Ni-Ti alloy intravascular stent with surface microstructure

Abstract

The invention discloses a Ni-Ti alloy intravascular stent with a surface microstructure. The Ni-Ti alloy intravascular stent comprises L supporting rings, and the L supporting rings are connected through connecting ribs to form a supporting tube; the number of the supporting rings is N, the N supporting rings are evenly distributed in the annular direction, and every two adjacent supporting rings are connected. The supporting ring is composed of two inclined N-shaped modules, and the two inclined N-shaped modules are symmetrically connected to form an M-shaped supporting ring. The N support rings are annularly connected to form a WM type support ring; and the upper and lower layers of adjacent support rings in the axial direction are connected through a connecting rib. Finite element analysis is adopted, and it is verified that the WM stent has the mechanical properties of being small in expansion and contraction rate and good in flexibility. A stent-blood vessel-plaque system model is established for simulation analysis, and it is verified that the stent can well cover the diseased region. The inner surface of the stent is subjected to microstructure design, so that the inner surface of the stent has a'hemolytic 'effect, and the occurrence rate of intravascular restenosis is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of vascular stents, and in particular to a Ni-Ti alloy vascular stent with a surface microstructure. Background Art

[0002] Due to the poor biocompatibility of bare metal stents, metal inflammation occurs locally in the blood vessels, and the endothelium of the blood vessels hyperplasia occurs. When the blood vessels are stretched open by the stents, restenosis sometimes occurs. According to existing statistical data, the incidence of vascular restenosis caused by bare metal stents is relatively high, reaching 20%-30%. Specifically, restenosis is caused by the damage to the blood vessels and the proliferation of new endothelial tissue in the blood vessels after the stents are implanted in the blood vessels, thus forming thrombi and gradually causing vascular restenosis. Summary of the invention

[0003] In order to solve the above problems existing in the prior art, the present invention aims to design a Ni-Ti alloy vascular stent with a surface microstructure which can improve the function of the existing vascular stent and reduce the restenosis rate after stent implantation.

[0004] In order to achieve the above-mentioned object, the technical scheme of the present invention is as follows: a Ni-Ti alloy vascular stent with a surface microstructure, comprising L support rings, the L support rings are connected by connecting ribs to form a support tube; the support rings include N support rings, the N support rings are evenly distributed along the circumferential direction, and adjacent support rings are connected in pairs; the support ring is composed of two oblique N-type modules, and the two oblique N-type modules are symmetrically connected to form an M-type support ring; the N support rings are connected along the circumferential direction to form a WM-type support ring; the upper and lower support rings adjacent to each other in the axial direction are connected by connecting ribs;

[0005] The inner surface of the support ring is provided with a shark skin-like surface microstructure, the surface microstructure is triangular, the microstructure height h is 0.025-0.065 mm, and the spacing w between the microstructures is 0.1±0.05 mm.

[0006] Furthermore, one end of the connecting rib is connected to the central low point of the upper M-shaped support ring, and the other end is connected to a high point on one side of the adjacent lower M-shaped support ring.

[0007] Furthermore, the connecting rib is a Z-shaped connecting rib, and both corners are acute angles, with an angle between 60° and 80°.

[0008] Furthermore, the outer diameter R of the entire stent is 2.5-4.0 mm; and the axial length L is 7-40 mm.

[0009] Furthermore, the outer diameter R of the entire stent is 3±0.5 mm; and the axial length L is 9.2±2 mm.

[0010] Furthermore, the thickness T of the entire bracket does not exceed 0.2 mm.

[0011] Furthermore, the thickness T of the entire stent is 0.125±0.05 mm.

[0012] Furthermore, the axial length L1 of the support ring is 2±0.5 mm, the axial distance L2 between the apex of the M-shaped support ring and the middle V-shaped bottom is 1.6±0.5 mm; and the axial length L3 of the connecting rib is 0.125±0.05 mm.

[0013] Furthermore, the M segment and the W segment of the WM-type support ring have the same structure and size, and are in opposite directions along the axial direction.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] 1. The present invention adopts finite element analysis to verify that the WM bracket has the mechanical properties of small expansion and contraction rate and good flexibility.

[0016] 2. The present invention establishes a stent-blood vessel-plaque system model for simulation analysis, and verifies that the stent can cover the lesion site well.

[0017] 3. Since the present invention performs microstructural design on the inner surface of the stent, the inner surface of the stent has "hemophobicity", thereby reducing the incidence of restenosis in the blood vessel. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a structural schematic diagram of the present invention;

[0019] Figure 2 It is a schematic diagram of the size parameters of the present invention;

[0020] Figure 3 It is a schematic diagram of a finite element model of the present invention;

[0021] Figure 4 It is a schematic diagram of the shape of the present invention after expansion in the artery-plaque system;

[0022] Figure 5 Cross-sectional view of the fluid domain for simplified surface microstructure support.

[0023] Figure 2 Middle: 1. Support ring, 2. Connecting ribs. DETAILED DESCRIPTION

[0024] The present invention is further described below in conjunction with the accompanying drawings.

[0025] The present invention is further described below in conjunction with the accompanying drawings.

[0026] like Figure 1-5As shown, a Ni-Ti alloy vascular stent with a surface microstructure includes a support ring 1 and a connecting rib 2, wherein the support ring 1 provides support for the diseased blood vessel after the stent is implanted to ensure the stability of the stent in the blood vessel, while the connecting rib 2 effectively improves the axial flexibility of the stent through its unique shape design and improves its adaptability in the blood vessel.

[0027] The support ring 1 of the bracket in the present invention is an innovative structure of unequal height support rings 1, including L support rings 1, which are connected by connecting ribs 2 to form a support tube; the support ring 1 includes N support rings 1, which are evenly distributed along the circumferential direction and adjacent support rings 1 are connected in pairs; the support ring 1 is composed of two oblique N-type modules, which are symmetrically connected to form an M-type support ring 1; N support rings 1 are connected along the circumferential direction to form a WM-type support ring 1; one end of the connecting rib 2 is connected to the central low point of the upper M-type support ring 1, and the other end is connected to the high point on one side of the adjacent lower M-type support ring 1. See for details. Figure 1 .

[0028] The connecting rib 2 uses a straight rod type connecting rib 2, and on this basis, a Z-shaped bending structure is further designed. Both corners of the Z-shaped connecting rib 2 are acute angles, and the angle is between 60° and 80°. Figure 1 As shown, the support ring 1 and the connecting rib 2 of the bracket are arranged at intervals, that is, the two ends of the connecting rib 2 are respectively connected to the two support rings 1. The inner surface of the support ring 1 is provided with a shark skin-like surface microstructure, the surface microstructure is triangular, the microstructure height is 0.025mm-0.065mm, and the interval between the microstructures is 0.1mm.

[0029] The support structure design parameters of the present invention are as follows Figure 2 As shown, the length of the stent currently used in clinical practice is generally in the range of 7-40mm. In the present invention, the length is determined as L equal to 9.2±2mm. The diameter R of the stent in clinical practice generally has specifications such as 2.5mm, 2.75mm, 3mm, 3.5mm, 4.0mm, etc. In the present invention, the diameter is determined as R equal to 3±0.5mm. There is no clear requirement for the thickness of the stent used in clinical practice, which can be determined based on the radial support force required for the diseased blood vessel. It is generally believed that the stent thickness T should not exceed 0.2mm, and preferably the thickness T is 0.125±0.05mm, the rib width L3 is 0.125±0.05mm, the support ring 1 height L1 is 2±0.5mm, and L2 is 1.6±0.5mm.

[0030] The structure of the present invention is analyzed as follows:

[0031] 1. Study on Mechanical Properties of Ni-Ti Alloy Stent

[0032] The present invention uses finite element analysis software to simulate the compression and self-expansion of the stent and analyze the radial support performance and the compliance performance of the stent. Figure 3 As shown in the figure, a finite element model of the stent is created. The radial support performance test experiment of the stent is a process in which a plurality of unit blocks are evenly arranged around the stent, and the unit blocks are evenly moved inward to squeeze the stent so that its diameter gradually decreases.

[0033] The stent was compressed to the minimum size and unloaded to a radius of 2mm to obtain a stress cloud map. The maximum stress value of the stent when compressed to the minimum size was 893.81MPa, and the stress value of the stent when unloaded to a radius of 2mm was 211.39MPa. The maximum radial expansion force generated when the stent was compressed was 9.24N. The strain on the stent was small and the radial expansion force was large, making the stent more stable. The stent would experience axial shortening during the compression and expansion process, but the stent would not shorten much after expansion. The axial expansion rate of the stent was 2.58%. The vascular stent with a small expansion rate could accurately cover the plaque at the diseased blood vessel.

[0034] The present invention adopts finite element analysis for compliance, specifically the cantilever beam method: the left end of the bracket is fixed, a square thin plate is drawn on one end face of the bracket, the thin plate is fixed and constrained, the left end face of the bracket is bound with the thin plate to constrain the right end face of the bracket to apply a pressure of 0.3N. The bending displacement and bending stiffness of the bracket are analyzed. The maximum deformation of the bending displacement of the WM bracket is 1.923mm. The larger the bending displacement, the smaller the bending stiffness and the better the compliance.

[0035] The present invention successfully verifies by finite element analysis that the WM bracket has good mechanical properties.

[0036] 2. Ni-Ti alloy stent-vessel-plaque coupling analysis

[0037] The present invention establishes a stent-vessel-plaque system model for simulation analysis, and the simulation process is divided into three processes: pre-expansion, compression and free expansion. Pre-expansion refers to the pre-expansion of the stent by 1.5 mm before implantation into the diseased blood vessel; then compression and free expansion are performed, and the compression analysis step time is set to 1 s, and the free expansion analysis step time is also 1 s. The first step: gradually compress the stent by 2 mm along the thin-walled cylinder; the second step: translate the thin-walled cylinder by 14 mm along the direction of the blood vessel, and the stent is gradually unloaded and freely expanded to contact the blood vessel and support the plaque.

[0038] During modeling, the plaque was simplified to be evenly distributed in the circumferential direction. The designed stent was for the treatment of coronary artery stenosis. The blood vessel length was set to 15 mm, the radius was 2.28 mm, the total blood vessel wall thickness was 0.9 mm, the intima layer, the middle layer and the adventitia layer accounted for 27%, 36% and 40% of the total blood vessel wall thickness respectively. The specific arterial parameters were inner diameter 1.38 mm, length 15 mm, wall thickness 0.9 mm, intima thickness 0.24 mm, middle thickness 0.32 mm, adventitia thickness 0.34 mm, and plaque size parameters were thickness 0.35 mm and length 4 mm.

[0039] After the modeling is completed, simulation is performed to show the shape of the stent after expansion in the artery-plaque system. Figure 4 As shown. First, the stress and strain of the stent after implantation in the blood vessel are analyzed. The maximum stress area and the maximum strain area are mainly concentrated in the arc of the support ring 1. Since the shape recovery of the middle area of ​​the stent is limited by the artery-plaque system, the stress value of the area where the stent contacts the plaque is higher than the stress at both ends of the stent that do not contact the plaque, and the failure form of the Ni-Ti alloy stent is related to strain. As the stent expands, the strain of the stent gradually decreases, and the strain at the arc of the stent is higher than that in other areas of the support ring 1, with a maximum strain of 0.08mm / mm. In other words, the stent can support the diseased blood vessels well and is not bent.

[0040] The radial and axial changes of the stent during the entire implantation process are then analyzed. After the stent is expanded, it can completely open the blood vessel, and the radial displacement reaches a stable state. As the thin-walled cylinder is withdrawn, the diameter of the stent gradually decreases to the minimum diameter, and then the stent significantly elongates during the expansion process. The supporting area for the diseased blood vessel also gradually increases with the expansion process, so that the narrow part that was originally not covered is also covered. The stent achieves the purpose of covering the diseased area very well.

[0041] 3. Fluid dynamics analysis of the surface microstructure of Ni-Ti alloy stent

[0042] According to the principle of bionics, the microstructure design is carried out on the inner surface of the stent to make the inner surface of the stent have "hemophobicity", thereby reducing the incidence of restenosis in the vascular stent. To facilitate simulation calculation, the vascular stent is simplified into a thin-walled cylinder, and a shark skin-like triangular micro-convex structure is designed on the inner surface. The axial section of the fluid domain ( Figure 5)'s length L is 10mm, its width D is 3mm, the spacing w between the microstructures is 0.1mm, and a stent inner surface model with triangular micro-convex microstructures of heights of 0.025mm, 0.035mm, 0.045mm, 0.055mm, and 0.065mm respectively is established. After fluid simulation of the simplified stent cylinder with triangular microstructures of different heights, the blood flow characteristics such as blood flow velocity and blood pressure are studied, and it is concluded that the microstructure with a height of 0.035mm is the most effective in improving the blood flow velocity near the wall, and has the best effect on improving the blood flow velocity near the wall, covers a wider mainstream area, and has a more uniform overall velocity distribution.

[0043] It was concluded that the vascular stent with a surface microstructure height of 0.035 mm achieved the purpose of reducing the incidence of restenosis within the vascular stent.

[0044] The product obtained by the method of the present invention can improve the function of existing vascular stents, reduce the restenosis rate of blood vessels after stent implantation, and provide new ideas for the design and development of new vascular stents.

[0045] The present invention is not limited to this embodiment, and any equivalent concepts or changes within the technical scope disclosed by the present invention are included in the protection scope of the present invention.

Claims

1. A Ni-Ti alloy vascular stent with a surface microstructure, characterized in that: The invention comprises L support rings (1), wherein the L support rings (1) are connected via connecting ribs (2) to form a support tube; the support ring (1) comprises N support rings (1), wherein the N support rings (1) are evenly distributed along the annular direction and adjacent support rings (1) are connected in pairs; the support ring (1) is composed of two oblique N-type modules, wherein the two oblique N-type modules are symmetrically connected to form an M-type support ring (1); the N support rings (1) are connected along the annular direction to form a WM-type support ring (1); and two support rings (1) in an upper and lower layers adjacent to each other in the axial direction are connected via connecting ribs (2); The inner surface of the support ring (1) is provided with a shark skin-like surface microstructure, the surface microstructure is triangular, the microstructure height h is 0.025-0.065 mm, and the spacing w between the microstructures is 0.1±0.05 mm.

2. The Ni-Ti alloy vascular stent with a surface microstructure according to claim 1, characterized in that: One end of the connecting rib (2) is connected to the central low point of the upper M-shaped support ring (1), and the other end is connected to a high point on one side of the adjacent lower M-shaped support ring (1).

3. The Ni-Ti alloy vascular stent with a surface microstructure according to claim 1, characterized in that: The connecting rib (2) is a Z-shaped connecting rib (2), and both corners are acute angles, with an angle between 60° and 80°.

4. The Ni-Ti alloy vascular stent with a surface microstructure according to claim 1, characterized in that: The outer diameter R of the entire stent is 2.5-4.0 mm; the axial length L is 7-40 mm.

5. The Ni-Ti alloy vascular stent with a surface microstructure according to claim 1, characterized in that: The outer diameter R of the entire stent is 3±0.5 mm; the axial length L is 9.2±2 mm.

6. The Ni-Ti alloy vascular stent with a surface microstructure according to claim 1, characterized in that: The thickness T of the entire bracket does not exceed 0.2 mm.

7. The Ni-Ti alloy vascular stent with a surface microstructure according to claim 1, characterized in that: The thickness T of the entire stent is 0.125±0.05mm.

8. The Ni-Ti alloy vascular stent with a surface microstructure according to claim 1, characterized in that: The axial length L1 of the support ring (1) is 2±0.5 mm, the axial distance L2 between the apex of the M-shaped support ring (1) and the middle V-shaped bottom is 1.6±0.5 mm; and the axial length L3 of the connecting rib (2) is 0.125±0.05 mm.

9. The Ni-Ti alloy vascular stent with a surface microstructure according to claim 1, characterized in that: The M section and the W section of the WM-type support ring (1) have the same structure and size, and are in opposite directions along the axial direction.

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