Facile Preparation of Core-Shell Nanocomposite Microgels

Abstract

Microgels with alginate (Alg) gel cores and shells of SiO₂ nanoparticles (so-called colloidosomes) were prepared by self-assembly of SiO₂ nanoparticles at ALG aqueous solution–hexane interfaces and subsequent in situ gelation caused by Ca²⁺ ions that were released from calcium-ethylenediamine tetraacetic acid chelate by decreasing the pH value through the slow hydrolysis of D-Gluconic-δ-lactone. The packing density of SiO₂ nanoparticles in the shell was about 0.906, indicating that the SiO₂ nanoparticles were present monolayer on the surfaces of the colloidosomes. The half release times of insulin microcrystals were 4 h for Alg gel microspheres and 10 h for Alg/SiO₂ colloidosomes at pH 7.4, compared to 1.5 h for bare insulin. The half release times of insulin microcrystals were 12 min for Alg gel microspheres and 30 min for Alg/SiO₂ colloidosomes at pH 1.2, compared to 30 s for bare insulin. The release rates of insulin from the colloidosomes with core–shell structure were slower than that from bare insulin crystals due to the dual barriers of the hydrogel cores and the close-packed inorganic shells. The release curves were nicely fitted by the Weibull equation and the release followed Fickian diffusion.

Keywords:

• alginate hydrogel
• colloidosome
• controlled release
• core–shell structure
• self-assembly

Acknowledgements

This work was supported by the National Natural Science Foundation of China (21274046) and the Natural Science Foundation of Guangdong Province (S2012020011057).