Patent ID: 7214348

Claim:
A microfluidic device comprising: a substrate having a first surface, a second surface opposing the first surface, and a thickness; a first channel formed in the substrate and extending in a first direction, the first channel having a first cross-sectional area defined by at least a first minimum dimension and a first depth, the first depth extending in a direction normal to the first surface and toward the second surface; a second channel formed in the substrate and extending in a second direction, the second channel having a second cross-sectional area defined by at least a second minimum dimension and a second depth, the second depth extending in a direction normal to the first surface and toward the second surface; a fluid communication formed in the substrate between the first channel and the second channel and having a third cross-sectional area defined by at least a third minimum dimension, wherein the third cross-sectional area is less than the first cross-sectional area; and a particulate flow-restricting material disposed in the first channel and comprising flow-restricting particles, wherein at least 10% by weight of the flow-restricting particles comprises flow-restricting particles having a particle diameter that is less than the third minimum dimension.