Gas and particle dynamics in transdermal powdered drug delivery
Transdermal powdered drug delivery is an emerging technology for the injection of drugs through human skin, in which particles of solid drug are entrained in a high-speed gas flow and directed towards the skin at a high enough velocity to penetrate the outer layer of dead cells. Hand-held devices based on this idea offer a means of safe, painless and effective delivery of many drugs and vaccines. This thesis describes a programme of research into the fluid dynamics which determine the particle velocity distribution, the most important mechanical characteristic of the system, in prototype drug delivery devices. Pressure measurements are described which enable characterisation of the gas flow in the drug delivery devices. These are complemented by optical particle detection experiments, which provide a record of the timing of drug particle delivery with respect to the gas flow. Doppler Global Velocimetry (DGV) has been used to measure the velocity field of drug particles. Various tasks involved in the application of DGV to these flow-fields are described. In particular, the use of time-integrated DGV for measurements of unsteady, short-duration flows is discussed. Time-integrated DGV, applied at a range of operating conditions, has provided information on the variation of particle delivery velocity with particle size and with total mass of particles. Time-resolved DGV measurements reveal that particles first emerge in a slow-moving cloud which is driven by transient starting process in the gas flow, followed by a faster stream of particles entrained in a quasi-steady gas flow. The experimental results are complemented by numerical computations of certain aspects of the drug delivery flows. These computations are compared with experimental results, and used to gain additional information on the functioning of the system as a whole.