[ 0028 ] fig1 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 . in the illustrated embodiment , the package 10 comprises ajar 14 , a lid 16 , and an overcap 18 . in fig1 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 fig3 . as shown more fully in fig1 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 . 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 . 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 . 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 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 fig1 - 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 . 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 . 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 . 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 . 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 . 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 fig1 but other configurations may be selected . in the embodiments depicted in fig1 - 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 . 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 . moreover , the snap locks 106 may have different lengths , as illustrated in fig4 . 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 . the embodiment of fig1 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 fig5 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 . fig6 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 . 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 .
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 .