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Figure 5B and C, we found that the surface temperature of the hydrogel can reach 60 °C, which is higher
than the critical solution temperature (LCST) of 37 °C of PNIPAM. As a result, the PNIPAM layer will
dehydrate and shrink and thus induce the bending motion [Figure 5B]. Finally, the two arms of the actuator
will touch with each other and form a closed loop at 80 s. Besides, the recovery behavior of the actuator in
alkaline solutions is shown in Figure 5D. Both PNIPAM and PDMAEMA have a high swelling rate at low
-
temperatures, but the LCST of PDMAEMA decreases at higher pH values, i.e., with increasing OH
concentrations, PDMAEMA shows a lower swelling while the PNIPAM layer does not have a pH response.
Therefore, in a low-temperature alkaline environment, the swelling performance of the PNIPMA layer is
more remarkable than that of the PDMAEMA layer, which can promote a faster recovery of the bilayer
hydrogel to its original shape. For our actuator, the bilayer hydrogel takes about 300 s to recover to its
starting state. In Figure 5E, we fabricated a four-arm gripper that can be actuated to bend towards the
PNIPMA side under the alternating magnetic field for 115 s. The actuator can catch a 3 g bottle cap.
[40]
Compared with the reported hydrogel actuators actuated by the direct current , our LME composite-based
hydrogel actuators can be controlled wirelessly by the applied electromagnetic field in an untethered
manner.

CONCLUSION
In this work, we proposed a simple yet efficient method of magnetic aggregation to fabricate initially
conductive LME with high stretchability, conductance stability, printability, and magnetic responsiveness.
This method allows the LM ferrofluid microparticles to be aggregated to form conductive networks in the
bottom of the elastomer. Compared to the traditional preparation methods for conductive LME composites,
our method does not require any post-sintering step that simplifies the preparation process. In addition, this
method also reduces the consumption of LM, which benefits the creation of lightweight and low-cost
stretchable LM conductors. We also demonstrated the applications of the initially conductive LME
composite in high-resolution circuits, magnetically controllable switches, and thermally responsive soft
hydrogel actuators. We believe these stretchable LME conductors may find wide applications in stretchable
electronic devices, soft robotics, and intelligent human-machine interactions.

DECLARATIONS
Authors’ contributions
Data curation, formal analysis, investigation, methodology, writing original draft: Peng M, Li G, Ma B, Liu
Y, Zhang Y
Conceptualization: Yan S, Ma X
Methodology: Peng M, Li G, Ma B, Liu Y, Zhang Y
Visualization: Peng M, Ma B, Li G
Data analysis: Peng M, Li G, Ma B, Liu Y
Data curation, formal analysis, and supervision: Peng M, Li G, Ma B
Conceptualization, funding acquisition, project administration, resources, supervision and writing, review
and editing: Yan S, Ma X

Availability of data and materials
Not applicable.

Financial support and sponsorship
Yan S thanks for the financial support from the Guangdong Basic and Applied Basic Research Foundation
(2021A1515110277 and 2021QN02Y387) and the Shenzhen Natural Science Fund (20200811205344001).