Sodium tripolyphosphate crosslinking enhancement on shikonin-loaded gelatin emulsions with high structure stability and its application in 4D printing

Shikonin was loaded into gelatin complex nanoparticles induced by sodium tripolyphosphate crosslinking enhancement, which could stabilize high internal phase emulsions for possible four-dimensional printing. Complex nanoparticles (446 nm) based emulsions possess excellent red colors and centrifugation stability. Rheology results indicate that sodium tripolyphosphate can promote the emulsions to own the outstanding thixotropy properties (high thixotropic hysteresis loop area 6646 Pa s⁻¹, and high recovery rate), shear-thinning behavior (power law index<1), yield stress (around 169 Pa), viscoelastic performance (high elastic modulus with high mechanic strength), and thermal resistance. Optical microscopy suggests the low-size, stable droplets with good freezing-thawing and heating endurance in emulsions. Finally, gelatin-shikonin complex nanoparticles based emulsions presents the excellent four-dimensional printability with great dynamic response to pH. This study provides important implications for producing stable emulsions for four-dimensional printing of novel, colorful, functional food products.