# Design and Analysis: Servo-Tube-Powered Liquid Jet Injector for Drug Delivery Applications
## 3 Results and Discussions
### Penetration of the Liquid Jet Produced by the Present Prototype  
It was also possible to examine the device's ability to penetrate and deposit medication in real tissue. This short series of tests made it possible to verify whether different targets could be attained by utilizing two different pressure curves, water as a test fluid and a 150 \(\upmu\)m nozzle. The volume chosen for the initial penetration study was 0.4 mL, which corresponds to 10 mm of downward travel. In order to ensure the proper volume of fluid was delivered for each sample, the chamber was filled and then primed once; at that point, the sample was placed underneath, and the injection was performed. Test samples of 40 mm to 45 mm thick pig thigh, obtained from the consumer market, weighing from 26 g to 35 g, were created and brought to room temperature. The samples were then placed, as illustrated in Figure 17, under the injector, utilizing a spacer to compress the samples up against the orifice so there would be no standoff distance. The first set of tests looked at the injector's ability to achieve different depths with the outer skin removed, as the tensile strength of pork skin increases as the tissue dries.  
Figure 16: Results showing the capability of the present prototype to shape the pressure profile and deliver different multiple pulse injections: (**a**) two pulses, (**b**) three pulses and (**c**) four pulses. The pulsed injections in each case were delivered at a frequency of approximately 10 Hz, and each pulse was approximately 0.2 mL of injectate.  
The penetration of the pork tissue delivered promising results; the two different profiles were able to deposit at different depths. Furthermore, the samples were weighed pre- and post-injection to determine the level of completeness. In Table 6, the pre-injection and post-injection weights were obtained using an OHAUS Scout SPX421. The pre-injection weight for the profile corresponded to 31.7 g and post-injection at 32.1 g, indicating a delivery efficiency of 100%. However, it should be noted that the weight of the sample could only be obtained within 0.1 g; thus, a more accurate scale should reveal a delivery efficiency of less than 100%. These numbers should be used to give a general behavior of delivery efficiency, and more detailed penetration studies that quantify the effect of backsplash should be conducted.  
It is worth noting that, due to the current experimental limitation and facility constraints, the results in Table 6 for two pressure profiles are provided mainly for illustration purposes to demonstrate the injection capability of the present prototype. A more systematic investigation of the present needle-free jet injector prototype in a well-controlled porcine tissue model, similar to the study by [PERSON] et al. [56], is required in future work.  
\begin{table}
\begin{tabular}{l c c} \hline \hline
**Profile** & **Initial View** & **Dissected View** \\ \hline Test 1 & & \\ (15 MPa injection) & & \\ \hline Test 2 & & \\ (7.5 MPa injection) & & \\ \hline \hline \end{tabular}
\end{table}
Table 6: Penetration Test (Porcine Tissue).  
Figure 17: Close-up of porcine tissue and jet injector nozzle.