Physicists from the Max Planck Institute for Dynamics and Self-Organization found that chemically active vesicles can spontaneously switch between attracting, repelling, or chasing each other. Jakob Metson said, "Remarkably, these nonreciprocal interactions between the vesicles emerge spontaneously by breaking the symmetry of the chemical reactions." This model helps explain lifelike behavior.
In nonreciprocal active matter, agents act differently on each other, seemingly in violation of Newton's third law. This principle can result in various active matter traits, such as self-propulsion, molecular regulation and collective motion.
A new model describes how such nonreciprocal interactions can emerge spontaneously between chemically active vesicles. Physicists from the Department of Living Matter Physics at the Max Planck Institute for Dynamics and Self-Organization (MPI-DS) found that such vesicles can dynamically switch between ignoring, attracting, repelling and chasing each other.
The study is published in the journal Newton.
"In our work, we describe a fundamentally new class of intelligent active matter systems," says Jakob Metson, first author of the study. "Remarkably, these nonreciprocal interactions between the vesicles emerge spontaneously by breaking the symmetry of the chemical reactions," he adds.
Chemical gradients drive changing interactions
The driving force behind this mechanism is the enzymatic activity within the semipermeable vesicles. This can cause a chemical concentration gradient between the interior of a vesicle and its surroundings, defining the behavior of the vesicles. Nonreciprocity can emerge between two vesicles if the chemical concentration inside one is higher than in its surroundings, while the concentration inside the other is lower than in its surroundings.
Furthermore, as the enzymatic reactions continue, this dynamic state may change over time, either spontaneously or in a controlled way. Manipulating the chemical reactions externally, for example, by adding more reactants, can be used to alter the interactions. All the vesicles can be prepared identically, yet their interactions are highly dynamic and depend on their evolving chemical state.
A framework for lifelike behavior
Ramin Golestanian, director at MPI-DS, says, "This conceptual framework provides a remarkable degree of flexibility for the emergent properties of the active suspension. The conceptual paradigm that underlies our work is that of emergent symmetries and their associated spontaneous symmetry breaking."
At the origins of life, protocells with similar properties are thought to have emerged. The study's new framework thus offers a perspective on how the properties defining life, such as signaling, sensing and movement, can emerge.