Magnetic-Nanorod-Mediated Nanowarming with Uniform and Rate-Regulated Heating

Rewarming cryopreserved samples requires fast heating to avoid devitrification, a challenge previously attempted by magnetic nanoparticle-mediated hyperthermia. Here, we introduce Fe₃O₄@SiO₂ nanorods as the heating elements to manipulate the heating profile to ensure safe rewarming and address the issue of uneven heating due to inhomogeneous particle distribution. The magnetic anisotropy of the nanorods allows their prealignment in the cryoprotective agent (CPA) during cooling and promotes subsequent rapid rewarming in an alternating magnetic field with the same orientation to prevent devitrification. More importantly, applying an orthogonal static magnetic field at a later stage could decelerate heating, effectively mitigating local overheating and reducing CPA toxicity. Furthermore, this orientational configuration offers more substantial heating deceleration in areas of initially higher heating rates, therefore reducing temperature variations across the sample. The efficacy of this method in regulating heating rate and improving rewarming uniformity has been validated using both gel and porcine artery models.