A soft-matter technique for nanoengineering surfaces is to graft or otherwise associate polymers to a hard surface. These polymer brushes are fascinating in their own right (you can read about our work on polymers grafted to the inside of capillaries or polyelectrolyte brushes subject to normal electric fields on this site) but they can also be used as components in microfluidic devices.
An idea of ours is to use a polymer brush to improve Field-Flow Fractionation (FFF). We have developed an ideal theory that accounts for retardation of flow within the brush and the free energy cost of solutes to entering the brush (which depends on the difference between particle size and grafting density (or brush height if the particle is large enough)), which suggests that there is a size range in which separation can be greatly improved by the presence of the brush and are currently running MPCD simulations on this system.
More to come on this project once we publish our work.