Haversian system of shape memory alloy bone stent and 4D printing preparation method and application

Abstract

The application discloses a shape memory alloy bone support simulating a Haversian system and a 4D printing preparation method and application. In the 4D printing preparation method, the stress state and functional requirements of the bone support are fully considered, a bone support porous structure with a Haversian system is designed by using a functional bionic method, and the bone support is prepared by using a 4D printing technology. The inner layer porous structure simulating cancellous bone designed in the preparation method not only has good elasticity and toughness, but also is beneficial to cell adhesion, cell growth, blood supply maintenance; the outer layer porous structure simulating cortical bone with a Haversian system meets the requirements of good compression resistance and bending resistance of the outer layer, and the Haversian system is beneficial to the growth of blood vessels and nerves, and is beneficial to bone metabolism and repair. The shape memory alloy bone support simulating the Haversian system has wide application prospects in bone implants.

Description

Technical Field

[0001] The present invention belongs to the fields of additive manufacturing, metal materials and biomedical engineering, and specifically relates to a shape memory alloy bone scaffold imitating a Haversian system and a 4D printing preparation method and application. Background Art

[0002] As people age, their bone density gradually decreases, their bone structure changes, and their bone strength weakens, leading to an increased risk of fractures. As the aging population intensifies, society's demand for the quantity and quality of bone implants is increasing. Hard bone is the most common type of bone in the human body, and is mainly responsible for support, protection, and movement. Hard bones include long bones, short bones, flat bones, and irregular bones. Considering strength and durability, hard bones are often replaced by metal implants. The commonly used materials for orthopedic implants are mostly titanium alloys, magnesium alloys, nickel-titanium alloys, etc. Among them, nickel-titanium alloys have high strength, low modulus, excellent biocompatibility, and unique superelasticity and shape memory effects, and have great potential in the direction of biomedical bone scaffolds.

[0003] From the Haversian anatomy, we know that bones are porous structures with highly complex pores. The cancellous bone fills the interior of the bone, and its porosity is usually above 30%, which has high elasticity. The outer layer is cortical bone with a Haversian system, with a porosity as low as 5%, and its compressive strength is higher than that of cancellous bone. The periosteum, outer ring periosteum, Haversian canal (Haver's canal), osteons, interosseous plates, Volkmann canal (Volkmann canal), inner ring bone plates and endosteum together form a complex Haversian system ( Figure 1 The Haversian canal is a longitudinal canal containing blood vessels and nerves that provide nutrients and oxygen to bone cells and excrete metabolic waste. The Volkmann canal, which runs through the bone and connects with the central canal, serves as a crucial pathway for blood vessels and nerves to enter the bone. Cortical bone, cancellous bone, and the Haversian system together constitute the complete skeletal structure. They are structurally and functionally interconnected and work together to maintain the normal physiological function of bone tissue.

[0004] In order to facilitate the rehabilitation of patients and avoid stress shielding, most bone implants adopt a porous structure. However, in the existing research, most of the bone scaffolds designed are single porosity, which cannot truly meet the complex functional requirements of the implant. In order to further meet the needs of patients, bionic design inspired by bone has attracted the attention of many scholars. For example, CN117100460A effectively improves the stress shielding effect by designing the scaffold surface with holes, improves the connectivity of the pores, and provides favorable conditions for cell growth. CN110876817B discloses a bionic bone device with a multi-layer structure and a preparation method thereof, which improves the bone repair performance. In Science Advances 2020(12), a bone simulation scaffold with Haversian canal and Volkmann canal is designed and prepared, in which the cancellous bone is designed as a reticular structure, but the cortical bone is a longitudinal hole solid structure. The ceramic scaffold has good mechanical properties and biocompatibility. At present, there are few reports on the design and preparation of shape memory alloy porous bone scaffolds with Haversian system. Therefore, the stress state and functional requirements of the scaffold are considered in this patent, and a shape memory alloy scaffold with Haversian system is designed and prepared, in which the inner layer cancellous bone and the outer layer cortical bone are both porous structures.

[0005] The preparation methods of porous bone scaffolds mainly include traditional mechanical processing, spark plasma sintering, hot isostatic pressing, direct foaming, high temperature self-propagating and other processes. However, the pore size and shape prepared by these traditional methods are randomly distributed, and the quantitative control is limited. It is difficult to prepare high porosity bone scaffolds, and the instability of the preparation process cannot provide stable mechanical properties of the bone scaffold, and the material utilization rate is low. Emerging additive manufacturing technologies include laser directed energy deposition, laser powder bed melting, selective electron beam melting, and arc additive manufacturing 3D printing technologies, which can achieve high controllability and interconnection of bone scaffold holes. In particular, laser powder bed melting 3D printing of shape memory alloy, also known as 4D printing, can precisely control the laser beam and energy density, so that the pore size, porosity accuracy and performance stability of the bone scaffold are guaranteed. SUMMARY

[0006] In order to overcome the deficiencies and shortcomings of the prior art, the primary purpose of the present application is to provide a 4D printing preparation method of a shape memory alloy bone scaffold with a Haversian system. The Haversian system of human anatomy is applied to the design of shape memory alloy porous bone scaffolds, and the 4D printing process is used to prepare the bone scaffold, so that the mechanical property stability and mass transfer performance of the bone scaffold are closer to the natural bone, providing an effective way for bone scaffold design and preparation.

[0007] The second object of the present application is to provide a shape memory alloy bone scaffold with a Haversian system prepared by the above-mentioned 4D printing preparation method.

[0008] The third object of the present application is to provide an application of the shape memory alloy bone scaffold with a Haversian system.

[0009] The primary object of the present application is achieved by the following technical solutions:

[0010] A 4D printing preparation method of a shape memory alloy bone scaffold with a Haversian system, comprising the following steps,

[0011] Step one, three-dimensional modeling design of the shape memory alloy bone scaffold with a Haversian system

[0012] Designing the inner layer of the porous structure of the cancellous bone and the outer layer of the porous structure of the cortical bone with a Haversian system Figure 2 , performing Boolean sum operation by using three-dimensional modeling software, so that the cross section of the inner layer of the porous structure of the cancellous bone and the outer layer of the porous structure of the cortical bone with a Haversian system is radially fused to form a complete shape memory alloy bone scaffold with a Haversian system;

[0013] Step two, three-dimensional model slicing processing

[0014] Importing the STL files of the inner layer of the porous structure of the cancellous bone and the outer layer of the porous structure of the cortical bone with a Haversian system into a slicing software for slicing processing, and importing the sliced files into a 4D printing additive manufacturing system;

[0015] Step three, 4D printing process preparation of the shape memory alloy bone scaffold with a Haversian system

[0016] First, preheat the NiTi alloy substrate, place the shape memory alloy powder in the powder cabin, then adjust the oxygen content of the forming cabin, and respectively give the forming process parameters of the inner layer of the porous structure of the cancellous bone and the outer layer of the porous structure of the cortical bone with a Haversian system, and obtain the shape memory alloy bone scaffold with a Haversian system after forming; according to the rod diameter and the thickness of the curved surface, different laser power and scanning speed are respectively given to the inner layer of the porous structure of the cancellous bone and the outer layer of the porous structure of the cortical bone with a Haversian system.

[0017] Preferably, the inner layer of the cancellous bone porous structure in step one is a strut-based porous unit, which is one of octahedron, regular cube, body-centered cube, face-centered cube, dodecahedron or diamond, with a unit size of 0.6-1.8 mm, a strut diameter of 140-500 μm, a pore size of 80-1200 μm, and a porosity of 50-90%.

[0018] Preferably, the outer layer of the cortical bone porous structure with Haversian system in step one is a triply periodic minimal surface-based porous unit, which is one of Gyroid, Diamond, Neovius or Lidinoid, with a unit size of 0.6-1.8 mm, a surface thickness of 150-450 μm, a pore size of 80-1200 μm, and a porosity of 10%-80%.

[0019] Preferably, the outer layer of the cortical bone porous structure with Haversian system in step one is designed longitudinally as concentrically arranged Haversian channels and transversely as concentrically arranged Volkmann channels.

[0020] Preferably, the Haversian channels have a diameter of 80-500 μm and a number of 12-36; and the Volkmann channels have a diameter of 80-500 μm and a number of 12-36.

[0021] Preferably, the three-dimensional modeling software in step one includes 3D Max, Rhino, Fusion 360, SolidWorks, UG, Materialise Magics, and nTopology.

[0022] Preferably, the preheating temperature of the NiTi alloy substrate in step three is 190-210℃; the shape memory alloy powder is one of NiTi, NiTiNb, NiTiCr, NiTiFe and NiTiCu, with a particle size of 15-53 μm; and the oxygen content in the forming cabin is controlled to be less than 100 ppm.

[0023] Preferably, the laser power for the inner layer of the cancellous bone porous structure in step three is 70-200 W, and the scanning speed is 400-2000 mm / s; and the laser power for the outer layer of the cortical bone porous structure with Haversian system is 80-220 W, and the scanning speed is 600-2200 mm / s.

[0024] Preferably, the inner layer of the spongy bone porous structure forming process parameters in step three: the spot diameter is 75-85 μm, the scanning interval is 60-100 μm, the layer thickness is 30-40 μm, and the printing strategy is to rotate the laser path by 65-75° every other layer.

[0025] The outer layer of the cortical bone porous structure with Haversian system forming process parameters: the spot diameter is 75-85 μm, the scanning interval is 60-100 μm, the layer thickness is 30-40 μm, and the printing strategy is to rotate the laser path by 65-75° every other layer.

[0026] The second object of the present application is achieved by the following technical solutions:

[0027] A shape memory alloy bone scaffold with a Haversian system is prepared by the 4D printing preparation method.

[0028] Preferably, the shape memory alloy bone scaffold with a Haversian system comprises an inner layer of spongy bone porous structure and an outer layer of cortical bone porous structure with Haversian system.

[0029] The third object of the present application is achieved by the following technical solutions:

[0030] The shape memory alloy bone scaffold with a Haversian system is applied to a bone implant.

[0031] Specifically, the specific size parameters of the bone implant depend on the bone site, and the bone site is humerus, ulna, radius, metacarpal bone, phalangeal bone, femur, tibia, fibula, metatarsal bone, tarsal bone, phalangeal bone, sternum, rib or pelvic bone.

[0032] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0033] In the 4D printing preparation method of the shape memory alloy bone scaffold with the Haversian system of the application, the stress state and functional requirements of the bone scaffold are fully considered, the bone scaffold porous structure with the Haversian system is designed by using a functional bionic method, and the bone scaffold is prepared by using a 4D printing process. The inner layer cancellous bone porous structure designed in the preparation method not only meets the good elasticity and toughness of the inner layer, but also is beneficial to cell adhesion and cell growth, and maintains blood supply; the outer layer cortical bone porous structure with the Haversian system meets the good compression and bending resistance of the outer layer, and the Haversian system is more conducive to the growth of blood vessels and nerves, and maintains bone metabolism and repair. The file after slicing is imported into the 4D printing additive manufacturing system; and subsequent process parameters are conveniently assigned. The shape memory alloy bone scaffold with the Haversian system prepared by the application not only has good biocompatibility and can meet the growth function of osteoblasts, blood vessels and nerves, but also has good mechanical properties, can avoid stress shielding effect and has certain bearing capacity. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 It is a schematic diagram of bone structure with Haversian system;

[0035] Figure 2 It is a schematic diagram of structure composition of shape memory alloy bone scaffold with Haversian system;

[0036] Figure 3 It is a three-dimensional diagram of shape memory alloy bone scaffold with Haversian system in Example 1;

[0037] Figure 4 It is a real object diagram of Gyroid three-periodic minimal surface structure and octahedral structure in Example 1;

[0038] Figure 5 It is a performance diagram of Gyroid three-periodic minimal surface structure in Example 1;

[0039] Figure 6 It is a performance diagram of octahedral structure in Example 1;

[0040] Figure 7 It is a three-dimensional diagram of shape memory alloy bone scaffold with Haversian system in Example 3;

[0041] Figure 8 It is a three-dimensional diagram of shape memory alloy bone scaffold with Haversian system in Example 5;

[0042] Figure 9 It is a flowchart of preparation process of shape memory alloy bone scaffold with Haversian system;

[0043] Figure 10 For the three-period minimal surface porous structure in Comparative Example 1 that cannot be shaped;

[0044] Figure 11 For the octahedral porous structure performance chart in Comparative Example 2. DETAILED DESCRIPTION

[0045] The present application will be further described in conjunction with specific examples and drawings, but the embodiments of the present application are not limited thereto. The materials used in the examples of the present application can be purchased by commercially available methods.

[0046] Example 1

[0047] A 4D printing preparation method of a shape memory alloy bone scaffold imitating a Haversian system, comprising the following steps,

[0048] Step 1: Design of a shape memory alloy bone scaffold imitating a Haversian system

[0049] Inner layer: porous structure imitating cancellous bone, unit type is an octahedral structure based on struts, unit size is 0.6 mm, strut diameter is 140 μm, pore size is 450 μm, and porosity is 50%;

[0050] Outer layer: porous structure imitating cortical bone with a Haversian system, unit type is a Gyroid three-period minimal surface structure, unit size is 0.6 mm, surface thickness is 225 μm, pore size is 600 μm, porosity is 25%, 36 Haversian canals with a diameter of 450 μm arranged in concentric circles are designed longitudinally in the outer layer, and 36 Volkmann canals with a diameter of 450 μm arranged in concentric circles are designed transversely in the outer layer.

[0051] Step 2: Preparation of a shape memory alloy bone scaffold imitating a Haversian system

[0052] 1) The STL files of the inner layer porous structure imitating cancellous bone and the outer layer porous structure imitating cortical bone with a Haversian system are respectively imported into a slicing software for slicing processing, and the sliced files are imported into a 4D printing additive manufacturing system.

[0053] 2) 4D printing process for preparing a shape memory alloy bone scaffold imitating a Haversian system

[0054] Preheat the NiTi alloy substrate to 190℃, put the NiTi shape memory alloy powder with particle size of 15-53 μm into the powder cabin, and control the oxygen content of the 4D printing forming cabin to 100 ppm. The process parameters of the inner layer of the porous structure simulating cancellous bone are as follows: the laser power is 90 W, the scanning speed is 400 mm / s, the spot diameter is 75 μm, the scanning interval is 60 μm, the layer thickness is 30 μm, and the printing strategy is that the laser path is rotated by 65° every other layer. The process parameters of the outer layer of the porous structure simulating cortical bone with Haversian system are as follows: the laser power is 80 W, the scanning speed is 600 mm / s, the spot diameter is 75 μm, the scanning interval is 60 μm, the layer thickness is 30 μm, and the printing strategy is that the laser path is rotated by 65° every other layer. Figure 3 A three-dimensional diagram of the shape memory alloy bone scaffold simulating Haversian system in this embodiment, Figure 4 A physical diagram of the Gyroid three-periodic minimal surface structure and the octahedral structure in this embodiment, Figure 5 A diagram of the Gyroid three-periodic minimal surface structure in this embodiment, and Figure 6 A performance diagram of the octahedral structure in this embodiment.

[0055] Example 2

[0056] A 4D printing preparation method of a shape memory alloy bone scaffold simulating Haversian system, comprising the following steps,

[0057] Step 1: Design of shape memory alloy bone scaffold simulating Haversian system

[0058] Inner layer: porous structure simulating cancellous bone, the unit type is a strut-based octahedral structure, the unit size is 0.6 mm, the rod diameter is 140 μm, the pore diameter is 450 μm, and the porosity is 50%;

[0059] Outer layer: porous structure simulating cortical bone with Haversian system, the unit type is a Gyroid three-periodic minimal surface structure, the unit size is 0.6 mm, the surface thickness is 225 μm, the pore diameter is 600 μm, the porosity is 25%, 36 Haversian pipes with a diameter of 250 μm arranged in concentric circles are designed in the longitudinal direction of the outer layer, and 36 Volkmann pipes with a diameter of 250 μm arranged in concentric circles are designed in the transverse direction of the outer layer.

[0060] Step 2: Preparation of shape memory alloy bone scaffold simulating Haversian system

[0061] 1) Import the STL files of the inner layer of the porous structure simulating cancellous bone and the outer layer of the porous structure simulating cortical bone with Haversian system into the slicing software for slicing, and then import the sliced files into the 4D printing additive manufacturing system.

[0062] 2) 4D printing process for preparing a shape memory alloy bone scaffold simulating a Haversian system

[0063] Preheat the NiTi alloy substrate to 210°C, place the NiTi shape memory alloy powder with a particle size of 15-53 μm in the powder compartment, and control the oxygen content of the 4D printing forming compartment to 100 ppm. The process parameters for the inner layer of the porous structure simulating cancellous bone are: laser power 200 W, scanning speed 2000 mm / s, spot diameter 75 μm, scanning interval 60 μm, layer thickness 30 μm, and printing strategy: laser path rotation by 65° every other layer. The process parameters for the outer layer of the porous structure simulating cortical bone with a Haversian system are: laser power 220 W, scanning speed 2200 mm / s, spot diameter 75 μm, scanning interval 60 μm, layer thickness 30 μm, and printing strategy: laser path rotation by 65° every other layer.

[0064] Example 3

[0065] A 4D printing method for preparing a shape memory alloy bone scaffold simulating a Haversian system, comprising the following steps,

[0066] Step 1: Design of a shape memory alloy bone scaffold simulating a Haversian system

[0067] Inner layer: porous structure simulating cancellous bone, unit type: diamond structure based on struts, unit size: 1.8 mm, strut diameter: 400 μm, pore diameter: 900 μm, porosity: 80%;

[0068] Outer layer: porous structure simulating cortical bone with a Haversian system, unit type: Lidinoid tri-periodic minimal surface structure, unit size: 1.8 mm, surface thickness: 200 μm, pore diameter: 600 μm, porosity: 25%, 36 Haversian channels with a diameter of 450 μm arranged in concentric circles are designed longitudinally in the outer layer, and 36 Volkmann channels with a diameter of 450 μm arranged in concentric circles are designed transversely in the outer layer.

[0069] Step 2: Preparation of a shape memory alloy bone scaffold simulating a Haversian system

[0070] 1) Import the STL files of the inner layer of the porous structure simulating cancellous bone and the outer layer of the porous structure simulating cortical bone with a Haversian system into the slicing software for slicing, and then import the sliced files into the 4D printing additive manufacturing system.

[0071] 2) 4D printing process for preparing a shape memory alloy bone scaffold simulating a Haversian system

[0072] Preheat the NiTi alloy substrate to 190℃, put the NiTi shape memory alloy powder with particle size of 15-53 μm into the powder cabin, and control the oxygen content of the 4D printing forming cabin to 100 ppm. The process parameters of the inner layer of the porous structure simulating cancellous bone are as follows: the laser power is 70 W, the scanning speed is 600 mm / s, the spot diameter is 75 μm, the scanning interval is 60 μm, the layer thickness is 30 μm, and the printing strategy is that the laser path is rotated by 65° every other layer. The process parameters of the outer layer of the porous structure simulating cortical bone with Haversian system are as follows: the laser power is 90 W, the scanning speed is 400 mm / s, the spot diameter is 75 μm, the scanning interval is 60 μm, the layer thickness is 30 μm, and the printing strategy is that the laser path is rotated by 65° every other layer. Figure 7 A three-dimensional diagram of the shape memory alloy bone scaffold simulating Haversian system in this embodiment.

[0073] Example 4

[0074] A 4D printing preparation method of a shape memory alloy bone scaffold simulating Haversian system, comprising the following steps,

[0075] Step 1: Design of shape memory alloy bone scaffold simulating Haversian system

[0076] Inner layer: porous structure simulating cancellous bone, unit type is diamond structure based on strut, unit size is 0.9 mm, strut diameter is 200 μm, pore diameter is 900 μm, and porosity is 80%;

[0077] Outer layer: porous structure simulating cortical bone with Haversian system, unit type is Lidinoid three-periodic minimal surface structure, unit size is 1 mm, surface thickness is 100 μm, pore diameter is 600 μm, porosity is 25%, 36 Haversian ducts with a diameter of 300 μm arranged in concentric circles are designed in the longitudinal direction of the outer layer, and 36 Volkmann ducts with a diameter of 300 μm arranged in concentric circles are designed in the transverse direction of the outer layer.

[0078] Step 2: Preparation of shape memory alloy bone scaffold simulating Haversian system

[0079] 1) Import the STL files of the inner layer of the porous structure simulating cancellous bone and the outer layer of the porous structure simulating cortical bone with Haversian system into the slicing software for slicing, and then import the sliced files into the 4D printing additive manufacturing system.

[0080] 2) 4D printing process for preparing shape memory alloy bone scaffold simulating Haversian system

[0081] Preheat the NiTi alloy substrate to 190℃, put the NiTi shape memory alloy powder with particle size of 15-53 μm into the powder cabin, and control the oxygen content of the 4D printing forming cabin to 100 ppm. The process parameters of the inner layer of the porous structure simulating cancellous bone are as follows: the laser power is 200 W, the scanning speed is 2200 mm / s, the spot diameter is 75 μm, the scanning interval is 60 μm, the layer thickness is 30 μm, and the printing strategy is that the laser path is rotated by 65° every other layer. The process parameters of the outer layer of the porous structure simulating cortical bone with Haversian system are as follows: the laser power is 220 W, the scanning speed is 2000 mm / s, the spot diameter is 75 μm, the scanning interval is 60 μm, the layer thickness is 30 μm, and the printing strategy is that the laser path is rotated by 65° every other layer.

[0082] Example 5

[0083] A 4D printing preparation method of a shape memory alloy bone scaffold simulating Haversian system, comprising the following steps,

[0084] Step 1: Design of a shape memory alloy bone scaffold simulating Haversian system

[0085] Inner layer: porous structure simulating cancellous bone, unit type is body-centered cubic structure based on strut, unit size is 0.9 mm, rod diameter is 200 μm, pore size is 500 μm, and porosity is 85%;

[0086] Outer layer: porous structure simulating cortical bone with Haversian system, unit type is Diamond three-period minimal surface structure, unit size is 1 mm, surface thickness is 100 μm, pore size is 120 μm, porosity is 75%, 36 Haversian tubes with a diameter of 450 μm arranged in concentric circles are designed in the longitudinal direction of the outer layer, and 36 Volkmann tubes with a diameter of 450 μm arranged in concentric circles are designed in the transverse direction of the outer layer.

[0087] Step 2: Preparation of a shape memory alloy bone scaffold simulating Haversian system

[0088] 1) Import the STL files of the inner layer of the porous structure simulating cancellous bone and the outer layer of the porous structure simulating cortical bone with Haversian system into the slicing software for slicing, and then import the sliced files into the 4D printing additive manufacturing system.

[0089] 2) 4D printing process for preparing a shape memory alloy bone scaffold simulating Haversian system

[0090] Preheat the NiTi alloy substrate to 190℃, put the NiTi shape memory alloy powder with particle size of 15-53 μm into the powder cabin, and control the oxygen content of the 4D printing forming cabin to 100 ppm. The process parameters of the inner layer of the porous structure simulating cancellous bone are as follows: the laser power is 130 W, the scanning speed is 1400 mm / s, the spot diameter is 75 μm, the scanning interval is 60 μm, the layer thickness is 30 μm, and the printing strategy is that the laser path is rotated by 65° every other layer. The process parameters of the outer layer of the porous structure simulating cortical bone with Haversian system are as follows: the laser power is 160 W, the scanning speed is 1200 mm / s, the spot diameter is 75 μm, the scanning interval is 60 μm, the layer thickness is 30 μm, and the printing strategy is that the laser path is rotated by 65° every other layer. Figure 8 A three-dimensional diagram of the shape memory alloy bone scaffold simulating Haversian system in this embodiment.

[0091] Example 6

[0092] A 4D printing preparation method of a shape memory alloy bone scaffold simulating Haversian system, comprising the following steps,

[0093] Step 1: Design of shape memory alloy bone scaffold simulating Haversian system

[0094] Inner layer: porous structure simulating cancellous bone, unit type is body-centered cubic structure based on strut, unit size is 0.9 mm, rod diameter is 200 μm, pore diameter is 500 μm, and porosity is 85%;

[0095] Outer layer: porous structure simulating cortical bone with Haversian system, unit type is Diamond three-period minimal surface structure, unit size is 1 mm, surface thickness is 100 μm, pore diameter is 120 μm, porosity is 75%, 36 Haversian tubes with a diameter of 80 μm arranged in concentric circles are designed in the longitudinal direction of the outer layer, and 36 Volkmann tubes with a diameter of 80 μm arranged in concentric circles are designed in the transverse direction of the outer layer.

[0096] Step 2: Preparation of shape memory alloy bone scaffold simulating Haversian system

[0097] 1) Import the STL files of the inner layer of the porous structure simulating cancellous bone and the outer layer of the porous structure simulating cortical bone with Haversian system into the slicing software for slicing processing, and then import the sliced files into the 4D printing additive manufacturing system.

[0098] 2) 4D printing process for preparing shape memory alloy bone scaffold simulating Haversian system

[0099] Preheat the NiTi alloy substrate to 190℃, put the NiTi shape memory alloy powder with particle size of 15-53 μm into the powder cabin, and control the oxygen content of the 4D printing forming cabin to 100 ppm. The process parameters of the inner layer of the porous structure simulating cancellous bone are as follows: the laser power is 130 W, the scanning speed is 1400 mm / s, the spot diameter is 75 μm, the scanning interval is 60 μm, the layer thickness is 30 μm, and the printing strategy is that the laser path is rotated by 65° every other layer. The process parameters of the outer layer of the porous structure simulating cortical bone with Haversian system are as follows: the laser power is 160 W, the scanning speed is 1200 mm / s, the spot diameter is 75 μm, the scanning interval is 60 μm, the layer thickness is 30 μm, and the printing strategy is that the laser path is rotated by 65° every other layer.

[0100] Example 7

[0101] A 4D printing preparation method of a shape memory alloy bone scaffold simulating Haversian system, comprising the following steps,

[0102] Step 1: Design of shape memory alloy bone scaffold simulating Haversian system

[0103] Inner layer: porous structure simulating cancellous bone, unit type is body-centered cubic structure based on strut, unit size is 0.9 mm, rod diameter is 200 μm, pore size is 500 μm, and porosity is 85%;

[0104] Outer layer: porous structure simulating cortical bone with Haversian system, unit type is Diamond three-period minimal surface structure, unit size is 1 mm, surface thickness is 100 μm, pore size is 120 μm, porosity is 75%, 12 Haversian tubes with a diameter of 80 μm arranged in concentric circles are designed in the longitudinal direction of the outer layer, and 12 Volkmann tubes with a diameter of 80 μm arranged in concentric circles are designed in the transverse direction of the outer layer.

[0105] Step 2: Preparation of shape memory alloy bone scaffold simulating Haversian system

[0106] 1) Import the STL files of the inner layer of the porous structure simulating cancellous bone and the outer layer of the porous structure simulating cortical bone with Haversian system into the slicing software for slicing processing, and then import the sliced files into the 4D printing additive manufacturing system.

[0107] 2) 4D process preparation of shape memory alloy bone scaffold simulating Haversian system

[0108] The NiTi alloy substrate is preheated to 190°C, the NiTi shape memory alloy powder with a particle size of 15-53 μm is placed in the powder cabin, and the oxygen content of the 4D printing forming cabin is controlled to 100 ppm. The process parameters of the inner layer of the porous structure simulating cancellous bone: laser power is 130 W, scanning speed is 1400 mm / s, spot diameter is 75 μm, scanning interval is 60 μm, layer thickness is 30 μm, and printing strategy is to rotate the laser path by 65° every other layer. The process parameters of the outer layer of the porous structure simulating cortical bone with Haversian system: laser power is 160 W, scanning speed is 1200 mm / s, spot diameter is 75 μm, scanning interval is 60 μm, layer thickness is 30 μm, and printing strategy is to rotate the laser path by 65° every other layer.

[0109] Comparative Example 1

[0110] A 4D printing preparation method of a shape memory alloy bone scaffold simulating Haversian system, comprising the following steps,

[0111] Step 1: Design of shape memory alloy bone scaffold simulating Haversian system

[0112] Inner layer: porous structure simulating cancellous bone, cell type is octahedral structure based on strut, cell size is 0.6 mm, strut diameter is 140 μm, pore size is 450 μm, and porosity is 50%;

[0113] Outer layer: porous structure simulating cortical bone with Haversian system, cell type is Gyroid three-periodic minimal surface structure, cell size is 0.6 mm, surface thickness is 225 μm, pore size is 600 μm, porosity is 25%, 36 Haversian ducts with a diameter of 450 μm arranged in concentric circles are designed longitudinally in the outer layer, and 36 Volkmann ducts with a diameter of 450 μm arranged in concentric circles are designed transversely.

[0114] Step 2: Preparation of shape memory alloy bone scaffold simulating Haversian system

[0115] 1) Import the STL files of the inner layer of the porous structure simulating cancellous bone and the outer layer of the porous structure simulating cortical bone with Haversian system into the slicing software for slicing, and then import the sliced files into the 4D printing additive manufacturing system.

[0116] 2) 4D process preparation of shape memory alloy bone scaffold simulating Haversian system

[0117] The NiTi alloy substrate is preheated to 160°C, the NiTi shape memory alloy powder with a particle size of 15-53 μm is placed in the powder cabin, and the oxygen content of the 4D printing forming cabin is controlled to 100 ppm. The process parameters of the inner layer of the porous structure simulating cancellous bone are: laser power 90 W, scanning speed 400 mm / s, spot diameter 75 μm, scanning interval 60 μm, layer thickness 30 μm, and printing strategy: laser path rotation 65° every other layer. The process parameters of the outer layer of the porous structure simulating cortical bone with Haversian system are: laser power 70 W, scanning speed 1500 mm / s, spot diameter 75 μm, scanning interval 60 μm, layer thickness 30 μm, and printing strategy: laser path rotation 65° every other layer.

[0118] The sample of the three-period minimal surface simulating cortical bone in Comparative Example 1 cannot be formed due to the combined influence of the substrate preheating temperature and the process parameters of laser power and scanning speed (low power and high scanning speed), as shown in Figure 10 .

[0119] Comparative Example 2

[0120] A 4D printing preparation method of a shape memory alloy bone scaffold simulating Haversian system, comprising the following steps,

[0121] Step 1: Design of a shape memory alloy bone scaffold simulating Haversian system

[0122] Inner layer: porous structure simulating cancellous bone, cell type is octahedral structure based on strut, cell size is 0.6 mm, rod diameter is 140 μm, pore diameter is 450 μm, and porosity is 50%;

[0123] Outer layer: porous structure simulating cortical bone with Haversian system, cell type is Gyroid three-period minimal surface structure, cell size is 0.6 mm, surface thickness is 225 μm, pore diameter is 600 μm, porosity is 25%, 36 Haversian pipes with a diameter of 450 μm arranged in concentric circles are designed in the longitudinal direction of the outer layer, and 36 Volkmann pipes with a diameter of 450 μm arranged in concentric circles are designed in the transverse direction of the outer layer.

[0124] Step 2: Preparation of a shape memory alloy bone scaffold simulating Haversian system

[0125] 1) Import the STL files of the inner layer of the porous structure simulating cancellous bone and the outer layer of the porous structure simulating cortical bone with Haversian system into the slicing software for slicing, and then import the sliced files into the 4D printing additive manufacturing system.

[0126] 2) 4D printing process to prepare a shape memory alloy bone scaffold simulating Haversian system

[0127] The NiTi alloy substrate is preheated to 190 DEG C, the NiTi shape memory alloy powder with a particle size of 15-53 μm is placed in the powder cabin, and the oxygen content of the 4D printing forming cabin is controlled to 100 ppm. The process parameters of the inner layer of the porous structure simulating cancellous bone are as follows: the laser power is 230 W, the scanning speed is 2300 mm / s, the spot diameter is 75 μm, the scanning interval is 60 μm, the layer thickness is 30 μm, and the printing strategy is that the laser path is rotated by 65 DEG every other layer. The process parameters of the outer layer of the porous structure simulating cortical bone with Haversian system are as follows: the laser power is 80 W, the scanning speed is 600 mm / s, the spot diameter is 75 μm, the scanning interval is 60 μm, the layer thickness is 30 μm, and the printing strategy is that the laser path is rotated by 65 DEG every other layer.

[0128] The sample of the octahedral porous structure for the porous structure simulating cancellous bone is affected by the process parameters of the laser power and the scanning speed (high power and high scanning speed) in the comparative example 2, defects are generated in the sample, the porous structure is locally failed during the compression experiment, and the mechanical property is poor, as shown in Figure 11 .

[0129] As can be seen by comparing the examples 1 to 7 and the comparative examples 1 to 2, the shape memory alloy bone scaffold simulating the Haversian system prepared by using the moderate laser power and the moderate scanning speed has good preparability, good biocompatibility, can meet the ingrowth function of the osteoblasts, blood vessels and nerves, and good mechanical property, can overcome the stress shielding effect, and is beneficial to the rehabilitation of the patient.

[0130] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above examples, and any changes, modifications, substitutions, combinations and simplifications made without departing from the spirit and principles of the present application should be equivalent replacement methods, and all are included in the protection scope of the present application.

Claims

1. A 4D printing method for preparing a shape memory alloy bone scaffold imitating the Haversian system, characterized in that: The following steps are included: Step 1: 3D modeling and design of shape memory alloy bone scaffolds imitating the Haversian system An inner layer cancellous bone-mimicking porous structure and an outer layer cortical bone-mimicking porous structure with a Haversian system are designed, and a Boolean sum operation is performed using three-dimensional modeling software to make the cross-sections of the inner layer cancellous bone-mimicking porous structure and the outer layer cortical bone-mimicking porous structure with a Haversian system radially fuse to form a complete shape memory alloy bone scaffold that mimics the Haversian system; the inner layer cancellous bone-mimicking porous structure is a porous unit based on struts, and the porous unit based on struts is one of octahedron, regular cube, body-centered cube, face-centered cube, dodecahedron or diamond, and its unit size is 0.6~1.8mm, its rod diameter is 140~500μm, its pore size is 80~1200μm, and its porosity is 50~90%; the outer layer cortical bone-mimicking porous structure with a Haversian system is a porous unit based on a three-periodic minimal surface, and the porous unit based on the three-periodic minimal surface is Gyroid, Diamond, One of the Neovius or Lidinoid, whose cell size is 0.6~1.8mm, whose surface thickness is 150~450μm, whose pore size is 80~1200μm, and whose porosity is 10%~80%; Step 2: 3D model slicing The STL files of the inner layer simulated cancellous bone porous structure and the outer layer simulated cortical bone porous structure with Haversian system are imported into the slicing software for slicing processing, and the sliced ​​files are imported into the 4D printing additive manufacturing system; Step 3: 4D printing process to prepare Haversian-like shape memory alloy bone scaffold First, a NiTi alloy substrate is preheated, and shape memory alloy powder is placed in a powder chamber. Then, the oxygen content in the forming chamber is adjusted, and forming process parameters are assigned to an inner layer of a cancellous bone-mimicking porous structure and an outer layer of a cortical bone-mimicking porous structure with a Haversian system. After forming, a shape memory alloy bone scaffold with a Haversian system is obtained. Different laser powers and scanning speeds are assigned to the inner layer of the cancellous bone-mimicking porous structure and the outer layer of the cortical bone-mimicking porous structure with a Haversian system according to the rod diameter and the curved surface thickness. The laser power of the inner layer of the cancellous bone-mimicking porous structure is 70-200W, and the scanning speed is 400-2000mm / s; the laser power of the outer layer of the cortical bone-mimicking porous structure with a Haversian system is 80-220W, and the scanning speed is 600-2200mm / s.

2. The 4D printing preparation method of the Haversian system-mimicking shape memory alloy bone scaffold according to claim 1, characterized in that: In step 1, the outer layer of the simulated cortical bone porous structure with the Haversian system is designed to be a simulated Haversian tube arranged in concentric circles in the longitudinal direction and a simulated Volkmann tube arranged in concentric circles in the transverse direction.

3. The 4D printing preparation method of the Haversian system-mimicking shape memory alloy bone scaffold according to claim 2, characterized in that: The diameter of the simulated Haversian tubes is 80-500 μm, and the number thereof is 12-36; the diameter of the simulated Volkmann tubes is 80-500 μm, and the number thereof is 12-36.

4. The 4D printing preparation method of the Haversian system-mimicking shape memory alloy bone scaffold according to claim 1, characterized in that: In step 3, the preheating temperature of the NiTi alloy substrate is 190-210° C.; the shape memory alloy powder is one of NiTi, NiTiNb, NiTiCr, NiTiFe, and NiTiCu, and the particle size of the shape memory alloy powder is 15-53 μm; and the oxygen content in the forming chamber is controlled within 100 ppm.

5. The 4D printing preparation method of the Haversian system-mimicking shape memory alloy bone scaffold according to claim 1, characterized in that: The process parameters for forming the inner layer cancellous bone-mimicking porous structure in step 3 are as follows: a spot diameter of 75-85 μm, a scanning pitch of 60-100 μm, a layer thickness of 30-40 μm, and a printing strategy of rotating the laser path by 65-75° every other layer. The outer layer has a Haversian system with a porous structure imitating cortical bone. The forming process parameters are as follows: a spot diameter of 75-85 μm, a scanning interval of 60-100 μm, a layer thickness of 30-40 μm, and a printing strategy of rotating the laser path by 65-75° every other layer.

6. A shape memory alloy bone scaffold imitating the Haversian system, characterized in that: The shape memory alloy bone scaffold imitating the Haversian system is prepared by the 4D printing preparation method according to any one of claims 1 to 5.

7. Use of the shape memory alloy bone scaffold simulating the Haversian system according to claim 6 in bone implants.

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