Patella claw with shape memory function and manufacturing method thereof

Abstract

The present application relates to the technical field of intelligent medical instrument manufacturing, and discloses a patella claw with shape memory function and a manufacturing method thereof, which comprises a center connecting part with an arc and 3-8 claw arms extending outward from the center connecting part, and the end of the claw arm is provided with a barb; the patella claw is made of a nickel-titanium shape memory alloy material, and the chemical components of the nickel-titanium shape memory alloy material comprise, by weight percentage, 50%-56% of nickel (Ni), 0.15% or less of oxygen (O), 0.05% or less of carbon (C), 0.005% or less of hydrogen (H), 0.05% or less of nitrogen (N), and the balance of titanium (Ti). Through the implementation of a two-stage graded heat treatment process of solid solution homogenization + constrained aging setting, the present application solves the problems of complex thermal history and huge internal stress generated in the additive manufacturing process, ensures that the patella claw can rapidly respond to body temperature and restore the preset shape after being implanted into the human body, realizes the continuous active pressurization fixing function, and thus can enhance the biological response force of the final product.

Description

Technical Field

[0001] This invention relates to the field of intelligent medical device manufacturing technology, and in particular to a patellar claw with shape memory function and its manufacturing method. Background Technology

[0002] Patellar fractures are common intra-articular fractures in orthopedic clinics. Treatment requires anatomical reduction and strong internal fixation to enable patients to start knee joint rehabilitation exercises early. Among the many internal fixation devices, nickel-titanium shape memory alloy patellar claws, due to their unique shape memory effect and superelasticity, can provide continuous longitudinal compression and cohesion force. They not only provide reliable fixation but also effectively prevent the separation and displacement of fracture fragments. They have become an important medical device for treating patellar fractures. This active clamping characteristic makes them superior to traditional Kirschner wire tension bands or stainless steel wire ligation in clinical efficacy.

[0003] However, despite the excellent biomechanical properties of nickel-titanium shape memory alloys, their extremely high work hardening rate and superelasticity make the forming and processing of the material extremely difficult. Traditional manufacturing processes mainly rely on precision casting or machining, which have significant limitations. On the one hand, machining is difficult to handle the high hardness and high elasticity of nickel-titanium alloys, resulting in severe tool wear and low processing efficiency, making it difficult to manufacture complex and intricate features. On the other hand, casting processes are prone to casting defects such as shrinkage cavities and porosity, and the coarse grains lead to a decrease in the material's fatigue resistance. Patellar claws produced by traditional processes are mostly standard sizes, which cannot match the complex anatomical curvature of the patella surface of different patients. During surgery, doctors often need to manually bend and shape them based on experience, which not only increases the difficulty of the operation but also easily destroys the material's preset memory recovery force, leading to fixation failure or fracture caused by stress concentration.

[0004] With the development of digital medical technology, selective laser melting (SLM)-based metal additive manufacturing technology has made it possible to manufacture personalized implants, enabling precise customization based on the patient's anatomical structure. However, directly applying SLM technology to the manufacture of nickel-titanium shape memory alloys still faces severe technical challenges. Due to the extremely rapid heating and cooling rates brought about by the laser beam during the SLM process, huge residual thermal stress accumulates inside the formed part, which can easily lead to warping or even cracking of the part during printing or peeling from the substrate. At the same time, the shape memory function of nickel-titanium alloys is highly sensitive to chemical composition and microstructure. The high energy density of nickel easily causes burn-off and volatilization, leading to fluctuations in the Ni / Ti atomic ratio in the matrix. This makes it difficult to predict and control the phase transition temperature of the material. Existing conventional heat treatment methods often cannot simultaneously eliminate the melt pool defects unique to additive manufacturing and precisely control the phase transition temperature. As a result, the prepared patellar claw either loses its shape memory function or the recovery temperature does not conform to the human physiological environment, failing to generate sufficient cohesion force at a body temperature of 37°C, thus affecting the biomechanical response of the final product. Therefore, this invention designs a patellar claw with shape memory function and its manufacturing method based on the above-mentioned problems. Summary of the Invention

[0005] The purpose of this invention is to provide a patellar claw with shape memory function and its manufacturing method, which solves the problem that existing manufacturing processes are difficult to achieve personalized precision molding of complex anatomical structures of nickel-titanium alloy patellar claws while accurately controlling the phase transition temperature of the material to ensure that it has stable shape memory function and excellent biomechanical properties in the human body environment.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: a patellar claw with shape memory function, comprising a central connecting part with an arc and 3 to 8 claw arms extending outward from the central connecting part, wherein the ends of the claw arms are provided with barbs;

[0007] The patellar claw is made of a nickel-titanium shape memory alloy, the chemical composition of which, by weight percentage, includes:

[0008] Nickel (Ni) 50%-56%, oxygen (O) ≤0.15%, carbon (C) ≤0.05%, hydrogen (H) ≤0.005%, nitrogen (N) ≤0.05%, balance is titanium (Ti).

[0009] A method for manufacturing a patellar claw with shape memory function includes the following steps:

[0010] S1. First, construct a three-dimensional digital model of the patellar claw and slice it, while preparing nickel-titanium alloy spherical powder.

[0011] S2. Subsequently, under a vacuum or inert gas protection environment, based on the data from the slice processing, the nickel-titanium alloy spherical powder is melted layer by layer using a selective laser melting process to obtain a patellar claw blank.

[0012] S3. Then, the patellar claw blank is subjected to graded heat treatment, which includes a first stage of solution homogenization treatment and a second stage of constrained aging and shaping treatment to eliminate internal stress and set the phase transformation temperature.

[0013] S4. Finally, the patellar claw blank after the graded heat treatment is subjected to surface post-treatment to remove surface impurities and reduce roughness, thereby obtaining the patellar claw with shape memory function.

[0014] Preferably, in the step of preparing nickel-titanium alloy spherical powder, the physical property parameters of the selected nickel-titanium alloy spherical powder are: particle size range 15. -53 Sphericity ≥90%, Hall flow rate ≤50s / 50g, loose density 3.5g / cm³-4.5g / cm³;

[0015] In the step of constructing the 3D digital model and performing slicing, the thickness of the claw arm is set to 1mm-2.5mm, and the width of the claw arm is set to 2mm-5mm; the length of the barb is set to 1.5mm-3mm, and the angle between the barb and the tangent of the claw arm is set to 30-60 degrees; the layer thickness of the slicing process is set to 20. -50 .

[0016] Preferably, in the step of obtaining the patellar claw blank using selective laser melting, the laser scanning parameters are set as follows: laser power 120W-350W, scanning speed 400mm / s-1200mm / s, and scanning spacing 60mm. -120 ; and through formula Controlling volumetric energy density In the range of 40J / mm³-120J / mm³, among which For laser power, For scanning speed, For scanning spacing, The thickness is the layer thickness.

[0017] Preferably, the selective laser melting process further includes setting environmental control and scanning strategy: using high-purity argon in an inert gas protected environment with oxygen content controlled at ≤100ppm, and preheating the substrate to 80℃-200℃ before forming; the scanning strategy adopts a strip combination with interlayer rotation of 67° or 90°.

[0018] Preferably, in the step of performing graded heat treatment on the patellar claw blank, the first stage of solution homogenization treatment specifically involves heating the patellar claw blank to 800℃-950℃ under vacuum or argon protection, holding it at that temperature for 1 hour to 4 hours, and then cooling it to room temperature in the furnace.

[0019] Preferably, in the step of performing graded heat treatment on the patellar claw blank, the second stage of constrained aging and shaping treatment specifically involves: fixing the patellar claw blank after the solution homogenization treatment in a shaping mold, heating it to 400℃-550℃, holding it at that temperature for 30 minutes-90 minutes, and immediately subjecting it to ice water quenching at 0℃-5℃ or rapid air cooling after the holding period, so as to control the austenitic phase transformation end temperature of the material between 25℃-35℃.

[0020] Preferably, the post-surface treatment step of the patellar claw blank includes a low-temperature electrolytic polishing process, specifically: using a mixed solution of 70 vol%-90 vol% methanol and 10 vol%-30 vol% sulfuric acid or perchloric acid as the electrolyte; controlling the electrolyte temperature at -20℃-0℃, and polishing the patellar claw blank at a voltage of 10V-30V for a polishing time of 30 seconds-180 seconds.

[0021] Preferably, the surface post-treatment further includes sandblasting before the low-temperature electrolytic polishing treatment, with 100-200 mesh alumina ceramic sand as the sandblasting medium and a spraying pressure of 0.3MPa-0.6MPa.

[0022] Preferably, the surface post-treatment after the low-temperature electrolytic polishing treatment further includes cleaning and sterilization treatment, specifically: ultrasonically cleaning the patellar claw blank with acetone, anhydrous ethanol and deionized water in sequence, and finally performing high-pressure steam sterilization or ethylene oxide sterilization and packaging.

[0023] In summary, the present invention has at least one of the following beneficial technical effects:

[0024] 1. This invention solves the complex thermal history and huge internal stress problems generated in additive manufacturing by implementing a two-stage graded heat treatment process of solution homogenization and constrained aging. The first stage of high-temperature solution treatment eliminates interlayer stress and resets the microstructure, while the second stage of modulus-constrained aging and rapid quenching precisely controls the nickel-rich strengthening phase. The dispersed precipitation behavior of ) thus reduces the austenitic phase transformation end temperature of the material ( The temperature is precisely locked between 25℃ and 35℃, ensuring that the patellar claw can quickly respond to body temperature and restore the preset shape after implantation, thus achieving continuous active pressure fixation and enhancing the biological responsiveness of the final product.

[0025] 2. This invention significantly improves the compatibility of the implant with the anatomical surface of the human patella by designing a radial claw arm structure with barbs in the central connecting part and setting a specific angle of 30-60 degrees between the barbs and the tangent of the claw arm. This biomimetic structural design utilizes the restoring force generated by the shape memory effect and the mechanical locking action of the barbs to form a dual fixation mechanism, effectively preventing the device from slipping or falling off during frequent flexion and extension movements of the knee joint after surgery, and solving the fixation failure problem caused by poor fit of traditional internal fixation devices.

[0026] 3. By strictly limiting the low content range of interstitial elements such as oxygen, carbon, and hydrogen in the raw material nickel-titanium alloy powder, this invention eliminates microscopic defects that cause material embrittlement at the source. The low content of interstitial elements effectively prevents the formation of brittle oxides or hydrides at grain boundaries, significantly improving the fracture toughness and fatigue resistance of the material, and can meet the stringent safety requirements of long-term orthopedic implants.

[0027] 4. This invention employs low-temperature electrolytic polishing surface treatment technology, which removes semi-molten powder from the surface and reduces surface roughness while avoiding damage to the pre-set shape memory function due to heat generated during the polishing process. The low-temperature environment effectively inhibits the pitting corrosion reaction of the nickel-titanium substrate, promotes the formation of a uniform and dense titanium oxide passivation film on the surface, significantly improves the corrosion resistance and biocompatibility of the finished product, and reduces the risk of inflammatory reactions after implantation.

[0028] 5. This invention employs selective laser melting (SLM) additive manufacturing technology, combined with a specific volumetric energy density, to precisely control the energy input at... Within this range, it effectively overcomes the problems of difficult subtractive processing, serious material waste, and geometric limitations of traditional nickel-titanium alloys. This energy density range achieves the best balance between melt fluidity and solidification rate, avoiding unfused pores caused by too low energy or keyhole pores caused by too high energy. This results in a solid structure with extremely high density and isotropic mechanical properties, ensuring the structural integrity of the patellar claw under stress. Attached Figure Description

[0029] Figure 1 This is a perspective view of the present invention;

[0030] Figure 2 This is a schematic diagram showing the structure of the present invention;

[0031] Figure 3 This is a side view of the present invention;

[0032] Figure 4 This is one of the schematic diagrams of the method flow of the present invention;

[0033] Figure 5 This is a second schematic diagram of the method flow of the present invention;

[0034] Figure 6 This is the third schematic diagram of the method flow of the present invention;

[0035] Figure 7 This is the fourth schematic diagram of the method flow of the present invention;

[0036] Figure 8 This is the fifth schematic diagram of the method flow of the present invention.

[0037] Among them, 1. central connecting part; 2. claw arm; 3. barb. Detailed Implementation

[0038] The following is in conjunction with the appendix Figure 1 - Appendix Figure 8 The present invention will be further described in detail below.

[0039] The present invention provides a patellar claw with shape memory function, including a central connecting part 1 with an arc and 3 to 8 claw arms 2 extending outward from the central connecting part 1, and the end of the claw arm 2 is provided with barbs 3;

[0040] The patellar claw is made of a nickel-titanium shape memory alloy, whose chemical composition by weight percentage includes:

[0041] Nickel (Ni) 50%-56%, oxygen (O) ≤0.15%, carbon (C) ≤0.05%, hydrogen (H) ≤0.005%, nitrogen (N) ≤0.05%, balance is titanium (Ti).

[0042] A method for manufacturing a patellar claw with shape memory function includes the following steps:

[0043] S1. First, construct a three-dimensional digital model of the patellar claw and perform slicing. Simultaneously, prepare nickel-titanium alloy spherical powder. The physical properties of the selected nickel-titanium alloy spherical powder are as follows: particle size range 15... -53 The sphericity is ≥90%, the Hall flow rate is ≤50s / 50g, and the loose density is 3.5g / cm³-4.5g / cm³. In the step of constructing the 3D digital model and performing slicing, the thickness of claw arm 2 is set to 1mm-2.5mm, and the width is set to 2mm-5mm; the length of barb 3 is set to 1.5mm-3mm, and the angle between barb 3 and the tangent of claw arm 2 is set to 30-60 degrees; the layer thickness for slicing is set to 20. -50 ;

[0044] Specifically, pre-alloyed nickel-titanium (NiTi) spherical powder is first selected as the raw material. In order to ensure the stability and biosafety of the subsequent shape memory effect, the chemical composition of the powder must be strictly controlled. The nickel (Ni) content is 50%-56% by weight, and the balance is titanium (Ti). At the same time, the impurity content must be strictly controlled, with oxygen (O) ≤0.15%, carbon (C) ≤0.05%, hydrogen (H) ≤0.005%, and nitrogen (N) ≤0.05%. The low content of interstitial elements (O, C, N, H) helps to prevent material embrittlement and improve fatigue life.

[0045] In terms of physical properties, the powder particle size range is controlled within 15. -53 Furthermore, the sphericity is ≥90% to ensure that the powder has good flowability (Hall flow rate ≤50s / 50g) and bulk density (loose packing density 3.5g / cm³-4.5g / cm³) during the powder spreading process, thereby ensuring the density of the printed parts;

[0046] A 3D model of the patellar claw was constructed using CAD software. This model includes a central connecting part 1 with an arc conforming to the surface curvature of the human patella, and 3 to 8 claw arms 2 radiating outwards from the central connecting part 1. The thickness of the claw arms 2 is set to 1mm-2.5mm, and the width to 2mm-5mm, to balance structural strength and the feeling of a foreign body after implantation. The ends of the claw arms 2 are designed with barbs 3, with a length of 1.5mm-3.0mm. The angle between the axis of the barbs 3 and the tangent of the claw arm 2 is set to 30°-60°. This angle design aims to enhance gripping force and prevent dislodgement. The model was imported into slicing software for discretization, and the slice thickness was set to 20 mm. -50 This layer thickness range can balance molding accuracy and printing efficiency.

[0047] S2. Subsequently, under vacuum or inert gas protection, based on the data from the slice processing, a selective laser melting process is used to melt the nickel-titanium alloy spherical powder layer by layer to obtain a patellar claw blank. In the step of obtaining the patellar claw blank using the selective laser melting process, the laser scanning parameters are set as follows: laser power 120W-350W, scanning speed 400mm / s-1200mm / s, scanning spacing 60... -120 ; and through formula Controlling volumetric energy density In the range of 40J / mm³-120J / mm³, among which For laser power, For scanning speed, For scanning spacing, To determine the layer thickness, the selective laser melting process also includes setting environmental control and scanning strategies: high-purity argon is used in an inert gas protected environment with an oxygen content controlled at ≤100ppm, and the substrate is preheated to 80℃-200℃ before forming; the scanning strategy uses a combination of strips with interlayer rotation of 67° or 90°.

[0048] Specifically, this step uses a high-energy laser beam to melt and stack discrete metal powder layer by layer into a solid, namely a titanium bone claw blank. This process is carried out under strictly controlled atmosphere and energy density to avoid material hydrogenation and internal defects.

[0049] Molding environment control: In order to prevent the titanium alloy from oxidizing violently at high temperature, the molding chamber needs to be evacuated and filled with high-purity argon (purity ≥99.90%), and the argon content should always be maintained at ≤100ppm. In addition, the substrate is preheated to 80℃-200℃ before printing begins. This preheating operation helps to reduce the temperature gradient when the molten pool solidifies, thereby reducing the accumulation of thermal stress during the molding process.

[0050] Laser scanning parameters and strategies: The setting of process parameters directly determines the stability of the molten pool and the density of the formed parts. Specific parameters are as follows: Laser power (P): 120W-350W; Scanning speed (v): 400mm / s-1200mm / s; Scanning interval (h): 60 -120 ;

[0051] Energy density control: through the volumetric energy density formula (where t is the layer thickness) By comprehensively adjusting the above parameters, E is controlled between 40J / mm³ and 120J / mm³. Within this energy density range, the powder can be fully melted, avoiding the formation of unfused pores (too low energy) or keyhole pores (too high energy).

[0052] Scanning strategy: A strip scanning strategy with interlayer rotation of 67° or 90° is adopted to interrupt the continuous growth direction of interlayer grains and reduce the anisotropy of material mechanical properties.

[0053] S3. Then, the patellar claw blank is subjected to graded heat treatment. The graded heat treatment includes the first stage of solution homogenization treatment and the second stage of constrained aging and shaping treatment to eliminate internal stress and set the phase transformation temperature. In the step of graded heat treatment of the patellar claw blank, the first stage of solution homogenization treatment is as follows: the patellar claw blank is heated to 800℃-950℃ under vacuum or argon protection and held for 1 hour to 4 hours, and then cooled to room temperature in the furnace. In the step of graded heat treatment of the patellar claw blank, the second stage of constrained aging and shaping treatment is as follows: the patellar claw blank after solution homogenization treatment is fixed in the shaping mold, heated to 400℃-550℃ and held for 30 minutes to 90 minutes. After the holding time is completed, it is immediately subjected to ice water quenching at 0℃-5℃ or rapid air cooling to control the austenitic phase transformation end temperature of the material between 25℃-35℃.

[0054] Specifically, SLM-molded patellar claw hairs often have extremely high residual stress and their phase transition temperature does not meet clinical requirements. This step, through solution homogenization and constrained aging graded treatment, endows the product with specific shape memory function.

[0055] The first stage: solution homogenization treatment. The patellar claw hair is placed in a vacuum furnace or argon-protected furnace and heated to 800℃-950℃. It is held for 1 hour to 4 hours and then cooled to room temperature with the furnace. The high temperature treatment can eliminate the thermal history and element segregation in the microstructure accumulated during the SLM process, homogenize the matrix structure, and completely release the internal residual stress, preparing for the subsequent aging precipitation.

[0056] The second stage: Constrained aging and shaping treatment. The solution-treated patellar claw blank is placed into a pre-prepared shaping mold. The mold cavity has the final designed clamping curvature. Under the constraint of the mold, the blank is heated to 400℃-550℃ and held for 30-90 minutes. After the holding time, the blank, along with the mold or removed from the workpiece, is immediately subjected to ice water quenching at 0℃-5℃ or rapid air cooling. During the medium-temperature aging process, nickel-rich... The dispersed precipitation of phases strengthens the matrix and alters the atomic ratio of Ni / T in the matrix, thereby adjusting the martensitic transformation temperature. By controlling the above parameters, the austenitic transformation end temperature of the material can be controlled. The temperature is precisely set between 25℃ and 35℃ to ensure that the patellar claw can automatically recover the set clasp shape and generate continuous pressure after being implanted in the human body (approximately 37℃).

[0057] S4. Finally, the patellar claw blank after graded heat treatment undergoes surface post-treatment to remove surface impurities and reduce roughness, thus obtaining a patellar claw with shape memory function. The surface post-treatment step includes low-temperature electrolytic polishing, specifically: using a mixed solution of 70 vol%-90 vol% methanol and 10 vol%-30 vol% sulfuric acid or perchloric acid as the electrolyte; controlling the electrolyte temperature at -20℃-0℃ and operating at a voltage of 10V-30V. The patellar claw blank is polished for 30-180 seconds. The surface post-treatment before the low-temperature electrolytic polishing process also includes sandblasting. The sandblasting medium is 100-200 mesh alumina ceramic sand, and the blasting pressure is 0.3MPa-0.6MPa. The surface post-treatment after the low-temperature electrolytic polishing process also includes cleaning and sterilization. Specifically, the patellar claw blank is ultrasonically cleaned with acetone, anhydrous ethanol, and deionized water in sequence. Finally, it is sterilized by high-pressure steam or ethylene oxide sterilization and packaged.

[0058] Specifically, the surface of the heat-treated patellar claw blank has an oxide layer and semi-molten powder, which need to be surface-treated to meet the biological requirements of the implant.

[0059] Sandblasting: Alumina ceramic sand with a particle size of 100-200 mesh is used to blast the workpiece surface under a pressure of 0.3MPa-0.6MPa. It is mainly used to physically remove semi-molten powder particles adhering to the surface.

[0060] Low-temperature electrolytic polishing: The low-temperature electrolytic polishing process further reduces surface roughness and improves corrosion resistance. Electrolyte: Composed of 70 vol%-90 vol% methanol and 10 vol%-30 vol% sulfuric acid or perchloric acid; Parameters: Electrolyte temperature controlled at -20℃-0℃, voltage 10V-30V, polishing time 30s-180s. The low-temperature environment helps to control the chemical reaction rate, avoid pitting corrosion on the nickel-titanium alloy surface, and form a uniform and dense titanium oxide passivation film.

[0061] Cleaning and sterilization: Finally, ultrasonic cleaning is performed sequentially using acetone, anhydrous ethanol, and deionized water, followed by sterilization and packaging using high-pressure steam or ethylene oxide to obtain the finished product.

[0062] To demonstrate the advantages of this invention in shape memory recovery, the following embodiments and comparative examples are designed:

[0063] Example 1: Patellar claw prepared according to the above steps;

[0064] Comparative Example 1: Compared with Example 1, the difference is that the content of interstitial oxygen (O) in the nickel-titanium alloy spherical powder used is 0.25 wt.% (exceeding the range of "≤0.15 wt.%)", and all other contents are the same;

[0065] Comparative Example 2: Compared with Example 1, the difference is that in the graded heat treatment in step S3, the first stage of solution homogenization treatment is omitted, and the blank after SLM forming is directly subjected to the second stage of constrained aging and shaping treatment. The rest are the same.

[0066] Comparative Example 3: Compared with Example 1, the difference is that in the graded heat treatment in step S3, the second stage of constrained aging and shaping treatment is omitted, and only the first stage of solution homogenization treatment is performed before surface treatment as the finished product. The rest are the same.

[0067] Comparative Example 4: Compared with Example 1, the difference is that in the second stage of heat treatment in step S3, the cooling method after the heat preservation is changed to furnace cooling to room temperature or natural air cooling (instead of 0℃-5℃ ice water quenching), and the rest are the same.

[0068] At this point, shape memory recovery rate and fatigue resistance performance tests were conducted, as follows:

[0069] Shape memory recovery rate test

[0070] Experimental sample preparation: Two patellar claws prepared in Example 1, Comparative Example 2 (without solution treatment), Comparative Example 3 (without aging), and Comparative Example 4 (without ice water quenching) were selected as test samples. The claw arm bending angle of all samples under their initial design state was recorded before testing. (That is, the angle between the tangent of the claw arm and the central axis; the standard state is set in this experiment as follows) );

[0071] Experimental steps:

[0072] Low-temperature deformation: First, prepare a low-temperature container filled with an ice-water mixture, maintaining the temperature at 0℃±1℃. Immerse each group of samples in the ice water for 5 minutes to allow them to fully transform into the martensitic phase. While still submerged, use mechanical tools to forcibly unfold all the claw arms of the patellar claw to a horizontal and straight state (i.e., the unfolding angle is...). And maintain this deformed state at low temperature for 30 seconds;

[0073] Temperature recovery: Prepare a water bath containing constant temperature phosphate buffer (PBS, simulated body fluid), and strictly control the temperature at 37℃±0.5℃. Quickly remove the sample that is flat at low temperature and put it into the 37℃ water bath.

[0074] Measurement and Calculation: Observe and record the shape recovery process of the sample in a 37℃ water bath. After the shape stabilizes (approximately 60 seconds), remove the sample and, without applying external force, use an image measuring instrument to measure the final angle of each claw arm after recovery. The shape memory recovery rate is calculated according to the formula. :

[0075]

[0076] in, The angle after deformation. For the restored angle, For the initial angle ( ), The closer to 100%, the better the memory function. Specific experimental data are shown in the table below:

[0077] Fatigue performance test

[0078] Experimental sample preparation: Two finished patellar claws were selected from Example 1, Comparative Example 1 (high oxygen / high impurity content), and Comparative Example 2 (no solid solution treatment). All samples had the same surface condition (all were sandblasted and electropolished).

[0079] Experimental steps

[0080] Installation and environmental setup: Using a dynamic fatigue testing machine equipped with an environmental chamber, the central connecting part of the patellar claw is fixed to the lower clamp, and a specially designed claw hook clamp is fixed to the end barbs of all claw arms. The environmental chamber is filled with circulating physiological saline at 37℃±1℃ to simulate the corrosive fatigue environment in the body.

[0081] Loading parameter settings: The displacement control mode is used for cyclic loading. The claw arm 2 is slightly opened to put it in a tensioned state (simulating the pretension after holding the scale bone). Based on the pretension, the claw arm 2 is subjected to reciprocating opening motion. The displacement amplitude of the end of the claw arm 2 is set to 2.0mm (simulating the deformation of the claw arm caused by the micro-movement of the fracture fragments during knee flexion and extension). Frequency: 5Hz (sine wave).

[0082] Termination conditions and records: Continuously apply cyclic loading until any claw arm 2 breaks or develops a visible crack, which is considered a failure. Record the total number of cycles at the time of failure. If the circuit does not break after 500,000 cycles, the experiment is stopped and recorded as ">500,000". The specific experimental data is shown in the table below:

[0083]

[0084] Based on the above experimental data and test results, the effects of the technical solution of this invention are summarized as follows: The test results of the shape memory recovery rate fully confirm the key role of the two-stage graded heat treatment process in regulating the intelligent properties of nickel-titanium alloys in this invention. Selective laser melting and forming introduces complex microstructure anisotropy and huge residual internal stress. If not treated or treated improperly (such as omitting the solution or aging steps in the comparative example), the lattice defects inside the material will severely hinder the reversible phase transformation between martensite and austenite, leading to the loss or incomplete recovery of the memory effect. This invention, through the high-temperature solution homogenization in the first stage, completely eliminates the thermal history generated during the printing process; combined with the constrained aging and rapid freezing process in the second stage, it promotes the formation of nickel-rich strengthening phases (…). The diffuse precipitation of ) and this specific microstructure evolution not only strengthens the matrix but also precisely guides the phase transformation path, ensuring that the finished product can quickly and accurately recover to the preset cohesive shape under human body temperature. The test results of fatigue performance profoundly reveal the decisive influence of the synergistic effect of raw material composition control and manufacturing process on the service life of implants. Nickel-titanium alloys are extremely sensitive to stress concentration and impurities. This invention limits the content of interstitial elements such as oxygen and hydrogen in the powder, effectively avoiding the formation of brittle inclusions such as oxides or hydrides at grain boundaries, eliminating the source of fatigue crack initiation. Comparative data shows that excessive impurity content can lead to early brittle fracture of the device under cyclic loading. In addition, combined with the above-mentioned solid solution stress relief treatment, this invention successfully eliminates the interlayer stress concentration phenomenon unique to additive manufacturing, so that the patellar claw can still maintain excellent structural integrity and fatigue fracture resistance when facing the dynamic mechanical environment of high-frequency flexion and extension of the knee joint.

[0085] In summary, the manufacturing method provided by this invention deeply integrates the energy density control of laser additive manufacturing with subsequent surface and heat treatment modifications, overcoming the shortcomings of traditional subtractive manufacturing in achieving both complex structures and excellent performance. Experiments have demonstrated that this technical approach not only achieves precise molding of the complex biomimetic barb structure of the patellar claw, but also obtains excellent comprehensive performance with high density, high shape recovery rate, and long fatigue life through precise control of microstructures. It effectively solves the problems of poor functional stability and low biomechanical fit in existing technologies, meeting the stringent requirements of orthopedic implants for long-term implantation safety and functionality.

[0086] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A patellar claw with shape memory function, comprising a curved central connecting portion (1) and 3 to 8 claw arms (2) extending outward from said central connecting portion (1), characterized in that, The claw arm (2) is provided with a barb (3) at its end; The patellar claw is made of a nickel-titanium shape memory alloy, the chemical composition of which, by weight percentage, includes: Nickel (Ni) 50%-56%, oxygen (O) ≤0.15%, carbon (C) ≤0.05%, hydrogen (H) ≤0.005%, nitrogen (N) ≤0.05%, balance is titanium (Ti).

2. A method for manufacturing a patellar claw with shape memory function, characterized in that, A patellar claw with shape memory function according to claim 1 includes the following steps: S1. First, construct a three-dimensional digital model of the patellar claw and slice it, while preparing nickel-titanium alloy spherical powder. S2. Subsequently, under a vacuum or inert gas protection environment, based on the data from the slice processing, the nickel-titanium alloy spherical powder is melted layer by layer using a selective laser melting process to obtain a patellar claw blank. S3. Then, the patellar claw blank is subjected to graded heat treatment, which includes a first stage of solution homogenization treatment and a second stage of constrained aging and shaping treatment to eliminate internal stress and set the phase transformation temperature. S4. Finally, the patellar claw blank after the graded heat treatment is subjected to surface post-treatment to remove surface impurities and reduce roughness, thereby obtaining the patellar claw with shape memory function.

3. The method for manufacturing a patellar claw with shape memory function according to claim 2, characterized in that, In the step of preparing nickel-titanium alloy spherical powder, the physical property parameters of the selected nickel-titanium alloy spherical powder are: particle size range 15. -53 Sphericity ≥90%, Hall flow rate ≤50s / 50g, loose density 3.5g / cm³-4.5g / cm³; In the step of constructing the three-dimensional digital model and performing slicing, the thickness of the claw arm (2) is set to 1mm-2.5mm, and the width of the claw arm (2) is set to 2mm-5mm; the length of the barb (3) is set to 1.5mm-3mm, and the angle between the barb (3) and the tangent of the claw arm (2) is set to 30-60 degrees; the layer thickness of the slicing process is set to 20. -50 .

4. A method for manufacturing a patellar claw with shape memory function according to claim 2 or 3, characterized in that, In the step of obtaining the patellar claw blank using selective laser melting, the laser scanning parameters are set as follows: laser power 120W-350W, scanning speed 400mm / s-1200mm / s, and scanning spacing 60mm. -120 ; and through formula Controlling volumetric energy density In the range of 40J / mm³-120J / mm³, among which For laser power, For scanning speed, For scanning spacing, The thickness is the layer thickness.

5. A method for manufacturing a patellar claw with shape memory function according to claim 4, characterized in that, The steps of selective laser melting process also include setting environmental control and scanning strategy: high-purity argon is used in an inert gas protected environment, and the oxygen content is controlled at ≤100ppm. The substrate is preheated to 80℃-200℃ before molding. The scanning strategy adopts a strip combination with interlayer rotation of 67° or 90°.

6. A method for manufacturing a patellar claw with shape memory function according to claim 2, characterized in that, In the step of graded heat treatment of the patellar claw blank, the first stage of solution homogenization treatment specifically involves heating the patellar claw blank to 800℃-950℃ under vacuum or argon protection, holding it at that temperature for 1 hour to 4 hours, and then cooling it to room temperature in the furnace.

7. A method for manufacturing a patellar claw with shape memory function according to claim 6, characterized in that, In the step of graded heat treatment of the patellar claw blank, the second stage of constrained aging and shaping treatment specifically involves fixing the patellar claw blank after the solution homogenization treatment in a shaping mold, heating it to 400℃-550℃, holding it at that temperature for 30 minutes to 90 minutes, and immediately performing ice water quenching or rapid air cooling at 0℃-5℃ after the holding time, so as to control the austenitic phase transformation end temperature of the material between 25℃ and 35℃.

8. A method for manufacturing a patellar claw with shape memory function according to claim 2, characterized in that, The post-surface treatment of the patellar claw blank includes a low-temperature electrolytic polishing process, specifically: using a mixed solution of 70 vol%-90 vol% methanol and 10 vol%-30 vol% sulfuric acid or perchloric acid as the electrolyte; controlling the electrolyte temperature at -20℃-0℃, and polishing the patellar claw blank at a voltage of 10V-30V for 30 seconds-180 seconds.

9. A method for manufacturing a patellar claw with shape memory function according to claim 8, characterized in that, The surface post-treatment also includes sandblasting before the low-temperature electrolytic polishing treatment. The sandblasting medium is 100-200 mesh alumina ceramic sand, and the spraying pressure is 0.3MPa-0.6MPa.

10. A method for manufacturing a patellar claw with shape memory function according to claim 8, characterized in that, The surface post-treatment, following the low-temperature electrolytic polishing treatment, also includes cleaning and sterilization treatment, specifically: ultrasonic cleaning of the patellar claw blank is performed sequentially using acetone, anhydrous ethanol, and deionized water, and finally high-pressure steam sterilization or ethylene oxide sterilization packaging is performed.

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