Biomimetic Locomotion on Water of a Porous Natural Polymeric Composite

Abstract

Observation of the natural world can provide invaluable information on the mechanisms that semi‐aquatic 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. This study presents 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−1. The structural characteristics of the natural polymeric composite are carefully analyzed and associated to its spontaneous movement. Surface tension experiments are also presented that connect the essential oil release with the locomotion of the porous composite films. This research work opens novel routes toward bioinspired natural materials that can be used for mimicking and studying the motion of bioorganisms and microorganisms, and for applications such as energy harvesting, aquatic pollution monitoring, drug delivery, to name few.

Hydrodynamic Signatures of Stationary Marangoni-Driven Surfactant Transport

“…Our result is quite robust, as we demonstrated for two surfactants varying in their CMC values by factor 100, and can be used with other surfactants. We used these signatures to determine that CA released from a gel tablet spreads in an adsorbed phase, a result that bears upon Marangoni-driven self-assembly [27][28][29][30][31][32] and propulsion [33][34][35][36]. Assumptions about surfactant dynamics, such as made in Ref.…”

Metal–Organic Framework “Swimmers” with Energy-Efficient Autonomous Motility

“…Beyond gels, polymer capsules from Pumera’s laboratory have been shown , to move with velocities up to 150 mm·s –1 ( v max = 8.96 mm –2 ·s –1 ), though without directional control. Recently, disks (7 mm in radius, 0.055 mm thick) of cellulose acetate imbibed with peppermint oil were shown to move on water with velocities up to 150 mm·s –1 and v max = 17.73 mm –2 ·s –1 . For these particles, the content of the peppermint oil fuel was also measured (6.7 mg in a 10 mg particle), allowing for the estimation of ε K,max ∼ 0.023 μJ·g –1 , that is, significantly lower than that for our MOFs or for several gel systems.…”

“…The ability to self-propelseen in animals, individual cells, and micro-organismshas inspired the design of a wide range of artificial systems capable of autonomous locomotion. Examples include droplets (sometimes tactic − ) driven by interfacial reactions, segmented nanorods , powered by the catalytic decomposition of H 2 O 2 , micromotors fueled by catalytic reactions, − light, , electric, , and magnetic , fields, polymer capsules, , exfoliating particles, as well as numerous forms of the so-called camphor boats based on gels − or polymers . In particular, camphor boats spread surface-active chemicals onto the interface at which they rest, thus establishing surface tension gradients, which, in turn, set up convective Marangoni flows in the surrounding fluid. − These flows then power the boats to perform different types of motion (continuous, oscillatory, or intermittent , ) and, if many boats are present, can drive formation of dynamic structures, including open-lattice arrays or swarms in which smaller particles assemble behind and follow larger “leaders” .…”

Multifunctional and biodegradable self-propelled protein motors

“…However, self-propelled motor systems have significant limitations that constrain their overall performance: low efficiency (i.e., high volume of fuel is required for sustained locomotion), short mobility lifetime (due to a finite amount of fuel), lack of locomotion direction control (i.e., random non-directional locomotion), and difficult miniaturization (size is limited by fuel storage capacity and fuel-friendly fabrication processes) 13 . Despite recent research on highly absorbent materials for improved fuel storage, such as polymer hydrogels 12,14,15 and metal-organic frameworks 16–18 , most self-propelled surface motors in the literature are non-functional, with low efficiency, low to moderate mobility lifetime and speeds, and uncontrolled random locomotion 7,13 . Furthermore, the materials of the motor, the fuel, and/or the swimming media might be toxic to physical and biological environments, posing biocompatibility, biodegradability, and sustainability challenges that need to be addressed to expand the applications of such motor systems to real world scenarios.…”