Surgical assembly 24 for enabling uniform deposition of a particulate material to a surface of an intracorporeal patient cavity, the assembly comprising an ion emitter 25 having an ion emission zone 26 locatable within the cavity； a dispenser 27 having outlet 28 locatable within the cavity for dispensing the particulate and a processor for determining a location of the ion emission zone based upon the outlet position within the cavity. The particulate material may be a therapeutic or diagnostic agent. The emission zone position may depend upon an electrical potential field. The processor may determine the emission zone based upon the cavity topography. There may be at least two spaced apart ion emitters between the outlet and the cavity surface. The ion emitter may have a surface that complements the cavity surface. Also a surgical spray instrument comprising a body, a transfer tube, a propellant actuator for causing a particulate in a propellant to pass along and out of the tube and arranged along the tube an ion emitter having an ion emission zone. Also a surgical spray instrument assembly comprising the surgical spray instrument and a DC supply, the ion emitter of the instrument being coupled with supply pole.
