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Chen et al. Soft Sci. 2026, 6, 48 Page 15 of 19

tests using L-929 fibroblast cells exposed to the MBF’s 100% sample extract, as well as diluted concentrations
(25%, 50%, and 75%) are first performed. As shown in Supplementary Figure 14, the cells maintained over
90% viability across all extract concentrations, with no obvious differences compared to the negative control
group. In contrast, the positive control group exhibited substantial cell damage, confirming the cytotoxicity
of harmful substances. These results demonstrate that the MBF possesses excellent biocompatibility, making
it suitable for vascular systems.

To validate the MBF’s angioplasty capability in a biologically relevant environment, we utilized a porcine
placenta model for ex vivo testing. The porcine placenta is well-recognized for its vascular anatomy, which
closely resembles the small arteries of the human brain, making it an ideal model for such demonstrations .
[55]
At 00:08, the MBF was steered by a repulsive magnetic field, achieving a 75° counterclockwise deflection to
enter a 2 mm diameter vessel branch. After withdrawing from this branch at 00:31, the MBF was directed by
an attractive magnetic field, producing a 15° clockwise deflection into a narrower branch with a diameter of
1.1 mm. Upon withdrawal from this branch at 00:38, the MBF was repulsed again, with a 15°
counterclockwise deflection, successfully entering a 1.8 mm diameter vessel branch [Figure 5B and
Supplementary Video 4]. Finally, the MBF’s phase-change balloon was activated via microwave heating to
perform angioplasty within the porcine placenta’s vessels. As shown in Figure 5C and Supplementary Video
5, the balloon expanded radially and widened the vascular lumen, demonstrating the feasibility of
microwave-triggered balloon expansion in small and tortuous vascular pathways.

DISCUSSION
This study presents a MBF for catheter-free angioplasty in small and tortuous arteries by integrating a
magnetically deflectable tip with a phase-change balloon in a single platform. The current results from in
vitro evaluation using a 3D cerebrovascular phantom, ex vivo validation in porcine placenta models, and
biocompatibility tests support the feasibility of this design in the present study. By combining vascular
navigation and balloon expansion within one device, the MBF provides a potential approach to address the
limited navigation and delivery capability of conventional guidewire-catheter systems in narrow and
complex vascular pathways.

At the same time, the present study is based on in vitro and ex vivo validation, whereas in vivo environments
involve additional physiological factors such as blood flow, pulsatile pressure, vascular compliance, and
dynamic device-tissue interactions. These factors will be important considerations in the next stage of
evaluation. For the microwave-heating mechanism, although an empirical resonance-related optimum of the
nitinol core was identified in the current setup, its behavior under more realistic tissue-loaded and
physiological dielectric conditions still requires further investigation. Future work will therefore extend the
evaluation to flow-enabled and pulsatile vascular platforms, followed by in vivo studies, to further assess
thermal safety, including tissue viability, vascular-wall injury, local fluid temperature, and
coagulation-related responses, as well as navigation stability and angioplasty performance under
physiological conditions. More detailed electromagnetic characterization, including SAR-related analysis,
will also be pursued to better quantify microwave energy deposition. In this process, additional
safety-oriented control strategies, such as real-time temperature monitoring and automatic microwave
shutoff near the upper limit of the actuation window, will also be explored to further reduce the risk of
overheating. In parallel, the present sealed phase-change design and passive-cooling-based deflation
mechanism can be further improved by enhancing balloon integrity, minimizing leakage risk, and
integrating active deflation strategies - such as pressure-triggered microchannels - to improve procedural
efficiency. The integration of real-time imaging and advanced electromagnetic navigation may also further
enhance device controllability and treatment guidance [56,57] .