Carotid artery stent

Abstract

The invention provides a carotid artery stent which comprises a plurality of supporting rings arranged in parallel in the axial direction, each supporting ring extends in the circumferential direction and comprises a plurality of supporting units, the multiple supporting units are connected end to end to form a ring-shaped structure, and a connecting assembly is arranged between every two adjacent supporting rings. The supporting units in the supporting rings are connected with the supporting units in the adjacent supporting rings in the axial direction through the connecting assemblies, and the supporting units can be contained in the connecting assemblies. According to the embodiment of the invention, the problems that the stent is difficult to compress and load, and the stent is difficult to release or instantly released and rushed out due to overlarge pushing resistance in the release process are solved, the radial force and flexibility of the stent are considered, and meanwhile, the easy loading and releasing capability is achieved.

Description

Technical Field

[0001] The embodiments of the present disclosure relate to the technical field of stents, and in particular, to a carotid artery stent. Background Art

[0002] The carotid artery is one of the main blood vessels for blood to flow from the heart to the brain and other parts of the body. Carotid artery stenosis can lead to insufficient blood supply to the brain, causing brain hypoxia. Carotid artery stenosis is mostly caused by carotid atherosclerosis, which has a high incidence rate. Carotid atherosclerosis here refers to the gradual formation of hardened plaques in the carotid intima, which ruptures and falls off or forms mural thrombi, causing vascular stenosis and abnormal carotid blood supply. At present, the main treatments for carotid stenosis include medical medication, carotid endarterectomy (CEA) and carotid angioplasty and stenting (CAS). Among them, carotid artery stenting (CAS) is an interventional treatment method that uses devices such as stents or balloon catheters to eliminate or reduce carotid artery stenosis and thrombosis, and improve blood perfusion of organs in the area supplied by the carotid blood vessels; carotid endarterectomy (CEA) is a method of removing thickened carotid intima atherosclerotic plaques to prevent plaque shedding and stroke.

[0003] With the continuous advancement of neurointerventional technology and the improvement of surgical instruments, CAS has gradually become an effective alternative treatment for CEA, and its therapeutic effect is not inferior to CEA. Carotid artery stent implantation is to place a stent in the narrowed blood vessels of the carotid artery to keep the blood vessels dilated. The vascular stent is a ring-shaped metal mesh structure, the main material of which is stainless steel, nickel-titanium alloy or cobalt-chromium alloy, woven or laser cut. It is compressed into a small diameter catheter and sent into the lesion site, and then released. After release, the stent will self-expand and open the blood vessel, which can effectively treat carotid stenosis, maintain blood flow in the blood vessels, and thus effectively reduce cerebrovascular disease. Summary of the invention

[0004] In order to solve the problems existing in the prior art, an embodiment of the present disclosure provides a carotid artery stent.

[0005] In view of this, an embodiment of the present disclosure provides a carotid artery stent, comprising a plurality of support rings arranged in parallel along the axial direction, each of the support rings extending along the circumferential direction and comprising a plurality of support units, the plurality of support units being connected end to end to form a ring-like structure, a connecting assembly being arranged between the support rings of two adjacent circles, the support units in the support rings being axially connected to the support units in the support rings of the adjacent circle through the connecting assembly, and the support units being capable of being received in the connecting assembly.

[0006] In some embodiments, the waveforms of any two adjacent turns of the support rings along the axial direction are arranged synchronously or are arranged with a dislocation.

[0007] In some embodiments, multiple turns of the support rings are arranged axially to form a tapered structure with non-equal diameters extending, and the diameters of the support rings increase linearly in sequence along the axial direction.

[0008] In some embodiments, the taper of the tapered structure is within the range of 1-20°.

[0009] In some embodiments, the support unit includes a wave crest portion and a wave trough portion, and the wave crest portion and the wave trough portion are connected by a wave rod portion.

[0010] In some embodiments, the width of the rod body of the wave rod portion is set to be thick-thin-thick.

[0011] In some embodiments, the connection assembly includes a plurality of connecting rods arranged at radial intervals. Two adjacent connecting rods and the support unit between the two connecting rods form a quadrilateral closed-loop structure. One end of each connecting rod is connected to the wave trough portion of one support unit, and the other end thereof is connected to the wave crest portion of another support unit in the support ring of the adjacent turn.

[0012] In some embodiments, the wave rod portion is a straight rod, an arc rod, or a special-shaped rod with a bent section and / or the connecting rod is a straight rod, an arc rod, or a special-shaped rod with a bent section.

[0013] In some embodiments, the structures of the connecting rods in the same column in the radial direction in the same connection assembly are the same, and the connecting rods in the adjacent two columns of the connection assemblies are arranged at intervals or with a dislocation in the axial direction.

[0014] In some embodiments, the connecting rod includes a first bent section and a second bent section, and a first groove and a second groove are respectively formed at the positions of the first bent section and the second bent section. The wave crest portion of one support unit connected to any one of the connecting rods can be recessed into the first groove, and the wave trough portion of another support unit connected to any one of the connecting rods can be recessed into the second groove.

[0015] The embodiments of the present disclosure solve the problems of difficult compression loading of the stent, and the situation that the stent is not easily released or instantaneously released and rushed out due to excessive pushing resistance during the release process, taking into account the radial force and flexibility of the stent, and achieving easy loading and release capabilities at the same time.

[0016] To make the above objects, features, and advantages of the embodiments of the present disclosure more obvious and understandable, the following specifically enumerates preferred embodiments and, in conjunction with the accompanying drawings, makes the following detailed description. Description of the Drawings

[0017] In the drawings, which are not necessarily to scale, the same reference numerals may describe similar components in different views. The same reference numerals with alphabetical suffixes or different alphabetical suffixes may represent different instances of similar components. The drawings generally illustrate various embodiments by way of example and not limitation, and are used in conjunction with the specification and the claims to explain the disclosed embodiments. Where appropriate, the same reference numerals are used throughout the drawings to refer to the same or similar parts. Such embodiments are illustrative and are not intended to be an exhaustive or exclusive embodiment of the apparatus or method. The drawings described herein are used to provide a further understanding of the present disclosure and form a part of this application. The illustrative embodiments and descriptions thereof of the present disclosure are used to explain the present disclosure and do not constitute an improper limitation of the present disclosure. In the drawings:

[0018] Figure 1 is a schematic plan view of a carotid artery stent provided by an embodiment of the present disclosure;

[0019] Figure 2 is an enlarged partial structural view of a support unit in the carotid artery stent provided by an embodiment of the present disclosure;

[0020] Figure 3 is a schematic view of a support unit in the carotid artery stent provided by an embodiment of the present disclosure being trapped within a connecting rod;

[0021] Figure 4 is a schematic structural view of a carotid artery stent having a tapered structure provided by an embodiment of the present disclosure;

[0022] Figure 5 is a schematic view of the connection of a connecting rod in the carotid artery stent provided by an embodiment of the present disclosure.

[0023] The above-mentioned drawings include the following reference numerals:

[0024] 100 - support ring; 110 - support unit; 111 - peak portion; 112 - wave rod portion; 113 - valley portion; 120 - connection assembly; 121 - connecting rod; 121a - first bending section; 121b - second bending section; 130 -

[0025] closed-loop structure; 210 - delivery catheter. Detailed Embodiments

[0026] Next, specific embodiments of the present disclosure will be described in detail in conjunction with the drawings, but this is not a limitation of the present disclosure.

[0027] It should be understood that various modifications can be made to the embodiments disclosed herein. Therefore, the above description should not be regarded as limiting, but merely as an example of the embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the present disclosure.

[0028] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present disclosure and, together with the general description of the present disclosure given above and the detailed description of the embodiments given below, serve to explain the principles of the present disclosure.

[0029] These and other features of the present disclosure will become apparent from the following description of the preferred forms of the embodiments given as non - limiting examples with reference to the accompanying drawings.

[0030] It should also be understood that although the present disclosure has been described with reference to some specific examples, those skilled in the art can surely implement many other equivalent forms of the present disclosure, which have the features as claimed and thus are all within the protection scope defined hereby.

[0031] When taken in conjunction with the accompanying drawings, the above and other aspects, features, and advantages of the present disclosure will become more apparent in view of the following detailed description.

[0032] Specific embodiments of the present disclosure will be described hereinafter with reference to the accompanying drawings; however, it should be understood that the disclosed embodiments are merely examples of the present disclosure and can be implemented in various ways. Well - known and / or repetitive functions and structures are not described in detail to avoid obscuring the present disclosure with unnecessary or redundant details. Therefore, the specific structural and functional details disclosed herein are not intended to be limiting, but merely as a basis for the claims and a representative basis for teaching those skilled in the art to use the present disclosure in substantially any suitable detailed structure in a variety of ways.

[0033] It should be noted that the terms "first", "second", etc. in the specification and claims of the present disclosure and in the above - mentioned accompanying drawings are used to distinguish similar objects and do not necessarily have to be used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present disclosure described herein can be implemented in an order different from those illustrated or described herein. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non - exclusive inclusion. For example, a process, method, system, product, or device that comprises a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these process, method, product, or device.

[0034] This specification may use phrases such as "in one embodiment", "in another embodiment", "in yet another embodiment", or "in other embodiments", all of which may refer to one or more of the same or different embodiments according to the present disclosure.

[0035] An embodiment of the present disclosure provides a carotid artery stent, which is a stent structure that can balance radial force and can well conform to the internal carotid artery and the common carotid artery. As shown Figures 1-5 in the figure, it includes a plurality of support rings 100, and the plurality of support rings 100 are arranged side by side along the axial direction, and each support ring 100 extends circumferentially. The number of the support rings 100 here can be set according to the actual requirements of the length of the carotid artery stent. Preferably, the number of the support rings 100 is 10 - 30. The support rings 100 of the present disclosure are made of nitinol alloy material.

[0036] Specifically, the support ring 100 includes a plurality of support units 110, and the plurality of support units 110 are connected end to end to form a ring-shaped structure. The number of the support units 110 in each support ring 100 here is set according to actual needs. Preferably, the number of the support units 110 on the circumference of the single-loop support ring 100 is 10 - 60.

[0037] The support ring 100 in this embodiment is a waveform structure, preferably formed by V-shaped units. Among them, the waveforms of any two adjacent loops of the support rings 100 along the axial direction can be arranged synchronously or in a staggered arrangement. Preferably, in the same carotid artery stent, all the support rings 100 have the same waveform structure, that is, a waveform with the same wavelength and amplitude; the wavelength here can be adjusted according to the different outer diameters of the stent. Preferably, its wavelength is 1 - 5 mm.

[0038] In this embodiment, the radial dimensions of each support ring 100 are the same, so that multiple loops of waveform support rings 100 arranged along the axial direction form a linear structure with equal diameter extension.

[0039] Of course, in order to meet the special requirements of different blood vessels, the carotid artery stent provided by the present disclosure can also form a non-equal-diameter extension structure, such as a tapered structure. In one embodiment, multiple loops of waveform support rings 100 arranged along the axial direction form a non-equal-diameter extension tapered structure. Specifically, the diameters of the support rings 100 along the axial direction increase linearly in sequence, so as to form a linearly transitional tapered structure, so as to be able to adapt to the large diameter difference structure at the bifurcation of the common carotid artery and the internal carotid artery.

[0040] For the carotid artery stent according to the embodiments of the present disclosure, whether it adopts a straight structure or a tapered structure, its diameter ranges from 2 mm to 12 mm, and its length is 20 - 80 mm. When the carotid artery stent with a tapered structure is adopted, the difference between the minimum diameter and the maximum diameter of the tapered structure along the axial direction is between 1 - 4 mm. For example, a tapered structure stent with a specification of 6 - 9 mm can be adopted, where the minimum diameter is 6 mm, the maximum diameter is 9 mm, and the difference is 3 mm. The taper of the tapered structure in this embodiment is within the range of 1 - 20°.

[0041] In this embodiment, the carotid artery stent is axially arranged as a non-uniform-diameter extended tapered structure, for example, the diameter increases or decreases uniformly in sequence, so as to form a tapered carotid artery stent with a linearly decreasing size, which can better conform to the different blood vessel size requirements of the common carotid artery and the internal carotid artery and is more adaptable to the anatomical structure of the blood vessels. When the carotid artery stent is implanted, the carotid artery stent can closely adhere to the blood vessel wall and will not form a suspended state locally, so as to conform to the different blood vessel size requirements of the common carotid artery and the internal carotid artery, be more adaptable to the anatomical structure of the blood vessels, and effectively prevent continuous pressure on the carotid sinus due to excessive radial force.

[0042] In addition, since the carotid artery stent adopts a uniformly changing transitional tapered structure, there is no stage where the diameter suddenly increases or decreases, and there is no smooth transition section either. The diameter of the carotid artery stent changes uniformly, which can not only take into account adapting to different diameter blood vessel sizes of the carotid artery, but also effectively cover all plaque positions of the atherosclerotic lesion site of the carotid artery. It can prevent continuous pressure on the carotid sinus due to excessive radial force caused by poor compliance, resulting in the risk of hypotension or blood vessel rupture in patients.

[0043] The support unit 110 described herein includes a peak portion 111 and a valley portion 113, and the peak portion 111 and the valley portion 113 are connected by a wave rod portion 112. The peak portion 111 and the valley portion 113 are preferably arc-shaped structures.

[0044] As Figure 2 shown, the wave rod portion 112 of the support unit 110 can be a straight rod, an arc rod, or a special-shaped rod formed by a bending section. Among them, the special-shaped rod formed by a bending section means that there is at least one bending section on the straight rod or the arc rod. The use of the special-shaped rod can strengthen the bending and stretching of the wave rod portion 112 and facilitate the stent loading and release performance. Among them, the bending degree and the number of the bending sections can be set according to actual needs.

[0045] Preferably, the width or thickness of the rod body of the wave rod portion 112 of the support unit 110 varies. For example, the width of the rod body is set as "thick-thin-thick", which can avoid strain concentration on the rod body and ensure excellent bending performance of the wave rod portion 112.

[0046] Furthermore, a connection component 120 is provided between two adjacent support rings 100, and the connection component 120 is used to axially connect different support rings 100. Here, the support unit 110 in the support ring 100 can be connected to another support unit 110 adjacent in the radial direction, or can be axially connected to the support unit 110 in the adjacent row of support rings 100 through the connection component 120. In this embodiment, the support units 110 of two adjacent support rings 100 can be received in the connection component 120. Especially when the carotid artery stent is loaded in the delivery catheter, the axial length between the carotid arteries can be reduced, and the carotid artery stent can be axially dilated after release.

[0047] Specifically, the connection component 120 includes a plurality of connecting rods 121 arranged at radial intervals. Each connecting rod 121 here connects two support units 110 in two adjacent support rings respectively. Here, two adjacent connecting rods 121 and the support unit 110 between the two connecting rods 121 form a quadrilateral closed-loop structure 130. Among them, one connecting rod 121, the support unit 110 on one side, the other connecting rod 121, and the support unit 100 on the other side are connected end to end to form the closed-loop structure 130. The closed-loop structure 130 here can improve the axial connection stability between two adjacent support rings 100, especially improve the axial connection strength of the carotid artery stent. At the same time, the characteristics of the quadrilateral can be used to adjust the relative position in the radial direction between two adjacent support rings 100, allowing a certain movement space between the support ring 100 and other support rings 100. The number of the connecting rods 121 in this embodiment and the interval between two adjacent connecting rods 121 are determined according to the balance between the actually required radial support force and flexibility.

[0048] Furthermore, one end of each connecting rod 121 is connected to the wave trough portion 113 of one support unit 100, and the other end is connected to the wave peak portion 111 of another support unit 100 in the adjacent support ring 100.

[0049] In the same connection component 120, a plurality of the connecting rods 121 are arranged at intervals, and the connecting rods 121 are arranged between the trough portion 113 of one support unit 100 located in different circles and the peak portion 111 of another support unit 100. As Figure 3 shown, the connecting rod 121 in this embodiment is a straight rod, an arc rod or a special-shaped rod with a bent section.

[0050] The connecting rod 121 with a special-shaped rod structure can enhance the bending and stretching performance of the carotid artery stent in the axial direction. At the same time, it can release the stress concentration phenomenon generated by the inward bending of the peak portion 111 and the trough portion 113 of the support unit 110, so as to facilitate the compression and loading of the carotid artery stent. Preferably, the connecting rod 121 is, for example, an S-shaped structure.

[0051] Furthermore, in the same radial column of the same connection component 120, the structures of the connecting rods 121 are the same, for example, presented as the same S-shaped structure arrangement. The connecting rods 121 in the same column of adjacent connection components 120 are arranged in the same S-shaped structure, or can also be arranged in the opposite inverted S-shaped structure. The arrangement structure in which two adjacent columns of the connecting rods 121 are arranged in the opposite S-shape can buffer the internal stress between two adjacent circles of the support rings 100 and improve the service life of the support rings 100.

[0052] Furthermore, the connecting rods 121 in two adjacent columns of the connection component 120 are arranged at intervals or staggered in the axial direction. This arrangement can enhance the supporting force of the connection component 120 on the support ring 100 and improve the flexibility of the carotid artery stent.

[0053] In order to enable the support units 110 of the adjacent two circles of the support rings 100 to be received within the connection assembly 120, the structure of the connecting rod 121 here is related to the relative positions of the wave crest portions 111 and the wave trough portions 113 having a connection relationship. Among them, the connecting rod 121 is, for example, an S-shaped structure having two bent segments, respectively including a first bent segment 121a and a second bent segment 121b, and a first groove and a second groove are respectively formed at the positions of the first bent segment 121a and the second bent segment 121b. After the carotid artery stent is loaded, the wave crest portion 111 of one support unit 110 connected to any one of the connecting rods 121 sinks into the first groove, and the wave trough portion 113 of another support unit 110 connected to any one of the connecting rods 121 sinks into the second groove. When the carotid artery stent needs to be loaded into the delivery catheter 210, the axial length of the carotid artery stent needs to be shortened. In this way, the wave crest portion 111 and the wave trough portion 113 of each support unit 110 can be respectively compressed and received within the first groove and the second groove of the corresponding connecting rod 121, so that the adjacent support units 110 in the axial direction are tightly connected and the axial length of the carotid artery stent is reduced, thereby facilitating the carotid artery stent to be tightly fitted and loaded into the delivery catheter 210.

[0054] In the above structure, by adopting the connecting rod 121 composed of bent segments, the ends of the wave crest or wave trough of the support unit can be perfectly compressed and received during the loading process, forming a seamless and tight fit, so that the force of the carotid artery stent can be effectively conducted in the axial and radial directions during the release process, achieving easy loading and release capabilities.

[0055] During the process of pushing the carotid artery stent, the wave crest portion 111 of the support unit 110 is stressed and transmitted through the connecting rod 121 to the wave trough portion 113 of the support unit 110 of the adjacent circle of the support ring 100, and then continuously transmitted through the wave rod portion 112, thereby realizing the effective conduction of force and achieving easy loading and release capabilities.

[0056] In this embodiment, the connection between the support rings 110 is realized through the connection component 120. The connecting rods 121 between adjacent support rings 110 are arranged radially, and a closed-loop structure is formed between the connecting rods 121 and the support unit 110, so that the connection components 120 are regularly arranged or staggered axially. The projections of the axially adjacent closed-loop structures in the axial direction do not overlap or only partially overlap. Such a structure takes into account the radial supporting force, and the spaced connection components 120 ensure that the radial supporting force is not too large. At the same time, the support unit 110 not connected to the connecting rod 121 can improve the flexibility of the stent, so that the carotid artery stent can maintain a good shape when bent or stretched.

[0057] The method for manufacturing the carotid artery stent according to the embodiment of the present disclosure includes the following steps:

[0058] (1) Laser cutting: Cut a nickel-titanium alloy tube with a predetermined specification into a mesh shape as required. Here, the predetermined specification is an outer diameter of 2 - 12 mm, a wall thickness of 0.1 - 0.4 mm, and a length of 20 - 80 mm.

[0059] (2) Etching and shaping: Etch and blank the stent after laser cutting, remove the slag generated by laser cutting, and perform heat treatment and shaping expansion with a special mold to form a stent with a linear structure or a tapered structure having a diameter of 4 - 10 mm.

[0060] (3) Pickling and polishing: Use chemical reagents to remove the oxide layer on the surface of the stent, and at the same time, electrochemical polishing can be performed to improve the surface quality of the stent.

[0061] The embodiment of the present disclosure solves the problems of difficult compression and loading of the stent, and the situation that the stent is not easily released or instantaneously released and rushed out due to excessive pushing resistance during the release process, taking into account the radial force and flexibility of the stent, and achieving easy loading and release capabilities at the same time.

[0062] In the above embodiments of the present disclosure, the descriptions of the respective embodiments have their own emphases. For parts not detailed in a certain embodiment, reference may be made to the relevant descriptions of other embodiments.

[0063] For the sake of description, spatial relative terms such as "above...", "over...", "on the upper surface of...", "above" etc. can be used here to describe as shown in the figure

[0064] The spatial positional relationship of a device or feature shown with other devices or features. It should be understood that the spatially relative terms are intended to encompass different orientations in use or operation in addition to the orientation depicted in the figures for the device. For example, if the device in the figure is inverted, a device described as "above" or "over" other devices or structures will then be positioned "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both the orientations of "above" and "below". The device can also be positioned in other different ways, rotated 90 degrees or in other orientations, and the spatially relative descriptions used herein are to be interpreted accordingly.

[0065] In addition to the above, it should also be noted that the "one embodiment", "another embodiment", "embodiment", etc. mentioned in this specification refer to the specific features, structures or characteristics described in connection with that embodiment being included in at least one embodiment generally described in this application. The same expression appearing in multiple places in the specification does not necessarily refer to the same embodiment.

[0066] Furthermore, when describing a specific feature, structure or characteristic in connection with any one embodiment, it is intended that implementing such feature, structure or characteristic in connection with other embodiments also falls within the scope of this disclosure.

[0067] In the above embodiments, the descriptions of the various embodiments each have their own emphasis. For parts not detailed in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0068] The above are only the preferred embodiments of this disclosure and are not used to limit this disclosure. For those skilled in the art, various changes and modifications can be made to this disclosure. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this disclosure shall be included within the protection scope of this disclosure.

Claims

1. A carotid artery stent, characterized in that, It includes a plurality of support rings arranged side by side along the axis. Each of the support rings extends circumferentially and includes a plurality of support units. The plurality of support units are connected end to end to form a ring-shaped structure. A connection component is arranged between adjacent two rings of the support rings. The support units in the support ring are axially connected to the support units in the support ring of the adjacent ring through the connection component. The support unit can be received in the connection component.

2. The carotid artery stent according to claim 1, characterized in that, The waveforms of any two adjacent rings of the support rings along the axis are arranged synchronously or form a staggered arrangement.

3. The carotid artery stent according to claim 1, wherein Multiple rings of the support rings are axially arranged to form a tapered structure with non-uniform diameter extension, and the diameters of the support rings increase linearly in sequence along the axis.

4. The carotid artery stent according to claim 3, characterized in that, The taper of the tapered structure is within the range of 1-20°.

5. The carotid artery stent according to claim 3, wherein, The support unit includes a crest portion and a trough portion, and the crest portion and the trough portion are connected by a wave rod portion.

6. The carotid artery stent according to claim 5, wherein, The width of the rod body of the wave rod portion is set as thick-thin-thick.

7. The carotid artery stent according to claim 5, characterized in that, The connection component includes a plurality of connecting rods arranged at radial intervals. The adjacent two connecting rods and the support unit between the two connecting rods form a quadrilateral closed-loop structure. One end of each connecting rod is connected to the trough portion of one support unit, and the other end is connected to the crest portion of another support unit in the support ring of the adjacent ring.

8. The carotid artery stent according to claim 7, wherein The wave rod portion is a straight rod, an arc rod or a special-shaped rod with a bent section and / or the connecting rod is a straight rod, an arc rod or a special-shaped rod with a bent section.

9. The carotid artery stent according to claim 8, characterized in that, The structures of the connecting rods in the same column in the radial direction in the same connection component are the same, and the connecting rods in the adjacent two columns of the connection components are arranged at intervals or staggered in the axial direction.

10. The carotid artery stent according to claim 8, wherein, The connecting rod includes a first bent section and a second bent section. A first groove and a second groove are respectively formed at the positions of the first bent section and the second bent section. The crest portion of one support unit connected to any one of the connecting rods can be recessed into the first groove, and the trough portion of another support unit connected to any one of the connecting rods can be recessed into the second groove.

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