Different types of exit dies are used to shape the extrudate to the desired profile. These dies include sheet and film dies used in transdermal film applications, strand dies used for medical tubing and some drug-eluting devices, shape dies used in blow molding, and co- extrusion dies used in reservoir device designs. Different downstream auxiliary components are also used in the finishing process, including water baths and air knives for cooling, conveyor belts for moving the extruded product from the die to the end of the line, strand-cutters for cutting the extrudate into tubing or rods, and spoolers for extrudate collection. Pelletizers are used for cutting the extrudate into smaller pieces for direct capsule filling and, in the case of some devices, for injection molding to form the final product.
As with any dosage form, material selection is critical in the development of a successful product. For most applications, the polymer should be thermoplastic, stable at the temperatures used in the process, and chemically compatible with the API during extrusion. For solid oral dosage forms, water soluble polymers are usually chosen from among well-known polymers already used in pharmaceutical products such as poly(ethylene glycol) and poly(vinylpyrrolidinone). With the increased interest in using HME for pharmaceutical products, major polymer suppliers are also beginning to offer polymers specifically designed for pharmaceutical applications. For drug-eluting devices, the polymers are generally water-insoluble, with most products under development using either ethylene vinyl acetate copolymers (EVAs) or polyurethanes.