Artificial cilia for active micro-fluidic mixing

Abstract

In lab-on-chip devices, on which complete (bio-)chemical analysis laboratories are miniaturized and integrated, it is essential to manipulate fluids in sub-millimetre channels and sub-microlitre chambers. A special challenge in these small micro-fluidic systems is to create good mixing flows, since it is almost impossible to generate turbulence. We propose an active micro-fluidic mixing concept inspired by nature, namely by micro-organisms that swim through a liquid by oscillating microscopic hairs, cilia, that cover their surface. We have fabricated artificial cilia consisting of electro-statically actuated polymer structures, and have integrated these in a micro-fluidic channel. Flow visualization experiments show that the cilia can generate substantial fluid velocities, up to 0.6 mm s(-1). In addition, very efficient mixing is obtained using specially designed geometrical cilia configurations in a micro-channel. Since the artificial cilia can be actively controlled using electrical signals, they have exciting applications in micro-fluidic devices.

Artificial cilia fabricated using magnetic fiber drawing generate substantial fluid flow

“…1d), consisting of a chamber containing the artificial cilia and a side channel providing a recirculation pathway for the fluid. This differs from previous studies, where tests were always performed in a closed chamber or channel, resulting in the combination of a ciliadriven forward flow near the ciliated surface and a recirculation backflow along the opposite surface and along the periphery within the chamber or channel itself, which made the quantification of the ''net flow'' hard to achieve Vilfan et al 2010;Wang et al 2013;den Toonder et al 2008;Shields et al 2010). By reducing (not eliminating) backflow within the main cilia chamber and observing the flow profile in the recirculation pathway, our device provides a straightforward manner to characterize the ''pumping efficiency'' of our artificial cilia.…”

“…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.…”

“…Recently, we reported a self-assembling in situ fabrication method of artificial cilia (Wang et al 2013) able to generate a net flow of up to 5 lm/s. Although the fabrication process is more cost-effective than for earlier examples, Vilfan et al 2010;Evans et al 2007;den Toonder et al 2008) expensive magnetic beads were used and the flow generated was rather low for practical lab-on-a-chip applications.…”

“…The maximum induced fluid flow speeds that were observed were also similar, namely in the order of micrometers per second. Den Toonder et al (2008) fabricated microbeams, or ''flaps'', about ten times bigger than natural cilia from bilayer films of polyimide and chromium using microsystems technologies. These artificial cilia were integrated directly into a microfluidic channel and actuated electrostatically between a bent and a flat state at frequencies up to a 200 Hz, generating a substantial net flow velocity of more than 500 lm/s.…”

Getting drowned in a swirl: Deformable bead-spring model microswimmers in external flow fields

“…Moreover, activated droplets may self-propel over liquid surfaces and through bulk fluids [21,61,63,[88][89][90][91], which implies induced fluid flows and thus classifies them as deformable microswimmers. An interaction with imposed surrounding flow fields becomes important when rheological properties of active systems are considered [92], when the features of self-propelled microswimmers are exploited in microfluidic devices [93,94], or when microorganisms orient themselves in external shear flows [95].…”