Freezing under gaseous pressure: Effect on cells and proposed mechanism

Abstract

When cellular materials are saturated with gas under pressure (e.g., nitrogen at 1,000 psig) and subsequently frozen under gaseous pressure, much of the gas is retained even upon thawing at atmospheric pressure. This effect is modified by the type of gas used to pressurize the system and by the type of biological material. Only certain gases such as nitrogen and methane are effective, while others such as carbon dioxide and nitrous oxide are not. Gases which pass through artificial membranes quickly are usually less effective than those which pass through slowly. Pressure-frozen substances when viewed as sections under the microscope have more opacity than ordinarily frozen ones, probably because of entrapped gas bubbles. After thawing, numerous gas bubbles are easily visible microscopically. If the material is then air-dried, the gas remains in the tissue and prevents shriveling. Pressure-freezing-air-drying offers an alternative to freeze-drying for the preservation of tissues without shriveling.