Formation and characterization of filled hydrogel beads based on calcium alginate: Factors influencing nanoemulsion retention and release

• Nanoemulsions can be entrapped in alginate hydrogel beads.
• Emulsification technique impacts retention and release of oil droplets.
• Release rate can be controlled by alginate and calcium concentration.
• Curcumin-loaded micelles rapidly diffuse out of hydrogel beads.
• Curcumin-loaded lipid droplets remain entrapped in the hydrogel beads.

Filled hydrogel particles fabricated from natural lipids and biopolymers can be utilized as tailor-made encapsulation and delivery systems. In the present study, the impact of nanoemulsion fabrication method (low energy versus high energy) on the retention and release of a lipophilic bioactive component (curcumin) and of lipid droplets from calcium alginate beads was investigated. Initially, curcumin was dissolved within an oil phase, and then the oil phase was encapsulated within the hydrogel beads using a two-step process. First, nanoemulsions composed of the same constituents (medium chain triglycerides, Tween 60, curcumin, and phosphate buffer) were prepared using either low energy (spontaneous emulsification) or high energy (microfluidization) homogenization. Second, the nanoemulsions were mixed with alginate solutions (0.25–1.5%), and then the resulting mixture was dripped into calcium solutions (10–500 mM) to form filled hydrogel beads. Unloaded beads became more spherical and rigid with increasing alginate and calcium concentrations. Turbidity and spectrophotometry measurements showed that the amount and extent of curcumin and lipid droplet release from the hydrogel beads decreased with increasing alginate and calcium concentration, which was attributed to a reduction in the pore size of the hydrogel matrix. In particular, a high amounts of curcumin released were observed in delivery systems containing high Tween 60 concentrations, which was attributed to rapid diffusion of curcumin-loaded surfactant micelles out of the beads. These results have important implications for the design of delivery systems to entrap and control the release of lipophilic bioactive components within filled hydrogel particles.

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