Janus Nanohybrids Enable Superflash Warming and High‐Affinity Ice Confinement for Cross‐Scale Cryopreservation

Abstract Strong hydration of cryoprotective agents reduces the glass transition temperature of water and suppresses ice formation. However, lethal cooling and warming remain a critical obstacle to cross‐scale cryopreservation of clinical biospecimens. Herein, a snowman‐like Janus nanohybrid composed of magnetic iron tetraoxide and photothermal polypyrrole is reported. Its cranial–corporal asymmetry enables heterogeneous hydration for a record high efficiency of ice confinement, reducing mean ice crystal area by 98.4%. Molecular dynamics simulations reveal that Janus architecture simultaneously enhances interactions with ice and strengthens the local hydration anisotropy, accounting for the effective inhibition of ice growth. Superflash warming over 920 °C min ^‒1 by magnetically rotating its anisotropic structure for uniform heat dissipation narrows the hostile temperature window in micro‐/macroscopic scenarios, as further confirmed by Monte Carlo modeling. This design enables cost‐effective post‐thaw magnetic retrieval, eliminating the need for heavy centrifuges, well‐suited for scalable and on‐site applications. As a result, cryopreserved samples from single cells, bacteria, to porcine trachea retain near‐complete viability and functionality. Therefore, this study offers a promising technique to bridge the gap between microscale cell storage and whole‐organ preservation.