Marangoni Effect Enabling Autonomously Miniatured Swimmers: Mechanisms, Design Strategy, and Applications

Miniature swimmers hold considerable potential for precision tasks in the confined environments, yet challenges persist with a simple, sustained, and controllable actuation for their large-scale applications in real-world scenarios. Marangoni-propelled miniature swimmers (MPMSs), leveraging surface-tension-gradient-driven interfacial flows, emerg as a promising solution due to simple implementation and scalable operation. The Marangoni effect, characterized by interfacial flow caused by surface tension gradients, offers a promising propulsion mechanism for the object movement at the liquid surfaces. Leveraging this effect, MPMSs have attracted great interest all over the world. In this regard, this review provides an overview of the latest advancement in the design and application of MPMSs, highlighting the synergy of various responsive materials and structural engineering to enable on-demand surface tension gradients for sustained Marangoni propulsion of the MPMSs. First, it systematically introduces different mechanisms for the generation of surface tension gradient to actuate these swimmers. Subsequently, it elaborately discusses the preparation materials and specialized structural designs employed in MPMSs while elucidating the correlation between propulsion mechanisms and swimmer design strategies. Furthermore, potential practical applications of MPMSs across various scenarios are presented briefly. Finally, remaining challenges along with possible solutions are presented.