A bionic heterogeneous composite structure bone implant and a preparation method thereof

Abstract

The application discloses a kind of bionic heterogeneous composite structure bone implants and preparation method thereof, it is related to medical implant technical field, including the cross structure of inner layer, the negative Poisson's ratio structure of middle layer and the honeycomb structure of outer layer, cross structure, negative Poisson's ratio structure, honeycomb structure are jointly formed bionic composite structure, after bionic composite structure of double network crosslinking is immersed in drug-containing solution and is handled to load medicine, obtain bionic heterogeneous composite structure.The application realizes the bionic adaptation and intelligent optimization of mechanical property, solves stress shielding problem;The application significantly accelerates and enhances bone integration and vascularization process, realizes the leap-forward promotion of biological activity;The application develops intelligent treatment new mode based on in-vivo microenvironment response, realizes on-demand, accurate drug delivery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of medical implant, in particular to a bionic heterogeneous composite structure bone implant and a preparation method thereof. BACKGROUND

[0002] Large segmental bone defect is a major challenge in clinical orthopedics, often caused by high-energy trauma, tumor resection or debridement of osteomyelitis. The self-healing ability of large segmental bone defect is extremely limited, and usually requires the implantation of bone repair materials to provide mechanical support and induce bone regeneration. The ideal implant should have the following characteristics: (1) matching mechanical properties with host bone to avoid stress shielding effect; (2) excellent porous structure to promote bone tissue ingrowth and vascularization; (3) biological activity to accelerate the process of bone integration and, if necessary, drug delivery function to prevent and treat infection.

[0003] Currently, the commonly used bone implants in clinical practice mainly include metal implants, bioceramics and polymer materials. Among them, titanium alloy (especially TC4) is widely used as a bone repair and replacement material for load-bearing sites due to its high specific strength, excellent corrosion resistance and good biocompatibility. However, traditional solid or homogeneous porous titanium alloy implants have significant drawbacks: first, their elastic modulus (110-120 GPa) is much higher than that of human cortical bone (about 18-20 GPa), which can cause severe stress shielding effect when bearing load, leading to bone resorption and long-term loosening failure around the implant; second, their biologically inert surface is not conducive to cell adhesion, proliferation and differentiation, and the bone integration rate is slow.

[0004] To overcome the above problems, various improvement schemes have been proposed in the prior art. One mainstream scheme is to use additive manufacturing (such as laser selective melting, SLM) to prepare porous titanium alloy scaffolds, which reduces the elastic modulus by designing the pore structure. For example, the porous structure design based on three-period minimal surface (TPMS) has achieved a certain degree of modulus reduction and pore structure interconnection, but the complex curved surface characteristics of TPMS structure make it difficult to completely clean the residual powder after printing, which may cause biocompatibility problems; at the same time, its smooth curved surface is not conducive to cell anchoring, and the single pore structure cannot meet the contradictory demands of mechanical support and rapid vascularization at the same time.

[0005] Another solution is to construct a metal-biomaterial composite implant to combine the mechanical advantages of metal and the osteogenic activity of biomaterials. For example, the method of filling hydrogel (such as gelatin, sodium alginate) into a porous titanium scaffold aims to provide a three-dimensional growth environment for cells and load biological factors. However, this method has obvious bottlenecks: first, the interface bonding force between metal and hydrophilic hydrogel is weak, and it is easy to debond and separate in the physiological environment, resulting in functional failure; second, the mechanical strength of conventional hydrogel is generally low and cannot effectively share the load; third, the release behavior of the drugs or growth factors loaded by it is mostly passive diffusion mode, which cannot respond to complex in vivo microenvironment (such as infection, inflammation) to achieve intelligent on-demand release, and the utilization rate is low and may produce side effects.

[0006] Therefore, there is an urgent need in the art for a new composite implant for large bone defect repair, which can achieve perfect adaptation of mechanical properties and directional guidance of biological functions from the structure, form a stable and firm composite from the material, and break through the limitations of passive release from the function to achieve intelligent response to external temperature stimulation and on-demand control of the release behavior of therapeutic agents.

[0007] Therefore, a bionic heterogeneous composite structure bone implant and a preparation method thereof are proposed to solve the above problems. SUMMARY

[0008] To achieve the above object, the present application provides the following technical scheme: a preparation method of a bionic heterogeneous composite structure bone implant, comprising the following steps:

[0009] Step 1, based on a three-dimensional modeling software, the modeling of the cross-shaped structure of the inner layer, the negative Poisson's ratio structure of the middle layer and the honeycomb structure of the outer layer is completed respectively, and then the cross-shaped structure, the negative Poisson's ratio structure and the honeycomb structure are combined to form a bionic composite structure;

[0010] Step 2, based on laser selective melting additive manufacturing technology, the bionic composite structure is printed and formed by using NiTi alloy powder;

[0011] Step 3, a PNIPAM pre-polymer solution and a GelMA mixed solution are prepared, and the PNIPAM pre-polymer solution and the GelMA mixed solution are mixed to obtain a hydrogel precursor solution;

[0012] Step 4, the hydrogel precursor solution is injected into a silica gel mold in which the bionic composite structure is placed, and the bionic composite structure is covered, and then light-chemical synergistic double network crosslinking is carried out through 405nm blue light irradiation and thermal initiation;

[0013] Step 5, the bionic composite structure after double network crosslinking is immersed in a drug-containing solution for post-treatment and drug loading to obtain a bionic heterogeneous composite structure.

[0014] As preferred, the cross-shaped structure is composed of a plurality of cross-shaped structure cells, the cross-shaped structure cell comprises a central circular inner ring, a cylindrical support one and an L-shaped support, the cylindrical support one is located at the center of the central circular inner ring for subsequent array connection of the cross-shaped structure cells, an L-shaped support is connected to the central circular inner ring, the L-shaped support rotates around the center of the central circular inner ring every 90° for 3 times to form a cross-shaped structure cell; one cross-shaped structure cell is arrayed 5 times along the x-axis, the plurality of cross-shaped structure cells after arraying are connected through the cylindrical support one, and the arraying distance is 4.65 mm; the end face of the L-shaped support far away from the central circular inner ring of the uppermost one of the L-shaped supports on the central circular inner ring is selected as a mirror surface, the structure after arraying 5 times is mirrored once, then the end face of the L-shaped support facing the positive direction of the z-axis is selected as a mirror surface, the structure is mirrored once, then the end face of the L-shaped support facing the positive direction of the z-axis is selected as a mirror surface again, and the obtained structure is mirrored once again, and finally the inner-layer cross-shaped structure is obtained.

[0015] As preferred, the negative Poisson's ratio structure is composed of a plurality of negative Poisson's ratio structure cells, the negative Poisson's ratio structure cell comprises two cross beams, four inner recess supports, a cylindrical support two and four connecting cylinders, the two cross beams are symmetrically distributed upward and downward, the four inner recess supports are symmetrically arranged between the two cross beams, the two ends of the inner recess supports are connected with the ends of the two cross beams respectively, the central positions of the four inner recess supports are provided with one connecting cylinder respectively, the cylindrical support two is located at the center of the two cross beams, and the two ends of the cylindrical support two are connected with the two cross beams respectively to support the two cross beams; one negative Poisson's ratio structure cell is arrayed 3 times along the x-axis, the arraying distance is 14 mm, the negative Poisson's ratio structure cells are connected through the connecting cylinders, the two negative Poisson's ratio structure cells at the two ends of the arrayed structure are arrayed once along the positive direction of the y-axis, the arraying distance is 14 mm, and the two negative Poisson's ratio structure cells are connected through the connecting cylinders, the connecting cylinder end face of the structure after arraying along the y-axis and facing the positive direction of the y-axis is selected as a mirror surface to mirror once, and finally the mirrored structure is arrayed 3 times along the z-axis, the arraying distance is 14 mm, and the two cross beams are closely connected to obtain the middle-layer negative Poisson's ratio structure.

[0016] As preferred, the honeycomb structure comprises a honeycomb wall and a circular hole, the honeycomb wall is provided with a large honeycomb-shaped groove structure and a small honeycomb-shaped groove structure, a plurality of large honeycomb-shaped groove structures are arranged at equal intervals on the inner wall of the honeycomb wall, a plurality of small honeycomb-shaped groove structures are arranged at equal intervals on the outer wall of the honeycomb wall, and a plurality of circular holes in a grid array are arranged through the honeycomb wall.

[0017] As preferred, step 2 is specifically:

[0018] The model of the biomimetic composite structure obtained in step 1 is saved in stl. format, imported into Magics software for slicing processing, and then copied into an SLM device, and NiTi spherical powder with a particle size of 15-53 μm is used for printing, with the printing parameters being: a light spot diameter of 80 μm, a laser power of 150 W, a scanning speed of 800 mm / s, a scanning interval of 0.08 mm, a layer thickness of 0.03 mm, a scanning strategy of a 2.5 mm chessboard scanning, and a layer rotation angle of 67°.

[0019] As preferred, in step 3, the preparation process of the PNIPAM pre-polymer solution is as follows:

[0020] First, 15 g of N-isopropyl acrylamide is dissolved in 10 ml of PBS solution, 0.12 g of N,N'-methylene bisacrylamide is added as a PNIPAM network crosslinking agent, then 0.15 g of ammonium persulfate is added as a PNIPAM polymerization initiator, and after dissolving under magnetic stirring at 500 rpm, 50 μL of tetramethyl ethylenediamine is added as a PNIPAM polymerization accelerator to obtain a PNIPAM pre-polymer solution;

[0021] In step 3, the preparation process of the GelMA mixed solution is as follows:

[0022] First, 8 g of methacrylated gelatin is dissolved in 10 ml of PBS solution at 60°C in a water bath, 1.5 g of nano-hydroxyapatite is ultrasonically dispersed for 5 min at a power of 300 W to achieve bone integration / mechanical reinforcement, then 0.2 g of hydroxypropyl cellulose is added to raise the phase transition temperature from 32°C to 37.5°C, and finally a photoinitiator is added to achieve GelMA photocuring in the dark, and finally a GelMA mixed solution is formed;

[0023] In step 3, the hydrogel precursor solution is composed of the PNIPAM pre-polymer solution and the GelMA mixed solution in a volume ratio of 1:1, and after vortex mixing for 30 s, a milky white suspension is formed.

[0024] As preferred, in step 4, the specific method of double network crosslinking is as follows:

[0025] First, the biomimetic composite structure covered with the hydrogel precursor solution is irradiated with 405 nm blue light to form a first heavy network, and then it is transferred to a 37°C incubator for 30 min of heat-induced PNIPAM polymerization, and the gel changes from transparent to milky white, i.e., the double network crosslinking is completed.

[0026] As preferred, in step 5, the specific process of post-processing and drug loading is as follows:

[0027] The biomimetic composite structure after double network crosslinking in step 4 is immersed in a drug-containing solution, which is a 10 mg / ml vancomycin solution, and is swelled at 4°C for 24 h to achieve efficient drug loading in a low-temperature state.

[0028] The application also provides a bionic heterogeneous composite structure bone implant prepared by the method.

[0029] The application has the following beneficial effects:

[0030] The application realizes bionic adaptation and intelligent optimization of mechanical properties, and solves the stress shielding problem. The application combines bionic structure design with NiTi super-elastic alloy to construct a multi-level composite structure of outer honeycomb structure, middle negative Poisson's ratio structure and inner cross-shaped structure. The middle negative Poisson's ratio structure and the inner cross-shaped structure significantly improve the bending resistance and torsional resistance, so that they are highly matched with the biomechanical properties of bone tissue. The NiTi alloy material provides excellent super-elasticity to realize material-structure-function integrated molding. The design and optimization of the structure and the material enable the load to be effectively transmitted to the surrounding bone tissue through the implant, fundamentally avoiding bone resorption and long-term loosening failure of the implant caused by stress shielding, and greatly improving the long-term stability of the implant.

[0031] The application significantly accelerates and enhances the process of bone integration and vascularization, and realizes a leap in biological activity. Instead of passively waiting for bone growth, the application creates an excellent osteogenic environment through multiple active strategies. Firstly, the outer honeycomb structure network provides a directional guiding path for cell migration and vascular growth, greatly improving the vascularization efficiency. Secondly, the double-network hybrid hydrogel provides excellent cell "anchoring points", which significantly improve the activity of osteoblasts, surpassing traditional porous titanium alloys. Thirdly, the hydrogel can load vancomycin anti-inflammatory drugs, which work synergistically with the physical structure to realize efficient bone repair combining "physical guidance" and "chemical induction".

[0032] The application develops a new intelligent treatment mode based on the response of the in-vivo microenvironment, and realizes on-demand and precise drug delivery. The application breaks through the limitations of passive drug release of traditional implants and constructs an intelligent closed-loop system of "perception-response-release". By integrating temperature-sensitive (PNIPAM) hydrogel, the implant can sensitively perceive the local temperature rise caused by infection. When the temperature is > 37.5℃, the hydrogel undergoes phase transition and shrinks, extruding the internal drugs for rapid release, while maintaining slow release under normal physiological conditions. This "on-demand treatment" mode greatly improves the drug utilization efficiency and provides a solution for the prevention and treatment of postoperative infection. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The design flowchart of the bionic composite structure of the application is shown in the figure.

[0034] Figure 2 The design diagram of the cross-shaped structure cell in the application is shown in the figure.

[0035] Figure 3Design drawing for negative Poisson's ratio structure cell in the application;

[0036] Figure 4 Design drawing for honeycomb structure in the application;

[0037] Figure 5 Enlarged drawing for honeycomb structure in the application;

[0038] Figure 6 Flow chart for preparation of bionic heterogeneous composite structure in the application;

[0039] Figure 7 Physical drawing for bionic composite structure in the application;

[0040] Figure 8 Physical drawing for bionic heterogeneous composite structure in the application.

[0041] In the figure: 1, cross-shaped structure cell; 101, central circular inner ring; 102, cylindrical support 1; 103, L-shaped support; 2, cross-shaped structure; 3, negative Poisson's ratio structure cell; 31, cross beam; 32, inner recessed support; 33, cylindrical support 2; 34, connecting cylinder; 4, negative Poisson's ratio structure; 5, honeycomb structure; 51, honeycomb wall; 52, circular hole; 511, large honeycomb groove structure; 512, small honeycomb groove structure; 6, bionic composite structure; 7, PNIPAM pre-polymer liquid; 8, GelMA mixed liquid; 9, hydrogel precursor solution; 10, 405 nm blue light; 11, bionic heterogeneous composite structure; 12, drug-containing solution. DETAILED DESCRIPTION

[0042] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the application.

[0043] The application will be further described in detail below according to the drawings and embodiments.

[0044] As shown in the figure, a preparation method of a bionic heterogeneous composite structure bone implant comprises the following steps: Figures 1 to 8

[0045] Step 1, based on a three-dimensional modeling software, modeling of the cross-shaped structure 2 of the inner layer, the negative Poisson's ratio structure 4 of the middle layer and the honeycomb structure 5 of the outer layer is respectively completed, and then the cross-shaped structure 2, the negative Poisson's ratio structure 4 and the honeycomb structure 5 are combined to form a bionic composite structure 6;

[0046] Among them, as shown in the figure, the cross-shaped structure 2 comprises a central circular inner ring 101, a cylindrical support 1 102 and an L-shaped support 103; the negative Poisson's ratio structure 4 comprises a cross beam 31, an inner recessed support 32 and a cylindrical support 2 33; the honeycomb structure 5 comprises a honeycomb wall 51 and a circular hole 52; the bionic composite structure 6 comprises the cross-shaped structure 2, the negative Poisson's ratio structure 4 and the honeycomb structure 5. Figure 1 Figure 2 ​​As shown, the cross-shaped structure 2 is composed of a plurality of cross-shaped structure cells 1, which include a central circular inner ring 101, a cylindrical support 102 located at the center of the central circular inner ring 101 for subsequent array connection of cross-shaped structure cells 1, and an L-shaped support 103 connected to the central circular inner ring 101, which rotates around the center of the central circular inner ring 101 every 90° for a total of three times to form a cross-shaped structure cell 1. The size of the cross-shaped structure cell 1 is: d = 12 mm, e = 14 mm, f = 4 mm, g = 1.5 mm, and h = 2 mm, where f is the outer diameter of the central circular inner ring 101, g is the diameter of the cylindrical support 102, the length of the cylindrical support 102 is 4.65 mm, and h is the thickness of the L-shaped support 103. Five times arraying of a cross-shaped structure cell 1 along the x-axis, and connecting the multiple cross-shaped structure cells 1 after arraying through the cylindrical support 102 with a distance of 1.5 mm; selecting the end face of one L-shaped support 103 farthest from the central circular inner ring 101 as the mirror surface, mirroring the structure once after arraying five times, then selecting the end face of an L-shaped support 103 facing the positive direction of the z-axis as the mirror surface, mirroring the structure once, and then selecting the end face of another L-shaped support 103 facing the positive direction of the z-axis as the mirror surface, mirroring the obtained structure once, finally obtaining a cross-shaped structure 2 with an inner layer size of 27.9 mm along the x-axis, 28 mm along the y-axis, and 56 mm along the z-axis;

[0047] As Figure 1 and Figure 3As shown, the negative Poisson's ratio structure 4 is composed of a plurality of negative Poisson's ratio structure cells 3, the negative Poisson's ratio structure cell 3 including two cross beams 31, four concave struts 32, one cylindrical support II 33, and four connecting cylinders 34 respectively distributed at the center positions of the four concave struts 32. The two cross beams 31 are symmetrically distributed up and down with a distance of 10 mm. The four concave struts 32 are symmetrically arranged between the two cross beams 31, and the two ends of the concave struts 32 are respectively connected with the end portions of the two cross beams 31. The cylindrical support II 33 is located at the center of the two cross beams 31, and the two ends of the cylindrical support II 33 are respectively connected with the two cross beams 31, thereby supporting the two cross beams 31. The connecting cylinders 34 are respectively distributed at the center positions of the four concave struts 32, thereby connecting the negative Poisson's ratio structure cells 3 in sequence, and the diameter of the connecting cylinders 34 is 1.5 mm. The negative Poisson's ratio structure cell 3 simulates the curve characteristics of the tortoise shell, and optimizes the concave prismatic structure in the typical negative Poisson's ratio structure to a concave arc structure, thereby further improving the mechanical bearing characteristics. The size of the negative Poisson's ratio structure cell 3 is as follows: a = 12 mm, b = 14 mm, c = 10 mm, d1 = 14 mm, e1 = 1.5 mm, wherein a is the width of the negative Poisson's ratio structure cell 3, b is the height of the negative Poisson's ratio structure cell 3, c is the height of the cylindrical support II 33, d1 is the distance between the end faces of the two oppositely distributed connecting cylinders 34, and e1 is the diameter of the connecting cylinder 34. The concave arc structure is designed according to the Bezier curve, which has excellent smoothness and is beneficial to improve the mechanical properties. The Bezier curve equation is as follows:

[0048] x(t) = (1-t) 2 x0+2(1-t)tx1+t 2 x2

[0049] y(t) = (1-t) 2 y0+2(1-t)ty1+t 2 y2

[0050] wherein t is a parameter in the range of [0, 1], x0, y0 are the starting point coordinates of the curve, x1, y1 are the midpoint coordinates of the curve, and x2, y2 are the terminal point coordinates of the curve.

[0051] The negative Poisson's ratio structure cell 3 is arrayed along the x-axis three times with an array spacing of 14 mm, the negative Poisson's ratio structure cells 3 are connected through the connecting cylinders 34, the two negative Poisson's ratio structure cells 3 at the ends of the structure after arraying are arrayed along the y-axis positive direction once with an array spacing of 14 mm, and are also connected through the connecting cylinders 34, then the end face of the connecting cylinder 34 of the structure after arraying along the y-axis in the direction of the y-axis positive direction is mirrored once, and finally the mirrored structure is closely arrayed along the z-axis three times with an array spacing of 14 mm and is closely connected through the cross beams 31, so as to obtain the negative Poisson's ratio structure 4 of the middle layer with a size of 56 mm in the x-axis direction, 56 mm in the y-axis direction, and 56 mm in the z-axis direction, and the size of the position in the negative Poisson's ratio structure 4 for accommodating the cross-shaped structure 2 is 28 mm in the x-axis direction, 28 mm in the y-axis direction, and 56 mm in the z-axis direction.

[0052] As shown in Figure 1 , Figure 4 and Figure 5 , the honeycomb structure 5 imitates the honeycomb structure characteristics and is designed with circular holes on the wall, which is beneficial to the improvement of mechanical properties and the release of hydrogel, including the honeycomb wall 51 and the circular hole 52, the honeycomb wall 51 is provided with large honeycomb-shaped groove structures 511 and small honeycomb-shaped groove structures 512, the inner wall of the honeycomb wall 51 is provided with a plurality of large honeycomb-shaped groove structures 511 at equal intervals, the spacing between the large honeycomb-shaped groove structures 511 is 1.69 mm, the outer wall of the honeycomb wall 51 is provided with a plurality of small honeycomb-shaped groove structures 512 at equal intervals, the spacing between the small honeycomb-shaped groove structures 512 is 2.27 mm, the honeycomb wall 51 is provided with a plurality of circular holes 52 in a grid array distribution in a penetrating manner, the spacing between the circular holes 52 is 4 mm, the size of the honeycomb structure 5 is: j=60 mm, k=56 mm, l=2 mm, n=1.15 mm, o=0.87 mm, m=3 mm, wherein j is the width of the honeycomb structure 5, k is the height of the honeycomb structure 5, l is the diameter of the circular hole 52, n is the edge length of the regular hexagonal section of the large honeycomb-shaped groove structure 511, o is the edge length of the regular hexagonal section of the small honeycomb-shaped groove structure 512, and m is the thickness of the honeycomb wall 51.

[0053] Step 2, based on the selective laser melting (SLM) additive manufacturing technology, the bionic composite structure 6 is printed and formed by using NiTi alloy powder, specifically:

[0054] The model of the biomimetic composite structure 6 obtained in step 1 is saved in stl. format, imported into Magics software for slicing processing, and then copied into an SLM device, and printing is performed using NiTi spherical powder with a particle size of 15-53 μm, with the printing parameters being: a light spot diameter of 80 μm, a laser power of 150 W, a scanning speed of 800 mm / s, a scanning interval of 0.08 mm, a layer thickness of 0.03 mm, a scanning strategy of a 2.5 mm chessboard scanning, and a layer rotation angle of 67°;

[0055] Step 3, preparing a PNIPAM prepolymer solution 7 and a GelMA mixed solution 8, and performing double-network mixing of the PNIPAM prepolymer solution 7 and the GelMA mixed solution 8 to obtain a hydrogel precursor solution 9;

[0056] The preparation process of the PNIPAM prepolymer solution 7 is as follows:

[0057] First, 15 g of N-isopropyl acrylamide (NIPAM) is dissolved in 10 ml of a PBS solution, 0.12 g of N,N'-methylene bisacrylamide (MBAA) is added as a PNIPAM network crosslinking agent, then 0.15 g of ammonium persulfate (APS) is added as a PNIPAM polymerization initiator, after dissolution under magnetic stirring at 500 rpm, 50 μL of tetramethyl ethylenediamine (TEMED) is added as a PNIPAM polymerization accelerator, and the PNIPAM prepolymer solution 7 is obtained;

[0058] The preparation process of the GelMA mixed solution 8 is as follows:

[0059] First, 8 g of methacrylated gelatin (GelMA) is dissolved in 10 ml of a PBS solution under a 60°C water bath, 1.5 g of nano-hydroxyapatite (nHA) is ultrasonically dispersed for 5 min under a power of 300 W to realize bone integration / mechanical reinforcement, then 0.2 g of hydroxypropyl cellulose (HPC) is added to raise the phase transition temperature from 32°C to 37.5°C to realize accurate response to body temperature, when the local temperature at the implantation site increases (>37.5°C), the burst release of the drug is triggered, and finally a light initiator (LAP) is added in the dark to realize GelMA photocuring, and the GelMA mixed solution 8 is finally formed;

[0060] The hydrogel precursor solution 9 is composed of the PNIPAM prepolymer solution 7 and the GelMA mixed solution 8 in a volume ratio of 1:1, and after vortex mixing for 30 s, a milky white suspension is formed;

[0061] Step 4, the hydrogel precursor solution 9 is injected into a silica gel mold in which the biomimetic composite structure 6 is placed, covering the biomimetic composite structure 6, and then light-chemical synergistic double-network crosslinking is performed through 405 nm blue light 10 irradiation and thermal initiation;

[0062] The specific method of double-network crosslinking is as follows:

[0063] First, irradiate the biomimetic composite structure 6 covered with the hydrogel precursor solution 9 with 405nm blue light 10 (15mW / cm2, 45s) to form a first heavy network, and then transfer to a 37℃ incubator for 30min to heat initiate the polymerization of PNIPAM, and the gel changes from transparent to milky white (the sign of phase change completion), that is, the double-network crosslinking is completed;

[0064] Step 5, immerse the biomimetic composite structure 6 after double-network crosslinking in the drug-containing solution 12 for post-processing and drug loading to obtain the biomimetic heterogeneous composite structure 11;

[0065] The specific process of post-processing and drug loading is as follows:

[0066] Immerse the biomimetic composite structure 6 after double-network crosslinking in step 4 in the drug-containing solution 12, which is a 10mg / ml vancomycin solution, and swell at 4℃ for 24h to realize efficient drug loading in a low-temperature state.

[0067] In summary, the present application realizes the bionic adaptation and intelligent optimization of mechanical properties, and solves the problem of stress shielding. The present application combines bionic structure design with NiTi super-elastic alloy to construct a multi-level composite structure of outer honeycomb structure 5, middle negative Poisson's ratio structure 4 and inner cross-shaped structure 2. The middle negative Poisson's ratio structure 4 and the inner cross-shaped structure 2 significantly improve the bending resistance and torsional resistance, so that they are highly matched with the biomechanical properties of bone tissue, and the NiTi alloy material provides excellent super-elasticity to realize material-structure-function integrated molding. The design and optimization of the structure and the material enable the load to be effectively transmitted to the surrounding bone tissue through the implant, which fundamentally avoids bone resorption and long-term loosening failure of the implant caused by stress shielding, and greatly improves the long-term stability of the implant.

[0068] The present application significantly accelerates and enhances the process of bone integration and vascularization, and realizes a leap in biological activity. Instead of passively waiting for bone growth, the present application creates an excellent osteogenic environment through multiple active strategies. Firstly, the outer honeycomb structure network provides a directional guiding path for cell migration and vascular ingrowth, greatly improving the vascularization efficiency; secondly, the double-network mixed hydrogel provides excellent cell "anchoring points", which significantly improve the activity of osteoblasts, surpassing traditional porous titanium alloy; thirdly, the hydrogel can load vancomycin anti-inflammatory drugs, which synergistically act with the physical structure to realize efficient bone repair combining "physical guidance" and "chemical induction".

[0069] The application develops a new intelligent treatment mode based on in-vivo microenvironment response, and realizes on-demand and precise drug delivery. The application breaks through the limitation of passive drug release of traditional implants, and constructs an intelligent closed-loop system of "perception-response-release". By integrating temperature-sensitive (PNIPAM) hydrogel, the implant can sensitively perceive the local temperature rise caused by infection. When the temperature is greater than 37.5 DEG C, the phase change of the hydrogel occurs, the internal drug is extruded and released quickly, and under normal physiological conditions, the hydrogel maintains low-speed sustained release. This "on-demand treatment" mode greatly improves the drug utilization efficiency, and provides a revolutionary solution for the prevention and treatment of postoperative infection.

[0070] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a biomimetic heterogeneous composite bone implant, characterized in that, Includes the following steps: Step 1: Based on 3D modeling software, model the inner cross-shaped structure (2), the middle negative Poisson's ratio structure (4), and the outer honeycomb structure (5) respectively, and then combine the cross-shaped structure (2), the negative Poisson's ratio structure (4), and the honeycomb structure (5) into a biomimetic composite structure (6). Step 2: Based on laser selective melting additive manufacturing technology, NiTi alloy powder is used to print the biomimetic composite structure (6) into shape; Step 3: Prepare PNIPAM prepolymer solution (7) and GelMA mixture (8). Mix PNIPAM prepolymer solution (7) and GelMA mixture (8) in a double network to obtain hydrogel precursor solution (9). Step 4: The hydrogel precursor solution (9) is injected into the silicone mold containing the biomimetic composite structure (6) and covered with the biomimetic composite structure (6). The photo-chemical synergistic dual network crosslinking is carried out by irradiation with 405nm blue light (10) and thermal initiation. Step 5: Immerse the biomimetic composite structure (6) after dual-network cross-linking into the drug-containing solution (12) for post-treatment and drug loading to obtain the biomimetic heterogeneous composite structure (11).

2. The method for preparing a biomimetic heterogeneous composite bone implant according to claim 1, characterized in that, The cross-shaped structure (2) is composed of multiple cross-shaped structural cells (1). The cross-shaped structural cell (1) includes a central circular inner ring (101), a cylindrical support (102), and an L-shaped pillar (103). The cylindrical support (102) is located at the center of the central circular inner ring (101) and is used for subsequent array connection of cross-shaped structural cells (1). An L-shaped pillar (103) is connected to the central circular inner ring (101). The L-shaped pillar (103) is rotated once every 90° around the center of the central circular inner ring (101) for a total of 3 rotations to form the cross-shaped structural cell (1). A cross-shaped structural cell (1) is tightly arranged along the x-axis. The array is repeated 5 times. After the array, multiple cross-shaped structural cells (1) are connected by cylindrical supports (102), and the array distance is 4.65 mm. The end face of the L-shaped support (103) located at the top of the central circular inner ring (101) away from the central circular inner ring (101) is selected as the mirror face. The structure after the array is repeated 5 times is mirrored once. Finally, the end face of the L-shaped support (103) facing the positive z-axis is selected as the mirror face, and the structure is mirrored once. Then, the end face of the L-shaped support (103) facing the positive z-axis is selected as the mirror face again, and the resulting structure is mirrored once more. Finally, the inner cross-shaped structure (2) is obtained.

3. The method for preparing a biomimetic heterogeneous composite bone implant according to claim 2, characterized in that, The negative Poisson's ratio structure (4) is composed of multiple negative Poisson's ratio structural cells (3). Each negative Poisson's ratio structural cell (3) includes two crossbeams (31), four concave pillars (32), a cylindrical support (33), and four connecting cylinders (34). The two crossbeams (31) are symmetrically distributed vertically. The four concave pillars (32) are symmetrically arranged between the two crossbeams (31). The two ends of the concave pillars (32) are connected to the ends of the two crossbeams (31), respectively. A connecting cylinder (34) is set at the center of each of the four concave pillars (32). The cylindrical support (33) is located at the center of the two crossbeams (31), and the two ends of the cylindrical support (33) are connected to the two crossbeams (31), respectively. The structure serves to support the two cross beams (31). A negative Poisson's ratio structural cell (3) is arrayed three times along the x-axis with an array spacing of 14 mm. The negative Poisson's ratio structural cells (3) are connected by connecting cylinders (34). The two negative Poisson's ratio structural cells (3) located at both ends of the structure after arraying are arrayed once along the positive y-axis with an array spacing of 14 mm. They are also connected by connecting cylinders (34). The structure after arraying along the y-axis is mirrored once with the end face of the connecting cylinder (34) facing the positive y-axis as the mirror plane. Finally, the mirrored structure is tightly arrayed three times along the z-axis with an array spacing of 14 mm. It is tightly connected by cross beams (31) to obtain the negative Poisson's ratio structure (4) in the middle layer.

4. The method for preparing a biomimetic heterogeneous composite bone implant according to claim 3, characterized in that, The honeycomb structure (5) includes a honeycomb wall (51) and round holes (52). The honeycomb wall (51) is provided with a large honeycomb groove structure (511) and a small honeycomb groove structure (512). The inner wall of the honeycomb wall (51) is provided with multiple large honeycomb groove structures (511) at equal intervals, and the outer wall of the honeycomb wall (51) is provided with multiple small honeycomb groove structures (512) at equal intervals. The honeycomb wall (51) is provided with multiple round holes (52) arranged in a grid array.

5. The method for preparing a biomimetic heterogeneous composite bone implant according to claim 4, characterized in that, Step 2 is as follows: The model of the biomimetic composite structure (6) obtained in step 1 was saved as an STL file, imported into Magics software for slicing, and then copied into an SLM device. NiTi spherical powder with a particle size of 15-53 μm was used for printing. The printing parameters were: spot diameter of 80 μm, laser power of 150 W, scanning speed of 800 mm / s, scanning spacing of 0.08 mm, layer thickness of 0.03 mm, scanning strategy of 2.5 mm checkerboard scanning, and interlayer rotation angle of 67°.

6. The method for preparing a biomimetic heterogeneous composite bone implant according to claim 5, characterized in that, In step 3, the preparation process of PNIPAM prepolymer solution (7) is as follows: First, 15g of N-isopropylacrylamide was dissolved in 10ml of PBS solution, and 0.12g of N,N'-methylenebisacrylamide was added as a PNIPAM network crosslinking agent. Then, 0.15g of ammonium persulfate was added as a PNIPAM polymerization initiator. After dissolving by magnetic stirring at 500rpm, 50μL of tetramethylethylenediamine was added as a PNIPAM polymerization accelerator to obtain the PNIPAM prepolymer solution (7). In step 3, the preparation process of the GelMA mixture (8) is as follows: First, 8g of methacrylamide gelatin was dissolved in 10ml of PBS solution in a 60℃ water bath. Then, 1.5g of nano-hydroxyapatite was added and ultrasonically dispersed for 5min at 300W power to achieve bone integration / mechanical strengthening. Subsequently, 0.2g of hydroxypropyl cellulose was added to raise the phase transition temperature from 32℃ to 37.5℃. Finally, a photoinitiator was added in the dark to achieve GelMA photocuring, and finally a GelMA mixture was formed (8). In step 3, the hydrogel precursor solution (9) is composed of PNIPAM prepolymer (7) and GelMA mixture (8) in a volume ratio of 1:

1. After vortex mixing for 30s, a milky white suspension is formed.

7. The method for preparing a biomimetic heterogeneous composite bone implant according to claim 6, characterized in that, The specific method for cross-linking the two networks in step 4 is as follows: First, the biomimetic composite structure (6) covered with hydrogel precursor solution (9) is irradiated with 405nm blue light (10) to form the first network. Then, it is transferred to a 37℃ incubator and kept at the temperature for 30min. Thermal initiation of PNIPAM polymerization occurs, and the gel changes from transparent to milky white, thus completing the cross-linking of the double network.

8. The method for preparing a biomimetic heterogeneous composite bone implant according to claim 7, characterized in that, The specific process of post-processing and drug loading in step 5 is as follows: The biomimetic composite structure (6) after cross-linking the dual networks in step 4 was immersed in a drug-containing solution (12), which was a vancomycin solution of 10 mg / ml. The solution was swollen at 4°C for 24 h to achieve efficient drug loading at low temperature.

9. A biomimetic heterogeneous composite bone implant, characterized in that, It is prepared by the method as described in claim 8.

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