Steady streaming particle traps
A microfluidic fluid flow system ( 100 ) is disclosed having a fluid chamber or channel ( 150 ) with inlet and outlet ports ( 104, 106 ), allowing the fluid channel to be filled with a fluid. One or more flow obstructions or perturbances, such as cylinders ( 152 ), are provided in the channel. An oscillatory boundary condition is applied, for example, with a piezoelectric driver ( 130 ), that is selected to induce a conservative, low-intensity steady streaming flow in the channel. The low-intensity streaming flow produces distinct eddies that can be utilized, for example, for fluid-dynamically trapping or retaining particles ( 90 ) such as cells ( 92 ) at well defined locations in the channel. The system may be used to trap and study individual cells or for concentrating or filtering particles in a fluid.
1. A method for fluid-dynamically trapping one or more particles in a fluid, the method comprising the steps of:
providing a channel with at least one channel feature that causes deviation from unidirectional flow;
filling the channel with a fluid containing a plurality of particles having a diameter of at least 20 μm; and
oscillating a boundary of the fluid at a frequency and an amplitude to generate a low-intensity steady streaming flow such that eddies are generated at fixed locations in the fluid, wherein the low-intensity steady streaming is driven by time-averaged Reynolds stresses resulting from inertial terms in the boundary layer in oscillating flow;
wherein the fluid exerts a force that moves at least one of the plurality of particles into one of the eddies.
2. The method of claim 1 , wherein the eddies are created by a conservative effect that does not require compression of the fluid.
3. The method of claim 1 , wherein at least one of the eddies fluid dynamically retains at least one of the plurality of particles.
4. The method of claim 1 , wherein some of the plurality of particles become concentrated within the eddies relative to the fluid in the channel away from the eddies.
5. The method of claim 1 , wherein the channel feature is an obstruction in the channel.
6. The method of claim 5 , wherein the channel includes a pair of oppositely disposed sidewalls, and the obstruction is disposed between the sidewalls and spaced apart from the sidewalls.
7. The method of claim 6 , wherein the obstruction is a cylinder.
8. The method of claim 5 , wherein the channel includes a pair of oppositely disposed sidewalls and the obstruction is a protrusion from one of the sidewalls.
9. The method of claim 1 , wherein the channel further comprises at least one inlet port and at least one outlet port, and wherein there is a net fluid flow through the channel.
10. The method of claim 1 , wherein the plurality of particles contained in the fluid are cells.
11. The method of claim 10 , wherein the cells are motile and capable of exerting a motile force, and wherein the eddies generate a trapping force that is greater than the motile force of the cells.
12. The method of claim 1 , wherein at least some of the plurality of particles contained in the fluid are denser than the fluid.
13. The method of claim 1 , wherein the eddies generate a trapping force that is controlled by the oscillation amplitude.
14. The method of claim 1 , wherein the size of the eddies is controlled by the oscillation frequency.
15. The method of claim 1 , wherein the channel includes a plurality of channel features, with at least one eddy associated with each channel feature.
16. The method of claim 15 , wherein at least one of the channel features is a cylindrical obstruction.
17. The method of claim 15 , wherein the channel further comprises an inlet port and an outlet port, and wherein there is a net fluid flow through the channel.
18. The method of claim 1 , further comprising the step of recovering the plurality of particles in the eddy.
19. A method of isolating cells at positions within a fluid, the method comprising:
immersing at least one cell in a fluid;
providing a channel having at least one channel feature that causes deviation from unidirectional flow;
filling the channel with the fluid; and
oscillating a boundary of the fluid at a frequency and an amplitude to generate a low-intensity steady streaming flow in the fluid such that an eddy is generated in the fluid, and fluid dynamically trapping at least one cell in the eddy, wherein the low-intensity steady streaming is driven by time-averaged Reynolds stresses resulting from inertial terms in the boundary layer in oscillating flow.
20. The method of claim 19 , wherein the at least one channel feature is a cylinder.
21. The method of claim 19 , wherein the at least one channel feature is a protrusion from a channel wall.
22. The method of claim 19 , wherein the at least one cell is denser than the fluid.
23. The method of claim 19 , wherein the at least one cell is motile and capable of generating a motile force, and wherein the eddy produces a trapping force that is greater than the motile force of the cell.
24. The method of claim 19 , wherein the channel further comprises at least one inlet port and at least one outlet port, and wherein there is a net fluid flow through the channel.
25. The method of claim 19 , wherein the eddy produces a trapping force that is controlled by the oscillation amplitude.
26. The method of claim 19 , wherein the size of the eddy is controlled by the oscillation frequency.
27. The method of claim 19 , wherein the at least one channel feature comprises a plurality of channel features, and wherein the low-intensity steady streaming generates at least one eddy associated with each channel feature.
28. The method of claim 27 , wherein plurality of channel features are cylinders.
29. The method of claim 27 , wherein the channel further comprises at least one inlet port and at least one outlet port, and wherein there is a net fluid flow through the channel.
30. The method of claim 19 , further comprising the step of recovering the cell trapped in the eddy.