Bionic collective intelligence of synthetic active matters by ion-exchange reaction

Abstract

In complex systems, a large ensemble of elementary components are involved to form parallel network interactions without centralized control, where nontrivial collective behaviors, intricate information processing, and adaptation emerge. Active matter, for its intrinsic non-equilibrium property, is a paradigm model of complex systems. Specifically, active matters define those matters in an entropically disfavored state that are able to continuously convert energy into mechanical work. Normally, active matters can self-propel with directional motion and self-organize into complex collective motion by interacting with neighbouring units that coexist in one system. Schools of fish, flocks of birds, and bacterial colonies are examples of living active matters in biological complex systems. Recently, synthetic active matter has aroused interest due to its potential in biomedical applications, as well as serving as the perfect model system for non-equilibrium physics. Notably, highly functional active nanoparticles have been proposed as minuscule robots for complex tasks. However, due to the limited size, it is challenging to incorporate sophisticated logic circuits into individual active particle, limiting their functionality. Therefore, the collective intelligence emerging from the interaction network of millions of individual simple particles should be explored to enable advanced functions. In this thesis, I present a bionic collective intelligence in a synthetic active matter system with non-reciprocal interaction, which is realized by the simple ion-exchange reaction. First, inspired by the microbial symbiosis system, a minimal complex system composed of two chemically coupled species is proposed, where the “waste” product of one is the “nutrient” for another. The experiment is achieved with the self-propelled ZnO nanorod and chemically active sulfonated polystyrene microbeads (sulfonated PS). The ion-exchange reaction can couple self-propelled ZnO nanorods and sulfonated PS together, where the Zn2+ and H+ are “nutrient” and “waste” exchanging between the two active species. Chemical communication is established that enhances the reactivity and motion of both nanorods and the microbeads, resulting in the non-reciprocal interaction via the long-ranged attractive/repulsive osmosis coupling. Subsequently, the ZnO-sulfonated PS active system emerges the sophisticated dynamic self-organization, active swarming and consensus decision-making behaviors. The quantitative analysis of the individual particle motion, the interparticle interaction and the in-situ chemical gradients reveal that the communication-dependent activity, i. e. separation-dependent reactivity, promotes the non-reciprocal interaction and the distinctive intelligent collective dynamics. A coarse-grained model simulation further confirms that both inter-particle osmotic interactions and the separation-dependent activity are essential to the observed collective intelligence. With the understanding of the underlying mechanism of the intelligent collective motion of the active ion-exchanging particle system, we take this idea to new grounds by synthesizing highly functional active particles as nanorobots and applying the quorum decision-making behavior of the robots for precise drug delivery to the dental biofilm and locally kill the bacteria.