Closure device

The present invention relates generally to a medical device for closing an opening or defect in an organ within a living body, e.g. a septal defect in a heart or a percutaneous puncture in a vessel wall (such as walls in arteries or other blood vessels), and in particular to an expandable and repositionable closure device, which can be remotely maneuvered from an initial positioning configuration to a final configuration in which the opening or defect is closed.

BACKGROUND OF THE INVENTION

The closing of an opening in an organ of a patient is a medical procedure that frequently has to be practised by doctors or other trained medical personnel. The opening may be a hole created by the doctor for a specific and usually temporary purpose, or the opening can be a congenital or acquired defect. An example of the former would be a puncture hole created in a patient's femoral artery to obtain access to the coronary system, while an example of the latter is a septal defect in a patient's heart. For descriptive and illustrative purposes the present invention will be described with reference to such a septal defect, although such techniques can be applied to other fields of application.

As is well-known, the human heart is divided into four chambers: the left atrium, the right atrium, the left ventricle, and the right ventricle. The atria are separated from each other by the interatrial septum, and the ventricles are separated by the interventricular septum.

Either congenitally or by acquisition, abnormal openings or holes can form between the chambers of the heart, causing shunting of blood through the opening or hole. For example, with an atrial septal defect, blood is shunted from the left atrium to the right atrium, which produces an over-load of the right side of the heart. In addition to left-to-right shunts such as occur in patent ductus arteriosus from the aorta to the pulmonary artery, the left side of the heart has to work harder because some of the blood will recirculate through the lungs instead of going to the rest of the body. The ill effects of such lesions usually cause added strain on the heart with ultimate failure if not corrected.

One way to cure a septal defect in the septum of a heart is to position and anchor a specially designed closure device at the septum such that both sides of the septal defect are spanned by the closure device to thereby close the defect. Examples of such septal defect closure devices are known from the U.S. Pat. Nos. 5,853,422; 6,024,756; 6,117,159 and 6,312,446 to Huebsch et al., which disclose a closure device comprising a cylindrical shaft of metal or polymeric material with concentric parallel cuts through the wall of the device to thereby create flattened support struts. The centers of the support struts are intended to move radially away from the longitudinal axis of the device in a hinge like fashion in response to movements of the proximal and distal ends of the device towards the centre thereof.

A similar septal defect closure device is also disclosed in the international application WO 2005/006990 A2.

SUMMARY OF THE INVENTION

In the conventional designs, discussed above, no particular measures are taken to ensure that the struts actually move radially outwards, and not move radially inwards.

Within the medical field it is of utmost importance that closure devices work properly, and a general object of the present invention is therefore to improve a closure device of the aforementioned type in such a way that a more reliable device is obtained, whose correct movement pattern is guaranteed.

According to the present invention, a septal defect closure device comprises an elongated tubular member in which a first set of longitudinal slits or cuts has been made on a first side of a shorter uncut central portion and a second set of longitudinal slits or cuts has been made on the opposite side of the central portion. On each side of the central portion, the slits extend towards the ends of the tubular member to terminate a short distance before the respective end, such that uncut proximal and distal end portions are formed. The tubular member, which is made from a flexible and preferably resorbable material, has thereby been provided with proximal and distal sets of struts or ribs. The distal ends of the distal struts are flexibly connected to the distal end portion of the tubular member, while the proximal ends of the distal struts are flexibly connected to the central portion. Similarly, the proximal ends of the proximal struts are flexibly connected to the proximal end portion of the tubular member, while the distal ends of the proximal struts are flexibly connected to the central portion. The struts are further each provided with a weakened section, which can act as a hinge, such that each strut in effect is divided into two articulated arms.

When the septal defect closure device during use is compressed such that the distal and proximal end portions are forced towards each other, the weakened sections of the struts move radially out from the longitudinal central axis of the closure device, and the respective arms of the struts assume an essentially perpendicular angle to the central axis of the closure device. The septal defect closure device comprises further a central cylindrical locking member, which preferably is separate from the tubular member and which over its length comprises several portions with different diameters. In use, the cylindrical locking member is inserted into the tubular member such that the distal end portion of the tubular member abuts a distal end rim of the locking member, and the proximal end portion of the tubular member is then pushed over a proximal end rim of the locking member. In the compressed state, the central, proximal and distal portions of the tubular member fit snugly over respective portions of the central locking member, and the closure device is held in the compressed state by the enlarged distal and proximal rim portions of the locking member, which prevents the closure device from resuming its original shape.

For this particular kind of closure device it is crucial that the struts and thereby the hinge sections move outwards (and not inwards), such that an expanded closure device is provided. In accordance with the present invention, this is accomplished by arranging the two articulated arms of each strut slightly inclined with respect to each other. Also in the introduction phase, when the closure device has an essentially longitudinal shape, the hinge section of each strut will thereby be slightly further out from the central axis of the closure device than the proximal and distal ends of the struts. This angled relation between the two articulated arms of each strut ensures that the struts move outwards when the closure device is compressed and expanded by forcing the proximal and distal end portions of the closure device towards each other.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a human heart having an atrial as well as a ventricular septal defect.

FIG. 2 is a schematic illustration of a human heart having a septal defect, which is to be closed by means of a medical procedure that, in a first step, involves the positioning of a septal defect closure device according to the present invention.

FIG. 3 illustrates an intermediate step in the medical procedure, in which a distal portion of the closure device of FIG. 2 is expanded in order to locate the septal defect from the distal side of the septal defect.

FIG. 4 illustrates another intermediate step in the medical procedure, in which a proximal portion of the closure device of FIG. 2 is expanded in order to locate the septal defect from the proximal side of the septal defect.

FIG. 5 illustrates the completion of the medical procedure, wherein the closure device of FIG. 2 has been secured in the septum surrounding the septal defect.

FIG. 6 shows a septal defect closure device according to the invention in a positioning configuration before the longitudinal compression of the closure device.

FIG. 7 shows the closure device of FIG. 6 in an intermediate semi-compressed state.

FIG. 8 shows a locking member which constitutes a separate part of a septal defect closure device.

FIG. 9 shows the closure device of FIG. 6 locked in a final compressed state.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A schematic cross-sectional view of a human heart 1 is shown in FIG. 1. The heart 1, with its left ventricle 2, left atrium 3, right ventricle 4 and right atrium 5, suffers from an atrial septal defect 6 as well as a ventricular septal defect 7. Below a medical procedure will be discussed in which an atrial septal defect is closed. It should, however, be clear that a septal defect closure device according to the present invention equally well could be employed to close a ventricular septal defect like ventricular septal defect 7 of FIG. 1. It should further be noticed that the septal defects 6, 7 can be accessed from different vessels, e.g. from the superior or inferior vena cava, or from the aorta. This implies, in turn, that throughout the present description terms like “distal” and “proximal” should always be seen from the end of a delivering catheter, through which a septal defect closure device is delivered (and not from any particular chamber or vessel of a heart).

In conjunction with FIGS. 2 to 5, a medical procedure will be briefly described, in which a septal defect closure device according to one embodiment of the present invention is employed to close a septal defect in the septum of a heart; and thereafter different positions and parts of the closure device itself will be described in detail in conjunction with FIGS. 6 to 9.

FIG. 2 illustrates a septal defect closure device 10 according to the present invention, which by means of a delivering catheter 11 has been introduced into an atrial septal defect 12 in the atrial septum 13 of a heart 14. The closure device 10 is of the same general construction that has been generally described above, and comprises an elongated tubular member in which distal and proximal sets of struts have been provided. The distal struts extend from a central portion of the closure device 10 to a distal end portion thereof, and the proximal struts extend from a proximal end portion of the closure device 10 to the central portion. As already discussed, each strut is provided with a thinner and thereby weaker section that can act as a hinge, and each strut is thereby effectively divided into two hinge-connected arms. In FIG. 2, the closure device 10 is shown in an initial positioning configuration, in which the arms of each strut are substantially—but not perfectly—aligned with each other. In this uncompressed positioning configuration, the closure device 10 has therefore a generally elongated tubular shape, which facilitates the introduction of the closure device 10 into the artery and heart of a patient. As indicated above and also previously discussed, a special feature of the closure device 10 is that the arms of each strut exhibit a small angle in relation to each other, something that will be thoroughly explained below. Here, it suffices to say that this angle exists also in the introduction phase; and it should therefore be understood that the above statement saying that the closure device 10 in this state has a generally tubular shape should not be taken literally but seen from a practical point of view.

To ascertain correct positioning of the closure device 10 with respect to the septal defect 12, the distal set of struts can be moved radially outwards from the central axis of the closure device 10, such that a partly expanded configuration is obtained. The radial movements of the distal struts are effectuated by partially compressing the closure device 10 through the maneuvering of a mechanical actuator (not shown in the figures). In this semi-expanded locating configuration, the closure device 10 is retracted until the distal struts abut the distal side of the atrial septum 13 surrounding the septal defect 12. The septal defect 12 can thereby be located by a doctor, who in this phase of the medical procedure will feel a marked increase in resistance against further retraction. This intermediate step of the medical procedure is depicted in FIG. 3.

A special advantage of the present invention is significant in the intermediate step illustrated in FIG. 3. Without the measures according to the invention, the arms of each strut would initially be perfectly aligned with each other; and when the distal portion of the closure device is longitudinally compressed to achieve the configuration shown in FIG. 3, there is a risk that some of the struts instead bend inwards. By arranging the two arms of each distal strut set such that they are not perfectly aligned with each other, but exhibit a small inclination, it is ensured that each arm moves outwards, and the closure device will therefore assume the proper configuration as illustrated in FIG. 3.

As an alternative or complement, the proximal set of struts can be moved radially outwards from the central axis of the closure device 10, such that another partly expanded configuration is obtained. As before, the radial movements of the proximal struts are accomplished by partially compressing the closure device 10 through the maneuvering of the mechanical actuator mentioned above. In this second semi-expanded locating configuration, the closure device 10 is advanced out of the catheter 11 until the proximal struts abut the proximal side of the atrial septum 13 surrounding the septal defect 12. The septal defect 12 can thereby be located by a doctor who in this phase of the medical procedure will feel a marked increase in resistance against further advancement. This intermediate step of the medical procedure is depicted in FIG. 4. It may be mentioned that the closure device 10 can be reversibly moved between the elongated, essentially tubular positioning configuration of FIG. 2 and either of the intermediate configurations shown in FIG. 3 and FIG. 4, respectively.

Also when the proximal portion of the closure device 10 is compressed to achieve the configuration shown in FIG. 4, the present invention provides the same advantage. By arranging the two arms of each proximal strut set such that they are not perfectly aligned with each other, but exhibit a small inclination, it is ensured that each arm moves outwards, and the closure device will therefore assume the proper configuration as illustrated in FIG. 4.

When the atrial septum 13 and thereby the septal defect 12 have been correctly located, either by the step shown in FIG. 3 or by the step of FIG. 4, or by both steps, the closure device 10 is fully expanded such that the proximal struts as well as the distal struts are forced radially outwards by maneuvering of the mechanical actuator mentioned above. In this closing configuration, the closure device 10 spans both the distal side and the proximal side of the septal defect 12, and is then held in this position. As can be seen in FIG. 5, the closure device 10 sandwiches the atrial septum 13 to thereby close the septal defect 12 therein. It can be mentioned that the term “close” or similar terms used herein in conjunction with the description of the closing of a septal defect should not be taken too literally. Such terms are meant to encompass all stages from actually sealing or closing off a septal defect to merely restricting the flow of blood therethrough, the important thing being that the closure device permits and facilitates healing of the septal (or other type of) defect over time. To improve the sealing capability of a closure device of the present type, it is conceivable that the distal and/or proximal struts at least partly are covered by a thin membrane or formed integrally with a thin membrane, which preferably is made from a resorbable material. This feature may in particular be advantageous when the closure device is used to seal a puncture hole in a vessel wall.

An embodiment of a septal defect closure device 20 according to the present invention is illustrated in FIG. 6. FIG. 6 shows the closure device 20 in a first or positioning configuration in which the closure device 20 has the general shape of an elongated, essentially tubular member 21, through which a number of longitudinal, parallel cuts or slits have been made to thereby form a first or distal set of struts 22 and a second or proximal set of struts 23. The first strut set 22 extends between a first end portion 24 of the tubular member 21 and a central portion 25 thereof, while the second strut set 23 extends between the central portion 25 and a second end portion 26 of the tubular member 21. The first and second end portions 24, 26 as well as the central portion 25 are uncut and are shorter than the slit portions of the tubular member 21. Somewhere along the length of the first set of struts 22, the tubular member 21 has been provided with a circumferential weakened section 27 in that material has been removed from this ring-shaped section of the tubular member 21. The weakened thinner section 27 of each strut 22 will thereby act as a hinge or articulation 27, which effectively divides each strut 22 into two articulated arms: a first or distal arm 22a and a second or proximal arm 22b. Similarly, the struts in second set of struts 23 are each provided with hinge section 28, which in effect divides each strut 23 into two articulated arms: a first or distal arm 23a and a second or proximal arm 23b.

To facilitate the expanding movement of the closure device 20, each arm 22a, 22b, 23a, 23b can at the end that is opposite to the central weakened sections 27, 28 be provided with a recess or weakened section, which acts as a hinge, similarly to the weakened sections 27, 28. In FIG. 6, the distal arms 22a of the first strut set 22 are provided with hinge sections 22c, while the proximal arms 22b have hinge sections 22d; and the distal arms 23a of the second strut set 23 are provided with hinge sections 23c, while the proximal arms 23b have hinge sections 23d. In effect, each arm 22a, 22b, 23a, 23b is provided with two articulation points. It should also be mentioned that if the struts are made from a material being flexible enough, it is possible that no extra hinge sections, like hinge sections 22c, 22d, 23c, 23d, are provided as the material in itself can act as an articulation or a hinge. Also in the latter case, each arm is, however, effectively provided with two articulation points.

A special feature of the present invention should be clearly visible in FIG. 6, where it can be seen that the first and second strut sets 22, 23 are arranged such that the weakened hinge sections 27, 28 are further out from the longitudinal central axis of the closure device 20 than are the first end portion 24, the central portion 25, and the second end portion 26. The arms 22a, 22b of the first strut set 22 have thereby assumed an outwardly angled relation to each other; and the arms 23a, 23b of the second strut set 23 have a similar outwardly angled relation to each other. It is, however, within the scope of the present invention that either the first arms 22a, 22b or the second arms 23a, 23b exhibit such a positive deviation from a perfect alignment. The angled relation of the arms of a strut set is characterized by a tilt angle which is positive when the arms of a strut set point slightly outwards from the central axis of a tubular member (one example of a positive tilt angle is shown in FIG. 6). The provision of a tilt angle should be guaranteed in the positioning configuration of a closure device, i.e. when a strut set is outside a delivering catheter and before any longitudinal compression of this strut set by a mechanical actuator. This tilt angle, which can be regarded as a deviation from a perfect alignment (straight line), can range from 1° to 10°, and more preferably from 3° to 720 . The tilt angle is defined as the angle under which a first line extending through the two articulation points of a first arm of a strut set intersects with a second line extending through the two articulation points of a second arm of this strut set. It is particularly important to keep this definition in mind when—in order to create hinge points for a strut arm—material is removed from opposite sides at the two ends of the arm. In this latter case, the struts could actually appear to be aligned along a straight line, but as long as the articulation points of the arms of the struts are not aligned, a tilt angle is provided in accordance with the definition above (with the tilt angle being positive when the articulation point(s) where the two arms meet are further away from the longitudinal central axis than the articulation points at each end of each strut set). The provision of a tilt angle should be guaranteed in the positioning configuration of a closure device, i.e. when a strut set is outside a delivering catheter and before the onset of any longitudinal compression of this strut set.

It should further be emphasized that the term “tubular” is merely intended to indicate the general shape of an elongated, cylindrical member, which comprises a number of struts, the ends of which are connected to shorter ring-shaped members, and which in a first positioning configuration assumes an essentially tubular shape. In other words, a tubular member, like tubular member 21, does not actually have to be cut or slit in order to create distal and proximal struts. On the contrary, a tubular member, having struts with weakened hinge-sections as well as ring-shaped central, distal and proximal end portions, can advantageously be directly produced in this form, e.g. by injection molding. It should in particular be noted that the angled relation between the arms of each strut preferably is created already during the manufacturing of a closure device. If the closure device is produced by injection moulding, the mould is outlined such that the weakened sections are further out from the central axis of the closure device than are the central portion and the end portions.

In FIG. 7, the closure device 20 of FIG. 6 is depicted in a semi-expanded state in which the distal and proximal end portions 24, 26 of the closure device 20 have been moved towards the central portion 25. The hinge sections 27, 28 of the first and second struts 22, 23 have thereby been forced to move outwards from the central axis of the closure device 20, and the articulated arms 22a, 22b and 23a, 23b have assumed an angled relation to the central axis of the closure device 20. Here it should be recognized that the configuration shown in FIG. 7 partly is for illustrative purposes; in practice either of the two end portions 24, 26 could be moved towards the central portion 25, to assume the locating configurations shown in FIG. 3 and FIG. 4, respectively. The semi-expanded configuration of FIG. 7 could, however, also be used to determine the proper position for the closure device 20, and can also be regarded as a configuration prior to a fully closed configuration described below in conjunction with FIG. 9. With reference to FIG. 6 and FIG. 7, the present invention can be summarized as guaranteeing that the transition from the initial configuration shown in FIG. 6 to the semi-expanded state of FIG. 7 actually takes place without any problem.

As can be seen in FIG. 7, the closure device 20 comprises further a locking member 30, which is separately illustrated in FIG. 8. The locking member 30, which in this example is a separate part of closure device 20, comprises a hollow body 31, which along is length is provided with several portions with different outer diameters. More specifically, the body 31 of the locking member 30 comprises a distal end rim 32, a distal portion 33, an intermediate portion 34, a proximal portion 35, and a proximal end rim 36. The distance between the distal end rim 32 and the proximal end rim 36 is considerably smaller than the length of the tubular member 21. As the observant reader already may have appreciated, the respective outer diameters of the locking member 30 are related to the respective diameters of the tubular member 21 of the closure device 20. Thus, the diameter of the distal end rim 32 is larger than the inner diameter of the distal end portion 24 of the tubular member 20, while the inner diameter of the distal end portion 24 is larger than the other diameters of the body 31 of the locking member 30, such that the distal end portion 24 of the tubular member 21 can slide over the locking member 30 until the distal end portion 24 abuts the distal end rim 32. The outer diameter of the distal portion 33 of the locking member 30 is adapted to the inner diameter of distal end portion 24 of the tubular member 21, while the diameter of the intermediate portion 34 is adapted to the diameter of the central portion 25 of the tubular member 21. The inner diameter of the proximal end portion 26 of the tubular member 21 is adapted to the outer diameter of the proximal portion 35 of the locking member 30, and is slightly less than the diameter of the proximal end rim 36. During use, the proximal end portion 26 of the tubular member 21, which is made from a somewhat elastic material, must therefore be forced over the proximal end rim 36 and can then slide on the proximal portion 35. As can be seen in FIG. 8, the locking member 30 comprises preferably a recess 37, which provides the proximal end rim 36 with a certain resilience which facilitates the sliding of the proximal end portion 26 of the closure device 20 over the proximal rim 36 of the locking member 30. Here it should also be mentioned that the present invention is equally applicable to a closure device having a unitary structure, i.e. when a locking member or some other type of locking arrangement is integral with an elongated tubular member.

In FIG. 9, the closure device 20 is shown in a closed and locked state, in which the distal and proximal end portions 24, 26 of the tubular member 21 have been fully moved towards each other until the central portion 25 is positioned over the intermediate portion 34 of the locking member 30 and the proximal end portion 26 has been moved over the proximal end rim 36 of the locking member 30. The closure device 20 is held in this compressed state due to the enlarged distal and proximal end rims 32, 36 of the locking member 30, which have diameters larger than the distal end portion 24 and the proximal end portion 26, respectively.

In FIGS. 6, 7 and 9, the central portion 25 of the tubular member 21 has been depicted with a longitudinal length approximately equal to the lengths of the distal and proximal end portions 24, 26. The length of a central portion of a tubular member can, however, be varied, e.g., be longer, and can in particular be adjusted to the thickness of a particular septum at which the corresponding closure device is to be placed.

Another way to facilitate the adaptation of a septal defect closure device to septa having different thicknesses is to arrange the distal set of struts and the proximal set of struts as two separate members. Such an arrangement would effectively correspond to cutting a tubular member like the tubular member 21 of FIG. 6 into two separate tubular members. These two tubular members would then independently of each other be movable along the length of a common locking member similar to locking member 30 of FIG. 8. Also in this case, at least one of the two tubular members would comprise two arms that exhibit an angle with respect to each other, as has been defined above.

The septal defect closure device has been shown with proximal and distal struts having equal lengths. It is, however, possible to provide a closure device having proximal struts with one length and distal struts with a different length. It may, for example, be desirable to arrange a closure device in such a way that the left part of the closure device, i.e. the part that is implanted into the left atrium of a heart, is smaller than the right part of the closure device, to thereby reduce the amount of artificial material introduced into the left atrium, which in turn may reduce the formation of thrombogenic material therein. In this context, it should be recognized that it is not mandatory that a heart is accessed via the venous system, as is shown in FIGS. 2 to 5, but the heart could be accessed via the arterial side. This implies that if a doctor wishes to place a smaller part of a closure device at the left side of a heart than at the right side of the heart, then this smaller part (i.e. the shorter struts) will constitute the distal set of struts if the heart is accessed via the venous system, whereas the smaller part will constitute the proximal set of struts if the heart is accessed through the arterial system.

It has already been mentioned that the length of the distal struts can differ from the length of the proximal struts; and it is also possible to have different lengths of the articulated arms within a strut set, such that, for example, the distal arms are longer than the proximal arms, or vice versa. The arms that actually contact a septum or a vessel wall can, for example, be shorter than the arms that do not contact the septum or the vessel wall, to thereby ensure a reliable closing of a septal defect in the septum or a puncture hole in the vessel wall.

As already has been stated, a closure device can comprise a central locking member that is separate from a tubular member. A two-piece closure device is generally easier and thereby cheaper to manufacture. If, for example, the closure device is produced by injection moulding, the moulds—i.e. one mould for the locking member and one mould for the tubular member—can be given comparatively less complicated shapes than if the closure device was to be moulded in a single mould.

It is in particular anticipated that a locking member is made from a first material and that a tubular member is made from a second material, something which in practice may require that the locking member is separate from the tubular member. With different materials some specific advantages can be achieved. If, for example, the closure device is a resorbable closure device, then the resorption time of the material in the locking member can be different from the resorption time of the material in the tubular member, such that the locking force between the two members during the degradation of the closure device is reduced and ultimately lost in a controllable and predictable way. In this respect it may be advantageous if the material of the tubular member has a shorter resorption time than the material of the locking member. Further, whether or not the materials are resorbable materials, different requirements are put on the different pieces. For example, the material in the hinge portions of a tubular member must be flexible and have a high tenacity, whereas the locking member must have a rather high stiffness. Also in a resorbable closure device it can be necessary to have one material in a locking member and another material in a tubular member, because of the different dimensions involved. It can, for example, be necessary to have a material with a relatively long resorption time in the thin hinge portions of the tubular member in order to match the resorption time of the material in a thick-walled locking member.

The closure device according to the present invention is preferably made from a resorbable material. Examples of resorbable materials for the tubular member and the locking member may include, but are not limited to, those materials made from aliphatic polyesters, polyether esters, and polycarbonates. More specifically, synthetic resorbable polymers such as homopolymers and copolymers made from any of the monomers lactide, glycolide, epsilon-caprolactone, trimethylene carbonate, and paradioxanone are advantageous because of their long clinical use.

The tubular member could preferably be made from a semi-crystalline material with a lower tensile modulus than the locking member. As previously stated, the device could, e.g. because of the hinge portions, have a more flexible material in the tubular member. Such material is preferably made from a block copolymer characterized by having a soft middle part characterized by having a glass transition temperature below room temperature and a semi-crystalline part at each end of the soft middle part. The semi-crystalline part could be polymerized from any of the monomers glycolide, lactide, or paradioxanone. Since polyparadioxanone is a relatively soft and pliable material compared to polyglycolide and polylactide, the tubular member can be made from pure polyparadioxanone itself.

The locking member can be made from any of the above materials, but to secure the locking mechanism it is advantageous if the material is stiffer than the material used in the tubular member. The material should also preferably resorb at a somewhat slower pace than the tubular member. The locking member could also be made from amorphous or semi-crystalline material, and preferably from homopolymers or copolymers where the main monomer component is lactide, caprolactone, or paradioxanone.

A particular advantage of the groups of synthetic resorbable polymers mentioned above is that various mechanical properties can be accomplished by simply changing the monomer composition in the homopolymer or copolymer. Further, in contrast to natural biopolymers, these materials can be molded and machined into complex structures, and by varying the monomer composition large time spans can be achieved for their resorption times.

It may be appreciated that it can be advantageous to provide a radiopaque closure device which is visible in an X-ray machine. When the closure device is made from a synthetic resorbable polymer, a radiopaque closure device can conveniently be produced by mixing the polymer with a suitable radiopaque agent. A suitable radiopaque agent is barium sulfate, which can be blended into the polymer or copolymer in an amount between 5% and 50%, and more preferably in an amount of 15% to 30%, to obtain the opacity needed in order to locate the closure device during an X-ray observation. Radiopaque materials can be used in a tubular member of the closure device, but is preferably used in the locking member, which marks the centre of the device. The radiopaque agent, e.g. barium sulfate, can—instead of being mixed with the polymer—be introduced into preformed holes in the closure device, which are then sealed by a synthetic resorbable material. As an alternative, preformed holes can be plugged with a resorbable material containing a large amount of a radiopaque agent, e.g. barium sulfate.

Other aspects, features, variations, and ways of using the present invention are described in the U.S. patent applications and filed under attorney docket numbers 030481/0249 (entitled “Closure Device”); 030481/0254 (entitled “Closure Device”); and 030481/0258 (entitled “Closure Device and Insertion Assembly”) concurrently herewith. The entire contents of these related applications are incorporated herein by reference. Features in these different applications may be combined with each other Although the present invention has been described with reference to specific embodiments, also shown in the appended drawings, it will be apparent for those skilled in the art that many variations and modifications can be done within the scope of the invention as described in the specification and defined with reference to the claims below. The arms and struts need not have the shape shown in the drawings. It is possible to have different lengths of the articulated arms within a strut set, such that, for example, the distal arms are longer than the proximal arms, or vice versa. The weakened strut sections discussed above can be replaced with other designs that provide the desired hinge-like action. The hinge action could, for example, be accomplished by real hinges arranged along the struts. Also in this last case, the hinges should, however, exhibit a small angle also in the introduction phase to ensure proper expansion of the closure device.

Closure device

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