Pneumatic capillary gun for ballistic delivery of microparticles
  A pneumatic gun for ballistic delivery of microparticles to soft targets is proposed and demonstrated. The particles are accelerated by a high speed flow of Helium in a capillary tube. Vacuum suction applied to a concentric, larger diameter tube is used to divert substantially all of the flow of Helium from the gun nozzle, thereby preventing the gas from hitting and damaging the target. Speed of ejection of micron-sized gold particles from the gun nozzle, and their depth of penetration into agarose gels are reported. 
Dmitry Rinberg, Claire Simonnet and Alex Groisman