Solving Solubility

Around two thirds of the products used in the pharmaceutical industry are in solid form, such as tablets and pills. Consequently, a lot of effort has been put into research on particle generation processes. The standard processes – crushing/milling and crystallisation/precipitation – are still the most commonly used. However, supercritical fluid (SCF) technologies present a new and interesting route for particle formation, which avoids most of the drawbacks of the traditional methods. Supercritical processes give micro or even nanoparticles with a narrow size distribution. They can also be used in co-process with excipients or host molecules like cyclodextrins.

USING SUPERCRITICAL CO2

The supercritical state is also known as the fourth state of matter. Above a certain critical temperature and pressure (30.7°C and 73.8 bar respectively for CO2), the boundaries between gas and liquid disappear. Beyond this critical point, the substance has the viscosity of a gas and the density of a liquid. Supercritical CO2 (scCO2) is the most commonly-used system in nanoparticle generation. The main reason is linked to the intrinsic solvent properties of the supercritical CO2: the viscosity of a gas, the density of liquid and the fact that the critical state of CO2 can be easily reached. The treatment is generally carried out at about 40°C and it allows us to handle temperature-sensitive molecules. Furthermore, CO2 is cheap, non-toxic, noninflammable, easily available and can also be recycled. Supercritical carbon dioxide is considered as a ‘green’ solvent; after depressurisation, it leaves no residue, unlike an organic solvent.