Small particles are of great interest in a variety of applications. Spray drying is a common technique for particle synthesis, but it is limited with respect to sizes below 10 μm. Therefore, a new laboratory-scale spray dryer was designed to address this issue. A novel aerosol generator consisting of a piezo crystal in a swirl chamber was designed to obtain droplets in the low micrometer range. After drying and cooling, particles were deposited in a molten carrier, using melt electrostatic precipitation. The median particle size of three pharmaceutical drug substances was 2 μm. The size distribution was particularly narrow, with span values of about 1.1. Spray drying is a sufficient technique to produce small drug particles below 5 μm with ultrasonic atomization at high frequencies. Electrostatic precipitation in a molten carrier is a suitable method to capture these particles.
Low aqueous solubility of drug substances is still one major challenge in pharmaceutical development. A general approach is the reduction of drug particle size to increase dissolution rate as well as solubility. Spray drying has been proposed as appropriate continuous manufacturing technique for micronized particles, which means a median diameter of less than 10 µm. For the production of sub-micron particles by spray drying small droplets are necessary and therefore an ultrasonic nebulizer operating at a frequency of 3 MHz and suitable for acetone is used. In this study a new apparatus was designed and the process parameters were determined. The aerosol consists of fine droplets of dissolved drug in acetone and is transported in carbon dioxide saturated with acetone. After evaporation the acetone vapour is removed by condensation. The resulting dry drug particles are separated from the carbon dioxide gas stream by electrostatic precipitation. The product has been analysed with laser diffraction method. Micronized drug particles were obtained at various process conditions. The presented technique was found to be appropriate for continuous manufacturing of micronized particles. The particles have been investigated regarding the particle size and shape.
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