A key disadvantage of the microfluidic ratchet mechanism is sample throughput, which at 5 µl per hour for the prototype studied here is significantly less than other methods, such as DLD, which is capable of inhibiting clot formation42 and processing 10 ml of whole blood per minute12. This limited throughput results from the ratchet transport process requiring oscillatory flow, which significantly improved selectivity, but at the cost of throughput. The throughput of the prototype device studied here is sufficient for many leukocyte assays, including flow cytometry, ELISA, and chemotaxis. However, we also recognize there are many applications where greater throughput is desired. In these situations, throughput can be increased by parallelizing the mechanism, as well as optimizing the device design for the specific application, as we have done for a device to enrich for circulating tumor cells, which has a sample throughput of 1 ml/hour36.