Medical stent and method of forming the same

Abstract

The present application relates to the field of medical devices, and provides a medical stent, which comprises a tubular mesh structure composed of a plurality of interconnected wave rods, and an enhanced imaging area is arranged on at least one wave rod, and a development wire winding is wound around the enhanced imaging area, which is beneficial to enhance the development performance of the medical stent, and does not increase the delivery resistance of the medical stent. Further, the wave rod is further provided with a limiting structure located at both ends of the development wire winding in the enhanced imaging area, which can avoid displacement or uncoiling of the development wire winding, so that the accuracy of the development image obtained by using the medical stent is higher. The present application further provides a forming method of the above medical stent, which has a lower cost and the formed medical stent has the same or similar advantages.

Description

Technical Field

[0001] This invention relates to the field of medical devices, and in particular to medical stents and methods for forming them. Background Technology

[0002] Cardiovascular and cerebrovascular diseases have gradually become one of the leading causes of disability and death in humans. Endovascular stenting intervention surgery delivers medical stents through catheters to the lesion site in the blood vessel, and achieves blood vessel recanalization by expanding and opening the lesion. Due to its characteristics of minimal invasiveness, high safety and high effectiveness, it has become an important means of treating cardiovascular and cerebrovascular diseases.

[0003] To facilitate accurate positioning, deployment, and adjustment of medical stents during surgery, and to assess stent displacement or thrombosis during postoperative follow-up, images of the stents need to be observed under X-ray or other medical imaging equipment. Therefore, medical stents require good image-contrast performance. This is particularly important for intracranial vessels with skull interference. However, due to considerations regarding the mechanical properties, corrosion resistance, and biocompatibility of medical stents, the stent body material is typically stainless steel, cobalt-chromium alloy, nickel-titanium alloy, magnesium alloy, or polymers. These materials have relatively poor visibility under X-ray and other medical imaging equipment, resulting in less than ideal image-contrast effects.

[0004] To enhance the imaging performance of medical stents, a common method is to widen and / or thicken the stent's waveband. However, this method increases the amount of metal required to manufacture the stent. From a clinical perspective, this increases the risk of biocompatibility and the likelihood of thrombosis. On the other hand, the increased metal content can cause the stent to harden, leading to increased resistance when the stent is pushed into the blood vessel.

[0005] Another method to enhance the imaging performance of medical stents is to wrap imaging wires around the stent from the proximal end to the distal end. However, the cost of manufacturing imaging wires that wrap the entire stent around the stent is high, and the imaging wires are prone to loosening. This can cause the imaging wires to slide (displace) on the wave rod of the medical stent during delivery, which increases the resistance of delivery and affects the accuracy of the imaging image. Summary of the Invention

[0006] To overcome the problems existing in current methods for enhancing the imaging performance of medical stents, this invention provides a medical stent and a method for forming a medical stent, which can enhance the imaging performance of the medical stent on the one hand, and will not cause significant resistance to the delivery of the medical stent in blood vessels on the other hand, and the imaging image has high accuracy.

[0007] According to one aspect of the present invention, a medical stent is provided, comprising a tubular mesh structure consisting of a plurality of interconnected wave rods, wherein an enhanced imaging region is provided on at least one of the wave rods, and an imaging wire winding is wound around the wave rod in the enhanced imaging region, the imaging wire winding comprising at least one layer of imaging wire coil formed by winding imaging wire.

[0008] Optionally, the wave rod is further provided with a limiting structure in the enhanced developing area. The limiting structure is located at both ends of the developing wire winding and is used to restrict the development wire winding from moving or unwinding on the wave rod.

[0009] Optionally, the difference between the width of the limiting structure and the width of the wave rod at the location where the developing wire winding is wound is greater than or equal to the difference between the thickness of the developing wire winding and the radius of the developing wire, and less than or equal to the thickness of the developing wire winding.

[0010] Optionally, the medical stent includes a plurality of the enhanced imaging zones, and the plurality of enhanced imaging zones are distributed in a staggered manner along the axial direction of the tubular mesh structure.

[0011] Optionally, the plurality of developing filament windings are spirally distributed along the axial direction of the tubular mesh structure.

[0012] Optionally, the width of the wave bar in the enhanced developing area is greater than or equal to the width of the wave bar outside the enhanced developing area, and the width of the wave bar at the location where the developing wire is wound is in the range of 0.2 mm to 0.4 mm.

[0013] Optionally, each layer of the developing wire coil includes 8 to 10 cycles.

[0014] Optionally, the diameter of the developing filament ranges from 0.001 inches to 0.003 inches.

[0015] Optionally, the developing wire is made of one or more of the following materials: gold, silver, platinum, rhodium, iridium, palladium, rhenium, tungsten, and tantalum.

[0016] Optionally, one or more of the enhanced imaging zones may be provided on the same wave rod.

[0017] Optionally, in a plane perpendicular to the extension of the wave rod, the cross-section of the limiting structure is one or more combinations of circular arc, triangle, square, trapezoid, and other polygons.

[0018] Optionally, within the plane of the unfolded tubular mesh structure, the cross-section of the limiting structure is a combination of one or more of the following: circular arc, triangle, square, trapezoid, and other polygons.

[0019] According to another aspect of the present invention, the present invention also provides a method for forming a medical stent, the method comprising: forming a stent with a tubular mesh structure, the tubular mesh structure further comprising a plurality of interconnected wave rods; and providing an enhanced imaging region on at least one of the wave rods, and forming an imaging wire winding by winding at least one layer of an imaging wire coil with a spiral structure in the enhanced imaging region.

[0020] The medical stent provided by this invention has an enhanced imaging zone on at least one wave rod, and an imaging wire winding is wound around the enhanced imaging zone. This enhances the imaging performance of the medical stent without increasing its transport resistance. Furthermore, the wave rod is provided with limiting structures at both ends of the imaging wire winding in the enhanced imaging zone. These limiting structures prevent displacement or unwinding of the imaging wire winding, thereby ensuring high accuracy of the imaging images obtained using the medical stent.

[0021] The method for forming the medical stent provided by the present invention first forms a stent with a tubular network structure, wherein the tubular network structure further includes a plurality of interconnected wave rods. Then, an enhanced imaging zone is formed on at least one of the wave rods, and at least one layer of helical imaging wire coil is wound around the enhanced imaging zone to form an imaging wire winding. The formed medical stent has the same or similar advantages as the medical stent of the present invention, and the method for forming the medical stent has a lower cost. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a medical stent according to an embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of the unfolded plan of a medical stent according to an embodiment of the present invention.

[0024] Figure 3 This is a schematic diagram of the enhanced development area according to an embodiment of the present invention.

[0025] Figure 4 This is a schematic diagram of the wave rod and developing wire winding in another embodiment of the present invention.

[0026] Figure 5 This is a schematic diagram of the enhanced developing area and the limiting structure according to an embodiment of the present invention.

[0027] Figures 6(a) to 6(f) This is a schematic diagram of the enhanced developing area and the limiting structure in another embodiment of the present invention.

[0028] Figure 7 This is a flowchart of a method for forming a medical stent according to an embodiment of the present invention.

[0029] Explanation of reference numerals in the attached figures:

[0030] 10-Medical stent; 100-Wave rod; 100a-Enhanced imaging zone; 110-Illuminating wire winding; 120-Limiting structure. Detailed Implementation

[0031] The medical stent and its formation method of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of the present invention will become clearer from the following description. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the present invention.

[0032] As described in the background art, existing methods to enhance the imaging performance of medical stents include widening and / or thickening the waveband of the stent as a whole, or wrapping an imaging wire around the stent as a whole. However, widening and / or thickening the waveband as a whole increases the metal content of the medical stent, which is not conducive to the treatment effect and makes it more difficult to deliver the medical stent in the catheter. On the other hand, wrapping an imaging wire around the stent as a whole is costly to manufacture, and the imaging wire is prone to loosening and displacement during delivery, affecting the accuracy of the imaging image.

[0033] Figure 1 This is a schematic diagram of a medical stent according to an embodiment of the present invention. Figure 2 This is a schematic planar view of a medical stent according to an embodiment of the present invention. Those skilled in the art should understand that the medical stent of this embodiment of the present invention, in practical applications, is... Figure 1 The tubular structure shown is illustrated, but for clarity, it can be visualized through... Figure 2 The following description is based on a schematic diagram of the unfolded plane. The text below primarily refers to... Figure 2 The medical stent of the present invention will be described in an embodiment. Figure 3 This is a schematic diagram of the enhanced development area according to an embodiment of the present invention. The following is a description of the process in conjunction with... Figures 1 to 3 A medical stent according to an embodiment of the present invention will be described.

[0034] Reference Figures 1 to 3 In one embodiment of the present invention, the medical stent 10 includes a tubular mesh structure, the tubular mesh structure further includes a plurality of interconnected wave rods 100, an enhanced imaging region 100a is provided on at least one wave rod 100, and a radiopaque wire winding 110 is wound around the wave rod 100 in the enhanced imaging region 100a, the radiopaque wire winding 110 including at least one layer of radiopaque wire coil formed by winding radiopaque wire.

[0035] Specifically, the medical stent 10 can be a metal stent or a non-metal stent. The medical stent 10 includes, for example... Figure 1The tubular mesh structure shown can be configured such that each mesh element acts as a wave loop, composed of multiple wave rods. The tubular mesh structure may include, for example, multiple nodes connecting multiple wave rods 100, which can also be considered as edges of the wave loop. Figure 1 and Figure 2 In the illustrated embodiment, each wave ring consists of four wave rods 100, but the invention is not limited thereto. Multiple interconnected wave rods 100 can also form wave rings of other shapes, with multiple wave rings serving as the grid of the tubular mesh structure.

[0036] To enhance imaging performance, the medical stent of this embodiment has an enhanced imaging region 100a on at least one wave rod 100, and an imaging wire winding 110 is wound around the enhanced imaging region 100a. Furthermore, the medical stent 10 of this embodiment has multiple enhanced imaging regions 100a and corresponding imaging wire windings 110.

[0037] Specifically, multiple enhanced imaging zones 100a can be uniformly distributed along the surface of the medical stent 10 (tubular mesh structure), for example, they can be uniformly distributed along the axial and / or circumferential directions of the medical stent 10. Further, the multiple enhanced imaging zones 100a can be staggered along the axial direction of the tubular mesh structure (i.e., not on a single axis, but on multiple axial lines on the outer circumferential surface of the tubular mesh structure), so that the image displayed under imaging conditions reflects the morphology of the medical stent 10 in both the axial and circumferential directions. Preferably, the multiple enhanced imaging zones 100a are spirally distributed along the axial direction of the medical stent 10. The technical advantage of this is that, on the one hand, it helps the image displayed under imaging conditions to uniformly reflect the overall outline of the medical stent 10; on the other hand, it can reduce the number of imaging wire windings 110, reduce the transport resistance of the medical stent 10, and save manufacturing costs.

[0038] The position of the enhanced developing area 100a on the wave rod 100 can be set as needed. For ease of winding, the enhanced developing area 100a can be located in the middle region of the wave rod 100, that is, the enhanced developing area 100a is located in the middle region of the wave rod 100. However, it is not limited to this. The enhanced developing area 100a and the developing wire winding 110 can also be located in the end region of the wave rod 100. In addition, for the same wave rod 100, one enhanced developing area 100a can be set and the developing wire winding 110 can be set in the enhanced developing area 100a. However, it is not limited to this. Multiple enhanced developing areas 100a can also be set on the same wave rod 100. Figure 4 This is a schematic diagram of the wave rod and developing wire winding in another embodiment of the present invention. (Refer to...) Figure 4 In another embodiment, three enhanced development zones 100a are provided on the same wave rod 100.

[0039] The developing wire winding 110 is formed by winding a developing wire that enhances the developing area 100a around the wave rod 100. The material of the developing wire can enhance the clarity of the developed image under irradiation by an X-ray machine or related medical imaging equipment. In this embodiment, it is used to enhance the developing performance of the medical stent 10. Here, "developing performance" refers to the visibility of the developed image of the medical stent under irradiation by an X-ray machine or related medical imaging equipment. The clearer the developed image, the better the developing performance. The developing wire can be made of a metal material, such as one or a combination of gold, silver, platinum, rhodium, iridium, palladium, rhenium, tungsten, and tantalum. The diameter (or wire diameter) of the developing wire ranges from 0.001 inches to 0.008 inches. Considering both developing effect and transport resistance, it is preferable to select a developing wire with a diameter range of 0.001 inches to 0.003 inches to form the developing wire winding 110.

[0040] The cross-section of the developing wire can be circular, elliptical, triangular, square, trapezoidal, or a combination of other polygons. For ease of manufacturing, a circular cross-section developing wire can be chosen. For the same developing wire winding 110, one or more developing wire coils can be included. A developing wire coil refers to a coil formed on the same plane after the developing wire is wound around the enhanced developing area 100a of the wave rod 100. Each developing wire coil is formed by tightly winding the developing wire in the same direction and angle, with adjacent coils either close together or without gaps. The number of turns of the same developing wire coil can be determined based on the length of the enhanced developing area 100a on the wave rod 100 and the desired developing effect. In this embodiment, each layer of the developing wire coil can include 5 to 15 winding cycles; preferably, each layer includes 8 to 10 winding cycles to balance the developing effect and transport resistance.

[0041] To limit the position and density of the radiopaque wire winding 110, and to prevent displacement or unwinding of the radiopaque wire winding 110 during delivery or after insertion into the blood vessel, thus affecting radiopaque performance and image accuracy, refer to... Figure 3 In this embodiment, for the wave rod 100 with the enhanced imaging zone 100a, the wave rod 100 is also provided with a limiting structure 120 in the enhanced imaging zone 100a. Furthermore, in order to enhance the imaging effect of the medical stent 10 in the enhanced imaging zone 100a, in some embodiments, the imaging performance of the medical stent 10 is further enhanced by increasing the width of the wave rod at the enhanced imaging zone 100a, thereby simultaneously increasing the width of the imaging wire winding 110 at that location and increasing the metal content of the enhanced imaging zone 100a, without needing to widen or thicken the wave rod 100 of the medical stent 10 as a whole, thus having almost no impact on the transport resistance of the medical stent 10. Figure 5 This is a schematic diagram of the enhanced developing area and the limiting structure according to an embodiment of the present invention. Figures 6(a) to 6(f) This is a schematic diagram of the enhanced developing area and the limiting structure in other embodiments of the present invention. See below for reference. Figure 5 and Figures 6(a) to 6(f) The enhanced developing area and the limiting structure of the present invention will be described.

[0042] Reference Figure 5 Since the outer diameter of the radiopaque wire winding 110 is related to the width of the wave rod 100 in the enhanced radiopaque area 100a and the thickness of the radiopaque wire winding 110, in order to enhance the radiopaque performance of the medical stent 10, in addition to increasing the outer diameter of the radiopaque wire winding 110 by increasing the diameter of the radiopaque wire and the number of layers of the radiopaque wire coil, in some embodiments, the width of the wave rod 100 in the enhanced radiopaque area 100a can be set to be greater than or equal to the width of other areas on the same wave rod 100 other than the enhanced radiopaque area 100a. Here, "width" refers to the distance between the two edges of the wave rod extending along the surface of the medical stent 10 (i.e., the unfolded plane of the medical stent 10) and perpendicular to the extension direction of the wave rod. Specifically, in this embodiment, the range of the wave rod width D at the location where the radiopaque wire winding 110 is wound in the enhanced radiopaque area 100a can be set to 0.08 mm to 0.5 mm, and more preferably, the range of the wave rod width D at the location where the radiopaque wire winding 110 is wound can be set to 0.2 mm to 0.4 mm.

[0043] The limiting structure 120 is located at both ends of the developing wire winding 110 and is used to restrict the movement or unwinding of the developing wire winding 110 on the wave rod 100. Specifically, the limiting structure 120 may include a set of stops located at both ends of the developing wire winding 110, the stops being ear-shaped and disposed at both ends of the developing wire winding 110. When the developing wire is wound into a spiral structure in the enhanced developing zone 100a of the wave rod 100, the limiting structure 120 can also be used to fix both ends of the developing wire coil, thereby giving the limiting structure 120 an anti-unwinding effect (e.g., maintaining the spiral structure of the developing wire coil and preventing the developing wire coil from loosening). (See reference...) Figure 5 and Figures 6(a) to 6(f) Within the unfolded plane of the medical stent 10, the cross-section of the limiting structure 120 can be a combination of one or more of the following: an arc shape, a triangle, a square, a trapezoid, and other polygons. Furthermore, within the plane perpendicular to the extension direction of the wave rod 100, the cross-section of the limiting structure 120 can also be a combination of one or more of the following: an arc shape, a triangle, a square, a trapezoid, and other polygons. Additionally, a set of limiting structures 120 located at both ends of the radiopaque wire winding 110 can be positioned on the same side (see Figure 6(b)) or opposite side (see Figure 6(a)) of the corresponding wave rod 100, or a pair can be positioned on each side (see Figure 6(a)). Figures 6(d) to 6(f)Alternatively, a pair can be set on one side and one on the other side (see Figure 6(c)), etc. The specific arrangement can be determined by a combination of factors such as the position of the wave rod 100 on the support 10, the position of the enhanced imaging area 100a on the wave rod 100, and the number of such areas.

[0044] Reference Figure 5 To limit the displacement or unwinding of the radiopaque wire winding 110, the width D' of the limiting structure 120 is greater than the width D of the wave rod where the radiopaque wire winding 110 is wound. Here, the width D' of the limiting structure 120 refers to the distance between the apex of the limiting structure 120 and the opposite edge of the wave rod 100 where the radiopaque wire winding 110 is wound, along the surface (unfolded plane) of the medical support 10 and perpendicular to the extension direction of the wave rod 100. To prevent the radiopaque wire winding 110 from slipping past the limiting structure 120, in this embodiment, the difference between the width D' of the limiting structure 120 and the corresponding width D of the wave rod where the radiopaque wire winding 110 is wound (i.e., D'-D) is preferably greater than or equal to the difference between the thickness of the radiopaque wire winding 110 (the distance from the inner diameter of the innermost radiopaque wire coil to the outer diameter of the outermost radiopaque wire coil, i.e., the product of the number of turns of the radiopaque wire coil and the diameter of the radiopaque wire) and the radius of the radiopaque wire. Furthermore, to avoid an excessively large width D' of the limiting structure 120 leading to increased delivery resistance of the medical stent 10, preferably, the difference between the width D' of the limiting structure 120 and the width D of the corresponding wave rod where the radiopaque wire winding 110 is wound (i.e., D'-D) is less than or equal to the thickness of the corresponding radiopaque wire winding 110. For example, when the radiopaque wire winding 110 includes n layers of radiopaque wire coils (n is an integer greater than or equal to 1), where the diameter of the radiopaque wire is d, the range of the difference between the width D' of the limiting structure 120 and the width D of the corresponding wave rod where the radiopaque wire winding 110 is wound (i.e., D'-D) can be set to (n-0.5)d to nd.

[0045] As described above, the medical stent 10 of this embodiment, by providing an enhanced imaging region 100a on the wave rod 100 and winding an imaging wire 110 around the enhanced imaging region 100a, enhances the imaging performance of the medical stent 10 without increasing the transport resistance of the medical stent 10. Furthermore, the wave rod 100 is also provided with limiting structures 120 located at both ends of the imaging wire 110 in the enhanced imaging region 100a. The limiting structures 120 can prevent the imaging wire 110 from shifting or unwinding, thereby ensuring higher accuracy of the imaging image obtained using the medical stent 10.

[0046] The present invention also includes a method for forming a medical stent. Figure 7 This is a flowchart of a method for forming a medical stent according to an embodiment of the present invention. (Refer to...) Figure 7 The method for forming a medical stent according to an embodiment of the present invention includes the following steps:

[0047] S1: A support forming a tubular mesh structure, wherein the tubular mesh structure further includes a plurality of interconnected wave rods;

[0048] S2: An enhanced developing zone is provided on at least one of the wave rods, and at least one layer of developing wire coil with a spiral structure is wound in the enhanced developing zone to form a developing wire winding.

[0049] In step S1, the tubular mesh structure can be formed using laser cutting or weaving methods, with laser cutting being preferred. Those skilled in the art can refer to existing technologies for describing the process of forming medical stents using laser cutting.

[0050] In step S2, preferably, the enhanced developing zone also includes limiting structures located at both ends of the developing wire winding to restrict the development wire winding from moving or unwinding on the corresponding wave rod.

[0051] The medical stent 10 of this invention can be formed using the above-described method for forming a medical stent. By providing a radiopaque wire winding on at least one wave rod to form an enhanced radiopaque region, the radiopaque performance of the medical stent is improved without increasing the transport resistance of the medical stent, and the method for forming the medical stent has a low cost. By providing limiting structures at both ends of the radiopaque wire winding, displacement or unwinding of the radiopaque wire winding can be prevented, thereby ensuring high accuracy of the radiopaque image obtained using the medical stent.

[0052] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. Regarding the methods disclosed in the embodiments, since they correspond to the structures disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to the structural descriptions.

[0053] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the invention. Any person skilled in the art can make possible variations and modifications to the technical solutions of the present invention using the disclosed methods and techniques without departing from the spirit and scope of the invention. For example, the medical stents of the present invention include, but are not limited to, vascular stents, and can also be any of the following human lumen stents: biliary stents, esophageal stents, intestinal stents, urethral stents, prostate stents, orthopedic stents, etc. Furthermore, the vascular stents can be coronary stents, cerebral artery stents, aortic stents, renal artery stents, peripheral artery stents, venous stents, etc. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention are within the protection scope of the present invention.

Claims

1. A medical stent, characterized in that, The device includes a tubular mesh structure composed of multiple interconnected wave rods. Enhanced development zones are provided on the wave rods. A developer wire winding is wound around each wave rod in the enhanced development zone. The developer wire winding includes at least one layer of developer wire coil formed by winding developer wire. A limiting structure is provided on each wave rod in the enhanced development zone. The limiting structure is located at both ends of the developer wire winding and is used to restrict the movement or unwinding of the developer wire winding on the wave rod. The multiple developer wire windings are staggered along the axial direction of the tubular mesh structure. The width of the portion of the wave rod covered by the developer wire winding is greater than the width of the portion of the limiting structure located on the side opposite to the developer wire winding.

2. The medical stent as described in claim 1, characterized in that, The difference between the width of the limiting structure and the width of the wave rod at the location where the developing wire winding is wound is greater than or equal to the difference between the thickness of the developing wire winding and the radius of the developing wire, and less than or equal to the thickness of the developing wire winding.

3. The medical stent as described in claim 1, characterized in that, The plurality of developing filament windings are spirally distributed along the axial direction of the tubular mesh structure.

4. The medical stent as described in claim 1, characterized in that, The width of the wave rod at the location where the developing wire is wound is in the range of 0.2mm to 0.4mm.

5. The medical stent as described in claim 1, characterized in that, Each layer of the developing wire coil comprises 8 to 10 cycles.

6. The medical stent according to any one of claims 1 to 5, characterized in that, The diameter of the developing filament ranges from 0.001 inches to 0.003 inches.

7. The medical stent according to any one of claims 1 to 5, characterized in that, The developing wire is made of one or more of the following materials: gold, silver, platinum, rhodium, iridium, palladium, rhenium, tungsten, and tantalum.

8. The medical stent according to any one of claims 1 to 5, characterized in that, One or more of the enhanced imaging zones are provided on the same wave rod.

9. The medical stent according to any one of claims 1 to 5, characterized in that, In a plane perpendicular to the extension of the wave rod, the cross-section of the limiting structure is one or more combinations of circular arc, triangle, square and trapezoid.

10. The medical stent according to any one of claims 1 to 5, characterized in that, Within the plane of the unfolded tubular mesh structure, the cross-section of the limiting structure is one or more combinations of circular arc, triangle, square and trapezoid.

11. A method for forming a medical stent, characterized in that, include: A support forming a tubular mesh structure, wherein the tubular mesh structure further includes a plurality of interconnected wave rods; as well as Enhanced developing zones are provided on multiple wave rods. At least one layer of developing wire coil with a spiral structure is wound around the enhanced developing zones to form developing wire windings. The wave rods are provided with limiting structures in the enhanced developing zones. The limiting structures are located at both ends of the developing wire windings to restrict the movement or unwinding of the developing wire windings on the wave rods. The multiple developing wire windings are staggered along the axial direction of the tubular mesh structure. The width of the portion of the wave rod covered by the developing wire windings is greater than the width of the portion of the limiting structure located on the side opposite to the developing wire windings.

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