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Abstract
Recently, polymeric nano/micro capsules with an aqueous core have been gaining attention for the encapsulation of hydrophilic guest molecules such as proteins. The objective of this thesis has been to synthesize polymeric capsules with an aqueous core based on the technique called “inverse (mini)emulsion periphery RAFT polymerization” (IEPP or IMEPP). IEPP is a relatively new technique but offers various advantages such as a reaction free core environment, which is suitable for encapsulation of sensitive guest molecules.
Various guest molecules can be encapsulated within polymeric capsules in a one-pot approach via the IEPP method. Water droplets in the inverse emulsion act as soft templates for the subsequent polymerization and containers for guest molecules. IEPP utilizes amphiphilic polymers which serve as both steric stabilizers and macroRAFT agents. The subsequent polymerization process is controlled via the RAFT process, leading to the shell formation at the outer surface of the water droplets. The diameter of capsules is governed by the initial water droplet diameter which can be tuned by varying emulsification conditions.
The IEPP process was successfully applied for the fabrication of polymeric capsules with diameters from submicron to over ten microns in combination with an emulsification technique called “membrane emulsification”. This size range cannot be achieved by conventional emulsification techniques such as ultrasonication. Regardless of the initial droplet diameter, the polymeric shell can be formed via the IEPP process, allowing size control from nano to micro scale with narrow size distributions. Two different guest molecules, sulforhodamine B and fluorescein-labelled bovine serum albumin were successfully encapsulated with high encapsulation efficiency.
Vegetable oils were tested as a continuous phase to eliminate the need for toxic organic solvents. Micrometer-sized polymeric capsules were successfully synthesized via IEPP in vegetable oil which is non-toxic and environmental friendly compared to common organic solvents.
By utilizing a photoinitiation system, polymeric nanocapsules were successfully synthesized via IMEPP at room temperature. A model enzyme, glucose oxidase which undergoes denaturation under high temperature, was successfully encapsulated within the polymeric nanocapsules. The encapsulated enzyme can function in an organic solvent mixture where the native enzyme immediately loses its enzymatic activity.