Influence of Different Polyelectrolytes on Layer-by-Layer Microcapsule Properties: Encapsulation Efficiency and Colloidal and Temperature Stability

The fabrication of colloidal and temperature stable microcapsules for encapsulation of biomolecules based on matrix-assisted layer-by-layer (LbL) encapsulation by polyelectrolyte self-assembly has been demonstrated. In brief, the process is based on the emulsification of a hydrogel in warm oil for microdroplet formation. The hydrogel acts as a matrix for the later encapsulation process and can be loaded with biomolecules. After microdroplets of, for example, protein loaded hydrogel are formed by emulsification, cooling leads to solidification of the droplets to form microbeads, followed by encapsulation of the hydrogel microbeads with polyelectrolyte multilayers through an LbL self-assembly process to form polymeric capsules. Colloidal stability, encapsulation efficiency, and temperature stability of the LbL hydrogel microcapsules composed from different polyelectrolytes with various ionic strengths and charge densities have been studied. Microcapsules fabricated with strong polyelectrolytes showed better colloidal stability, while microcapsules fabricated with weak polyelectrolytes showed better encapsulation efficiency and temperature stability. After temperature treatment, microcapsules fabricated with different polyelectrolytes exhibited different morphological changes from complete rupturing over broken microcapsules with deformed hollow shells to intact microcapsules. Among all the studied polyelectrolyte pairs, the PAH/PSS polyelectrolyte system was found to be the best material to fabricate microcapsules with good colloidal and temperature stability and high encapsulation efficiency. Microcapsules with PSS as the outermost layer remained similar in size after temperature treatment, while microcapsules with PAH as the outermost layer shrunk by 76% in capsule volume. The present study provides a detailed overview on properties and design of LbL microcapsules as a function of polyelectrolyte materials and layer number. As a result of the versatility of loading LbL hydrogel microcapsules with various biomolecules or mixtures, potential applications are in the fields of diagnostics, drug delivery, and life sciences.