An extrusion printing process parameter design method based on rheological properties of biological materials

Abstract

The application discloses a kind of based on the rheological property of biological material extrusion printing process parameter design method, it relates to additive technology field.The present application solves the problem of low filament diameter precision in the existing biological material 3D printing due to the neglect of material rheological property, and the printing parameters obtained are not ideal, and further lead to low precision.The application builds a 3D printing device that can control key parameters separately, realizes 3D printing of target material under different parameters and records printing precision, builds a printing precision prediction model based on experimental data and optimizes printing parameters, and completes filament printing with high diameter precision.Through rheological test, analyze rheological data, determine the optimal temperature and extrusion speed;Through the 3D printing device that can control temperature and extrusion speed separately, explore the relationship between printing precision and process parameters in the printing process.The application is used for the additive printing of tissue or organ for transplantation surgery.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of additive manufacturing technology, in particular to an extrusion printing process parameter design method based on the rheological properties of biological materials, which is used for 3D printing of human tissue organs. BACKGROUND

[0002] In the field of biological medicine, tissue engineering technology has become an important means to serve regenerative medicine. This technology uses healthy cells and biocompatible materials as raw materials to prepare tissues or organs that can be applied to transplantation surgery to alleviate the problem of donor shortage. Because tissues and organs usually have complex three-dimensional structures, additive manufacturing technology represented by 3D printing technology has become the best means in the field of biological manufacturing.

[0003] The typical feature of this technology is to extrude the material from the nozzle in the cartridge, build continuous filaments with a diameter of a few hundred microns, and then deposit them on the platform in a predetermined trajectory, and build a three-dimensional tissue organ structure through layer-by-layer stacking. Because the biological ink is usually a high-molecular polymer with complex rheological properties, its unique viscoelasticity makes it have strict requirements for the printing environment: when the temperature is high or the shear rate of the material is large, the material exhibits Newtonian viscosity, its viscosity decreases and its flowability increases, resulting in poor forming of the printed filaments; when the temperature is low or the shear rate of the material is low, the material exhibits Hookean elasticity, its viscosity is high and its flowability is poor, causing plastic deformation of the printed filaments, resulting in filament expansion and even rupture.

[0004] In the 3D printing process, two printing parameters have a direct impact on the printing conditions: the internal temperature of the printing nozzle affects the temperature the material is subjected to; the extrusion speed affects the shear rate the material is subjected to. Deformation of the filaments caused by inappropriate printing parameters (temperature and extrusion speed) can cause a large deviation between the actual diameter of the filaments and the designed value, i.e., low filament diameter precision. As the basic component of the three-dimensional structure, the error of the filaments will be gradually magnified in the 3D printing process, causing a large error in the overall structure, making it difficult to achieve a tissue organ structure with high precision.

[0005] Currently, to obtain ideal filament printing process parameters, the trial-and-error method is usually used to control the temperature and extrusion speed until ideal filament diameter is obtained. In this process, the process parameters need to be adjusted repeatedly, which not only consumes time but also lacks reliability and repeatability. The reason for this phenomenon is that the rheological properties of biological materials are ignored, and the printing parameters are not designed according to the rheological characteristics of different materials. Therefore, to obtain printing process parameters (temperature and extrusion speed) that can extrude ideal filaments, there is an urgent need for a method based on the rheological properties of biological materials to guide the design of process parameters, ultimately achieving the improvement of the printing precision of the printed filaments.

[0006] In summary, in the existing 3D printing of biological materials, the rheological properties of the materials are ignored, the obtained printing parameters are not ideal, and the problem of low filament diameter precision is caused. SUMMARY

[0007] The purpose of the present application is to solve the problem of low filament diameter precision caused by ignoring the rheological properties of the materials in the existing 3D printing of biological materials, and to provide an extrusion printing process parameter design method based on the rheological properties of biological materials.

[0008] The technical solution of the present application is:

[0009] An extrusion printing process parameter design method based on the rheological properties of biological materials comprises the following steps:

[0010] Step one: obtain the complex modulus-temperature curve and the viscosity-shear rate curve at a certain temperature of the polymer material to be printed;

[0011] Step two: analyze the complex modulus-temperature curve and find the change rule of the complex modulus of the 3D printing material with temperature;

[0012] Step three: analyze the viscosity-shear rate curve at the most suitable 3D printing temperature obtained in step two, and find the change rule of the viscosity of the 3D printing material with shear rate;

[0013] Step three one: convert the shear rate in the viscosity-shear rate by:

[0014]

[0015] wherein is the shear rate; v is the extrusion speed of the fluid; d is the inner diameter of the pipe;

[0016] Step three two: convert the shear rate to obtain the viscosity-3D printing extrusion speed curve;

[0017] Step three three: select the extrusion speed at low viscosity value for printing to ensure the smooth progress of 3D printing;

[0018] Step four: prepare a 3D printing equipment that can control temperature and extrusion speed respectively;

[0019] Step five: use the 3D printing equipment that can control temperature and extrusion speed respectively to perform 3D printing of target materials at different temperatures and extrusion speeds, and record the filament diameter;

[0020] Step six: Organize the experimental data, and take the temperature, extrusion speed and filament diameter data in different experimental groups as the coordinate values of x, y and z respectively to obtain a set of three-dimensional column chart;

[0021] Import the experimental data in the three-dimensional column chart into the analysis software, and fit to obtain the variation surface of the filament diameter under different temperatures and extrusion speeds as the prediction model for controlling the filament diameter by adjusting the two printing parameters;

[0022] Step seven: Optimize the printing parameters through the prediction model:

[0023] Step seven one: Determine the target printing filament diameter;

[0024] Step seven two: Select appropriate temperature and extrusion speed in the surface of the prediction model according to the diameter as the high-filament-precision printing parameters of the target material;

[0025] Step eight: Perform 3D printing on the target material by using the parameters optimized in step seven two, and verify the 3D printing precision.

[0026] Further, the way to obtain the complex modulus variation curve with temperature and the viscosity variation curve with shear rate at a certain temperature in step one is as follows:

[0027] Use a rotary rheometer with temperature control function to obtain the complex modulus variation curve with temperature by performing vibration temperature scanning analysis test on the target material;

[0028] Obtain the viscosity variation curve with shear rate at a certain temperature by performing steady shear scanning analysis test on the target material.

[0029] Further, the analysis process of the complex modulus variation curve with temperature in step two is as follows:

[0030] Due to the particularity of high polymer materials, they exhibit both Newtonian viscosity and Hookean elasticity in physical properties, i.e. viscoelasticity of high polymer materials;

[0031] The complex modulus is a rheological property used to describe the viscoelasticity of high polymer materials, which is divided into storage modulus G’ and dissipation modulus G”; among them, the storage modulus G’ is used to measure the Hookean elasticity of the material, and the dissipation modulus G” is used to measure the Newtonian viscosity of the material;

[0032] When the storage modulus G’ is greater than the dissipation modulus G”, it indicates that the Hookean elasticity of the high polymer material dominates, and the high polymer material exhibits solid-like elasticity, at this time the material flowability is poor, which causes plastic deformation of the printing filament, resulting in filament expansion and rupture;

[0033] When the storage modulus G' is less than the dissipation modulus G”, it indicates that the Newtonian viscosity of the polymer material is dominant, and the polymer material exhibits a fluidity similar to that of a liquid. At this time, the ability to form filaments printed is relatively weak.

[0034] Therefore, by analyzing the curve of the complex modulus changing with temperature, it can be concluded that as the temperature increases, the material gradually changes from a solid to a liquid. When the storage modulus G' intersects with the dissipation modulus G” curve, the material has properties between those of a solid and a liquid.

[0035] Furthermore, the 3D printing equipment in step four, which allows for separate control of temperature and extrusion speed, includes: a servo motor, coupling, lead screw, lead screw nut, L-shaped pressure plate, nozzle push rod, temperature-controlled printing nozzle, and frame; the frame is vertically arranged, the servo motor is vertically mounted on the upper part of the frame, the output shaft of the servo motor is connected to one end of the lead screw located on the frame, the lead screw nut is mounted on the lead screw, the vertical section of the L-shaped pressure plate is connected to the lead screw nut, the horizontal section of the L-shaped pressure plate is connected to the nozzle push rod, the nozzle push rod is inserted into the temperature-controlled printing nozzle, and under the follow of the L-shaped pressure plate, it achieves lifting and lowering to extrude the polymer material in the temperature-controlled printing nozzle.

[0036] Furthermore, the 3D printing equipment that allows for separate control of temperature and extrusion speed also includes a bearing housing, which is horizontally mounted on the lower part of the frame, with the other end of the lead screw installed inside the bearing housing.

[0037] Preferably, the temperature-controlled printhead has both heating and cooling functions.

[0038] Furthermore, in step eight, the verification process for 3D printing accuracy is as follows:

[0039] If the 3D printing accuracy meets the requirements, then a design of three-dimensional printing parameters to improve the accuracy of the extruded filament diameter has been completed.

[0040] If the requirements are not met, repeat step seven until the 3D printing accuracy meets the requirements. At this point, the design of 3D printing parameters to improve the accuracy of the extruded filament diameter is complete.

[0041] Compared with the prior art, the present invention has the following advantages:

[0042] 1. This invention obtains optimal printing parameters by conducting rheological tests on the target material and analyzing the rheological curves. By constructing a 3D printing device that can control key parameters individually, 3D printing of the target material under different parameters is achieved, and the printing accuracy is recorded. Based on the experimental data, a printing accuracy prediction model is constructed, and the printing parameters are optimized to complete the printing of filaments with high diameter accuracy.

[0043] 2. This invention proposes a parameter optimization method for achieving high-precision printing of 3D printing filaments. This design method enables high-precision printing of polymer filaments, with a simple and clear design process and high efficiency in obtaining optimal parameters, which is of great significance for the high-precision in vitro construction of tissues and organs with complex structures. For example... Figures 1 to 7 As shown, rheological tests were conducted to analyze rheological data and determine the optimal temperature and extrusion speed. A 3D printing device capable of separately controlling temperature and extrusion speed was constructed to print filaments at different temperatures and extrusion speeds, and the filament diameter was measured to explore the relationship between printing accuracy and process parameters. Poly(L-lactide-caprolactone) (PLCL), a commonly used polymer in biomanufacturing, was used as the printing material to verify the feasibility of the designed method. Figure 5 The results of the printing experiment are shown below. The results were analyzed using a computer, and a fitting was obtained as shown below. Figure 6 The prediction model is shown. Based on the prediction model, parameters were optimized and filament printing experiments were conducted, ultimately yielding... Figure 7 The filament shown has a diameter accuracy within 5μm. Without this method, the absolute diameter error of the printed PLCL filament can reach 22μm. With this method, the absolute error of the filament is reduced by 77.3%, effectively improving the diameter accuracy of the 3D printed filament. Attached Figure Description

[0044] Figure 1 This is a flowchart of a three-dimensional printing parameter design method for improving the accuracy of extruded filament diameter according to the present invention;

[0045] Figure 2 This is a structural diagram of the designed extrusion 3D printing device;

[0046] Figure 3 This is the modulus-temperature curve of the PLCL;

[0047] Figure 4 This is the viscosity-shear rate curve at the optimal printing temperature for PLCL.

[0048] Figure 5 The diameter of 3D printed PLCL filaments under different temperatures and extrusion speeds;

[0049] Figure 6 It is a PLCL filament accuracy prediction model under different temperatures and extrusion speeds;

[0050] Figure 7 They are high-precision PLCL filaments with different diameters;

[0051] Figure 8 This is a viscosity-extrusion speed curve for PLCL.

[0052] The components include: 1. Servo motor, 2. Coupling, 3. Lead screw, 4. Lead screw nut, 5. L-shaped pressure plate, 6. Printhead push rod, 7. Temperature-controlled printing nozzle, and 8. Frame. Detailed Implementation

[0053] Specific implementation method one: Combining Figures 1 to 8 This embodiment describes the following steps:

[0054] Step 1: Obtain the curve of the modulus of the polymer material to be printed as a function of temperature and the curve of the viscosity as a function of shear rate at a certain temperature; where "a certain temperature" is the temperature value near the intersection of the storage modulus G' and the dissipation modulus G" curves in the modulus-temperature curve.

[0055] Step 2: Analyze the curve of the mold amount as a function of temperature to find the variation law of the mold amount of the 3D printing material with temperature;

[0056] Step 3: At the optimal 3D printing temperature obtained in Step 2, analyze the viscosity variation curve with shear rate to find the law of viscosity variation of 3D printing material with shear rate.

[0057] Step 31: Convert the shear rate in the viscosity-shear rate equation:

[0058]

[0059] in d is the shear rate; v is the fluid extrusion velocity; d is the pipe inner diameter;

[0060] Since the 3D printing process is driven by a lead screw pushing the nozzle push rod, the following can be calculated based on the cross-sectional area of ​​the push rod and the cross-sectional area of ​​the nozzle: For fluid in the pipe: A1 / A2=V2 / V1; where A is the area at the cross-section and V is the flow velocity at the cross-section;

[0061] Step 32: Obtain the viscosity variation curve as a function of 3D printing extrusion speed by converting the shear rate;

[0062] Step 33: Select an extrusion speed with a low viscosity value for printing to ensure smooth 3D printing;

[0063] Low viscosity means that the viscosity curve decreases sharply with increasing shear rate, then the rate of decrease slows down, and finally remains almost constant. The viscosity value used here is the value when the viscosity is almost constant. Figure 4 The viscosity value of the middle finger is less than 80,000 mPas;

[0064] Step 4: Prepare 3D printing equipment that can control the temperature and extrusion speed separately;

[0065] Step 5: Using 3D printing equipment that can control the temperature and extrusion speed separately, 3D print the target material at different temperatures and extrusion speeds, and record the filament diameter;

[0066] Step 6: Organize the experimental data, and use the temperature, extrusion speed and filament diameter data in different experimental groups as x, y and z coordinate values ​​respectively to obtain a set of three-dimensional bar charts;

[0067] The experimental data in the three-dimensional bar chart were imported into Origin or Excel analysis software, and the variation surface of the filament diameter under different temperatures and extrusion speeds was obtained by fitting. This surface serves as a predictive model for controlling the filament diameter by adjusting two printing parameters.

[0068] Step 7: Optimize printing parameters using a predictive model:

[0069] Step 71: Determine the diameter of the target printing filament;

[0070] Step 72: Select appropriate temperature and extrusion speed on the surface of the prediction model based on the diameter, as the high-precision printing parameters for the target material filament; the appropriate temperature is: based on the target printing filament diameter in Step 71, select the point where the diameter is located on the prediction surface, and find the corresponding temperature and extrusion speed parameters.

[0071] Step 8: 3D print the target material using the parameters selected in Step 72, and verify the 3D printing accuracy.

[0072] Specific Implementation Method Two: Combining Figure 3 This embodiment describes the method for obtaining the curves of the complex modulus as a function of temperature and the curves of the viscosity as a function of shear rate at a certain temperature in step one of this embodiment.

[0073] Using a rotational rheometer with temperature control, the complex modulus as a function of temperature was obtained by performing vibration temperature scanning analysis on the target material.

[0074] By performing steady-state shear scanning analysis on the target material, the viscosity variation curve with shear rate at a certain temperature was obtained.

[0075] This setup facilitates the provision of necessary data to subsequently determine the temperature and extrusion rate of the polymer material. Other components and connections are the same as in Specific Embodiment 1.

[0076] Specific implementation method three: Combining Figures 3 to 6 The following describes the process of analyzing the curve of the composite modulus changing with temperature in step two of this embodiment:

[0077] Due to the special nature of polymer materials, they exhibit both Newtonian viscosity and Hooke's elasticity in their physical properties, i.e., the viscoelasticity of polymer materials.

[0078] Complex modulus is a rheological property used to describe the viscoelasticity of polymer materials. It is divided into storage modulus G' and dissipation modulus G”. Among them, storage modulus G' is used to measure the Hooke elasticity of the material, and dissipation modulus G” is used to measure the Newtonian viscosity of the material.

[0079] When the storage modulus G' is greater than the dissipation modulus G”, it indicates that the Hooke elasticity of the polymer material is dominant, and the polymer material exhibits elasticity similar to that of a solid. At this time, the material has poor fluidity, which causes the printing filament to undergo plastic deformation, resulting in the filament expanding and breaking.

[0080] When the storage modulus G' is less than the dissipation modulus G”, it indicates that the Newtonian viscosity of the polymer material is dominant, and the polymer material exhibits a fluidity similar to that of a liquid. At this time, the ability to form filaments printed is relatively weak.

[0081] Therefore, by analyzing the curve of the complex modulus changing with temperature, it can be concluded that as the temperature increases, the material gradually changes from a solid to a liquid. When the storage modulus G' intersects with the dissipation modulus G” curve, the material has properties between those of a solid and a liquid.

[0082] This setup facilitates accurate determination of the optimal printing temperature. Other components and connections are the same as in implementation method one or two.

[0083] Specific implementation method four: Combination Figure 2 This embodiment describes a 3D printing equipment in step four that allows for separate control of temperature and extrusion speed, comprising: a servo motor 1, a coupling 2, a lead screw 3, a lead screw nut 4, an L-shaped pressure plate 5, a nozzle push rod 6, a temperature-controlled printing nozzle 7, and a frame 8.

[0084] The frame 8 is set vertically, and the servo motor 1 is installed vertically on the upper part of the frame 8. The output shaft of the servo motor 1 is connected to one end of the lead screw 3 located on the frame 8. The lead screw nut 4 is installed on the lead screw 3. The vertical section of the L-shaped pressure plate 5 is connected to the lead screw nut 4, and the horizontal section of the L-shaped pressure plate 5 is connected to the nozzle push rod 6. The nozzle push rod 6 is inserted into the temperature-controlled printing nozzle 7 and, under the follow of the L-shaped pressure plate 5, achieves lifting and lowering to extrude the polymer material in the temperature-controlled printing nozzle 7.

[0085] In this configuration, since the extrusion printing process parameter design method based on the rheological properties of biomaterials of the present invention requires a device capable of precise temperature control and a precise printing speed to achieve optimal printing accuracy, the printing temperature is controlled by a temperature-controlled printhead 7 in this embodiment. The L-shaped pressure plate 5 and the printhead push rod 6 are raised and lowered by the screw nut 4 moving up and down on the screw 3, thereby controlling the extrusion speed. Other components and connections are the same as in any of the specific embodiments one to three.

[0086] Specific Implementation Method Five: Combining Figure 2 To illustrate this embodiment, the 3D printing equipment in this embodiment, which can control the temperature and extrusion speed separately, also includes a bearing housing, which is horizontally installed at the lower part of the frame 8, and the other end of the lead screw 3 is installed inside the bearing housing.

[0087] This configuration facilitates the smooth rotation of the lead screw 3 and ensures the accuracy of the lead screw nut 4 during lifting and lowering. Other components and connections are the same as in any of the specific embodiments one through four.

[0088] Specific Implementation Method Six: Combination Figure 2 This embodiment describes a temperature-controlled printhead 7 that has both heating and cooling functions.

[0089] With this configuration, the heating function in this embodiment, including but not limited to resistance wires and heating rods, and the cooling function, including but not limited to cooling plates, are flexible and convenient to use, and primarily enable rapid and precise temperature control. Other components and connections are the same as in any one of embodiments one through five.

[0090] Specific implementation method seven: Combination Figure 1 This embodiment describes the process of verifying 3D printing accuracy in step eight, which is as follows:

[0091] If the 3D printing accuracy meets the requirements, then a design of three-dimensional printing parameters to improve the accuracy of the extruded filament diameter has been completed.

[0092] If the requirements are not met, repeat step seven until the 3D printing accuracy meets the requirements. At this point, the design of 3D printing parameters to improve the accuracy of the extruded filament diameter is complete.

[0093] This setup ensures optimal precision and quality of the printed filaments through verification. Other components and connections are identical to any one of the specific implementation methods one through six.

[0094] Combination Figures 1 to 7 Explanation of the working process of this invention:

[0095] The above-mentioned objective is achieved through the following technical solution:

[0096] Step 1: Using a rotational rheometer with temperature control, the complex modulus as a function of temperature is obtained by performing vibrational temperature scanning analysis on the target material; the viscosity as a function of shear rate at a certain temperature is obtained by performing steady-state shear scanning analysis on the target material.

[0097] Step 2: Analyze the curve of modulus versus temperature to find the optimal temperature for 3D printing. Due to the special properties of polymer materials, they often exhibit both Newtonian viscosity and Hookean elasticity in their physical properties, i.e., viscoelasticity of polymer materials. Complex modulus is a rheological property used to describe the viscoelasticity of polymer materials, and it is divided into storage modulus (G') and dissipation modulus (G''). Storage modulus measures the material's Hooke's elasticity, while dissipation modulus measures its Newtonian viscosity. When G' is greater than G'', Hooke's elasticity dominates, and the material exhibits solid-like elasticity. In this case, the material's flowability is poor, causing plastic deformation of the printed filament, leading to filament expansion and breakage. When G' is less than G'', Newtonian viscosity dominates, and the material exhibits liquid-like flowability. In this case, the printed filament's forming ability is weak. Therefore, by analyzing the curve of complex modulus versus temperature, we can conclude that as temperature increases, the material gradually transforms from a solid to a liquid. When the storage modulus G' and dissipation modulus G' curves intersect, the material exhibits properties intermediate between a solid and a liquid.

[0098] Step 3: Analyze the viscosity versus shear rate curve at the optimal 3D printing temperature obtained in Step 2. Polymer materials are composed of long-chain macromolecular clusters with variable volume. When extruded into the circular channel of a 3D printer nozzle, they typically exhibit shear thinning. That is, as the extrusion speed increases, the shear rate rises, causing the long-chain macromolecular clusters inside the material to deform along the fluid flow direction, increasing the flow velocity and ultimately reducing the apparent viscosity of the material. Therefore, by converting the shear rate in the viscosity-shear rate conversion, we can obtain the viscosity versus 3D printing extrusion speed curve. Selecting the extrusion speed with the lowest viscosity value ensures smooth 3D printing. According to polymer fluid dynamics, the conversion between the shear rate and extrusion speed inside the circular tube is as follows:

[0099]

[0100] in is the shear rate; v is the fluid extrusion speed; d is the pipe inner diameter.

[0101] Step 4: Develop a new type of 3D printing equipment that can separately control temperature and extrusion speed. The mechanical structure of this equipment is as follows: Figure 2As shown, its components include: 1-servo motor, 2-coupling, 3-lead screw, 4-lead screw nut, 5-L-shaped pressure plate, 6-printer push rod, 7-temperature-controlled print head. The connection relationship is as follows: 1. The motor shaft at the lower end of the servo motor is connected to 3. Lead screw via 2. Coupling; 4. Lead screw nut is installed on the outside of the lead screw; 5. The upper end of the L-shaped pressure plate is connected to the lead screw nut; 5. The lower end of the L-shaped pressure plate is connected to the top of 6. Printer push rod; 6. Printer push rod is inserted into the channel inside 7. Temperature-controlled print head and can move up and down. The connection methods mentioned above include, but are not limited to, threaded connections, welding, pin connections, etc.; 7. The temperature control housing can achieve heating or cooling: heating methods include, but are not limited to, heating rods, heating wires, etc., and cooling methods include, but are not limited to, cooling plates, etc. Its working process is as follows: the target material is loaded into 7. Temperature-controlled print head, and the print head temperature is adjusted through its internal temperature control system, thereby controlling the temperature that the target material is subjected to. Subsequently, by controlling the rotation of servo motor 1, the rotation is transmitted to lead screw 3. Through the meshing between lead screw 3 and lead screw 4 nuts, the reciprocating motion of 5-L-shaped pressure plate is controlled at a fixed speed. This extrudes the target material, achieving 3D printing of fine filaments.

[0102] Step 5: Using this printing equipment, 3D print the target material at different temperatures and extrusion speeds, and record the filament diameter;

[0103] Step Six: Organize the experimental data. Use the temperature, extrusion speed, and filament diameter data from different experimental groups as x, y, and z coordinate values, respectively, to obtain a set of three-dimensional bar charts. Import the experimental data from this chart into analysis software and fit it to obtain the surface curve of filament diameter variation under different temperatures and extrusion speeds. This surface curve serves as a predictive model for controlling filament diameter by adjusting two printing parameters.

[0104] Step 7: The printing parameters can be optimized through the prediction model: First, determine the diameter of the target printing filament, and then select the appropriate temperature and extrusion speed on the surface of the prediction model based on the diameter as the high-precision printing parameters for the target material.

[0105] Step 8: Using this parameter to 3D print the target material, determine whether the printing accuracy meets the requirements. This completes the verification of a 3D printing parameter design method to improve the accuracy of extruded filament diameter.

[0106] Example:

[0107] Printing material: A biodegradable polymer, poly(L-lactide-caprolactone) (PLCL):

[0108] The purchased PLCL particles were placed in a rotational rheometer, and the complex modulus-temperature curve of the PLCL was obtained using the oscillating temperature scan analysis mode. Figure 3 );

[0109] Based on the obtained curves, it was found that the material exhibits solid properties at lower temperatures and liquid properties at higher temperatures, with printing at 130℃-137℃ being the most suitable. To further understand the variation of material viscosity with extrusion speed, the temperature at the intersection of the G' and G” curves (134.5℃) was selected as the printing temperature for steady-state shear sweep analysis, obtaining the material viscosity variation curve with shear rate. Figure 4 ).

[0110] Based on the obtained curve, and considering that the nozzle diameter used in the 3D printing experiment was 100 μm, the curve of material viscosity changing with extrusion speed was obtained after conversion. Figure 8 It was determined that the viscosity change was relatively stable when the extrusion speed varied between 1.2 and 2.5 mm / s, which is a suitable 3D printing speed.

[0111] Based on the above conclusions, 130, 134.5, and 137℃ were selected as temperature parameters; 1.2, 1.7, and 2.2 mm / s were selected as extrusion speed parameters. Printing experiments were conducted using the proposed 3D printing equipment, and the diameter of the printed filaments was recorded. Figure 5 Inside.

[0112] Obtained through fitting Figure 6 The curved surface in the graph allows us to obtain the extrusion speed and temperature parameters corresponding to different target filament diameters. By selecting different temperature parameters and printing, we can obtain... Figure 7 The printing of the filaments was shown, and the printing accuracy of the filaments was measured. The final accuracy was controlled within 5μm, verifying the feasibility.

[0113] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. 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 of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for designing extrusion printing process parameters based on the rheological properties of biomaterials, characterized in that: It includes the following steps: Step 1: Obtain the curves of the molding weight of the polymer material to be printed as a function of temperature and the curves of the viscosity as a function of shear rate at a certain temperature; Step 2: Analyze the curve of the mold amount as a function of temperature to find the variation law of the mold amount of the 3D printing material with temperature; Step 3: At the optimal 3D printing temperature obtained in Step 2, analyze the viscosity variation curve with shear rate to find the law of viscosity variation of 3D printing material with shear rate. Step 31: Convert the shear rate in the viscosity-shear rate equation: in d is the shear rate; v is the fluid extrusion velocity; d is the pipe inner diameter; Step 32: Obtain the viscosity variation curve as a function of 3D printing extrusion speed by converting the shear rate; Step 33: Select Printing is performed at extrusion speeds with low viscosity values ​​to ensure smooth 3D printing. Step 4: Prepare 3D printing equipment that can control the temperature and extrusion speed separately; Step 5: Using 3D printing equipment that can control the temperature and extrusion speed separately, 3D print the target material at different temperatures and extrusion speeds, and record the filament diameter; Step 6: Organize the experimental data, and use the temperature, extrusion speed and filament diameter data in different experimental groups as x, y and z coordinate values ​​respectively to obtain a set of three-dimensional bar charts; The experimental data in the three-dimensional bar chart were imported into the analysis software, and the variation surface of the filament diameter under different temperatures and extrusion speeds was obtained by fitting. This surface serves as a predictive model for controlling the filament diameter by adjusting two printing parameters. Step 7: Optimize printing parameters using a predictive model: Step 71: Determine the diameter of the target printing filament; Step 72: Based on the diameter, select appropriate temperature and extrusion speed on the surface of the prediction model as the high-precision printing parameters for the target material filament; Step 8: 3D print the target material using the parameters selected in Step 72, and verify the 3D printing accuracy.

2. The method for designing extrusion printing process parameters based on the rheological properties of biomaterials according to claim 1, characterized in that: The method for obtaining the curves of the change of complex modulus with temperature and the curves of the change of viscosity with shear rate at a certain temperature in step one is as follows: Using a rotational rheometer with temperature control, the complex modulus as a function of temperature was obtained by performing vibration temperature scanning analysis on the target material. By performing steady-state shear scanning analysis on the target material, the viscosity variation curve with shear rate at a certain temperature was obtained.

3. The method for designing extrusion printing process parameters based on the rheological properties of biomaterials according to claim 1, characterized in that: The analysis process for the curve of the change of the complex modulus with temperature in step two is as follows: Due to the special nature of polymer materials, they exhibit both Newtonian viscosity and Hooke's elasticity in their physical properties, i.e., the viscoelasticity of polymer materials. Complex modulus is a rheological property used to describe the viscoelasticity of polymer materials. It is divided into storage modulus G' and dissipation modulus G”. Among them, storage modulus G' is used to measure the Hooke elasticity of the material, and dissipation modulus G” is used to measure the Newtonian viscosity of the material. When the storage modulus G' is greater than the dissipation modulus G”, it indicates that the Hooke elasticity of the polymer material is dominant, and the polymer material exhibits elasticity similar to that of a solid. At this time, the material has poor fluidity, which causes the printing filament to undergo plastic deformation, resulting in the filament expanding and breaking. When the storage modulus G' is less than the dissipation modulus G”, it indicates that the Newtonian viscosity of the polymer material is dominant, and the polymer material exhibits a fluidity similar to that of a liquid. At this time, the ability to form filaments printed is relatively weak. Therefore, by analyzing the curve of the complex modulus changing with temperature, it can be concluded that as the temperature increases, the material gradually changes from a solid to a liquid. When the storage modulus G' intersects with the dissipation modulus G” curve, the material has properties between those of a solid and a liquid.

4. The method for designing extrusion printing process parameters based on the rheological properties of biomaterials according to claim 3, characterized in that: The 3D printing equipment in step four, which can control the temperature and extrusion speed separately, includes: a servo motor (1), a coupling (2), a lead screw (3), a lead screw nut (4), an L-shaped pressure plate (5), a nozzle push rod (6), a temperature-controlled printing nozzle (7), and a frame (8). The frame (8) is set vertically, and the servo motor (1) is installed vertically on the upper part of the frame (8). The output shaft of the servo motor (1) is connected to one end of the lead screw (3) located on the frame (8). The lead screw nut (4) is installed on the lead screw (3). The vertical section of the L-shaped pressure plate (5) is connected to the lead screw nut (4). The horizontal section of the L-shaped pressure plate (5) is connected to the nozzle push rod (6). The nozzle push rod (6) is inserted into the temperature-controlled printing nozzle (7) and, under the follow of the L-shaped pressure plate (5), it realizes the lifting and lowering of the polymer material extrusion in the temperature-controlled printing nozzle (7).

5. The method for designing extrusion printing process parameters based on the rheological properties of biomaterials according to claim 4, characterized in that: The 3D printing equipment that can control the temperature and extrusion speed separately also includes a bearing housing, which is horizontally installed at the bottom of the frame (8), and the other end of the lead screw (3) is installed in the bearing housing.

6. The method for designing extrusion printing process parameters based on the rheological properties of biomaterials according to claim 5, characterized in that: The temperature-controlled printhead (7) has heating and cooling functions.

7. The method for designing extrusion printing process parameters based on the rheological properties of biomaterials according to claim 6, characterized in that: Step eight involves verifying the accuracy of 3D printing as follows: If the 3D printing accuracy meets the requirements, then a design of three-dimensional printing parameters to improve the accuracy of the extruded filament diameter has been completed. If the requirements are not met, repeat step seven until the 3D printing accuracy meets the requirements. At this point, the design of 3D printing parameters to improve the accuracy of the extruded filament diameter is complete.

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