Osmosis in aqueous two-phase system and its application in protein encapsulation

Abstract

Encapsulation is a process where the active pharmaceutical ingredient (API) is preserved in a cage of excipient, such as a polymeric particle. The vulnerable API is protected against degradation before reaching the target site. Conventional encapsulating techniques include emulsion evaporation or spray drying. However, among these techniques, it is inevitable to use an organic solvent to dissolve polymers. Much evidence proves that the oil-water interface denatures proteins once they are adsorbed to and aggregate at the interface. Also, the harsh temperature and pressure change involved could destroy the functional structure of the active ingredients, lending to reduced loading efficiency.

Therefore, the osmo-solidification of the all-aqueous emulsion has been developed to preserve proteins. Enzymes such as beta-galactosidase and alpha-amylase can be well preserved in the osmo-solidified particles. This technique is superior to the other conventional techniques since it is organic solvent-free, and the process takes place under room temperature and pressure. This provides bio-friendly conditions to manipulate the biomolecules. However, the parameters and mechanisms that modulate the size and structure of the particles are unknown. Moreover, factors affecting the encapsulation of biomolecules are still unknown. These unsolved questions greatly hinder the technique from being translated for pharmaceutical applications.

In the present work, we study the mechanism that governs the size and structure of the particles. We report that the size of the particles depends on the spreading of the droplets. Moreover, the formation of skin in the all-aqueous emulsion is induced at a high BSA concentration. To our best knowledge, this is the first report revealing the formation of skin at the aqueous-aqueous interface. The solid layer of the skin significantly affects the size and structure of the particles. We also investigate the partitioning behavior of proteins in the all-aqueous emulsions. The partitioning of proteins governs their encapsulation efficiency in the osmo-solidified particles. Four factors that affect partitioning, including the molecular weight of polyethylene glycol (PEG), the NaCl concentration, the protein charge, and the droplet generating system, are evaluated. Implications for the industry to employ osmo-solidification are discussed. This thesis improves important information on designing an efficient drug carrier via osmo-solidification.