Biomimetic locomotion on water of a porous natural polymeric composite

Observation of the natural world can provide invaluable information on the mechanisms that semiaquatic living organisms or bacteria use for their self-propulsion. Microvelia, for example, uses wax excreted from its legs to move on water in order to escape from predators or reach the bank of the river. Mimicking such mechanism, few self-propelled materials on water, as camphor, have been previously developed, but weak points like slow locomotion, short movement duration or shape-restrictions still need to be improved. Herein we present a totally green self-assembled porous system, formed by the combination of a natural polymer with an essential oil, that spontaneously moves on water for hours upon expulsion of the oil, with high velocities reaching 15 cm/s. The structural characteristics of the natural polymeric composite are carefully analyzed and associated to its spontaneous movement. Surface tension change experiments are also presented that connect the essential oil release with the locomotion of the porous composite films. This research work opens novel routes towards bio-inspired natural materials that can be used for mimicking and studying the motion of bio-organisms and microorganisms, and for applications such as energy harvesting, aquatic pollution monitoring, drug delivery, to name few.