Freeze drying: past, present and future.

In 1890 Alt man dried pieces of frozen tissue by placing ¡hem in a vacuum desiccator at —20 °C. Since then the freeze drying technique has been constantly improved. In ¡939 the freeze drying process was placed for the first time on an engineering basis, and 1940 saw the large-scale production of dried plasma for wartime use. The first book unfreeze drying by Flosdorfin 1949 was followed by the first symposium on this subject held in London in ¡952 and biennial courses initiated in 1958 by Rey in France. New advances were reported and stress was made to obtain uniformity and time reduction of the freeze drying cycles and a better understanding of the principles and basis which govern them. The ever increasing needs for freeze-dried products is demanding more basic and applied research in this technique and t lie Jut lire will no doubt see the development of equipment and systems which will allow freeze drying of a wide variety of products, in shorter cycles and at lower costs. Let us look at the past. If we were to ask ourselves how long the technique of freeze drying has been in use, we would find it very difficult to put a date on it, especially if one considers that the natives of Peru (1) still preserve potatoes by first freezing them and afterwards exposing them to the heat of the sun and finally submitting them to the cold, circulating air of their high, mountainous region. The selfsame procedures that were used by their forefathers, the Incas, hundreds of years ago, and as a result they produced a stable dried product retaining most of the nutritional properties of the natural tuber. It is also interesting to note that their end product closely resembles that of a freeze-dried potato processed in one of our most advanced lyophilization machines today. No doubt, if we had the time to delve deeper into this form of historical research, we would find many more such examples. Flosdorf (2) has pointed out that low-temperature evaporation of water under vacuum to produce freezing, followed by sublimation of ice is so old that Wollaston (3) was apologetic in demonstrating it before the Royal Society of London in 1813. In his paper, Wollaston explained with simplicity and clarity, the relation of vapor pressure to temperature, and the cooling effect of evaporation. Use of desiccation dates back as early as the 18th century, when it was found that cowpox vaccine could be preserved and shipped as a powder. In 1890 Altmann (4), in order to make histological sections, dried pieces of frozen tissue by placing them in a vacuum desiccator at 2 0 °C. In 1906 d'Arsonval and Bordas (5) in France, described a freeze drying ensemble which we would recognize today. The first clearly recorded use of sublimation is that of Shackell (6) in 1909, who applied it to biological substances. His observations were recognized and the procedure was subsequently applied to a variety of biological materials such as complement, antisera, rabies virus, and bacteria. Chemical desiccants were used exclusively for the removal of water vapor in these early procedures. The first reference to freeze drying in the Presented at a symposium on Lyophilizalion at the Annual Meeting of the Parenteral Drug Association in New York City, November 7-9, 1980. Received February 8, 1980. Accepted for publication May 17. 1980 Journal of the Parenteral Drug Association 352 on September 3, 2013 journal.pda.org Downloaded from