Characterization of polysaccharide multilayered capsules for tissue engineering applications

Abstract

Cell encapsulation has been widely studied as an alternative therapy for almost every human diseases and disorders. This technique enables the inclusion of various types of living cells inside spherical systems which, among other capabilities, mimic the environment provided by the extracellular matrix. This new therapeutic approach has already proved to be successful either in vitro or in vivo studies, thus becoming one of the most promising tools in tissue engineering and regenerative medicine. The main goal of this thesis was to explore some of the potential of cell encapsulation using simple and versatile techniques that can be performed in physiological and friendly conditions to the cells. In a first approach, cells were encapsulated in liquid-core capsules using a three step methodology: (i) the precipitation of a polymer solution of alginate into a bath of calcium chloride (ionotropic gelation), (ii) deposition of polyelectrolyte multilayers onto the surface of the beads, in a process called layer-by-layer. (iii) use of EDTA to liquefy the alginate core. Two different natural-based polymers were used, alginate, the most studied copolymer for cell encapsulation and chitosan, a polymer widely explored in a variety of biomedical applications. Both polymers were proved to be biocompatible, biodegradable and can be manipulated under physiological conditions. All the capsules produced exhibited spherical shape, smooth surface and liquid-core. The results shown that encapsulated cells were viable and proliferating few days after the alginate-chitosan multilayer buildup, which suggests that the develop capsules posses a semipermeable membrane which allows the correct diffusion of nutrients and metabolites. A preliminary study was started to test the feasibility of culturing anchorage-dependent cells in PLLA solid microparticles previously treated with human serum fibronectin followed by the encapsulation of the whole set in alginate-chitosan liquid-core capsules. The results are still very incipient but very promising.