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Chen et al. Soft Sci. 2026, 6, 48 Page 3 of 19

In this work, we propose a magnetic balloon fiberbot (MBF) for catheter-free angioplasty in small arteries by
seamlessly integrating a magnetically bendable tip with a phase-change balloon [Figure 1A]. The magnetic
tip allows for enhanced navigation to the complex small arteries, while the balloon is wirelessly inflated via
low-power microwave heating (e.g., 50 W at a distance of 15 cm) (see Comparison Supplementary Table 1).
The microwave energy is efficiently absorbed by the carbon nanotubes (CNTs) coating and further amplified
by optimizing the embedded nitinol core through an electromagnetic resonance effect. By carefully
controlling the heating power and distance, the temperature of MBF can be quickly raised to 42-50 °C,
enabling effective balloon expansion while limiting excessive heating of surrounding tissue. To ensure
targeted vascular widening, axial pre-stretching of the balloon minimizes undesired axial elongation during
inflation, allowing for primary radial expansion. The performance of the MBF was validated through in vitro
experiments using a 3D cerebrovascular phantom and ex vivo studies with porcine placenta models,
demonstrating effective navigation, controlled balloon expansion, and biocompatibility.

EXPERIMENTAL
Materials
Polydimethylsiloxane (PDMS) (Sylgard 184) was purchased from Dow Corning Co., Ltd. NdFeB particles
(5μm) were commercially obtained from Magnequench Co., Ltd. CNTs were purchased from XFNano Co.,
Ltd. Ecoflex 0030 and mold release agent (Release 200) were purchased from Smooth On Co., Ltd. Novec
7000 and Novec 649 were commercially obtained from 3M Co., Ltd. Hexane and anhydrous ethanol were
purchased from Hushi Co., Ltd. Medical-grade polyvinylidene fluoride (PVDF) heat-shrinkable tubing was
purchased from Zhongxin Co., Ltd. The superelastic nitinol wire (nitinol core) was commercially obtained
from Mingfeng Co., Ltd. The anticoagulated porcine whole blood was purchased from Yuechi Co., Ltd. All
the chemicals were used without further purification.

Preparation for the MBF
Fabrication of magnetic tip
Magnetic tip was fabricated by injecting ferromagnetic composite ink into a mold, followed by curing,
demolding, and magnetizing. Firstly, Part A and Part B of Sylgard 184 were mixed in a ratio of 10:1, placed in
a planetary mixer (ARV-310, Thinky, Japan), and blended at 2,000 rpm for 3 min. Following this, NdFeB
particles were added to the blended Sylgard 184 with different volume ratios, and then blended at 2,000 rpm
for 5 min to obtain the ferromagnetic composite ink. Finally, the obtained ferromagnetic composite ink was
injected into a PTFE tubular mold, with a diameter of 1mm. To create a channel for the nitinol core, a
temporary metal wire was placed in the center of the PTFE tubular mold prior to injection. After curing in
an oven at 60 °C for 2 h, the tubular mold was removed, and the temporary metal wire was extracted, leaving
a central hole. The resulting slender cylindrical rod was placed into a pulse magnetizer for magnetization,
ultimately obtaining the magnetic tip.

Fabrication of the phase-change balloon
The phase-change balloon consists of three integrated components: an inner nitinol core, an outer
functionalized Ecoflex tube serving as the balloon wall, and an enclosed phase-change liquid. In this
configuration, the nitinol core functions as the central structural backbone and also contributes to
microwave-heating enhancement through electromagnetic resonance, while the functionalized Ecoflex tube,
incorporating a CNT layer, serves as the microwave-absorbing and heat-generating balloon wall. The
phase-change liquid sealed inside the tube undergoes liquid-to-gas transition upon heating, thereby driving
balloon expansion. These three components were assembled into an integrated balloon structure as described
below.