Preparation of nanosize alginate gel using pluronic-based nano-carrier as a template

•Nano alginate gel was prepared using a pluronic-based nano-carrier as a template.•No organic solvent or chemical reaction was used.•Positively charged proteins were efficiently loaded and slowly released.•Pluronic shell provided neutral surface charge and good dispersion of nanogel.

Nanosize (∼50 nm) alginate gel was made by loading alginate into the pluronic nano-carrier, followed by adding calcium ions to induce calcium ion-induced crosslinking inside the nano-carrier without using any organic solvent during the preparation. The alginate gel formation inside the nano-carrier did not alter the size or the surface charge of the nano-carrier, and the residence of alginate inside the nano-carrier in physiological buffer was greatly increased by calcium ion complexation. Also, this complex nanogel could be re-dispersed after lyophilization without aggregation. In addition, proteins were efficiently loaded into the alginate gel-filled nano-carrier by simple co-incubation at 4 °C, followed by increase to 37 °C, and this alginate gel-filled nano-carrier showed prolonged release of proteins over one month while preserving the bioactivity of proteins. Therefore, pluronic-based nanogel was effective for easy preparation of nanosize alginate gel in it. The presence of pluronic shell of the composite nanogel did not hinder the loading or sustained release of positively charged proteins from negatively charged alginate gel inside, but rather provided the neutralization of surface charge and enhanced stability of the nanosize alginate gel.

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