Programmable Multi-Axially Aligned Aerogels via Sequential Freeze-Casting for Tailored Anisotropy and Tunable...

Biological materials achieve exceptional mechanical resilience and multifunctionality through a hierarchical, multi-axial alignment, a structural complexity that remains challenging to replicate in synthetic porous materials. Conventional freeze-casting, while promising for mimicking aligned structures, is typically constrained to unidirectional anisotropy when governed by a single temperature gradient, resulting in poor transverse mechanical stability. Here, we present the Sequential Hybridization by Infiltration and Freeze-casting Technique (SHIFT), a platform that temporally separates primary scaffold formation and secondary architecture formation to enable the programmable construction of multi-axial aerogel architectures. By utilizing the primary structure as a geometric template during the secondary freeze-casting of an infiltrated precursor solution, SHIFT allows for controlled tuning of the secondary alignment angle (0°-90°) and spatial density. Mechanical analysis reveals that orthogonal alignment significantly suppresses mechanical anisotropy, achieving an anisotropy ratio of 2.87, closely matching that of natural cuttlebone (2.89), whereas programming the secondary alignment at oblique angles (30°-60°) enhances cyclic recovery. Furthermore, by integrating radial and vertical freezing strategies, multidirectional volumetric mass transport is achieved. This approach offers a versatile strategy to reduce the dependence of structural formation on a single freezing direction, unlocking new possibilities for engineering porous materials with programmable mechanical and transport properties.