A medical catheter having a composite sandwich structure and a method of making the same

Abstract

This invention discloses a medical catheter with a composite sandwich structure and its preparation method, comprising a catheter base and a sandwich composite structure bonded to the outer surface of the catheter base. The sandwich composite structure, from the inside out, comprises: an inner polyimide layer coated on the outer surface of the catheter base; a polyether block amide intermediate layer coated on the outer surface of the inner polyimide layer; and an outer polyimide layer coated on the outer surface of the polyether block amide intermediate layer. The inner polyimide layer, the polyether block amide intermediate layer, and the outer polyimide layer are formed into an integral structure through a combination of chemical bonding and physical interlocking. This invention achieves multi-layer functional synergy while ensuring strong interlayer bonding, thereby improving the overall performance of the catheter in complex vascular environments. It exhibits excellent pushing force, torsional control, flexibility, and flexural strength, with a smooth inner wall and structural stability.

Description

Technical Field

[0001] This invention relates to the field of medical device technology, and in particular to a medical catheter with a composite sandwich structure and its preparation method. Background Technology

[0002] In interventional medicine, such as cardiovascular, neurological, and peripheral vascular interventional surgeries, catheters are core instruments. Their performance directly affects the success rate and safety of the procedure. To achieve good pushing force and torque transmission, the catheter wall needs to have high rigidity and strength. However, this can lead to an overly rigid catheter, resulting in poor flexibility when passing through tortuous blood vessels, causing significant irritation to the vascular wall, and even posing a risk of perforation. Conversely, using overly soft materials in pursuit of flexibility can make catheter pushing difficult, causing it to accumulate in the blood vessel like "noodles" and fail to reach the target location. Currently, most common catheters are made of a single polymer material or a simple coating structure. These types of catheters are prone to problems such as high frictional resistance, insufficient flexibility, and easy kinking when pushed through tortuous blood vessels, affecting the precision and safety of the surgical procedure.

[0003] To further improve catheter performance, existing technologies have attempted to employ multi-layered composite structures or surface coatings, such as coating the catheter surface with a polyimide coating to improve strength and temperature resistance, or coating it with a hydrophilic coating to reduce the coefficient of friction. However, the adhesion between a single coating and the substrate is limited, and the coating is prone to peeling or cracking under repeated bending or long-term use. Moreover, the coating has a single function and it is difficult to simultaneously achieve strength, flexibility, and surface lubrication. In addition, if different coatings are only physically stacked together, the interfacial adhesion is weak, which can easily lead to interlayer separation, affecting the reliability and durability of the overall catheter structure. Summary of the Invention

[0004] The purpose of this invention is to provide a medical catheter with a composite sandwich structure and its preparation method. While achieving multi-layer functional synergy, it ensures strong interlayer bonding, thereby improving the overall performance of the catheter in complex vascular environments. It has excellent pushing force, torsional control, flexibility and flexural strength, smooth inner wall and stable structure.

[0005] The above-mentioned technical objective of the present invention is achieved through the following technical solution: a medical catheter with a composite sandwich structure, comprising a tube base and a sandwich composite structure composited on the outer surface of the tube base, wherein the sandwich composite structure comprises, from the inside to the outside:

[0006] An inner polyimide layer is coated on the outer surface of the tube substrate;

[0007] A polyether block amide intermediate layer is coated on the outer surface of the inner polyimide layer;

[0008] An outer polyimide layer is coated on the outer surface of the polyether block amide intermediate layer;

[0009] The inner polyimide layer, the polyether block amide intermediate layer, and the outer polyimide layer form an integral structure through a combination of chemical bonding and physical interlocking.

[0010] By adopting the above technical solution, the inner and outer polyimide layers provide a high-strength, high-modulus structural framework, ensuring the catheter's pushing force and flexural strength. The polyether block amide intermediate layer contributes excellent flexibility and elasticity, enabling the catheter to have good tracking and compliance in tortuous blood vessels. The three layers are bonded together through strong interfaces to form a whole, achieving a balance of rigidity and flexibility. The comprehensive mechanical properties are superior to any single material or simple double-layer structure. The dual effect of chemical bonding and physical interlocking ensures that the sandwich composite structure does not delaminate or peel under harsh conditions such as repeated bending and torsional deformation, greatly improving the structural integrity and service life of the catheter. In addition, the outermost layer is fully cured polyimide with a smooth surface and low coefficient of friction, which is beneficial for travel in blood vessels. At the same time, polyimide has excellent biocompatibility and chemical stability, and the polyether block amide intermediate layer also has good biocompatibility. This three-layer sandwich structure achieves strong interfacial bonding while cleverly distributing the rigid and flexible regions of the material, giving the catheter excellent pushing, passage, and fatigue resistance.

[0011] A further provision of the present invention is that the polyether block amide intermediate layer is chemically bonded to the inner polyimide layer and the outer polyimide layer respectively through intermolecular forces.

[0012] By adopting the above technical solution, a large number of interaction points are formed at the contact interface between the polyether block amide intermediate layer and the inner polyimide layer and the outer polyimide layer. The sum of these points constitutes a strong interfacial adhesion force and provides a good initial bonding interface for the physical interlocking structure, which facilitates cooperation with the physical interlocking and improves the stability of the sandwich composite structure.

[0013] A further provision of the present invention is that the polyether block amide intermediate layer is melt-treated and solidified under the constraint of the inner polyimide layer and the outer polyimide layer, thereby forming a microscopic physical interlock at the interface.

[0014] By adopting the above technical solution, the two adjacent layers in the sandwich composite structure are firmly locked together, which can effectively transfer and disperse interlayer stress, especially when subjected to shear force and peeling force, and exhibits extremely strong resistance. In addition, the combination of chemical bonding and physical interlocking achieves a strong all-round bonding from the molecular level to the microscopic level.

[0015] A further feature of the present invention is that the tube substrate is made of polytetrafluoroethylene, and the tube substrate is connected to the inner polyimide layer by a combination of chemical bonding and physical interlocking.

[0016] By adopting the above technical solution, a high-strength polyimide layer is firmly bonded to the PTFE substrate through a combination of chemical bonding and physical interlocking. This is equivalent to putting a hard shell on the soft PTFE tube, which not only retains the advantages of the PTFE core, but also enhances the axial strength, compression resistance and kinking resistance of the entire tube, thus expanding the application scenarios of PTFE conduits under high pressure and high torsional loads.

[0017] A further provision of the present invention is that the surface of the tube substrate is subjected to an activation treatment.

[0018] By adopting the above technical solution, the originally difficult-to-bond PTFE surface is transformed into a bondable active surface, which facilitates the construction of a strong interface.

[0019] Secondly, this application provides a method for preparing a medical catheter with a composite sandwich structure, used to prepare a medical catheter with a composite sandwich structure as described above, employing the following technical solution: including the following steps:

[0020] S1: Surface activation treatment is performed on the polytetrafluoroethylene tube substrate to obtain a bondable active surface on its outer surface;

[0021] S2: Coat the outer surface of the activated tube substrate with a polyimide prepolymer solution and perform a first-stage curing treatment to form a partially cross-linked inner polyimide layer;

[0022] S3: Coating the outer surface of the inner polyimide layer with a polyether block amide solution, and drying it to form a polyether block amide intermediate layer;

[0023] S4: Coat the outer surface of the polyether block amide intermediate layer with a polyimide prepolymer solution and perform a second-stage curing treatment; wherein, the second-stage curing treatment causes the newly coated polyimide prepolymer to form a fully cured outer polyimide layer and promotes the further curing of the inner polyimide layer, while the polyether block amide intermediate layer melts and tightly bonds with the inner and outer polyimide layers under the constraint of the inner and outer polyimide layers, thereby obtaining the medical catheter.

[0024] By adopting the above technical solution, the inner polyimide layer is first partially cured. The partially cured inner PI surface still has a certain degree of reactivity and swelling capacity, which is conducive to the wetting and initial bonding with the polyether block amide solution. Then, PEBA is coated and finally cured together at high temperature. In the final high-temperature curing stage, the inner polyimide layer and the outer polyimide layer undergo further imidization crosslinking reaction at the same time and interact with the intermediate molten PEBA to achieve the integration of the three-layer structure.

[0025] A further provision of the present invention is that the surface activation treatment in step S1 is at least one of plasma treatment and chemical etching treatment.

[0026] By adopting the above technical solutions, they can be flexibly selected or combined according to production conditions and performance requirements to ensure that the PTFE substrate obtains a stable and uniform activated surface.

[0027] A further provision of the present invention is that the first stage curing process in step S2 includes: first evaporating the solvent at 80°C to 120°C, and then carrying out partial imidization and crosslinking reactions at 150°C to 250°C.

[0028] By adopting the above technical solution, the low-temperature stage mainly removes the solvent to prevent bubbles or coating defects caused by rapid solvent evaporation; the medium-temperature stage promotes the polyimide prepolymer to undergo partial imidization cyclization reaction and preliminary cross-linking to form a partially cured PI layer with certain strength but still retaining some activity and a certain swelling capacity. This not only provides support for subsequent coatings but also reserves chemical and physical space for interfacial interaction with the polyether block amide intermediate layer.

[0029] A further provision of the present invention is that the drying process in step S3 is carried out at a temperature of 60°C to 80°C.

[0030] By adopting the above technical solution, the solvent in the polyether block amide solution can be effectively removed to form a continuous PEBA film layer. At the same time, it can avoid excessive softening of the polyether block amide intermediate layer or further violent reaction of the inner polyimide layer, ensuring that the coated polyether block amide intermediate layer maintains an independent and clear layered structure, so that a controlled interlocking interface is formed during the final high-temperature curing.

[0031] A further provision of the present invention is that the second stage curing process in step S4 adopts a stepped heating program, and its final curing temperature is not lower than 300°C, so that the polyimide layer is completely imidized.

[0032] By adopting the above technical solution, the stepped heating is not simply a matter of curing and bonding the three layers separately. Instead, in a heat treatment process, the three layers of materials undergo their key phase transitions or reactions simultaneously, and complete the interface fusion under mutually constrained conditions, ultimately forming a sandwich integrated structure that combines chemical and physical processes and has no clear weak interface.

[0033] In summary, the present invention has the following beneficial effects:

[0034] 1. The system employs a tubular base and a sandwich composite structure bonded to the outer surface of the base. From the inside out, the sandwich composite structure comprises an inner polyimide layer coated on the outer surface of the base, a polyether block amide intermediate layer coated on the outer surface of the inner polyimide layer, and an outer polyimide layer coated on the outer surface of the polyether block amide intermediate layer. These three layers are chemically bonded and physically interlocked to form a single structure. The inner and outer polyimide layers provide a high-strength, high-modulus structural framework, ensuring the catheter's pushing force and flexural strength, allowing for precise manipulation of the distal end. The polyether block amide intermediate layer contributes excellent flexibility and elasticity, enabling the catheter to have good tracking and compliance in tortuous blood vessels, allowing it to easily pass through these vessels and reducing trauma to the vessel wall. During bending, the outer polyimide layer is under tension, the inner polyimide layer is under tension, and the polyether block amide intermediate layer provides elasticity. Deformation absorption and stress dispersion, combined with a strong interface, form a unified whole, achieving a balance of rigidity and flexibility. This improves the catheter's resistance to bending fatigue, making it less prone to permanent creases or breakage under extreme bending conditions, thus enhancing surgical safety. Its comprehensive mechanical properties are superior to any single material or simple double-layer structure. The dual effect of chemical bonding and physical interlocking ensures that the sandwich composite structure does not delaminate or peel under harsh conditions such as repeated bending and torsional deformation, greatly improving the structural integrity and service life of the catheter. In addition, the outermost layer is fully cured polyimide with a smooth surface and low coefficient of friction, which is beneficial for travel within blood vessels. At the same time, polyimide has excellent biocompatibility and chemical stability. The middle layer of polyether block amide also has good biocompatibility. This three-layer sandwich structure achieves strong interface bonding while cleverly distributing the rigid and flexible regions of the material, giving the catheter excellent delivery, passage, and fatigue resistance.

[0035] 2. The tubing base is made of polytetrafluoroethylene (PTFE). PTFE has a smooth inner wall, an extremely low coefficient of friction, and stable chemical properties. It possesses excellent chemical inertness, lubricity, and biocompatibility, making it suitable as a guidewire channel or fluid channel. The tubing base and the inner polyimide layer are connected through a combination of chemical bonding and physical interlocking. This combination of chemical bonding and physical interlocking firmly bonds the high-strength inner polyimide layer to the PTFE tubing base, essentially giving the soft PTFE tubing base a hard outer shell. This retains the advantages of the PTFE core while enhancing the axial strength, compression resistance, and kinking resistance of the entire tubing, expanding the application scenarios of PTFE catheters under high pressure and high torsional loads. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a medical catheter with a composite sandwich structure according to the present invention.

[0037] Figure 2 This is a flowchart of a method for preparing a medical catheter with a composite sandwich structure according to the present invention.

[0038] In the diagram: 1. Tube base; 2. Inner polyimide layer; 3. Polyether block amide intermediate layer; 4. Outer polyimide layer. Detailed Implementation

[0039] The invention will now be further described with reference to the accompanying drawings.

[0040] A medical catheter with a composite sandwich structure, such as Figure 1 As shown, it includes a tube base 1 and a sandwich composite structure bonded to the outer surface of the tube base 1. The sandwich composite structure includes, from the inside to the outside:

[0041] An inner polyimide (PI) layer is coated on the outer surface of the tube substrate 1;

[0042] A polyether block amide (Pebax, abbreviated as PEBA) intermediate layer is coated on the outer surface of the inner polyimide layer 2;

[0043] An outer polyimide (PI) layer is coated on the outer surface of the polyether block amide intermediate layer 3;

[0044] The inner polyimide layer 2, the polyether block amide intermediate layer 3, and the outer polyimide layer 4 form an integral structure through a combination of chemical bonding and physical interlocking. Through the above structural design, the inner polyimide layer 2 and the outer polyimide layer 4 provide a high-strength, high-modulus structural framework, ensuring the catheter's pushing force and flexural strength. The polyether block amide intermediate layer 3 contributes excellent flexibility and elasticity, enabling the catheter to have good tracking and compliance in tortuous blood vessels. The three layers are bonded together through strong interfaces to form a whole, achieving a balance of rigidity and flexibility. The comprehensive mechanical properties are superior to any single material or simple double-layer structure. The dual effect of chemical bonding and physical interlocking ensures that the sandwich composite structure does not delaminate or peel under harsh conditions such as repeated bending and torsional deformation, greatly improving the structural integrity and service life of the catheter. In addition, the outermost layer is fully cured polyimide with a smooth surface and low coefficient of friction, which is beneficial for travel in blood vessels. At the same time, polyimide has excellent biocompatibility and chemical stability, and the polyether block amide in the intermediate layer also has good biocompatibility. This three-layer sandwich structure achieves strong interfacial bonding while cleverly distributing the rigid and flexible regions of the material, giving the catheter excellent pushing, passage, and fatigue resistance.

[0045] Preferably, the polyether block amide interlayer 3 is chemically bonded to the inner polyimide layer 2 and the outer polyimide layer 4 through intermolecular forces. Specifically, the polyether block amide molecular chain contains polar amide bonds and flexible ether bonds, while the polyimide molecular chain contains numerous polar groups such as imide rings and carbonyl groups. During the preparation process, when PEBA comes into contact with incompletely cured PI or a reactive PI surface, the polar groups (such as C=O, NH, etc.) between the two can generate strong intermolecular forces, such as hydrogen bonds and dipole-dipole interactions. This molecular-scale interaction forms the basis of the interlayer chemical bonding. Through the above structural design, a large number of interaction points are formed at the contact interface between the polyether block amide interlayer 3 and the inner polyimide layer 2 and the outer polyimide layer 4. These points together constitute a strong interfacial adhesion force and provide a good initial bonding interface for the physical interlocking structure, facilitating cooperation with the physical interlocking structure and improving the stability of the sandwich composite structure.

[0046] Preferably, the polyether block amide interlayer 3 is melt-treated and solidified under the constraint of the inner polyimide layer 2 and the outer polyimide layer 4, thereby forming a micro-mechanical interlocking structure at the interface to achieve the physical interlocking. Specifically, during the high-temperature curing stage of the preparation process, the PEBA interlayer softens or even melts, and its molecular chain segment mobility is enhanced. At this time, sandwiched between the partially solidified or microporous / rough PI layers of the inner and outer polyimide layers, the molten PEBA will penetrate into the micro-depressions, pores or molecular chain gaps on the surface of the PI layer under pressure (such as coating shrinkage stress or capillary force). Subsequently, during the cooling and curing process, the PEBA recrystallizes or solidifies, and its solidified entity is "anchored" in the microstructure of the PI layer, forming an interlocking interface, that is, forming physical interlocking. Through the above structural design, the two adjacent layers in the sandwich composite structure are firmly locked together, which can effectively transfer and disperse interlayer stress, especially when subjected to shear force and peeling force, showing extremely strong resistance; in addition, the combination of chemical bonding and physical interlocking achieves a strong all-round bonding from the molecular level to the microscopic level.

[0047] Preferably, the tube base 1 is made of polytetrafluoroethylene (PTFE). PTFE has a smooth inner wall, an extremely low coefficient of friction, and stable chemical properties. It has excellent chemical inertness, lubricity, and biocompatibility, making it suitable as a guide wire channel or fluid channel. The tube base 1 and the inner polyimide layer 2 are connected by a combination of chemical bonding and physical interlocking. The high-strength inner polyimide layer 2 is firmly bonded to the PTFE tube base 1 by a combination of chemical bonding and physical interlocking. This is equivalent to putting a hard outer shell on the soft PTFE tube base 1, which not only retains the advantages of the PTFE core but also enhances the axial strength, compression resistance, and kinking resistance of the entire tube, expanding the application scenarios of PTFE catheters under high pressure and high torsional loads.

[0048] Preferably, the surface of the tube substrate 1 undergoes activation treatment. Activation treatment refers to introducing oxygen- and nitrogen-containing active groups (such as -COOH, -OH, C=O, etc.) into the PTFE surface through methods such as plasma treatment or chemical etching (e.g., sodium-naphthalene complex treatment), thereby generating a certain surface roughness. The introduced active groups can chemically react with the active groups in the subsequently coated PI prepolymer or form strong intermolecular forces, achieving chemical bonding. The surface roughness allows the liquid prepolymer to penetrate these micro-rough structures when the prepolymer solution of the inner polyimide layer 2 is coated and initially cured. After curing, the PI solid is mechanically anchored in the microstructure of the PTFE surface, forming a physical interlock. Through activation treatment, the originally difficult-to-bond PTFE surface is transformed into a bondable active surface, facilitating the construction of a strong interface.

[0049] In addition, this embodiment also provides a method for preparing a medical catheter with a composite sandwich structure, used to prepare a medical catheter with a composite sandwich structure as described above, such as... Figure 2 As shown, the following technical solution is adopted, including the following steps:

[0050] S1: The polytetrafluoroethylene tube substrate 1 is subjected to surface activation treatment to obtain a bondable active surface on its outer surface;

[0051] S2: Coat the outer surface of the activated tube substrate 1 with a polyimide prepolymer solution and perform a first-stage curing treatment to form a partially cross-linked inner polyimide layer 2.

[0052] S3: Coating the outer surface of the inner polyimide layer 2 with a polyether block amide solution, and drying it to form a polyether block amide intermediate layer 3;

[0053] S4: Coat the outer surface of the polyether block amide intermediate layer 3 with a polyimide prepolymer solution and perform a second-stage curing treatment; wherein, the second-stage curing treatment causes the newly coated polyimide prepolymer to form a fully cured outer polyimide layer 4, and promotes the further curing of the inner polyimide layer 2, while the polyether block amide intermediate layer 3 melts and tightly bonds with the inner polyimide layer 2 and the outer polyimide layer 4 under the constraint of the inner polyimide layer 2 and the outer polyimide layer 4, thereby obtaining the medical catheter.

[0054] The inner polyimide layer 2 is partially cured first. The partially cured inner PI surface still has a certain degree of reactivity and swelling capacity, which is beneficial for wetting and initial bonding with the polyether block amide solution. Then, PEBA is coated and finally cured together at high temperature. In the final high-temperature curing stage, the inner polyimide layer 2 and the outer polyimide layer 4 undergo further imidization crosslinking reaction at the same time and interact with the intermediate molten PEBA to achieve the integration of the three-layer structure.

[0055] Preferably, the surface activation treatment in step S1 is at least one of plasma treatment and chemical etching treatment. Plasma treatment is a dry treatment that is clean and environmentally friendly. It can effectively introduce active groups and slightly etch the surface, making it suitable for medical devices with high cleanliness requirements. Chemical etching (such as sodium-naphthalene treatment) can more drastically change the chemical properties of the PTFE surface, introduce a large number of polar groups, and achieve stronger adhesion. It can be flexibly selected or combined according to production conditions and performance requirements to ensure that the PTFE substrate obtains a stable and uniform activated surface.

[0056] Preferably, the first stage of curing in step S2 includes: first evaporating the solvent at 80°C to 120°C, and then carrying out partial imidization and crosslinking reactions at 150°C to 250°C. The low-temperature stage (80-120°C) mainly removes the solvent to prevent bubbles or coating defects caused by rapid solvent evaporation. The medium-temperature stage (150-250°C) promotes the partial imidization cyclization reaction and preliminary crosslinking of the polyimide prepolymer to form a partially cured PI layer with a certain strength but still retaining some activity (such as unreacted carboxyl groups and amyl acid structures) and a certain swelling capacity. This layer can provide support for subsequent coatings and reserve chemical and physical space for interfacial interaction with the polyether block amide intermediate layer 3.

[0057] Preferably, the drying process in step S3 is carried out at a temperature of 60°C to 80°C. This temperature range is higher than the boiling point of commonly used solvents for PEBA (such as ethanol, isopropanol, etc.), which can effectively remove the solvent in the polyether block amide solution and form a continuous PEBA film layer. At the same time, this temperature is much lower than the melting point of PEBA (usually >150°C) and the imidization temperature of PI, which can avoid excessive softening of the polyether block amide intermediate layer 3 or further violent reaction of the inner polyimide layer 2, ensuring that the coated polyether block amide intermediate layer 3 maintains an independent and clear layered structure, so that a controlled interlocking interface is formed during the final high-temperature curing.

[0058] Preferably, the second-stage curing process in step S4 employs a stepped heating procedure, with a final curing temperature not lower than 300°C, ensuring complete imidization of the outer polyimide layer 4 coating. As a preferred embodiment, the stepped heating refers to raising the temperature from room temperature to 250°C at a certain rate, holding it at that temperature for a period of time, and then raising it to above 300°C and holding it thereafter. Slow heating facilitates the complete removal of solvents and small molecule byproducts (such as water) generated during imidization, preventing pinholes or defects in the coating. A final temperature not lower than 300°C ensures complete conversion of the polyamic acid. To achieve optimal mechanical properties and chemical stability for the outer polyimide layer 4, the polyether block amide interlayer 3 sandwiched between the inner polyimide layer 2 and the outer polyimide layer 4 undergoes a melting-flowing-re-curing process at this high temperature. Under the clamping and constraint of the inner and outer polyimide layers 2 and 4, the molten PEBA and PI interface undergo sufficient inter-diffusion and penetration, forming a strong microscopic interlocking upon cooling. This process design ensures that the sandwich structure achieves optimal interfacial bonding while maintaining the best performance of each material. The stepped heating is not simply about curing and bonding the three layers separately, but rather allowing them to undergo their key phase transitions or reactions simultaneously (complete imidization of PI, melting and re-curing of PEBA) during a single heat treatment process. Under mutually constrained conditions, the interfacial fusion is completed, ultimately forming a chemically and physically integrated sandwich structure without clearly defined weak interfaces.

[0059] To more clearly illustrate the above preparation method, specific examples are provided below for a clear and complete description. It should be noted that the examples described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0060] A medical catheter with a composite sandwich structure, wherein the base 1 of the tube body is a PTFE tube with an inner diameter of 0.5 mm and a wall thickness of 0.1 mm.

[0061] Its preparation method is as follows:

[0062] Surface activation treatment (S1): The PTFE tube substrate 1 is placed in a plasma treatment device and treated with oxygen plasma at a pressure of 50Pa and a power of 100W for 3 minutes to activate its outer surface.

[0063] Coating and partially curing the inner polyimide layer 2 (S2): The activated PTFE tube is immersed in a 15% polyamic acid (PAA) / N-methylpyrrolidone (NMP) solution and coated by dip coating; it is dried in an oven at 100°C for 10 minutes to remove most of the solvent, and then transferred to an oven for heat treatment at 200°C for 30 minutes to partially imidize, forming the inner polyimide layer 2 with a thickness of about 5 μm.

[0064] Coating polyether block amide intermediate layer 3 (S3): Immerse the tube with the inner PI layer into a 10% PEBA-7233 / ethanol solution and coat it by lifting; dry at 70°C for 15 minutes to form a PEBA intermediate layer with a thickness of about 10 μm.

[0065] Coating and final curing of the outer polyimide layer 4 (S4): The tube body is immersed in the above PAA / NMP solution again for pull coating; then step curing is performed: first, drying at 100°C for 10 minutes, then curing at 250°C for 1 hour, and finally curing at 320°C for 30 minutes. During this process, the newly coated PAA is completely imidized to form the outer polyimide layer 4 (thickness of about 5μm), the inner polyimide layer 2 is further completely cured, and the PEBA intermediate layer melts at high temperature and is re-cured under the constraint of the inner and outer PI layers, forming a tight bond with both.

[0066] The above description is only a preferred embodiment of the present invention. Therefore, all equivalent changes or modifications made to the structure, features and principles described in the claims of this patent application are included in the scope of this patent application.

Claims

1. A medical catheter with a composite sandwich structure, characterized in that, It includes a tube base (1) and a sandwich composite structure attached to the outer surface of the tube base (1), wherein the sandwich composite structure comprises, from the inside to the outside: An inner polyimide layer (2) is coated on the outer surface of the tube substrate (1); A polyether block amide intermediate layer (3) is coated on the outer surface of the inner polyimide layer (2); An outer polyimide layer (4) is coated on the outer surface of the polyether block amide intermediate layer (3); The inner polyimide layer (2), the polyether block amide intermediate layer (3), and the outer polyimide layer (4) form an integral structure through a combination of chemical bonding and physical interlocking; the polyether block amide intermediate layer (3) achieves chemical bonding with the inner polyimide layer (2) and the outer polyimide layer (4) through intermolecular forces; the polyether block amide intermediate layer (3) is melt-treated and solidified under the constraint of the inner polyimide layer (2) and the outer polyimide layer (4), thereby forming a microscopic physical interlock at the interface; Its preparation method includes the following steps: S1: The tube substrate (1) made of polytetrafluoroethylene is subjected to surface activation treatment so that its outer surface has a bondable active surface; S2: Coat the outer surface of the activated tube substrate (1) with a polyimide prepolymer solution and perform a first-stage curing process to form a partially cross-linked inner polyimide layer (2); S3: Coating the outer surface of the inner polyimide layer (2) with a polyether block amide solution, and drying it to form a polyether block amide intermediate layer (3); S4: Coat the outer surface of the polyether block amide intermediate layer (3) with a polyimide prepolymer solution and perform a second-stage curing process; wherein, the second-stage curing process causes the newly coated polyimide prepolymer to form a fully cured outer polyimide layer (4) and promotes the further curing of the inner polyimide layer (2), while causing the polyether block amide intermediate layer (3) to melt and tightly bond with the inner polyimide layer (2) and the outer polyimide layer (4) under the constraint of the inner polyimide layer (2) and the outer polyimide layer (4), thereby obtaining the medical catheter.

2. A method for preparing a medical catheter with a composite sandwich structure, used to prepare a medical catheter with a composite sandwich structure as described in claim 1, characterized in that, Includes the following steps: S1: The tube substrate (1) made of polytetrafluoroethylene is subjected to surface activation treatment so that its outer surface has a bondable active surface; S2: Coat the outer surface of the activated tube substrate (1) with a polyimide prepolymer solution and perform a first-stage curing process to form a partially cross-linked inner polyimide layer (2); S3: Coating the outer surface of the inner polyimide layer (2) with a polyether block amide solution, and drying it to form a polyether block amide intermediate layer (3); S4: Coat the outer surface of the polyether block amide intermediate layer (3) with a polyimide prepolymer solution and perform a second-stage curing process; wherein, the second-stage curing process causes the newly coated polyimide prepolymer to form a fully cured outer polyimide layer (4) and promotes the further curing of the inner polyimide layer (2), while causing the polyether block amide intermediate layer (3) to melt and tightly bond with the inner polyimide layer (2) and the outer polyimide layer (4) under the constraint of the inner polyimide layer (2) and the outer polyimide layer (4), thereby obtaining the medical catheter.

3. The method for preparing a medical catheter with a composite sandwich structure according to claim 2, characterized in that: The surface activation treatment in step S1 is at least one of plasma treatment and chemical etching treatment.

4. The method for preparing a medical catheter with a composite sandwich structure according to claim 2, characterized in that: The first stage of curing in step S2 includes: first evaporating the solvent at 80°C to 120°C, and then carrying out partial imidization and crosslinking reactions at 150°C to 250°C.

5. The method for preparing a medical catheter with a composite sandwich structure according to claim 2, characterized in that: The drying process in step S3 is carried out at a temperature of 60°C to 80°C.

6. The method for preparing a medical catheter with a composite sandwich structure according to claim 2, characterized in that: The second stage of curing in step S4 adopts a stepped heating program, and its final curing temperature is not lower than 300℃, so that the polyimide layer (4) is completely imidized.

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