Facile method for forming ionically cross-linked chitosan microcapsules from Pickering emulsion templates

Abstract

Microcapsules with an oil-core hold great promise as an effective delivery system for lipophilic active ingredients used in myriad applications. Herein, we describe a facile technique for preparing chitosan microcapsules (CMCs) containing tocotrienol using oil-in-water (O/W) Pickering emulsions droplets as templates. The CMCs were fabricated under mild and safe processing conditions i.e., at ambient temperature and in the absence of organic solvents. Chitosan (CS) was precipitated above its pKa value to form a particulate emulsifier that could assemble at the O/W interface. The adsorbed particles were subsequently ionically cross-linked with sodium tripolyphosphate (TPP) at different pH values (i.e., 2–8.5) to form oil-core microcapsules. The Pickering emulsions (CPEs) and CMCs were characterized using laser light scattering, optical microscopy, confocal laser scanning microscopy (CLSM), and Fourier transform infrared spectroscopy (FTIR). The results showed that the size of the CMCs and oil leakage was affected by the pH used in the cross-linking process. The increase in the CMCs' sizes was attributed to the extended conformation of CS polymer chains at low cross-linking pH. The oil leakage was ascribed to the CMCs' porous microstructures, which resulted from the swelling and/or dissolution of some parts of the shell at low cross-linking pH. The varied porous microstructure exhibited by the CMCs was found to be dependent on the cross-linking pH. Therefore, by tuning the cross-linking conditions, one may obtain tailor-made microcapsules that are well suited for the rapid or controlled release of lipophilic compounds.