Recent Progress of Artificial Cilia: From Bioinspired Design, Facile Fabrication to Practical Application†

As well known, cilia play an irreplaceable role in sensing and movement of natural organisms because they can respond to external signals and generate net flow in complex environments. Based on these findings, scientists further explored the functions of natural cilia and have developed many artificial cilia in the past nearly thirty years. This review provides an overview of recent progress of artificial cilia. Firstly, we summarize the characteristics of natural cilia. Subsequently, we introduce the fabrication methods including template, magnetic assembly, lithography, and 3D printing. Then we discuss the stimulus actuation of artificial cilia from two major modes: contact control and remote control. In addition, five typical types of applications, including adhesion regulation, intelligent control, mobile microrobot, biological sensor and anti-counterfeiting, were reviewed in detail. Finally, we present the challenges and future development in the fields of advanced artificial cilia.

Key Scientists

From 1994 to 1997, research teams including Bohringer, Donald, and Macdonald from Cornell University and Suh and Kovacs from Stanford University reported on the application of artificial cilia in the field of micro-electro-mechanical systems (MEMS) technology,^[1-3] while Fujita from the University of Tokyo and Stemme from KTH were also conducting research in artificial cilia fields at the same time. In 2006, Krijnen's team designed a combination of cricket cerci cilia and MEMS technology to further extend the application of artificial cilia to flow sensors.^[4] In 2007, Superfine's crew introduced the polycarbonate track-etched (PCTE) membrane method into the fabrication of artificial cilia, achieving the fabrication of high aspect ratio cilia in a liquid free environment.^[5] Since 2008, Toonder's lab has been focusing on the research of artificial cilia and have made outstanding contributions in lab on chip and achieve various stimuli responsive actuation of artificial cilia.^[6-8] In 2010, Alexeev's research team used computer simulations to design a hydrodynamic model of ciliary strike.^[9] Since 2017, Jiang and his coworkers have made progress in the application of directional manipulation of artificial cilia, including research on solids, droplets and bubbles.^[10-13] In 2020—2024, Sitti's research group has introduced cilia into the field of bioinspired microrobot and realized the programmed actuation of artificial cilia from the perspectives of electricity, photothermal and magnetic.^[14-19] In 2022, Jeong's group innovated the traditional magnetic assembly method to fabricate three-dimensional nanoscale cilia with regular spatial distribution and controllable geometry.^[20-21]