Novel techniques for microencapsulation of probiotic bacteria

Microencapsulation of living cells such as probiotic bacteria can be used for the protection of the cells from harsh conditions such as low pH and mechanical stress in the digestive system. In this thesis we demonstrate various novel strategies to microencapsulate living yeast cells as a model for probiotic bacteria. We prepared and used sporopollenin microcapsules to encapsulate yeast cells by compressing the sporopollenin particles into a pellet which was exposed to an aqueous suspension of yeast cells in the presence of a biocompatible surface active agent. We also demonstrate that the viability of the cells is preserved after the microencapsulation. We fabricated novel shellac-yeast cells composite microcapsules programmed to release the cells upon change of pH in a narrow range. This was achieved by either spray drying or sprays co-precipitating dispersion of yeast cells in aqueous solution of ammonium shellac doped with a pH-sensitive polyelectrolyte. We also demonstrate that yeast cells retain their viability even when treated with aqueous solutions of low pH. In addition, the pH-triggered release of yeast cells from these composite microcapsules and their disintegration rates were investigated. We developed a theoretical model for the kinetics of yeast cells release from the microcapsules triggered by (i) pH change and (ii) the growth of the cells in a culture media. In a separate strategy of microencapsulation of living cells, we used templates of Pickering emulsions stabilised with latex nanoparticles to fabricate colloidosomes loaded with viable probiotics. Depending on the method of transfer, we have shown that magnetic colloidosomes containing pH-sensitive polyelectrolyte loaded with living cells can be prepared using Pickering emulsion templates. In addition, we demonstrate two strategies to strengthen the stability of water-in-oil Pickering emulsion droplets by interlocking the adsorbed latex particle monolayer: by (i) using oppositely charged polyelectrolyte adsorption or (ii) using polyelectrolyte pre-coated yeast cells which act as cross-linkers inside the water-in-oil droplets. Furthermore, we report the fabrication of 3 D multicellular cellosomes of living cells by using water-in-oil emulsion templates as intermediate. We have used two strategies to assemble yeast cells pre-coated with polyelectrolytes in water-in-oil emulsion droplets stabilised with either surfactant or solid particles. The emulsion droplets containing oppositely charged yeast cells linked together by electrostatical interactions were shrunken to compact structures upon addition of dry octanol and subsequently transferred into water to fabricate cellosomes. In summary, this thesis contributes an arsenal of new methods for microencapsulation of living cells for the purpose of their protection and triggered release. The results of this thesis can be used in the formulation of better probiotic products, protection and release of cells implants, tissue engineering and development of live vaccines

Novel techniques for microencapsulation of probiotic bacteria

Microencapsulation of living cells such as probiotic bacteria can be used for the protection of the cells from harsh conditions such as low pH and mechanical stress in the digestive system. In this thesis we demonstrate various novel strategies to microencapsulate living yeast cells as a model for probiotic bacteria. We prepared and used sporopollenin microcapsules to encapsulate yeast cells by compressing the sporopollenin particles into a pellet which was exposed to an aqueous suspension of yeast cells in the presence of a biocompatible surface active agent. We also demonstrate that the viability of the cells is preserved after the microencapsulation.We fabricated novel shellac-yeast cells composite microcapsules programmed to release the cells upon change of pH in a narrow range. This was achieved by either spray drying or sprays co-precipitating dispersion of yeast cells in aqueous solution of ammonium shellac doped with a pH-sensitive polyelectrolyte. We also demonstrate that yeast cells retain their viability even when treated with aqueous solutions of low pH. In addition, the pH-triggered release of yeast cells from these composite microcapsules and their disintegration rates were investigated. We developed a theoretical model for the kinetics of yeast cells release from the microcapsules triggered by (i) pH change and (ii) the growth of the cells in a culture media.In a separate strategy of microencapsulation of living cells, we used templates of Pickering emulsions stabilised with latex nanoparticles to fabricate colloidosomes loaded with viable probiotics. Depending on the method of transfer, we have shown that magnetic colloidosomes containing pH-sensitive polyelectrolyte loaded with living cells can be prepared using Pickering emulsion templates. In addition, we demonstrate two strategies to strengthen the stability of water-in-oil Pickering emulsion droplets by interlocking the adsorbed latex particle monolayer: by (i) using oppositely charged polyelectrolyte adsorption or (ii) using polyelectrolyte pre-coated yeast cells which act as cross-linkers inside the water-in-oil droplets.Furthermore, we report the fabrication of 3 D multicellular cellosomes of living cells by using water-in-oil emulsion templates as intermediate. We have used two strategies to assemble yeast cells pre-coated with polyelectrolytes in water-in-oil emulsion droplets stabilised with either surfactant or solid particles. The emulsion droplets containing oppositely charged yeast cells linked together by electrostatical interactions were shrunken to compact structures upon addition of dry octanol and subsequently transferred into water to fabricate cellosomes.In summary, this thesis contributes an arsenal of new methods for microencapsulation of living cells for the purpose of their protection and triggered release. The results of this thesis can be used in the formulation of better probiotic products, protection and release of cells implants, tissue engineering and development of live vaccines