Recent & Upcoming Talks

2022

Sebastian Fürthauer

Abstract

Living cells move, deform and divide. The engine of these behaviors is the cytoskeleton, a highly crosslinked network of polymer filaments and molecular scale motors that use chemical energy to do work. We develop a theory that predicts how the micro-scale properties of molecular motors and crosslinks tune the networks emergent material properties and generate predictable, and possibly controllable, behaviors. I will present how this theory is constructed, and discuss its implications for cytoskeletal networks in vitro and in vivo, highlighting how it has helped to quantitatively understand motor driven microtubule fluxes in a system made from XCTK2 motors and stabilized microtubules, and how it resolved long-standing puzzles about the motion of microtubules in spindles. I will then discuss some future research directions and sketch how the approach taken here can be generalized to describe different and larger biological assemblies such as cells and tissues and form the basis for a quantitative physics of living materials.

Date

May 17, 2022 9:00 AM — 11:00 AM

Event

Xiamen University Seminar, BIO SMAT Seminar

Location

Xiamen University, virtual

Project

Sebastian Fürthauer

Abstract

Living cells move, deform and divide. The engine of these behaviors is the cytoskeleton, a highly crosslinked network of polymer filaments and molecular scale motors that use chemical energy to do work. We develop a theory that predicts how the micro-scale properties of molecular motors and crosslinks tune the networks emergent material properties and generate predictable, and possibly controllable, behaviors. I will present how this theory is constructed, and discuss its implications for cytoskeletal networks in vitro and in vivo, highlighting how it has helped to quantitatively understand motor driven microtubule fluxes in a system made from XCTK2 motors and stabilized microtubules, and how it resolved long-standing puzzles about the motion of microtubules in spindles. I will then discuss some future research directions and sketch how the approach taken here can be generalized to describe different and larger biological assemblies such as cells and tissues and form the basis for a quantitative physics of living materials.

Date

May 5, 2022 11:00 AM — 12:00 PM

Event

ISTA Slam Seminar, opens an external URL in a new window

Location

IST Austria

Project

Sebastian Fürthauer

Abstract

Living cells move, deform and divide. The engine of these behaviors is the cytoskeleton, a highly crosslinked network of polymer filaments and molecular scale motors that use chemical energy to do work. We develop a theory that predicts how the micro-scale properties of molecular motors and crosslinks tune the networks emergent material properties and generate predictable, and possibly controllable, behaviors. I will present how this theory is constructed, and discuss its implications for cytoskeletal networks in vitro and in vivo, highlighting how it has helped to quantitatively understand motor driven microtubule fluxes in a system made from XCTK2 motors and stabilized microtubules, and how it resolved long-standing puzzles about the motion of microtubules in spindles. I will then discuss some future research directions and sketch how the approach taken here can be generalized to describe different and larger biological assemblies such as cells and tissues and form the basis for a quantitative physics of living materials.

Date

Apr 26, 2022 4:00 PM — 6:00 PM

Event

IAP Seminar, opens an external URL in a new window

Location

TU-Wien, hybrid

1040 Wien, Wiedner Hauptstrasse, DB gelb 05 B, Wien

Project

Sebastian Fürthauer, Anup Kanale, Feng Ling, Hanliang Guo, Eva Kanso

Abstract

In many biology, fluid transport often emerges from the coordinated activity of thousands of multi-ciliated cells, each containing hundreds of cilia. Given the sheer number of cilia in these system, a continuum theory is needed to fully analyze large ciliary carpets. Here, we formulate a continuum theory by systematically coarse graining a simple model for cilia that treats them as immersed spheres forced along circular trajectories above a surface. We analyze the stability of isotropic and synchronized states and show that they are unstable to small perturbations, which implies dynamic pattern formation. To challenge the theory, we performed numerical simulations on discrete systems. We report quantitative agreement between theory and in-silico experiments.

Date

03.16.2022 16:00 — 15:00

Event

APS March meeting 2022

Location

APS march meeting, Chicago

Project

Brato Chakrabarti, Sebastian Fürthauer, Michael Shelley

Abstract

Active particles, such as motor proteins and motile micro-organisms, convert chemical energy from a reservoir to do mechanical work in their environment. We are interested in cases where this energy conversion process involves a periodic duty cycle, such as a cyclic swimming stroke or a periodic stepping of a motor, and can be mapped onto a phase variable. We study the hydrodynamics of a suspension of such particles. For an orientationally aligned suspension of active particles, a stability analysis predicts that both the phase-ordered and disordered states are unstable. Nonlinear simulations of such aligned suspensions reveal the formation of chimera states. The phase dynamics can further trigger alignment instabilities that are unique to these systems and are absent in classical active fluids with time-periodic force dipoles. We find that in channels, a combination of the alignment and phase instability allows these active particles to self-organize and generate unidirectional pumping.

Date

03.16.2022 16:00 — 15:00

Event

APS March meeting 2022

Location

APS march meeting, Chicago

Project

Abstract

Motile cilia are slender, hair-like cellular appendages that spontaneously oscillate under the action of internal molecular motors and are typically found in dense arrays. These active filaments coordinate their beating to generate metachronal waves that drive long-range fluid transport and locomotion. Until now, our understanding of their collective behavior largely comes from the study of minimal models that coarse-grain the relevant biophysics and the hydrodynamics of slender structures. Here we build on a detailed biophysical model to elucidate the emergence of metachronal waves on millimeter scales from nanometer-scale motor activity inside individual cilia. Our study of a 1D lattice of cilia in the presence of hydrodynamic and steric interactions reveals how metachronal waves are formed and maintained. We find that in homogeneous beds of cilia these interactions lead to multiple attracting states, all of which are characterized by an integer charge that is conserved. This even allows us to design initial conditions that lead to predictable emergent states. These ideas from a 1D lattice of cilia generalize to 2D carpets and we show that in nonuniform ciliary tissues, boundaries and inhomogeneities provide a robust route to metachronal waves.

Date

03.15.2022 16:00 — 15:00

Event

APS March meeting 2022

Location

APS march meeting, Chicago

Project

Peter Foster, Sebastian Fürthauer, Nikta Fakhri

Abstract

Actomyosin is a canonical example of an active material, driven out of equilibrium in part through the injection of energy by myosin motors. This influx of energy allows actomyosin networks to generate cellular-scale contractility, which underlies cellular processes ranging from division to migration. While the molecular players underlying actomyosin contractility have been well characterized, how cellular-scale deformation in disordered actomyosin networks emerges from filament-scale interactions is not well understood. Here, we address this question in vivo using the meiotic surface contraction wave of starfish oocytes. Using pharmacological treatments targeting actin polymerization, we find that the rate of cellular deformation is not a monotonic function of cortical actin density, but is instead peaked near the wild type density. To understand this, we develop an active fluid model coarse-grained from filament-scale interactions and find quantitative agreement with the measured data. This model further predicts the dependence of the strain rate on the concentrations of active motors and passive actin crosslinkers, which we experimentally verify. Taken together, this work is an important step towards bridging the molecular and cellular length scales for cytoskeletal networks.

Date

03.15.2022 12:30 — 06:00

Event

APS March meeting 2022

Location

APS march meeting, Chicago

Project

Abstract

Cells, the building blocks of life, move deform and perform mechanical work autonomously. Internally, these abilities are powered by self organized networks of chiral filaments and motor molecules, which are collectively called the cytoskeleton. We construct the theoretical framework that allows us to derive the large scale material properties of cytoskeletal networks from microscale interactions. In this talk, I will highlight how the handedness of motor-filament interactions shapes the emergent material properties. In particular, I will discuss the emergence of chiral contributions to the stress tensor and their macroscopic consequences.

Date

03.14.2022 12:30 — 06:00

Event

APS March meeting 2022

Location

APS march meeting, Chicago

Project

Abstract

Living cells move, deform and divide. The engine of these behaviors is the cytoskeleton, a highly crosslinked network of polymer filaments and molecular scale motors that use chemical energy to do work. We develop a theory that predicts how the microscale properties of molecular motors and crosslinks tune the networks emergent material properties and generate predictable, and possibly controllable, behaviors. I will present how this theory is constructed, and discuss its implications for cytoskeletal networks in vitro and in vivo, highlighting how it has helped to quantitatively understand motor driven microtubule fluxes in a system made from XCTK2 motors and stabilized microtubules, and how it resolved longstanding puzzles about the motion of microtubules in spindles. I will then discuss some future research directions and sketch how the approach taken here can be generalized to describe different and larger biological assemblies such as cells and tissues and form the basis for a quantitative physics of living materials.

Date

01.26.2022 14:15 — 15:30

Event

Invited talk at TU Berlin

Location

TU Berlin, virtual

2021

Abstract

How bulk cytoplasm generates forces to separate post-anaphase microtubule (MT) asters in Xenopus laevis and other large eggs remains unclear. Previous models proposed that dynein-based, inward organelle transport generates length-dependent pulling forces that move centrosomes and MTs outwards while other components of cytoplasm are static. We imaged aster movement by dynein and actomyosin forces in Xenopus egg extracts and observed outward co-movement of MTs, endoplasmic reticulum (ER), mitochondria, acidic organelles, F-actin, keratin and soluble fluorescein. Organelles exhibited a burst of dynein-dependent inward movement at the growing aster periphery, then mostly halted inside the aster, while dynein-coated beads moved to the aster center at a constant rate, suggesting organelle movement is limited by brake proteins or other sources of drag. Based on these observations, we are developing active gel models for aster separation movement, in which all components of the cytoplasm comprise a mechanically integrated aster gel that moves collectively in response to dynein and actomyosin forces.

Date

12.11.2021 00:01 — 23:59

Event

James presents a poster and a short talk on microtubule aster motion at ASCB, opens an external URL in a new window

Location

virtual

Abstract

Motile cilia are slender, hair-like cellular appendages that spontaneously oscillate under the action of internal molecular motors and are typically found in dense arrays. These active filaments coordinate their beating to generate metachronal waves that drive long-range fluid transport and locomotion. Until now, our understanding of their collective behavior largely comes from the study of minimal models that coarse-grain the relevant biophysics and the hydrodynamics of slender structures. Here we build on a detailed biophysical model to elucidate the emergence of metachronal waves on millimeter scales from nanometer-scale motor activity inside individual cilia. Our study of a 1D lattice of cilia in the presence of hydrodynamic and steric interactions reveals how metachronal waves are formed and maintained. We find that in homogeneous beds of cilia these interactions lead to multiple attracting states, all of which are characterized by an integer charge that is conserved. This even allows us to design initial conditions that lead to predictable emergent states. Finally, and very importantly, we show that in nonuniform ciliary tissues, boundaries and inhomogeneities provide a robust route to metachronal waves. # Talk start and end times.

Date 

11.23.2021 12:40 — 15:15

Event

Brato gives a talk about our work on in cilia at APS DFD, opens an external URL in a new window

Location

Phoenix, USA

Abstract

In order to survive, cells need to organize their functions tightly in space and time. A prime example is the mitotic spindle, which segregates chromosomes between the daughter cells during cell division. To achieve this, the spindle first needs to assemble at the right time, then it needs to move to the center of the cell, finally it needs to transport the correct chromosome to the correct location - such that after cell division both daughter cells end up with a complete copy of the genetic information. Using this example, I will introduce some key concepts of how cellular processes are coordinated in space and time, and illustrate how we seek to better understand these mechanisms using the methods of theoretical and numerical physics.

Date

11.10.2021 16:00 — 11.01.2021 15:00

Event

Guest Lecture in Emerging Fields in Architecture, opens an external URL in a new window

Location

TU-Wien, virtual

Much of our current understanding of the physics of the cytoskeleton - the structure that allows cells to change and maintain their shapes, and to move - comes from phenomenological theories that capture its behavior in terms of a few material properties such as viscosities elasticities and active stresses. How these properties are set by microscale processes is often less well understood. We seek to bridge this gap by deriving a theory for the large length and time scale physics of cytoskeletal materials based on microscopic interaction rules that can be measured in the lab.