Development of encapsulation technique for nano-biomaterials using chitosan-based cryogel

Abstract

Curcumin was chosen as the present model biomaterial. A technique was developed and investigated to encapsulate the oil-soluble curcumin into a hydrogel system. The curcumin loaded oil-in-water nano-emulsion was prepared using a chitosan colloidal suspension, and the emulsion was converted into hydrogel by using cryotropic gelation. The cryogel based oil encapsulation was carried out with a ternary system of colloidal chitosan, κ-carrageenan, carboxy methylcellulose sodium salt (NaCMC) suspensions and the effects of the freezing condition (unidirectional freezing rate with and without post-freezing incubation) as well as initial concentration ratio of carrageenan to NaCMC on the properties of the nanocapsules were experimentally studied. The effects of chitosan concentration (1.5, 2.0 and 3.0%), К-carrageenan:NaCMC ratio of the polymer suspension (1:9, 4:6 and 6:4) and MW of chitosan (low, medium and high) on sol-gel formation were investigated. The effects of cooling rate during unidirectional freezing (-0.5, -1, and -2 °C/min) on the morphology of the freeze-dried cryogel specimens and the release behavior of curcumin from the specimens were determined. So were the effects of pH of the phosphate-buffered media on the swelling of the specimens. The key findings are as follows. The encapsulation yields were found to vary from ca 83.9 to 99.6% when a high-MW chitosan was used, and they were influenced by the cooling protocols during freezing, indicating that the gel formation kinetics was related to the degree of encapsulation. The release curves showed that both a burst release and a first order release were achieved simply by changing the freezing conditions. Controlled release of the encapsulated curcumin in an aqueous system could be maintained for 4 days, and the releasable amount of curcumin was found to range from 41.1 to 59.9%. The encapsulation yield as well as the release pattern and releasable amount of curcumin were influenced by the cooling protocol used during freezing. Irrespective of the introduced oil phase composition, controlled release of curcumin was achievable when the cooling rate was sufficiently high at -2 °C/min. When cold incubation was carried out, the release rate became slower than the corresponding case of no incubation because crosslinking was enhanced during the incubation period.