Pen-drawn Marangoni swimmer

Abstract

Pen-drawing is an intuitive, convenient, and creative fabrication method for delivering emergent and adaptive design to real devices. To demonstrate the application of pen-drawing to robot construction, we developed pen-drawn Marangoni swimmers that perform complex programmed tasks using a simple and accessible manufacturing process. By simply drawing on substrates using ink-based Marangoni fuel, the swimmers demonstrate advanced robotic motions such as polygon and star-shaped trajectories, and navigate through maze. The versatility of pen-drawing allows the integration of the swimmers with time-varying substrates, enabling multi-step motion tasks such as cargo delivery and return to the original place. We believe that our pen-based approach will significantly expand the potential applications of miniaturized swimming robots and provide new opportunities for simple robotic implementations.

Fig. 1. Overview of pen-drawn Marangoni swimmers.

a Fabrication of pen-drawn Marangoni swimmers. The motion trajectory of the swimmers is determined according to the drawing pattern and concentration of the camphor ink. Different concentrations of camphor inks can be used together for programming a complex motion. b Complex motion trajectory programmed by a combination of different functional modules. c Versatile applicability of pen-drawn Marangoni swimmers on diverse substrates. The pen-based approach enables patterning of camphor engines on a 3D structure. d Multistep motion programming by integrating a time-varying substrate. The folded paper is gradually unfolded when it is placed on the water surface. A camphor engine drawn on the folded region is activated when it touches the water surface. Scale bars: 1 µm (a) and 5 cm (b–d). SEM scanning electron microscopy, PVB polyvinyl butyral.

Fig. 2. Controllable motion of pen-drawn Marangoni swimmers.

a–c Speed of swimmer according to the drawing pattern. a Drawing pattern of camphor engine. b Speed of swimmers for different drawing patterns. c Average speed of swimmers between 10 s and 20 s (n = 3). d Speed of swimmers under different camphor concentrations. The same drawing pattern (iii) was used in this experiment (n = 3). Error bars represent standard deviation (SD). e Different motion trajectories according to the camphor engine arrangement and estimated motion trajectories simulated by FEA. Color bars represent the normalized speed based on the highest speed (red) and zero-speed (blue) in each simulation. f Motion programming using different concentrations of camphor inks. Scale bars: 1 cm (e) and 5 cm (f).

Fig. 3. Complex motion programming by combining different functional modules.

a Programming of a star-shaped trajectory. Unstable equilibrium resulting from symmetric camphor engines creates an oscillation motion. The oscillation module and rotation module are combined to realize a swimmer with a star-shaped trajectory. b Programming of a polygonal trajectory. Opposing camphor engines with different concentrations create an intermittent movement (see also Supplementary Fig. 2). A combination of intermittent movement module and rotation module results in a polygonal (square) trajectory. Scale bars: 1 cm (black) and 5 cm (blue).

Fig. 4. Practical applications of functional module combination for complex motion programming.

a–c Path-finding swimming robot. a The black engine generates dominant propelling power to move forward. Red engine is a steering actuator to change directions when encountering obstacles. b Combination of these two modules enables the swimmers to navigate a narrow winding path. c Demonstration of escape from the SNU-shaped maze. d Robot soccer on a water surface with programmable Marangoni swimmers. Scale bars: 1 cm.

Fig. 5. Versatile applicability of pen-drawn Marangoni swimmers on various substrates.

The pen-based approach allows the fabrication of Marangoni swimmers with various substrates: a acrylic plate, b paper origami, c natural surfaces like leaves, and d 3D printed structures. Scale bars: 1 cm (a, d), 5 cm (b), and 3 cm (c). See also Supplementary Movie 5.

Fig. 6. Multistep motion programming on a time-dependent transformable substrate.

a–c Two-step motion programming of the rocket-shaped paper substrate. a The hinge of the folded paper is unfolded by the expansion of the compressed cellulose fiber when it touches the water surface. This phenomenon facilitates multistep activation of the camphor engines. b Speed of the swimmer is boosted as the second-stage engine is activated. c Different motion trajectories can be programmed depending on the location of the second-stage engine. d, e Three-step motion programming via different folding angles. d Larger folding angle implies a longer time for unfolding and activation. Camphor engines in the green, blue, and orange areas are first, second, and third-stage engines, respectively. e The swimmer rotates clockwise, anticlockwise, and moves straight in the first, second, and third stages, respectively. Scale bars: 5 cm (c) and 1 cm (e).

Fig. 7. Multistep motion programming using water-soluble bridges and its application in cargo delivery.

a Multistep motion programming by disassembly of the swimmers connected by a water-soluble bridge. b Cargo delivery and return using multistep motion programming. The swimmer returns to the original position after it releases the cargo at the target position. Scale bars: 5 cm (a) and 1 cm (b).