Many biological entities—from cells and bacteria to animals—have the remarkable ability to convert stored or ambient energy into directed motion. Similar processes also occur in a variety of artificial systems, such as vibrated granular matter and engineered microswimmers. This common property—shared across systems spanning vastly different length scales and physical domains—is the defining feature of active matter.
 

Active matter is now one of the fastest-growing areas in condensed matter and statistical physics. It presents several novel and challenging aspects. At the level of individual units, the mechanisms underlying motility are often highly nontrivial, arising from biochemical regulation and complex force generation. Such self-propulsion is fundamentally different from the thermal or externally driven motion of passive particles, leading to nontrivial interactions and feedback with the surrounding environment.
 

Equally rich and unexpected physics emerges at the collective level, when many active units interact, as in cell colonies, bacterial suspensions, or flocks of birds. Self-propulsion can dramatically alter the statistical properties of these systems. In contrast to more familiar nonequilibrium systems, where energy is typically injected at the boundaries, in active matter the energy input is local—at the level of each individual unit. As a result, these systems often display remarkable and novel behaviors, such as the emergence of large-scale collective patterns or ratchet effects.
 

Research in this field is pursued from several complementary perspectives within the department. From a theoretical standpoint, active matter is investigated as a paradigmatic problem in nonequilibrium statistical physics, both in terms of stochastic processes and mesoscopic field theories. More broadly, several groups employ physics-based approaches to study living systems, with the aim of providing quantitative descriptions of emergent phenomena and identifying general principles across scales and biological functions.

Theoretical Active Matter
Activity modifies the behavior of a system both at the level of individual units and at large scales. A central theoretical question is to understand how activity affects collective properties in the presence of interactions, and how the resulting nonequilibrium features can be described and quantified. Simplified stochastic models can often be solved using methods from stochastic thermodynamics and nonequilibrium statistical physics, providing useful benchmarks for more complex situations. Models of self-propelled particles are widely used to investigate numerically phase transitions and collective patterns in strongly interacting systems. Hydrodynamic theories, describing the problem at a coarse-grained level, allow analytical predictions concerning stability properties and critical behavior. Lorenzo Caprini and Matteo Paoluzzi work extensively in this field, with applications to granular, magnetic, and chiral active materials, as well as tissue dynamics, in close collaboration with researchers at the Institute for Complex Systems. Irene Giardina focuses on problems related to collective motion and cell proliferation.

Collective Behavior in Interacting Biological Systems
Collective behavior is widespread in biological systems across many species and scales, ranging from cell colonies to flocks of birds, insect swarms, and animal groups on the move. In many cases, the collective patterns that emerge are not driven by leaders or external signals, but arise spontaneously from mutual interactions between individuals. In this respect, these systems represent paradigmatic examples of interacting living active matter.Understanding how to describe such living aggregates, and whether simplified models can quantitatively account for their behavior, remains a challenging problem. The COBBS Lab (Collective Behavior in Biological Systems)—a joint laboratory between the Department of Physics and the Institute for Complex Systems—studies collective behavior in a variety of biological systems, including bird flocks, insect swarms, and cell colonies, using a multidisciplinary approach. The group performs experiments both in the laboratory and in the field, and combines them with statistical physics models and theoretical approaches to interpret the data. COBBS members include Irene Giardina (full professor, Sapienza), Andrea Cavagna (Research Directors, ISC-CNR), Stefania Melillo and Leonardo Parisi (Senior researchers, ISC-CNR) together with  several postdoc, PhD and Master Students.

Active Matter and Synthetic Biology of Living Microorganisms
At the micrometer scale, living organisms present a number of challenging problems related to locomotion, interactions with the environment, and the internal mechanisms underlying their functioning. The Di Leonardo Lab addresses several of these issues using microscopy, optical micromanipulation, and microfabrication techniques. The group investigates bacterial swimming motility, focusing on the origins, consequences, and applications of these motions, ranging from fundamental questions in statistical physics and fluid mechanics to the design of micromachines and microrobots. Another major line of research concerns the synthetic biology of the cell. Microorganisms provide a vast repertoire of molecular devices and circuits shaped by evolution; through genetic engineering, these components can be harnessed to reprogram microorganisms for applications in miniaturized laboratories and complex biological environments.  Members of the group include  Roberto Di Leonardo (full professor, Sapienza), Silvio Bianchi, Claudio Maggi, Giacomo Frangipane, Filippo Saglibeni, and Nicola Pellicciotta (CNR researchers), and several postodcs, PhD and master students.
 

Life Nanosciences
Research in this area is carried out in close collaboration with the IIT Center for Life Nano & Neuro-Science, directed by Giancarlo Ruocco. Using a multidisciplinary approach, the center develops advanced genetic, molecular, electrophysiological, computational, imaging, and perturbation tools to investigate the biological processes underlying brain function and RNA physiology. Researchers from the Department involved in this activity include Giancarlo Ruocco and Mattia Miotto, together with a broad group of condensed matter researchers associated with the center. More information can be found at IIT Center for Life Nano & Neuro-Science.

People:

Lorenzo Caprini (theoretical active matter) is a tenure-track researcher in Theoretical Physics working in the field of statistical physics and active matter. His research focuses on nonequilibrium systems, collective phenomena, microswimmers, active fluids, and the role of inertia and chirality in active systems. He combines analytical theory, numerical simulations, and experiments to investigate emergent behavior in interacting active particles. His work has contributed to the understanding of motility-induced phase separation, active crystals, and transport phenomena in driven systems. He has been recently awarded the 2025 IUPAP Early Career Scientist Prize in Statistical Physics.

Roberto Di Leonardo (active matter, synthetic biology, microscopy) is a full professor in Experimental Condensed Matter working at the interface of soft matter, biophysics, and nonlinear dynamics. His research explores microswimmers, optical manipulation, active colloids, and biological transport processes, often through innovative experimental techniques. He has made important contributions to the study of active matter and light-controlled microscopic systems.

Mattia Miotto (Life nanosciences) is a tenure-track researcher in Applied Physics with interests spanning active matter, machine learning, and biological physics. His work focuses on data-driven approaches to collective behavior and nonequilibrium dynamics, combining computational methods with theoretical modeling to uncover emergent structures and interactions in complex systems.

Irene Giardina (theoretical active matter, physics of living systems, system biology) is Full Professor in Theoretical Physics. She worked for several years on problems related to glassy and non-equilibrium behaviour in condensed matter systems (spin glasses/structural glasses) and interdisciplinary applications. In 2005 she started working on biological systems and founded with Andrea Cavagna, the COBBS Lab, the first lab to collect 3D large-scale experimental data in the field on flocking and swarming behaviour, and to build theory starting directly from the data. In 2021 she was awarded, together with Andrea Cavagna, the Delbruck prize in Biological Physics of the American Physical Society.

Matteo Paoluzzi (theoretical active matter) is an Associate Professor in Theoretical Physics working in statistical physics and complex systems, with a focus on active matter, collective behavior, and nonequilibrium phenomena. His research combines theory and numerical simulations to study emergent dynamics in systems of interacting active particles, glasses, and biological collectives. He has contributed to the understanding of phase transitions, transport, and self-organization in driven systems.

Giancarlo Ruocco (Life nanoscience) is a Full Professor of Experimental Condensed Matter known for his work on disordered systems, liquid matter, biophysics, and complex systems. His research combines scattering techniques, spectroscopy, and statistical physics to investigate the dynamics of glasses, biomolecules, and living systems. He has also played a major role in promoting interdisciplinary research and large-scale scientific initiatives.