A microfluidic pumping mechanism driven by non-equilibrium osmotic effects

A mechanism is presented which drives a fluid flow using two chemically reacting molecular species and osmotic effects. For concreteness the mechanism is discussed in the context of a tube which at each end has a capping membrane which is permeable to the fluid but impermeable to the two molecular species. The chemical reactions occur at sites embedded in the capping membrane. Labeling the two chemical species A and B, at one end the reactions split each molecule of species B into two molecules of species A. On the other end two molecules of species A are fused together to form a single molecule of species B. A mathematical model of the solute diffusion, fluid flow, and osmotic effects is presented and used to describe the non-equilibrium steady-state flow rate generated. Theoretical and computational results are given for how the flow rate depends on the relative diffusivities of the solute species and the geometry of the system. An interesting feature of the pump is that for the same fixed chemical reactions at the tube ends, fluid flows can be driven in either direction through the tube, with the direction depending on the relative diffusivities of the solute species. The theoretical results are compared with three-dimensional numerical simulations of the pump.