4D printing of poly-Pickering high internal phase emulsions to assembly a thermo-responsive shape-memory hierarchical macroporous scaffold

Because of their enormous potential in biofabrication, adsorption, catalysis, and energy conversion applications, there has been substantial attention to fabricating 4D printed hierarchically porous structures from the molecular level to the macroscopic dimensions. To this end, an understanding of the structure-feature relationship of smart materials in 4D printing is necessary to design innovative constructs, which are not limited to any specific degree of freedom. Here, we report on the fabrication of thermo-responsive macroporous polymerized-high internal phase emulsions (poly-HIPEs) through 3D printing of Pickering-type HIPEs. The oil-in-water Pickering-HIPE-based inks contained methylcellulose/kappa-carrageenan blend (non-crosslinked) as a continuous phase, which was colloidally stabilized by a hybrid of cellulose nanocrystals and cellulose nanofibers. The Pickering-HIPE-based inks showed a non-linear and time-dependent oscillatory response with excellent viscoelastic interfacial properties. The poly-Pickering-HIPEs were readily fabricated by in-situ crosslinking of Pickering-HIPEs during hot-melt extrusion-based printing, which produced a series of 3D printed thermo-responsive hierarchical macroporous structures. The 4D printed objects presented a highly interconnected open-cell porous structure, which was thermo-responsive in nature. Moreover, these 4D structures showed high mechanical strength with outstanding self-recovery performance. Our results offer the prospect of developing a thermo-responsive macroporous construct having shape memory features at different temperatures by regulating emulsion formulation.