The invention provides mechanisms to improve particle atomisation in a needleless syringe. If the particles are more evenly distributed across the cross-section of the device at the time at which they are entrained, a better footprint of particle penetration is obtainable. The particles are initially located between first and second closure means and the pressure at which said closure means open can be made to be different. Also, a transfer duct which fluidly connects a location upstream of the second closure means to a location between the first and second closure means can be provided. Furthermore, the closure means can be constituted by rupturable membranes which are scored or indented so as to provide controlled rupturing.