Bioactive long-term release from biodegradable microspheres preserves implanted ALG-PLO-ALG microcapsules from in vivo response to purified alginate

Current Status of Alginate in Drug Delivery

Alginate is one of the natural polymers that are often used in drug- and protein-delivery systems. The use of alginate can provide several advantages including ease of preparation, biocompatibility, biodegradability, and nontoxicity. It can be applied to various routes of drug administration including targeted or localized drug-delivery systems. The development of alginates as a selected polymer in various delivery systems can be adjusted depending on the challenges that must be overcome by drug or proteins or the system itself. The increased effectiveness and safety of sodium alginate in the drug- or protein-delivery system are evidenced by changing the physicochemical characteristics of the drug or proteins. In this review, various routes of alginate-based drug or protein delivery, the effectivity of alginate in the stem cells, and cell encapsulation have been discussed. The recent advances in the in vivo alginate-based drug-delivery systems as well as their toxicities have also been reviewed.

Microparticles, Microspheres, and Microcapsules for Advanced Drug Delivery

Microparticles, microspheres, and microcapsules are widely used constituents of multiparticulate drug delivery systems, offering both therapeutic and technological advantages. Microparticles are generally in the 1–1000 µm size range, serve as multiunit drug delivery systems with well-defined physiological and pharmacokinetic benefits in order to improve the effectiveness, tolerability, and patient compliance. This paper reviews their evolution, significance, and formulation factors (excipients and procedures), as well as their most important practical applications (inhaled insulin, liposomal preparations). The article presents the most important structures of microparticles (microspheres, microcapsules, coated pellets, etc.), interpreted with microscopic images too. The most significant production processes (spray drying, extrusion, coacervation, freeze-drying, microfluidics), the drug release mechanisms, and the commonly used excipients, the characterization, and the novel drug delivery systems (microbubbles, microsponges), as well as the preparations used in therapy are discussed in detail.

A bridging SF/Alg composite scaffold loaded NGF for spinal cord injury repair

Neurons loss and axons degeneration after spinal cord injury (SCI) gradually give rise to result in functional motor and sensory impairment. A bridging biomaterial scaffold that allows the axons to grow through has been investigated for the repair of injured spinal cord. In this study, we introduced a silk fibroin (SF)-based neurobridge as scaffold enriched with/without nerve growth factor (NGF) that can be utilized as a therapeutic approach for spinal cord repair. NGF released from alginate (Alg) microspheres on SF scaffold (SF/Alg composites scaffolds) to the central lesion site of SCI significantly enhanced the sparing of spinal cord tissue and increased the number of surviving neurons. This optimal multi-disciplinary approach of combining biomaterials, controlled-release microspheres and neurotrophic factors offers a promising treatment for the injured spinal cord.

Current status of hepatocyte xenotransplantation

The treatment of acute liver failure, a condition with high mortality, comprises optimal clinical care, and in severe cases liver transplantation. However, there are limitations in availability of organ donors. Hepatocyte transplantation is a promising alternative that could fill the medical need, in particular as the bridge to liver transplantation. Encapsulated porcine hepatocytes represent an unlimited source that could function as a bioreactor requiring minimal immunosuppression. Besides patients with acute liver failure, patients with alcoholic hepatitis who are unresponsive to a short course of corticosteroids are a target for hepatocyte transplantation. In this review we present an overview of the innate immune barriers in hepatocyte xenotransplantation, including the role of complement and natural antibodies; the role of phagocytic cells and ligands like CD47 in the regulation of phagocytic cells; and the role of Natural Killer cells. We present also some illustrations of physiological species incompatibilities in hepatocyte xenotransplantation, such as incompatibilities in the coagulation system. An overview of the methodology for cell microencapsulation is presented, followed by proof-of-concept studies in rodent and nonhuman primate models of fulminant liver failure: these studies document the efficacy of microencapsulated porcine hepatocytes which warrants progress towards clinical application. Lastly, we present an outline of a provisional clinical trial, that upon completion of preclinical work could start within the upcoming 2-3 years.

Multifunctional hydrogel-based scaffold for improving the functionality of encapsulated therapeutic cells and reducing inflammatory response

Since the introduction of cell immunoisolation as an alternative to protect transplanted cells from host immune attack, much effort has been made to develop this technology into a realistic clinical proposal. Several promising approaches have been investigated to resolve the biotechnological and biosafety challenges related to cell microencapsulation. Here, a multifunctional hydrogel-based scaffold consisting of cell-loaded alginate-poly-l-lysine-alginate (APA) microcapsules and dexamethasone (DXM)-loaded poly(lactic-co-glycolic) acid (PLGA) microspheres embedded in alginate hydrogel is developed and evaluated. Initially, the feasibility of using an alginate hydrogel for enclosing APA microcapsules was studied in a xenogeneic approach. In addition, the performance of the local release of DXM was addressed. The in vitro studies confirmed the correct adaptation of the enclosed cells to the scaffolds in terms of metabolic activity and viability. The posterior implantation of the hydrogel-based scaffolds containing cell-loaded microcapsules revealed that the hematocrit levels were maintained high and constant, and the pericapsular overgrowth was reduced in the DXM-treated rats for at least 2months. This multifunctional scaffold might have a synergistic effect: (1) providing a physical support for APA microcapsules, facilitating administration, ensuring retention and recuperation and preventing dissemination; and (2) reducing post-transplantation inflammation and foreign body reaction, thus prolonging the lifetime of the implant by the continuous and localized release of DXM.

Alginate-Poly(ethylene glycol) Hybrid Microspheres for Primary Cell Microencapsulation

The progress of medical therapies, which rely on the transplantation of microencapsulated living cells, depends on the quality of the encapsulating material. Such material has to be biocompatible, and the microencapsulation process must be simple and not harm the cells. Alginate-poly(ethylene glycol) hybrid microspheres (alg-PEG-M) were produced by combining ionotropic gelation of sodium alginate (Na-alg) using calcium ions with covalent crosslinking of vinyl sulfone-terminated multi-arm poly(ethylene glycol) (PEG-VS). In a one-step microsphere formation process, fast ionotropic gelation yields spherical calcium alginate gel beads, which serve as a matrix for simultaneously but slowly occurring covalent cross-linking of the PEG-VS molecules. The feasibility of cell microencapsulation was studied using primary human foreskin fibroblasts (EDX cells) as a model. The use of cell culture media as polymer solvent, gelation bath, and storage medium did not negatively affect the alg-PEG-M properties. Microencapsulated EDX cells maintained their viability and proliferated. This study demonstrates the feasibility of primary cell microencapsulation within the novel microsphere type alg-PEG-M, serves as reference for future therapy development, and confirms the suitability of EDX cells as control model.

Functionalized PEG hydrogels through reactive dip-coating for the formation of immunoactive barriers

Influencing the host immune system via implantable cell-delivery devices has the potential to reduce inflammation at the transplant site and increase the likelihood of tissue acceptance. Towards this goal, an enzymatically-initiated, dip-coating technique is adapted to fabricate conformal hydrogel layers and to create immunoactive polymer coatings on cell-laden poly(ethylene glycol) (PEG) hydrogels. Glucose oxidase (GOx)-initiated dip coatings enable the rapid formation of uniform, PEG-based coatings on the surfaces of PEG hydrogels, with thicknesses up to 500 μm where the thickness is proportional to the reaction time. Biofunctional coatings were fabricated by thiolating biomolecules that were subsequently covalently incorporated into the coating layer via thiol-acrylate copolymerization. The presence of these proteins was verified via fluorescent confocal microscopy and a modified ELISA, which indicated IgG concentrations as high as 13 ± 1 ng/coated cm² were achievable. Anti-Fas antibody, known to induce T cell apoptosis, was incorporated into coatings, with or without the addition of ICAM-1 to promote T cell interaction with the functionalized coating. Jurkat T cells were seeded atop functionalized coatings and the induction of apoptosis was measured as an indicator of coating bioactivity. After 48 h of interaction with the functionalized coatings, 61 ± 9% of all cells were either apoptotic or dead, compared to only 18 ± 5% of T cells on non-functionalized coatings. Finally, the cytocompatibility of the surface-initiated GOx coating process was confirmed by modifying gels with either encapsulated β-cells or 3T3 fibroblasts within a gel that contained a PEG methacrylate coating.