Regulating emulsion properties through tannin acid-mediated gelatin/cellulose nanocrystal complexes: From low-oil emulsion to high internal phase emulsion gel for 3D printing

In this study, a stabilized low-oil emulsion and high internal phase emulsion gels (HIPE gels) integrated preparation method is proposed. Highly stable low-oil emulsions, prepared using tight ternary complexes formed by incorporating tannic acid (TA) into gelatin/cellulose nanocrystals (GLT/CNC) complexes mainly through strengthening hydrogen-bonding interaction. The subsequent heating-centrifugation process was used to enable the conversion of GLT/CNC/TA stabilized low-oil emulsions to stabilized HIPE gels, and systematically investigated the regulation of emulsion properties by TA concentrations. The ternary complexes formed by appropriate concentration of TA (0.6 %) can form stable low-oil emulsions with smallest average particle (36.1 ± 0.25 μm) size and best rheological properties, while the rheological properties of HIPE gels were similarly regulated by the TA concentration (0 %, 0.2 %, 0.6 %, 1.0 %, 1.2 %). Heating induced flocculation of low-oil emulsions without causing demulsification, allowed for the subsequent centrifugation to yield stable HIPE gels, significantly superior to the GLT/CNC/TA-stabilized HIPE gels prepared by conventional methods that typically exhibit thermal instability. TA effectively promoted the interfacial adsorption of GLT/CNC and tight stacking of oil droplets to build a more stable network structure in the continuous phase. HIPE gels with 0.6 % TA demonstrated excellent 3D printability with optimal dimensional resolution and surface quality, presenting a novel strategy for HIPE gel preparation and versatile emulsion applications.