A filamentary structure extruded from a nozzle during 3D printing comprises a continuous filament including filler particles dispersed therein. At least some fraction of the filler particles in the continuous filament comprise high aspect ratio particles having a predetermined orientation with respect to a longitudinal axis of the continuous filament. The high aspect ratio particles may be at least partially aligned along the longitudinal axis of the continuous filament. In some embodiments, the high aspect ratio particles may be highly aligned along the longitudinal axis. Also or alternatively, at least some fraction of the high aspect ratio particles may have a helical orientation comprising a circumferential component and a longitudinal component, where the circumferential component is imparted by rotation of a deposition nozzle and the longitudinal component is imparted by translation of the deposition nozzle.