arXiv subjects

Anupam Sengupta

Publications and source records attributed to Anupam Sengupta.

21 records · Page 2Linked to original sources

arXiv2020

Microbial Active Matter: A Topological Framework

Topology transcends boundaries that conventionally delineate physical, biological and engineering sciences. Our ability to mathematically describe topology, combined with our access to precision tracking and manipulation approaches, has triggered a fresh appreciation of topological ramifications, specifically in mediating key functions in biological systems spanning orders of magnitude in length and time scales. Microbial ecosystems, a frequently encountered example of living matter, offer a rich test bed where the role of topological defects and their mechanics can be explored in the context of microbial composition, structure and functions. Emergent processes, triggered by anisotropy and activity characteristic of such structured, out-of-equilibrium systems, underpin fundamental properties in microbial systems. An inevitable consequence of anisotropy is the long-range orientational (or positional) correlations, which give rise to topological defects nucleating due to spontaneous symmetry breaking. The scene stealer of this emerging cross-disciplinary field is the topological defects: singularities embedded within the material field that elicit novel, if not unexpected, dynamics that are at the heart of active processes underpinning soft and living matter systems. In this short review, I have put together a summary of the key recent advances that highlight the interface of liquid crystal physics and the physical ecology of microbes; and combined it with original experimental data on sessile species as a case to demonstrate how this interface offers a biophysical framework that could help to decode and harness active microbial processes in 'true' ecological settings. Topology and its functional manifestations - a crucial and well-timed topic - offer a rich opportunity for both experimentalists and theoreticians willing to take up an exciting journey across scales and disciplines.

physics.bio-ph↗

arXiv2018

Geometry and mechanics of microdomains in growing bacterial colonies

Bacterial colonies are abundant on living and nonliving surfaces and are known to mediate a broad range of processes in ecology, medicine, and industry. Although extensively researched, from single cells to demographic scales, a comprehensive biomechanical picture, highlighting the cell-to-colony dynamics, is still lacking. Here, using molecular dynamics simulations and continuous modeling, we investigate the geometrical and mechanical properties of a bacterial colony growing on a substrate with a free boundary and demonstrate that such an expanding colony self-organizes into a "mosaic" of microdomains consisting of highly aligned cells. The emergence of microdomains is mediated by two competing forces: the steric forces between neighboring cells, which favor cell alignment, and the extensile stresses due to cell growth that tend to reduce the local orientational order and thereby distort the system. This interplay results in an exponential distribution of the domain areas and sets a characteristic length scale proportional to the square root of the ratio between the system orientational stiffness and the magnitude of the extensile active stress. Our theoretical predictions are finally compared with experiments with freely growing E. coli microcolonies, finding quantitative agreement.

cond-mat.soft↗

arXiv2017

Cross-talk between topological defects in different fields revealed by nematic microfluidics

Topological defects are singularities in material fields that play a vital role across a range of systems: from cosmic microwave background polarization to superconductors, and biological materials. Although topological defects and their mutual interactions have been extensively studied, little is known about the interplay between defects in different fields -- especially when they co-evolve -- within the same physical system. Here, using nematic microfluidics, we study the cross-talk of topological defects in two different material fields -- the velocity field and the molecular orientational field. Specifically, we generate hydrodynamic stagnation points of different topological charges at the center of star-shaped microfluidic junctions, which then interact with emergent topological defects in the orientational field of the nematic director. We combine experiments, and analytical and numerical calculations to demonstrate that a hydrodynamic singularity of given topological charge can nucleate a nematic defect of equal topological charge, and corroborate this by creating $-1$, $-2$ and $-3$ topological defects in $4-$, $6-$, and $8-$arm junctions. Our work is an attempt toward understanding materials that are governed by distinctly multi-field topology, where disparate topology-carrying fields are coupled, and concertedly determine the material properties and response.

cond-mat.soft↗