Metachronal waves with programmable densely packed magnetic artificial cilia

Biological cilia exhibit a consorted collective movement in a metachronal wave. It is yet unclear how these collective movement contribute to the biological functions of cilia or how these waves are generated in the first place. Hence, it is useful to create artificial cilia that can reconstitute metachronal waves to generate insights and to help develop applications that make use of these mechanisms. However, almost all of the artificial cilia to date that are capable of having metachronal motion have a large pitch-to-width ratio, hence are too sparsely distributed to study the interciliary flow or their influence on the collective functions of natural cilia. For example, magnetic artificial cilia, the most common ones due to the remote actuation mechanism and high obtainable frequency, are all placed relatively far apart because of attractive forces from magnetic interaction between cilia. Hence, creating a system with densely packed magnetic artificial cilia that allows tuning of the cilia spacing, phase difference and wavelengths is needed for modeling natural cilia. In this study, the magnetic artificial cilia were fabricated by molding magnetic thermoplastic elastomer in micromolds fabricated with femtosecond laser-assisted etching (FLAE) technique. The design was assisted by a COMSOL model. Experiment and simulation results show the same vortex structures generated by the cilia, which are critical in understanding the mechanism of metachronal-induced flow.