Hydrodynamic metamaterials are microfabricated structures that have can be used to manipulate particles to flow along particular paths. They are analogous to traditional optical materials, except rather than modifying the propagation of electromagnetic light waves, these metamaterials modify the propagation of particles through a microfluidic channel.
One class of hydrodynamic metamaterials is an asymmetric array of posts placed within a microfluidic flow channel. The posts are oriented vertically, while flow occurs in the horizontal plane. The asymmetry arises, because each subsequent column of posts is vertically offset from the previous column by a small distance. As a result, the rows of posts are at an angle, α, relative to the direction of flow. Small particles and molecules follow the streamlines of fluid through the channel, and propagate in the direction of flow. Large particles the asymmetry of the channel, and propagate at an angle α relative to the flow direction.
These properties can be exploited to build devices. The figure on the left shows a hydrodynamic metamaterial with two different asymmetric post arrays. Particles entering this metamaterials are focused into a streamline along the center of the channel.
- Morton, K.J., Loutherback, K., Inglis, D.W., Tsui, O.K., Sturm, J.C., Chou, S.Y., & Austin, R.H. "[Hydrodynamic metamaterials: Microfabricated arrays to steer, refract, and focus streams of biomaterials]." Proc. Nat'l Acad Sci. (2008), 105(21), 7434-7438.