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Yu et al. Soft Sci. 2026, 6, 19 Page 7 of 24

Fabrication process and material performance of the MSG
Based on the core objective of achieving rapid underwater response and high adaptability in grasping, the
performance of magnetically actuated flexible grippers is highly dependent on the magneto-mechanical
coupling characteristics of the material system. Previous studies in the field of magnetically driven soft
robotics have demonstrated that the dispersion, filling ratio, and magnetization strength of magnetic
particles within the elastomeric matrix are critical factors influencing actuation efficiency, mechanical
flexibility, and fatigue life [45,46] . Accordingly, this section systematically introduces the formulation and
processing of Ecoflex0020/NdFeB composites and verifies their underwater applicability through multiscale
characterization.

The fabrication process of the flexible gripper is illustrated in Figure 2A, comprising four steps: molding of
the main body, construction of microstructural needle surfaces, magnetization, and modular assembly.
Ecoflex0020 silicone elastomer was selected as the matrix material due to its excellent elasticity and
biocompatibility, ensuring stability and safety in underwater environments. The magnetic filler consisted of
NdFeB particles (400 mesh), providing sufficient magnetic responsiveness. The molds were fabricated using
3D-printed PLA, ensuring structural precision and reproducibility. During the micro-needle fabrication step,
customized molds (conical micro-needles, height: 500 μm, density: 180 needles/cm ) were employed to
2
generate structured distributions on the gripper surface, thereby enhancing surface friction and adaptability
to biological objects. Finally, the single modules were magnetized using a pulsed magnetic field of 2.5 T and
assembled mechanically.

To validate whether the fabricated grippers met the desired actuation performance, samples were subjected
to a series of physical property tests, including mechanical characterization (stress-strain behavior, Young’s
modulus), magnetic response [magnetization (M) vs. magnetic field (H) curves (M-H curves), bending
angles under magnetic fields], and surface friction performance of the micro-needles. As shown in Figure 2B,
the stress-strain curves of four gripper samples with different NdFeB weight fractions under 0%-150% strain
revealed that samples with higher NdFeB content exhibited smaller strain under the same stress, indicating
reduced flexibility compared to samples with lower filler content. Figure 2C shows the variation in Young’s
modulus and surface remanence with increasing NdFeB weight fraction. Since Young’s modulus reflects
material stiffness, samples with higher filler content exhibited stronger rigidity, which could potentially
induce excessive impact and damage when grasping underwater objects. Notably, the 70 wt% samples
displayed a significantly higher modulus than the other three compositions. The test results indicate that, as
the mass fraction of NdFeB increases, the samples’ surface remanent magnetization progressively grows.
Increased surface remanence enhances the MSG’s magnetic actuation force within the magnetic-drive
system, thereby directly increasing the MSG’s payload capacity. Consequently, when designing MSG
materials, a trade-off must be carefully considered between improving magnetic responsiveness and
preserving the required flexibility. We acknowledge that the Ecoflex0020/NdFeB composite exhibits
time-varying inelastic behavior (Mullins-type cyclic softening, rate dependence, and creep/relaxation), which
may affect the dynamic actuation response of the gripper during grasping. Due to instrument limitations and
project schedule constraints, only quasi-static elastic characterization is reported. However, the
event-varying inelastic behavior of the material cannot be ignored; therefore, we present a complete
experimental protocol for subsequent experiments, with the planned tests as follows: Mullins Cyclic Testing.
N = 50 cycles are performed between peak engineered strain ε = 20% and 0%, at a nominal strain rate of
max
10%/s; the cycles are also repeated at ε = 10% and 30% to probe amplitude dependence. Measurement
max
outputs: Tangent modulus Et(c), residual strain, and hysteresis energy Wh(c) per cycle. Sample size n ≥
3/cycle. Depth-depth rate [dynamic mechanical analysis (DMA)] Testing. DMA (shear or tensile modes),
frequency sweep f = 0.1-50 Hz, small strain amplitude 0.5%-2%, temperature points including 25 and 5 °C
(approximate deep-sea temperature). Outputs: Storage modulus E′(f), loss modulus E′′(f), tan δ(f). Sample