Magnetic-Nanorod-Mediated Nanowarming with Uniform\nand Rate-Regulated Heating

Rewarming\ncryopreserved samples requires fast heating to avoid\ndevitrification, a challenge previously attempted by magnetic nanoparticle-mediated\nhyperthermia. Here, we introduce Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub> nanorods as the heating elements to manipulate the heating\nprofile to ensure safe rewarming and address the issue of uneven heating\ndue to inhomogeneous particle distribution. The magnetic anisotropy\nof the nanorods allows their prealignment in the cryoprotective agent\n(CPA) during cooling and promotes subsequent rapid rewarming in an\nalternating magnetic field with the same orientation to prevent devitrification.\nMore importantly, applying an orthogonal static magnetic field at\na later stage could decelerate heating, effectively mitigating local\noverheating and reducing CPA toxicity. Furthermore, this orientational\nconfiguration offers more substantial heating deceleration in areas\nof initially higher heating rates, therefore reducing temperature\nvariations across the sample. The efficacy of this method in regulating\nheating rate and improving rewarming uniformity has been validated\nusing both gel and porcine artery models.