Patent Publication Number: US-11375710-B2

Title: Packaging system for tissue grafts

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The Present application is a Continuation-In-Part of U.S. patent application Ser. No. 15/402,806, filed on Jan. 10, 2017, now allowed, the disclosure of which is hereby incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to packaging for tissue grafts, and in particular, to packaging systems that include a tissue graft retainer for tissue grafts. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a tissue graft packaging system having a retainer. The retainer includes: a first member having a first inner surface including first engagement means, a first plurality of channel sidewalls extending along the first inner surface, a first plurality of channels defined by the first plurality of channel sidewalls, and a first outer surface; a second member having a second inner surface including second engagement means configured to removeably engage the first engagement means, a second plurality of channel sidewalls extending along the second inner surface, a second plurality of channels defined by the second plurality of channel sidewalls, and a second outer surface; and a vent on said first member and extending from said first inner surface to said first outer surface, or on said second member and extending from said second inner surface to said second outer surface, or both. The first and second pluralities of channel sidewalls are configured to form a continuous interior space between the first and second members. When the first and second members are assembled, the vent is in fluid communication with the first and second plurality of channels and the continuous interior space and allows moisture to escape from said retainer. 
     The present invention is also directed to processes for drying and rehydrating tissue grafts using the tissue graft packaging system and its retainer, wherein the retainer has at least one first side passageway and at least one end passageway. The packaging process includes the steps of assembling a retainer having a first member, a second member and a vent, with a tissue graft therein, and drying the tissue graft while contained in the retainer. The method for using the resulting dried tissue graft includes rehydrating the tissue graft by contacting with a biocompatible fluid prior to use in a medical procedure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The patent application file contains at least one drawing executed in color. Copies of this patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee. 
       The present invention will be further explained with reference to the attached drawings, wherein like features are referred to by like numerals throughout the several views, and the features of successive embodiments are labeled using the reference numbers for similar features of the previous embodiment increased by 200. The drawings shown are not necessarily to scale, with emphasis instead generally being placed upon illustrating the principles of the present invention. 
         FIG. 1  is a perspective, exploded view of a tissue graft packaging system in connection with an embodiment of the present invention; 
         FIG. 2  is a perspective, exploded view of a tissue graft retainer used with the packaging system of  FIG. 1 , along with a tissue graft and backing therefor, all according to the present invention; 
         FIG. 3  is a perspective view of a first member of the tissue graft retainer of  FIG. 2 ; 
         FIG. 3A  is an enlarged perspective view of a portion of the first member of the tissue graft retainer of  FIG. 3 ; 
         FIG. 4  is a top plan view of the first member of the tissue graft retainer of  FIG. 2 ; 
         FIG. 5  is a right side elevational view of the first member of the tissue graft retainer of  FIG. 2 ; 
         FIG. 6  is a perspective view of a second member of the tissue graft retainer of  FIG. 2 ; 
         FIG. 7  is a perspective view of the tissue graft retainer of  FIG. 2 , showing the first and second members assembled together; 
         FIG. 7A  is an enlarged perspective view of a portion of the assembled tissue graft retainer of  FIG. 7 ; 
         FIG. 8  is a left side elevational view of the assembled tissue graft retainer of  FIG. 7 ; 
         FIG. 9  is a sectional view, taken through line  9 - 9  in  FIG. 7 , of the assembled tissue graft retainer of  FIG. 7 ; 
         FIG. 10  is a rear end elevational view of the assembled tissue graft retainer of  FIG. 7 ; 
         FIG. 11  is a front end elevational view of the assembled tissue graft retainer of  FIG. 7 ; 
         FIG. 12  is top plan view of the assembled tissue graft retainer of  FIG. 7 , with a portion of the second member broken away to show the tissue graft, backing and cryopreservation media therein; 
         FIG. 13  is a perspective view of an alternative embodiment of the tissue graft retainer of  FIG. 2 , in its assembled configuration showing a plurality of apertures; 
         FIG. 14  is a perspective view of a first member of the tissue graft retainer of  FIG. 13 ; 
         FIG. 15  is a top plan view of the first member of  FIG. 14 ; 
         FIG. 16  is a right side elevational view of the first member of  FIG. 14 ; 
         FIG. 17  is a front elevational view of the first member of  FIG. 14 ; 
         FIG. 18  is a perspective view of a first member of another alternative embodiment of the tissue graft retainer of  FIG. 13 , having a plurality of apertures; 
         FIG. 19  is a perspective view of another alternative embodiment of the tissue graft retainer of  FIG. 2 , in its assembled configuration showing a plurality of elongated openings; 
         FIG. 20  is a perspective view of a first member of the tissue graft retainer of  FIG. 19 ; 
         FIG. 21  is a top plan view of the first member of  FIG. 19 ; 
         FIG. 22  is a right side elevational view of the first member of  FIG. 19 ; 
         FIG. 23  is a front elevational view of the first member of  FIG. 19 ; 
         FIG. 24  is a perspective view of a first member of another alternative embodiment of the tissue graft retainer of  FIG. 19 , having elongated openings; 
         FIG. 25  is a top plan view of the first member of  FIG. 24 ; 
         FIG. 26  is a graph showing the results of cell viability testing on the tissue graft retainer of  FIG. 7  (left) and a clamshell (i.e., one piece) tissue graft retainer (right); 
         FIG. 27  is a micrograph showing the results of cell viability testing on the tissue graft retainer of  FIG. 7  (top left and right) and a clamshell (i.e., one piece) tissue graft retainer (bottom left and right); 
         FIG. 28  is a graph showing the results of cell viability testing on the tissue graft retainer of  FIG. 7 , based on freezer storage times; 
         FIG. 29  is graph showing the results of studies on the separation force required for the members of the tissue graft retainer of  FIG. 7 ; and 
         FIG. 30  is another graph showing the results of studies on the separation force required for the members of the tissue graft retainer of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Detailed embodiments of the present invention are disclosed herein. It should be understood that the disclosed embodiments are merely illustrative of the invention that may be embodied in various forms. In addition, each of the examples given in connection with the various embodiments of the invention is intended to be illustrative, and not restrictive. Further, the figures are not necessarily to scale, and some features may be exaggerated to show details of particular components. In addition, any measurements, specifications and the like shown in the figures are intended to be illustrative, and not restrictive. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as examples for teaching one skilled in the art to variously employ the present invention. 
     The present invention generally relates to a packaging system for the storage, containment and transportation of tissue grafts (e.g., allografts, autografts, xenografts, tissue-engineered grafts, etc.), and in particular, tissue grafts that are cryopreserved (i.e., tissue grafts that are maintained in cryopreservation media) to maintain at least a portion of their viability. The description of the packaging system and retainer of the present invention are described below. The packaging system may also be employed with non-cryopreserved tissue grafts, as discussed below. 
     An embodiment of the packaging system  10  of the present invention is schematically shown in  FIG. 1 , and includes a retainer  12  and other components that are described below. As further disclosed below, the retainer  12  holds a cryopreserved tissue graft securely therein, but is also constructed with features that enable cryopreservation media to flow to the tissue graft and suspend the tissue graft therein, which protects the viable cells of the tissue graft throughout its shelf life. Such a tissue graft may include, for example, a viable allograft dermis graft. In another embodiment, the retainer may also hold a non-cryopreserved (i.e., dehydrated, lyophilized, refrigerated etc.) tissue graft. It is understood that in any of the non-cryopreserved configurations of the tissue graft, the cryopreservation media may be replaced with any media/solution compatible to the tissue graft, regardless of whether or not the solution has cryopreservation capabilities. Further, it is understood that in any of the non-cryopreserved configurations of the tissue graft, the cryopreservation media may be omitted and not replaced, thus creating a configuration of the tissue graft without any media/solution present. 
     Referring now to  FIG. 2 , one embodiment of the retainer  12  of the present invention is illustrated, including a first member  14  and a separate second member  16  that cooperate to engage one another and contain a tissue graft  18  and, optionally, a backing  20  for the tissue graft  18 . In this embodiment, the first and second members  14 ,  16  are separate, and not permanently connected to one another, such as by a hinge. Providing the first and second members  14 ,  16  as separate from one another prevents bowing of the retainer  12  when subjected to cryopreservation temperatures, and thereby enables the retainer  12  to remain closed in a relatively flat configuration to retain the tissue graft  18  therein. 
     In an embodiment, the first and second members  14 ,  16  are structurally identical to one another (i.e., having the same structural features, dimensions, configurations and shapes as one another). The first member  14  of this embodiment is further described below, with the understanding that the description is also applicable to the second member  16 . 
     In alternate embodiments, the first and second members  14 ,  16  are not structurally identical. In both embodiments where the first and second members  14 ,  16  are and are not structurally identical, the structure of the first member  14  may be symmetrical to the structure of the second member  16 . More particularly, in being symmetrical to each other, the first and second members  14 ,  16  correspond in size, shape, and relative position of their respective structural features on opposite sides of a median plane and/or a dividing line between them, and thereby fit together to engage one another in a symmetrical fashion. The first and second members  14 ,  16  may therefore engage one another via their respective structural features, whether identical, symmetrical, or both, as further described below. 
     In the embodiment illustrated in  FIGS. 1-12 , the first and second members  14 ,  16  (which are structurally identical) are arranged to be symmetrical to one another in that their respective surfaces (and associated structural features) are inverted with respect to one another on opposite sides of a median plane that is substantially parallel to the surfaces of the first and second members  14 ,  16 . 
     With reference to  FIGS. 2-5 , the first member  14  of the retainer  12  illustrated in  FIG. 2  is substantially planar, and includes a first end  22  having a first corner tab  23 , an opposed second end  24  having a second corner tab  25 , and opposed first and second sides  26 ,  28  extending between the first and second ends  22 ,  24 . In an embodiment, the first corner tab  23 , second corner tab  25  and all other corners and edges of the first member  14  are rounded, so as to avoid puncturing the pouches in which the retainer  12  is contained. Such pouches are described below. 
     In an embodiment, the second corner tab  25  includes first indicia  29 , for purposes of correctly aligning the first member  14  with the second member  16  when assembling the retainer  12 , as further described below. The first indicia  29  may be an alphanumeric symbol (e.g., the numeral 2, as shown in  FIGS. 2 and 3 ) or other symbol that can be readily identified during packaging of the tissue graft. 
     The first member  14  further includes a first inner surface  30  that is positioned proximate the graft  18  upon assembly of the retainer  12  of the packaging system  10 , and a first outer surface  32  that is a positioned distal the tissue graft  18  upon assembly of the retainer  12  (see  FIGS. 2-5 ). The first inner surface  30  includes a first plurality of channels  34  that extend longitudinally between the first and second ends  22 ,  24  of the first member  14  (see  FIGS. 2-4 ). The first channels  34  are defined by a first plurality of channel sidewalls  35  that extend longitudinally between the first and second ends  22 ,  24  of the first member  14 . In an alternate embodiment, the first channels  34  and first channel sidewalls  35  extend longitudinally between the first and second sides  26 ,  28  of the first member  14 . The channel sidewalls  35  each have a rounded apex, as illustrated in  FIGS. 2-3A . All of the first channels  34  have the same dimensions, and are evenly distributed across the first inner surface  30 , as illustrated in  FIGS. 2-4 . In alternate embodiment(s), the first channels  34  may have different dimensions from each other and/or an uneven spacing/distribution across the first inner surface  30 . 
     In alternate embodiment(s), the first channels  34  and sidewalls  35  may extend in different directions in relation to the first and second ends  22 ,  24  of the first member  14  and may be defined by sidewalls of different dimensions or shape. 
     In other alternate embodiment(s), the first inner surface  30  may not include a plurality of channels, and/or may include a plurality of protrusions, recesses, holes, or openings. 
     In still other alternate embodiments(s), the first inner surface  30  may include one or more structural features that are not channels or channel walls, through which and/or around which cryopreservation media may flow. Such structural features may include, but are not limited to, one or more elements formed as part of the first member  14  and/or the first inner surface  30 , such as one or more grid patterns, one or more segments, one or more squares, or one or more dots. Such elements may be formed as part of a larger pattern/design on the first inner surface  30 . 
     With continued reference to  FIGS. 3-5 , the first end  22  of the first member  14  includes a first end protrusion  36  that extends upwardly from the first inner surface  30 . The second end  24  includes a second end raised area  38  that extends upwardly from the first inner surface  30 , and defines a second end recess  40  (i.e., a groove or indentation) therein. The first end protrusion  36  and second end recess  40  constitute first engagement means of the first member  14  and are configured to removably engage similar, complimentary structures included on the second member  16 , as will be described further below. 
     In an embodiment, the first end  22  also includes an additional (i.e., supplemental) first end protrusion  42  that extends upwardly from the first inner surface  30 , and the second end raised area  38  of the second end  24  also defines an additional (i.e., supplemental) second end recess  44 . The additional first end protrusion  42  and additional second end recess  44  are both positioned closer to the first channels  34  and first channel sidewalls  35  than the first end protrusion  36  and second end  40  recess, respectively. The additional first end protrusion  42  and additional second end recess  44  are configured to removably engage similar, complimentary structures included on the second member  16 , as will be described further below. 
     The first side  26  of the first member  14  includes a first side protrusion  46  that extends upwardly from the first inner surface  30 . The first side  26  also includes a first side raised area  48  that extends upwardly from the first inner surface  30  and defines a first side recess  50  (i.e., a groove or indentation) therein. The first side protrusion  46  is positioned proximate the second end  24 , while the first side raised area  48  and first side recess  50  are positioned proximate the first end  22 . The first side protrusion  46  and first side recess  50  are configured to removably engage similar, complimentary structures included on the second member  16 , as will be described further below. The first engagement means of the first member  14  also includes the first side protrusion  46  and first side recess  50 . 
     The first side protrusion  46  and first side raised area  48  cooperate to define a first side inlet  52  between them (see  FIGS. 2-5 ). The first side inlet  52  is in fluid communication with the first channels  34 , and facilitates the flow of cryopreservation media into the retainer  12  and to the tissue graft  18  and the suspension of the tissue graft  18  therein, which protects the viable cells of the tissue graft  18  throughout its shelf life, as will be described further below. 
     Referring to  FIGS. 2-4 , the second side  28  of the first member  14  includes similar structures as those of the first side  26 . More particularly, the second side  28  includes a second side protrusion  54  that extends upwardly from the first inner surface  30 . The second side  28  also includes a second side raised area  56  that extends upwardly from the first inner surface  30  and defines a second side recess  58  (i.e., a groove or indentation) therein. The second side protrusion  54  is positioned proximate the second end  24 , while the second side raised area  56  and second side recess  58  are positioned proximate the first end  22 . The second side protrusion  54  and second side recess  58  are configured to removably engage similar, complimentary structures included on the second member  16 , as will be described further below. The first engagement means of the first member  14  also includes the second side protrusion  54  and second side recess  58 . 
     The second side protrusion  54  and second side raised area  56  cooperate to define a second side inlet  60  between them (see  FIGS. 2-5 ). Like the first side inlet  52 , the second side inlet  60  is in fluid communication with the first channels  34 , and facilitates the flow of cryopreservation media into the retainer  12  and to the tissue graft  18  and the suspension of the tissue graft  18  therein, which protects the viable cells of the tissue graft  18  throughout its shelf life, as will be described further below. 
     In the embodiment illustrated herein, the second member  16  and the first member  14  are identical (i.e., having the same structural features, dimensions, configurations and shapes as one another). The construction and operation of the second member  16  is described below. 
     With reference to  FIGS. 2 and 6 , the second member  16  of the retainer  12  is substantially planar, and includes a third end  62  having a third corner tab  63 , an opposed fourth end  64  having a fourth corner tab  65 , and opposed third and fourth sides  66 ,  68  extending between the third and fourth ends  62 ,  64 . In an embodiment, the third corner tab  63 , fourth corner tab  65  and all other corners and edges of the second member  16  are rounded so as to avoid puncturing the pouches in which the retainer  12  is contained. Such pouches are described below. 
     In an embodiment, the fourth corner  65  includes second indicia  69 , for purposes of correctly aligning the second member  16  with the first member  14  when assembling the retainer  12 . The second indicia  69  may be an alphanumeric symbol (e.g., the numeral 2, as shown in  FIG. 6 ) or other symbol that can be readily identified during packaging of the tissue graft  18 . The second indicia  69  is preferably identical to the first indicia  29  on the first member  14 , so as to simplify the packaging process. In alternate embodiments, the first indicia  29  and second indicia  69  are different, so as to allow the end user to distinguish one side of the tissue graft  18  from the other. 
     The second member  16  further includes a second inner surface  70  that is positioned proximate the tissue graft  18  upon assembly of the retainer  12  of the packaging system  10 , and a second outer surface  72  that is a positioned distal the tissue graft  18  upon assembly of the retainer  12  (see  FIGS. 2, 6 and 12 ). The second inner surface  70  of the second member  16  includes a second plurality of channels  74  that extend longitudinally between the third and fourth ends  62 ,  64  of the second member  16 . The second channels  74  are defined by a second plurality of channel sidewalls  75  that extend longitudinally between the third and fourth ends  62 ,  64  of the second member  16 . In an alternate embodiment, the second channels  74  and second channel sidewalls  75  extend longitudinally between the first and second sides  66 ,  68  of the second member  16 . The channel sidewalls  75  each have a rounded apex, as illustrated in  FIG. 6 . All of the second channels  74  have the same dimensions, and are evenly distributed across the second inner surface  70 , as illustrated in  FIG. 6 . In alternate embodiments, the second channels  74  may have different dimensions from each other and/or an uneven spacing/distribution across the second inner surface  70 . 
     In alternate embodiment(s), the second channels  74  and sidewalls  75  may extend in different directions in relation to the third and fourth ends  62 ,  64  of the second member  16  and may be defined by sidewalls of different dimensions or shape. 
     In other alternate embodiment(s), the second inner surface  70  may not include a plurality of channels, and/or may include a plurality of protrusions, recesses, holes, or openings. 
     In still other alternate embodiments(s), the second inner surface  70  may include one or more structural features that are not channels or channel walls, through which and/or around which cryopreservation media may flow. Such structural features may include, but are not limited to, one or more elements formed as part of the second member  16  and/or the second inner surface  70 , such as one or more grid patterns, one or more segments, one or more squares, or one or more dots. Such elements may be formed as part of a larger pattern/design on the second inner surface  70 . 
     The second channels  74  also have the same dimensions, spacing/distribution and orientation (i.e., extending longitudinally along the same axis and direction) as the first channels  34 . In an alternate embodiment, the second channels  74  may have one or more different dimensions, distribution and/or orientation from the first channels  34 . For example, in an embodiment, the second channels  74  extend longitudinally between the third and fourth sides  66 ,  68  of the second member  16 , and the first channels  34  extend longitudinally between the first and second ends  22 ,  24  of the first member  14 , such that the second channels  74  are oriented perpendicularly to the first channels  34  upon assembly of the retainer  12 . 
     Upon assembly of the retainer  12 , the first channels  34  and second channels  74  do not mate. More particularly, the first channel sidewalls  35  do not come into contact with the second channel sidewalls  75  when the first and second members  14 ,  16  are connected to each other via their respective first and second engagement means (see  FIGS. 7A and 9 ). This arrangement facilitates the creation of a continuous interior space (i.e., a gap)  122  between the first and second members  14 ,  16  in which the tissue graft  18  is maintained, as illustrated in  FIG. 9  and further described below. 
     With continued reference to  FIG. 6 , the third end  62  of the second member  16  includes a third end protrusion  76  that extends upwardly from the second inner surface  70 . The fourth end  64  includes a fourth end raised area  78  that extends upwardly from the second inner surface  70 , and defines a fourth end recess  80  (i.e., a groove or indentation) therein. The third end protrusion  76  and fourth end recess  80  constitute second engagement means of the second member  16 . The third end protrusion  76  is configured to insertably and removably engage the second end recess  40  of the first member  14  (i.e., upon assembly of the retainer  12 ), while the first end protrusion  36  of the first member  14  is configured to insertably and removably engage the fourth end recess  80 , as further described below. For example, the third end protrusion  76  may be oval-shaped and the second end recess  40  may be oval-shaped but slightly smaller than the third end protrusion  76  so as to facilitate an interference fit therewith, and the first end protrusion  36  and fourth end recess  80  may be similarly shaped and sized so as to also facilitate an interference fit therewith. For example, the third end protrusion  76  may be oval-shaped and the second end recess  40  may be oval-shaped but slightly smaller than the third end protrusion  76  so as to facilitate an interference fit therewith, and the first end protrusion  36  and fourth end recess  80  may be similarly shaped and sized so as to also facilitate an interference fit therewith. In an alternate embodiment, the third end protrusion  76  has the same dimensions as the second end recess  40 , so as to facilitate a press-fit therebetween, and the first end protrusion  36  has the same dimensions as fourth end recess  80 , so as to facilitate a press-fit therebetween. 
     In an embodiment, the third end  62  also includes an additional (i.e., supplemental) third end protrusion  82  that extends upwardly from the second inner surface  70 , and the fourth end raised area  78  of the fourth end  64  also defines an additional (i.e., supplemental) fourth end recess  84 . The additional third end protrusion  82  and additional fourth end recess  84  are both positioned closer to the second channels  74  and second channel sidewalls  75  than the third end protrusion  76  and fourth end  80  recess, respectively. 
     The additional third end protrusion  82  is configured to insertably and removably engage the additional second end recess  44  of the first member  14  (i.e., upon assembly of the retainer  12 ), and functions to facilitate the correct alignment of the first and second members  14 ,  16 . Similarly, the additional first end protrusion  42  of the first member  14  is configured to insertably and removably engage the additional fourth end recess  84 , and also functions to facilitate the correct alignment of the first and second members  14 ,  16  upon assembly of the retainer  12 . The additional first end protrusion  42 , additional second end recess  44 , additional third end protrusion  82  and additional fourth end recess  84  thereby function as alignment guides for the tissue graft processor/packager, as further discussed below. 
     The third side  66  of the second member  16  includes a third side protrusion  86  that extends upwardly from the second inner surface  70 . The third side  66  also includes a third side raised area  88  that extends upwardly from the second inner surface  70  and defines a second side recess  90  (i.e., a groove or indentation) therein. The third side protrusion  86  is positioned proximate the fourth end  64 , while the third side raised area  88  and third side recess  90  are positioned proximate the third end  62 . The second engagement means of the second member  16  also includes the third side protrusion  86  and third side recess  90 . 
     As illustrated in  FIG. 7 , the third side protrusion  86  is configured to insertably and removably engage the first side recess  50  of the first member  14  (i.e., upon assembly of the retainer  12 ), while the first side protrusion  46  of the first member  14  is configured to insertably and removably engage the third side recess  90  of the second member  16 . 
     The third side protrusion  86  and third side raised area  88  cooperate to define a third side inlet  92  between them (see  FIG. 6 ). The third side inlet  92  is in fluid communication with the second channels  74 , and facilitates the flow of cryopreservation media into the retainer  12  and to the tissue graft  18  and the suspension of the tissue graft  18  therein, which protects the viable cells of the tissue graft  18  throughout its shelf life, as will be described further below. 
     The fourth side  68  of the second member  16  includes similar structures as those of the third side  66 . More particularly, the fourth side  68  of the second member  16  includes a fourth side protrusion  94  that extends upwardly from the second inner surface  70 . The fourth side  68  also includes a fourth side raised area  96  that extends upwardly from the second inner surface  70  and defines a fourth side recess  98  (i.e., a groove or indentation) therein. The fourth side protrusion  94  is positioned proximate the fourth end  64 , while the fourth side raised area  96  and fourth side recess  98  are positioned proximate the third end  62 . The second engagement means of the second member  16  also includes the fourth side protrusion  94  and fourth side recess  98 . 
     As illustrated in  FIG. 7 , the fourth side protrusion  94  is configured to insertably and removably engage the second side recess  58  of the first member  14  (i.e., upon assembly of the retainer  12 ), while the second side protrusion  54  of the first member  14  is configured to insertably and removably engage the fourth side recess  98  of the second member  16 . 
     The fourth side protrusion  94  and fourth side raised area  96  cooperate to define a fourth side inlet  100  between them (see  FIG. 6 ). Like the third side inlet  92 , the fourth side inlet  100  is in fluid communication with the second channels  74 , and facilitates the flow of cryopreservation media into the retainer  12  and to the tissue graft  18  and the suspension of the tissue graft  18  therein, which protects the viable cells of the tissue graft  18  throughout its shelf life, as will be described further below. 
     The first and second members  14 ,  16  of the retainer  12  may be formed (e.g., via thermoforming, or any suitable alternate manufacturing method) from any biologically inert material that can operably withstand cryopreservation temperatures (e.g., &lt;0° C. to −196° C.). Such materials include, but are not limited to, polyethylene terephthalate glycol-modified (PETG), high-impact polystyrene (HIPS), polystyrene, polypropylene, or any plastic derivative of the foregoing materials. In an embodiment, the material is transparent or translucent, such that the tissue graft  18  may be visible through the retainer  12  during packaging, handling and surgery (or use in other, non-surgical medical procedures). In alternate embodiments, the first and/or second members  14 ,  16  are made of an opaque material, or a semi-opaque material. The first and/or second members  14 ,  16  can be made of the same material or different materials. 
     In an embodiment, the first and second members  14 ,  16  of the retainer  12  are identical (i.e., having the same structural features, dimensions, configurations and shapes as one another), which simplifies both the manufacturing and operation of the retainer  12 . In an embodiment, the size of the first and second members  14 ,  16  may range from 1 cm×1 cm to 15 cm×15 cm. Such sizes include, but are not limited to, a 1 cm diameter, a 3 cm×3 cm square, a 5 cm×5 cm square, a 10 cm×10 cm square, and a 7.5 cm×15 cm rectangle. In alternate embodiments, the first member  14  may have a different size, shape and/or configuration than the second member  16 . 
     For illustrative purposes,  FIGS. 7-11  show the retainer  12  as assembled (i.e., with the first and second members  14 ,  16  connected to each other by way of their respective first and second engagement means), but without containing the tissue graft  18  (or its backing  20 ) within.  FIG. 12  shows a portion of the second member  16  of the assembled retainer  12  broken away to reveal the tissue graft  18 , backing  20  and cryopreservation media  104  therein. Reference to the foregoing figures, and  FIGS. 1 and 2 , will be made throughout the following discussion of the operation and assembly of the retainer  12  and other components of the tissue packaging system  10  of the present invention, and the associated tissue graft  18  and backing  20 , where applicable. 
     While the retainer  12  and tissue packaging system  10  of the present invention are described below in connection with a cryopreserved viable tissue graft  18  having a sheet-like configuration (i.e., a planar, single-layer graft), it is understood that the retainer  12  and tissue packaging system  10  may also be used for other viable tissue grafts and tissue-engineered scaffolds with seeded cells that also require cryopreservative media, as well as sheet-like decellularized tissue grafts, and non-sheet-shaped tissue grafts, such as three-dimensional tissue grafts. The retainer  12  may also be used with non-cryopreserved tissue grafts or tissue-engineered scaffolds, such as those stored at refrigerated temperature or room (i.e., ambient) temperature. If desired, an alternate solution may be substituted for the cryopreservation solution, and such alternate solution may optionally not have any cryopreservation capabilities. Alternatively, the solution may be omitted from the retainer  12  completely. Tissue-engineered scaffolds as described above for use with the retainer  12  can be either naturally-occurring, naturally-derived, synthetic, or a combination thereof. Further, the retainer  12  and tissue packaging system  10  may alternatively be used with multiple (i.e., two or more) tissue grafts. 
     Donor tissues are processed for preparation of a tissue graft  18  that may be used as an allograft in various surgical and other medical procedures (e.g., ophthalmological, genitourinary, wound healing, burn care, surgical anti-adhesion, dental, orthopaedic, plastic and reconstructive surgery, etc.). Generally, the donor tissue is processed (e.g., removed from any adjacent tissue(s), cleaned to remove blood and blood clots and soaked in an antibiotic solution) and cut into a number of tissue grafts  18  having a sheet (i.e., single layer) configuration. Such tissue grafts  18  can be of any dimension, as discussed in the Examples herein. 
     The finished tissue graft  18  is then placed into the retainer  12 , cryopreserved (optionally via controlled rate freezing (e.g., 1° C./min.) and maintained in cryopreservation media until it is thawed, shortly before its use in surgery (or other medical applications), as described further below. The tissue graft  18  may optionally be supported by, and packaged with, a backing  20  (see  FIGS. 2 and 12 ) that is maintained in contact with (i.e., removeably secured to) the tissue graft  18 . In an embodiment, the backing  20  is maintained in contact with the tissue graft  18  via surface tension between them. In an embodiment, the two sides of the backing  20  have different surfaces, namely, a meshed side and non-meshed side, and the tissue graft  18  is placed on the meshed side to provide surface tension between the backing  20  and the tissue graft  18 , and thereby secure the tissue graft  18  to the backing  30 . In an embodiment, the backing  20  is labeled to indicate which side of the tissue graft  18  is face-down or face-up (i.e., in the event that a first side of the tissue graft  18  is different from a second side thereof), which enables a healthcare provider (e.g., a surgeon) to easily identify each side. The backing  20  may alternatively be directly applied to the first or second side of the tissue graft  18  for such identification purposes. In other embodiments, the backing  20  can include other sidedness indicators such as texture, marking and/or color. 
     The backing  20  is maintained in contact with (i.e., removeably secured to) the tissue graft  18  (e.g., via surface tension) so as to enable a healthcare provider to remove the backing  20  easily (e.g., after the tissue graft  18  is applied to a wound), as also described below. 
     With continued reference to  FIGS. 2 and 12 , the tissue graft  18 , and the optional backing  20 , is placed on the first inner surface  30  of the first member  14  of the retainer  12 , so as to engage the first channel sidewalls  35  thereof and thereby be in contact with the first channels  34 . The tissue graft  18 , and the backing  20 , may alternatively be placed on the second inner surface  70  of the second member  16  of the retainer  12 , so as to engage the second channel sidewalls  75  thereof and thereby be in contact with the second channels  74 . 
     As illustrated in  FIG. 12 , and also in  FIG. 2 , the first and second members  14 ,  16  of the retainer  12  have a larger surface area than that of the tissue graft  18  and its backing  20 . In an embodiment, the backing  20  itself has a larger surface area than that of the tissue graft  18 , such that at least one edge of the backing  20  does not come into contact with the tissue graft  18 , and therefore facilitates the separation of the backing  20  from the tissue graft  18  by the healthcare provider. 
     In other embodiments, the first and/or second members  14 ,  16  of the retainer  12  have a surface area that is the same size as or smaller than that of the tissue graft  18  and its backing  20 . In yet other embodiments, the backing  20  has a surface area that is the same size as or smaller than that of the tissue graft  18 . 
     The first and second members  14 ,  16  are then secured to one another via their respective first and second engagement means (by, i.e., a tissue graft processor/packager), with the tissue graft  18 , and the optional backing  20 , being enclosed within the continuous interior space  122  between the first and second members  14 ,  16 . More particularly, in the embodiment illustrated in  FIGS. 7-12 , the retainer  12  is assembled by at least the steps of (1) removably inserting (i.e., snapping) the third end protrusion  76  of the second member  16  into the second end recess  40  of the first member  14 , and (2) removably inserting (i.e., snapping) the first end protrusion  36  of the first member  14  into the fourth end recess  80  of the second member  16 . The first and second members  14 ,  16  are further secured to one another by the steps of (3) removably inserting (i.e., snapping) the third side protrusion  86  of the second member  16  into the first side recess  50  of the first member  14 ; (4) removably inserting (i.e., snapping) the first side protrusion  46  of the first member  14  into the third side recess  90  of the second member  16 ; (5) removably inserting (i.e., snapping) the fourth side protrusion  94  of the second member  16  into the second side recess  58  of the first member  14 ; and (6) removably inserting (i.e., snapping) the second side protrusion  54  of the first member  14  into the fourth side recess  98  of the second member  16 . In alternate embodiments, fewer than all of these steps (i.e., fewer than all of the foregoing protrusions and recesses) may be used to secure the first and second members  14 ,  16  of the retainer  12  together. 
     The first and second members  14 ,  16  are configured and manufactured such that when secured to one another, a minimum retention force is required to maintain the interconnection of the first and second members  14 ,  16 , with the tissue graft  18  between them. In an embodiment, the minimum retention force is 18 Newtons (18 N). 
     In alternate embodiments, the aforementioned minimum retention force may be less than or greater than 18 N. For example, the minimum retention force may range from 5 N to 100 N, and may be, without limitation, 8 N, 9 N, 10 N, 20 N or 30 N. In another alternate embodiment, there is no minimum retention force required to maintain the interconnection of the first and second members  14 ,  16  (i.e., the “minimum” retention force is 0 N). 
     The first and second indicia  29 ,  69  on the corner tabs  25 ,  65  of the first and second members  14 ,  16 , respectively, may be used by the tissue graft processor/packager to align the first and second members  14 ,  16  according to the proper orientation upon assembly. As illustrated in  FIG. 7 , the first and second indicia  29 ,  69  are aligned on the same side of the assembled retainer  12  (i.e., the side corresponding to the first side  26  of the first member  14  and the aligned, adjacent third side  66  of the second member  16 ). The first and second indicia  29 ,  69  thereby facilitate efficient and accurate assembly of the retainer  12 . 
     As indicated above, the additional third end protrusion  82  insertably and removably engages the additional second end recess  44  to facilitate the correct alignment of the first and second members  14 ,  16  upon assembly of the retainer  12  (i.e., by the tissue graft processor/packager). Similarly, the additional first end protrusion  42  insertably and removably engages the additional fourth end recess  84  to facilitate the correct alignment of the first and second members  14 ,  16  upon assembly of the retainer  12 . In assembling the retainer  12 , the tissue graft processor/packager would removably insert (i.e., snap) the additional third end protrusion  82  of the second member  16  into the additional second end recess  44  of the first member  14 , and removably insert (i.e., snap) the additional first end protrusion  42  of the first member  14  into the additional fourth end recess  84  of the second member  16 . 
     Upon assembly of the first and second members  14 ,  16  of the retainer  12 , the first side inlet  52  and third side inlet  92  cooperate to form a first side passageway  102  through which cryopreservation media  104  flows into and out of the assembled retainer  12  (see  FIGS. 7 and 9 ). Likewise, the second side inlet  60  and fourth side inlet  100  cooperate upon assembly of the first and second members  14 ,  16  to form a second side passageway  106  through which cryopreservation media  104  flows into and out of the assembled retainer  12  (see  FIGS. 7-9 ). 
     Upon assembly of the retainer  12 , first and second members  14 ,  16  also cooperate to form end passageways through which cryopreservation media  104  flows into and out of the assembled retainer  12 . More particularly, the fourth side raised area  96  cooperates with the second end raised area  38  to form a first end passageway  101  between them, and the third side raised area  88  cooperates with the second end raised area  38  to form a second end passageway  103  between them (see  FIG. 10 ). In addition, the second side raised area  56  cooperates with the third end raised area  78  to form a third end passageway  105  between them, and the first side raised area  48  cooperates with the third end raised area  78  to form a fourth end passageway  107  between them (see  FIG. 11 ). The first, second, third and fourth end passageways  101 ,  103 ,  105 ,  107  are in fluid communication with said first and second pluralities of channels  34 ,  74 . 
     The respective components of the first and second members  14 ,  16  (e.g., the first and second channel sidewalls  35 ,  75  and/or first and second inner surfaces  30 ,  70 ) are configured such that they minimally contact the tissue graft  18  between them when the first and second members  14 ,  16  are secured to one another. 
     In an embodiment, such minimal contact may constitute no contact (i.e., touching) between the respective components of the first and/or second members  14 ,  16  and the tissue graft  18 . In another embodiment, such minimal contact may constitute light contact between the respective components of the first and/or second members  14 ,  16  and the tissue graft  18 , such that the components do not exert an amount of pressure on the tissue graft  18  sufficient to compromise and/or damage the viability of the tissue thereof (e.g., by crushing, pinching or compressing the tissue graft  18 ). More particularly, the tissue graft  18  is maintained within the continuous interior space  122 , which provides sufficient space (i.e., clearance) between the first channels  34  of the first member  14  and the second channels  74  of the second member  16 , so as to facilitate the suspension of the tissue graft  18  in the cryopreservation media  104 , and minimal contact between the tissue graft  18  and the first and second channel sidewalls  35 ,  75  and/or first and second inner surfaces  30 ,  70 . In an embodiment, the clearance between the apexes of the first channel walls  35  and the apexes of the second channel walls is at least slightly greater than the average thickness of the tissue graft  18  (and, if present, the backing  20 ), such that the continuous interior space  122  has a height that is greater than the height (i.e., thickness) of the tissue graft  18 , or the combined height (i.e., thickness) of the tissue graft  18  and backing  20 . In another embodiment, the continuous interior space  122  has a height that is approximately the same height (i.e., thickness) of the tissue graft  18 , or the combined height (i.e., thickness) of the tissue graft  18  and backing  20 . 
     In an embodiment, the first and second channel sidewalls  35 ,  75  are also not in constant contact with the tissue graft  18  (i.e., the tissue graft  18  moves within the continuous interior space  122 , suspended in the cryopreservation media  104 , so that the tissue graft  18  may, at various times, be supported by the first inner surface  30  and the first channel sidewalls  35  thereof, or be supported by the second inner surface  70  and the second channel sidewalls  75  thereof, or float in the cryopreservation media  104  between the first and second inner surfaces  30 ,  70 ). The first and second channel sidewalls  35 ,  75  therefore do not block/impede the cryopreservation media  104  from reaching any portion of the tissue graft  18 , which could otherwise adversely affect the viability of the tissue graft  18 . 
     While the tissue graft  18  may move within the retainer  12  (i.e., within the continuous interior space  122 , while suspended in the cryopreservation media  104 ), the various complimentarily-engaged protrusions and recesses of the interconnected first and second members  14 ,  16  (i.e., the first and second engagement means) prevent egress of the tissue graft  18  outside of the retainer  12 . In the meantime, the first and second side passageways  102 ,  106  and first, second, third and fourth end passageways  101 ,  103 ,  105 ,  107  are dimensioned such that the cryopreservation media  104  may freely flow into the retainer  12  to suspend the tissue graft  18  therein, but not large enough to permit passage of the tissue graft  18  therethrough. 
     Once the tissue graft  18  has been secured within the retainer  12 , the retainer  18  is placed into an inner pouch  108 , as illustrated in  FIG. 1 . The inner pouch  108  is then filled with an amount (i.e., volume) of cryopreservation media  104 . In an embodiment, 20 ml of cryopreservation media  104  is used, although other volumes are contemplated. In an embodiment, the cryopreservation media  104  is a solution containing a cryoprotectant known in the art, such as dimethyl sulfoxide (DMSO). Other types of cryoprotectant may alternatively be used. 
     The inner pouch  108  is then sealed, containing the retainer  12 , tissue graft  18  and cryopreservation media  104  therein. As indicated above, the cryopreservation media  104  flows freely from the inner pouch  108  (outside of the retainer  12 ) into the retainer  12  through the first and second side passageways  102 ,  106  thereof and the first, second, third and fourth end passageways  101 ,  103 ,  105 ,  107  thereof, and through its first and second channels  34 ,  74 , to immerse the tissue graft  18  therein, and thereby preserve the viability of the cells of the tissue graft  18  throughout its shelf life. 
     One or more labels  110 ,  112  may be applied to the outside of the sealed inner pouch  108 . Such labels  110 ,  112  may convey information about the tissue graft  18 , including its orientation (e.g., which side of the graft is face-down on the backing  20  or face-up) and donor and/or lot numbers (e.g., via alphanumeric and/or bar code). The sealed inner pouch  108  is then placed within an outer pouch  114 , which is then sealed. A label  116  may be applied to the outside of the sealed outer pouch  114 . The label  116  may also convey information about the tissue graft  18  (e.g., its donor and/or lot numbers (e.g., via alphanumeric and/or bar code)). 
     The outer pouch  114  is then loaded into controlled rate freezer (e.g., a CryoMed™ controlled rate freezer, Thermo Fischer Scientific, Waltham, Mass.), by which the tissue graft  18  is cryopreserved. Once the desired cryopreservation temperature has been attained, the outer pouch  114  is removed from the controlled rate freezer and stored in a freezer under approved storage conditions (e.g., −80° C.). Cryopreservation temperatures may range from &lt;0° C. to −196° C., and may include, by way of example only, −20° C., −40° C., −70° C., −80° C., and −100° C. 
     Prior to supplying the cryopreserved tissue graft  18  to a hospital or other end user, the outer pouch  114  containing same is placed in a carton  118 , which may include a label  120  with information regarding the cryopreserved tissue graft  18  (e.g., its donor and/or lot numbers (e.g., via alphanumeric and/or bar code)) and/or the use thereof. The carton  118  may be made from any suitable material (e.g., corrugated cardboard, paperboard, etc.). In an embodiment, the carton  118  is laminated so that it can better withstand freezing temperatures/conditions. 
     A package insert containing instructions for use and other information (not shown) may also be placed inside the carton  118 . Such instructions for use may include how to thaw and rinse the cryopreserved tissue graft  18  prior to surgery (or other medical procedure performed by a healthcare provider), a method that is facilitated by the design of the retainer  12 , as further described below. 
     In an embodiment, the following graft defrosting and preparation protocol is followed prior to a surgery, or other medical procedure performed by a healthcare provider, involving the implantation or application of the tissue graft  18 . The carton  118  containing the outer pouch  114 , inner pouch  108 , retainer  12  and tissue graft  18  is removed from the hospital (or surgical center or other end user) freezer and delivered to the surgical suite (i.e., operating room or other surgical area), or applicable medical treatment area. The outer pouch  114  is removed from the carton  118  and opened, enabling a healthcare provider to retrieve the sealed inner pouch  108  and pass it into a sterile field within the surgical suite. The inner pouch  108  contains the tissue graft  18 , the backing  20 , and retainer  12 , as well as the cryopreservation media  104 . In an embodiment, the cryopreservation media  104  is a first color (e.g., yellow). 
     The sealed inner pouch  108  is placed into a first basin containing enough thawing solution (e.g., saline or other appropriate biocompatible liquid) to completely submerge the inner pouch  108  therein, or enough thawing solution to at least contact a surface of the inner pouch  108 . Placement of the inner pouch  108  in the thawing solution facilitates the thawing of the tissue graft  18  still sealed therein. The thawing solution may be room temperature, or a higher temperature, such as 37° C., or any appropriate temperature up to and including 40° C. 
     The tissue graft  18  is completely thawed when no more ice is visible. In one embodiment, the cryopreservation media  104  turns a second color (e.g., red) to indicate that the tissue graft  18  is completely thawed. Alternatively, the cryopreservation media  104  may not undergo a change in color upon complete thawing of the tissue graft  18 . 
     The inner pouch  108  is then removed from the first basin and opened, wherein the cryopreservation media  104  is discarded and the retainer  12  containing the tissue graft  18  is removed from the inner pouch  108  and placed into a second basin containing a rinse solution to remove residual cryopreservation media  104 . In an embodiment, the rinse solution may constitute 5% dextrose in lactated ringer&#39;s solution, which maintains the cell viability of the tissue graft  18 . Alternatively, the rinse solution may constitute physiological saline solution (i.e., 0.9% saline w/v). The retainer  12  is fully submerged in the rinse solution for at least 5 minutes, generally not more than one hour, and at most for four hours. The first and second side passageways  102 ,  106 , and first, second, third and fourth end passageways  101 ,  103 ,  105 ,  107  of the retainer  12  facilitate the flow of residual cryopreservation media  104  out of the retainer  12 , as well as the flow of the rinse solution into and out of the retainer  18 , to more effectively rinse the tissue graft  18 . 
     Once the residual cryopreservation media  104  has been rinsed from the tissue graft  18 , it is ready for use. The retainer  12  is opened by disengaging the first engagement means (e.g., the first end protrusion  36 , second end recess  40 , first side protrusion  46 , first side recess  50 , second side protrusion  54 , and/or second side recess  58 ) from the second engagement means (e.g., the third end protrusion  76 , fourth end recess  80 , third side protrusion  86 , third side recess  90 , fourth side protrusion  94  and/or fourth side recess  98 ) to separate the first and second members  14 ,  16  from each other. 
     The tissue graft  18  is then removed from the retainer  12  with its backing  20 , and a healthcare provider may manipulate the tissue graft  18  based on which side the healthcare provider prefers to be placed downward to face a patient&#39;s body (e.g., to be in contact with a wound). As indicated in the embodiment disclosed above, the backing  20  may be directly applied to the first or second side of the tissue graft  18  for identifying that side (i.e., in the event that the first side of the tissue graft  18  is different from the second side). The opposing side of the tissue graft  18  is therefore exposed (i.e., not in contact with or covered by the backing  20 ). A healthcare provider can lift the tissue graft  18  off of the backing  20  with a forceps (e.g., starting by lifting a corner of the tissue graft  18 ) in order to expose the underlying side of the tissue graft  18  and place it facing downward on a wound. Alternatively, the healthcare provider can place the exposed side of the tissue graft  18  facing downward on the wound by leaving the tissue graft  18  on the backing  20  until after the tissue graft  18  is applied to the wound, and then carefully removing the backing  20  from opposite side of the tissue graft  18 . The backing  20  is maintained on the tissue graft  18  (e.g., by surface tension) to enable its removal without disrupting the placement of the tissue graft  18  on the wound. The healthcare provider may, alternatively, not make any distinction or decision to orient a certain side of the tissue graft  18  downward. 
     Alternatively, the tissue graft  18  could be removed from the backing  20  and used in other wound care or medical applications other than those where it is layered down onto a wound bed. Such applications include, for example, balling, rolling or otherwise shaping the tissue graft  18  prior to placement onto a wound; cutting the tissue graft  18  into smaller pieces prior to placement onto a wound; “stuffing” the tissue graft  18  into a wound, etc. The tissue graft  18  could also be removed from the backing  20  and used in any non-wound care medical or surgical application, including, but not limited to, placement onto or within another allograft or non-allograft medical product prior to use; placement as a layer between human tissues during orthopaedic or general surgery procedures; use for replacement of a naturally-occurring membrane in the human body (e.g., tympanic membrane, pericardium, omentum, interstitial membranes, and other membranes or sheet-like structures), etc. The tissue graft  18  could also be removed from the backing  20  and used for in vitro diagnostic or research applications, including but not limited to, cell culture, tissue culture, microbiology, bioreactors, or other tissue engineering applications. 
     As mentioned above, in some embodiments, the retainer described and contemplated herein may hold a non-cryopreserved (i.e., dehydrated, lyophilized, refrigerated etc.) tissue graft. In some such embodiments, at least a portion of moisture (often, but not always, water or water vapor) present in the tissue graft is separated or removed from the tissue graft, such as by dehydration, lyophilizing, or other drying technique. Drying of the tissue graft may occur prior to, or after, the retainer and tissue graft are assembled (e.g., as shown in  FIGS. 2, 12, 13 and 19 ). When performed after assembly of the retainer and tissue graft, there must be a way for the moisture to escape from the retainer during drying. The escape of moisture during drying may be permitted by the various passageways of the assembled retainer described in detail above (e.g., see the first and second side passageways  102 ,  106  and the first, second, third and fourth end passageways  101 ,  103 ,  105 ,  107  of the assembled retainer shown in  FIGS. 8-11 , all of which allow cryopreservative, lyophilizing, or other media to flow in and out of the assembled retainer). However, depending on the volume of moisture to be removed and the time period required for drying (e.g., how quickly drying is to be accomplished), those passageways may not be sufficient. 
     With reference now to  FIGS. 13-25 , in some alternative embodiments, to address the need to allow fluid (i.e., liquid or vapor) to escape from the retainer during and after drying, the retainer comprises one or more vents through which moisture (i.e., a liquid or gaseous fluid which may or may not comprise water) may escape from the retainer during and after drying. As described in further detail below,  FIGS. 13-25  show various alternative embodiments of the retainer in which the first member, or second member, or both members, of a retainer, have different types and/or quantities of vents for allowing escape of moisture from assembled retainers. As will be described in further detail below, the vents generally comprise one or more openings each of which extends entirely through whichever member on which it is included. 
     It is noted that  FIGS. 13-17, 18, 19-24 and 24-25  depict second, third, fourth, and fifth embodiments, respectively, of the retainer described and contemplated here. Features illustrated in  FIGS. 13-17 ,  FIG. 18 ,  FIGS. 19-24  and  FIGS. 24-25  which correspond, either identically or substantially, to the features described above with respect to the embodiment of  FIGS. 2-12  have been designated by corresponding reference numerals increased by 200, 400, 600 and 800, respectively. Unless otherwise stated, the embodiments of  FIGS. 13-25  are constructed, assembled and operated in the same basic manner as the embodiment of  FIGS. 2-12 . It is further noted that although not shown in  FIGS. 13-25 , as with the embodiment described above with  FIGS. 2-12 , the second member of each embodiment of the second, third, fourth and fifth embodiments of the retainer described below is structurally identical to its corresponding first member (i.e., having the same structural features, dimensions, configurations and shapes as one another). Finally, in each of the following second, third, fourth and fifth embodiment described below, it should be understood that the description of the first member for each embodiment is also applicable to the second member thereof. 
     In some embodiments of the retainer, one or both of the first and second members may include vents comprising a plurality of apertures, which may have the same or different size and shape, and which may or may not be arranged in a pattern, such as one or more rows, and may or may not be evenly spaced. For example, in a second embodiment of a retainer  212  shown in  FIGS. 13-17 , the first member  214  may include a vent which comprises a plurality of apertures  330  arranged in two rows  332 ,  334 . Each of the plurality of apertures  330  extends through the first member  214 , i.e., from the first inner surface  230  to the first outer surface  232  (see  FIGS. 13, 16 and 17 ). Each of the apertures  330  is positioned in a first channel  234  and in between adjacent first sidewalls  235 , and is in fluid communication with the first channels  234  of the first member  214 . As used herein, fluid communication means that at least some reasonably measurable flow of fluid (i.e., liquid or vapor phase) is permitted. As shown in  FIG. 13 , since each of the apertures  330  extends through the first member  214 , from the first inner surface  230  to the first outer surface  232 , they are visible on the first outer surface  232  of the first member  214  and are also in fluid communication with the exterior environment of the retainer  212 , even when the retainer  212  is assembled. Furthermore, when the retainer  212  is assembled, each aperture  330  is also in fluid communication with the second channels of a second member and a continuous interior space formed between the first and second members  214 ,  216  (not shown, but see  FIGS. 7A and 9  showing analogous second channels  74  of the analogous second member  16  and a continuous interior space  122  of the assembled retainer  12 ). Accordingly, the plurality of apertures  330  allows at least a portion of moisture to escape from inside to outside the retainer  212 , i.e., through one or more of the plurality of apertures  330 , in the event the retainer  212  is assembled with a tissue graft therein and then subjected to drying, such as lyophilizing. As mentioned above, the second member  216  (shown only partially in  FIG. 13 ) may or may not also include a vent comprising a plurality of apertures. 
     Neither the quantity of apertures  330  or the quantity of rows  332 ,  334  is particularly limited. For example, without limitation,  FIG. 18  shows a third embodiment in which the vent comprises a greater quantity of apertures  430  which are arranged on the first member  414  in four rows  532 ,  534 ,  536 ,  538 . It is noted, that when apertures  330 ,  430  are arranged in rows  332 ,  334 ,  532 ,  534 ,  536 ,  538 , the rows need not extend across all channels  234 ,  434  of the first member  214 ,  414 , respectively, and they need not be evenly spaced across the first member  214 ,  414 . For efficacy, a minimum total of four apertures (on the first member, or on the second member, or on both) is recommended. Moreover, the apertures  330 ,  530  need not be arranged in rows  332 ,  334 ,  532 ,  534 ,  536 ,  538  at all, but rather, they may be arranged in some other pattern (e.g., circular, waves, etc.), or not in any organized pattern (i.e., randomly). In some embodiments, where both the first and second members  214 ,  216  include a plurality of apertures  330 , the quantities of apertures  330  on each member  214 ,  216  need not be the same, and the patterns, if any, of the apertures  330  need not be the same. 
     Each aperture  330 ,  530  should have a minimum diameter of about 1 micron (0.001 millimeter, “mm”) and a maximum diameter of about 3.5 mm. For example, without limitation, each aperture  330 ,  530  may have a minimum diameter of about 25 microns, or about 50 microns, or about 75 microns, or about 100 microns. For example, without limitation, each aperture  330 ,  530  may have a maximum diameter of about 3 mm, or about 2.5 mm, or about 2 mm, or about 1.5 mm. In some embodiments, each aperture  330 ,  530  has a diameter from about 1 micron to about 3.5 mm, or any desired value therebetween, as determinable by persons of ordinary skill in the relevant art. Although the apertures  330 ,  530  are shown with each having a circular shape, they may have other shapes (including without limitation, square, triangle, rectangle, diamond, irregular, etc.). Accordingly, where the apertures  330 ,  530  are not circular, each aperture  330 ,  530  may have an open area from about 0.75 square micron and about 9.6 mm, or any desired value therebetween. The apertures  330 ,  530  need not be the same size and shape, as long as at least half of the apertures are each within the minimum and maximum dimensions stated above. 
     In some embodiments of the retainer, one or both of the first and second members may include vents comprising one or more elongated openings, or “slits,” which may have the same or different size and shape, and which may or may not be arranged in a pattern or be evenly spaced. For example, in a fourth embodiment of a retainer  612  shown in  FIGS. 19-23 , the first member  614  may include a vent which comprises two slits  740 ,  742  which extend across all of the first channels  634  and are evenly spaced across the width of the first member  614 . Each of the slits  740 ,  742  extends through the first member  614 , i.e., from the first inner surface  630  to the first outer surface  632  (see  FIGS. 19, 22 and 23 ). Each of the slits  740 ,  742  is in fluid communication with the first channels  634  of the first member  614 . As shown in  FIG. 19 , since each of the slits  740 ,  742  extends through the first member  614 , from the first inner surface  630  to the first outer surface  632 , they are visible on the first outer surface  632  of the first member  614  and are in fluid communication with the exterior environment of the retainer  612 , even when the retainer  612  is assembled. Furthermore, when the retainer  612  is assembled, each slit  740 ,  742  is also in fluid communication with the second channels of a second member and a continuous interior space formed between the first and second members  614 ,  616  (not shown, but see  FIGS. 7A and 9  showing analogous second channels  74  of the analogous second member  16  and a continuous interior space  122  of the assembled retainer  12 ). Accordingly, the slits  740 ,  742  allow at least a portion of moisture to escape from inside to outside the retainer  612 , i.e., through one or both of the slits  740 ,  742 , in the event the retainer  612  is assembled with a tissue graft therein and then subjected to drying, such as lyophilizing. As mentioned above, the second member  616  (shown only partially in  FIG. 19 ) may or may not also include a vent comprising one or more slits. 
     Neither the quantity or spacing of slits  740 ,  742  is particularly limited. For example, without limitation, as shown in a fifth embodiment in  FIGS. 24-25 , the vent comprises a greater quantity, i.e., four, slits  940 ,  942 ,  944 ,  946 , which may be arranged, evenly spaced, on the first member  814 . It is noted that, when the vent comprises one or more slits, the slits need not extend across all of the first channels  634 ,  834  of the first member  614 ,  814 , respectively, and they need not be evenly spaced across the first member  614 ,  814 , as shown in  FIGS. 19-25 . Instead, it is contemplated that one or more slits may be provided, each of which may, independently, extend across two or more of the first channels  634 ,  834  and may or may not be aligned with one another on the first member  614 ,  814 . For efficacy, a minimum of one slit (i.e, positioned either on the first member  614 , or on the second member  616 ) is recommended, and at least one slit on each of the first and second members  614 ,  616  is preferred. Moreover, the slits  740 ,  742 ,  940 ,  942 ,  944 ,  946  need not have linear shapes, but rather, they may have elongated shapes of varied width, or wave-like shapes, or some other nonlinear shape, or not have any regular or organized shape. Where both the first  614  and second members  616  include one or more slits  740 ,  742 ,  940 ,  942 ,  944 ,  946 , the quantities of slits on each members need not be the same, and the spacing and shape, if any, of the slits need not be the same. 
     Each slit  740 ,  742 ,  940 ,  942 ,  944 ,  946  should have a minimum width of about 1 micron (0.001 millimeter, “mm”) and a maximum width of about 7 mm. For example, without limitation, the slits  740 ,  742 ,  940 ,  942 ,  944 ,  946  may have a minimum width of about 25 microns, or about 50 microns, or about 75 microns, or about 100 microns. For example, without limitation, the slits  740 ,  742 ,  940 ,  942 ,  944 ,  946  may have a maximum width of about 6.75 mm, or about 6.5 mm, or about 6.25 mm, or about 6 mm, or about 5.5 mm, or about 5 mm, or about 4.5 mm, or about 4 mm, or about 3.5 mm or about 3 mm. In some embodiments, each slit has a width from about 1 micron to about 7 mm, or any desired value therebetween, as determinable by persons of ordinary skill in the relevant art. Although the slits  740 ,  742 ,  940 ,  942 ,  944 ,  946  are shown having an elongated rectangular shape, they may have other shapes (including without limitation, elongated triangle, elongated diamond, elongated oval, irregular, etc.). The slits  740 ,  742 ,  940 ,  942 ,  944 ,  946  need not be the same size and shape, as long as at least half of the slits present are each within the minimum and maximum dimensions stated above. 
     An assembled retainer  12 ,  212 ,  612  (see, e.g.,  FIGS. 12, 13 and 19 , respectively), may be used to hold a tissue graft therein, as described above, followed by drying of the tissue graft, such as by heating or lyophilizing. For example, a tissue graft may be secured within a retainer by assembling first and second members as described above (see, e.g.,  FIGS. 7A and 12 ), and where one or both of the first and second members have a vent as described above in connection with any of the second, third, fourth and fifth embodiments of  FIGS. 13-25 , or alternatives thereto. The assembled retainer and tissue graft therein may then be subjected to a drying technique, such as heating, lyophilizing, etc., whereupon moisture separated from the tissue graft will escape from the retainer through the vent (e.g., plurality of apertures  330 ,  530 , or one or more slits  740 ,  742 ,  940 ,  942 ,  944 ,  946 , in the first and/or second members of the retainer). This facilitates and increases the efficacy and efficiency of the drying technique employed to dry the tissue graft. The time required for drying a tissue graft contained in a retainer having one or more vents is shortened as compared to a retainer lacking a vent. 
     Where drying will be accomplished by lyophilizing, the assembled retainer and tissue graft therein may, optionally, be placed in an open container (e.g., a tray, etc.) containing an amount (i.e., volume) of lyophilizing media (not shown). In an embodiment, 20 ml of lyopreservation media is used, although other volumes are contemplated. In an embodiment, the lyophilizing media is a solution containing a lyophilizing agent, such as, without limitation, glucose, trehalose, dextran, hydroxyethyl starch (HES), catechins (e.g., epigallocatechin gallate (EGCG)), sorbitol, xylitol, and combination thereof. Other types of lyophilizing agents may also be used. The lyophilizing media flows freely into the retainer through one or more of the various passageways  102 ,  106 ,  101 ,  103 ,  105 ,  107  (described above) and into the first and second channels of the first and second members, respectively, to immerse the tissue graft therein. After the lyophilizing media contacts the tissue graft in the retainer, the retainer and tissue graft therein are subjected to lyophilizing, such as in a lyophilizing apparatus, as is well known and understood by persons of ordinary skill in the art. 
     Additionally, in some embodiments, after contact with the lyophilizing media as described above, but prior to actually lyophilizing, excess lyophilizing media may be rinsed (i.e., separated and removed) from the tissue graft by contacting the assembled retainer containing the tissue graft with (e.g., transferring it to a container containing) a biocompatible fluid (e.g., without limitation, an HBSS or PBS solution). Such pre-lyophilizing rinsing may reduce the presence of dried residue (e.g., sugar crystals from trehalose or another sugar) on the lyophilized tissue graft at the end. In such embodiments, the vent would also aid in the exit and entry of the biocompatible solution and other fluids during the rinsing and lyophilizing processes. 
     Prior to use in a medical procedure (e.g., surgery or other medical procedure performed by a healthcare provider), a dried tissue graft may be rehydrated by a healthcare provider or assistant thereto, either while contained in the retainer or after opening the retainer and removing the dried tissue graft. Rehydrating the tissue graft while in the retainer may be facilitated by the design of the retainer which includes various passageways  102 ,  106 ,  101 ,  103 ,  105 ,  107  and a vent (e.g., apertures  330 ,  530  and/or slits  740 ,  742 ,  940 ,  942 ,  944 ,  946  in one or both of the first  214 ,  414 ,  614 ,  814  and second members, as described above). It is expected that both the passageways  102 ,  106 ,  101 ,  103 ,  105 ,  107  and vent will allow rehydration fluid to flow into the retainer and contact the dried tissue graft therein. Alternatively, the dried tissue graft may be removed from the retainer prior to rehydration by contacting with a rehydration fluid. Once the dried tissue graft is rehydrated and removed from the retainer, it is ready for use. 
     As will be recognized by persons of ordinary skill in the relevant art, the rehydration fluid may be any biocompatible fluid including, without limitation, an aqueous buffer (e.g., phosphate buffered saline (“PBS”)), a buffered or non-buffered isotonic solution (e.g., an aqueous sodium chloride solution), a lactated Ringer&#39;s solution, a cell culture media (e.g., Dulbecco&#39;s Modified Eagle&#39;s Medium (DMEM) or Basal Medium Eagle (BME)), platelet rich plasma (PRP), lecithin, alginate, hyaluronic acid (HA), a derivative or salt of HA (e.g., sodium hyaluronate), and mixtures thereof. 
     It should be understood that, although the foregoing description of vents in or on containers capable of containing tissue grafts therein, to facilitate drying the tissue graft while in the container, is provided in connection with the particular retainers described hereinabove, the tissue graft container is not particularly limited and such vents may be provided on or in any type of tissue graft container. In other words, the container need not be a retainer which includes first and second elements as described above. Rather, any type of container having an interior space, or compartment, which is formed by one or more components when in their closed configuration and is capable of containing a tissue graft (or other tissue form) therein, could be provided with vents to facilitate the escape of moisture and other fluid from the container when assembled, closed, or sealed (i.e., in a closed configuration) with a tissue graft therein. Such containers include boxes, bags, packages, pouches, etc., regardless of whether the container comprises a single component which forms the interior space to contain and hold a tissue graft therein when closed or sealed, or comprises two or more components which cooperate to form the interior space or compartment to contain and hold a tissue graft therein when assembled or connected together in a closed configuration. The interior space is typically at least partially enclosed, with only limited fluid communication with the exterior environment of the container. In some cases, the interior space is fully enclosed with essentially no fluid communication with the exterior environment. 
     Typical single component containers for holding tissue grafts include, for example without limitation, a pouch or bag which is closed or sealed to form an interior space. In such embodiments, one or more vents would be provided on and extending through the entire thickness, and all layers present, of the pouch or bag, thereby providing fluid communication between the exterior environment and the interior space of the sealed pouch or bag. The one or more vents may comprise an aperture, a plurality of apertures, an elongated slit, a plurality of elongated slits, or combinations thereof. 
     Several types of containers for holding tissue graft exist that comprise two or more components which cooperate to form the interior space within which a tissue graft is held when the components are assembled or connected together in their closed configuration. Such multiple component containers include, for example without limitation, a container base or tray with a lid (e.g., connected with a hinge device or by an integral hinge), a container including two or more complementary elements, trays or parts which cooperate to form a container having an interior space (e.g., similar to the channels  34 ,  74  and continuous interior space  122  formed by the assembled retainer described above), and other multiple component package designs capable of containing a tissue graft in an interior space thereof when the components are in their closed configuration. The one or more vents would be positioned or located on at least one component and extend entirely through that component to provide fluid communication between the interior space (wherein a tissue graft would be held) and the environment exterior to the assembled or otherwise closed container. The one or more vents may comprise an aperture, a plurality of apertures, an elongated slit, a plurality of elongated slits, or combinations thereof. 
     It will be understood that the embodiments described herein are merely exemplary and that a person of ordinary skill in the art may make many variations and modifications without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as defined in the appended claims. While not meant to be limiting, some of the possible variations and modifications are described below. 
     The retainer of the packaging system  10  of the present invention may be formed of two interconnected members rather than two separate members. Such a retainer may have a “clamshell” configuration, or otherwise have a hinge element between the interconnected members to facilitate the opening and closing thereof. 
     The first and second engagement means of the retainer could also include a “butterfly” closure. More particularly, the first engagement means may include two outer tabs positioned on an end or side of the first member of the retainer, and the second engagement means may include one middle tab positioned on a corresponding end or side of the second member of the retainer, wherein the middle tab is depressed, or snapped, between the two outer tabs to secure the tissue graft within the first and second members. 
     In other alternate embodiments, the first and second members  14 ,  16  of the retainer  12  may be secured together (i.e., on either side of the tissue graft) by external engagement means. Such external engagement means include, but are not limited to, one or more clamps, one or more retaining rings, one or more pieces of adhesive tape or labels affixed to both first and second members, one or more rubber bands, and/or the inner pouch  108  that is sized and shaped to have a cavity that is only slightly larger than the assembled retainer  12 , such that the first and second members  14 ,  16  are secured to one another as a result of tightly fitting inside the cavity of the inner pouch  108 . 
     In an alternate embodiment, a plurality of smaller tissue grafts, (e.g., particles or “mini sheets”) may be packaged in the system of the present invention. 
     EXAMPLES 
     The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to make and use the described invention, and are not intended to limit the scope of what the inventors regard as their invention nor are they intended to represent that the experiments below are all or the only experiments performed. Efforts have been made to ensure accuracy with respect to numbers used (e.g., amounts, temperatures, etc.) but some experimental errors and deviations should be accounted for. Unless indicated otherwise, temperature is in degrees centigrade, force is measured in Newtons (N), and energy is measured in Joules (J). 
     Example 1 
     Assessment of the Ability to Contain the Tissue Graft 
     The ability of the retainer to contain the tissue graft may be assessed by measuring the minimum and maximum clearance between the assembled/closed retainer members within and around the perimeter and degree of parallelism, where the clearance must be greater than the smallest dimension of the tissue graft within the perimeter and the clearance around the perimeter must be less than the smallest dimension of the tissue graft to prevent the tissue graft from migrating to the outside of the retainer. For example, if the tissue graft is 2 cm×2 cm×50-200 μm, the clearance within the perimeter must be greater than 50 μm and the clearance around the perimeter must be less than 200 μm. The length of any negative space that may be present in the perimeter of the retainer may also be measured, where it is less than the greatest dimension of the tissue graft. For example, if the tissue graft is 2 cm×2 cm×50-200 μm, the negative space in the perimeter must be less than 2 cm. These dimensions and aspects may be measured using any device or instrument for measuring dimension including but not limited to, calipers, gauge blocks, a feeler gauge, a micrometer, or a comparator. 
     Example 2 
     Assessment of the Ability to Contain the Tissue Graft and Allow the Tissue Graft to Maintain its Shape 
     The ability of the retainer to contain the tissue graft may be assessed by enclosing the tissue graft within the two members of the retainer and submerging the retainer and tissue graft in liquid (e.g., saline, water, lactated ringers, or dextrose), so that the liquid is fully dispersed within the two members of the retainer and the tissue graft is fully submerged. The retainer may remain static while submerged in the liquid, or it may be agitated or shaken. A visual observation may be made to determine if the tissue graft remained within the perimeter of the retainer, moved within the perimeter of the retainer, or migrated outside the perimeter of the retainer. Visual observation may also be made to determine if the tissue graft maintained its shape while contained within the retainer. 
     Example 3 
     Assessment of Cytotoxicity and Compatibility for Direct Contact with Tissue Graft 
     The retainer may be analyzed to identify potential cytotoxic effects that may occur when the retainer is in direct or indirect contact with a patient or that may occur by migration of extractables from the retainer to the tissue graft. The analysis may be performed on a portion of the retainer or on the tissue graft after contact with the retainer utilizing methods including, but not limited to, physicochemical testing, non-volatile residue, residue on ignition, extractable metals, buffering capacity, pH, biological reactivity, identity of materials or additives by infrared spectrophotometry, ultraviolet visible spectroscopy, thermal analysis, differential scanning calorimetry, total organic carbon, acidity, alkalinity, in vitro biological reactivity by agar diffusion test, direct contact test, or elution test, in vivo biological reactivity by systemic injection test, intracutaneous test, or implantation test in which the degree of reactivity is measured on a scale of 0 to 4, where 0 indicates no reactivity and 4 indicates a severe cytotoxic reaction. 
     Example 4 
     Assessment of Ability to Withstand Cryogenic Temperature 
     The retainer&#39;s ability to withstand ultra low temperatures may be assessed by measuring the material strength when subjected to subzero temperatures by methods including, but not limited to, flexural strength, durability, impact strength, and dynamic mechanical analysis where the retainer is capable to withstand up to 1770 Newtons. 
     To further quantify the ability of the material to withstand frozen storage, multi-axial impact testing similar to ASTM D 3763 was performed at ambient and ultra low temperatures. The provided materials were cut into 4×4 inch plaque specimens. For this test method, a plunger with a steel rod is allowed to impact a test specimen, and impact data, including force, time, and deflection, is recorded using a load cell which is incorporated within the hemispherical end of the steel rod. From this data, the energy absorbed by the sample during the impact, and through failure, is determined. The results are shown in Table 1 below. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 Energy at 
                 Energy at 
                 Peak 
                 Displacement 
                   
               
               
                   
                   
                 Peak 
                 50% Peak 
                 Force 
                 at Peak Force 
                 Failure 
               
               
                 Material 
                 Test Temp 
                 Force (J) 
                 Force (J) 
                 (N) 
                 (mm) 
                 Mode 
               
               
                   
               
             
            
               
                 PETG 
                  23 C. 
                 9.64 (2.6%)  
                 14.20 (2.5%) 
                 1230 (0.7%)  
                 16.40 (1.3%)  
                 Ductile 
               
               
                 PETG 
                 −70 C. 
                 8.35 (39.8%) 
                  9.93 (54.6%) 
                 1770 (12.0%) 
                 12.50 (16.6%) 
                 Mixed 
               
               
                   
               
            
           
         
       
     
     Example 5 
     Assessment of Ability to Maintain Viability of Tissue Graft 
     The retainer&#39;s ability to maintain the viability of endogenous cells in the tissue graft may be assessed by the following methods, but not limited to, quantitation of adenosine triphosphate (ATP) and fluorescent staining. 
     In the following study, a comparison was made between a two-piece retainer design with channels and protrusions and a one-piece hinged clamshell retainer, which does not contain the channels or protrusions and creates a significantly larger clearance between the two sides. The intent was to determine the effect of the channels and the clearance between the two sides of the retainer on cell viability. Tissue samples (i.e., representing the tissue graft) were prepared and split evenly between the two test groups. Samples were processed, packaged in each respective retainer, sealed into pouches with cryoprotectant solution (i.e., cryopreservative media), cryopreserved to −100° C., and stored at −80° C. Samples were tested after the following time points: 48 hours, 2 weeks, and 1 month after cryopreservation and frozen storage. Tissue samples were then analyzed by CellTiter-Glo® Luminescent Cell Viability Assay (Promega, Madison, Wis.). In addition, samples were stained using ethidium homodimer-1 and calcein and viewed under fluorescence microscope. 
     Using the measurement of ATP present, an analysis was made to quantify if a difference in cell viability existed between the two-piece retainer and clamshell retainer. This was done by a statistical T-test which uses a comparison of mean responses to determine if a difference exists. The results in Table 2 and  FIG. 26  below show that the two-piece retainer exerts no negative effect on the viability of the cells within the tissue sample compared to the clamshell. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Analysis of Variance for Retainer Clearance 
               
               
                 Versus ATP at Final Timpoint (1 Month) 
               
            
           
           
               
               
               
               
               
               
            
               
                 Source 
                 DF 
                 ADj SS 
                 ADj MS 
                 F-Value 
                 P-Value 
               
               
                   
               
               
                 Type 
                 1 
                 150.8 
                 150.8 
                 0.33 
                 0.582 
               
               
                   
               
            
           
         
       
     
     Fluorescent staining of live and dead cells was performed on both groups to qualitatively measure the effect of the channels in the retainer. If the channels were in constant contact with the tissue graft it may have affected the viability by not allowing appropriate media to reach the tissue graft. At the conclusion of the 1 month study the result showed that there was no impact made by the channels to the viability of the cells.  FIG. 27  shows the 48 hour timepoint versus the 1 month timepoint for the retainer having two separate members and clamshell. 
     In another study, the ability of donor tissue to be cryopreserved to −100° C. while suspended in cryopreservative media contained in a retainer and pouch package and subsequently stored in a −80° C. freezer was analyzed utilizing similar process and methods as described above. Tissue samples were analyzed over a 24 month period of frozen storage and as shown in  FIG. 28 , ATP levels were maintained throughout the duration of the study. 
     Example 6 
     Quantitative Assessment of the Release Force 
     The ability of the retainer to maintain closure is necessary to prevent migration of the tissue graft out of the retainer or during preparation for clinical use. Therefore, it is important to determine acceptability of the retainer received from a supplier prior to use. Acceptability may be determined by visual observation of the retainer&#39;s ability to remain closed after exposure to sterilization, processing, changing temperature environments and handling that may occur during packaging of tissue grafts, submersion in solution, cryopreservation, shipping, and long term storage. 
     In addition, the force required to engage and release the closure mechanism may be measured by force gauge or other instrument. The method employs a test fixture with mechanism to hold one member of the retainer in a fixed location and move the second member of the retainer in perpendicular direction and in parallel orientation towards the first member until the closure is fully engaged. A pre-determined compressive force is then applied for a pre-determined length of time. Next, the second member is moved away from the first member until the closure is fully released. The force required to release the closure is measured, by force gauge or other force measuring equipment. 
     The specified application force and minimum threshold for release force was determined by measuring the force required to engage and open parts that had been deemed unacceptable, such as not maintaining a closed system or opening after exposure to temperature changes such as cryopreservation and storage, against parts that were deemed acceptable through the same examination methods. 
       FIG. 29  shows the mean difference between the acceptable and unacceptable parts that were measured for release force. 
     The data generated also provided the threshold as shown in  FIG. 30 . Using a Main Effects plot through a binary logistic regression, which shows the interaction between separation force and lot acceptability, a threshold limit of 18 N has at least 75% probability of identifying a potential failure before use. 
     The method described may be used as a Quality Control measure during the manufacture of the retainer and/or as a Quality Control measure prior to or any time after packaging the tissue graft in a closed retainer to reduce the likelihood of failures. The method may also be utilized to assess ease of opening the package when the tissue graft is prepared and used for medical treatment. 
     Example 7 
     Ability of the Channels and Inlets to Allow Flow of Cryopreservation and Rinsing Fluid 
     The channels and inlets are intended to allow communication of cryopreservation media and the tissue graft as well as communication of a rinsing fluid and the tissue graft during static or agitated soak or by pouring or injecting fluid with syringe or other device. The amount of fluid that is exchanged is influenced by the shape, dimensions, orientation, and distribution of channels and can be assessed by a dye penetration method where the retainer is submerged in a dye solution that allows visible contrast against the retainer material, such as Toluidine Blue, and a visual observation of the direction of fluid flow and amount of fluid that is passed through the retainer can be made. 
     Example 8 
     Quantification of Residual c Cryopreservation Media Remaining after Rinsing 
     Prior to use of the tissue graft for medical treatment, the tissue graft may be rinsed with one or more solutions including, but not limited to, Lactated Ringers in 5% dextrose saline solution, water, saline or irrigant. To provide containment and facilitate ease of use and handling of the tissue graft, it may be rinsed while contained in the retainer. Following a standard rinsing method, residual cryopreservation media remaining on the tissue graft may be quantified by methods including, but not limited to, gas chromatography, liquid chromatography, spectroscopy, or other chemical analysis methods. 
     In the following study, remaining levels of cryopreservation media were analyzed after rinsing by gas chromatography with a flame ionization detector. Samples from three different tissue donors were rinsed by submerging the tissue graft suspended in the retainer in Lactated Ringers in 5% dextrose saline solution for 5 minutes and comparing to non-rinsed control samples. The average level of residual cryopreservation media for samples undergoing the rinse procedure was 2.94±0.92% by weight, and the average level for samples that did not undergo the rinse procedure was 9.70±1.44% by weight. Therefore the retainer was determined to provide adequate fluid flow of the rinsing solution and cryopreservation media. 
     Example 9 
     Assessment of Optional Backing 
     The tissue graft may optionally be supported by and packaged with a backing to maintain its shape during cryopreservation, ensuring sufficient exposure to cryopreservation media, and to facilitate ease of application for medical treatment. Materials may be considered unsuitable if it were not biocompatible as measured by methods described in Example 3, visually damaged during sterilization, processing, freezing, or shipping, caused damage to the tissue during processing or during removal for clinical use, or has a negative effect on cell viability measured by methods described in Example 5. 
     Alternatively, in the following study, materials were scored on a scale of 1 to 5 for the ability to hold the tissue graft in place during processing and packaging and the ability to release the tissue graft during various anticipated clinical uses as described in Table 3. A score of 1 was regarded to completely fulfill the criteria and a score of 5 was regarded as not fulfilling the criteria. Table 3 shows resulting ranking scores for various materials. 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Test Article 
                 1 
                 2 
                 3 
                 4 
                 5 
                 5-2 
                 6 
                 7 
                 8 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 Processing Average Score 
                 1.00 
                 1.00 
                 1.67 
                 1.67 
                 1.00 
                 1.33 
                 1.58 
                 2.33 
                 2.00 
               
               
                 End Use Average Score 
                 3.25 
                 3.25 
                 2.50 
                 2.50 
                 1.38 
                 1.13 
                 3.00 
                 2.38 
                 2.75 
               
               
                 Overall Average Score 
                 2.13 
                 2.13 
                 2.00 
                 2.00 
                 1.19 
                 1.19 
                 2.22 
                 2.25 
                 2.25