Continuous manufacturing of co-crystals using spray drying: A comprehensive review

Co-crystals have gained significant interest in pharmaceutical and material sciences as an effective solid-state modification strategy to improve solubility, stability, dissolution behavior, and bioavailability of active substances. Solvent evaporation, mixing, and slurry-based processes are examples of conventional co-crystallization techniques that often encounter problems with scalability, repeatability, and limited control over particle properties. Because of its rapid solvent removal, precise control of the process, and industrial scalability, spray drying has become a potential continuous manufacturing method for co-crystal synthesis. The use of spray drying for co-crystal manufacturing is critically examined in this paper, starting with the basic concepts of co-crystal formation, including kinetic and thermodynamic aspects and supramolecular synthon-based design techniques. There includes an in-depth discussion of the fundamentals of spray drying, equipment setups, and important operating parameters such as feed rate, atomization mode, and inlet temperature. The focus is placed on the processes that are controlling droplet-to-particle transformation as well as the effects of solvent selection, solubility, and supersaturation on co-crystal formation and quality. The efficiency of spray drying for producing higher quality co-crystals with regulated particle size and morphology is demonstrated by a few pharmaceutical case studies. Performance evaluation methods are examined together with characterization techniques that are frequently used to verify co-crystal formation, including as Particle X-ray Diffraction, spectroscopic, thermal, and microscopic investigations. The use of experiment design, mathematical modeling, integration with downstream processing, and recent developments in continuous spray drying systems are highlighted. Finally, future prospects involving quality-by-design implementation, regulatory considerations, and emerging multi-component co-crystal systems are discussed, reinforcing spray drying as a robust and industrially viable platform for continuous co-crystal manufacturing.