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Many biological materials in nature are in fact complex composites,which involve not only solid phases(e.g.,plant tissues)but also the liquid phase,particularly the water.And it is noteworthy that in these biological materials,the liquid phase is essential to their optimal global mechanical performance and plays critical roles in their functionalities,such as the ability to change their shape in response to external stimuli(e.g.,environmental humidity).Inspired by the nature,water-responsive actuation has been reported for the soft synthetic materials including gels and polymers,but not for rigid materials such as the metals.Here we report that,by "mixing" gold and water together at nanoscale,a new nanocomposite can be obtained which offers tunable strength and shape-changing capability.The new nanocomposite was prepared by infiltrating the nanoporous gold(npg)with water,where the npg samples are macroscopic materials and are prepared by a corrosion process called dealloying.We found that by controlling the water-content in this nanocomposite,the material's compression strength can be tuned recoverably by as large as 23 MPa,which exceeds 50%of the strength of dry npg sample.And using similar procedure,the material's dimension can be changed elastically up to 1.26%(volume strain: 3.7%).Furthermore,the reversible bending can be achieved in gold/npg bilayer foils,with tip displacement reaching 20 mm,in response to cyclic water-filling and partial drying.Both strength-tuning and shape-changing effects originate from the large stress of water-capillarity in nanoscale pore channels.Compared to previous electrochemical methods that can tune the strength [1] and change the shape of npg [2,3] as well,current approach is obviously easier to operate,more energy-efficient and eco-friendly.The new metal-water nanocomposites may act as "artificial muscle" in future to propel the micro-robots by harvesting the energy from environment.