Abstract:
A method of manufacturing a bag ( 20 ) for the cryopreservation of thermolabile liquids. The manufacturing method is characterized by being versatile, simple and inexpensive and allows to manufacture single and multi-compartment bags without modifying the main sealing molds ( 31, 32 ). The relative size and the number of the compartments ( 28 ) can be modified without change in the molds. Only a closure sealing tool ( 50 ) must be adjusted as a function of the number of chosen compartments ( 28 ). The process is compatible with standard high frequency sealing processes. This method provides bags ( 20 ) with uniformly thick walls and with a predetermined bag volume.

Description:
FIELD OF THE INVENTION 
     The invention relates to a method for forming flexible bags, a system for manufacturing the bags and to the bag itself. More specifically, the invention relates to bags that contain blood substances or any biological or cellular substance. The invention in particular relates to a bag allowing cryogenic preservation while saving the internal bag substance from any cryogenic-preservation damaging effect. 
     BACKGROUND OF THE INVENTION 
     The preservation of blood and cellular biological thermolabile substances involves storage at very low temperatures. Thermolabile substances are substances that are easily altered or decomposed by heat. They can be contained in bags of plastics material; however, storage at very low temperatures creates stresses in the plastics materials and their joints and accordingly the bags used for this purpose must meet stringent requirements. 
     U.S. Pat. No. 5,928,214 described a bag of plastics material for containing biological liquid samples in particular for the cryopreservation of such samples, the bag being of the type made of facing plastics films joined around a sealed peripheral edge. The facing plastics films define a volume for containing a sample, in particular with several compartments communicating with one another by heat-sealable regions. This bag was described in connection with a system for concentrating white blood cells wherein the bag containing stem cells was divided into compartments limited by a heat seal that divided the stem cell freezing bag into two intimately attached but independent white cell containers with heat seals at the dividing locations. The larger main chamber keeps the bulk of the white cells and a smaller chamber is used for storage of a smaller fraction which can be separated from the main compartment without thawing. 
     U.S. Pat. Nos. 6,146,124; 6,232,115 and 6,808,675 describe respectively a mold, a bag useful for the cryopreservation of thermolabile substances and a method to manufacture the bag. The method uses a first mold having a portal-shaped recess and a recess with a planar surface having a radiused periphery circumscribing the planar surface and a peripheral ledge that circumscribes the radiused periphery. A sheet of plastics material is placed over the first mold and caused to conform to its shape. This formed sheet—which forms a half-shell of the bag—is then placed facing a similar formed sheet, or a flat sheet, and the two sheets are joined together by high frequency sealing around the periphery. 
     This manufacturing method is thus done in three different steps: individual pre-shaping of the two films with two different molds, one per film; positioning the two shaped films and the connector/tubes; and sealing of the bag borders with the connector and tubes 
     This process allows manufacture of a bag with a 3-D shape therefore a reduced space for the storage. However, the process requires the aforementioned three steps, and if different bags with different compartments are to be produced, different two-part molds are needed. 
     Bags can also be formed by folding over a planar film and joining the peripheries by a seam. 
     The standard process for making flat plastic bags is by high-frequency welding around the periphery of two flat films. The tool is composed of two matrices which seal the borders of the film and the connector and tube sealing is included in the same step. This procedure is simple, however the bag keeps a 2-D shape and its storage capacity is limited. This therefore does not meet the specifications of certain types of bags which require a volume that fits in a specific protection cassette, for instance with 25 mL capacity for cryogenic storage. This simple process is thus inapplicable for bags which must have a given volume. 
     SUMMARY OF THE INVENTION 
     The invention relates to a simplified method of manufacturing a bag in particular for the cryopreservation of thermolabile liquids. The manufacturing method is versatile, simple and inexpensive and allows manufacture of single and multi-compartment bags without modifying the molds. Also, for any bag of given volume, the size of the bag&#39;s compartments and the number of these compartments can be modified without change in the main sealing molds. Moreover, the process can easily be adapted for making a large range of bags of different volume, for example from 10 ml to 500 ml. The method is compatible with standard high frequency sealing processes. This method provides bags with uniformly thick walls and with a predetermined bag volume. The invention results in bags with a substantially homogenous cross section so that the thickness of the bag containing any molecular substance is reduced which is very advantageous when several bags are placed together for storage. 
     According to a main aspect of the invention, there is provided a method of manufacturing a bag of plastics material for containing biological samples in particular for the cryopreservation of such samples, the bag being of the type made of facing spaced-apart layers of plastics film joined around a sealed peripheral edge whereby the facing spaced-apart plastics layers define a volume for containing a sample. 
     The inventive method comprises firstly placing between two superposed layers of a film of plastics material a molding insert having a shape, width and thickness that correspond to the inside shape, width and thickness of the bag to be formed. The layers are then formed into a part-formed bag whose inner shape, width and thickness are defined by the molding insert. The part-formed bag is made of spaced-apart layers that are closed around a portion of the bag periphery by joined edges, leaving open edges along one side that form an opening for removal of the molding insert. The joined edges of the part-formed bag are then sealed around a portion of the bag periphery, leaving the aforesaid opening in one side, the molding insert is removed from the part-formed bag through this opening, and the open edges of the spaced-apart layers of the part-formed bag are brought together along the opening. Lastly, the brought-together edges are sealed to form a bag that is closed around substantially its entire periphery by the sealed joined edges. 
     Preferably, the superposed layers are formed by folding over a film of plastics material. However, it is also possible to use two different films superposed one on the other. 
     The invention also proposes a mold for manufacturing a bag according to the above-defined as well as the mould in combination with a plurality of interchangeable closure sealing tools for forming the bag into one compartment or a plurality of compartments at choice. 
     The main sealing mold used to generate the overall natural shape of the bag is independent of the number of compartments, so it can stay the same for different configurations of the final bag (one or more compartments), only the sealing closure tool must change according to the desired number of compartments. 
     This new method can be used to produce bags of different final volume (for example, from 10 to 500 ml), but in this case the main molds must be adjusted for each different bag volume. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be further described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is a perspective view of a molding assembly with a folded film inserted between separated mold parts and with a molding insert in an outer position; 
         FIG. 2  is a corresponding perspective view of the molding assembly with a folded film inserted between the separated mold parts and with the molding insert being inserted; 
         FIG. 3  shows the pressed-together mold parts for the sealing operation; 
         FIG. 4  is a perspective view of the molding assembly with the mold parts after separation, and with the molding insert in its outer removed position, the part-formed bag being shown resting in the lower mold part; 
         FIG. 5  shows a closure sealing tool forming the finished bag after insertion of a connector and tube in the open side and sealing this side. 
         FIG. 6  shows the resulting one-compartment bag after opening of FIG.  5 &#39;s closure sealing tool. 
         FIG. 7  shows another closure sealing tool for forming a two-compartment bag after insertion of a connector and tube in the open side and sealing this side. 
         FIG. 8  shows the resulting two-compartment bag after opening of FIG.  7 &#39;s closure sealing tool. 
     
    
    
     DETAILED DESCRIPTION 
     The invention addresses the issues mentioned above. In order to store cryogenic preservation bags there is a need to realize a bag with a built-in volume shape. The invention consists in manufacturing such a bag with a simple and versatile process. 
     In general terms, the manufacturing process consists in positioning an insert  40  between one folded film  10 ′, 10 ″ or two flat planar films for forming the bag walls ( FIG. 1 ), before making a standard sealing by high frequency on three sides of the bags. 
     Introduction of the insert  40  between a folded film  10 ′, 10 ″ is shown in  FIG. 2 . The insert  40  generates a natural volume in the bag and so increases the nominal capacity at the same time. 
     Then the two matrices  31 , 32  are closed around the film and the insert  40 , as shown in  FIG. 3 . There is no film stretching during the forming process due to the fact that the film naturally follows the shape of the insert without mechanical strains. This results in a finished bag with uniformly thick walls, which is important for withstanding the low temperatures during cryogenic storage. 
     The insert  40  used during the sealing between the generally planar films  10 ′, 10 ″ provides the bag&#39;s 3-D shape. This geometry provides space efficient storage for the finished and filled bags  20 . The sealing process is then activated as illustrated in  FIG. 3 . 
     On  FIG. 4  one can see that once the matrices are reopened we have a part-formed bag  22  with an inherent volume. 
     The second step is to insert the tubes  25  and connectors  26  and to seal the fourth side of the bag with a standard HF method, to form the bag  20  as illustrated in  FIGS. 5 and 6 . 
     This solves the space and storage problem described above as the thickness of the bag  20  will remain constant, reducing thus the thickness of the bag and saving precious storage place. 
     The manufacturing process is simplified by comparison to the prior art. In order to create a built-in volume and 3-D shape in the bag, the process uses 1 or 2 generally planar films positioned on each side of an insert  40  having the appropriate length, width and thickness. Then standard HF sealing methods is used to seal three sides of the bag. 
     In particular, the inventive method can for example be implemented by the following series of steps. 
     Two superposed layers  10 ′, 10 ″ formed by folding over a film  10  of plastics material are positioned between the spaced-apart lower part  31  and upper part  32  of a main sealing mould  30 , as shown in  FIG. 1 . A molding insert  40  that has a shape, width and thickness that corresponds to the inside shape, width and thickness of the bag to be formed is placed between the layers  10 ′, 10 ″ in the main sealing mould  30 , as shown in  FIG. 2 . On its insertable end section  41  that fits in the cavity  35  of the main sealing mold  30 , the insert  40  has rounded edges  42  corresponding to the rounded shape of the bag&#39;s edges. 
     This cavity  34  in the main sealing mold  30  corresponds to the outside shape and dimensions of the bag  20  to be manufactured. Cavity  34  is closed around a portion of its periphery, namely around three sides, corresponding to a portion of the periphery of the bag to be manufactured. This cavity  34  has an opening  35  that opens into a lateral face of the two mold parts  31 , 32 . 
     The molding insert  40  has an inserted position in which the insertable end section  41  is situated in the cavity  34  between the two mold parts  31 , 32  when they are placed together. This end section  41  of the molding insert has a shape and thickness that corresponds to the inside shape and thickness of the bag  20  to be formed in the cavity  34  and is insertable into and removable laterally from the cavity  34  via the opening  35  by inserting or removing the insert  40  when the two mold parts  31 , 32  are placed together or spaced apart. 
     The mould parts  31 , 32  are positioned using standard mechanical alignment methods schematically illustrated by way of example as columns  33  by which they are slidably mounted together. By bringing together the two mould parts as shown in  FIG. 3 , the layers  10 ′, 10 ″ are formed into a part-formed bag  22  whose inner shape, width and thickness are defined by the molding insert  40 . The part-formed bag  22  (see  FIG. 4 ) is made of spaced-apart layers of the plastics film that are closed around three edges of the bag periphery by joined edges  21 , leaving open edges  23  along one side that form an opening  24  for removal of the molding insert  40 . The joined edges  21  of the part-formed bag  22  around the three edges of the bag periphery are sealed using high-frequency sealing between the two mould parts  31 , 32 , leaving the opening  24  in one side, that will be sealed in the subsequent operation. As can be seem in  FIG. 3  the open edges that will be sealed in the subsequent operation protrude from the side of the closed sealing mold  30 . 
     The molding insert  40  is removed from the part-formed bag  22  through opening  24 , as shown in  FIG. 4 . 
     The part-formed bag  22  is then inserted in a closure sealing tool  50 ,  FIG. 5 , which in this example is adapted for forming a one-compartment bag. The closure sealing tool  50  has a lower tool part  51  and an upper tool part  52  with facing corresponding recesses  54  for receiving tubes  25 , portals  26  or any other connectors that are inserted in the previously-described opening  24  in the part-formed bag  22 . 
     The lower and upper parts  51 , 52  of the closure sealing tool are as before positioned using standard mechanical alignment methods schematically illustrated by way of example as columns  33  by which they are slidably mounted together. This allows the two parts to be brought together, as shown in  FIG. 5  in order to bring together the open edges of the spaced-apart layers of the part-formed bag  22  along the opening  24 . The brought-together edges are then sealed by high-frequency sealing to form a bag that is closed around substantially its entire periphery by the sealed joined edges  21 , leaving apertures at the locations of the tubes/portals or connectors  25 / 26 . In this example, the peripheral sealed edge  21  surrounds and defines a single internal compartment  28 . 
       FIGS. 7 and 8  show a special sealing closure tool  50  for forming the bag  20  with a sealed area  27  whereby the bag  20  is divided into two (or more) compartments  28  that communicate with one another at  29  adjacent the edge of the bag opposite said brought-together edges along the opening  24 . For this purpose, the upper tool part  51  has a projection  55  at the location for forming the sealed area  27 . This projection  55  presses together the plastics layers at the location of the sealed area  27  when the tool parts  51 , 52  are brought together. High-frequency sealing is then made along the joined edges at the location of the opening  24 , and along the projection  55   
     In this way, the bag of given size and shape produced using the main sealing mold  30  can have one or and desired number of compartments  28  and the relative sizes of the compartments can be varied at will without any need to change the main sealing mold  30 , making the process very versatile. 
     The invention also contemplates filling the bag  20  with a sample through an aperture ( 25 , 26 ), whereupon the aperture is sealed and the sample in the bag is frozen. In particular, the finished bag  20  can be filled with a biological sample followed by sealing the compartments  28  of multi-compartment bags from one another by sealing together the facing parts  29  of the films where the compartments communicate. 
     Usually, as described, the bags  20  are of overall generally rectangular shape, and the first sealing step takes place by sealing together the joined edges of the part-formed bag  22  along three sides of the rectangular bag, the opening  24  in the part-formed bag being located usually along a long side of the rectangular bag where the apertures for tubes  25  and connectors  26  are located.