Preparation method and application of oriented freezing and mechanical stretching induced anisotropic hydrogel
Through unidirectional freezing assembly and mechanical stretching, anisotropic hydrogel with a directional channel structure is induced, and the dissociation mechanism of metal coordination bonds is regulated by ultraviolet light programming, the problem of difficult traditional hydrogels to replicate complex deformation and limited response speed is solved, achieving efficient water molecule transmission and fast and controllable 3D deformation.
Patent Information
- Application Number
- CN202510368215.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-26
- Publication Date
- 2025-05-27
AI Technical Summary
Traditional homogeneous hydrogels are limited by isotropic network structures, making it difficult to replicate the complex multi-dimensional coordinated deformation behavior of biological tissues, and the dense crosslinking network limits the transmission of water molecules, resulting in limited response speed.
The 3D ordered cellular network structure is constructed through unidirectional cryogenic assembly technology, and combined with mechanical stretch induction and Fe3+ secondary crosslinking strategies, anisotropic hydrogel with a directional channel structure is formed. Then, the dissociation mechanism of metal coordination bonds is regulated through ultraviolet light programming, and a gradient crosslinking network is built to achieve controllable 3D deformation under light and thermal stimulation.
It significantly improves the diffusion efficiency of water molecules in the hydrogel network, imparts accurate mechanical anisotropy to the material, and realizes fast and controllable multimodal 3D deformation, expanding the potential of hydrogels in complex application scenarios such as bionic robots and intelligent grasping.
Smart Images
Figure CN120040655A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a preparation method and application of an anisotropic hydrogel induced by directional freezing combined with mechanical stretching, belonging to the field of nanotechnology. Background Art
[0002] Flexible intelligent drive systems, with their bionic deformation ability and biocompatible characteristics, have shown breakthrough application potential in fields such as soft robots, flexible electronic sensors, and wearable medical devices. For example, by mimicking the movement mechanism of sea cucumber epidermis, hydrogel actuators can achieve directional curling through ion concentration gradients; in addition, stimulus-responsive materials that simulate plant tropic growth can construct self-regulating drug delivery systems, etc. As the core material for bionic actuation, hydrogels can achieve deformation from microscale to macroscale under the regulation of external stimuli due to their osmotic pressure-driven reversible swelling-deswelling characteristics. However, traditional homogeneous hydrogels are limited by the isotropic network structure and can only produce isotropic expansion / contraction deformation under homogeneous stimuli, making it difficult to replicate the complex multi-dimensional cooperative deformation behavior of biological tissues.
[0003] To break the deformation limitation of isotropic hydrogels, researchers have developed bionic orientation structure construction strategies. Typical technical paths include external field regulation methods such as electric / magnetic field-induced directional assembly of nano-fillers and mechanical pre-stretching-induced polymer chain orientation. In particular, the mechanical stretching-induced strategy realizes cross-scale precise regulation of network topology by synchronously reconstructing the molecular chain orientation arrangement and the spatial distribution of nano-reinforcing phases, providing a new paradigm for the design of structure-function integrated hydrogels. However, the dense cross-linked networks prepared by these methods will significantly limit the transport of water molecules, resulting in a certain limitation of the response speed.
[0004] Optimizing the driving performance of hydrogels requires a synergistic improvement between the "structural orientation degree" and the "mass transfer efficiency". The honeycomb-like porous structure constructed based on the ice template method can significantly improve the diffusion rate of water molecules. By synchronously constructing open porous channels and an ion-crosslinked fixed orientation polymer three-dimensional network structure in the hydrogel network, the present invention not only endows the material with excellent anisotropic mechanical properties but also can regulate the 3D deformation mode through ultraviolet light programming, realizing precise and complex driving of the hydrogel actuator under light and heat stimuli, and significantly expanding the potential of hydrogels in complex application scenarios such as bionic robots and intelligent grasping. Summary of the Invention
[0005] Aiming at the deficiencies of the above-mentioned existing technologies, the present invention provides a preparation method and application of an orientation freezing combined with mechanical stretching-induced anisotropic hydrogel. The present invention uses unidirectional freezing to induce photopolymerization, and then combines mechanical stretching orientation technology with a secondary crosslinking strategy to successfully prepare a hydrogel actuator with high anisotropy and rapid response ability, and further realizes the rapid and controllable 3D deformation of the APPF hydrogel actuator by utilizing the characteristics of ultraviolet light controllable programming crosslinking-decrosslinking.
[0006] In the preparation method of the orientation freezing combined with mechanical stretching-induced anisotropic hydrogel of the present invention, first, N-isopropylacrylamide (NIPAM), acrylic acid (AA), silver nanowires (AgNW), a crosslinking agent, and a photoinitiator are uniformly mixed in a specific ratio, and a AgNW / PNIPAM / PAA primary hydrogel with a three-dimensional ordered honeycomb network structure is assembled by unidirectional freezing technology-assisted ultraviolet photopolymerization; subsequently, the polymer network is induced to orient along the stretching direction by mechanical stretching, and Fe 3+ is crosslinked with the carboxyl groups in the polymer network to fix the stretching deformation, and an excellent photothermal response AgNW / PNIPAM / PAA / Fe 3+ hydrogel (APPF) with open mass transfer channels is successfully prepared. Then, by using the ultraviolet light-regulated selective dissociation mechanism of metal coordination bonds, a gradient crosslinking network from the irradiated surface to the non-irradiated surface is constructed to realize the controllable 3D deformation of the APPF hydrogel under light and heat stimuli.
[0007] The preparation method of the orientation freezing combined with mechanical stretching-induced anisotropic hydrogel of the present invention includes the following steps:
[0008] Step 1: Prepare the AgNW / PNIPAM / PAA hydrogel precursor solution
[0009] In a low-temperature environment of 5-10 °C, monomer 1, monomer 2, a crosslinking agent, and a photoinitiator are successively ultrasonically dissolved in deionized water, and the bubbles generated by dissolution are removed by vacuum drying; the prepared hydrogel precursor solution is transferred to an ice bath environment for storage; finally, silver nanowires are added to the precursor solution, and after mixing evenly, the AgNW / PNIPAM / PAA hydrogel precursor solution is obtained.
[0010] In Step 1, the monomer 1 is N-isopropylacrylamide (NIPAM), and the addition amount is 14%-16% of the mass of the hydrogel precursor solution; the monomer 2 is acrylic acid (AA), and the addition amount is 1.6%-3.2% of the mass of the hydrogel precursor solution; the crosslinking agent is N,N'-methylenebisacrylamide, and the addition amount of the crosslinking agent is 0.3%-0.4% of the mass of the monomer; the photoinitiator is 2-hydroxy-2-methyl-1-phenyl-1-propanone, and the addition amount of the photoinitiator is 6.5%-7.5% of the mass of the monomer, and the addition amount of silver nanowires is 0.6%-1.2% of the mass of the hydrogel precursor solution.
[0011] Furthermore, the mass ratio between monomer 1 and monomer 2 is 10:1 - 9:2.
[0012] In Step 1, the silver nanowires are prepared by the following method:
[0013] Add 10 g of PVP solid powder and 400 mL of glycerol into a 1000 mL beaker. After mechanical stirring evenly, place it at 160 °C and heat for 30 min to dissolve PVP. After the above solution cools to room temperature, stir gently and add AgNO 3 solution (5 g of AgNO 3 dissolved in 3 mL of deionized water) and NaCl solution (300 mg of NaCl dissolved in 2 mL of deionized water) in sequence. After sufficient stirring, place it in an oven at 180 °C and react for 16 hours. When the solution color turns grayish green, the silver nanowires can be prepared. Finally, repeatedly centrifuge and wash with water and ethanol to remove the PVP on the surface of the silver nanowires to obtain pure silver nanowires.
[0014] Step 2: Unidirectional freezing ultraviolet photopolymerization forming
[0015] Inject the AgNW / PNIPAM / PAA hydrogel precursor solution obtained in Step 1 into a prefabricated mold and immediately transfer it to a unidirectional freezing platform. Control the low temperature of the platform. After the mold and the internal precursor solution are completely frozen, perform ultraviolet light irradiation polymerization in a low temperature environment to obtain a primary hydrogel.
[0016] In Step 2, the temperature of the unidirectional freezing cold platform is set to -20 °C to -40 °C; the low temperature environment for polymerization is -10 °C to -20 °C, and the ultraviolet light irradiation polymerization time is 3 min.
[0017] Step 3: Mechanical stretching - secondary crosslinking synergistic orientation
[0018] Stretch the primary hydrogel obtained in Step 2 mechanically along the direction perpendicular to the unidirectional freezing ice crystal growth direction and fix it with a clamp. Then immerse it in an aqueous ferric chloride solution to complete secondary crosslinking. Then dynamically swell with deionized water for a period of time to remove the surface free Fe 3+ and finally obtain an anisotropic hydrogel with a directional pore structure.
[0019] In Step 3, the mechanical stretching is to stretch the primary hydrogel to 150% of its original length; the concentration of the aqueous ferric chloride solution is 0.06 - 0.10 mol / L, the soaking time is 18 h; the dynamic swelling time of deionized water is 2 min; finally, an anisotropic APPF hydrogel with a directional pore structure is obtained.
[0020] The application of the present invention for preparing an anisotropic hydrogel by combining directional freezing and mechanical stretching is to irradiate the anisotropic APPF hydrogel with ultraviolet light of a specific wavelength and intensity. By controlling the irradiation area and irradiation time, the ultraviolet light is used to selectively dissociate the induced metal coordination bonds, that is, Fe 3+ and COO - The selective dissociation of the coordination bonds constructs a polymer network crosslinking density gradient between the irradiated surface and the non-irradiated surface, endowing the APPF hydrogel with the ability to generate multi-modal controllable three-dimensional deformation under light and heat stimuli.
[0021] The wavelength of the ultraviolet light with the specific wavelength and intensity is 365 nm, and the intensity is 18 W / cm 2 , and the irradiation time is 0.5 - 1 min.
[0022] The beneficial effects of the present invention are as follows:
[0023] When preparing the hydrogel actuator of the present invention, first, a 3D ordered honeycomb network structure is constructed by the unidirectional freezing assembly technology, and then a mechanical stretching induction combined with Fe 3+ secondary crosslinking strategy is adopted to make the polymer chains in the 3D network align along the stretching direction, forming an anisotropic hydrogel with a directional pore structure. Finally, through the programmable dissociation mechanism of ultraviolet light-induced metal coordination bonds, a gradient crosslinking network is constructed inside the hydrogel from the irradiated area to the non-irradiated area. The optimized directional pore structure significantly improves the diffusion efficiency of water molecules in the hydrogel network. The oriented polymer network endows the material with precise mechanical anisotropy, while the gradient crosslinking structure formed by ultraviolet light programming realizes the differential response of polymer chains under light and heat stimuli. Under the synergistic action of the three, the hydrogel can quickly complete complex 3D deformations with adjustable deformation directions and amplitudes under a hot water bath or near-infrared stimulation.
[0024] In summary, the present invention proposes a preparation method for an anisotropic hydrogel by combining directional freezing and mechanical stretching. First, a three-dimensional honeycomb hydrogel network is constructed by the ice template method, and then an anisotropic APPF hydrogel is obtained by mechanical stretching induction orientation and metal ion secondary crosslinking locking. The optimization of the three-dimensional honeycomb network to a highly ordered oriented structure is realized under the synergistic action of the open interconnected pores induced by the ice template and the mechanically stressed oriented network, providing a fast transmission channel for water molecule transport, enabling the hydrogel actuator to achieve rapid reversible anisotropic deformation under external stimuli. Further, through the controllable induction of local de-crosslinking of Fe 3+ by ultraviolet light, the controllable programming of the stimulus response is realized. The APPF hydrogel exhibits fast programmable multi-modal 3D deformation ability. The present invention provides a new idea and theoretical basis for the preparation of flexible intelligent hydrogel actuators. Brief Description of the Drawings
[0025] Figure 1 Scanning electron microscope image of AgNWs prepared according to the present invention. From Figure 1 it can be seen that the size distribution of AgNWs is uniform, with a diameter of about 60 - 100 nm and a length of 10 - 15 μm.
[0026] Figure 2 Scanning electron microscope image of the surface of anisotropic APPF hydrogel with porous open channels prepared according to the present invention. From Figure 2 it can be seen that the APPF hydrogel retains a highly ordered orientation structure through stretching orientation and secondary crosslinking, and the hydrogel network presents a long and ordered layered structure in the stretching direction.
[0027] Figure 3 Scanning electron microscope image of the cross-section of anisotropic APPF hydrogel with porous open channels prepared according to the present invention. From Figure 3 it can be seen that the hydrogel retains a highly ordered orientation structure through unidirectional freezing, and the hydrogel network presents a layered structure in the vertical direction.
[0028] Figure 4 Stress-strain curve of the anisotropic APPF hydrogel prepared according to the present invention. Figure 4 It can be calculated that the Young's modulus of the anisotropic hydrogel along the parallel direction (APPF∥) is 2.48 times that of the Young's modulus in the stretching perpendicular direction (APPF⊥), showing obvious mechanical anisotropy, which provides a basis for anisotropic response deformation.
[0029] Figure 5 Temperature response photo of the three-dimensional deformation of the APPF hydrogel under thermal stimulation prepared according to the present invention. From Figure 5 the three-dimensional deformation of the "U" pattern of the hydrogel can be realized by means of ultraviolet light programming.
[0030] Figure 6 Light response temperature change curve of the anisotropic APPF hydrogel prepared according to the present invention. From Figure 6 it can be seen that due to the photothermal conversion effect of silver nanowires, the hydrogel has a good heating effect under light illumination, providing a basis for light response deformation.
[0031] Figure 7 Shows a programmable 3D deformation actuator realized by regulating the ultraviolet light irradiation time according to the present invention. This device can simulate the lifting mechanism of a jack under near-infrared light excitation to achieve efficient lifting of heavy objects. Detailed implementation mode
[0032] The reagent raw materials and equipment used in the present invention are all commercially available products and can be purchased through the market.
[0033] Example 1: Synthesis of silver nanowires
[0034] Add 10 g of PVP solid powder and 400 mL of glycerol to a 1000 mL beaker. After mechanical stirring until homogeneous, place it in an oven at 160 °C and heat for 30 min to dissolve the PVP. After the above solution cools to room temperature, gently stir and sequentially add AgNO 3 solution (5 g of AgNO 3 dissolved in 3 mL of deionized water) and NaCl solution (300 mg of NaCl dissolved in 2 mL of deionized water). After sufficient stirring, place it in an oven at 180 °C and react for 16 h. When the solution color turns grayish green, silver nanowires are prepared. Finally, repeatedly centrifuge and wash with water and ethanol to remove the PVP on the surface of the silver nanowires to obtain pure silver nanowires.
[0035] Example 2: Preparation of anisotropic APPF hydrogel with porous open channels and ultraviolet light-induced Fe 3+ Controlled dissociation
[0036] 1. Prepare the thermosensitive PNIPAM / PAA hydrogel precursor solution
[0037] At a low temperature of 0 - 10 °C, sequentially weigh 0.72 g of NIPAM, 80 μL of AA, 3 mg of N,N'-methylenebisacrylamide, and 50 μL of 2-hydroxy-2-methyl-1-phenyl-1-propanone and dissolve them in 3 ml of deionized water. Sonicate until completely dissolved, and use a vacuum drying oven to remove the bubbles generated during the dissolution process. Store the prepared hydrogel precursor solution in an ice bath.
[0038] 2. Prepare the AgNW / PNIPAM / PAA primary hydrogel
[0039] Add 1 mL of 30 mg / ml silver nanowires to the prepared AgNW / PNIPAM / PAA hydrogel precursor solution and mix evenly. Take the above-prepared solution and drop it into a unidirectional freezing mold. Adjust the cold plate temperature to -20 °C. After the system is completely frozen, perform ultraviolet light irradiation polymerization in a low-temperature environment at -10 °C for 3 min to obtain the primary hydrogel.
[0040] 3. Prepare the APPF hydrogel with porous open channels
[0041] Stretch the above-obtained primary hydrogel mechanically along the direction perpendicular to the unidirectional freezing ice crystal growth direction to 150% of its original length and fix it with a clamp. Immerse it in 0.08 mol / L ferric chloride solution for 18 h and then swell in deionized water for 2 min to finally obtain an anisotropic APPF hydrogel with a directional pore structure.
[0042] 4. Ultraviolet light-induced Fe in the APPF hydrogel network 3+ Controlled dissociation
[0043] The anisotropic APPF hydrogel with the above-mentioned directional pore structure is placed on an ultraviolet irradiation platform for spatial selective cross-linking, and irradiated under ultraviolet light with a specific wavelength of 365 nm and an intensity of 18 W / cm 2 After 30 s of irradiation, an APPF hydrogel that can undergo 3D deformation under light and heat stimuli is finally obtained.
[0044] Example 3: Preparation of anisotropic APPF hydrogel with porous open channels and ultraviolet light-induced Fe 3+ Controllable dissociation
[0045] 1. Preparation of thermosensitive PNIPAM / PAA hydrogel precursor solution
[0046] At a low temperature of 0 - 10 °C, 0.68 g of NIPAM, 120 μL of AA, 3 mg of N,N'-methylenebisacrylamide, and 50 μL of 2-hydroxy-2-methyl-1-phenyl-1-propanone are successively weighed and dissolved in 3 ml of deionized water. After ultrasonic treatment until completely dissolved, the bubbles generated during the dissolution process are removed using a vacuum drying oven, and the prepared hydrogel precursor solution is stored in an ice bath.
[0047] 2. Preparation of AgNW / PNIPAM / PAA hydrogel
[0048] 1 mL of 20 mg / ml silver nanowires is added to the prepared AgNW / PNIPAM / PAA hydrogel precursor solution and mixed evenly. The above-prepared solution is dropped into a unidirectional freezing mold, the temperature of the cold plate is adjusted to -30 °C, and after the system is completely frozen, ultraviolet light irradiation polymerization is carried out in a low-temperature environment of -10 °C for 2 min to obtain a primary hydrogel.
[0049] 3. Preparation of APPF hydrogel with porous open channels
[0050] The above-obtained primary hydrogel is mechanically stretched along the direction perpendicular to the unidirectional freezing ice crystal growth direction to 175% of its original length and fixed with a clamp. After being immersed in 0.10 mol / L ferric chloride solution for 18 h, it is swollen in deionized water for 2 min, and finally an anisotropic APPF hydrogel with a directional pore structure is obtained.
[0051] 4. Ultraviolet light-induced Fe in the APPF hydrogel network 3+ Controllable dissociation
[0052] The anisotropic APPF hydrogel with the above-mentioned directional pore structure is placed on an ultraviolet irradiation platform for spatial selective cross-linking, and at a specific wavelength of 365 nm and 18 W / cm 2Irradiation treatment was carried out under ultraviolet light of a certain intensity. After 1 minute of irradiation, an APPF hydrogel that can undergo 3D deformation under light and heat stimuli was finally obtained.
[0053] In this invention, a three-dimensional ordered honeycomb network structure was constructed by a unidirectional freezing assembly technique for a PNIPAM / PAA hydrogel and silver nanowire composite system. Then, mechanical stretching was used to induce the polymer network to be orderly arranged along the stress direction, and the interaction between Fe 3+ and carboxyl groups was used to fix the orderly oriented network structure, and finally an anisotropic hydrogel with a directional pore structure was obtained. Further, an APPF hydrogel with 3D responsive deformation to light and heat was prepared by an ultraviolet light programming method. The synergistic effect of the open through-pores formed by ice crystal growth and the stretched and oriented polymer network provides a fast channel for the transmission of water molecules in the hydrogel network. Therefore, this hydrogel can rapidly complete multi-modal controllable complex 3D deformations under a hot water bath or near-infrared stimulation, such as realizing a "U"-shaped pattern design and driving deformations such as a "jack".
Claims
1. A method for preparing anisotropic hydrogel induced by oriented freezing combined with mechanical stretching, characterized in that: Firstly, N-isopropylacrylamide, acrylic acid, silver nanowires, crosslinking agent and photoinitiator were uniformly mixed in a specific ratio, and the AgNW / PNIPAM / PAA primary hydrogel with a three-dimensional ordered honeycomb network structure was assembled by unidirectional freezing technology-assisted UV polymerization; then, the polymer network was induced to be oriented along the stretching direction by mechanical stretching, and the iron ions Fe 3+ Crosslinking with carboxyl groups in the polymer network to fix the tensile deformation resulted in the preparation of an anisotropic structure of AgNW / PNIPAM / PAA / Fe with open mass transfer channels. 3+ Hydrogel, referred to as APPF hydrogel.
2. The preparation method according to claim 1, characterized in that The steps include: Step 1: Preparation of AgNW / PNIPAM / PAA hydrogel precursor Under a low temperature environment of 5-10°C, monomer 1, monomer 2, crosslinker, and photoinitiator are ultrasonically dissolved in deionized water in turn, and bubbles generated by the dissolution are removed by vacuum drying; the prepared hydrogel precursor solution is transferred to an ice bath environment for storage; finally, silver nanowires are added to the precursor solution, and the mixture is evenly mixed to obtain the AgNW / PNIPAM / PAA hydrogel precursor solution; The monomer 1 is N-isopropyl acrylamide, and the monomer 2 is acrylic acid; Step 2: One-way frozen UV polymerization The AgNW / PNIPAM / PAA hydrogel precursor solution obtained in step 1 is injected into the mold and immediately transferred to a one-way freezing platform, and the platform temperature is controlled. After the mold and the internal precursor solution are completely frozen, ultraviolet light irradiation polymerization is performed in a low temperature environment to obtain a primary hydrogel; Step 3: Mechanical stretching-secondary cross-linking synergistic orientation The primary hydrogel obtained in step 2 was mechanically stretched perpendicular to the growth direction of the unidirectional frozen ice crystals and fixed with a clamp, then immersed in an aqueous solution of ferric chloride to complete the secondary crosslinking, and then dynamically swollen with deionized water for a period of time to remove the surface free Fe 3+ , and finally an anisotropic APPF hydrogel with a directional pore structure was obtained.
3. The preparation method according to claim 2, characterized in that: In step 1, the amount of monomer 1 added is 14%-16% of the mass of the hydrogel precursor solution; the amount of monomer 2 added is 1.6%-3.2% of the mass of the hydrogel precursor solution.
4. The preparation method according to claim 2, characterized in that: In step 1, the crosslinking agent is N,N'-methylenebisacrylamide, and the amount of the crosslinking agent added is 0.3%-0.4% of the monomer mass; the photoinitiator is 2-hydroxy-2-methyl-1-phenyl-1-propanone, and the amount of the photoinitiator added is 6.5%-7.5% of the monomer mass.
5. The preparation method according to claim 2, characterized in that: In step 1, the amount of silver nanowires added is 0.6%-1.2% of the mass of the hydrogel precursor solution.
6. The preparation method according to claim 2 or 5, characterized in that The silver nanowires are prepared by the following method: PVP solid powder and propylene glycol are added to a reactor, mechanically stirred and heated at 160°C for 30 min to dissolve PVP; after the solution is cooled to room temperature, AgNO3 solution and NaCl solution are added in sequence with stirring, and reacted at 180°C. When the color of the solution turns gray-green, silver nanowires can be prepared; finally, the PVP on the surface of the silver nanowires is removed by repeated centrifugal washing with water and ethanol to obtain pure silver nanowires.
7. The preparation method according to claim 2, characterized in that: In step 2, the temperature of the one-way freezing cold platform is set to -20°C to -40°C; the low temperature environment for polymerization is -10°C to -20°C; and the ultraviolet light irradiation polymerization time is 3 min.
8. The preparation method according to claim 2, characterized in that: In step 3, the concentration of the ferric chloride aqueous solution is 0.06-0.10 mol / L, and the soaking time is 18 h.
9. Use of an anisotropic hydrogel induced by oriented freezing combined with mechanical stretching prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The anisotropic APPF hydrogel is placed under ultraviolet light of specific wavelength and intensity for irradiation treatment, and the ultraviolet light-induced selective dissociation of the metal coordination bonds is achieved by controlling the irradiation area and irradiation time, that is, Fe 3+ With COO - The selective dissociation of coordination bonds constructs a polymer network cross-linking density gradient between the irradiated and non-irradiated surfaces, giving APPF hydrogel the ability to produce multimodal controllable three-dimensional deformation under light and heat stimulation.
10. The use according to claim 9, characterized in that: The wavelength of the ultraviolet light of specific wavelength and intensity is 365 nm and the intensity is 18 W / cm 2 , irradiation time is 0.5-1min.