CN114642764B - Construction Method of Fractal Scaffold for Bone Tissue Engineering - Google Patents

Abstract

The invention relates to the technical field of biomedical materials, in particular to a method for constructing a bone tissue engineering shape-divided support. The method comprises the following steps: obtaining a physical geometry of a target bone replacement; determining a 2D fractal tree curve according to the physical geometric dimension of the target bone substitute; carrying out circumferential array on the 2D shape-divided tree curve by using the axis of the target bone defect to construct a 2D shape-divided layer; designing 2D concentric circular curves at the bifurcating positions of the 2D fractal tree curves, and forming a 2D circular layer by using the 2D concentric circular curves with different diameters; on the basis of the 2D shaping layer and the 2D annular layer, a 3D shaping layer and a 3D annular layer are created according to the diameter of the tows and the height of the target bone substitute; the materials are axially stacked layer by layer to construct a fractal support of the bone tissue engineering. The invention solves the technical problem that the radial gradient pore change of the existing scaffold is relatively lacked during construction.

Description

Fractal-shaped Scaffold Construction Method for Bone Tissue Engineering

technical field

The invention relates to the technical field of biomedical materials, in particular to a method for constructing a fractal-shaped scaffold for bone tissue engineering.

Background technique

Critical bone defect is one of the important problems in orthopedics today, seriously affecting people's health and quality of life. Although autologous bone grafting has been the gold standard of treatment, the amount of available bone limits its widespread use in the clinic. In this context, tissue engineering was proposed in 1987 with the aim of obtaining artificial substitutes for tissue replacement and regeneration. An ideal bone scaffold (material) should have biological activity, mechanical support, permeability and biodegradability, etc. Among them, the interconnected porous structure can effectively promote cell proliferation and ingrowth as well as transport of nutrients and oxygen, and promote tissue regeneration.

In order to simulate the gradient pore structure of "bone marrow cavity-cancellous bone-cortical bone" of natural bone, computer-aided design (CAD) including Voronoi tessellation method, triple periodic minimal surface (TPMS), topology optimization, etc. ) method has been used to design a bone scaffold model with a gradient structure, but the fabrication techniques of the scaffold obtained by the above method are mainly selective laser melting (SLM), electron beam melting (EBM) and stereolithography (SLA).

Although the existing technology can realize the design of the controllable gradient pore scaffold, the matching manufacturing process, such as the high temperature of the processing and the toxicity of the photosensitive material, is not friendly to cells, or even harmful, which cannot meet the needs of bio-3D printing bone tissue engineering. Scaffolds require radially gradient pore structures.

Extrusion 3D printing has been widely used due to its advantages of simple operation, wide range of available materials, and cell printing. At present, although some scaffolds with axially gradient pores are designed by adjusting parameters such as extrusion filament diameter and distribution spacing (Bittner S M, Smith B T, Diaz-Gomez L, et al. Fabrication and mechanical characterization of 3D printed vertical uniform and gradient scaffolds forbone and osteochondral tissue engineering[J].Acta biomaterialia,2019,90:37-48), but for scaffold The study of gradient changes along the radial direction is lacking. That is to say, the existing research on extruded 3D printed gradient pore scaffolds mainly focuses on axial stacking to realize the axial gradient pore distribution of the scaffold, and lacks how to realize the gradient pore change that mimics natural bone from cancellous bone to cortical bone. Therefore, how to design and prepare a biomimetic gradient-pore bone tissue engineering scaffold based on extrusion 3D printing is a major problem faced by 3D printing technology in tissue engineering.

Contents of the invention

An embodiment of the present invention provides a method for constructing a fractal scaffold for bone tissue engineering, to at least solve the technical problem that the gradient pore change is relatively lacking when the existing scaffold is constructed.

According to an embodiment of the present invention, a method for constructing a fractal-shaped scaffold for bone tissue engineering is provided, comprising the following steps:

obtaining the physical geometry of the target bone substitute;

Determining a 2D fractal tree curve based on the physical geometry of the target bone substitute;

The 2D fractal tree curve is arranged in a circular array with the axis of the target bone defect to construct a 2D fractal layer;

Design 2D concentric ring curves at the bifurcation positions of 2D fractal tree curves, and use 2D concentric ring curves of different diameters to form 2D ring layers;

On the basis of the 2D fractal layer and the 2D ring layer, a 3D fractal layer and a 3D ring layer are created according to the diameter of the filament bundle and the height of the target bone substitute, and the 3D fractal layer and the 3D ring layer are axially stacked to construct bone tissue engineering Fractal shape bracket 3D model.

Further, the method also includes:

Divide the 3D model of the fractal scaffold for bone tissue engineering into n-1 areas along the radial direction, and calculate the porosity of each area respectively, where n is an integer ≥ 2;

By adjusting the parameters involved including fractal primary patterns, iteration rules, iteration times, bifurcation angles at all levels of 2D fractal tree curves, the number of circular arrays of 2D fractal tree curves, and tow diameter parameters, pores with radial gradients can be obtained 3D model of fractal-shaped scaffolds for bone tissue engineering.

Further, the method also includes:

The obtained 2D fractal layer curve and 2D ring layer curve of the bone tissue engineering fractal-shaped scaffold 3D model with radial gradient pores are constructed based on the programming software combined with the manufacturing code definition rules of commercial printers and the printer’s feeding motion parameters. Manufacturing codes for gradient pore tissue engineering scaffolds;

Modify and adjust the parameters involved in the printer's feeding movement until the diameter of the actual filament extruded by the 3D printer is close to the filament diameter of the 3D model of the fractal scaffold for bone tissue engineering with radial gradient pores;

In the parametric design software, the design of the entire 3D model and the acquisition of the manufacturing code, and the subsequent 3D printing preparation of the bracket are realized.

Further, before preparing the fractal-shaped scaffold for bone tissue engineering by 3D printing, the method also includes:

Polylactic acid-glycolic acid copolymer (PLGA) and 1,4-dioxane are prepared by magnetic stirring at a ratio of 0.8-1.2g/2-3ml for 8-12 hours to prepare printing ink; the printing ink material is a or multiple combinations of biomaterials, or cell bioinks containing one or more combinations.

Further, the physical geometric dimensions of the target bone substitute are determined according to the CT or MRI medical image data through Mimics medical processing software.

Further, the 2D fractal tree curve is determined according to the inner diameter size, the outer diameter size, the fractal primary pattern, the iteration rule, and the number of iterations in the physical geometric size of the target bone substitute.

Further, on the basis of the 2D fractal layer and the 2D ring layer, the circle with the same diameter as the 3D printer extrudes the tow, using its center as a reference point to move along the lines of the 2D fractal layer and the 2D ring layer and the center of the circle Normals are always coincident with 2D lines, and this circle extrudes offset to form a 3D fractal layer and a 3D torus layer, which support each other. The bottom layer is the 3D fractal layer, and then the position of the 3D ring layer is shifted axially by a value of the interlayer distance, and then stacked layer by layer along the axial direction until the height of the target bone defect is reached, and the bone tissue is completed. Construction of 3D model of engineering fractal shape bracket.

Further, the obtained 2D fractal layer curve and 2D ring layer curve of the bone tissue engineering fractal-shaped scaffold 3D model with radial gradient pores are combined with the manufacturing code definition rules of commercial printers and the printer’s feeding motion parameters, through the Python programming language. Construction of fabrication codes for radially gradient-porous tissue engineering scaffolds.

Further, the parameters of the printer's feeding movement include the extrusion pressure of the printing ink, the movement speed of the printing head, the height of the printing head from the bottom receiving platform, and the rheological properties of the ink.

Further, in the parametric design software Grasshopper that comes with Rhino, the design of the entire 3D model and the acquisition of manufacturing codes are realized, and the "design-manufacturing" workflow of 3D printing radial gradient porosity bone tissue engineering fractal scaffolds is constructed. This work Streams can be modified parametrically with one click according to target needs.

Furthermore, the fractal-shaped scaffolds for bone tissue engineering prepared by 3D printing were three-dimensionally reconstructed by Micro-CT SkyScan1176, and the overall and radial porosity of each region were evaluated on the basis of the reconstruction.

Furthermore, the fractal scaffold for bone tissue engineering with the number of iterations N≥3 has the characteristic that the porosity gradually decreases from the inside to the outside, and the porosity gradient decreases more and more significantly with the increase of the number of iterations.

Further, the method also includes:

Parametrically construct the fractal scaffold design-manufacturing workflow for bone tissue engineering, and obtain the manufacturing code (G-code);

The fractal scaffolds for bone tissue engineering were printed and prepared, and their porosity was evaluated by CT three-dimensional reconstruction.

A storage medium stores program files capable of implementing any one of the above methods for constructing fractal-shaped scaffolds for bone tissue engineering.

A processor, the processor is used to run a program, wherein, when the program is running, any one of the methods for constructing fractal-shaped scaffolds for bone tissue engineering described above is executed.

The bone tissue engineering fractal scaffold construction method in the embodiment of the present invention proposes a fractal tree curve with an iterative function based on bionics and fractal design. The fractal tree curve uses the axis of the target bone defect as a circular array to construct a 2D fractal layer, and builds a 2D ring layer based on this. The 2D fractal layer and the 2D ring layer are stretched and offset to construct a 3D fractal layer and a 3D ring layer. The present invention uses the fractal layer and the ring layer to support each other and builds a stable 3D printed bone tissue engineering fractal shape through layer-by-layer stacking. stand.

Description of drawings

The accompanying drawings described here are used to provide a further understanding of the present invention and constitute a part of the application. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations to the present invention. In the attached picture:

Fig. 1 is the flow chart of the construction method of bone tissue engineering fractal-shaped scaffold of the present invention;

Figure 2 is a graph of the fractal tree proposed based on the Koch Snowflake;

Fig. 3 is the schematic diagram (A1, B1, C1, D1) and iteration rule diagram (A2, B2, C2, D2) of fractal shape tree curve iteration 0-3 times;

Figure 4 is a schematic diagram of the design and manufacture of a fractal scaffold for bone tissue engineering based on extrusion 3D printing;

Figure 5 is a diagram of the pore gradient variation of 90° tow orthogonality (a common stacking method for extrusion 3D printing) and iterations 0-3 times of bone tissue engineering fractal-shaped scaffolds;

Fig. 6 is the rule that the bone tissue engineering scaffold is equally divided into six regions a-f along the radial direction;

Fig. 7 is a "design-manufacture" work flow chart of 3D printing radial gradient porosity bone tissue engineering fractal-shaped scaffold;

Figure 8 is a physical map of the bone tissue engineering fractal-shaped scaffold obtained by extrusion 3D printing at 90° orthogonal (90°), iteration 0 (N=0) and iteration 3 (N=3);

Figure 9 shows the overall porosity and local porosity of the 90° orthogonal (90°), iteration 0 (N=0) and iteration 3 (N=3) bone tissue engineering scaffolds prepared by 3D printing.

Detailed ways

In order to enable those skilled in the art to better understand the solutions of the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only It is an embodiment of a part of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

It should be noted that the terms "first" and "second" in the description and claims of the present invention and the above drawings are used to distinguish similar objects, but not necessarily used to describe a specific sequence or sequence. It is to be understood that the data so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein can be practiced in sequences other than those illustrated or described herein. Furthermore, the terms "comprising" and "having", as well as any variations thereof, are intended to cover a non-exclusive inclusion, for example, a process, method, system, product or device comprising a sequence of steps or elements is not necessarily limited to the expressly listed instead, may include other steps or elements not explicitly listed or inherent to the process, method, product or apparatus.

Example 1

According to an embodiment of the present invention, a method for constructing a fractal-shaped scaffold for bone tissue engineering is provided, as shown in Fig. 1, comprising the following steps:

S101: Obtain the physical geometry size of the target bone substitute;

S102: Determine the 2D fractal tree curve according to the physical geometry of the target bone substitute;

S103: Performing a circular array on the 2D fractal tree curve with the axis of the target bone defect to construct a 2D fractal layer;

S104: Design 2D concentric ring curves at the bifurcation positions of the 2D fractal tree curves, and use 2D concentric ring curves of different diameters to form a 2D ring layer;

S105: Create a 3D fractal layer and a 3D ring layer according to the diameter of the wire bundle and the height of the target bone substitute, and the 3D fractal layer and the 3D ring layer are axially stacked layer by layer to construct a fractal-shaped scaffold for bone tissue engineering;

S106: Parametrically construct the bone tissue engineering fractal-shaped scaffold design-manufacturing workflow, and obtain the manufacturing code;

S107: Prepare fractal-shaped scaffolds for bone tissue engineering by 3D printing and evaluate their porosity by CT three-dimensional reconstruction.

The bone tissue engineering fractal scaffold construction method in the embodiment of the present invention proposes a fractal tree curve with an iterative function based on bionics and fractal design. The fractal tree curve uses the axis of the target bone defect as a circular array to construct a 2D fractal layer, and builds a 2D ring layer accordingly. On the basis of the 2D fractal layer and the 2D ring layer, the same diameter as the 3D printer extruded filament The circle moves along the lines of the 2D fractal layer and the 2D ring layer with its center as the reference point, and the center normal of the circle always coincides with the 2D line. The 3D model of the fractal scaffold for bone tissue engineering is constructed by stacking layers of mutual support. The present invention uses fractal layers and ring layers to support each other and builds a structurally stable 3D printed fractal scaffold for bone tissue engineering through layer-by-layer stacking.

Among them, the method also includes:

Divide the 3D model of the fractal scaffold for bone tissue engineering into n-1 areas along the radial direction, and calculate the porosity of each area respectively, where n is an integer ≥ 2;

By adjusting the parameters involved including fractal original patterns, iteration rules, iteration times, bifurcation angles at all levels of 2D fractal tree curves, the number of circular arrays of 2D fractal tree curves, and the distance between layers, etc., a radial gradient is obtained. Porous bone tissue engineering fractal scaffold 3D model.

Among them, the method also includes:

The obtained 2D fractal layer curve and 2D ring layer curve of the bone tissue engineering fractal-shaped scaffold 3D model with radial gradient pores are constructed based on the programming software combined with the manufacturing code definition rules of commercial printers and the printer’s feeding motion parameters. Manufacturing codes for gradient pore tissue engineering scaffolds;

Modify and adjust the parameters of the printer's feeding motion involved until the actual extruded filament diameter of the 3D printer is close to the interlayer distance of the 3D model of the fractal scaffold for bone tissue engineering with radial gradient pores;

In the parametric design software, the design of the entire 3D model and the acquisition of the manufacturing code, and the subsequent 3D printing preparation of the bracket are realized.

Wherein, before obtaining the physical geometry size of the target bone substitute, the method further includes:

Polylactic acid-glycolic acid copolymer (PLGA) and 1,4-dioxane are prepared by magnetic stirring at a ratio of 0.8-1.2g/2-3ml for 8-12 hours to prepare printing ink; the printing ink material is a or multiple combinations of biomaterials, or cell bioinks containing one or more combinations.

Wherein, the physical geometric dimensions of the target bone substitute are determined according to the CT or MRI medical image data through the Mimics medical processing software.

Wherein, the 2D fractal tree curve is determined according to the inner diameter size, the outer diameter size, the fractal primary pattern, the iteration rule, and the number of iterations in the physical geometric size of the target bone substitute.

Among them, on the basis of the 2D fractal layer and the 2D ring layer, the 3D fractal layer and the 3D ring layer are created according to the diameter of the filament bundle and the height of the target bone substitute, and the axial stacking of the 3D model of the fractal-shaped scaffold for bone tissue engineering includes :

A circle with the same diameter as the 3D printer extrudes the tow, moves along the lines of the 2D fractal layer and the 2D ring layer with its center as the reference point, and the center normal of the circle always coincides with the 2D line, and the circle is stretched and offset to form a 3D The fractal layer and the 3D ring layer, the bottom layer is the 3D fractal layer, and then the value of the distance between the layers is offset along the axial direction to locate the position of the 3D ring layer, and then piled up sequentially along the axial direction until the target bone defect is reached to complete the construction of the 3D model of the fractal scaffold for bone tissue engineering.

Among them, the obtained 2D fractal layer curve and 2D ring layer curve of the bone tissue engineering fractal-shaped scaffold 3D model with radial gradient pores, combined with the manufacturing code definition rules of commercial printers, and the printer’s feeding motion parameters, were used in the parametric design software The GhPython battery is used in Grasshopper to construct the fabrication code for radially gradient pore tissue engineering scaffolds through the Python programming language.

Among them, the printer feeding movement parameters include the extrusion pressure of the printing ink, the movement speed of the printing head, the height of the printing head from the receiving platform at the bottom, and the rheological properties of the ink.

Among them, in the parametric design software Grasshopper that comes with Rhino, the design of the entire 3D model and the acquisition of manufacturing codes are realized, and the "design-manufacturing" workflow of 3D printing radial gradient porosity bone tissue engineering fractal-shaped scaffolds is constructed. This workflow One-click parametric modification can be performed according to the target needs.

Among them, the Micro-CT imaging system SkyScan1176 was used to reconstruct the three-dimensional scaffold to obtain the porosity of the whole and each part.

The method for constructing the bone tissue engineering fractal-shaped scaffold of the present invention will be described in detail below with specific examples:

The invention belongs to the technical field of biomedical materials, and specifically relates to a method for constructing a fractal scaffold for bone tissue engineering with radially gradient pores based on bionics and fractal design, and builds a parameterized scaffold "design-manufacture" workflow. The invention builds a bionic bone tissue engineering fractal-shaped scaffold with porosity gradient changes along the radial direction under computer-aided design, so that the structure has controllable gradient pores; the constructed scaffold imitates the pores of natural bone from cancellous bone to cortical bone Morphology, can be used for repair and regeneration of tissue engineering; secondary development of existing commercial 3D printers to complete the preparation of scaffolds. Utilizing the fractal bone tissue engineering scaffold of the present invention, tissue engineering scaffolds with different gradient pores and different performances can be prepared according to actual needs.

The present invention relates to a method for constructing a bone tissue engineering fractal scaffold with radial gradient pores based on bionics and fractal design, specifically related to the design of fractal tree curves, the construction of bone tissue engineering fractal scaffolds, and the "design- The construction of the "manufacturing" work data flow and its scaffold construction method, which can control the gradient porosity of the scaffold according to the porosity change of the natural bone.

The purpose of the present invention is to solve the deficiencies in the radial gradient pore structure design of bone tissue engineering scaffolds in the prior art, and provide a method for constructing a bone tissue engineering fractal scaffold with radial gradient pores based on bionics and fractal design, and The "design-manufacture" workflow for secondary development of existing commercial 3D printers to build brackets. According to this method, controllable gradient pores based on extrusion 3D printing can be obtained, which can be used for bone tissue and other tissue repair and regeneration. Specifically, the present invention can dynamically change the scaffold model according to the size parameters of the patient's bone defect, and construct a "design-manufacture" workflow for bone tissue engineering fractal-shaped scaffolds, and re-develop existing commercial 3D printers so that they can prepare Designed radial gradient porosity scaffolds for bone tissue engineering. At the same time, the secondary development of existing commercial 3D printers saves manufacturing costs.

Concrete steps of the present invention are summarized as follows:

1) Poly(lactic-co-glycolic acid) (PLGA) and 1,4-dioxane were magnetically stirred at a ratio of 1 g/2.5 ml for 10 hours to prepare printing ink. The printing ink material can be one or more combinations of biomaterials, or one or more combinations of cell bioinks.

2) Determine the physical geometric dimensions (such as inner diameter, outer diameter, height, etc.) of the target bone substitute based on medical image data such as CT or MRI by using medical processing software such as Mimics.

3) Determine the 2D fractal tree curve according to the inner and outer diameters of the target bone substitute in step 2), the original fractal pattern, the iteration rule, and the number of iterations.

4) The 2D fractal tree curve obtained in step 3) is used as a circular array with the axis of the target bone defect to construct a 2D fractal layer.

5) According to the 2D fractal layer determined in step 4), in order to realize mutual support between the layers of the 3D stent, a 2D concentric ring curve is designed at the bifurcation position of the 2D fractal tree curve, and the concentric 2D ring curves of different diameters form a 2D circle ring layer.

6) According to the 2D fractal layer determined in step 5), it is assumed that each 2D fractal layer includes n 2D concentric ring curves, and n is an integer ≥ 2.

7) On the basis of the 2D fractal layer and the 2D circular ring layer obtained in step 4) and step 5), the interlayer distance (ie filament diameter) and the number of axial arrays are determined according to the height of the target bone substitute. The 2D fractal layer and the 2D ring layer can form the 3D fractal layer and the 3D ring layer by stretching and offsetting the circle whose diameter is the distance between the layers along the line. The bottom layer is the 3D fractal layer, and then the position of the 3D ring layer is shifted axially by a value of the interlayer distance, and then piled up sequentially along the axial direction until the height of the target bone defect is reached, that is, bone tissue engineering is completed. Construction of 3D model of fractal shape scaffold.

8) Divide the 3D model of the bracket obtained in step 7) into n-1 regions along the radial direction, and calculate the porosity of each region respectively, where n comes from step 6).

9) By adjusting steps 3)-step 8), the original fractal patterns, iteration rules, number of iterations, bifurcation angles at all levels of 2D fractal tree curves, the number of circular arrays of 2D fractal tree curves, and interlayer The 3D model of the fractal-shaped scaffold for bone tissue engineering with radially gradient pores was obtained.

10) Extract the 2D fractal layer curve and the 2D circular layer curve of the bracket 3D model obtained in step 9), based on the parametric design software Grasshopper in combination with the manufacturing code (G-code) definition rules of commercial printers, printer feed movement and other parameters to come Construction of fabrication codes for radially gradient-porous tissue engineering scaffolds.

11) Modify and adjust the printer feeding motion parameters involved in step 10) until the actual extruded filament diameter of the 3D printer is close to the interlayer distance of the 3D model of the bracket. Among them, the printer feeding movement parameters include the extrusion pressure of the printing ink, the movement speed of the printing head, the height of the printing head from the receiving platform at the bottom, and the rheological properties of the ink.

12) The above step 3)-step 11) is implemented in the parametric design software Grasshopper that comes with Rhino to achieve the design of the entire 3D model and the acquisition of the manufacturing code (G-code), and the subsequent 3D printing preparation of the bracket, that is, the construction A "design-manufacture" workflow for 3D printing of fractal-shaped scaffolds for bone tissue engineering with radial gradient pores can be modified with one-click parameterization according to the target needs.

13) Based on step 1) and step 12), perform 3D printing to prepare fractal-shaped scaffold for bone tissue engineering, and perform low-temperature freeze-drying treatment on it.

14) Perform three-dimensional reconstruction on the fractal-shaped bone tissue engineering scaffold prepared in step 13), and combine with step 8) to obtain the porosity of the whole and each local area through Boolean operations, and evaluate the radial gradient porosity.

Key technical points of the present invention are:

1. The present invention applies bionics and fractals to design 2D fractal tree curves.

2. The 2D fractal tree curve proposed in the present invention constitutes a 2D fractal layer by arraying around the axis of the target bone defect.

3. In order to realize the structural stability of the 3D printing stent in the present invention, it is proposed to set 2D concentric ring curves at the bifurcation points of the 2D fractal layer curves, and the concentric 2D ring curves with different diameters constitute the 2D ring layer.

4. In the present invention, the 2D fractal layer and the 2D ring layer take the circle whose diameter is the distance between the layers to stretch and offset along the line to form the 3D fractal layer and the 3D ring layer, which are piled up layer by layer along the axial direction until the target bone defect is reached. Height, that is, to complete the construction of the 3D model of the fractal-shaped scaffold for bone tissue engineering.

5. In the present invention, the design of the entire 3D model and the acquisition of the manufacturing code (G-code) are realized in the parametric design software Grasshopper that comes with Rhino, and the subsequent 3D printing preparation of the bracket is constructed to build a one-click parametric "Design-fabrication" workflow for 3D printing fractal-shaped scaffolds with radially gradient pores for bone tissue engineering.

6. The present invention proposes the design and preparation of a fractal-shaped scaffold for bone tissue engineering with radial pore gradients that can be used for extrusion-type bio-3D printing.

7. Fractal-shaped scaffolds for bone tissue engineering with radial pore gradients designed in the present invention include but are not limited to extrusion 3D printing.

8. The printing ink involved in the present invention may include one or more of biomaterials such as polymer materials and hydrogels.

9. The printing ink involved in the present invention may contain one or more cells.

The protection points of the present invention are at least:

1. The fractal tree curve with iteration function designed based on bionics and fractals proposed by the present invention. The fractal tree curve is iterated for 3 times or more (N≥3), and the design of the fractal scaffold for bone tissue engineering with radially gradient pores can be realized by constructing the fractal layer and the ring layer.

2. In the present invention, the fractal layer and the ring layer are used to support each other to build a structurally stable 3D printed radial gradient pore bone tissue engineering fractal scaffold through layer-by-layer stacking.

3. The fractal-shaped scaffold for bone tissue engineering proposed in the present invention can be adjusted according to the size of the target bone defect.

4. In the present invention, based on the parametric design software Grasshopper, the "design-manufacture" workflow of 3D printing radial gradient porosity bone tissue engineering fractal-shaped scaffolds is constructed. The fractal original pattern, iteration rule, number of iterations, bifurcation angles of all levels of 2D fractal tree curves, the number of circular arrays of 2D fractal tree curves, the distance between layers, and the definition of manufacturing code (G-code) can be modified by one key The target bone tissue engineering scaffold can be easily obtained with parameters such as rules and printer feeding movement.

5. The fractal-shaped scaffold for bone tissue engineering with radial gradient pores designed in the present invention can be prepared by extrusion 3D printing technology.

6. The present invention divides the 3D model of the bracket and the 3D reconstruction model equally along the radial direction, and calculates the porosity of each region to evaluate the gradient pore change in the radial direction.

Compared with the prior art, the present invention has brought many advantages, at least as follows:

1. The fractal scaffold for bone tissue engineering with radial gradient pores of the present invention realizes controllable radial gradient pores based on extrusion 3D printing, and is suitable for the preparation of radial gradient bone tissue engineering scaffolds of different scales.

2. The "design-manufacturing" workflow of 3D printing radial gradient porous bone tissue engineering fractal-shaped scaffolds was established, and the design and manufacturing parameters can be adjusted according to different needs to obtain target scaffolds.

3. The "design-manufacture" workflow of the radial gradient pore tissue engineering scaffold built by the present invention can complete the secondary development of common commercial ordinary/industrial/medical extrusion 3D printers according to the manufacturing code rules of different printers , to reduce manufacturing costs.

4. The present invention proposes an evaluation rule for evaluating gradient pores at equal radial intervals.

The present invention proves to be feasible through experimental verification, and concrete implementation case is as follows:

A. Inspired by Koch snowflakes (as shown in Figure 2A-B) and Koch curves (as shown in Figure 2C), the fractal tree curves are designed in the parametric software Grasshopper that comes with Rhino6.0, showing iterations 0-3 respectively The second curve result (as shown in Figure 2D). Figure 2A is a 2D snowflake model, Figure 2B is a Koch snowflake that has been iterated 3 times in a regular triangle, and Figure 2C and 2D are Koch curves and fractal tree curves that have been iterated 0-3 times, respectively.

B. The main parameters affecting the fractal tree curve are the number of iterations and the bifurcation angles at all levels (as shown in Figure 3), especially the odd-numbered area lines of the fractal tree curve are all along the radial direction, as shown in the lines FG and HI of Figure 3C2.

C. Bone tissue engineering fractal scaffolds are formed by stacking 3D fractal layers and 3D ring layers to support each other. The 3D fractal layer and 3D ring layer are respectively passed by the 2D fractal layer curve and the 2D ring layer curve to determine the distance between layers. The 2D fractal layer curve is formed by a circular array of the fractal tree curve with the tail line cut off, and the bone defect axis, and the 2D circular layer curve is constructed by the bifurcation point of the fractal tree curve. A 2D concentric ring curve. Taking three iterations of the fractal tree curve as an example, the schematic diagram of the design and fabrication of the fractal scaffold for bone tissue engineering based on extrusion 3D printing is shown (as shown in Figure 4).

D. Based on the same overall porosity of the scaffold, design a common 90° orthogonal and iterative 0-3 fractal tree curve to construct a 3D model of bone tissue engineering fractal scaffold, and calculate the porosity of each local area of the model separately (as shown in FIG. 5 ), divide the bracket into six regions a to f equally along the radial direction (as shown in FIG. 6 ). With the gradual increase of the number of iterations, especially the 3rd iteration, the gradient of the porosity of the bone tissue engineering fractal-shaped scaffolds gradually became obvious, and its trend was similar to that of cancellous bone to cortical bone from sparse to dense. The fractal tree curve can realize the radial gradient pores of the fractal scaffold for bone tissue engineering when the fractal iteration is three times or more.

E. According to the normal adult femoral CT reconstruction model, a hollow cylinder with an inner diameter of 8 mm, an outer diameter of 22 mm, and a height of 3 mm was selected as the target bracket.

F. Construction of fractal-shaped scaffolds for bone tissue engineering with radial gradient pores by 3 iterations. Among them, the bifurcation angles of the fractal tree curves are 40°, 30°, and 12.8°; It is composed of rings with a pitch of 1.1167mm.

G. The "design-manufacturing" workflow of 3D printing radial gradient porosity bone tissue engineering fractal scaffolds was built in Grasshopper, which can parametrically change the physical geometric dimensions (inner diameter, outer diameter and height) and fractal parameters of the target bone defect , manufacturing code rules, etc. to construct the "design-manufacture" workflow of radially gradient pore tissue engineering scaffolds (as shown in Figure 7). Among them, Fig. 7A is a flow chart of this workflow, and Fig. 7B-J is a battery diagram of the realization of this workflow in Grasshopper software. Among them, Figure 7B is the geometric parameters of the target bone defect, Figure 7C is the fractal parameters required by the fractal tree curve, Figure 7D is the battery customized for the fractal scaffold design, and Figure 7E is the porosity gradient change analysis based on Grasshopper and Origin , Fig. 7F is the CAD model of the fractal scaffold for bone tissue engineering exported and used in Abaqus, Comsol and other software for simulation of mechanical properties, permeability and other parameters. Fig. 7G is the 2D design of the fractal scaffold for bone tissue engineering, including the fractal layer and the ring layer Curve, Fig. 7H is the parameter writing rule of the manufacturing code of commercial printer Bioscaffolder 3.1 used for this invention, Fig. 7I is the manufacturing code (G-code) generation instruction based on GhPython writing, Fig. 7J is the manufacturing code format ( *.nc).

H. Combining steps C and G to obtain a manufacturing code (G-code) that can be used to guide the movement of the 3D printer.

I. Polylactic-co-glycolic acid (PLGA) and 1,4-dioxane were prepared as printing ink after magnetic stirring at a ratio of 1g/2.5ml for 10 hours. The bottom of the stent forming platform is a fixed -30°C low-temperature cooling platform, so that the ink can be cooled and formed after deposition.

J. After finishing the printing head height positioning of commercial printer Bioscaffolder 3.1 and its control software GeSiM and the cryogenic cooling platform altimeter operation, by uploading the manufacturing code (G-code) obtained by the second development of the present invention obtained by step 1 to control The printing head deposits ink along the specified path to complete the preparation of the fractal-shaped scaffold for bone tissue engineering with radial gradient pores proposed by the present invention. Among them, the inner diameter of the print head is 0.26mm, the extrusion pressure is 400kPa, and the moving speed is 9mm/s.

K. After the 3D printing of the scaffold, the 1,4-dioxane was removed by a low-temperature freeze dryer to complete the final molding of the scaffold (as shown in Figure 8).

L. Using the Micro-CT imaging system SkyScan1176 to collect CT images of bone tissue engineering scaffolds prepared by 3D printing at 90° orthogonal (90°), iteration 0 (N=0) and iteration 3 (N=3) , and use its own software such as NRecon, DataViewer, CTAn, CTvox to perform three-dimensional reconstruction of the bracket (as shown in Figure 9a-c).

M. Perform Boolean operations on the CT reconstructed stent model to obtain the overall porosity of the stent and the porosity of each part of the equidistant area along the radial direction (as shown in Figure 9), where n.s. indicates that there is no significant difference in the one-way analysis of variance, and * indicates p ≤0.05 means that there is a significant difference between the data, ** means that p ≤ 0.01 means that there is a significant difference between the data, *** means that p ≤ 0.001 means that there is a very significant difference between the data. As a result, there is no significant difference in the overall porosity among the 90° orthogonal (90°), iteration 0 (N=0) and iteration 3 (N=3) bone tissue engineering scaffolds (as shown in Figure 9D). For the local porosity, each area of 90° orthogonal (90°) scaffold a-f is basically level and there is no significant difference (Fig. 9A and Fig. 9E), the results of iteration 0 (N=0) and iteration 3 (N=3) There are obvious significant differences in each region of scaffold a-f (Fig. 9B-C and Fig. 9E). Among them, the porosity of the scaffold gradually increases from the inside to the outside of the iteration 0 (N=0) (Fig. 9B and 9E), and the porosity of the scaffold gradually decreases from the inside to the outside of the iteration 3 (N=3). The "medullary cavity-cancellous bone-cortical bone" gradient structure with gradually decreasing porosity of natural bone (Fig. 9C and Fig. 9E).

The alternatives of the present invention are as follows:

The 3D printing radial gradient bone tissue engineering fractal-shaped scaffold proposed by the present invention includes but is not limited to bone tissue engineering, tissue engineering, and functionally graded scaffold/material.

As a further improvement of the present invention, the "design-manufacturing" workflow can be completed in multiple software or one software, and at the same time, this workflow can control different print heads of a printer or multiple 3D printers of the same brand or different brands. Work.

As an improvement of the present invention, the original curve of the fractal tree curve designed based on fractals can be modified into other line combinations.

As an improvement of the present invention, the 3D model of the scaffold can be designed as a linear or non-linear variable gradient porosity bone tissue engineering scaffold along the radial direction.

As another improvement of the present invention, the software required for scaffolding workflow construction includes, but is not limited to, Rhino, Grasshopper, Python, and GeSiM.

As another improvement of the present invention, the types of 3D printers used for scaffold workflow construction include but are not limited to extrusion printing (Extrusion printing), inkjet printing (Inkjet printing), laser assisted printing (Laserassisted printing), wherein extrusion Printing includes but is not limited to Bioscaffolder 3.1 printers.

As another improvement of the present invention, the preparation technology includes but not limited to SLM, EBM, SLA and other 3D printing or additive manufacturing technologies.

As a further improvement of the present invention, the printing ink includes but is not limited to two or more of biological materials such as PLGA, polylactic acid (PLA), calcium phosphate (β-TCP), hydroxyapatite (HA), and hydrogel. The combination of species and their different proportioning schemes.

As a further improvement of the present invention, the printed bio-ink may contain one or more types of cells.

Example 2

A storage medium stores program files capable of implementing any one of the above methods for constructing fractal-shaped scaffolds for bone tissue engineering.

Example 3

A processor, the processor is used to run a program, wherein, when the program is running, any one of the methods for constructing fractal-shaped scaffolds for bone tissue engineering described above is executed.

The serial numbers of the above embodiments of the present invention are for description only, and do not represent the advantages and disadvantages of the embodiments.

In the above-mentioned embodiments of the present invention, the descriptions of each embodiment have their own emphases, and for parts not described in detail in a certain embodiment, reference may be made to relevant descriptions of other embodiments.

In the several embodiments provided in this application, it should be understood that the disclosed technical content can be realized in other ways. Wherein, the system embodiments described above are only illustrative, for example, the division of units can be divided into a logical function, and there may be other division methods in actual implementation, for example, multiple units or components can be combined or integrated into Another system, or some features may be ignored, or not implemented. In another point, the mutual coupling or direct coupling or communication connection shown or discussed may be through some interfaces, and the indirect coupling or communication connection of units or modules may be in electrical or other forms.

A unit described as a separate component may or may not be physically separated, and a component shown as a unit may or may not be a physical unit, that is, it may be located in one place, or may be distributed over multiple units. Part or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, each unit may exist separately physically, or two or more units may be integrated into one unit. The above-mentioned integrated units can be implemented in the form of hardware or in the form of software functional units.

If the integrated unit is realized in the form of a software function unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the essence of the technical solution of the present invention or the part that contributes to the prior art or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium , including several instructions to make a computer device (which may be a personal computer, server or network device, etc.) execute all or part of the steps of the methods in various embodiments of the present invention. The aforementioned storage media include: U disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), mobile hard disk, magnetic disk or optical disk and other media that can store program codes. .

The above is only a preferred embodiment of the present invention, it should be pointed out that, for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications can also be made. It should be regarded as the protection scope of the present invention.

Claims (9)

1. A bone tissue engineering shape-divided scaffold construction method is characterized by comprising the following steps:

obtaining a physical geometry of a target bone replacement;

determining a 2D fractal tree curve according to the physical geometric dimension of the target bone substitute;

carrying out circumferential array on the 2D shape-divided tree curve by using the axis of the target bone defect to construct a 2D shape-divided layer;

designing 2D concentric circular curves at the bifurcating positions of the 2D fractal tree curves, and forming a 2D circular layer by using the 2D concentric circular curves with different diameters;

on the basis of the 2D shape-dividing layer and the 2D ring layer, a 3D shape-dividing layer and a 3D ring layer are created according to the diameter of the tows and the height of the target bone substitute, and the 3D shape-dividing layer and the 3D ring layer are axially stacked to construct a bone tissue engineering shape-dividing support 3D model;

the method further comprises the following steps:

equally dividing the bone tissue engineering fractal-shaped scaffold 3D model into n-1 regions along the radius direction, and respectively calculating the porosity of each region, wherein n is an integer more than or equal to 2;

and obtaining the bone tissue engineering fractal-shaped support 3D model with radial gradient pores by adjusting the related parameters including the fractal primary pattern, the iteration rule, the iteration times, the bifurcation angles of the 2D fractal-shaped tree curves, the number of circumferential arrays of the 2D fractal-shaped tree curves and the diameter of the tows.

2. The method for constructing a bone tissue engineering fractal scaffold according to claim 1, wherein the method further comprises:

constructing a manufacturing code for the radial gradient pore tissue engineering scaffold based on a programming software, a manufacturing code definition rule of a commercial printer and a printer feeding motion parameter, wherein the 2D fractal layer curve and the 2D circular ring layer curve of the obtained bone tissue engineering fractal-shaped scaffold 3D model with the radial gradient pores;

modifying and adjusting related feeding motion parameters of a printer until the diameter of the actually extruded tows of the 3D printer is close to that of the tows of the bone tissue engineering fractal support 3D model with radial gradient pores;

and realizing the design of the whole 3D model and the acquisition of manufacturing codes in parameterized design software, and then carrying out 3D printing preparation on the bracket.

3. The method for constructing a bone tissue engineering fractal-shaped scaffold according to claim 1, wherein before 3D printing and manufacturing the bone tissue engineering fractal-shaped scaffold, the method further comprises:

polylactic-co-glycolic acid (PLGA) and 1, 4-dioxane in a proportion of 0.8-1.2g/2-3ml are magnetically stirred for 8-12 hours to prepare printing ink; wherein the printing ink material is one or more combined biological materials or cell biological ink containing one or more combinations.

4. The method for constructing a bone tissue engineering fractal scaffold according to claim 1, wherein the physical geometry of the target bone substitute is determined by means of Mimics medical processing software from CT or MRI medical image data.

5. The bone tissue engineering fractal scaffold construction method according to claim 1, wherein a 2D fractal tree curve is determined according to the inner diameter size, the outer diameter size, the fractal primary pattern, the iteration rule and the iteration times of the physical geometry of the target bone substitute.

6. The method for constructing a bone tissue engineering shape-divided scaffold according to claim 1, wherein on the basis of the 2D shape-divided layer and the 2D annular layer, a circle with the same diameter as the extruded filament bundle of the 3D printer moves along the line of the 2D shape-divided layer and the 2D annular layer with the center as a reference point and the central normal line of the circle is always coincident with the 2D line, and the circle is stretched and offset to form the 3D shape-divided layer and the 3D annular layer which are supported with each other; the bottom layer is a 3D fractal layer, the position of the 3D circular layer is located by shifting a numerical value of the interlayer distance along the axial direction, and then the 3D circular layer is sequentially stacked layer by layer along the axial direction until the height of the target bone defect is reached, so that the construction of the bone tissue engineering fractal support 3D model is completed.

7. The bone tissue engineering fractal-shaped scaffold construction method according to claim 2, wherein a 2D fractal layer curve and a 2D ring layer curve of which the iteration times N of the obtained bone tissue engineering fractal-shaped scaffold 3D model with the radial gradient pores is more than or equal to 3 are combined with a manufacturing code definition rule of a printer and a printer feeding motion parameter, and a manufacturing code for the radial gradient pore tissue engineering scaffold is constructed by a Python programming language.

8. The method for constructing a bone tissue engineering shape-divided scaffold according to claim 2, wherein the printer feed motion parameters comprise extrusion air pressure of printing ink, motion speed of a printing head, height of the printing head from a bottom receiving platform, and rheological properties of the ink.

9. The method for constructing the bone tissue engineering fractal-shaped scaffold as claimed in claim 2, wherein the steps of obtaining the design and manufacturing codes of the whole 3D model in the parametric design software Grasshopper of the Rhino, 3D printing preparation of the scaffold, and constructing the design-manufacturing workflow of the 3D printing radial gradient pore bone tissue engineering fractal-shaped scaffold are realized, and the workflow can be modified in a one-key parametric mode according to the target requirement.

Images