Engineering a Clinically Translatable Bioartificial Pancreas to Treat Type I Diabetes

Polyethersulfone Polymer for Biomedical Applications and Biotechnology

Polymers stand out as promising materials extensively employed in biomedicine and biotechnology. Their versatile applications owe much to the field of tissue engineering, which seamlessly integrates materials engineering with medical science. In medicine, biomaterials serve as prototypes for organ development and as implants or scaffolds to facilitate body regeneration. With the growing demand for innovative solutions, synthetic and hybrid polymer materials, such as polyethersulfone, are gaining traction. This article offers a concise characterization of polyethersulfone followed by an exploration of its diverse applications in medical and biotechnological realms. It concludes by summarizing the significant roles of polyethersulfone in advancing both medicine and biotechnology, as outlined in the accompanying table.

Recent Advances in Alginate-Based Hydrogels for Cell Transplantation Applications

With its exceptional biocompatibility, alginate emerged as a highly promising biomaterial for a large range of applications in regenerative medicine. Whether in the form of microparticles, injectable hydrogels, rigid scaffolds, or bioinks, alginate provides a versatile platform for encapsulating cells and fostering an optimal environment to enhance cell viability. This review aims to highlight recent studies utilizing alginate in diverse formulations for cell transplantation, offering insights into its efficacy in treating various diseases and injuries within the field of regenerative medicine.

Inflammation-induced subcutaneous neovascularization for the long-term survival of encapsulated islets without immunosuppression

Cellular therapies for type-1 diabetes can leverage cell encapsulation to dispense with immunosuppression. However, encapsulated islet cells do not survive long, particularly when implanted in poorly vascularized subcutaneous sites. Here we show that the induction of neovascularization via temporary controlled inflammation through the implantation of a nylon catheter can be used to create a subcutaneous cavity that supports the transplantation and optimal function of a geometrically matching islet-encapsulation device consisting of a twisted nylon surgical thread coated with an islet-seeded alginate hydrogel. The neovascularized cavity led to the sustained reversal of diabetes, as we show in immunocompetent syngeneic, allogeneic and xenogeneic mouse models of diabetes, owing to increased oxygenation, physiological glucose responsiveness and islet survival, as indicated by a computational model of mass transport. The cavity also allowed for the in situ replacement of impaired devices, with prompt return to normoglycemia. Controlled inflammation-induced neovascularization is a scalable approach, as we show with a minipig model, and may facilitate the clinical translation of immunosuppression-free subcutaneous islet transplantation.

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.

Enhancing longevity of immunoisolated pancreatic islet grafts by modifying both the intracapsular and extracapsular environment

Type 1 diabetes mellitus (T1DM) is a chronic metabolic disease characterized by autoimmune destruction of pancreatic β cells. Transplantation of immunoisolated pancreatic islets might treat T1DM in the absence of chronic immunosuppression. Important advances have been made in the past decade as capsules can be produced that provoke minimal to no foreign body response after implantation. However, graft survival is still limited as islet dysfunction may occur due to chronic damage to islets during islet isolation, immune responses induced by inflammatory cells, and nutritional issues for encapsulated cells. This review summarizes the current challenges for promoting longevity of grafts. Possible strategies for improving islet graft longevity are also discussed, including supplementation of the intracapsular milieu with essential survival factors, promotion of vascularization and oxygenation near capsules, modulation of biomaterials, and co-transplantation of accessory cells. Current insight is that both the intracapsular as well as the extracapsular properties should be improved to achieve long-term survival of islet-tissue. Some of these approaches reproducibly induce normoglycemia for more than a year in rodents. Further development of the technology requires collective research efforts in material science, immunology, and endocrinology. STATEMENT OF SIGNIFICANCE: Islet immunoisolation allows for transplantation of insulin producing cells in absence of immunosuppression and might facilitate the use of xenogeneic cell sources or grafting of cells obtained from replenishable cell sources. However, a major challenge to date is to create a microenvironment that supports long-term graft survival. This review provides a comprehensive overview of the currently identified factors that have been demonstrated to be involved in either stimulating or reducing islet graft survival in immunoisolating devices and discussed current strategies to enhance the longevity of encapsulated islet grafts as treatment for type 1 diabetes. Although significant challenges remain, interdisciplinary collaboration across fields may overcome obstacles and facilitate the translation of encapsulated cell therapy from the laboratory to clinical application.

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.

In Vivo Stable Allogenic Cartilage Regeneration in a Goat Model Based on Immunoisolation Strategy Using Electrospun Semipermeable Membranes

Tissue engineering is a promising strategy for cartilage defect repair. However, autologous cartilage regeneration is limited by additional trauma to the donor site and a long in vitro culture period. Alternatively, allogenic cartilage regeneration has attracted attention because of the unique advantages of an abundant donor source and immediate supply, but it will cause immune rejection responses (IRRs), especially in immunocompetent large animals. Therefore, a universal technique needs to be established to overcome IRRs for allogenic cartilage regeneration in large animals. In the current study, a hybrid synthetic-natural electrospun thermoplastic polyurethane/gelatin (TPU/GT) semipermeable membrane to explore the feasibility of stable allogenic cartilage regeneration by an immunoisolation strategy is developed. In vitro results demonstrated that the rationally designed electrospun TPU/GT membranes has ideal biocompatibility, semipermeability, and an immunoisolation function. In vivo results further showed that the semipermeable membrane (SPM) efficiently blocked immune cell attack, decreased immune factor production, and cell apoptosis of the regenerated allogenic cartilage. Importantly, TPU/GT-encapsulated cartilage-sheet constructs achieved stable allogeneic cartilage regeneration in a goat model. The current study provides a novel strategy for allogenic cartilage regeneration and supplies a new cartilage donor source to repair various cartilage defects.

Comparative Study of Two Common In Vitro Models for the Pancreatic Islet with MIN6

BACKGROUND

Islet transplantation is currently considered the most promising method for treating insulin-dependent diabetes. The two most-studied artificial islets are alginate-encapsulated β cells or β cell spheroids. As three-dimensional (3D) models, both artificial islets have better insulin secretory functions and transplantation efficiencies than cells in two-dimensional (2D) monolayer culture. However, the effects of these two methods have not been compared yet. Therefore, in this study, cells from the mouse islet β cell line Min6 were constructed as scaffold-free spheroids or alginate-encapsulated dispersed cells.

METHODS

MIN6 cell spheroids were prepared by using Agarose-base microwell arrays. The insulin secretion level was determined by mouse insulin ELISA kit, and the gene and protein expression status of the MIN6 were performed by Quantitative polymerase chain reaction and immunoblot, respectively.

RESULTS

Both 3D cultures effectively promoted the proliferation and glucose-stimulated insulin release (GSIS) of MIN6 cells compared to 2D adherent cells. Furthermore, 1% alginate-encapsulated MIN6 cells demonstrated more significant effects than the spheroids. In general, three pancreatic genes were expressed at higher levels in response to the 3D culture than to the 2D culture, and pancreatic/duodenal homeobox-1 (PDX1) expression was higher in the cells encapsulated in 1% alginate than that in the spheroids. A western blot analysis showed that 1% alginate-encapsulated MIN6 cells activated the phosphoinositide 3-kinase (PI3K)/serine/threonine protein kinase (AKT)/forkhead transcription factor FKHR (FoxO1) pathway more than the spheroids, 0.5% alginate-, or 2% alginate-encapsulated cells did. The 3D MIN6 culture, therefore, showed improved effects compared to the 2D culture, and the 1% alginate-encapsulated MIN6 cells exhibited better effects than the spheroids. The upregulation of PDX1 expression through the activation of the PI3K/AKT/FoxO1 pathway may mediate the improved cell proliferation and GSIS in 1% alginate-encapsulated MIN6 cells.

CONCLUSION

This study may contribute to the construction of in vitro culture systems for pancreatic islets to meet clinical requirements.

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.

Traction of 3D and 4D Printing in the Healthcare Industry: From Drug Delivery and Analysis to Regenerative Medicine

Three-dimensional (3D) printing and 3D bioprinting are promising technologies for a broad range of healthcare applications from frontier regenerative medicine and tissue engineering therapies to pharmaceutical advancements yet must overcome the challenges of biocompatibility and resolution. Through comparison of traditional biofabrication methods with 3D (bio)printing, this review highlights the promise of 3D printing for the production of on-demand, personalized, and complex products that enhance the accessibility, effectiveness, and safety of drug therapies and delivery systems. In addition, this review describes the capacity of 3D bioprinting to fabricate patient-specific tissues and living cell systems (e.g., vascular networks, organs, muscles, and skeletal systems) as well as its applications in the delivery of cells and genes, microfluidics, and organ-on-chip constructs. This review summarizes how tailoring selected parameters (i.e., accurately selecting the appropriate printing method, materials, and printing parameters based on the desired application and behavior) can better facilitate the development of optimized 3D-printed products and how dynamic 4D-printed strategies (printing materials designed to change with time or stimulus) may be deployed to overcome many of the inherent limitations of conventional 3D-printed technologies. Comprehensive insights into a critical perspective of the future of 4D bioprinting, crucial requirements for 4D printing including the programmability of a material, multimaterial printing methods, and precise designs for meticulous transformations or even clinical applications are also given.

Optimization of an O2-balanced bioartificial pancreas for type 1 diabetes using statistical design of experiment

A bioartificial pancreas (BAP) encapsulating high pancreatic islets concentration is a promising alternative for type 1 diabetes therapy. However, the main limitation of this approach is O₂ supply, especially until graft neovascularization. Here, we described a methodology to design an optimal O₂-balanced BAP using statistical design of experiment (DoE). A full factorial DoE was first performed to screen two O₂-technologies on their ability to preserve pseudo-islet viability and function under hypoxia and normoxia. Then, response surface methodology was used to define the optimal O₂-carrier and islet seeding concentrations to maximize the number of viable pseudo-islets in the BAP containing an O₂-generator under hypoxia. Monitoring of viability, function and maturation of neonatal pig islets for 15 days in vitro demonstrated the efficiency of the optimal O₂-balanced BAP. The findings should allow the design of a more realistic BAP for humans with high islets concentration by maintaining the O₂ balance in the device.

Polymer nanotherapeutics to correct autoimmunity

The immune system maintains homeostasis and protects the body from pathogens, mutated cells, and other harmful substances. When immune homeostasis is disrupted, excessive autoimmunity will lead to diseases. To inhibit the unexpected immune responses and reduce the impact of treatment on immunoprotective functions, polymer nanotherapeutics, such as nanomedicines, nanovaccines, and nanodecoys, were developed as part of an advanced strategy for precise immunomodulation. Nanomedicines transport cytotoxic drugs to target sites to reduce the occurrence of side effects and increase the stability and bioactivity of various immunomodulating agents, especially nucleic acids and cytokines. In addition, polymer nanomaterials carrying autoantigens used as nanovaccines can induce antigen-specific immune tolerance without interfering with protective immune responses. The precise immunomodulatory function of nanovaccines has broad prospects for the treatment of immune related-diseases. Besides, nanodecoys, which are designed to protect the body from various pathogenic substances by intravenous administration, are a simple and relatively noninvasive treatment. Herein, we have discussed and predicted the application of polymer nanotherapeutics in the correction of autoimmunity, including treating autoimmune diseases, controlling hypersensitivity, and avoiding transplant rejection.

The Cell-Isolation Capsules with Rod-Like Channels Ensure the Survival and Response of Cancer Cells to Their Microenvironment

Current macrocapsules with semipermeable but immunoprotective polymeric membranes are attractive devices to achieve the purpose of immunoisolation, however, their ability to allow diffusion of essential nutrients and oxygen is limited, which leads to a low survival rate of encapsulated cells. Here, a novel method is reported by taking advantage of thermotropic liquid crystals, sodium laurylsulfonate (SDS) liquid crystals (LCs), and rod-like crystal fragments (LCFs) to develop engineered alginate hydrogels with rod-like channels. This cell-isolation capsule with an engineered alginate hydrogel-wall allows small molecules, large molecules, and bacteria to diffuse out from the capsules freely but immobilizes the encapsulated cells inside and prevents cells in the microenvironment from moving in. The encapsulated cells show a high survival rate with isolation of host immune cells and long-term growth with adequate nutrients and oxygen supply. In addition, by sharing and responding to the normal molecular and vesicular microenvironment (NMV microenvironment), encapsulated cancer cells display a transition from tumorous phenotypes to ductal features of normal epithelial cells. Thus, this device will be potentially useful for clinical application in cell therapy by secreting molecules and for establishment of patient-derived xenograft (PDX) models that are often difficult to achieve for certain types of tumors, such as prostate cancer.

Targeting the extracellular matrix for immunomodulation: applications in drug delivery and cell therapies

Host immune cells interact bi-directionally with their extracellular matrix (ECM) to receive and deposit molecular signals, which orchestrate cellular activation, proliferation, differentiation, and function to maintain healthy tissue homeostasis. In response to pathogens or damage, immune cells infiltrate diseased sites and synthesize critical ECM molecules such as glycoproteins, proteoglycans, and glycosaminoglycans to promote healing. When the immune system misidentifies pathogens or fails to survey damaged cells effectively, maladies such as chronic inflammation, autoimmune diseases, and cancer can develop. In these conditions, it is essential to restore balance to the body through modulation of the immune system and the ECM. This review details the components of dysregulated ECM implicated in pathogenic environments and therapeutic approaches to restore tissue homeostasis. We evaluate emerging strategies to overcome inflamed, immune inhibitory, and otherwise diseased microenvironments, including mechanical stimulation, targeted proteases, adoptive cell therapy, mechanomedicine, and biomaterial-based cell therapeutics. We highlight various strategies that have produced efficacious responses in both pre-clinical and human trials and identify additional opportunities to develop next-generation interventions. Significantly, we identify a need for therapies to address dense or fibrotic tissue for the treatment of organ tissue damage and various cancer subtypes. Finally, we conclude that therapeutic techniques that disrupt, evade, or specifically target the pathogenic microenvironment have a high potential for improving therapeutic outcomes and should be considered a priority for immediate exploration. A schematic showing the various methods of extracellular matrix disruption/targeting in both fibrotic and cancerous environments. a Biomaterial-based cell therapy can be used to deliver anti-inflammatory cytokines, chemotherapeutics, or other factors for localized, slow release of therapeutics. b Mechanotherapeutics can be used to inhibit the deposition of molecules such as collagen that affect stiffness. c Ablation of the ECM and target tissue can be accomplished via mechanical degradation such as focused ultrasound. d Proteases can be used to improve the distribution of therapies such as oncolytic virus. e Localization of therapeutics such as checkpoint inhibitors can be improved with the targeting of specific ECM components, reducing off-target effects and toxicity.

Methacrylated Gellan Gum/Poly-l-lysine Polyelectrolyte Complex Beads for Cell-Based Therapies

Cell encapsulation strategies using hydrogel beads have been considered as an alternative to immunosuppression in cell-based therapies. They rely on layer-by-layer (LbL) deposition of polymers to tune beads' permeability, creating a physical barrier to the host immune system. However, the LbL approach can also create diffusion barriers, hampering the flow of essential nutrients and therapeutic cell products. In this work, the polyelectrolyte complex (PEC) methodology was used to circumvent the drawbacks of the LbL strategy by inducing hydrogel bead formation through the interaction of anionic methacrylated gellan gum (GG-MA) with cationic poly-l-lysine (PLL). The interfacial complexation between both polymers resulted in beads with a cell-friendly GG-MA hydrogel core surrounded by a PEC semipermeable membrane. The beads showed great in vitro stability over time, a semi-permeable behavior, and supported human adipose-derived stem cell encapsulation. Additionally, and regarding immune recognition, the in vitro and in vivo studies pointed out that the hydrogel beads behave as an immunocompatible system. Overall, the engineered beads showed great potential for hydrogel-mediated cell therapies, when immunoprotection is required, as when treating different metabolic disorders.

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.

Wearable Glucose Monitoring and Implantable Drug Delivery Systems for Diabetes Management

The global cost of diabetes care exceeds $1 trillion each year with more than $327 billion being spent in the United States alone. Despite some of the advances in diabetes care including continuous glucose monitoring systems and insulin pumps, the technology associated with managing diabetes has largely remained unchanged over the past several decades. With the rise of wearable electronics and novel functional materials, the field is well-poised for the next generation of closed-loop diabetes care. Wearable glucose sensors implanted within diverse platforms including skin or on-tooth tattoos, skin-mounted patches, eyeglasses, contact lenses, fabrics, mouthguards, and pacifiers have enabled noninvasive, unobtrusive, and real-time analysis of glucose excursions in ambulatory care settings. These wearable glucose sensors can be integrated with implantable drug delivery systems, including an insulin pump, glucose responsive insulin release implant, and islets transplantation, to form self-regulating closed-loop systems. This review article encompasses the emerging trends and latest innovations of wearable glucose monitoring and implantable insulin delivery technologies for diabetes management with a focus on their advanced materials and construction. Perspectives on the current unmet challenges of these strategies are also discussed to motivate future technological development toward improved patient care in diabetes management.

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.

Xenogeneic stem cell transplantation: Research progress and clinical prospects

Organ transplantation is the ultimate treatment for end-stage diseases such as heart and liver failure. However, the severe shortage of donor organs has limited the organ transplantation progress. Xenogeneic stem cell transplantation provides a new strategy to solve this problem. Researchers have shown that xenogeneic stem cell transplantation has significant therapeutic effects and broad application prospects in treating liver failure, myocardial infarction, advanced type 1 diabetes mellitus, myelosuppression, and other end-stage diseases by replacing the dysfunctional cells directly or improving the endogenous regenerative milieu. In this review, the sources, problems and solutions, and potential clinical applications of xenogeneic stem cell transplantation will be discussed.

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.

The Current Status of Bioartificial Pancreas Devices

Type 1 diabetes mellitus is a common and highly morbid disease for which there is no cure. Treatment primarily involves exogenous insulin administration, and, under specific circumstances, islet or pancreas transplantation. However, insulin replacement alone fails to replicate the endocrine function of the pancreas and does not provide durable euglycemia. In addition, transplantation requires lifelong use of immunosuppressive medications, which has deleterious side effects, is expensive, and is inappropriate for use in adolescents. A bioartificial pancreas that provides total endocrine pancreatic function without immunosuppression is a potential therapy for treatment of type 1 diabetes. Numerous models are in development and take different approaches to cell source, encapsulation method, and device implantation location. We review current therapies for type 1 diabetes mellitus, the requirements for a bioartificial pancreas, and quantitatively compare device function.

Transcriptome analysis of the transdifferentiation of canine BMSCs into insulin producing cells

Background

Bone marrow mesenchymal stem cells are a potential resource for the clinical therapy of certain diseases. Canine, as a companion animal, living in the same space with human, is an ideal new model for human diseases research. Because of the high prevalence of diabetes, alternative transplantation islets resource (i.e. insulin producing cells) for diabetes treatment will be in urgent need, which makes our research on the transdifferentiation of Bone marrow mesenchymal stem cells into insulin producing cells become more important.

Result

In this study, we completed the transdifferentiation process and achieved the transcriptome profiling of five samples with two biological duplicates, namely, “BMSCs”, “islets”, “stage 1”, “stage 2” and “stage 3”, and the latter three samples were achieved on the second, fifth and eighth day of induction. A total of 11,530 differentially expressed transcripts were revealed in the profiling data. The enrichment analysis of differentially expressed genes revealed several signaling pathways that are essential for regulating proliferation and transdifferentiation, including focal adhesion, ECM-receptor interaction, tight junction, protein digestion and absorption, and the Rap1 signaling pathway. Meanwhile, the obtained protein–protein interaction network and functional identification indicating involvement of three genes, SSTR2, RPS6KA6, and VIP could act as a foundation for further research.

Conclusion

In conclusion, to the best of our knowledge, this is the first survey of the transdifferentiation of canine BMSCs into insulin-producing cells according with the timeline using next-generation sequencing technology. The three key genes we pick out may regulate decisive genes during the development of transdifferentiation of insulin producing cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07426-3.

Applying Immunomodulation to Promote Longevity of Immunoisolated Pancreatic Islet Grafts

Islet transplantation is a promising therapy for insulin-dependent diabetes, but large-scale application is hampered by the lack of a consistent source of insulin-producing cells and need for lifelong administration of immunosuppressive drugs, which are associated with severe side effects. To avoid chronic immunosuppression, islet grafts can be enveloped in immunoisolating polymeric membranes. These immunoisolating polymeric membranes protect islet grafts from cell-mediated rejection while allowing diffusion of oxygen, nutrients, and insulin. Although clinical trials have shown the safety and feasibility of encapsulated islets to control glucose homeostasis, the strategy does up till now not support long-term graft survival. This partly can be explained by a significant loss of insulin-producing cells in the immediate period after implantation. The loss can be prevented by combining immunoisolation with immunomodulation, such as combined administration of immunomodulating cytokines or coencapsulation of immunomodulating cell types such as regulatory T cells, mesenchymal stem cells, or Sertoli cells. Also, administration of specific antibodies or apoptotic donor leucocytes is considered to create a tolerant microenvironment around immunoisolated grafts. In this review, we describe the outcomes and limitations of these approaches, as well as the recent progress in immunoisolating devices. Impact statement Immunoisolation by enveloping islets in semipermeable membranes allows for successful transplantation of islet grafts in the absence of chronic immunosuppression, but the duration of graft survival is still not permanent. The reasons for long-term final graft failure is not fully understood, but combining immunoisolation with immunomodulation of tissues or host immune system has been proposed to enhance the longevity of grafts. This article reviews the recent progress and challenges of immunoisolation, as well as the benefits and feasibility of combining encapsulation approaches with immunomodulation to promote longevity of encapsulated grafts.

Impact of electrostatic potential on microcapsule-formation and physicochemical analysis of surface structure: Implications for therapeutic cell-microencapsulation

Cell-encapsulation is used for preventing therapeutic cells from being rejected by the host. The technology to encapsulate cells in immunoprotective biomaterials, such as alginate, commonly involves application of an electrostatic droplet generator for reproducible manufacturing droplets of similar size and with similar surface properties. As many factors influencing droplet formation are still unknown, we investigated the impact of several parameters and fitted them to equations to make procedures more reproducible and allow optimal control of capsule size and properties. We demonstrate that droplet size is dependent on an interplay between the critical electric potential (U_c,), the needle size, and the distance between the needle and the gelation bath, and that it can be predicted with the equations proposed. The droplet formation was meticulously studied and followed by a high-speed camera. The X-ray photoelectron analysis demonstrated optimal gelation and substitution of sodium with calcium on alginate surfaces while the atomic force microscopy analysis demonstrated a low but considerable variation in surface roughness and low surface stiffness. Our study shows the importance of documenting critical parameters to guarantee reproducible manufacturing of beads with constant and adequate size and preventing batch-to-batch variations.

Cell-laden alginate hydrogels for the treatment of diabetes

INTRODUCTION

Diabetes mellitus is an ever-increasing medical condition that currently suffers 1 of 11 adults who may have lifelong commitment with insulin injections. Cell-laden hydrogels releasing insulin may provide the ultimate means of correcting diabetes. Here, we provide insights of this cell-based approach including latest preclinical and clinical progress both from academia and industry.

AREA COVERED

The present article focuses on reviewing latest advances in cell-laden hydrogels both from the technological and biological perspective. The most relevant clinical results including clinical trials are also discussed.

EXPERT OPINION

Current progress in technological issues (stem cells, devices, biomaterials) have contributed cell encapsulation science to have a very relevant progress in the field of diabetes treatment.

Chemical Degradation of PSF-PUR Blend Hollow Fiber Membranes-Assessment of Changes in Properties and Morphology after Hydrolysis

In this study, we focused on obtaining polysulfone-polyurethane (PSF-PUR) blend partly degradable hollow fiber membranes (HFMs) with different compositions while maintaining a constant PSF:PUR = 8:2 weight ratio. It was carried out through hydrolysis, and evaluation of the properties and morphology before and after the hydrolysis process while maintaining a constant cut-off. The obtained membranes were examined for changes in ultrafiltration coefficient (UFC), retention, weight loss, morphology assessment using scanning electron microscopy (SEM) and MeMoExplorer™ Software, as well as using the Fourier-transform infrared spectroscopy (FT-IR) method. The results of the study showed an increase in the UFC value after the hydrolysis process, changes in retention, mass loss, and FT-IR spectra. The evaluation in MeMoExplorer™ Software showed the changes in membranes' morphology. It was confirmed that polyurethane (PUR) was partially degraded, the percentage of ester bonds has an influence on the degradation process, and PUR can be used as a pore precursor instead of superbly known polymers.

3D perfusion culture of mouse insulinoma in macro-porous scaffolds enhanced insulin production response

To address the remaining issue of poor cell immobilization and insufficient mass transfer in scaffold-based tissue engineering approach for future islet transplantation, we employed a macro-porous poly-l-lactide (PLLA) scaffold immobilizing mouse insulinoma cells and studied its function toward an implantable pancreatic tissue in 7-day perfusion culture. The murine pancreatic β cells could be immobilized in the PLLA scaffold at a high density of 10⁷ cells per cm³ close to the estimated range in normal pancreas. The perfusion culture promoted the 3D cellular organization as observed with live/dead staining and histological staining. The insulin production was significantly enhanced in comparison with static 2D culture and 3D rotational suspension culture by two and six folds, respectively (p < 0.001). As enhanced insulin response was only observed where both the perfusion and 3D cellular organization were present, this could represent important elements in engineering a functional bioartificial pancreas.

Recent advances in the design of implantable insulin secreting heterocellular islet organoids

Islet transplantation has proved one of the most remarkable transmissions from an experimental curiosity into a routine clinical application for the treatment of type I diabetes (T1D). Current efforts for taking this technology one-step further are now focusing on overcoming islet donor shortage, engraftment, prolonged islet availability, post-transplant vascularization, and coming up with new strategies to eliminate lifelong immunosuppression. To this end, insulin secreting 3D cell clusters composed of different types of cells, also referred as heterocellular islet organoids, spheroids, or pseudoislets, have been engineered to overcome the challenges encountered by the current islet transplantation protocols. β-cells or native islets are accompanied by helper cells, also referred to as accessory cells, to generate a cell cluster that is not only able to accurately secrete insulin in response to glucose, but also superior in terms of other key features (e.g. maintaining a vasculature, longer durability in vivo and not necessitating immunosuppression after transplantation). Over the past decade, numerous 3D cell culture techniques have been integrated to create an engineered heterocellular islet organoid that addresses current obstacles. Here, we first discuss the different cell types used to prepare heterocellular organoids for islet transplantation and their contribution to the organoids design. We then introduce various cell culture techniques that are incorporated to prepare a fully functional and insulin secreting organoids with select features. Finally, we discuss the challenges and present a future outlook for improving clinical outcomes of islet transplantation.

Preferences of Type 1 Diabetic Patients on Devices for Islet Transplantation

Transplantation of pancreatic islets within a biomaterial device is currently under investigation in clinical trials for the treatment of patients with type 1 diabetes (T1D). Patients’ preferences on such implants could guide the designs of next-generation implantable devices; however, such information is not currently available. We surveyed the preferences of 482 patients with T1D on the size, shape, visibility, and transplantation site of islet containing implants. More than 83% of participants were willing to receive autologous stem cells, and there was no significant association between implant fabricated by one’s own stem cell with gender (χ² (1, n = 468) = 0.28; P = 0.6) or with age (χ² (4, n = 468) = 2.92; P = 0.6). Preferred location for islet transplantation within devices was under the skin (52.7%). 48.3% preferred microscopic disks, and 32.3% preferred a thin device (like a credit card). Moreover, 58.4% preferred the implant to be as small as possible, 25.4% did not care about visibility, and 16.2% preferred their implants not to be visible. Among female participants, 81% cared about the implant visibility, whereas this number was 64% for male respondents (χ² test (1, n = 468) = 16.34; P < 0.0001). 22% of those younger than 50 years of age and 30% of those older than 50 did not care about the visibility of implant (χ² test (4, n = 468) = 23.69; P < 0.0001). These results suggest that subcutaneous sites and micron-sized devices are preferred choices among patients with T1D who participated in our survey.

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.

Generation of insulin-secreting organoids: a step toward engineering and transplanting the bioartificial pancreas

Diabetes is a major health issue of increasing prevalence. ß‐cell replacement, by pancreas or islet transplantation, is the only long‐term curative option for patients with insulin‐dependent diabetes. Despite good functional results, pancreas transplantation remains a major surgery with potentially severe complications. Islet transplantation is a minimally invasive alternative that can widen the indications in view of its lower morbidity. However, the islet isolation procedure disrupts their vasculature and connection to the surrounding extracellular matrix, exposing them to ischemia and anoikis. Implanted islets are also the target of innate and adaptive immune attacks, thus preventing robust engraftment and prolonged full function. Generation of organoids, defined as functional 3D structures assembled with cell types from different sources, is a strategy increasingly used in regenerative medicine for tissue replacement or repair, in a variety of inflammatory or degenerative disorders. Applied to ß‐cell replacement, it offers the possibility to control the size and composition of islet‐like structures (pseudo‐islets), and to include cells with anti‐inflammatory or immunomodulatory properties. In this review, we will present approaches to generate islet cell organoids and discuss how these strategies can be applied to the generation of a bioartificial pancreas for the treatment of type 1 diabetes.

A green tea-triggered genetic control system for treating diabetes in mice and monkeys

Cell-based therapies are recognized as the next frontier in medicine, but the translation of many promising technologies into the clinic is currently limited by a lack of remote-control inducers that are safe and can be tightly regulated. Here, we developed therapeutically active engineered cells regulated by a control system that is responsive to protocatechuic acid (PCA), a metabolite found in green tea. We constructed multiple genetic control technologies that could toggle a PCA-responsive ON/OFF switch based on a transcriptional repressor from Streptomyces coelicolor We demonstrated that PCA-controlled switches can be used for guide RNA expression-mediated control of the CRISPR-Cas9 systems for gene editing and epigenetic remodeling. We showed how these technologies could be used as implantable biocomputers in live mice to perform complex logic computations that integrated signals from multiple food metabolites. Last, we used our system to treat type 1 and type 2 diabetes in mice and cynomolgus monkeys. This biocompatible and versatile food phenolic acid-controlled transgenic device opens opportunities for dynamic interventions in gene- and cell-based precision medicine.

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.

Hacking Human Beings with Machine Biology to Increase Lifespan

Imagine a world where machines can program cells to deliver therapeutics in a remote-controlled, time-specific, and targeted manner. Or, what if physicians could collect data continuously to establish intimate links between therapy and disease progression? Such machine biology systems could empower physicians beyond imagination and give rise to personalized treatments.

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.

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.

Conformal Coating of Stem Cell-Derived Islets for β Cell Replacement in Type 1 Diabetes

The scarcity of donors and need for immunosuppression limit pancreatic islet transplantation to a few patients with labile type 1 diabetes. Transplantation of encapsulated stem cell-derived islets (SC islets) might extend the applicability of islet transplantation to a larger cohort of patients. Transplantation of conformal-coated islets into a confined well-vascularized site allows long-term diabetes reversal in fully MHC-mismatched diabetic mice without immunosuppression. Here, we demonstrated that human SC islets reaggregated from cryopreserved cells display glucose-stimulated insulin secretion in vitro. Importantly, we showed that conformally coated SC islets displayed comparable in vitro function with unencapsulated SC islets, with conformal coating permitting physiological insulin secretion. Transplantation of SC islets into the gonadal fat pad of diabetic NOD-scid mice revealed that both unencapsulated and conformal-coated SC islets could reverse diabetes and maintain human-level euglycemia for more than 80 days. Overall, these results provide support for further evaluation of safety and efficacy of conformal-coated SC islets in larger species.

Fluorocapsules allow in vivo monitoring of the mechanical stability of encapsulated islet cell transplants

Clinical trials that have used encapsulated islet cell therapy have been few and overall disappointing. This is due in part to the lack of suitable methods to monitor the integrity vs. rupture of transplanted microcapsules over time. Fluorocapsules were synthesized by embedding emulsions of perfluoro-15-crown-5-ether (PFC), a bioinert compound detectable by 19F MRI, into dual-alginate layer, Ba2+-gelled alginate microcapsules. Fluorocapsules were spherical with an apparent smooth surface and an average diameter of 428 ± 52 μm. After transplantation into mice, the 19F MRI signal of capsules remained stable for up to 90 days, corresponding to the total number of intact fluorocapsules. When single-alginate layer capsules were ruptured with alginate lyase, the 19F MRI signal dissipated within 4 days. For fluoroencapsulated luciferase-expressing mouse βTC6 insulinoma cells implanted into autoimmune NOD/ShiLtJ mice and subjected to alginate-lyase induced capsule rupture in vivo, the 19F MRI signal decreased sharply over time along with a decrease in bioluminescence imaging signal used as a measure of cell viability in vivo. These results indicate that maintenance of capsule integrity is essential for preserving transplanted cell survival, where a decrease in 19F MRI signal may serve as a predictive imaging surrogate biomarker for impending failure of encapsulated islet cell therapy.

Polymeric Approaches to Reduce Tissue Responses Against Devices Applied for Islet-Cell Encapsulation

Immunoisolation of pancreatic islets is a technology in which islets are encapsulated in semipermeable but immunoprotective polymeric membranes. The technology allows for successful transplantation of insulin-producing cells in the absence of immunosuppression. Different approaches of immunoisolation are currently under development. These approaches involve intravascular devices that are connected to the bloodstream and extravascular devices that can be distinguished in micro- and macrocapsules and are usually implanted in the peritoneal cavity or under the skin. The technology has been subject of intense fundamental research in the past decade. It has co-evolved with novel replenishable cell sources for cure of diseases such as Type 1 Diabetes Mellitus that need to be protected for the host immune system. Although the devices have shown significant success in animal models and even in human safety studies most technologies still suffer from undesired tissue responses in the host. Here we review the past and current approaches to modulate and reduce tissue responses against extravascular cell-containing micro- and macrocapsules with a focus on rational choices for polymer (combinations). Choices for polymers but also choices for crosslinking agents that induce more stable and biocompatible capsules are discussed. Combining beneficial properties of molecules in diblock polymers or application of these molecules or other anti-biofouling molecules have been reviewed. Emerging are also the principles of polymer brushes that prevent protein and cell-adhesion. Recently also immunomodulating biomaterials that bind to specific immune receptors have entered the field. Several natural and synthetic polymers and even combinations of these polymers have demonstrated significant improvement in outcomes of encapsulated grafts. Adequate polymeric surface properties have been shown to be essential but how the surface should be composed to avoid host responses remains to be identified. Current insight is that optimal biocompatible devices can be created which raises optimism that immunoisolating devices can be created that allows for long term survival of encapsulated replenishable insulin-producing cell sources for treatment of Type 1 Diabetes Mellitus.

Layer-by-Layer Cerium Oxide Nanoparticle Coating for Antioxidant Protection of Encapsulated Beta Cells

In type 1 diabetes, the replacement of the destroyed beta cells could restore physiological glucose regulation and eliminate the need for exogenous insulin. Immunoisolation of these foreign cellular transplants via biomaterial encapsulation is widely used to prevent graft rejection. While highly effective in blocking direct cell-to-cell contact, nonspecific inflammatory reactions to the implant lead to the overproduction of reactive oxygen species, which contribute to foreign body reaction and encapsulated cell loss. For antioxidant protection, cerium oxide nanoparticles (CONPs) are a self-renewable, ubiquitous, free radical scavenger currently explored in several biomedical applications. Herein, 2-12 alternating layers of CONP/alginate are assembled onto alginate microbeads containing beta cells using a layer-by-layer (LbL) technique. The resulting nanocomposite coatings demonstrate robust antioxidant activity. The degree of cytoprotection correlates with layer number, indicating tunable antioxidant protection. Coating of alginate beads with 12 layers of CONP/alginate provides complete protection to the entrapped beta cells from exposure to 100 × 10-6 m H2 O2 , with no significant changes in cellular metabolic activity, oxidant capacity, or insulin secretion dynamics, when compared to untreated controls. The flexibility of this LbL method, as well as its nanoscale profile, provides a versatile approach for imparting antioxidant protection to numerous biomedical implants, including beta cell transplantation.

Interconnected Toroidal Hydrogels for Islet Encapsulation

Islet encapsulation and transplantation promises to improve upon current treatments for type 1 diabetes mellitus, though several limitations remain. Macroscale devices have been designed for in vivo transplantation and retrieval, but traditional geometries do not support clinically adequate mass transfer of nutrients to and insulin from the encapsulated tissue. Microcapsule technologies have improved mass transfer properties, but their clinical translation remains challenging as their complete retrieval is difficult, should the graft become a safety concern. Here, the design, characterization and testing of a novel encapsulation structure, comprised of elastomer-reinforced interconnected toroidal hydrogels is reported. These donut-shaped hydrogels feature a high surface area, higher than conventional spherical capsules of the same volume, bestowing suitable mass transport conditions, while allowing interconnection and reversible deformation for intraperitoneal implantation and retrieval. Diabetes correction up to 12 weeks and complete retrieval is achieved in a diabetic mouse model, providing a proof-of-concept for the potential application as a type 1 diabetes cell replacement therapy.

Applications of stem cells and bioprinting for potential treatment of diabetes

Currently, there does not exist a strategy that can reduce diabetes and scientists are working towards a cure and innovative approaches by employing stem cell-based therapies. On the other hand, bioprinting technology is a novel therapeutic approach that aims to replace the diseased or lost β-cells, insulin-secreting cells in the pancreas, which can potentially regenerate damaged organs such as the pancreas. Stem cells have the ability to differentiate into various cell lines including insulin-producing cells. However, there are still barriers that hamper the successful differentiation of stem cells into β-cells. In this review, we focus on the potential applications of stem cell research and bioprinting that may be targeted towards replacing the β-cells in the pancreas and may offer approaches towards treatment of diabetes. This review emphasizes on the applicability of employing both stem cells and other cells in 3D bioprinting to generate substitutes for diseased β-cells and recover lost pancreatic functions. The article then proceeds to discuss the overall research done in the field of stem cell-based bioprinting and provides future directions for improving the same for potential applications in diabetic research.

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.

Cell-Surface Engineering for Advanced Cell Therapy

Stem cells opened great opportunity to overcome diseases that conventional therapy had only limited success. Use of scaffolds made from biomaterials not only helps handling of stem cells for delivery or transplantation but also supports enhanced cell survival. Likewise, cell encapsulation can provide stability for living animal cells even in a state of separateness. Although various chemical reactions were tried to encapsulate stolid microbial cells such as yeasts, a culture environment for the growth of animal cells allows only highly biocompatible reactions. Therefore, the animal cells were mostly encapsulated in hydrogels, which resulted in enhanced cell survival. Interestingly, major findings of chemistry on biological interfaces demonstrate that cell encapsulation in hydrogels have a further a competence for modulating cell characteristics that can go beyond just enhancing the cell survival. In this review, we present a comprehensive overview on the chemical reactions applied to hydrogel-based cell encapsulation and their effects on the characteristics and behavior of living animal cells.

Islet encapsulation

Review of emerging advances and persisting challenges in the engineering and translation of islet encapsulation technologies.