Cobalt chromium L605-based heart stent material and preparation method thereof

Abstract

The invention belongs to the technical field of biomedical materials, and particularly relates to a heart stent material based on cobalt chromium L605 and a preparation method of the heart stent material. The cobalt-chromium L605 alloy pipe material comprises the following raw materials: a cobalt-chromium L605 alloy pipe material, an organic solvent, an alkaline cleaning solution, an acidic activation solution, a neutralization solution, an electrolyte, a citric acid passivation solution and tetraisopropyl titanate. Through a continuous process of cleaning and decontamination, activation, electrolytic polishing, controlled passivation and nano TiO2 compact layer reinforcement, surface defects, passivation film quality and ion barrier capability are systematically optimized on the premise of not changing mechanical properties of a matrix; controllable and uniform treatment is used for replacing a traditional strong corrosion or thick coating method, excellent corrosion resistance, low ion release, excellent deformation compatibility and consistency of inner and outer surface treatment are synchronously achieved, and a more stable and reliable pipe base is provided for follow-up stent machining.

Description

Technical Field

[0001] This invention belongs to the field of biomedical materials technology, specifically relating to a cobalt-chromium L605-based cardiac stent material and its preparation method. Background Technology

[0002] Cardiovascular stents, as crucial implantable devices used in interventional therapy to restore or maintain vascular patency, rely heavily on the long-term safety and effectiveness of their materials within the body fluid environment. After implantation, stents must withstand the long-term effects of pulsatile blood flow, cyclic mechanical loads, and a complex biochemical microenvironment. Localized corrosion, increased metal ion release, or blood compatibility issues induced by surface defects on the material surface can further lead to risks such as inflammatory reactions, thrombosis, and restenosis. Therefore, stent materials not only need high strength and good fatigue resistance but also require a stable, controllable, and repeatable surface state at the microscopic level to meet the consistency and reliability requirements of implanted medical devices.

[0003] Cobalt-chromium alloys are widely used in balloon-expandable cardiac stents due to their high strength and excellent fatigue resistance. Materials such as cobalt-chromium L605 alloy can support thinner stent structures, which helps reduce vascular injury and improve delivery performance. However, cobalt-chromium alloys may still have potential problems in body fluid environments, including active local electrochemical reactions, corrosion sensitivity at micro-defects, and the migration and release of metal ions. In particular, stents are usually manufactured from thin-diameter, thin-walled precision tubing. During the drawing, straightening, heat treatment, cutting, and subsequent cleaning processes, surface processing layers, drawing marks, micro-pits, or residual contaminants are inevitably introduced; these inhomogeneities can become corrosion initiation points and ion release channels. At the same time, cleaning and treating the inner lumen of the thin tubing is more difficult, and it is easy to have sufficient outer surface treatment but insufficient inner lumen treatment, resulting in inconsistent inner and outer surface conditions, which affects overall durability and batch consistency.

[0004] To improve the corrosion resistance and biocompatibility of metal scaffold materials, existing technologies typically employ surface treatments such as electropolishing, chemical passivation, plasma treatment, or coating modification. Among these, electropolishing can reduce surface roughness and processing defects, passivation can form an oxide film on the surface to reduce electrochemical activity, and coating methods can achieve a certain degree of barrier and functionalization through polymer or inorganic layers. However, existing solutions still have several shortcomings: First, some methods focus on improving a single aspect, such as only reducing roughness or only enhancing the passivation film, but lack overall synergy in defect source removal, film quality reconstruction, and ion migration channel closure, resulting in limited long-term stability improvement; Second, thick or brittle coatings may experience microcracks, delamination, or particle shedding under large deformation conditions such as support gripping and expansion, which may bring new safety hazards; Third, there is insufficient capacity for simultaneous processing of the inner cavity of thin-walled tubes with small diameters, and common processing techniques cannot guarantee the consistency of the inner and outer surfaces, with large batch fluctuations; Fourth, some coating or film formation processes are sensitive to conditions such as hydrolysis, polycondensation, and curing. If there is a lack of clear and controllable process windows, problems such as film discontinuity, pinhole defects, or insufficient stability may occur, which is not conducive to engineering scale-up and quality control. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a cobalt-chromium L605-based cardiac stent material and its preparation method.

[0006] The technical effects described in this invention are achieved through the following technical solution: a cobalt-chromium L605-based cardiac stent material, comprising the following raw materials: cobalt-chromium L605 alloy tubing, organic solvent, alkaline cleaning solution, acidic activation solution, neutralizing solution, electrolyte, citric acid passivation solution, and tetraisopropyl titanate. Furthermore, the cobalt-chromium L605 alloy tube has an outer diameter of 1.2–2 mm, a wall thickness of 0.08–0.18 mm, and an inner diameter of 1.04–1.64 mm. Furthermore, the organic solvent is either anhydrous ethanol or isopropanol; Furthermore, the alkaline cleaning solution is prepared by dissolving sodium carbonate and fatty alcohol polyoxyethylene ether in deionized water; the final concentration of sodium carbonate is 2-5 wt%; and the final concentration of fatty alcohol polyoxyethylene ether is 0.1-0.3 wt%. Furthermore, the acidic activation solution is prepared by adding sulfuric acid to deionized water; the final concentration of the sulfuric acid is 3-6 wt%. Furthermore, the neutralizing solution is a sodium bicarbonate aqueous solution with a concentration of 1-3 wt%; Furthermore, the electrolyte is prepared by dissolving phosphoric acid and sulfuric acid in deionized water; the final concentration of the phosphoric acid is 65–75 wt%; and the final concentration of the sulfuric acid is 10–20 wt%. Furthermore, the citric acid passivation solution is prepared by adding citric acid and hydrogen peroxide to deionized water; the final concentration of the citric acid is 4-8 wt%; and the final concentration of the hydrogen peroxide is 1-3 wt%. Furthermore, another aspect of the present invention provides a method for preparing a cobalt-chromium L605-based cardiac stent material, specifically comprising the following steps: S101: Place the cobalt-chromium L605 alloy pipe in an organic solvent for ultrasonic cleaning, then rinse with deionized water and dry. S102: Immerse the L605 alloy pipe that has been treated in step S101 in an alkaline cleaning solution and circulate the liquid through the inner cavity of the pipe; then rinse with deionized water until the pH of the rinsing solution is 6.5-7.5 and there is no foam residue. S103: Simultaneously treat the outer surface and inner cavity of the pipe after step S102 with an acidic activation solution to remove the surface passivation layer and processing layer, and obtain an activated substrate; immediately after completion, rinse with deionized water to pH 6.5-7.5, and then neutralize with a neutralizing solution; S104: The pipe processed in step S103 is clamped in an electropolishing fixture, and the outer wall and inner cavity are electropolished using an electrolyte solution; after polishing, it is rinsed in multiple stages and neutralized using a neutralizing solution, and then cleaned and dried. S105: The pipes processed in step S104 are placed in a citric acid passivation solution for controlled passivation to form a passivation film; after passivation, they are rinsed and dried. S106: The pipes that have completed step S105 are subjected to film densification treatment in a mild oxidizing environment; then rinsed and dried. S107: Deposit a dense layer of nano-scale TiO2 on the tube passivation film after step S106; perform low-temperature film stabilization treatment; then rinse and dry to obtain cardiac stent material; Further, in step S102, the soaking parameters are: temperature 40-50℃, time 10-15min; Further, in step S102, the circulating fluid parameters are: the fluid flow linear velocity in the inner cavity is 0.3 to 0.8 m / s; Further, in step S103, the specific operation of the acid activation solution treatment is as follows: the two ends of the pipe treated in step S102 are connected to the circulation loop through PTFE joints, and the acid activation solution is continuously pumped into the inner cavity of the pipe with a flow rate of 0.3 to 0.8 m / s at an internal linear velocity using a peristaltic pump and then returned to the storage bottle; at the same time, the entire pipe is immersed in the same acid activation solution, and the outer wall is simultaneously activated for 1 to 3 minutes at room temperature. Further, in step S104, the specific operation of the electrolytic polishing treatment is as follows: the two ends of the pipe are sealed and connected with PTFE acid-resistant insulating clamps to form a liquid-flowing circuit in the inner cavity; a graphite plate cathode is arranged in the electropolishing tank; the entire pipe is immersed in the electrolyte; a slender graphite cathode rod is inserted into the center of the inner cavity of the pipe, covered with an insulating sleeve, exposing only the effective working section, and ensuring that the cathode rod is concentric with the pipe wall; the electrolyte temperature is 35-45℃, the voltage is 8-15V, and the anode current density is 0.2-0.45A / cm². 2 The processing time is 60–120 s, and the linear velocity of the electrolyte in the inner cavity is 0.5–1.5 m / s; Further, in step S104, the multi-stage rinsing operation is as follows: Stage 1 involves immediately immersing the outer wall in a large amount of deionized water and shaking for 30-60 seconds, followed by flushing the inner cavity with deionized water for 1-2 minutes at a linear velocity of 0.8-1.5 m / s; Stage 2 involves flushing the outer wall with flowing deionized water for 2-5 minutes, followed by flushing the inner cavity with deionized water for 2-5 minutes at the same flow rate; Stage 3 involves washing with neutralizing solution for 1-3 minutes, simultaneously introducing neutralizing solution into the inner cavity for 1-3 minutes at a linear velocity of 0.3-0.8 m / s; Stage 4 involves flushing the outer wall with deionized water for 2-5 minutes, followed by flushing the inner cavity with deionized water for 4-8 minutes at a linear velocity of 0.8-1.5 m / s; the pH of the final outer wall rinsing solution and the inner cavity effluent is 6.5-7.5; the conductivity of the final rinsing solution is ≤5 µS / cm. It should be noted that in all processing steps, the drying parameters are: nitrogen blowing for 1 to 3 minutes, followed by hot air drying at 40 to 60°C for 10 to 30 minutes; Further, in step S105, the specific operation of the passivation treatment is as follows: the outer wall of the pipe is completely immersed in citric acid passivation solution; at the same time, the passivation solution is circulated into the inner cavity, the passivation temperature is 40-55℃, the passivation time is 25-45min, and the fluid circulation speed in the inner cavity is 0.3-0.8m / s. Further, in step S106, the specific operation of the membrane densification treatment is as follows: the pipe after the treatment in step S105 is immersed in deionized water at 70-80°C, and the inner cavity is circulated with deionized water at the same temperature for 10-25 minutes, with a circulating fluid velocity of 0.3-0.8 m / s in the inner cavity. Further, in step S107, the specific operation of depositing the TiO2 dense layer is as follows: S1: Dissolve tetraisopropyl titanate in anhydrous ethanol and stir until homogeneous to obtain a tetraisopropyl titanate solution; add deionized water and glacial acetic acid to anhydrous ethanol and mix to form a hydrolyzed phase, then slowly add it dropwise to the tetraisopropyl titanate solution over 5-10 min, bring the volume to a final volume with anhydrous ethanol, stir at 800 rpm until homogeneous, and age at room temperature for 40-80 min to obtain a sol. S2: Immerse the outer wall of the pipe treated with S106 in the sol for 40-90s, while simultaneously circulating the sol through the inner cavity at a linear velocity of 0.2-0.4m / s for 2-3min; lift and level at 1-3mm / s for 120-180s; pre-cur at 60-80℃ for 10min, and repeat the coating 2-3 times to achieve a final film thickness of 30-60nm; Further, in step S1, the molar ratio of tetraisopropyl titanate, deionized water, and glacial acetic acid is 1:3-5:0.4-0.8; the final concentration of tetraisopropyl titanate after being diluted with anhydrous ethanol is 0.1-0.15 mol / L. Further, in step S107, the specific operation of the low-temperature film stabilization treatment is as follows: air atmosphere, 80-110℃ for 10-30 min; 120-180℃ for 40-80 min; It should be noted that, in all processing steps, the specific parameters for rinsing are as follows: the pH of the rinsing solution on the outer wall and the effluent from the inner cavity after rinsing is 6.5 to 7.5; the conductivity of the rinsing solution is ≤5µS / cm.

[0007] The beneficial effects of this invention are as follows: Compared with existing technologies, this invention addresses the pain points of localized corrosion induction, metal ion release, and subsequent surface functional layer failure due to deformation in thin-walled tubes used in stents within bodily fluid environments. It constructs a continuous surface engineering system encompassing cleaning and decontamination, surface activation, electropolishing, controlled passivation, film densification, and nano-TiO2 dense layer reinforcement. This system does not alter the main alloy composition or the mechanical fundamentals of the tube. Through systematic regulation of surface micro-defect sources, passivation film quality, and ion migration channels, it achieves an overall improvement in corrosion resistance and low ion release performance, while maintaining compatibility with stent compression and expansion deformation conditions. This provides a more stable material substrate for subsequent stent cutting, polishing, and assembly. Specifically, the key to this invention lies in the organic coupling of two pathways: "morphological finishing" and "chemical film reconstruction." The initial organic degreasing and alkaline cleaning focus on removing drawing lubricant residues and polar contaminants, preventing oil and particles from forming a shielding zone during subsequent acid activation and electropolishing, thus improving treatment uniformity from the source. Acid activation is not about pursuing strong corrosion, but rather about removing unstable surface impurities and activating the substrate in a controlled manner, allowing subsequent electropolishing to proceed on a more uniform interface. Electropolishing further reduces drawing marks, micro-pits, and potential crack initiation points, lowering the probability of pitting corrosion and fatigue initiation, while providing a more continuous and less defective film substrate for the passivation film. The subsequent controlled passivation and mild densification treatment using a citric acid system transforms the naturally formed, batch-fluctuating oxide film into a reproducible, chemically more stable engineered passivation film, significantly reducing porosity and weak points, and inhibiting film damage caused by ion exchange and localized acidification in body fluids. Finally, a nanoscale TiO2 dense layer is constructed on top of the engineered passivation film. This dense inorganic network provides secondary closure of ion migration channels, forming a gradient barrier structure of substrate-passivation film-dense layer, thereby achieving more reliable ion shielding and corrosion inhibition without relying on thick coatings.

[0008] This invention also addresses and balances common performance conflicts in stent material surface engineering. Firstly, while traditional thick-film coatings provide barrier properties, they are prone to microcracks and particle detachment during stent clamping and expansion, potentially inducing inflammatory reactions or thrombosis. This invention employs a strategy of superimposing a nano-scale dense layer with an engineered passivation film, replacing thick-layer stacking with thin-layer densification. This achieves effective barrier properties while also allowing for easier deformation in tandem with the substrate, structurally reducing the potential for delamination and powdering. Secondly, while strong acid and oxidation treatments can quickly clean the surface, they can easily lead to localized over-etching and defect amplification, especially in narrow-diameter cavities where consistency is difficult to guarantee. This invention, through controlled activation, graded rinsing and neutralization, and simultaneous fluid flow within the cavity, prevents residual active ions from accumulating in micro-crack areas, avoiding the formation of localized corrosion initiation points. Simultaneously, it ensures simultaneous completion of internal and external surface treatments, addressing the pain point of inadequate treatment of narrow-tube cavities. Thirdly, while sol-gel TiO2 layers possess good barrier potential, uncontrollable hydrolysis and film formation can easily lead to sol instability, uneven film layers, or increased defects. This invention employs a combined strategy of hydrolysis regulation and slow dripping, leveling pre-curing and multiple thin coatings, and low-temperature stable film curing to transform the film formation process from "random gelation" to "controllable deposition and layer-by-layer densification," thereby improving the continuity, adhesion stability, and batch consistency of the coating.

[0009] In summary, this invention achieves a continuous modification path from contaminant removal, defect reduction, film reconstruction to nanoscale barrier reinforcement through the synergistic design of the process chain. Within the same system, it simultaneously ensures corrosion resistance, low ion release, internal and external surface consistency, and stability under deformation conditions. This method can be implemented using common cleaning, pump circulation, and electropolishing equipment. The process window is clear, and the repeatability is high, making it suitable for the engineering fabrication and large-scale consistency control of L605 precision thin-walled tubing for support systems. Attached Figure Description

[0010] Figure 1 The graph shows the mass results of the weight gain particles in the erosion resistance test of the support pipes in Example 1 and Comparative Examples 1-4. Figure 2 The graph shows the turbidity results of the circulating liquid in the erosion resistance test of the support pipes in Example 1 and Comparative Examples 1-4. Figure 3 Here are SEM images of the pipes at each stage of Example 1; Figure 3 (a) The initial pipe surface of Example 1 without surface engineering treatment; Figure 3 (b) is the homogenized substrate surface obtained after acid activation and electropolishing in Example 1; Figure 3 (c) The surface morphology of Example 1 after further forming a dense surface layer on the basis of passivation and densification; Figure 4 XPS images of the pipes at each stage of Example 1. Detailed Implementation

[0011] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Unless otherwise specified, the raw materials involved in the present invention are all purchased through conventional commercial channels. Experimental methods without specific conditions are conventional methods and conditions well known in the art, or according to the conditions recommended by the instrument manufacturer.

[0012] Example 1: A cardiac stent material based on cobalt-chromium L605, comprising the following raw materials: cobalt-chromium L605 alloy tubing, organic solvent, alkaline cleaning solution, acidic activation solution, neutralizing solution, electrolyte, citric acid passivation solution, and tetraisopropyl titanate. The cobalt-chromium L605 alloy tube has an outer diameter of 1.6 mm, a wall thickness of 0.12 mm, and an inner diameter of 1.36 mm. The method for preparing the cobalt-chromium L605-based cardiac stent material specifically includes the following steps: S101: Place the cobalt-chromium L605 alloy pipe in anhydrous ethanol for ultrasonic cleaning, then rinse with deionized water and dry. S102: The L605 alloy pipe that has been treated in step S101 is immersed in an alkaline cleaning solution at 45°C for 12 minutes, and the liquid is circulated in the inner cavity of the pipe at a linear velocity of 0.5 m / s; then it is rinsed with deionized water until the pH of the rinsing solution is 7 and there is no foam residue. The alkaline cleaning solution is prepared by dissolving sodium carbonate and fatty alcohol polyoxyethylene ether in deionized water; the final concentration of sodium carbonate is 4 wt%; and the final concentration of fatty alcohol polyoxyethylene ether is 0.2 wt%. S103: Connect both ends of the pipe treated in step S102 to the circulation loop through PTFE connectors. Use a peristaltic pump to continuously pump the acidic activation solution into the inner cavity of the pipe at a flow rate of 0.5 m / s within the cavity and return it to the storage bottle. Simultaneously, immerse the entire pipe in the same acidic activation solution to perform synchronous activation treatment on the outer wall at room temperature for 2 minutes. After completion, immediately rinse with deionized water until pH 7, then rinse the outer wall with neutralization solution and simultaneously introduce it into the inner cavity for neutralization for 3 minutes. Finally, rinse thoroughly with deionized water until the specified conductivity is achieved. The acidic activation solution is a 5wt% sulfuric acid aqueous solution; The neutralizing solution is a 2wt% sodium bicarbonate aqueous solution; S104: Seal and connect both ends of the pipe treated in step S103 using PTFE acid-resistant insulating clamps to form a liquid-flowing circuit within the inner cavity. Arrange a graphite cathode plate in the electropolishing tank, immersing the entire pipe in the electrolyte. Insert a slender graphite cathode rod into the center of the pipe's inner cavity, covering it with an insulating sleeve, exposing only the effective working section, and ensuring that the cathode rod is concentric with the pipe wall; the electrolyte temperature is 40℃, the voltage is 12V, and the anolyte current density is 0.35A / cm². 2 The processing time was 90 seconds, and the linear velocity of the electrolyte in the inner cavity was 1.2 m / s. After polishing, a multi-stage rinsing process was performed. The first stage involved immediately immersing the outer wall in a large amount of deionized water and shaking for 45 seconds, followed by rinsing the inner cavity with deionized water for 1.5 minutes at a linear velocity of 1.2 m / s. The second stage involved rinsing the outer wall with flowing deionized water for 4 minutes, followed by rinsing the inner cavity with deionized water for 4 minutes at the same flow rate. The third stage involved washing with neutralizing solution for 2 minutes, followed by simultaneous rinsing of the inner cavity with neutralizing solution for 2 minutes at a linear velocity of 0.5 m / s. The fourth stage involved rinsing the outer wall with deionized water for 4 minutes, followed by rinsing the inner cavity with deionized water for 6 minutes at a linear velocity of 1.2 m / s. The pH of the final outer wall rinsing solution and the inner cavity effluent was 7. The conductivity of the final rinsing solution was ≤5 µS / cm. The solution was then neutralized with neutralizing solution, followed by nitrogen blowing for 2 minutes and hot air drying at 50°C for 20 minutes. The electrolyte is prepared by dissolving phosphoric acid and sulfuric acid in deionized water; the final concentration of the phosphoric acid is 70 wt%; and the final concentration of the sulfuric acid is 15 wt%. S105: Completely immerse the outer wall of the pipe treated in step S104 in citric acid passivation solution; simultaneously, circulate the passivation solution into the inner cavity, passivation temperature 50℃, passivation time 35min, inner cavity circulation flow rate 0.5m / s; after passivation, rinse until the pH of the outer wall rinsing solution and the inner cavity effluent is 7; the conductivity of the rinsing solution is ≤5µS / cm; blow dry with nitrogen for 2min, and dry with hot air at 50℃ for 20min; The citric acid passivation solution was prepared by adding citric acid and hydrogen peroxide to deionized water; the final concentration of the citric acid was 6 wt%; and the final concentration of the hydrogen peroxide was 2 wt%. S106: Immerse the pipe after step S105 in deionized water at 75°C and circulate the deionized water in the inner cavity at the same temperature for 20 minutes, with a circulation velocity of 0.5 m / s. Then rinse until the pH of the rinsing solution on the outer wall and the effluent from the inner cavity is 7; the conductivity of the rinsing solution is ≤5 µS / cm; blow dry with nitrogen for 2 minutes, and then dry with hot air at 50°C for 20 minutes. S107: Deposit a dense nano-scale TiO2 layer on the passivation film of the tube after step S106; treat in air atmosphere at 100℃ for 20 min; treat at 150℃ for 60 min; rinse until the pH of the rinsing solution on the outer wall and the effluent from the inner cavity is 7; the conductivity of the rinsing solution is ≤5µS / cm; blow dry with nitrogen for 2 min, and then dry with hot air at 50℃ for 20 min to obtain the cardiac stent material.

[0013] In step S107, the specific operation of depositing the TiO2 dense layer is as follows: S1: Dissolve 0.1 mol tetraisopropyl titanate in 700 mL of anhydrous ethanol and stir until homogeneous to obtain a tetraisopropyl titanate solution; add 0.48 mol deionized water and 0.072 mol glacial acetic acid to 200 mL of anhydrous ethanol and mix well to form a hydrolyzed phase, then slowly add it dropwise to the tetraisopropyl titanate solution over 8 min, bring the volume to 1000 mL with anhydrous ethanol, stir at 800 rpm until homogeneous, and age at room temperature for 60 min to obtain a sol; S2: Immerse the outer wall of the pipe treated with S106 in the sol for 60s, and simultaneously circulate the sol through the inner cavity at a linear velocity of 0.3m / s for 2.5min; lift and level at 2mm / s for 150s; pre-cur at 70℃ for 10min, and repeat the coating twice to achieve a final film thickness of 50nm.

[0014] Example 2: A cardiac stent material based on cobalt-chromium L605, comprising the following raw materials: cobalt-chromium L605 alloy tubing, organic solvent, alkaline cleaning solution, acidic activation solution, neutralizing solution, electrolyte, citric acid passivation solution, and tetraisopropyl titanate. The cobalt-chromium L605 alloy tube has an outer diameter of 2 mm, a wall thickness of 0.18 mm, and an inner diameter of 1.64 mm. The method for preparing the cobalt-chromium L605-based cardiac stent material specifically includes the following steps: S101: Place the cobalt-chromium L605 alloy pipe in anhydrous ethanol for ultrasonic cleaning, then rinse with deionized water and dry. S102: Immerse the L605 alloy pipe treated in step S101 in an alkaline cleaning solution at 50°C for 15 minutes, and circulate the liquid in the inner cavity of the pipe at a linear velocity of 0.8 m / s; then rinse with deionized water until the pH is 6.5 and there is no foam residue. The alkaline cleaning solution is prepared by dissolving sodium carbonate and fatty alcohol polyoxyethylene ether in deionized water; the final concentration of sodium carbonate is 5 wt%; and the final concentration of fatty alcohol polyoxyethylene ether is 0.3 wt%. S103: Connect both ends of the pipe treated in step S102 to the circulation loop through PTFE connectors. Use a peristaltic pump to continuously pump the acidic activation solution into the inner cavity of the pipe at a flow rate of 0.8 m / s within the cavity and return it to the storage bottle. Simultaneously, immerse the entire pipe in the same acidic activation solution to perform synchronous activation treatment on the outer wall at room temperature for 3 minutes. After completion, immediately rinse with deionized water until pH 6.5, then rinse the outer wall with neutralization solution and simultaneously introduce it into the inner cavity for neutralization for 3 minutes. Finally, rinse thoroughly with deionized water until the specified conductivity is achieved. The acidic activation solution is a 6wt% sulfuric acid aqueous solution; The neutralizing solution is a 3 wt% sodium bicarbonate aqueous solution; S104: The two ends of the pipe treated in step S103 are sealed and connected using PTFE acid-resistant insulating clamps to form a liquid-flowing circuit within the inner cavity. A graphite cathode is placed in the electropolishing tank, and the entire pipe is immersed in the electrolyte. A slender graphite cathode rod is inserted into the center of the inner cavity of the pipe, covered with an insulating sleeve, exposing only the effective working section, and ensuring that the cathode rod is concentric with the pipe wall; the electrolyte temperature is 45℃, the voltage is 15V, and the anode current density is 0.45A / cm². 2 The processing time was 120 seconds, and the linear velocity of the electrolyte in the inner cavity was 1.5 m / s. After polishing, a multi-stage rinsing process was performed. The first stage involved immediately immersing the outer wall in a large amount of deionized water and shaking for 60 seconds, followed by rinsing the inner cavity with deionized water for 2 minutes at a linear velocity of 1.5 m / s. The second stage involved rinsing the outer wall with flowing deionized water for 5 minutes, followed by rinsing the inner cavity with deionized water for 5 minutes at the same flow rate. The third stage involved washing with neutralizing solution for 3 minutes, followed by simultaneous rinsing of the inner cavity with neutralizing solution for 3 minutes at a linear velocity of 0.8 m / s. The fourth stage involved rinsing the outer wall with deionized water for 5 minutes, followed by rinsing the inner cavity with deionized water for 8 minutes at a linear velocity of 1.5 m / s. The pH of the final outer wall rinsing solution and the inner cavity effluent was 6.5. The conductivity of the final rinsing solution was ≤5 µS / cm. The solution was then neutralized with neutralizing solution, followed by nitrogen blowing for 3 minutes and hot air drying at 60°C for 10 minutes. The electrolyte is prepared by dissolving phosphoric acid and sulfuric acid in deionized water; the final concentration of the phosphoric acid is 75 wt%; and the final concentration of the sulfuric acid is 20 wt%. S105: Completely immerse the outer wall of the pipe treated in step S104 in citric acid passivation solution; simultaneously, circulate the passivation solution into the inner cavity, passivation temperature 55℃, passivation time 45min, inner cavity circulation flow rate 0.8m / s; after passivation, rinse until the pH of the outer wall rinsing solution and the inner cavity effluent is 6.5; the conductivity of the rinsing solution is ≤5µS / cm; dry with nitrogen for 3min, and dry with hot air at 60℃ for 10min; The citric acid passivation solution was prepared by adding citric acid and hydrogen peroxide to deionized water; the final concentration of the citric acid was 8 wt%; and the final concentration of the hydrogen peroxide was 3 wt%. S106: Immerse the pipe after step S105 in deionized water at 80℃ and circulate the inner cavity with deionized water at the same temperature for 25 minutes, with a circulation velocity of 0.8 m / s. Then rinse until the pH of the rinsing solution on the outer wall and the effluent from the inner cavity is 6.5; the conductivity of the rinsing solution is ≤5µS / cm; blow dry with nitrogen for 3 minutes, and then dry with hot air at 60℃ for 10 minutes. S107: Deposit a dense nano-scale TiO2 layer on the tube passivation film after step S106; treat in air atmosphere at 110℃ for 10 min; treat at 180℃ for 40 min; rinse until the pH of the rinsing solution on the outer wall and the effluent from the inner cavity is 6.5; the conductivity of the rinsing solution is ≤5µS / cm; dry with nitrogen for 3 min, and then dry with hot air at 60℃ for 10 min to obtain the cardiac stent material.

[0015] In step S107, the specific operation of depositing the TiO2 dense layer is as follows: S1: Dissolve 0.15 mol tetraisopropyl titanate in 700 mL of anhydrous ethanol and stir until homogeneous to obtain a tetraisopropyl titanate solution; add 0.45 mol deionized water and 0.06 mol glacial acetic acid to 200 mL of anhydrous ethanol and mix well to form a hydrolyzed phase, then slowly add it dropwise to the tetraisopropyl titanate solution over 5 min, and bring the volume to 1000 mL with anhydrous ethanol. Stir at 800 rpm until homogeneous, and age at room temperature for 80 min to obtain a sol. S2: Immerse the outer wall of the pipe treated with S106 in the sol for 90s, and simultaneously circulate the sol through the inner cavity at a linear velocity of 0.4m / s for 2min; lift and level at 3mm / s for 120s; pre-cur at 80℃ for 10min, and repeat the coating 3 times to achieve a final film thickness of 60nm.

[0016] Example 3: A cardiac stent material based on cobalt-chromium L605, comprising the following raw materials: cobalt-chromium L605 alloy tubing, organic solvent, alkaline cleaning solution, acidic activation solution, neutralizing solution, electrolyte, citric acid passivation solution, and tetraisopropyl titanate; The cobalt-chromium L605 alloy tube has an outer diameter of 1.2 mm, a wall thickness of 0.08 mm, and an inner diameter of 1.04 mm. The method for preparing the cobalt-chromium L605-based cardiac stent material specifically includes the following steps: S101: Place the cobalt-chromium L605 alloy pipe in isopropanol for ultrasonic cleaning, then rinse with deionized water and dry. S102: Immerse the L605 alloy pipe treated in step S101 in an alkaline cleaning solution at 40℃ for 10 minutes, and circulate the liquid in the inner cavity of the pipe at a linear velocity of 0.3m / s; then rinse with deionized water until the pH of the rinsing solution is 7.5 and there is no foam residue. The alkaline cleaning solution is prepared by dissolving sodium carbonate and fatty alcohol polyoxyethylene ether in deionized water; the final concentration of sodium carbonate is 2 wt%; and the final concentration of fatty alcohol polyoxyethylene ether is 0.1 wt%. S103: Connect both ends of the pipe treated in step S102 to the circulation loop through PTFE connectors. Use a peristaltic pump to continuously pump the acidic activation solution into the inner cavity of the pipe at a flow rate of 0.3 m / s within the cavity and return it to the storage bottle. Simultaneously, immerse the entire pipe in the same acidic activation solution to perform synchronous activation treatment on the outer wall at room temperature for 1 min. After completion, immediately rinse with deionized water until pH 7.5, then rinse the outer wall with neutralization solution and simultaneously introduce it into the inner cavity for neutralization for 3 min. Finally, rinse thoroughly with deionized water until the specified conductivity is achieved. The acidic activation solution is a 3wt% sulfuric acid aqueous solution; The neutralizing solution is a 1 wt% sodium bicarbonate aqueous solution; S104: Seal and connect both ends of the pipe treated in step S103 using PTFE acid-resistant insulating clamps to form a liquid-flowing circuit within the inner cavity. Arrange a graphite cathode plate in the electropolishing tank, immersing the entire pipe in the electrolyte. Insert a slender graphite cathode rod into the center of the pipe's inner cavity, covering it with an insulating sleeve, exposing only the effective working section, and ensuring that the cathode rod is concentric with the pipe wall; electrolyte temperature 35℃, voltage 8V, anolyte current density 0.2A / cm². 2 The processing time was 60 seconds, and the linear velocity of the electrolyte in the inner cavity was 0.5 m / s. After polishing, a multi-stage rinsing process was performed. The first stage involved immediately immersing the outer wall in a large amount of deionized water and shaking for 30 seconds, followed by rinsing the inner cavity with deionized water for 1 minute at a linear velocity of 0.8 m / s. The second stage involved rinsing the outer wall with flowing deionized water for 2 minutes, followed by rinsing the inner cavity with deionized water for 2 minutes at the same flow rate. The third stage involved washing with neutralizing solution for 1 minute, followed by simultaneous rinsing of the inner cavity with neutralizing solution for 1 minute at a linear velocity of 0.3 m / s. The fourth stage involved rinsing the outer wall with deionized water for 2 minutes, followed by rinsing the inner cavity with deionized water for 4 minutes at a linear velocity of 0.8 m / s. The pH of the final rinsing solution for the outer wall and the effluent from the inner cavity was 7.5. The conductivity of the final rinsing solution was ≤5 µS / cm. The solution was then neutralized with neutralizing solution, followed by nitrogen blowing for 1 minute and hot air drying at 40°C for 30 minutes. The electrolyte is prepared by dissolving phosphoric acid and sulfuric acid in deionized water; the final concentration of the phosphoric acid is 65 wt%; and the final concentration of the sulfuric acid is 10 wt%. S105: Completely immerse the outer wall of the pipe treated in step S104 in citric acid passivation solution; simultaneously, circulate the passivation solution into the inner cavity, passivation temperature 40℃, passivation time 25min, inner cavity circulation flow rate 0.3m / s; after passivation, rinse until the pH of the outer wall rinsing solution and the inner cavity effluent is 7.5; the conductivity of the rinsing solution is ≤5µS / cm; blow dry with nitrogen for 1min, and dry with hot air at 40℃ for 30min; The citric acid passivation solution was prepared by adding citric acid and hydrogen peroxide to deionized water; the final concentration of the citric acid was 4 wt%; and the final concentration of the hydrogen peroxide was 1 wt%. S106: Immerse the pipe after step S105 in deionized water at 70℃ and circulate the inner cavity with deionized water at the same temperature for 10 minutes, with a circulation velocity of 0.3 m / s. Then rinse until the pH of the rinsing solution on the outer wall and the effluent from the inner cavity is 7.5; the conductivity of the rinsing solution is ≤5µS / cm; blow dry with nitrogen for 1 minute, and then dry with hot air at 40℃ for 30 minutes. S107: Deposit a dense nano-scale TiO2 layer on the tube passivation film after step S106; treat in air atmosphere at 80℃ for 30 min; treat at 120℃ for 40 min; rinse until the pH of the rinsing solution on the outer wall and the effluent from the inner cavity is 7.5; the conductivity of the rinsing solution is ≤5µS / cm; blow dry with nitrogen for 1 min, and then dry with hot air at 40℃ for 30 min to obtain the cardiac stent material.

[0017] In step S107, the specific operation of depositing the TiO2 dense layer is as follows: S1: Dissolve 0.1 mol tetraisopropyl titanate in 700 mL of anhydrous ethanol and stir until homogeneous to obtain a tetraisopropyl titanate solution; add 0.5 mol deionized water and 0.08 mol glacial acetic acid to 200 mL of anhydrous ethanol and mix well to form a hydrolyzed phase, then slowly add it dropwise to the tetraisopropyl titanate solution over 10 min, bring the volume to 1000 mL with anhydrous ethanol, stir at 800 rpm until homogeneous, and age at room temperature for 40 min to obtain a sol; S2: Immerse the outer wall of the pipe treated with S106 in the sol for 40s, and simultaneously circulate the sol through the inner cavity at a linear velocity of 0.2m / s for 3min; lift and level at 1mm / s for 180s; pre-cur at 60℃ for 10min, and repeat the coating twice, with a final film thickness of 30nm.

[0018] Comparative Example 1: The main difference between Comparative Example 1 and Example 1 is that the electropolishing treatment in step S104 is omitted in Comparative Example 1; the remaining steps and parameters are the same as in Example 1.

[0019] Comparative Example 2: The main difference between Comparative Example 2 and Example 1 is that the passivation solution in step S105 of Comparative Example 2 uses only citric acid aqueous solution and does not add hydrogen peroxide; the remaining steps and parameters are consistent with those of Example 1.

[0020] Comparative Example 3: The main difference between Comparative Example 3 and Example 1 is that the film densification treatment in step S106 is omitted in Comparative Example 3; the remaining steps and parameters are consistent with those in Example 1.

[0021] Comparative Example 4: The main difference between Comparative Example 4 and Example 1 is that in Comparative Example 4, step S107 does not use the tetraisopropyl titanate sol-gel system to deposit a dense TiO2 layer, but instead replaces tetraisopropyl titanate with tetraethyl silicate to deposit a dense SiO2 layer; the remaining steps and parameters are consistent with those of Example 1.

[0022] Performance testing: Mechanical performance testing: The mechanical properties of the cardiac stent materials in Examples 1-3 and Comparative Examples 1-4 were tested based on GB / T 228.1-2021 and GB / T 3075-2021. The test results are shown in Table 1 below.

[0023] Table 1. Mechanical property results of cardiac stent materials in the examples and comparative examples

[0024] Based on the results in Table 1, all groups in the examples used L605 alloy as the main component. The surface treatment temperature window was relatively mild, and no heat treatment that altered the matrix structure was introduced. The tensile strength and yield strength only varied slightly within the statistical fluctuation range, demonstrating that surface engineering does not sacrifice the load-bearing capacity of the matrix. Comparative Example 1 showed the worst fatigue performance and low elongation: After omitting electropolishing, defects such as drawing marks / microgrooves remained, making it easier for cracks to initiate at surface defects and propagate under cyclic loading, resulting in a significant decrease in fatigue strength. At the same time, tensile fracture occurred more easily and elongation decreased slightly. Comparative Example 3 was the worst: The lack of film densification resulted in insufficient convergence of passivation film defects, making it easier for micro-defects / weak areas to form at the interface of the subsequent dense layer. Under the combined action of cyclic loading and corrosive media, micro-cracks were more likely to occur, resulting in fatigue strength lower than the system with densification steps. Comparative Examples 2 and 4 are at an intermediate level: The oxidation-reconstruction strength of the passivation system in Comparative Example 2 is insufficient, resulting in slightly poor stability of the engineered passivation film. Even with a TiO2 layer, it is more susceptible to the influence of interfaces and defects. Although Comparative Example 4 still has a dense layer, the SiO2 layer is weaker than the TiO2 system in terms of interface matching and deformation synergy, resulting in a higher risk of cracks / delamination and thus lower fatigue strength than the example using TiO2.

[0025] Erosion resistance test: The tubing prepared in Example 1 and Comparative Examples 1-4 was fixed in the cavity, ensuring that the fluid only passed through the inner cavity. The rinsing medium was PBS + 0.5% albumin, and the linear velocity in the inner cavity was controlled at 1 m / s. Rinsing was performed continuously for 24 hours, with samples taken every 2 hours. After rinsing, a certain volume of circulating liquid (100 mL) was filtered through a 0.22 μm filter membrane. The filter membrane was dried at 60℃ for 30 min and then weighed (the difference before and after drying is the particle mass). A blank control was set up, i.e., the same PBS + 0.5% albumin was used, and the same 24-hour circulation was performed, but no sample was placed, resulting in a blank circulating liquid. The blank circulating liquid was filtered and weighed in the same way. The increase in particle mass = increase in filter membrane weight of the sample group - increase in filter membrane weight of the blank group. The turbidity (NTU) of the circulating liquid was measured simultaneously. The test results are as follows: Figure 1 and Figure 2 As shown.

[0026] based on Figure 1 and Figure 2 Analysis of the results showed that Example 1 consistently exhibited the lowest particle quality and turbidity. This was primarily due to the fact that electropolishing first reduced drawing marks and micro-defect sources, followed by controlled passivation and densification, which led to the convergence of passivation film defects and reduced porosity. Ultimately, a continuous, closed TiO2 nano-density layer was formed, reducing microcrack initiation and debris shedding under internal erosion conditions, resulting in a low-starting-point, low-increase erosion release curve. In Comparative Example 1, after removing electropolishing, the inner wall grooves and defect sources remained, making it easier for fluid shearing and micro-disturbances to trigger localized erosion / microcrack propagation, resulting in the highest particle quality and turbidity throughout the process, with the most significant accumulation over time. In Comparative Example 3, after removing densification, the passivation film defects were difficult to fully converge, and the dense layer interface was more prone to forming weak areas, leading to accelerated shedding in the middle and later stages (12-24h), exhibiting a significant increase in the later stages. Comparative Example 2, lacking peroxide synergy in its passivation system, exhibited insufficient stability and density of the engineered passivation film. Even with a subsequent TiO2 layer, it was more susceptible to interface and defect influences, resulting in moderate particle size and turbidity. Comparative Example 4, while still possessing a dense layer, showed weaker interface matching and deformation synergy compared to the TiO2 system. Under internal erosion, it was more prone to microcracks or localized delamination, leading to an overall performance slightly inferior to Example 1 but similar to Comparative Example 2.

[0027] Biocompatibility testing: The cardiac stents prepared in Examples 1-3 were cut into samples (approximately 10 × 10 mm each), and sequentially ultrasonicated with anhydrous ethanol for 10 min, rinsed three times with deionized water, and dried with nitrogen. They were then sterilized by immersion in ethylene oxide for 30 min followed by UV irradiation on each side for 30 min. Cytotoxicity was assessed using the extraction method, with DMEM (containing 10% fetal bovine serum) as the extraction medium, at a sample surface area to volume ratio of 3 cm³. 2 Extraction was performed at 37℃ and 5% CO2 for 24 h and 72 h respectively; the supernatant was filtered (0.22 μm) to obtain the extract. L929 fibroblasts were seeded into 96-well plates at a density of 1×10⁶ m² / mL.4 Cells / well were cultured for 24 hours until adherence, then treated with 100% and 50% extract solutions respectively. A negative control (complete culture medium) and a positive control (0.1% Triton X-100) were also included. After incubation for 24 hours and 72 hours respectively, CCK-8 assays were performed. 10 μL of CCK-8 was added to each well, and the cells were incubated at 37°C for 2 hours. Readings were taken at 450 nm. Biocompatibility (%) was calculated as (OD value of each experimental group - OD value of the positive control group) / (OD value of the negative control group - OD value of the positive control group) × 100%. The test results are shown in Tables 2-5 below. For the hemolysis test, fresh anticoagulated whole blood (EDTA) was used. Red blood cells were washed three times with PBS to prepare a 2% (v / v) red blood cell suspension. Samples (surface area 1 cm²) were then... 2 10 mL of red blood cell suspension was added to a centrifuge tube, incubated in a 37°C water bath for 60 min, centrifuged at 1000 rpm for 5 min, and the supernatant was collected. The absorbance was measured at 540 nm. The negative control was PBS, and the positive control was deionized water. The hemolysis rate (%) was calculated as (absorbance of each experimental group - absorbance of the negative control group) / (absorbance of the positive control group - absorbance of the negative control group) × 100%. The test results are shown in Table 6 below.

[0028] Table 2. Cytotoxicity test results of 100% extract (stock solution extracted for 24 hours) of cardiac stent tubing from the example

[0029] Table 3. Cytotoxicity test results of 100% extract (stock solution extracted for 72 hours) of cardiac stent tubing from the example.

[0030] Table 4. Cytotoxicity test results of 50% extract (24h extraction) of cardiac stent tubing in the example. The 50% extract refers to the solution obtained by mixing 100% extract stock solution with complete culture medium at a volume ratio of 1:1.

[0031] Table 5. Cytotoxicity test results of 50% extract (72h extraction) of cardiac stent tubing in the examples. The 50% extract refers to the solution obtained by mixing 100% extract stock solution with complete culture medium at a volume ratio of 1:1.

[0032] Table 6. Results of hemolysis rate test of cardiac stent tubing in the example

[0033] Based on the results analysis in Tables 2-6 above, all embodiments of the present invention employ a complete surface engineering chain, which can effectively reduce processing residues and surface defect sources, forming a more stable engineered passivation film and nanoscale dense layer, thereby reducing the release of potential metal ions and microparticles during the extraction process, and having a smaller impact on cell metabolic activity and erythrocyte membrane integrity. There are slight differences between the embodiments, but the overall level is still maintained, showing excellent biocompatibility.

[0034] Spectrum test: Figure 3 The images shown are SEM (Scanning Electron Microscope) images of the pipes at each stage of Example 1. Figure 4 XPS images of the pipes at each stage of Example 1.

[0035] based on Figure 3 and Figure 4 Results analysis, Figure 3 (a) The initial pipe surface without surface engineering treatment; Figure 3 (b) is the homogenized substrate surface obtained after acid activation and electropolishing; Figure 3 (c) Surface morphology after further formation of a dense surface layer based on controlled passivation / densification; the untreated L605 pipe surface still retains obvious processing textures and directional grooves, and the surface undulations and micro-slit structure provide potential channels for localized corrosion and ion migration. After acid activation and electropolishing, the macroscopic grooves on the surface are significantly reduced, and the substrate tends to be more uniform, indicating that the unstable processing layer and defect sources are reduced, providing a continuous and controllable film-forming interface for subsequent film construction. On this basis, through controlled passivation and film densification treatment, the surface further exhibits more continuous and uniform coverage characteristics, and the macroscopic texture is weakened, suggesting that the film layer has a sealing and reconstruction effect on surface defects and potential channels. XPS spectra showed that the untreated sample (curve (c)) was dominated by L605 matrix element signals, with characteristic peaks of Co 2p and Cr 2p visible, while only O 1s signals associated with the natural oxide film were observed, indicating that its surface was still in a state of matrix exposure accompanied by a thin natural oxide layer. After acid activation and electropolishing (curve (b)), the matrix peaks were still clearly visible, but the O 1s signal was relatively enhanced, indicating that the surface gradually transformed from processing residues and an unstable surface layer to a cleaner, more uniform substrate state that was more conducive to the formation of a stable oxide / passivation interface. Furthermore, after controlled passivation / densification and the completion of the dense layer construction (curve (a)), obvious Ti 2p characteristic signals appeared in the spectrum, while matrix-related peaks such as Co 2p and Cr 2p were relatively attenuated, indicating that a continuous titanium-containing dense layer was formed on the surface and had an effective shielding effect on the matrix. The above XPS chemical evidence is consistent with the morphological evolution from the striped processing state to the uniform coverage state in SEM.

[0036] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A cardiac stent material based on cobalt-chromium L605, characterized in that, Its composition includes the following raw materials: cobalt-chromium L605 alloy pipe, organic solvent, alkaline cleaning solution, acidic activation solution, neutralizing solution, electrolyte, citric acid passivation solution and tetraisopropyl titanate; The cobalt-chromium L605 alloy tube has an outer diameter of 1.2–2 mm, a wall thickness of 0.08–0.18 mm, and an inner diameter of 1.04–1.64 mm. The organic solvent is either anhydrous ethanol or isopropanol.

2. The cardiac stent material based on cobalt-chromium L605 according to claim 1, characterized in that, The alkaline cleaning solution is prepared by dissolving sodium carbonate and fatty alcohol polyoxyethylene ether in deionized water; the final concentration of sodium carbonate is 2-5 wt%; the final concentration of fatty alcohol polyoxyethylene ether is 0.1-0.3 wt%; the acidic activation solution is prepared by adding sulfuric acid to deionized water; the final concentration of sulfuric acid is 3-6 wt%.

3. The cardiac stent material based on cobalt-chromium L605 according to claim 1, characterized in that, The neutralizing solution is a 1-3 wt% sodium bicarbonate aqueous solution; the electrolyte is prepared by dissolving phosphoric acid and sulfuric acid in deionized water; the final concentration of the phosphoric acid is 65-75 wt%; and the final concentration of the sulfuric acid is 10-20 wt%.

4. The cardiac stent material based on cobalt-chromium L605 according to claim 1, characterized in that, The citric acid passivation solution is prepared by adding citric acid and hydrogen peroxide to deionized water; the final concentration of the citric acid is 4-8 wt%; and the final concentration of the hydrogen peroxide is 1-3 wt%.

5. A method for preparing a cobalt-chromium L605-based cardiac stent material according to any one of claims 1-4, characterized in that, Specifically, the following steps are included: S101: Place the cobalt-chromium L605 alloy pipe in an organic solvent for ultrasonic cleaning, then rinse with deionized water and dry. S102: Immerse the L605 alloy pipe that has been treated in step S101 in an alkaline cleaning solution and circulate the solution through the inner cavity of the pipe; then rinse with deionized water until no foam residue remains. S103: Simultaneously treat the outer surface and inner cavity of the pipe after step S102 with an acidic activation solution to remove the surface passivation layer and processing layer, and obtain an activated substrate; immediately rinse with deionized water after completion, and then neutralize with a neutralizing solution; S104: The pipe processed in step S103 is clamped in an electropolishing fixture, and the outer wall and inner cavity are electropolished using an electrolyte solution; after polishing, it is rinsed in multiple stages and neutralized using a neutralizing solution, and then cleaned and dried. S105: The pipes processed in step S104 are placed in a citric acid passivation solution for controlled passivation to form a passivation film; after passivation, they are rinsed and dried. S106: The pipes that have completed step S105 are subjected to film densification treatment in an oxidation source environment; then rinsed and dried. S107: Deposit a dense layer of nanoscale TiO2 on the tube passivation film after step S106; stabilize the film; then rinse and dry to obtain the cardiac stent material.

6. The method for preparing a cobalt-chromium L605-based cardiac stent material according to claim 5, characterized in that, In step S103, the specific operation of the acid activation solution treatment is as follows: the two ends of the pipe treated in step S102 are connected to the circulation loop through PTFE joints, and the acid activation solution is continuously pumped into the inner cavity of the pipe and returned to the storage bottle at a flow rate of 0.3 to 0.8 m / s using a peristaltic pump; at the same time, the entire pipe is immersed in the same acid activation solution to perform synchronous activation treatment on the outer wall for 1 to 3 minutes at room temperature.

7. The method for preparing a cobalt-chromium L605-based cardiac stent material according to claim 5, characterized in that, In step S104, the specific operation of the electropolishing treatment is as follows: The two ends of the pipe are sealed and connected using PTFE acid-resistant insulating clamps to form a liquid-flowing circuit within the inner cavity. A graphite cathode is arranged in the electropolishing tank, and the entire pipe is immersed in the electrolyte. A slender graphite cathode rod is inserted into the center of the inner cavity of the pipe, covered with an insulating sleeve, exposing only the effective working section, and ensuring that the cathode rod is concentric with the pipe wall. The electrolyte temperature is 35–45℃, the voltage is 8–15V, and the anode current density is 0.2–0.45A / cm². 2 The processing time is 60–120 seconds, and the linear velocity of the electrolyte in the inner cavity is 0.5–1.5 m / s.

8. The method for preparing a cobalt-chromium L605-based cardiac stent material according to claim 5, characterized in that, In step S104, the multi-stage rinsing operation is as follows: Stage 1 involves immediately immersing the outer wall in a large amount of deionized water and shaking for 30-60 seconds, followed by flushing the inner cavity with deionized water for 1-2 minutes at a linear velocity of 0.8-1.5 m / s; Stage 2 involves flushing the outer wall with flowing deionized water for 2-5 minutes, followed by flushing the inner cavity with deionized water for 2-5 minutes at the same flow rate; Stage 3 involves washing with neutralizing solution for 1-3 minutes, followed by simultaneous flushing of the inner cavity with neutralizing solution for 1-3 minutes at a linear velocity of 0.3-0.8 m / s; Stage 4 involves flushing the outer wall with deionized water for 2-5 minutes, followed by flushing the inner cavity with deionized water for 4-8 minutes at a linear velocity of 0.8-1.5 m / s; the pH of the final outer wall rinsing solution and the inner cavity effluent is 6.5-7.5; the conductivity of the final rinsing solution is ≤5 µS / cm.

9. The method for preparing a cobalt-chromium L605-based cardiac stent material according to claim 5, characterized in that, In step S105, the passivation treatment specifically involves: completely immersing the outer wall of the pipe in citric acid passivation solution; simultaneously circulating the passivation solution into the inner cavity, with a passivation temperature of 40–55°C, a passivation time of 25–45 min, and a circulating flow rate of 0.3–0.8 m / s within the inner cavity; In step S106, the membrane densification treatment specifically involves: immersing the pipe after step S105 in deionized water at 70–80°C, and circulating deionized water at the same temperature into the inner cavity for 10–25 min, with a circulating flow rate of 0.3–0.8 m / s within the inner cavity; In step S107, the membrane stabilization treatment specifically involves: air atmosphere treatment at 80–110°C for 10–30 min; and treatment at 120–180°C for 40–80 min.

10. The method for preparing a cobalt-chromium L605-based cardiac stent material according to claim 5, characterized in that, In step S107, the specific operation of depositing the TiO2 dense layer is as follows: S1: Dissolve tetraisopropyl titanate in anhydrous ethanol and stir until homogeneous to obtain a tetraisopropyl titanate solution; add deionized water and glacial acetic acid to anhydrous ethanol and mix to form a hydrolyzed phase, then slowly add it dropwise to the tetraisopropyl titanate solution over 5-10 min, bring the volume to a final volume with anhydrous ethanol, stir at 800 rpm until homogeneous, and age at room temperature for 40-80 min to obtain a sol. S2: Immerse the outer wall of the pipe treated with S106 in the sol for 40-90s, while simultaneously circulating the sol through the inner cavity at a linear velocity of 0.2-0.4m / s for 2-3min; lift and level at 1-3mm / s for 120-180s; pre-cur at 60-80℃ for 10min, and repeat the coating 2-3 times to achieve a final film thickness of 30-60nm; In step S1, the molar ratio of tetraisopropyl titanate, deionized water and glacial acetic acid is 1:3-5:0.4-0.8; the final concentration of tetraisopropyl titanate after being diluted with anhydrous ethanol is 0.1-0.15 mol / L.

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