Programmable Shape-Morphing in Homogeneous Hydrogels via Interfacial Confinement

Here, we design a geometric strategy to induce anisotropic deformation in homogeneous hygroscopic hydrogels through interfacial confinement. By mechanically interlocking the hydrogel with a microporous substrate, we suppress lateral expansion at the base and redirect isotropic volume gain into directional displacement.

Systematic variation of sample thickness reveals a morphological transition: thin films undergo quasi-uniaxial vertical swelling, whereas thick films develop mushroom-like architectures featuring coexisting interfacial anisotropy and distal isotropy. Meanwhile, the ionic osmotic pressure (∼10⁷ Pa) overwhelmingly exceeds the elastic penalty imposed by the constraint (∼10⁵ Pa), which makes the equilibrium water uptake of the corresponding hydrogels irrespective of boundary geometry.