Dual-bionic foam with enhanced energy absorption and superhydrophobicity realized by multiple constrained unidirectional foaming

Inspired by the anisotropic cellular architecture of basal wood and the seta-spatulate formations of gecko toes, we engineer dual-bionic foams featuring a highly oriented interior cellular structure and a seta-like biomimetic surface through an ingenuous multiple constraint unidirectional foaming (MCUF) method using supercritical carbon dioxide as the blowing agent. By integrating circumferential and surface constraints, the dual-bionic foam is regulated to grow unidirectionally forming highly aligned cells with an aspect ratio of ∼ 18. By emulating the microstructure of the constrained surface mesh and the spontaneous viscoelastic contraction of the stretched polymer tips, the dual-bionic foam simultaneously constructs seta-like surface microstructures in the MCUF process. Unlike conventional bending-based deformation mechanism, the cell wall bulking-based impact response mechanism of dual-bionic foam results in a significant enhancement in compressive strength and a special progressive folding deformation mechanism, which leads to a high energy dissipation upon impact. The biomimetic surface features a double re-entrant microstructure, bestowing exceptional superhydrophobic properties with a water contact angle of ∼ 163°. The unique dual-functional attributes of these foams make them highly suitable for applications requiring both energy absorption and self-cleaning capabilities. Moreover, the scalable MCUF method is adaptable to various thermoplastic polymers, broadening the potential applications of dual-bionic porous materials.