Combining protein fibrosis with dynamic non-covalent crosslink to improve the mechanical properties of high internal phase emulsion and its application in hollow model printing

This study hypothesized that the 3D printing performance of high internal phase emulsions (HIPEs) would be synergistically enhanced by protein fibrosis and dynamic non-covalent crosslink. Soy β-conglycinin (7S) was modified by fibrillation, then combined with three different crosslinking agents (tannic acid (TA), sodium alginate (SA), and calcium chloride (CaCl₂)) through non-covalent bonds to form HIPEs for 3D printing. The determination of molecular interaction confirmed that protein fibril (7F) could bond with TA, SA and Ca²⁺ through hydrogen bond, electrostatic interaction and coordinate bond, respectively. TEM revealed that the shape of protein changed from spherical to branched dendritic structure after fibrillation, three crosslinking agents further induced aggregation of 7F, leading to changes in secondary structure, particle size and surface hydrophobicity. The interfacial rheology analysis suggested that SA and TA could significantly decrease the interfacial tension, the permeation and rearrangement rate of 7F, facilitating the formation of dense and thick interfacial film, as observed in microscopy images. Ca²⁺ induced an increase in protein hydrophobicity and affected its interfacial properties with opposite effects to the other two crosslinking agents. However, it could effectively improve the freeze-thaw stability of HIPEs. Compared with 7S, HIPEs formed of 7F had substantially higher G′ due to amyloid fibril entanglement. Bonding with crosslinking agents further increased the G′ of HIPEs. HIPEs formed of 7F-SA showed the highest G′, viscosity, hardness and relatively low creep values, which enabled the HIPEs to rapidly recover the structure after extrusion, thus exhibiting excellent self-supporting performance and printing accuracy in hollow model printing.