Methods and devices are disclosed for providing the controlled formation of planar homogeneous or heterogeneous materials using microfluidic devices. In one embodiment, a planar array of microfluidic channels is employed to produce a flowing liquid sheet having heterogeneous structure by spatially and temporally controlling dispensing of polymer liquid from selected microchannels. The resulting liquid sheet is solidified to produce a planar heterogeneous material that may be continuously drawn and/or fed from the plurality of microfluidic channels. The polymer liquid may include a payload that may be selectively incorporated into the heterogeneous structure. In some embodiments, the local material composition is controllable, thereby allowing control over local and bulk material properties, such as the permeability and the elasticity, and of creating materials with directionally dependent properties.