Multi-layered and foam-gel composites as a Model for Needle Free Jet Injections

Needle-free jet injections is a growing area of research as an alternative to needle-and-syringe inoculations. To further study this area, it is crucial to understand the fluid dispersion inside the targeted tissue. Due to the cost and limited availability of skin a transparent in vitro model made to represent tissue layers is needed. Previous studies have used single-layer gel substrates with mechanical properties reminiscent of tissue layers. However, typical drug delivery target tissues (intradermal, subcutaneous, muscle) are each composed of a complex system of fibers and cells with differing mechanical properties. In this study we construct a multi-layered hydrogel with various concentrations to match the mechanical properties of each layer of tissue; This study explores both the transient dynamics and final shape of the fluid bolus from jet injection in such substrates. The results of our research involving multi-layered hydrogel are in better agreement with ex vivo dispersion patterns compared to the results obtained for single-layer gels. We also consider a novel substrate using gel-soaked sponges as a proxy for subcutaneous tissue.