3D Printed Vascularized Device for Subcutaneous Transplantation of Human Islets

Advances and challenges of the cell-based therapies among diabetic patients

Diabetes mellitus is a significant global public health challenge, with a rising prevalence and associated morbidity and mortality. Cell therapy has evolved over time and holds great potential in diabetes treatment. In the present review, we discussed the recent progresses in cell-based therapies for diabetes that provides an overview of islet and stem cell transplantation technologies used in clinical settings, highlighting their strengths and limitations. We also discussed immunomodulatory strategies employed in cell therapies. Therefore, this review highlights key progresses that pave the way to design transformative treatments to improve the life quality among diabetic patients.

Encapsulation and immune protection for type 1 diabetes cell therapy

Type 1 Diabetes (T1D) involves the autoimmune destruction of insulin-producing β-cells in the pancreas. Exogenous insulin injections are the current therapy but are user-dependent and cannot fully recapitulate physiological insulin secretion dynamics. Since the emergence of allogeneic cell therapy for T1D, the Edmonton Protocol has been the most promising immunosuppression protocol for cadaveric islet transplantation, but the lack of donor islets, poor cell engraftment, and required chronic immunosuppression have limited its application as a therapy for T1D. Encapsulation in biomaterials on the nano-, micro-, and macro-scale offers the potential to integrate islets with the host and protect them from immune responses. This method can be applied to different cell types, including cadaveric, porcine, and stem cell-derived islets, mitigating the issue of a lack of donor cells. This review covers progress in the efforts to integrate insulin-producing cells from multiple sources to T1D patients as a form of cell therapy.

Therapeutic approaches for Type 1 Diabetes: Promising cell-based approaches to achieve ultimate success

Type 1 Diabetes mellitus (T1DM) is a chronic metabolic disorder characterized by pancreatic β-cells destruction. Despite substantial advances in T1DM treatment, lifelong exogenous insulin administration is the mainstay of treatments, and constant control of glucose levels is still a challenge. Endogenous insulin production by replacing insulin-producing cells is an alternative, but the lack of suitable donors is accounted as one of the main obstacles to its widespread application. The research and trials overview demonstrates that endogenous production of insulin has started to go beyond the deceased-derived to stem cells-derived insulin-producing cells. Several protocols have been developed over the past couple of years for generating insulin-producing cells (IPCs) from various stem cell types and reprogramming fully differentiated cells. A straightforward and quick method for achieving this goal is to investigate and apply the β-cell specific transcription factors as a direct strategy for IPCs generation. In this review, we emphasize the significance of transcription factors in IPCs development from different non-beta cell sources, and pertinent research underlies the marked progress in the methods for generating insulin-producing cells and application for Type 1 Diabetes treatment.

Stem cells therapy for diabetes: from past to future

Diabetes mellitus is a chronic disease of carbohydrate metabolism characterized by uncontrolled hyperglycemia due to the body's impaired ability to produce or respond to insulin. Oral or injectable exogenous insulin and its analogs cannot mimic endogenous insulin secreted by healthy individuals, and pancreatic and islet transplants face a severe shortage of sources and transplant complications, all of which limit the widespread use of traditional strategies in diabetes treatment. We are now in the era of stem cells and their potential in ameliorating human disease. At the same time, the rapid development of gene editing and cell-encapsulation technologies has added to the wings of stem cell therapy. However, there are still many unanswered questions before stem cell therapy can be applied clinically to patients with diabetes. In this review, we discuss the progress of strategies to obtain insulin-producing cells from different types of stem cells, the application of gene editing in stem cell therapy for diabetes, as well as summarize the current advanced cell encapsulation technologies in diabetes therapy and look forward to the future development of stem cell therapy in diabetes.

Visible light photocrosslinking of sugar beet pectin for 3D bioprinting applications

Herein, we report the hydrogelation of sugar beet pectin (SBP) via visible light-mediated photocrosslinking and its applications in extrusion-based 3D bioprinting. Rapid hydrogelation (<15 s) was achieved by applying 405 nm visible light to an SBP solution in the presence of tris(bipyridine)ruthenium(II) chloride hexahydrate ([Ru(bpy)₃]²⁺) and sodium persulfate (SPS). The mechanical properties of the hydrogel could be tuned by controlling the visible light irradiation time and concentrations of SBP, [Ru(bpy)₃]²⁺, and SPS. High-fidelity 3D hydrogel constructs were fabricated by extruding inks containing 3.0 wt% SBP, 1.0 mM [Ru(bpy)₃]²⁺, and 1.0 mM SPS. Human hepatoblastoma (HepG2) cells encapsulated in SBP hydrogels remained viable and metabolically active after 14 d of culture. Overall, this study demonstrates the feasibility of applying SBP and a visible light-mediated photocrosslinking system to the 3D bioprinting of cell-laden constructs for tissue engineering applications.

Engineering a versatile and retrievable cell macroencapsulation device for the delivery of therapeutic proteins

Encapsulated cell therapy holds a great potential to deliver sustained levels of highly potent therapeutic proteins to patients and improve chronic disease management. A versatile encapsulation device that is biocompatible, scalable, and easy to administer, retrieve, or replace has yet to be validated for clinical applications. Here, we report on a cargo-agnostic, macroencapsulation device with optimized features for protein delivery. It is compatible with adherent and suspension cells, and can be administered and retrieved without burdensome surgical procedures. We characterized its biocompatibility and showed that different cell lines producing different therapeutic proteins can be combined in the device. We demonstrated the ability of cytokine-secreting cells encapsulated in our device and implanted in human skin to mobilize and activate antigen-presenting cells, which could potentially serve as an effective adjuvant strategy in cancer immunization therapies. We believe that our device may contribute to cell therapies for cancer, metabolic disorders, and protein-deficient diseases.

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.

Cell Encapsulation and 3D Bioprinting for Therapeutic Cell Transplantation

The promise of cell therapy has been augmented by introducing biomaterials, where intricate scaffold shapes are fabricated to accommodate the cells within. In this review, we first discuss cell encapsulation and the promising potential of biomaterials to overcome challenges associated with cell therapy, particularly cellular function and longevity. More specifically, cell therapies in the context of autoimmune disorders, neurodegenerative diseases, and cancer are reviewed from the perspectives of preclinical findings as well as available clinical data. Next, techniques to fabricate cell-biomaterials constructs, focusing on emerging 3D bioprinting technologies, will be reviewed. 3D bioprinting is an advancing field that enables fabricating complex, interconnected, and consistent cell-based constructs capable of scaling up highly reproducible cell-biomaterials platforms with high precision. It is expected that 3D bioprinting devices will expand and become more precise, scalable, and appropriate for clinical manufacturing. Rather than one printer fits all, seeing more application-specific printer types, such as a bioprinter for bone tissue fabrication, which would be different from a bioprinter for skin tissue fabrication, is anticipated in the future.

Characterization of human islet function in a convection-driven intravascular bioartificial pancreas

Clinical islet transplantation for treatment of type 1 diabetes (T1D) is limited by the shortage of pancreas donors and need for lifelong immunosuppressive therapy. A convection-driven intravascular bioartificial pancreas (iBAP) based on highly permeable, yet immunologically protective, silicon nanopore membranes (SNM) holds promise to sustain islet function without the need for immunosuppressants. Here, we investigate short-term functionality of encapsulated human islets in an iBAP prototype. Using the finite element method (FEM), we calculated predicted oxygen profiles within islet scaffolds at normalized perifusion rates of 14-200 nl/min/IEQ. The modeling showed the need for minimum in vitro and in vivo islet perifusion rates of 28 and 100 nl/min/IEQ, respectively to support metabolic insulin production requirements in the iBAP. In vitro glucose-stimulated insulin secretion (GSIS) profiles revealed a first-phase response time of <15 min and comparable insulin production rates to standard perifusion systems (~10 pg/min/IEQ) for perifusion rates of 100-200 nl/min/IEQ. An intravenous glucose tolerance test (IVGTT), performed at a perifusion rate of 100-170 nl/min/IEQ in a non-diabetic pig, demonstrated a clinically relevant C-peptide production rate (1.0-2.8 pg/min/IEQ) with a response time of <5 min.

The future treatment for type 1 diabetes: Pig islet- or stem cell-derived β cells?

Replacement of β cells is only a curative approach for type 1 diabetes (T1D) patients to avoid the threat of iatrogenic hypoglycemia. In this pursuit, islet allotransplantation under Edmonton's protocol emerged as a medical miracle to attain hypoglycemia-free insulin independence in T1D. Shortage of allo-islet donors and post-transplantation (post-tx) islet loss are still unmet hurdles for the widespread application of this therapeutic regimen. The long-term survival and effective insulin independence in preclinical studies have strongly suggested pig islets to cure overt hyperglycemia. Importantly, CRISPR-Cas9 technology is pursuing to develop "humanized" pig islets that could overcome the lifelong immunosuppression drug regimen. Lately, induced pluripotent stem cell (iPSC)-derived β cell approaches are also gaining momentum and may hold promise to yield a significant supply of insulin-producing cells. Theoretically, personalized β cells derived from a patient's iPSCs is one exciting approach, but β cell-specific immunity in T1D recipients would still be a challenge. In this context, encapsulation studies on both pig islet as well as iPSC-β cells were found promising and rendered long-term survival in mice. Oxygen tension and blood vessel growth within the capsules are a few of the hurdles that need to be addressed. In conclusion, challenges associated with both procedures, xenotransplantation (of pig-derived islets) and stem cell transplantation, are required to be cautiously resolved before their clinical application.

Implantable niche with local immunosuppression for islet allotransplantation achieves type 1 diabetes reversal in rats

Pancreatic islet transplantation efficacy for type 1 diabetes (T1D) management is limited by hypoxia-related graft attrition and need for systemic immunosuppression. To overcome these challenges, we developed the Neovascularized Implantable Cell Homing and Encapsulation (NICHE) device, which integrates direct vascularization for facile mass transfer and localized immunosuppressant delivery for islet rejection prophylaxis. Here, we investigated NICHE efficacy for allogeneic islet transplantation and long-term diabetes reversal in an immunocompetent, male rat model. We demonstrated that allogeneic islets transplanted within pre-vascularized NICHE were engrafted, revascularized, and functional, reverting diabetes in rats for over 150 days. Notably, we confirmed that localized immunosuppression prevented islet rejection without inducing toxicity or systemic immunosuppression. Moreover, for translatability efforts, we showed NICHE biocompatibility and feasibility of deployment as well as short-term allogeneic islet engraftment in an MHC-mismatched nonhuman primate model. In sum, the NICHE holds promise as a viable approach for safe and effective islet transplantation and long-term T1D management.

3D Bioprinting for Pancreas Engineering/Manufacturing

Diabetes is the most common chronic disease in the world, and it brings a heavy burden to people's health. Against this background, diabetic research, including islet functionalization has become a hot topic in medical institutions all over the world. Especially with the rapid development of microencapsulation and three-dimensional (3D) bioprinting technologies, organ engineering and manufacturing have become the main trends for disease modeling and drug screening. Especially the advanced 3D models of pancreatic islets have shown better physiological functions than monolayer cultures, suggesting their potential in elucidating the behaviors of cells under different growth environments. This review mainly summarizes the latest progress of islet capsules and 3D printed pancreatic organs and introduces the activities of islet cells in the constructs with different encapsulation technologies and polymeric materials, as well as the vascularization and blood glucose control capabilities of these constructs after implantation. The challenges and perspectives of the pancreatic organ engineering/manufacturing technologies have also been demonstrated.

Type 1 diabetes and engineering enhanced islet transplantation

The development of new therapeutic approaches to treat type 1 diabetes mellitus (T1D) relies on the precise understanding and deciphering of insulin-secreting β-cell biology, as well as the mechanisms responsible for their autoimmune destruction. β-cell or islet transplantation is viewed as a potential long-term therapy for the millions of patients with diabetes. To advance the field of insulin-secreting cell transplantation, two main research areas are currently investigated by the scientific community: (1) the identification of the developmental pathways that drive the differentiation of stem cells into insulin-producing cells, providing an inexhaustible source of cells; and (2) transplantation strategies and engineered transplants to provide protection and enhance the functionality of transplanted cells. In this review, we discuss the biology of pancreatic β-cells, pathology of T1D and current state of β-cell differentiation. We give a comprehensive view and discuss the different possibilities to engineer enhanced insulin-secreting cell/islet transplantation from a translational perspective.

Cell delivery systems: Toward the next generation of cell therapies for type 1 diabetes

Immunoprotection and oxygen supply are vital in implementing a cell therapy for type 1 diabetes (T1D). Without these features, the transplanted islet cell clusters will be rejected by the host immune system, and necrosis will occur due to hypoxia. The use of anti-rejection drugs can help protect the transplanted cells from the immune system; yet, they also may have severe side effects. Cell delivery systems (CDS) have been developed for islet transplantation to avoid using immunosuppressants. CDS provide physical barriers to reduce the immune response and chemical coatings to reduce host fibrotic reaction. In some CDS, there is architecture to support vascularization, which enhances oxygen exchange. In this review, we discuss the current clinical and preclinical studies using CDS without immunosuppression as a cell therapy for T1D. We find that though CDS have been demonstrated for their ability to support immunoisolation of the grafted cells, their functionality has not been fully optimized. Current advanced methods in clinical trials demonstrate the systems are partly functional, physically complicated to implement or inefficient. However, modifications are being made to overcome these issues.

Vascularization in Bioartificial Parenchymal Tissue: Bioink and Bioprinting Strategies

Among advanced therapy medicinal products, tissue-engineered products have the potential to address the current critical shortage of donor organs and provide future alternative options in organ replacement therapy. The clinically available tissue-engineered products comprise bradytrophic tissue such as skin, cornea, and cartilage. A sufficient macro- and microvascular network to support the viability and function of effector cells has been identified as one of the main challenges in developing bioartificial parenchymal tissue. Three-dimensional bioprinting is an emerging technology that might overcome this challenge by precise spatial bioink deposition for the generation of a predefined architecture. Bioinks are printing substrates that may contain cells, matrix compounds, and signaling molecules within support materials such as hydrogels. Bioinks can provide cues to promote vascularization, including proangiogenic signaling molecules and cocultured cells. Both of these strategies are reported to enhance vascularization. We review pre-, intra-, and postprinting strategies such as bioink composition, bioprinting platforms, and material deposition strategies for building vascularized tissue. In addition, bioconvergence approaches such as computer simulation and artificial intelligence can support current experimental designs. Imaging-derived vascular trees can serve as blueprints. While acknowledging that a lack of structured evidence inhibits further meta-analysis, this review discusses an end-to-end process for the fabrication of vascularized, parenchymal tissue.

Hyaluronic acid methacrylate/pancreatic extracellular matrix as a potential 3D printing bioink for constructing islet organoids

Islet transplantation has poor long-term efficacy because of the lack of extracellular matrix support and neovascularization; this limits its wide application in diabetes research. In this study, we develop a 3D-printed islet organoid by combining a pancreatic extracellular matrix (pECM) and hyaluronic acid methacrylate (HAMA) as specific bioinks. The HAMA/pECM hydrogel was validated in vitro to maintain islet cell adhesion and morphology through the Rac1/ROCK/MLCK signaling pathway, which helps improve islet function and activity. Further, in vivo experiments confirmed that the 3D-printed islet-encapsulated HAMA/pECM hydrogel increases insulin levels in diabetic mice, maintains blood glucose levels within a normal range for 90 days, and rapidly secretes insulin in response to blood glucose stimulation. In addition, the HAMA/pECM hydrogel can facilitate the attachment and growth of new blood vessels and increase the density of new vessels. Meanwhile, the designed 3D-printed structure was conducive to the formation of vascular networks and it promoted the construction of 3D-printed islet organoids. In conclusion, our experiments optimized the HAMA/pECM bioink composition and 3D-printed structure of islet organoids with promising therapeutic effects compared with the HAMA hydrogel group that can be potentially used in clinical applications to improve the effectiveness and safety of islet transplantation in vivo. STATEMENT OF SIGNIFICANCE: The extraction process of pancreatic islets can easily cause damage to the extracellular matrix and vascular system, resulting in poor islet transplantation efficiency. We developed a new tissue-specific bioink by combining pancreatic extracellular matrix (pECM) and hyaluronic acid methacrylate (HAMA). The islet organoids constructed by 3D printing can mimic the microenvironment of the pancreas and maintain islet cell adhesion and morphology through the Rac1/ROCK/MLCK signaling pathway, thereby improving islet function and activity. In addition, the 3D-printed structures we designed are favorable for the formation of new blood vessel networks, bringing hope for the long-term efficacy of islet transplantation.

Emerging local immunomodulatory strategies to circumvent systemic immunosuppression in cell transplantation

INTRODUCTION

Cell transplantation is a promising curative therapeutic strategy whereby impaired organ functions can be restored without the need for whole organ transplantation. A key challenge in allotransplantation is the requirement for life-long systemic immunosuppression to prevent rejection, which is associated with serious adverse effects such as increased risk of opportunistic infections and the development of neoplasms. This challenge underscores the urgent need for novel strategies to prevent graft rejection while abrogating toxicity-associated adverse events.

AREAS COVERED

We review recent advances in immunoengineering strategies for localized immunomodulation that aim to support allograft function and provide immune tolerance in a safe and effective manner.

EXPERT OPINION

Immunoengineering strategies are tailored approaches for achieving immunomodulation of the transplant microenvironment. Biomaterials can be adapted for localized and controlled release of immunomodulatory agents, decreasing the effective dose threshold and frequency of administration. The future of transplant rejection management lies in the shift from systemic to local immunomodulation with suppression of effector and activation of regulatory T cells, to promote immune tolerance.

Integrating Additive Manufacturing Techniques to Improve Cell-Based Implants for the Treatment of Type 1 Diabetes

The increasing global prevalence of endocrine diseases like type 1 diabetes mellitus (T1DM) elevates the need for cellular replacement approaches, which can potentially enhance therapeutic durability and outcomes. Central to any cell therapy is the design of delivery systems that support cell survival and integration. In T1DM, well-established fabrication methods have created a wide range of implants, ranging from 3D macro-scale scaffolds to nano-scale coatings. These traditional methods, however, are often challenged by their inherent limitations in reproducible and discrete fabrication, particularly when scaling to the clinic. Additive manufacturing (AM) techniques provide a means to address these challenges by delivering improved control over construct geometry and microscale component placement. While still early in development in the context of T1DM cellular transplantation, the integration of AM approaches serves to improve nutrient material transport, vascularization efficiency, and the accuracy of cell, matrix, and local therapeutic placement. This review highlights current methods in T1DM cellular transplantation and the potential of AM approaches to overcome these limitations. In addition, emerging AM technologies and their broader application to cell-based therapy are discussed.

Engineering β Cell Replacement Therapies for Type 1 Diabetes: Biomaterial Advances and Considerations for Macroscale Constructs

While significant progress has been made in treatments for type 1 diabetes (T1D) based on exogenous insulin, transplantation of insulin-producing cells (islets or stem cell-derived β cells) remains a promising curative strategy. The current paradigm for T1D cell therapy is clinical islet transplantation (CIT)-the infusion of islets into the liver-although this therapeutic modality comes with its own limitations that deteriorate islet health. Biomaterials can be leveraged to actively address the limitations of CIT, including undesired host inflammatory and immune responses, lack of vascularization, hypoxia, and the absence of native islet extracellular matrix cues. Moreover, in efforts toward a clinically translatable T1D cell therapy, much research now focuses on developing biomaterial platforms at the macroscale, at which implanted platforms can be easily retrieved and monitored. In this review, we discuss how biomaterials have recently been harnessed for macroscale T1D β cell replacement therapies.

Emerging strategies for beta cell transplantation to treat diabetes

Beta cell replacement has emerged as an attractive therapeutic alternative to traditional exogenous insulin administration for management of type 1 diabetes (T1D). Beta cells deliver insulin dynamically based on individual glycometabolic requirements, providing glycemic control while significantly reducing patient burden. Although transplantation into the portal circulation is clinically available, poor engraftment, low cell survival, and immune rejection have sparked investigation of alternative strategies for beta cell transplantation. In this review, we focus on current micro- and macroencapsulation technologies for beta cell transplantation and evaluate their advantages and challenges. Specifically, we comment on recent methods to ameliorate graft hypoxia including enhanced vascularization, reduction of pericapsular fibrotic overgrowth (PFO), and oxygen supplementation. We also discuss emerging beta cell-sourcing strategies to overcome donor shortage and provide insight into potential approaches to address outstanding challenges in the field.

Bioprinting Technology in Skin, Heart, Pancreas and Cartilage Tissues: Progress and Challenges in Clinical Practice

Bioprinting is an emerging additive manufacturing technique which shows an outstanding potential for shaping customized functional substitutes for tissue engineering. Its introduction into the clinical space in order to replace injured organs could ideally overcome the limitations faced with allografts. Presently, even though there have been years of prolific research in the field, there is a wide gap to bridge in order to bring bioprinting from "bench to bedside". This is due to the fact that bioprinted designs have not yet reached the complexity required for clinical use, nor have clear GMP (good manufacturing practices) rules or precise regulatory guidelines been established. This review provides an overview of some of the most recent and remarkable achievements for skin, heart, pancreas and cartilage bioprinting breakthroughs while highlighting the critical shortcomings for each tissue type which is keeping this technique from becoming widespread reality.

A 3D bioprinted hybrid encapsulation system for delivery of human pluripotent stem cell-derived pancreatic islet-like aggregates

Islet transplantation is a promising treatment for type 1 diabetes. However, treatment failure can result from loss of functional cells associated with cell dispersion, low viability, and severe immune response. To overcome these limitations, various islet encapsulation approaches have been introduced. Among them, macroencapsulation offers the advantages of delivering and retrieving a large volume of islets in one system. In this study, we developed a hybrid encapsulation system composed of a macroporous polymer capsule with stagger-type membrane and assemblable structure, and a nanoporous decellularized extracellular matrix (dECM) hydrogel containing pancreatic islet-like aggregates using 3D bioprinting technique. The outer part (macroporous polymer capsule) was designed to have an interconnected porous architecture, which allows insulin-producingβ-cells encapsulated in the hybrid encapsulation system to maintain their cellular behaviors, including viability, cell proliferation, and insulin-producing function. The inner part (nanoporous dECM hydrogel), composed of the 3D biofabricated pancreatic islet-like aggregates, was simultaneously placed into the macroporous polymer capsule in one step. The developed hybrid encapsulation system exhibited biocompatibilityin vitroandin vivoin terms of M1 macrophage polarization. Furthermore, by controlling the printing parameters, we generated islet-like aggregates, improving cell viability and functionality. Moreover, the 3D bioprinted pancreatic islet-like aggregates exhibited structural maturation and functional enhancement associated with intercellular interaction occurring at theβ-cell edges. In addition, we also investigated the therapeutic potential of a hybrid encapsulation system by integrating human pluripotent stem cell-derived insulin-producing cells, which are promising to overcome the donor shortage problem. In summary, these results demonstrated that the 3D bioprinting approach facilitates the fabrication of a hybrid islet encapsulation system with multiple materials and potentially improves the clinical outcomes by driving structural maturation and functional improvement of cells.

Tackling Ischemic Reperfusion Injury With the Aid of Stem Cells and Tissue Engineering

Ischemia is a severe condition in which blood supply, including oxygen (O), to organs and tissues is interrupted and reduced. This is usually due to a clog or blockage in the arteries that feed the affected organ. Reinstatement of blood flow is essential to salvage ischemic tissues, restoring O, and nutrient supply. However, reperfusion itself may lead to major adverse consequences. Ischemia-reperfusion injury is often prompted by the local and systemic inflammatory reaction, as well as oxidative stress, and contributes to organ and tissue damage. In addition, the duration and consecutive ischemia-reperfusion cycles are related to the severity of the damage and could lead to chronic wounds. Clinical pathophysiological conditions associated with reperfusion events, including stroke, myocardial infarction, wounds, lung, renal, liver, and intestinal damage or failure, are concomitant in due process with a disability, morbidity, and mortality. Consequently, preventive or palliative therapies for this injury are in demand. Tissue engineering offers a promising toolset to tackle ischemia-reperfusion injuries. It devises tissue-mimetics by using the following: (1) the unique therapeutic features of stem cells, i.e., self-renewal, differentiability, anti-inflammatory, and immunosuppressants effects; (2) growth factors to drive cell growth, and development; (3) functional biomaterials, to provide defined microarchitecture for cell-cell interactions; (4) bioprocess design tools to emulate the macroscopic environment that interacts with tissues. This strategy allows the production of cell therapeutics capable of addressing ischemia-reperfusion injury (IRI). In addition, it allows the development of physiological-tissue-mimetics to study this condition or to assess the effect of drugs. Thus, it provides a sound platform for a better understanding of the reperfusion condition. This review article presents a synopsis and discusses tissue engineering applications available to treat various types of ischemia-reperfusions, ultimately aiming to highlight possible therapies and to bring closer the gap between preclinical and clinical settings.

Tissue engineering and 3D printing of bioartificial pancreas for regenerative medicine in diabetes

Diabetes is a severe chronic disease worldwide. In various types of diabetes, the pancreatic beta cells fail to secrete sufficient insulin, at some point, to regulate blood glucose levels. Therefore, the replacement of dysfunctional pancreas, islets of Langerhans, or even the insulin-secreting beta cells facilitates physiological regulation of blood glucose levels. However, the current lack of sufficient donor human islets for cell replacement therapy precludes a routine and absolute cure for most of the existing diabetes cases globally. It is envisioned that tissue engineering of a bioartificial pancreas will revolutionize regenerative medicine and the treatment of diabetes. In this review, we discuss the anatomy and physiology of the pancreas, and identify the clinical considerations for engineering a bioartificial pancreas. Subsequently, we dissect the bioengineering problem based on the design of the device, the biomaterial used, and the cells involved. Last but not least, we highlight current tissue engineering challenges and explore potential directions for future work.

Modulating the foreign body response of implants for diabetes treatment

Diabetes Mellitus is a group of diseases characterized by high blood glucose levels due to patients' inability to produce sufficient insulin. Current interventions often require implants that can detect and correct high blood glucose levels with minimal patient intervention. However, these implantable technologies have not reached their full potential in vivo due to the foreign body response and subsequent development of fibrosis. Therefore, for long-term function of implants, modulating the initial immune response is crucial in preventing the activation and progression of the immune cascade. This review discusses the different molecular mechanisms and cellular interactions involved in the activation and progression of foreign body response (FBR) and fibrosis, specifically for implants used in diabetes. We also highlight the various strategies and techniques that have been used for immunomodulation and prevention of fibrosis. We investigate how these general strategies have been applied to implants used for the treatment of diabetes, offering insights on how these devices can be further modified to circumvent FBR and fibrosis.

Tissue Engineering Strategies for Improving Beta Cell Transplantation Outcome

Purpose of Review

Beta cell replacement therapy as a form of islet transplantation is a promising alternative therapy with the possibility to make selected patients with type 1 diabetes (T1D) insulin independent. However, this technique faces challenges such as extensive activation of the host immune system post-transplantation, lifelong need for immunosuppression, and the scarcity of islet donor pancreas. Advancement in tissue engineering strategies can improve these challenges and allow for a more widespread application of this therapy. This review will discuss the recent development and clinical translation of tissue engineering strategies in beta cell replacement therapy.

Recent Findings

Tissue engineering offers innovative solutions for producing unlimited glucose responsive cells and fabrication of appropriate devices/scaffolds for transplantation applications. Generation of pancreatic organoids with supporting cells in biocompatible biomaterials is a powerful technique to improve the function of insulin-producing cell clusters. Fabrication of physical barriers such as encapsulation strategies can protect the cells from the host immune system and allow for graft retrieval, although this strategy still faces major challenges to fully restore physiological glucose regulation.

Summary

The three main components of tissue engineering strategies including the generation of stem cell-derived insulin-producing cells and organoids and the possibilities for therapeutic delivery of cell-seeded devices to extra-hepatic sites need to come together in order to provide safe and functional insulin-producing devices for clinical beta cell replacement therapy.

Bioengineered Islet Cell Transplantation

Purpose of Review

β cell replacement via whole pancreas or islet transplantation has greatly evolved for the cure of type 1 diabetes. Both these strategies are however still affected by several limitations. Pancreas bioengineering holds the potential to overcome these hurdles aiming to repair and regenerate β cell compartment. In this review, we detail the state-of-the-art and recent progress in the bioengineering field applied to diabetes research.

Recent Findings

The primary target of pancreatic bioengineering is to manufacture a construct supporting insulin activity in vivo. Scaffold-base technique, 3D bioprinting, macro-devices, insulin-secreting organoids, and pancreas-on-chip represent the most promising technologies for pancreatic bioengineering.

Summary

There are several factors affecting the clinical application of these technologies, and studies reported so far are encouraging but need to be optimized. Nevertheless pancreas bioengineering is evolving very quickly and its combination with stem cell research developments can only accelerate this trend.

3D Bioprinting and the Future of Surgery

Introduction: The disciplines of 3D bioprinting and surgery have witnessed incremental transformations over the last century. 3D bioprinting is a convergence of biology and engineering technologies, mirroring the clinical need to produce viable biological tissue through advancements in printing, regenerative medicine and materials science. To outline the current and future challenges of 3D bioprinting technology in surgery. Methods: A comprehensive literature search was undertaken using the MEDLINE, EMBASE and Google Scholar databases between 2000 and 2019. A narrative synthesis of the resulting literature was produced to discuss 3D bioprinting, current and future challenges, the role in personalized medicine and transplantation surgery and the global 3D bioprinting market. Results: The next 20 years will see the advent of bioprinted implants for surgical use, however the path to clinical incorporation will be fraught with an array of ethical, regulatory and technical challenges of which each must be surmounted. Previous clinical cases where regulatory processes have been bypassed have led to poor outcomes and controversy. Speculated roles of 3D bioprinting in surgery include the production of de novo organs for transplantation and use of autologous cellular material for personalized medicine. The promise of these technologies has sparked an industrial revolution, leading to an exponential growth of the 3D bioprinting market worth billions of dollars. Conclusion: Effective translation requires the input of scientists, engineers, clinicians, and regulatory bodies: there is a need for a collaborative effort to translate this impactful technology into a real-world healthcare setting and potentially transform the future of surgery.

Cell microencapsulation technologies for sustained drug delivery: Clinical trials and companies

In recent years, cell microencapsulation technology has advanced, mainly driven by recent developments in the use of stem cells or the optimization of biomaterials. Old challenges have been addressed from new perspectives, and systems developed and improved for decades are now being transferred to the market by novel start-ups and consolidated companies. These products are mainly intended for the treatment of diabetes mellitus (DM), but also cancer, central nervous system (CNS) disorders or lysosomal diseases, among others. In this review, we analyze the results obtained in clinical trials to date and define the global key players that will lead the cell microencapsulation market to bring this technology to the clinic in the future.

Enhanced In Vivo Vascularization of 3D-Printed Cell Encapsulation Device Using Platelet-Rich Plasma and Mesenchymal Stem Cells

The current standard for cell encapsulation platforms is enveloping cells in semipermeable membranes that physically isolate transplanted cells from the host while allowing for oxygen and nutrient diffusion. However, long-term viability and function of encapsulated cells are compromised by insufficient oxygen and nutrient supply to the graft. To address this need, a strategy to achieve enhanced vascularization of a 3D-printed, polymeric cell encapsulation platform using platelet-rich plasma (PRP) and mesenchymal stem cells (MSCs) is investigated. The study is conducted in rats and, for clinical translation relevance, in nonhuman primates (NHP). Devices filled with PRP, MSCs, or vehicle hydrogel are subcutaneously implanted in rats and NHP and the amount and maturity of penetrating blood vessels assessed via histopathological analysis. In rats, MSCs drive the strongest angiogenic response at early time points, with the highest vessel density and endothelial nitric oxide synthase (eNOS) expression. In NHP, PRP and MSCs result in similar vessel densities but incorporation of PRP ensues higher levels of eNOS expression. Overall, enrichment with PRP and MSCs yields extensive, mature vascularization of subcutaneous cell encapsulation devices. It is postulated that the individual properties of PRP and MSCs can be leveraged in a synergistic approach for maximal vascularization of cell encapsulation platforms.

Expanding sacrificially printed microfluidic channel-embedded paper devices for construction of volumetric tissue models in vitro

We report a method for expanding microchannel-embedded paper devices using a precisely controlled gas-foaming technique for the generation of volumetric tissue models in vitro. We successfully fabricated hollow, perfusable microchannel patterns contained in a densely entangled network of bacterial cellulose nanofibrils using matrix-assisted sacrificial three-dimensional printing, and demonstrated the maintenance of their structural integrity after gas-foaming-enabled expansion in an aqueous solution of NaBH₄. The resulting expanded microchannel-embedded paper devices showed multilayered laminar structures with controllable thicknesses as a function of both NaBH₄ concentration and expansion time. With expansion, the thickness and porosity of the bacterial cellulose network were significantly increased. As such, cellular infiltration was promoted comparing to as-prepared, non-expanded devices. This simple technique enables the generation of truly volumetric, cost-effective human-based tissue models, such as vascularized tumor models, for potential applications in preclinical drug screening and personalized therapeutic selection.

3D Bioprinting and Translation of Beta Cell Replacement Therapies for Type 1 Diabetes

Type 1 diabetes (T1D) is an autoimmune disorder in which the body's own immune system selectively attacks beta cells within pancreatic islets resulting in insufficient insulin production and loss of the ability to regulate blood glucose (BG) levels. Currently, the standard of care consists of BG level monitoring and insulin administration, which are essential to avoid the consequences of dysglycemia and long-term complications. Although recent advances in continuous glucose monitoring and automated insulin delivery systems have resulted in improved clinical outcomes for users, nearly 80% of people with T1D fail to achieve their target hemoglobin A1c (HbA1c) levels defined by the American Diabetes Association. Intraportal islet transplantation into immunosuppressed individuals with T1D suffering from impaired awareness of hypoglycemia has resulted in lower HbA1c, elimination of severe hypoglycemic events, and insulin independence, demonstrating the unique potential of beta cell replacement therapy (BCRT) in providing optimal glycemic control and a functional cure for T1D. BCRTs need to maximize cell engraftment, long-term survival, and function in the absence of immunosuppression to provide meaningful clinical outcomes to all people living with T1D. One innovative technology that could enable widespread translation of this approach into the clinic is three-dimensional (3D) bioprinting. Herein, we review how bioprinting could facilitate translation of BCRTs as well as the current and forthcoming techniques used for bioprinting of a BCRT product. We discuss the strengths and weaknesses of 3D bioprinting in this context in addition to the road ahead for the development of BCRTs. Impact statement Significant research developments in beta cell replacement therapies show its promise in providing a functional cure for type 1 diabetes (T1D); yet, their widespread clinical use has been difficult to achieve. This review provides a brief overview of the requirements for a beta cell replacement product followed by a discussion on both the promise and limitations of three-dimensional bioprinting in facilitating the fabrication of such products to enable translation into the clinic. Advancements in this area could be a key component to unlocking the safety and effectiveness of beta cell therapy for T1D.

Integration of nano- and biotechnology for beta-cell and islet transplantation in type-1 diabetes treatment

Regenerative medicine using human or porcine β‐cells or islets has an excellent potential to become a clinically relevant method for the treatment of type‐1 diabetes. High‐resolution imaging of the function and faith of transplanted porcine pancreatic islets and human stem cell–derived beta cells in large animals and patients for testing advanced therapy medicinal products (ATMPs) is a currently unmet need for pre‐clinical/clinical trials. The iNanoBIT EU H2020 project is developing novel highly sensitive nanotechnology‐based imaging approaches allowing for monitoring of survival, engraftment, proliferation, function and whole‐body distribution of the cellular transplants in a porcine diabetes model with excellent translational potential to humans. We develop and validate the application of single‐photon emission computed tomography (SPECT) and optoacoustic imaging technologies in a transgenic insulin‐deficient pig model to observe transplanted porcine xeno‐islets and in vitro differentiated human beta cells. We are progressing in generating new transgenic reporter pigs and human‐induced pluripotent cell (iPSC) lines for optoacoustic imaging and testing them in transplantable bioartificial islet devices. Novel multifunctional nanoparticles have been generated and are being tested for nuclear imaging of islets and beta cells using a new, high‐resolution SPECT imaging device. Overall, the combined multidisciplinary expertise of the project partners allows progress towards creating much needed technological toolboxes for the xenotransplantation and ATMP field, and thus reinforces the European healthcare supply chain for regenerative medicinal products.

Biomaterials for Personalized Cell Therapy

Cell therapy has already had an important impact on healthcare and provided new treatments for previously intractable diseases. Notable examples include mesenchymal stem cells for tissue regeneration, islet transplantation for diabetes treatment, and T cell delivery for cancer immunotherapy. Biomaterials have the potential to extend the therapeutic impact of cell therapies by serving as carriers that provide 3D organization and support cell viability and function. With the growing emphasis on personalized medicine, cell therapies hold great potential for their ability to sense and respond to the biology of an individual patient. These therapies can be further personalized through the use of patient-specific cells or with precision biomaterials to guide cellular activity in response to the needs of each patient. Here, the role of biomaterials for applications in tissue regeneration, therapeutic protein delivery, and cancer immunotherapy is reviewed, with a focus on progress in engineering material properties and functionalities for personalized cell therapies.

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.

Engineering the vasculature for islet transplantation

The microvasculature in the pancreatic islet is highly specialized for glucose sensing and insulin secretion. Although pancreatic islet transplantation is a potentially life-changing treatment for patients with insulin-dependent diabetes, a lack of blood perfusion reduces viability and function of newly transplanted tissues. Functional vasculature around an implant is not only necessary for the supply of oxygen and nutrients but also required for rapid insulin release kinetics and removal of metabolic waste. Inadequate vascularization is particularly a challenge in islet encapsulation. Selectively permeable membranes increase the barrier to diffusion and often elicit a foreign body reaction including a fibrotic capsule that is not well vascularized. Therefore, approaches that aid in the rapid formation of a mature and robust vasculature in close proximity to the transplanted cells are crucial for successful islet transplantation or other cellular therapies. In this paper, we review various strategies to engineer vasculature for islet transplantation. We consider properties of materials (both synthetic and naturally derived), prevascularization, local release of proangiogenic factors, and co-transplantation of vascular cells that have all been harnessed to increase vasculature. We then discuss the various other challenges in engineering mature, long-term functional and clinically viable vasculature as well as some emerging technologies developed to address them. The benefits of physiological glucose control for patients and the healthcare system demand vigorous pursuit of solutions to cell transplant challenges. STATEMENT OF SIGNIFICANCE: Insulin-dependent diabetes affects more than 1.25 million people in the United States alone. Pancreatic islets secrete insulin and other endocrine hormones that control glucose to normal levels. During preparation for transplantation, the specialized islet blood vessel supply is lost. Furthermore, in the case of cell encapsulation, cells are protected within a device, further limiting delivery of nutrients and absorption of hormones. To overcome these issues, this review considers methods to rapidly vascularize sites and implants through material properties, pre-vascularization, delivery of growth factors, or co-transplantation of vessel supporting cells. Other challenges and emerging technologies are also discussed. Proper vascular growth is a significant component of successful islet transplantation, a treatment that can provide life-changing benefits to patients.

Supporting Survival of Transplanted Stem-Cell-Derived Insulin-Producing Cells in an Encapsulation Device Augmented with Controlled Release of Amino Acids

Pancreatic islet transplantation is a promising treatment for type I diabetes, which is a chronic autoimmune disease in which the host immune cells attack insulin-producing beta cells. The impact of this therapy is limited due to tissue availability and dependence on immunosuppressive drugs that prevent immune rejection of the transplanted cells. These issues can be solved by encapsulating stem cell-derived insulin-producing cells in an immunoprotective device. However, encapsulation exacerbates ischemia, and the lack of vasculature at the implantation site post-transplantation worsens graft survival. Here, an encapsulation device that supplements nutrients to the cells is developed to improve the survival of encapsulated stem cell-derived insulin-producing cells in the poorly vascularized subcutaneous space. An internal compartment in the device is fabricated to provide zero-order release of alanine and glutamine for several weeks. The amino acid reservoir sustains viability of insulin-producing cells in nutrient limiting conditions in vitro. Moreover, the reservoir also increases cell survival by 30% after transplanting the graft in the subcutaneous space.

Therapies for Type 1 Diabetes: Current Scenario and Future Perspectives

Type 1 diabetes (T1D) is caused by autoimmune destruction of insulin-producing β cells located in the endocrine pancreas in areas known as islets of Langerhans. The current standard-of-care for T1D is exogenous insulin replacement therapy. Recent developments in this field include the hybrid closed-loop system for regulated insulin delivery and long-acting insulins. Clinical studies on prediction and prevention of diabetes-associated complications have demonstrated the importance of early treatment and glucose control for reducing the risk of developing diabetic complications. Transplantation of primary islets offers an effective approach for treating patients with T1D. However, this strategy is hampered by challenges such as the limited availability of islets, extensive death of islet cells, and poor vascular engraftment of islets post-transplantation. Accordingly, there are considerable efforts currently underway for enhancing islet transplantation efficiency by harnessing the beneficial actions of stem cells. This review will provide an overview of currently available therapeutic options for T1D, and discuss the growing evidence that supports the use of stem cell approaches to enhance therapeutic outcomes.

Biofabrication strategies for creating microvascular complexity

Design and fabrication of effective biomimetic vasculatures constitutes a relevant and yet unsolved challenge, lying at the heart of tissue repair and regeneration strategies. Even if cell growth is achieved in 3D tissue scaffolds or advanced implants, tissue viability inevitably requires vascularization, as diffusion can only transport nutrients and eliminate debris within a few hundred microns. This engineered vasculature may need to mimic the intricate branching geometry of native microvasculature, referred to herein as vascular complexity, to efficiently deliver blood and recreate critical interactions between the vascular and perivascular cells as well as parenchymal tissues. This review first describes the importance of vascular complexity in labs- and organs-on-chips, the biomechanical and biochemical signals needed to create and maintain a complex vasculature, and the limitations of current 2D, 2.5D, and 3D culture systems in recreating vascular complexity. We then critically review available strategies for design and biofabrication of complex vasculatures in cell culture platforms, labs- and organs-on-chips, and tissue engineering scaffolds, highlighting their advantages and disadvantages. Finally, challenges and future directions are outlined with the hope of inspiring researchers to create the reliable, efficient and sustainable tools needed for design and biofabrication of complex vasculatures.

Paving the way for successful islet encapsulation

Type 1 diabetes mellitus (T1DM) is a disorder that decimates pancreatic β-cells which produce insulin. Direct pancreatic islet transplantation cannot serve as a widespread therapeutic modality owing to the need for lifelong immunosuppression and donor shortage. Therefore, several encapsulation techniques have been developed to enclose the islets in semipermeable vehicles that will allow oxygen and nutrient input as well as insulin, other metabolites and waste output, while accomplishing immunoisolation. Although encapsulation technology continues to face significant obstacles, recent advances in material science, stem cell biology and immunology potentially serve as pathways to success. This review summarizes the accomplishments of the past 5 years.

Concise Review: Canine Diabetes Mellitus as a Translational Model for Innovative Regenerative Medicine Approaches

Diabetes mellitus (DM) is a common spontaneous endocrine disorder in dogs, which is defined by persistent hyperglycemia and insulin deficiency. Like type 1 diabetes (T1D) in people, canine DM is a complex and multifactorial disease in which genomic and epigenomic factors interact with environmental cues to induce pancreatic β‐cell loss and insulin deficiency, although the pathogenesis of canine DM is poorly defined and the role of autoimmunity is further controversial. Both diseases are incurable and require life‐long exogenous insulin therapy to maintain glucose homeostasis. Human pancreatic islet physiology, size, and cellular composition is further mirrored by canine islets. Although pancreatic or isolated islets transplantation are the only clinically validated methods to achieve long‐term normoglycemia and insulin independence, their availability does not meet the clinical need; they target a small portion of patients and have significant potential adverse effects. Therefore, providing a new source for β‐cell replacement is an unmet need. Naturally occurring DM in pet dogs, as a translational platform, is an untapped resource for various regenerative medicine applications that may offer some unique advantages given dogs' large size, longevity, heterogenic genetic background, similarity to human physiology and pathology, and long‐term clinical management. In this review, we outline different strategies for curative approaches, animal models used, and consider the value of canine DM as a translational animal/disease model for T1D in people. stem cells translational medicine2019;8:450–455

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.

Generation of Human Stem Cell-Derived Pancreatic Organoids (POs) for Regenerative Medicine

Insulin-dependent diabetes mellitus or type 1 diabetes mellitus (T1DM) is an auto-immune condition characterized by the loss of pancreatic β-cells. The curative approach for highly selected patients is the pancreas or the pancreatic islet transplantation. Nevertheless, these options are limited by a growing shortage of donor organs and by the requirement of immunosuppression.Xenotransplantation of porcine islets has been extensively investigated. Nevertheless, the strong xenoimmunity and the risk of transmission of porcine endogenous retroviruses, have limited their application in clinic. Generation of β-like cells from stem cells is one of the most promising strategies in regenerative medicine. Embryonic, and more recently, adult stem cells are currently the most promising cell sources exploited to generate functional β-cells in vitro. A number of studies demonstrated that stem cells could generate functional pancreatic organoids (POs), able to restore normoglycemia when implanted in different preclinical diabetic models. Nevertheless, a gradual loss of function and cell dead are commonly detected when POs are transplanted in immunocompetent animals. So far, the main issue to be solved is the post-transplanted islet loss, due to the host immune attack. To avoid this hurdle, nanotechnology has provided a number of polymers currently under investigation for islet micro and macro-encapsulation. These new approaches, besides conferring PO immune protection, are able to supply oxygen and nutrients and to preserve PO morphology and long-term viability.Herein, we summarize the current knowledge on bioengineered POs and the stem cell differentiation platforms. We also discuss the in vitro strategies used to generate functional POs, and the protocols currently used to confer immune-protection against the host immune attack (micro- and macro-encapsulation). In addition, the most relevant ongoing clinical trials, and the most relevant hurdles met to move towards clinical application are revised.

The emerging field of pancreatic tissue engineering: A systematic review and evidence map of scaffold materials and scaffolding techniques for insulin-secreting cells

A bioartificial endocrine pancreas is proposed as a future alternative to current treatment options. Patients with insulin-secretion deficiency might benefit. This is the first systematic review that provides an overview of scaffold materials and techniques for insulin-secreting cells or cells to be differentiated into insulin-secreting cells. An electronic literature survey was conducted in PubMed/MEDLINE and Web of Science, limited to the past 10 years. A total of 197 articles investigating 60 different materials met the inclusion criteria. The extracted data on materials, cell types, study design, and transplantation sites were plotted into two evidence gap maps. Integral parts of the tissue engineering network such as fabrication technique, extracellular matrix, vascularization, immunoprotection, suitable transplantation sites, and the use of stem cells are highlighted. This systematic review provides an evidence-based structure for future studies. Accumulating evidence shows that scaffold-based tissue engineering can enhance the viability and function or differentiation of insulin-secreting cells both in vitro and in vivo.

Modulating physical, chemical, and biological properties in 3D printing for tissue engineering applications

Over the years, 3D printing technologies have transformed the field of tissue engineering and regenerative medicine by providing a tool that enables unprecedented flexibility, speed, control, and precision over conventional manufacturing methods. As a result, there has been a growing body of research focused on the development of complex biomimetic tissues and organs produced via 3D printing to serve in various applications ranging from models for drug development to translational research and biological studies. With the eventual goal to produce functional tissues, an important feature in 3D printing is the ability to tune and modulate the microenvironment to better mimic in vivo conditions to improve tissue maturation and performance. This paper reviews various strategies and techniques employed in 3D printing from the perspective of achieving control over physical, chemical, and biological properties to provide a conducive microenvironment for the development of physiologically relevant tissues. We will also highlight the current limitations associated with attaining each of these properties in addition to introducing challenges that need to be addressed for advancing future 3D printing approaches.