A cellulose nanocrystal-reinforced solvent-responsive double-layer hydrogel actuator and a preparation method and application thereof
By introducing cellulose nanocrystals into the hydrogel actuator to construct an asymmetric structure, the problem of the hydrogel actuator's inability to achieve complex deformation was solved, and a high-strength, reversible solvent-responsive bilayer hydrogel actuator was prepared, which is suitable for soft robots and intelligent graspers.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NINGBO UNIV
- Filing Date
- 2025-05-28
- Publication Date
- 2026-05-19
AI Technical Summary
Existing hydrogel actuators can only achieve simple dimensional changes when they swell or shrink uniformly, making it difficult to achieve complex deformations. Furthermore, the fabrication process of high-cost heterogeneous structures is complex.
A bilayer hydrogel actuator reinforced with cellulose nanocrystals is constructed by adding different concentrations of cellulose nanocrystals to two polymer layers to create an asymmetric structure with pore size differences. This allows for bending deformation through solvent responsiveness, and the bilayer hydrogel is formed layer by layer by UV curing.
A hydrogel actuator with high mechanical strength, reversible solvent responsiveness and adjustable bending angle has been developed, which is suitable for soft robots and intelligent grippers, and has simple preparation and good interfacial bonding.
Smart Images
Figure CN120535779B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a bilayer hydrogel actuator, and more particularly to a solvent-responsive bilayer hydrogel actuator reinforced with cellulose nanocrystals, its preparation method, and its application. Background Technology
[0002] Hydrogels are materials with a three-dimensional network structure formed by the cross-linking of hydrophilic polymer chains. Due to their excellent water retention, biocompatibility, and stimulus-responsive properties, they have become important functional materials in fields such as flexible actuators, soft robotics, and intelligent devices. Hydrogel actuators are devices composed of hydrogels that can respond to specific environments. Their power primarily originates from the repulsion or absorption of water molecules by the polymer chains. Changes in water molecules drive changes in macroscopic shape, converting other forms of energy into mechanical energy. If a hydrogel actuator exhibits uniform swelling or contraction in all directions, it can only achieve simple dimensional changes and cannot accomplish complex deformations. Currently, methods to enable complex deformations in hydrogels typically involve applying heterogeneous excitation methods such as local electric fields or light to isotropic hydrogels, or designing hydrogels with bilayer heterogeneous structures or cross-linked gradient structures, generating deformation driving forces through differences in swelling / contraction.
[0003] Cellulose nanocrystals (CNCs) have attracted widespread attention due to their low cost, strong biocompatibility, and high mechanical strength. Their excellent hydrophilicity also lays the foundation for their integration with hydrogels. Introducing cellulose nanocrystals into hydrogels allows them to form a three-dimensional network through hydrogen bonding. On one hand, different amounts of cellulose nanocrystals affect the density of the three-dimensional network; introducing different cellulose nanocrystal contents into the hydrogel structure can create hydrogel actuators with different functions. On the other hand, the introduction of cellulose nanocrystals can significantly improve the mechanical strength of the hydrogel, addressing the problem of poor mechanical properties in hydrogel actuators. Most hydrogel actuators with heterogeneous structures are costly and have complex fabrication processes. Currently, there are no research reports on hydrogel actuators with bilayer heterogeneous structures based on cellulose nanocrystals. Summary of the Invention
[0004] The purpose of this invention is to address the above-mentioned shortcomings by providing a solvent-responsive bilayer hydrogel actuator reinforced with cellulose nanocrystals, which has high mechanical strength, reversible solvent responsiveness, and adjustable bending angle, as well as its preparation method and application.
[0005] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:
[0006] A solvent-responsive bilayer hydrogel actuator reinforced with cellulose nanocrystals is disclosed, comprising a first hydrogel layer and a second hydrogel layer, both polymerized and crosslinked. The raw materials for preparing both the first and second hydrogel layers are acrylamide monomer, a cellulose nanocrystal suspension, a crosslinking agent, and an initiator. Different contents of cellulose nanocrystals in the bilayer hydrogel enable bilayer heterogeneous hydrogel actuators with varying network densities.
[0007] Preferably, the concentration of the cellulose nanocrystal suspension used in the first layer of hydrogel is 1wt%-6wt%, and the concentration of the cellulose nanocrystal suspension used in the second layer of hydrogel is 0.5wt%.
[0008] Preferably, the thickness ratio of the first hydrogel layer to the second hydrogel layer is 1:1.
[0009] Preferably, the crosslinking agent is N,N-methylenebisacrylamide (Bis), and the initiator is a photoinitiator: 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone (Irgacure 2959).
[0010] This invention also provides a method for preparing the above-mentioned cellulose nanocrystal-reinforced solvent-responsive bilayer hydrogel actuator, characterized by comprising the following steps:
[0011] 1. A certain amount of acrylamide (AM) monomer, crosslinking agent and photoinitiator are added to cellulose nanocrystal suspensions of different concentrations and stirred evenly with a magnetic stirrer to obtain a prepolymer solution of hydrogel.
[0012] 2. The prepolymer solution of the first layer of hydrogel is injected into a self-made mold and cured by ultraviolet (UV) light to form the first hydrogel layer;
[0013] 3. Pour the prepolymer solution of the second layer onto the first layer of hydrogel prepared in step S2, and cure it again with UV light to form the second hydrogel layer, thus obtaining a solvent-responsive bilayer hydrogel actuator reinforced with cellulose nanocrystals.
[0014] Preferably, in the prepolymer solution of the hydrogel described in step S1, the amount of polyacrylamide monomer added is 10% of the mass of the cellulose nanocrystal suspension, and the amount of crosslinking agent and photoinitiator added is 3% of the mass of the polyacrylamide monomer.
[0015] The present invention also provides the application of the above-mentioned cellulose nanocrystal-reinforced solvent-responsive bilayer hydrogel actuator as a smart gripper in different liquids.
[0016] Preferably, the intelligent gripper is cross-shaped; it consists of two strip-shaped double-layer hydrogel actuators (80mm×10mm×2mm), the two double-layer hydrogel actuators are intersected and perforated at the center, and the shape is fixed by two upper and lower silicone films.
[0017] Preferably, the intelligent gripper swells in water and deswells in ethanol, utilizing the swelling characteristics in different solvents to achieve the intelligent gripping function.
[0018] The basic principles of this invention are explained as follows: 1) By adding different amounts of cellulose nanocrystals to a two-layer polyacrylamide (PAM) hydrogel to construct an asymmetric structure, the pore size between the two layers of the cured bilayer hydrogel differs. This difference leads to different swelling rates in water and deswell rates in ethanol. When the bilayer hydrogel, which is fully swollen in water, is transferred to ethanol, the non-uniform deswelling shrinkage on both sides induces bending deformation. 2) Cellulose nanocrystals, as a nano-reinforcing phase, form a cross-linked network with the polymer chains on their surface hydroxyl groups, effectively improving the cross-linking density and mechanical strength of the hydrogel. 3) By controlling the difference in cellulose nanocrystal content between the two layers of hydrogel, the bending angle can be controlled.
[0019] Compared with the prior art, the advantages of the present invention are as follows:
[0020] 1. This invention introduces cellulose nanocrystals into acrylamide hydrogel, which not only significantly improves the mechanical properties of acrylamide hydrogel, but also has potential applications in soft robotics, intelligent grippers and other fields based on its excellent mechanical strength and reversible driving characteristics.
[0021] 2. The bilayer hydrogel actuator prepared by the present invention also imparts a difference in network pore size along the thickness direction to the bilayer hydrogel by changing the content of cellulose nanocrystals between the two layers. The difference in pore size leads to different swelling rates and deswelling rates, and exhibits bending response characteristics in ethanol and aqueous solutions.
[0022] 3. This invention is prepared by layer-by-layer polymerization. The double-layer structure has the same material and has the advantages of simple preparation and strong interfacial bonding.
[0023] 4. This invention achieves a wide range of adjustable bending angles in ethanol by adjusting the concentration difference of cellulose nanocrystals between the two layers. The specific bending angle depends on the concentration difference of cellulose nanocrystals between the two layers.
[0024] 5. The bilayer hydrogel actuator prepared by the present invention can achieve reversible deformation in ethanol and water. After multiple bending / recovery cycles, the bilayer hydrogel actuator does not delaminate or degrade in performance. Attached Figure Description
[0025] Figure 1 Microstructure diagrams of PAM hydrogels with different CNC contents are shown, where (a) represents a CNC suspension concentration of 6 wt%, (b) represents a CNC suspension concentration of 3 wt%, and (c) represents a CNC suspension concentration of 0.5 wt%.
[0026] Figure 2 The swelling rate (a) and water retention rate (b) of hydrogels with different CNC contents in water are shown.
[0027] Figure 3 Tensile stress-strain curves for different CNC hydrogels;
[0028] Figure 4 The bending angle of the bilayer hydrogel actuator in ethanol varies with the CNC concentration of the first hydrogel layer. The horizontal axis 1-6 in the figure represents Examples 1-6, respectively.
[0029] Figure 5 Bending / recovery cycle test of bilayer hydrogel actuator in ethanol / deionized water;
[0030] Figure 6 It is the process by which a double-layer hydrogel actuator acts as a smart gripper to capture objects in an ethanol environment. Detailed Implementation
[0031] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. These examples are only for illustrating the present invention and should not be construed as limiting the scope of protection of the present invention.
[0032] I. Specific Implementation Example: Fabrication of a solvent-responsive bilayer hydrogel actuator reinforced with cellulose nanocrystals.
[0033] Example 1: A method for preparing a solvent-responsive bilayer hydrogel actuator reinforced with cellulose nanocrystals, comprising the following steps:
[0034] 1. Weigh 1g of acrylamide monomer, 0.03g of crosslinking agent N,N'-methylenebisacrylamide, and 0.03g of photoinitiator 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone, dissolve them in 10g of cellulose nanocrystal suspension with a concentration of 1wt%, and stir evenly with a magnetic stirrer to obtain the prepolymer solution of the first layer of hydrogel;
[0035] 2. Weigh 1g of acrylamide monomer, 0.03g of crosslinking agent N,N'-methylenebisacrylamide, and 0.03g of photoinitiator 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone, dissolve them in 10g of 0.5wt% cellulose nanocrystal suspension, and stir evenly with a magnetic stirrer to obtain the prepolymer solution of the second layer hydrogel;
[0036] 3. Transfer the prepolymer solution of the first hydrogel layer into a silicone mold, and irradiate it with ultraviolet light for 4 minutes to obtain the first hydrogel layer;
[0037] 4. Transfer the prepolymer solution of the second hydrogel to the top of the first hydrogel. After irradiation with ultraviolet light for 4 minutes, a second hydrogel layer is formed, resulting in a solvent-responsive bilayer hydrogel actuator reinforced with cellulose nanocrystals, denoted as C1A / C. 0.5 A.
[0038] Example 2 is the same as Example 1 above, except that: in step S1, the concentration of the cellulose nanocrystal suspension is 2 wt% during the preparation of the prepolymer solution of the first layer of hydrogel, and a solvent-responsive bilayer hydrogel actuator reinforced with cellulose nanocrystals is finally obtained, denoted as C2A / C. 0.5 A.
[0039] Example 3 is the same as Example 1 above, except that: in step S1, the concentration of the cellulose nanocrystal suspension is 3 wt% during the preparation of the prepolymer solution of the first layer of hydrogel, and a solvent-responsive bilayer hydrogel actuator reinforced with cellulose nanocrystals is finally obtained, denoted as C3A / C. 0.5 A.
[0040] Example 4 is the same as Example 1 above, except that: in step S1, the concentration of the cellulose nanocrystal suspension is 4 wt% during the preparation of the prepolymer solution of the first layer of hydrogel, and a solvent-responsive bilayer hydrogel actuator reinforced with cellulose nanocrystals is finally obtained, denoted as C4A / C. 0.5 A.
[0041] Example 5 is the same as Example 1 above, except that: in step S1, the concentration of the cellulose nanocrystal suspension is 5 wt% during the preparation of the prepolymer solution of the first layer of hydrogel, and a solvent-responsive bilayer hydrogel actuator reinforced with cellulose nanocrystals is finally obtained, denoted as C5A / C. 0.5 A.
[0042] Example 6 is the same as Example 1 above, except that: in step S1, the concentration of the cellulose nanocrystal suspension is 6 wt% during the preparation of the prepolymer solution of the first layer of hydrogel, and a solvent-responsive bilayer hydrogel actuator reinforced with cellulose nanocrystals is finally obtained, denoted as C6A / C. 0.5 A.
[0043] A control group and a cellulose nanocrystal-reinforced hydrogel were prepared by preparing a single-layer hydrogel, including the following steps:
[0044] 1. Weigh 1g of acrylamide monomer, 0.03g of crosslinking agent N,N'-methylenebisacrylamide, and 0.03g of photoinitiator 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone, and dissolve them in 10g of cellulose nanocrystal suspension with a concentration of x wt% (x=0.5,1,2,3,4,5,6). Stir the solution evenly with a magnetic stirrer to obtain a prepolymer solution of hydrogel.
[0045] 2. Transfer the prepolymer solution of the hydrogel into a silicone mold and place it under a UV lamp for 4 minutes to obtain a monolayer hydrogel, denoted as C. x A, where x = 0.5, 1, 2, 3, 4, 5, 6.
[0046] II. Characterization and Performance Testing.
[0047] 1. Microstructure of a single-layer hydrogel.
[0048] The monolayer hydrogels prepared in the control group were soaked in deionized water for 2 days to remove unreacted monomers and achieve a fully swollen state. After freeze-drying, their cross-sectional morphology was observed using a scanning electron microscope.
[0049] Figure 1 The CNC content was shown to be 6 wt% ( Figure 1 a) 3wt% Figure 1 (b) and 0.5wt% ( Figure 1 c) Microscopic image of the hydrogel. It can be observed that the hydrogel exhibits a honeycomb structure. Furthermore, with increasing CNC content, the pore size of the three-dimensional network structure of the hydrogel gradually decreases, indicating that the cross-linking density of the hydrogel network structure increases with increasing CNC content.
[0050] 2. Kinetics of reswelling and deswelling of monolayer hydrogels.
[0051] The monolayer hydrogel prepared in the control group was immersed in deionized water for 2 days and then transferred to an ethanol solution for deswelling kinetics testing. After the deswelling kinetics test, it was immersed in deionized water again for reswelling kinetics testing.
[0052] The deswelling kinetics are described using water retention ratio (WR), which is defined as follows:
[0053] WR = (W t de -W d ) / (W s -W d )×100%. Where, W t de W is the mass of the hydrogel at time t after it has been soaked in ethanol. sW is the mass of the hydrogel after it has fully swelled in deionized water. d It is the mass of the hydrogel after it has swollen to equilibrium in ethanol.
[0054] In the study of reswelling kinetics, the swelling ratio is defined as follows: SR = (W t re -W d ) / W d ×100%. Where, W t re W is the mass at a certain point in time during the re-swelling process of the hydrogel. d It is the mass of the hydrogel at which it swells to equilibrium in ethanol.
[0055] Figure 2 The swelling behavior of hydrogels with different CNC contents in deionized water was demonstrated. Figure 2 (a) and deswelling behavior in ethanol ( Figure 2 (b) It can be observed that with the increase of CNC content, the hydrogel exhibits a lower swelling rate and a slower deswelling rate. Combined with... Figure 1 It can be concluded that the larger the pore size of the three-dimensional network structure of PAM hydrogel, the higher the swelling rate and the faster the deswelling rate.
[0056] 3. Mechanical property testing of monolayer hydrogels.
[0057] The tensile samples were prepared using the same prepolymer solution as the control group. After being formed by a specially designed dumbbell mold, they were soaked in deionized water for 2 days and then subjected to tensile testing using a soft matter mechanical testing machine.
[0058] Its tensile stress-strain curve is as follows Figure 3 As shown, from Figure 3 As can be seen, with the increase of CNC content, the strength of the hydrogel increases, while its toughness decreases.
[0059] 4. Solvent response behavior of bilayer hydrogel actuators.
[0060] The bilayer hydrogels prepared in Examples 1-6 were cut into strips of 35mm × 7mm. After fixing one end, they were immersed in an ethanol solution. When the hydrogels reached desolvation equilibrium in the ethanol, their bending angles were recorded.
[0061] Figure 4 The graph shows the variation of the bending angle of the bilayer hydrogel actuator in ethanol with the CNC concentration of the second hydrogel layer. It can be seen that the higher the CNC concentration in the first hydrogel layer, i.e., the greater the concentration difference of CNC between the two layers, the larger the bending angle of the hydrogel. This indicates that the bilayer hydrogel actuator has good solvent response characteristics and a wide adjustable range of bending angles.
[0062] 5. Cyclic testing of bilayer hydrogel actuators in ethanol / deionized water
[0063] The bilayer hydrogel prepared in Example 3 was cut into strips of 35mm × 7mm, and then subjected to 10 cycles of alternating ethanol / deionized water immersion, and the bending angle after reaching swelling / deswelling equilibrium was recorded each time.
[0064] Figure 5 The changes in bending angle of the bilayer hydrogel actuator during 10 swelling-shrinkage cycles were demonstrated. During the 10 swelling-shrinkage cycles, the actuator did not exhibit delamination or bending angle attenuation, demonstrating tight interfacial bonding, excellent reusability, and reversible bending deformation.
[0065] III. Application Example: Grasping objects in an ethanol environment.
[0066] Using the bilayer hydrogel actuator C3A / C in Example 3 0.5 A cross-shaped gripper is constructed to grasp objects in an ethanol solution.
[0067] The cross-shaped gripper is composed of two strip-shaped double-layer hydrogels (80mm×10mm×2mm). The two hydrogels cross and perforate at the center and are fixed in shape by two upper and lower silicone films.
[0068] Figure 6 The complete working process of the gripping device constructed based on the bilayer hydrogel actuator in an ethanol environment was recorded. Experimental results show that the driving force generated by the dehydration and shrinkage of the bilayer hydrogel actuator in ethanol solution can effectively drive the device to complete the gripping action. In the test, the device successfully achieved stable gripping of wax blocks in ethanol, fully demonstrating its practical operability in ethanol medium and expanding the application of this bilayer hydrogel actuator.
[0069] In summary, the cellulose nanocrystal-reinforced solvent-responsive bilayer hydrogel actuator provided by this invention exhibits reversible solvent responsiveness, tight interfacial bonding, and excellent mechanical properties. The difference in swelling and shrinkage between the two layers caused by the CNC concentration gradient, especially the driving force generated by dehydration shrinkage, can drive the hydrogel to move in ethanol. Furthermore, by changing the difference in CNC concentration between the two layers, the bending angle of the actuator can be effectively adjusted. Based on these properties, this hydrogel actuator holds promise for applications in soft robotics, intelligent graspers, and other fields.
[0070] The foregoing description is not intended to limit the invention, nor is the invention limited to the examples given. Any changes, modifications, additions, or substitutions made by those skilled in the art within the scope of the invention should also be considered within the protection scope of the invention.
Claims
1. The application of a cellulose nanocrystal-reinforced solvent-responsive bilayer hydrogel actuator as a smart grasper in ethanol solution, characterized in that: This actuator is a bilayer hydrogel with a heterogeneous structure, achieved through polymerization and crosslinking. It comprises a first and a second hydrogel layer, prepared using a layer-by-layer polymerization method. The different contents of cellulose nanocrystals in the bilayer hydrogel result in differences in pore size between the two layers after curing. The raw materials for preparing the first and second hydrogel layers are acrylamide monomer, cellulose nanocrystal suspension, crosslinking agent, and initiator. The concentration of the cellulose nanocrystal suspension used in the first hydrogel layer is 1wt%-6wt%, and the concentration of the cellulose nanocrystal suspension used in the second hydrogel layer is 0.5wt%.
2. The application according to claim 1, characterized in that: The crosslinking agent is N,N-methylenebisacrylamide, the initiator is the photoinitiator 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone, and the polymerization method is ultraviolet light polymerization.
3. The application according to claim 1, characterized in that: The thickness ratio of the first hydrogel layer to the second hydrogel layer is 1:
1.
4. The application according to claim 1, characterized in that... The method for preparing the cellulose nanocrystal-reinforced solvent-responsive bilayer hydrogel actuator includes the following steps: S1. Acrylamide monomer, crosslinking agent and photoinitiator are added to cellulose nanocrystal suspensions of different concentrations and stirred evenly with a magnetic stirrer to obtain a prepolymer solution of hydrogel. S2. The prepolymer solution of the first layer of hydrogel is injected into a silicone mold and cured by ultraviolet light to form the first hydrogel layer. The concentration of the cellulose nanocrystal suspension used in the prepolymer solution of the first layer of hydrogel is 1wt%-6wt%. S3. Pour the prepolymer solution of the second layer onto the first layer of hydrogel prepared in step S2, and cure it again with ultraviolet light to form the second hydrogel layer, thereby obtaining a solvent-responsive bilayer hydrogel actuator reinforced with cellulose nanocrystals. The concentration of the cellulose nanocrystal suspension used in the second hydrogel layer is 0.5wt.
5. The application according to claim 4, characterized in that: In the prepolymer solution of the hydrogel described in step S1, the amount of acrylamide monomer added is 10% of the mass of the cellulose nanocrystal suspension, and the amount of crosslinking agent and photoinitiator added is 3% of the mass of polyacrylamide monomer.
6. The application according to claim 1, characterized in that: The intelligent gripper is cross-shaped and consists of two strip-shaped double-layer hydrogel actuators. The two double-layer hydrogel actuators cross and perforate at the center and are fixed in shape by two upper and lower silicone films.