Systems, devices and methods for freezing and thawing biological materials

Abstract

There are provided a system and a method for cryopreserving a liquid biological material disposed in a bag having a longitudinal axis. The system comprises a bag holder for holding the bag, so that the biological material therein has a surface area S, and a volume V, a tank containing a cryogenic fluid, a mechanism for the immersion of the bag holder into the tank along the longitudinal axis, an opening in the tank for insertion therethrough of the bag holder, and a guide member extending from the opening into the tank. There are further provided a system and a method for warming a cryopreserved liquid biological material disposed in a bag. The system comprises a heat source, a warming device having a space for placing the bag therein, connected to the heat source and adapted to transfer heat from the heat source to the bag, and means for maintaining the heat source in heat transfer contact with a cryogenically preserved portion of the material to allow receiving the heat by said cryogenically preserved portion.

1 . A system for cryopreserving a liquid biological material disposed in a bag having a longitudinal axis, the system comprising:
 a bag holder for holding said bag, so that the biological material therein has a surface area S, and a volume V;   a tank containing a cryogenic fluid;   a mechanism for the immersion of said bag holder into said tank along said longitudinal axis;   an opening in said tank for insertion therethrough of the bag holder; and   a guide member extending from said opening into said tank and adapted for engaging walls of said bag holder, when the bag holder is being immersed into the tank via said opening, to reduce widening of the bag during its being frozen by the cryogenic fluid.   
     
     
         2 . A system according to  claim 1 , comprising means to prevent ratio between that of the surface area S and that of the volume V of said biological material from increasing during the immersion to more than 4:3. 
     
     
         3 . A system according to  claim 1  or  2 , wherein the guide member comprises a plurality of guides in the form of tongues depending into said tank from said opening. 
     
     
         4 . A system according to any one of  claims 1  to  3 , wherein the guides are spaced by a proximal distance at a proximal portion of the guide member and a distal distance at a distal portion of the guide member, said distal distance being equal to or lesser than said proximal distance. 
     
     
         5 . A system according to any one of  claims 1  to  4 , wherein said tank comprises a cover, wherein the proximal portion of the guide member is attached to said cover at the opening's periphery. 
     
     
         6 . A system according to  claim 5 , wherein the cover has an inner surface facing the interior of the tank, and the proximal portion is attached to the inner surface. 
     
     
         7 . A system according to any one of  claims 1  to  6 , comprising a means for keeping level of said cryogenic fluid in said tank within no less than 3 cm below the maximal fluid level during the immersion of the bag with the biological material. 
     
     
         8 . A system according to any one of  claims 1  to  7 , wherein said tank comprises level sensors for monitoring a level of the cryogenic fluid within the tank. 
     
     
         9 . A system according to any one of  claims 1  to  8 , wherein the bag holder is in the form of a cartridge comprising a pair of frame members. 
     
     
         10 . A system according to  claim 9 , wherein said frame members constitute side walls of the cartridge, for placing the bag with the biological material in a space created therebetween. 
     
     
         11 . A system according to any one of  claims 1  to  10 , wherein the bag holder comprises stiffening members for keeping a width of the bag uniform. 
     
     
         12 . A system according to any one of  claims 1  to  11 , comprising a temperature control block for setting an immersion temperature of said bag, prior to said immersion, to a pre-determined value higher than a temperature of said cryogenic fluid. 
     
     
         13 . A system according to  claim 12 , wherein said temperature control block is adapted for setting said immersion temperature to between about 0° C. and about 30° C. 
     
     
         14 . A system according to any one of  claims 1  to  13 , comprising a velocity control means allowing to select a pre-determined value of said immersion velocity and to maintain said pre-determined value constant during said immersion. 
     
     
         15 . A system for cryopreserving a liquid biological material disposed in a bag having a longitudinal axis, the system comprising:
 a bag holder for holding said bag, so that the biological material therein has a surface area S, and a volume V;   a tank containing a cryogenic fluid;   a mechanism for the immersion of said bag holder into said tank along said longitudinal axis at an immersion velocity, wherein said immersion velocity may be of a plurality of values; and   a velocity control means allowing to select a pre-determined value of said immersion velocity from said plurality of values, and to maintain said pre-determined value constant during said immersion.   
     
     
         16 . A system according to  claim 15 , wherein said tank comprises an opening in said tank for insertion therethrough of the bag holder, at said immersion velocity, said opening having an opening width. 
     
     
         17 . A system according to any one of  claim 15  or  16 , comprising means to prevent ratio between that of the surface area S and that of the volume V of said biological material from increasing during the immersion to more than 4:3. 
     
     
         18 . A system according to any one of  claim 16  or  17 , comprising a guide member extending from said opening into said tank and adapted for engaging walls of said bag holder, when the bag holder is being immersed into the tank via said opening, to reduce widening of the bag during its being frozen by the cryogenic fluid. 
     
     
         19 . A system according to  claim 18 , wherein the guide member comprises a plurality of guides in the form of tongues depending into said tank from said opening. 
     
     
         20 . A system according to  claim 19 , wherein the guides are spaced by a proximal distance at a proximal portion of the guide member and a distal distance at a distal portion of the guide member, said distal distance being equal to or lesser than said proximal distance. 
     
     
         21 . A system according to any one of  claims 18  to  20 , wherein said tank comprises a cover, wherein the proximal portion of the guide member is attached to said cover at the opening's periphery. 
     
     
         22 . A system according to  claim 21 , wherein the cover has an inner surface facing the interior of the tank, and the proximal portion is attached to the inner surface. 
     
     
         23 . A system according to any one of  claims 15  to  22 , comprising a means for keeping level of said cryogenic fluid in said tank within no less than 3 cm below the maximal fluid level during the immersion of the bag with the biological material. 
     
     
         24 . A system according any one of  claims 15  to  23 , wherein said tank comprises level sensors for monitoring a level of the cryogenic fluid within the tank. 
     
     
         25 . A system according to any one of  claims 15  to  24 , wherein the bag holder is in the form of a cartridge comprising a pair of frame members. 
     
     
         26 . A system according to  claim 25 , wherein said frame members constitute side walls of the cartridge, for placing the bag with the biological material in a space created therebetween. 
     
     
         27 . A system according to  claim 26 , wherein the bag is of a shape substantially complementary to a shape of said space. 
     
     
         28 . A system according to any one of  claims 25  to  27 , wherein the frame members are perforated to reduce the thermal mass of the frame. 
     
     
         29 . A system according to any one of  claims 15  to  28 , wherein the bag holder comprises stiffening members for keeping a width of the bag uniform. 
     
     
         30 . A system according to any one of  claims 15  to  29 , comprising a temperature control block for setting an immersion temperature of said bag, prior to said immersion, to a pre-determined value higher than a temperature of said cryogenic fluid. 
     
     
         31 . A system according to  claim 30 , wherein said temperature control block is adapted for setting said immersion temperature to between about 0° C. and about 30° C. 
     
     
         32 . A system for cryopreserving a liquid biological material disposed in a bag having a longitudinal axis, the system comprising:
 a bag holder for holding said bag, so that the biological material therein has a surface area S, and a volume V;   a tank containing a cryogenic fluid;   a mechanism for the immersion of said bag holder into said tank along said longitudinal axis; and   a temperature control setting an immersion temperature of said bag, prior to said immersion, to a pre-determined value higher than a temperature of said cryogenic fluid,   
     
     
         33 . A system according to  claim 32 , temperature control block is adapted for setting said immersion temperature to between about 0° C. and about 30° C. 
     
     
         34 . A system according to any one of  claim 32  or  33 , wherein said tank comprises an opening in said tank for insertion therethrough of the bag holder, at said immersion velocity, said opening having an opening width. 
     
     
         35 . A system according to any one of  claims 32  to  34 , comprising means to prevent ratio between that of the surface area S and that of the volume V of said biological material from increasing during the immersion to more than 4:3. 
     
     
         36 . A system according to any one of  claim 34  or  35 , comprising a guide member extending from said opening into said tank and adapted for engaging walls of said bag holder, when the bag holder is being immersed into the tank via said opening, to reduce widening of the bag during its being frozen by the cryogenic fluid. 
     
     
         37 . A system according to  claim 36 , wherein the guide member comprises a plurality of guides in the form of tongues depending into said tank from said opening. 
     
     
         38 . A system according to  claim 37 , wherein the guides wherein the guides are spaced by a proximal distance at a proximal portion of the guide member and a distal distance at a distal portion of the guide member, said distal distance being equal to or lesser than said proximal distance. 
     
     
         39 . A system according to any one of  claims 36  to  38 , wherein said tank comprises a cover, wherein the proximal portion of the guide member is attached to said cover at the opening's periphery. 
     
     
         40 . A system according to  claim 39 , wherein the cover has an inner surface facing the interior of the tank, and the proximal portion is attached to the inner surface. 
     
     
         41 . A system according to any one of  claims 32  to  40 , comprising means for keeping level of said cryogenic fluid in said tank within no less than 3 cm below the maximal fluid level during the immersion of the bag with the biological material. 
     
     
         42 . A system according to any one of  claims 32  to  41 , wherein said tank comprises level sensors for monitoring a level of the cryogenic fluid within the tank. 
     
     
         43 . A system according to any one of  claims 32  to  42 , wherein the bag holder is in the form of a cartridge comprising a pair of frame members. 
     
     
         44 . A system according to  claim 43 , wherein said frame members constitute side walls of the cartridge, for placing the bag with the biological material in a space created therebetween. 
     
     
         45 . A system according to  claim 44 , wherein the bag is of a shape substantially complementary to a shape of said space. 
     
     
         46 . A system according to any one of  claims 43  to  45 , wherein the frame members are perforated to reduce the thermal mass of the frame. 
     
     
         47 . A system according to any one of  claims 43  to  46 , wherein the frame members comprise a common pivot axis. 
     
     
         48 . A system according to  claim 47 , wherein the frame members are adapted to move with respect to said pivot axis and with respect to each other, thereby changing a position of the bag holder between an open and a closed positions. 
     
     
         49 . A system according to  claim 48 , wherein the bag holder, while in said closed position, has a shape that corresponds to a shape of the opening. 
     
     
         50 . A system according to any one of  claims 32  to  49 , wherein the bag holder comprises stiffening members for keeping a width of the bag uniform. 
     
     
         51 . A system according to any one of  claims 32  to  50 , wherein the cryogenic fluid is a liquid. 
     
     
         52 . A system according to any one of  claims 32  to  51 , comprising a velocity control means allowing to select a pre-determined value of said immersion velocity, and to maintain said pre-determined value constant during said immersion. 
     
     
         53 . A system for cryopreserving a liquid biological material disposed in a bag having a longitudinal axis, the system comprising:
 a bag holder for holding said bag, so that the biological material therein has a surface area S, and a volume V;   a tank containing a cryogenic fluid;   a mechanism for the immersion of said bag holder into said tank along said longitudinal axis; and   means to prevent ratio between that of the surface area S and that of the volume V of said biological material from increasing during the immersion to more than 4:3.   
     
     
         54 . A system according to  claim 53 , wherein said tank comprises an opening in said tank for insertion therethrough of the bag holder, at said immersion velocity, said opening having an opening width. 
     
     
         55 . A system according to  claim 54 , comprising a guide member extending from said opening into said tank and adapted for engaging walls of said bag holder, when the bag holder is being immersed into the tank via said opening, to reduce widening of the bag during its being frozen by the cryogenic fluid. 
     
     
         56 . A system according to  claim 55 , wherein the guide member comprises a plurality of guides in the form of tongues depending into said tank from said opening. 
     
     
         57 . A system according to  claim 56 , wherein the guides wherein the guides are spaced by a proximal distance at a proximal portion of the guide member and a distal distance at a distal portion of the guide member, said distal distance being equal to or lesser than said proximal distance. 
     
     
         58 . A system according to any one of  claims 55  to  57 , wherein said tank comprises a cover, wherein the proximal portion of the guide member is attached to said cover at the opening's periphery. 
     
     
         59 . A system according to  claim 58 , wherein the cover has an inner surface facing the interior of the tank, and the proximal portion is attached to the inner surface. 
     
     
         60 . A system according to any one of  claims 53  to  59 , a means for keeping level of said cryogenic fluid in said tank within no less than 3 cm below the maximal fluid level during the immersion of the bag with the biological material. 
     
     
         61 . A system according to any one of  claims 53  to  60 , wherein said tank comprises level sensors for monitoring a level of the cryogenic fluid within the tank. 
     
     
         62 . A system according to any one of  claims 53  to  61 , wherein the bag holder is in the form of a cartridge comprising a pair of frame members. 
     
     
         63 . A system according to  claim 62 , wherein said frame members constitute side walls of the cartridge, for placing the bag with the biological material in a space created therebetween. 
     
     
         64 . A system according to  claim 63  wherein the bag is of a shape substantially complementary to a shape of said space. 
     
     
         65 . A system according to any one of  claims 62  to  64 , wherein the frame members are perforated to reduce the thermal mass of the frame. 
     
     
         66 . A system according to any one of  claims 62  to  65 , wherein the frame members comprise a common pivot axis. 
     
     
         67 . A system according to  claim 66 , wherein the frame members are adapted to move with respect to said pivot axis and with respect to each other, thereby changing a position of the bag holder between an open and a closed positions. 
     
     
         68 . A system according to  claim 67 , wherein the bag holder, while in said closed position, has a shape that corresponds to a shape of the opening. 
     
     
         69 . A system according to any one of  claims 53  to  68 , wherein the bag holder comprises stiffening members for keeping a width of the bag uniform. 
     
     
         70 . A system according to any one of  claims 54  to  69 , comprising a temperature control block for setting an immersion temperature of said bag, prior to said immersion, to a pre-determined value higher than a temperature of said cryogenic fluid. 
     
     
         71 . A system according to  claim 70 , wherein said temperature control block is adapted for setting said immersion temperature to between about 0° C. and about 30° C. 
     
     
         72 . A system according to any one of  claims 54  to  71 , comprising a velocity control means allowing to select a pre-determined value of said immersion velocity, and to maintain said pre-determined value constant during said immersion. 
     
     
         73 . A method for cryopreserving a liquid biological material disposed in a bag having a longitudinal axis, the method comprising:
 placing the bag in a bag holder; and   immersing said bag holder into a cryogenic fluid in a direction parallel to said longitudinal axis at an invariant immersion velocity selected so as to ensure that the thermal curve of the biological material at least at three different locations along the longitudinal axis of the bag is essentially as shown in  FIG. 11 .   
     
     
         74 . A method according to  claim 73 , wherein said bag holder is immersed into a tank containing said cryogenic fluid. 
     
     
         75 . A method according to  claim 74 , wherein said bag holder is immersed into said tank through an opening at said invariant immersion velocity. 
     
     
         76 . A method according to any one of  claims 73  to  75 , comprising means to prevent ratio between that of the surface area S and that of the volume V of said biological material from increasing during the immersion to more than 4:3. 
     
     
         77 . A method according to any one of  claim 75  or  76 , comprising engaging walls of said bag holder by a guide member extending from said opening into said tank and adapted for engaging walls of said bag holder, when the bag holder is being immersed into the tank via said opening, to reduce widening of the bag during its being frozen by the cryogenic fluid. 
     
     
         78 . A method according to  claim 77 , wherein the guide member comprising a plurality of guides in the form of tongues depending into said tank from said opening. 
     
     
         79 . A method according to  claim 78 , wherein the guides are spaced by a proximal distance at a proximal portion of the guide member and a distal distance at a distal portion of the guide member, said distal distance being equal to or lesser than said proximal distance. 
     
     
         80 . A method according to any one of  claims 77  to  79 , wherein said tank comprises a cover, wherein the proximal portion of the guide member is attached to said cover at the opening's periphery. 
     
     
         81 . A method according to  claim 80 , wherein the cover has an inner surface facing the interior of the tank, and the proximal portion is attached to the inner surface, 
     
     
         82 . A method according to any one of  claims 74  to  81 , comprising keeping level of said cryogenic fluid in said tank within no less than 3 cm below the maximal fluid level during the immersion of the bag with the biological material. 
     
     
         83 . A method according to any one of  claims 74  to  82 , comprising monitoring a level of the cryogenic fluid within the tank by level sensors. 
     
     
         84 . A method according to any one of  claims 73  to  83 , wherein the bag holder is in the form of a cartridge comprising a pair of frame members. 
     
     
         85 . A method according to  claim 84 , wherein said frame members constitute side walls of the cartridge, for placing the bag with the biological material in a space created therebetween. 
     
     
         86 . A method according to  claim 85 , wherein the bag is of a shape substantially complementary to a shape of said space. 
     
     
         87 . A method according to any one of  claims 84  to  86 , wherein the frame members are perforated to reduce the thermal mass of the frame. 
     
     
         88 . A method according to any one of  claims 84  to  87 , wherein the frame members comprise a common pivot axis. 
     
     
         89 . A method according to  claim 88 , comprising moving the frame members with respect to said pivot axis and with respect to each other, thereby changing a position of the bag holder between an open and a closed positions. 
     
     
         90 . A method according to any one of  claims 89 , wherein the bag holder, while in said closed position, has a shape that corresponds to a shape of the opening. 
     
     
         91 . A method according to any one of  claims 73  to  90 , wherein the bag holder comprises stiffening members for keeping a width of the bag uniform. 
     
     
         92 . A method according to any one of  claims 73  to  91 , comprising a temperature control block for setting an immersion temperature of said bag, prior to said immersion, to a pre-determined value higher than a temperature of said cryogenic fluid. 
     
     
         93 . A method according to  claim 92 , wherein said temperature control block is adapted for setting said immersion temperature to between about 0° C. and about 30° C. 
     
     
         94 . A method according to any one of  claims 73  to  93 , wherein the cryogenic fluid is a liquid. 
     
     
         95 . A method for cryopreserving a liquid biological material disposed in a bag having a longitudinal axis, the method comprising:
 placing the bag in a bag holder; and   immersing said bag holder into a cryogenic fluid in a direction parallel to said longitudinal axis at an invariant immersion velocity selected so as to ensure that cooling behavior of the biological material at least at three different locations along the longitudinal axis of the bag is defined by a curve having initial curved portion, central essentially linear portion and final curved portion, the central portions corresponding to more than half of the range of temperatures, and at least the central portions being parallel at said at least three locations.   
     
     
         96 . A method according to  claim 95 , wherein said bag holder is immersed into a tank containing said cryogenic fluid. 
     
     
         97 . A method according to  claim 96 , wherein said bag holder is immersed into said tank through an opening at said invariant immersion velocity. 
     
     
         98 . A method according to any one of  claims 95  to  97 , comprising means to prevent ratio between that of the surface area S and that of the volume V of said biological material from increasing during the immersion to more than 4:3. 
     
     
         99 . A method according to any one of  claims 97  to  98 , comprising engaging walls of said bag holder a guide member extending from said opening into said tank and adapted for engaging walls of said bag holder, when the bag holder is being immersed into the tank via said opening, to reduce widening of the bag during its being frozen by the cryogenic fluid. 
     
     
         100 . A method according to  claim 99 , wherein the guide member comprising a plurality of guides in the form of tongues depending into said tank from said opening. 
     
     
         101 . A method according to  claim 100 , wherein the guides are spaced by a proximal distance at a proximal portion of the guide member and a distal distance at a distal portion of the guide member, said distal distance being equal to or lesser than said proximal distance. 
     
     
         102 . A method according to any one of  claims 99  to  101 , wherein said tank comprises a cover, wherein the proximal portion of the guide member is attached to said cover at the opening's periphery. 
     
     
         103 . A method according to  claim 102 , wherein the cover has an inner surface facing the interior of the tank, and the proximal portion is attached to the inner surface. 
     
     
         104 . A method according to any one of  claims 96  to  103 , comprising keeping level of said cryogenic fluid in said tank within no less than 3 cm below the maximal fluid level during the immersion of the bag with the biological material. 
     
     
         105 . A method according to any one of  claims 96  to  104 , comprising monitoring a level of the cryogenic fluid within the tank by level sensors. 
     
     
         106 . A method according to any one of  claims 95  to  105 , wherein the bag holder is in the form of a cartridge comprising a pair of frame members. 
     
     
         107 . A method according to  claim 106 , wherein said frame members constitute side walls of the cartridge, for placing the bag with the biological material in a space created therebetween. 
     
     
         108 . A method according to  claim 107 , wherein the bag is of a shape substantially complementary to a shape of said space. 
     
     
         109 . A method according to any one of  claims 106  to  108 , wherein the frame members are perforated to reduce the thermal mass of the frame. 
     
     
         110 . A method according to any one of  claims 106  to  108 , wherein the frame members comprise a common pivot axis. 
     
     
         111 . A method according to  claim 110 , comprising moving the frame members with respect to said pivot axis and with respect to each other, thereby changing a position of the bag holder between an open and a closed positions. 
     
     
         112 . A method according to  claim 111 , wherein the bag holder, while in said closed position, has a shape that corresponds to a shape of the opening. 
     
     
         113 . A method according to any one of  claims 95  to  112 , wherein the bag holder comprises stiffening members for keeping a width of the bag uniform. 
     
     
         114 . A method according to any one of  claims 95  to  113 , comprising a temperature control block for setting an immersion temperature of said bag, prior to said immersion, to a pre-determined value higher than a temperature of said cryogenic fluid. 
     
     
         115 . A method according to  claim 114 , wherein said temperature control block is adapted for setting said immersion temperature to between about 0° C. and about 30° C. 
     
     
         116 . A method according to any one of  claims 95  to  115 , wherein the cryogenic fluid is a liquid. 
     
     
         117 . A system for warming a cryopreserved liquid biological material disposed in a bag, the system comprising:
 a heat source;   a warming device having a space for placing said bag therein, connected to the heat source and adapted to transfer heat from the heat source to the bag;   means for maintaining the heat source in heat transfer contact with a cryogenically preserved portion of said material to allow receiving said heat by said cryogenically preserved portion.   
     
     
         118 . A system according to  claim 117 , wherein the warming device comprises an empty space for accommodating of any liquefied material apart from the cryopreserved material. 
     
     
         119 . A system according to  claim 118 , wherein said space is a part of the bag. 
     
     
         120 . A system according to any one of  claims 117  to  119 , wherein the warming device comprises a pair of plates creating said space for the bag therebetween. 
     
     
         121 . A system according to  claim 120 , wherein at least one of said plates is used as the heat source. 
     
     
         122 . A system according to any one of  claim 120  or  121 , wherein at least one of said plates is adapted to move with respect to the other plate in a direction perpendicular to a longitudinal axis of said bag, thereby applying pressure on the bag. 
     
     
         123 . A system according to any one of  claims 117  to  122 , wherein the heat source is adapted to continually supply heat to the warming device until all the cryopreserved material is liquefied and removed. 
     
     
         124 . A system according to any one of  claims 117  to  123 , wherein the warming device is adapted to store heat supplied by the heat source. 
     
     
         125 . A system according to any one of  claims 117  to  124 , wherein the warming device comprising heat storage means and the heat source is adapted to supply heat to said heat storage means of the warming device only prior to a warming process, during which the heat stored in the warming device is supplied to the bag. 
     
     
         126 . A system according to any one of  claims 117  to  125 , wherein said bag has a cryopreserved material section filled with the cryopreserved material before said warming and an empty section constituting said empty space, which is free of the cryopreserved material and is adapted to accommodate said liquefied material. 
     
     
         127 . A system according to any one of  claims 117  to  126 , wherein the heat source is an electrical heater. 
     
     
         128 . A method for warming a cryopreserved liquid biological material disposed in a bag, the method comprising:
 providing a heat source;   providing a warming device and placing said bag within a space therein;   connecting the warming device to the heat source adapted to transfer heat from the heat source to the bag; and   removing of a liquefied material thereby preventing it from receiving said heat.   
     
     
         129 . A method according to  claim 128 , comprising accommodating of said liquefied material apart from the cryopreserved material in an empty space of said bag. 
     
     
         130 . A method according to  claim 129 , wherein the warming device comprises a pair of plates creating said space for the bag therebetween, 
     
     
         131 . A method according to  claim 130 , using at least one of said plates as heat source. 
     
     
         132 . A method according to any one of  claim 130  or  131 , comprising moving of at least one of said plates with respect to the other plate in a direction perpendicular to a longitudinal axis of said bag, thereby applying pressure on the bag. 
     
     
         133 . A method according to any one of  claim 128  or  132 , comprising continually supplying heat to the warming device by the heat source until all the cryopreserved material is liquefied and removed. 
     
     
         134 . A method according to any one of  claim 128  or  133 , wherein the warming device is adapted to store heat supplied by the heat source. 
     
     
         135 . A method according to any one of  claim 128  or  134 , wherein the warming device comprising heat storage means and the heat source is adapted to supply heat to said heat storage means of the warming device only prior to a warming process, during which the heat stored in the warming device is supplied to the bag. 
     
     
         136 . A method according to any one of  claim 128  or  135 , wherein said bag has a cryopreserved material section filled with the cryopreserved material before said warming and an empty section constituting said empty space, which is free of the cryopreserved material and is adapted to accommodated said liquefied material. 
     
     
         137 . A method according to any one of  claim 128  or  136 , wherein the heat source is an electrical heater. 
     
     
         138 . A method according to any one of  claim 128  or  137 , wherein the heat source is a warm water. 
     
     
         139 . A system for warming a cryopreserved liquid biological material disposed in a bag having a longitudinal axis, the system comprising:
 a heat source;   a warming device having a space for placing said bag therein and fluid accommodating means for accommodating a fluid therein, the device adapted to transfer heat from the fluid to the bag; and   means for maintaining a liquefied material within the bag evenly dispersed along said longitudinal axis thereby improving heat transfer between said fluid and said cryopreserved material.   
     
     
         140 . A system according to  claim 139 , wherein the warming device comprises a pair of plates creating said space for the bag therebetween. 
     
     
         141 . A system according to  claim 140 , wherein the fluid accommodating means are channels comprised within at least one of said plates. 
     
     
         142 . A system according to any one of  claims 139  to  141 , wherein the device comprises an empty space for accommodating of any liquefied material apart from the cryopreserved material. 
     
     
         143 . A system according to any one of  claims 140  to  142 , wherein at least one of said plates is adapted to move with respect to the other plate in a direction perpendicular to said axis, thereby applying pressure on the bag. 
     
     
         144 . A system according to any one of  claims 139  to  143 , comprising an immersion tank filled with said fluid. 
     
     
         145 . A system according to  claim 144 , comprising a pump for pushing said fluid from said tank to said fluid accommodating means. 
     
     
         146 . A system according to any one of  claims 139  to  145 , wherein the fluid is warm water. 
     
     
         147 . A method for warming a cryopreserved liquid biological material disposed in a bag having a longitudinal axis, the method comprising
 providing a heat source;   providing a warming device having a space for placing said bag therein and fluid accommodating means for accommodating a fluid therein, for transferring heat from the fluid to the bag;   providing for maintaining a liquefied material within the bag evenly dispersed along said longitudinal axis thereby improving heat transfer between said fluid and said cryopreserved material; and   removing from the bag a liquefied material thereby preventing it from receiving said heat during warming of cryopreserved material left in the bag.   
     
     
         148 . A method according to  claim 147 , wherein the warming device comprises a pair of plates creating said space for the bag therebetween. 
     
     
         149 . A method according to  claim 148 , wherein the fluid accommodating means are channels comprised within at least one of said plates. 
     
     
         150 . A method according to any one of  claims 147  to  149 , comprising removing from the bag a liquefied material thereby preventing it from receiving said heat during warming of cryopreserved material left in the bag. 
     
     
         151 . A method according to any one of  claims 148  to  149 , comprising moving at least one of said plates with respect to the other plate in a direction perpendicular to said axis, thereby applying pressure on the bag. 
     
     
         152 . A method according to any one of  claims 148  to  151 , comprising providing an immersion tank filled with said fluid. 
     
     
         153 . A method according to  claim 152 , comprising providing a pump for pushing said fluid from said tank to said fluid accommodating means. 
     
     
         154 . A method according to any one of  claims 148  to  153 , wherein the fluid is warm water.