Rapid, Targeted Magnetic Hyperthermia with Auxiliarily‑Guided γ‑Fe₂O₃/Polyurethane Electrospun Fibers

Abstract

We present a facial electrospinning technique that precisely deposits magnetic polyurethane (PU) nanofibers decorated with superparamagnetic γ‑Fe₂O₃ nanoparticles. A conical aluminum auxiliary electrode extends the jet‑stabilization zone, enabling four‑fold control over deposition area. The resulting composite membranes reach 43 °C within 70 s under a 12.5 Oe, 153 kHz alternating magnetic field (AMF), outperforming membranes fabricated without the auxiliary electrode. This method offers a manipulable route for producing magnetic fibers and localized magnetic hyperthermia suitable for cancer therapy.

Background

Magnetic hyperthermia exploits the heat generated by superparamagnetic nanoparticles in an AMF, selectively raising tumor temperatures to 41–45 °C without harming healthy tissue. Traditional systemic delivery of iron oxide nanoparticles suffers from rapid clearance and poor tumor accumulation, limiting therapeutic efficacy. Embedding γ‑Fe₂O₃ nanoparticles within electrospun fibers addresses these issues by localizing the heating source and ensuring intimate contact with tumor tissue.

Conventional electrospinning mixes pre‑synthesized nanoparticles into polymer solutions, but yields membranes that are difficult to apply uniformly to irregular tumor surfaces and may detach during treatment. In situ electrospinning—depositing fibers directly onto target tissues—circumvents these limitations. Prior work has used airflow or magnetic fields to guide deposition, yet these approaches add complexity or only affect magnetic polymers. Introducing a conical auxiliary electrode provides a simple, universal means to refine deposition geometry while preserving fiber integrity.

Methods

Materials

γ‑Fe₂O₃ nanoparticles (10 nm, 99.5 % purity, Shanghai Macklin Biochemical Co.) and high‑molecular‑weight polyurethane (WHT‑8170, Yantai Wanhua Polyurethanes) were dissolved in N,N‑dimethylformamide (DMF, 99.5 %) without further purification.

Preparation of γ‑Fe₂O₃/PU Composite Fibers

Nanoparticles were dispersed in DMF by 4 h ultrasonication, followed by mixing with a PU/DMF solution (1.8 g PU in 7.5 g DMF). The blend was stirred vigorously for 30 min, then sonicated for 24 h at 50 °C before electrospinning.

Electrospinning Setup

A handheld gun‑shaped spinner incorporated a 4 cm diameter conical auxiliary electrode beneath the needle tip (0.7 mm ID). The 5 mL syringe pumped the solution at 33 µL min⁻¹ while a voltage of 10–15 kV was applied over a 10 cm tip‑collector distance. The collector could be aluminum foil, skin, or tumor tissue. Fibrous membranes were collected for 5, 10, 15, and 20 min, yielding samples labeled γ‑Fe₂O₃/PU‑A5, –A10, –A15, and –A20. Control membranes were fabricated identically but without the auxiliary electrode, labeled γ‑Fe₂O₃/PU‑5, –10, –15, and –20.

Characterization

SEM (Hitachi TM‑1000) revealed fiber morphology; TEM (JEM‑200EX) assessed nanoparticle dispersion; XRD (Rigaku RINT2000) identified crystalline phases; FTIR (Thermo Nicolet iN10) confirmed chemical structure; TGA (10 °C min⁻¹, N₂ atmosphere) evaluated thermal stability; VSM (Quantum Design) measured magnetic properties. Magnetic heating was assessed by placing cylindrical membranes in a 30 mm copper coil (12.5 Oe, 153 kHz) and recording temperature with an infrared detector.

Results and Discussion

Precise Deposition via Auxiliary Electrode

With the electrode, the jet‑stabilization zone extended to 4 cm versus 0.96 cm without it, reducing deposition diameter from 4.6 cm to 1.8 cm. This confinement allows rapid, localized fiber deposition and significantly thicker membranes (four‑fold increase after 30 min) compared to conventional spinning.

Morphology and Composition

SEM images show bead‑free, porous fibers with mean diameters of 1.39 µm (without electrode) and 1.67 µm (with electrode). Embedding γ‑Fe₂O₃ slightly reduced diameter to 0.85 µm and increased surface roughness, while the auxiliary electrode introduced modest surface irregularities due to limited solvent evaporation.

TEM confirmed uniform dispersion of 10 nm nanoparticles, largely encapsulated within fibers—critical for preventing leaching during hyperthermia. XRD patterns displayed broad PU peaks and characteristic γ‑Fe₂O₃ reflections (220, 311, 400, 511, 440). FTIR spectra revealed no new bonds, indicating physical mixing. VSM curves displayed superparamagnetic behavior: γ‑Fe₂O₃ nanoparticles (58.3 emu g⁻¹ at 15 kOe) versus composites (≈10 emu g⁻¹). TGA showed composite onset decomposition at ~260 °C, suitable for AMF application; residual weight indicated ~19–20 wt % nanoparticle loading.

Magnetic Hyperthermia Performance

Under AMF, membranes with the auxiliary electrode achieved higher temperature rises and faster heating rates. For a 15 min–spun membrane, the equilibrium temperature reached 44.3 °C at 0.42 °C s⁻¹, compared to 24.4 °C (0.24 °C s⁻¹) for the non‑electrode counterpart. Cyclic heating tests over three AMF cycles showed stable temperature profiles, demonstrating robust repeatability.

In Situ Application

Using the portable spinner, magnetic fibers were deposited onto a human hand surface, covering a scar with a seamless, skin‑like membrane while sparing surrounding tissue—illustrating the method’s precision and versatility for clinical scenarios.

Conclusions

Integrating a conical auxiliary electrode into a handheld electrospinning system enables rapid, precise deposition of γ‑Fe₂O₃/PU composite membranes with superior magnetic heating efficiency and cyclic stability. This technique offers a practical platform for localized magnetic hyperthermia in cancer therapy, potentially enhancing synergistic effects with chemotherapy, radiotherapy, or immunotherapy.

Abbreviations

• AMF – Alternating magnetic field
• DMF – N,N‑Dimethylformamide
• FTIR – Fourier transform infrared spectroscopy
• INOPs – Iron oxide nanoparticles
• MES – Magnetic electrospinning
• PU – Polyurethane
• SEM – Scanning electron microscopy
• TEM – Transmission electron microscopy
• TGA – Thermogravimetric analysis
• VSM – Vibration sample magnetometer
• XRD – X‑ray powder diffraction