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Ren et al. Soft Sci. 2026, 6, 6 Page 11 of 33

hydrogel ceramic laminates for dehydration programmed morphing and sintered ceramic architectures. Reproduced with permission from
Ref. [86] . Copyright 2024, Springer Nature; (G) Thermally reconfigurable micro metastructures using transparent hydrogel artificial muscles
for pixel-level information display. Reproduced with permission from Ref. [87] . Copyright 2023, Springer Nature; (H) Stimuli-responsive
hydrogel blocks assembled with DH parameters for true 3D-to-3D microscale transformers. Reproduced with permission from Ref. [88] .
Copyright 2020, American Association for the Advancement of Science. 4D: Four-dimensional; LCEs: liquid crystal elastomers; DLP:
digital light processing; DH: Denavit–Hartenberg; 3D: three-dimensional; UV: ultraviolet; LC: liquid crystal; AP: acid-poly(ethylene glycol)
diacrylate; LP: laser power.

printed architecture can be reconfigured multiple times for different tasks [Figure 4C]. To introduce optical
addressability, Feng et al. prepared a photoswitchable WO nanoparticle-doped SMP nanocomposite for
2.9
DLP . Utilizing trace amounts of WO below 0.20 wt.‰ to provide controlled photothermal absorption,
[95]
2.9
the printed structures exhibited remotely and spatially controllable, reversible shape morphing with high
stretchability in the rubbery state and fatigue resistance over repeated cycling [Figure 4D].

In practical applications, SMPs offer many advantages including large recoverable strains, high shape
fixation, low density, and adjustable activation temperatures, broadening their applications in robotics,
aerospace, and biomedicine. Key limitations include response times governed by thermal diffusion; creep
and residual strain under cyclic loading; environmental sensitivity to moisture or solvents; and long-term
stability of network structures and additives.

Magnetic nanocomposite polymers
Magnetic nanocomposite polymers combine a soft polymer matrix (elastomer, hydrogel, or
thermoplastics/thermosets) with dispersed magnetic fillers. These magnetic materials are typically iron oxide
(Fe O /γ-Fe O ) nanoparticles, metallic Fe/Co/Ni, or micro- to nanoscale hard magnets such as NdFeB
2
3
3
4
[Figure 4E] [96-98] . Their magneto-mechanical response arises from field-particle interactions. In soft-magnetic
systems, field-induced magnetization generates dipole–dipole forces and torques that reconfigure the matrix.
In hard-magnetic systems with remanent magnetization, preprogrammed magnetization vectors produce
deterministic bending, twisting, or folding under uniform or rotating fields, while magnetic field gradients
provide the net force for locomotion . In this way, complex deformations and multi-degree-of-freedom
[99]
behaviors are achieved at micro- to millimeter scales.

Deng et al. developed a laser-rewritable magnetic composite film consisting of an elastomer matrix and
magnetic particles encapsulated by a phase-change polymer . Transient laser heating melts the coating to
[100]
reorient particles under a programming field, enabling a single actuation field to induce multistate switches
and multimodal 3D morphing in soft robots [Figure 4F]. Using coaxial printing, Zhang et al. produced
hybrid magnetic-mechanical-electrical core-sheath fibers that integrate a magnetoactive sheath with a
conductive core [101] . This material system enables programmable magnetization, somatosensory feedback,
magnetic actuation, and simultaneous wireless energy transfer, as demonstrated in a flexible catheter, a
durable gripper, and an untethered soft robot [Figure 4G]. By applying a magnetic field during DIW of an
elastomer loaded with ferromagnetic microparticles, Kim et al. aligned particles at the nozzle to program
ferromagnetic domains [102] . The resulting printed composites transformed rapidly between complex 3D
shapes under magnetic fields, unlocking auxetic metamaterials, reconfigurable soft electronics, and soft
robots with high power density [Figure 4H].

For 4D-printed soft microrobots, magnetic nanocomposite polymers offer wireless, rapid, and deep
penetration control through fluids or tissues. They are also compatible with multiple fabrication routes
(DIW, DLP, SLA, TPP, and molding), and offer multifunctionality such as imaging contrast, localized
heating, and embedded sensing. Key limitations include challenges with filler dispersion and sedimentation,
narrowed printability windows due to increased viscosity, particle aggregation and oxidation, and trade-offs
between magnetic loading and mechanical compliance or fatigue life. Other disadvantages include the scale