Role of freeze drying in nanotechnology

Governments worldwide have spent more money on nanotechnology between 1997 and 2005 than on the Apollo project. The spending trend is still going upwards. Drying is an indispensable operation in the fabrication of nanosized materials. Hence, it is no surprise to find a large number of papers published in the past decade on drying and nano-related materials. This article reviews the literature and highlights the opportunities and challenges of freeze drying in nanotechnology. Freeze drying has found application in the production of nanoparticles for electrochemical, environmental, engineered materials, and pharmaceutical industries. The retention of the homogenous properties typically found in a solution, the small size of particles produced, and the long shelf life obtained for pharmaceutical applications are the primary reasons for choosing freeze drying. The relatively cheap operation cost compared to supercritical fluid extraction is another reason. Freezing was found to be a very important step in obtaining desired particle size and properties. Primary drying of solvent sublimation should be carried out at a temperature below the collapse temperature. Cryoprotectants are frequently necessary in preserving the original properties of active pharmaceutical ingredients. Spray freezing into liquid was found to be an optimal operation in order to minimize the air-liquid interfacial loss of bioactivity. A continuous freeze-drying process for production of granules of nanoparticles would be in demand, a dream that freeze-drying researchers have had for over a decade. This freeze drying may be carried out under vacuum or at atmospheric pressure using proper gases.