Laterally Dispersing Nozzles for Needle-assisted Jet Injection

Most transdermal drug delivery systems are designed to inject drugs through the skin in a direction normal to the skin surface. However, in some applications, such as local anaesthesia, it is desirable to disperse the drug in a direction parallel to the surface of the skin. In this paper we present nozzles for needle-assisted jet injection that are designed to laterally disperse the fluid drug at a chosen depth in tissue. These nozzles were manufactured by laser machining holes in the walls of 0.57 mm (24 G) hypodermic needles, and sealing the ends of the needles. An existing controllable jet injection system was used to test the nozzles. High-speed video recordings were taken to examine the shape of the high-speed jets emitted from the orifices, and jet injections into post mortem porcine tissue were performed to evaluate the resulting dispersion pattern. These injections demonstrated the ability of these nozzles to achieve a widely spread dispersion at a depth of 3 mm to 4 mm in tissue. We observed that the widest dispersion occurred at the same depth as the orifices, and dispersion was greater in the direction of the jets. Further investigation, including an in vivo study, is now required to evaluate whether this technique can reduce the time, cost or pain associated with transdermal local anaesthetic delivery.