Application of a small molecule assembled hydrogel in the preparation of 4D printing ink

Abstract

The present invention discloses the application of a small molecule assembled hydrogel in the preparation of 4D printing ink. First, the organic small molecule hexadecyl maleate is synthesized. Then, in the presence of a very small amount of surfactant sodium dodecyl sulfate, its aqueous solution self-assembles into a flat liquid crystal bilayer structure above the Krafft point (37°C). Utilizing the special phase change characteristics of the system, a stable gel state is formed below the Krafft point to obtain a printable ink composed of small molecule non-polymers. The ink meets the rheological properties required for direct ink writing, including shear thinning, shear yield, and rapid recovery of modulus after shear stress disappears. The small molecule assembled hydrogel ink prepared by the present invention can achieve stable fiber printing by self-regulating viscosity through temperature, without the need for a photocuring step. Large-area anisotropic arrangement of liquid crystal bilayers is achieved through 3D printing, and the color change of thermally responsive printed objects is achieved.

Description

Technical Field

[0001] The present invention relates to application of a small molecule assembled hydrogel in preparing 4D printing ink, belonging to the technical field of small molecule materials. Background Art

[0002] 3D printing builds objects by depositing materials layer by layer, allowing precise control over the dimensions and properties of complex printed structures. The most widely used printing method is extrusion-based, which boasts the ability to print a wide range of materials. Direct ink writing, an extrusion-based additive manufacturing technique, has been extensively developed and researched for its low cost, simplicity, and wide range of materials. Newer 4D printing technologies add a temporal dimension to 3D printing. 4D printing was initially defined as static 3D printed objects that change shape under appropriate external stimuli, such as light, temperature, pH, magnetic fields, and electric fields. With increasing research, 4D printing has expanded to include the generation of changes in physical and chemical properties and functionality, leading to innovative developments in areas such as biomimetic materials, autonomous robotics, smart textiles, and drug delivery. However, practical applications still face numerous challenges, and the exploration of complex 4D property variations is crucial. Among the various 3D printing inks, hydrogels are one of the most widely used. However, traditional 3D printing inks use polymers. To ensure printability, these inks are typically modified chemically, with the addition of rheology modifiers and fillers. Photolithography is often required at the tip of the needle to ensure fiber stability during printing.

[0003] This invention provides a novel 4D printing ink composed of small molecules. Through its assembly structure and unique phase transition, the ink increases viscosity, suppresses diffusion during printing, and ultimately achieves stable printing of printed fibers. The ink flows as a liquid during extrusion and solidifies as a solid after extrusion. Temperature control during extrusion suppresses diffusion and ensures fiber stability. Temperature-induced phase transitions in the printed product produce color changes, ultimately enabling color-shifting 4D printing. This developed color-responsive 4D printing method is expected to help explore the full potential of 4D printing. Summary of the Invention

[0004] This invention aims to provide a method for preparing 4D printing inks using small molecule assembled hydrogels. This method utilizes the unique phase transition of the lamellar bilayer structure self-assembled in aqueous solution by the organic small molecule hexadecyl maleate, as well as the change in bilayer spacing during the phase transition, to achieve 4D printing of inks. This method produces a 3D printable hydrogel model that changes ink viscosity and color solely through phase transitions stimulated by external temperature.

[0005] The present invention first synthesizes the organic small molecule hexadecyl maleate (HGM), then dissolves HGM in deionized water with a small amount of the ionic surfactant sodium dodecyl sulfate (SDS) as a cosolvent. Above the Krafft point (37°C), the organic small molecules self-assemble into a lamellar liquid crystal color solution. By controlling the HGM content, the interlayer spacing is controlled to between 150 and 300 nm. This solution is then placed in an environment below the Krafft point, undergoing a phase transition to obtain a small molecule assembly ink. The ink's stable gel state, shear thinning properties, and shear yield properties make it suitable for use as a 3D printing ink. The hydrogel ink is loaded into a syringe and extruded under pressure. The 3D printing platform is temperature-controlled, allowing the hydrogel ink to be printed into complex three-dimensional structures in one step. First, the ink is assembled from small molecules, resulting in weak intermolecular forces and minimal extrusion pressure, reducing printing costs. Second, the ink's viscosity is affected by temperature. Printing the ink from room temperature onto a low-temperature cooling platform (>0°C) controls diffusion during printing, ensuring the stability of the printed fibers and significantly controlling the print resolution. Finally, the printed product undergoes a phase change under temperature stimulation, resulting in a periodic change in the spacing between the bilayers and a change in color, thus achieving 4D printing.

[0006] The application of the small molecule assembled hydrogel of the present invention in preparing 4D printing ink comprises the following steps:

[0007] The small molecule assembled hydrogel is placed in a 50CC injection syringe, and the syringe device is installed on the 3D printing platform. The extrusion pressure is provided by an air pump, and the pressure regulator controls the air pressure. The small molecule assembled hydrogel is extruded through a 30-34G needle. After 3D modeling, the printed model is exported to GCODE format using slicing software. The memory card is connected to the 3D printer, and the printer moves along the prescribed path. By continuously adjusting the movement speed and extrusion pressure, the hydrogel ink can be evenly written on the substrate.

[0008] The printing platform is a constant temperature cooling platform with an adjustable temperature range of 0-25°C. The vertical distance between the printing needle and the cooling platform is 150-200μm.

[0009] The initial movement speed of the 3D printing device of the present invention is set to 2-10 mm / s, and the extrusion pressure is 1-3 psi.

[0010] The small molecule assembled hydrogel is prepared by the following method:

[0011] Step 1: First, synthesize cetyl maleate. Mix 20-30g of maleic anhydride and 48-72g of cetyl alcohol. React at 110°C for 10-30 minutes under nitrogen, then continue to react at 130°C for 20-40 minutes, stirring under nitrogen and reflux for 50-60 minutes. After the reaction is complete, cool the mixture and add n-hexane solution to the mixture until a crude white crystal product precipitates. Recrystallize the crude product from ethanol to obtain a purified sample.

[0012] Step 2: Synthesis of hexadecyl maleate. Under a nitrogen atmosphere, dissolve 10-15 g of the hexadecyl maleate purified in Step 1 in 8-12 mL of toluene and react with 6.5-9.7 g of glycidol at 106-110°C in the presence of a catalyst. Reflux the mixture at 105-110°C under a nitrogen atmosphere for 4-6 hours, evaporating the toluene during the reflux process. Purify the crude product using a silica gel column, and then recrystallize the purified product to obtain the final sample.

[0013] Step 3: Dissolve the hexadecyl maleate synthesized in step 2 and a small amount of sodium lauryl sulfate in deionized water, mix the mixture, and place it in a 45-65°C water bath for self-assembly for 20-24 hours to obtain a brightly colored solution.

[0014] Step 4: Place the colored solution from step 3 at an ambient temperature of 1-37°C for 2-5 minutes to obtain a stable gel product.

[0015] In step 1, the flow rate of nitrogen is controlled at 0.5-2 mL / s.

[0016] In step 1, n-hexane is added when the reaction mixture is cooled to 70-80° C. after the reflux reaction is completed. 40-60 mL of n-hexane solution is added with vigorous stirring. A large amount of white crystals will precipitate during this process.

[0017] In step 1, the ethanol recrystallization is performed 3-5 times, and then the ethanol is removed in a vacuum drying oven at 42-45° C. to obtain cetyl maleate, which has a melting point of 69-71° C.

[0018] In step 2, the flow rate of nitrogen is controlled at 0.5-2 mL / s, and the catalyst is 18-24 mg of pyridinium p-toluenesulfonate.

[0019] In step 2, the eluent used for silica gel column purification is a mixture of n-hexane and ethyl acetate in a volume ratio of 3:2, and then the solvent is removed by rotary evaporation at 42-45° C. and a pressure of 10-20 kPa.

[0020] In step 2, the recrystallization is performed using a mixed solution of acetone / n-hexane (volume ratio 1 / 1) for 2-3 times, and the mixture is placed in a vacuum drying oven at 42-45° C. to remove the solvent. The final product, hexadecyl maleate, has a melting point of 50-52° C.

[0021] In step 3, the amount of self-assembly solution components used is 35-60 mg of hexadecyl maleate, 6×10 -2 -10×10 -2 mg, prepared into 1-3 mL of water system.

[0022] The beneficial effects of the present invention are embodied in:

[0023] The present invention provides a method for preparing a novel small molecule assembly 4D printing ink that only requires phase change under external temperature stimulation to achieve ink viscosity change and color change. First, the ink for 3D printing is prepared by preparing an organic small molecule hexadecyl maleate (HGM), and then HGM is dissolved in about 50°C water in conjunction with a very small amount of ionic surfactant sodium dodecyl sulfate (SDS). The surfactant properties of the HGM molecule are utilized and it forms a flat bilayer structure when the critical micelle concentration is exceeded. When the critical micelle concentration is exceeded, it dissolves and self-assembles. By controlling the HGM content, the interlayer spacing is controlled between 150-300nm to obtain a colored solution. The color of the final assembled sample can be adjusted by changing the HGM or SDS content. That is, at the same HGM concentration, increasing the amount of SDS will reduce the final interlayer spacing of the bilayer assembly and the solution color will shift blue; at the same SDS content, increasing the amount of HGM will also reduce the final interlayer spacing of the bilayer assembly and the solution color will shift blue. The assembled solution system is placed at 0-37°C for a period of time to obtain a small molecule assembled hydrogel. The ink has stable gel state and shear thinning, shear yield and other characteristics, making it suitable for use as 3D printing ink. The hydrogel ink is loaded into a syringe and extruded by pressure. The temperature of the 3D printing platform is controllable, and the hydrogel ink is printed into a complex three-dimensional structure in one step. First, the ink is assembled from small molecules, the intermolecular force is weak, and the printing extrusion pressure is extremely small, which reduces the printing cost. Secondly, the viscosity of the ink is affected by temperature. The normal temperature ink is printed on a low temperature cold stage (>0°C) to control the diffusion phenomenon of the print, achieve the stability of the printed fiber, and greatly control the resolution of the print. Finally, the printed product undergoes a phase change under temperature stimulation, resulting in a change in the periodic bilayer interlayer spacing, thereby producing a change in color. The present invention provides a theoretical basis for the preparation of 4D small molecule assembled hydrogel ink. At the same time, this type of 4D small molecule assembled hydrogel provides a new method and new ideas for the development of new 4D printing inks.

[0024] Compared to traditional polymer hydrogel inks, the 4D printing small molecule assembled hydrogel ink of the present invention is a periodic layered structure self-assembled from the organic small molecule hexadecyl maleate. It has a simple structure, is easy to obtain, and can undergo a transition between solution and gel phases around its Krafft point with temperature changes. The printing process does not require an additional photocuring step and can be directly extruded. This phase transition is solely due to temperature, and the ink viscosity can be adjusted by temperature, thereby printing stable fibers and controlling the printing resolution to avoid severe diffusion. The intermolecular forces in the gel assembled from small molecules are hydrogen bonds and van der Waals forces, making the gel state easily destructible. The printing pressure is far lower than the extrusion pressure of conventional 3D printing. The final printed product undergoes a phase transition near the Krafft point, with the interlayer spacing of the periodic layered structure changing, and Bragg diffraction emits a different color than before the phase transition. The small molecule assembled hydrogel ink is obtained solely through a special phase transition of the small molecule self-assembled solution, and the two phases are reversible and recyclable. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Optical photographs of solution-hydrogel transformation of small molecule assembly at different concentrations.

[0026] Figure 2 The effect of different HGM contents and temperatures on the color and interlayer spacing of the system under the same SDS content.

[0027] Figure 3 The effect of different SDS contents and temperatures on the color and interlayer spacing of the system under the same HGM content.

[0028] Figure 4 This is an optical photograph of the sample printed on the modified 3D printing platform. Figure 2 It can be seen that the small molecule hydrogel ink has good rheological properties and stability.

[0029] Figure 5 The rheological curves of small molecule assembled hydrogels at different temperatures. Figure 3 It can be seen that as the temperature decreases, the ink viscosity gradually increases.

[0030] Figure 6 The fiber resolution micrographs obtained under the same printing parameters and different platform temperatures. Figure 4 It can be seen that lowering the temperature can significantly improve the printing resolution.

[0031] Figure 7 4D printed color-changing devices. 3D hydrogel devices change color as the temperature changes.

[0032] Figure 8 This is the H NMR spectrum of the intermediate product hexadecyl maleate.

[0033] Figure 9 This is the H NMR spectrum of the final product hexadecyl maleate. DETAILED DESCRIPTION

[0034] The reagents, raw materials and equipment used in the present invention are all commercially available products and can be purchased on the market.

[0035] Example 1: Synthesis of organic small molecule surfactants

[0036] 1. Synthesis of Cetyl Maleate

[0037] 21.56 g of maleic anhydride and 52.12 g of 1-hexadecanol were added to a 150 mL three-necked flask, stirred with a nitrogen flow of 1 mL / s, heated in an oil bath at 110°C for 20 min, then raised to 130°C and heated for 30 min; cooled to 70°C, stirred rapidly, and 50 mL of n-hexane was added, resulting in the precipitation of a large amount of white crystals; cooled to room temperature; placed the product in a 45°C vacuum drying oven to remove the n-hexane, then recrystallized three times with ethanol, and placed in a 45°C vacuum drying oven again to remove the ethanol to obtain the intermediate product, hexadecyl maleate.

[0038] 2. Synthesis of Cetyl Maleate

[0039] 11.56 g of hexadecyl maleate, 6.714 mL of glycidol, 10 mL of toluene and 20 mg of catalyst pyridinium p-toluenesulfonate were added to a 50 mL three-necked flask, and the mixture was stirred and heated at a constant temperature of 108° C. in an oil bath with a nitrogen flow rate of 1 mL / s for 5 h. After the reaction was completed, the mixture was cooled to room temperature and purified by a silica gel column with n-hexane / ethyl acetate (volume ratio 3 / 2) as the eluent. The precipitated solution from the silica gel column was evaporated to remove the solvent using a rotary evaporator at a temperature of 45° C. and a pressure of 20 kPa. The product was recrystallized twice with acetone / n-hexane (volume ratio 1 / 1) and then placed in a vacuum drying oven at 45° C. to remove the solvent, thereby obtaining the final product, the amphiphilic surfactant hexadecyl maleate.

[0040] Example 2: Preparation of small molecule assembled hydrogel

[0041] Take 49.18 mg of small molecule hexadecyl maleate and 0.086 mg of sodium lauryl sulfate and dissolve them in 2 mL of deionized water to prepare a 2.4 wt% HGM solution. Self-assemble in a 50°C water bath for 24 hours. During this period, gently shake the glass bottle every four hours to accelerate the assembly. After the assembly is completed, a bright purple solution is formed.

[0042] Another 40.82 mg of small molecule hexadecyl maleate and 0.071 mg of sodium lauryl sulfate were dissolved in 2 mL of deionized water to prepare a 2.0 wt% HGM solution. The above steps were repeated to obtain a bright green solution after the assembly was completed.

[0043] Another 32.52 mg of small molecule hexadecyl maleate and 0.057 mg of sodium lauryl sulfate were dissolved in 2 mL of deionized water to prepare a 1.6 wt% HGM solution. The above steps were repeated to obtain a bright pink solution.

[0044] The three solutions were placed at room temperature for five minutes to obtain gel ink.

[0045] Example 3: 3D printing of small molecule assembled hydrogel ink

[0046] The 1.6wt%, 2.0wt%, and 2.4wt% HGM printable small molecule assembly hydrogel inks synthesized in Example 2 were placed in two 50cc syringes. The syringe device was installed in the 3D printing platform system. The extrusion pressure was provided by an air pump, and the pressure regulator controlled the pressure. The small molecule assembly hydrogel ink was extruded through a 34G (60μm) needle. By continuously adjusting the movement speed and extrusion pressure, the hydrogel ink was able to write evenly on the substrate. Printing was performed on a temperature-controlled cold stage at a constant temperature. The fiber diameter was controlled by temperature. The cold stage temperature was set to three groups: 25°C, 15°C, and 5°C. The syringe needle was 150μm vertically from the cold stage plane. The initial movement speed of the 3D printing device of the present invention was set to 5mm / s, and the extrusion pressure was 1psi.

[0047] The present invention provides a method for preparing a novel small molecule assembly 4D printing ink that only requires phase change under external temperature stimulation to achieve ink viscosity change and color change. First, the ink used for 3D printing is prepared by preparing an organic small molecule hexadecyl maleate, and then HGM is dissolved in about 50°C water in conjunction with a very small amount of ionic surfactant sodium dodecyl sulfate (SDS). The surfactant properties of the HGM molecule are utilized and it forms a flat bilayer structure when the critical micelle concentration is exceeded. When the critical micelle concentration is exceeded, it dissolves and self-assembles. By controlling the HGM content, the interlayer spacing is controlled between 150-300nm to obtain a colored solution. The color of the final assembled sample can be adjusted by changing the HGM or SDS content. That is, at the same HGM concentration, increasing the amount of SDS will reduce the final interlayer spacing of the bilayer assembly and the solution color will shift blue; at the same SDS content, increasing the amount of HGM will also reduce the final interlayer spacing of the bilayer assembly and the solution color will shift blue. The assembled solution system is placed at 0-37°C (excluding 37°C) for a period of time to obtain a small molecule assembled hydrogel. The ink has stable gel state and shear thinning, shear yield and other characteristics, making it suitable for use as 3D printing ink. The hydrogel ink is loaded into a syringe and extruded by pressure. The 3D printing platform can control the temperature and print the hydrogel ink into a complex three-dimensional structure in one step. First, the ink is assembled from small molecules, the intermolecular force is weak, and the printing extrusion pressure is extremely small, which reduces the printing cost. Secondly, the viscosity of the ink is affected by temperature. The normal temperature ink is printed on a low temperature cold stage (>0°C) to control the diffusion phenomenon of the print, achieve the stability of the printed fiber, and greatly control the resolution of the print. Finally, the printed product undergoes a phase change under temperature stimulation, resulting in a change in the periodic bilayer interlayer spacing, thereby producing a change in color. The present invention provides a theoretical basis for the preparation of 4D small molecule assembled hydrogel ink. At the same time, this type of 4D small molecule assembled hydrogel provides a new method and new ideas for the development of new 4D printing inks.

Claims

1. Application of a small molecule assembled hydrogel in the preparation of 4D printing ink, characterized by: The organic small molecule hexadecyl maleate was dissolved in deionized water, and the ionic surfactant sodium lauryl sulfate was used as a cosolvent. Above the Krafft point, the organic small molecules self-assembled into a lamellar liquid crystal color solution. The interlayer spacing was controlled between 150-300 nm by controlling the content of hexadecyl maleate. The dosage of each component in the self-assembly solution was 35-60 mg of hexadecyl maleate, 6×10 sodium lauryl sulfate, and 10 -2 -10×10 -2 mg, prepared into 1-3 mL water system; The solution is then placed in an environment below the Krafft point to undergo phase change to obtain a small molecule assembled hydrogel; the small molecule assembled hydrogel is placed in an injection syringe, and the syringe device is installed on a 3D printing platform. An air pump provides extrusion pressure, and a pressure regulator controls the air pressure. The small molecule assembled hydrogel is extruded through a 30-34G needle. By adjusting the movement speed and extrusion pressure, the hydrogel ink can be evenly written on the substrate.

2. The use according to claim 1, characterized in that: The printing platform is a constant temperature cooling platform with an adjustable temperature range of 0-25°C. The vertical distance between the printing needle and the cooling platform is 150-200μm.

3. The use according to claim 1, characterized in that: Hexadecyl maleate and sodium lauryl sulfate are dissolved in deionized water and mixed, and self-assembled in a 45-65°C water bath for 20-24 hours to obtain a brightly colored solution; the colored solution is placed at an ambient temperature of 1-37°C for 2-5 minutes to obtain a stable gel product.

4. The use according to claim 1, characterized in that: The moving speed was set to 2-10 mm / s and the extrusion pressure was set to 1-3 psi.

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