Controlling length and areal density of artificial cilia through the dipolar assembly of ferromagnetic nanoparticles

Abstract

Artificial cilia have been explored for use in microrobotics, MEMS, and lab-on-a-chip devices for applications ranging from micromixers, microfluidic pumps, locomotion, acoustic detection, and heat transfer. We have previously demonstrated the ability to assemble dense brushes of magnetically actuated artificial cilia through the dipolar assembly of 24 nm ferromagnetic cobalt nanoparticles. With little more than a strategically placed permanent magnet, the nanoparticles assemble at room temperature in less than 60 s. Despite areal densities exceeding 1 cilium/mm 2 , diameters below 25 nm, aspect ratios exceeding 400, and flexural rigidities below 3 Â 10 À28 N m 2 , these seemingly delicate structures resist collapse upon each other or the underlying substrate. The current study investigates the ability to rationally control their average length and areal density by changing the nanoparticle concentration and the dimensions of the rectangular capillary tube containing the dispersion. We find that the length and areal density obey a simple conservation of mass relationship with concentration and capillary height such that the product of the former is directly proportional to the product of the latter. Detailed statistical analysis supports a mechanism in which the role of the external field is to align pre-existing chains with the external field, assist stacking of chains along the axis of the field, and then draw them towards the ends of the permanent magnets, where the magnetic field gradient is steepest.

Forces and shapes as determinants of micro-swimming: effect on synchronisation and the utilisation of drag

“…This swimmer is a good candidate for forming the basis of future micro-carriers, a claim supported as much by its simplicity of design as by the number of experimental micro-swimmer systems that are based on linearly connected beads. 1,[3][4][5]7,12 A simpler variant of this design, the three-sphere swimmer introduced by Naja and Golestanian, 32 has already proved its immense utility by establishing many basic properties of micro-swimming in spite of sparseness of body elements. [33][34][35][36] Starting with a force-based description 37 and considering only ellipsoids of revolution for the beads in our swimmer, we here determine the optimal forcing parameters as well as the ellipsoidal aspect ratios that lead to the fastest and the most efficient swimming.…”

Effect of bunching of cilia and their interplay on muco-ciliary transport

“…Extending the scope further, we find that the study of the synchronized movement of cilia has inspired to mimic them and develop 'artificial cilia'. These artificial cilia, apart from application in MEMS and micro-robotics, have been used on labon-a-chip devices for varied applications including microfluidic pumps, acoustic detection, and heat transfer (Khaderi [23], Breidenich [24]).…”

Polymer brushes and their possible applications in artificial cilia research

“…In addition, the principle did not work in conductive fluids, including certain biological fluids, because the electrical field may damage biological components of cells. Therefore, magnetic-actuated cilia have been developed to overcome these three primary limitations, and have become the most studied artificial cilia (45)(46)(47). They are made from a polymer matrix film consisting of embedded magnetic nanoparticles in response to the external magnetic field (48).…”