Nanoparticle-Mediated Bubble Suppression During Droplet Solidification for Mechanical Reinforcement.

Droplet-based 3D printing can fabricate complex structures, but quantitative regulation over droplet solidification and the mechanical performance of printed components remains essential for its load-bearing and multi-functional applications. Leveraging the intrinsic transparency of ice, we innovatively propose a nanoparticle-mediated strategy to suppress trapped air bubbles during water droplet solidification and thereby reinforce the mechanical performance of printed components. We develop a unified influencing factor to integrate the effects of nanoparticle concentration, diameter, and type on droplet nucleation and freezing characteristics. We uncover that the addition of nanoparticles raises nucleation temperature, refines ice dendrites, reduces freezing rate, and ultimately diminishes trapped air bubbles. These effects enable mechanical reinforcement of components and quantitative regulation of their compressive strength. The bubble volume fraction is reduced by ∼35% while the compressive strength is increased by up to 39%, exceeding the reported average values by more than two times. The low-cost strategy requires no external physical fields and introduces negligible changes to the hydrodynamic properties of raw printing materials. These findings elucidate the physical mechanisms governing nanoparticle-mediated bubble suppression during droplet solidification and further provide a viable pathway for the controllable fabrication of high-performance composite printing materials.