Double-layer biliary stent

Abstract

The present invention discloses a double-layer biliary stent. The stent mainly includes: a first-layer stent, which is a hollow tubular structure, and at least one through hole is arranged on the side wall of the first-layer stent; a second-layer stent, which is located inside the first-layer stent and is a hollow tubular structure, and at least one positioning sheath is arranged on the side wall of the second-layer stent, and the positioning sheath can switch between a state of protruding from the through hole and a state of retreating to the inside of the first-layer stent through the relative rotation of the second-layer stent and the first-layer stent. In the present invention, when the biliary stent is removed, the positioning sheath can enter the outer layer stent, and will not scratch the bile duct tissue due to protrusion, thereby avoiding the risk of discomfort or inflammation and infection of the patient.

Description

1.1.1 Technical Field

[0002] The invention relates to the technical field of medical materials, and in particular to a double-layer biliary stent. 1.1.2 Background Art

[0004] Biliary stents generally refer to stents installed between the duodenal papilla and the bile duct. Biliary duct stenosis and obstruction may be caused by gallstones, bile duct cancer and abnormal tissue proliferation. If the bile duct is blocked, it will cause symptoms such as jaundice, liver inflammation and even sclerosis. Biliary stents can treat bile duct stenosis.

[0005] The front and back of the stent are connected, which allows bile to be discharged smoothly when the stent is inside the bile duct. Currently, most common biliary stents on the market have a positioning sheath that is opened on one side, which can easily cause scratches and bleeding in the bile duct when the doctor installs or removes it. 1.1.3 Summary of the invention

[0007] Based on the above reasons, an object of the present invention is to provide a double-layer biliary stent that can reliably allow bile to flow out and avoid damaging the bile duct.

[0008] In order to achieve the above-mentioned purpose, an embodiment of the present invention provides a double-layer biliary stent. The double-layer biliary stent comprises:

[0009] The first layer support is a hollow tubular structure, and at least one through hole is provided on the side wall of the first layer support;

[0010] The second layer bracket is located inside the first layer bracket and is a hollow tubular structure. At least one positioning sheath is provided on the side wall of the second layer bracket. The positioning sheath can switch between a state of protruding from the through hole and a state of retreating into the inside of the first layer bracket through relative rotation of the second layer bracket and the first layer bracket.

[0011] Optionally, the positioning pin is formed by tilting a portion of the side wall of the second layer bracket relative to the rest of the side wall of the second layer bracket.

[0012] Optionally, a first through hole is provided on the side wall of the first end side of the first layer support, and a second through hole is provided on the side wall of the second end side of the first layer support, and the first through hole and the second through hole are provided on the same side relative to the axis of the first layer support;

[0013] A first positioning sheath is provided on the side wall of the first end side of the second layer bracket, and a second positioning sheath is provided on the side wall of the second end side of the second layer bracket, and the first positioning sheath and the second positioning sheath are arranged at the same side relative to the axis of the second layer bracket;

[0014] When the double-layer biliary stent is in use, the second positioning sheath can switch between a state of protruding from the second through hole and a state of retreating into the first layer of the stent through relative rotation of the second layer of the stent and the first layer of the stent, and when the second positioning sheath is in the state of protruding from the second through hole, the first positioning sheath is fixed to the first layer of the stent.

[0015] Optionally, the first positioning sheath and the second positioning sheath are tilted relative to each other along the direction in which the second layer of the bracket extends.

[0016] Optionally, a third through hole is provided on the side wall of the second end side of the first layer support, which is opposite to the second through hole, and the third through hole and the second through hole do not overlap in the extension direction of the first layer support;

[0017] A fourth through hole facing opposite to the second positioning sheath is provided on the side wall of the second end side of the second layer bracket. When the second positioning sheath protrudes from the second through hole, the fourth through hole is communicated with the third through hole.

[0018] Optionally, the length of the first layer of supports is smaller than the length of the second layer of supports.

[0019] Optionally, the first end side is an operating end side, and the second end side is a distal end side away from the operating end side.

[0020] An inner diameter of an end portion on the second end side of the first layer support is smaller than an outer diameter of an end portion on the second end side of the second layer support.

[0021] Optionally, the positioning sheath has an arc-shaped outer edge.

[0022] Optionally, the first layer support and the second layer support are made of at least one material selected from the group consisting of polycarbonate, thermoplastic polyurethane elastomer, polyurethane, polyethylene, nylon, polyether-polyamide block copolymer, and polyvinylidene fluoride.

[0023] Optionally, the first layer support and the second layer support are in any one of an arc shape, an angle shape and a double ring shape.

[0024] Beneficial effects of the present invention

[0025] In the double-layer biliary stent of the embodiment of the present invention, at least one through hole is arranged on the side wall of the first-layer stent, and at least one positioning sheath is arranged on the side wall of the second-layer stent. The positioning sheath can switch between a state of protruding from the through hole and a state of retreating to the inside of the first-layer stent through the relative rotation of the second-layer stent and the first-layer stent. That is, when the stent is taken out of the patient's body, the positioning sheath can be retreated to the inside of the first-layer stent through the through hole through the relative rotation of the second-layer stent and the first-layer stent. Therefore, the bile duct tissue will not be scratched due to the protrusion of the positioning sheath, thereby avoiding the risk of discomfort or inflammatory infection to the patient. 1.1.4 BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic structural diagram of a double-layer biliary stent provided in an embodiment of the present invention.

[0028] Figure 2 A schematic diagram of the structure of the first-layer bracket provided in an embodiment of the present invention.

[0029] Figure 3 A schematic diagram of the structure of the second-layer bracket provided in an embodiment of the present invention.

[0030] Figure 4 A schematic structural diagram of a positioning sheath provided in an embodiment of the present invention.

[0031] Figure 5 A schematic cross-sectional view of the second end side (distal end side) of the double-layer biliary stent provided in an embodiment of the present invention.

[0032] Figure 6 A schematic cross-sectional view of the first end side (proximal side) of a double-layer biliary stent provided in an embodiment of the present invention.

[0033] Description of Reference Numerals

[0034] 1-first layer bracket; 11-first through hole; 12-second through hole; 13-third through hole;

[0035] 2-second layer support; 21-second positioning sheath; 22-second positioning sheath; 23-fourth through hole. 1.1.5 DETAILED DESCRIPTION

[0037] Here, exemplary embodiments will be described in detail, and examples thereof are shown in the accompanying drawings. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention.

[0038] Figure 1 is a schematic diagram of the structure of a double-layer biliary stent according to an exemplary embodiment. Figure 1 The double-layer biliary stent includes: a first-layer stent 1 and a second-layer stent 2.

[0039] This embodiment improves the traditional biliary stent by changing the original single-layer biliary stent into a double-layer biliary stent, which can reduce the damage to the bile duct caused by the doctor when removing or replacing the biliary stent.

[0040] Specifically, the first-layer bracket 1 is an outer-layer bracket, which adopts a hollow tubular structure, and at least one through hole is set on the side wall of the first-layer bracket 1; the second-layer bracket 2 is an inner-layer bracket, which is located inside the first-layer bracket 1 and is a hollow tubular structure, and at least one positioning sheath is set on the side wall of the second-layer bracket 2. The positioning sheath can switch between a state of protruding from the through hole and a state of retreating to the inside of the first-layer bracket through the relative rotation of the second-layer bracket 2 and the first-layer bracket 1.

[0041] In the above-mentioned double-layer biliary stent, when in the drainage state, the positioning sheath on the side wall of the second-layer stent 2 protrudes through the through hole of the first-layer stent 1, so that the inner cavity of the second-layer stent 2 is connected with the bile duct; when the stent is taken out of the patient's body, the second-layer stent 2 and the first-layer stent 1 can be relatively rotated to make the positioning sheath retreat from the state of protruding through the through hole to the inside of the first-layer stent 1. Therefore, when the doctor removes the stent, the positioning sheath of the inner stent shrinks into the outer stent and will not scratch the bile duct tissue due to protrusion, thereby avoiding the risk of discomfort or inflammation and infection of the patient.

[0042] In one embodiment, Figure 2 As shown, a first through hole 11 is provided on the side wall of the first end side (proximal side) of the first layer bracket 1, and a second through hole 12 is provided on the side wall of the second end side (distal side) of the first layer bracket 1. Figure 2 As shown, the first through hole 11 and the second through hole 12 are arranged on the same side relative to the axis of the first layer of the bracket 1, so that the direction of the second through hole 12 and even the positioning sheath extending from the second through hole 12 can be determined by observing the direction of the first through hole 11. Of course, the first through hole 11 and the second through hole 12 can also be arranged on opposite sides of the bracket axis, or in other relative position relationships.

[0043] A third through hole 13 facing in the opposite direction to the second through hole 12 may also be provided on the side wall of the second end side (distal side) of the first layer of the stent 1, and the third through hole 13 and the second through hole 12 do not overlap in the extension direction of the first layer of the stent 1. Since two through holes communicating with the bile duct cavity are provided on the distal side of the first layer of the stent 1, it is beneficial for bile to be discharged quickly. Moreover, even if one of the two through holes is blocked by gallstones or other tissues, the other through hole can still ensure communication with the bile duct cavity. The third through hole 13 faces in the opposite direction to the second through hole 12, which can avoid the situation where both through holes are blocked as much as possible.

[0044] The overall shape of the first-layer stent 1 is not particularly limited as long as it is a tubular shape suitable for insertion into a cavity such as a bile duct. Figure 2 The overall arc shape is schematically shown in the figure, but it is not limited to this, and the overall shape can be appropriately changed according to the application site.

[0045] In one embodiment, Figure 3 As shown, a first positioning sheath 21 is provided on the side wall of the first end side (proximal side) of the second layer stent 2 (inner layer stent), and a second positioning sheath 22 is provided on the side wall of the second end side (distal side) of the second layer stent 2. Figure 3 As shown, the first positioning sheath 21 and the second positioning sheath 22 are arranged on the same side relative to the axis of the second layer stent 2, so that the position of the distal positioning sheath in the body can be known by observing the position of the proximal positioning sheath 31. Of course, the positions of the two positioning sheaths can also be arranged on opposite sides of the axis of the second layer stent, or in other positional relationships.

[0046] like Figure 3 and Figure 4 As shown, the positioning pin is formed by tilting a portion of the side wall of the second-layer bracket 2 relative to the rest of the side wall of the second-layer bracket 2. Thus, the positioning sheath can be integrally formed on the second-layer bracket 2, which not only saves the cost of the bracket, but also helps the positioning sheath to smoothly switch between a state of protruding from the through hole and a state of retreating to the inside of the first-layer bracket.

[0047] In one embodiment, the positioning sheath has an arc-shaped outer edge. The arc-shaped outer edge shape can not only reduce the damage caused by the positioning sheath to the patient when fixed in the bile duct, but also can rotate and retract more smoothly when cooperating with the first layer of stent 1.

[0048] Exemplarily, when the first layer stent 1 and the second layer stent 2 are assembled together (for example, when the double-layer biliary stent is in use), as shown in FIG. Figure 1 , Figure 4 , Figure 5 , Figure 6As shown, the second positioning sheath 22 protrudes through the second through hole 12, and the first positioning sheath 21 can protrude through the first through hole 11 like the second positioning sheath, or it can not extend into the through hole but be stuck at the edge near the first through hole 11, such as the end edge of the first layer bracket 1 or the concave portion provided at the end edge. By making the second layer bracket 2 rotate relative to the first layer bracket 1, the second positioning sheath 22 can switch between the state of protruding from the second through hole 12 and the state of retreating into the inside of the first layer bracket 1. In the retreat state, the second positioning sheath 22 is retracted inside the first layer bracket 1.

[0049] Optionally, the first positioning sheath 21 and the second positioning sheath 22 of this embodiment can be as follows Figure 3 As shown, the second-layer stent 2 is tilted relative to each other along the extending direction of the second-layer stent 2. This structure can easily and stably position the second-layer stent 2 relative to the first-layer stent 1, and more firmly position the second-layer stent 2 in the bile duct in a simple manner.

[0050] In addition, since the positioning sheath on the first end side and the positioning sheath on the second end side are set in the same direction (for example, at a position corresponding to the extension direction of the stent), the doctor can check whether the positioning sheath on the first end side is retracted, and can judge whether the positioning sheath on the second end side is retracted. For example, when the first positioning sheath 21 on the first end side (the end closer to the bile duct entrance) is misaligned by 180 degrees with the first through hole 11, it can represent that the second positioning sheath 22 on the second end side (the end farther from the bile duct entrance) has been retracted, which is convenient for the doctor to check and operate and facilitates the operation.

[0051] In the above embodiment, since the outer stent has a corresponding opening at the protruding position of the positioning sheath, the remote opening (the second through hole 12) can make the first positioning sheath 21 protrude from the outer stent and allow bile to flow out from the second through hole 12 to prevent bile from accumulating in the bile duct and causing bile duct lesions or inflammation. The proximal opening (the first through hole 11) allows the physician to determine whether the remote positioning sheath is in an open state during clinical surgery. At the same time, the hole can also serve as a channel for bile to flow out.

[0052] In addition, a fourth through hole 23 facing in the opposite direction to the second positioning sheath 22 may be provided on the side wall of the second end side (distal side) of the second layer stent 2, and the fourth through hole 23 is connected with the third through hole 13 when the second positioning sheath 22 protrudes from the second through hole 12. The front and back of the stent are connected so that bile can be discharged smoothly when the stent is inside the bile duct. In this embodiment, the bile duct stent is provided with a hole structure on the side wall (the third through hole 13 of the first layer stent 1 and the fourth through hole 23 of the second layer stent 2), which can ensure the smooth discharge of bile when a through hole on the distal side is blocked by gallstones.

[0053] It should be understood that the present embodiment does not limit the structure and number of the positioning sheaths, and the positioning sheaths can be a single-piece, double-piece, or four-piece or more sheet structure, and the number can be determined according to the surgical requirements to position the biliary stent more firmly in the bile duct. The positioning sheaths of the inner stent of the present embodiment correspond one-to-one with the through holes of the outer stent.

[0054] Optionally, the length of the first layer support 1 in this embodiment is smaller than the length of the second layer support 2 .

[0055] The length of the first layer support 1 is smaller than the length of the second layer support 2. Figure 6 As shown, the first positioning sheath 21 of the inner biliary stent can be easily fixed to the first layer stent 1, which can prevent the outer biliary stent from sliding toward the duodenal end or deep into the tissue. The length of the first layer stent 1 is less than that of the second layer stent 2, which can also facilitate the doctor to position the biliary stent, and can also help the doctor to judge the positional relationship between the first layer stent 1 and the second layer stent 2. For example, when the first positioning sheath 21 is misaligned with the first through hole 11 by 180 degrees, it can represent that the second positioning sheath 22 has been retracted, or the first positioning sheath 21 has shrunk into the first layer stent 1, which can represent that the second positioning sheath 22 has been retracted, or the first positioning sheath 21 protrudes through the first through hole 11 of the first layer stent 1, which can represent that the second positioning sheath 22 has also protruded. This is convenient for doctors to check and operate, and facilitates the operation.

[0056] Optionally, the first end side of this embodiment is the operation end side, and the second end side is the distal end side away from the operation end side; and the inner diameter of the end of the second end side of the first layer stent is smaller than the outer diameter of the end of the second end side of the second layer stent, that is, the inner diameter of the most distal opening of the outer layer biliary stent is slightly smaller than the outer diameter of the inner layer biliary stent. This can more reliably prevent the second layer stent (inner layer stent) 2 from coming off the distal end side of the first layer stent (outer layer stent) 1.

[0057] The length and outer diameter of the double-layer biliary stent of this embodiment can be determined or used according to the symptoms of different patients. The inner diameter of the most distal opening of the outer biliary stent is slightly smaller than the outer diameter of the inner biliary stent, so that the first positioning sheath 21 of the inner biliary stent can fix the outer biliary stent in the first positioning sheath 21. Figure 6 As shown, the outer biliary stent can be prevented from sliding toward the duodenal end or deep into the tissue.

[0058] Regarding the material of the double-layer biliary stent, in one embodiment, the first-layer stent 1 and the second-layer stent 2 can be made of at least one material selected from the group consisting of polycarbonate, thermoplastic polyurethane elastomer, polyurethane, polyethylene, nylon, polyether-polyamide block copolymer, and polyvinylidene fluoride.

[0059] The inner layer stent and the outer layer stent of this embodiment are made of the same material. The biliary stent is generally made of a material with a certain elasticity and rigidity, such as polycarbonate, thermoplastic polyurethane elastomer, polyurethane, polyethylene, nylon, polyether-polyamide block copolymer, polyvinylidene fluoride, etc., or a mixture of one or more of the above materials to prevent the stent from damaging the bile duct.

[0060] In one embodiment, the cross-sectional shape of the first layer stent 1 and the second layer stent 2 can be arc-shaped, angled, double-ring-shaped, etc., which are highly applicable and can be applied to a variety of symptoms or physical conditions. The use of the biliary stent of the present invention is not limited to the use of one double-layer stent at a time. Multiple stents can be used for a single affected area during a single operation, and the number is determined by the actual clinical evaluation of the physician. It should be understood that the present invention has a variety of different designs for the outer diameter and length of the biliary stent, which can be selected by the physician after evaluating the patient's physical condition and symptoms.

[0061] Regarding the manufacturing method of the double-layer biliary stent, it can be prepared by injection molding, processing molding, extrusion coating molding and casting molding. As long as the double-layer biliary stent of the above-mentioned embodiment of the present invention can be manufactured, the manufacturing method is not particularly limited, but a method that can be mass-produced is preferred.

[0062] The following is a description of the use of the double-layer biliary stent of this embodiment in an actual process.

[0063] The physician first evaluates the patient's condition before the operation, and then determines the appropriate surgical method, and uses the double-layer biliary stent of this embodiment for endoscopic biliary drainage. For example, during the operation, the physician will first pass the biliary endoscope through the mouth, esophagus, stomach, and deep into the opening of the duodenal papilla, that is, the bile duct outlet, and first pass a non-radioactive guide wire into the bile duct, and then push the double-layer biliary stent of this embodiment into the bile duct along the guide wire. At this time, the positioning sheath (second positioning sheath 22) on the distal side can be completely protruding from the outer layer of the biliary stent, or contracted in the outer layer of the biliary stent; then insert the balloon catheter into the inner layer of the biliary stent, and after the balloon is inflated, due to the friction between the balloon and the inner wall of the stent, the balloon catheter is rotated and the inner layer of the biliary stent is driven, so that the positioning sheath on the distal side of the inner layer of the biliary stent can be ejected from the notch (second through hole 12) of the outer layer of the biliary stent. The proximal positioning sheath (first positioning sheath 21) will not enter the bile duct, but will be fixed to the proximal end edge of the first layer stent 1 (outer layer stent) as a stop mechanism outside the mastoid. In the above steps, the doctor will observe and ensure with the help of X-ray whether the double-layer biliary stent has successfully reached the affected area, and the time the stent is placed in the patient's body is based on the doctor's assessment, and is generally installed in the patient's body for about 1 to 3 months.

[0064] When the patient needs to remove the stent or replace it, the physician can rotate the inner biliary stent to shrink the positioning sheath of the inner biliary stent into the outer biliary stent, and remove the inner and outer biliary stents. Specifically, during the disassembly process, the physician will first pass the biliary endoscope through the mouth, esophagus, stomach, and deep into the opening of the duodenal papilla, find the location of the biliary stent, guide the guide wire into the new double-layer biliary stent, and then pass the balloon catheter into the double-layer biliary stent through the guide wire, and expand the balloon to support the inner wall of the inner stent, and rotate it counterclockwise or clockwise. At this time, the inner biliary stent begins to rotate with the direction of the balloon catheter due to friction, and the positioning sheath on the distal side will be driven back to the hole (second through hole 12) due to the structural design of the corresponding hole bevel, and finally fixed in the wall of the outer stent, and then pulled out of the bile duct together with the balloon catheter. After removing the inner biliary stent, remove the outer biliary stent in the same way as above.

[0065] The double-layer biliary stent of the above embodiment can be taken out of the patient by rotating the second-layer stent 2 so that the through hole of the first-layer stent 1 can place the positioning sheath inside the first-layer stent 1, so that the bile duct tissue will not be scratched due to the protrusion, thereby avoiding the patient's discomfort or the risk of inflammation and infection. The first-layer stent 1 has a corresponding through hole at the protruding position of the positioning sheath, so that the positioning sheath can protrude from the first-layer stent 1 and bile can flow out through the hole to prevent bile from accumulating in the bile duct and causing bile duct lesions or inflammation. At the same time, the positioning sheath is designed with an arc curve, which can reduce the damage to the patient when it is fixed in the bile duct, and can be better rotated and retracted when it cooperates with the first-layer stent 1. In addition, the inner diameter of the most remote opening (the second through hole 12) of the outer-layer biliary stent is slightly smaller than the outer diameter of the inner-layer biliary stent, and the length of the outer-layer biliary stent is slightly shorter than that of the inner-layer biliary stent. In this way, the first positioning sheath 21 can fix the outer-layer biliary stent in the first positioning sheath 21 to prevent the outer-layer biliary stent from sliding toward the duodenal end or deep tissue.

[0066] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not disclosed in this disclosure. The specification and examples are to be considered exemplary only, and the true scope and spirit of the present invention are indicated by the following claims.

[0067] For example, the application of the stent of the present invention is not limited to the bile duct, but can also be applied to other lumens in the body that require drainage.

[0068] It should be understood that the present invention is not limited to the exact construction that has been described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. A double-layer biliary stent, characterized in that: include: The first layer support is a hollow tubular structure, and at least one through hole is arranged on the side wall of the first layer support; The second-layer bracket is located inside the first-layer bracket and is a hollow tubular structure, and at least one positioning sheath is provided on the side wall of the second-layer bracket, and the positioning sheath can be switched between a state of protruding from the through hole and a state of retreating into the inside of the first-layer bracket through relative rotation of the second-layer bracket and the first-layer bracket; The positioning pin is formed by tilting a portion of the side wall of the second layer bracket relative to the remaining portion of the side wall of the second layer bracket; The length of the first layer of brackets is shorter than the length of the second layer of brackets.

2. The double-layer biliary stent according to claim 1, characterized in that: A first through hole is provided on the side wall of the first end side of the first layer support, and a second through hole is provided on the side wall of the second end side of the first layer support, and the first through hole and the second through hole are provided on the same side relative to the axis of the first layer support; A first positioning sheath is provided on the side wall of the first end side of the second layer bracket, and a second positioning sheath is provided on the side wall of the second end side of the second layer bracket, and the first positioning sheath and the second positioning sheath are arranged at the same side relative to the axis of the second layer bracket; When the double-layer biliary stent is in use, the second positioning sheath can switch between a state of protruding from the second through hole and a state of retreating into the first layer of the stent through relative rotation of the second layer of the stent and the first layer of the stent, and when the second positioning sheath is in the state of protruding from the second through hole, the first positioning sheath is fixed to the first layer of the stent.

3. The double-layer biliary stent according to claim 2, characterized in that: The first positioning sheath and the second positioning sheath are tilted in a manner opposite to each other along a direction in which the second layer stent extends.

4. The double-layer biliary stent according to claim 2, characterized in that: A third through hole is provided on the side wall of the second end side of the first layer support, which is opposite to the second through hole, and the third through hole and the second through hole do not overlap in the extension direction of the first layer support; A fourth through hole facing opposite to the second positioning sheath is provided on the side wall of the second end side of the second layer bracket. When the second positioning sheath protrudes from the second through hole, the fourth through hole is communicated with the third through hole.

5. The double-layer biliary stent according to claim 2, characterized in that: The first end side is an operation end side, and the second end side is a distal end side away from the operation end side. An inner diameter of an end portion on the second end side of the first layer support is smaller than an outer diameter of an end portion on the second end side of the second layer support.

6. The double-layer biliary stent according to claim 1, characterized in that: The positioning sheath has an arc-shaped outer edge.

7. The double-layer biliary stent according to claim 1, characterized in that: The first layer support and the second layer support are made of at least one material selected from the group consisting of polycarbonate, polyurethane, polyethylene, nylon, and polyvinylidene fluoride.

8. The double-layer biliary stent according to claim 1, characterized in that: The shapes of the first layer bracket and the second layer bracket are any one of an arc shape, an angle shape and a double ring shape.

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