Functional Comparison of the Single-Layer Agarose Microbeads and the Developed Three-Layer Agarose Microbeads as the Bioartificial Pancreas: An In Vitro Study

Progress technology in microencapsulation methods for cell therapy

Cell encapsulation in microcapsules allows the in situ delivery of secreted proteins to treat different pathological conditions. Spherical microcapsules offer optimal surface-to-volume ratio for protein and nutrient diffusion, and thus, cell viability. This technology permits cell survival along with protein secretion activity upon appropriate host stimuli without the deleterious effects of immunosuppressant drugs. Microcapsules can be classified in 3 categories: matrix-core/shell microcapsules, liquid-core/shell microcapsules, and cells-core/shell microcapsules (or conformal coating). Many preparation techniques using natural or synthetic polymers as well as inorganic compounds have been reported. Matrix-core/shell microcapsules in which cells are hydrogel-embedded, exemplified by alginates capsule, is by far the most studied method. Numerous refinement of the technique have been proposed over the years such as better material characterization and purification, improvements in microbead generation methods, and new microbeads coating techniques. Other approaches, based on liquid-core capsules showed improved protein production and increased cell survival. But aside those more traditional techniques, new techniques are emerging in response to shortcomings of existing methods. More recently, direct cell aggregate coating have been proposed to minimize membrane thickness and implants size. Microcapsule performances are largely dictated by the physicochemical properties of the materials and the preparation techniques employed. Despite numerous promising pre-clinical results, at the present time each methods proposed need further improvements before reaching the clinical phase.

Generation of monodisperse alginate microbeads and in situ encapsulation of cell in microfluidic device

A microfluidic method for the in situ production of monodispersed alginate hydrogels using chaotic mixing is described. Aqueous droplets comprising of alginate and calcium as a cross-linking agent were formed as an immiscible continuous phase, and then the alginate and calcium in the droplet came into contact and were rapidly mixed. Gelation of the hydrogel was achieved in situ by the chaotic mixing of the droplets in the microfluidic device. Important operating parameters included: the capillary number (Ca) and the flow rate of the continuous phase, which mainly influenced the formation of three distinctive flow regimes, such as fluctuation, stable droplets, and laminar flow. Under the stable formation of droplets regime, monodispersed alginate microbeads having a narrow size distribution (below 3% of CV) were produced in the microfluidic device and the size of the microbeads, ranging from 60 to 95 microm, could be easily modulated by varying the flow rate, viscosity, and interfacial tension. In addition, this approach can be applied to the encapsulation of yeast cells in alginate hydrogels with a high monodispersity. This simple microfluidic technique for the production of monodispersed hydrogels and encapsulation of biomolecules shows strong potential for use in biosensors, cell sensors, drug delivery systems, and cell transplantation applications.

Biological and Biomaterial Approaches for Improved Islet Transplantation

Islet transplantation may be used to treat type I diabetes. Despite tremendous progress in islet isolation, culture, and preservation, the clinical use of this modality of treatment is limited due to post-transplantation challenges to the islets such as the failure to revascularize and immune destruction of the islet graft. In addition, the need for lifelong strong immunosuppressing agents restricts the use of this option to a limited subset of patients, which is further restricted by the unmet need for large numbers of islets. Inadequate islet supply issues are being addressed by regeneration therapy and xenotransplantation. Various strategies are being tried to prevent beta-cell death, including immunoisolation using semipermeable biocompatible polymeric capsules and induction of immune tolerance. Genetic modification of islets promises to complement all these strategies toward the success of islet transplantation. Furthermore, synergistic application of more than one strategy is required for improving the success of islet transplantation. This review will critically address various insights developed in each individual strategy and for multipronged approaches, which will be helpful in achieving better outcomes.