Cracking-directed dynamic liquid bridging for autonomous microdroplet recession and enrichment

Abstract

The precise control and manipulation of microdroplets (diameter < 20 µm) on solid substrates holds critical importance across diverse applications, such as environmental air quality assessment, targeted pharmaceutical delivery, clinical diagnostics, and public health initiatives. A key challenge in this field is contact angle hysteresis, caused by interfacial adhesion and frictional forces, which pin droplets and impede their mobility. To overcome this, we introduced a crack-mediated capillary bridging strategy that enables the efficient capture and directional transport of microdroplets. This approach utilizes a stretchable elastomeric substrate engineered with precision to incorporate island-like microstructures. Upon application of longitudinal tensile stress, the substrate undergoes controlled fracture, yielding densely packed, directionally oriented surface cracks. These fissures induce localized capillary forces of significant magnitude, effectively counteracting adhesion-induced resistance and facilitating programmable droplet motion. To validate the practical utility of this platform, experiments were conducted to capture airborne pathogenic agents, demonstrating a 14.2-fold enhancement in enrichment efficiency relative to conventional flat surfaces. These findings highlight the versatility of the proposed mechanism, offering promising avenues for advancing technologies in biosensing, pollutant analysis, and related interdisciplinary fields. The integration of fracture mechanics with capillary-driven fluid dynamics presented herein establishes a foundational framework for next-generation microfluidic systems.