A device comprising a first region comprising a first array of obstacles through which particles can be flowed, wherein the first array of obstacles deterministically directs particles having a hydrodynamic size above a critical size in a first direction and particles having a hydrodynamic size below the critical size in a second direction. The first array of obstacles form a network of gaps, wherein a fluid passing through the gaps is divided unequally into a major flux and a minor flux so that particles having the hydrodynamic size above the critical size are displaced in the network and particles having the hydrodynamic size below the critical size are not displaced in the network. The device further comprises a bypass channel disposed in fluid communication with the first region, wherein the first array of obstacles directs the particles having the hydrodynamic size above the critical size either toward or away from the bypass channel.