Development of Smart Fractal Nanostructure for Promoting Heterogeneous Ice Nucleation

Our development of smart fractal ice nano-nucleators (SF-INNs) leverages their structural advantages, which inherently maximizes the number of active sites for heterogeneous ice nucleation. Owing to their radially attached nanocrystalline structure, SF-INNs expose an extensive array of grain boundaries. The rapid precipitation and subsequent radial attachments of nanocrystallites promote the exposure of facets with high Miller indices, intrinsically strained, five-fold twinned nanocrystals, and increasing point defects due to kinetically-limited precipitation. This unique fractal structure culminates in the elevating of freezing temperature compared to Euclidean-shaped ice nucleators. Additionally, the branched fractal structure of SF-INNs facilitates heterogenic ice formation within its nanoconfined region, leading to the production of numerous self-similar small fractal fragments. This fragmentation is primarily driven by nanoconfinement-induced delayed ice nucleation, similar to frost heaving. The shear stress can be easily relieved through grain boundary sliding within the radially stacked SF-INN, making itself prone to cryo-responsive fragmentation. Such cold-responsive attributes significantly enhance ice nucleating activity, presenting a powerful strategy to increase the efficacy of cryotherapy by enhancing cellular ice formation and in vivo tumor coverage. This research marks a paradigmatic leap in utilizing fractal nanoparticles for ice nano-nucleators.