Liquid metal universal grippers for gentle, adaptable, multiscale manipulation

Domain: chemistry
Published: 2026-03-06
Editorial outcome: minor_revision

Abstract
The amoeba can flow like liquid to change its morphology to effectively capture and excrete
various prey. Inspired by the amoeba, we present a liquid metal universal gripper capable of
effective grasping and active releasing of targets with various shapes, sizes, and stiffnesses in
liquid and air. We unveil a surface tension induced active release mechanism enabling tunable
active release of micro-objects. The gripper operates across 14 orders of magnitude in weight (from
10-12 g to 200 g) and achieves a low gripping contact pressure of ~10 Pa for handling delicate
items. It can capture and release moving objects within milliseconds without precise alignment.
An environment-agnostic surface activity design extends its functionality to a non-electrolyte
environment. The gripper offers notable performance metrics over existing robotic grippers in
multiscale operation, low contact pressure, and tunable releasing speed, representing a notable
solution for living organisms and microscale objects.

Introduction
In the long-life river, living beings evolved an extensive assortment of manipulative organs and
behaviors for survival in the competitive natural world. These efficient manipulative organs and
behaviors have inspired the creation of versatile robotic grippers. Human-like multi-fingered
manipulator works well for rigid and regular-shaped objects but has limitations with fragile,
irregular-shaped, small-scale, or high dynamic items1-3. Caging grippers, enclosing objects in
containers by pneumatically-actuated soft materials or kirigami structures, can reduce contact
pressure and achieve high payload capability4-8. But these methods cannot tightly fix targets and
may suffer low manipulation accuracy. Universal grippers utilizing interlocking mechanisms by
shape memory polymers, jamming granular materials and phase-changing materials, have
demonstrated versatility in grasping objects of various shapes. However, they usually require
auxiliary systems (vacuum or thermal devices) or external force assistance, facing limitations when
handling dynamic or delicate objects9-13. Grippers that employ adhesion forces are commonly used
for microscale or lightweighted objects manipulation. But they encounter significant challenges in
releasing14,15. Although some robotic grippers outperform humans in specific tasks, current
manipulation technologies continue to face significant challenges. These arise from the vast
diversity of target objects in terms of shape, stiffness (ranging from soft to rigid), size (from
microscale to macroscale), and operational environments-particularly when dealing with
microscale and lightweighted objects or dynamic targets such as living organisms.

Results
The gripper cavity was fabricated by 3D printing flexible silicone (Fig. 1c). The soft tube on the
left is connected to the interior gripper cavity to inject FLM. A hollow interlayer (thickness of 1
mm), termed electrolyte interlayer, is embedded into the cavity wall to store the electrolyte injected
from the tube on the right (Fig. 2a). The essence of the LiMU gripper lies in the development of
an environment-agnostic surface activity design. We used microchannels (diameter of 800 μm) to
connect the electrolyte interlayer and the inner wall of the gripper cavity. We adhered a layer of
porous gauze to the inner wall of the gripper cavity, which absorbs the electrolyte from the
electrolyte interlayer, maintains a localized electrolyte environment for the FLM droplet and acts
as a leakage barrier for the electrolyte. A copper wire is inserted into the left tube and immersed
into the FLM. We used a copper foil (thickness of ~40 μm) to cover the bottom of the gripper
cavity. The inner edge of the copper foil is embedded between the gauze and the inner wall of the
gripper cavity to avoid direct contact with the FLM.

Inspired by the root reinforcement mechanism of plants37, we designed root-like micropillars
(radius of 0.5 mm, height of 2 mm) on the inner wall of the gripper cavity (Fig. 2b). Copper
powders are glued to the micropillars and processed with the copper-gallium alloy formation
procedure38,39. Due to the firm metallic bond between the copper and gallium, the FLM droplet is
firmly restricted in the gripper cavity. Single micropillar can provide 0.34 N equivalent adhesion.
For the LiMU gripper equipped with six micropillars, there exists an upper limit on its diameter of
~40 mm, as detailed in ‘Gripper Size Analysis of LiMU Gripper’ in Methods.

The gripper cavity was fixed on the bottom of an electromagnetic coil, which can generate a high
magnetic field strength of 4000 Gs. Both the viscosity and yield stress of FLM in the gripper cavity
can be regulated under the magnetorheological effect induced by the magnetic field, thus enabling
the LiMU gripper to grasp the wrapped payload against gravity25,40. The LiMU gripper can be
mounted to a robotic arm by the flange on the top of the electromagnetic coil.

Similar to the capturing behavior of amoeba, the LiMU gripper can conformably wrap around
target objects with complex shapes by reducing the high surface tension of FLM to near zero41.
Fig. 3a and Supplementary Video 3 illustrate the wrapping process of FLM in a 3D-printed mold
(Supplementary Fig. 4a) in an electrolyte (0.5 mol/L NaOH solution). The injected FLM initially
forms a droplet at the top of the mold chamber and cannot wrap the preset structure features
(Supplementary Fig. 4b). Once applying a positive voltage of 5 V, FLM becomes oxidized
(reflected by its tarnished color) and fills the whole mold chamber in ~3 s. All structural features
of the mold chamber, such as concave channels and convex corners, are neatly enveloped
(Supplementary Fig. 4c).

The distinctive wrapping capability of the LiMU gripper is due to the FLM’s control over
electrochemical interfacial tension and its ability to eliminate Marangoni instabilities23,24. When
increasing the applied oxidative potential above the oxidation threshold, the surface tension of the
FLM can be reduced to a moderate range under the action of electrocapillary, which is insufficient
to trigger wrapping behavior. However, when the applied voltage exceeds the oxidation threshold,
an oxide layer begins to form on the surface due to electrochemical reactions. In NaOH solution,
the oxide dissolution competes with its electrochemical formation, dynamically maintaining the
oxide layer at a specific thickness and reducing the surface tension to nearly zero. This allows the
FLM to wrap around the target. It is also important to note that excessive high voltage eventually
leads to the growth of a thicker oxide layer, which may halt the wrapping capability of the FLM.

The wrapping of FLM in the gripper cavity is governed by the balance of the spreading forces
(gravity and injection), viscous force and surface tension, as shown in Fig. 3b (see “Wrapping
Mechanism by Electrochemistry” in Methods for details). We further evaluate the wrapping
performance of a FLM droplet in the mold filled with NaOH solution of different concentrations,
as well as in different electrolytes, including seawater (see Fig. 3c and “Wrapping performance of
a FLM droplet” in Methods). The FLM functions effectively in various electrolytes, with the
fastest wrapping speed observed in NaOH solution.

Fig. 3d and Supplementary Video 4 illustrate the detailed wrapping process of the LiMU gripper
to capture a glass ball (diameter of 6 mm) in NaOH solution (the gauze in the gripper cavity is
removed in electrolyte for a clear observation, the same below). By applying a positive voltage of
5 V to lower the surface tension of FLM, the glass ball is completely wrapped within 3 seconds.
The wrapping time of the LiMU gripper can be accelerated to ~1 second by increasing the applied
voltages, electrolyte concentration, and Fe content within the FLM (see Fig. 3e and “Wrapping
performance of the LiMU gripper” in Methods). The wrapping time increases with the target
objects' size, implying a maximum wrapping size limit exists (SFig. 3f).

To enable the operation of the LiMU gripper in the air, we use a layer of porous gauze to adhere
to the inner wall of the gripper cavity, which absorbs the electrolyte and provides a local liquid
environment for the upper part of the FLM droplet for electrochemical control (see Fig. 2b). When
the upper part of the FLM droplet is oxidized, it lowers its interfacial tension and wraps around
the object. Upon reduction, the Marangoni effect rapidly transports the electrolyte to the exposed
surface of the FLM droplet, restoring the surface tension of the entire droplet to enable object
release. Such an environment-agnostic surface activity design of FLM to enable its operation
outside the liquid environment was demonstrated by the both of simulation and experiment (see
Supplementary Fig. 3, Supplementary Video 4, “Simulation for environment-agnostic surface
activity design outside the liquid environment” and “Experiment for environment-agnostic surface
activity design outside the liquid environment” in Methods).

To demonstrate the FLM’s ability to adapt to various morphologies automatically for universal
gripping, we used the LiMU gripper to capture a rubber ring, a conch, and a stone with complex
shapes, in both liquid and air (Fig. 3g). Compared to universal grippers based on shape memory
polymers, phase-changing metals, and granular materials9-13, the LiMU gripper exhibits several
advantages. First, its very low surface tension allows it to seamlessly conform to complex object
features, outperforming membrane and polymer materials. Second, the wrapping process is
spontaneous, requiring no auxiliary systems (vacuum pumps, thermal devices) and external force
assistance, which minimizes stress on the object and exhibits strong adaptability to various targets
and environments.

The electromagnetic coil fixed on the top of the gripper cavity can generate a magnetic field to
induce the magnetorheological effect of the FLM25. This effect significantly increases the shear
yield stress (i.e. stiffness) of FLM within milliseconds, allowing the gripper to securely grasp
objects by interlocking with their structural features. The combination of excellent wrapping and
stiffness tuning provides substantial gripping capability. Notably, capturing small fish underwater
poses a challenge for many existing grippers due to the mucus layer on the fish. In contrast, our
LiMU gripper successfully grasps a goldfish fry (body length: ~18 mm) underwater, as shown in
Fig. 4a and Supplementary Video 5. After release, the fish swims freely.

The FLM under the magnetorheological effect can be treated as an elastic medium. By modeling
the target object as a sphere with the diameter of 𝐷, the payload capacity of the LiMU gripper can
be estimated similarly to the tensile strength of the ball-and-socket joint. The LiMU gripper
pinches the sphere around the gripper-sphere contact line, with a pinching stress 𝜎∗ applied on the
thin band of width centered at the embedding angle 𝜃 (Supplementary Fig. 9). Grasping
mechanism and payload characterization of the LiMU gripper are illustrated in Fig. 4b (see
“Grasping mechanism of the LiMU gripper” and “Experiment setup for payload capacity test of
the LiMU gripper” in Methods). Both the grasping mechanism and payload capacity
characterization show that the payload capacity of the LiMU gripper closely relates to the
embedded angle 𝜃. For 𝜃 ≤ 𝜋/2, the friction and suction effects predominate and the payload is
very limited (≤ 30 gf). For 𝜃 ≥ 𝜋/2, geometric interlock occurs between FLM and the wrapped
sphere, and the payload depends on the shear yield stress of FLM. The payload increases
substantially to ~120 gf when 𝜃 = 𝜋. Therefore, the payload of the LiMU gripper in the interlock
state far exceeds that without interlock.

The Fe content in FLM and applied magnetic field intensity are also critical for the payload
capacity. Higher Fe content and magnetic field intensity increase the shear yield stress of FLM
(Fig. 4c), which enhances the payload capacity. The payload reaches saturation (~200 gf) when
the Fe content surpasses 40% and the magnetic field strength exceeds 4000 Gs. Fig. 4d and
Supplementary Fig. 5b demonstrate the LiMU gripper grasps heavy objects such as a pepper (165.2
g), a broccoli (157.8 g) and an orange (164.3 g) in air (also see Supplementary Video 6).

The payload capacity of the LiMU gripper is strongly dependent on its size, as shown in Fig. 4e.
As the gripper size expands from 4 mm to 10 mm (gripper cavity diameter), the payload increases
sharply from ~145 g to ~205 g, and eventually saturates at ~210 g when the gripper size exceeds
20 mm. This trend arises because a larger gripper thickens the wrapped FLM layer, enhancing the
shear yield stress until it plateaus42,43, consistent with ‘Production of Functional Liquid Metal
(FLM)’ and ‘Grasping Mechanism of the LiMU Gripper’ sections in Methods. Interestingly, from
the perspective of payload-to-gripper mass ratio, smaller grippers demonstrate a clear advantage
in grasping efficiency. For a 4 mm gripper, the payload-to-gripper mass ratio reaches as high as
~1290. As the gripper size increases to 12 mm, this ratio drops sharply to ~35, and when the gripper
exceeds 20 mm, the ratio approaches zero. This indicates the potential advantage of the LiMU
gripper in small-scale manipulations.

The LiMU gripper, enabled by variable stiffness FLM, demonstrates an ultra-gentle grasping
capability for handling fragile objects. We developed a contact pressure measurement system to
quantify the pressure exerted by the LiMU gripper (see Supplementary Fig. 5c and “Contact
pressure measurement of the LiMU gripper” in Methods). The contact pressure is minimal (~10
Pa) when subjected to a magnetic field of ~500 Gs (Fig. 4f and Supplementary Video 7). As the
magnetic field strength increases, the contact pressure gradually rises, reaching saturation at ~60
Pa when the field exceeds 2500 Gs. Fig. 4g and Supplementary Video 8 demonstrate the LiMU
gripper successfully transporting a delicate piece of tofu (yield stress: ~3920 Pa) in the air, with
no damage occurring throughout the process. Fig. 4h (and Supplementary Table 1) shows that the
LiMU gripper applies notably low contact pressure, outperforming most reported grippers and
remaining well below the yield stress of many soft-bodied organisms and fragile objects. This
makes the LiMU gripper an ideal choice for handling delicate and sensitive targets, particularly
living organisms.

The wrapping process of the LiMU gripper typically takes a few seconds (Fig. 3d), somewhat
limiting its use for manipulating stationary objects. To address this, the LiMU gripper can be
adapted for rapid capture of dynamic objects by immersing the target directly into oxidized FLM
with low surface tension. The LiMU gripper demonstrates its swift grasping ability by successfully
capturing a fast-moving cockroach, one of the fastest insects on land, as shown in Fig. 5a (see also
Supplementary Video 9 and "Experiment setup for dynamic grasping" in Methods). The entire
grasping process takes only ~200 ms, while the cockroach moves at a speed of ~30 mm/s. The
success rate was 100% in 20 cycles.

Unlike conventional contact grippers, the LiMU gripper does not require precise alignment to
capture irregularly shaped, moving objects. It can swiftly capture and firmly grip an object by
immersing only part of the target into the FLM. Fig. 5b and Supplementary Video 10 demonstrate
the grasping and transport of a wriggling earthworm. The earthworm is securely held within the
gripper as it twists and is ultimately transferred to a grassy area unharmed.

Industrial robotic manipulators face significant challenges when accurately grasping parts from a
disordered and overlapping pile, even with the aid of precision visual servoing44. The LiMU
gripper demonstrates strong potential for addressing this bin-picking problem. As shown in Fig.
5c and Supplementary Video 11, a 6-DOF robotic arm equipped with a LiMU gripper as the end
effector was employed to transfer the stones of varying shapes and sizes to four pre-programmed
locations, operating independently of visual servoing. During grasping, the LiMU gripper was
positioned randomly above the stones and then descent to a specific height to contact with the
stones. In four attempts, the gripper successfully grasps and precisely places four parts into
indentations, all without the need for visual assistance.

Releasing a macroscopic object is straightforward for most grippers due to gravity. However,
releasing micro-scale objects through contact becomes challenging because of microscale effects,
such as Van der Waals, capillary, electrostatic, and surface tension forces45,46. The standout feature
of the LiMU gripper is its ability to restore the FLM's high surface tension electrochemically,
enabling the active release of wrapped objects by leveraging the significant contrast in surface
energy between the FLM and the objects. This active release mechanism effectively overcomes
challenges associated with microscale effects, making the gripper particularly efficient at releasing
lightweight and microscale objects. Fig. 6a and Supplementary Video 12 demonstrate the active
release of a lightweight goose feather (~19 mg), which initially adhered to the FLM within the
gripper and could not be released naturally. Upon reduction of the FLM, the goose feather is
rapidly launched away, separating from the FLM droplet in under 60 ms. This active release
behavior is controlled by the surface tension regulation of the FLM. The underlying mechanism is
explained in detail using the model shown in Supplementary Fig. 6 (see “Surface tension induced
active release mechanism” in Methods). In brief, upon reduction, the restored high surface tension
of the deformed FLM propels the feather, similar to how a bow launches an arrow. Notably, no
significant residues of FLM and electrolyte are found on the surfaces of the released objects after
~50 times repeated grasping and release cycles (see Supplementary Fig. 7).

The surface tension induced active release is especially pronounced when releasing smaller objects.
We quantitatively explore this capability by actively releasing human hair (length ~10 mm,
diameter ~70 μm, weight ~0.05 mg) in water using the LiMU gripper (Fig. 6b and Supplementary
Video 13). At 5.5 ms, the magnetic field used for grasping is removed, and a reductive voltage of
15 V is applied simultaneously for active release. By 11.5 ms, the hair launches and completely
detaches from the FLM surface. The hair undergoes a high acceleration, moving from rest to a
velocity of 696 mm/s (~8700 body lengths/s) in just 6 ms (Fig. 6c), resulting in a peak acceleration
of 411.84 m/s² (~42 G). This acceleration surpasses that of other reported grippers (Fig. 6d,
Supplementary Table 2). Microscale objects, such as microchips (Mini-Led chip 0201, weight ~0.1
mg), microfibers (diameter of 20 μm, weight ~0.58 μg) and microspheres (diameter ~10 μm,
weight ~1.21 pg) can also be captured by LiMU gripper and active released (see ‘Grasping
microfibers and microspheres’ in Methods, the high-speed microscopic photography in
Supplementary Fig. 8 and Supplementary Video 14).

The surface tension induces ultrafast active release by the LiMU gripper can be used to construct
catapult actuators for high-performance micro jumping robots. It enables the rapid release of
energy in a simpler manner, with higher power and faster response, surpassing the current catapult
actuators such as light-driven hydrogel actuator, magnetic-driven bistable soft actuator, and
combustion actuator47-49. It should also be noted that excessively high release acceleration may
induce damage to sensitive objects to be manipulated or affect operational accuracy50,51. As seen
in the " Surface Tension-Induced Active Release Mechanism" in Methods, the active release speed
can be regulated by the applied reductive voltage. Fig. S11 shows the control the active release
acceleration and speed of a human hair by regulating the reductive voltage. As the reductive
voltage increases from 4 to 15 V, the maximum acceleration and speed of the human hair during
the active release process exhibit a linear correlation with the applied reductive voltage, increasing
from 29.3 to 398.8 m/s² and 186 (~2325 body lengths/s) to 696 mm/s (~8700 body lengths/s),
respectively. When the applied reductive voltage exceeds 15 V, the maximum acceleration and
speed of the human hair show a downward trend due to the intense electrolysis effect. Nevertheless,
in the extended applications of the LiMU gripper, an appropriate voltage for active release should
be selected according to specific application scenarios to achieve a trade-off between operational
efficiency and task requirements, such as safety and accuracy.

In life science research and applications such as assisted reproduction and gene editing, cell and
embryo manipulations are commonly performed using micropipettes52,53. This approach, however,
is often characterized by operational complexity, high risk of sample damage, and a reliance on
expensive peripheral equipment like precision injection pumps. The LiMU gripper demonstrates
significant potential as a promising technological alternative in these fields. In a laboratory study
on zebrafish embryos, embryos fertilized within 6 hours were selected and transferred with the
LiMU gripper (LiMU group) and a conventional pipette (control group), see detailed setup in
‘Experiment Setup and Assessment for Zebrafish Embryo Manipulation’ in Methods. The process
of grasping, transferring, and actively releasing a zebrafish embryo from a sample pool using the
LiMU gripper is detailed in Fig. 7a. In a statistical analysis of 200 embryos manipulated by the
LiMU gripper, a success rate of 99% is achieved. The two recorded failures all occur during the
grasping, with an average operational duration of 3.9 s/cycle. In contrast, conventional pipetting
requires relatively precise control over both aiming and air pressure regulation for suction and
release, resulting in lower efficiency, as shown in Supplementary Video 15. This method attained
a success rate of only 72%, with failures occurring at various stages, and an average duration of
20 s/cycle. This set of experiments demonstrates that the LiMU gripper holds a significant
advantage in manipulation efficiency.

We then conduct a subsequent systematic evaluation of both cell viability and embryo survival in
the manipulated zebrafish embryos to validate the biocompatibility of the LiMU gripper for
handling sensitive biological tissues. Fig. 7b, c show that fluorescent staining images with reactive
oxygen species (ROS) probe and statistical analysis of ROS for two groups of zebrafish embryos
immediately after the manipulation. No significant difference in oxidative stress is observed
between the two groups. Fig. 7d presents a morphological comparison of randomly selected and
tracked zebrafish embryos from both groups on days 0, 1, and 4. Fig. 7e shows the body length
measurements of hatched zebrafish larvae on day 4. No obvious tissue damage is detected. Fig. 7f
shows the heatmaps of 12-hour locomotion trajectories for three randomly selected hatched
zebrafishes from both groups on day 5. Fig. 7g shows the motion distance of the trajectories.
There is no significant difference in mobility between two groups. These evaluations demonstrate
the good biocompatibility of the LiMU gripper for handling sensitive biological tissues.

Methods
Production of Functional Liquid Metal (FLM)
The fabrication process for obtaining magnetic functional liquid metal (FLM) is illustrated in
Supplementary Fig. 2. In brief, we mixed 3 mL EGaIn (75 wt % Ga and 25 wt % In, purity: 99.99 %,
Changsha SanTech Material) and Fe particles (diameter of ~ 50 µm, Shanghai Yu-sui Welding
Material) in a beaker with the presence of a hydrochloric acid (HCl) solution (8 wt%, freshly made
before all experiments) for ~30 min stirring at room temperature. We next removed the HCl
solution and thoroughly washed the mixture with deionized (DI) water to obtain FLM. The shear
yield stress of the FLM is expressed as42,43,54:
𝜎 = ∑𝑃
4𝐴𝜇0𝜋𝜒2𝐻2
(1)
𝑓 𝑖=1
3
𝐶1
where 𝑃 denotes the number of chains of the FLM, related to the size and volume fraction of iron
particles in FLM. 𝜇 is the vacuum magnetic susceptibility, 𝜒 is the magnetic susceptibility of iron
0
particles, 𝐻 is the applied magnetic field intensity. 𝐶 is a constant related to size, coating layer,
1
and the neighboring space of iron particles. 𝐴 = ∑
𝑁1−1 1
, where 𝑁 is the number of iron particles
𝑘=1 𝑘4 1
in a single chain. 𝐴 increases with the rise of the FLM scale expands, and finally reaches saturation
(~1.0823); the shear yield stress of the FLM exhibits a similar trend.

Wrapping Mechanism by Electrochemistry
The FLM is subjected to gravity, injection, viscous, and capillary forces. Its hydrodynamic model
can be expressed as:
𝐺 +𝐹 −𝐹 −𝐹 = 𝑚 𝑎 (2)
0 𝑖 𝜇 𝑙 0 0
where 𝐺 = 𝑚 𝑔 = 2𝜌0𝑔𝜋(𝑅′3 −𝑟′3
)
, denotes the gravity of the FLM. 𝜌 is the density of the FLM.
0 0 0
3
𝑅′ is the radius of the gripper cavity. 𝑟′ is the diameter of the target object. 𝐹 = ∆𝑃𝜋(𝑅′2 −𝑟′2 ) ,
𝑖
denotes the injection force. ∆𝑃 is the injection pressure. 𝐹 = 𝐶2𝐿(𝑡)𝑑𝐿(𝑡)
, denotes the viscous force.
𝜇
𝑑𝑡
𝐶 is a constant related to the viscosity of the FLM, 𝐿(𝑡) denotes the displacement of the FLM.
2
𝐹 = 2𝐾 𝜋𝑐𝑜𝑠𝜁(𝑅′ + 𝑟′), denotes the capillary force of the FLM. 𝛾 is the surface tension
𝑙 𝑠 𝑠
coefficient of the FLM. 𝜁 is the contact angle.

When 𝐺 +𝐹 ≤ 𝐹, the FLM remains stationary. When 𝐺 +𝐹 > 𝐹, the wrapping is triggered.
0 𝑖 𝑙 0 𝑖 𝑙
The acceleration of the FLM can be calculated as:
𝑎 = 𝑔+
3∆𝑃(𝑅′+ 𝑟′)
−
3𝐶2𝐿(𝑡)𝑑𝐿(𝑡)
−
3𝛾𝑠𝑐𝑜𝑠𝜁(𝑅′+ 𝑟′)
(3)
0 2𝜌0(𝑅′2 +𝑅′ 𝑟′+ 𝑟′2 ) 2𝜌0𝜋(𝑅′3 −𝑟′3 )𝑑𝑡 𝜌0(𝑅′3 −𝑟′3 )
As can be seen from Fig. 3f and Equation 3, when the size of the object being gripped approaches
that of the gripper (𝑟′ → 𝑅′), the space between the object and the gripper cavity decreases, giving
rise to microscale effects (𝑅′−𝑟′＜0.5 mm). Compared with surface tension and viscous force,
gravity no longer dominates, which may reduce the fluidity of the FLM and thus prolong the
wrapping time of the LiMU gripper.

Gripper Size Analysis of LiMU Gripper
The FLM droplet is adhered to micropillars in the gripper cavity, relying on Cu-Ga metallic bonds
to prevent falling from gravity, as shown in Fig. 2b. To investigate the micropillar configuration
in the gripper cavity, we modeled the micropillar as a cylinder uniformly arranged inside the
gripper cavity, as shown in Supplementary Fig. 10.

Metallic bonding force provided by each micropillar can be calculated as:
𝐹 = 𝐹 +𝐹 (4)
𝑚 𝑚𝑏 𝑚𝑠
where 𝐹 = 𝜎 𝑆 , denotes the metallic bonding force provided by the base surface 𝑆 . 𝐹 =
𝑚𝑏 0 1 1 𝑚𝑠
𝜎 𝑆 , denotes the metallic bonding force provided by the side surface 𝑆 . 𝜎 is the bonding force
0 2 2 0
of CuGa interface (~1241 mN/m2)55.
2
Suppose there are N micropillars in the gripper cavity, the FLM droplet can be adhered should be
satisfied by:
𝑁𝐹 ≥ 𝐺 (5)
𝑚
where 𝐺 = 4 𝜌 𝜋𝑅′3𝑔, denotes the gravity of the FLM droplet; where 𝜌 is the density of the FLM
0 0
3
droplet, and 𝑅′ is the radius of the gripper cavity. The number of micropillars has an upper limit
𝜋𝑅′𝑠𝑖𝑛𝛼
inside the gripper cavity. For instance, 𝑁 ≤ , as illustrated in Supplementary Fig. 10.
𝑟
Therefore, the gripper size is restricted inherently, as follows:
𝑅′ ≤ √ 3𝐹𝑚𝑠𝑖𝑛𝛼 (6)
4𝑟𝜌0𝑔
For the LiMU gripper design in Supplementary Fig. 10, the maximum gripper size is ~40 mm.

Wrapping Performance of a FLM Droplet
We further evaluate the wrapping performance of a FLM droplet in the mold filled with different
electrolytes including seawater and air. As shown in Fig. 3c, a FLM droplet was submerged in
seawater, sodium carbonate (Na CO ) solution (0.5 mol/L), or NaOH solution (0.5 mol/L). In
2 3
addition, the wrapping performance was also examined in the air (a mold covered by a thin layer
of 0.5 mm NaOH solution). In general, applying an appropriate oxidative potential is necessary
for successful wrapping. When the applied voltage is too small (<1 V), no wrapping behavior was
observed. Conversely, significant electrolysis of the solution can be observed when the applied
voltage exceeds 5 V. The appropriate oxide voltage windows vary depending on the environment,
with 1-5 V for NaOH solution and air, 2-5 V for seawater, and 1-3 V for Na CO solution. In the
2 3
operating windows, increasing voltage can accelerate the wrapping process in seawater, NaOH
solution, and air. In the case of Na₂CO₃ solution, the wrapping time initially decreased and then
increased, with the optimal oxide voltage observed at 2 V. The wrapping process solely relies on
the force of gravity in NaOH solution, Na CO solution, and air, without the need for additional
2 3
injection process. However, a minimum injection velocity of 1 mL/min is required for the case of
seawater. Thus, the NaOH solution is the optimal choice for wrapping. Even in the air, FLM can
quickly fill the mold with the aid of a thin layer of NaOH solution.

Wrapping Performance of LiMU Gripper
We verified the wrapping performance of FLM in various environments (Fig. 3c). The LiMU
gripper was submerged in seawater, sodium carbonate (Na CO ) solution (0.5 mol/L), or NaOH
2 3
solution (0.5 mol/L). In addition, the wrapping performance was also examined in the air. In
general, applying an appropriate oxidative potential is necessary for successful wrapping. When
the applied voltage is too small (<1 V), no wrapping behavior was observed. Conversely,
significant electrolysis of the solution can be observed when the applied voltage exceeds 5 V. The
appropriate oxide voltage windows vary depending on the environment, with 1-5 V for NaOH
solution and air, 2-5 V for seawater, and 1-3 V for Na CO solution. In the operating windows,
2 3
increasing voltage can accelerate the wrapping process in seawater, NaOH solution, and air. In the
case of Na₂CO₃ solution, the wrapping time initially decreased and then increased, with the optimal
oxide voltage observed at 2 V. The wrapping process solely relies on the force of gravity in NaOH
solution, Na CO solution, and air, without the need for additional injection process. However, a
2 3
minimum injection velocity of 1 mL/min is required for the case of seawater. Thus, the NaOH
solution is the optimal choice for wrapping. Even in the air, FLM can quickly fill the mold with
the aid of a thin layer of NaOH solution.

In NaOH solution, we investigated the wrapping time of the LiMU gripper (inner diameter of the
gripper cavity: 10 mm) as it wrapped a 3D-printed PLA hemisphere (diameter of 8 mm) under
different applied voltages, as shown in Fig. 3e. The LiMU gripper failed to wrap the hemisphere
when the voltage was less than 1 V. The wrapping time decreased to ~1 second as the voltage
increased from 1 V to 5 V. A high voltage (> 5 V) induces significant hydrolysis and generates
hydrogen bubbles near the FLM droplet to compromise the wrapping performance.

Fe content is positively correlated to the viscosity of the FLM25, which further affects the wrapping
performance of the LiMU gripper. Fig. 3e shows that the wrapping time decreases as the Fe content
reduces from 40 % to 10 %, due to the lower viscosity of the FLM. Using a constant applied
voltage of 5 V, we further examined the time required for wrapping 3D-printed PLA hemispheres
of various diameters in NaOH solutions of differing concentrations (Fig. 3f). When increasing the
size of the target objects, the space between the object and the gripper cavity is decreased, thus
increasing the flow resistance of the FLM and increasing the wrapping time (see “Wrapping
Mechanism by Electrochemistry” in Methods for details). The wrapping time can be reduced by
increasing the concentration of the NaOH solution.

Simulation for Environment-Agnostic Surface Activity Design outside Liquid Environment
The hydrodynamic behavior of the environment-agnostic surface activity design was simulated
with COMSOL. By applying a negative voltage to the FLM droplet, the potential distribution along
the FLM droplet surface is governed by the following equations:
∇⋅𝐉⃗ = 0 (7)
𝐉⃗ = 𝜎𝐄⃗⃗ (8)
𝐄⃗⃗ = −∇𝑈 (9)
where 𝜎 is the electric conductivity of the electrolyte, 𝐉⃗ is the current density, 𝐄⃗⃗ is the electric field
intensity, and 𝑈 is the voltage. By inputting the initial configuration (Supplementary Fig. 3c (i))
to the electric currents module of COMSOL, the potential distribution of the FLM surface can be
obtained, as seen in Supplementary Fig. 3c (ii).

The potential difference across the droplet and the surface tension between the FLM and electrolyte
follow Lippman’s equation:
𝛾 = 𝛾 − 1 𝐶𝑣2 (10)
0
2
where 𝛾 is the surface tension, 𝛾 is the surface tension at the point of zero charge, 𝐶 is the
0
capacitance of the electric double layer (EDL) per unit area, 𝑣 is the potential difference. The
surface tension distribution of the FLM droplet can be obtained (Supplementary Fig. 3c (iii)).

The Marangoni effect, which causes fluid flow, occurs when a tension gradient exists on the FLM-
electrolyte interface. In the creeping flow modules of COMSOL, the fluid satisfies the Navier-
Stokes equation and incompressible fluid continuity equation and considered as steady flow:
𝜌(𝐮⃗⃗⃗ ⋅∇𝐮⃗⃗⃗) = ∇⋅[−𝑝𝐼 +𝐾]+𝐅⃗ (11)
𝐾 = 𝜇[∇𝐮⃗⃗⃗ +(∇𝐮⃗⃗⃗)𝑇] (12)
∇⋅𝐮⃗⃗⃗ = 0 (13)
where 𝐾 is the shear stress matrix, 𝐮⃗⃗⃗ is the fluid velocity, 𝜌 is the fluid density, 𝑝 is pressure, 𝜇 is
viscosity, 𝐅⃗ is external force per unit volume of fluid received.

The hydrodynamic behavior of surface activity can be obtained by linking the electric currents and
creeping flow modules with stress conditions on the surface of the FLM droplet:
[−𝑝𝐼 +𝐾]𝐧⃗⃗⃗ = ∇ 𝛾 (14)
𝜏
where 𝐼 is the identity matrix and 𝐧⃗⃗⃗ is the unit vector normal to the surface.

The simulated flow field is illustrated in Supplementary Fig. 3d, which is consistent with the
experiment results.

Experiment for Environment-Agnostic Surface Activity Design outside Liquid Environment
In non-electrolyte environments like the air, only the top hemisphere of the FLM droplet in the
gripper cavity contacts the electrolyte in the gauze. The bottom hemisphere of the FLM droplet is
exposed to air. However, the LiMU gripper is still applicable in non-electrolyte environments with
the aid of the surface tension control system, which induced the formation of Marangoni flows that
allow the electrolyte to move to the region exposed to air. We illustrated the effect caused by
Marangoni flows using a FLM droplet with half of it immersed in NaOH solution and the other
exposed to the air, as shown in Supplementary Fig. 3a. The induced Marangoni effect enables the
electrolyte to wrap the exposed surface of the FLM in a very short time, thus maintaining the
electrical activity of the whole FLM droplet (Supplementary Fig. 3b).

A FLM droplet (volume of 130 μL, diameter of 6 mm) was restricted in a rounded groove located
in the center of a 3D-printed circular container (diameter of 5 cm, PLA, 3D printed by HORI
printer). NaOH solution (0.5 mol/L) was filled in the container with a depth of 0.5 mm. A circular
copper wire (diameter of 0.8 mm) was twined around the internal wall of the container, and another
copper wire was inserted into the FLM droplet. The two copper wires were connected to the DC
power supply (IT6432, ITECH, China) as electrodes. Copper powder (diameter of 300 nm) was
sprinkled into the NaOH solution as an indicator. When applying a negative voltage to the FLM
droplet, we observed that the electrolyte flows towards the FLM droplet along a specific radial
direction, passing the top hemisphere of the droplet, and sequentially flowing back along the
circumferential direction. Interestingly, we first observed that two independent vortices were
formed symmetrically along the radial direction, as shown in Supplementary Video 4. When
moving the electrode to shift the FLM droplet away from the center, the flow direction always
keeps along the radial direction towards the center of the circular container.

Grasping Mechanism of LiMU gripper
The payload characterization under different embedded angles (sphere diameter: 10 mm, magnetic
field intensity: 3000 GS) is shown in Fig. 4c. For spheres with embedding angle 𝜃 ≤ 𝜋/2 (Fig. 4b
(i)), the friction and suction play major roles. The payload 𝐹 equals to the maximum resultant
𝑝
force of the friction and suction in the vertical direction, and can be formulated as 𝐹 = 𝐹 +𝐹 ,
𝑝 𝑠 𝑓
where the suction force is expressed as:
𝐹 = 𝜋𝐷2𝜎∗(𝜇𝑠𝑖𝑛𝜃−𝑐𝑜𝑠𝜃)𝑠𝑖𝑛3𝜃 (15)
𝑠
The friction force is expressed as:
𝐹 = 2𝜋𝐷2𝜎∗(𝜇𝑠𝑖𝑛𝜃 −𝑐𝑜𝑠𝜃)𝑠𝑖𝑛2𝜃 (16)
𝑓
where 𝐷 denotes the diameter of the sphere, and 𝜇 denotes the static friction coefficient at the
gripper-sphere contact area. The above theory implying that the payload is nearly zero when the
embedding angle blew a critical embedding angle tan−11/𝜇. The payload characterization
experiment also confirmed that the payload is very limited (~10 gf) when the embedding angle is
less than 60°. For spheres with embedding angle 𝜃 ≥ 𝜋/2, the FLM and the wrapped sphere is
geometrically interlocked. Furthermore, when 𝜃 − 𝜋/2 ≫ 1, only minimum interlocking occurs
(Fig. 4b (ii)). The payload 𝐹 mainly contributed to the bend force for the wrapped sphere to slip
𝑝
out, and is expressed as:
𝐹 ≈ ( 𝜋 )𝐸𝐷2(𝑡/𝑙)3 (17)
𝑝 2
where 𝐸 is the equivalent elastic modulus of FLM, and 𝑙 is the thickness of the FLM wrapped
around the sphere, and 𝑡 is the bending arm length. When 𝜃 ≥ 𝜋/2, there is a high level of
interlocking. The payload 𝐹 depends on the shear yield stress of the FLM 𝜎 , and can be
𝑝 𝑓
formulated as:
𝐹 ≈ (2𝜋𝐷𝑡2/𝑙)𝜎 (18)
𝑝 𝑓
We can see that the payload increases significantly (~30 gf to ~120 gf) with the increase in the
embedding angle from 90° to 180°. The payload of LiMU gripper in the interlock state far exceeds
that when no interlock occurs. As concluded, the geometrically interlocked of the FLM to the
surface features of the target object dominates the payload capacity of the LiMU gripper.

Experiment Setup for Payload Capacity Test of LiMU gripper
We developed a robotic testing system to quantitatively characterize the payload capacity of the
LiMU gripper, as shown in Supplementary Fig. 5a. The LiMU gripper was mounted to a 6-DOF
robotic arm (AUBO-i5, AUBO Robotics Technology Co., LTD). The inner diameter of the gripper
cavity is 26 mm, and the volume of the injected FLM droplet is 2.5 mL. A DC power supply
(IT6432, ITECH, China) was used to drive the electromagnetic coil. For comparability, a 3D-
printed sphere hook (diameter of 10 mm) was pre-immersed in the FLM with a certain embedding
angle and connected to a force sensor (LY-103, Bengbu Ocean Sensing System Engineering Co.,
LTD) with a cotton rope. During the experiment, the robot arm was controlled to move far away
from the force sensor along the axial direction of the force sensor. The real-time force-
displacement data was recorded by a computer. The maximum payload can be obtained by
analyzing the yield point of the force-displacement curve.

Contact Pressure Measurement of LiMU Gripper
Supplementary Fig. 5c illustrates the contact pressure measurement system. A small highly
stretchable rubber balloon (elastic modulus: ~3 MPa, thickness of ~0.05 mm) was tightly hooped
in a glass capillary (outer diameter of 10 mm, inner diameter of 2 mm) using a rubber band. The
rubber balloon was filled with purple litmus solution as an indicator. We adhered a scale label to
the glass capillary to record the height of the indicator fluid. The 3D-printed cylindrical container
was filled with FLM, and an electromagnetic coil was fixed below the container. The wrapping
and grasping of the LiMU gripper to the balloon can be replicated by immersing the entire balloon
into the FLM and then activating a magnetic field with specific intensity. The contact pressure
exerted by the LiMU gripper to grasp the balloon can be determined by measuring the change in
internal pressure within the balloon once the magnetic field is activated. This contact pressure 𝑃
was precisely measured by monitoring the corresponding change in height of the indicator fluid,
which is expressed as 𝑃 = 𝜌 𝑔∆ℎ, where 𝜌 denotes the density of the purple litmus solution, 𝑔
𝑠 𝑠
denotes the gravitational acceleration, and ∆ℎ denotes the change in height of the indicator.

Experiment Setup for Dynamic Grasping
We used the LiMU gripper to catch a cockroach to demonstrate its ability of dynamic grasping.
The diameter of the cavity is 20 mm. The volume of the filled FLM droplet is about 1 mL. The
adopted electrolyte is water. The oxide voltage is 5 V. The magnetic field strength for grasping is
about 2500 Gs. The LiMU gripper was installed at the robotic arm's end, suspended 10 mm above
the tube. The cockroach can crawl freely in a transparent acrylic tube. A camera was placed on the
side of the acrylic tube, perpendicular to the LiMU gripper, to record the process and analyze the
position of the cockroach. When the cockroach was detected in the trapping area below the LiMU
gripper, the robotic arm was activated to move downward to fixed height of 3 mm to grasp the
cockroach (see also Supplementary Video 9). The entire grasping process took only ~200
milliseconds, while the cockroach's movement speed was ~30 mm/s.

Surface Tension Induced Active Release Mechanism
When applying an electric field for active releasing, the force induced by the surface tension of the
FLM, denoted by 𝐹 = 𝛾 𝑙 , undergoes a significant increase as the increasing of the surface
𝛾 𝑠 𝑖
tension coefficient 𝛾 of FLM, where 𝑙 denotes the intersection line where the feather rod, FLM,
𝑠 𝑖
and air meet. As shown in Supplementary Fig. 6, the surface tension generates a launch force 𝐹,
𝑙
that acts on the road of the immersed feather in a vertical direction,
𝐹 = 𝐹 𝑠𝑖𝑛𝜑 (19)
𝑙 𝛾
where 𝜑 = 𝛿 +𝛽 −180°, denotes the tilt angle between the launch force and the horizontal
direction; 𝛽 represents the immersion angle and is related to the depth at which the feather rod is
immersed in the FLM; 𝛿 = ~145° is the contact angle between the FLM and the feather rod. The
dynamic changes on the surface of the FLM caused by the feather launch can be ignored. The
gravity and buoyancy can be ignored for the small and lightweight target object. Thus, the
dynamics of the object during the active release can be formulated as:
𝐹 −𝐹 = 𝑚𝑎 (20)
𝑙 𝜏
where 𝐹 = 𝜇 𝑉 formulates the viscous drag forces of the feather, 𝜇 denotes the combined
𝜏 𝑣 𝑓 𝑣
viscous coefficient of the air and FLM; 𝑉 denotes the velocity of the feather; 𝑎 and 𝑚 denote the
𝑓
acceleration and the mass of the feather respectively.

The feather experiences two phases when launched out of the FLM droplet. When the feather is
immersed deeper in the FLM droplet (Supplementary Fig. 6a), both the immersion angle 𝛽 and the
tilt angle 𝜑 remain constant and the launch force 𝐹 acts on the road of the feather is maximum.
𝑙
As the feather road is ejected from the FLM droplet surface (Supplementary Fig. 6b), the launch
force 𝐹 decrease to 0 with the decrease of the immersion angle 𝛽 until the feather is completely
𝑙
separate from the FLM droplet.

The reduction rate of FLM exhibits a closely linear correlation with applied reduction voltage25,26,
which release speed can be regulated by the applied electric field. Reducing the reduction voltage
can slow the release speed to zero.

Grasping Microfibers and Microspheres
During grasping, we gently press the oxidized FLM droplet of LiMU gripper onto a paper bed
covered with microfibers and microspheres. The grasped micro-objects exhibit uncertain states:
some may be immersed in the FLM droplet, while others adhere to the surface via oxides. As
described in the wrapping mechanism, the oxidized FLM surface possesses an oxide layer (Ga
2
O
3
)
with strong adhesion to various materials.

Experiment Setup and Assessment of Zebrafish Embryo Manipulation
Zebrafish embryo manipulation: A LiMU gripper with a cavity diameter of 4 mm was mounted
at the bottom of a 3D-printed hollow sleeve (length: 100 mm, diameter: 8 mm) for handling
zebrafish embryos (AB wild-type, diameter: ~1 mm, purchased from Beyotime Biotech. Inc).
The
voltage for grasping is set to 5 V, and voltage for active release is set to 15 V. Zebrafish embryos
were submerged in culture medium (Hanks' Balanced Salts Solution, purchased from Sigma-
Aldrich) and maintained in a recirculating aquaculture system at a constant temperature of 28.5°C
under a 14-hour light/10-hour dark (14L:10D) photoperiod cycle. The experiment employed both
the LiMU gripper and a pipette (purchased from Beyotime Biotech. Inc) to grasp and transfer 200
zebrafish embryos from the culture dish to a target dish for further evaluation.

Cell viability and embryo survival: To assess potential cellular oxidative damage of zebrafish
embryos immediately after the manipulation, intracellular ROS levels in zebrafish embryos were
assayed using the fluorescent probe DCFH-DA (Solarbio, D6470). Briefly, embryos successfully
transferred by either the LiMU gripper or a micropipette were randomly selected (n = 12 per group),
treated with the DCFH-DA probe for 30 minutes, and then imaged under an Olympus BX60
microscope with 504 nm excitation.

The morphology evaluation was performed to assess the zebrafish embryo development of the two
groups (n = 12 per group). The embryos were imaged under a microscope (Olympus BX16
Microscope) on days 0, 1, and 4 post-manipulations and the body length of the resulting larvae
were measured on day 4.

Behavioral tests were performed to assess embryonic development of the two groups (n = 12 per
group) on day 5. The free-swimming trajectories of hatched zebrafish larvae were recorded for one
hour in a controlled incubation chamber maintained at 28.5°C. Locomotor activity was
automatically tracked by the Zebrabox video system, and data were processed using Zebralab 3.11
software (Viewpoint, France).

Vision Recording and Processing
Human hair release was recorded with a high-speed camera (Memrecam HX-7S, nac Image
Technology, Japan; frame rate: 2000 fps). The release of microchips, microfibers, and
microspheres was captured by a high-speed camera (UPT030/M, WorkPower Technology Co., LTD,
China; frame rate: 815 fps) equipped with a microscopic lens (M Plan 20/10×, Mitutoyo, Japan).
The trajectory of the released objects was analyzed using MATLAB with the template-based object
tracking algorithm56. The velocity and acceleration of hair movement were obtained by taking the
first- and second-order derivatives of the trajectory data, respectively. The remaining experimental
videos were obtained with a DSILR camera (Canon 5D, Japan).

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "I appreciate the authors efforts to address my initial comments. It helps to know that the authors aren’t claiming breakthroughs in terms of novel material science or material architectures. While this lessens the uniqueness of this approach, it doesn’t diminish its potential value as an approach for soft robot gripping. Therefore, I think this work could be suitable for publication Nature Communications after the authors make some final revisions based on the comments below:\n1. In some ways, this gripper has advantages over other “universal grippers” in the variety of lightweight objects that it can pick up. However, it’s not clear how scalable this gripper is and if it can be engineered to lift heavier objects. Somewhere, the authors should report the payload capacity as a function of gripper mass and also provide some discussion or calculations on how this ratio might change with gripper size. Because of its reliance on surface tension, I presume that the scaling laws support the highest ratio of payload to gripper weight at smaller length scales. Such a calculation could be added to the “Grasping mechanism of the LiMU gripper” subsection within Methods.\n2. Similar to the above comment, what is the theoretical limit on how large or small the gripper can be? All of the examples appear to be of centimeter and millimeter scale objects. How would the gripper perform if it was 10s or 100s of centimeter in diameter? I would imagine that the size would also influence the gripping speed and so it would help to have some discussion or calculations around this. Again, just a theoretical calculation in the Methods or SI would be sufficient here.\n3. I’m still not convinced that this gripper “ mimic[s] the hunting behavior of amoeba.” While it’s fine to refer to the amoeba as a source of inspiration, I feel that the analogy distracts from the main contributions of this work. I suggest that the authors downplay the connection with natural amoeba and removing the images of natural endocytosis and exocytosis shown in Fig. 1a. While I definitely see parallels between the gripper and the amoeba, I feel that the same arguments could be applied to the granular jamming gripper and aren’t unique to the liquid metal based approach.", "reviewer_3": "While I appreciate the authors' efforts to address the concerns raised, I find that the responses are only partially satisfactory, and several key issues remain unresolved. I cannot recommend the manuscript for publication unless the authors adequately address the concerns outlined below.\nFirst, I remain unconvinced about the practical utility of the proposed gripper. To substantiate its relevance, the authors should clearly demonstrate how this system could replace or improve upon existing manipulation techniques in real-world scenarios, particularly in biomedical contexts involving living organisms, or in the handling of microscale components in microelectronics assembly and manufacturing. Without such demonstrations or a compelling application roadmap, the broader impact of this technology remains speculative.\nSecond, although the reported acceleration of 42 G is noteworthy, it is unclear whether achieving such an extreme release speed is necessary or beneficial. In fact, overly high acceleration could risk damaging fragile or sensitive targets, especially in biomedical or microscale applications. A more balanced discussion regarding the trade-offs between release speed and object safety would improve the manuscript.\nThird, the relevance of the acceleration data presented in Figure 6d is questionable. In microscale manipulation, the critical challenge lies in achieving reliable and controllable grasping and release, particularly in the presence of dominant surface forces. Release speed alone is of limited significance in such regimes. For example, the analogy between the gripper’s release of a feather and the launch of a rocket is unconvincing. These mechanisms operate on fundamentally different physical principles, serve distinct purposes, and exist on vastly different length and force scales."}, "author_response": "We thank the reviewer for the positive comments and time spent evaluating the manuscript.\n1. In some ways, this gripper has advantages over other “universal grippers” in the variety of lightweight objects that it can pick up. However, it’s not clear how scalable this gripper is and if it can be engineered to lift heavier objects. Somewhere, the authors should report the payload capacity as a function of gripper mass and also provide some discussion or calculations on how this ratio might change with gripper size. Because of its reliance on surface tension, I presume that the scaling laws support the highest ratio of payload to gripper weight at smaller length scales. Such a calculation could be added to the “Grasping mechanism of the LiMU gripper” subsection within Methods.\nWe appreciate the reviewers' recognition of the advantages of the LiMU gripper in handling lightweight objects, and we are also grateful for the constructive comments provided by the reviewer.\nThe scalability of the LiMU gripper depends foremost on the size of the gripper itself. The lower size limit of the LiMU gripper is not theoretically constrained, but rather depends on engineering capabilities. The minimum diameter of the LiMU gripper that can be fabricated by using conventional 3D printing technology is ~4 mm (gripper cavity diameter). Smaller-sized LiMU grippers may require micro-nano scale 3D printing or MEMS technology for production. However, the LiMU gripper has a theoretical upper limit on its size, which depends on the maximum size of the functional liquid metal (FLM) droplet that can be constrained by the micropillars on the inner wall of the gripper cavity. We have conducted a detailed theoretical analysis on the maximum size limit of the LiMU gripper. Please refer to the new section \"Gripper Size Analysis of LiMU gripper\" in the Methods in the revised manuscript. A single micropillar can provide an equivalent adhesion force of ~0.34 N. For a LiMU gripper equipped with six micropillars, there is an upper limit on its size of ~40 mm.\nWe are grateful for the insightful suggestion to link the payload capacity with the gripper size (or mass), so as to conduct a comprehensive evaluation of the scalability of the LiMU gripper. As suggested by the reviewer, we performed experiments to evaluate the relationship of the payload force to the different gripper sizes and masses, which is illustrated in Fig.4e in the revised manuscript. The results verified that the payload capacity of the LiMU gripper is strongly dependent on its size. As the gripper size expands from 4 mm to 10 mm, the payload increases sharply from ~145 g to ~205 g, and eventually saturates at ~210 g when the gripper size exceeds 20 mm. Interestingly, from the perspective of payload-to-gripper mass ratio, smaller grippers demonstrate a clear advantage in grasping efficiency. For a 4 mm gripper, the payload-to-gripper mass ratio reaches as high as ~1290. As the gripper size increases to 12 mm, this ratio drops sharply to ~35, and when the gripper exceeds 20 mm in size, the ratio approaches zero. This indicates the potential advantage of the LiMU gripper in small-scale manipulations.\nOne key point to emphasize is that the LiMU gripper’s ability to grasp heavy objects does not rely on surface tension; rather, it results from the increased stiffness of the FLM when subjected to magnetic fields due to the magnetorheological effect.\nTo clarify the scalability of this gripper, we added a new section of \" Gripper Size Analysis of LiMU gripper \" and a new figure of Fig. 4e. Meanwhile, we updated the section of “Production of Functional Liquid Metal (FLM)” in the Methods in the revised manuscript, as given below:\nPage 8, line 122\nInspired by the root reinforcement mechanism of plants29, we design root-like micropillars (radius of 0.5 mm, height of 2 mm) on the inner wall of the gripper cavity (Fig. 2b). Copper powders are glued to the micropillars and processed with the copper-gallium alloy formation procedure30,31. Due to the firm metallic bond between the copper and gallium, the FLM droplet is firmly restricted in the gripper cavity. A single micropillar can provide ~0.34 N equivalent adhesion. For the LiMU gripper equipped with six micropillars, there exists an upper limit on its diameter of ~40 mm, as detailed in ‘Gripper Size Analysis of LiMU Gripper’ in Methods.\nPage 13, line 226\nThe payload capacity of the LiMU gripper is strongly dependent on its size, as shown in Fig. 4e. As the gripper size expands from 4 mm to 10 mm (gripper cavity diameter), the payload increases sharply from ~145 g to ~205 g, and eventually saturates at ~210 g when the gripper size exceeds 20 mm. This trend arises because a larger gripper thickens the wrapped FLM layer, enhancing the shear yield stress until it plateaus34,35, consistent with ‘Production of Functional Liquid Metal (FLM)’ and ‘Grasping Mechanism of LiMU Gripper’ sections in Methods. Interestingly, from the perspective of payload-to-gripper mass ratio, smaller grippers demonstrate a clear advantage in grasping efficiency. For a 4 mm gripper, the payload-to-gripper mass ratio reaches as high as ~1290. As the gripper size increases to 12 mm, this ratio drops sharply to ~35, and when the gripper exceeds 20 mm, the ratio approaches zero. This indicates the potential advantage of the LiMU gripper in small-scale manipulations.\nFig. 4e Relationship of the payload force (payload-to-gripper mass ratio: the mass ratio of payload to FLM droplet inside the LiMU gripper) to the different gripper sizes and masses.\nMethods\nPage 27, line 513\nProduction of Functional Liquid Metal (FLM)\nThe fabrication process for obtaining magnetic functional liquid metal (FLM) is illustrated in Supplementary Fig. 2. In brief, we mixed 3 mL EGaIn (75 wt % Ga and 25 wt % In, purity: 99.99 %, Changsha SanTech Material) and Fe particles (diameter of ~ 50 µm, Shanghai Yu-sui Welding Material) in a beaker with the presence of a hydrochloric acid (HCl) solution (8 wt%, freshly made before all experiments) for ~30 min stirring at room temperature. We next removed the HCl solution and thoroughly washed the mixture with deionized (DI) water to obtain FLM. The shear yield stress of the FLM is expressed as :\n34,35,43\n𝜎f = E\n4Aµo\n(1)\nP ___ 71-\nX2H2 4.1 3 C\n1\nwhere 𝑃 denotes the number of chains of the FLM, related to the size and volume fraction of iron particles in FLM. 𝜇o is the vacuum magnetic susceptibility, 𝜒 is the magnetic susceptibility of iron particles, 𝐻 is the applied magnetic field intensity. 𝐶 is a constant related to size, coating layer, and the neighboring space of iron particles. 𝐴 = E\nk=11\nk 4\n, where 𝑁 is the number of iron particles in a single chain. 𝐴 increases with the rise of the FLM scale expands, and finally reaches saturation (~1.0823); the shear yield stress of the FLM exhibits a similar trend.\nPage 28, line 546\nGripper Size Analysis of LiMU Gripper\nThe FLM droplet is adhered to micropillars in the gripper cavity, relying on Cu-Ga metallic bonds to prevent falling from gravity, as shown in Fig. 2b. To investigate the micropillar configuration in the gripper cavity, we modeled the micropillar as a cylinder uniformly arranged inside the gripper cavity, as shown in Supplementary Fig. 10.\nMetallic bonding force provided by each micropillar can be calculated as:\n𝐹m = 𝐹mb + 𝐹ms (4)\nwhere 𝐹mb = 𝜎o𝑆1, denotes the metallic bonding force provided by the base surface 𝑆1. 𝐹ms = 𝜎o𝑆2, denotes the metallic bonding force provided by the side surface 𝑆2. 𝜎o is the bonding force of CuGa2 interface (~1241 mN/m2)44.\nSuppose there are N micropillars in the gripper cavity, the FLM droplet can be adhered should be satisfied by:\n𝑁 𝐹m ≥ 𝐺 (5)\nwhere 𝐺 = 3 𝜌o𝜋𝑅'3𝑔, denotes the gravity of the FLM droplet; where 𝜌o is the density of the FLM droplet, and 𝑅' is the radius of the gripper cavity. The number of micropillars has an upper limit inside the gripper cavity. For instance, 𝑁 ≤ 71-Rᇲsina r ________ , as illustrated in Supplementary Fig. 10.\nTherefore, the gripper size is restricted inherently, as follows:\n(6)\n𝑅' ≤ ,j 3Fmsina 4rPo9\nFor the LiMU gripper design in Supplementary Fig. 10, the maximum gripper size is ~40 mm.\nSupplementary Information\nSupplementary Figure 10. Schematic illustration of the FLM droplet restricted by micropillars.\nReferences\n34. Peng, Y. & Pei, P. Microstructure evolution based particle chain model for shear yield stress of magnetorheological fluids. J. Intell. Mater. Syst. Struct. 32, 49-64 (2021).\n35. Peng, X. & Li, H. Analysis of the magnetomechanical behavior of MRFs based on micromechanics incorporating a statistical approach. Smart Mater. Struct. 16, 2477 (2007).\n44. Zhang, X. et al. Improving the Thermal Performance of Liquid Metal Thermal Interface Materials: The Role of Intermetallic Compounds at the Gallium/Copper Interface. Adv. Mater. Interfaces 12, 2500041 (2025).\n2. Similar to the above comment, what is the theoretical limit on how large or small the gripper can be? All of the examples appear to be of centimeter and millimeter scale objects. How would the gripper perform if it was 10s or 100s of centimeter in diameter? I would imagine that the size would also influence the gripping speed and so it would help to have some discussion or calculations around this. Again, just a theoretical calculation in the Methods or SI would be sufficient here.\nWe appreciate the constructive comments provided by the reviewer. Please see our response to the first comment regarding how large or small the gripper can be. This section responds to the gripping speed comment.\nThe LiMU gripper goes through two stages during gripping - wrapping and grasping. During the wrapping, the FLM with the low surface tension flows in the space between the gripper cavity and the targeted object, thereby enclosing the object. The hydrodynamic behavior of the FLM during wrapping is closely related to the gripper size. An excessively small gripper size restricts the space for FLM flow, and the resulting microscale effects reduce the fluidity of the FLM, prolonging the wrapping time of the LiMU gripper, as shown in Fig. 3b, Fig. 3f and \" Wrapping Mechanism by Electrochemistry\" in Methods in the revised manuscript. The grasping of the LiMU gripper is attributed to the magnetorheological effect of the FLM. By applying a magnetic field, the shear yield stress (i.e. stiffness) of the FLM droplets in the LiMU gripper increased significantly within milliseconds, endowing the LiMU gripper with payload capacity to hold the target object. Therefore, the grasping speed of the LiMU gripper is less affected by the gripper size. All the corrections are highlighted in the revised manuscript, as given below:\nPage 9 line 153\nThe wrapping of FLM in the gripper cavity is governed by the balance of the spreading forces (gravity and injection), viscous force, and surface tension, as shown in Fig. 3b (see “Wrapping Mechanism by Electrochemistry” in Methods for details).\nFig. 3b Wrapping mechanism of the LiMU gripper.\nPage 11 line 176\nThe wrapping time increases with the target objects' size, implying a maximum wrapping size limit exists (Fig. 3f).\nMethods\nPage 27, line 528\nWrapping Mechanism by Electrochemistry\nThe FLM is subjected to gravity, injection, viscous, and capillary forces. Its hydrodynamic model can be expressed as:\n𝐺o + 𝐹 - 𝐹µ - 𝐹 = 𝑚o𝑎o (2)\nwhere 𝐺o = 𝑚0 𝑔 = ____________ , denotes the gravity of the FLM. 𝜌o is the density of the FLM. 𝑅' is the radius of the gripper cavity. 𝑟' is the diameter of the target object. 𝐹 = ∆𝑃𝜋(𝑅'ଶ - 𝑟'ଶ), denotes the injection force. ∆𝑃 is the injection pressure. 𝐹µ= dt , denotes the viscous force. 𝐶ଶ is a constant related to the viscosity of the FLM, 𝐿(𝑡) denotes the displacement of the FLM. 𝐹 = 2𝛾௦ 𝜋𝑐𝑜𝑠𝜁(𝑅' + 𝑟') , denotes the capillary force of the FLM. 𝛾௦ is the surface tension coefficient of the FLM. 𝜁 is the contact angle.\nWhen 𝐺o + 𝐹 ≤ 𝐹 , the FLM remains stationary. When 𝐺o + 𝐹 > 𝐹 , the wrapping is triggered. The acceleration of the FLM can be calculated as:\n𝑎o = 𝑔+ ଶ ଷ p ∆బ (ே ா 'మ ା ே ା ◌ ா ') ' ଷ మL ( t )dL(t ଷఊ ே ೞ ா ' ◌ା ௦ ' ) '◌ା 'మ) ଶpబn- pబ(ே◌ா'య ◌ି 'య) (3)\nAs can be seen from Fig. 3f and Equation 3, when the size of the object being gripped approaches that of the gripper (𝑟→ 𝑅), the space between the object and the gripper cavity decreases, giving rise to microscale effects (𝑅- 𝑟'<0.5 mm). Compared with surface tension and viscous force, gravity no longer dominates, which may reduce the fluidity of the FLM and thus prolong the wrapping time of the LiMU gripper.\nPage 30, line 608\nWrapping Performance of LiMU Gripper\nWhen increasing the size of the target objects, the space between the object and the gripper cavity is decreased, thus increasing the flow resistance of the FLM and increasing the wrapping time (see “Wrapping Mechanism by Electrochemistry” in Methods for details). The wrapping time can be reduced by increasing the concentration of the NaOH solution.\n3. I’m still not convinced that this gripper “ mimic[s] the hunting behavior of amoeba.” While it’s fine to refer to the amoeba as a source of inspiration, I feel that the analogy distracts from the main contributions of this work. I suggest that the authors downplay the connection with natural amoeba and removing the images of natural endocytosis and exocytosis shown in Fig. 1a. While I definitely see parallels between the gripper and the amoeba, I feel that the same arguments could be applied to the granular jamming gripper and aren’t unique to the liquid metal based approach.\nWe appreciate the reviewer's comments. As suggested, we have removed the amoeba’s analogy in Fig. 1 and modified the expressions in the revised manuscript to downplay the connection between the LiMU gripper and the amoeba, as given below:\nPage 6, line 78\nInspired by the hunting behavior of the amoeba, we report a liquid metal universal gripper (LiMU gripper) by regulating the surface tension and stiffness of functional liquid metal (FLM) with electric and magnetic fields, realizing notable grasp and active release performance in both air and liquids (see Fig. 1b, Supplementary Fig. 1, and Supplementary Video 1).\nFigure 1\nFig. 1 | Conception of the LiMU gripper. a, Morphological transitions of FLM via regulating its surface tension. b, The working mechanism of the LiMU gripper. c, The design and actual image of the LiMU gripper. Scale bar: 2 mm. d-i, Grasp and active release performance of the LiMU gripper. Scale bars: 5 mm. j, Comparison of this work and various grippers in terms of gripping scale and response time.\nReviewer #3:\nWhile I appreciate the authors' efforts to address the concerns raised, I find that the responses are only partially satisfactory, and several key issues remain unresolved. I cannot recommend the manuscript for publication unless the authors adequately address the concerns outlined below.\nWe thank the reviewer for comments and time spent evaluating the manuscript.\n1. First, I remain unconvinced about the practical utility of the proposed gripper. To substantiate its relevance, the authors should clearly demonstrate how this system could replace or improve upon existing manipulation techniques in real-world scenarios, particularly in biomedical contexts involving living organisms, or in the handling of microscale components in microelectronics assembly and manufacturing. Without such demonstrations or a compelling application roadmap, the broader impact of this technology remains speculative.\nWe appreciate the constructive comments provided by the reviewer. We conducted additional experiments to show that the LiMU gripper holds significant application potential in biological sample manipulation in life science research, such as assisted reproduction and cell/embryo manipulations. Compared with the traditional micropipette, the LiMU gripper exhibits distinct advantages in manipulation precision and efficiency, ease of use, cost-effectiveness, and biocompatibility. In research areas such as assisted reproduction and neural development, frequent manipulation of zebrafish embryos is routinely required. We therefore compared the performance of the LiMU gripper and traditional micropipettes in manipulating zebrafish embryos (Fig. 7a, Supplementary Video 15, and \"Experiment Setup and Assessment for Zebrafish Embryo Manipulation\" in Methods). After 200 manipulation trials, the LiMU gripper achieved a 99% success rate and an average operational duration of 3.9 seconds per cycle. In contrast, conventional pipetting requires relatively precise control over both aiming and air pressure regulation for suction and release, resulting in lower efficiency, which attained a success rate of only 72% and an average duration of 20 seconds.\nWe then conducted a subsequent systematic evaluation of both cell viability and embryo survival in the manipulated zebrafish embryos to validate the biocompatibility of the LiMU gripper for handling sensitive biological tissues (Figure 7). These results show that there is no significant difference between the LiMU gripper technology and the traditional micropipettes. These evaluations demonstrate the good biocompatibility of the LiMU gripper for handling sensitive biological tissues.\nIn the revised manuscript, we added Figure 7, a new section of \"Experiment Setup and Assessment for Zebrafish Embryo Manipulation\" in Methods, and Supplementary Video 15, as given below:\nPage 20, line 340\nIn life science research and applications such as assisted reproduction and gene editing, cell and embryo manipulations are commonly performed using micropipettes41,42. This approach, however, is often characterized by operational complexity, high risk of sample damage, and a reliance on expensive peripheral equipment like precision injection pumps. The LiMU gripper demonstrates significant potential as a promising technological alternative in these fields. In a laboratory study on zebrafish embryos, embryos fertilized within 6 hours were selected and transferred with the LiMU gripper (LiMU group) and a conventional pipette (control group), see detailed setup in ‘Experiment Setup and Assessment for Zebrafish Embryo Manipulation’ in Methods. The process of grasping, transferring, and actively releasing a zebrafish embryo from a sample pool using the LiMU gripper is detailed in Fig. 7a. In a statistical analysis of 200 embryos manipulated by the LiMU gripper, a success rate of 99% is achieved. The two recorded failures all occur during the grasping, with an average operational duration of 3.9 s/cycle. In contrast, conventional pipetting requires relatively precise control over both aiming and air pressure regulation for suction and release, resulting in lower efficiency, as shown in Supplementary Video 15. This method attained a success rate of only 72%, with failures occurring at various stages, and an average duration of 20 s/cycle. This set of experiments demonstrates that the LiMU gripper holds a significant advantage in manipulation efficiency.\nWe conduct a subsequent systematic evaluation of both cell viability and embryo survival in the manipulated zebrafish embryos to validate the biocompatibility of the LiMU gripper for handling sensitive biological tissues. Figs. 7b, c show that fluorescent staining images with reactive oxygen species (ROS) probe and statistical analysis of ROS for two groups of zebrafish embryos immediately after the manipulation. No significant difference in oxidative stress is observed between the two groups. Fig. 7d presents a morphological comparison of randomly selected and tracked zebrafish embryos from both groups on days 0, 1, and 4. Fig. 7e shows the body length measurements of hatched zebrafish larvae on day 4. No obvious tissue damage is detected. Fig. 7f shows the heatmaps of 12-hour locomotion trajectories for three randomly selected hatched zebrafishes from both groups on day 5. Fig. 7g shows the motion distance of the trajectories. There is no significant difference in mobility between the two groups. These evaluations demonstrate the good biocompatibility of the LiMU gripper for handling sensitive biological tissues.\nFigure 7\nFig. 7 | LiMU gripper for biomedical manipulation. a, Process of grasping, transferring, and actively releasing a zebrafish embryo by the LiMU gripper. Scale bar: 4 mm. b, Fluorescent staining images with ROS probe for two groups of zebrafish embryos. c, Reactive oxygen species (ROS) for two groups of zebrafish embryos. d, Morphological comparison of randomly selected and tracked zebrafish embryos from both groups. e, Body length measurements of hatched zebrafish larvae on day 4. f, Heatmaps of 12-hour locomotion trajectories for three randomly selected hatched zebrafishes from both groups on day 5. g, Motion distance of the trajectories.\nMethods\nPage 36, line 763\nExperiment Setup and Assessment for Zebrafish Embryo Manipulation\nZebrafish embryo manipulation: A LiMU gripper with a cavity diameter of 4 mm was mounted at the bottom of a 3D-printed hollow sleeve (length: 100 mm, diameter: 8 mm) for handling zebrafish embryos (AB wild-type, diameter: ~1 mm, purchased from Beyotime Biotech. Inc). The voltage for grasping is set to 5 V, and voltage for active release is set to 15 V. Zebrafish embryos were submerged in culture medium (Hanks' Balanced Salts Solution, purchased from Sigma-Aldrich) and maintained in a recirculating aquaculture system at a constant temperature of 28.5°C under a 14-hour light/10-hour dark (14L:10D) photoperiod cycle. The experiment employed both the LiMU gripper and a pipette (purchased from Beyotime Biotech. Inc) to grasp and transfer 200 zebrafish embryos from the culture dish to a target dish for further evaluation.\nCell viability and embryo survival: To assess potential cellular oxidative damage of zebrafish embryos immediately after the manipulation, intracellular ROS levels in zebrafish embryos were assayed using the fluorescent probe DCFH-DA (Solarbio, D6470). Briefly, embryos successfully transferred by either the LiMU gripper or a micropipette were randomly selected (n = 12 per group), treated with the DCFH-DA probe for 30 minutes, and then imaged under an Olympus BX60 microscope with 504 nm excitation.\nThe morphology evaluation was performed to assess the zebrafish embryo development of the two groups (n = 12 per group). The embryos were imaged under a microscope (Olympus BX16 Microscope) on days 0, 1, and 4 post-manipulations and the body length of the resulting larvae was measured on day 4.\nBehavioral tests were performed to assess embryonic development of the two groups (n = 12 per group) on day 5. The free-swimming trajectories of hatched zebrafish larvae were recorded for one hour in a controlled incubation chamber maintained at 28.5 °C. Locomotor activity was automatically tracked by the Zebrabox video system, and data were processed using Zebralab 3.11 software (Viewpoint, France).\nReferences\n41. Chow, Y. T. et al. Liquid Metal-Based Multifunctional Micropipette for 4D Single Cell Manipulation. Adv. Sci. 5, 1700711 (2018).\n42. Zhang, X. P. et al. Controlled Aspiration and Positioning of Biological Cells in a Micropipette. IEEE. T. Bio-med. Eng. 59, 1032-1040 (2012).\n2. Second, although the reported acceleration of 42 G is noteworthy, it is unclear whether achieving such an extreme release speed is necessary or beneficial. In fact, overly high acceleration could risk damaging fragile or sensitive targets, especially in biomedical or microscale applications. A more balanced discussion regarding the trade-offs between release speed and object safety would improve the manuscript.\nWe thank the reviewer for the comment. In scenarios of non-sensitive targeted objects, such as constructing catapult actuators for high-performance micro-jumping robots, the surface tension-induced ultrafast active release by the LiMU gripper possesses enormous application potential. It enables the rapid release of energy in a simpler manner, with higher power and faster response, surpassing the current catapult actuators such as light-driven hydrogel actuators, magnetic-driven bistable soft actuators, and combustion actuators.\nIt should also be noted that excessively high release acceleration may cause damage to sensitive objects that are being manipulated or affect operational accuracy. However, the active release speed can be regulated by the applied reductive voltage, which is clarified in the \"Surface Tension-Induced Active Release Mechanism\" in the Methods. Furthermore, we also investigated how to control the active release acceleration and speed of a human hair by regulating the reductive voltage, as shown in Fig. S11.\nMoreover, in our response to Comment 1, we conducted a systematic evaluation of both cell viability and embryo survival rate in the manipulated zebrafish embryos to validate the biocompatibility of the LiMU gripper for handling sensitive biological tissues, compared with the widely used micropipettes. Noted that the applied reductive voltage during the manipulation of the zebrafish embryo by the LiMU gripper was 15 V. The evaluation in Fig. 7 shows that there is no significant difference between the LiMU gripper technology and traditional micropipettes, which demonstrates the good biocompatibility of the LiMU gripper for handling sensitive biological tissues.\nIn the revised manuscript, we added a new paragraph of discussion in the main text, and a new figure of Fig. S11 in the Supplementary Information, as given below:\nPage 19, line 322\nThe surface tension induces ultrafast active release by the LiMU gripper can be used to construct catapult actuators for high-performance micro jumping robots. It enables the rapid release of energy in a simpler manner, with higher power and faster response, surpassing the current catapult actuators such as light-driven hydrogel actuator, magnetic-driven bistable soft actuator, and combustion actuator39-41.\nIt should also be noted that excessively high release acceleration may induce damage to sensitive objects to be manipulated or affect operational accuracy42,43. As given in the \"Surface Tension-Induced Active Release Mechanism\" in Methods, the active release speed can be regulated by the applied reductive voltage. Fig. S11 shows the control of the active release acceleration and speed of a human hair by regulating the reductive voltage. As the reductive voltage increases from 4 to 15 V, the maximum acceleration and speed of the human hair during the active release process exhibit a linear correlation with the applied reductive voltage, increasing from 29.3 to 398.8 m/s2 and 186 (~2325 body lengths/s) to 696 mm/s (~8700 body lengths/s), respectively. When the applied reductive voltage exceeds 15 V, the maximum acceleration and speed of the human hair show a downward trend due to the intense electrolysis effect. Nevertheless, in the extended applications of the LiMU gripper, an appropriate voltage for active release should be selected according to specific application scenarios to achieve a trade-off between operational efficiency and task requirements, such as safety and accuracy.\nSupplementary Figure 11. Active release acceleration and speed of a human hair by regulating the reductive voltage.\nReferences\n39. Wang, X. et al. Beyond surface tension-dominated water surface jumping. Nat. Commun. 16, 3034 (2025).\n40. Tang, D. et al. Bistable soft jumper capable of fast response and high takeoff velocity. Sci. Rob. 9, eadm8484 (2024).\n41. Aubin, C. A. et al. Powerful, soft combustion actuators for insect-scale robots. Science 381, 1212-1217 (2023).\n42. Chen, F. et al. Laser-driven hierarchical “gas-needles” for programmable and high-precision proximity transfer printing of microchips. Sci. Adv. 9, eadk0244 (2023).\n43. Li, A. et al. Drop-printing with dynamic stress release for conformal wrap of bioelectronic interfaces. Science 389, 1127-1132 (2025).\n3. Third, the relevance of the acceleration data presented in Figure 6d is questionable. In microscale manipulation, the critical challenge lies in achieving reliable and controllable grasping and release, particularly in the presence of dominant surface forces. Release speed alone is of limited significance in such regimes. For example, the analogy between the gripper’s release of a feather and the launch of a rocket is unconvincing. These mechanisms operate on fundamentally different physical principles, serve distinct purposes, and exist on vastly different length and force scales.\nWe appreciate the insightful comment. According to the suggestion of the reviewer, we removed confusing descriptions, such as rocket, fighter, animal and human behavior, from the previous Fig. 6d. Meanwhile, we compared the performance of active release speed of the LiMU gripper with the existing high-performance catapult actuators of micro jumping robots in Fig. 6d, as given below:\nPage 19, line 316\nThis acceleration surpasses that of other reported grippers and robots (Fig. 6d, Supplementary Table 2).\nSupplementary Information\nCategory Body length (m) Acceleration (m/s2) Reference\nLight-driven hydrogel actuator 3.5 × 10−2 5.8 × 102 (17)\nBistable soft actuator 1.0 × 10−1 1.0 × 103 (18)\nInflatable soft jumper 3.5 × 10−2 5.8 × 103 (19)\nHopcopter jumper 1.0 × 10−1 2.3 × 102 (20)\nSpringtail-inspired jumper 6.0 × 10−2 1.4 × 103 (21)\nEPN-inspired jumper 1.2 × 10−1 2.6 × 103 (22)\nReferences\n17. Wang, X. et al. Beyond surface tension-dominated water surface jumping. Nat. Commun. 16, 3034 (2025).\n18. Tang, D. et al. Bistable soft jumper capable of fast response and high takeoff velocity. Sci. Rob. 9, eadm8484 (2024).\n19. Gorissen, B., Melancon, D., Vasios, N., Torbati, M. & Bertoldi, K. Inflatable soft jumper inspired by shell snapping. Sci. Rob. 5, eabb1967 (2020).\n20. Hsiao, Y.-H. et al. Hybrid locomotion at the insect scale: Combined flying and jumping for enhanced efficiency and versatility. Sci. Adv. 11, eadu4474 (2025).\n21. Ramirez Serrano, F., Hyun, N.-s. P., Steinhardt, E., Lechère, P.-L. & Wood, R. J. A springtail-inspired multimodal walking-jumping microrobot. Sci. Rob. 10, eadp7854 (2025).\n22. Kumar, S. et al. Reversible kink instability drives ultrafast jumping in nematodes and soft robots. Sci. Rob. 10, eadq3121 (2025)."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have adequately addressed my previous comments. This article is now well suited for publication.", "reviewer_3": "I appreciate the authors’ efforts to explore more practical grasping scenarios for the LIMU gripper and to incorporate the scaling analysis into the revised manuscript. Overall, the quality of the work has improved substantially, and from a technical point of view I do not have major concerns. However, I believe that the way the significance of the soft gripper is described, and the way the data are interpreted, are still below the standard expected for Nature Communications and should be further refined to avoid overclaiming. I also strongly encourage the authors to provide a fair and transparent comparison with existing grippers in the manuscript (e.g., in Fig. 1j and Fig. 6d). Finally, the language throughout should be further polished before this work can be considered for publication. Here are my concerns about the manuscript:\n1. In the abstract, the authors claim that their gripper “exhibits notable advantages over existing robotic grippers in adaptability, multiscale operation, low contact pressure, and fast manipulation speed.” However, the presented data indicate clear scale limitations, especially when handling heavier objects (e.g., >100 g) or objects with large volume-to-weight ratios. The current results suggest that the gripper performs best for relatively small and light objects rather than heavy ones. The abstract should be revised to more accurately reflect these limitations and to avoid overly broad claims.\n2.More data points are needed to complete the Ashby map in Fig. 1i. As it stands, the map appears under-populated and does not support the broader comparative conclusions the authors claimed here.\n3. I am still not fully convinced that achieving a releasing acceleration of 42 g is a key contribution of this work relative to existing grippers. I acknowledge that high acceleration is important for applications such as jumping robots, but for grasping and manipulation tasks, extremely fast release may not be necessary or even desirable. It may be more compelling to emphasize and quantify the tunability of releasing speed and contact pressure, which are indeed challenging to achieve in a controlled manner with many other grippers.\n4. In Fig. 6d, I am not convinced by the choice to normalize acceleration by body length (BL) of the gripper. This metric is commonly used for comparing high-speed locomotion (e.g., jumping, swimming, flying), but its relevance to gripper performance is not clearly justified here. In addition, including jumping robots in the same comparison panel may mix different regimes and be misleading. The authors should either provide a strong justification for this normalization and comparison or consider revising/removing this analysis."}, "author_response": "We thank the reviewer for comments and time spent evaluating the manuscript.\n1. In the abstract, the authors claim that their gripper “exhibits notable advantages over existing robotic grippers in adaptability, multiscale operation, low contact pressure, and fast manipulation speed.” However, the presented data indicate clear scale limitations, especially when handling heavier objects (e.g., >100 g) or objects with large volume-to-weight ratios. The current results suggest that the gripper performs best for relatively small and light objects rather than heavy ones. The abstract should be revised to more accurately reflect these limitations and to avoid overly broad claims.\nWe clarified the upper limit of the LiMU gripper in the abstract, as given below: Page 3, line 32\nThe gripper operates across 14 orders of magnitude in weight (from 10-12 g to 200 g) and achieves a low gripping contact pressure of ~10 Pa for handling delicate items.\n2. More data points are needed to complete the Ashby map in Fig. 1j. As it stands, the map appears under-populated and does not support the broader comparative conclusions the authors claimed here.\nWe thank the reviewer for the comment. We added more data points accordingly in Fig. 1j and updated the references in the revised manuscript, as given below:\nPage 5, line 59\nFig. 1j Comparison of this work and various grippers in terms of gripping scale and response time.\n29. Li, S., Vogt, D. M., Rus, D. & Wood, R. J. Fluid-driven origami-inspired artificial muscles. Proc. Natl. Acad. Sci. U. S. A. 114, 13132-13137 (2017).\n30. Hong, Y. et al. Boundary curvature guided programmable shape-morphing kirigami sheets. Nat. Commun. 13, 530 (2022).\n31. Lyu, B. et al. Humanoid finger with rigid-flexible-soft structure. Nat. Commun. 16, 9905 (2025).\n32. Wu, S. et al. High-Load Shape Memory Microgripper with Embedded Resistive Heating and Magnetic Actuation. Adv. Funct. Mater. 35, 2421798 (2025)..\n33. Kim, J. et al. Shape memory polymer surfaces with controllable roughness for multiscale switchable dry adhesion. Nat. Commun. 16, 4954 (2025).\n34. Liu, F. et al. Stable manipulating objects with unknown surface morphology via integration of magnetic artificial muscle and adhesive structures. Microsyst. Nanoeng. 11, 164 (2025).\n35. Lee, J. Y. et al. Shape-Adaptive Universal Soft Parallel Gripper for Delicate Grasping Using a Stiffness-Variable Composite Structure. IEEE Trans. Ind. Electron. 68, 12441-12451 (2021)..\n36. Eisenhaure, J. & Kim, S. Laser-Driven Shape Memory Effect for Transfer Printing Combining Parallelism with Individual Object Control. Adv. Mater. Technol. 1, 1600098 (2016).\n3. I am still not fully convinced that achieving a releasing acceleration of 42 g is a key contribution of this work relative to existing grippers. I acknowledge that high acceleration is important for applications such as jumping robots, but for grasping and manipulation tasks, extremely fast release may not be necessary or even desirable. It may be more compelling to emphasize and quantify the tunability of releasing speed and contact pressure, which are indeed challenging to achieve in a controlled manner with many other grippers.\nWe thank the reviewer for the comment. Per the reviewers' comments, we revised the abstract by deleting the description of the gripper's active release acceleration reaching 42G, while emphasizing advantages of the LiMU gripper in terms of low contact pressure and tunable releasing speed. See the revised abstract.\nPage 3, line 31\nWe unveil a surface tension induced active release mechanism enabling tunable active release of micro-objects.\nPage 3, line 36\nThe gripper offers notable performance metrics over existing robotic grippers in multiscale operation, low contact pressure, and tunable releasing speed, representing a notable solution for living organisms and microscale objects.\n4. In Fig. 6d, I am not convinced by the choice to normalize acceleration by body length (BL) of the gripper. This metric is commonly used for comparing high-speed locomotion (e.g., jumping, swimming, flying), but its relevance to gripper performance is not clearly justified here. In addition, including jumping robots in the same comparison panel may mix different regimes and be misleading. The authors should either provide a strong justification for this normalization and comparison or consider revising/removing this analysis.\nWe thank the reviewer for the comment. Per the reviewers' comments, we removed the body length statistics in Figs. 6c and 6d and deleted the comparison with jumping robots in Fig. 6d. We also updated Table S2 in the revised Supporting Information.\nPage 18, line 302\nFigs. 6c-d c, Recorded velocity and acceleration of a human hair during active releasing. d, Comparison of the active release max acceleration of the LiMU gripper with other robotic grippers.\nSupporting Information\n13. Ngo, T.-H., Tran, H.-V., Nguyen, T.-A., Dao, T.-P. & Wang, D.-A. Design and kinetostatic modeling of a compliant gripper for grasp and autonomous release of objects. Adv. Robot. 32, 717-735 (2018).\n14. Avci, E. et al. Piezo-actuated parallel mechanism for biological cell release at high speed. Biomed. Microdevices 17, 98 (2015).\n15. Chen, T., Chen, L., Sun, L., Weibin, R. & Qing, Y. in 2010 IEEE/RSJ International Conference on Intelligent Robots and Systems. 6137-6142.\n16. Avci, E. et al. High-Speed Automated Manipulation of Microobjects Using a Two-Fingered Microhand. IEEE Trans. Ind. Electron. 62, 1070-1079 (2015)."}]

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