Self-assembly of plant polyphenols-grafted soy proteins to manufacture a highly stable antioxidative emulsion gel for direct-ink-write 3D printing

The practicable application of 3D printing in the pharmaceutical and food sectors directly relates to the preparation of highly stable bioactive printable inks. Here, three different polyphenols (rosemary polyphenols, thyme polyphenols, and basil polyphenols) were individually grafted onto soy protein isolate through a free-radical grafting method to produce a precursor printable ink for potential applications in developing 3D printed structures. The morphological feature, emulsion rheology experiments, quartz crystal microbalance with dissipation monitoring techniques, and interfacial shear rheology were used to monitor emulsification features and interfacial rheology (i.e., adsorption kinetics, viscoelastic features, and interfacial adsorbed layers) of precursor inks. Compared to soy-based ink, polyphenols-grafted soy protein inks developed more stable emulsions with finer droplets. Also, the interfacial adsorption properties of protein particles were improved after the grafting process, in which the surface dilatational viscoelastic moduli and interfacial pressure were boosted. The ink including soy protein-g-rosemary polyphenols (with greater hydrophobicity) showed a smaller size, stiffer structure, and stronger surface absolute potential than inks soy protein-g-thyme and basil soy protein-g-basil, showing outstanding printing performance. Overall, this work suggests that by compatibilization of the plant polyphenols and the soy proteins, offering an opportunity of adopting plant-based inks in the 3D printing of advanced materials.