3D printing metamaterial piezoelectric bone defect repair stent and preparation method thereof

Abstract

The invention belongs to the crossing field of biomedical engineering and additive manufacturing, and particularly relates to a 3D printing metamaterial piezoelectric bone defect repair scaffold, and the pore structure of the scaffold is formed by compounding three extremely small curved surface units, namely Gyandroid, SchwarzP and Diamond, which are defined by mathematical expressions; the porosity of the stent is 30%-70%, and the pore diameter range is 0.1-1 mm; the stent is made of a piezoelectric composite material composed of polyvinylidene fluoride (PVDF), polylactic acid and barium titanate, the piezoelectric composite material comprises the following components in percentage by mass: 30%-55% of polyvinylidene fluoride (PVDF), 20%-45% of polylactic acid (PLA) and 10%-25% of barium titanate (BaTiO3), and the sum of the mass percentages of all the components is 100%. Precise regulation and control of a macrostructure and a microstructure are achieved through a multi-material 3D printing technology, and the system has the mechanical adaptability, degradation controllability and the function of actively promoting bone regeneration and is suitable for large-section bone defect repair scenes such as craniomaxillofacial and long bones of four limbs.

Description

Technical Field

[0001] The present invention belongs to the cross - field of biomedical engineering and additive manufacturing, and particularly relates to a 3D - printed metamaterial piezoelectric bone defect repair scaffold and a preparation method thereof. Background Art

[0002] Bone defect is one of the most common diseases in orthopedics. Trauma, infection, tumor resection, and congenital diseases can all lead to bone loss. Currently, common clinical treatment methods cannot meet the needs of treating large bone defects. Therefore, there is an increasing amount of research on artificial bone graft materials. How to create an artificial bone scaffold suitable for clinical treatment has become a research hotspot in orthopedics.

[0003] An ideal artificial bone scaffold should have good mechanical properties and bioactivity. However, its mechanical properties largely depend on the material system of the artificial bone scaffold and its internal structure. Currently, bone repair materials used clinically mainly face three major problems:

[0004] 1. Mechanical property problems: The elastic modulus of traditional inert materials such as titanium alloy and PEEK (>50 GPa) is significantly higher than that of cancellous bone (0.12 GPa), resulting in a stress - shielding effect, leading to bone resorption (Wolff's law), and the loosening rate after 5 years is as high as 15% - 25%.

[0005] 2. Low efficiency of bone ingrowth: Although hydroxyapatite ceramic scaffolds have osteoconductivity, they have no osteoinductive activity, and bone ingrowth is slow. The failure rate of repairing large - size defects (>5 cm) is relatively high.

[0006] 3. Limitations in manufacturing processes: Traditional foaming and sintering methods cannot precisely control the pore structure, and the pore size deviation is large, making it difficult to construct a multi - level pore structure that mimics trabecular bone.

[0007] Therefore, those skilled in the art have provided a 3D - printed metamaterial piezoelectric bone defect repair scaffold to solve the problems raised in the above - mentioned background art. Summary of the Invention

[0008] The purpose of the present invention is to provide a 3D - printed metamaterial piezoelectric bone defect repair scaffold to solve the defect that traditional bone repair scaffolds are difficult to balance mechanical load - bearing, biological conduction, and active electrical stimulation functions. To achieve this purpose, the scaffold is based on the triply periodic minimal surface (TPMS) topology and is realized through the gradient pore design of composite piezoelectric materials and the innovation of additive manufacturing processes. The technical solutions are as follows:

[0009] A 3D printed metamaterial piezoelectric bone defect repair stent, the pore structure of the stent is composed of a composite of three minimal surface units, Gyroid, SchwarzP, and Diamond, defined by a mathematical expression; the porosity of the stent is 30%-70%, and the pore size ranges from 0.1 to 1 mm; the material of the stent is a piezoelectric composite material composed of polyvinylidene fluoride, polylactic acid, and barium titanate.

[0010] In a preferred embodiment, the piezoelectric composite material is as follows by mass percentage: polyvinylidene fluoride (PVDF) 30%-55%, polylactic acid (PLA) 20%-45%, barium titanate (BaTiO 3 ) 10%-25%, and the sum of the mass percentages of each component is 100%.

[0011] In a preferred embodiment, the mathematical expressions of the minimal surface units in a three-dimensional Cartesian coordinate system are: Gyroid structure: sin(x)cos(y)+sin(y)cos(z)+sin(z)cos(x)=0; SchwarzP structure: cosh(x)cos(y)+cosh(y)cos(z)+cosh(z)cos(x)=C, where C is a constant determined according to specific designs; Diamond structure: cos(x)sin(y)+cos(y)sin(z)+cos(z)sin(x)=0.

[0012] In a preferred embodiment, a method for 3D printing a metamaterial piezoelectric bone defect repair stent includes the following steps:

[0013] Step S1: Filament preparation: Mix PVDF, PLA, and BaTiO 3 in a designed ratio and perform vacuum drying with a vacuum drying humidity ≤ 3% RH. Prepare a printing filament with a diameter of 1.75 ± 0.05 mm under the following temperature conditions by a twin-screw extruder: During the extrusion process, the temperature settings of each zone of the screw are precisely regulated according to the melting points and processing characteristics of each component. The melting section temperature of PVDF is set at 160-180°C, the melting section temperature of PLA is set at 150-170°C, and the dispersion section temperature of BaTiO 3 is slightly higher than the melting points of the two, and each component is fully melted and mixed, and BaTiO 3 is uniformly dispersed in the polymer matrix;

[0014] Step S2 Structure Printing: The scaffold is printed using fused deposition modeling technology under the following process parameters: During the printing process, the printing nozzle temperature is set between 170 - 200 °C according to the characteristics of the filament material, the printing platform temperature is controlled at 40 - 60 °C to ensure good melting spreading and forming effect of the filament. The printing speed is set at 30 - 60 mm / s, the layer height is set at 0.1 - 0.3 mm. The pore structures, according to their Gyroid, SchwarzP, and Diamond structures, need to be formed strictly in accordance with their respective mathematical expressions in a three-dimensional Cartesian coordinate system. The design model is converted into printing instructions through slicing software to precisely control the movement path of the nozzle and the material extrusion volume;

[0015] Step S3 Post-treatment: The printed part is placed in a vacuum oven and heated to 70 - 80 °C at a rate of 2 °C / min for annealing treatment for 3.0 h ± 0.5 h. After annealing, it is immersed in phosphate buffered saline with pH = 7.4 for surface activation treatment.

[0016] The technical effects achieved by the present invention are:

[0017] The core advantages of the present invention are reflected in the synergistic effect of structural design, material function, and process innovation, and the systematic improvement of bone repair performance is achieved through multi-level principle optimization:

[0018] Mechanical Adaptability Optimization: The gradient pore design follows the bionics principle of natural bone tissue. The outer high-density Diamond unit disperses stress concentration through continuous surface topology, the middle Schwarz P unit realizes modulus transition with the help of curvature gradient, and the inner Gyroid through-network effectively alleviates the interfacial shear stress, making the overall mechanical response of the scaffold dynamically match the load-bearing requirements of the host bone. Under dynamic load conditions, the gradient pore structure significantly reduces the stress shielding effect through the energy dissipation mechanism, ensuring the effective conduction of mechanical stimuli to the newly formed bone tissue.

[0019] Electroactive Induction Mechanism: Based on the multiphase synergistic effect of piezoelectric composites, the scaffold generates directional bioelectric signals through the piezoelectric effect under physiological loads. The polar β-phase crystals of PVDF and BaTiO 3 Induce a continuous surface potential, which activates the osteogenesis-related signal pathway by regulating the cell membrane potential and ion channel activity, and promotes extracellular matrix mineralization and directional bone tissue regeneration at the molecular level.

[0020] Enhanced Osteoconduction Efficiency: The through-pore network constructs a three-dimensional connected biotransport channel, combined with surface hydrophilic modification to enhance protein adsorption ability, providing an ideal microenvironment for cell migration, angiogenesis, and nutrient transport. The gradient pore size design simultaneously meets the dual requirements of early cell adhesion (small pore size area) and long-range tissue infiltration (large pore size area), realizing precise spatial and temporal regulation during the bone regeneration process.

[0021] Degradation matching characteristics: Through the compound design of degradable polymers and piezoelectric fillers, the degradation behavior of the scaffold shows multi-stage response characteristics. The hydrolysis of PLA dominates the initial degradation to maintain structural stability, the hydrophobic barrier of PVDF delays the mid-term degradation rate, and finally, the synchronous disintegration with the replacement of new bone is achieved through the peeling of the filler-matrix interface. This degradation kinetics ensures that the mechanical support is gradually transferred to the new bone during the regeneration process, avoiding the risk of structural collapse.

[0022] Breakthrough in process compatibility: 3D printing technology breaks through the technical limitations of the post-treatment of traditional piezoelectric materials. Description of the Drawings

[0023] Figure 1 It is a schematic structural diagram of a 3D printed metamaterial piezoelectric bone defect repair scaffold;

[0024] Figure 2 It is a schematic structural diagram of the pores in the fusion mechanism of a 3D printed metamaterial piezoelectric bone defect repair scaffold;

[0025] Figure 3 It is a schematic structural diagram of the piezoelectric material in a 3D printed metamaterial piezoelectric bone defect repair scaffold;

[0026] Figure 4 It is a schematic diagram of the piezoelectric signal of the piezoelectric material in a 3D printed metamaterial piezoelectric bone defect repair scaffold. Detailed Description of the Invention

[0027] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention will be given in conjunction with the drawings of the specification.

[0028] Example 1 (Structure of the 3D Printed Metamaterial Piezoelectric Bone Defect Repair Scaffold)

[0029] Referring to Figures 1-4 , this example provides a 3D printed metamaterial piezoelectric bone defect repair scaffold, which has a gradient pore distribution and piezoelectric-mechanical coupling characteristics.

[0030] The overall scaffold is cylindrical and is divided into three layers from the outside to the inside: an outer layer (A), a middle layer (B), and an inner layer (C).

[0031] The outer layer (A) is composed of a Diamond structure, and its mathematical expression is:

[0032] cos(x)sin(y)+cos(y)sin(z)+cos(z)sin(x) = 0, the porosity is 35% ± 2%, and the average pore diameter is 50μm ± 8μm;

[0033] The middle layer (B) is composed of Schwarz P structure, and its mathematical expression is: cosh(x)cos(y)+cosh(y)cos(z)+cosh(z)cos(x) = C, where C is a constant determined according to specific design; the pore gradient increases to 45% ± 3%, and the pore diameter expands to 80μm ± 10μm;

[0034] The inner layer (C) is composed of Gyroid structure, and its mathematical expression is:

[0035] sin(x)cos(y)+sin(y)cos(z)+sin(z)cos(x) = 0, the porosity is 70% ± 3%, and the pore diameter reaches 120μm ± 15μm.

[0036] The material of the stent is a piezoelectric composite material composed of polyvinylidene fluoride, polylactic acid and barium titanate, and the mass percentages are as follows: polyvinylidene fluoride (PVDF) 30% - 55%, polylactic acid (PLA) 20% - 45%, barium titanate (BaTiO 3 ) 10% - 25%, and the sum of the mass percentages of each component is 100%.

[0037] Example 2 (Preparation process of 3D printed metamaterial piezoelectric bone defect repair stent)

[0038] This example specifically discloses the production method of the stent described in Example 1, including the following steps:

[0039] Step S1: Filament preparation: Mix PVDF, PLA and BaTiO 3 in the designed proportion and conduct vacuum drying (vacuum drying humidity ≤ 3%RH). Prepare a printing filament with a diameter of 1.75 ± 0.05mm under the following temperature conditions by a twin-screw extruder: During the extrusion process, the temperature of each zone of the screw is precisely controlled according to the melting points and processing characteristics of each component. For example, the melting section temperature of PVDF is set at 160 - 180°C, the melting section temperature of PLA is set at 150 - 170°C, and the temperature of the dispersion section of BaTiO 3 is slightly higher than the melting points of the two to ensure that each component is fully melted and mixed and BaTiO 3 is evenly dispersed in the polymer matrix;

[0040] Step S2 Structure Printing: The scaffold is printed using the fused deposition modeling (FDM) technique under the following process parameters: During the printing process, the printing nozzle temperature is set between 170 - 200 °C according to the characteristics of the filament material, and the printing platform temperature is controlled at 40 - 60 °C to ensure good melting and spreading of the filament and forming effect. The printing speed is set at 30 - 60 mm / s, the layer height is set at 0.1 - 0.3 mm, and the pore structure, according to its Gyroid, SchwarzP, and Diamond structures, needs to be formed strictly according to their respective mathematical expressions in a three-dimensional Cartesian coordinate system. The design model is converted into printing instructions through slicing software to precisely control the movement path of the nozzle and the material extrusion amount, realizing the precise construction of complex three-dimensional porous structures;

[0041] Step S3 Post-processing: The printed part is placed in a vacuum oven and heated to 70 - 80 °C at a rate of 2 °C / min for annealing treatment for 3.0 h ± 0.5 h. After annealing, it is immersed in phosphate-buffered saline with pH = 7.4 for surface activation treatment.

[0042] The core advantages of the present invention are reflected in the synergistic effect of structural design, material function, and process innovation, and the systematic improvement of bone repair performance is achieved through multi-level principle optimization:

[0043] Mechanical Adaptability Optimization: The gradient pore design follows the bionics principle of natural bone tissue. The outer high-density Diamond unit disperses stress concentration through continuous surface topology, the middle Schwarz P unit realizes modulus transition with the help of curvature gradient, and the inner Gyroid through-network effectively relieves interface shear stress, making the overall mechanical response of the scaffold dynamically match the load-bearing requirements of the host bone. Under dynamic load conditions, the gradient pore structure significantly reduces the stress shielding effect through the energy dissipation mechanism, ensuring the effective conduction of mechanical stimuli to the newly formed bone tissue.

[0044] Electroactive Induction Mechanism: Based on the multiphase synergistic effect of piezoelectric composites, the scaffold generates directional bioelectric signals through the piezoelectric effect under physiological loads. The polar β-phase crystals of PVDF and BaTiO 3 Induce a continuous surface potential, which regulates the cell membrane potential and ion channel activity through this potential, activates the osteogenesis-related signaling pathway, and promotes extracellular matrix mineralization and bone tissue directional regeneration at the molecular level.

[0045] Bone Conduction Efficiency Enhancement: The through-pore network constructs a three-dimensional connected biotransport channel, combined with surface hydrophilic modification to enhance protein adsorption ability, providing an ideal microenvironment for cell migration, angiogenesis, and nutrient transport. The gradient pore size design simultaneously meets the dual requirements of early cell adhesion (small pore size area) and long-range tissue infiltration (large pore size area), realizing precise spatial and temporal regulation during the bone regeneration process.

[0046] Degradation matching characteristics: Through the compound design of degradable polymers and piezoelectric fillers, the degradation behavior of the scaffold exhibits multi-stage response characteristics. The hydrolysis of PLA dominates the initial degradation to maintain structural stability, the hydrophobic barrier of PVDF delays the mid-term degradation rate, and finally, the synchronous disintegration with the replacement of new bone is achieved through the peeling of the filler-matrix interface. This degradation kinetics ensures that the mechanical support is gradually transferred to the new bone during the regeneration process, avoiding the risk of structural collapse.

[0047] Breakthrough in process compatibility: The 3D printing technology breaks through the technical limitations of the post-treatment of traditional piezoelectric materials.

[0048] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention. The structures, devices, and operation methods not specifically described and explained in the present invention are implemented according to the conventional means in the art without special explanation and limitation.

Claims

1. A 3D printed metamaterial piezoelectric bone defect repair scaffold, characterized in that: The pore structure of the support is composed of three minimal surface units defined by mathematical expressions, namely Gyroid, SchwarzP and Diamond; the porosity of the support is 30%-70%, and the pore size range is 0.1-1mm; the material of the support is a piezoelectric composite material composed of polyvinylidene fluoride, polylactic acid and barium titanate.

2. A 3D printed metamaterial piezoelectric bone defect repair scaffold according to claim 1, characterized in that: The piezoelectric composite material is composed of 30%-55% polyvinylidene fluoride (PVDF), 20%-45% polylactic acid (PLA), and 10%-25% barium titanate (BaTiO3), and the sum of the mass percentages of the components is 100%.

3. A 3D printed metamaterial piezoelectric bone defect repair scaffold according to claim 1, characterized in that: The mathematical expression of the minimal surface unit in the three-dimensional Cartesian coordinate system is: Gyroid structure: sin(x)cos(y)+sin(y)cos(z)+sin(z)cos(x)=0; SchwarzP structure: cosh(x)cos(y)+cosh(y)cos(z)+cosh(z)cos(x)=C, wherein C is a constant determined according to the specific design; Diamond structure: cos(x)sin(y)+cos(y)sin(z)+cos(z)sin(x)=0.

4. A method for preparing a 3D printed metamaterial piezoelectric bone defect repair scaffold according to any one of claims 1 to 3, characterized in that: The following steps are involved: Step S1: filament preparation: PVDF, PLA and BaTiO3 are mixed according to the designed ratio and vacuum dried, the vacuum drying humidity is ≤3% RH, and a printing filament with a diameter of 1.75±0.05 mm is prepared by a twin-screw extruder under the following temperature conditions: during the extrusion process, the temperature setting of each zone of the screw is precisely controlled according to the melting point and processing characteristics of each component, the temperature of the PVDF melting section is set at 160-180°C, the temperature of the PLA melting section is set at 150-170°C, and the temperature of the BaTiO3 dispersion section is slightly higher than the melting points of the two, the components are fully melted and mixed, and the BaTiO3 is evenly dispersed in the polymer matrix; Step S2 structure printing: the bracket is printed using fused deposition modeling technology under the following process parameters: during the printing process, the temperature of the print head is set between 170-200°C according to the material properties of the filament, the temperature of the printing platform is controlled at 40-60°C to ensure good melting, spreading and molding effects of the filament, the printing speed is set at 30-60mm / s, the layer height is set at 0.1-0.3mm, the pore structure must be strictly in accordance with its Gyroid, SchwarzP and Diamond structures according to their respective mathematical expressions, and molded in a three-dimensional Cartesian coordinate system, the design model is converted into a printing instruction through the slicing software, and the nozzle movement path and material extrusion amount are accurately controlled; Step S3 post-treatment: Place the printed part in a vacuum oven and heat it to 70-80°C at a rate of 2°C / min, anneal it for 3.0h±0.5h, and after annealing, immerse it in phosphate buffered saline with pH=7.4 for surface activation treatment.

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