Human red blood cells can be stored for three months or longer at temperatures below —80 C if they are mixed with glycerol. Before the red blood cells can be used, however, they must be washed free of glycerol. Both the initial equilibration with glycerol before storage and the removal of the glycerol from the cells after storage involve fractional centrifugation. In order to accomplish this without bacterial contamination and with a minimum of hemolysis, the apparatus here described has been developed. Experience with 175 units of red blood cells so processed showed that sterility had been maintained, loss by hemolysis did not exceed 20%, and the time required for the processing had been significantly shortened.
Ketchel MM, Tullis JL, Tinch RJ, Driscoll SG, Surgenor DM. USE OF BIOMECHANICAL EQUIPMENT FOR THE LONG-TERM PRESERVATION OF ERYTHROCYTES. JAMA. 1958;168(4):404-408. doi:10.1001/jama.1958.03000040040009