Dual-Responsive "Egg-Box" Shaped Microgel Beads Based on W/O/W Double Emulsions for Colon-Targeted Delivery of Synbiotics.

In this study, for enhancing the resistance of probiotics to environmental factors, we designed a microgel beads delivery system loaded with synbiotics. Multiple droplets of W/O/W emulsions stabilized with zein-apple pectin hybrid nanoparticles (ZAHPs) acted as the inner "egg," whereas a three-dimensional network of poly-L-lysine (PLL)-alginate-CaCl (Ca) crosslinked gel layers served as the outermost "box." ZAHPs with a mass ratio of 2:1 zein-to-apple pectin showed excellent wettability (three-phase contact angle = 89.88°). The results of the ζ-potentials and Fourier transform infrared spectroscopy demonstrate that electrostatic interaction forces and hydrogen bonding were the main forces involved in the formation of ZAHPs. On this basis, we prepared W/O/W emulsions with other preparation parameters and observed their microstructures by optical microscopy and confocal laser scanning microscope. The multi-chambered structures of W/O/W emulsions were successfully visualized. Finally, the W/O/W emulsions were coated with PLL-alginate-Ca using the solution extrusion method. The results of the in vitro colonic digestion stage reveal that the survival rate of probiotics in the microgel beads was about 75.11%, which was significantly higher than that of the free. Moreover, probiotics encapsulated in microgel beads also showed positive storage stability. Apple pectin would serve as both an emulsifier and a prebiotic. Thus, the results indicate that the "egg-box" shaped microgel beads, designed on the basis of pH-sensitive and enzyme-triggered mechanisms, can enhance the efficiency of probiotics translocation in the digestive tract and mediate spatiotemporal controlled release.