Microfluidic propulsion by the metachronal beating of magnetic artificial cilia: a numerical analysis

In this work we study the effect of metachronal waves on the flow created by magnetically-driven plate-like artificial cilia in microchannels using numerical simulations. The simulations are performed using a coupled magneto-mechanical solid-fluid computational model that captures the physical interactions between the fluid flow, ciliary deformation and applied magnetic field. When a rotating magnetic field is applied to super-paramagnetic artificial cilia, they mimic the asymmetric motion of natural cilia, consisting of an effective and recovery stroke. When a phase-difference is prescribed between neighbouring cilia, metachronal waves develop. Due to the discrete nature of the cilia, the metachronal waves change direction when the phase difference becomes sufficiently large, resulting in antiplectic as well as symplectic metachrony. We show that the fluid flow created by the artificial cilia is significantly enhanced in the presence of metachronal waves and that the fluid flow becomes unidirectional. Antiplectic metachrony is observed to lead to a considerable enhancement in flow compared to symplectic metachrony, when the cilia spacing is small. Obstruction of flow in the direction of the effective stroke for the case of symplectic metachrony was found to be the key mechanism that governs this effect

Transport and mixing by metachronal waves in nonreciprocal soft robotic pneumatic artificial cilia at low Reynolds numbers

Cilia are widely employed by living systems to manipulate fluid flow in various functions, such as feeding, pumping, and locomotion. Mimicking the intricate ciliary asymmetry in combination with collective metachronal beating may find wide application in fluid transport and mixing in microfluidic systems. Here, we numerically analyze the metachronal beating of pneumatic artificial cilia. We specifically address three aspects of ciliary motion: (i) pumping in the backflow region, (ii) mixing in the cilia region, and (iii) the transport—mixing transition region. Our results show that antiplectic metachrony leads to the highest mixing efficiency and transport rate in two distinct regions, i.e., below and above the ciliary surface, respectively. We find that the ciliary motion strongly enhances the diffusivity when advection is dominant at high Péclet numbers, with a factor 3 for symplectic metachrony and a factor 4 for antiplectic metachrony and synchronous beating. In addition, we find an increase with a factor 1.5 for antiplectic metachrony and a decrease with a factor 2.5 for symplectic metachrony compared with synchronous beating for fluid pumping. To investigate the higher transport rate compared to symplectic metachrony, we develop a simple two-cilia model and demonstrate that the shielding of flow between neighboring cilia is the main reason for the higher antiplectic transport rate

Metachronal patterns by magnetically-programmable artificial cilia surfaces for low Reynolds number fluid transport and mixing

Motile cilia can produce net fluid flows at low Reynolds number because of their asymmetric motion and metachrony of collective beating. Mimicking this with artificial cilia can find application in microfluidic devices for fluid transport and mixing. Here, we study the metachronal beating of nonidentical, magnetically-programmed artificial cilia whose individual non-reciprocal motion and collective metachronal beating pattern can be independently controlled. We use a finite element method that accounts for magnetic forces, cilia deformation and fluid flow in a fully coupled manner. Mimicking biological cilia, we study 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 cilia and explore the underlying physical mechanism. Our results show that shielding effects between neighboring cilia lead to a primary flow that is larger for antiplectic than for symplectic metachronal waves. The secondary flow can be fully explained by the propagation direction of the metachronal wave. Finally, we show that the mixing rate can be strongly enhanced by laeoplectic and diaplectic metachrony resulting in large velocity gradients and vortex-like flow patterns.</p

A novel breast cancer model of early stage invasion:using microfluidic methods to mimic a heterogeneous physical tumor microenvironment

The majority of breast cancer deaths are not caused by the primary tumor, but by metastasis to other organs. In this work, we propose a novel in vitro breast cancer model that focuses on dissecting the influence of the biophysical properties of the extracellular matrix (ECM) on the onset of cancer invasion. Based on microfluidic technology, it will provide us with the necessary tools to independently vary different material and cell properties, while it provides the cells with a physiologically relevant environment.<br/

Artificial mini-heart:An internal micropump based on magnetically actuated artificial cilia that can induce flows in a microfluidic channel network

Here we report the fabrication of an internal micropump based on magnetically actuated artificial cilia (MAAC) that functions like an artificial mini-heart. The micropump can provide versatile flows in a microfluidic channel network, when the MAAC are actuated to perform a tilted conical movement. Compared to other pumping methods, this in-situ micro-pump does not need tubing or electrical connections, which reduces the usage of reagents by minimizing “dead volumes”, allows the construction of a more compact system, avoids undesirable electrical effects and accommodates a wide range of fluids

Artificial mini-heart:An internal micropump based on magnetically actuated artificial cilia that can induce flows in a microfluidic channel network

Here we report the fabrication of an internal micropump based on magnetically actuated artificial cilia (MAAC) that functions like an artificial mini-heart. The micropump can provide versatile flows in a microfluidic channel network, when the MAAC are actuated to perform a tilted conical movement. Compared to other pumping methods, this in-situ micro-pump does not need tubing or electrical connections, which reduces the usage of reagents by minimizing “dead volumes”, allows the construction of a more compact system, avoids undesirable electrical effects and accommodates a wide range of fluids

A concise review of microfluidic particle manipulation methods

Particle manipulation is often required in many applications such as bioanalysis, disease diagnostics, drug delivery and self-cleaning surfaces. The fast progress in micro- and nano-engineering has contributed to the rapid development of a variety of technologies to manipulate particles including more established methods based on microfluidics, as well as recently proposed innovative methods that still are in the initial phases of development, based on self-driven microbots and artificial cilia. Here, we review these techniques with respect to their operation principles and main applications. We summarize the shortcomings and give perspectives on the future development of particle manipulation techniques. Rather than offering an in-depth, detailed, and complete account of all the methods, this review aims to provide a broad but concise overview that helps to understand the overall progress and current status of the diverse particle manipulation methods. The two novel developments, self-driven microbots and artificial cilia-based manipulation, are highlighted in more detail