A polylactic acid / nano-hydroxyapatite composite wire for 3D printing and a preparation method and application thereof

Abstract

The application relates to the technical field of nanocomposites, in particular to a polylactic acid / nano-hydroxyapatite composite wire for 3D printing and a preparation method and application thereof. The method comprises the following steps: S1, preparing polylactic acid / nano-hydroxyapatite composite microspheres with different average particle diameters through an emulsion solvent volatilization method; S2, performing particle grading on the composite microspheres with different average particle diameters to obtain graded raw materials; and S3, melt-extruding and traction-stretching the graded raw materials to obtain a composite wire. The application effectively realizes the uniform dispersion of nano-hydroxyapatite in a polylactic acid matrix by combining composite microspherization and particle grading. The obtained wire has a diameter of 1.75+ / -0.03 mm, a nano-hydroxyapatite mass fraction of 3-15%, and a breaking strength of 37.52-54.84 MPa. The wire is suitable for FDM 3D printing and can be used for preparing bone repair scaffolds and has excellent biocompatibility and mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of nanocomposite materials technology, specifically to a polylactic acid / nanohydroxyapatite composite filament for 3D printing, its preparation method, and its application. Background Technology

[0002] 3D printing technology, as an innovative rapid prototyping technology, has been widely used in many fields such as medical, aerospace, automotive manufacturing, and construction in recent years. Based on digital model files (such as STL files), this technology manufactures three-dimensional objects by layering materials, offering significant advantages such as short manufacturing cycles, high customizability, and the ability to create complex structures.

[0003] Fused deposition modeling (FDM) technology boasts advantages such as low cost, high material utilization, and applicability to a variety of materials, giving it a continuously growing application potential in industrial and medical fields. The performance of FDM printing filaments plays a decisive role in the quality and performance of 3D printed products. Polylactic acid (PLA) possesses both biocompatibility and controllable degradation characteristics, and its degradation products can be metabolized by the human body without toxic residues, making it an ideal material for drug delivery and bone repair scaffolds. However, PLA lacks osteogenic activity, and its acidic degradation products may induce inflammation. Nano-hydroxyapatite (nHAP), a major inorganic component of human bones and teeth, exhibits good cell affinity and osteogenic activity, guiding the formation of new bone tissue. Therefore, combining nHAP with PLA using FDM technology holds promise for constructing complex biomimetic three-dimensional bone scaffold materials: PLA provides a biodegradable framework, nHAP enhances mechanical properties and imparts osteogenic activity, and FDM technology constructs the complex biomimetic structure. This synergistic construction of components and structure is expected to significantly improve bone repair outcomes.

[0004] However, the key to preparing high-quality PLA / nHAP composite filaments suitable for FDM technology lies in the uniform compounding and filament fabrication techniques of PLA and nHAP. Among these, ensuring the uniform dispersion of nHAP within the PLA matrix is ​​a major issue affecting the quality of PLA / nHAP composite filaments and the performance of 3D-printed scaffolds. High nHAP content helps improve the osteogenic activity of the material, but high content inevitably leads to agglomeration during compounding with polylactic acid. Currently, melt blending and solution dispersion are two commonly used processes for mixing PLA and nHAP raw materials. The former is simple, but suffers from the problem of nHAP agglomeration and difficulty in uniform dispersion; the latter, in solution, can improve the uniformity of nHAP dispersion, thereby reducing agglomeration and facilitating the acquisition of uniform micro / nano composite structures.

[0005] Therefore, there is an urgent need to develop a composite filament preparation method suitable for FDM 3D printing that can achieve highly uniform dispersion of nano-hydroxyapatite in a polylactic acid matrix and flexibly control the content of nano-hydroxyapatite in the composite filament. Summary of the Invention

[0006] In view of this, the present invention provides a polylactic acid / nanohydroxyapatite composite filament for 3D printing, its preparation method, and its application. PLA is the main component, with the composite active functional ingredient nHAP added to enhance mechanical properties and osteogenic activity. Structurally, nHAP and PLA are composite microspheres formed by emulsion solvent evaporation. After particle gradation of composite microspheres with different particle sizes, they are used as raw materials, and then the composite filament is prepared by melt extrusion. FDM technology is used to construct an ordered and complex structured PLA / nHAP porous scaffold material, achieving uniform dispersion of nHAP and enhancing mechanical properties and osteogenic activity, thus giving it good biosafety, mechanical properties, and biodegradability.

[0007] The technical solution of this invention is implemented as follows: In a first aspect, the present invention proposes a method for preparing polylactic acid / nanohydroxyapatite composite filaments for 3D printing, comprising the following steps: S1. Polylactic acid is dissolved in an organic solvent to form a polylactic acid solution, and nano-hydroxyapatite is dispersed in the organic solvent to form a nano-hydroxyapatite dispersion. The polylactic acid solution and the nano-hydroxyapatite dispersion are mixed to obtain a mixed phase. The mixed phase is added to an aqueous solution containing polyvinyl alcohol (PVA), stirred, and the organic solvent is evaporated. The mixed phase is solidified into microspheres, which are then separated and dried to obtain polylactic acid / nano-hydroxyapatite composite microspheres. Repeat the above process to prepare at least two types of polylactic acid / nanohydroxyapatite composite microspheres with different average particle sizes; S2. The composite microspheres with at least two different average particle sizes are subjected to particle gradation to obtain graded raw materials; S3. The graded raw materials are melt-extruded and stretched to obtain composite wire.

[0008] Preferably, the polylactic acid in step S1 is racemic polylactic acid with a weight-average molecular weight of 100,000-200,000; and the particle size range of the composite microspheres is 10-80 μm.

[0009] More preferably, in step S1, the organic solvent for dissolving polylactic acid includes dichloromethane, and the organic solvent for dispersing nano-hydroxyapatite includes dichloromethane.

[0010] Preferably, the particle size distribution in step S2 is used to prepare wires with a nano-hydroxyapatite content ≤5wt%, specifically by mixing two types of composite microspheres with average particle sizes of 30-35μm and 10-15μm at a mass ratio of (18-20):1.

[0011] Preferably, the particle size distribution in step S2 is used to prepare wires with a nano-hydroxyapatite content of 5wt%-10wt%, specifically by mixing two types of composite microspheres with average particle sizes of 50-55μm and 20-25μm at a mass ratio of (18-20):1.

[0012] Preferably, the particle size distribution in step S2 is used to prepare wires with a nano-hydroxyapatite content of 10wt%-15wt%, specifically by mixing two types of composite microspheres with average particle sizes of 75-80μm and 30-35μm at a mass ratio of (18-20):1.

[0013] Preferably, the particle size distribution in step S2 is used to prepare wires with a nano-hydroxyapatite content of 5wt%-10wt%, specifically by mixing three types of composite microspheres with average particle sizes of 75-80μm, 50-55μm and 10-15μm in a mass ratio of (18-20):(3-5):1.

[0014] Preferably, the melt extrusion in step S3 is performed using an extruder with a screw speed of 20-25 r / min, a feed cooling temperature of 40-50℃, and a barrel heating temperature of 155-165℃.

[0015] Preferably, the traction stretching in step S3 is performed using a wire drawing machine with a rotation speed of 140-160 r / min and a room temperature cooling water bath.

[0016] In a second aspect, the present invention provides a polylactic acid / nanohydroxyapatite composite filament for 3D printing obtained by the preparation method described in the first aspect, wherein the diameter of the composite filament is 1.75±0.03mm, and the nanohydroxyapatite accounts for 3-15% of the mass fraction of polylactic acid.

[0017] Thirdly, the present invention provides an application of the polylactic acid / nanohydroxyapatite composite filament for 3D printing as described in the second aspect in the field of biomedical bone repair.

[0018] Compared with the prior art, the advantages of the present invention are as follows: (1) The emulsion solvent evaporation method of the present invention has the advantages of mild conditions, high safety and simple operation, which can avoid the thermal degradation of PLA caused by melt blending. Compared with melt blending, the process of composite microsphere formation of PLA and nHAP by emulsion solvent evaporation method helps to improve the uniformity of raw material composite. Furthermore, by adjusting the process parameters of emulsion solvent evaporation method, the size of composite microspheres can be controlled as needed. By further adjusting the particle size distribution, raw materials with good flowability and high bulk density can be obtained, which is conducive to the extrusion molding of high-quality composite wires, improving the dispersion uniformity of nHAP in PLA, obtaining a uniform micro-nano composite structure, and improving the thermal stability and mechanical properties of the wire.

[0019] (2) This invention combines FDM technology to construct a three-dimensional scaffold with a complex biomimetic structure using composite wires. PLA provides a biodegradable framework, while nHAP enhances mechanical properties and imparts osteogenic activity. This synergistic construction of components and structure is expected to significantly improve bone repair effects. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the gradation of the two-stage microspheres of the present invention; Figure 2 This is a schematic diagram of the gradation of the three-dimensional microspheres of the present invention; Figure 3 Transmission electron microscopy morphology of nHAP provided by the present invention; Figure 4 The morphology of the PLA / nHAP composite microspheres obtained in Example 1 is shown in the image. Figure 5 The elemental distribution map of the PLA / nHAP composite microspheres obtained in Example 1 is shown. Figure 6 The image shows a scanning electron microscope (SEM) image of the PLA / nHAP 3D printing composite filament obtained in Example 1. Figure 7 The elemental distribution diagram is shown for the composite wire obtained in Example 1. Figure 8 Scanning electron microscope image of the PLA / 10%nHAP inhomogeneous composite wire prepared for Comparative Example 1; Figure 9 Elemental distribution diagram of PLA / 10%nHAP non-uniform composite wire prepared for Comparative Example 1; Figure 10 Thermogravimetric curves of the wires obtained in Embodiment 2 and Comparative Example 2 of the present invention are shown. Figure 11 The fracture strength diagrams are of the wires obtained in Embodiments 1-3, 5-6 and Comparative Examples 1-2 of the present invention. Figure 12 Scanning electron microscope image and elemental distribution map of the 3D printed scaffold in Application Example 1; Figure 13 The image shows the cell compatibility test results of the 3D-printed scaffold in Application Example 1. Figure 14 AM / PI fluorescence staining image of cells on the surface of the 3D printed scaffold in Application Example 2; Figure 15 The images show cross-sectional scanning electron microscope (SEM) images of the shaped wires obtained in Example 1 and Comparative Example 3. Figure 16 The image shows the morphology of the PLA / nHAP composite microspheres obtained in Comparative Example 4. Detailed Implementation

[0022] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0023] In this invention, the emulsion solvent evaporation method offers advantages such as mild conditions, high safety, and simple operation, avoiding the thermal degradation of PLA caused by melt blending. Compared to melt blending, using the emulsion solvent evaporation method for the composite microsphere formation of PLA and nHAP helps improve the uniformity of the composite material. Furthermore, by adjusting the process parameters of the emulsion solvent evaporation method, the size of the composite microspheres can be controlled as needed. Further, through particle size distribution, raw materials with good flowability and high bulk density can be obtained, which is beneficial for the extrusion molding of high-quality composite wires. In addition, large-size microspheres are easier to composite with high nHAP content. Therefore, to prepare composite wires with high nHAP content, large-scale composite microspheres can be used as extrusion raw materials; while for composite wires with low nHAP content, using small-scale composite microspheres is beneficial for achieving wire molding at lower temperatures.

[0024] In addition, the purpose of particle size selection is to achieve the densest particle packing, reduce the gaps between particles, which is beneficial for wire extrusion molding and reduces internal porosity defects in the wire. Figure 1 Here is a schematic diagram of two size gradations: Let the diameter of the large-scale microsphere be D1. When four microspheres are stacked, a gap is formed in the middle. Assume that the diameter of the largest microsphere that can be filled is D2. The center of the circle forms a square with a side length of D1. The diameter of the largest filling microsphere is D2 = BC - D1, where (BC) 2 =2 (D1) 2; The relationship between D1 and D2 is: D2 = 1.4142D1 - D1 = 0.4142D1. Therefore, the two-stage particle size matching is as shown in the following table;

[0025] The mass ratio of D1 and D2 microspheres is calculated by volume ratio. Figure 1 In a cubic structural unit (dashed box range), the number ratio of D1 microspheres to D2 microspheres is 4:3. Therefore, the converted mass ratio is approximately 18.76:1. Finally, the three-size grading is equivalent to adding some 50-μm microspheres to replace some 80-μm microspheres based on the two-size grading of 80 μm and 30 μm, which is beneficial to reducing pore defects and can also meet the wire preparation requirements with 5% < C nHAP ≤ 10%. The three-stage particle size matching is as Figure 2 shown.

[0026] In addition, when preparing wires with different nHAP contents, the selection of different-sized microspheres for particle grading is based on the comprehensive consideration of two factors: the amount of nHAP encapsulated in the microspheres and the melting temperature of the microspheres. The amount of nHAP encapsulated in the microspheres is related to osteogenic activity. A high content corresponds to high biological activity, but the encapsulation amount is also related to the microsphere size. Small-sized microspheres can only encapsulate a low content of nHAP. If high biological activity, i.e., high nHAP content, is required, large-sized microspheres need to be prepared. In addition, during extrusion molding, first, the microsphere raw materials need to be in a molten state and air needs to be discharged, and then they are extruded into wires. The microsphere size is related to the melting temperature and the void volume. The smaller the size, the easier it is for the particles to achieve dense packing, and the fewer the voids between the particles, which helps to reduce pore defects inside the wire; and the lower the melting temperature, the melting extrusion molding can be achieved at a lower temperature.

[0027] Therefore, for the preparation of wires with nHAP content ≤ 5%, small-sized microspheres can achieve the required encapsulation amount, and small-sized microspheres are also beneficial to reducing pore defects and can be extruded at a lower temperature. For the preparation of wires with 5% < C nHAP ≤ 10%, small-sized microspheres can no longer meet the nHAP content requirements, so medium-sized microspheres need to be prepared. For the preparation of wires with 10% < CnHAP ≤ 15%, large-sized microspheres are needed to encapsulate a high content of nHAP, and at this time, the extrusion molding temperature needs to be increased.

[0028] Ultimately, the mechanical properties of the wire are related to the nHAP content and internal porosity defects. At low nHAP content levels, nHAP acts as a nanoparticle dispersion toughening agent. The dispersed particles hinder the propagation of the main crack, causing the crack tip to bend between particles, generating line tension, thus increasing the fracture energy and producing a toughening effect. However, as the nHAP content increases, nHAP agglomeration becomes severe, leading to internal defects and a decrease in mechanical properties. The thermal properties of the wire are positively correlated with the nHAP content. The high thermal stability of nHAP ceramic particles (above 700℃) can reduce heat conduction, thereby improving thermal stability.

[0029] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0030] In this document, the terms “containing,” “comprising,” or “including” are open-ended expressions, meaning they include the contents specified in this invention but do not exclude other aspects.

[0031] In this document, the terms “optional,” “optionally,” or “optional” generally refer to an event or condition that may, but may not, occur, and the description includes both cases in which the event or condition occurs and cases in which the event or condition does not occur.

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0033] Unless otherwise specified, all reagents used in this invention can be purchased from the market. Specifically, polyvinyl alcohol (PVA) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., and racemic polylactic acid (PLA) was purchased from Jinan Daigang Bioengineering Co., Ltd.; the raw materials used to prepare nHAP, calcium chloride dihydrate (CaCl2·2H2O, analytical grade), were purchased from Sinopharm Group, and disodium hydrogen phosphate dodecahydrate (Na2HPO4·12H2O, analytical grade) and sodium hydroxide (NaOH, analytical grade) were purchased from Shanghai Maclean's.

[0034] Preferably, the nano-hydroxyapatite (nHAP) used in this invention is synthesized by a precipitation method, and the preparation process includes the following steps: Na₂HPO₄ (0.02 mol / L) and CaCl₂ (0.0334 mol / L) solutions were prepared separately, maintaining a Ca / P molar ratio of 1.67. The two solutions were magnetically stirred for 1 h, and then the phosphate solution was added dropwise to the calcium salt solution under continuous stirring. The pH of the mixed solution was adjusted to 9-10 using 0.1 mol / L NaOH solution. The mixture was then placed in a constant temperature water bath at 37℃ or 80℃, and the reaction was continued for 3 h (37℃) or 1 h (80℃) at the corresponding temperatures. After the reaction, the mixture was allowed to stand at room temperature for 12 h. Impurities were removed by centrifugation (5000 rpm, 5 min) combined with four washes with ultrapure water. The precipitate was collected and freeze-dried, and finally ground to obtain nano-hydroxyapatite (nHAP) powder.

[0035] Preferably, the present invention provides a process for preparing PLA / nHAP composite microspheres by emulsion solvent evaporation, comprising the following steps: (1) Dissolve polyvinyl alcohol (PVA) in deionized water to prepare a PVA solution; dissolve racemic polylactic acid (PLA, weight-average molecular weight of 100,000-200,000) in dichloromethane to prepare a PLA organic solution; dissolve nano-hydroxyapatite (nHAP, short rod-shaped, 40-60 nm in length and 10-15 nm in diameter, such as...) Figure 3 (As shown) Add to dichloromethane and sonicate for 15 min to prepare an nHAP dispersion of 1.5-7.5 mg / ml; (2) Mix the above nHAP dispersion with PLA organic solution and stir continuously for 20 min (the mass fraction of nHAP in PLA is adjusted to 3%, 5%, 8%, 10% or 15% as needed) to obtain a mixed phase; slowly add the mixed phase to the above PVA solution and stir at 1000-1500 rpm to evaporate the dichloromethane, and then let it stand at room temperature (25-35℃) for 12 h to obtain a suspension containing microspheres; (3) The above suspension was centrifuged (5000 rpm, 5 min), washed 4 times with ultrapure water, and the precipitate was freeze-dried to obtain PLA / nHAP composite microspheres with nHAP content of 3%, 5%, 8%, 10% or 15%.

[0036] Furthermore, the average particle size of the composite microspheres can be controlled by changing the PLA concentration, PVA concentration in step (1), the volume ratio of PVA solution to PLA organic solution in step (2), and the stirring speed.

[0037] Preparation Example 1 This preparation example provides a method for preparing PLA / nHAP composite microspheres with an average particle size of 13.6±4.1 μm. The method is based on the above basic steps, with the following settings: in step (1), the concentration of PVA (weight average molecular weight of 100,000) is 5 mg / mL, the concentration of PLA is 50 mg / mL, and the concentration of nHAP dispersion is 4.5 mg / mL; in step (2), the volume ratio of PVA solution to PLA organic solution is 10:1, and the stirring speed is 1500 rpm.

[0038] The average particle size of the obtained composite microspheres is 13.6±4.1 μm. Meanwhile, under this condition, by adjusting the mass fraction of nHAP in PLA in step (2) to 3%, 5%, 8%, 10% or 15%, composite microspheres with corresponding nHAP content and average particle size of 10-15 μm can be obtained respectively.

[0039] The electron microscopy image of the composite microspheres with 5% nHAP content and 13.6±4.1 μm obtained in this preparation example is shown below. Figure 4-5 As shown, nHAP exhibits good dispersion in the composite microspheres.

[0040] Preparation Example 2

[0041] This preparation example provides a method for preparing PLA / nHAP composite microspheres with an average particle size of 20.7±8.5 μm. The only difference between this example and the preparation example 1 is that the PLA concentration in step (1) is 10 mg / mL and the stirring speed in step (2) is 1000 rpm.

[0042] The average particle size of the obtained composite microspheres is 20.7±8.5 μm. Meanwhile, under this condition, by adjusting the mass fraction of nHAP in PLA in step (2) to 3%, 5%, 8%, 10% or 15%, composite microspheres with corresponding nHAP content and average particle size of 20-25 μm can be obtained respectively.

[0043] Preparation Example 3 This preparation example provides a method for preparing PLA / nHAP composite microspheres with an average particle size of 33±11.9 μm. The only difference between this example and the preparation example 1 is that the concentration of PVA (weight average molecular weight of 200,000) is 9 mg / mL in step (1) and the stirring speed is 1000 rpm in step (2).

[0044] The average particle size of the obtained composite microspheres is 33±11.9 μm. Meanwhile, under this condition, by adjusting the mass fraction of nHAP in PLA in step (2) to 3%, 5%, 8%, 10% or 15%, composite microspheres with corresponding nHAP content and average particle size of 30-35 μm can be obtained respectively.

[0045] Preparation Example 4 This preparation example provides a method for preparing PLA / nHAP composite microspheres with an average particle size of 50±10.5 μm. The only difference between this example and the preparation example 1 is that the stirring speed in step (2) is 1000 rpm.

[0046] The average particle size of the resulting composite microspheres is 50±10.5 μm. Meanwhile, under this condition, by adjusting the mass fraction of nHAP in PLA in step (2) to 3%, 5%, 8%, 10% or 15%, composite microspheres with corresponding nHAP content and average particle size of 50-55 μm can be obtained respectively.

[0047] Preparation Example 5 This preparation example provides a method for preparing PLA / nHAP composite microspheres with an average particle size of 80±18.7 μm. The only difference between this example and the preparation example 1 is that the volume ratio of PVA solution to PLA organic solution in step (2) is 30:1 and the stirring speed is 1000 rpm.

[0048] The average particle size of the obtained composite microspheres is 80±18.7 μm. Meanwhile, under this condition, by adjusting the mass fraction of nHAP in PLA in step (2) to 3%, 5%, 8%, 10% or 15%, composite microspheres with corresponding nHAP content and average particle size of 75-80 μm can be obtained respectively.

[0049] Example 1 This embodiment provides a method for preparing polylactic acid / nanohydroxyapatite composite filaments for 3D printing, including the following steps: (1) Referring to Preparation Example 1 and Preparation Example 3, the nHAP content was controlled at 5%, and PLA / nHAP composite microspheres with 5% nHAP content and average particle size of 10-15 μm and 30-35 μm were prepared respectively; the two composite microspheres were mixed according to the mass ratio W 30-35μm :W 10-15μm The mixture is prepared at a ratio of 18:1 and used as a raw material for wire extrusion molding. (2) Set the barrel heating temperature to 200℃, and put in high-density polyethylene to clean the extruder until the extruded wire is transparent; (3) The barrel heating temperature was set to 155℃, the feed cooling temperature to 40℃, and the screw speed to 20r / min. Composite microsphere particle-graded raw materials were fed in for extrusion and stretching. The wire drawing machine speed was 140r / min. After water cooling at 25℃, PLA / 5%nHAP composite wire was obtained. The diameter of the obtained wire was 1.75±0.03mm and nHAP was uniformly dispersed in it. Its elemental distribution diagram and electron micrograph are shown below. Figure 6 , Figure 7As shown, the axial tensile test of the wire was conducted according to GB / T 1040, and the breaking strength of the wire was 45.31 MPa. Figure 11 As shown in (a) of the diagram.

[0050] Example 2 This embodiment provides a method for preparing polylactic acid / nanohydroxyapatite composite filaments for 3D printing, including the following steps: (1) Referring to Preparation Example 2 and Preparation Example 4, the nHAP content was controlled at 10%, and PLA / nHAP composite microspheres with 10% nHAP content and average particle size of 20-25 μm and 50-55 μm were prepared respectively; the two composite microspheres were mixed according to the mass ratio W 50-55μm :W 20-25μm The mixture is prepared at a ratio of 19:1 and used as a raw material for wire extrusion molding. (2) Set the barrel heating temperature to 200℃, and put in high-density polyethylene to clean the extruder until the extruded wire is transparent; (3) The barrel heating temperature is set to 165℃, the feed cooling temperature to 45℃, and the screw speed to 22r / min. Composite microsphere particle-graded raw materials are fed in for extrusion and stretching. The wire drawing machine speed is 150r / min. After water cooling at 25℃, PLA / 10%nHAP composite wire is obtained. The diameter of the obtained wire is 1.75±0.03mm, and its thermal decomposition temperature is 350℃. Figure 10 As shown, the fracture strength is 54.84 MPa. Figure 11 As shown in (a) of the example. The fracture strength is significantly improved compared to Example 1, indicating that the uniformly composited nHAP plays a role in particle dispersion toughening, and the particle dispersion toughening effect is enhanced with the increase of nHAP content.

[0051] The filaments obtained in Example 2 were further tested according to the systemic toxicity test requirements recommended in GB / T 16886.11-2021 "Biological Evaluation of Medical Devices Part 11: Systemic Toxicity Testing". The filaments were extracted with 0.9% sodium chloride injection (polar) and cottonseed oil (non-polar). The polar extract was administered to 5 KM mice via tail vein injection, and the non-polar extract was administered to 5 KM mice via intraperitoneal injection. Five KM mice were selected as controls for each extraction medium, and the corresponding extraction medium was administered using the same method at a dose of 50 mL / kg. The animals' responses were observed daily for 3 consecutive days, and their weight was measured. The number of animal deaths caused by the obtained filament extracts was 0, as shown in Table 1.

[0052] Table 1. Statistics on the number of animal deaths caused by the obtained wire extract.

[0053] Following the material-mediated pyrogen testing specifications in GB / T 16886.11-2021 "Biological Evaluation of Medical Devices Part 11: Systemic Toxicity Testing", New Zealand rabbits were tagged, weighed, and quarantined. They were then pre-fed for 8 days in a standard laboratory animal facility to acclimatize to the laboratory environment. One hour before the experiment, the rabbits were withheld from feeding and placed in a loosely positioned rabbit cage. 20g of ethylene oxide-sterilized filament was added to 100ml of 0.9% sodium chloride injection solution and incubated at 37℃ for 72h. The filament extract was then slowly infused into the rabbits' circulatory system via the marginal ear vein. A thermometer was inserted into the anus, and body temperature was measured every 30 minutes for a total of 8 measurements. The cumulative temperature rise in the New Zealand rabbits was 0.4℃ (<1.3℃), as shown in Table 2.

[0054] Table 2. Statistics on temperature rise in New Zealand rabbits obtained from the detection of pyrogens mediated by wires.

[0055] According to GB / T16886.10-2017 Standard for Biological Evaluation of Medical Devices: Stimulation and Sensitization Tests, three 2g portions of ethylene oxide-sterilized filaments were extracted with 10ml of 0.9% sodium chloride injection (polar) and cottonseed oil (non-polar), respectively, and the dissolution program was maintained at 37℃ for 72 hours. 0.10g of 1-chloro-2,4-dinitrobenzene was dissolved in acetone to prepare a 20.00ml positive control solution, mixed thoroughly, and labeled for later use. Before the experiment, quarantined guinea pigs were ear-tagged and weighed. After quarantine, they were randomly divided into four groups according to weight: a polar test group, a polar control group, a non-polar test group, and a non-polar control group, with 10 guinea pigs in each test group and 5 guinea pigs in each control group. The guinea pigs in each group were pre-housed in the laboratory animal room for 11 days. Before the experiment, the hair near the scapula on the back of the guinea pigs was removed, with a hair removal area of ​​3cm × 3cm. The above-mentioned extract was injected intradermally into the animals of each experimental group according to the standard procedure for induction. Six days after the intradermal induction phase, local induction was performed. Fourteen days after the local induction phase, the animals were challenged with the thread extract. The animals were wrapped with absorbent gauze for 24±2 hours. The skin condition of the experimental area was observed and described and graded 24±2 hours and 48±2 hours after the absorbent gauze was removed. The negative control group and the positive control group were operated on in the same manner. The prepared thread did not cause sensitization of the animal skin, as shown in Table 3.

[0056] Table 3. Statistics of Stimulation and Sensitization Tests of the Obtained Wires

[0057] Example 3 This embodiment provides a method for preparing polylactic acid / nanohydroxyapatite composite filaments for 3D printing, including the following steps: (1) Referring to Preparation Example 3 and Preparation Example 5, the nHAP content was controlled at 15%, and PLA / nHAP composite microspheres with 15% nHAP content and average particle size of 30-35 μm and 75-80 μm were prepared respectively; the two composite microspheres were mixed according to the mass ratio W 75-80μm :W 30-35μm The mixture is prepared at a ratio of 20:1 and used as a raw material for wire extrusion molding. (2) Set the barrel heating temperature to 200℃, and put in high-density polyethylene to clean the extruder until the extruded wire is transparent; (3) The barrel heating temperature was set to 165℃, the feed cooling temperature to 50℃, and the screw speed to 25r / min. Composite microsphere particle-graded raw materials were fed in for extrusion and stretching. The wire drawing machine speed was 160r / min. After water cooling at 35℃, PLA / 15%nHAP composite wire was obtained. The diameter of the obtained wire was 1.75±0.03mm, and the tensile strength of the wire was 37.52MPa. Figure 11 As shown in (a) of Example 2, the fracture strength decreased significantly because 15% nHAP was difficult to uniformly encapsulate in the microspheres. The aggregated nHAP could not fully exert the toughening effect of particle dispersion, and instead existed in the form of defects, causing a decrease in strength.

[0058] Example 4 This embodiment provides a method for preparing polylactic acid / nanohydroxyapatite composite filaments for 3D printing, including the following steps: (1) Referring to Preparation Examples 3, 4 and 5, the nHAP content was controlled at 10%, and PLA / nHAP composite microspheres with 10% nHAP content and average particle sizes of 30-35 μm, 50-55 μm and 75-80 μm were prepared respectively; the three composite microspheres were mixed according to the mass ratio W 75-80μm :W 50-55μm :W 30-35μm The mixture was prepared in a ratio of 19:4:1 and used as a raw material for wire extrusion molding. (2) Set the barrel heating temperature to 200℃, and put in high-density polyethylene to clean the extruder until the extruded wire is transparent; (3) The barrel heating temperature was set to 160℃, the feed cooling temperature to 45℃, and the screw speed to 22r / min. Composite microsphere particle graded raw materials were fed into the extrusion and stretching process. The wire drawing machine speed was 150r / min. After water cooling at 25℃, PLA / 10%nHAP composite wire was obtained. The diameter of the obtained wire was 1.75±0.03mm, and the breaking strength of the wire was 54.30MPa. There was no significant difference in breaking strength compared with Example 2.

[0059] Example 5 The difference between this embodiment and Example 1 is that step (1) is the same as in Example 1 and Example 3, and the nHAP content is controlled to be 3%, while the rest is the same as in Example 1.

[0060] The resulting wire had a breaking strength of 44.93 MPa. Compared with Example 1, the breaking strength was slightly lower, indicating that the uniformly composited nHAP played a role in particle dispersion toughening. As the nHAP content increased, the particle dispersion toughening effect was enhanced.

[0061] Example 6 The difference between this embodiment and Example 2 is that step (1) is the same as in Example 2 and Example 4, and the nHAP content is controlled to be 8%, while the rest is the same as in Example 2.

[0062] The resulting wire had a breaking strength of 51.62 MPa; the breaking strength was higher than that of Example 1 but lower than that of Example 2, which also indicates that the uniformly composited nHAP played a role in particle dispersion toughening, and the particle dispersion toughening effect was enhanced as the nHAP content increased.

[0063] Comparative Example 1 This comparative example provides a method for preparing non-uniform composite wires, i.e., without the preparation of composite microspheres, including the following steps: (1) Set the barrel heating temperature to 200℃, and put in high-density polyethylene to clean the extruder until the extruded wire is transparent.

[0064] (2) The barrel heating temperature was set to 165℃, the feed cooling temperature to 45℃, and the screw speed to 22r / min. PLA granules and 10% nHAP powder by mass were fed into the extrusion and stretching process. The wire drawing machine speed was 150r / min. After water cooling, PLA / 10%nHAP non-uniform composite wire was obtained. The nHAP in the obtained wire was not uniformly dispersed, such as... Figure 8 , Figure 9 As shown; Figure 11 As shown, the fracture strength was 52.57±7.92MPa, which was lower than that of the sample in Example 2. Moreover, the error of the average fracture strength was large, indicating poor mechanical property stability. This suggests that nHAP was unevenly distributed in the wire and the sample quality was unstable.

[0065] Comparative Example 2 This comparative example provides a method for preparing PLA wires without the preparation of composite microspheres, including the following steps: (1) Set the barrel heating temperature to 200℃, and put in high-density polyethylene to clean the extruder until the extruded wire is transparent.

[0066] (2) The barrel heating temperature is set to 165℃, the feed cooling temperature to 45℃, and the screw speed to 25r / min. PLA granules are fed in for extrusion and stretching. The wire drawing machine speed is 150r / min. After water cooling, PLA wire is obtained. The thermal decomposition temperature of the obtained wire is 330℃. Figure 10 As shown, the fracture strength is 41.56 MPa. Figure 11 As shown in (a) of Example 1, it can be seen that the composite of nHAP plays a role in particle dispersion and toughening.

[0067] Comparative Example 3 This comparative example provides a method for preparing polylactic acid / nanohydroxyapatite composite filaments for 3D printing, including the following steps: (1) Referring to Preparation Example 5, the nHAP content was controlled to be 10% to prepare PLA / nHAP composite microspheres with 10% nHAP content and an average particle size of 75-80μm; without particle size distribution, they were used as raw materials for wire extrusion molding. (2) Set the barrel heating temperature to 200℃, and put in high-density polyethylene to clean the extruder until the extruded wire is transparent; (3) The barrel heating temperature was set to 155℃, the feed cooling temperature to 40℃, and the screw speed to 20r / min. Microsphere raw materials were fed in for extrusion and stretching. The wire drawing machine speed was 140r / min. After water cooling at 25℃, PLA / 10% nHAP composite wire was obtained. The tensile strength of the obtained wire was 43.43MPa, which was lower than that of Example 1. Further scanning electron microscopy revealed that, as Figure 15 As shown in (a) and (b), the wire has many pore defects, leading to a decrease in breaking strength; while the defects in the wire of Example 1 are significantly reduced after particle size distribution, such as... Figure 15 As shown in (c) and (d) in the figure. A comparison between Example 1 and Comparative Example 3 reveals that, under the same extrusion process conditions, small-scale composite microspheres with particle size distribution are more conducive to eliminating internal defects, while large-scale composite microspheres without particle size distribution are more prone to internal defects due to insufficient air removal; for large-scale microspheres, higher temperatures are required to help the microspheres melt and eliminate pores.

[0068] Comparative Example 4 This comparative example provides a method for preparing polylactic acid / nanohydroxyapatite composite filaments for 3D printing, including the following steps: (1) Referring to Preparation Example 1, the nHAP content was controlled to be 10% to prepare PLA / nHAP composite microspheres with 10% nHAP content and an average particle size of 10-15 μm; without particle size distribution, they were used as raw materials for wire extrusion molding. (2) Set the barrel heating temperature to 200℃, and put in high-density polyethylene to clean the extruder until the extruded wire is transparent; (3) The barrel heating temperature was set to 155℃, the feed cooling temperature to 40℃, the screw speed to 20r / min, the microsphere raw material was fed in for extrusion and stretching, the wire drawing machine speed was 140r / min, and PLA / 10% nHAP composite wire was obtained after water cooling at 25℃. The fracture strength of the obtained wire was 48.73MPa. Under the same extrusion process conditions, small-scale microspheres are easy to melt and extrude and eliminate pore defects, but due to the agglomeration of nHAP, the particle dispersion toughening effect was not well exerted.

[0069] Because preparing microspheres with a particle size of 10-15 μm and a 10% nHAP content results in a decrease in the quality of the composite microspheres due to the high nHAP content, the small-sized microspheres cannot uniformly encapsulate so much nHAP. Some nHAP will adsorb onto the microsphere surface and aggregate, such as... Figure 16 As shown, this will affect the uniformity of the composite wire.

[0070] Application Example 1 This application example provides the fabrication process of the 3D-printed bone repair scaffold using the filament obtained in Example 2, including the following steps: (1) Set the printing temperature to 160℃, the printing platform temperature to 45℃, the layer height to 0.1mm, the wall thickness to 0.8mm, the infill density to 30%, the infill pattern to be linear, the printing speed to 30mm / s, and the printing platform attachment type to Brim.

[0071] (2) The PLA / 10%nHAP filament obtained in Example 2 was used to print layer by layer to obtain a 3D-printed bone repair scaffold with a mesh structure. The nHAP in the obtained mesh structure scaffold was evenly dispersed, such as... Figure 12 As shown, cells were cultured using a co-culture method. After culture, cytotoxicity was assessed using a CCK-8 assay kit. The cell viability after co-culturing with the scaffold was 107.5%. Figure 13 As shown.

[0072] Application Example 2 This application example provides the fabrication process of the 3D-printed bone repair scaffold using the filament obtained in Example 2, including the following steps: (1) Set the printing temperature to 160℃, the printing platform temperature to 45℃, the layer height to 0.1mm, the wall thickness to 0.8mm, the infill density to 30%, the infill pattern to be linear, the printing speed to 30mm / s, and the printing platform attachment type to Brim.

[0073] (2) PLA / 10%nHAP filament was used to print layer by layer, resulting in a 3D-printed bone repair scaffold with an umbrella-like structure. After co-culturing with cells, the scaffold underwent a cell live / dead staining experiment. Green fluorescence indicated live cells, and red fluorescence indicated dead cells. The resulting scaffold promoted cell adhesion and proliferation, such as... Figure 14 As shown.

[0074] In summary, this invention successfully obtained PLA / nHAP composite microspheres with average particle sizes of 10-15 μm, 20-25 μm, 30-35 μm, 50-55 μm, and 75-80 μm by controlling the preparation parameters of the emulsion solvent evaporation method. Furthermore, for different nHAP content targets, the microspheres of corresponding particle sizes were graded according to a specific mass ratio, and after melt extrusion and traction stretching, composite wires with a diameter of 1.75 ± 0.03 mm and uniform nHAP dispersion were obtained. Mechanical testing showed that the wire's breaking strength reached 37.52-54.84 MPa with minimal performance fluctuations. Thermogravimetric analysis showed that its thermal decomposition temperature was higher than that of pure PLA.

[0075] Compared with methods such as directly mixing nHAP powder and using ungraded microspheres of a single particle size, the filament of this invention exhibits significantly reduced internal porosity defects and greatly improved nHAP dispersion uniformity. Biological evaluation confirmed that the filament has no acute systemic toxicity, no pyrogenic reaction, and no skin sensitization. The bone repair scaffold obtained by FDM printing using this filament shows good cell compatibility and can promote cell adhesion and proliferation. The composite microsphereization and particle gradation strategy provided by this invention offers a reliable technical solution for the stable preparation of highly dispersed, high-content PLA / nHAP composite filaments, and has broad application prospects in the field of biomedical 3D printing.

[0076] The embodiments described above are some, but not all, of the embodiments of the present invention; the detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention; all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for preparing polylactic acid / nanohydroxyapatite composite filaments for 3D printing, characterized in that, Includes the following steps: S1. Polylactic acid is dissolved in an organic solvent to form a polylactic acid solution, and nano-hydroxyapatite is dispersed in the organic solvent to form a nano-hydroxyapatite dispersion. The polylactic acid solution and the nano-hydroxyapatite dispersion are mixed to obtain a mixed phase. The mixed phase is added to an aqueous solution containing polyvinyl alcohol, stirred to allow the organic solvent to evaporate, and the mixed phase is solidified into microspheres. After separation and drying, polylactic acid / nano-hydroxyapatite composite microspheres are obtained. Repeat the above process to prepare at least two types of polylactic acid / nanohydroxyapatite composite microspheres with different average particle sizes; S2. The composite microspheres with at least two different average particle sizes are subjected to particle gradation to obtain graded raw materials; S3. The graded raw materials are melt-extruded and stretched to obtain composite wire.

2. The preparation method according to claim 1, characterized in that, The polylactic acid mentioned in step S1 is racemic polylactic acid with a weight-average molecular weight of 100,000-200,000; the particle size range of the composite microspheres is 10-80 μm.

3. The preparation method according to claim 1, characterized in that, The particle gradation mentioned in step S2 is used to prepare wires with a nano-hydroxyapatite content ≤5wt%. Specifically, two types of composite microspheres with average particle sizes of 30-35μm and 10-15μm are mixed at a mass ratio of (18-20):

1.

4. The preparation method according to claim 1, characterized in that, The particle gradation mentioned in step S2 is used to prepare wires with a nano-hydroxyapatite content of 5wt%-10wt%. Specifically, two types of composite microspheres with average particle sizes of 50-55μm and 20-25μm are mixed at a mass ratio of (18-20):

1.

5. The preparation method according to claim 1, characterized in that, The particle gradation mentioned in step S2 is used to prepare wires with a nano-hydroxyapatite content of 10wt%-15wt%. Specifically, two types of composite microspheres with average particle sizes of 75-80μm and 30-35μm are mixed at a mass ratio of (18-20):

1.

6. The preparation method according to claim 1, characterized in that, The particle gradation mentioned in step S2 is used to prepare wires with a nano-hydroxyapatite content of 5wt%-10wt%. Specifically, three composite microspheres with average particle sizes of 75-80μm, 50-55μm and 10-15μm are mixed in a mass ratio of (18-20):(3-5):

1.

7. The preparation method according to claim 1, characterized in that, The melt extrusion described in step S3 uses an extruder with a screw speed of 20-25 r / min, a feed cooling temperature of 40-50℃, and a barrel heating temperature of 155-165℃.

8. The preparation method according to claim 1, characterized in that, The traction and stretching described in step S3 is performed using a wire drawing machine with a rotation speed of 140-160 r / min and a cooling water bath at 25-35℃.

9. A polylactic acid / nanohydroxyapatite composite filament for 3D printing obtained by the preparation method according to any one of claims 1-8, characterized in that, The composite wire has a diameter of 1.75±0.03mm, and the nano-hydroxyapatite accounts for 3-15% of the mass fraction of polylactic acid.

10. The application of the polylactic acid / nanohydroxyapatite composite filament for 3D printing as described in claim 9 in the field of biomedical bone repair.

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