From University of Göttingen [Georg-August-Universität Göttingen](DE): “Creating order by mechanical deformation in dense active matter”


From University of Göttingen [Georg-August-Universität Göttingen](DE)

24.09.2021

Contacts:
Dr Rituparno Mandal
Institute of Theoretical Physics
University of Göttingen
rituparno.mandal@theorie.physik.uni-goettingen.de
Tel: +49 (0)551 39 26958

Professor Peter Sollich
Institute of Theoretical Physics
University of Göttingen
peter.sollich@theorie.physik.uni-goettingen.de

Researchers at Göttingen University use computer simulation to investigate models of living system.

1
A snapshot of the researchers’ simulation showing orientational ordering under steady shear deformation. Colours code the orientation of the self-propulsion forces, e.g. blue for downward and red for upward; neighbouring particles tend to be oriented in similar directions. Photo: Dr Rituparno Mandal.

Living or biological systems cannot be easily understood using the standard laws of physics, such as thermodynamics, as scientists would for gases, liquids or solids. Living systems are active-demonstrating fascinating properties such as adapting to their environment or repairing themselves. Exploring the questions posed by living systems using computer simulations, researchers at the University of Göttingen have now discovered a novel type of ordering effect generated and sustained by a simple mechanical deformation, specifically steady shear. The results were published in PNAS.

Understanding living systems, such as tissues formed by cells, poses a significant challenge because of their unique properties, such as adaptation, self-repair and self-propulsion. Nonetheless, they can be studied using models that treat them as just an unusual, “active” form of physical matter. This can reveal extraordinary dynamical or mechanical properties. One of the puzzles is how active materials behave under shear (the deformation produced by moving the top and bottom layers sideways in opposite directions, like sliding microscope cover plates against each other). Researchers at the Institute for Theoretical Physics, University of Göttingen explored this question and discovered a novel type of ordering effect that is generated and sustained by steady shear deformation. The researchers used a computer model of self-propelling particles where each particle is driven by a propulsion force that changes direction slowly and randomly. They found that while the flow of the particles looks similar to that in ordinary liquids, there is a hidden order revealed by looking at the force directions: these tend to point towards the nearest (top or bottom) plate, while particles with sideways forces aggregate in the middle of the system.

“We were exploring the response of a model active material under steady driving, where the system is sandwiched between two walls, one stationary and the other moving to generate shear deformation. What we saw was that at a sufficiently strong driving force, an interesting ordering effect emerges,” comments Dr Rituparno Mandal, Institute for Theoretical Physics at the University of Göttingen. “We now also understand the ordering effect using a simple analytical theory and the predictions from this theory match surprisingly well with the simulation.”

Senior author Professor Peter Sollich, also from the Institute for Theoretical Physics, University of Göttingen, explains, “Often an external force or driving force destroys ordering. But here the driving by shear flow is key in providing mobility to the particles that make up the active material, and they actually need this mobility to achieve the observed order. The results will open up exciting possibilities for researchers investigating the mechanical responses of living matter.”

This research was made possible thanks to funding from the European Union’s Horizon 2020 research and innovation programme under a Marie Skłodowska-Curie grant.

See the full article here.

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The University of Göttingen [Georg-August-Universität Göttingen] (DE), is a public research university in the city of Göttingen, Germany. Founded in 1734 by George II, King of Great Britain and Elector of Hanover, and starting classes in 1737, the Georgia Augusta was conceived to promote the ideals of the Enlightenment. It is the oldest university in the state of Lower Saxony and the largest in student enrollment, which stands at around 31,600.

Home to many noted figures, it represents one of Germany’s historic and traditional institutions. As of October 2020, 44 Nobel Prize winners have been affiliated with the University of Göttingen as alumni, faculty members or researchers.

The University of Göttingen was previously supported by the German Universities Excellence Initiative, holds memberships to the U15 Group of major German research universities and to the Coimbra Group of major European research universities. Furthermore, the university maintains strong connections with major research institutes based in Göttingen, such as those of the Max Planck Society(DE) and the Leibniz Association [Leibniz-Gemeinschaft or Wissenschaftsgemeinschaft Gottfried Wilhelm Leibniz](DE). With approximately 9 million media units, the Göttingen State and University Library ranks among the largest libraries in Germany.

Partner institutions

Within the Göttingen Campus the university is organizationally and personally interlinked with the following independent and semi-independent institutions:

Max Planck Institute for Biophysical Chemistry (Karl Friedrich Bonhoeffer Institute)
Max Planck Institute for Experimental Medicine
Max Planck Institute for Dynamics and Self-Organization, formerly Max Planck Institute for Flow Research
Max Planck Institute for the Study of Religious and Ethnic Diversity, formerly Max Planck Institute for History
Max Planck Institute for Solar System Research, formerly Max Planck Institute for Aeronomy
German Primate Center – Leibniz Institute for Primate Research
German Aerospace Center