Abstract: The invention provides pneumatic shuttering of a focused or collimated aerosol particle stream. The aerosol stream can be collimated by an annular sheath of inert or non-inert gas. The apparatus propagates a sheathed aerosol stream through a series of aerodynamic lenses along the axis of a flow cell. The final lens is typically positioned above a substrate, so that direct material deposition is provided. A substantially perpendicularly-flowing gas external to the aerodynamic lens system is used to redirect the particle stream away from the flow axis and through an exhaust port, thereby shuttering the collimated aerosol stream. The pneumatic shutter enables printing of discreet structures, with on/off shuttering times of approximately 1 to 100 milliseconds.