Lyophilisation

Lyophilisation, also called freeze-drying, is a dehydration process in which a frozen aqueous sample is placed under reduced pressure so that water sublimes directly from the solid to the vapour phase, bypassing the liquid state. The process typically comprises three stages: freezing, primary drying (sublimation of ice) and secondary drying (desorption of residual bound water).

Because the sample never returns to a liquid phase, thermally labile molecules such as peptides retain their conformation and activity. The resulting cake — a lyophilised powder — is stable at ambient or refrigerated temperatures for long periods and is reconstituted for use by adding a defined volume of sterile diluent.