Preparation method and application of a biodegradable medical composite magnesium alloy pipe

Abstract

This application relates to a method for preparing a biodegradable medical composite magnesium alloy tubing and its application, comprising: providing a high-purity magnesium outer layer billet with a magnesium purity ≥ 99.98 wt% and a low-zinc magnesium-zinc-calcium alloy inner layer billet containing 0.5-2.5 wt% Zn and 0.1-0.8 wt% Ca; setting a magnesium-based interface transition layer with a lower Zn and Ca content than the inner layer between the two to be composited surfaces; coaxially nesting the low-zinc magnesium-zinc-calcium alloy inner layer billet within the high-purity magnesium outer layer billet, and setting an extrusion mandrel in the central through hole to obtain a composite tubular billet; hot-extruded the composite tubular billet to obtain a composite tube blank; rolling the composite tube blank in multiple passes, and annealing it after deformation to obtain a biodegradable medical composite magnesium alloy tubing. The magnesium alloy tubing prepared by this application has a low initial degradation rate in the outer layer, high support strength in the inner layer, and the interface gradient transition zone reduces the risk of interlayer corrosion.

Description

Technical Field

[0001] This application relates to the field of alloy materials, and in particular to a method for preparing a biodegradable medical composite magnesium alloy tubing and its application. Background Technology

[0002] In recent years, biodegradable magnesium alloy vascular stents have attracted widespread attention because they can be gradually degraded and absorbed after providing mechanical support, avoiding the chronic inflammation and late-stage thrombosis caused by permanent stents. Magnesium is an essential trace element for the human body, and its degradation products can be safely metabolized, exhibiting good biocompatibility. Furthermore, the elastic modulus and radial support capacity of magnesium alloys are closer to the clinical requirements of metallic stents, effectively preventing vascular elastic recoil in the early stages of implantation.

[0003] However, commonly used magnesium-zinc alloys corrode rapidly in physiological environments, often losing their mechanical integrity before complete vascular tissue remodeling. While high-purity magnesium exhibits excellent corrosion resistance and cell compatibility, its low strength results in insufficient radial support for the tubing, making it prone to early collapse or shrinkage and failing to meet clinical requirements. To combine the advantages of both materials, current research has attempted to prepare composite tubing made from high-purity magnesium and magnesium alloys. However, the mechanical fitting or diffusion bonding processes employed generally suffer from poor interfacial bonding, susceptibility to galvanic corrosion, and complex procedures. Furthermore, these methods do not fully utilize the differences in grain size, texture orientation, and interfacial bonding between the inner and outer layers caused by dynamic recrystallization and deformation mechanisms during plastic deformation processes such as extrusion and drawing, making it difficult to achieve synergistic control of mechanical and degradation properties. Summary of the Invention

[0004] To improve the delamination problem caused by galvanic corrosion at the interface of high-purity magnesium and magnesium-zinc alloy composite pipes, this application provides a method for preparing biodegradable medical composite magnesium alloy pipes and their application.

[0005] This application provides a method for preparing a biodegradable medical composite magnesium alloy tubing, which adopts the following technical solution: A method for preparing a biodegradable medical composite magnesium alloy tubing includes the following steps: S1. Raw material preparation: Provide high-purity magnesium outer layer billet and low-zinc magnesium-zinc-calcium alloy inner layer billet, wherein the magnesium purity of the high-purity magnesium outer layer billet is ≥99.98wt%, and the low-zinc magnesium-zinc-calcium alloy inner layer billet includes Zn 0.5-2.5wt%, Ca 0.1-0.8wt%, and the balance Mg; S2. Interface preconstruction: A magnesium-based interface transition layer is set between the high-purity magnesium outer layer billet and the low-zinc magnesium-zinc-calcium alloy inner layer billet to be composite contact surface. The Zn and Ca contents in the magnesium-based interface transition layer are lower than the Zn and Ca contents in the low-zinc magnesium-zinc-calcium alloy inner layer billet. S3. Nested assembly: The low-zinc magnesium-zinc calcium alloy inner layer blank is coaxially nested inside the high-purity magnesium outer layer blank, and an extrusion core rod is set in the central through hole to obtain a composite tubular blank. S4. Hot extrusion composite: Hot extrusion is performed on the composite tubular blank to obtain the composite tubular blank; S5. Deformation, sizing, and annealing: The composite tube blank is rolled in multiple passes and then annealed after deformation to obtain a biodegradable medical composite magnesium alloy tube with an outer layer of high-purity magnesium and an inner layer of low-zinc magnesium-zinc-calcium alloy.

[0006] By adopting the above technical solution, a magnesium-based interface transition layer is pre-placed between the high-purity magnesium outer layer and the low-zinc Mg-Zn-Ca inner layer. This layer undergoes hot extrusion and multi-pass rolling annealing to allow it to plastically deform synchronously with the substrates on both sides, forming a gradient transition zone with gradually changing Zn and Ca content at the interface. This gradient transition zone reduces the corrosion potential difference between the outer and inner layers, thereby inhibiting interfacial galvanic corrosion and interlayer delamination. Simultaneously, the high-purity magnesium outer layer improves the low degradation rate and biocompatibility in the early stages of implantation, while the low-zinc magnesium-zinc-calcium alloy inner layer provides sufficient radial support strength. These three elements work synergistically to achieve a match between degradation rate and mechanical properties during the vascular remodeling cycle.

[0007] Preferably, the low-zinc magnesium-zinc-calcium alloy inner layer billet contains 1.0-1.5 wt% Zn, 0.3-0.5 wt% Ca, and the balance is Mg.

[0008] By adopting the above technical solution, and preferably with Zn and Ca contents within the above range, the alloy has a better match between strength and plasticity, which helps to control the degradation rate of the inner layer itself and reduces the phenomenon that excessive Zn content leads to an increase in the second phase, which accelerates local corrosion, or excessive Ca content introduces coarse Ca-containing phases, which affects processing performance.

[0009] Preferably, the cross-sectional area ratio of the high-purity magnesium outer layer blank to the low-zinc magnesium-zinc-calcium alloy inner layer blank is (4-10):(1-4); the thickness of the high-purity magnesium layer in the resulting pipe is 50-600μm, and the thickness of the low-zinc magnesium-zinc-calcium alloy layer is 50-500μm.

[0010] By adopting the above technical solution, the outer high-purity magnesium effectively coats the inner layer in the early stage of degradation, delaying the penetration of corrosive media into the interface and inner layer; the inner layer retains sufficient thickness to bear mechanical support, reducing the overall radial strength reduction caused by the inner layer being too thin.

[0011] Preferably, the magnesium-based interface transition layer is a Mg-Zn-Ca transition alloy, wherein the Zn content in the Mg-Zn-Ca transition alloy is 10%-80% of the Zn content in the low-zinc magnesium-zinc-calcium alloy inner layer blank, and the Ca content is 10%-80% of the Ca content in the low-zinc magnesium-zinc-calcium alloy inner layer blank.

[0012] By adopting the above technical solution, the interface transition layer adopts a Mg-Zn-Ca transition alloy, with Zn and Ca contents ranging from 10% to 80% of the inner layer. Its composition is between the high-purity magnesium of the outer layer and the Mg-Zn-Ca of the inner layer. During hot extrusion and subsequent rolling annealing, the Zn and Ca elements in the transition layer diffuse to both sides in a limited manner, forming a compositional gradient in the interface region, which helps to gradually transition the corrosion potential along the radial direction.

[0013] Preferably, the magnesium-based interface transition layer is a Mg-Zn-Ca transition alloy foil, which is disposed between the inner surface of the high-purity magnesium outer layer blank and the outer surface of the low-zinc magnesium-zinc-calcium alloy inner layer blank, and the thickness of the Mg-Zn-Ca transition alloy foil before hot extrusion is 5-80 μm.

[0014] By adopting the above technical solution and using transition alloy foil as the interface layer, the operation is simple and suitable for the assembly of tubular blanks. The foil deforms synchronously with the flow of the inner and outer metal layers during hot extrusion, which can form a continuous interface transition zone and reduce the occurrence of local poor bonding caused by discontinuous interface layers.

[0015] Preferably, the magnesium-based interface transition layer is a Mg-Zn-Ca transition alloy powder layer, which is formed by coating Mg-Zn-Ca alloy powder onto the inner surface of a high-purity magnesium outer layer blank and / or the outer surface of a low-zinc magnesium-zinc-calcium alloy inner layer blank, followed by vacuum degreasing and pre-compaction.

[0016] By adopting the above technical solution, the alloy powder coating method forms an interface transition layer, which is suitable for blanks with different diameters and surface conditions. After coating, vacuum degreasing and pre-compacting can reduce organic residues and interlayer porosity, and reduce the possibility of inclusions or unbonded defects at the interface after extrusion.

[0017] Preferably, in step S4, the hot extrusion temperature is 350-450℃ and the extrusion ratio is 1:(100-400); before hot extrusion, the composite tubular billet is preheated for 10-60 minutes under inert gas protection.

[0018] By adopting the above technical solution, the extrusion composite conditions are preferably within the above range. Magnesium and magnesium alloys have good plastic flowability. The three-layer material can fully fill the interface gaps and undergo dynamic recrystallization, which promotes the interfacial metallurgical bonding. Furthermore, preheating under inert gas protection before extrusion helps to reduce the oxidation of the billet surface, thereby improving the composite quality.

[0019] Preferably, in step S5, during multi-pass rolling, the deformation amount of each pass is 5%-30%, and the cumulative deformation amount is 20%-80%; the annealing temperature is 180-250℃, and the holding time is 5-30min.

[0020] By adopting the above technical solution, and preferably within the range of rolling deformation, the microstructure of the interface region can be further refined. Furthermore, preferably within the range of annealing temperature and holding time, it helps to eliminate the processing stress generated by rolling, promote grain recovery and local recrystallization near the interface, and improve the dimensional stability of the pipe.

[0021] Preferably, in step S5, after annealing, a micro-arc oxidation treatment is performed on the outer surface of the pipe to form a micro-arc oxidation ceramic layer; the micro-arc oxidation ceramic layer is formed only on the outer surface of the pipe and has a thickness of 2-5 μm.

[0022] By adopting the above technical solution, micro-arc oxidation treatment is performed on the outer surface of the pipe after annealing to form a ceramic layer, which slows down the corrosion rate of the outer surface of the pipe in the early stage of implantation. Moreover, the ceramic layer is only formed on the outer surface, which reduces the difficulties and unevenness in the preparation of the inner hole coating.

[0023] Preferably, after the micro-arc oxidation treatment, a polycaprolactone sealing layer is coated on the outer surface of the micro-arc oxidized ceramic layer, the thickness of which is 0.5-3 μm.

[0024] By adopting the above technical solution, coating the ceramic layer surface with polycaprolactone can fill the micropores on the ceramic layer surface, reduce the channels through which corrosive media directly contact the magnesium matrix. Polycaprolactone itself is degradable and has good flexibility, which improves the sealing effect and enhances the conformal deformation ability of the coating, further improving the corrosion resistance stability of the pipe in the early stage of implantation.

[0025] In summary, this application includes at least one of the following beneficial technical effects: The three-layer structure design of high-purity magnesium outer layer, low-zinc Mg-Zn-Ca inner layer and magnesium-based interface transition layer enables the pipe to have high radial support in the early stage. At the same time, the high-purity magnesium outer layer and the interface gradient structure together reduce the risk of initial corrosion and interface galvanic corrosion. By synergistically controlling the deformation and dynamic recrystallization behavior of the inner and outer layers through hot extrusion, multi-pass rolling and short-time annealing, a compositional gradient and recrystallization structure continuity are formed at the interface, thereby improving the stability of the interface bonding. A thin micro-arc oxide ceramic layer and a sealing layer are formed on the outer surface of the pipe, while no coating is applied to the inner surface. This improves the initial corrosion resistance of the outer surface and reduces the difficulty in preparing the inner hole coating and the risk of cracking during subsequent processing. Detailed Implementation

[0026] Figure 1 This is an interfacial metallographic image of the biodegradable medical composite magnesium alloy tubing obtained in Example 1 of this application.

[0027] Figure 2 This is a cross-sectional metallographic image of the biodegradable medical composite magnesium alloy tubing obtained in Example 2 of this application. Detailed Implementation

[0028] The present application will be further described in detail below with reference to the embodiments: Raw material description: All raw materials used in the examples are commercially available; Example 1

[0029] S1. Raw material preparation: High-purity magnesium outer layer billet with a magnesium purity of 99.99wt% is used and processed into a hollow cylindrical billet with an outer diameter of 20mm, a length of 30mm, and a central inner hole diameter of 10mm; under argon protection, high-purity magnesium ingot is melted at 720℃ and held for 20min, pure zinc particles and Mg-Ca intermediate alloy are added, stirred evenly and poured into a preheated mold, cooled and machined to obtain a low-zinc magnesium zinc-calcium alloy inner layer billet. The composition of the low-zinc magnesium zinc-calcium alloy inner layer billet is Zn 0.5wt%, Ca 0.1wt% and balance Mg, and it is processed into a hollow cylindrical billet with an outer diameter of 10mm, a length of 30mm, and a central inner hole diameter of 3mm. S2. Interface preconstruction: A 5μm Mg-Zn-Ca transition alloy foil is used as the magnesium-based interface transition layer. The composition of the Mg-Zn-Ca transition alloy foil is 0.05wt% Zn, 0.01wt% Ca, and the balance Mg. The Zn and Ca contents in the transition alloy foil are 10% of the Zn and Ca contents in the low-zinc magnesium-zinc-calcium alloy inner layer blank, respectively. The Mg-Zn-Ca transition alloy foil is placed and attached to the inner surface of the high-purity magnesium outer layer blank in an argon glove box. S3. Nested assembly: The low-zinc magnesium-zinc-calcium alloy inner layer billet is coaxially nested inside the high-purity magnesium outer layer billet, with the Mg-Zn-Ca transition alloy foil located between the two; a heat-resistant steel extrusion core rod coated with boron nitride release agent is inserted into the central through hole of the low-zinc magnesium-zinc-calcium alloy inner layer billet to obtain a composite tubular billet. S4. Hot extrusion composite: The composite tubular billet is placed in an argon protective atmosphere and preheated at 350℃ for 10 min. Then, it is hot extruded at 350℃ with an extrusion ratio of 1:100 to obtain a composite tubular billet with an outer layer of high-purity magnesium, an inner layer of low-zinc magnesium-zinc-calcium alloy, and a magnesium-based interface transition layer in the middle. S5. Deformation, Sizing, and Annealing: The composite tube blank is rolled in multiple passes, with a deformation of 5% per pass and a cumulative deformation of 20%. After rolling, it is annealed at 180℃ for 5 minutes under argon protection. After cooling to room temperature, a polytetrafluoroethylene (PTFE) core wire is inserted into the inner hole of the annealed tube and both ends are sealed, exposing only the outer surface of the tube. A short-time micro-arc oxidation treatment is performed in a phosphate-containing micro-arc oxidation electrolyte to form a 2μm thick micro-arc oxidation ceramic layer on the outer surface of the tube. The tube is then removed, rinsed with deionized water, and dried. After removing the inner hole sealing core wire, it is confirmed that there is no coating on the inner surface. Then, the outer surface of the tube is dipped in a 1wt% polycaprolactone (CAS No.: 24980-41-4) solution. After removal, the solvent is evaporated at room temperature in the absence of dust, and then vacuum dried at 35℃ for 6 hours to form a 0.5μm thick polycaprolactone sealing layer on the outer surface of the micro-arc oxidation ceramic layer, resulting in a biodegradable medical composite magnesium alloy tube. Example 2

[0030] S1. Raw material preparation: High-purity magnesium outer layer billet with a magnesium purity of 99.99wt% is used and processed into a hollow cylindrical billet with an outer diameter of 30mm, a length of 40mm, and a central inner hole diameter of 16mm; under argon protection, high-purity magnesium ingot is melted at 720℃ and held for 20min, pure zinc particles and Mg-Ca intermediate alloy are added, stirred evenly and poured into a preheated mold, cooled and machined to obtain a low-zinc magnesium-zinc-calcium alloy inner layer billet. The composition of the low-zinc magnesium-zinc-calcium alloy inner layer billet is Zn 2.5wt%, Ca 0.8wt% and balance Mg, and it is processed into a hollow cylindrical billet with an outer diameter of 16mm, a length of 40mm, and a central inner hole diameter of 5mm. S2. Interface Preconstruction: Mg-Zn-Ca transition alloy powder is used as the raw material for the magnesium-based interface transition layer. The composition of the Mg-Zn-Ca transition alloy powder is 2.0wt% Zn, 0.64wt% Ca, and the balance Mg. The Zn and Ca contents in the transition alloy powder are 80% of the Zn and Ca contents in the low-zinc magnesium-zinc-calcium alloy inner layer blank, respectively. Mg-Zn-Ca transition alloy powder with a particle size of 15μm is dispersed in anhydrous ethanol to form a slurry. The slurry is uniformly coated on the inner surface of the high-purity magnesium outer layer blank and the outer surface of the low-zinc magnesium-zinc-calcium alloy inner layer blank. Then, it is vacuum treated at 80℃ and -0.09MPa for 60min to remove the ethanol. Then, it is radially pre-compacted in an inert atmosphere to form a Mg-Zn-Ca transition alloy powder layer as the magnesium-based interface transition layer. S3. Nested assembly: The low-zinc magnesium-zinc-calcium alloy inner layer blank is coaxially nested inside the high-purity magnesium outer layer blank; a heat-resistant steel extrusion core rod coated with boron nitride release agent is inserted into the central through hole of the low-zinc magnesium-zinc-calcium alloy inner layer blank to obtain a composite tubular blank. S4. Hot extrusion composite: The composite tubular blank is preheated at 450℃ for 60 minutes under argon protection, and then hot extruded at 450℃ with an extrusion ratio of 1:400 to obtain the composite tubular blank. S5. Deformation, Sizing, and Annealing: The composite tube blank is rolled in multiple passes, with a deformation of 30% per pass and a cumulative deformation of 80%. After rolling, it is annealed at 250℃ for 30 minutes under vacuum. After cooling to room temperature, a polytetrafluoroethylene (PTFE) core wire is inserted into the inner hole of the annealed tube and both ends are sealed, leaving only the outer surface of the tube exposed. Micro-arc oxidation is performed in a phosphate-containing micro-arc oxidation electrolyte to form a 5μm thick micro-arc oxidation ceramic layer on the outer surface of the tube. The tube is then removed, rinsed with deionized water, and dried. After removing the inner hole sealing core wire, it is confirmed that there is no coating on the inner surface. The outer surface of the tube is then dipped in a 6wt% polycaprolactone solution. After removal, the solvent is evaporated at room temperature in the absence of dust, and then vacuum dried at 40℃ for 8 hours to form a 3μm thick polycaprolactone sealing layer on the outer surface of the micro-arc oxidation ceramic layer, thus obtaining a biodegradable medical composite magnesium alloy tube. Example 3

[0031] S1. Raw material preparation: High-purity magnesium outer layer billet with a magnesium purity of 99.99wt% is used and processed into a hollow cylindrical billet with an outer diameter of 24mm, a length of 35mm, and a central inner hole diameter of 12mm; under argon protection, high-purity magnesium ingot is melted at 720℃ and held for 20min, pure zinc particles and Mg-Ca intermediate alloy are added, stirred evenly and poured into a preheated mold, cooled and machined to obtain a low-zinc magnesium-zinc-calcium alloy inner layer billet. The composition of the low-zinc magnesium-zinc-calcium alloy inner layer billet is Zn 1.25wt%, Ca 0.4wt% and balance Mg, and it is processed into a hollow cylindrical billet with an outer diameter of 12mm, a length of 35mm, and a central inner hole diameter of 4mm. S2. Interface preconstruction: A 40μm thick Mg-Zn-Ca transition alloy foil is used as the magnesium-based interface transition layer. The composition of the Mg-Zn-Ca transition alloy foil is 0.56wt% Zn, 0.18wt% Ca, and the balance Mg. The Zn and Ca contents in the transition alloy foil are 45% of the Zn and Ca contents in the low-zinc magnesium-zinc-calcium alloy inner layer blank, respectively. The Mg-Zn-Ca transition alloy foil is placed and attached to the inner surface of the high-purity magnesium outer layer blank in an argon glove box. S3. Nested assembly: The low-zinc magnesium-zinc-calcium alloy inner layer blank is coaxially nested inside the high-purity magnesium outer layer blank; a heat-resistant steel extrusion core rod coated with boron nitride release agent is inserted into the central through hole of the low-zinc magnesium-zinc-calcium alloy inner layer blank to obtain a composite tubular blank. S4. Hot extrusion composite: The composite tubular blank is placed in an argon protective atmosphere and preheated at 400℃ for 30 minutes. Then, it is hot extruded at 400℃ with an extrusion ratio of 1:250 to obtain the composite tubular blank. S5. Deformation, Sizing, and Annealing: The composite tube blank is rolled in four passes, with a deformation of approximately 15% per pass and a cumulative deformation of 50%. After rolling, it is annealed at 210℃ for 15 minutes under vacuum. After cooling to room temperature, a polytetrafluoroethylene (PTFE) core wire is inserted into the inner hole of the annealed tube and both ends are sealed, leaving only the outer surface of the tube exposed. Micro-arc oxidation is performed in a phosphate-containing micro-arc oxidation electrolyte to form a 3.5μm thick micro-arc oxidation ceramic layer on the outer surface of the tube. The tube is then removed, rinsed with deionized water, and dried. After removing the inner hole sealing core wire, it is confirmed that there is no coating on the inner surface. The outer surface of the tube is then dipped in a 3wt% polycaprolactone solution. After removal, the solvent is evaporated at room temperature in the absence of dust, and then vacuum dried at 38℃ for 8 hours to form a 1.5μm thick polycaprolactone sealing layer on the outer surface of the micro-arc oxidation ceramic layer, resulting in a biodegradable medical composite magnesium alloy tube. Example 4

[0032] Example 4 is based on Example 3. The difference between Example 4 and Example 3 is that the thickness of the Mg-Zn-Ca transition alloy foil before hot extrusion in Example 4 is 2 μm. Example 5

[0033] Example 5 is based on Example 3. The difference between Example 5 and Example 3 is that the thickness of the Mg-Zn-Ca transition alloy foil before hot extrusion in Example 5 is 120 μm. Example 6

[0034] Example 6 is based on Example 3. The difference between Example 6 and Example 3 is that the hot extrusion temperature in Example 6 is 300°C. Example 7

[0035] Example 7 is based on Example 3. The difference between Example 7 and Example 3 is that the hot extrusion temperature in Example 7 is 500°C. Example 8

[0036] Example 8 is based on Example 3. The difference between Example 8 and Example 3 is that the annealing temperature in Example 8 is 120°C. Example 9

[0037] Example 9 is based on Example 3. The difference between Example 9 and Example 3 is that the annealing temperature in Example 9 is 320°C. Example 10

[0038] Example 10 is based on Example 3. The difference between Example 10 and Example 3 is that the thickness of the micro-arc oxidation ceramic layer in Example 10 is 1 μm. Example 11

[0039] Example 11 is based on Example 3. The difference between Example 11 and Example 3 is that the thickness of the micro-arc oxidation ceramic layer in Example 11 is 8 μm. Example 12

[0040] Example 12 is based on Example 3. The difference between Example 12 and Example 3 is that no polycaprolactone sealing layer is provided in Example 12. Example 13

[0041] Example 13 is based on Example 3. The difference between Example 13 and Example 3 is that in Example 13, the outer high-purity magnesium billet is replaced with a low-zinc magnesium-zinc-calcium alloy billet with the same composition as the inner layer. Example 14

[0042] Example 14 is based on Example 3. The difference between Example 14 and Example 3 is that in Example 14, the Zn content in the low zinc magnesium zinc calcium alloy inner layer billet is 3.5 wt%, the Ca content is 0.4 wt%, and the balance is Mg. The Zn content and Ca content in the magnesium-based interface transition layer are 45% of the Zn content and Ca content in the inner layer billet, respectively. Example 15

[0043] Example 15 is based on Example 3. The difference between Example 15 and Example 3 is that in Example 15, the Zn content in the low-zinc magnesium-zinc-calcium alloy inner layer billet is 1.25wt%, the Ca content is 1.2wt%, and the balance is Mg. The Zn content and Ca content in the magnesium-based interface transition layer are 45% of the Zn content and Ca content in the inner layer billet, respectively.

[0044] Comparative Example 1 Comparative Example 1 is based on Example 3. In Comparative Example 1, the magnesium-based interface transition layer is replaced with a Mg-Zn-Ca alloy foil with the same composition as the low-zinc magnesium-zinc-calcium alloy inner layer blank, which has the composition of Zn 1.25wt%, Ca 0.4wt% and balance Mg.

[0045] Comparative Example 2 Comparative Example 2 is based on Example 3, except that the magnesium-based interface transition layer is replaced with pure magnesium foil.

[0046] Comparative Example 3 Comparative Example 3 is based on Example 3, but without the magnesium-based interface transition layer.

[0047] Comparative Example 4 Comparative Example 4 is based on Example 3. Comparative Example 4 does not involve the preparation of a composite structure. It only uses high-purity magnesium billet with a magnesium purity of 99.99 wt%. After the same hot extrusion, rolling, annealing, and micro-arc oxidation and polycaprolactone sealing treatment on the outer surface, a single-layer high-purity magnesium pipe is obtained.

[0048] Comparative Example 5 Comparative Example 5 is based on Example 3. However, Comparative Example 5 does not use a high-purity magnesium outer layer and a magnesium-based interface transition layer. It only uses a low-zinc magnesium-zinc-calcium alloy billet with Zn 1.25wt%, Ca 0.4wt%, and the balance Mg. After the same hot extrusion, rolling, annealing, and micro-arc oxidation and polycaprolactone sealing treatment on the outer surface, a single-layer low-zinc magnesium-zinc-calcium alloy pipe is obtained. Example

[0049] The composite magnesium alloy tube prepared in Example 3 was laser-cut into a stent skeleton structure, and then electrochemically polished and cleaned to obtain a biodegradable magnesium alloy vascular stent.

[0050] Performance testing The following performance tests were performed on the samples of Examples 1-15 and Comparative Examples 1-5: (1) Radial compression support performance Cut short pipe samples with a length of 5 mm from each group of pipes and place them between two parallel pressure plates of a universal testing machine, ensuring that the pipe axis is parallel to the pressure plates. Compress the pipe at a speed of 0.1 mm / min until the outer diameter of the pipe is reduced by 10%. Record the radial compression force per unit length and the elastic recovery rate after unloading. Test each sample 3 times, take the average value, and fill in the test results in Table 1. (2) Tensile properties Using GB / T 228.1-2021 as the testing reference, the tensile properties of the specimens were tested. Each specimen was tested 3 times, and the average value was taken. The test results were filled in Table 1. (3) In vitro degradation and pH changes Using GB / T 16886.12-2023, GB / T 16886.15-2022, and GB / T 6920-1986 as testing references, phosphate buffer, Hank's simulated body fluid, or other physiological simulated solutions were used as immersion media. After the samples were cleaned, dried, and weighed with anhydrous ethanol, the sample surface area was divided into 1 cm³ of immersion solution volume. 2 Soak the sample in 20 mL of solution at 37±1℃ for 28 days. After 28 days, remove the solution, measure the pH value, remove the corrosion products, weigh the sample, and calculate the weight loss rate. Test each sample three times, take the average value, and fill in the test results in Table 1.

[0051] Table 1 Performance test results of Examples 1-15 and Comparative Examples 1-5

[0052] As shown in Table 1, the radial compressive force of Examples 1-3 is 0.72-0.91 N / mm, the elastic recovery rate is 80.8%-88.2%, and the weight loss rate after 28 days of immersion is 7.5%-12.4%, indicating that the composite magnesium alloy pipe prepared in this application has good mechanical support and controllable degradation comprehensive performance.

[0053] In Examples 4 and 5, the thickness of the Mg-Zn-Ca transition alloy foil before hot extrusion is not within the range specified in this application. When the transition alloy foil is too thin, the interfacial composition gradient and metallurgical bonding continuity are insufficient, and the mechanical properties and degradation stability decrease. When the transition alloy foil is too thick, a wider composition transition zone and local microstructure inhomogeneity are formed.

[0054] The hot extrusion temperatures in Examples 6 and 7 are not within the range specified in this application. When the hot extrusion temperature is insufficient, the magnesium alloy has insufficient plastic flow capacity and insufficient dynamic recrystallization at the interface closure. When the hot extrusion temperature is too high, grain growth and excessive interface diffusion occur.

[0055] In Examples 8 and 9, the annealing temperatures are not within the range specified in this application. When the annealing temperature is insufficient, the residual rolling stress is not released sufficiently, and stress-assisted corrosion occurs during degradation. When the annealing temperature is too high, the grains coarsen and the strengthening effect is weakened.

[0056] In Examples 10 and 11, the thickness of the micro-arc oxidation ceramic layer is not within the range specified in this application. When the thickness of the micro-arc oxidation ceramic layer is too thin, the barrier effect is insufficient; when the thickness of the micro-arc oxidation ceramic layer is too thick, the excessively thick coating increases the risk of brittle cracking under subsequent compression deformation.

[0057] In Example 12, the absence of a polycaprolactone sealing layer allowed corrosive media to penetrate the magnesium matrix more easily.

[0058] In Example 13, the outer layer was replaced with a low-zinc magnesium-zinc-calcium alloy of the same composition, which improved the overall strength. However, the outer layer no longer had the barrier effect of the slow initial degradation of high-purity magnesium, and the pH and weight loss rate increased significantly.

[0059] In Example 14, the Zn content was 3.5 wt%, the second phase increased, local microgalvanic corrosion was enhanced, degradation was the fastest and elongation decreased.

[0060] In Example 15, the Ca content was 1.2 wt%, and the coarse Ca-containing phase and uneven structure resulted in decreased plasticity and corrosion stability.

[0061] Comparative Example 1 uses a transition alloy foil with the same composition as the inner layer, which fails to form an effective composition gradient between the high-purity magnesium outer layer and the inner alloy layer, resulting in an increase in the interfacial galvanic corrosion rate.

[0062] Comparative Example 2 used pure magnesium foil, but the transition layer was too close to the outer layer, and there was a significant difference in composition between the high-purity magnesium and the inner low-zinc alloy, resulting in decreased stability.

[0063] Comparative Example 3, without a transition layer, suffers from decreased interface bonding and component buffering performance.

[0064] Comparative Example 4 is a single-layer high-purity magnesium pipe, which degrades slowly and has a high elongation, but its radial compressive strength and tensile strength are significantly insufficient, making it difficult to provide sufficient early support.

[0065] Comparative Example 5 is a single-layer low-zinc magnesium-zinc-calcium alloy pipe with high mechanical strength, but its degradation rate is too fast and its pH rises significantly.

[0066] Combination Figure 1 It can be seen that the biodegradable medical composite magnesium alloy tubing prepared in Example 1 has an outer high-purity magnesium layer with a thickness of about 500 μm and an inner low-zinc magnesium alloy layer with a thickness of about 100 μm, and the outer layer can cover the inner layer.

[0067] Combination Figure 2 It can be seen that the biodegradable medical composite magnesium alloy tubing prepared in Example 2 has an outer layer of high-purity magnesium that completely covers the inner layer of low-zinc magnesium alloy, with a clear interface boundary.

[0068] This specific embodiment is merely an explanation of this application and is not intended to limit it. Based on the above description, those skilled in the art can make various changes and modifications without departing from the technical concept of this application. The technical scope of this application is not limited to the contents of the specification but must be determined according to the scope of the claims.

Claims

1. A method for preparing a biodegradable medical composite magnesium alloy tubing, characterized in that: Includes the following steps: S1. Raw material preparation: Provide high-purity magnesium outer layer billet and low-zinc magnesium-zinc-calcium alloy inner layer billet, wherein the magnesium purity of the high-purity magnesium outer layer billet is ≥99.98wt%, and the low-zinc magnesium-zinc-calcium alloy inner layer billet includes Zn 0.5-2.5wt%, Ca 0.1-0.8wt%, and the balance Mg; S2. Interface preconstruction: A magnesium-based interface transition layer is set between the high-purity magnesium outer layer billet and the low-zinc magnesium-zinc-calcium alloy inner layer billet to be composite contact surface. The Zn and Ca contents in the magnesium-based interface transition layer are lower than the Zn and Ca contents in the low-zinc magnesium-zinc-calcium alloy inner layer billet. S3. Nested assembly: The low-zinc magnesium-zinc calcium alloy inner layer blank is coaxially nested inside the high-purity magnesium outer layer blank, and an extrusion core rod is set in the central through hole to obtain a composite tubular blank. S4. Hot extrusion composite: Hot extrusion is performed on the composite tubular blank to obtain the composite tubular blank; S5. Deformation, sizing, and annealing: The composite tube blank is rolled in multiple passes and then annealed after deformation to obtain a biodegradable medical composite magnesium alloy tube with an outer layer of high-purity magnesium and an inner layer of low-zinc magnesium-zinc-calcium alloy.

2. The method for preparing a biodegradable medical composite magnesium alloy tubing according to claim 1, characterized in that: The low-zinc magnesium-zinc-calcium alloy inner layer billet contains 1.0-1.5 wt% Zn, 0.3-0.5 wt% Ca, and the balance is Mg.

3. The method for preparing a biodegradable medical composite magnesium alloy tubing according to claim 1, characterized in that: The cross-sectional area ratio of the high-purity magnesium outer layer blank to the low-zinc magnesium-zinc-calcium alloy inner layer blank is (4-10):(1-4); the thickness of the high-purity magnesium layer in the resulting pipe is 50-600μm, and the thickness of the low-zinc magnesium-zinc-calcium alloy layer is 50-500μm.

4. The method for preparing a biodegradable medical composite magnesium alloy tubing according to claim 1, characterized in that: The magnesium-based interface transition layer is a Mg-Zn-Ca transition alloy, wherein the Zn content in the Mg-Zn-Ca transition alloy is 10%-80% of the Zn content in the low-zinc magnesium-zinc-calcium alloy inner layer blank, and the Ca content is 10%-80% of the Ca content in the low-zinc magnesium-zinc-calcium alloy inner layer blank.

5. The method for preparing a biodegradable medical composite magnesium alloy tubing according to claim 4, characterized in that: The magnesium-based interface transition layer is a Mg-Zn-Ca transition alloy foil, which is sandwiched between the inner surface of the high-purity magnesium outer layer blank and the outer surface of the low-zinc magnesium-zinc-calcium alloy inner layer blank, and the thickness of the Mg-Zn-Ca transition alloy foil before hot extrusion is 5-80 μm.

6. The method for preparing a biodegradable medical composite magnesium alloy tubing according to claim 4, characterized in that: The magnesium-based interface transition layer is a Mg-Zn-Ca transition alloy powder layer, which is formed by coating Mg-Zn-Ca alloy powder onto the inner surface of a high-purity magnesium outer layer blank and / or the outer surface of a low-zinc magnesium-zinc-calcium alloy inner layer blank, followed by vacuum degreasing and pre-compaction.

7. The method for preparing a biodegradable medical composite magnesium alloy tubing according to claim 1, characterized in that: In step S4, the hot extrusion temperature is 350-450℃ and the extrusion ratio is 1:(100-400); before hot extrusion, the composite tubular billet is preheated for 10-60 minutes under inert gas protection.

8. The method for preparing a biodegradable medical composite magnesium alloy tubing according to claim 1, characterized in that: In step S5, during multi-pass rolling, the deformation amount of each pass is 5%-30%, and the cumulative deformation amount is 20%-80%; the annealing temperature is 180-250℃, and the holding time is 5-30min.

9. The method for preparing a biodegradable medical composite magnesium alloy tubing according to claim 1, characterized in that: In step S5, after annealing, a micro-arc oxidation treatment is performed on the outer surface of the pipe to form a micro-arc oxidation ceramic layer; the micro-arc oxidation ceramic layer is formed only on the outer surface of the pipe and has a thickness of 2-5 μm; the method for preparing a biodegradable medical composite magnesium alloy pipe is characterized in that: after the micro-arc oxidation treatment, a polycaprolactone sealing layer is coated on the outer surface of the micro-arc oxidation ceramic layer, and the thickness of the polycaprolactone sealing layer is 0.5-3 μm.

10. The application of the biodegradable medical composite magnesium alloy tubing prepared by the method according to any one of claims 1-9 in the preparation of biodegradable vascular stents or cavity support devices.

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