Basic aspects and future trends in the freeze-drying of pharmaceuticals

Freeze-drying, as a unit operation in chemical engineering, is a complex multistage process which has to be carefully adjusted to each individual case. Its essential feature, drying from the frozen state, makes it particularly attractive for the stabilization of labile hydrated organic compounds of biological origin. However, it offers equal opportunities for the preparation of three-dimensional porous matrices for diversified physical and chemical applications. As such it is both an advanced technology for the long term preservation of unstable material and a refined operation for the development of new structures. Since freeze-drying, also called lyophilization, has been known for almost a century, and has given rise to numerous publications, this paper will not attempt to give a comprehensive review of its evolution but will focus on some of its basic requirements and potential trends.