​A collaboration led by the Chinese University of Hong Kong has discovered that millions of bacterial cells in suspension in a liquid can self-organize into highly robust collective oscillatory motion, even though the individual cells move in an erratic manner, with random directional changes. Using a mathematical model, a researcher from IRAMIS has deciphered the mechanisms underlying such behavior, thus providing evidence for a new family of "active" matter, in which a long-range order arises from "weak" synchronization between cells.

This work improves the knowledge of self-organization processes in biological systems. Collective oscillations are ubiquitous in nature and play a vital role in many processes such as embryogenesis, organ growth, and the synchronization of neural networks. Multicellular systems studied before now usually emerged from long-distance couplings between individual cells. In the present case, however, there is no long-range coupling between cells, nor any local oscillation mode. This explains why this type of motion has not been detected up to this point.

As an emerging interdisciplinary discipline, the science of "active" matter investigates systems in which the injected energy generates motion. Research on active matter can focus on any living organism—from cell assemblies to herds of animals—in which each element is self-propelled, or on synthetic materials resulting from self-organization processes. Bio-inspired self-assembly principles could be used for the development of materials, fabrics, or even complete active devices.