Behavior of capillary valves in centrifugal microfluidic devices prepared by three-dimensional printing

This paper details the behavior of capillary valves in centrifugal microfluidic devices prepared by three-dimensional (3D), or solid-object, printing. Microfluidic structures containing valve channels with different widths, heights, and radial distances from the center of rotation were studied and compared with extant capillary valve theories. Due to the printing process, the produced valve channels possessed a ridged or scalloped pattern. Hence, actual channel widths at the widest and narrowest points of the ridged pattern were determined, and used in comparisons between theoretical and empirical values. In addition, variations in contact angle resulting from the ridged pattern were measured and employed in theoretical calculations. For 1-mm high valve channels, the critical angular frequency (rpm) required to overcome capillary valve pressure was found to be independent of width. However, as the height of the valve channel was reduced, the critical rpm was found to become progressively more width-dependent increasing more rapidly for narrower channels. Both of these observations point to a role for feature sharpness, as well as the geometry of the valve channel opening, in valve behavior. Otherwise, valves followed a predictable trend of increasing critical rpm with decreased valve height and decreased radial distance from the rotation center. Using these results as a guide, then, it is possible to prepare centrifugal microfluidic devices by 3D printing with operability comparable to devices prepared by other microfabrication techniques.