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Page 12 of 24 Yu et al. Soft Sci. 2026, 6, 19

ciliate-like microneedles on the contact surface-one of the key design elements enabling high-reliability
underwater grasping. The microneedles increase the contact friction coefficient and effective contact area,
thereby amplifying surface frictional forces and improving capture reliability. Porous magnetic soft grippers
enhance gripper compliance and gripping versatility by introducing porous structures, while also increasing
gripping force through increased surface roughness . However, such methods primarily rely on the overall
[38]
improvement of structural porosity and surface roughness to achieve performance improvements,
Furthermore, the maximum known mass that porous grippers can grasp is 42 g, while the maximum mass
that the MSG in this study can grasp is 54.1 g, which is 28.8% higher than that of porous grippers. Therefore,
microneedle structures have advantages in the field of flexible gripping. And the biomimetic microneedles
proposed in this study specifically increase the actual contact area under lubricating water film conditions
and improve interfacial friction, thereby significantly improving the static friction coefficient and anti-slip
capability without increasing the volume of magnetic materials or significantly altering the overall flexibility
of the gripper. This structural design can be seen as a supplement to existing strategies and provides a new
engineering path for achieving stable, low-damage gripping under water lubrication conditions. Although
comparable data on friction coefficients or slip thresholds are insufficient in existing literature, multiple
studies consistently demonstrate that surface morphology and internal structure have a significant impact on
gripping performance, which provides a guarantee for the design motivation of using microneedles to
improve the gripping ability of lubricated interfaces.

The frictional benefit of microneedles was quantified in Figure 2F. The microneedles are also compliant and
deform upon contact, further enlarging the effective contact area. Figure 3C reports grasping tests in which
the MSG (60 wt% NdFeB) retrieved a sphere bearing hanging masses; at the same drive current the
microneedle-equipped gripper sustained a greater load than the smooth variant. At 6 A the microneedle
augmentation increased grasping force by approximately 20%, demonstrating the structure’s important role
in enhancing capture capability.

A review of the literature provides reported damage thresholds for representative marine organisms and
deep-sea mineral targets, which can be used as reference benchmarks to evaluate grasping force and
biological safety in this study. Previous studies indicate that the tensile strength of jellyfish body walls is
approximately 0.17 MPa, while their compressive strength is about 1.43 MPa . Sea cucumbers exhibit
[55]
distinct mechanical responses within a stress range of 0.3-3 MPa . The average fracture force of coralline
[56]
algae has been measured to be approximately 20-26 N . The compressive strength of mineral nodules has
[57]
been reported to fall within the range of 0.346-2.286 MPa (346-2,286 kPa) . In contrast, certain crustaceans
[58]
or hard-shelled organisms (e.g., turtles) possess substantially higher mechanical tolerance thresholds, with
reported values on the order of 1 GPa or higher . By comparing the maximum grasping force of the gripper
[59]
developed in this study with these damage thresholds, potential damage during grasping can be effectively
avoided; Quantitative analysis of the contact stress between the gripper and the target through numerical
simulation provides a preliminary verification of the “non-destructive gripping” concept proposed in this
study (the gripping process is illustrated in Supplementary Figure 1, and the contact stress distribution of the
gripped target is shown in Supplementary Figure 2). Simulation results show that the maximum contact
stress borne by the gripped target is approximately 9.2 kPa. Comparison of this stress level with the
mechanical damage thresholds of typical marine organisms and deep-sea minerals reported in the literature
reveals that, under the simulated contact conditions, the local stress applied by the gripper to the target is
significantly lower than the tolerance thresholds of many types of organisms and minerals, supporting the
feasibility of non-destructive gripping from the perspective of stress level. It should be noted that the above
conclusions are based on specific numerical models and boundary conditions. Different contact
configurations, material parameters, or more stringent operating conditions may induce stress
concentration, leading to higher local stress peaks. Therefore, further research should conduct extended