The high speed penetration of particles into the human dermis is of interest for targeted drug delivery by transdermal powder injection. However, performing well-controlled single impact experiments with micron scale particles on dermal tissues is difficult. Therefore, the suitability of the use of a dimensionally scaled up 'model' system utilizing steel balls impacting a gelatin to simulate the perforation of micron sized gold particles into human skin was investigated. A finite element (FE) model of a 'calibration' system consisting of a 2 μm gold sphere impacting the human dermis at 651 m/s was used to extract the combinations of possible epidermal material properties which allowed an FE predicted penetration able to match measured data from an existing study in the literature. Novel scaling laws were developed to link the 'model' and 'calibration' systems, and impact experiments were performed on gelatins of various formulations to determine the formulation that produced a penetration which, when scaled, matched that of the calibration system. The resulting material properties of the gelatin were appropriately scaled and used to choose the best combination of skin material properties. In this manner, a quasi static elastic modulus of 2.25 MPa was found for skin, in good agreement with reported values from the literature.
Further experiments were performed with steel, polymethyl-methacrylate, titanium, and tungsten carbide balls impacting the gelatin, in order to determine the effects of particle size and density on penetration depth. FE simulations of both the model and calibration systems confirmed the scaling relationships and impact behavior found in these experiments. Both the FE model and the steel-gelatin experiments were able to predict the penetration trends found by other investigators in the examination of typical particles used for vaccine delivery. It can therefore be concluded that scaled up systems utilizing ballistic gelatins can be used to investigate the performance of transdermal powder injection technology.