Development of an NIR imaging technique in ex-vivo studies for needle-free jet injection systems

A major challenge in the study of the physical mechanism behind needle-free jet injection (NFJI) systems is the lack of visualization techniques or tools to study the penetration and dispersion characteristics of the high-velocity microjet inside the skin tissue. Current imaging techniques used to assess skin permeation require a minimum temporal resolution of 1 ms, whereas a temporal resolution in the order of 100 mu s is needed to study the penetration and dispersion phases of a NFJI system. In this study, we propose near-infrared (NIR) fluorescent and absorbance/transmission imaging techniques to achieve the temporal resolution required for visualization of NFJI studies. Fluorescent signals up to 2.5 mm could be obtained with a normal ex vivo porcine sample. However, absorbance/transmission imaging could not produce the required contrast in the normal ex vivo sample. Also, we apply a tissue clearing technique to improve the image acquisition for higher depth. In the cleared tissue sample, the lowest measured dimensional error was observed at a temporal resolution up to 50 and 10 mu s for NIR fluorescent and absorbance/transmission imaging techniques, respectively.