| abstract |
Microfluidic systems and methods including those that provide control of fluid flow are provided. Such systems and methods can be used, for example, to control pressure-driven flow based on the influence of channel geometry and the viscosity of one or more fluids inside the system. One method includes flowing a plug of a low viscosity fluid and a plug of a high viscosity fluid in a channel including a flow constriction region and a non-constriction region. In one embodiment, the low viscosity fluid flows at a first flow rate in the channel and the flow rate is not substantially affected by the flow constriction region. When the high viscosity fluid flows from the non-constriction region to the flow constriction region, the flow rates of the fluids decrease substantially, since the flow rates, in some systems, are influenced by the highest viscosity fluid flowing in the smallest cross-sectional area of the system (e.g., the flow constriction region). This causes the fluids to flow at the same flow rate at which the high viscosity fluid flows in the flow constriction region. Accordingly, by designing microfluidic systems with flow constriction regions positioned at particular locations and by choosing appropriate viscosities of fluids, a fluid can be made to speed up or slow down at different locations within the system without the use of valves and/or without external control. |