Narrow tube spray drying with precise drying history control for particle engineering

Lactose is one of the most commonly used pharmaceutical excipients and is typically found in the amorphous state in spray drying. Amorphous particles are prone to phase transition, hence, controlling the degree of crystallinity in lactose is paramount to ensure its stability and bio-availability. It is widely known that drying temperature plays a vital role in affecting the crystallinity of particles in spray drying. There are contrasting reports on the effect of spray drying inlet temperature on lactose crystallinity. This discrepancy arises due to the inlet
or outlet drying temperature being used to delineate the drying history of the crystallisation process precluding any in-situ control of drying history. There are no detailed studies on how the drying history and particle development throughout the drying time affects crystallisation. This research aims to address the current limitation by introducing a modified narrow tube spray dryer which will allow precise control of the drying history. It comprises of a series of 10 narrow copper tubes with inner diameter of 1.7 cm. By taking advantage of the small narrow tube, individual segments of the tube wall can be heated independently. This allows different drying history to be created and controlled in the tube dryer. An elevation of particle temperature at the intermediate stage of drying results in significant crystallinity in lactose particles. Scanning Electron Microscope (SEM) images show lactose particle with singular cubic crystalline structure was obtained; in contrast to spherical lactose particle. This could be due to the intensification of critical crystallisation period at the intermediate stage as noted in the literature of single droplet studies. Varying the intensity of the intermediate period causes significant changes in crystallisation, providing a direct process control of lactose drying. With this newly developed equipment, detailed drying history condition can be manipulated and studied to engineer the desired particle properties.