04117881 is referenced by 75 patents and cites 10 patents.

Blood cells, blood marrow, and other similar biological tissue is frozen while in a polyethylene bag placed in abutting relationship against opposed walls of a pair of heaters. The bag and tissue are cooled with refrigerating gas at a time programmed rate at least equal to the maximum cooling rate needed at any time during the freezing process. The temperature of the bag, and hence of the tissue, is compared with a time programmed desired value for the tissue temperature to derive an error indication. The heater is activated in response to the error indication so that the temperature of the tissue follows the desired value for the time programmed tissue temperature. The tissue is heated to compensate for excessive cooling of the tissue as a result of the cooling by the refrigerating gas. In response to the error signal, the heater is deactivated while the latent heat of fusion is being removed from the tissue while the tissue is changing phase from liquid to solid.

Title
System for and method of freezing biological tissue
Application Number
5/806440
Publication Number
4117881
Application Date
June 14, 1977
Publication Date
October 3, 1978
Inventor
Thomas A Cygnarowicz
New Carrollton
MD, US
Thomas E Williams
Millersville
MD, US
Agent
John O Tresansky
John R Manning
Robert D Marchant
Assignee
The United States of America represented by the Administrator of the National Aeronautics and Space Administration
DC, US
IPC
F25B 13/00
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