@phdthesis{21423,
  abstract     = {Biological systems, such as cytoskeletal filaments and multicellular collectives, exhibit rich 
self-organization driven by their intrinsic activity and physical constraints. Across scales, 
geometry plays a central role: the shape of active units and the structure of their environment 
strongly influence how order emerges in these far-from-equilibrium systems. In this thesis, 
we combine minimal active-matter models with bottom-up in vitro experiments to identify 
the principles by which geometry and activity shape collective behavior in biological matter. 
At the subcellular scale, we investigate how the physical properties of chiral FtsZ filaments 
govern their large-scale organization. Using a mesoscopic model validated by reconstituted 
filament assays, we show that filament shape, intrinsic curvature, and flexibility, together with 
activity-driven straightening, determine whether filaments form chiral rings, polar bands, or 
nematic-like states. Our model shows that small changes in filament mechanics produce large 
shifts in collective structures, revealing how the geometry of individual filaments amplifies 
through activity to control patterns relevant for bacterial cytokinesis. 
At the cellular scale, we examine how geometry of the external environment influences 
collective cancer cell migration. Experiments in controlled microfabricated obstacle 
environments demonstrate that geometric disorder alone can induce a transition from 
collective to single-cell invasion. A minimal model of active particles in disordered geometries 
reproduces these effects, demonstrating that cell dissemination results both from local 
geometrical constraints and a global integration of spatial disorder over time. Surprisingly, 
this transition is accompanied by a change in the universality class of interface dynamics, 
revealing that cell-environment interactions can shift the collective behavior of an invasive 
front purely through mechanics.  
In the last system, we study how cell-intrinsic geometry and chirality affect collective motion 
in confined and unconfined settings. Using a minimal model inspired by in vitro experiments, 
we analyze motile cells that exhibit persistent rotation due to intrinsic left-right asymmetry. 
In circular confinement, this simplified chiral model reproduces several experimentally 
observed features within specific parameter regimes. At high densities in unconfined 
environments, however, intrinsic chirality becomes masked even before the onset of the 
jamming transition. These results show that single-cell geometric asymmetry does not 
necessarily translate into large-scale chiral flows, offering new insight into how forces and 
symmetries shape collective motion in dense cellular systems. 
Overall, this work uncovers how geometric constraints – embedded in the intrinsic 
architecture of an active filament or encoded in the complexity of a microenvironment 
couple to active forces to generate different classes of complex behaviors. },
  author       = {Dunajova, Zuzana},
  isbn         = {978-3-99078-076-3},
  issn         = {2663-337X},
  pages        = {110},
  publisher    = {Institute of Science and Technology Austria},
  title        = {{Geometry-driven self-organization of migrating cells and chiral filaments}},
  doi          = {10.15479/AT-ISTA-21423},
  year         = {2026},
}