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Chen et al. Soft Sci. 2026, 6, 3 Page 7 of 26

To overcome these constraints, spray-assisted programming has been introduced as a minimalist and highly
adaptable strategy . A magnetically responsive coating composed of polyvinyl alcohol, gluten, and iron
[72]
particles is uniformly sprayed onto diverse substrates, including 1D filaments, thin sheets, and 3D objects.
The resulting magnetic film (approximately 100-250 μm thick) preserves the underlying geometry while
imparting actuation capabilities several hundred times its own weight. Robots fabricated using this method
can be reprogrammed and disintegrated on demand and have demonstrated potential in catheter navigation
and targeted drug delivery. Three-dimensional-printing-assisted programming provides substantially greater
flexibility in design and control. Extrusion-based direct ink writing enables layer-by-layer deposition of
shear-thinning magnetic inks, with ferromagnetic particles reoriented in situ using a magnetic field applied
at the print nozzle [142,143,145] . This allows voxel-level programming of magnetic domains throughout a 3D
architecture. Light-based printing techniques, such as ultraviolet lithography and photopolymerization, offer
even higher spatial resolution . By orienting pre-magnetized particles before local curing, these systems can
[59]
encode intricate 3D magnetization profiles capable of multi-axis bending, twisting, large-angle
reconfiguration, and coupled deformation modes. These strategies have supported the development of
auxetic metamaterials, reconfigurable soft electronics, and microrobots for manipulation and drug delivery.

As magnetic soft robots approach submillimeter dimensions, traditional methods become increasingly
restrictive. Microassembly-assisted programming addresses this limitation by enabling bottom-up
construction of complex 3D magnetic architectures from microscale components. This strategy affords
arbitrary geometry, multi-material integration, and high-resolution magnetization encoding. Resulting
robots can achieve sophisticated mechanical behaviors, including reversible shape reconfiguration, peristaltic
pumping, targeted biopsy, and robust locomotion in curved, fluid-filled tubular environments . The
[60]
expanded flexibility in design offered by microassembly is particularly well-suited for biomedical
microrobotics. Finally, modular strategies have begun linking advanced magnetization control with
functional payload integration. Approaches based on adhesive micro-patterning or localized assembly enable
the precise placement of magnetized elements alongside pH-responsive membranes, localization electronics,
or therapeutic layers . These developments point toward future soft robotic systems that combine high-
[61]
resolution magnetic encoding with sensing, actuation, and therapeutic functionalities.

Magnetic soft material-tissue interactions
Toxicity
Superparamagnetic iron oxide nanoparticles are widely employed as magnetic fillers, due to their high
magnetic resonance traceability [146,147] and magnetothermal conversion efficiency in hyperthermia
therapies [148-152] . However, challenges arise when ferromagnetic particles are incorporated into soft
matrices [153-155] . Ferromagnetic particles such as NdFeB are prone to corrosion in the aqueous environments
of hydrogels owing to their high iron content. As a result, bare NdFeB particles are generally considered to
cause moderate cytotoxicity. NdFeB magnets coated with corrosion-resistant metals or metal alloys have
shown good biocompatibility and have been employed in orthodontic and orthotic devices [153,156] . Similarly, a
layer of biocompatible and non-cytotoxic silica can be applied to the particle surface to prevent
corrosion [76,98] . Magnetic soft robots fabricated by embedding silica-coated NdFeB particles in alginate
hydrogels or PDMS matrices have exhibited low cytotoxicity when co-cultured with gastric epithelial cells
and mouse bone mesenchymal stem cells . Notably, for intravascular applications, hemocompatibility of
[66]
the magnetic soft materials must be rigorously assessed, often requiring surface modifications to prevent
thrombogenesis [157,158] .

Mechanical properties and physical damage
Material stability is a critical determinant of long-term biocompatibility, encompassing parameters such as
mechanical stiffness, degradation kinetics, and surface morphology. One key advantage of magnetic soft
materials is their low elastic modulus [8,12,159] . This property closely matches that of soft tissues such as the