenogeneic islets transplanted into the omental tissue bilayer sac (OB; n = 4) and diabetic (n = 1) NHPs. Changes in the expression of cytokines after implantation were limited to 2-6-fold changes in blood, most of which did not persist over the first 4 weeks after implantation. Flow cytometry of PBMCs following transplantation showed minimal changes in IFNγ or TNFα expression on xenoantigen-specific CD4+  or CD8+  T cells compared to unstimulated cells, and these occurred mainly in the first 4 weeks. Microbeads were readily retrievable for assessment at day 90 and day 180 and at retrieval were without microscopic signs of degradation or foreign body responses (FBR). In vitro and immunohistochemistry studies of explanted microbeads indicated the presence of functional xenogeneic islets at day 30 post transplantation in all biopsied NHPs. These results from a small pilot study revealed that CXCL12-microencapsulated xenogeneic islets abrogate inflammatory and adaptive immune responses to the xenograft. This work paves the way toward future larger scale studies of the transplantation of alginate microbeads with CXCL12 and porcine or human stem cell-derived beta cells or allogeneic islets into diabetic NHPs without systemic immunosuppression.

3D printed elastomeric biomaterial mitigates compaction during in vitro vasculogenesis

A key parameter for the success of most cellular implants is the formation of a complete and comprehensive intra-implant vessel network. Pre-vascularization, the generation of vessel structures in vitro prior to transplantation, provides accelerated implant perfusion via anastomosis, but scalability and ease of integration hinder clinical translation. For fibrin-based vasculogenesis approaches, the remodeling and degradation of the fragile, hydrogel matrix during the formation of vessel-like structures results in rapid, cell-mediated construct compaction leading to dense, capillary-like structures with ineffective network coverage. To resolve these challenges, vasculogenic hydrogels were embedded within a highly porous, biostable three-dimensional (3D) polydimethylsiloxane (PDMS) scaffold. Using reverse-casting of 3D-printed molds, scaffolds exhibited highly interconnected and reproducible pore structures. Pore size was optimized via in vivo screening of intra-device angiogenesis. The inclusion of the PDMS frame with vasculogenic hydrogels significantly reduced fibrin compaction in vitro, resulting in easily manipulated constructs with predictable dimensionality and increased surface area compared to fibrin hydrogel alone. Globally, vascular morphogenesis was altered by the PDMS frame, with significantly larger and less dense network structures. Vasculogenic proteomic evaluation showed a temporal impact of the addition of the PDMS frame, indicating altered cellular proliferation and migration signaling. This work establishes a platform for improving the generation of translational pre-vascularized networks for greater flexibility to meet the needs of clinically scaled, engineered tissues. STATEMENT OF SIGNIFICANCE: Competent intra-implant vascularization is a significant issue hindering the success of engineered tissues. Pre-vascularization approaches, whereby a vascular network is formed in vitro and subsequently implanted into the host to anastomose, is a promising approach but it is limited by the compacted, dense, and poorly functional microcapillary structures typically formed using soft hydrogels. Herein, we have uniquely addressed this challenge by adding a 3D printed PDMS-based open framework structure that serves to prevent hydrogel compaction. Globally, we observed distinct differences in overall construct geometry, vascular network density, compaction, and morphogenesis, indicating that this PDMS framework lead to elevated maturity of this in vitro network while retaining its global dimensions. Overall, this novel approach elevates the translational potential of pre-vascularized constructs.

Engineering Modular, Oxygen-Generating Microbeads for the In Situ Mitigation of Cellular Hypoxia

Insufficient oxygenation is a key obstacle in the design of clinically scalable tissue-engineered grafts. In this work, an oxygen-generating composite material, termed OxySite, is created through the encapsulation of calcium peroxide (CaO2 ) within polydimethylsiloxane and formulated into microbeads for ease in tissue integration. Key material parameters of reactant loading, porogen addition, microbead size, and an outer rate-limiting layer are modulated to characterize oxygen generation kinetics and their suitability for cellular applications. In silico models are developed to predict the local impact of different OxySite microbead formulations on oxygen availability within an idealized cellular implant. Promising OxySite microbead variants are subsequently coencapsulated with murine β-cells within macroencapsulation devices, resulting in improved cellular metabolic activity and function under hypoxic conditions when compared to controls. Additionally, the coinjection of optimized OxySite microbeads with murine pancreatic islets within a confined transplant site demonstrates ease of integration and improved primary cell function. These works highlight the broad translatability delivered by this new oxygen-generating biomaterial format, whereby the modularity of the material provides customization of the oxygen source to the specific needs of the cellular implant.

Combinatorial islet protective therapeutic approaches in β-cell transplantation: Rationally designed solutions using a target product profile

While progress has been made in the development of islet cell transplantation (ICT) as a viable alternative to the use of exogenous insulin therapy in the treatment of type 1 diabetes, it has not yet achieved its full potential in clinical studies. Ideally, ICT would enable lifelong maintenance of euglycemia without the need for exogenous insulin, blood glucose monitoring or systemic immune suppression. To achieve such an optimal result, therapeutic approaches should simultaneously promote long-term islet viability, functionality, and localized immune protection. In practice, however, these factors are typically tackled individually. Furthermore, while the requirements of optimal ICT are implicitly acknowledged across numerous publications, the literature contains few comprehensive articulations of the target product profile (TPP) for an optimal ICT product, including key characteristics of safety and efficacy. This review aims to provide a novel TPP for ICT and presents promising tried and untried combinatorial approaches that could be used to achieve the target product profile. We also highlight regulatory barriers to the development and adoption of ICT, particularly in the United States, where ICT is only approved for use in academic clinical trials and is not reimbursed by insurance carriers. Overall, this review argues that the clear definition of a TPP in addition to the use of combinatorial approaches could help to overcome the clinical barriers to the widespread adoption of ICT for the treatment of type 1 diabetes.

Tissue engineering approaches and generation of insulin-producing cells to treat type 1 diabetes

Tissue engineering (TE) has become a new effective solution to a variety of medical problems, including diabetes. Mesenchymal stem cells (MSCs), which have the ability to differentiate into endodermal and mesodermal cells, appear to be appropriate for this function. The purpose of this review was to evaluate the outcomes of various researches on the insulin-producing cells (IPCs) generation from MSCs with TE approaches to increase efficacy of type 1 diabetes treatments. The search was performed in PubMed/Medline, Scopus and Embase databases until 2021. Studies revealed that MSCs could also differentiate into IPCs under certain conditions. Therefore, a wide range of protocols have been used for this differentiation, but their effectiveness is very different. Scaffolds can provide a microenvironment that enhances the MSCs to IPCs differentiation, improves their metabolic activity and up-regulate pancreatic-specific transcription factors. They also preserve IPCs architecture and enhance insulin production as well as protect against cell death. This systematic review offers a framework for prospective research based on data. In vitro and in vivo evidence suggests that scaffold-based TE can improve the viability and function of IPCs.

A predictive computational platform for optimizing the design of bioartificial pancreas devices

The delivery of encapsulated islets or stem cell-derived insulin-producing cells (i.e., bioartificial pancreas devices) may achieve a functional cure for type 1 diabetes, but their efficacy is limited by mass transport constraints. Modeling such constraints is thus desirable, but previous efforts invoke simplifications which limit the utility of their insights. Herein, we present a computational platform for investigating the therapeutic capacity of generic and user-programmable bioartificial pancreas devices, which accounts for highly influential stochastic properties including the size distribution and random localization of the cells. We first apply the platform in a study which finds that endogenous islet size distribution variance significantly influences device potency. Then we pursue optimizations, determining ideal device structures and estimates of the curative cell dose. Finally, we propose a new, device-specific islet equivalence conversion table, and develop a surrogate machine learning model, hosted on a web application, to rapidly produce these coefficients for user-defined devices.

Microencapsulation-based cell therapies

Mapping a new therapeutic route can be fraught with challenges, but recent developments in the preparation and properties of small particles combined with significant improvements to tried and tested techniques offer refined cell targeting with tremendous translational potential. Regenerating new cells through the use of compounds that regulate epigenetic pathways represents an attractive approach that is gaining increased attention for the treatment of several diseases including Type 1 Diabetes and cardiomyopathy. However, cells that have been regenerated using epigenetic agents will still encounter immunological barriers as well as limitations associated with their longevity and potency during transplantation. Strategies aimed at protecting these epigenetically regenerated cells from the host immune response include microencapsulation. Microencapsulation can provide new solutions for the treatment of many diseases. In particular, it offers an advantageous method of administering therapeutic materials and molecules that cannot be substituted by pharmacological substances. Promising clinical findings have shown the potential beneficial use of microencapsulation for islet transplantation as well as for cardiac, hepatic, and neuronal repair. For the treatment of diseases such as type I diabetes that requires insulin release regulated by the patient's metabolic needs, microencapsulation may be the most effective therapeutic strategy. However, new materials need to be developed, so that transplanted encapsulated cells are able to survive for longer periods in the host. In this article, we discuss microencapsulation strategies and chart recent progress in nanomedicine that offers new potential for this area in the future.

Microencapsulated islet transplantation alleviates podocyte injury in diabetic nephropathy via inhibiting Notch-1 signaling

OBJECTIVE

Podocyte injury has a critical role in the pathogenesis of diabetic nephropathy (DN). Microencapsulated islet transplantation (MIT) is identified as an effective method for improving the clinical condition of DN. This study aimed to explore the role and mechanism of MIT in alleviating podocyte injury in DN.

METHODS

A mouse model of DN was constructed using streptozotocin (STZ). Mice were divided into 3 groups: the untreated diabetic nephropathy group (DN group), the microencapsulated islet transplantation-treated group (MIT group) and the control group. The mice were raised for 6 weeks posterior to islet transplantation to identify the role of MIT. Renal function and structure of glomerular filtration barrier were assessed by urine analysis, histopathological examination, and transmission electron microscopy. The expression levels of several proteins including Caspase-3, Bcl2/Bax, β-galactosidase, Ki-67, synaptopodin, WT-1, Jagged-1, Notch-1, and Hes-1 in renal tissues were identified via immunohistochemistry (IHC), immunofluorescence (IF), and western blotting techniques.

RESULTS

Compared with the DN group, the MIT group presented decreased levels of blood glucose, urinary albumin/creatinine, urea nitrogen, and serum creatinine while their body weight gradually increased. Glomerular injury in the MIT group was significantly better than that in the DN group. The MIT group indicated significantly decreased expression of Caspase-3, β-galactosidase, Bax/Bcl-2, and Ki-67 when compared with DN group, while the proportion of synaptopodin- and WT-1-positive cells was significantly increased (P < 0.05). The protein expression of Jagged-1, Notch-1, and Hes-1 in the glomerulus of the MIT group was significantly lower than that in the DN group (P < 0.05).

CONCLUSION

MIT alleviates podocyte injury induced by DN by inhibiting Notch-1 signaling. The identification of signaling pathways influencing podocyte restoration can help evaluate personalized medicine efficacy for patients treated with islet transplantation.

Cell encapsulation in alginate-based microgels using droplet microfluidics; a review on gelation methods and applications

Cell encapsulation within the microspheres using a semi-permeable polymer allows the two-way transfer of molecules such as oxygen, nutrients, and growth factors. The main advantages of cell encapsulation technology include controlling the problems involved in transplanting rejection in tissue engineering applications and reducing the long-term need for immunosuppressive drugs following organ transplantation to eliminate the side effects. Cell-laden microgels can also be used in 3D cell cultures, wound healing, and cancerous clusters for drug testing. Since cell encapsulation is used for different purposes, several techniques have been developed to encapsulate cells. Droplet-based microfluidics is one of the most valuable techniques in cell encapsulating. This study aimed to review the geometries and the mechanisms proposed in microfluidic systems to precisely control cell-laden microgels production with different biopolymers. We also focused on alginate gelation techniques due to their essential role in cell encapsulation applications. Finally, some applications of these microgels and researches will be explored.

Highly Efficient Differentiation of Human Pluripotent Stem Cells into Pancreatic Progenitors Co-expressing PDX1 and NKX6.1

Diabetes is a complex metabolic disorder, with no available treatment. Islet transplantation is currently practiced beta cell replacement therapy option, however, with major limitations. Human pluripotent stem cells (hPSCs) can be used as a scalable source for generation of insulin-secreting cells as hPSCs have high proliferative capacity and can differentiate into any tissue type. In vitro stepwise protocols have been designed for differentiating hPSCs into pancreatic lineages that finally give rise to beta cells; however, these hPSC-derived beta cells are dissimilar to adult human beta cells in key aspects of gene expression and functionality. Alternatively, pancreatic progenitors, when transplanted in the body, have been shown to mature into functional insulin-secreting beta cells, capable of reversing hyperglycemia. These pancreatic progenitors require the co-expression of PDX1, a transcription factor (TF) regulating pancreatic development, and NKX6.1, another TF key for beta cell maturation and function, to produce glucose-responsive beta cells. Given the crucial role played by NKX6.1, we optimized an in vitro differentiation protocol to enhance the generation of pancreatic progenitors co-expressing PDX1 and NKX6.1 by modulating cell density, matrix availability, and cellular dissociation.

Artificial Cell Encapsulation for Biomaterials and Tissue Bio-Nanoengineering: History, Achievements, Limitations, and Future Work for Potential Clinical Applications and Transplantation

Pancreatic β-cell loss and failure with subsequent deficiency of insulin production is the hallmark of type 1 diabetes (T1D) and late-stage type 2 diabetes (T2D). Despite the availability of parental insulin, serious complications of both types are profound and endemic. One approach to therapy and a potential cure is the immunoisolation of β cells via artificial cell microencapsulation (ACM), with ongoing promising results in human and animal studies that do not depend on immunosuppressive regimens. However, significant challenges remain in the formulation and delivery platforms and potential immunogenicity issues. Additionally, the level of impact on key metabolic and disease biomarkers and long-term benefits from human and animal studies stemming from the encapsulation and delivery of these cells is a subject of continuing debate. The purpose of this review is to summarise key advances in this field of islet transplantation using ACM and to explore future strategies, limitations, and hurdles as well as upcoming developments utilising bioengineering and current clinical trials.

Injectable biomaterial shuttles for cell therapy in stroke

Ischemic stroke (IS) is the leading cause of disability and contributes to a significant socio-economic cost in the western world. Brain repair strategies investigated in the pre-clinical models include the delivery of drug or cell-based therapeutics; which is hindered by the complex anatomy and functional organization of the brain. Biomaterials can be instrumental in alleviating some of these challenges by providing a structural support, localization, immunomodulation and/or modulating cellular cross-talk in the brain. This review addresses the significance of and challenges associated with cell therapy in an ischemic brain. This is followed by a detailed insight into the biomaterial-based delivery systems which have been designed to provide sustained trophic factor delivery for endogenous repair and to support transplanted cell survival and integration. A biomaterial intervention uses a multifaceted approach in enhancing the survival and engraftment of cells during transplantation and this has driven them as potential candidates for the treatment of IS. The biological processes that are activated as a response to the biomaterials and how to modulate them is one of the key factors contributing to the success of the biomaterial-based therapeutic approach. Future perspectives highlight the need of a combinative approach of merging the material design with disease biology to fabricate effective biomaterial-based intervention of stroke.

Immunoengineering Biomaterials in Cell-Based Therapy for Type 1 Diabetes

Type 1 diabetes (T1D) is caused by low insulin production and chronic hyperglycemia due to the destruction of pancreatic β-cells. Cell transplantation is an attractive alternative approach compared to insulin injection. However, cell therapy has been limited by major challenges including life-long requirements for immunosuppressive drugs in order to prevent host immune responses. Encapsulation of the transplanted cells can solve the problem of immune rejection, by providing a physical barrier between the transplanted cells and the recipient's immune cells. Despite current disputes in cell encapsulation approaches, thanks to recent advances in the fields of biomaterials and transplantation immunology, extensive effort has been dedicated to immunoengineering strategies in combination with encapsulation technologies to overcome the problem of the host's immune responses. The current review summarizes the most commonly used encapsulation and immunoengineering strategies combined with cell therapy which has been applied as a novel approach to improve cell replacement therapies for the management of T1D. Recent advances in the fields of biomaterial design, nanotechnology, as well as deeper knowledge about immune modulation had significantly improved cell encapsulation strategies. However, further progress requires the combined application of novel immunoengineering approaches and islet/ß-cell transplantation.

Advances in Encapsulation and Delivery Strategies for Islet Transplantation

Type 1 diabetes mellitus (T1DM) is a chronic metabolic disease caused by the destruction of pancreatic β-cells in response to autoimmune reactions. Shapiro et al. conducted novel islet transplantation with a glucocorticoid-free immunosuppressive agent in 2000 and achieved great success; since then, islet transplantation has been increasingly regarded as a promising strategy for the curative treatment of T1DM. However, many unavoidable challenges, such as a lack of donors, poor revascularization, blood-mediated inflammatory reactions, hypoxia, and side effects caused by immunosuppression have severely hindered the widespread application of islet transplantation in clinics. Biomaterial-based encapsulation and delivery strategies are proposed for overcoming these obstacles, and have demonstrated remarkable improvements in islet transplantation outcomes. Herein, the major problems faced by islet transplantation are summarized and updated biomaterial-based strategies for islet transplantation, including islet encapsulation across different scales, delivery of stem cell-derived beta cells, co-delivery of islets with accessory cells and immunomodulatory molecules are highlighted.

A therapeutic vascular conduit to support in vivo cell-secreted therapy

A significant barrier to implementation of cell-based therapies is providing adequate vascularization to provide oxygen and nutrients. Here we describe an approach for cell transplantation termed the Therapeutic Vascular Conduit (TVC), which uses an acellular vessel as a scaffold for a hydrogel sheath containing cells designed to secrete a therapeutic protein. The TVC can be directly anastomosed as a vascular graft. Modeling supports the concept that the TVC allows oxygenated blood to flow in close proximity to the transplanted cells to prevent hypoxia. As a proof-of-principle study, we used erythropoietin (EPO) as a model therapeutic protein. If implanted as an arteriovenous vascular graft, such a construct could serve a dual role as an EPO delivery platform and hemodialysis access for patients with end-stage renal disease. When implanted into nude rats, TVCs containing EPO-secreting fibroblasts were able to increase serum EPO and hemoglobin levels for up to 4 weeks. However, constitutive EPO expression resulted in macrophage infiltration and luminal obstruction of the TVC, thus limiting longer-term efficacy. Follow-up in vitro studies support the hypothesis that EPO also functions to recruit macrophages. The TVC is a promising approach to cell-based therapeutic delivery that has the potential to overcome the oxygenation barrier to large-scale cellular implantation and could thus be used for a myriad of clinical disorders. However, a complete understanding of the biological effects of the selected therapeutic is absolutely essential.

Immunological considerations and challenges for regenerative cellular therapies

The central goal of regenerative medicine is to replace damaged or diseased tissue with cells that integrate and function optimally. The capacity of pluripotent stem cells to produce unlimited numbers of differentiated cells is of considerable therapeutic interest, with several clinical trials underway. However, the host immune response represents an important barrier to clinical translation. Here we describe the role of the host innate and adaptive immune responses as triggers of allogeneic graft rejection. We discuss how the immune response is determined by the cellular therapy. Additionally, we describe the range of available in vitro and in vivo experimental approaches to examine the immunogenicity of cellular therapies, and finally we review potential strategies to ameliorate immune rejection. In conclusion, we advocate establishment of platforms that bring together the multidisciplinary expertise and infrastructure necessary to comprehensively investigate the immunogenicity of cellular therapies to ensure their clinical safety and efficacy.

Exosome loaded immunomodulatory biomaterials alleviate local immune response in immunocompetent diabetic mice post islet xenotransplantation

Foreign body response (FBR) to biomaterials compromises the function of implants and leads to medical complications. Here, we report a hybrid alginate microcapsule (AlgXO) that attenuated the immune response after implantation, through releasing exosomes derived from human Umbilical Cord Mesenchymal Stem Cells (XOs). Upon release, XOs suppress the local immune microenvironment, where xenotransplantation of rat islets encapsulated in AlgXO led to >170 days euglycemia in immunocompetent mouse model of Type 1 Diabetes. In vitro analyses revealed that XOs suppressed the proliferation of CD3/CD28 activated splenocytes and CD3+ T cells. Comparing suppressive potency of XOs in purified CD3+ T cells versus splenocytes, we found XOs more profoundly suppressed T cells in the splenocytes co-culture, where a heterogenous cell population is present. XOs also suppressed CD3/CD28 activated human peripheral blood mononuclear cells (PBMCs) and reduced their cytokine secretion including IL-2, IL-6, IL-12p70, IL-22, and TNFα. We further demonstrate that XOs mechanism of action is likely mediated via myeloid cells and XOs suppress both murine and human macrophages partly by interfering with NFκB pathway. We propose that through controlled release of XOs, AlgXO provide a promising new platform that could alleviate the local immune response to implantable biomaterials.

Regulation of Blood Glucose Using Islets Encapsulated in a Melanin-Modified Immune-Shielding Hydrogel

Islet transplantation is currently a promising treatment for type 1 diabetes mellitus. However, the foreign body reaction and retrieval difficulty often lead to transplantation failure and hinder the clinical application. To address these two challenges, we propose a balanced charged sodium alginate-polyethyleneimine-melanin (SA-PEI-Melanin) threadlike hydrogel with immune shielding and retrievable properties. The attractiveness of this study lies in that the introduction of melanin can stimulate insulin secretion, especially under near-infrared (NIR) irradiation. After demonstrating a good immune-shielding effect, we performed an in vivo transplantation experiment. The results showed that the blood glucose level in the SA-PEI-Melanin group was stably controlled below the diabetic blood glucose criterion, and this blood glucose level could be further adjusted after NIR irradiation. In addition, the evaluation after retrieving the SA-PEI-Melanin hydrogel indicated that the islets still maintained a normal physiological function, further proving its excellent immunological protection. This study provides a new approach for the accurate regulation of blood glucose in patients with type 1 diabetes mellitus and contributes to developing a promising transplant system to reconcile real-time and precise light-defined insulin secretion regulation.

C-Peptide as a Therapy for Type 1 Diabetes Mellitus

Diabetes mellitus (DM) is a complex metabolic disease affecting one-third of the United States population. It is characterized by hyperglycemia, where the hormone insulin is either not produced sufficiently or where there is a resistance to insulin. Patients with Type 1 DM (T1DM), in which the insulin-producing beta cells are destroyed by autoimmune mechanisms, have a significantly increased risk of developing life-threatening cardiovascular complications, even when exogenous insulin is administered. In fact, due to various factors such as limited blood glucose measurements and timing of insulin administration, only 37% of T1DM adults achieve normoglycemia. Furthermore, T1DM patients do not produce C-peptide, a cleavage product from insulin processing. C-peptide has potential therapeutic effects in vitro and in vivo on many complications of T1DM, such as peripheral neuropathy, atherosclerosis, and inflammation. Thus, delivery of C-peptide in conjunction with insulin through a pump, pancreatic islet transplantation, or genetically engineered Sertoli cells (an immune privileged cell type) may ameliorate many of the cardiovascular and vascular complications afflicting T1DM patients.

Transplantation of encapsulated human Leydig-like cells: A novel option for the treatment of testosterone deficiency

Previous studies have demonstrated that the transplantation of alginate-poly-ʟ-lysine-alginate (APA)-encapsulated rat Leydig cells (LCs) provides a promising approach for treating testosterone deficiency (TD). Nevertheless, LCs have a limited capacity to proliferate, limiting the efficacy of LC transplantation therapy. Here, we established an efficient differentiation system to obtain functional Leydig-like cells (LLCs) from human stem Leydig cells (hSLCs). Then we injected APA-encapsulated LLCs into the abdominal cavities of castrated mice without an immunosuppressor. The APA-encapsulated cells survived and partially restored testosterone production for 90 days in vivo. More importantly, the transplantation of encapsulated LLCs ameliorated the symptoms of TD, such as fat accumulation, muscle atrophy and adipocyte accumulation in bone marrow. Overall, these results suggest that the transplantation of encapsulated LLCs is a promising new method for testosterone supplementation with potential clinical applications in TD.

Development of a Bioartificial Vascular Pancreas

Transplantation of pancreatic islets has been shown to be effective, in some patients, for the long-term treatment of type 1 diabetes. However, transplantation of islets into either the portal vein or the subcutaneous space can be limited by insufficient oxygen transfer, leading to islet loss. Furthermore, oxygen diffusion limitations can be magnified when islet numbers are increased dramatically, as in translating from rodent studies to human-scale treatments. To address these limitations, an islet transplantation approach using an acellular vascular graft as a vascular scaffold has been developed, termed the BioVascular Pancreas (BVP). To create the BVP, islets are seeded as an outer coating on the surface of an acellular vascular graft, using fibrin as a hydrogel carrier. The BVP can then be anastomosed as an arterial (or arteriovenous) graft, which allows fully oxygenated arterial blood with a pO2 of roughly 100 mmHg to flow through the graft lumen and thereby supply oxygen to the islets. In silico simulations and in vitro bioreactor experiments show that the BVP design provides adequate survivability for islets and helps avoid islet hypoxia. When implanted as end-to-end abdominal aorta grafts in nude rats, BVPs were able to restore near-normoglycemia durably for 90 days and developed robust microvascular infiltration from the host. Furthermore, pilot implantations in pigs were performed, which demonstrated the scalability of the technology. Given the potential benefits provided by the BVP, this tissue design may eventually serve as a solution for transplantation of pancreatic islets to treat or cure type 1 diabetes.

Effect of alginate matrix engineered to mimic the pancreatic microenvironment on encapsulated islet function

Islet transplantation is emerging as a therapeutic option for type 1 diabetes, albeit, only a small number of patients meeting very stringent criteria are eligible for the treatment because of the side effects of the necessary immunosuppressive therapy and the relatively short time frame of normoglycemia that most patients achieve. The challenge of the immune-suppressive regimen can be overcome through microencapsulation of the islets in a perm-selective coating of alginate microbeads with poly-l-lysine or poly- l-ornithine. In addition to other issues including the nutrient supply challenge of encapsulated islets a critical requirement for these cells has emerged as the need to engineer the microenvironment of the encapsulation matrix to mimic that of the native pancreatic scaffold that houses islet cells. That microenvironment includes biological and mechanical cues that support the viability and function of the cells. In this study, the alginate hydrogel was modified to mimic the pancreatic microenvironment by incorporation of extracellular matrix (ECM). Mechanical and biological changes in the encapsulating alginate matrix were made through stiffness modulation and incorporation of decellularized ECM, respectively. Islets were then encapsulated in this new biomimetic hydrogel and their insulin production was measured after 7 days in vitro. We found that manipulation of the alginate hydrogel matrix to simulate both physical and biological cues for the encapsulated islets enhances the mechanical strength of the encapsulated islet constructs as well as their function. Our data suggest that these modifications have the potential to improve the success rate of encapsulated islet transplantation.

Facilitating islet transplantation using a three-step approach with mesenchymal stem cells, encapsulation, and pulsed focused ultrasound

BACKGROUND

The aim of this study was to examine the effect of a three-step approach that utilizes the application of adipose tissue-derived mesenchymal stem cells (AD-MSCs), encapsulation, and pulsed focused ultrasound (pFUS) to help the engraftment and function of transplanted islets.

METHODS

In step 1, islets were co-cultured with AD-MSCs to form a coating of AD-MSCs on islets: here, AD-MSCs had a cytoprotective effect on islets; in step 2, islets coated with AD-MSCs were conformally encapsulated in a thin layer of alginate using a co-axial air-flow method: here, the capsule enabled AD-MSCs to be in close proximity to islets; in step 3, encapsulated islets coated with AD-MSCs were treated with pFUS: here, pFUS enhanced the secretion of insulin from islets as well as stimulated the cytoprotective effect of AD-MSCs.

RESULTS

Our approach was shown to prevent islet death and preserve islet functionality in vitro. When 175 syngeneic encapsulated islets coated with AD-MSCs were transplanted beneath the kidney capsule of diabetic mice, and then followed every 3 days with pFUS treatment until day 12 post-transplantation, we saw a significant improvement in islet function with diabetic animals re-establishing glycemic control over the course of our study (i.e., 30 days). In addition, our approach was able to enhance islet engraftment by facilitating their revascularization and reducing inflammation.

CONCLUSIONS

This study demonstrates that our clinically translatable three-step approach is able to improve the function and viability of transplanted islets.

Glucosamine potentiates the differentiation of adipose-derived stem cells into glucose-responsive insulin-producing cells

Background

Islet transplantation might be a logical strategy to restore insulin secretion for the treatment of diabetes, however, the scarcity of donors poses an obstacle for such a treatment. As an alternative islet source, differentiation of stem cells into insulin-producing cells (IPCs) has been tried. Many protocols have been developed to improve the efficiency of differentiation of stem cells into IPCs. In this study, we investigated whether glucosamine supplementation during differentiation of human adipose-derived stem cells (hADSCs) into IPCs can improve the insulin secretory function.

Methods

Glucosamine was added to the original differentiation medium at different stages of differentiation of hADSCs into IPCs for 12 days and insulin secretion was analyzed.

Results

Addition of glucosamine alone to the growth medium of hADSCs did not affect the differentiation of hADSCs to IPCs. Supplementation of the differentiation medium with glucosamine at a later stage (protocol G3) proved to have the greatest effect on IPC differentiation. Basal and glucose-stimulated insulin secretion (GSIS) was significantly increased and the expression of insulin and C-peptide was increased in differentiated IPCs as compared with that in differentiated IPCs using the conventional protocol (protocol C). In addition, the expression of beta-cell specific transcription factors such as pancreatic and duodenal homeobox1 (PDX1) and neurogenin 3 (NGN3) was also increased. Furthermore, the expression of genes related to insulin secretion, including synaptotagmin 4 (Syt4), glucokinase (Gck) and glucose transporter 2 (Glut2), was also increased.

Conclusions

We conclude that glucosamine supplementation potentiates the differentiation of hADSCs into IPCs.

Surrogate testes: Allogeneic spermatogonial stem cell transplantation within an encapsulation device may restore male fertility

Toxic insult to the gonads by chemotherapy or radiotherapy can lead to permanent infertility. It's an important health concern because each year more than 4000 male patients are at risk of azoospermia in the United States due to gonadotoxicity of the regimens used. There are also several benign/genetic diseases whose natural course can result in infertility without gonadotoxic therapy. Considering the fact that most of these people are cured and survive with the advent of modern medicine, infertility is related to serious psychological and relationship implications and parenthood is a significant issue for those patients. Semen cryopreservation option is available for postpubertal adolescent and adult men, while children do not have this storing option since they do not have mature spermatozoa. However, their testes contain spermatogonial stem cells (SSCs), which are initiators of spermatogenesis. Promising findings in animal studies and human cell lines have encouraged scientists that SSCs may be hope for restoring fertility option of patients who cannot produce functional sperm and who have no other choice to preserve their future fertility. For this reason, several centers around the world already began to collect and cryopreserve testicular tissue or cells with anticipation that SSC-based therapies will be available in the near future; however, an optimal transplantation design in humans is yet to be developed. Here we propose an allogeneic testicular stem cell transplantation with an encapsulation device to restore fertility in patients with infertility. We endeavor to discuss the reliability of this method with the current literature and bring the evidence on its feasibility.

Stem Cell Therapy for Diabetes: Beta Cells versus Pancreatic Progenitors

Diabetes mellitus (DM) is one of the most prevalent metabolic disorders. In order to replace the function of the destroyed pancreatic beta cells in diabetes, islet transplantation is the most widely practiced treatment. However, it has several limitations. As an alternative approach, human pluripotent stem cells (hPSCs) can provide an unlimited source of pancreatic cells that have the ability to secrete insulin in response to a high blood glucose level. However, the determination of the appropriate pancreatic lineage candidate for the purpose of cell therapy for the treatment of diabetes is still debated. While hPSC-derived beta cells are perceived as the ultimate candidate, their efficiency needs further improvement in order to obtain a sufficient number of glucose responsive beta cells for transplantation therapy. On the other hand, hPSC-derived pancreatic progenitors can be efficiently generated in vitro and can further mature into glucose responsive beta cells in vivo after transplantation. Herein, we discuss the advantages and predicted challenges associated with the use of each of the two pancreatic lineage products for diabetes cell therapy. Furthermore, we address the co-generation of functionally relevant islet cell subpopulations and structural properties contributing to the glucose responsiveness of beta cells, as well as the available encapsulation technology for these cells.

Encapsulation boosts islet-cell signature in differentiating human induced pluripotent stem cells via integrin signalling

Cell replacement therapies hold great therapeutic potential. Nevertheless, our knowledge of the mechanisms governing the developmental processes is limited, impeding the quality of differentiation protocols. Generating insulin-expressing cells in vitro is no exception, with the guided series of differentiation events producing heterogeneous cell populations that display mixed pancreatic islet phenotypes and immaturity. The achievement of terminal differentiation ultimately requires the in vivo transplantation of, usually, encapsulated cells. Here we show the impact of cell confinement on the pancreatic islet signature during the guided differentiation of alginate encapsulated human induced pluripotent stem cells (hiPSCs). Our results show that encapsulation improves differentiation by significantly reshaping the proteome landscape of the cells towards an islet-like signature. Pathway analysis is suggestive of integrins transducing the encapsulation effect into intracellular signalling cascades promoting differentiation. These analyses provide a molecular framework for understanding the confinement effects on hiPSCs differentiation while confirming its importance for this process.

Clinical Applications of Cell Encapsulation Technology

Cell encapsulation comprises immunoisolation three-dimensional systems for housing therapeutic cells that secrete bioactive compounds de novo and in a sustained manner. This allows transplantation of multiple allo- or xenogeneic cells without the aid of immunosuppressant drugs. Recent advances in the field have provided improvements to these cell-based drug delivery systems, which have gained the attention of the scientific community and inspired many biotechnological companies to develop their own product candidates. From micro- to macroencapsulation devices, this chapter describes some of the most important approaches that are being currently tested in late-stage clinical trials and are likely to reach the market as future game changers. Most studies involve the treatment of diabetes, eye disorders, and diseases of the central nervous system. However, many other pathologies are also amenable to benefit from this technology. Latest advances to overcome major pending challenges related to biosafety and efficacy are also discussed.

Engineering Strategies to Improve Islet Transplantation for Type 1 Diabetes Therapy

Type 1 diabetes is an autoimmune disease in which the immune system attacks insulin-producing beta cells of pancreatic islets. Type 1 diabetes can be treated with islet transplantation; however, patients must be administered immunosuppressants to prevent immune rejection of the transplanted islets if they are not autologous or not engineered with immune protection/isolation. To overcome biological barriers of islet transplantation, encapsulation strategies have been developed and robustly investigated. While islet encapsulation can prevent the need for immunosuppressants, these approaches have not shown much success in clinical trials due to a lack of long-term insulin production. Multiple engineering strategies have been used to improve encapsulation and post-transplantation islet survival. In addition, more efficient islet cryopreservation methods have been designed to facilitate the scaling-up of islet transplantation. Other islet sources have been identified including porcine islets and stem cell-derived islet-like aggregates. Overall, islet-laden capsule transplantation has greatly improved over the past 30 years and is moving towards becoming a clinically feasible treatment for type 1 diabetes.

Review of Advanced Hydrogel-Based Cell Encapsulation Systems for Insulin Delivery in Type 1 Diabetes Mellitus

: Type 1 Diabetes Mellitus (T1DM) is characterized by the autoimmune destruction of β-cells in the pancreatic islets. In this regard, islet transplantation aims for the replacement of the damaged β-cells through minimally invasive surgical procedures, thereby being the most suitable strategy to cure T1DM. Unfortunately, this procedure still has limitations for its widespread clinical application, including the need for long-term immunosuppression, the lack of pancreas donors and the loss of a large percentage of islets after transplantation. To overcome the aforementioned issues, islets can be encapsulated within hydrogel-like biomaterials to diminish the loss of islets, to protect the islets resulting in a reduction or elimination of immunosuppression and to enable the use of other insulin-producing cell sources. This review aims to provide an update on the different hydrogel-based encapsulation strategies of insulin-producing cells, highlighting the advantages and drawbacks for a successful clinical application.

Stem Cell Therapies for Treating Diabetes: Progress and Remaining Challenges

Restoration of insulin independence and normoglycemia has been the overarching goal in diabetes research and therapy. While whole-organ and islet transplantation have become gold-standard procedures in achieving glucose control in diabetic patients, the profound lack of suitable donor tissues severely hampers the broad application of these therapies. Here, we describe current efforts aimed at generating a sustainable source of functional human stem cell-derived insulin-producing islet cells for cell transplantation and present state-of-the-art efforts to protect such cells via immune modulation and encapsulation strategies.

The Role of Stiffness in Cell Reprogramming: A Potential Role for Biomaterials in Inducing Tissue Regeneration

The mechanotransduction is the process by which cells sense mechanical stimuli such as elasticity, viscosity, and nanotopography of extracellular matrix and translate them into biochemical signals. The mechanotransduction regulates several aspects of the cell behavior, including migration, proliferation, and differentiation in a time-dependent manner. Several reports have indicated that cell behavior and fate are not transmitted by a single signal, but rather by an intricate network of many signals operating on different length and timescales that determine cell fate. Since cell biology and biomaterial technology are fundamentals in cell-based regenerative therapies, comprehending the interaction between cells and biomaterials may allow the design of new biomaterials for clinical therapeutic applications in tissue regeneration. In this work, we present the most relevant mechanism by which the biomechanical properties of extracellular matrix (ECM) influence cell reprogramming, with particular attention on the new technologies and materials engineering, in which are taken into account not only the biochemical and biophysical signals patterns but also the factor time.

Characterization of Polyethylene Glycol-Reinforced Alginate Microcapsules for Mechanically Stable Cell Immunoisolation

Islet transplantation within mechanically stable microcapsules offers the promise of long-term diabetes reversal without chronic immunosuppression. Reinforcing the ionically gelled network of alginate (ALG) hydrogels with covalently linked polyethylene glycol (PEG) may create hybrid structures with desirable mechanical properties. This report describes the fabrication of hybrid PEG-ALG interpenetrating polymer networks and the investigation of microcapsule swelling, surface modulus, rheology, compression, and permeability. It is demonstrated that hybrid networks are more resistant to bulk swelling and compressive deformation and display improved shape recovery and long-term resilience. Interestingly, it is shown that PEG-ALG networks behave like ALG during microscale surface deformation and small amplitude shear while exhibiting similar permeability properties. The results from this report's in vitro characterization are interpreted according to viscoelastic polymer theory and provide new insight into hybrid hydrogel mechanical behavior. This new understanding of PEG-ALG mechanical performance is then linked to previous work that demonstrated the success of hybrid polymer immunoisolation devices in vivo.

Stem cell therapies for Type 1 diabetes: current status and proposed road map to guide successful clinical trials

Many people with Type 1 diabetes struggle with the burden of self-management and are unable to achieve optimal glycaemic control without risk of hypoglycaemia. Future therapies with the potential to reduce the risk for short- and long-term complications while simultaneously reducing the burden of diabetes are therefore attractive. β-cell replacement is one strategy which might achieve this. Islet transplantation is limited by organ supply and the risks of long-term immunosuppression. Encapsulated stem-cell-derived β cells have the potential to address both of these issues and phase I/II clinical trials of encapsulated pancreatic progenitors have begun. A significant risk associated with the translation of stem-cell science to the clinical management of Type 1 diabetes is an underestimation of the complexity of the process and a mismatch between the hype and the expectations of both people with Type 1 diabetes and the public. We provide an update on progress in clinical trials of encapsulated stem-cell-derived β cells and propose a road map for the design and conduct of future trials to facilitate the translation of this exciting science to clinical care.

Type 1 Diabetes Mellitus reversal via implantation of magnetically purified microencapsulated pseudoislets

Microencapsulation of pancreatic islets for the treatment of Type I Diabetes Mellitus (T1DM) generates a high quantity of empty microcapsules, resulting in high therapeutic graft volumes that can enhance the host's immune response. We report a 3D printed microfluidic magnetic sorting device for microcapsules purification with the objective to reduce the number of empty microcapsules prior transplantation. In this study, INS1E pseudoislets were microencapsulated within alginate (A) and alginate-poly-L-lysine-alginate (APA) microcapsules and purified through the microfluidic device. APA microcapsules demonstrated higher mechanical integrity and stability than A microcapsules, showing better pseudoislets viability and biological function. Importantly, we obtained a reduction of the graft volume of 77.5% for A microcapsules and 78.6% for APA microcapsules. After subcutaneous implantation of induced diabetic Wistar rats with magnetically purified APA microencapsulated pseudoislets, blood glucose levels were restored into normoglycemia (<200 mg/dL) for almost 17 weeks. In conclusion, our described microfluidic magnetic sorting device represents a great alternative approach for the graft volume reduction of microencapsulated pseudoislets and its application in T1DM disease.

Coatings on mammalian cells: interfacing cells with their environment

The research community is intent on harnessing increasingly complex biological building blocks. At present, cells represent a highly functional component for integration into higher order systems. In this review, we discuss the current application space for cellular coating technologies and emphasize the relationship between the target application and coating design. We also discuss how the cell and the coating interact in common analytical techniques, and where caution must be exercised in the interpretation of results. Finally, we look ahead at emerging application areas that are ideal for innovation in cellular coatings. In all, cellular coatings leverage the machinery unique to specific cell types, and the opportunities derived from these hybrid assemblies have yet to be fully realized.

Oxygenation strategies for encapsulated islet and beta cell transplants

Human allogeneic islet transplantation (ITx) is emerging as a promising treatment option for qualified patients with type 1 diabetes. However, widespread clinical application of allogeneic ITx is hindered by two critical barriers: the need for systemic immunosuppression and the limited supply of human islet tissue. Biocompatible, retrievable immunoisolation devices containing glucose-responsive insulin-secreting tissue may address both critical barriers by enabling the more effective and efficient use of allogeneic islets without immunosuppression in the near-term, and ultimately the use of a cell source with a virtually unlimited supply, such as human stem cell-derived β-cells or xenogeneic (porcine) islets with minimal or no immunosuppression. However, even though encapsulation methods have been developed and immunoprotection has been successfully tested in small and large animal models and to a limited extent in proof-of-concept clinical studies, the effective use of encapsulation approaches to convincingly and consistently treat diabetes in humans has yet to be demonstrated. There is increasing consensus that inadequate oxygen supply is a major factor limiting their clinical translation and routine implementation. Poor oxygenation negatively affects cell viability and β-cell function, and the problem is exacerbated with the high-density seeding required for reasonably-sized clinical encapsulation devices. Approaches for enhanced oxygen delivery to encapsulated tissues in implantable devices are therefore being actively developed and tested. This review summarizes fundamental aspects of islet microarchitecture and β-cell physiology as well as encapsulation approaches highlighting the need for adequate oxygenation; it also evaluates existing and emerging approaches for enhanced oxygen delivery to encapsulation devices, particularly with the advent of β-cell sources from stem cells that may enable the large-scale application of this approach.

Nanotechnology in cell replacement therapies for type 1 diabetes

Islet transplantation is a promising long-term, compliance-free, complication-preventing treatment for type 1 diabetes. However, islet transplantation is currently limited to a narrow set of patients due to the shortage of donor islets and side effects from immunosuppression. Encapsulating cells in an immunoisolating membrane can allow for their transplantation without the need for immunosuppression. Alternatively, "open" systems may improve islet health and function by allowing vascular ingrowth at clinically attractive sites. Many processes that enable graft success in both approaches occur at the nanoscale level-in this review we thus consider nanotechnology in cell replacement therapies for type 1 diabetes. A variety of biomaterial-based strategies at the nanometer range have emerged to promote immune-isolation or modulation, proangiogenic, or insulinotropic effects. Additionally, coating islets with nano-thin polymer films has burgeoned as an islet protection modality. Materials approaches that utilize nanoscale features manipulate biology at the molecular scale, offering unique solutions to the enduring challenges of islet transplantation.

Cell encapsulation: Overcoming barriers in cell transplantation in diabetes and beyond

Cell-based therapy is emerging as a promising strategy for treating a wide range of human diseases, such as diabetes, blood disorders, acute liver failure, spinal cord injury, and several types of cancer. Pancreatic islets, blood cells, hepatocytes, and stem cells are among the many cell types currently used for this strategy. The encapsulation of these "therapeutic" cells is under intense investigation to not only prevent immune rejection but also provide a controlled and supportive environment so they can function effectively. Some of the advanced encapsulation systems provide active agents to the cells and enable a complete retrieval of the graft in the case of an adverse body reaction. Here, we review various encapsulation strategies developed in academic and industrial settings, including the state-of-the-art technologies in advanced preclinical phases as well as those undergoing clinical trials, and assess their advantages and challenges. We also emphasize the importance of stimulus-responsive encapsulated cell systems that provide a "smart and live" therapeutic delivery to overcome barriers in cell transplantation as well as their use in patients.

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-I diabetes. Microspheres for islet encapsulation have enabled long-term glycaemic control in diabetic rodent models; yet human patients transplanted with equivalent microsphere formulations have experienced only transient islet-graft function, owing to a vigorous foreign-body reaction (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. Although one month post-implantation all formulations elicited significant FBR and PFO, three chemically modified, immune-modulating alginate formulations elicited 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.

The rat pancreatic body tail as a source of a novel extracellular matrix scaffold for endocrine pancreas bioengineering

Background

Regenerative medicine and tissue engineering are promising approaches for organ transplantation. Extracellular matrix (ECM) based scaffolds obtained through the decellularization of natural organs have become the preferred platform for organ bioengineering. In the field of pancreas bioengineering, acellular scaffolds from different animals approximate the biochemical, spatial and vascular relationships of the native extracellular matrix and have been proven to be a good platform for recellularization and in vitro culture. However, artificial endocrine pancreases based on these whole pancreatic scaffolds have a critical flaw, specifically their difficult in vivo transplantation, and connecting their vessels to the recipient is a major limitation in the development of pancreatic tissue engineering. In this study, we focus on preparing a novel acellular extracellular matrix scaffold derived from the rat pancreatic body tail (pan-body-tail ECM scaffold).

Results

Several analyses confirmed that our protocol effectively removes cellular material while preserving ECM proteins and the native vascular tree. DNA quantification demonstrated an obvious reduction of DNA compared with that of the natural organ (from 931.9 ± 267.8 to 11.7 ± 3.6 ng/mg, P < 0.001); the retention of the sGAG in the decellularized pancreas (0.878 ± 0.37) showed no significant difference from the natural pancreas (0.819 ± 0.1) (P > 0.05). After transplanted with the recellularized pancreas, fasting glucose levels declined to 9.08 ± 2.4 mmol/l within 2 h of the operation, and 8 h later, they had decreased to 4.7 ± 1.8 mmol/l (P < 0.05).

Conclusions

The current study describes a novel pancreatic ECM scaffold prepared from the rat pancreatic body tail via perfusion through the left gastric artery. We further showed the pioneering possibility of in vivo circulation-connected transplantation of a recellularized pancreas based on this novel scaffold. By providing such a promising pancreatic ECM scaffold, the present study might represent a key improvement and have a positive impact on endocrine pancreas bioengineering.

Polymeric Scaffolds for Pancreatic Tissue Engineering: A Review

In recent years, there has been an alarming increase in the incidence of diabetes, with one in every eleven individuals worldwide suffering from this debilitating disease. As the available treatment options fail to reduce disease progression, novel avenues such as the bioartificial pancreas are being given serious consideration. In the past decade, the research focus has shifted towards the field of tissue engineering, which helps to design biological substitutes for repair and replacement of non-functional or damaged organs. Scaffolds constitute an integral part of tissue engineering; they have been shown to mimic the native extracellular matrix, thereby supporting cell viability and proliferation. This review offers a novel compilation of the recent advances in polymeric scaffolds, which are used for pancreatic tissue engineering. Furthermore, in this article, the design strategies for bioartificial pancreatic constructs and their future applications in cell-based therapy are discussed.

Collagen type VI interaction improves human islet survival in immunoisolating microcapsules for treatment of diabetes

Collagens are the most abundant fibrous protein in the human body and constitute the main structural element of the extracellular matrix. It provides mechanical and physiological support for cells. In the pancreas, collagen VI content is more than double that of collagen I or IV. It is a major component of the islet-exocrine interface and could be involved in islet-cell survival. To test the impact of collagen VI on human encapsulated pancreatic islets-cells, we tested the effects of exogenous collagen type VI on in vitro functional survival of alginate encapsulated human islet-cells. Concentrations tested ranged from 0.1 to 50 µg/ml. Islets in capsules without collagen type VI served as control. Islet-cell interaction with collagen type VI at concentrations of 0.1 and 10 µg/ml, promoted islet-cell viability (p<0.05). Although no improvement in glucose induced insulin secretion (GSIS) was observed, islets in capsules without incorporation of collagen type VI showed more dysfunction and oxygen consumption rates was improved by inclusion of collagen type VI. Our results demonstrate that incorporation of collagen type VI in immunoisolated human islets supports in vitro viability and survival of human pancreatic islets.