A compound ampoule for large-volume controllable jet injection

We present a new design for a needle-free injector ampoule, using two concentric pistons to pressurize the fluid during the injection. The smaller, inner piston is used to provide an initial high-velocity piercing jet; it then engages the outer piston to deliver the remaining drug via a low-velocity jet. The goal of this design is to enable needle-free delivery of relatively large volumes to controlled depths in tissue, a task impractical with conventional ampoules and actuators. We demonstrate this concept by constructing a 1.2mL ampoule, measuring the jet velocity it produces in free air, and performing a set of injections into post-mortem porcine tissue. The ampoule smoothly produces the two desired phases of an injection, with a smooth transition of jet velocity as the two pistons engage. The injection is able to penetrate porcine skin to a controlled depth and deliver fluid to the subcutaneous and/or intramuscular layers, though further investigation is required to ensure that all of the fluid delivered can be retained at the desired depth.