Magnetic field-directed chain and layered architectures control deformation-mode-dependent viscoelasticity in ultra-soft hydrogel composites

Controlling the spatial organization of particulate reinforcements offers a route to tailor the mechanical response of soft composites. Here, carbonyl iron microparticles are magnetically organized during pre-gelation of a self-healing oxidized laminarin/gelatin hydrogel into random, chain-like, and layered architectures. A controlled pre-gelation window combined with triaxial and biaxial magnetic fields limits particle sedimentation and enables homogeneous centimetre-scale specimens for shear, torsion, compression, and tension testing. Quasi-static measurements and axial–torsional dynamic mechanical analysis reveal a strong coupling between particle architecture and loading mode. Layered structures provide the greatest reinforcement under shear and torsion, whereas chain-like structures dominate under compression and also enhance tensile stiffness, although at the expense of extensibility. Extending the Sequence of Physical Processes framework beyond shear reveals intra-cycle signatures consistent with interlamellar sliding, particle contacts, alignment, and structural instabilities. Large-amplitude cyclic shear tests further show rapid recovery of the linear viscoelastic response. Overall, these results establish a direct processing–architecture–property relationship and show that particle organization can be used to tailor stiffness and energy dissipation in ultra-soft hydrogel composites.