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• W27835331 abstract "Diseases of deficient or subnormal metabolic or secretory cell function, such as diabetes mellitus, are on the increase due to an aging population and increased incidence of metabolic syndrome. At present, the only means of reversal is allograft transplantation. However, the amount of tissue available for transplantation precludes this as a viable option for treating the majority of the patient population. In addition, the required immunosuppressive drug regimen is associated with many long-term side effects. The use of microencapsulation cell therapy to transplant foreign cells or tissue for providing site-specific and dynamic delivery of cell-synthesized molecules is an attractive alternative treatment to replace the lost function in the host tissue. In microencapsulation, the transplant material is covered with a semi-permeable membrane prior to transplantation to shield it from the immune system of recipients. The membrane allows for the transportation of nutrients and therapeutic agents but is relatively impermeable to the larger molecules and cells of the recipient’s immune system. This technique avoids the requirement for immunosuppressive drugs, enlarges the amount of available transplant material and provides long-term and continuous drug delivery to sites that are difficult to access in the body. Microencapsulation of cell spheroids in an immunoselective, highly biocompatible, biomembrane such as alginate/polycation/alginate (APA) offers a way to create viable implantation options. Traditionally the encapsulation process has been achieved through the injection/extrusion of alginate/cell mixtures into a calcium chloride solution to produce calcium alginate capsules around the cells. While an immuno-isolating membrane can be established around the cells, the microcapsules generated have substantial dead space leading to an unnecessarily large transplant volume. A novel alternative is explored in this thesis, in which a two-phase emulsion process is used to produce thin coherent alginate membranes around cell spheroids. A thorough investigation has been used to establish the emulsion process parameters that are critical to the formation of a coherent alginate coat both on a model spheroid system of polymer beads and subsequently on cell spheroids. Optical and Fluorescence microscopy are used to assess the morphology and coherence of the calcium alginate/poly-L-ornithine/alginate (APA) capsules produced. The developed coherent APA microcapsule can provide an immunoselective and highly biocompatible membrane for cellular or tissue transplantation. However, this technique is not applicable for xenograft transplantation, as small peptides and other foreign molecules released from the xenogenic transplant material can diffuse through the coherent microcapsules and trigger the indirect response of the host immune system. This thesis explored a novel approach in which alginate is biotinylated using carbodiimide crosslinking chemistry to facilitate subsequent immobilisation of biomolecules to further augment the biofunctionality of the microcapsules via a streptavidin-biotin conjugation. A thorough investigation has been conducted to optimize and characterize alginate biotinylation via carbodiimide chemistry by a 4’-hydroxyazobenzene-2-carboxylic acid (HABA) based assay and by ATR-FTIR, H-NMR and XPS. To minimize the formation of by-product, a theoretical 40% activation of the carboxylic group on the alginate was employed to manufacture an optimal modification of ~10% biotinylated alginate. Confocal fluorescence microscopy was used to assess the conjugation of streptavidin and assembly of antibodies on the microcapsules. Local immunosuppressive capacity was assimilated on the APA microcapsules by binding of anti-tumor necrosis factor-alpha (TNF-α) antibodies via streptavidin¬biotin conjugation, shown from the clear reduction of TNF-α in in-vitro medium. Conventional alginate/poly-L-ornithine (AP) membranes fail in long-term transplantations of immortal cell lines. Continuous cell proliferation inside the microcapsule causes rapid rupture of the membranes causing immediate immune rejection. This restricts the applicability of immortal cell lines for the development of cell-based drug delivery systems. This thesis examines a novel layer-by-layer (LbL) membrane using polystyrene sulfonate and polyallylamine hydrochloride (PSS/PAH) on top of the coherent AP membrane. Assembly of the LbL membrane was followed by electrophoresis, and the surface morphologies and structure were characterized and examined by cryo-scanning electron microscope (Cryo-SEM) and transmission electron microscopy (TEM). Unlike the standard AP membrane, the LbL multilayer membrane withstood the internal pressure generated by continuous cell proliferation of microencapsulated HEK-293 and Min-6 cells. The new membrane did not affect insulin secretion and diffusion by the Min-6 cell line. This thesis demonstrates that using the two-phase emulsion method, coherent alginate microcapsule can be readily and controllably manufactured for the microencapsulation of a cell spheroid. This coherent alginate microcapsule can be further enhanced with biofunctional and mechanical argumentation on the alginate/PLO membrane, enabling it as a robust cell-based drug delivery system suitable for a variety of medical applications." @default.
• W27835331 created "2016-06-24" @default.
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• W27835331 date "2008-01-01" @default.
• W27835331 modified "2023-09-27" @default.
• W27835331 title "Self Assembled Nano-coats for Protection of Foreign Tissue Transplants" @default.
• W27835331 hasPublicationYear "2008" @default.
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