Tailoring Flexible Arrays for Artificial Cilia Actuators

Abstract

Soft actuators refer to active devices made of flexible or compliant materials which can respond to and be motivated by external triggers such as magnetic fields, electric fields, acoustic waves, light fields, chemical reagents, and so on. [1][2][3] Recent years have witnessed the rapid development of soft actuators. Thanks to the great endeavors ever paid to this field, a large variety of smart soft actuators with multiple actuation mechanisms and diverse structures, including film-shaped, tube-shaped, cilia-shaped, etc., have been designed and fabricated, [4][5][6][7] playing an increasingly important role in electronics, [8] robotics engineering, [9] artificial intelligence, [10] fluid manipulation, [11] biomedicine, [12] and life science. [13] Among these intriguing soft actuators, the artificial cilia actuator, which is composed of a cilia-like array, is a representative example. Such artificial cilia can be fabricated through numerous strategies, from top-down approaches such as FES and template replication [14][15][16][17] to bottom-up ones such as self-assembly. [18][19][20] These fabricated artificial cilia not only exhibit high flexibility, sensitivity, tailorability, and controllability but also can be simultaneously imparted with various functions after specific modification.To better tailor the artificial cilia and to further improve their performances in complicated and changeable environments, researchers seek inspirations from nature. Cilia are ubiquitous in nature and can be found in a wide range of species including microbiome, plant stems, fish skins, legs of insects, and airways of mammals. [21][22][23] These natural cilia have been reported to exhibit the functions of guiding movements, sensing ambient environments, clearing foreign matters, etc. By mimicking and recapitulating the natural cilia, scientists have developed swimming cilia robots, multilegged cilia carpets, micropillar sensors, slippery cilia surfaces, and other artificial cilia actuators. [24][25][26] In addition, to achieve the intelligent manipulation and remote control, different single-factor or multi-factor actuation methods of the artificial cilia have also been investigated. [27][28][29] To date, these artificial cilia have found applications in a wide spectrum of fields, including microfluidics, droplet manipulation, flexible electronics, and soft robots. [30][31][32] In this review, we present the recent progress on the tailoring and applications of the artificial cilia actuators. Different from existing reviews in this field which only involve artificial cilia in some sections, this review provides a profound, comprehensive, and exclusive summary of artificial cilia actuators for the first time. We first introduce some typical examples of natural cilia, their properties and functions, as well as the bionic cilia derived from them. We then summarize the actuation mechanisms of the artificial cilia, and emphasize the magnetically actuated artificial cilia and multi-responsive artificial cilia in particular. In the follo...

Transport and mixing by metachronal waves in nonreciprocal soft robotic pneumatic artificial cilia at low Reynolds numbers

“…This effective beating mechanism of natural cilia has been mimicked in artificial ciliary systems for fluid manipulation in microfluidic "lab-on-a-chip" devices. [6][7][8][9][10][11] There are various ways of actuating artificial cilia, using, for instance, electric fields, magnetic fields, sound, or light. 10,12 Cilia are successfully applied in microfluidic devices supported by a broad range of studies on fluid propulsion by artificial cilia using theoretical/numerical [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] and experimental [6][7][8][9][30][31][32] methods.…”

Metachronal patterns by magnetically-programmable artificial cilia surfaces for low Reynolds number fluid transport and mixing

“…[18][19][20][21] Much work has been done on cilia material design and fabrication, that can be actuation strategies, and cilia motion optimization. 22 Cilia can be fabricated by various methods, such as self-assembly techniques, 23 casting processes, 24,25 and photolithography, 26 and actuated in many ways, for instance, by electric fields, 27 magnetic fields, [28][29][30] light 31,32 and pH. 33 The experimental realization of metachronal motion has recently become possible by using pneumatic 34 or magnetic cilia.…”

Microscopic artificial cilia – a review

“…In general, the cilia fabrication methods can be broadly classified into template-based and template-free fabrication methods. 30 …”