“…For instance, gas generation at the surface of object via catalytic reaction can lead to the powerful propulsion of objects. , In addition, Marangoni flow caused by a surface tension gradient can also work as a driving force to move objects over a liquid surface. , Surface tension gradient is generally generated by dissolution of surface-active chemicals from the objects, which can create concentration gradients of the chemicals at the liquid surface. For example, the Stenus beetle, − soap boats, camphor crystals, organic solvent-loaded objects, , and depolymerizable plastics can move over the water surface via Marangoni flow, which was generated by the ejection of surface-active chemicals that expand over the water surface. Surface tension gradients generated based on temperature gradients, which are induced by light irradiation, have been also utilized to generate powerful propulsion forces to move small objects. ,− Recently, liquid marbles coated by particles with light-to-heat photothermal property were demonstrated to move over water surface by local heating via irradiation with a near-infrared (NIR) laser, which generates a temperature gradient. − …”