Melt electrostatic direct writing method for preparing polymer fiber scaffolds with continuous gradient structure

Abstract

The present invention belongs to the field of polymer additive manufacturing technology and relates to a melt electrostatic direct writing preparation method for a polymer fiber scaffold with a continuous and gradient structure. The method first designs a basic homogeneous pattern according to the transition interface characteristics of the tissue to be repaired, and discretizes it into a dense and ordered point array. Then, a nonlinear transformation function is designed according to the structural change characteristics at the transition interface. f and g , using nonlinear transformation function f and g , the points are mapped one by one to , thus obtaining a point array. The point array is then equidistantly sampled to obtain the desired printing path. Finally, based on the desired printing path, melt electrostatic direct writing is performed to produce a polymer fiber scaffold with a continuously gradient structure. This invention utilizes a curved printing process to mimic the smooth transition interface between tissues, enhancing the structural and mechanical biomimetic properties of the polymer fiber scaffold.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer additive manufacturing and relates to a melt electrostatic direct writing preparation method of a polymer fiber support with a continuous and gradient structure. Background Art

[0002] Melt electrostatic writing (MEW) is a novel method for preparing thermoplastic polymer fiber scaffolds. It offers the following advantages: The printing process does not require organic solvents, eliminating the biotoxicity concerns associated with organic solvents; It prints fibers at high resolution, enabling the printing of micron or submicron-sized fibers comparable to cell diameters; It can process a wide range of materials; and its microstructure is customizable. Based on these advantages, MEW scaffolds can closely mimic the complex structure and biomechanical properties of the extracellular matrix and regulate cell behaviors such as adhesion, proliferation, migration, and differentiation, thereby promoting tissue regeneration and reconstruction. Consequently, MEW scaffolds have found widespread application in tissue engineering and regenerative medicine (TERM).

[0003] The MEW scaffold structure aims to mimic the extracellular matrix structure of native tissue in the human body and improve the degree of biomimetic properties. However, there are a large number of different transition zone tissue structures in the human body, such as bone and cartilage tissue, tendon / ligament-bone interface tissue, heart valve tissue, etc. Therefore, the preparation of bionic scaffolds with heterogeneous structures has important tissue engineering significance.

[0004] Currently, there are two main strategies for the design of heterogeneous bionic scaffolds: interlayer gradient and intralayer gradient.

[0005] For interlayer gradient design, for example, in Reference 1 (Bioinspired stratified electrowritten fiber-reinforced hydrogel constructs with layer-specific induction capacity for functional osteochondral regeneration - ScienceDirect[J].Biomaterials,266[2025-06-17].DOI:10.1016 / j.biomaterials.2020.120385.), a three-layer scaffold was designed to simulate the gradual transition from cartilage to subchondral bone by increasing the fiber spacing layer by layer and changing the interlayer angle; in Reference 2 (MeltElectrowriting of Graded Porous Scaffolds to Mimic the Matrix Structure of the Human Trabecular Meshwork. ACS Biomater Sci Eng 2022, 8, 3899.), a three-layer scaffold similar to the human trabecular meshwork was constructed by regulating the fiber spacing and orientation; in Reference 3 (Designing Outside the Box: Unlocking the Geometric Freedom of Melt Electrowriting using Microscale Layer Shifting[J].Advanced Materials, 2020, 32(28).DOI:10.1002 / adma.202001874.) further proposed an interlayer path offset strategy, which constructed a new structure by increasing the displacement layer by layer, significantly improving the design freedom of the MEW bracket.

[0006] However, although the interlayer gradient design is relatively simple, it is not suitable for situations where the structural gradient characteristics are coplanar with the fiber direction, such as tendon / ligament-bone interface tissue and heart valve tissue. For these application scenarios, the strategy of "partitioned homogeneous structure design + inter-region splicing" is currently mainly used to achieve intra-layer gradient. For example, the document 4 (Fabrication of bioinspired grid-crimp micropatterns by melt electrospinning writing for bone-ligament interface study[J].Biofabrication, 2022, 14(2).DOI:10.1088 / 1758-5090 / ac4ac8.) designed a grid-crimp pattern, with a 0 / 90° grid at the bone end and a wavy pattern at the ligament end. The two interface areas are composed of overlapping patterns.

[0007] Reference 5 (Spatially Heterogeneous Tubular Scaffolds for In Situ HeartValve Tissue Engineering Using Melt Electrowriting[J].Advanced FunctionalMaterials, 2022, 32(21).) Based on reference 4, an enhanced suture structure was additionally designed in the interface area using a dedicated algorithm;

[0008] Different from the heterogeneous patterns formed by partitioning, reference 6 (Melt electrowriting of high-precision diamond-square bi-phasic scaffolds and influence on mechanical characteristics through path planning[J].Materials Letters, 2025, 385(000).DOI:10.1016 / j.matlet.2025.138175.) prepared a diamond-square biphasic scaffold, using clever path design to make the square grid pattern transition to the diamond in a continuous manner, forming a seamless printing path.

[0009] However, the above-mentioned intra-layer gradient design strategy still has key limitations: first, the internal structure of each region is homogeneous, but when it is spliced ​​or connected at the interface, the continuity and smoothness of the structure of each region do not match, there are structural mutations and significant inter-regional interfaces, and both the structure and mechanical properties deviate from the continuous gradient characteristics of the extracellular matrix of natural tissue. Under cyclic tensile loads, such discontinuous transition structures will cause stress concentration at the interface and premature failure due to the mismatch of the deformation behavior of adjacent regions; second, as the microstructure domains and their transition interfaces need to be independently parameterized, the complexity of path generation increases exponentially, which restricts the large-scale preparation of biomimetic gradient scaffolds.

[0010] Therefore, it is of great significance to study a melt electrostatic direct writing method for preparing a polymer fiber scaffold with continuous gradient structure to solve the above problems. Summary of the Invention

[0011] The purpose of the present invention is to solve the problems existing in the prior art and to provide a melt electrostatic direct writing method for preparing a polymer fiber scaffold with a continuous and gradient structure.

[0012] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0013] A melt electrostatic direct writing method for preparing a polymer fiber scaffold with a continuous and gradient structure comprises the following steps:

[0014] Step 1: Design a basic homogeneous pattern based on the transition interface characteristics of the tissue to be repaired and discretize it into a dense and ordered point array: ;

[0015] Step 2: Design nonlinear transformation functions f and g according to the structural change characteristics at the transition interface. Use the nonlinear transformation functions f and g to transform the points of R Mapped one by one ,in , , i is the point number, thus getting the point sequence ;

[0016] Step 3: Point Array After equidistant sampling (to reduce point density), the expected printing path is obtained ;

[0017] Step 4: Based on the expected printing path, melt electrostatic direct writing is performed to produce a polymer fiber scaffold with a continuous gradient structure.

[0018] As the preferred technical solution:

[0019] In the melt electrostatic direct writing method for preparing a structurally continuous gradient polymer fiber scaffold as described above, the basic homogeneous pattern in step 1 is a continuous closed line that can be completed in one stroke; and the distance between adjacent dots in the dense and orderly dot array is less than 0.1 μm.

[0020] In the melt electrostatic direct writing preparation method of a structural continuous gradient polymer fiber scaffold as described above, in step 1, if the transition interface of the tissue to be repaired is a ligament-bone interface or a tendon-bone interface, the basic homogeneous pattern is a 0 / 90° grid, and the grid side length of the basic homogeneous pattern is 0.02~2 mm; if the transition interface of the tissue to be repaired is a heart valve, the basic homogeneous pattern is a honeycomb grid or a diamond grid, and the grid side length of the basic homogeneous pattern is 0.05~2 mm.

[0021] As described above, in the melt electrostatic direct writing method for preparing a polymer fiber scaffold with a continuous gradient structure, the nonlinear transformation functions f and g in step 2 satisfy the Jacobian formula This holds true for any point sequence in the basic homogeneous pattern R.

[0022] The choice of nonlinear transformation function is determined by the deformation effect expected by the user. If a wave effect is expected, a univariate trigonometric transformation can be selected. , where and is the wave number, and is the phase shift, 、 Indicates the amplitude of wave deformation. As its value increases, the wave fluctuation becomes more obvious. If a periodic density effect is expected, a two-variable trigonometric transformation can be selected. or , where 、 Indicates the intensity of periodic oscillation deformation. The larger the value, the more severe the deformation. 、 To fine-tune the parameters of the deformation feature, Adjust the linear displacement in the X direction, Adjust the linear displacement in the Y direction; if you want to produce a ripple effect, you can first list the origin coordinates Convert to polar coordinates ,Right now , , and then complete the ripple transformation in polar coordinate form, that is, , where represents the reference coefficient in the radial equation, 、 Determines the intensity of the ripples and affects the contrast intensity of the pattern. represents the frequency, which determines how many waves appear within a given radial distance. Represents the exponential decay factor, by adjusting The amplitude of the ripple can be reduced as the radial distance increases, and finally Convert back to Cartesian coordinate form , where the parameters can be =1, =0.025, =0, =10 or =1, =0.025, =0.5, =20, etc. If a flower-shaped effect is expected, use the flower-shaped transformation in polar coordinate form , where the cosine term The angular periodicity is determined, where n is an integer that directly determines the number of petals (e.g., n=5 generates five-fold rotational symmetry), and the exponential decay factor Adjust the size of the petals along the radial direction, Controls the size gradient from the center to the edge, is the base coefficient, Controls the intensity of the flower effect, where the parameter can be =2, =1, =1, n=8 or =2, =5, =5, n=4, etc. If a vortex effect is expected, the vortex transformation in polar coordinate form is used. , where represents the base coefficient, E represents the radial attenuation rate of angular displacement, and the formula produces a spiral effect through two coupling mechanisms: radial expansion regulation, Introduced radial expansion ( >0) or shrinkage ( <0), and decays exponentially with the increase of radius R; Angle accumulation: A gradual distortion deformation is created, where the parameters Controls the maximum distortion strength at the origin (R=0), where the parameter can be =1, =2, =0.1, =3, etc., as a special case of vortex transformation, such as =0, a local circular expansion (B4>0) or contraction (B4<0) effect is produced; in the above nonlinear transformation functions, A1~A5, B1~B4, C1~C5, D1~D2, E, ~ , etc. are user-adjustable parameters.

[0023] One or more nonlinear transformations in step 2 can be flexibly combined and applied in sequence to achieve a composite transformation, that is, the initial point sequence R is transformed once to obtain r1, r1 is transformed twice to obtain r2, and so on, until the desired pattern point sequence r is obtained. n .

[0024] Composite transformations can also be obtained by combining nonlinear transformations with linear transformations; linear transformations include translations, rotations, or general canonical transformations; the translation transformation function is , , the rotation transformation function is , , the regular transformation function is , ,in .

[0025] The combination of nonlinear transformation and linear transformation is generally used as a unit in the following way: "first linear transformation + nonlinear transformation + second linear transformation", where the second linear transformation is the inverse transformation of the first linear transformation; a combination can contain any number of units.

[0026] If the deformation region needs to be limited, the coefficients (A1, A2, C1, C1, etc.) in the above-mentioned single-variable or double-variable trigonometric transformation functions or the exponential decay terms ( 、 、 and ) can be replaced by the restricted factor , Corresponding to a specific limited area (the limited area is customized by the user), inside the limited area ( ) applies full deformation, external ( ) does not deform, in the boundary transition area, The value linearly decays from 1 to 0 from the inner edge to the outer edge of the transition area.

[0027] In the melt electrostatic direct writing method for preparing a structurally continuous gradient polymer fiber scaffold as described above, the sampling distance in step 3 is 10-200 μm. The sampling distance refers to selecting a point at a certain distance (e.g., 10 μm), and deleting points with a distance less than this value.

[0028] In the melt electrostatic direct writing method for preparing a polymer fiber scaffold with a continuously gradient structure, the specific process of step 4 is as follows: selecting an appropriate jet lag length value and jet deposition rate, generating the actual motion trajectory and motion rate of the XY moving platform based on the expected printing path and curve printing theory, and executing the printing process, including the following steps:

[0029] Step a: Based on the expected fiber diameter Calculating the jet deposition rate , and monitor the current jet lag length value l in real time, where The melt flow rate can be adjusted by the feed air pressure; the online monitoring device for melt electrowriting jet lag in patent CN202510392215.0 is used to monitor the jet lag length in the curve printing process in real time by adjusting the feed air pressure; the online monitoring device for melt electrowriting jet lag includes a servo motor, an industrial camera, an annular guide rail and a load-bearing bracket. The servo motor and the industrial camera are both fixed on the slider of the annular guide rail. The servo motor drives the industrial camera to move along the annular guide rail. The annular guide rail is fixed to the gantry of the melt electrowriting equipment through the load-bearing bracket. The annular guide rail is coaxial with the center line of the melt electrowriting nozzle; the servo motor drives the industrial camera to move on the annular guide rail at a certain speed, takes pictures in real time during the movement and obtains the jet lag length in the curve printing process; the speed at which the servo motor drives the industrial camera to move on the annular guide rail is ; Where R is the radius of the annular guide rail, in mm; 、 and are the local curvature of the deposition trajectory, the unit tangent vector and the deposition rate at the real-time deposition point of the fiber, respectively. The unit of the local curvature of the deposition trajectory is mm -1 , the unit of the unit tangent vector is 1, and the unit of the deposition rate is mm / s;

[0030] Step b: Adjust process parameters such as voltage and inter-electrode spacing so that the electrostatic direct writing system can control the jet lag length within the range of 1-3 mm under stable printing conditions to ensure the stability of the printing process, and continuously adjust the printing path based on the monitored jet lag length l;

[0031] Step c: Generate the actual motion trajectory of the XY mobile platform based on the curve printing theory under steady state and movement rate And input into the motion platform controller of the electrostatic direct writing system to implement the printing process.

[0032] As described above, the melt electrostatic direct writing method for preparing a polymer fiber scaffold with a continuous gradient structure, the fiber diameter in step a is 5~50 μm.

[0033] The actual motion trajectory of the XY moving platform in step c is the melt electrostatic direct writing method for preparing a polymer fiber scaffold with a continuous gradient structure as described above. and movement rate , calculated by formulas (1) to (4);

[0034] (1);

[0035] (2);

[0036] (3);

[0037] (4);

[0038] in, Represents the difference operation, i is the point number.

[0039] As described above, a melt electrostatic direct writing method for preparing a structural continuous gradient polymer fiber scaffold is provided, wherein the material of the polymer fiber scaffold is polycaprolactone (PCL), polylactic acid (PLA) or polylactic acid-glycolic acid copolymer (PLGA).

[0040] Beneficial effects:

[0041] (1) The present invention improves the flexibility of melt electrostatic direct writing printing path design through matrix or function transformation, while increasing the freedom of personalized design and the interactivity of the design process, lowering the threshold of printing path design and greatly improving the customizability of path design.

[0042] (2) The present invention utilizes nonlinear transformation functions f and g to produce a polymer fiber scaffold with continuous structural gradient, which can imitate the smooth transition interface between tissues and ensure the smooth connection and transition at the interface between different tissues, thereby improving the structural and mechanical biomimetic degree of the polymer fiber scaffold, making the stress distribution more uniform when the designed scaffold bears load, improving the stress concentration phenomenon, and also greatly improving the diversity and richness of the microscopic pattern; in addition, the present invention can meet the situation where the structural gradient feature is coplanar with the fiber direction, that is, realizing the gradient of structure within the same layer, which is of great significance to the melt electrostatic direct writing technology and its facing tissue engineering and biomedical fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 Schematic diagram of a 0 / 90° grid as the basic homogeneous pattern of the present invention;

[0044] Figure 2 This is a schematic diagram of a basic homogeneous pattern after functional heterogeneity in the present invention;

[0045] Figure 3 Schematic diagram of the interface of the transition interface of the organization in the present invention;

[0046] Figure 4 A schematic diagram of a transition interface organized in the prior art;

[0047] Figure 5Schematic diagram of the same transition interface selected during simulated tensile testing of a continuously graded polymer fiber scaffold of the present invention and a scaffold directly stacked in the prior art; in the figure, a is a schematic diagram of the transition interface selected for the continuously graded polymer fiber scaffold of the present invention, and b is a schematic diagram of the transition interface selected for the scaffold directly stacked in the prior art;

[0048] Figure 6 for Figure 5 Figure 2 shows the simulated tensile test results of the same transition interface selected in [1]. In the figure, a is the simulation result of the continuous gradient polymer fiber scaffold of the present invention, and b is the simulation result of the scaffold directly superimposed in the prior art. S, Mises, stands for Mises stress, which is an equivalent stress index widely used in engineering fields, and its unit is MPa.

[0049] Figure 7 This is a printed physical image of the continuous gradient polymer fiber scaffold of the present invention and the scaffold directly superimposed in the prior art; in the figure, a is a printed physical image of the continuous gradient polymer fiber scaffold of the present invention, and b is a printed physical image of the scaffold directly superimposed in the prior art;

[0050] Figure 8 The stress-strain curve diagram of the continuous gradient polymer fiber scaffold of the present invention and the scaffold directly superimposed in the prior art. DETAILED DESCRIPTION

[0051] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0052] The test methods for the relevant performance indicators in the present invention are as follows:

[0053] Elastic modulus, yield stress, and tensile strength: A structural continuous gradient polymer fiber scaffold and a directly stacked scaffold were used as specimens. A high-strength, high-modulus fiber tensile tester was used. The 5 mm × 12 mm specimens were secured with pneumatic clamps at 20°C and 65% relative humidity to reduce slippage. The specimens were then stretched at a rate of 40 mm / min while force-displacement data was continuously recorded until fracture. The elastic modulus, yield strength, and tensile strength were calculated based on the obtained stress-strain curves.

[0054] A melt electrostatic direct writing method for preparing a polymer fiber scaffold with a continuously gradient structure, comprising the following steps:

[0055] Step 1: Design a basic homogeneous pattern based on the transition interface characteristics of the tissue to be repaired and discretize it into a dense and ordered point array: If the transition interface of the tissue to be repaired is a ligament-bone interface or a tendon-bone interface, the basic homogeneous pattern is a 0 / 90° grid composed of continuous closed lines that can be completed in one stroke, and the grid side length of the basic homogeneous pattern is 0.02-2 mm. If the transition interface of the tissue to be repaired is a heart valve, the basic homogeneous pattern is a honeycomb grid or a diamond grid composed of continuous closed lines that can be completed in one stroke, and the grid side length of the basic homogeneous pattern is 0.05-2 mm. The distance between adjacent points of the dense and orderly point array is less than 0.1 μm.

[0056] Step 2: Design nonlinear transformation functions f and g according to the structural change characteristics at the transition interface. Use the nonlinear transformation functions f and g to transform the points of R Mapped one by one ,in , , i is the point number, thus getting the point sequence ; Nonlinear transformation functions f and g satisfy the Jacobi form This holds true for any point sequence in the basic homogeneous pattern R;

[0057] Step 3: Point Array The expected printing path is obtained after equidistant sampling ; Among them, the sampling distance is 10~200 μm;

[0058] Step 4: Select appropriate jet lag length and jet deposition rate, generate the actual motion trajectory and motion rate of the XY moving platform based on the expected printing path and curve printing theory, and execute the printing process, including the following steps:

[0059] Step a: Based on the expected fiber diameter Calculating the jet deposition rate , and monitor the current jet lag length value l in real time, where is the melt flow rate; the fiber material is polycaprolactone (PCL), polylactic acid (PLA) or polylactic acid-glycolic acid copolymer (PLGA), and the fiber diameter 5~50 μm;

[0060] Step b: Adjusting process parameters so that the electrostatic direct writing system can control the jet lag length within the range of 1-3 mm under stable printing conditions and continuously adjusting the printing path according to the monitored jet lag length l;

[0061] Step c: Generate the actual motion trajectory of the XY mobile platform based on the curve printing theory under steady state and movement rate And input into the motion platform controller of the electrostatic direct writing system to implement the printing process; among them, the actual motion trajectory of the XY moving platform and movement rate , calculated by formulas (1) to (4);

[0062] (1);

[0063] (2);

[0064] (3);

[0065] (4);

[0066] in, Indicates differential operation, i is the point number;

[0067] Based on the expected printing path, melt electrostatic direct writing is performed to produce a polymer fiber scaffold with continuous gradient structure.

[0068] Taking the preparation of bone-ligament tissue bionic scaffold as an example, the above preparation method is adopted, wherein:

[0069] In step 1, the transition interface of the tissue to be repaired is the ligament-bone interface, and the basic homogeneous pattern is a 0 / 90° grid composed of continuous closed lines that can be completed in one stroke, such as Figure 1 As shown, the grid side length of the basic homogeneous pattern is 500 μm, and the adjacent dot distance of the dense and orderly dot array is 0.09 μm;

[0070] In step 2, a wave effect is expected to be generated according to the structure of the bone-ligament tissue biomimetic scaffold to be prepared, so a univariate trigonometric transformation is selected, and the wave effect is limited to the left side of the bone-ligament tissue biomimetic scaffold and smoothly transitioned to a straight line effect (i.e., area It decays linearly from 1 to 0, achieving the transition from curve to straight line. The amplitude changes smoothly to prevent discontinuous jumps in the deformation boundary and stress concentration under the force of the bracket. The pattern of the ligament-bone interface is as follows: Figure 3 As shown, to simulate the structural gradient from ligament to bone, the point array is obtained (According to the point list The obtained basic homogeneous pattern after deformation is as follows Figure 2 As shown); where the univariate trigonometric transformation is: , where is 1, and Both are 1, and They are and , from which we get the point sequence The specific operations are as follows:

[0071] Take the points contained in the basic pattern (0, 0), (0.1, 0), (0.2, 0) as an example, point (0, 0) after the deformation equation , , the coordinates are (0, 0.5), similarly we can get (0.1, 0.5), (0.2, 0.49), the remaining points can be calculated using the same method to obtain the deformed coordinates;

[0072] The sampling distance in step 3 is 100 μm;

[0073] In step 4, the printing temperature is 23°C, the printing humidity is 35%, the fiber material is polycaprolactone (manufacturer is Swedish Perstorp, model number is CAPA6500), and the fiber diameter is is 30 μm, and the melt flow rate Q is 7.63 μL / h;

[0074] First, the fiber deposition rate is calculated as 3 mm / s, and then calculate the local curvature of each ordered point array according to formulas (1) to (4): With the unit tangent vector ,by (0, 0.5), (0.1, 0.5), Taking (0.2, 0.49) as an example, the ordered point sequence is calculated by formulas (1) and (2): The local curvature at 0.996 mm -1 , the unit tangent vector (1.1, −0.05);

[0075] Then, the actual motion trajectory of the XY mobile platform is generated based on the curve printing theory under steady state and movement rate , and input the motion platform controller of the electrostatic direct writing system to perform the printing process to obtain the bone-ligament tissue bionic scaffold; wherein, the number of printing layers is 8, and the printing path is continuously adjusted according to the observed real-time jet lag length l during the printing process. For example, if the jet lag length l is 1 mm, then Point real-time trajectory ,rate 4.23 mm / s.

[0076] The final structure of the continuous gradient polymer fiber scaffold (such as Figure 7 Middle a, Figure 8 The elastic modulus of the steel is 134.2 MPa, the yield stress is 17.9 MPa, and the tensile strength is 22.5 MPa.

[0077] Referring to the reference 4 (Fabrication of bioinspired grid-crimp micropatterns by meltelectrospinning writing for bone-ligament interface study[J].Biofabrication,2022, 14(2).DOI:10.1088 / 1758-5090 / ac4ac8.), a scaffold with 8 layers directly stacked (i.e., the tissue pattern on one side is printed first, and then the tissue pattern on the other side is printed, ensuring that the two parts have a certain area of ​​overlap to form a whole), wherein the transition interface is as follows Figure 4 As shown; directly stacked brackets (such as Figure 7 Middle b, Figure 8 The elastic modulus of the steel is 66.9 MPa, the yield strength is 13.2 MPa, and the tensile strength is 17.8 MPa.

[0078] Abaqus software was used to perform tensile tests on the same transition interface of the structured continuous gradient polymer fiber scaffold and the directly superimposed scaffold model to observe whether the stress distribution is uniform. The results are as follows: Figure 5 As shown in the figure, it can be seen that compared with the direct stacking structure, the stress distribution in the tensile direction of the continuous gradual transition method is more uniform, and the stress concentration phenomenon is improved;

[0079] The above-prepared continuous gradient polymer fiber scaffold and the directly stacked scaffold were directly subjected to tensile testing, and the results are as follows: Figure 6 As shown in the figure, it can be seen that under the same strain, the structural continuous gradient polymer fiber scaffold has a higher tensile strength (UTS) or yield strength and a larger elastic modulus, which is conducive to bearing a larger load.

Claims

1. A melt electrostatic direct writing method for preparing a polymer fiber scaffold with a continuous gradient structure, characterized in that The steps include: Step 1: Design a basic homogeneous pattern based on the transition interface characteristics of the tissue to be repaired and discretize it into a dense and ordered point array: ; Step 2: Design nonlinear transformation functions f and g according to the structural change characteristics at the transition interface. Use the nonlinear transformation functions f and g to transform the points of R Mapped one by one ,in , , i is the point number, thus getting the point sequence ; Step 3: Point Array The expected printing path is obtained after equidistant sampling ; Step 4: Based on the expected printing path, melt electrostatic direct writing is performed to produce a polymer fiber scaffold with a continuous gradient structure.

2. The method for preparing a polymer fiber scaffold with a continuous and gradient structure by melt electrostatic direct writing according to claim 1, characterized in that: The basic homogeneous pattern in step 1 is a continuous closed line that can be completed in one stroke; the distance between adjacent dots in the dense and orderly dot array is less than 0.1 μm.

3. The melt electrostatic direct writing method for preparing a polymer fiber scaffold with a continuous and gradient structure according to claim 1, characterized in that: In step 1, if the transition interface of the tissue to be repaired is the ligament-bone interface or the tendon-bone interface, the basic homogeneous pattern is a 0 / 90° grid with a grid side length of 0.02-2 mm. If the transition interface of the tissue to be repaired is a heart valve, the basic homogeneous pattern is a honeycomb grid or a diamond grid with a grid side length of 0.05-2 mm.

4. The method for preparing a polymer fiber scaffold with a continuous and gradient structure by melt electrostatic direct writing according to claim 1, characterized in that: In step 2, the nonlinear transformation functions f and g satisfy the Jacobian This holds true for any point sequence in the basic homogeneous pattern R.

5. The melt electrostatic direct writing method for preparing a polymer fiber scaffold with a continuous and gradient structure according to claim 1, characterized in that: The sampling distance in step 3 is 10~200 μm.

6. The melt electrostatic direct writing method for preparing a polymer fiber scaffold with a continuously gradient structure according to claim 1, characterized in that: The specific process of step 4 is as follows: select the appropriate jet lag length value and jet deposition rate, generate the actual motion trajectory and motion rate of the XY mobile platform based on the expected printing path and curve printing theory, and execute the printing process, including the following steps: Step a: Based on the expected fiber diameter Calculating the jet deposition rate , and monitor the current jet lag length value l in real time, where is the melt flow rate; Step b: Adjusting process parameters so that the electrostatic direct writing system controls the jet lag length within the range of 1 to 3 mm under a stable printing state, and continuously adjusting the printing path according to the monitored jet lag length l; Step c: Generate the actual motion trajectory of the XY mobile platform based on the curve printing theory under steady state and movement rate And input into the motion platform controller of the electrostatic direct writing system to implement the printing process.

7. The melt electrostatic direct writing method for preparing a polymer fiber scaffold with a continuously gradient structure according to claim 6, characterized in that: Fiber diameter in step a 5~50 μm.

8. The melt electrostatic direct writing method for preparing a polymer fiber scaffold with a continuously gradient structure according to claim 6, characterized in that: The actual motion trajectory of the XY mobile platform in step c and movement rate , calculated by formulas (1) to (4); （1）； （2）； （3）； （4）； in, Represents the difference operation, i is the point number.

9. The melt electrostatic direct writing method for preparing a polymer fiber scaffold with a continuously gradient structure according to claim 1, characterized in that: The material of the polymer fiber scaffold is polycaprolactone, polylactic acid or polylactic acid-glycolic acid copolymer.

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