Convenient one-step approach based on stimuli-responsive sol-gel transition properties to directly build chitosan-alginate core-shell beads

Herein, chitosan-alginate core-shell gel beads are directly fabricated by a convenient one-step dripping approach. In particular, the approach exquisitely utilizes both the pH-responsive sol-gel transition property of chitosan and the calcium-responsive sol-gel transition property of alginate. The approach has a variety of benefits such as the simple method, the environmentally-friendly route (without using organic solvents and toxic reagents), the mild conditions (in aqueous solution at room temperature), and the easy post-treatment for the beads. Morphology observation from optical microscopy and scanning electron microscopy demonstrates that the resulting chitosan-alginate beads have a clear core-shell structure with a well-defined border between the core and the shell. The chitosan-alginate core-shell beads shows a good sphericity and monodispersity. Comparison experiments indicate that the shell thickness and the core state (solid or liquid) of the core-shell beads can be modulated by altering the preparation conditions (solution concentrations or pHs). Loading experiments demonstrate that the core-shell structure of the chitosan-alginate beads can be utilized to respectively load various components (e.g., fluorescent dyes, drugs, and nanoparticles) in different layers. Release studies reveal that the chitosan-alginate core-shell beads have attractive capabilities to regulate drug release through the pH-responsive sol-gel transition of the chitosan core as well as the thickness control of the alginate shell.