Twin-screw wet granulation in continuous pharmaceutical manufacturing

Wet granulation is a critical unit operation in the manufacturing of solid dosage forms. However, conventional wet granulation techniques are limited by significant batch-to-batch variability and scale-up challenges, making them difficult to meet the demands of continuous pharmaceutical manufacturing and robust quality control. As an emerging continuous granulation technology, Twin-Screw Wet Granulation (TSWG) has attracted extensive attention in pharmaceutical research and industrial applications due to its advantages of continuous processing, modular design, controllable mixing and shear, and reduced scale-up effects. This review systematically summarizes and critically evaluates the core technologies and underlying mechanisms of TSWG, including equipment configuration, screw design, and granulation mechanisms. The relationships between formulation variables, equipment parameters, and process conditions with critical quality attributes (CQAs) of granules, such as particle size distribution, porosity, and mechanical strength, are comprehensively analyzed. Furthermore, the application of Process Analytical Technology (PAT) for real-time monitoring is discussed, together with recent advances in process modeling and optimization using Discrete Element Method-Computational Fluid Dynamics (DEM-CFD) coupled models, Population Balance Models (PBMs), Machine Learning (ML), and Artificial Intelligence (AI). The potential of integrating AI with PAT, machine vision, and data-driven models for granule quality prediction, online monitoring, and intelligent process control is also highlighted. Finally, the current challenges of TSWG are addressed, including process scale-up consistency, adaptation to raw material batch variability, and control of active pharmaceutical ingredient (API) polymorphic stability. Future development is expected to rely on interdisciplinary integration to advance technological innovation and support Quality by Design (QbD) paradigm in pharmaceutical manufacturing.