Device And Method For Improving The Function Of A Heart Valve

Abstract

A device for improving the function of a heart valve comprises: a support member formed from a shape memory material, and a restraining member providing a restraining action on a course of the support member. The support member may abut one side of the valve conforming to the shape of the valve annulus upon said shape memory material assuming an activated shape while the restraining member restrains the course of the support member. The restraining action is removable for allowing the support member to assume a desired, altered course. The restraining member may be biodegradable to be degraded within a patient or may be detachable from the support member to be withdrawn. The support member according to another embodiment presents a shape change in that an increased cross-section is associated with a shortened length of the support member. The support member according to yet another embodiment has a first and a second activated shape.

Claims

1. A device for improving the function of a heart valve comprised of valve tissue including an annulus and a plurality of leaflets for allowing and preventing blood flow, the device comprising: a support member at least partially formed from a shape memory material operable to assume an activated shape and an inactivated shape, and a restraining member, which is arranged to provide a restraining action on a course of the support member, said support member being configured to abut one side of the valve and being arranged to conform to the shape of at least a part of the valve annulus upon said shape memory material assuming said activated shape while the restraining member exerts the restraining action on the course of the support member, and the restraining member being formed of a biodegradable material to be degraded when the device is implanted in a patient, wherein degradation of the restraining member removes the restraining action and allows the support member to assume a desired, altered course.

2. The device according to claim 1, wherein the support member is arranged to be brought into the activated shape by receiving induced heating at selective portions of the support member.

3. The device according to claim 1, wherein the support member is arranged to assume a reduced radius of curvature upon the restraining action being removed.

4. The device according to claim 1, wherein the restraining member is formed so as to control the rate of degradation in a patient.

5. The device according to claim 1, wherein the support member is a first support member and the device further comprises a second support member at least partially formed from said shape memory material and connected to said first support member, said second support member being configured to abut an opposite side of the valve, whereby a portion of the valve tissue is trapped between said first and second support members upon said shape memory material assuming said activated shape.

6. The device according to claim 5, wherein the first and second support members are loop-shaped.

7. The device according to claim 6, wherein the first and second support members are D-shaped.

8. The device according to claim 5, wherein an outer boundary of the second support member is greater than an outer boundary of the first support member.

9. The device according to claim 6, wherein the first loop-shaped support member is continuous with the second loop-shaped support member to form a coil-shape.

10. A device for improving the function of a heart valve comprised of valve tissue including an annulus and a plurality of leaflets for allowing and preventing blood flow, the device comprising: a support member being configured to abut one side of the valve and being arranged to conform to the shape of at least a part of the valve annulus, said support member having an inherent adaptation to a shape change such that an increased cross-section of at least part of the support member is associated with a shortened length of the support member, whereby the support member is susceptible to an expansion of a cross-section of the support member when the support member has conformed to the shape of at least part of the valve annulus such that the support member assumes a desired, altered shape.

11. The device according to claim 10, wherein the support member is arranged to assume a reduced radius of curvature in the altered shape.

12. The device according to claim 10, wherein the support member is a first support member and the device further comprises a second support member connected to said first support member, said second support member being configured to abut an opposite side of the valve and being arranged to conform to the shape of at least a part of the valve annulus, whereby a portion of the valve tissue is trapped between said first and second support members, said second support member having an inherent adaptation to a shape change such that an increased cross-section of at least part of the support member is associated with a shortened length of the support member.

13. The device according to claim 12, wherein the first and second support members are loop-shaped.

14. The device according to claim 13, wherein an outer boundary of the second support member is greater than an outer boundary of the first support member.

15. The device according to claim 13, wherein the first loop-shaped support member is continuous with the second loop-shaped support member to form a coil-shape.

16. The device according to claim 12, wherein the first and second support members are tubular.

17. The device according to claim 12, wherein the first and second support members have a U-shaped cross-section.

18. The device according to claim 16, wherein the first and second support members are adapted to receive a balloon therein for expanding the cross-section of at least part of the support member.

19. The device according to claim 12, wherein the first and second support members are belt-shaped.

20. The device according to claim 12, wherein the first and second support members are formed from a mesh-like structure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The invention will now be described in further detail by way of example under reference to the accompanying drawings.

[0057] FIG. 1 schematically illustrates a patient with a heart shown in cross-section and a device of the present invention schematically illustrated as supporting the mitral valve.

[0058] FIG. 1A is a cross-sectional view of the left ventricle showing the mitral valve in perspective.

[0059] FIG. 2 is a perspective view of a device according to a first embodiment of the invention, wherein first and second support members of the device are shown in an inactivated shape suitable for insertion into a patient.

[0060] FIG. 3 is a perspective view of the device in FIG. 2, wherein the first and second support members have assumed an activated shape but are restrained by a restraining member.

[0061] FIG. 4 is a perspective view of the device in FIG. 2, wherein the first and second support members have assumed a desired, activated shape after release of the restrain from the restraining member.

[0062] FIG. 5 is a perspective view of an alternative device according to the first embodiment of the invention.

[0063] FIG. 6 is a perspective view of the device of FIG. 5 having assumed a desired, activated shape.

[0064] FIG. 7 is a perspective view of yet another alternative device according to the first embodiment of the invention.

[0065] FIG. 8 is a perspective view of the device of FIG. 8 having assumed a desired, activated shape.

[0066] FIG. 9 is a cross-sectional view of the device in FIG. 4.

[0067] FIG. 10 is a perspective view of a device according to a second embodiment of the invention, wherein first and second support members of the device are shown in a first shape having a small cross-section.

[0068] FIG. 11 is a perspective view of the device in FIG. 10, wherein the cross-section has been increased and the first and second support members have assumed an altered shape.

[0069] FIGS. 12a-c are cross-sectional views of the device according to the second embodiment.

[0070] FIG. 13 is a perspective view of a device according to a third embodiment of the invention, wherein the device is in an inactivated shape.

[0071] FIG. 14 is a perspective view of the device in FIG. 13, wherein the device is in a first activated shape.

[0072] FIG. 15 is a perspective view of the device in FIG. 13, wherein the device is in a second activated shape.

[0073] FIG. 16 is a perspective view of a device according to a fourth embodiment of the invention, wherein the device comprises only one support member.

[0074] FIG. 17 is a perspective view of the device in FIG. 16, wherein the device has assumed an altered shape.

[0075] FIGS. 18a-b are partially sectioned perspective views of the mitral valve and the device according to the first embodiment of the invention during implantation of the device.

[0076] FIG. 19 is a partially sectioned perspective view showing the device of the invention after having been turned into position.

[0077] FIGS. 20a-b are cross-sectional views illustrating fixation of the device to the heart valve.

[0078] FIG. 21 is a cross-sectional view of the implanted device in FIG. 18.

[0079] FIG. 22 is a perspective view showing the implanted device after the restraining member has been degraded.

DETAILED DESCRIPTION OF THE INVENTION

[0080] FIG. 1 illustrates a patient 10 having a heart 12 shown in cross-section including a left ventricle 14 and a right ventricle 16. The concepts of the present invention are suitable to be applied, for example, to a mitral valve 18 which supplies blood into left ventricle 14. Mitral valve 18, as better shown in FIG. 1A, includes an annulus 20 and a pair of leaflets 22, 24 which selectively allow and prevent blood flow into left ventricle 14. It will be appreciated that the term valve tissue is used extensively throughout this disclosure in reference to the drawings. The inventive principles are equally applicable when referring to any valve tissue such as annulus tissue, leaflet tissue or other attached vessel tissue. Leaflets 22, 24 are supported for coaptation by chordae tendinae or chords 26, 28 extending upwardly from respective papillary muscles 30, 32. Blood enters left ventricle 14 through mitral valve 18 and is expelled during subsequent contraction of heart 12 through aortic valve 34. It will be appreciated that the present invention is applicable to tricuspidal heart valves as well.

[0081] A device 40 according to a first embodiment of the present invention is shown in FIGS. 2-4. The device comprises a first and a second support member 42, 44. The first support member 42 is continuous with the second support member 44. The first and second support members 42, 44 are formed from a shape memory material, such as alloys based on e.g. Nitinol, copper-zinc-aluminium, or copper-aluminium-nickel, or a shape memory polymer, which may be polynorborene-, polyisoprene-, styrene butadiene-, and polyurethane-based materials and vinyl acetate- and polyester-based compounds.

[0082] The first and second support members 42, 44 have an inactivated shape and an activated shape. In the inactivated shape, the support members 42, 44 are flexible and may be easily deformed. In the activated shape, the support members 42, 44 have a strong strive towards assuming a desired, preprogrammed shape. The support members 42, 44 may enter an activated shape by being exposed to a temperature above a transition temperature. Thus, the device 40 may be inserted in a low invasive manner, the support member 42, 44 being in the inactivated shape. The device 40 may then assume the desired shape when placed in the proper position in the patient by the support members 42, 44 being brought to their activated shape. The support members 42, 44 may be arranged to be brought into the activated shape by receiving induced heating at selective portions of the support members 42, 44. By selectively heating the support members 42, 44, selective portions of the support members 42, 44 may be brought to the activated shape and the heating controls what shape the support members 42, 44 will assume. The selective heating may be accomplished by a catheter with a heating element, which may be brought in contact with selective parts of the support members 42, 44.

[0083] The device 40 further comprises a restraining member 45. The restraining member 45 is arranged to prevent the support members 42, 44 from fully assuming the desired activated shape. The restraining member 45 is coil-shaped and is formed from a biodegradable material, such as a material based on polyglycolic acid, copolymers of glycolic acid and lactic acid, or various lactide polymers. The biodegradable material will be degraded or resorbed when implanted in a patient. The time period for degradation will depend on the particular material and the thickness of the restraining member 45. Thus, this may be controlled by the design of the restraining member 45.

[0084] As shown in FIGS. 2-3, the first and second support members 42, 44 may be wound around the restraining member 45. This allows the restraining member 45 to restrain the support members 42, 44 from assuming the preprogrammed shape. As shown in FIG. 2, the device 40 may be arranged in a generally elongate shape in the inactivated shape of the support members 42, 44. This elongate shape is suitable for placing the device 40 inside a catheter for insertion into a patient. The coil-shaped restraining member 45 is thus stretched out for allowing it to be placed inside a catheter.

[0085] In FIG. 3, the device 40 is shown with the support members 42, 44 being in an activated shape. The restraining member 45 has assumed its coil-shape and prevents the support members 42, 44 from fully obtaining the activated shape. The restraining member 45 forces the support members 42, 44 to follow a coil-shape having a larger radius of curvature than the preprogrammed shape.

[0086] When implanted in a patient, the restraining member 45 will be degraded. In FIG. 4, the device 40 is shown after the restraining member 45 has been degraded and the first and second support members have fully assumed the activated, preprogrammed shape. The first and second support members 42, 44 now form a general coiled configuration in the form of a spiral or key ring-type configuration with two loops.

[0087] Alternatively, the restraining member 45 may be withdrawn during implantation of the device 40 in a patient. Thus, the restraining member 45 may be withdrawn when the first and second support members 42, 44 have been properly placed allowing the support members 42, 44 to fully assume the activated shape. This implies that a surgeon may see the result of the full shape change of the support members 42, 44 during implantation of the device 40 and may directly get an indication of the success of the surgery.

[0088] As a further alternative, the restraining member may be implemented as one or more bars extending between different positions on the first and second support members 42, 44. These bars may thus keep the positions on the support members 42, 44 at a fixed distance to each other and, in this way, prevent the support members 42, 44 to fully assume the activated shape. The bars may be formed from a biodegradable material as described above. Alternatively, the bars may be detached from the support members 42, 44 and removed during implantation, or the bars may be cut during implantation in order to remove the restraining action of the bars.

[0089] According to an alternative shown in FIGS. 5-6, a device 340 comprises a first and a second support member 342, 344. The first support member 342 is continuous with the second support member 344. The first and second support members 342, 344 are formed from a shape memory material. The first and second support members 342, 344 are coated with a biodegradable sheath 345. During manufacture of the device 340, the first and second support members 342, 344 may be immersed in a biodegradable material being in a liquid state. The first and second support members 342, 344 may be immersed into the biodegradable material in an inactivated, flexible state, while being held in a coil-shape that may fit for placing the device within a heart such that the first and second support members may conform to the shape of at least a part of the valve annulus at opposite sides of the valve. The first and second support members 342, 344 may thus be embedded in a biodegradable sheath 345. When the biodegradable sheath 345 is degraded within a patient, the first and second support members 342, 344 are allowed to assume the activated shape, wherein a reduced radius of the coil-shape is obtained as illustrated in FIG. 6.

[0090] According to yet another alternative illustrated in FIGS. 7-8, a device 440 comprises a first and a second support member 442, 444. The first support member 442 is continuous with the second support member 444. The first and second support members 442, 444 are formed from a shape memory material. The first and second support members 442, 444 are tubular. The device 440 further comprises an elongate restraining member 445 that may be arranged extending within the tubular first and second support members 442, 444. The restraining member 445 may be pushed to extend through the entire first and second support members 442, 444 in order to force the first and second support members 442, 444 to a coil-shape with a large radius. By withdrawing the restraining member 445 from inside the support members 442, 444, the support members 442, 444 are allowed to assume an activated shape wherein the coil-shape has a decreased radius as illustrated in FIG. 8.

[0091] The second support member 44 has an outer boundary which is greater than the outer boundary of the first support member 42. The support members 42, 44 have corresponding shapes with the second support member 44 being in larger scale than the first support member 42. This is advantageous in creating a pinch of the valve tissue between the first and second support members 42, 44, as will be described below with reference to FIG. 14. An end of the second support member 44 and the corresponding end of the restraining member 45, which will lead the coil during insertion of the device 40 at the valve, has a greater pitch than the rest of the coil. This implies that the leading end of the coil during rotation into position in the valve will project from immediate contact with the valve tissue and, therefore, the risk that the coil is caught by the chords is diminished.

[0092] The device 40 is shown in cross-section in FIG. 9. The first and second support members 42, 44 have a round cross-sectional shape. Opposed surfaces 46 of the first and second support members 42, 44 provide a pinch to trap valve tissue therebetween. The round cross-section is also advantageous in creating a pinch of the valve tissue which will not harm the leaflets in their movement during normal heart action, as will be further described below with reference to FIG. 21.

[0093] A device 140 according to a second embodiment of the present invention is shown in FIGS. 10-12. The device 140 comprises a first and a second support member 142, 144. The first support member 142 is continuous with the second support member 144. The first and second support members 142, 144 are formed from a mesh-type or netlike structure, such as stents.

[0094] The first and second support members 142, 144 have an inherent adaptation to a shape change such that an increased cross-section of at least part of the support member 142, 144 is associated with a shortened length of the support member 142, 144. This foreshortening is accomplished in that the mesh-type structure, when expanded in cross-section, pulls the ends of the support members 142, 144 towards each other.

[0095] The support members 142, 144 present a shape change that may be controlled. The shape change will not occur until a force is applied for increasing the cross-section of at least part of the first and second support members 142, 144. This implies that the second embodiment as well as the first embodiment provides a possibility to place a device in relation to a heart valve and, thereafter, control the point of time when the device placed at the heart valve is going to perform a change of shape.

[0096] In FIG. 10, the device 140 is shown with the support members 142, 144 arranged in a first shape suitable for being attached to the heart valve. In this first shape the support members 142, 144 conform to the shape of the heart valve annulus, such that the support members 142, 144 may be attached to the annulus along the entire course of the support members 142, 144. The first and second support members 142, 144 form a general coiled configuration in the form of a spiral or key ring-type configuration with two loops, such that the support members 142, 144 may abut opposite sides of a heart valve.

[0097] In FIG. 11, the device 140 is shown after the support members 142, 144 have been exposed to a force increasing the cross-section of the support members 142, 144. The increased cross-section has forced the support members 142, 144 to shorten. The first and second support members 142, 144 now form a coiled configuration having a decreased radius of curvature to accommodate to the shortened length of the support members 142, 144.

[0098] In FIGS. 12a-c, different cross-sections of the first and second support members 142, 144 are illustrated. In FIG. 12a, the support members 142, 144 are tubular having a circular cross-section. In FIG. 12b, the support members 142, 144 have a U-shaped cross-section. Both these cross-sections are suitable for receiving an inflatable balloon inside the cross-sectional structure. Inflation of the balloon will thus force the cross-section to increase radially. In FIG. 12c, the support members 142, 144 are belt-shaped having a linear cross-section. This cross-section may be increased by pulling the edges of the belt apart.

[0099] A device 540 according to a third embodiment is shown in FIGS. 13-15. The device 540 comprises a first and a second support member 542, 544. The first support member 542 is continuous with the second support member 544. The first and second support members 542, 544 are formed from a shape memory material. The shape memory material is treated to form a first and a second activated shape. The first and second support members 542, 544 may thus assume two different shapes depending on the temperature of the device 540. In an inactivated shape as illustrated in FIG. 13, the device 540 is flexible and may be arranged in an elongate form in order to facilitate introduction of the device to a heart of a patient via a catheter. The device 540 may be cooled during introduction in the catheter in order to maintain its inactivated shape. The device 540 may then be heated to a first temperature by utilizing the body temperature. Then, the device 540 is brought to the first activated shape as illustrated in FIG. 14 forming a coil-shape with a large radius suitable for placing the first and second support members 542, 544 in contact with opposite sides of a heart valve and fixing the position of the support members 542, 544 to the valve annulus. The device 540 may further be heated to a second temperature by further utilizing the body temperature. Then, the device is brought to the second activated shape as illustrated in FIG. 15. The device 540 in the second activated shape forms a coil-shape with a smaller radius suitable for diminishing a radius of the valve annulus.

[0100] A device 240 according to a fourth embodiment of the present invention is shown in FIGS. 16-17. The device 240 comprises only one support member 242. The support member 242 is arranged to be placed only on one side of a heart valve.

[0101] The support member 242 may be formed from a shape memory material having an inactivated shape and an activated shape. In the inactivated shape, the support member 242 is flexible and may be easily deformed. In the activated shape, the support member 242 has a strong strive towards assuming a desired, preprogrammed shape. The device 240 may be inserted in a low invasive manner, the support member 242 being in the inactivated shape. The device 240 may then assume the desired shape when placed in the proper position in the patient by the support member 242 being brought to their activated shape. The device 240 may further comprise a restraining member (not shown), which is arranged to prevent the support member 242 from fully assuming the desired activated shape. The restraining member may thus control the point of time when the support member 242 is fully brought to its desired activated shape. The support member 242 may be wound around the restraining member or the restraining member may extend between two positions on the support member fixating the distance between these positions.

[0102] The support member 242 may alternatively be formed from a mesh-type or netlike structure having an inherent adaptation to a shape change such that an increased cross-section of at least part of the support member 242 is associated with a shortened length of the support member 242. The support member 242 presents a shape change that may be controlled. The shape change will not occur until a force is applied for increasing the cross-section of at least part of the support member 242.

[0103] According to a further alternative, the support member 240 may be formed from a shape memory material treated to form a first and a second activated shape.

[0104] In FIG. 16, the device 240 is shown with the support member 242 being in a first shape conforming to the shape of the annulus of the heart valve to be treated.

[0105] In FIG. 17, the device 240 is shown after the support member 242 has been allowed to perform a change of shape to assume the desired shape. Either a restraining action of a restraining member has been removed or a cross-section of the support member 242 has been increased in order to activate the shape change. The support member 242 has now changed shape to decrease a radius of curvature for remodelling the heart valve and decreasing the size of the heart valve annulus.

[0106] Referring now to FIGS. 18-22, a method for repairing a heart valve by means of the device according to the first embodiment will be described. The concept of this method may be applied to the device according to the second, third or fourth embodiments as well, as would be understood by a person skilled in the art. As been described above, the shape change of the device may be activated in different ways, depending on the embodiment of the device. However, the point of time when the shape change is activated may be controlled irrespective of which embodiment is used. Thus, it may be ascertained that the device is firmly attached to the heart valve before the shape change occurs, such that the heart valve may be properly remodelled as will be described below.

[0107] First, access to the heart valve is achieved by means of conventional catheter techniques, including making puncture in a vessel and guiding the catheter through the vascular system into the heart. In FIG. 18a, the device 40 is shown when being inserted to the mitral valve 18. The device 40 is being carried in a catheter 50, which extends from the outside of the patient into the heart. The device 40 may be pushed out of the catheter 50 using a gripping tool (not shown) extending through the catheter 50. When pushed out of the catheter 50, the restraining member 45 assumes its coil-shape. An end of the restraining member and the second support member 44 is brought to the opening of the mitral valve 18 at a commissure between the leaflets 22, 24, as shown in FIG. 18b. The end is led through the opening and the device 40 is turned 360 degrees. Thus, the second support member 44 will be rotated into place on one side of the valve 18, whereas the first support member 42 is placed on the opposite side of the valve 18.

[0108] The first and second support members 42, 44 are now brought to their activated shape by e.g. heating them above a transition temperature. The heating may be provided by the body temperature of the patient or by means of heating energy being transmitted through a conductor (not shown) in the catheter. This implies that the first and second support members 42, 44 strive towards assuming the preprogrammed shape. The first and second support members 42, 44 on opposite sides of the valve will now be drawn towards each other for securely trapping valve tissue therebetween. The restraining member 45 will prevent the first and second support members 42, 44 from fully assuming the activated shape and, thus, from reducing the radius of curvature of the coil-shape. In this way, the device 40 is arranged in engagement with the valve 18, as shown in FIG. 19.

[0109] The support members 42, 44 are now placed on opposite sides of the valve 18 pinching valve tissue therebetween to maintain a shape of the valve 18. The support members 42, 44 may have roughened, opposed surfaces 46 to better keep the leaflets 22, 24 from slipping through the pinch. This implies that the position of the support members 42, 44 relative the heart valve is initially fixed.

[0110] The device 40 may now be secured to the valve 18 for strengthening the fixation of the relative position between the support members 42, 44 and the valve tissue. The support members 42, 44 may comprise respective bores 54 through the opposed support members for receiving separate fasteners 56. The fasteners 56 may be threaded or unthreaded pins and may be pushed into position extending through bores in both support members and valve tissue therebetween. The fastener may have an end 58 with larger diameter than the bores 54 such that the fastener 56 may not fall through the bore 54. In this way, the device 40 is firmly attached to the valve 18 for keeping the valve annulus 20 in its reshaped form, as illustrated in FIG. 20a. Many alternative embodiments of the fasteners may be contemplated. As shown in FIG. 20a, the fasteners 56 may have an end 60 with an expandable diameter for securing the fastener 56 after it has been pushed through the bores 54. Alternatively, the fastener 56 may have a curved portion 60 for gripping around one of the support members, such that the fastener 56 may extend through a bore 54 in one support member and around the other support member, as illustrated in FIG. 20b. As further alternatives, the fasteners may be clips, sutures, or projections that are extendable from at least one of the support members for engaging the valve tissue.

[0111] As illustrated in FIG. 21, the second support member 44 is slightly displaced radially with respect to the first support member 42. This implies that the first and second support members 42, 44 are not arranged directly on top of each other. The pinch between the first and second support members is therefore not sharply defined in a radial direction of the valve. This implies that a pinching force between the support members is not focussed to a specific radial position of the valve. As a result, the pinching force does not affect the movement of the leaflets during normal heart action and there is a diminished risk of rupture in the leaflets at the pinch. The support members are interrelated in such manner that the outer boundary of the first support member 42 has a diameter corresponding to a line through the center of the second support member 44. Thus, the support members 42, 44 overlap somewhat such that tissue is not allowed to move through the pinch and the shape of the valve is maintained. Further, the cross-section of the support members 42, 44 is round, which also gives a soft contact between the support members and the valve tissue to further diminish the risk of rupture in the leaflets.

[0112] After the device 40 has been placed at the heart valve forming a pinch of the valve tissue, the catheter 50 will be retracted and the device 40 is left in the patient. The restraining member 45 will be degraded in the patient during a time period of a few weeks. During this time, the support members 42, 44 will grow into the valve tissue for further securing the support members 42, 44 to the valve. When the restraining member 45 has been degraded, the support members 42, 44 are able to fully assume the activated shape. Thus, the support members 42, 44 will reduce the radius of curvature of the coil-shape and bring the pinched valve tissue in the shape change so as to remodel the valve, as illustrated in FIG. 22. The leaflets 22, 24 are thus brought closer together for ensuring that they may close the valve properly.

[0113] It should be emphasized that the preferred embodiments described herein are in no way limiting and that many alternative embodiments are possible within the scope of protection defined by the appended claims.

[0114] For example, the access to the heart valve may be achieved endoscopically or with open heart surgery. In such case, the device 40 may have a coil-shape already during insertion into the heart.

[0115] Many different shapes may be contemplated for the loop-shaped support members. For example, the support members may have elliptical, circular or D-shaped forms. One or both support members need not make an angular turn of 360 such as to have a C or U-shape instead.

[0116] Further, different shape changes may be contemplated. The course of the support member may be changed such that a radius of curvature is increased locally. Further, the course of the support member may be changed to introduce a depression or recess in the course of the support member.

[0117] Although the invention has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention. Accordingly, it is to be understood that the drawings and descriptions herein are proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof.