A method for preparing high-precision 3D printed hydrogels by extrusion with salt crystallization assistance

Abstract

This invention provides a method for preparing a salt crystallization-assisted extrusion-based high-precision 3D printing hydrogel. The method involves mixing a salt solution and a hydrogel solution to prepare a printing ink, depositing a layer of crystal nuclei on the forming platform of an extrusion 3D printer, printing a hydrogel model using the 3D printer, and finally curing it through photo-linking and deionized water washing to obtain a hydrogel with high precision, high porosity, and good biocompatibility. This preparation method utilizes salt crystallization at room temperature to maintain the stability of the printed structure, overcoming the problems of low printing precision and easy structural collapse in existing hydrogel printing technologies. It has no sample size limitations, especially in the Z-axis direction, allowing for the preparation of large-sized samples. Furthermore, it can prepare porous hydrogels through crystallization; and the salt used can be completely removed by deionized water washing, leaving no residue. The resulting hydrogel exhibits high biocompatibility.

Description

Technical Field

[0001] This invention belongs to the field of 3D printing technology, specifically relating to a method for preparing a salt crystallization-assisted extrusion-based high-precision 3D printed hydrogel. Background Technology

[0002] Extrusion 3D printing of hydrogels offers strong material compatibility, the ability to handle high-viscosity materials, and the capacity for printing complex structures and multifunctional applications. These characteristics make it a promising technology for tissue engineering, drug delivery, and regenerative medicine.

[0003] Extrusion-based 3D printing of hydrogels utilizes the shear-thinning effect of hydrogels, resulting in a low viscosity during extrusion. However, once the material leaves the nozzle, the shear force disappears, and the viscosity rapidly increases, preventing the material from flowing and spreading during deposition and preserving the printed shape and detail. However, hydrogels typically exhibit a soft, wet texture and low modulus. When the weight of the printed structure exceeds its yield stress, the hydrogel is prone to deformation or even collapse, directly impacting the stability and accuracy of the printed structure.

[0004] To ensure sufficient mechanical strength in the printed part (hydrogel) to improve structural fidelity, rapid curing mechanisms (such as photocuring and thermal curing) can be used. However, this method is prone to nozzle clogging, causing the printing process to terminate. Alternatively, the printing ink can be frozen at low temperatures to preserve the hydrogel's structure; however, this method requires extremely low temperatures to generate sufficient heat, and the size of the printed sample is limited along the Z-axis.

[0005] Therefore, it is necessary to provide a hydrogel suitable for 3D printing to solve the problem of low printing accuracy of current hydrogels and promote the development of tissue engineering and regenerative medicine. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a method for preparing high-precision 3D printed hydrogels using salt crystallization-assisted extrusion. This method overcomes the issues of low printing accuracy and structural collapse in existing hydrogel printing technologies, significantly improving the structural retention and accuracy of hydrogel printing. The hydrogel prepared by this method exhibits high precision, high porosity, and good biocompatibility.

[0007] A method for preparing a salt crystallization-assisted extrusion-based high-precision 3D printed hydrogel includes the following steps:

[0008] (1) Mix the hydrogel monomer, photoinitiator, thickener and water evenly to prepare a hydrogel solution; dissolve the salt in water to prepare a salt solution;

[0009] (2) Prepare printing ink by mixing hydrogel solution and salt solution;

[0010] (3) Lay a layer of crystal nuclei on the forming platform of the 3D printer, and use printing ink as raw material to print a pre-set hydrogel scaffold using an extrusion 3D printer.

[0011] (4) The printed hydrogel scaffold is photocrosslinked and then cleaned with deionized water to remove salt crystals, thus obtaining the extruded high-precision 3D printed hydrogel.

[0012] In step (1) above:

[0013] Deionized water is preferred for preparing hydrogel solutions; purified water is preferred for preparing salt solutions.

[0014] Preferably, the hydrogel monomer is one or more of acrylamide, acrylic acid, methacrylamide gelatin, methacrylamide hyaluronic acid, methacrylamide chitosan, and methacrylamide silk fibroin. Acrylamide is more preferred.

[0015] Preferably, the mass ratio of hydrogel monomer to water in the hydrogel solution is (0.1 to 1.4):1.

[0016] As a further preferred embodiment, when the hydrogel monomer is selected from acrylamide and / or acrylic acid, the mass ratio of hydrogel monomer to water in the hydrogel solution is (0.7 to 1.1):1. Even more preferably, it is 0.9:1.

[0017] As a further preferred embodiment, when the hydrogel monomer is selected from one or more of methacrylated gelatin, methacrylated hyaluronic acid, methacrylated chitosan, and methacrylated silk fibroin, the mass ratio of the hydrogel monomer to water in the hydrogel solution is (0.1–0.5):1. Even more preferably, it is 0.3:1.

[0018] Preferably, the photoinitiator is lithium phenyl (2,4,6-trimethylbenzoyl) phosphate. A photoinitiator is a substance that generates free radicals under light and further initiates the polymerization of hydrogel monomers.

[0019] Preferably, the mass ratio of hydrogel monomer to photoinitiator is (1-200):1.

[0020] As a further preferred embodiment, when the hydrogel monomer is selected from acrylamide and / or acrylic acid, the mass ratio of the hydrogel monomer to the photoinitiator is (80-120):1. Even more preferred is 108:1.

[0021] As a further preferred embodiment, when the hydrogel monomer is selected from one or more of methacrylamide gelatin, methacrylamide hyaluronic acid, methacrylamide chitosan, and methacrylamide silk fibroin, the mass ratio of the hydrogel monomer to the photoinitiator is (5-15):1. Even more preferably, it is 12:1.

[0022] As a further preferred option, when the hydrogel monomer is one or both of acrylamide and acrylic acid, a crosslinking agent is also added to the hydrogel solution.

[0023] As a further preferred option, the crosslinking agent is N,N'-methylenebisacrylamide.

[0024] Preferably, the mass ratio of hydrogel monomer to crosslinking agent is (15-150):1. More preferably, it is (40-60):1. The preferred mass ratio of hydrogel monomer to crosslinking agent is 54:1.

[0025] Preferably, the salt is sodium acetate or a mixture of sodium acetate and carbamide. Further, anhydrous sodium acetate is preferred.

[0026] As a further preferred embodiment, when the salt is sodium acetate, the mass ratio of sodium acetate to water in the salt solution is (0.2–1.7):1. Even more preferred is (1–1.5):1. As a further preferred embodiment, when the salt is sodium acetate, the mass ratio of sodium acetate to water in the salt solution is 1.2:1.

[0027] As a further preferred embodiment, when the salt is a mixture of sodium acetate and carbamide, the mass ratio of sodium acetate to water in the salt solution is (0.2–1.7):1; and the mass ratio of carbamide to water is (0.2–0.8):1. As even more preferred, when the salt is a mixture of sodium acetate and carbamide, the mass ratio of sodium acetate to water in the salt solution is (1–1.5):1; and the mass ratio of carbamide to water is (0.3–0.6):1. As a further preferred embodiment, when the salt is a mixture of sodium acetate and carbamide, the mass ratio of sodium acetate to water in the salt solution is 1.25:1; and the mass ratio of carbamide to water is 0.5:1.

[0028] Preferably, the thickener is one or more of polyacrylamide, polyacrylic acid, polyethylene glycol, gelatin, cellulose or its derivatives, starch or its derivatives, fumed silica, and carbomer. More preferably, polyacrylamide is used.

[0029] As a further preferred option, the molecular weight of the polyacrylamide is 1 million to 14 million. Even more preferred is 5 million to 10 million. Even more preferred is 7 million.

[0030] Preferably, the mass ratio of thickener to water in the hydrogel solution is 0.005:1 to 1:5. More preferably, it is (0.01 to 0.05):1.

[0031] In step (2) above:

[0032] Preferably, the volume ratio of the hydrogel solution to the salt solution in the printing ink is 1:17 to 10:1. More preferably, it is 1:(1 to 4).

[0033] In step (3) above,

[0034] As a preferred option, the 3D printing parameters are: barrel temperature of 50-80℃, nozzle temperature of 40-80℃, printing speed of 75-4000mm / min, extrusion flow rate of 0.01-0.5mL / min, and nozzle diameter of 80-1000μm.

[0035] As a further preferred option, the 3D printing parameters are: barrel temperature of 55-65℃, nozzle temperature of 55-65℃, printing speed of 1000-3000mm / min, extrusion flow rate of 0.01-0.05mL / min, and nozzle diameter of 100-400μm.

[0036] Preferably, the printer is kept at room temperature (25°C), which is lower than the crystallization temperature of salts in the printing ink. This helps the printing ink cool down quickly after leaving the print head and become supersaturated.

[0037] Preferably, the distance between the print head and the forming platform is 15–100 μm to ensure that the extruded ink can directly contact the forming platform.

[0038] Preferably, the wavelength of the light source used for photocrosslinking is 380–500 nm. More preferably, the wavelength of the light source used for photocrosslinking is 405 nm.

[0039] Preferably, the printed hydrogel scaffold is subjected to a first photocrosslinking, and then the printed hydrogel scaffold is rotated 180° and subjected to a second photocrosslinking; wherein the photocrosslinking time for the first and second photocrosslinking is independently 3 to 10 minutes. As a further preferred embodiment, the photocrosslinking time for both the first and second photocrosslinking is 5 minutes.

[0040] Preferably, the crystal nucleus is sodium acetate trihydrate powder.

[0041] Preferably, a glass plate is used as the forming platform for the 3D printer. The forming platform is used to receive the ink after printing.

[0042] As a preferred option, the specific operation of laying a layer of crystal nuclei on the 3D printer forming platform is as follows:

[0043] After soaking the molding platform in an aqueous solution of sodium acetate trihydrate, remove it and let it air dry naturally until there is no liquid on the surface of the molding platform.

[0044] As a further preferred embodiment, the mass ratio of sodium acetate trihydrate to water in the aqueous solution is (1-1.5):1. Even more preferably, it is 1.3:1.

[0045] Preferably, the 3D printer is an extrusion 3D printer, including pneumatic extrusion and mechanical extrusion. Mechanical extrusion is more preferred.

[0046] In step (4) above,

[0047] As a preferred method, the specific steps for cleaning the cured hydrogel scaffold with deionized water to remove salt crystals are as follows:

[0048] Immerse the cured hydrogel scaffold in deionized water for 60 minutes, then remove it; repeat 3 times.

[0049] This invention discloses a method for preparing a salt crystallization-assisted extrusion-based high-precision 3D printing hydrogel. The method involves mixing a salt solution with a hydrogel solution to prepare 3D printing ink. A layer of crystal nuclei is deposited on the forming platform of an extrusion 3D printer, and printing is performed using the printer. During the extrusion process, the printing ink gradually decreases in temperature after leaving the nozzle and crystallizes upon contact with the crystal nuclei on the forming platform. The printing ink rapidly solidifies through a crystalline phase transition, effectively maintaining the stability of the printed structure. Subsequent layer-by-layer stacking allows crystals to grow continuously from the previous layer upwards. Finally, photocrosslinking and deionized water washing steps remove the salt, resulting in a hydrogel with high precision, high porosity, and good biocompatibility.

[0050] The preparation method of this invention overcomes the problems of low printing accuracy and easy structural collapse in existing hydrogel printing technologies, significantly improves the structural retention ability and accuracy of hydrogel printing, and contributes to the development of tissue engineering and regenerative medicine.

[0051] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0052] (1) The salt crystallization-assisted extrusion high-precision 3D printing hydrogel preparation method of the present invention is a supplement to the existing 3D printing hydrogel preparation method, expands the existing 3D printing hydrogel manufacturing method, and the hydrogel obtained has the characteristics of high precision, high porosity and good biocompatibility.

[0053] (2) The salt crystallization-assisted extrusion high-precision 3D printing hydrogel preparation method of the present invention can maintain the stability of the printed structure by using salt crystallization at room temperature, overcoming the problems of low printing accuracy and easy collapse of the structure in the existing hydrogel printing technology. There is no limitation on sample size, especially in the Z-axis direction, large-sized samples can be prepared.

[0054] (3) The salt crystallization-assisted extrusion high-precision 3D printing hydrogel preparation method of the present invention can prepare porous hydrogel through crystallization.

[0055] (4) The salt crystallization-assisted extrusion high-precision 3D printing hydrogel preparation method of the present invention uses salt that can be completely removed by washing with deionized water without residue, and the resulting hydrogel has high biocompatibility. Attached Figure Description

[0056] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0057] Figure 1 This is a schematic diagram of the extrusion structure and printing and crystallization process of the 3D printer used in Example 1;

[0058] Figure 2 An optical photograph of the cross-linked and cured hydrogel scaffold in Example 1;

[0059] Figure 3 An optical photograph of the hydrogel prepared in Example 1 after being soaked in deionized water;

[0060] Figure 4 This is a micrograph of the high-precision hydrogel obtained in Example 1 after curing and cleaning. Detailed Implementation

[0061] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without creative effort are within the scope of protection of this application.

[0062] Example 1:

[0063] like Figure 1As shown, a method for preparing a salt crystallization-assisted extrusion-based high-precision 3D printed hydrogel includes the following steps:

[0064] (1) First, prepare the hydrogel solution: Weigh 5.4g of acrylamide, 0.1g of N,N'-methylenebispropionamide, 0.05g of phenyl (2,4,6-trimethylbenzoyl) lithium phosphate and 0.1g of polyacrylamide (molecular weight of 7 million) into 6mL of deionized water using an electronic balance and mix them. Stir the mixture magnetically to form a clear and transparent hydrogel solution. The hydrogel solution is then shielded from light to prevent interference from external light.

[0065] (2) Preparation of salt solution: Weigh 24g of anhydrous sodium acetate using an electronic balance and mix it with 20mL of pure water. Heat the mixture in a water bath for one hour to completely dissolve it into a clear and transparent solution, thus obtaining the salt solution.

[0066] (3) Mix the above hydrogel solution and salt solution evenly to obtain 3D printing ink, and perform light-shielding treatment. The purpose of light-shielding treatment is to prevent external light from interfering with the solution.

[0067] (4) Load the printing ink into the barrel of the mechanical extrusion 3D printer, set the barrel temperature and nozzle temperature to 60℃, set the printing speed to 3000mm / min, the distance between the nozzle and the forming platform to 15μm, the extrusion flow rate to 0.01mL / min, and the nozzle diameter to 100μm.

[0068] To lay a layer of crystal nuclei on the 3D printer forming platform (glass plate), the specific method is as follows: immerse the glass plate in an aqueous solution of sodium acetate trihydrate (where the mass ratio of sodium acetate trihydrate to water is 1.3:1), remove the glass plate and allow it to air dry naturally. When there is no liquid on the glass surface, a forming platform with sodium acetate trihydrate crystal nuclei on the surface is obtained.

[0069] The printing model was set up and generated by the printing software of Suzhou Yongqinquan Intelligent Equipment Co., Ltd. The generated parameters were: XY plane size 2cm*2cm, line spacing 2mm, layer height 30μm, and 500 layers in a grid pattern. Then, 3D printing was carried out at room temperature.

[0070] (5) After 3D printing, the printed model was photocrosslinked for 5 minutes using a 405nm wavelength light source. Then, the printed model was rotated 180° and photocrosslinked for another 5 minutes to obtain the cured hydrogel scaffold. Its optical photograph is shown below. Figure 2 As shown, by Figure 2 It can be seen that the hydrogel scaffold has high precision and structural integrity.

[0071] (6) Finally, the solidified hydrogel scaffold is soaked in deionized water for 60 minutes and then removed; this process is repeated three times to remove residual salt from the scaffold and finally obtain a high-precision hydrogel with high biocompatibility.

[0072] Optical photographs of the hydrogel support (high-precision hydrogel) after cleaning with deionized water, as shown below. Figure 3 As shown, by Figure 3 As can be seen, after cleaning to remove the salt, the support changed from white to translucent, while maintaining its structural integrity.

[0073] The cleaned hydrogel scaffold (high-precision hydrogel) was observed under a microscope, and the results are as follows: Figure 4 As shown; by Figure 4 It can be seen that the porous structure and layer texture in this high-precision hydrogel are clearly visible.

[0074] Example 2:

[0075] (1) Preparation of hydrogel solution: Using an electronic balance, weigh 0.6 g of lyophilized methacrylamide gelatin sample, 0.05 g of lithium phenyl (2,4,6-trimethylbenzoyl) phosphate powder and 0.1 g of polyacrylamide and add them to 2 mL of deionized water. Mix them by magnetic stirring to form a clear and transparent hydrogel solution. The hydrogel solution is then shielded from light to prevent interference from external light.

[0076] (2) Preparation of salt solution: Weigh 5g of anhydrous sodium acetate and 2g of carbamide using an electronic balance and mix them in 4mL of pure water. Heat in a water bath for one hour to completely dissolve them into a clear and transparent solution to obtain the salt solution.

[0077] (3) Using steps (3)-(6) in Example 1, a biocompatible methacrylamide gelatin hydrogel scaffold was obtained.

[0078] Example 3:

[0079] (1) 3D printing ink is obtained by using steps (1)-(3) in Example 1.

[0080] (2) Load the printing ink into the barrel of the mechanical extrusion 3D printer, set the barrel temperature and nozzle temperature to 60℃, set the printing speed to 1000mm / min, the distance between the nozzle and the forming platform to 100μm, the extrusion flow rate to 0.05mL / min, and the nozzle diameter to 350μm.

[0081] To lay a layer of crystal nuclei on the forming platform (glass plate) of a 3D printer, the specific method is as follows: immerse the glass plate in an aqueous solution of sodium acetate trihydrate (where the mass ratio of sodium acetate trihydrate to water is 1.3:1), remove the glass plate and allow it to air dry naturally. When there is no liquid on the glass surface, a forming platform with sodium acetate trihydrate crystal nuclei on the surface is obtained.

[0082] The printing model was set up and generated by the printing software of Suzhou Yongqinquan Intelligent Equipment Co., Ltd. The generated parameters were: XY plane size 2cm*2cm, line spacing 2mm, layer height 50μm, and 500 layers in a grid pattern. Then, 3D printing was carried out at room temperature.

[0083] (3) Using steps (5)-(6) in Example 1, a high-precision hydrogel with high biocompatibility is finally obtained.

[0084] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0085] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing a salt crystallization-assisted extrusion-based high-precision 3D printed hydrogel, characterized in that, Includes the following steps: (1) Mix the hydrogel monomer, photoinitiator, thickener and water evenly to prepare a hydrogel solution; dissolve the salt in water to prepare a salt solution; (2) Prepare printing ink by mixing hydrogel solution and salt solution; (3) A layer of crystal nuclei is laid on the forming platform of the 3D printer, and the pre-set hydrogel scaffold is printed using the printing ink as raw material and the extrusion 3D printer is used. (4) The printed hydrogel scaffold is subjected to photocrosslinking, and then the cured hydrogel scaffold is cleaned with deionized water to remove salt crystals, thus obtaining the extrusion-type high-precision 3D printed hydrogel. The salt is sodium acetate or a mixture of sodium acetate and carbamide; The crystal nucleus is sodium acetate trihydrate powder.

2. The method for preparing salt crystallization-assisted extrusion-based high-precision 3D printing hydrogel according to claim 1, characterized in that, The hydrogel monomer is one or more of acrylamide, acrylic acid, methacrylated gelatin, methacrylated hyaluronic acid, methacrylated chitosan, and methacrylated silk fibroin; In the hydrogel solution, the mass ratio of hydrogel monomer to water is (0.1~1.4):

1.

3. The method for preparing salt crystallization-assisted extrusion-based high-precision 3D printing hydrogel according to claim 2, characterized in that, When the hydrogel monomer is one or both of acrylamide and acrylic acid, a crosslinking agent is also added to the hydrogel solution. The crosslinking agent is N,N'-methylenebispropionamide.

4. The method for preparing salt crystallization-assisted extrusion-based high-precision 3D printing hydrogel according to claim 1, characterized in that, When the salt is sodium acetate, the mass ratio of sodium acetate to water in the salt solution is (0.2~1.7):1; When the salt is a mixture of sodium acetate and carbamide, the mass ratio of sodium acetate to water in the salt solution is (0.2~1.7):1; the mass ratio of carbamide to water is (0.2~0.8):

1.

5. The method for preparing salt crystallization-assisted extrusion-based high-precision 3D printing hydrogel according to claim 1, characterized in that, The thickener is one or more of the following: polyacrylamide, polyacrylic acid, polyethylene glycol, gelatin, cellulose or its derivatives, starch or its derivatives, fumed silica, and carbomer. In the hydrogel solution, the mass ratio of thickener to water is 0.005:1 to 1:

5.

6. The method for preparing salt crystallization-assisted extrusion-based high-precision 3D printing hydrogel according to claim 1, characterized in that, In printing ink, the volume ratio of hydrogel solution to salt solution is 1:17 to 10:

1.

7. The method for preparing salt crystallization-assisted extrusion-based high-precision 3D printing hydrogel according to claim 1, characterized in that, In step (3), the 3D printing parameters are: barrel temperature is 50~80 ℃, nozzle temperature is 40~80 ℃, printing speed is 75~4000 mm / min, extrusion flow rate is 0.01~0.5 mL / min, and nozzle diameter is 80~1000 μm.

8. The method for preparing salt crystallization-assisted extrusion-based high-precision 3D printing hydrogel according to claim 1, characterized in that, The wavelength of the light source used for photocrosslinking is 380~500 nm.

9. The method for preparing salt crystallization-assisted extrusion-based high-precision 3D printing hydrogel according to claim 1, characterized in that, The specific steps for cleaning the cured hydrogel scaffold with deionized water to remove salt crystals are as follows: Immerse the cured hydrogel scaffold in deionized water for 60 minutes, then remove it; repeat 3 times.

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