Method for continuous particle separation using obstacle arrays asymmetrically aligned to fields

A microfluidic for separating particles according to size comprising device: a microfluidic channel and a lattice comprising a network of gaps within the microfluidic channel, wherein the device employs a field that propels the particles being separated through the microfluidic channel; and characterized in that a flow field from the gaps is divided unequally into a major flux component and a minor flux component into subsequent gaps in the network, so that the average direction of the minor flux component is not parallel to the average field direction, and, when particles are introduced into the array, particles having a size smaller than a predetermined critical size are transported generally in the average direction of the field, and particles having a size at least as the critical size are transported generally in the average direction of the major flux component, thereby separating the particles according to size.