The 2025 Motile Active Matter Roadmap.

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.

Low efficiency of Janus microswimmers as hydrodynamic mixers.

The generation of fluid flows by autophoretic microswimmers has been proposed as a mechanism to enhance mass transport and mixing at the micro- and nanoscale. Here, we experimentally investigate the ability of model 2D active baths of photocatalytic silica-titania Janus microspheres to enhance the diffusivity of tracer particles at different microswimmer densities below the onset of collective behavior. Inspired by the similarities between our experimental findings and previous results for biological microorganisms, we then model our Janus microswimmers using a general squirmer framework, specifically treating them as neutral squirmers.

Simulation and time series analysis of responsive active Brownian particles (rABPs) with memory.

To realise the goals of active matter at the micro- and nano-scale, the next generation of microrobots must be capable of autonomously sensing and responding to their environment to carry out pre-programmed tasks. Memory effects are proposed to have a significant effect on the dynamics of responsive robotic systems, drawing parallels to strategies used in nature across all length-scales. Inspired by the integral feedback control mechanism by which Escherichia coli () are proposed to sense their environment, we develop a numerical model for responsive active Brownian particles (rABP) in which the rABPs continuously react to changes in the physical parameters dictated by their local environment.

Effect of particle stiffness and surface properties on the non-linear viscoelasticity of dense microgel suspensions.

Hypothesis: Particle surface chemistry and internal softness are two fundamental parameters in governing the mechanical properties of dense colloidal suspensions, dictating structure and flow, therefore of interest from materials fabrication to processing.

Experiments: Here, we modulate softness by tuning the crosslinker content of poly(N-isopropylacrylamide) microgels, and we adjust their surface properties by co-polymerization with polyethylene glycol chains, controlling adhesion, friction and fuzziness. We investigate the distinct effects of these parameters on the entire mechanical response from restructuring to complete fluidization of jammed samples at varying packing fractions under large-amplitude oscillatory shear experiments, and we complement rheological data with colloidal-probe atomic force microscopy to unravel variations in the particles' surface properties.