Abstract

Liquid needle free injectors are biomedical devices that deliver medication via the creation of high speed liquid jets without the use of hypodermic needles, have been a topic of interest in the scientific community for quite some time. This study focuses on the development and analysis of liquid jet injectors powered by air. Studies demonstrate that the majority of commercially available injectors are gas/air powered units; however there is no indication of a model that prescribes the performance characteristics of this particular type of injector. Consequently the main goal of this research is to develop and validate a model capable of predicting the behaviour of such devices.

In this study, the development and analysis of a model for air-powered injectors is accomplished first by constructing a prototype injector that functions in a very similar fashion and produces jets of similar geometry and velocities as the vast majority of commercially available units. Furthermore, the injector is designed in such a way that the parameters such as, driver pressure, injection chamber length and volume as well as nozzle geometry can be varied.

An initial evaluation of the prototype injector is performed to ensure it can be used to accurately conduct testing. The prototype injector is then used to validate a fluid mechanics model constructed based on previous work from Baker and Sanders [IEEE Trans. Biomed. Eng. 46:235-242, 1999]. Experiments that map stagnation pressures of the jet through the use of a piezoelectric force transducer are performed in order to validate the performance of the model. These experiments describe the peak and average stagnation pressures of the jet based on the effect of different parameters such as driver pressure (400-800 kPa), nozzle size (130-250 μm) and injection chamber length (10-25 mm). The results of these tests are then compared to the behaviour prescribed by the model. An analysis of these results indicates that the present model can accurately be used to predict the performance of air-powered needle free liquid jet injectors.