CFD investigation of powdered vaccine and gas dynamics in biolistic gun

Abstract

This paper presents the development of a new device for powder DNA/vaccine delivery system to human skin. The device consists of a convergent–divergent (C–D) nozzle followed by a constant area mixing duct. It accelerates helium gas to supersonic speeds in the C–D nozzle. The particles are entrained from parallel inlet which in turn energizes the boundary layer to prevent flow separation that has been observed in the existing devices. Further, the supersonic flow accelerates the powder micro solid particles through the constant area mixing duct to high speeds sufficient to breach the stratum corneum layer of the human skin to achieve the pharmaceutical effect. The dynamics of the gas/particles flow have been studied numerically to achieve the maximum particle impact velocity. Three different types of micro particles are tested, two of which are gold of diameters 1.8 and 5 μm and the third is polystyrene of diameter 38 μm. Numerical results obtained using semi-empirical particle penetration calculation confirms that the first type of microparticles penetrate distance ranging from 20 to 50 μm and the second type achieve depth from 20 to 57 μm. The third type of microparticles penetrates a distance ranging from 20 to 60 μm beneath the skin. The new device design reduces gas delivery pressure which is required to achieve the same impact conditions compared to the previous devices by 33%. The effect of different parameters on the particle impact conditions are also studied through a series of parametric studies of the driver gas pressure, the device length to diameter ratio (L/D), the particle type. We tested also the use of air instead of helium as driver gas and gas swirling effect. A semi-empirical particles penetration and particle impact parameter (PIP) calculation show a good agreement compared to experimental data.