Creases gate and steer droplets via elastocapillary repulsion

Creases, localized indentations arising from elastic instabilities at strained soft interfaces, autonomously gate and steer droplets via long-range elastocapillary repulsion. We demonstrate that creases impose a sharp, strain-tunable threshold for droplets: Droplets below a critical radius halt at a finite distance upstream, while larger droplets traverse the crease. Notably, small variations in strain near the creasing instability produce multifold increase in critical drop radius, demonstrating nonlinear mechanical control over gating. For the gated droplets, we reveal two distinct repulsion regimes based on size, each characterized by different force-distance scaling laws. A combination of experiments and modeling uncovers the physical origin of this size-dependent repulsion landscape, with larger droplets responding to variations in substrate slope while smaller droplets sense curvature gradients. Exploiting these features, we realize passive and active drop filtration based on droplet size and surface tension, and demonstrate programmable operations including path guidance, angular hysteretic memory, drop pulse modulation, and both sequential and combinational logic gating units-all controlled by reversible substrate deformation. These results position creases as multimodal regulators of droplet transport, bridging the physics of elastic instabilities with reconfigurable fluidic systems.