Fabrication of Double-Layered Alginate Capsules Using Coaxial Nozzle

Abstract

Multilayered encapsulation has been of great interest for various pharmaceutical, chemical, and food industries. Fabrication of well-defined capsules with more than one shell layer still poses a significant fabrication challenge. This study aims to investigate the feasibility of using a coaxial nozzle to fabricate double-layered (core–shell–shell) capsules during vibration-assisted dripping. A three-layered coaxial nozzle has been designed, manufactured, and tested for double-layered capsule fabrication when using sodium alginate solutions as the model liquid material for inner and outer shell layers and calcium chloride solution as the core fluid. To facilitate the droplet formation process, a vibrator has been integrated into the fabrication system to provide necessary perturbation for effective breakup of the fluid flow. It is demonstrated that double-layered alginate capsules can be successfully fabricated using the proposed three-layered coaxial nozzle fabrication system. During fabrication, increasing the core flow rate leads to an increase in capsule and core diameters while the inner and outer shell layer thicknesses decrease. Increasing annular flow rate results in an increase in capsule diameter and inner shell layer thickness while the outer shell layer thickness decreases. An increase in the sheath flow rate leads to an increase in capsule diameter and outer shell layer thickness but has no significant effect on the core diameter and inner shell layer thickness.