Activity-driven tissue alignment in proliferating spheroids

Soft Matter Royal Society of Chemistry 19:5 (2023) 921-931


Liam J Ruske, Julia M Yeomans


We extend the continuum theory of active nematic fluids to study cell flows and tissue dynamics inside multicellular spheroids, spherical, self-assembled aggregates of cells that are widely used as model systems to study tumour dynamics. Cells near the surface of spheroids have better access to nutrients and therefore proliferate more rapidly than those in the resource-depleted core. Using both analytical arguments and three-dimensional simulations, we find that the proliferation gradients result in flows and in gradients of activity both of which can align the orientation axis of cells inside the aggregates. Depending on environmental conditions and the intrinsic tissue properties, we identify three distinct alignment regimes: spheroids in which all the cells align either radially or tangentially to the surface throughout the aggregate and spheroids with angular cell orientation close to the surface and radial alignment in the core. The continuum description of tissue dynamics inside spheroids not only allows us to infer dynamic cell parameters from experimentally measured cell alignment profiles, but more generally motivates novel mechanisms for controlling the alignment of cells within aggregates which has been shown to influence the mechanical properties and invasive capabilities of tumors.

Itinerant Magnetism in the Triangular Lattice Hubbard Model at Half-doping: Application to Twisted Transition-Metal Dichalcogenides

ArXiv 2311.10146 (2023)


Yuchi He, Roman Rausch, Matthias Peschke, Christoph Karrasch, Philippe Corboz, Nick Bultinck, SA Parameswaran

Kekulé spirals and charge transfer cascades in twisted symmetric trilayer graphene

ArXiv 2310.16094 (2023)


Ziwei Wang, Yves H Kwan, Glenn Wagner, Nick Bultinck, Steven H Simon, SA Parameswaran

Entropy production and thermodynamic inference for stochastic microswimmers

ArXiv 2310.15311 (2023)


Michalis Chatzittofi, Jaime Agudo-Canalejo, Ramin Golestanian

Spin skyrmion gaps as signatures of strong-coupling insulators in magic-angle twisted bilayer graphene

Nature Communications Springer Nature 14 (2023) 6679


Jiachen Yu, Benjamin Foutty, Yves H Kwan, Mark E Barber, Kenji Watanabe, Takashi Taniguchi, Zhi-Xun Shen, Siddharth Ashok Parameswaran, Benjamin E Feldman


The flat electronic bands in magic-angle twisted bilayer graphene (MATBG) host a variety of correlated insulating ground states, many of which are predicted to support charged excitations with topologically non-trivial spin and/or valley skyrmion textures. However, it has remained challenging to experimentally address their ground state order and excitations, both because some of the proposed states do not couple directly to experimental probes, and because they are highly sensitive to spatial inhomogeneities in real samples. Here, using a scanning single-electron transistor, we observe thermodynamic gaps at even integer moiré filling factors at low magnetic fields. We find evidence of a field-tuned crossover from charged spin skyrmions to bare particle-like excitations, suggesting that the underlying ground state belongs to the manifold of strong-coupling insulators. From the spatial dependence of these states and the chemical potential variation within the flat bands, we infer a link between the stability of the correlated ground states and local twist angle and strain. Our work advances the microscopic understanding of the correlated insulators in MATBG and their unconventional excitations.