Fig. 4. Artificial cilia motion types. (a) (i) Tilted conical motion; (ii) time-lapse image showing top-view of cilia under tilted conical motion, where the red arrow indicates the direction of effective stroke and the yellow arrow indicates the rotation direction. Reproduced from ref. 27 with permission from John Wiley and Sons. (b) (i) 2D asymmetric motion with the swept area between the dotted lines representing forward and backward stroke; (ii) side-view image where the solid line indicates the effective stroke and the dashed line indicates the recovery stroke. Reproduced from ref. 101 with permission from the Royal Society of Chemistry. (c) (i) Metachronal wave motion and (ii) time-sequence images from showing the wave propagation. Reproduced from ref. 19 with permission under open license CC BY.