Speaker: (Edmond) Tingtao Zhou, California Institute of Technology

Time : 15:00 - 16.00 CEST (Rome/Paris)

Hosted at: SISSA, International School of Advanced Studies, Trieste, Italy

YouTube : https://youtu.be/bnZGUqET-HY

Organizers : Pavan Pranjivan Mehta* (pavan.mehta@sissa.it) and Arran Fernandez** (arran.fernandez@emu.edu.tr)

* SISSA, International School of Advanced Studies, Italy

** Eastern Mediterranean University, Northern Cyprus

Keywords: fractional laplacian, active matter, levy walk, anti-infection catheters

Abstract: Many active matter systems are known to perform Levy walks during migration or foraging. Such superdiffusive transport indicates long-range correlated dynamics. These behavior patterns have been observed for microswimmers such as bacteria in microfluidic experiments, where Gaussian noise assumptions are insufficient to explain the data [1].

In the first part of this talk, we introduce active Levy swimmers [2] to model such behavior. The focus is on ideal swimmers that only interact with the walls but not with each other, which reduces to the classical Levy walk model but now under confinement. We study the density distribution in the channel and force exerted on the walls by the Levy swimmers, where the boundaries require proper explicit treatment. We analyze stronger confinement via a set of coupled kinetics equations and the swimmers’ stochastic trajectories. Previous literature demonstrated that power-law scaling in a multiscale analysis in free space results in a fractional diffusion equation. We show that in a channel, in the weak confinement limit active Levy swimmers are governed by a modified Riesz fractional derivative. Leveraging recent results on fractional fluxes, we derive steady state solutions for the bulk density distribution of active Levy swimmers in a channel, and demonstrate that these solutions agree well with particle simulations. The profiles are non-uniform over the entire domain, in contrast to constant-in-the-bulk profiles of active Brownian and run-and-tumble particles. Our theory provides a mathematical framework for Levy walks under confinement with sliding no-flux boundary conditions and provides a foundation for studies of interacting active Levy swimmers.

In the second part of this talk, I will present a geometric design for anti-infection catheters. Urinary catheters cause lots of infections in hospitalized patients and cost about 30 million US dollars annually. Based on our understanding of microbial transport in channels, specifically how bacteria swim upstream due to flow-induced reorientation, we extend our model for active Levy swimmers to investigate their rheotaxis behaviors. Our modeling enables us to propose and experimentally demonstrate a novel catheter interior design that reduces bacterial contamination by 100-fold [3-5], potentially prevent urinary tract infections associated with indwelling catheters.

Biography: Dr. (Edmond) Tingtao Zhou received his B.S. in Physics from Peking University in China, where he worked on statistical physics of star formation. He then pursued his Ph.D. in Physics at MIT, where his thesis focused on materials sustainability by understanding how phase transitions in porous colloidal media, such as cement or batteries, lead to materials degradation. Currently, he is a Drinkward Postdoc Fellow at California Institute of Technology, where he combines statistical physics and fluid mechanics to study the fundamentals of living matter and its applications in biomedical and responsive materials.

Bibliography

[1] Figueroa-Morales, N., Rivera, A., Soto, R., Lindner, A., Altshuler, E. and Clément, É., 2020. E. coli “super-contaminates” narrow ducts fostered by broad run-time distribution. Science advances, 6(11), p.eaay0155.

[2] Zhou, T., Peng, Z., Gulian, M., & Brady, J. F. (2021). Distribution and pressure of active Lévy swimmers under confinement. Journal of Physics A: Mathematical and Theoretical, 54(27), 275002.

[3] Zhou, T., Wan, X., Huang, D.Z., Li, Z., Peng, Z., Anandkumar, A., Brady, J.F., Sternberg, P.W. and Daraio, C., 2024. AI-aided geometric design of anti-infection catheters. Science Advances, 10(1), p.eadj1741.

[4] Zhou, T. et al. "Anti-infection fluidic channel." U.S. Patent No. 12,128,189. 29 Oct. 2024.

[5] Zhou, T. et al. "Anti-infection fluidic channel." U.S. Patent No. 12,220,539. 11 Feb. 2025.