Abstract:
A packaging for an implantable medical device such as a heart valve wherein the implantable medical device is immersed in a liquid medium. The packaging comprises ajar and a lid assembly having a seal and a ridge therebetween, the ridge being adapted to contact the seal. At least one circumferential leg is interposed between the lid assembly and the jar. The leg maintains a predetermined spacing between the lid and the jar and may be loaded in compression. The lid assembly may comprise a lid and an overcap. The overcap may turn independently of the lid and may apply compressive pressure to the lid over the ridge and seal. The lid and overcap may be coupled together by, for example, mating snap hooks. At least one of the lid or overcap may have a plurality of snap hooks. At least one of the plurality of snap hooks may be of different length than other of the snap hooks, whereby an asymmetric force may be applied to the lid when the overcap is loosened from the jar.

Description:
TECHNICAL FIELD  
         [0001]    The present invention pertains to packaging for implantable prosthetic devices and in particular to leakproof packaging for prosthetic devices packaged in liquid media.  
         BACKGROUND ART  
         [0002]    Prosthetic heart valves are representative of numerous implantable medical devices that must be stored for long periods of time in a sterile package or in sealed, anti-bacterial packaging. Often such packages contain a liquid, which may have antibacterial properties to inhibit transmission of disease with the implantable device. To effectively package a heart valve in a liquid storage medium, it is important to have a container that can be manipulated within a sterile environment such as a glove box. The assembled container should provide a seal that will inhibit the loss of the liquid storage medium for a substantial period of time, for example, for as long as five years. Despite the need for a reliable seal, however, it should not be difficult for operating room staff to open the container in the sterile and constrained circumstances of open-heart surgery, where it is anticipated that the present invention will be used.  
           [0003]    Today, there are three major types of heart valves: mechanical valves, bioprosthetic or tissue valves, and polymer valves. The term “mechanical valve” as used herein, refers to a heart valve made exclusively of rigid synthetic materials and which comprises essentially no biological components. The term “bioprosthetic valve,” on the other hand, refers to a heart valve comprising at least some biological components such as tissue or tissue components (e.g., collagen). The biological components are obtained from a donor animal (typically bovine or porcine), and the valve may comprise either biological materials alone or biological materials with man-made supports or stents. Polymer valves, on the other hand, are heart valves made of at least some elastomeric polymer components, including specifically leaflet occluders made of elastomeric polymers. The present invention is suitable for use in connection with all three major types of heart valves.  
           [0004]    Mechanical heart valves are generally characterized by a rigid annular valve body supporting one or more occluders, with a sewing ring or sewing cuff circumscribing the annular valve body. Pyrolytic carbon is a material often used for the valve body or the occluders, although other materials such as metal, polymers or ceramics have also been proposed. The sewing ring is often comprised of silicone rubber with a polymeric fabric cover (e.g., Dacron™ fabric). A metal stiffening ring may be provided between the valve body and the sewing ring and a metal lock wire may be used to secure the stiffening ring and/or sewing ring to the valve body.  
           [0005]    A bi-leaflet mechanical valve typically comprises an annular valve body in which two opposed leaflet occluders are pivotally mounted. Monoleaflet mechanical heart valves typically comprise a single leaflet occluder coupled to the annular valve body. Monoleaflet valves typically open by pivoting movement, although some valves open by a combination of pivoting and translational movement. For both bi-leaflet and monoleaflet mechanical valves, the occluders are typically substantially rigid, although some designs incorporate flexible leaflets. In bi-leaflet valves, the leaflets move between a closed position in which the two leaflets are mated to prevent blood flow in the reverse direction, and an open position in which the occluders are pivoted away from each other to permit blood flow in the forward direction. In monoleaflet valves, the leaflet pivots and/or translates from the closed to the open position to allow blood flow. In each case, however, the energy of blood flow causes the occluders to move between their open and closed positions.  
           [0006]    Mechanical valves have also been made with flexible leaflets fabricated from manmade materials such as polyurethane, silicone rubber or other biocompatible polymer, for example, a valve described by Purdy, et al., U.S. Pat. No. 5,562,729, incorporated herein by reference. A sewing ring is provided for mounting flexible leaflet mechanical heart valves in a patient&#39;s heart.  
           [0007]    Bioprosthetic heart valves, in contrast to mechanical valves, comprise an annulus formed by an annular stent to which three flexible leaflets, comprised of a biological material such as bovine or porcine pericardium, are coupled. When blood flows in the forward direction, the energy of the blood flow deflects the leaflets away from the center of the annulus and allows blood to flow in the forward direction. When the pressure across the valve reverses and blood begins to flow in the reverse direction, the three leaflets engage each other in a coaptive region, occluding the valve body annulus and preventing the flow of blood through the valve in the reverse direction. The valve leaflets are made from tissue, such as specially treated porcine or bovine pericardial tissue.  
           [0008]    Mechanical heart valves have usually been packaged in containers that support the mechanical valve in such a way as to protect or isolate it from mechanical shocks. Representative packaging patents include Cromie, U.S. Pat. No. 4,101,031; Lubock et al., U.S. Pat. No. 4,801,015; Dohm et al., U.S. Pat. No. 5,720,391; and Caudillo et al., U.S. Pat. No. 5,823,342, all of which are hereby incorporated herein by reference in their entirety. Mechanical valves are typically shipped and stored in a sterilized condition in airtight containers. Because mechanical valves do not comprise biological materials, air is used as the medium in the containers. Inclusion of a liquid storage medium, such as an antibacterial solution, has been deemed unnecessary at best, and possibly damaging to the structural materials during storage, and has been avoided on the basis of added cost as well as the risk of possible harm to the valve. However, Pathak and Chinn have suggested, in a co-pending application filed contemporaneously with the present Application, that liquids may also be advantageously used in mechanical heart valve packaging.  
           [0009]    Bioprosthetic valves, on the other hand, are almost always shipped or stored in liquid media because of the need to maintain the biological components of the valve in a hydrated condition. In addition, the medium may have anti-bacterial properties or additives to ensure sterility and protect the biological components from bacterial degradation.  
           [0010]    To effectively package a heart valve—whether mechanical or bioprosthetic—in a liquid medium, it is important to have a container that can be manipulated within a sterile environment such as a glove box. The assembled container should provide a seal that will inhibit the loss of the liquid medium for a substantial period of time, for example, for as long as five years. In addition to the need for a reliable seal, however, the container should be easy for operating room staff to open in the sterile and constrained circumstances of open-heart surgery, where it is anticipated that the present invention will be used.  
         BRIEF SUMMARY OF THE INVENTION  
         [0011]    The present invention comprises packaging for an implantable prosthesis such as a heart valve, wherein the prosthesis is immersed in a liquid medium in the container, which may optionally have antibacterial properties. The packaging comprises ajar and a lid assembly having a seal and a ridge therebetween, the ridge being adapted to contact the seal. At least one circumferential leg is interposed between the lid assembly and the jar. The leg maintains a predetermined spacing between the lid and the jar and may be loaded in compression. The lid assembly may comprise a lid and an overcap. The overcap may turn independently of the lid and may apply compressive pressure to the lid over the ridge and seal. The lid and overcap may be coupled together by, for example, mating snap hooks. At least one of the lid or overcap may have a plurality of snap hooks. At least one of the plurality of snap hooks may be of a length different than the other snap hook(s), whereby an asymmetric force may be applied to the lid when the overcap is loosened from the jar.  
           [0012]    It is an object of the invention to provide a package for an implantable prosthetic device comprising ajar and lid assembly, the lid assembly having a lid connected to an overcap.  
           [0013]    Another object of the invention is to provide a package that is easily assembled in a sterile environment.  
           [0014]    Yet another object of the invention is to provide a package that maintains a seal for long periods of time but wherein resistance or friction associated with opening the package is reduced.  
           [0015]    A further object of the invention is to provide a package comprising ajar and lid assembly with a seal interposed between the jar and lid assembly.  
           [0016]    Another object of the invention is to provide a structure whereby a pre-load between the lid assembly and the jar that is not supported by the seal to maintain loads on the seal within acceptable parameters.  
           [0017]    A further feature of the invention is a pre-load structure comprising radially spaced annular legs adjacent an annular seal, the legs contacting an overcap and ajar and adapted to receive a compressive pre-load between the overcap and the jar.  
           [0018]    It is also an object of the invention to provide a lid assembly comprising a lid and overcap that are rotatably connected.  
           [0019]    Another feature of the invention is a lid and overcap that are connected by mating snap hooks.  
           [0020]    Yet another feature of the invention is an arm structure on an overcap for applying compressive force through a lid to a seal.  
           [0021]    These and other features and advantages of the invention will be apparent from the following description and accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    [0022]FIG. 1 is an isometric view of a container with a mechanical heart valve in antimicrobial fluid.  
         [0023]    [0023]FIG. 2 is an exploded isometric view of the container of FIG. 1.  
         [0024]    [0024]FIG. 3 is a cross sectional view of a region of the container of FIG. 1, taken along line  3 - 3 .  
         [0025]    [0025]FIG. 4 is a partial cross-sectional view of an overcap for the container of FIG. 1.  
         [0026]    [0026]FIG. 5 is a cross-sectional view of an alternative embodiment for the region of FIG. 3 for the container of FIG. 1.  
         [0027]    [0027]FIG. 6 is a cross-sectional view of a second alternative embodiment for the region of FIG. 3 for the container of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]    [0028]FIG. 1 is a perspective view of a package  10  for a prosthetic device such as heart valve  12 , shown in phantom lines. Heart valve  12  is a mechanical heart valve and is representative of the set of implantable medical devices such as bioprosthetic and polymer heart valves, suitable for use in the present invention. More particularly, package  10  may also be used with other implantable prosthetic devices such as mechanical heart valves with flexible polymeric or silicone rubber leaflets, such as the heart valve of Purdy et al., U.S. Pat. No. 5,562,729, or vascular grafts, such as the grafts of Lauterjung U.S. Pat. No. 5,824,036 or Lauterjung WO97/48350 (both incorporated herein by reference) or angioplasty rings, such as the rings of Campbell, U.S. Pat. No. 6,102,945 (incorporated herein by reference), or other implantable devices.  
         [0029]    In the illustrated embodiment, the package  10  comprises ajar  14 , a lid  16 , and an overcap  18 . In FIG. 1, a plan through section of these elements is shown in phantom lines. A portion of the plan through section, taken along line  3 - 3 , is also illustrated in FIG. 3.  
         [0030]    As shown more fully in FIGS. 1 and 2, the jar  14  comprises two parts, a container  20  and a seal  22 . The container has a circumferential wall  24  and a bottom  26  which define an interior  28  that contains the heart valve  12  or other implantable prosthetic device in liquid  30 . An upper circumferential edge  32  of the wall  24  abuts the lid  16 . A lip  34 , generally perpendicular to the wall  24 , extends radially outward from the edge  32  and forms an upper surface  36 . A circumferential groove  38  in the upper surface  36  receives the seal  22 , as will be described more particularly below. A rim  40  at an outer edge  42  of the lip  34  guides the lid  16  into position above the seal  22 . A cylindrical flange  43  extends downwardly from the outer edge  42  and supports a set of male threads  44 . A plurality of ribs  46  may be provided at periodic intervals between the wall  24  and the cylindrical flange  42 . The ribs  46  extend from the wall  24  to the cylindrical flange  43  and provide additional structural support for the cylindrical flange  43  and the lip  34  without significantly increasing the weight of the jar  14 .  
         [0031]    In a preferred embodiment, the container  20  is cast from a rigid material such as polypropylene, for example Himont 6323 polypropylene homopolymer in a particularly preferred embodiment. The elastometic seal  22  is then placed in the groove  38 . Alternatively, the seal  22  can be coupled to the container  20  by casting or another suitable method, and the jar  14  can be manipulated as a single piece, making it easier to assemble the package  10  in a sterile environment such as a glove box. The seal  22  may be comprised of an elastomeric polymer such as Kraton G2705™, available from Advanced Elastomer Systems, Inc., Akron, Ohio. The seal  22  should have a sufficient radial width to accommodate some variation in the placement of the lid  16 , as will be explained below. Alternatively, a separate, generally toroidal seal may be placed on the lip  34 .  
         [0032]    The lid  16  provides a leakproof interior  28  for the jar  14  by engaging the seal  22 . The lid  16  comprises a generally circular disc  50  that may be slightly convex. At an outer edge  52  of the disc  50 , a seal contact structure  53  extends around the entire periphery of the disc  50 . The seal contact structure  53  comprises a ring  56  having an inner edge  58 , an outer edge  60 , a top surface  62  and a bottom surface  64 . At a junction  66  between the top surface  62  and the outer edge  60  there is a circumferential snap hook  68 . In the preferred embodiment, the snap hook  68  comprises a cylindrical segment  69  that joins the ring  56  at a lower end of the cylindrical segment to a radially outwardly facing circumferential hook  70 . The snap hook  68  extends completely along the outer edge  60  of the lid  16 . The snap hook  68  could also be interrupted at selected intervals. Interruptions or breaks in the snap hook  68  would make it easier for the snap hook to be deflected inwardly to engage the overcap  12 , as will be described below. Because of the preferred structure of the overcap  12 , interruptions of the snap hook  68  are not considered necessary.  
         [0033]    In a preferred embodiment, two circumferential, cylindrical legs  72 ,  74  extend downwardly from the bottom surface  64  of the ring  56 . Preferably, an inner leg  72  is near the inner edge  58  of the ring  56  and an outer leg  74  is near the outer edge  60  of the ring  56 . In the preferred embodiment, the legs  72 ,  74  are continuous, but they may be interrupted by gaps or breaks as a matter of design discretion. The two legs  72 ,  74  are spaced sufficiently far away from each other to allow them to bracket the seal  22  when the lid  16  is placed on the jar  14 . The outer leg  74  guides the lid into position over the seal  22  by sliding down an inner surface  76  of the rim  40  on the jar  14 . The two legs  72 ,  74  limit the amount of force applied to seal  22 . In an alternative embodiment, the legs  72 ,  74  are not present and the force applied to seal  22  is controlled by the degree to which the lid  16  is tightened onto jar  14   
         [0034]    Between the two legs  72 ,  74  and extending downwardly from the bottom surface  64  of the ring  56 , there is a ridge  78 . The ridge  78  is continuous and preferably cylindrical. The ridge  78  is configured to contact the seal  22  when the lid  16  is on the jar  14  along the entire length of the seal, thereby closing the package  10  and providing a barrier sufficient to prevent the loss of liquid from within the package for an extended period of time. A tip  80  of the ridge  78  has a cross sectional radius selected such that the tip will provide sufficient localized contact pressure with the seal when the tip is forced into the seal to produce the desired sealing characteristics. In the embodiment of FIGS.  1 - 3 , legs  72  and  74 , as well as ridge  78 , are depicted as being integrally formed with the lid  16 . Other means of coupling the legs and the ridge to lid  16  are possible without departing from the scope of the invention.  
         [0035]    The two legs  72 ,  74  are sufficiently long to prevent the ridge  78  from being forced too far into the seal  22  and distorting or damaging the seal. Consequently, the lid  16  and jar  14  cooperate to produce a consistent seal with predictable characteristics without elaborate assembly devices. Moreover, when compressed by the overcap  18 , as described below, the two legs  72 ,  74  are preloaded in compression, which compensates for fluctuations in differential pressure across the seal  22  over a range of ambient conditions. Ambient air pressure does not remain constant. After the package  10  is assembled, it may be anticipated that ambient pressure will fall below the pressure in the package  10  from time to time. The preloading of the legs  72 ,  74  keeps the pressure difference across the lid from moving the tip  80  of the ridge  78  out of the seal  22 .  
         [0036]    The overcap  18  comprises a circumferential cylindrical wall  82  of any suitable shape. In the preferred embodiment, for example, the wall  82  has a right cylindrical lower section  84  surmounted by a frustro-conical upper section  86 . A plurality of vertical ridges  88  may be provided on an outer surface  90  of the wall  82  to improve grip friction when the overcap is turned. Other features to improve grip may be selected by those skilled in the art. A set of female threads  92  on an inner surface  94  of the wall  82  engages the male threads  44  on the jar  14 .  
         [0037]    A circumferential compression arm  96  extends radially inwardly from an upper edge  98  of the wall  82 . The compression arm  96  extends both inwardly from the wall  82  and then down towards the lid  16  so that a tip  100  can exert pressure against the top surface  62  of the seal contact structure  53  substantially directly over the ridge  78  and seal  22 .  
         [0038]    In the preferred embodiment, the arm  96  comprises a substantially planar flange  102  coupling the wall  82  to a downward facing frustro-conical ring  104 . The frustro-conical ring  104  ends at the tip  100  that contacts the lid  16 . It is preferred that the arm  96  be circularly continuous to apply uniform pressure completely around the lid  16 . Nevertheless, the arm could be interrupted without departing from the teachings of the invention.  
         [0039]    The overcap  18  further has one or more snap hooks  106  that extend axially downwardly from the arm  96 . The snap hooks  106  could also be attached to the wall  82 . The snap hooks  106  on the overcap  18  are configured to engage the snap hook  68  on the lid  16 . As noted above, the lid snap hook  68  is preferably circularly continuous. The overcap  18 , on the other hand, preferably has a plurality of snap hooks  106  spaced circularly around the overcap. This makes it easier for the overcap snap hooks  106  to bend outwardly as the lid  16  is snapped into the overcap. In addition, a slot  108  may be cut in the arm  96  of the overcap  18  radially inwardly from overcap snap hook  106  to increase the flexibility of the adjacent overcap snap hook  106 . In the preferred embodiment, four radially equally spaced slots and snap hooks have been provided on the overcap, as best shown in FIG. 1, but other configurations may be selected. In the embodiments depicted in FIGS.  1 - 3 , the snap hooks  68  and  106  are integrally formed with the lid  16  and the overcap  18 , respectively. Other ways of joining the snap hooks to the lid and overcap are possible without departing from the scope of the invention.  
         [0040]    In the packaging  10 , the lid  16  is snapped into the overcap  18  before sterilization. This provides a cap assembly  109  that is essentially a single piece and is consequently easier to manipulate than two separate pieces would be. Moreover, the anti-microbial packaging  10  should provide a consistent, reliable seal, but should also be relatively easy to open. The unitary overcap-and-lid configuration described herein reduces the initial torque needed to start opening the packaging  10  because one must only overcome the contact friction between the tip  100  of the arm  96  of the overcap and the top surface  62  of the seal contact structure  52  of the lid, rather than the contact friction between the seal  22  and the tip  80  of the ridge  78 . The seal  22  is elastomeric and the ridge  78  and seal are in continuous contact, whereas both the top surface  62  and the arm tip  100  may be relatively hard and have a low coefficient of friction and a relatively small contact area. This makes the task of opening the packaging easier, even after a long self-life.  
         [0041]    Moreover, the snap locks  106  may have different lengths, as illustrated in FIG. 4. When the overcap is unscrewed, the shortest snap lock  106   a  would begin to raise the lid first. If the lid is being held on the jar by an ambient atmospheric overpressure, the short snap lock  106   a  would begin to raise only a part of the lid, thus allowing the force developed by unscrewing the lid to be applied at a small part of the edge of the lid until the contact between the ridge  78  and the seal  22  has been broken and the pressure on both sides of the lid equalize. Thereafter, longer snap hooks  106   b  would raise the remaining portion of the lid.  
         [0042]    The embodiment of FIGS. 1 through 4 represent the preferred embodiment of the invention, but variations will suggest themselves to those of skill in the art. For example, as suggested by FIG. 5, the seal  22  could be incorporated into the lid  16  rather than the jar  14 , and the ridge  78  could be incorporated into the jar  14 . FIG. 6 suggests another variation, wherein the legs  72 ,  74  are incorporated into the jar  14  rather than the lid  16 . Moreover, the outside leg  74  may be combined with the rim  40  and a ledge  110  may function as the outside leg  74  of the ring  56 . Other variations will suggest themselves to those of skill in the art in view of the teachings presented herein.  
         [0043]    The foregoing descriptions concern preferred embodiments of the invention and are given by way of example only. The invention is not limited to any of the specific features described herein, but includes all variations thereof within the scope of the appended claims.