Structured Active Fluids via Interfacial Nanoparticle Assembly

The transport of ordinary liquids tends to be driven by pressure difference, whereas for active fluids (or biological matters), the transport is autonomous and/or isotropic, governed by the gradient in specific chemical. Wu et al. recently discovered the emergence of spontaneous directional flow of active fluids, consisting of microtubule filaments and kinesin molecular motors, upon their confinement in a variety of microfluidic channels [Science 24 Mar 2017: Vol. 355, Issue 6331]; when confined in loops of toroidal and cylindrical channels, the flow persisted in one direction, either clockwise or counterclockwise. Here, we observed the same active fluid confined in channels of similar geometries, which are made of a thin layer of nanoparticles. By extruding or molding a dispersion of charged nanoparticles in an immiscible solution of oppositely charged surfactants, liquids can be mechanically stabilized (or structured) in an arbitrary shape by jamming of nanoparticle surfactants at the liquid interface. The flow of active fluid and its consequence to overall structures are observed in situ by fluorescent microscopy. The interactions between the liquid interface and active fluid is also studied.