Contact-line-driven microfluidic devices and methods
In order to expand capabilities of anisotropic ratchet conveyor (ARC) systems beyond those of the simple systems that include only a single track of consistent rung spacing, disclosed herein are ARC devices, systems, and methods related to ARC gates that can selectively pause droplet transport; ARC switches that can select the direction of droplet transport between two tracks, each moving away from an intersection between the two tracks; and ARC junctions that can move a droplet towards, and then through, an intersection between two tracks.
1. A device configured to move a droplet on a surface between a first track and a second track, the device comprising a surface comprising:
a first track comprising a plurality of transverse arcuate regions having a different degree of hydrophobicity than a surrounding region;
a second track comprising a plurality of transverse arcuate regions having a different degree of hydrophobicity than the surrounding region, wherein the transverse arcuate regions of the first track and the second track are sized and spaced to induce asymmetric contact angle hysteresis when the droplet is vibrated; and
an intersection between the first track and the second track, wherein the intersection is configured to selectively transition the droplet between the first track and the second track under specific vibration characteristics.
2. The device of claim 1 , wherein the intersection is a junction configured to selectively transition a droplet from the second track to the first track, wherein the second track is configured to direct the droplet towards the junction.
3. The device of claim 1 , wherein the intersection is a switch configured to selectively transition a droplet from the first track to the second track, wherein the second track is configured to direct the droplet away from the junction.
4. The device of claim 1 , wherein the first track includes a first portion having a first duty cycle and the second track includes a second portion having a second duty cycle that is different the first duty cycle.
5. The device of claim 4 , wherein the first portion and the second portion are adjacent to the intersection, such that during operation the droplet is transferred between the first portion and the second portion.
6. The device of claim 1 , further comprising a source of vibratory motion configured to controllably vibrate the droplet.
7. The device of claim 1 , wherein the plurality of transverse arcuate regions and the surrounding region are optically flat.
8. The device of claim 1 , wherein the plurality of transverse arcuate regions and the surrounding region are coplanar.
9. The device of claim 1 , wherein the transverse arcuate regions define substantially circular arcs having a constant radius.
10. The device of claim 9 , wherein the constant radius is approximately equal to a radius of a footprint of the droplet.
11. The device of claim 9 , wherein the substantially circular arcs are equal to or less than ½ of a circle.
12. The device of claim 1 , wherein the plurality of transverse arcuate regions and the surrounding region are transparent at visible wavelengths.
13. The device of claim 1 , wherein the droplet has a degree of hydrophobicity closer to the degree of hydrophobicity of the transverse arcuate regions than that of the surrounding region.
14. The device of claim 1 , wherein the surrounding region is a hydrophobic material and the transverse arcuate regions are defined in the surrounding region by removing the hydrophobic material to expose a hydrophilic material underneath.
15. The device of claim 1 , wherein the device includes at least two device elements selected from the group consisting of a loop, a gate, a junction, and a switch, such that the at least two device elements are configured to manipulate the same droplet when operated.
16. A method of moving a droplet on a track on a surface of a device according to claim 1 , the method comprising:
depositing the droplet on the track such that a front portion of the droplet contacts a first of the plurality of arcuate regions of the track; and
vibrating the droplet at a frequency and amplitude sufficient to cause the droplet to deform such that the front portion of the droplet contacts a second of the plurality of arcuate regions of the track, thereby urging the droplet towards the second of the plurality of arcuate regions.
17. The method of claim 16 , the step of vibrating the droplet comprises a technique selected from the group consisting of acoustic vibration, electromagnetic vibration, and piezoelectric vibration.
18. The method of claim 16 , the step of vibrating the droplet comprises vibrating the surface.
19. The method of claim 16 , wherein the device is a switch and the step of vibrating the droplet comprises vibrating the droplet at a vibration signal sufficient to move the droplet from the first track to the second track, thereby moving the droplet away from the switch on the second track.
20. The method of claim 16 , wherein the device is a junction and the step of vibrating the droplet comprises vibrating the droplet at a vibration signal sufficient to move the droplet from the second track to the first track, thereby moving the droplet towards the junction on the second track, through the junction, and then away from the junction on the first track.