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Ren et al. Soft Sci. 2026, 6, 6 Page 21 of 33

Hybrid actuation
Multi-stimulus strategies are increasingly adopted in 4D-printed soft microrobots because a single stimulus
rarely satisfies the full set of requirements for navigation, reconfiguration, and task execution simultaneously.
A common and practical design paradigm is to decouple functions across stimuli - for example, using
magnetic fields for continuous, untethered positioning and steering - while leveraging a second stimulus,
such as chemical cues or temperature, to trigger localized shape morphing, gripping, or on-demand release.
A representative chemical magnetic example was reported by Xin et al., who fabricated pH-responsive,
shape-morphing microrobots by laser printing, where magnetic propulsion guided the robot to the target
region and a mild pH environment triggered programmed opening or closing for cargo handling and drug
release . Similarly, Hu et al. demonstrated a thermos-magnetic hybrid soft robot enabled by 4D printing, in
[136]
which temperature-dependent material response was combined with magnetic actuation to achieve
multimodal reconfiguration and motion . Despite these advantages, multi-stimulus systems also introduce
[137]
specific challenges, including stimulus cross-talk and calibration complexity, increased material and printing
burden for multi-functional integration, and safety constraints such as thermal management or chemical
compatibility in biomedical settings. Therefore, achieving robust multi-stimulus synergy typically requires
careful stimulus selection with sufficient orthogonality, as well as systematic characterization and control
strategies that remain reliable across realistic environments.

APPLICATIONS
The 4D printing technology transforms stimulus-responsive materials into microrobots capable of altering
their shape, stiffness, and functionality on demand, making it a highly promising manufacturing technique.
Previous review articles have demonstrated the significant application potential of 4D-printed soft
microrobots across biomedical, defense, and electronic fields [9,138] . This section focuses on showcasing the
latest representative application advancements, including targeted drug delivery, tissue engineering, stent,
sensing, and other applications.

Targeted drug delivery
The 4D-printed soft microrobots offer a compelling pathway for targeted drug delivery [139] . By coupling
stimuli-responsive architectures with shape-morphing mechanics, these devices can be deployed invasively,
and then expand, clamp, or conform to local physiological structures to resist flushing and anchor in
dynamic environments such as the stomach, bladder, airways, or vasculature. Activation and release can be
driven by clinically compatible cues, including magnetic fields, ultrasound, light, temperature, pH, or
enzyme activity, enabling the targeted delivery of small molecules and biologics.

Xin et al. developed environmentally adaptive shape morphing microrobots by programming differential
expansion in pH-responsive hydrogels . Propelled magnetically, a crab-like microrobot performed targeted
[136]
microparticle gripping, transport, and release, while a fish-like microrobot encapsulated doxorubicin at pH
~7.4 and released it in mildly acidic media to treat HeLa cells in a model vascular network [Figure 8A].
Building toward gastric resident delivery, Bellinger et al. designed a swallowable capsule that deployed a star-
shaped drug carrier in the stomach . The carrier unfolded to maintain residence and delivered antimalarial
[140]
doses for weeks before disassembly, thereby addressing compliance issue in treatment barriers [Figure 8B].
Extending organ retention to the gastrointestinal tract, Ghosh et al. created parasite-inspired
mechanochemical theragrippers capable of autonomously latching onto mucosa for about twenty-four
hours, extending the elimination half-life of ketorolac tromethamine by roughly sixfold [141] . This
demonstrated that shape-changing microdevices can prolong drug delivery [Figure 8C].

Tissue engineering
Tissue engineering aims to develop alternative tissues for regenerating and healing damaged tissues . The
[142]
4D-printed soft microrobots integrate biocompatible, stimulus-responsive architectures with living cells to