  Despite recent advances in artificial cilia technologies, the application of
metachrony, which is the collective wavelike motion by cilia moving
out-of-phase, has been severely hampered by difficulties in controlling densely
packed artificial cilia at micrometer length scales. Moreover, there has been
no direct experimental proof yet that a metachronal wave in combination with
fully reciprocal ciliary motion can generate significant microfluidic flow on a
micrometer scale as theoretically predicted. In this study, using an in-house
developed precise micro-molding technique, we have fabricated densely packed
magnetic artificial cilia that can generate well-controlled metachronal waves.
We studied the effect of pure metachrony on fluid flow by excluding all
symmetry-breaking ciliary features. Experimental and simulation results prove
that net fluid transport can be generated by metachronal motion alone, and the
effectiveness is strongly dependent on cilia spacing. This technique not only
offers a biomimetic experimental platform to better understand the mechanisms
underlying metachrony, it also opens new pathways towards advanced industrial
applications.
