Application of rheology to hot melt extrusion: Theory and practice

Hot melt extrusion (HME) has become a key manufacturing method in the pharmaceutical industry for developing novel drug delivery systems, due to its solvent-free nature, ease of operation, and ability to achieve one-step molding and continuous processing. The rheological properties of drug-polymer systems play a crucial role in determining the processability of formulations and the final product quality. This review systematically summarizes the shear-thinning and viscoelastic properties related to polymer melts, as well as the relevant rheological models. It aims to provide a theoretical basis for selecting excipients in HME formulations through the application of rheology and to guide the design of process parameters. Additionally, the review details the application of rheology in the scale-up and modeling of HME processes, exploring its potential for integration with continuous manufacturing, fused deposition modeling 3D printing, and machine learning, with the expectation of empowering HME drug development and playing a valuable role.