Degradable controllable hydroxyapatite / poly-l-lactic acid interface bone nail and manufacturing method thereof

Abstract

The application discloses a degradable controllable hydroxyapatite / PLLA interface bone nail and a manufacturing method thereof. The interface bone nail is formed by laser selective melting sintering of hydroxyapatite / PLLA composite powder. The hydroxyapatite / PLLA composite powder comprises 20-40% of hydroxyapatite and 60-80% of PLLA in terms of mass fraction. The manufacturing method comprises the following steps: placing the hydroxyapatite / PLLA composite powder processed through ball milling, extrusion granulation, powder crushing and spheroidization into a laser selective melting system, and printing the degradable controllable interface bone nail layer by layer. The bone nail surface is provided with openings, which are connected with the through holes in the nail body. The number of the openings can be adjusted to control the degradation rate of the bone nail in the human body while ensuring the fixing strength. Meanwhile, the new bone grows into the bone nail through the openings on the surface of the bone nail, thereby enhancing the fixing strength of the grafted ligament in the bone. The calcium and phosphorus generated by the degradation of the bone nail also contribute to the growth of the new bone.

Description

Technical Field

[0001] This invention belongs to the field of biomaterials technology, specifically relating to a bone nail using a degradable and controllable hydroxyapatite / L-polylactic acid interface and its manufacturing method. Background Technology

[0002] With the popularization of fitness for all, ligament injuries, such as cruciate ligament injuries in the knee, have become the most common sports-related injuries. Ligament injuries are difficult to heal on their own. If left untreated, repeated sprains can occur, leading not only to severe joint dysfunction but also damage to structures such as articular cartilage and the meniscus, resulting in premature aging of the joint and arthritis, significantly reducing the patient's quality of life. Currently, ligament reconstruction is widely considered the most effective means of restoring joint function. The specific method involves creating a tunnel in the bone to accommodate the ligament, and then using interfacial bone screws to fix the ligament tip to the inner wall of the bone tunnel. Although patients can regain their function through reconstruction surgery, every year some patients experience failed reconstruction healing, mainly due to poor healing of the interface between the ligament tip and the bone tunnel. Analysis suggests that this is related to the material of the interface bone screw. Currently, it is mainly made of metal or alloy in clinical practice, which brings many problems to the treatment process: (1) It cannot be degraded and the bone screw needs to be removed by a second surgery after the bone heals; (2) Its rigidity is much greater than that of cancellous bone, which leads to stress shielding; (3) It will produce toxic metal ions under wear conditions, which will lead to inflammation.

[0003] Polylactic acid (PLA) possesses excellent biocompatibility and biodegradability, and has been approved by the FDA for human implantation, making it an ideal material for preparing interfacial bone screws. Interfacial bone screws made with PLA gradually degrade in vivo, with degradation products becoming intermediates in the tricarboxylic acid cycle during carbohydrate metabolism, and then being completely metabolized into carbon dioxide and water by enzymes. Furthermore, during the degradation of PLA interfacial bone screws, the numerous neatly arranged longitudinal fibers within the bone tunnel are disrupted, creating pores that facilitate the migration and replacement of cancellous bone. However, the degradation rate of PLA interfacial bone screws in vivo is slow, requiring 7–10 years for complete degradation, thus delaying the healing time of the interface between the ligament and the bone tunnel. Clinically, the degradation rate of interfacial bone screws needs to be adjustable. Specifically, in the early postoperative period before new bone formation, the interfacial bone screw needs to have mechanical strength matching the bone to effectively fix the ligament ends and induce bone growth; in the mid-to-late postoperative period after new bone formation and complete recovery, the interfacial bone screw needs to gradually degrade until it is completely absorbed. Therefore, how to achieve an interface bone nail with a controllable degradation rate that can induce rapid healing between ligament grafts and bone has become an urgent clinical problem to be solved.

[0004] For example, the zinc-manganese-magnesium alloy interface screw for anterior cruciate ligament reconstruction and fixation disclosed in CN112957539A contains multiple metals, which may produce toxic metal ions under wear conditions, leading to inflammation. At the same time, it cannot control its own degradation rate to match the growth rate of new bone when fixing ligaments, which is not conducive to new bone growth. Summary of the Invention

[0005] One object of the present invention is to solve at least the above-mentioned problems and / or defects, and to provide at least the advantages described below.

[0006] To achieve these objectives and other advantages according to the present invention, a degradable and controllable hydroxyapatite / L-polylactic acid interface bone nail is provided, which is formed by selective laser melting and sintering of hydroxyapatite / L-polylactic acid composite powder, wherein the hydroxyapatite / L-polylactic acid composite powder comprises 20-40% by mass of hydroxyapatite and 60-80% by mass of L-polylactic acid.

[0007] Preferably, the threaded portion of the surface of the interface bone screw body has at least one opening, and the openings are regularly or irregularly distributed on the bone screw body.

[0008] Preferably, the diameter of the opening is 200–600 μm.

[0009] A method for fabricating a degradable and controllable hydroxyapatite / L-polylactic acid interface bone screw includes the following steps:

[0010] Step 1: Use computed tomography (CT) to scan the joint area where the patient's ligament is defective or torn to obtain joint data. Then, use image processing software to analyze and extract the data. Use three-dimensional data to accurately measure the shape and volume of the surrounding joints to determine the diameter of the bone tunnel that needs to be excavated. Finally, use computer-aided design software to design a three-dimensional model of the interface bone nail.

[0011] Step 2: Mix hydroxyapatite powder and L-polylactic acid powder to obtain hydroxyapatite / L-polylactic acid composite powder, and then ball mill the hydroxyapatite / L-polylactic acid composite powder in a ball mill.

[0012] Step 3: Place the ball-milled hydroxyapatite / L-polylactic acid composite powder into a twin-screw extruder and extrude it through a twin-screw extruder. Then, shear it to obtain sheared particles.

[0013] Step 4: Grind the sheared particles into powder using a cryogenic grinder;

[0014] Step 5: Spheroidize the powder from Step 4 using a spheroidizing device to obtain spheroidized powder;

[0015] Step 6: Import the three-dimensional model of the interface bone nail into the laser selective melting system, then place the spheroidized powder into the laser selective melting system, and print the degradable controllable interface bone nail layer by layer according to the three-dimensional model of the interface bone nail. During single-layer sintering, the laser is scanned twice, the first scan is in the X direction and the second scan is in the Y direction.

[0016] Preferably, in step one, the diameter of the interface bone nail is 0.5 to 1 mm smaller than the diameter of the bone tunnel.

[0017] Preferably, in step two, the ball milling speed is 180-250 rpm and the ball milling time is 1.5-2.5 h.

[0018] Preferably, in step three, the feed temperature of the twin-screw extruder is 170–180°C, the discharge temperature is 180–190°C, and the rotation speed is 95–115 rpm.

[0019] Preferably, in step four, the particle size of the pulverized powder is less than 70 μm, the temperature during the pulverization process is between -180°C and -150°C, and the main unit speed is between 45 and 47 rpm.

[0020] Preferably, in step five, the angle of repose of the spheroidized powder is ≤32°, the temperature of the spheroidizing equipment is set to 220~240℃, and the feed speed is 5~7rpm.

[0021] Preferably, in step six, the laser power is 1 to 1.3 W, the scanning rate is 90 to 110 mm / s, and the printing thickness is 0.1 to 0.3 mm.

[0022] Preferably, before mixing the hydroxyapatite powder and L-polylactic acid powder, the hydroxyapatite powder is reinforced with dextran, collagen, and calcium fluoride. The reinforcement method is as follows: The hydroxyapatite is modified by mixing calcium fluoride powder and hydroxyapatite powder in a mass ratio of 1:6, followed by high-temperature sintering at 1150–1200°C for 1–2 hours. This process decomposes some of the hydroxyapatite into fluorapatite, yielding hydroxyapatite containing fluorapatite, which is then ground into powder. Next, a 20 wt% dextran solution, a 0.01 mol / L sodium periodate solution, and a 0.01 mol / L potassium permanganate solution are weighed in a mass ratio of 10:3:1. The mixture is then processed using the sodium periodate solution and potassium permanganate solution... Potassium solution is used to oxidize and modify dextran to obtain oxidized dextran. Then, 70-80 parts by weight of hydroxyapatite powder containing fluorinated apatite, 5-10 parts by weight of oxidized dextran, and 10-20 parts by weight of collagen are weighed and mixed. The mixture is then added to 70-80 parts by weight of water and stirred thoroughly in a high-speed mixer at a speed of 800-1200 rpm for 0.5-1 h until a paste is formed. The paste is then placed in a freeze dryer and freeze-dried at -40°C for 12-24 h. After that, it is pulverized in a pulverizer at a speed of 1200-1600 rpm for 3-12 h. The pulverized mixture is then ground in a mill for 2-4 h at a speed of 150-180 rpm to obtain reinforced hydroxyapatite powder.

[0023] Hydroxyapatite containing a portion of fluorapatite, obtained by calcining a mixture of calcium fluoride and hydroxyapatite, provides heterogeneous nucleation for hydroxyapatite, resulting in well-crystallized hydroxyapatite. Furthermore, the addition of calcium fluoride powder increases the calcium-to-phosphorus ratio of the hydroxyapatite, which is beneficial for improving its stability. The further addition of oxidized dextran, along with collagen, allows for a self-assembly reaction with the hydroxyapatite, forming strong intermolecular forces—Schiff bases. Simultaneously, the cations Ca in the hydroxyapatite... 2+ Nucleophilic addition occurs, fundamentally enhancing the mechanical properties of the scaffold.

[0024] The present invention has at least the following beneficial effects:

[0025] (1) The degradable and controllable hydroxyapatite / L-polylactic acid interface bone nail used in this invention can undergo natural degradation and release calcium and phosphorus, which are easily absorbed and utilized by surrounding tissues, inducing the growth of new bone, thereby accelerating the interface healing between ligament grafts and bone.

[0026] (2) The present invention utilizes laser selective melting technology to prepare a degradable controllable interface bone nail, wherein the aperture size of the hole on the surface of the nail body is 200-600μm, which is conducive to the growth of new bone into the interior of the nail body, thereby maximizing the bonding surface between the bone nail and the bone, promoting bone growth and improving the fixation strength of the ligament graft in the bone after surgery.

[0027] (3) This invention utilizes laser selective melting technology to prepare degradable controllable interface bone nails. While ensuring its fixation strength, the number of through holes on the nail surface can be adjusted according to different ages and bone growth rates in different locations, thereby controlling the degradation rate of the interface bone nail in vivo and matching it with the new bone growth rate.

[0028] (4) The composite powder used in this invention is processed by extrusion granulation, crushing and spheroidization, and has the characteristics of uniform mixing, regular shape and good fluidity, which is beneficial to powder spreading in the printing process and avoids various defects and low forming accuracy in the sintering process.

[0029] (5) The hydroxyapatite containing a portion of fluorapatite obtained by calcining a mixture of calcium fluoride and hydroxyapatite provides heterogeneous nucleation for hydroxyapatite, resulting in good crystallinity. Furthermore, the addition of calcium fluoride powder increases the calcium-to-phosphorus ratio of the hydroxyapatite, which is beneficial for improving its stability. The addition of oxidized dextran, along with collagen, allows for a self-assembly reaction with the hydroxyapatite, forming strong intermolecular forces—Schiff bases. Simultaneously, the cations Ca in the hydroxyapatite... 2+ Nucleophilic addition occurs, fundamentally enhancing the mechanical properties of the scaffold.

[0030] In summary, this invention solves the problem of uncontrollable degradation of absorbable interfacial bone screws, which leads to slow or poor healing between ligament grafts and bone. The degradable hydroxyapatite / L-polylactic acid interfacial bone screw of this invention is naturally degradable, and its degradation products, including calcium and phosphorus, are easily absorbed by surrounding bone tissue, accelerating bone regeneration and thus speeding up the healing process between the ligament graft and bone. Furthermore, the use of laser selective melting technology to prepare an interfacial bone screw with perforated surfaces facilitates new bone ingrowth into the screw, maximizing the interface between the screw and bone. This promotes bone growth and improves the fixation strength of the ligament graft within the bone postoperatively. Simultaneously, while ensuring the fixation strength of the interfacial bone screw, the number of perforations on the screw surface can be adjusted according to different ages and bone growth rates at different locations, thereby regulating its degradation rate within the body to match the rate of new bone growth, ultimately achieving the goal of ligament reconstruction.

[0031] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached image description:

[0032] Figure 1 This is a front view structural diagram of Embodiment 1 of the present invention;

[0033] Figure 2 This is a sample image of Embodiment 1 of the present invention;

[0034] Figure 3 This is an image of Alizarin Red staining of stem cells from Example 1 of the present invention after 21 days of culture in interfacial bone nail extract.

[0035] Figure 4 This is a biocompatibility test diagram of Embodiment 1 of the invention. Detailed implementation method:

[0036] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0037] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not imply the presence or addition of one or more other elements or combinations thereof.

[0038] Example 1

[0039] A method for fabricating a degradable and controllable hydroxyapatite / L-polylactic acid interface bone screw includes the following steps:

[0040] A mixed powder containing 30% hydroxyapatite and 70% L-polylactic acid was weighed using an electronic balance. This mixed powder was then subjected to ball milling, extrusion granulation, pulverization, and spheroidization processes to obtain a composite powder with regular shape and good flowability. This powder was then placed in a laser selective melting system. The ball milling speed was 190 rpm, and the milling time was 2.2 hours. The ball-milled composite powder was then extruded and granulated, and sheared to obtain sheared particles. The temperature at the feed end of the twin-screw extruder was 173°C, the discharge end temperature was 183°C, and the extrusion speed was 95 rpm. The sheared particles were then pulverized into powder with a particle size less than 70 μm using a liquid nitrogen pulverizer. The pre-cooling temperature and pulverization temperature of the liquid nitrogen pulverizer were both -155°C, the main motor speed was 46 rpm, the fan speed was 9 rpm, and the discharge port speed was 6 rpm. The pulverized irregular powder was then placed in a vacuum drying oven and dried under vacuum conditions for 12 hours at a temperature of 60°C. The dried hydroxyapatite / L-polylactic acid composite powder was spheroidized using an air fluidized bed apparatus. The angle of repose after spheroidization was ≤34°. The heating temperature of the air fluidized bed apparatus was 225℃, and the feed speed was 6 rpm. Computed tomography (CT) was used to scan the joint area of ​​the patient's ligament defect or rupture to obtain joint data. Image processing software was then used to analyze and extract the data. The shape and volume of the surrounding joint were accurately measured using three-dimensional data to determine the diameter of the bone tunnel to be excavated. A model of the interface bone nail, 0.5 mm smaller than the diameter of the bone tunnel, was designed using computer-aided design software. After generating an STL file, it was imported into a laser selective melting system. Finally, a biodegradable interface bone nail was printed using high-energy laser. The scanning strategy was as follows: during single-layer sintering, the laser was scanned twice, first in the X direction and then in the Y direction. The laser power was 1W, the scanning rate was 100 mm / s, and the printing layer thickness was 0.2 mm.

[0041] Scanning electron microscopy revealed that a regularly shaped hydroxyapatite / L-polylactic acid composite powder was prepared by ball milling, extrusion granulation, pulverization and spheroidization processes, with a repose angle of 29.8°, showing good flowability.

[0042] It can be adjusted as follows Figure 1 The number of openings 1 in the controllable degradation interface bone screw shown can be adjusted to regulate its degradation rate in the human body, so that its degradation rate matches the rate of new bone growth.

[0043] Observe the prints produced using composite powder with good flowability, such as Figure 2 The degradable controllable interface bone screw shown in the figure has no obvious defects and has high shape accuracy.

[0044] Mechanical performance testing revealed that the fixation strength of the degradable controllable hydroxyapatite / L-polylactic acid interface bone nail is 612 MPa, which is higher than the maximum strength required for ligament daily activities (450 MPa), meeting the clinical implantation requirements.

[0045] Stem cell culture tests revealed that, just as Figure 3 As shown, degradable and controllable hydroxyapatite / L-polylactic acid interface bone nails promote stem cell growth.

[0046] Biocompatibility testing revealed that, as Figure 4 As shown, the degradable and controllable hydroxyapatite / L-polylactic acid interface bone screw can induce bone growth and has good bioactivity.

[0047] Example 2

[0048] A method for fabricating a degradable and controllable hydroxyapatite / L-polylactic acid interface bone screw includes the following steps:

[0049] A mixed powder containing 20% ​​hydroxyapatite and 80% L-polylactic acid was weighed using an electronic balance. This mixed powder was then subjected to ball milling, extrusion granulation, pulverization, and spheroidization processes to obtain a composite powder with regular shape and good flowability. This powder was then placed in a laser selective melting system. The ball milling speed was 180 rpm, and the milling time was 2.5 hours. The ball-milled composite powder was then extruded and granulated, and sheared to obtain sheared particles. The temperature at the feed end of the twin-screw extruder was 170°C, the discharge end temperature was 180°C, and the extrusion speed was 95 rpm. The sheared particles were then pulverized into powder with a particle size less than 70 μm using a liquid nitrogen pulverizer. The pre-cooling temperature and pulverization temperature of the liquid nitrogen pulverizer were both -150°C, the main motor speed was 45 rpm, the fan speed was 8 rpm, and the discharge port speed was 5 rpm. The pulverized irregular powder was then placed in a vacuum drying oven and dried under vacuum conditions for 12 hours at a temperature of 60°C. The dried hydroxyapatite / L-polylactic acid composite powder was spheroidized using an air fluidized bed apparatus. The angle of repose after spheroidization was ≤34°. The heating temperature of the air fluidized bed apparatus was 220℃, and the feed speed was 5 rpm. Computed tomography (CT) was used to scan the joint area of ​​the patient's ligament defect or rupture to obtain joint data. Image processing software was then used to analyze and extract the data. The shape and volume of the surrounding joint were accurately measured using three-dimensional data to determine the diameter of the bone tunnel to be excavated. A model of the interface bone nail, 0.5 mm smaller than the diameter of the bone tunnel, was designed using computer-aided design software. After generating an STL file, it was imported into a laser selective melting system. Finally, a biodegradable interface bone nail was printed using high-energy laser. The scanning strategy involved two laser scans during single-layer sintering: the first scan was in the X direction, and the second scan was in the Y direction. The laser power was 1W, the scanning rate was 100 mm / s, and the printing layer thickness was 0.2 mm.

[0050] Scanning electron microscopy revealed that a regularly shaped hydroxyapatite / L-polylactic acid composite powder was prepared by ball milling, extrusion granulation, pulverization and spheroidization processes, with a repose angle of 31.2°, showing good flowability.

[0051] The degradable controllable interface bone screws printed using composite powder with good flowability were observed to have no obvious defects and high shape accuracy.

[0052] Mechanical performance testing revealed that the fixation strength of the degradable controllable hydroxyapatite / L-polylactic acid interface bone nail is 596 MPa, which meets the clinical implantation requirements.

[0053] Stem cell culture tests have shown that degradable and controllable hydroxyapatite / L-polylactic acid interface bone nails promote stem cell growth.

[0054] Biocompatibility testing revealed that the degradable and controllable hydroxyapatite / L-polylactic acid interface bone screw can induce bone growth and has good bioactivity.

[0055] Example 3

[0056] A method for fabricating a degradable and controllable hydroxyapatite / L-polylactic acid interface bone screw includes the following steps:

[0057] A mixed powder containing 40% hydroxyapatite and 60% L-polylactic acid was weighed using an electronic balance. This mixed powder was then subjected to ball milling, extrusion granulation, pulverization, and spheroidization processes to obtain a composite powder with regular shape and good flowability. This powder was then placed in a laser selective melting system. The ball milling speed was 220 rpm, and the milling time was 2.2 hours. The ball-milled composite powder was then extruded and granulated, and sheared to obtain sheared particles. The temperature at the feed end of the twin-screw extruder was 175°C, the discharge end temperature was 185°C, and the extrusion speed was 95 rpm. The sheared particles were then pulverized into powder with a particle size less than 70 μm using a liquid nitrogen pulverizer. The pre-cooling temperature and pulverization temperature of the liquid nitrogen pulverizer were both -165°C, the main motor speed was 47 rpm, the fan speed was 10 rpm, and the discharge port speed was 6 rpm. The pulverized irregular powder was then placed in a vacuum drying oven and dried under vacuum conditions for 12 hours at a temperature of 60°C. The dried hydroxyapatite / L-polylactic acid composite powder was spheroidized using an air fluidized bed device. The angle of repose after spheroidization was ≤34°. The heating temperature of the air fluidized bed device was 235°C, and the feed speed was 7 rpm. Computed tomography was used to scan the joint area of ​​the patient's ligament defect or rupture to obtain joint data. Image processing software was then used to analyze and extract the data. The shape and volume of the surrounding joint were accurately measured using three-dimensional data to determine the diameter of the bone tunnel to be excavated. Then, computer-aided design software was used to design an interface bone nail model that was 0.5 mm smaller than the diameter of the bone tunnel. After generating an STL file, it was imported into the laser selective melting system. Finally, a biodegradable interface bone nail was printed using high-energy laser. The scanning strategy was that during single-layer sintering, the laser was scanned twice, first in the X direction and then in the Y direction. The laser power was 1W, the scanning rate was 100 mm / s, and the printing layer thickness was 0.2 mm.

[0058] Scanning electron microscopy revealed that a regularly shaped hydroxyapatite / L-polylactic acid composite powder was prepared by ball milling, extrusion granulation, pulverization, and fluidization processes, with a repose angle of 30.4°, exhibiting good flowability.

[0059] The degradable controllable interface bone screws printed using composite powder with good flowability were observed to have no obvious defects and high shape accuracy.

[0060] Mechanical performance testing revealed that the fixation strength of the degradable controllable hydroxyapatite / L-polylactic acid interface bone nail is 630 MPa, which meets the clinical implantation requirements.

[0061] Stem cell culture tests have shown that degradable and controllable hydroxyapatite / L-polylactic acid interface bone nails promote stem cell growth.

[0062] Biocompatibility testing revealed that the degradable and controllable hydroxyapatite / L-polylactic acid interface bone screw can induce bone growth and has good bioactivity.

[0063] Example 4

[0064] A method for fabricating a degradable and controllable hydroxyapatite / L-polylactic acid interface bone screw includes the following steps:

[0065] A mixed powder containing 30% hydroxyapatite and 70% L-polylactic acid was weighed using an electronic balance. Before ball milling the hydroxyapatite and L-polylactic acid powders, the hydroxyapatite was modified by weighing 15g of calcium fluoride powder and 90g of hydroxyapatite powder, mixing them evenly, and then sintering at a high temperature of 1150℃ for 1 hour to decompose some of the hydroxyapatite into fluorapatite, obtaining hydroxyapatite containing fluorapatite, which was then ground into powder. Then, 100g of 20wt% dextran solution, 30g of 0.01mol / L sodium periodate solution, and 10g of 0.01mol / L potassium permanganate solution were weighed and mixed. Potassium solution was added to dextran solution and magnetically stirred for 1 hour at room temperature in the dark. After dialysis for 2 days, oxidized dextran was obtained by freeze-drying. Then, 80g of hydroxyapatite powder containing fluorapatite, 5g of oxidized dextran, and 15g of collagen were weighed and mixed. The mixture was then added to 80 parts of water and stirred thoroughly in a high-speed mixer at 800 rpm for 1 hour until a paste was formed. The paste was then placed in a freeze dryer and freeze-dried at -40°C for 24 hours. After that, it was pulverized in a pulverizer at 1200 rpm for 3 hours. The pulverized mixture was then ground in a grinder for 2 hours at 180 rpm to obtain reinforced hydroxyapatite powder.

[0066] All other conditions are the same as in Implementation Case 1.

[0067] Hydroxyapatite containing a portion of fluorapatite, obtained by calcining a mixture of calcium fluoride and hydroxyapatite, provides heterogeneous nucleation for hydroxyapatite, resulting in well-crystallized hydroxyapatite. Furthermore, the addition of calcium fluoride powder increases the calcium-to-phosphorus ratio of the hydroxyapatite, which is beneficial for improving its stability. The further addition of oxidized dextran, along with collagen, allows for a self-assembly reaction with the hydroxyapatite, forming strong intermolecular forces—Schiff bases. Simultaneously, the cations Ca in the hydroxyapatite... 2+ Nucleophilic addition occurs, fundamentally enhancing the mechanical properties of the scaffold.

[0068] Scanning electron microscopy revealed that a regularly shaped hydroxyapatite / L-polylactic acid composite powder was prepared by ball milling, extrusion granulation, pulverization and spheroidization processes, with a repose angle of 27.4°, showing good flowability.

[0069] The degradable controllable interface bone screws printed using composite powder with good flowability were observed to have no obvious defects and high shape accuracy.

[0070] Mechanical performance testing revealed that the fixation strength of the degradable controllable hydroxyapatite / L-polylactic acid interface bone nail is 662 MPa, which meets the clinical implantation requirements.

[0071] Stem cell culture tests have shown that degradable and controllable hydroxyapatite / L-polylactic acid interface bone nails promote stem cell growth.

[0072] Biocompatibility testing revealed that the degradable and controllable hydroxyapatite / L-polylactic acid interface bone screw can induce bone growth and has good bioactivity.

[0073] Example 5

[0074] A method for fabricating a degradable and controllable hydroxyapatite / L-polylactic acid interface bone screw includes the following steps:

[0075] A mixed powder containing 20% ​​hydroxyapatite and 80% L-polylactic acid was weighed using an electronic balance. Before ball milling the hydroxyapatite and L-polylactic acid powders, the hydroxyapatite was modified by weighing 15g of calcium fluoride powder and 90g of hydroxyapatite powder, mixing them evenly, and then sintering at a high temperature of 1150℃ for 1 hour to decompose some of the hydroxyapatite into fluorapatite, obtaining hydroxyapatite containing fluorapatite, which was then ground into powder. Then, 100g of 20wt% dextran solution, 30g of 0.01mol / L sodium periodate solution, and 10g of 0.01mol / L potassium permanganate solution were weighed and mixed. Potassium solution was added to dextran solution and magnetically stirred for 1 hour at room temperature in the dark. After dialysis for 2 days, oxidized dextran was obtained by freeze-drying. Then, 80g of hydroxyapatite powder containing fluorapatite, 5g of oxidized dextran, and 15g of collagen were weighed and mixed. The mixture was then added to 80 parts of water and stirred thoroughly in a high-speed mixer at 800 rpm for 1 hour until a paste was formed. The paste was then placed in a freeze dryer and freeze-dried at -40°C for 24 hours. After that, it was pulverized in a pulverizer at 1200 rpm for 3 hours. The pulverized mixture was then ground in a grinder for 2 hours at 180 rpm to obtain reinforced hydroxyapatite powder.

[0076] All other conditions are the same as in Implementation Case 2.

[0077] Hydroxyapatite containing a portion of fluorapatite, obtained by calcining a mixture of calcium fluoride and hydroxyapatite, provides heterogeneous nucleation for hydroxyapatite, resulting in well-crystallized hydroxyapatite. Furthermore, the addition of calcium fluoride powder increases the calcium-to-phosphorus ratio of the hydroxyapatite, which is beneficial for improving its stability. The further addition of oxidized dextran, along with collagen, allows for a self-assembly reaction with the hydroxyapatite, forming strong intermolecular forces—Schiff bases. Simultaneously, the cations Ca in the hydroxyapatite... 2+ Nucleophilic addition occurs, fundamentally enhancing the mechanical properties of the scaffold.

[0078] Scanning electron microscopy revealed that a regularly shaped hydroxyapatite / L-polylactic acid composite powder was prepared by ball milling, extrusion granulation, pulverization and spheroidization processes, with a repose angle of 28.4°, showing good flowability.

[0079] The degradable controllable interface bone screws printed using composite powder with good flowability were observed to have no obvious defects and high shape accuracy.

[0080] Mechanical performance testing revealed that the fixation strength of the degradable controllable hydroxyapatite / L-polylactic acid interface bone nail is 651 MPa, which meets the clinical implantation requirements.

[0081] Stem cell culture tests have shown that degradable and controllable hydroxyapatite / L-polylactic acid interface bone nails promote stem cell growth.

[0082] Biocompatibility testing revealed that the degradable and controllable hydroxyapatite / L-polylactic acid interface bone screw can induce bone growth and has good bioactivity.

[0083] Comparative Example 1

[0084] All other conditions were the same as in Implementation Case 1, except that: a mixed powder of 10% hydroxyapatite and 90% L-polylactic acid was weighed using an electronic balance; and the fixation strength of the prepared degradable controllable interface bone nail was 425 MPa.

[0085] Comparative Example 2

[0086] All other conditions were the same as in Implementation Case 1, except that: a mixed powder of 50% hydroxyapatite and 50% L-polylactic acid was weighed using an electronic balance; and the fixation strength of the prepared degradable controllable interface bone nail was 428 MPa.

[0087] Comparative Example 3

[0088] All other conditions were the same as in Implementation Case 1, except that: a mixed powder of 30% hydroxyapatite and 70% L-polylactic acid was weighed using an electronic balance, and without ball milling, extrusion granulation, pulverization, or spheroidization, the mixed powder was directly placed into a laser selective melting system; scanning electron microscopy revealed that the hydroxyapatite / L-polylactic acid composite powder had an irregular shape, poor flowability, and an angle of repose of 40.2°, and the fixation strength of the prepared degradation-controllable interface bone nail was 385 MPa.

[0089] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. Other modifications can be easily made by those skilled in the art. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for fabricating a degradable and controllable hydroxyapatite / L-polylactic acid interface bone nail, characterized in that, The degradable and controllable hydroxyapatite / L-polylactic acid interface bone nail is formed by selective laser melting and sintering of hydroxyapatite / L-polylactic acid composite powder, wherein the hydroxyapatite / L-polylactic acid composite powder comprises 20-40% hydroxyapatite and 60-80% L-polylactic acid by mass fraction. The method for fabricating a degradable and controllable hydroxyapatite / L-polylactic acid interface bone screw specifically includes the following steps: Step 1: Use computed tomography (CT) to scan the joint area where the patient's ligament is defective or torn to obtain joint data. Then, use image processing software to analyze and extract the data. Use three-dimensional data to accurately measure the shape and volume of the surrounding joints to determine the diameter of the bone tunnel that needs to be excavated. Finally, use computer-aided design software to design a three-dimensional model of the interface bone nail. Step 2: Mix hydroxyapatite powder and L-polylactic acid powder to obtain hydroxyapatite / L-polylactic acid composite powder, and then ball mill the hydroxyapatite / L-polylactic acid composite powder in a ball mill. Step 3: Place the ball-milled hydroxyapatite / L-polylactic acid composite powder into a twin-screw extruder and extrude it through a twin-screw extruder. Then, shear it to obtain sheared particles. Step 4: Grind the sheared particles into powder using a cryogenic grinder; Step 5: Spheroidize the powder from Step 4 using a spheroidizing device to obtain spheroidized powder; Step 6: Import the three-dimensional model of the interface bone nail into the laser selective melting system, then place the spheroidized powder into the laser selective melting system, and print the degradable controllable interface bone nail layer by layer according to the three-dimensional model of the interface bone nail. When sintering a single layer, the laser is scanned twice, the first scan is in the X direction and the second scan is in the Y direction. Before mixing hydroxyapatite powder and L-polylactic acid powder, the hydroxyapatite powder was reinforced with dextran, collagen, and calcium fluoride. The reinforcement method was as follows: hydroxyapatite was modified by weighing calcium fluoride powder and hydroxyapatite powder at a mass ratio of 1:6, mixing them evenly, and then sintering at a high temperature of 1150–1200℃ for 1–2 hours. This process caused some of the hydroxyapatite to decompose and transform into fluorapatite, resulting in hydroxyapatite containing fluorapatite. The mixture was then ground. The mixture is prepared into powder. Then, a 20wt% dextran solution, a 0.01mol / L sodium periodate solution, and a 0.01mol / L potassium permanganate solution are weighed in a mass ratio of 10:3:

1. The dextran is oxidized and modified using the sodium periodate and potassium permanganate solutions to obtain oxidized dextran. Next, 70–80 parts by weight of hydroxyapatite powder containing fluoroapatite, 5–10 parts by weight of oxidized dextran, and 10–20 parts by weight of collagen are weighed and mixed. This mixture is then added to 70–80 parts by weight of water, and the mixture is stirred at a speed of 800–1200 rpm. The mixture is thoroughly stirred in a high-speed mixer at rpm for 0.5–1 hour until it becomes a paste. The paste is then placed in a freeze dryer at -40°C and freeze-dried for 12–24 hours. After that, it is pulverized in a pulverizer at 1200–1600 rpm for 3–12 hours. The pulverized mixture is then ground in a grinder for 2–4 hours at 150–180 rpm to obtain reinforced hydroxyapatite powder.

2. The method for fabricating a degradable and controllable hydroxyapatite / L-polylactic acid interface bone nail according to claim 1, characterized in that, The surface of the interface bone screw has at least one opening, which is regularly or irregularly distributed on the interface bone screw.

3. The method for fabricating a degradable and controllable hydroxyapatite / L-polylactic acid interfacial bone nail according to claim 2, characterized in that, The diameter of the opening is 200–600 μm.

4. The method for fabricating a degradable and controllable hydroxyapatite / L-polylactic acid interface bone nail according to claim 1, characterized in that, In step one, the diameter of the interface bone nail is 0.5 to 1 mm smaller than the diameter of the bone tunnel.

5. The method for fabricating a degradable and controllable hydroxyapatite / L-polylactic acid interface bone screw according to claim 1, characterized in that, In step two, the ball milling speed is 180-250 rpm and the ball milling time is 1.5-2.5 h.

6. The method for fabricating a degradable and controllable hydroxyapatite / L-polylactic acid interfacial bone screw according to claim 1, characterized in that, In step three, the feed temperature of the twin-screw extruder is 170–180°C, the discharge temperature is 180–190°C, and the rotation speed is 95–115 rpm.

7. The method for fabricating a degradable and controllable hydroxyapatite / L-polylactic acid interface bone nail according to claim 1, characterized in that, In step four, the particle size of the pulverized powder is less than 70 μm, the temperature during the pulverization process is between -180°C and -150°C, and the main unit speed is 45 to 47 rpm.

8. The method for fabricating a degradable and controllable hydroxyapatite / L-polylactic acid interfacial bone nail according to claim 1, characterized in that, In step five, the angle of repose of the spheroidized powder is ≤32°, the temperature of the spheroidizing equipment is set to 220~240 ℃, and the feed speed is 5~7 rpm.

9. The method for fabricating a degradable and controllable hydroxyapatite / L-polylactic acid interfacial bone nail according to claim 1, characterized in that, In step six, the laser power is 1 to 1.3W, the scanning rate is 90 to 110 mm / s, and the printing thickness is 0.1 to 0.3 mm.

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