Active matter physics involves the study of dynamic systems wherein each element interacts with its surroundings and converts the energy associated with these interactions into mechanical work. Found naturally in the biological world, active systems encompass a large range of length scales: from schooling of fish and flocking of birds- ranging a few meters across, to microscopic bacterial swarms. Motor proteins such as kinesin and myosin, which self propel along microtubules to transport cellular materials are also examples of active systems which constantly respond to their environment.

Biological active matter possesses the ability to ‘sense’ and respond to different chemical gradients. They are  capable of autonomously moving up (chemotaxis) or down (anti-chemotaxis) external gradients, and migrate collectively from one point to another. These systems possess the ability to ‘communicate’ between themselves to show non-trivial emergent behaviors, which cannot be directly inferred from single particle dynamics. Microscopic energy consumption and dissipation drive macroscopic processes, leading to constant remodeling of system configurations and various emergent phenomena. These intriguing systems are inherently out of equilibrium and require the knowledge of non-equilibrium statistical physics, fluid dynamics, reaction kinetics and rigid body dynamics, among others, for developing a good understanding of their behaviors.

Exact modeling of the dynamics of such systems, however, is very challenging as the particles not only experience local interaction forces, but also are subject to force fields generated by themselves during motion; thus making them essentially interact with complex potentials that might have spatio-temporal variations. Often these models are also quite problem specific and it would be interesting to check if there exist generic force equations for motion (like Newton’s laws in classical mechanics and Navier Stokes equations for fluids) which can be applicable for active systems across multiple length scales. In addition, questions such as: Where do the properties of these systems emerge from? What is the exact mechanism through which active particles interact with external stimuli and also with one another? Can these systems be modeled such that their behaviors can be predicted accurately? – are currently being probed rigorously.

Such unique systems can also be transformed to have a large range of applications. These endeavors not only help us in developing an understanding of various biological processes (such as force generation and activity in cellular media) through a physical perspective, but also in harnessing their properties to achieve specific goals (such as targeted drug delivery within in vivo environments) at the micro/nano scales. One of such intriguing active systems are enzymes. Known widely for their bio-catalytic efficiencies, the potential of enzymes to behave as active matter came as a surprise. These nanometer sized proteins are able to generate forces at highly viscous and inhomogeneous conditions, and not only enhance their own diffusions, but also transfer energy and increase the diffusions of nearby particles as well. Another important property of enzymes is their generation of 'active fluctuations' while reacting with a substrate. These fluctuations are able to travel across a distance of the order of micrometers, and influence the dynamics of faraway systems. The main focus of research in our lab is to probe these active fluctuations, and how they impact the dynamics of particles in artificially crowded media. We believe that the potential of enzymes as active systems has not yet been uncovered fully, and the quest to delve deeper into their kinetics and active fluctuations, will not only help us in understanding life processes in detail, but will also enable us to harness their energies to control the dynamics of crowders in systems.

 

An introductory video on the field of active matter physics can be found below.

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