Mechanisms of transport enhancement for self-propelled nanoswimmers in a porous matrix

Abstract

Micro/nanoswimmers convert diverse energy sources into directional movement, demonstrating significant promise for biomedical and environmental applications, many of which involve complex, tortuous, or crowded environments. Here, we investigated the transport behavior of self-propelled catalytic Janus particles in a complex interconnected porous void space, where the rate-determining step involves the escape from a cavity and translocation through holes to adjacent cavities. Surprisingly, self-propelled nanoswimmers escaped from cavities more than 20× faster than passive (Brownian) particles, despite the fact that the mobility of nanoswimmers was less than 2× greater than that of passive particles in unconfined bulk liquid. Combining experimental measurements, Monte Carlo simulations, and theoretical calculations, we found that the escape of nanoswimmers was enhanced by nuanced secondary effects of self-propulsion which were amplified in confined environments. In particular, active escape was facilitated by anomalously rapid confined short-time mobility, highly efficient surface-mediated searching for holes, and the effective abolition of entropic and/or electrostatic barriers at the exit hole regions by propulsion forces. The latter mechanism converted the escape process from barrier-limited to search-limited. These findings provide general and important insights into micro/nanoswimmer mobility in complex environments.

Advances in Chemically Powered Micro/Nanorobots for Biological Applications: A Review

“…Experiments and simulations showed that escape was influenced by confined space and the transition between barrier, and search was limited. [ 46 ] Electro‐hydrodynamic flows responsive microswimmers tuning motion and coupling for local dynamic control through internal reconfiguration. The shape and dielectric properties of microswimmers enable responsive advancement when heated.…”

Elucidating the Influence of Metal Surface Composition on Organic Adsorbate Binding Using Active Particle Dynamics

“…Active particles are colloids that convert environmental energy into directed mobility that exceeds Brownian motion . For example, Janus particles with a cap of catalytic metal (typically Pt) move autonomously in a fuel solution of H 2 O 2 . The Pt sites rapidly decompose H 2 O 2 , creating an asymmetric chemical gradient that acts to propel the particle .…”

Active Diffusion of Self-Propelled Particles in Flexible Polymer Networks

“…28,57 Considering a broader perspective, our work provides a relevant example of an active particle in a periodic confining potential 58 and is intimately related to the study of active particles in a porous matrix. 33,59 This paper is organized as follows. In section 2, we explain the model system investigated in this work.…”

“…As demonstrated in the studies using the Brownian tracer, ,− the accessible volume and its connectivity network drastically differ from the geometrical ratio, which is expected to result in size-dependent diffusion dynamics for the active tracer. Our model system serves as a prototype for the study of the active diffusion in the above-mentioned biological meshwork or artificial regular polymer matrices. , Considering a broader perspective, our work provides a relevant example of an active particle in a periodic confining potential and is intimately related to the study of active particles in a porous matrix. , …”