Magnetically-actuated artificial cilia for microfluidic propulsion

Abstract

Natural cilia are hair-like microtubule-based structures that are able to move fluid at low Reynolds number through asymmetric motion. In this paper we follow a biomimetic approach to design artificial cilia lining the inner surface of microfluidic channels with the goal to propel fluid. The artificial cilia consist of polymer films filled with magnetic nanoparticles. The asymmetric, nonreciprocating motion is generated by tuning an external magnetic field. To obtain the magnetic field and associated magnetization local to the cilia we solve the Maxwell equations, from which the magnetic torques can be deduced. To obtain the ciliary motion we solve the dynamic equations of motion which are then fully coupled to the fluid dynamic equations that describe fluid flow around the cilia. By doing so we show that by properly tuning the applied magnetic field, asymmetric ciliary motion can be generated that is able to propel fluid in a microchannel. The results are presented in terms of three dimensionless parameters that fully delineate the asymmetry and cycle time as a function of the relative contribution of elastic, inertial, magnetic and viscous fluid forces.

Fluid–structure interaction of three-dimensional magnetic artificial cilia

“…In a similar fashion, plate-like magnetic artificial cilia have also been synthesized and integrated in microfluidic systems to manipulate fluids (Fahrni et al 2009;Belardi et al 2011;Hussong et al 2011;Khaderi et al 2011a). The two-dimensional analysis is valid for cilia widths that are larger than the cilia length and channel height.…”

“…The two-dimensional analysis is valid for cilia widths that are larger than the cilia length and channel height. However, the synthesized cilia are, in general, three-dimensional structures and have a finite width (typically one fifth of their length) Khaderi et al (2011a), see figure 1. In these situations, the effect of the cilia width and the spacing between the cilia along the width direction play an important role in determining the fluid transported.…”

Artificial cilia fabricated using magnetic fiber drawing generate substantial fluid flow

“…In most of the previously published work on artificial cilia or flagella, a big drawback for real application is that the fabrication techniques adopted are tedious and costly, as they either require microsystem techniques like photolithography (den Toonder et al 2008;Vilfan et al 2010;Fahrni et al 2009;Belardi et al 2011;Khaderi et al 2011), or rely on expensive sacrificial materials (Evans et al 2007). In order to address this issue, our research is aimed at fabricating artificial cilia in a cost-efficient, cleanroom-free manner, while realizing an effective pumping function that can be practically used in lab-on-achip devices.…”

Propulsion of swimming microrobots inspired bymetachronal wavesin ciliates: from biology to material specifications

“…These velocities were thus considered for describing the velocity field condition set at the inlet boundary. Moreover, in order to model the apparent motion of the fluid with respect to the micro-swimmer, the external force term f e of (1) is derived from the accelerations in (11) and (12). This way, even if defined with respect to the frame fixed on the micro-swimmer, the model can accurately predict the effect of the resistive drag due to the movement of the microswimmer itself through the stress tensor σ.…”

“…Also, in looking for solutions within the eukaryotic realm, an elastic tail vaguely resembling eukaryotic flagella was developed for magnetically propelling a swimming microdevice [8,9]. Moreover, artificial single cilia mimicking their natural counterpart but relying on magnetic actuation, were investigated both for propulsion of microrobots [10] and for fluid transport in microfluidics [11,12].…”