The 2024 Motile Active Matter Roadmap (2411.19783v1)

Abstract: Activity and autonomous motion are fundamental aspects of many living and engineering systems. Here, the scale of biological agents covers a wide range, from nanomotors, cytoskeleton, and cells, to insects, fish, birds, and people. Inspired by biological active systems, various types of autonomous synthetic nano- and micromachines have been designed, which provide the basis for multifunctional, highly responsive, intelligent active materials. A major challenge for understanding and designing active matter is their inherent non-equilibrium nature due to persistent energy consumption, which invalidates equilibrium concepts such as free energy, detailed balance, and time-reversal symmetry. Furthermore, interactions in ensembles of active agents are often non-additive and non-reciprocal. An important aspect of biological agents is their ability to sense the environment, process this information, and adjust their motion accordingly. It is an important goal for the engineering of micro-robotic systems to achieve similar functionality. With many fundamental properties of motile active matter now reasonably well understood and under control, the ground is prepared for the study of physical aspects and mechanisms of motion in complex environments, of the behavior of systems with new physical features like chirality, of the development of novel micromachines and microbots, of the emergent collective behavior and swarming of intelligent self-propelled particles, and of particular features of microbial systems. The vast complexity of phenomena and mechanisms involved in the self-organization and dynamics of motile active matter poses major challenges, which can only be addressed by a truly interdisciplinary effort involving scientists from biology, chemistry, ecology, engineering, mathematics, and physics.

• The paper presents an extensive roadmap addressing the non-equilibrium dynamics and control challenges of motile active matter systems.
• It details key aspects such as transport in complex environments, the role of chirality, and emergent collective behaviors in both synthetic and biological systems.
• The research advocates advanced modeling and experimental innovations to drive practical applications like targeted drug delivery and environmental cleanup.

Motile active matter encompasses a range of systems characterized by autonomous motion and persistent energy consumption, manifesting both in natural entities like cells, insects, and humans, as well as synthetic micro-machines. The paper "The 2024. Motile Active Matter Roadmap" provides an extensive review and prospective guide on the understanding and engineering of such systems with substantial interdisciplinary contributions.

Overview of Motile Active Matter

Active Matter Characteristics: At its core, active matter involves numerous self-propelled agents operating far from equilibrium. This leads to complex behavior influenced by non-equilibrium dynamics, interactions that are often non-additive and non-reciprocal, and the agents' ability to sense and respond to environmental stimuli.

Challenges: A persistent challenge in the field is to understand and control the non-equilibrium nature of active matter, which invalidates traditional equilibrium concepts like free energy and detailed balance. The paper outlines a roadmap for addressing these challenges, emphasizing an interdisciplinary approach involving biology, chemistry, physics, engineering, and mathematics.

Key Areas of Focus

1. Transport and Feedback in Complex Environments: Active objects, from nanomotors to microorganisms, navigate through diverse and often heterogeneous environments like porous media or biological fluids. Understanding their behavior requires an integration of fluid dynamics, boundary interactions, and collective behavior.
2. Chirality and Active Matter: Chirality introduces fascinating dynamics into active matter systems, leading to non-equilibrium phenomena like non-reciprocal interactions and odd elasticity. This section touches on the use of idealized models to simplify the inherent complexity of chirality in biological and synthetic systems.
3. Microbots and Micromachines: The roadmap highlights the potential applications of intelligent micromachines capable of environmental sensing and response, which could revolutionize drug delivery, environmental cleanup, and more. It stresses the need for these systems to develop adaptive and autonomous functions akin to biological agents.
4. Emergent Collective Behavior: The paper explores the swarming and collective dynamics observed in groups of self-propelled particles, akin to bird flocks or fish schools. Understanding these dynamics can inform the design of synthetic systems with emergent group behaviors.
5. Application to Microbial Systems: Advances in controlling microbial motility through mechanical or chemical means could lead to novel technologies in medicine and bioengineering, such as controlling infection pathways or enhancing beneficial microbial activity.

Future Directions and Interdisciplinary Collaboration

The authors argue for a significant interdisciplinary effort to tackle the complexity of active matter phenomena. They propose focused research on:

• Advanced Modeling Techniques: Developing models that integrate different physical forces and interactions to predict active matter behavior accurately.
• Experimental Innovations: Enhancing experimental techniques to observe and manipulate active particles and agents at micro and macro scales.
• Technological Applications: Translating fundamental research into practical applications, particularly in biomedical fields for targeted drug delivery and minimally invasive surgery.

The roadmap underscores the necessity of collaborations crossing traditional domain boundaries to pioneer active matter science and engineering. By understanding the intricate behaviors of motile active systems, the field seeks not only to enhance artificial systems but also to glean insights into living systems that have naturally evolved these capabilities.