Many of us say we need to fight the system. But this does not apply to an active or living system. Examples of active systems include bacterial suspensions, cellular layers, and suspensions of cytoskeletal filaments powered by molecular motors. The more we know about these systems, the more useful this knowledge will be to us.
Applications of active systems include improved design of smart materials; better understanding of biological processes like cellular motility, wound healing, etc.; and better understanding of dynamics of living fluids.
In this study, flow of active fluids is studied. Active systems, or active fluids, are fluids that contain self-driven particles that are capable of generating flow without any external forces. In passive fluids, movement occurs solely due to external forces.
To better understand the behaviour of active fluids, active nematics are studied. Nematics are one of the simplest and most common types of liquid crystalline phases. They are a phase of liquid crystals where the molecules are aligned without a specific positional order but have an orientational order, a state between ‘liquids’ and ‘crystals’. Active nematic fluids combine the characteristics of nematic liquid crystals with the dynamics of active particles.
Active nematics are studied because they capture the dynamics of some of the active or living systems.
Confinements play a major role in dictating the dynamic state of active systems. When active nematics are confined in microchannels of square cross section, they exhibit a multitude of flow states, such as no fluid flow, unidirectional, oscillatory, etc.
Although the importance of boundaries in dictating the dynamics of active fluids has been stated, so far only channels with flat walls, cylindrical walls, and annular rings have been studied. The effect of non-uniformity of the channel walls on the dynamics of active fluids is yet to be addressed.
In this study, the authors Mr. Jaideep P. Vaidya and Prof. Sumesh P. Thampi from the Department of Chemical Engineering, Indian Institute of Technology (IIT) Madras, Chennai, India, and Prof. Tyler N. Shendruk from the School of Physics and Astronomy, The University of Edinburgh, Edinburgh, UK, have studied the effect of non-uniform boundary walls on the dynamics of active nematic fluids using a computational algorithm called AN-MPCD (active nematic multi-particle collision dynamics).
A corrugated channel was chosen as the non-uniform boundary channel. In a corrugated channel, the surface has ridges and grooves that make it uneven.
It was found that the uneven boundaries in corrugated channels play a significant role in determining the dynamics of confined active systems.
The work done by the authors also suggests the possible mechanism by which asymmetric notches/teeth on the channel wall can direct coherent flows of channel confined active nematics, as seen in experiments.
The authors feel that future studies should focus on validating this hypothesis and investigate the role of asymmetry of the channel corrugations to dictate the direction of coherent flow.
Prof. Amin Doostmohammadi, Associate Professor of Physics, from the Active Intelligent Matter Research Group, Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark, pointed out the importance of this study with the following comments: “Sperm flows, bacterial biofilms, and cellular assemblies are all examples of a class of material that could be described as active nematics. In these materials, activity describes the potent capability of biological entities to produce work, and nematics describes their tendency to self-organize into groups with same orientation. It has been well-known that such materials spontaneously start to flow if put under confinement of certain sizes. In this work, Vaidya et al., make an important step to show how the shape of the confinement further affects the ability of active nematics to generate spontaneous flows. In particular, using numerical simulations the authors show that the presence of corrugations in the walls of a confining channel can further enhance the establishment of spontaneous flows. Moving beyond the spontaneous flow generation, the authors show how at higher activities such corrugations provide niches for the generation of swirling flows of active nematics. These finding pave the way for the design of active microfluidics for transport of active and passive materials, and present new means for controlling flows of biological matter.”
Article by Akshay Anantharaman
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