The devices and systems described herein include one or more fluid paths, e.g., channels, and one or more selectively permeable obstacles arranged in the fluid path(s), each including a plurality of aligned nanostructures, e.g., nanotubes or nanorods, defining an outer surface of the obstacle and an internal network of voids. The obstacle(s) can further include binding moieties applied to the outer surface and/or to the surfaces of the individual nanostructures within the obstacle(s). The devices can be manufactured by forming the dense groupings of nanostructures to extend outwards and upwards from a substrate; forming a fluidic channel, bonding the fluidic channel to the substrate; and optionally applying binding moieties to the obstacles. The devices can be used to manipulate cells within fluid samples.