Biocompatible homogeneous particle formation via the self-complexation of chitosan with oleic acid and its application as an encapsulation material for a water-insoluble compound

Abstract

A simple, precise method for preparing submicrometer-sized homogeneous particles as potential delivery carriers for water-insoluble compounds was developed using self-complexation of chitosan (CHI) and oleic acid (OA). One-step mixing of a CHI aqueous solution and an ethanol solution containing fatty acids provided homogeneously turbid dispersions at ambient conditions. Mean particle diameters measured using dynamic light scattering and laser diffraction measurements ranged from 300 to 1000 nm with narrow diameter distributions (polydispersity index < 0.2, for 600-nm particles), depending on their preparation conditions. Scanning transmission electron microscopy (STEM) also indicated the formation of submicron-sized particles. Based on measurements of Fourier-transform infrared (FT-IR) spectra, fluorescent spectra with pyrene, and small angle X-ray scattering (SAXS), this study proposed particle formation via electrostatic complexation between positively charged CHI and negatively charged oleate ions, and aggregation of hydrophobic interaction between alkyl groups of OA. The diameter distribution of the particles did not change even after storage for three months at room temperature and pH 5.0. Furthermore, the hydrophobic bioactive compound curcumin was successfully encapsulated into complex particles without use of additional emulsifiers as dispersant for curcumin. Particle suspension encapsulating curcumin could be concentrated using evaporation of the aqueous dispersion medium without significant changes in their diameter. These findings demonstrate that CHI-OA complex particles are potentially advantageous for encapsulating/dispersing hydrophobic compounds in aqueous media in order to develop novel liquid-based foods and beverages with improved physicochemical stability and enhanced health functionality. • Biocompatible fine particles were obtained using a one-step procedure. • Homogenous particle size distribution could be maintained for a long time. • Particles formed via non-covalent interactions between chitosan and oleic acid. • Particle size was tunable (300–1000 nm) by adjusting preparation conditions. • Efficient encapsulation of the lipophilic compound curcumin was demonstrated.