Active matter is a broad field with many potential applications. A common thread underlying many of the current research lines is the study of systems powered by some internal energy source, as in the case of organisms moving thanks to food metabolism. In fact, self-propelling systems need to overcome the resistance of the surrounding medium, drawing the required energy from internal sources. The study of locomotion and self-propulsion in biological and bio-inspired artificial system appears, therefore, as an ideal testing ground to put the concepts and tools of active matter at work. We will report on recent progress coming from case-studies on the motility and collective feeding of unicellular organisms (flagellates and ciliates) and bio-inspired micro-robots, studied from the point of view of the mechanics of active matter.

As a geoscientist who has spent his career at universities and national laboratories studying fluid mechanics, I have had the opportunity to pursue a wide range of research topics—from fundamental studies of flow in Earth’s core and mantle convection to the monitoring of CO₂ sequestration. The technical challenges encountered over the years have often been novel and always engaging. The U.S. Magma Energy Project of the 1980s, which explored the theory and practice of drilling into a magma body to extract heat for electricity generation, inspired further work on volcanism and magma transport within the Earth. This research led to investigations of thermally driven circulations and forced magma flows in conduits as mechanisms for offsetting heat loss and preventing eruptive pathways from solidifying. Viscosity—a critical parameter in modeling magma flow—is notoriously difficult to constrain in volcanic environments and often requires indirect and innovative methods, including high-pressure experiments conducted under challenging and sometimes hazardous conditions. At the opposite end of the viscosity spectrum, tracing the movement of gases through subsurface pores and fractures has also been a major research theme. Technologies such as electrical-resistance tomography have proven effective in monitoring CO₂ sequestration at depths approaching 3,000 meters. Finally, understanding how gases migrate through the subsurface under the combined influence of imposed and atmospheric pressure variations remains an active challenge motivating ongoing research on multiple fronts. The motivations behind this applied research, as well as the technologies developed to address these problems, will be the primary focus of this presentation.