An encapsulation system for the immunoisolation of pancreatic islets

Encapsulation of HRP-Immobilized Silica Particles into Hollow-Type Spherical Bacterial Cellulose Gel: A Novel Approach for Enzyme Reactions within Cellulose Gel Capsules

We revealed that the encapsulation of enzyme-immobilized silica particles in hollow-type spherical bacterial cellulose (HSBC) gels enables the use of the inside of HSBC gels as a reaction field. The encapsulation of horseradish peroxidase (HRP)-immobilized silica particles (Si-HRPs, particle size: 40-50 μm) within HSBC gels was performed by using a BC gelatinous membrane produced at the interface between Komagataeibacter xylinus suspension attached onto an alginate gel containing Si-HRPs and silicone oil. After the biosynthesis of the BC gelatinous membrane, formed from cellulose nanofiber networks, the alginate gel was removed via immersion in a phosphate-buffered solution. Si-HRP encapsulated HSBC gels were reproducibly produced using our method with a yield of over 90%. The pore size of the network structure of the BC gelatinous membrane was less than 1 μm, which is significantly smaller than the encapsulated Si-HRPs. Consequently, the encapsulated Si-HRPs could neither pass through the BC gelatinous membrane nor leak from the interior cavity of the HSBC gel. The activity of the encapsulated HRPs was detected using the 3,3',5,5'-tetramethylbenzidine (TMB)-H2O2 system, demonstrating that this method can encapsulate the enzyme without inactivation. Since HSBC gels are composed of a network structure of biocompatible cellulose nanofibers, immune cells cannot enter the hollow interior, thus, the enzyme-immobilized particles encapsulated inside the HSBC gel are protected from immune-cell attacks. The encapsulation technique demonstrated in this study is expected to facilitate the delivery of enzymes and catalysts that are not originally present in the in vivo environment.

Postmodification with Polycations Enhances Key Properties of Alginate-Based Multicomponent Microcapsules

Postmodification of alginate-based microspheres with polyelectrolytes (PEs) is commonly used in the cell encapsulation field to control microsphere stability and permeability. However, little is known about how different applied PEs shape the microsphere morphology and properties, particularly in vivo. Here, we addressed this question using model multicomponent alginate-based microcapsules postmodified with PEs of different charge and structure. We found that the postmodification can enhance or impair the mechanical resistance and biocompatibility of microcapsules implanted into a mouse model, with polycations surprisingly providing the best results. Confocal Raman microscopy and confocal laser scanning microscopy (CLSM) analyses revealed stable interpolyelectrolyte complex layers within the parent microcapsule, hindering the access of higher molar weight PEs into the microcapsule core. All microcapsules showed negative surface zeta potential, indicating that the postmodification PEs get hidden within the microcapsule membrane, which agrees with CLSM data. Human whole blood assay revealed complex behavior of microcapsules regarding their inflammatory and coagulation potential. Importantly, most of the postmodification PEs, including polycations, were found to be benign toward the encapsulated model cells.

Unlocking Transplant Tolerance with Biomaterials

For patients suffering from organ failure due to injury or autoimmune disease, allogeneic organ transplantation with chronic immunosuppression is considered the god standard in terms of clinical treatment. However, the true "holy grail" of transplant immunology is operational tolerance, in which the recipient exhibits a sustained lack of alloreactivity toward unencountered antigen presented by the donor graft. This outcome is resultant from critical changes to the phenotype and genotype of the immune repertoire predicated by the activation of specific signaling pathways responsive to soluble and mechanosensitive cues. Biomaterials have emerged as a medium for interfacing with and reprogramming these endogenous pathways toward tolerance in precise, minimally invasive, and spatiotemporally defined manners. By viewing seminal and contemporary breakthroughs in transplant tolerance induction through the lens of biomaterials-mediated immunomodulation strategies-which include intrinsic material immunogenicity, the depot effect, graft coatings, induction and delivery of tolerogenic immune cells, biomimicry of tolerogenic immune cells, and in situ reprogramming-this review emphasizes the stunning diversity of approaches in the field and spotlights exciting future directions for research to come.

3D Bioprinting of Collagen-based Microfluidics for Engineering Fully-biologic Tissue Systems

Microfluidic and organ-on-a-chip devices have improved the physiologic and translational relevance of in vitro systems in applications ranging from disease modeling to drug discovery and pharmacology. However, current manufacturing approaches have limitations in terms of materials used, non-native mechanical properties, patterning of extracellular matrix (ECM) and cells in 3D, and remodeling by cells into more complex tissues. We present a method to 3D bioprint ECM and cells into microfluidic collagen-based high-resolution internally perfusable scaffolds (CHIPS) that address these limitations, expand design complexity, and simplify fabrication. Additionally, CHIPS enable size-dependent diffusion of molecules out of perfusable channels into the surrounding device to support cell migration and remodeling, formation of capillary-like networks, and integration of secretory cell types to form a glucose-responsive, insulin-secreting pancreatic-like microphysiological system.

Hydrogel-Composited Laminate for Islet Immune-Isolation to Treat Type 1 Diabetes

Challenges remain to be solved for the clinical translation of β-cell encapsulation technology in the treatment of type 1 diabetes (T1D). Successful delivery of β cells urgently needs the development of an encapsulation device with a thin dimension and rapid mass transport that offers stable immune isolation and complete retrieval. In this study, we focus on a laminate in which an islet-embedding alginate hydrogel layer (Alg) is sandwiched between two polymer layers (polyether sulfone, PES). Mechanical support by the PES layer protects the alginate from disintegrating after implantation and allows complete retrieval. The multilayered device has a thin membrane configuration (∼1 mm), and the edge of the laminate and the gaps between Alg and PES offer a semiopen structure that could be more permeable to molecules compared with the closed pocket of conventional macroencapsulation. Islets are suspended in the alginate solution and then encapsulated in the hydrogel layer in the middle of the laminate after gelation. Encapsulating syngeneic or xenogeneic islets in the laminate device corrected chemically induced T1D in mice for over 90 days in both the intraperitoneal space and the epididymal fat pad. The multilayered membrane system may therefore provide a translatable solution in β cell-transplantation therapy in T1D.

Production of alginate macrocapsule device for long-term normoglycaemia in the treatment of type 1 diabetes mellitus with pancreatic cell sheet engineering

Type 1 diabetes-mellitus (T1DM) is characterized by damage of beta cells in pancreatic islets. Cell-sheet engineering, one of the newest therapeutic approaches, has also been used to create functional islet systems by creating islet/beta cell-sheets and transferring these systems to areas that require minimally invasive intervention, such as extrahepatic areas. Since islets, beta cells, and pancreas transplants are allogeneic, immune problems such as tissue rejection occur after treatment, and patients become insulin dependent again. In this study, we aimed to design the most suitable cell-sheet treatment method and macrocapsule-device that could provide long-term normoglycemia in rats. Firstly, mesenchymal stem cells (MSCs) and beta cells were co-cultured in a temperature-responsive culture dish to obtain a cell-sheet and then the cell-sheets macroencapsulated using different concentrations of alginate. The mechanical properties and pore sizes of the macrocapsule-device were characterized. The viability and activity of cell-sheets in the macrocapsule were evaluatedin vitroandin vivo. Fasting blood glucose levels, body weight, and serum insulin & C-peptide levels were evaluated after transplantation in diabetic-rats. After the transplantation, the blood glucose level at 225 mg dl-1on the 10th day dropped to 168 mg dl-1on the 15th day, and remained at the normoglycemic level for 210 days. In this study, an alginate macrocapsule-device was successfully developed to protect cell-sheets from immune attacks after transplantation. The results of our study provide the basis for future animal and human studies in which this method can be used to provide long-term cellular therapy in T1DM patients.

Biomanufacturing Recombinantly Expressed Cripto-1 Protein in Anchorage-Dependent Mammalian Cells Growing in Suspension Bioreactors within a Three-Dimensional Hydrogel Microcarrier

Biotherapeutic soluble proteins that are recombinantly expressed in mammalian cells can pose a challenge when biomanufacturing in three-dimensional (3D) suspension culture systems. Herein, we tested a 3D hydrogel microcarrier for a suspension culture of HEK293 cells overexpressing recombinant Cripto-1 protein. Cripto-1 is an extracellular protein that is involved in developmental processes and has recently been reported to have therapeutic effects in alleviating muscle injury and diseases by regulating muscle regeneration through satellite cell progression toward the myogenic lineage. Cripto-overexpressing HEK293 cell lines were cultured in microcarriers made from poly (ethylene glycol)-fibrinogen (PF) hydrogels, which provided the 3D substrate for cell growth and protein production in stirred bioreactors. The PF microcarriers were designed with sufficient strength to resist hydrodynamic deterioration and biodegradation associated with suspension culture in stirred bioreactors for up to 21 days. The yield of purified Cripto-1 obtained using the 3D PF microcarriers was significantly higher than that obtained with a two-dimensional (2D) culture system. The bioactivity of the 3D-produced Cripto-1 was equivalent to commercially available Cripto-1 in terms of an ELISA binding assay, a muscle cell proliferation assay, and a myogenic differentiation assay. Taken together, these data indicate that 3D microcarriers made from PF can be combined with mammalian cell expression systems to improve the biomanufacturing of protein-based therapeutics for muscle injuries.

Nanotechnology in Kidney and Islet Transplantation: An Ongoing, Promising Field

Organ transplantation has evolved rapidly in recent years as a reliable option for patients with end-stage organ failure. However, organ shortage, surgical risks, acute and chronic rejection reactions and long-term immunosuppressive drug applications and their inevitable side effects remain extremely challenging problems. The application of nanotechnology in medicine has proven highly successful and has unique advantages for diagnosing and treating diseases compared to conventional methods. The combination of nanotechnology and transplantation brings a new direction of thinking to transplantation medicine. In this article, we provide an overview of the application and progress of nanotechnology in kidney and islet transplantation, including nanotechnology for renal pre-transplantation preservation, artificial biological islets, organ imaging and drug delivery.

Synthesis of Alginate Nanogels with Polyvalent 3D Transition Metal Cations: Applications in Urease Immobilization

Biocompatible nanogels are highly in demand and have the potential to be used in various applications, e.g., for the encapsulation of sensitive biomacromolecules. In the present study, we have developed water-in-oil microemulsions of sodium alginate sol/hexane/Span 20 as a template for controlled synthesis of alginate nanogels, cross-linked with 3d transition metal cations (Mn²⁺, Fe³⁺, and Co²⁺). The results suggest that the stable template of 110 nm dimensions can be obtained by microemulsion technique using Span 20 at concentrations of 10mM and above, showing a zeta potential of −57.3 mV. A comparison of the effects of the cross-links on the morphology, surface charge, protein (urease enzyme) encapsulation properties, and stability of the resulting nanogels were studied. Alginate nanogels, cross-linked with Mn²⁺, Fe³⁺, or Co²⁺ did not show any gradation in the hydrodynamic diameter. The shape of alginate nanogels, cross-linked with Mn²⁺ or Co²⁺, were spherical; whereas, nanogels cross-linked with Fe³⁺ (Fe–alginate) were non-spherical and rice-shaped. The zeta potential, enzyme loading efficiency, and enzyme activity of Fe–alginate was the highest among all the nanogels studied. It was found that the morphology of particles influenced the percent immobilization, loading capacity, and loading efficiency of encapsulated enzymes. These particles are promising candidates for biosensing and efficient drug delivery due to their relatively high loading capacity, biocompatibility, easy fabrication, and easy handling.

Core-Shell Microcapsules: Biofabrication and Potential Applications in Tissue Engineering and Regenerative Medicine

The construction of biomaterial scaffolds that accurately recreate the architecture of living tissues in vitro is a major challenge in the field of tissue engineering and regenerative medicine. Core-shell microcapsules...

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.

Cell microencapsulation technologies for sustained drug delivery: Latest advances in efficacy and biosafety

The development of cell microencapsulation systems began several decades ago. However, today few systems have been tested in clinical trials. For this reason, in the last years, researchers have directed efforts towards trying to solve some of the key aspects that still limit efficacy and biosafety, the two major criteria that must be satisfied to reach the clinical practice. Regarding the efficacy, which is closely related to biocompatibility, substantial improvements have been made, such as the purification or chemical modification of the alginates that normally form the microspheres. Each of the components that make up the microcapsules has been carefully selected to avoid toxicities that can damage the encapsulated cells or generate an immune response leading to pericapsular fibrosis. As for the biosafety, researchers have developed biological circuits capable of actively responding to the needs of the patients to precisely and accurately release the demanded drug dose. Furthermore, the structure of the devices has been subject of study to adequately protect the encapsulated cells and prevent their spread in the body. The objective of this review is to describe the latest advances made by scientist to improve the efficacy and biosafety of cell microencapsulation systems for sustained drug delivery, also highlighting those points that still need to be optimized.

A nanofibrous encapsulation device for safe delivery of insulin-producing cells to treat type 1 diabetes

Transplantation of stem cell-derived β (SC-β) cells represents a promising therapy for type 1 diabetes (T1D). However, the delivery, maintenance, and retrieval of these cells remain a challenge. Here, we report the design of a safe and functional device composed of a highly porous, durable nanofibrous skin and an immunoprotective hydrogel core. The device consists of electrospun medical-grade thermoplastic silicone-polycarbonate-urethane and is soft but tough (~15 megapascal at a rupture strain of >2). Tuning the nanofiber size to less than ~500 nanometers prevented cell penetration while maintaining maximum mass transfer and decreased cellular overgrowth on blank (cell-free) devices to as low as a single-cell layer (~3 micrometers thick) when implanted in the peritoneal cavity of mice. We confirmed device safety, indicated as continuous containment of proliferative cells within the device for 5 months. Encapsulating syngeneic, allogeneic, or xenogeneic rodent islets within the device corrected chemically induced diabetes in mice and cells remained functional for up to 200 days. The function of human SC-β cells was supported by the device, and it reversed diabetes within 1 week of implantation in immunodeficient and immunocompetent mice, for up to 120 and 60 days, respectively. We demonstrated the scalability and retrievability of the device in dogs and observed viable human SC-β cells despite xenogeneic immune responses. The nanofibrous device design may therefore provide a translatable solution to the balance between safety and functionality in developing stem cell-based therapies for T1D.

Pancreatic, but not myeloid-cell, expression of interleukin-1alpha is required for maintenance of insulin secretion and whole body glucose homeostasis

OBJECTIVE

The expression of the interleukin-1 receptor type I (IL-1R) is enriched in pancreatic islet β-cells, signifying that ligands activating this pathway are important for the health and function of the insulin-secreting cell. Using isolated mouse, rat, and human islets, we identified the cytokine IL-1α as a highly inducible gene in response to IL-1R activation. In addition, IL-1α is elevated in mouse and rat models of obesity and Type 2 diabetes. Since less is known about the biology of IL-1α relative to IL-1β in pancreatic tissue, our objective was to investigate the contribution of IL-1α to pancreatic β-cell function and overall glucose homeostasis in vivo.

METHODS

We generated a novel mouse line with conditional IL-1α alleles and subsequently produced mice with either pancreatic- or myeloid lineage-specific deletion of IL-1α.

RESULTS

Using this in vivo approach, we discovered that pancreatic (IL-1αPdx1-/-), but not myeloid-cell, expression of IL-1α (IL-1αLysM-/-) was required for the maintenance of whole body glucose homeostasis in both male and female mice. Moreover, pancreatic deletion of IL-1α led to impaired glucose tolerance with no change in insulin sensitivity. This observation was consistent with our finding that glucose-stimulated insulin secretion was reduced in islets isolated from IL-1αPdx1-/- mice. Alternatively, IL-1αLysM-/- mice (male and female) did not have any detectable changes in glucose tolerance, respiratory quotient, physical activity, or food intake when compared with littermate controls.

CONCLUSIONS

Taken together, we conclude that there is an important physiological role for pancreatic IL-1α to promote glucose homeostasis by supporting glucose-stimulated insulin secretion and islet β-cell mass in vivo.

Encapsulation of Activated Carbon into a Hollow-Type Spherical Bacterial Cellulose Gel and Its Indole-Adsorption Ability Aimed at Kidney Failure Treatment

For reducing side effects and improvement of swallowing, we studied the encapsulation of activated carbon formulations with a hollow-type spherical bacterial cellulose (HSBC) gel using two kinds of encapsulating methods: Methods A and B. In Method A, the BC gelatinous membrane was biosynthesized using Komagataeibacter xylinus (K. xylinus) at the interface between the silicone oil and cell suspension containing activated carbon. In Method B, the bacterial cellulose (BC) gelatinous membrane was formed at the interface between the cell suspension attached to the alginate gel containing activated carbon and the silicone oil. After the BC gelatinous membrane was biosynthesized by K. xylnus, alginate gel was removed by soaking in a phosphate buffer. The activated carbon encapsulated these methods could neither pass through the BC gelatinous membrane of the HSBC gel nor leak from the interior cavity of the HSBC gel. The adsorption ability was evaluated using indole, which is a precursor of the uremic causative agent. From curve-fitting, the adsorption process followed the pseudo-first-order and intra-particle diffusion models, and the diffusion of the indole molecules at the surface of the encapsulated activated carbon within the HSBC gel was dominant at the initial stage of adsorption. It was observed that the adsorption of the encapsulated activated carbon by the intraparticle diffusion process became dominant with longer adsorption times.

Size-Based Sorting of Emulsion Droplets in Microfluidic Channels Patterned with Laser-Ablated Guiding Tracks

We demonstrate an autonomous, high-throughput mechanism for sorting of emulsion droplets with different sizes concurrently flowing in a microfluidic Hele-Shaw channel. The aqueous droplets of varying radii suspended in olive oil are separated into different streamlines across the channel upon interaction with a shallow (depth ∼ 700 nm) inclined guiding track ablated into the polydimethylsiloxane-coated surface of the channel with focused femtosecond laser pulses. Specifically, the observed differences in the droplet trajectories along the guiding track arise due to the different scaling of the confinement force attracting the droplets into the track, fluid drag, and wall friction, with the droplet radius. In addition, the distance traveled by the droplets along the track also depends on the track width, with wider tracks providing more stable droplet guiding for any given droplet size. We systematically study the influence of the droplet size and velocity on the trajectory of the droplets in the channel and analyze the sensitivity of size-based droplet sorting for varying flow conditions. The droplet guiding and sorting experiments are complemented by modeling of the droplet motion in the channel flow using computational fluid dynamics simulations and a previously developed model of droplet guiding. Finally, we demonstrate a complete separation of droplets produced by fusion of two independent droplet streams at the inlet of the Hele-Shaw channel from unfused daughter droplets. The presented droplet sorting technique can find applications in the development of analytical and preparative microfluidic protocols.

Zwitterionically modified alginates mitigate cellular overgrowth for cell encapsulation

Foreign body reaction (FBR) to implanted biomaterials and medical devices is common and can compromise the function of implants or cause complications. For example, in cell encapsulation, cellular overgrowth (CO) and fibrosis around the cellular constructs can reduce the mass transfer of oxygen, nutrients and metabolic wastes, undermining cell function and leading to transplant failure. Therefore, materials that mitigate FBR or CO will have broad applications in biomedicine. Here we report a group of zwitterionic, sulfobetaine (SB) and carboxybetaine (CB) modifications of alginates that reproducibly mitigate the CO of implanted alginate microcapsules in mice, dogs and pigs. Using the modified alginates (SB-alginates), we also demonstrate improved outcome of islet encapsulation in a chemically-induced diabetic mouse model. These zwitterion-modified alginates may contribute to the development of cell encapsulation therapies for type 1 diabetes and other hormone-deficient diseases.

Encapsulation of Micro- and Milli-Sized Particles with a Hollow-Type Spherical Bacterial Cellulose Gel via Particle-Preloaded Droplet Cultivation

A hollow-type spherical bacterial cellulose (HSBC) gel prepared using conventional methods cannot load particles larger than the pore size of the cellulose nanofiber network of bacterial cellulose (BC) gelatinous membranes. In this study, we prepared a HSBC gel encapsulating target substances larger than the pore size of the BC gelatinous membranes using two encapsulating methods. The first method involved producing the BC gelatinous membrane on the surface of the core that was a spherical alginate gel with a diameter of 2 to 3 mm containing the target substances. With this method, the BC gelatinous membrane was biosynthesized using Gluconacetobacter xylinus at the interface between the cell suspension attached onto the alginate gel and the silicone oil. The second method involved producing the BC gel membrane on the interface between the silicone oil and cell suspension, as well as the spherical alginate gel with a diameter of about 1 mm containing target substances. After the BC gelatinous membrane was biosynthesized, an alginate gel was dissolved in a phosphate buffer to prepare an HSBC gel with the target substances. These encapsulated substances could neither pass through the BC gelatinous membrane of the HSBC gel nor leak from the interior space of the HSBC gel. These results suggest that the HSBC gel had a molecular sieving function. The HSBC gel walls prepared using these methods were observed to be uniform and would be useful for encapsulating bioactive molecules, such as immobilized enzymes in HSBC gel, which is expected to be used as a drug carrier.

Deep pool water-impacts of viscous oil droplets

We experimentally study the impacts of viscous, immiscible oil drops into a deep pool of water. Within the target liquid pool, the impacting drop creates a crater, whose dynamics are studied. It is found that the inertia of pool liquid and drop viscosity are the main factors that determine the crater's maximum depth, while the additional factor of mutual immiscibility between the drop and pool liquids leads to interesting interfacial dynamics along the oil-water interface. We discuss how this can change the crater dynamics in its retraction phase, making possible a type of double-entrainment, whereby a tiny air bubble is entrapped inside a water-entrained oil drop. Further, we report the observation of a type of 'fingering' that occurs along the oil-drop rim, which we discuss, arises as a remnant of the well-known crown-splash instability.

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.

Encapsulation of individual living cells with enzyme responsive polymer nanoshell

Cell delivery in cell therapy is typically challenged by the low cell survival rate and immunological rejection during cells injection and circulation. Encapsulation of cells with semipermeable hydrogels or membranes can improve cell viability by resisting high shear force and inhibit immune response with the physical isolation effect. Herein, the individual HeLa cells and human mesenchymal stem cells (hMSCs) were encapsulated with enzyme responsive polymer nanoshell. The encapsulation shell was prepared via the Layer-by-Layer (LbL) assembly of functionalized gelatin and click chemistry of peptide linker and gelatin. The encapsulated cells showed high cell viability and could resist the physical stress. Moreover, the encapsulation shell had a prolonged encapsulation sustaining period and could effectively prevent the invasion of external entities. In addition, on-site cell release was realized via enzymolysis of the encapsulation shell by human matrix metalloproteinase-7 (MMP-7), an overexpressed enzyme on tumor area. The finding of this study proved a potential approach in cell therapy, especially for cell-based cancer therapy.

Conformal coating by multilayer nano-encapsulation for the protection of human pancreatic islets: In-vitro and in-vivo studies

To improve the efficiency of pancreatic islet transplantation, we performed in-vitro and in-vivo experiments with isolated human pancreatic islets coated by multi-layer nano-encapsulation using differently charged polymers [chitosan and poly(sodium styrene sulfonate)] to obtain up to 9 layers. The islet coating (thickness: 104.2 ± 4.2 nm) was uniform, with ≥ 90% cell viability and well preserved beta- and alpha-cell ultrastructure. Nano-encapsulated islets maintained physiological glucose-stimulated insulin secretion by both static incubation and perifusion studies. Notably, palmitate- or cytokine-induced toxicity was significantly reduced in nano-coated islets. Xenotransplantation of nano-encapsulated islets under the kidney capsule of streptozotocin-induced C57Bl/6J diabetic mice allowed long term normal or near normal glycemia, associated with minimal infiltration of immune cell into the grafts, well preserved islet morphology and signs of re-vascularization. In summary, the multi-layer nano-encapsulation approach described in the present study provides a promising tool to effectively protect human islets both in-vitro andin-vivo conditions.

Pancreatic deletion of the interleukin-1 receptor disrupts whole body glucose homeostasis and promotes islet β-cell de-differentiation

Objective

Pancreatic tissue, and islets in particular, are enriched in expression of the interleukin-1 receptor type I (IL-1R). Because of this enrichment, islet β-cells are exquisitely sensitive to the IL-1R ligands IL-1α and IL-1β, suggesting that signaling through this pathway regulates health and function of islet β-cells.

Methods

Herein, we report a targeted deletion of IL-1R in pancreatic tissue (IL-1R^Pdx1−/−) in C57BL/6J mice and in db/db mice on the C57 genetic background. Islet morphology, β-cell transcription factor abundance, and expression of the de-differentiation marker Aldh1a3 were analyzed by immunofluorescent staining. Glucose and insulin tolerance tests were used to examine metabolic status of these genetic manipulations. Glucose-stimulated insulin secretion was evaluated in vivo and in isolated islets ex vivo by perifusion.

Results

Pancreatic deletion of IL-1R leads to impaired glucose tolerance, a phenotype that is exacerbated by age. Crossing the IL-1R^Pdx1−/− with db/db mice worsened glucose tolerance without altering body weight. There were no detectable alterations in insulin tolerance between IL-1R^Pdx1−/− mice and littermate controls. However, glucose-stimulated insulin secretion was reduced in islets isolated from IL-1R^Pdx1−/− relative to control islets. Insulin output in vivo after a glucose challenge was also markedly reduced in IL-1R^Pdx1−/− mice when compared with littermate controls. Pancreatic islets from IL-1R^Pdx1−/− mice displayed elevations in Aldh1a3, a marker of de-differentiation, and reduction in nuclear abundance of the β-cell transcription factor MafA. Nkx6.1 abundance was unaltered.

Conclusions

There is an important physiological role for pancreatic IL-1R to promote glucose homeostasis by suppressing expression of Aldh1a3, sustaining MafA abundance, and supporting glucose-stimulated insulin secretion in vivo.

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Pancreatic deletion of IL-1R impairs glucose tolerance in young and old male mice.

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Pancreatic deletion of IL-1R worsens glucose tolerance in obese db/db mice.

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Deletion of IL-1R triggers expression of the de-differentiation marker Aldh1a3.

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IL-1 signaling in pancreatic tissue influences islet health and function.

The journey of islet cell transplantation and future development

Intraportal islet transplantation has proven to be efficacious in preventing severe hypoglycemia and restoring insulin independence in selected patients with type 1 diabetes. Multiple islet infusions are often required to achieve and maintain insulin independence. Many challenges remain in clinical islet transplantation, including substantial islet cell loss early and late after islet infusion. Contributions to graft loss include the instant blood-mediated inflammatory reaction, potent host auto- and alloimmune responses, and beta cell toxicity from immunosuppressive agents. Protective strategies are being tested to circumvent several of these events including exploration of alternative transplantation sites, stem cell-derived insulin producing cell therapies, co-transplantation with mesenchymal stem cells or exploration of novel immune protective agents. Herein, we provide a brief introduction and history of islet cell transplantation, limitations associated with this procedure and methods to alleviate islet cell loss as a means to improve engraftment outcomes.

Engineering a Tumor Microenvironment-Mimetic Niche for Tissue Regeneration with Xenogeneic Cancer Cells

The insufficient number of cells suitable for transplantation is a long-standing problem to cell-based therapies aimed at tissue regeneration. Xenogeneic cancer cells (XCC) may be an alternative source of therapeutic cells, but their transplantation risks both immune rejection and unwanted spreading. In this study, a strategy to facilitate XCC transplantation is reported and their spreading in vivo is confined by constructing an engineering matrix that mimics the characteristics of tumor microenvironment. The data show that this matrix, a tumor homogenate-containing hydrogel (THAG), successfully creates an immunosuppressive enclave after transplantation into immunocompetent mice. XCC of different species and tissue origins seeded into THAG survive well, integrated with the host and developed the intrinsic morphology of the native tissue, without being eliminated or spreading out of the enclave. Most strikingly, immortalized human hepatocyte cells and rat β-cells loaded into THAG exert the physiological functions of the human liver and rat pancreas islets, respectively, in the mouse body. This study demonstrates a novel and feasible approach to harness the unique features of tumor development for tissue transplantation and regenerative medicine.

Structural changes in alginate-based microspheres exposed to in vivo environment as revealed by confocal Raman microscopy

A next-generation cure for type 1 diabetes relies on immunoprotection of insulin-producing cells, which can be achieved by their encapsulation in microspheres made of non-covalently crosslinked hydrogels. Treatment success is directly related to the microsphere structure that is characterized by the localization of the polymers constituting the hydrogel material. However, due to the lack of a suitable analytical method, it is presently unknown how the microsphere structure changes in vivo, which complicates evaluation of different encapsulation approaches. Here, confocal Raman microscopy (CRM) imaging was tailored to serve as a powerful new tool for tracking structural changes in two major encapsulation designs, alginate-based microbeads and multi-component microcapsules. CRM analyses before implantation and after explantation from a mouse model revealed complete loss of the original heterogeneous structure in the alginate microbeads, making the intentionally high initial heterogeneity a questionable design choice. On the other hand, the structural heterogeneity was conserved in the microcapsules, which indicates that this design will better retain its immunoprotective properties in vivo. In another application, CRM was used for quantitative mapping of the alginate concentration throughout the microbead volume. Such data provide invaluable information about the microenvironment cells would encounter upon their encapsulation in alginate microbeads.

3D Bioprinting for Artificial Pancreas Organ

Type 1 diabetes mellitus (T1DM) results from an autoimmune destruction of insulin-producing beta cells in the islet of the endocrine pancreas. Although islet transplantation has been regarded as an ideal strategy for T1D, transplanted islets are rejected from host immune system. To immunologically protect them, islet encapsulation technology with biocompatible materials is emerged as an immuno-barrier. However, this technology has been limited for clinical trial such as hypoxia in the central core of islet bead, impurity of islet bead and retrievability from the body. Recently, 3D bioprinting has been emerged as an alternative approach to make the artificial pancreas. It can be used to position live cells in a desired location with real scale of human organ. Furthermore, constructing a vascularization of the artificial pancreas is actualized with 3D bioprinting. Therefore, it is possible to create real pancreas-mimic artificial organ for clinical application. In conclusion, 3D bioprinting can become a new leader in the development of the artificial pancreas to overcome the existed islet.

Designing a retrievable and scalable cell encapsulation device for potential treatment of type 1 diabetes

Cell encapsulation has been shown to hold promise for effective, long-term treatment of type 1 diabetes (T1D). However, challenges remain for its clinical applications. For example, there is an unmet need for an encapsulation system that is capable of delivering sufficient cell mass while still allowing convenient retrieval or replacement. Here, we report a simple cell encapsulation design that is readily scalable and conveniently retrievable. The key to this design was to engineer a highly wettable, Ca²⁺-releasing nanoporous polymer thread that promoted uniform in situ cross-linking and strong adhesion of a thin layer of alginate hydrogel around the thread. The device provided immunoprotection of rat islets in immunocompetent C57BL/6 mice in a short-term (1-mo) study, similar to neat alginate fibers. However, the mechanical property of the device, critical for handling and retrieval, was much more robust than the neat alginate fibers due to the reinforcement of the central thread. It also had facile mass transfer due to the short diffusion distance. We demonstrated the therapeutic potential of the device through the correction of chemically induced diabetes in C57BL/6 mice using rat islets for 3 mo as well as in immunodeficient SCID-Beige mice using human islets for 4 mo. We further showed, as a proof of concept, the scalability and retrievability in dogs. After 1 mo of implantation in dogs, the device could be rapidly retrieved through a minimally invasive laparoscopic procedure. This encapsulation device may contribute to a cellular therapy for T1D because of its retrievability and scale-up potential.

Improved Histological Evaluation of Vascularity around an Immunoisolation Device by Correlating Number of Vascular Profiles to Glucose Exchange

The aim of this study was to determine which vessels are important for the exchange of small molecules, such as glucose, from the microcirculation into an immunoisolation device. Reasonably, those vessels should be the ones of interest in histological evaluations. In a previous study, we examined the diffusion of glucose from the microcirculation into immunoisolation devices that had been implanted subcutaneously in rats for various times (i.e., 1, 2, and 4 weeks and 3 months). The glucose kinetic data were then correlated with the number of vascular profiles within 15 and 250 μm from the device. Significant correlations were found only at 250 μm. To examine the relation further between function and vascularization, we used the histological samples from the previous study and counted vascular profiles within various distances between 15 and 400 μm from the device. The number was then correlated with the already available glucose kinetic data. The highest correlations were found at 75 and 100 μm (p < 0.05). We therefore suggest that vascular profiles within 100 μm should be used when evaluating the vascularity of tissue surrounding an immunoisolation device. We also studied neovascularization asymmetries between the side of the membrane facing the skin and that facing the muscle. At 1 and 2 weeks about half of the devices were mainly vascularized on the side facing the skin, whereas the rest were equally vascularized on the two sides. At 3 months, all devices were well vascularized, and no striking vascularization asymmetries were seen.

Factors Influencing Insulin Secretion from Encapsulated Islets

Adequate regulation of glucose levels by a microencapsulated pancreatic islet graft requires a minute-to-minute regulation of blood glucose. To design such a transplant, it is mandatory to have sufficient insight in factors influencing the kinetics of insulin secretion by encapsulated islets. The present study investigates factors influencing the glucose-induced insulin response of encapsulated islets in vitro. We applied static incubations and did the following observations. (i) Small islets (90–120 μm) showed a similar instead of a lower glucose-induced insulin response, suggesting that inclusion of only small islets, which are associated with lower protrusion and failing rates, has no consequences for the functional performance of the graft. (ii) A capsule diameter of 800 μm showed identical rather than lower glucose-induced insulin responses as smaller, 500-μm capsules. (iii) Capsule membranes constructed with a conventional permeability interfered with diffusion of insulin, as illustrated by a lower response of islets in capsules with a 10-min poly-L-lysine (PLL) membrane than islets in capsules with a 5-min PLL membrane. (iv) Irrespective of the tested porosity, the capsules provided sufficient immunoprotection because the 10-min PLL membranes did block diffusion of the cytokines IL-1β (17 kDa) and TNF-α (70 kDa) while the 5-min PLL membranes interfered with the diffusion of the vast majority of the cytokines. We conclude that capsules containing small islets (90–120 μm) and a membrane with a lower permeability than routinely applied is preferred in order to obtain a graft with adequate glucose-induced insulin responses.

In Vitro Culture Duration does Not Impact the Ability of Encapsulated Choroid Plexus Transplants to Prevent Neurological Deficits in an Excitotoxin-Lesioned Rat Model of Huntington's Disease

Delivery of neurotrophic molecules to the CNS is a potential treatment strategy for preventing the neuronal loss accompanying many neurological disorders. Choroid plexus (CP) epithelial cells secrete a cocktail of neurotrophic factors, and encapsulated CP transplants are neuroprotective in animal models of stroke and Huntington's disease (HD). Prior to clinical use, it is essential to identify and optimize parameters such as the length of time that transplant products such as encapsulated CP can be maintained. In the present study, neonatal porcine CP was encapsulated within alginate microcapsules and maintained in vitro for 1, 2, or 7 months. The encapsulated cells remained viable (>80%) at all time points and were transplanted unilaterally into the rat striatum. Seven days later, the same animals received unilateral injections of quinolinic acid (QA; 225 nmol) adjacent to the implant site. Separate groups of animals served as controls and received QA alone. After surgery, animals were periodically evaluated for weight loss and were tested for motor function 14 days post-QA. In controls, QA lesions produced a significant loss of body weight and impaired function of the contralateral forelimb. In contrast, implants of CP were potently neuroprotective as rats receiving CP transplants did not lose body weight and were not significantly impaired when tested for motor function. These benefits were independent of the length of time that the cells were held in vitro and demonstrate that the potential potency of alginate encapsulated CP cells can be retained for extremely long periods of time in vitro.

Microencapsulation of Cells Producing Therapeutic Proteins: Optimizing Cell Growth and Secretion

Microencapsulation of genetically engineered cells may have important applications as delivery systems for therapeutic proteins. However, optimization of the microcapsules with regard to mechanical stability, cell growth, and secretion of proteins is necessary in order to evaluate the future use of this delivery technology. We have explored the growth, survival, and secretion of therapeutic proteins from 293-EBNA cells producing endostatin (293 endo cells) and JJN3 myeloma cells producing hepatocyte growth factor (HGF) that have been embedded in various types of alginate capsules. Parameters that affect capsule integrity such as homogenous and inhomogenous gel cores and addition of an outer poly-l-lysine (PLL)–alginate coating were evaluated in relation to cell functions. When cells were encapsulated, the PLL layer was found to be absolutely required for the capsule integrity. The JJN3 and 293 endo cells displayed completely different growth and distribution patterns of live and dead cells within the microcapsules, as shown by 3D pictures reconstructed from images taken with confocal laser scanning microscopy (CLSM). Encapsulated JJN3 cells showed a bell-shaped growth and HGF secretion curve over a time period of 5 months. The 293 endo cells reached a plateau phase in growth after 23 days postencapsulation; however, after around 30 days a fraction of the microcapsules started to disintegrate. Microcapsule disintegration occurred with time irrespective of capsule and cell type, showing that alginate microcapsules possessing relatively high gel strength are not strong enough to keep proliferating cells within the microcapsules for prolonged time periods. Although this study shows that the stability of an alginate-based cell factory can be increased by a PLL–alginate coating, further improvement is necessary with regard to capsule integrity as well as controlling the cell growth before this technology can be used for therapy.

Cell Viability and Noninvasive In Vivo MRI Tracking of 3D Cell Encapsulating Self-Assembled Microcontainers

Several molecular therapies require the implantation of cells that secrete biotherapeutic molecules and imaging the location and microenvironment of the cellular implant to ascertain its function. We demonstrate noninvasive in vivo magnetic resonance imaging (MRI) of self-assembled microcontainers that are capable of cell encapsulation. Negative contrast was obtained to discern the microcontainer with MRI; positive contrast was obtained in the complete absence of background signal. MRI on a clinical scanner highlights the translational nature of this research. The microcontainers were loaded with cells that were dispersed in an extracellular matrix, and implanted both subcutaneously and in human tumor xenografts in SCID mice. MRI was performed on the implants, and microcontainers retrieved postimplantation showed cell viability both within and proximal to the implant. The microcontainers are characterized by their small size, three dimensionality, controlled porosity, ease of parallel fabrication, chemical and mechanical stability, and noninvasive traceability in vivo.

Advances in islet encapsulation technologies

Type 1 diabetes is an autoimmune disorder in which the immune system attacks and destroys insulin-producing islet cells of the pancreas. Although islet transplantation has proved to be successful for some patients with type 1 diabetes, its widespread use is limited by islet donor shortage and the requirement for lifelong immunosuppression. An encapsulation strategy that can prevent the rejection of xenogeneic islets or of stem cell-derived allogeneic islets can potentially eliminate both of these barriers. Although encapsulation technology has met several challenges, the convergence of expertise in materials, nanotechnology, stem cell biology and immunology is allowing us to get closer to the goal of encapsulated islet cell therapy for humans.

Current and Future Perspectives on Alginate Encapsulated Pancreatic Islet

Transplantation of pancreatic islets in immune protective capsules holds the promise as a functional cure for type 1 diabetes, also about 40 years after the first proof of principal study. The concept is simple in using semipermeable capsules that allow the ingress of oxygen and nutrients, but limit the access of the immune system. Encapsulated human islets have been evaluated in four small clinical trials where the procedure has been evaluated as safe, but lacking long-term efficacy. Host reactions toward the biomaterials used in the capsules may be one parameter limiting the long-term function of the graft in humans. The present article briefly discusses important capsule properties such as stability, permeability and biocompatibility, as well as possible strategies to overcome current challenges. Also, recent progress in capsule development as well as the production of insulin-producing cells from human stem cells that gives promising perspectives for the transplantation of encapsulated insulin-producing tissue is briefly discussed. Stem Cells Translational Medicine 2017;6:1053-1058.

Determination of the Mechanical Strength of Microcapsules

The promise of pancreatic islet transplantation is hindered by organ shortage, and the need for immunosuppression of transplant recipient in order to prevent rejection. Alginate microencapsulation can overcome these hurdles; however further optimization of this technique is required. Among the critical factors to be optimized is the durability of alginate microcapsules, which can be determined by their mechanical strength tests. Here we describe several simple and reliable methods to assist in assessing the mechanical strength of alginate beads.

The Diffusive Properties of Hydrogel Microcapsules for Cell Encapsulation

Hydrogel microcapsules have been used for decades to encapsulate cells and treat diseases ranging from neurodegenerative disorders to more systemic applications like Type I Diabetes. This cell encapsulation modality has been developed through more cumulative experiments than perhaps any other, owing to the relative ease of accessing the required materials, the commercial availability of droplet-generating instrumentation, and the mild microenvironment and unique permeability properties of hydrogels that are difficult to attain with alternative encapsulation systems employing thermoplastic materials. Because of their size and shape, microcapsules have an inherent advantage over macroencapsulation devices due to the more favorable surface area to volume ratio, which allows for greater efficiency in the amount of cellular cargo that is entrapped and enhanced nutrient exchange and efflux of secreted products. Unfortunately, with this significant positive benefit comes the caveat of difficult or impractical retrievability, highlighting the paradox that is particularly relevant as differentiated stem cell sources become more readily available. This chapter focuses on several techniques that can be used to evaluate the permeability and pore structure of hydrogel microcapsules, including a simplistic model for describing the diffusive behavior of alginate-polycation-alginate (APA) microcapsules with a liquid core, and an ancillary method to evaluate the ultrastructure of the APA membrane including morphometric analysis.

Controlled production of sub-millimeter liquid core hydrogel capsules for parallelized 3D cell culture

Liquid core capsules having a hydrogel membrane are becoming a versatile tool for three-dimensional culture of micro-organisms and mammalian cells. Making sub-millimeter capsules at a high rate, via the breakup of a compound jet in air, opens the way to high-throughput screening applications. However, control of the capsule size monodispersity, especially required for quantitative bioassays, was still lacking. Here, we report how the understanding of the underlying hydrodynamic instabilities that occur during the process can lead to calibrated core-shell bioreactors. The requirements are: i) damping the shear layer instability that develops inside the injector arising from the co-annular flow configuration of liquid phases having contrasting viscoelastic properties; ii) controlling the capillary instability of the compound jet by superposing a harmonic perturbation onto the shell flow; iii) avoiding coalescence of drops during jet fragmentation as well as during drop flight towards the gelling bath; iv) ensuring proper engulfment of the compound drops into the gelling bath for building a closed hydrogel shell. We end up with the creation of numerous identical compartments in which cells are able to form multicellular aggregates, namely spheroids. In addition, we implement an intermediate composite hydrogel layer, composed of alginate and collagen, allowing cell adhesion and thus the formation of epithelia or monolayers of cells.

Polyelectrolyte Multilayer Film Coating and Stability at the Surfaces of Oral Prosthesis Base Polymers: an in vitro and in vivo Study

A new type of coating involving a layer-by-layer technique has been recently reported. This coating is composed of a polyelectrolyte multilayer film that confers specific properties on surfaces to which it is applied. Here, we studied the applicability of such a technique to the coating of oral prostheses, by first testing the construction of polyelectrolyte multilayer films on several polymers used in oral prosthesis bases, and, subsequently, by studying the stability of these coatings in vitro, in human saliva, and in vivo in a rat model. We demonstrated that the multilayered films are able to coat the surfaces of all tested polymers completely, thus increasing their wettability. We also showed that saliva does not degrade the film after 7 days in vitro and after 4 days in vivo. Taken together, our results establish that the layer-by-layer technique is suitable for the coating of oral devices.

Microfluidic production of multiple emulsions and functional microcapsules

Recent advances in microfluidics have enabled the controlled production of multiple-emulsion drops with onion-like topology. The multiple-emulsion drops possess an intrinsic core-shell geometry, which makes them useful as templates to create microcapsules with a solid membrane. High flexibility in the selection of materials and hierarchical order, achieved by microfluidic technologies, has provided versatility in the membrane properties and microcapsule functions. The microcapsules are now designed not just for storage and release of encapsulants but for sensing microenvironments, developing structural colours, and many other uses. This article reviews the current state of the art in the microfluidic-based production of multiple-emulsion drops and functional microcapsules. The three main sections of this paper discuss distinct microfluidic techniques developed for the generation of multiple emulsions, four representative methods used for solid membrane formation, and various applications of functional microcapsules. Finally, we outline the current limitations and future perspectives of microfluidics and microcapsules.

Encapsulation of anti-carbonic anhydrase IX antibody in hydrogel microspheres for tumor targeting

Encapsulation is a well-established method of biomaterial protection, controlled release, and efficient delivery. Here we evaluated encapsulation of monoclonal antibody M75 directed to tumor biomarker carbonic anhydrase IX (CA IX) into alginate microbeads (SA-beads) or microcapsules made of sodium alginate, cellulose sulfate, and poly(methylene-co-guanidine) (PMCG). M75 antibody release was quantified using ELISA and its binding properties were assessed by immunodetection methods. SA-beads showed rapid M75 antibody release in the first hour, followed by steady release during the whole experiment of 7 days. In contrast, the M75 release from PMCG capsules was gradual, reaching the maximum concentration on the 7th day. The release was more efficient at pH 6.8 compared to pH 7.4. The released antibody could recognize CA IX, and target the CA IX-positive cells in 3D spheroids. In conclusion, SA-beads and PMCG microcapsules can be considered as promising antibody reservoirs for targeting of cancer cells.

Immunoisolation to prevent tissue graft rejection: Current knowledge and future use

This review focuses on the concept of immunoisolation and how this method has evolved over the last few decades. The concept of immunoisolation came out of the need to protect allogeneic transplant tissue from the host immune system and avoid systemic side effects of immunosuppression. The latter remains a significant hurdle in clinical translation of using tissue transplants for restoring endocrine function in diabetes, growth hormone deficiency, and other conditions. Herein, we review the most significant works studying the use of hydrogels, specifically alginate and poly (ethylene glycol), and membranes for immunoisolation and discuss how this approach can be applied in reproductive biology.