A fast opening on the bench
Researchers tested a capsule that combines a soft, monostable cover, a payload-carrying PLA base and a magnetothermally triggered phase-change hydrogel layer for microrobot delivery and release. On a printed platform, the capsule opened within 50 milliseconds after the hydrogel softened. The fitted initial ejection velocity was 1.017 metres per second, estimated from the translational motion of the PLA base.
The system demonstrations used NdFeB magnetic elastomer pieces as representative microrobots, included upright capsule configurations and extended to ex vivo porcine stomach tissue. In this setting, ex vivo means tissue tested outside a living body. The design was evaluated as a way to hold a payload during delivery, then release it for magnetic deployment.
Heating the latch
The baseline latch, called GC-Fe3O4, contained 20% (w/v) gelatin, 1% (w/v) carrageenan and 15% (w/v) Fe3O4 nanoparticles. The particles were heated by an alternating magnetic field, or AMF, while the hydrogel's temperature and mechanical response were measured.
At 37 °C, the gel retained approximately 1 kPa of storage modulus, a measure of how it responded to deformation in the test. After 60 seconds of AMF exposure, samples starting at 21 °C reached 30.8 to 41.4 °C, depending on concentration. Silicone-oil-coated hydrogels reached 41.1 to 56.1 °C.
The reported work-to-rupture measure, which indicates how much mechanical work the material took before breaking, was 0.034 mJ/mm3 for GC-Fe3O4, compared with 0.025 mJ/mm3 for G-Fe3O4 and 0.0037 mJ/mm3 for pure gelatin. The capsule used a 1 mm-thick GC-Fe3O4 layer.
Tuning the cover for release
High-speed tracking measured an average recovery speed of 1.21 m/s for the monostable, or single-state, cover, which detached from the base within 100 milliseconds. A bistable cover remained locked after inversion.
Mechanical characterization used tensile testing and 180-degree peel testing. The researchers also used a two-dimensional axisymmetric Abaqus finite-element computer model with the modified Riks method to assess cover stability.
The resulting stability map set boundaries for cover thickness, height and half-span, as well as the dimensions of the bonding section. In the design comparison, Design 1 had a strain-energy density more than one order of magnitude higher than the other configurations. Design 3 exceeded the rupture threshold when bonder thickness passed 0.9 mm.
The selected cover used a 5 mm half-span, a 2.6 mm height, a 1.5 mm thickness, a 3.5 mm bonder length and a 0.8 mm bonder thickness.
From platform to stomach tissue
In the same platform demonstration, target delivery took approximately 70 seconds, while the local temperature increased from approximately 20 °C to 41 °C. The opening itself occurred within 50 milliseconds after hydrogel softening.
On ex vivo porcine stomach tissue, the capsule remained closed during magnetic repositioning. Its estimated initial ejection velocity was approximately 0.486 m/s and reached 0.852 m/s before subsequent deceleration. The released microrobots remained magnetically controllable.
Where the evidence stops
The capsule has not yet been shown to deliver microrobots inside a living body. The authors identify long-term safety, deployment under normal gastrointestinal conditions and prolonged latch stability during gastric or intestinal exposure as unresolved.
The speed figures also need to be read as estimates. On the platform, the velocity was inferred from translational motion of the PLA base, and the tissue demonstration likewise reported estimated values.
Disclosures and data
The work reports support from Chinese national, provincial and 111 Project funding bodies. Four named authors report a patent application covering the capsule technology. The custom finite-element simulation code is available from the corresponding authors upon reasonable request, and other supporting data are stated to be available in the paper and supporting information.
Paper data and sources
Original title: A Bioinspired Magnetothermally Triggered Capsule for Rapid Microrobot Release
Authors: Mengfan Zhang, Zike Chen, Zhihao Lv et al.
Journal/Repository: arXiv
Status: Preprint, not yet peer-reviewed
First online: 2026-09-29
DOI: Not available
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