Using these methods, we introduced time-dependent programmable features for microswimmers, such as shape change and disassembly.
Photolithography enables not only high-throughput and multi-scale fabrication but also iterated photolithography cycles, enabling the integration of multiple functional materials in a single swimmer. As a result, we were able to introduce maskless photolithography 25, 26, 27 to fabricate Marangoni microswimmers. PVA has poor solubility in organic solvents and is not dissolved when additional fabrication procedures based on non-polar solvents are performed 23, 24. We introduced polyvinyl alcohol (PVA) as a fuel because it can be dissolved in water to lower the surface tension. In this study, a fuel for the highly programmable Marangoni microswimmers was introduced to overcome the fabrication problem. As a result, the current programmability of Marangoni microswimmers is limited. However, the described swimmers sporadically released their fuel to all sides without control, lowering their efficiency and programmability of motion.
Alternatively, a recent method reported machining of the fuel-immersed film in the designated conformation 16, 22. Previously reported methods loaded liquid- or solid-phase fuels on pre-made swimmers by pipetting 22 or hand assembly 12 that have limitations in throughput, precision and scale to achieve mass fabrication of swimmers below millimeter scale, even though they achieved advanced functions such as prolonged motion or environmental sensing. Furthermore, multiple parts with a distinct function that control the motion of the swimmers should be integrated into these swimmers. To program the motion of the swimmers, the fuel releasing component should be precisely positioned in the swimmers. As a result, a variety of methods or techniques that include washing with solutions cannot be incorporated into the fabrication process of these swimmers. Fuels used for Marangoni swimmers are usually surfactants that exhibit amphiphilic properties, which causes them to dissolve after any liquid contact that is required during fabrication 6, 10, 16, 21. Furthermore, although external stimuli-based methods show a high level of programmability, the external stimuli sources are much bulkier than the actual swimmers, limiting the practical applications of such swimmers.Īlthough Marangoni microswimmers demonstrated powerful and autonomous swimming, there is a limitation in the precise mass fabrication, thereby affecting their scale, degree of programmability and future development. In contrast, the motion of conventional swimmers that are less than a few hundred micrometers in size generally requires external stimuli, such as lasers or ultrasound, as energy source 17, 18, 19 this is because the smallest reported battery 20 has an area of ~2 mm 2 and there are substantial challenges in integrating such parts in microscale robotics. With a simple fuel releasing system, recent studies have demonstrated that the Marangoni swimmer in milli- or microscale can swim tens of minutes in a linear or circular motion without an external energy source or control 11, 12, 16. Without the mechanical systems for stroking water or external stimuli, Marangoni swimmers demonstrate powerful swimming performance by producing mechanical energy directly from the surfactant 6, 15. Inspired by nature’s Marangoni effect-based swimming principles, various studies on robots on the surface of the water, seawater and organic solvent/water mixture were introduced 5, 6, 7, 8, 9, 10, 11, 12, 13, 14. With an explosive speed of approximately twice the physical swimming speed, Microvelia uses the Marangoni effect to escape from predators 1, 4. These insects secrete surfactants that lower the surface tension of water and the Marangoni effect allows them to propel along the surface of the water from low to high surface tension areas. Marangoni effect is a mass transfer phenomenon between two liquid regions with different surface tension 2, 3. For example, Microvelia and Rove beetles can propel faster than the conventional physical swimming speed using the Marangoni effect 1. While the majority of life physically stroke water when swimming, few creatures can swim by other principles. In nature, over 1200 species of life have the ability to move on the surface of the water.
0 kommentar(er)
