*2.3.3 Supercritical fluid technology*

Materials that have pressure and temperature greater than their critical state (Pc and Tc) are supercritical fluids. The leading objective of supercritical fluid technology is to regulate cloud seeding and crystal development courses. The most conspicuous supercritical fluid used in the pharmaceutical arena is carbon dioxide, with critical temperature and pressure of 31.0°C and 7.39 atm, respectively, because of its nontoxicity, non-flammability, and low-cost properties [22, 33]. Numerous approaches of employing the supercritical fluid carbon dioxide to produce co-crystals are as

follows: (1) where CO2 is used as an anti-solvent known as gas anti-solvent crystallization (GAS). As an example, the SAS (supercritical anti-solvent crystallization) and AAS (atomization and anti-solvent crystallization) methods of supercritical fluid technology were successfully used in the formation of the indomethacin:saccharin co-crystal, (2) where the carbon dioxide is used as a liquid and molecular movement enhancer called co-crystallization with the supercritical solvent (CSS), (3) where CO2 is utilized as a solvent and molecular movement enhancer called supercritical anti-solvent crystallization (SAS), (4) where CO2 is used as corsage enhancer or anti-solvent called atomization and anti-solvent crystallization (AAS), (5) where CO2 is used as corsage enhancer or anti-solvent called supercritical fluid improved atomization (SEA), and (6) where CO2 is used as a solvent known as rapid expansion of supercritical solutions (RESS) [34].
