Knee joint prosthesis intramedullary nail and preparation method thereof

Abstract

The invention discloses a knee joint prosthesis intramedullary nail and a preparation method thereof, relates to the technical field of medical implant materials, and solves the technical problems that existing material fibers are insufficient in mechanical property, complex structural parts are difficult to prepare and the like. Comprising a core part, an outer layer and a middle layer located between the core part and the outer layer. The core part is made of a continuous carbon fiber reinforced polyaryletherketone material and comprises a bar center part in which carbon fibers are axially distributed in parallel and a surface layer winding part in which the carbon fibers are distributed in a staggered winding manner; the middle layer is a porous titanium material, the porosity is 30-70%, and the aperture is 20-500 [mu] m; the outer layer is obtained by coating chopped carbon fiber reinforced polyaryletherketone through injection molding and machining; and the length of the short carbon fiber is 50-800 microns. Through cooperation of core fiber orientation optimization, middle layer interface strengthening and outer layer injection molding toughening, the layering risk is avoided while high bending strength is kept, and an innovative solution with mechanical adaptability, complex structure processability and biological integration is provided.

Description

Technical Field

[0001] The present invention relates to the technical field of medical implant materials, and in particular to an intramedullary nail for a knee joint prosthesis and a preparation method thereof. Background Art

[0002] The incidence of bone tumors accounts for approximately 2% to 3% of all tumors in the body. Its clinical treatment focuses on radical resection combined with bone defect reconstruction, but postoperative bone defect reconstruction has always been a major challenge facing the field of orthopedics. Currently, the commonly used reconstruction and repair technologies in clinical practice include tumor bone deactivation and reimplantation, allogeneic bone reconstruction, fibula transplantation, biomaterial repair, and tumor prosthesis implantation. Among them, although traditional autologous bone transplantation has good biocompatibility, it is limited by insufficient donor sources, donor site dysfunction, and postoperative infection risks. Allogeneic bone transplantation has the risk of disease transmission and timeliness defects. Against this background, artificial orthopedic implant materials with the advantage of customization have gradually become the solution with the most development potential. Especially in the social context of increasing aging, frequent accidental injuries, and an increase in bone-related diseases, the demand for research and development of artificial orthopedic implant materials continues to grow.

[0003] Ideal materials for postoperative bone tumor repair must meet both biocompatibility and mechanical strength requirements. Currently, mainstream clinical products are generally made of metal materials, but these materials have significant drawbacks: their high density can scatter and block X-rays and radiotherapy radiation, severely impacting the accuracy of postoperative imaging assessments and potentially interfering with bone tumor patients requiring precise radiotherapy. To address this critical issue, researchers both domestically and internationally have begun exploring the application of carbon fiber-reinforced polyaryletherketone (CF / PEEK) composites. For example, Chinese patent document CN104188706A discloses a composite structure of an axial carbon fiber core layer and a ±45° fiber middle layer, and combines the surface vapor deposition metal layer technology to prepare bone fixation screws, but its preparation process makes it difficult to achieve the molding of step-shaped or grooved structures; Chinese patent document CN111729134A discloses the use of hot flow molding technology to prepare continuous CF / PEEK bone fixators, but the single fiber arrangement direction leads to significant anisotropy and insufficient bending and torsional mechanical properties; Chinese patent document CN119680024A proposes twisting and hot pressing of carbon fiber composite rope strands to prepare intramedullary nails, but twisting is not conducive to fiber alignment and cannot fully exert the mechanical properties of the fibers.

[0004] In summary, existing artificial orthopedic implant materials generally have technical bottlenecks such as insufficient mechanical properties and difficulty in molding complex structures, and it is urgent to develop new composite material molding processes. Summary of the Invention

[0005] In order to solve technical problems such as insufficient mechanical properties of existing material fibers and difficulty in preparing complex structural parts, the present invention proposes a knee joint prosthesis intramedullary nail and a preparation method thereof.

[0006] The technical solutions of the present invention are as follows:

[0007] A knee joint prosthesis intramedullary nail comprises a core, an outer layer and an intermediate layer between the core and the outer layer;

[0008] The core is a continuous carbon fiber reinforced polyaryletherketone material, including a rod center portion where carbon fibers are axially parallel and a surface winding portion where carbon fibers are staggered and wound;

[0009] The middle layer is a porous titanium material with a porosity of 30-70% and a pore size of 20-500 μm;

[0010] The outer layer is obtained by injection molding and coating short-cut carbon fiber reinforced polyaryletherketone, and then machining; the length of the short-cut carbon fiber is 50 to 800 μm.

[0011] Preferably, the polyaryletherketone is selected from polyetheretherketone or polyetherketoneketone. The polyaryletherketone has a tensile strength of ≥85 MPa and a crystallinity of ≥5%.

[0012] Preferably, the diameter of the central portion of the rod is 3 to 12 mm, and the weight percentage of carbon fiber in the central portion of the rod is 40 to 70%; since when the intramedullary nail is subjected to bending stress, the stress is mainly absorbed by the outer side, and the bending stress borne by the central portion of the rod is relatively small, the raw material used to manufacture the central portion is more preferably a prepreg with a carbon fiber content of 45 to 55% with a lower production cost.

[0013] The thickness of the surface winding portion is 0.4 to 2 mm, and the weight percentage of the carbon fiber in the surface winding portion is 45 to 70%. When the intramedullary nail is subjected to bending stress, in order to ensure sufficient bending resistance, the carbon fiber content should be as high as possible. Therefore, the raw material used to manufacture the winding layer is preferably a prepreg with a carbon fiber content of 60 to 70%.

[0014] In order to ensure that the porous titanium intermediate layer has sufficient adhesion thereto, the concentration of carbon fibers in the outermost 1 to 3 winding layers of the surface winding portion is lower than that in the inner winding layers, preferably 5 to 55%.

[0015] Preferably, the carbon fibers in the core, where the carbon fibers are continuously distributed, have a tensile strength of 4000 MPa or greater and a tensile modulus of 300 GPa or less; more preferably, the tensile strength is 5000 MPa or greater. High tensile strength increases the flexibility of continuous carbon fiber layup design, while low modulus reduces stress shielding in orthopedic implants.

[0016] Preferably, the tensile modulus of the carbon fibers in the chopped carbon fiber reinforced polyaryletherketone is ≤250 GPa, and the tensile strength is ≤4000 MPa. Low tensile strength and low elastic modulus are beneficial for increasing surface polishing efficiency and reducing stress shielding effects of orthopedic implants.

[0017] Preferably, the continuous carbon fibers in the surface winding portion and the continuous carbon fibers in the center portion of the rod are arranged in a staggered manner at an angle of ±30 to 60°.

[0018] In order to ensure that the winding layer generates sufficient holding force and tensile strength on the inner layer fibers, the more preferred angle range is ±40 to 45 degrees.

[0019] Preferably, the intermediate layer is obtained by plasma spraying titanium powder, the mesh size of the titanium powder is 300 mesh; the thickness of the intermediate layer is 50 to 200 μm.

[0020] Preferably, the outer layer is processed with steps and axially distributed grooves, and the percentage of carbon fiber in the outer layer is not less than 40%, more preferably 15-30%.

[0021] Preferably, in order to ensure a strong bond with the middle layer and the surface layer winding portion, the core surface is further processed with sunken holes or grooves.

[0022] The present invention also provides a method for preparing the above-mentioned knee joint prosthesis intramedullary nail, comprising the following steps:

[0023] S1. preparing a continuous carbon fiber / polyaryletherketone prepreg tape;

[0024] S2, melt-mixing the chopped carbon fiber and the polyaryletherketone in a twin-screw extruder to obtain chopped carbon fiber / polyaryletherketone composite pellets;

[0025] S3, cutting the continuous carbon fiber / polyaryletherketone prepreg into narrow strips, preheating the narrow strips and placing them in a preheated cylindrical die, extruding the polyaryletherketone through a screw and then melting it into the cylindrical die from the side, fully infiltrating the narrow strips under the action of pressure, cooling and shaping, and obtaining the center of the rod; or preheating the narrow strips and passing them through a cylindrical die heated to above the melting point of the polyaryletherketone, thermoforming them into a cylindrical shape in the die, and then pultruding and shaping them to obtain the center of the rod; or using a hot press plate with carbon fiber orientations of 0° / 45° / 90° / 135° as a profile, using a lathe to process it into a circular core along the 0° direction, in order to ensure that the core has sufficient compressive and tensile strength, the content of the 0° oriented carbon fiber ply is not less than 50%, and obtaining the center of the rod;

[0026] S4, winding a plurality of layers of continuous carbon fiber / polyether aryl ketone prepreg tapes on the surface of the central rod by staggered heating to obtain a core;

[0027] S5, plasma spraying titanium powder, the interfaces between titanium powder particles are fused and accumulated to obtain a porous titanium intermediate layer;

[0028] S6. Prepare the outer layer of the intramedullary nail by injection molding and coating; place the material in a preheated injection molding and coating mold, use the chopped carbon fiber / polyaryletherketone composite pellets for injection molding and coating to obtain an intramedullary nail blank, and then machine it to form steps and axially distributed grooves to obtain a knee joint prosthesis intramedullary nail.

[0029] Preferably, the width of the narrow strip is 4.0 to 8.0 mm, and the inner diameter of the cylindrical die is 4.0 to 10.0 mm.

[0030] Preferably, the preheating temperature of the cylindrical die is 400°C, and the preheating temperature of the injection molding die is 240-270°C.

[0031] Compared with the prior art, the present invention has the following specific beneficial effects:

[0032] The present invention optimizes the mechanical properties and biological functions of the intramedullary nail of the knee prosthesis through the coordinated design of the core, the middle layer and the outer layer. The core is made of continuous carbon fiber reinforced polyaryletherketone material. The central part of the rod has the advantage of axial load-bearing by axially parallel distribution of carbon fibers, while the surface winding part forms a circumferential reinforcement by staggered winding of carbon fibers to suppress delamination and cracking. The combination of the two enables the core to dissipate energy preferentially through fiber breakage rather than interlayer peeling under three-point bending load, thereby increasing the bending strength to more than 2000N. The porous titanium material in the middle layer uses the gradient modulus property to alleviate the sudden change of interfacial stress. At the same time, its three-dimensional interconnected pore structure enhances the interlayer bonding strength through mechanical interlocking and resin penetration, avoiding the expansion of cracks caused by direct contact between the core and the outer layer. The outer layer is injection-molded with short-cut carbon fiber reinforced polyaryletherketone. The random distribution of the short fibers imparts an isotropic reinforcement effect, effectively dispersing local stress and hindering crack propagation. This maintains processing fluidity while ensuring toughness. Combined with machining, the outer layer is precisely adapted to its shape. Mechanical drilling of the core surface before plasma spraying further enhances titanium powder adhesion through a groove structure, further enhancing bending strength. Compared to traditional multi-directional laminated composite materials, this invention achieves high bending strength while avoiding the risk of delamination through the synergistic effect of optimizing the orientation of the core fibers, strengthening the interface of the porous structure of the middle layer, and toughening the outer layer through injection molding. This provides an innovative solution for orthopedic implants that combines mechanical adaptability, complex structural processability, and biointegration. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic diagram of the structure of the injection-molded coated blank of the intramedullary nail described in Example 1;

[0034] Figure 2 Schematic diagram of the appearance of the intramedullary nail of the knee joint prosthesis obtained in Example 1;

[0035] Figure 3 This is a schematic cross-sectional view of the intramedullary nail described in Example 1. DETAILED DESCRIPTION

[0036] In order to make the technical solution of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the specification of the present invention. It should be noted that the following embodiments are only used to better understand the technical solution of the present invention and should not be understood as limiting the present invention.

[0037] Example 1.

[0038] Continuous carbon fiber with a tensile strength of 4900 MPa and a tensile modulus of 230 GPa was selected to prepare continuous carbon fiber reinforced polyetheretherketone prepreg tapes with carbon fiber weight contents of 65% and 50%, respectively. The preparation process is briefly described as follows:

[0039] The carbon fibers sized with stearic acid polyoxyethylene ether-5 were placed in a tunnel oven preheated to 380°C for a residence time of 90 seconds to obtain desized carbon fibers. The desized carbon fibers were immediately passed through an extrusion coating die without cooling. Polyetheretherketone (PEEK) with a melt index of 80 g / min was added to a single-screw extrusion coating machine. The extrusion speed and carbon fiber yarn release speed were adjusted to control the weight ratio of the sizing amount to the carbon fibers to be 35:65 and 50:50. The carbon fibers were cooled and shaped to obtain a carbon fiber / PEEK unidirectional prepreg.

[0040] Carbon fibers with a tensile strength of 3500 MPa and a tensile modulus of 230 GPa were selected and melt-mixed with polyetheretherketone (PEEK) with a melt index of 30 g / 10 min (380°C, 5 kg) in a twin-screw extruder to prepare chopped carbon fiber reinforced PEEK composite pellets with a carbon fiber content of 30%.

[0041] A prepreg tape with a 65% carbon fiber content was slit into 6.3mm-wide strips, preheated in an oven at 320°C for 60 seconds, and then passed through a circular die with an inner diameter of 8.05mm, preheated to 400°C. Within the die, the prepreg was extruded and thermoformed into a round rod, which was then cooled and shaped to produce a central rod with a diameter of 8.0mm.

[0042] The core of the intramedullary nail is obtained by firstly wrapping two layers of prepreg tape with a carbon fiber content of 65% at ±45° on the surface of the central rod, and then wrapping two layers of prepreg tape with a carbon fiber content of 50% at ±45°.

[0043] 300 mesh titanium powder was plasma sprayed onto the core surface, and the average spraying thickness was controlled to be 0.15 mm to obtain an intermediate layer.

[0044] The material is then placed in an injection molding mold preheated to 270°C and injection molded with chopped carbon fiber reinforced polyetheretherketone to obtain an intramedullary nail blank, such as Figure 1 As shown, the blank is then machined to form steps and axially distributed grooves to obtain Figure 2 The intramedullary nail is shown in Figure 1. Figure 3 shown.

[0045] Example 2.

[0046] In this embodiment, 20% of chopped carbon fiber reinforced polyetheretherketone composite material particles are used to prepare the outer layer of the intramedullary nail. Other conditions are the same as those in Example 1.

[0047] Example 3.

[0048] In this embodiment, before plasma spraying 300 mesh titanium powder and injection coating, 10 holes (3 mm in diameter and 1 mm in depth) were mechanically drilled at equal intervals on the core surface of the intramedullary nail. Other conditions were the same as those in Example 1.

[0049] Comparative Example 1.

[0050] The surface of the core of the intramedullary nail was not processed with the surface winding portion, and other conditions were the same as those in Example 1.

[0051] Comparative Example 2.

[0052] The center of the intramedullary nail was not sprayed with an intermediate layer, and other conditions were the same as those in Example 1.

[0053] Comparative Example 3.

[0054] Continuous carbon fiber with a tensile strength of 4900 MPa and a tensile modulus of 230 GPa was used to prepare a continuous carbon fiber-reinforced polyetheretherketone (PEEK) prepreg tape with a carbon fiber weight content of 65%. After slitting, the prepreg tape was placed in a 400 mm square mold and laid up to a thickness of 27 mm using a 0° / 45° / 90° / 135° pattern. The prepreg was then hot-pressed at 390°C and a surface pressure of 5 MPa for 30 minutes. The prepreg was then cooled at a rate of -5°C / min to 120°C to produce a continuous carbon fiber / PEEK molded sheet. The sheet was then slit and machined to produce an intramedullary nail.

[0055] Effect example.

[0056] Three-point bending strength test:

[0057] The intramedullary nails prepared in the embodiments and comparative examples were placed on a U-shaped bending strength test fixture with a span of 70 mm. Stress was applied at the center of the fixture at a speed of 1 mm / min, and the displacement-load curve was recorded. The maximum load value was taken as the bending strength in N.

[0058] The corresponding three-point bending strength test results are listed in Table 1.

[0059] Table 1

[0060] Experimental example Bending strength (N) Bending failure mode Example 1 2136 Stress point fracture, center layer / outer layer does not crack Example 2 2065 Stress point fracture Example 3 2109 Stress point fracture Comparative Example 1 1713 Delamination and cracking Comparative Example 2 1954 Stress point fracture, center layer / outer layer cracking Comparative Example 3 1038 / 1412 Delamination and cracking, anisotropy of bending strength

[0061] From the comparison results of the embodiment and comparative example 1, it can be seen that the core of the present invention adopts axially parallel distribution of continuous carbon fibers + surface winding part, the center part of the rod has axial load-bearing advantage, and the surface carbon fibers are staggered and wound to form a circumferential reinforcement. The surface winding part not only increases the bending strength of the intramedullary nail, but also prevents the stress stratification of the core part of the intramedullary nail and suppresses interlaminar shear failure.

[0062] From the comparison results of the embodiment and comparative example 2, it can be seen that the middle layer of porous titanium is located between the core and the outer layer, which reduces the interface stress concentration. The pore structure allows the outer layer injection molding resin to penetrate to form an anchoring structure, enhance the interlayer bonding, and effectively increase the bonding force between the layers.

[0063] In Example 3, grooves are formed by drilling the core to increase the adhesion area of the plasma sprayed titanium powder, improve the mechanical bite between the middle layer and the core, and also increase the mechanical bonding strength between the outer layer and the middle, thereby delaying the occurrence of cracks.

[0064] Comparative Example 3 uses a hot press plate with prepreg tapes laid up at 0° / 45° / 90° / 135° angles. The anisotropic arrangement of the carbon fibers weakens the axial strength and disperses the fibers' axial load-bearing capacity, resulting in a bending strength that is only 50% of that of the continuous axial core fibers of the present invention. Furthermore, the ply interfaces rely on resin bonding, lacking the mechanical interlocking and interlayer bonding reinforcement of porous titanium, making delamination failure more likely.

[0065] In summary, the core axial fibers of this application maximize load-bearing efficiency and avoid strength loss in multi-directional plies; the porous titanium intermediate layer balances mechanical matching and interface reinforcement, breaking through the interlaminar bonding bottleneck of traditional composite materials; and the outer layer of chopped fibers, injection molded, achieves low cost and high toughness, balancing biocompatibility and process feasibility. Compared to existing technologies, this invention provides an integrated solution for orthopedic implants that combines high strength, fatigue resistance, and ease of processing, with significant clinical application value.

[0066] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A knee joint prosthesis intramedullary nail, characterized in that: comprising a core, an outer layer and an intermediate layer between the core and the outer layer; The core is a continuous carbon fiber reinforced polyaryletherketone material, including a rod center portion where carbon fibers are axially parallel and a surface winding portion where carbon fibers are staggered and wound; The middle layer is a porous titanium material with a porosity of 30-70% and a pore size of 20-500 μm; The outer layer is obtained by injection molding and coating short carbon fiber reinforced polyether aryl ketone, and then machining; the length of the short carbon fiber is 50 to 800 μm.

2. The intramedullary nail of the knee joint prosthesis according to claim 1, characterized in that: The polyaryletherketone is selected from polyetheretherketone or polyetherketoneketone.

3. The intramedullary nail of the knee joint prosthesis according to claim 1, characterized in that: The diameter of the central part of the rod is 3-12 mm, and the weight percentage content of carbon fiber in the central part of the rod is 40-70%; the thickness of the surface winding part is 0.4-2 mm, and the weight percentage content of carbon fiber in the surface winding part is 45-70%.

4. The intramedullary nail of the knee joint prosthesis according to claim 1, characterized in that: The continuous carbon fibers in the surface winding portion and the continuous carbon fibers in the center portion of the rod are arranged in a staggered manner at an angle of ±30 to 60 degrees.

5. The intramedullary nail of the knee joint prosthesis according to claim 1, characterized in that: The intermediate layer is obtained by plasma spraying titanium powder, the mesh number of the titanium powder is 300 meshes; the thickness of the intermediate layer is 50 to 200 μm.

6. The intramedullary nail of the knee joint prosthesis according to claim 1, characterized in that: The outer layer is processed with steps and axially distributed grooves, and the percentage of carbon fiber in the outer layer is not less than 40%.

7. The intramedullary nail for knee joint prosthesis according to any one of claims 1 to 6, characterized in that: The core surface is further processed with inwardly sunken holes or grooves.

8. A method for preparing an intramedullary nail for a knee joint prosthesis according to any one of claims 1 to 7, characterized in that: The steps include: S1. preparing a continuous carbon fiber / polyether aryl ketone prepreg tape; S2, melt-mixing the chopped carbon fiber and the polyaryletherketone in a twin-screw extruder to obtain chopped carbon fiber / polyaryletherketone composite pellets; S3, cutting the continuous carbon fiber / polyaryletherketone prepreg into narrow strips, preheating the narrow strips and placing them in a preheated cylindrical die, extruding the polyaryletherketone through a screw and then melting it into the cylindrical die from the side, fully infiltrating the narrow strips under the action of pressure, cooling and shaping, and obtaining the center of the rod; or preheating the narrow strips and passing them through a cylindrical die heated to above the melting point of the polyaryletherketone, thermoforming them into a cylindrical shape in the die, and then pultruding and shaping them to obtain the center of the rod; or using a hot press plate with carbon fiber orientations of 0° / 45° / 90° / 135° as a profile, using a lathe to process it into a circular core along the 0° direction, wherein the content of the 0°-oriented carbon fiber layer is not less than 50%, to obtain the center of the rod; S4, winding a plurality of layers of continuous carbon fiber / polyether aryl ketone prepreg tapes on the surface of the central rod by staggered heating to obtain a core; S5, plasma spraying titanium powder to obtain a porous titanium intermediate layer; S6. Prepare the outer layer of the intramedullary nail by injection molding and coating; place the material in a preheated injection molding and coating mold, use the chopped carbon fiber / polyether aryl ketone composite pellets for injection molding and coating to obtain an intramedullary nail blank, and then machine it to form steps and axially distributed grooves to obtain a knee joint prosthesis intramedullary nail.

9. The method for preparing the intramedullary nail of a knee joint prosthesis according to claim 8, characterized in that: The width of the narrow strip is 4.0-8.0 mm, and the inner diameter of the cylindrical die is 4.0-10.0 mm.

10. The method for preparing the intramedullary nail of a knee joint prosthesis according to claim 8, characterized in that: The preheating temperature of the cylindrical die is 400°C, and the preheating temperature of the injection coating mold is 220-270°C.

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