Boundary-mediated phases of self-propelled Kuramoto particles, FA, Vittoria Sposini, Enzo Orlandini and Fulvio Baldovin, Phys. Rev. E 114, 025421 (2026)Active agents confined near boundaries develop distinct accumulation patterns depending on the microscopic drive behind their motion. This work examines how self-propulsion and velocity alignment, individually and combined, shape these patterns in self-propelled Kuramoto particles confined within circular walls. Under smooth, frictionless boundaries, the interplay of persistence and alignment produces three regimes: a dilute gas phase, a delocalized ring-like cluster, and localized disk-like clusters, with the system's moment of inertia and angular momentum both peaking in the delocalized regime. Introducing boundary friction fundamentally changes this picture: it destabilizes delocalized clusters, giving rise to coexisting boundary clusters and gas phases, and a new "trapped gas" phase where particles form small, non-rotating groups near the wall. 

By connecting these macroscopic accumulation patterns to the specific microscopic mechanism that produces them, our results offer a practical diagnostic tool: delocalized, ring-like structures signal self-propulsion-dominated motility with weak coordination, as in E. coli run-and-tumble motion or dilute Janus particles, while alignment-coupled self-propulsion produces cohesive clusters, a mechanism spanning scales from bird flocks to confined Quincke rollers. This has direct implications for interpreting boundary accumulation in biological systems, such as cell migration, and for guiding the design of bio-inspired robotic swarms.

Boundary-mediated phases of self-propelled Kuramoto particles, FA, Vittoria Sposini, Enzo Orlandini and Fulvio Baldovin, Phys. Rev. E 114, 025421 (2026) 

Epithelial tissues shift between solid-like and fluid-like states depending on physiological or pathological context, a plasticity central to morphogenesis, homeostasis, and disease. This fluidification arises through two routes: cell motility, generating directed motion through the tissue, and large, spatially heterogeneous shape fluctuations, which drive neighbor rearrangements via boundary deformations. While motility-driven fluidization is well studied, the role of heterogeneous shape fluctuations remains largely unexplored. My research develops a modeling framework that embeds experimentally measured distributions of molecular motor activity into cell-based models via superstatistics, linking molecular variability to tissue-scale rheology. This framework enables a systematic comparison of motility- and shape-fluctuation-driven fluidification, disentangling their relative contributions to epithelial dynamics in development and disease.

Phase separation is a hallmark of collective behavior in active systems, from bacterial biofilm aggregation to cell segregation in tissue development. These phenomena are commonly studied through simulations of self-propelled particle mixtures, where non-conservative forces mimic motility driven by sensing of nutrient or cell-density gradients. A simple model system is a collection of self-propelled particles evolving under Langevin dynamics, with bath temperature set by activity and white noise. When propulsion and density are high enough, this system undergoes Motility-Induced Phase Separation (MIPS), where traffic jams grow into dense droplets surrounded by a gaseous phase. The structure and dynamics of these droplets, and the link between macroscopic behavior and microscopic details, are fertile ground for biophysical research.

We find that droplet lifetime and shape depend non-monotonically on self-propulsion persistence, arising from competing mechanical stress components that stabilize or destabilize interface fluctuations. This work compares active and passive phase-separating systems mechanically, relating microscopic single-particle properties to observables such as condensation and evaporation rates.

The interplay between motility and deformation of endothelial and epithelial cells in monolayer plays a crucial role in regulating several biological processes such as wound-healing, cancer progression, and tissue morphogenesis. Finite element simulations of deformable cells can offer insights on the accessible phenotypes of a monolayers once the microscopic parameters of the model are set. Thus, computer simulations informed with single cell features represent a powerful tool to explore feedback mechanisms essential in biology. 

Deformable Particles (DPs) can be modeled in two dimensions as ring polymers where the monomer equation of motion is set by a shape energy function that includes compressibility, contractility, and curvature costs as well as interactions between monomers of different cells. This model allows for exploration of how deformability alters mechanical and dynamical properties of rigid disordered systems. For example the relaxation of the density field and the propagation of stress are altered by particle alignment.

Amorphous solids, such as grains and colloidal suspensions, are able to adapt and form a memory of a mechanical deformation when a periodic perturbation is applied to them. Cyclic shear is a reliable process to encode memories in colloidal suspensions and jammed solids, yet its emergence mechanism and the relation to the amorphous structure of the systems it develops in are not fully understood.

With recent computational advances for the production of extremely stable configurations of amorphous solids, we study memory encoding by cyclic shear as a function of the underlying stability of the amorphous structure in marginally stable and highly stable packings, the latter produced by minimizing the potential energy using both positional and radial degrees of freedom. We find that jammed solids need to be marginally stable in order to store a memory by cyclic shear. In particular, highly stable packings store memories only after overcoming brittle yielding and the mechanical training takes place in the shear band, the least stable portion of the system.

Marginal stability in memory training of jammed solids, FA, E Corwin and V Hagh, Physical Review E, 104, 044907 (2021)

The unconventional thermal properties of jammed amorphous solids are directly related to their vibrational density of states. While the vibrational spectrum of jammed soft spheres has been fully described, the vibrational spectrum of hard spheres, a model system for glass former liquids, is still unknown due to the difficulty of treating the non-analytic interaction potential representing collisions between impenetrable objects. 

We bypass this difficulty by using an effective interaction potential for the free energy of thermal hard spheres and minimizing it to mimic the rapid compression of hard spheres towards the jamming point. The resulting vibrational spectrum shows that the mechanical response of hard and soft spheres is unified at jamming. For hard-sphere packings, we observe low frequency modes which agree with those found in numerical simulations of jammed soft spheres. Our measurements of the vibrational structure demonstrate that the jamming universality extends away from the transition point: hard-sphere thermal systems below jamming exhibit the same vibrational spectra as thermal and athermal soft-sphere systems above the transition.

Vibrational properties of hard and soft spheres are unified at jamming, FA and E Corwin, Physical Review Letters, 124, 238002 (2021)