Patrick Onck1
Univ of Groningen1
Nature has developed astonishing concepts to manipulate fluids at small length scales and to enable micro-organisms to efficiently navigate through fluids at low Reynolds numbers. Motile biological cilia for instance can produce net fluid flows at low Reynolds numbers because of their asymmetric motion and emerging metachrony of collective beating. Mimicking this with magnetic artificial cilia can find application in microfluidic devices for fluid transport, mixing and directional particle transport. In addition to magnetic artificial cilia, also soft robotic magnetic micro-swimmers can be applied for future wireless medical robots for operation inside the human body. In this presentation I will discuss recent work we carried out [1-4] on the computational modelling of magnetically-actuated artificial cilia and soft-robotic magnetic micro-swimmers performed in close collaboration with experimental groups.<br/><br/>To generate fluid transport we studied the metachronal beating of magnetically-actuated artificial cilia whose individual non-reciprocal motion and collective metachronal beating patterns can be independently controlled [1,2]. We have developed a computational framework that is able to account for the magnetic actuation forces, the ciliary deformation, the coupled interaction with the surrounding fluid and the resulting fluid flow. We study arrays of magnetic cilia subject to a full range of metachronal driving patterns, including antiplectic, symplectic, laeoplectic and diaplectic waves. We analyse the induced primary flow, secondary flow and mixing rate as a function of the phase lag between the cilia and explore the underlying physical mechanism.<br/><br/>In addition, we developed a versatile particle transportation platform consisting of arrays of magnetic artificial cilia actuated by a rotating magnet [3]. By performing a tilted conical motion, the artificial cilia are capable of transporting particles on their tips, along designated directions that can be fully controlled by the externally applied magnetic field, at high resolution (particle precision), with varying speeds and for a range of particle sizes. The results show that the adhesion and friction between the particle and the cilia are essential ingredients of the mechanism underlying the multi-directional transportation. This work offers an advanced solution to controllable transport particles along designated paths in any direction over a surface, which has potential applications in diverse fields including lab-on-a-chip devices, in-vitro biomedical sciences, self-cleaning and antifouling.<br/><br/>In addition to magnetic artificial cilia, we also studied soft robotic magnetic micro-swimmers for future wireless medical robots operating inside channels, vessels, tubes and cavities of the human body, filled with flowing or stagnant biological fluids [4]. Driven by different external magnetic fields, the swimmer's motion can be changed between undulation crawling, undulation swimming, and helical crawling. By using computational modelling, we analyze the transport mechanisms of the soft robots and study the effect of different parameters to provide guidelines for the design of the robots in specific applications. Our design method provide unprecedented opportunities for studying ciliary biomechanics and creating cilia-inspired object manipulation, lab- and organ-on-a-chip devices, mobile microrobots wireless microfluidic pumping and bioengineering systems.<br/><br/>1. Dong, X. et al. Science Advances, 6(45), p.eabc9323 (2020).<br/>2. Zhang, R. et al. Soft Matter, 18, 3902 (2022).<br/>3. Zhang, S., et al. ACS Nano, 14(8), pp.10313-10323 (2020).<br/>4. Ren, Z. et al., Science Advances, 7(27): eabh2022 (2021).