Miniaturization in pharmaceutical extrusion technology: feeding as a challenge of downscaling

In recent years, extrusion technology has shifted the focus of pharmaceutical research due to versatile applications like pelletization, bioavailability improvement or manipulation of solid-state properties of drugs, continuous granulation, and the development of novel solid dosage forms. Meanwhile, a major effort has been devoted to the miniaturization of equipment in pharmaceutical extrusion technology, particularly with regard to the requirements of the development of new chemical entities and formulations. In the present study, a lab-scale twin-screw extruder was investigated in order to determine the limitations imposed by the feeding systems. The wet extrusion process was considered as challenging because both a powder and a liquid feeder have to be considered. Initially, the accuracy and uniformity of the powder and liquid feeder were tested independently of the extrusion process. After modification of the powder feeder, both feeders were investigated in conjunction with extrusion. Based on this, an optimization of the liquid feeder was required and completed. Both feeder modifications reduced the variability of the moisture content in the extrudates 10-fold. This led to a reliable small-scale extrusion process.