Effects of Nozzle Diameter and Injection Volume of Drug on Performance of a Needle-Free Injector

Among the techniques of subcutaneous drug delivery, the needle-free injection is relatively new. Compared to the hypodermic syringe, the needle-free injection avoids accidental stabbing and cross-infection. Although the needle-free injection technique has been exercised, the knowledge about instantaneous behaviors of the drug during the injection process have not been clarified. The present study aims to reveal drug flow characteristics of the needle-free injection. The effects of major operating parameters were investigated. An experimental work incorporating the measurement of instantaneous stagnation pressure and the visualization of drug diffusion in gel was conducted. The results show that the needle-free injection process is characterized by time-varying stagnation pressure. The peak stagnation pressure at the initial stage of injection is an important indicator of the aggressivity of the drug. The peak stagnation pressure decreases linearly with the increase of the nozzle diameter or the volume of injection. It is evidenced that the increase in the volume of injection causes an enlargement of the diffusion area of the liquid in the gel, which implies that the drug absorption rate is improved accordingly. Furthermore, with large nozzle diameter, the amount of the power consumed is high. Therefore, the maximum penetration depth of the liquid in gel increases with the nozzle diameter. However, the attainable lateral distance of the liquid is nearly insensitive to the nozzle diameter.