A curcumin sustained-release hydrogel prepared from Pickering emulsions stabilized by modified amorphous calcium phosphate nanoparticles

This study presents a method to prepare hydrogel from Pickering emulsions stabilized with amorphous calcium phosphate (ACP). Pickering emulsion was prepared by utilizing stearic acid (Sa)-modified ACP as the emulsifier, blended oil as the dispersed phase, and aqueous sodium alginate (SA) as the continuous phase. ACP releases calcium ions to crosslink with sodium alginate when the pH decreases, forming a hydrogel. Structural characterization and surface wettability of the modified ACP were assessed through FT-IR, XRD, and contact angle measurements. Droplet sizes in the emulsion were analyzed using optical microscopy, and the release of curcumin from the hydrogel was monitored using ultraviolet spectroscopy. These results demonstrate Sa was grafted onto the surface of ACP. Stabilization of the Pickering emulsion was achieved using 4 wt% Sa-ACP. Moreover, the droplet size exhibited a reduction with heightened particle concentration, oil-water ratio, and pH. The release of curcumin was optimized at 5 wt% SA and 0.75 w/v% Sa-ACP with 53.5% release. The Ca-alginate matrices prevented the release of the curcumin at pH 1.2 and the curcumin was vastly released at pH 7.4, exhibiting pH-responsive release characteristics. These results confirmed the Sa-ACP-stabilized Pickering emulsion hydrogel could be used as an effective delivery system. Graphical Abstract