Method for evaluating the formability of a reversible crosslinking self-healing 3D printing ink

Abstract

This invention discloses a method for evaluating the formability of reversible cross-linked self-healing 3D printing ink, belonging to the technical field of 3D printing material evaluation methods. This invention utilizes an extrusion 3D printer to print multi-layer scaffolds. By comparing the printed physical scaffolds with scaffold models based on finite element simulation, it analyzes collapse and fusion. Combined with the evaluation of the roundness of the fused scaffolds and the shape changes of the scaffolds after collapse, it constructs an evaluation method suitable for the formability of reversible cross-linked self-healing colloidal gel inks in 3D printing. It includes quantitative calculation methods for ink rheological properties, visualized deformation, and formability, applicable to the evaluation of various reversible cross-linked self-healing inks.

Description

Technical Field

[0001] This invention belongs to the technical field of 3D printing material evaluation methods, specifically relating to a method for evaluating the formability of a reversible cross-linked self-healing 3D printing ink. Background Technology

[0002] Extrusion 3D printing is a technology that melts or softens materials (such as plastics, metals, and biogels) and then extrudes and builds them layer by layer through a nozzle. Due to its flexibility and versatility, extrusion 3D printing plays a vital role in various industries and continuously drives technological innovation and application expansion. It is widely used in manufacturing, construction, food processing, and biomedical engineering. In the biomedical field, extrusion 3D printing is widely applied due to its simplicity, wide range of usable materials, and ease of cell printing. It can be used to print scaffolds with specific porosity and mechanical properties, which can be used for tissue engineering and drug testing.

[0003] The precision of extrusion 3D printing is determined by a combination of factors, including equipment precision, extrusion parameters, material formability, and nozzle design. Material formability is primarily determined by its rheological properties; ideal bio-inks should exhibit good shear-thinning behavior and appropriate yield stress. Shear-thinning behavior helps reduce shear forces on cells during printing, thus protecting cell viability; yield stress helps the printed structure maintain its shape and resist deformation caused by gravity or surface tension. Furthermore, the self-healing properties of inks are particularly important for printing high-shape-fidelity scaffolds. Self-healing hydrogels can restore their binding force and initial structure, properties, and function after extrusion. Combined with shear-thinning properties, this not only allows for the safe printing of cells but also ensures the shape stability of the printed structure. However, current research on ink self-healing primarily focuses on testing modulus recovery after high strain amplitude or high oscillation frequency, and a systematic evaluation method for self-healing is lacking. The evaluation of the impact of self-healing on 3D printing formability also requires further development.

[0004] Currently, inks used for extrusion 3D printing are mainly water-based gels, which can be composed of polymers (such as Pluronic F127), polysaccharides (such as chitosan and cellulose), proteins (such as silk fibroin and gelatin), and inorganic materials (such as hydroxyapatite, tricalcium phosphate, graphene, and glass). Most water-based gels have poor self-healing properties, primarily due to three reasons: First, the lack of reversible interactions, such as hydrogen bonds and hydrophobic interactions, constitutes a small proportion in hydrogels, and there is a lack of dynamically reversible chemical bonds, such as hydrazone bonds, imine bonds, and disulfide bonds. Second, the irreversibility of chemical cross-linking; some hydrogels form stable network structures through chemical cross-linking, but these cross-linking bonds (such as covalent bonds) are difficult to reform after being broken, limiting the self-healing ability of the hydrogel. Third, a single cross-linking mechanism may limit the ink's self-healing properties; a single cross-linking mechanism may not provide sufficient self-healing capacity. In contrast, combining multiple mechanisms of physical and chemical cross-linking can improve self-healing properties. To address the issue of low self-healing rates due to the lack of reversible cross-linking in hydrogel inks, we can improve self-healing properties by increasing the specific surface area, such as through colloidal gels constructed from nanoparticles; and by introducing numerous reversible interactions, such as abundant hydrogen bonds or van der Waals forces generated by interactions between hydrophilic polymers or protein surfaces. The rich variety of reversible cross-links and the dynamically reorganized mechanical entanglements within these inks result in diverse rheological properties, including varying viscoelasticity, strain rate dependence, flow characteristics, infinite-chain flow relaxation time, and finite relaxation time. Furthermore, the combination of these rheological properties leads to self-healing properties in terms of macroscopic modulus and viscosity. However, due to the lack of methods for evaluating the impact of self-healing on 3D printing formability, the influence of self-healing on printing remains unclear.

[0005] Currently, there are two main evaluation methods applicable to extrusion 3D printing: one is roundness (Pr). Ideally, ink fusion should not occur on orthogonal paths. Under the influence of gravity and low ink mechanical strength, fusion is unavoidable, so Pr is usually below 1. If the ink is difficult to extrude, when Pr exceeds 1, it may lead to serrated filaments. The second is the area change rate (Ar), which is the ratio of the actual printing gap to the ideal gap. The printing gap is usually smaller than the theoretical area without deformation, extrusion expansion, or fusion. However, when evaluating the formability of high-strength materials, Ar and Pr may not reflect significant differences between two inks in low-strength materials. In addition, self-healing inks based on reversible crosslinking usually have complex rheological properties, and different inks may have similar formability. Ar and Pr are difficult to accurately evaluate self-healing inks based on reversible crosslinking. This is because Ar is more significantly affected by ink viscosity, while Pr is more significantly affected by modulus. Essentially, Pr is suitable for evaluating the formability of medium-to-high strength inks, while Ar is more effective for medium-to-low strength inks.

[0006] In summary, while there is a consensus on the impact of ink strength on printing, the effect of ink self-healing properties on 3D printing, especially on formability, remains unclear. This has prompted researchers in additive manufacturing to investigate quantitative methods for self-healing properties and their impact on formability. Currently, most hydrogel inks exhibit poor self-healing properties and insufficient controllability of viscoelasticity, making them unsuitable for constructing inks with diverse rheological properties. Based on this, nanoscale particles are prepared using hydrogel building blocks. The larger specific surface area of ​​nanoparticles increases surface interactions, and the shear-thinning properties required for extrusion printing can be easily achieved through the movement and repositioning of the particle structure under high amplitude or shear. Furthermore, reversibly cross-linked inks can be constructed using natural polymers such as gelatin and silk fibroin, or hydrophilic inorganic materials such as hydroxyapatite and nanoclay, which possess abundant reversible interaction groups on their surfaces. This reversible interaction promotes colloidal network recombination after shearing is removed, thereby achieving ink self-healing, making it an ideal material for rheological research and 3D printing. By leveraging the rich surface interactions and diverse self-assembly structures of reversible cross-linked self-healing inks, viscoelasticity control of the ink can be achieved, which can be used to study the rationality of different printing evaluation methods. Analyzing the disadvantages of existing evaluation methods and constructing new, widely applicable formability evaluation parameters is of great significance for guiding the construction and extrusion parameters of 3D printing inks. Summary of the Invention

[0007] Therefore, the purpose of this invention is to provide a method for evaluating the formability of reversible cross-linked self-healing 3D printing inks. This invention achieves quantitative characterization of self-healing properties based on particulate cross-linked self-healing inks, analyzes the influence of viscoelasticity on the formability of extrusion 3D printing, and constructs a widely applicable method for evaluating ink formability.

[0008] The objective of this invention is achieved through the following means:

[0009] This invention provides a method for evaluating the moldability of reversible cross-linked self-healing 3D printing ink, comprising the following steps:

[0010] (1) Preparation of reversible cross-linking self-healing ink: Mix reversible cross-linking self-healing material with deionized water to prepare colloidal inks with different volume fractions;

[0011] (2) Test the rheological properties of reversible cross-linking self-healing ink: Take 0.35 ml of reversible cross-linking self-healing ink, apply it to the base plate of the rheometer, and then select a 20 mm parallel plate for testing. The working distance is set to 1 mm and the axial force is about 0.1 N.

[0012] (3) Stents with single-layer and eight-layer structures were printed using reversible cross-linking self-healing ink. After that, the process was allowed to wait 20 to 60 minutes to ensure that the scaffold relaxation was complete. The roundness Pr of the orthogonal unit regions of the printed scaffold was then calculated. The calculation method is Pr = L 2 / 16A, where L is the perimeter of the region and A is the area of ​​the region; calculate the rate of change of the area of ​​the orthogonal unit region of the printed scaffold, Ar, by calculating Ar = A / A0, where A is the actual area of ​​the tested region and A0 is the ideal area when the scaffold does not fuse or collapse; assign equivalent values ​​to Ar and Pr, and calculate the formability index Fid, which is calculated as follows:

[0013]

[0014] Where D P and D A The standard deviations of Pr and Ar are respectively, U P and U A are the average values ​​of Pr and Ar, respectively, and e is the natural constant.

[0015] (4) Using the storage modulus, composite viscosity, modulus self-healing rate and viscosity self-healing rate measured by the rheometer as variables, fit their relationship with Ar, Pr and Fid.

[0016] Based on the above technical solution, the reversible cross-linked self-healing material mentioned in step (1) further includes gelatin nanoparticles, silk fibroin nanoparticles and nano-clay.

[0017] Based on the above technical solution, the volume fractions mentioned in step (1) are 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 and 0.5 respectively.

[0018] Based on the above technical solution, further, the test described in step (2) mainly includes two consecutive test steps, which need to be tested after sample preparation:

[0019] A. At a fixed frequency of 1 Hz / s, continuous tests of time scan 1, amplitude scan 1, and time scan 2 are performed. The test time for time scan 1 and time scan 2 is 60 minutes, and the strain is controlled at 0.1%. The time of amplitude scan 1 is determined by the actual test of the rheometer, and it is only necessary to control the strain to change nonlinearly from 0.1% to 100%. The three tests are performed sequentially, and the average storage modulus G of time scan 1 and time scan 2 is calculated from the last 60 seconds of time scan 1 and the first 60 seconds of time scan 2. ’ 1 and G ’ 2. The modulus self-healing rate is G ’ 2 / G ’ 1;

[0020] B. At a fixed frequency of 1 Hz / s, continuous tests were performed with time scan 3, peak hold 1, and time scan 4. The test time for time scan 3 and time scan 4 was 60 minutes, and the strain rate was controlled at 0.1 s. -1 The peak value was maintained at 1 for 60 seconds, and the strain rate was controlled at 30 seconds. -1 The three tests were performed sequentially, and the average combined viscosity V of time scan 3 and time scan 4 was calculated from the last 60 seconds of time scan 3 and the first 60 seconds of time scan 4. ’ 1 and V ’ 2. Viscosity self-healing rate is G ’ 2 / G ’ 1.

[0021] Based on the above technical solution, further, the outer side of the bracket in step (3) is a cylindrical structure with a diameter of 20mm, and the inner side is a rectangular structure formed by six equally spaced horizontal and vertical paths arranged orthogonally, with each path having a length of 14.14mm; the bracket is composed of 8 layers of the above structure, with each layer having a thickness of 0.4mm.

[0022] Based on the above technical solution, further, in step (3), the value range of the formability index Fid is 0-1, and the larger the value, the better the formability.

[0023] Based on the above technical solution, further, in step (4), the fitting is performed using a fourth-order polynomial in Origin.

[0024] The advantages of this invention over the prior art are as follows:

[0025] This invention demonstrates the feasibility of Ar and Pr in gelatin nanoparticles, silk nanoparticles, and nanoclay materials, and establishes new parameters to quantify fidelity (Fid). This is applicable to the evaluation of the moldability of reversible cross-linked self-healing gels. By comparing the fidelity of different colloidal gels, the relationship between good and bad printability and rheological properties of materials is obtained, thereby guiding the rheological parameters for the design of bio-inks. Attached Figure Description

[0026] To more clearly illustrate the embodiments of the present invention, the accompanying drawings involved in the embodiments will be briefly described below.

[0027] Figure 1 An 8-layer orthogonal scaffold printed with gelatin, nanoclay, and silk fibroin inks;

[0028] Figure 2 The results are the rheological test results of gelatin (frequency scan, shear thinning, modulus self-healing and viscosity self-healing).

[0029] Figure 3The results of rheological tests on silk fibroin (frequency scan, shear thinning, modulus self-healing, and viscosity self-healing);

[0030] Figure 4 The results of rheological tests on nanoclay (frequency scan, shear thinning, modulus self-healing, and viscosity self-healing);

[0031] Figure 5 The local fusion of inks with different volume fractions of gelatin, silk fibroin and nano-clay after printing;

[0032] Figure 6 The significance of three evaluation parameters (Ar, Pr, and Fid) on colloidal inks with different volume fractions and components was analyzed. Where a is the Ar evaluation parameter, b is the Pr evaluation parameter, and c is the Fid evaluation parameter. Detailed Implementation

[0033] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.

[0034] Example 1

[0035] This embodiment controls the self-healing and viscoelasticity of colloidal particles by varying the surface interactions of the particles. Based on this, a quantitative analysis is performed, and a 3D-printed scaffold with an eight-layer structure and uniform orthogonal distribution is constructed. After printing with different self-healing inks, the collapse and fusion of the scaffold are visualized and analyzed. The relationship between existing evaluation parameters Pr and Ar and the self-healing and viscoelasticity of the ink is calculated. It is found that the existing evaluation parameters are only applicable within a limited range of rheological characteristics. Therefore, we combine the two evaluation parameters to construct an evaluation method with wider applicability.

[0036] Extrusion 3D printing is a technology widely used in tissue engineering and biomedicine. It constructs complex three-dimensional structures by precisely controlling the extrusion and assembly of bio-inks. The following is a detailed description of ink preparation and operational steps for extrusion 3D printing:

[0037] Preparation of bio-ink: Bio-ink is a key material in 3D printing and needs to have appropriate rheological properties to ensure the smooth progress of the printing process.

[0038] The surface of gelatin nanoparticles is rich in amino and carboxyl groups, making them more hydrophilic and easier to swell. The thickening of the hydration layer increases the volume fraction and interparticle chain entanglement, further fixing the colloidal structure. Therefore, the colloidal gel formed from gelatin nanoparticles exhibits high strength, low volume, and good self-healing properties. The soft gelatin nanoparticles can deform upon injection, making injection easier.

[0039] Nanoclay is a type of sheet-like montmorillonite. Upon absorbing water, the positively charged edges and negatively charged surfaces bond together through electrostatic interactions, forming a "house of cards" structure and a gel. This structure can be modified post-injection and exhibits self-healing properties.

[0040] Silk fibroin nanoparticles are less hydrophilic than gelatin nanoparticles and nanoclay. Silk fibroin and nanoclay, influenced by β-sheets, form nanoparticles. This results in almost no free chains on the surface, thus leading to higher stiffness than gelatin nanoparticles. The gelation of silk fibroin nanoparticles is primarily achieved through weaker van der Waals forces, hydrophobic interactions, and dense stacking. Due to the different compositions and interactions of these three materials, they exhibit different rheological properties. A comparison of the fidelity of various colloidal materials is therefore appropriate.

[0041] Gelatin nanoparticles (approximately 100 nm in dry state) were synthesized according to existing research (Hathout RM, Metally A A. Gelatin nanoparticles[J]. Pharmaceutical Nanotechnology: Basic Protocols, 2019: 71-78.). 10 g of gelatin was dissolved in 200 ml of deionized water and reacted at a constant temperature of 50°C with a magnetic stirring speed of 400 rpm for 30 minutes until the gelatin was completely dissolved. Acetone was then slowly added using a peristaltic pump to form an emulsion at a flow rate of 20 ml / min, with a total addition volume of 800 ml. After emulsification, glutaraldehyde, as a cross-linking agent, was added to fix the shape of the gelatin nanoparticles; the added glutaraldehyde volume was 1 ml. After 8 hours of reaction, 50 ml of 5M glycine solution was added to consume unreacted glutaraldehyde, and the reaction proceeded for 2 hours. The fixed nanoparticles were washed with ethanol, an ethanol-water mixture, and water.

[0042] Silk fibroin nanoparticles (approximately 115 nm in dry state) were supplied by Huanova Biotech (Shenzhen, China). Ethanol was added dropwise to the silk fibroin solution until complete emulsification. The nanoparticles were then washed three times with ethanol and water.

[0043] Laponite XLS(Lap,SiO2:MgO:Li2O:Na2O:P2O5=54.5:26:0.8:5.6:4.1)

[0044] It was purchased from BYK (Germany).

[0045] At room temperature, gelatin nanoparticles, silk fibroin nanoparticles, and Laponite XLS nanoparticles were dissolved in 5 mM HEPES solution to form a suspension of 5 mg / mL, and the pH was adjusted to 7 ± 0.1. After the suspension stabilized for 60 seconds, the diameter and surface zeta potential of the nanoparticles were measured using dynamic light scattering (DLS). Sixty data points were collected for each measurement, with a 1-second interval between each measurement. A total of three measurements were performed, and the results were averaged.

[0046] Table 1. Surface zeta potential and average hydration particle size of gelatin, nanoclay, and silk nanoparticles.

[0047]

[0048] Preparation of reversible cross-linked self-healing ink: Reversible cross-linked self-healing materials (gelatin nanoparticles, silk fibroin nanoparticles and nanoclay) were mixed with deionized water to prepare colloidal inks with different volume fractions of 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 and 0.5.

[0049] Rheological testing: The rheological properties of different colloidal systems were measured at room temperature using a DHR-2 rheometer (DHR, TA Instruments) with a 20 mm parallel plate and a 1000 μm operating gap. Strain-controlled testing was performed in this embodiment: frequency and strain were set to 1 Hz / s and 0.1%, respectively. Viscoelasticity was measured by frequency scanning from 100 Hz / s to 0.1 Hz / s. The self-healing ability of the modulus was measured by amplitude scanning, applying a slight strain (0.1%) over 20 seconds. After the material properties stabilized, a strain sufficient to disrupt the material structure (100%) was applied for 20 seconds, followed by rapid recovery to 0.1% strain. The self-healing ability of viscosity was measured by peak hold, with the same period as the modulus. Shear rates were set to 0.1 and 30 s, respectively. -1 The modulus and viscosity were averaged during the first five seconds of each cycle. Flow scanning measured the shear thinning behavior of these three materials at shear rates ranging from 0.1 to 30 s⁻¹. -1 The viscosity changes, and then the changes are recorded.

[0050] Ink was loaded into a 10 ml syringe with a 260-micron needle. During printing, the extrusion speed was 5 mm / s, and the extrusion volume was controlled to fill 60%, 80%, and 100% of the required needle volume. The height of the first layer was 0.7 mm, and the height of the second layer was 0.22 mm. A double-layer orthogonal support with a diameter of 20 mm × 20 mm was printed using an eight-row path, with each sample printed three times to evaluate its printability. Figure 5 ), Figure 5 In the diagram, 1-1 represents the first single-layer support printed when the volume fraction is 10%, 2-1 represents the first single-layer support printed when the volume fraction is 15%, 3-1 represents the first single-layer support printed when the volume fraction is 20%, and 4-1 represents the first single-layer support printed when the volume fraction is 25%.

[0051] Ink samples were printed using a 400-micron needle, which was used to calculate the collapse rate. The extrusion speed was 5 mm / s, and the needle fill ratio was 80%. The first layer was printed to a height of 0.95 mm, followed by each subsequent layer at a height of 0.4 mm, forming eight cylinders with a diameter of 20 mm; six rows of paths constituted the internal orthogonal structure. These supports were photographed 30 minutes after printing.

[0052] The printed supports were sampled using an equidistant sampling method, with eight grid spaces selected for each support. Twenty-four points of each sample were photographed using a 4x microscope. MATLAB captured the spatial images taken by the optical microscope. Boundaries were automatically located using contrast differences, and the boundary lengths and intervals were exported as pixels. These were then converted using the fixed resolution and scale of the optical microscope.

[0053] Pr (roundness) is determined by Pr = L 2 / 16A is calculated, where L is the perimeter and A is the area; Ar (area collapse ratio) is calculated by Ar = A / A0, where A0 is the area under ideal conditions when the filament does not expand or collapse. Based on the combination of Ar and Pr, and considering the large standard deviation caused by the instability of results at lower concentrations, a new printability evaluation algorithm Fid (fidelity) is established:

[0054]

[0055] Among them, D P and D A The standard deviations of Pr and Ar are respectively, U P and U A Let Pr and Ar be the average values, respectively, and e be the natural constant. The formability index Fid ranges from 0 to 1, with a higher value indicating better formability.

[0056] The storage modulus, composite viscosity, modulus self-healing rate, and viscosity self-healing rate measured by the rheometer were used as variables to fit their relationship with Ar, Pr, and Fid. The fitting was performed using a fourth-order polynomial in Origin, with the formula y = a0 + a1x + a2x. 2 +a3x 3 +a4x 4 Coefficient of determination R 2 The calculation is based on the ratio of the regression sum of squares (SSR) to the total sum of squares (SST), i.e., R0. 2 = SSR / SST. Where SSR is the variance explained by the regression model, and SST is the total variance of the dependent variable. The coefficient of determination R² ranges from 0 to 1.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for evaluating the moldability of a reversible cross-linked self-healing 3D printing ink, characterized in that, Includes the following steps: (1) Preparation of reversible cross-linking self-healing ink: Mix reversible cross-linking self-healing material with deionized water to prepare colloidal inks with different volume fractions; (2) Test the rheological properties of reversible cross-linking self-healing ink: Take 0.35 ml of reversible cross-linking self-healing ink, apply it to the base plate of the rheometer, and then select a 20 mm parallel plate for testing. The working distance is set to 1 mm and the axial force is about 0.1 N. (3) Stents with single-layer and eight-layer structures were printed using reversible cross-linking self-healing ink. After that, the process was allowed to wait 20 to 60 minutes to ensure that the scaffold relaxation was complete. The roundness Pr of the orthogonal unit regions of the printed scaffold was then calculated. The calculation method is Pr = L 2 / 16A, where L is the perimeter of the region and A is the area of ​​the region; calculate the rate of change of the area of ​​the orthogonal unit region of the printed scaffold, Ar, by calculating Ar = A / A0, where A is the actual area of ​​the tested region and A0 is the ideal area when the scaffold does not fuse or collapse; assign equivalent values ​​to Ar and Pr, and calculate the formability index Fid, which is calculated as follows: Where D P and D A The standard deviations of Pr and Ar are respectively, U P and U A are the average values ​​of Pr and Ar, respectively, and e is the natural constant; (4) Using the storage modulus, composite viscosity, modulus self-healing rate and viscosity self-healing rate measured by the rheometer as variables, fit their relationship with Ar, Pr and Fid.

2. The evaluation method according to claim 1, characterized in that, The reversible cross-linked self-healing material described in step (1) includes gelatin nanoparticles, silk fibroin nanoparticles, and nanoclay.

3. The evaluation method according to claim 1, characterized in that, The volume fractions mentioned in step (1) are 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 and 0.5 respectively.

4. The evaluation method according to claim 1, characterized in that, The test described in step (2) mainly includes two consecutive steps, which require separate sample preparation and testing: A. At a fixed frequency of 1 Hz / s, continuous tests of time scan 1, amplitude scan 1, and time scan 2 were performed. The test time for time scan 1 and time scan 2 was 60 minutes, and the strain was controlled at 0.1%. The time of amplitude scan 1 was determined by the actual test of the rheometer, and it was only necessary to control the strain to change nonlinearly from 0.1% to 100%. The three tests were conducted sequentially, and the average energy storage modulus G of time scan 1 and time scan 2 was calculated from the last 60 seconds of time scan 1 and the first 60 seconds of time scan 2. ’ 1 and G ’ 2. The modulus self-healing rate is G ’ 2 / G ’ 1; B. At a fixed frequency of 1 Hz / s, continuous tests were performed with time scan 3, peak hold 1, and time scan 4. The test time for time scan 3 and time scan 4 was 60 minutes, and the strain rate was controlled at 0.1 s. -1 The peak value was maintained at 1 for 60 seconds, and the strain rate was controlled at 30 seconds. -1 The three tests were performed sequentially, and the average combined viscosity V of time scan 3 and time scan 4 was calculated from the last 60 seconds of time scan 3 and the first 60 seconds of time scan 4. ’ 1 and V ’ 2. Viscosity self-healing rate is G ’ 2 / G ’ 1.

5. The evaluation method according to claim 1, characterized in that, The bracket described in step (3) has a cylindrical structure with a diameter of 20 mm on the outside and a rectangular structure formed by six equally spaced horizontal and vertical paths arranged orthogonally on the inside. Each path is 14.14 mm long. The bracket consists of 8 layers of the above structure, each layer being 0.4 mm thick.

6. The evaluation method according to claim 1, characterized in that, In step (3), the value range of the formability index Fid is 0-1, and the larger the value, the better the formability.

7. The evaluation method according to claim 1, characterized in that, In step (4), the fitting is performed using a fourth-order polynomial in Origin.

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