System for and method of freezing biological tissue
First Claim
1. A method of freezing blood cells, bone marrow, and other similar biological tissue located in a container against opposed walls of a pair of heaters, said container having a high thermal conductivity so that the tissue and container are at substantially the same temperature, comprising cooling the container with refrigerating fluid at a time programmed rate at least equal to the maximum cooling rate needed at any time during the freezing process, monitoring the temperature of a surface of the container to derive an indication of the tissue temperature, comparing the indication of the tissue temperature with a time programmed desired value for the tissue temperature to derive an error indication, and activating the heaters in response to the error indication so that the temperature of the tissue follows the desired value for the time programmed tissue temperature.
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Abstract
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.
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Citations
15 Claims
- 1. A method of freezing blood cells, bone marrow, and other similar biological tissue located in a container against opposed walls of a pair of heaters, said container having a high thermal conductivity so that the tissue and container are at substantially the same temperature, comprising cooling the container with refrigerating fluid at a time programmed rate at least equal to the maximum cooling rate needed at any time during the freezing process, monitoring the temperature of a surface of the container to derive an indication of the tissue temperature, comparing the indication of the tissue temperature with a time programmed desired value for the tissue temperature to derive an error indication, and activating the heaters in response to the error indication so that the temperature of the tissue follows the desired value for the time programmed tissue temperature.
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4. A method of freezing blood cells, bone marrow and other similar biological tissue comprising cooling the tissue with refrigerating fluid supplied to the tissue at a time programmed rate at least equal to the maximum cooling rate needed at any time during the freezing process, heating the tissue to compensate for excessive cooling of the tissue as a result of the cooling by the refrigerating fluid, and preventing heating of the tissue while the latent heat of fusion is being removed from the tissue while it is undergoing a change of state from liquid to solid.
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5. A method of freezing blood cells, bone marrow and other similar biological tissue, comprising cooling the tissue with refrigerating fluid at a time programmed rate at least equal to the maximum cooling rate needed at any time during the freezing process, deriving an indication of tissue temperature, comparing the indication of the tissue temperature with a time programmed desired value for the tissue temperature to derive an error indication, and heating the tissue in response to the error indication so that the temperature of the tissue follows the desired value for the time programmed tissue temperature.
- 6. Apparatus for freezing blood cells, bone marrow and other similar biological tissue adapted to be placed in a container having a high thermal conductivity so that the tissue and container are at substantially the same temperature, comprising a heater having a pair of opposed heating walls against which the container is adapted to abut, means for cooling the container with refrigerating fluid at a time programmed rate at least equal to the maximum cooling rate needed at any time during the freezing process, means for monitoring the temperature of a surface of the container to derive an indication of tissue temperature, means for comparing the indication of the tissue temperature with a time programmed desired value for the tissue temperature to derive an error indication, and means for activating the heater in response to the error indication so that the temperature of the tissue follows the desired value for the time programmed tissue temperature.
- 11. Apparatus for freezing blood cells, bone marrow and other similar biological tissue comprising means for cooling the tissue with refrigerating fluid at a time programmed rate at least equal to the maximum cooling rate needed at any time during the freezing process, means for deriving an indication of tissue temperature, means for comparing the indication of the tissue temperature with a time programmed desired value for the tissue temperature to derive an error indication, and means for heating the tissue in response to the error indication so that the temperature of the tissue follows the desired value for the time programmed tissue temperature.
- 14. Apparatus for controlling the temperature of a load to a high resolution, said load being located in a refrigerator adapted to freeze the load, comprising means for sensing the temperature of the load to derive a first signal indicative of the load temperature, means for comparing the first signal with a desired load temperature to derive a control signal having a duty cycle directly proportional to the deviation between the load and desired temperatures, an electric heater for heating the load, an electric switch for selectively connecting the heater to an AC power source that is connected to the switch to cut off the switch during each cycle of the power source, the power source having a period much less than each period of the control signal so that many cycles of the power source occur during one cycle of the control signal, said switch being responsive to the control signal so that the switch is activated to connect the power source to the heater during a portion of each cycle of the control signal while the duty cycle of the control signal is being derived.
Specification