Full‐field hygroscopic characterization of tough <scp>3D</scp>‐printed supramolecular hydrogels

Chain-extended ureido-pyrimidinone poly(ethylene glycol) (CE-UPy-PEG) is a supramolecular hydrogel with excellent mechanical properties and shape memory capabilities, making it highly suitable for 3D printing of complex biomimetic structures to mimic biomaterials. However, its transient hygroexpansion response under environmental change, specifically relative humidity (RH), which strongly affected by the sub-structure, poorly understood. Therefore, high-precision full-field fiber-swelling methodology applied 3D-printed CE-UPy-PEG fibers, enabling investigation influence PEG chain length (1.5, 3, 10 kg/mol studied here) RH rate from wet dry on longitudinal transverse surface strain evolution during multiple cycles. The directly influences fibers' hygroscopic properties, because only CE-UPy-PEG3k CE-UPy-PEG10k exhibit phase transformation semicrystalline amorphous at higher levels, fully described phenomenological model. Furthermore, all fibers display cyclic repeatability (shape memory), increased swelling longer chains lower rate, disappearance sub-millimeter-sized tube-like voids after wetting.