Materials that adapt dynamically to environmental changes are generally limited to two-state switching of single properties, and only a small number of strategies that may lead to materials with continuously adjustable characteristics have been reported. Dynamic fluid surfaces are a ubiquitous component of natural adaptive systems, from tear films on eyes to the mucous lining of lung and stomach, to the light-adaptive skeletons of brittle stars and the responsive skin of cephalopods. The fluid's ability to flow and configure itself around a variety of surfaces provides unique responsive mechanisms not possible with solid materials alone, yet synthetic adaptive materials design rarely goes beyond soft solids in the search for malleable surfaces. 

Inspired by these fluid surfaces, we have developed a new type of adaptive material. The material is made of a liquid film supported by a nanoporous elastic substrate. Such nanoporous networks ensure the retention of the lubricating liquid, which can flow and redistribute in response to external stimuli. As the substrate deforms, the liquid flows within the pores, causing the smooth and defect-free liquid surface to roughen through a continuous range of topographies. The substrate's elasticity makes these changes reversible. We show that a graded mechanical stimulus can be directly translated into finely tuned, dynamic adjustments of wettability and optical transparency. By stretching and relaxing the material, we reversibly stop and start droplets of water or oil sliding down the surface. The stimulus sensitivity for different types of droplets can be tuned by changing the amount of liquid infused in the porous network. Moreover, highly precise and reversible optical fine-tuning can be obtained with the same material.