Hydratable programmable shape memory artificial muscle, and preparation method and application thereof

Abstract

The application discloses a hydratable programmable shape memory artificial muscle and a preparation method and application thereof, and belongs to the technical field of polymer gels. The preparation method comprises the following steps: (1) under a solution environment, polyvinyl alcohol, sea squirt cellulose nanocrystals and polymerized monomers composed of acrylamide, acrylic acid and N,N'-methylene bisacrylamide are mixed and incubated to obtain a polymerized precursor dispersion liquid; (2) an initiator is added into the polymerized precursor dispersion liquid, and a fibrous hydrogel material is formed through a polymerization reaction process to obtain the shape memory artificial muscle. The raw materials of the method are widely available, the process is simple and fast, the prepared shape memory artificial muscle has super-high breaking elongation and toughness, shape programming and recovery processes under a high pre-stretching ratio and a constant stress can be realized, and when the shape memory artificial muscle is used for a bionic structure, antagonistic movement of an artificial arm is realized.

Description

Technical Field

[0001] This invention relates to the field of polymer gel technology, and in particular to a hydrated and programmable shape memory artificial muscle, its preparation method, and its application. Background Technology

[0002] Human skeletal muscles contract to enable various movements essential to the human body. Researchers are currently dedicated to creating artificial muscles with similar functions and have developed various types of artificial muscle materials. Shape memory polymers, in particular, due to the diversity of their shape programming mechanisms, allow shape memory artificial muscles to switch between temporary and permanent shapes. However, shape memory polymers often require external force for shape programming, making it difficult for shape memory polymer artificial muscles to achieve reversible movement without external force.

[0003] Human skeletal muscles cannot extend voluntarily; instead, they achieve reciprocating contraction and extension through the formation of antagonistic muscle pairs. However, shape memory polymers cannot simulate antagonistic movements because the modulus difference during shape programming and shape recovery is very small, preventing connected artificial muscles from stretching each other. To further develop shape memory polymers, water-triggered shape memory effects are currently being extensively studied. Hydrogels in their hydrated state exhibit low modulus and high toughness, enabling large-deformation shape programming. In their dehydrated state, the polymer network is fixed by hydrogen bonds, resulting in high modulus mechanical properties, thus fixing a temporary shape. The temporary shape can then recover to a permanent shape after hydration, achieving reversible actuation.

[0004] Chinese Patent Publication No. CN112940288A discloses a method for preparing shape memory hydrogels and their applications. The preparation method includes the following steps: Step 1, acrylamide, acrylic acid, and acrylamide adamantane are dissolved in a certain proportion in an aqueous dispersion of cyclodextrin-grafted sea squirt cellulose nanocrystals, incubated at 55°C for 2 hours, cooled in an ice-water bath, and ammonium persulfate initiator is added. The dispersion is then injected into a mold and polymerized at 55°C for 5 hours to obtain a single-crosslinked hydrogel; Step 2, the single-crosslinked hydrogel obtained in Step 1 undergoes a series of continuous orientation operations to obtain a helical hydrogel; Step 3, the helical hydrogel obtained in Step 2 is immersed in a fixative for 24 hours to obtain a shape memory hydrogel. This shape memory hydrogel has two chiral helical structures, which can achieve stretching and deformation in opposite directions under cyclic stimulation of ethanol-water solvent. However, the driving process of this hydrogel material as an artificial muscle is achieved in a swollen state, resulting in a low elastic modulus and low driving force and working capacity of the artificial muscle. Meanwhile, this shape memory hydrogel mimics the movement patterns of cucumber tendrils in nature through the shape memory effect, including climbing, winding, and spiraling contractions, but it cannot achieve antagonistic movements, which limits its application range.

[0005] Similarly, Chinese patent CN116426005A discloses a temperature-responsive hydrogel artificial muscle, its preparation method, and its application. The method includes: dissolving N-isopropylacrylamide, potassium 3-sulfonopropyl methacrylate, acrylamide, a crosslinking agent, an initiator, and a accelerator in a sulfuric acid-hydrolyzed aqueous dispersion of sea squirt cellulose nanocrystals to obtain a mixture; then injecting the mixture into a mold for polymerization to obtain a chemically crosslinked hydrogel; subjecting the chemically crosslinked hydrogel to continuous orientation to obtain a helical hydrogel; and immersing the helical hydrogel in a zirconium salt solution to obtain the hydrogel artificial muscle. This hydrogel artificial muscle utilizes the -SO group of the potassium 3-sulfonopropyl methacrylate segment in the hydrogel backbone. 3 With Zr 4+ The ionic coordination between the components fixes the initial columnar hydrogel into a spring-like structure, which can undergo stretching and deformation through temperature stimulation. The addition of sea squirt cellulose nanocrystals as a nanofiller enhances the mechanical properties of the initial columnar hydrogel and facilitates subsequent twisting and fixation. However, its function depends on the stretching and deformation of the spring-like helical structure, requiring controlled twisting and fixation, making the process complex.

[0006] Therefore, in addition to the existing motion mechanisms, a simple method for preparing shape memory artificial muscles is proposed to solve the above-mentioned technical problems and simulate the antagonistic movement of human skeletal muscles, which is of great significance for expanding the application fields of artificial muscles. Summary of the Invention

[0007] In view of the above-mentioned deficiencies of the prior art, in a first aspect of the present invention, a method for preparing a shape memory artificial muscle that is simple to process and hydrated and programmable is provided, comprising the following steps:

[0008] (1) In a solution environment, polyvinyl alcohol, sea squirt cellulose nanocrystals and polymer monomers composed of acrylamide, acrylic acid and N,N'-methylenebisacrylamide were mixed and incubated to obtain a polymerization precursor dispersion;

[0009] (2) An initiator is added to the polymerization precursor dispersion, and the mixture is processed by polymerization to form a fibrous hydrogel material, thereby obtaining shape memory artificial muscle.

[0010] Preferably, in step (1), the total content of the polyvinyl alcohol accounts for 0.1 wt.% to 10.0 wt.% of the polymerization precursor dispersion; and the total content of the polymeric monomers accounts for 20 wt.% to 30 wt.% of the polymerization precursor dispersion.

[0011] Preferably, in step (1), the mass ratio of acrylamide, acrylic acid and N,N'-methylenebisacrylamide in the polymer monomers is 1-9:1-9:0.0001-0.1.

[0012] Polyethylene glycol can affect the toughness of the resulting hydrogel material; furthermore, among the monomers, acrylic acid can enhance the hydration process of the dry hydrogel, but it can also affect the swelling step of the hydrogel. To achieve better finished product results, the amount of raw materials added in the above technical solutions is limited to an appropriate range.

[0013] Preferably, in step (1), the polymerization precursor dispersion is formed by incubating polyvinyl alcohol and polymeric monomers dissolved in an aqueous dispersion of sea squirt cellulose nanocrystals.

[0014] More preferably, the content of sea squirt cellulose nanocrystals in the aqueous dispersion of sea squirt cellulose nanocrystals is 0.1 wt.% to 5.0 wt.%.

[0015] Preferably, in step (1), the incubation temperature is 50-90°C and the incubation time is 1-5 hours.

[0016] Preferably, in step (2), the polymerization reaction is carried out at a temperature of 40–80°C for 1–8 hours.

[0017] In this invention, the reaction of acrylamide, acrylic acid, and N,N'-methylenebisacrylamide is achieved through free radical polymerization of the monomers. Under this reaction mechanism, the choice of initiators in the art is diverse and extensive. Thermal initiators such as ammonium persulfate and potassium persulfate, or photoinitiators such as azobisisobutyronitrile and photoinitiator 2959, are all common and suitable for the polymerization reaction described above, and no particular limitation is required. Furthermore, those skilled in the art can rationally select the amount of initiator to add to complete the polymerization based on the specific type of initiator available.

[0018] There are various ways to process hydrogel materials into a fibrous form, and the appropriate method can be selected according to the actual processing conditions. For example, in a laboratory preparation environment, fibrous hydrogel materials can be obtained by completing the polymerization reaction in a polytetrafluoroethylene pipe with a diameter of 1.5 mm; while under industrial-scale manufacturing conditions, other methods can also be used.

[0019] In a second aspect of the invention, a shape memory artificial muscle with high elongation at break and toughness, and temperature responsiveness is provided, which is manufactured using the method of the first aspect of the invention.

[0020] In a third aspect of the invention, an application of the shape memory artificial muscle of the second aspect of the invention is provided, specifically as an application of shape memory material in antagonistic motion of biomimetic structures.

[0021] Shape memory artificial muscles can be programmed to simulate desired muscle shapes by pre-stretching the hydrogel material under strain and stress control. Strain-controlled shape programming involves air-drying the hydrogel at a pre-stretch ratio (e.g., 800%) to fix its shape, while stress-controlled shape programming involves stretching the hydrogel under a constant external force and then air-drying to fix its shape. This process is to fix the temporary shape of the shape memory artificial muscle. During air-drying, the hydrogen bonds within the polymer network change from hydrated hydrogen bonds to inter-polymer chain hydrogen bonds, thus fixing the temporary shape. The fixed shape memory artificial muscle can be stretched in a hydrated state and contract autonomously upon heating. This is because, upon heating, the polymer network changes from a glassy state to a viscoelastic state, allowing polymer chain segments to slip, thus achieving a thermal contraction effect.

[0022] The preferred application method of shape memory artificial muscles is as follows:

[0023] Shape memory artificial muscles, under strain and stress control, are stretched and dried to form antagonistic muscle pairs that simulate agonist and antagonist muscles. These antagonist muscle pairs are assembled on both sides of the bionic arm as the biceps and triceps muscles. In response to temperature, the agonist muscles contract and the antagonist muscles elongate, thus achieving cyclic bending and elongation movements (antagonistic movements) of the arm.

[0024] Based on the above technical solutions, the design concept and principle of this invention are as follows: Polyvinyl alcohol, as a hydrophilic shape memory polymer, has the ability to undergo thermal phase transition. After heating, polyvinyl alcohol will change from a glassy state to a viscoelastic state, allowing for shape programming or recovery. Acrylamide, acrylic acid, and N,N'-methylenebisacrylamide, as hydrophilic monomers, are used to obtain a polymer network through free radical polymerization, which has hydrophilic and swelling capabilities. Therefore, the hydrogel can achieve shape programming in the swollen state. After adding polyvinyl alcohol, the hydrogel can achieve a thermal phase transition after drying. Through shape programming in the hydrogel state and the shrinkage-driven process of the fibers in the dry state, the antagonistic movement of the shape memory fibers is achieved. Sea squirt cellulose nanocrystals have high aspect ratio and high modulus mechanical properties. When added to the polymer network, they not only improve the toughness of the hydrogel, but also induce the formation of special wrinkled structures on the network surface during the shrinkage process of the shape memory fibers. This adjacent, ring-shaped, periodic fold structure is similar to the ring-shaped folds on the skin of some organisms such as leeches, which enables the fibers to achieve a further contraction effect. It can meet the requirements without twisting and fixing to form a spring-like helical structure, thus optimizing the material structure of artificial muscles and simplifying the preparation process.

[0025] This invention combines water-triggered shape memory effect with traditional thermally responsive shape memory materials to achieve shape programming of shape memory polymers in a hydrated state. The shape memory artificial muscle, after being stretched in a hydrogel state and then dried and fixed, forms shape memory fibers with high mechanical properties, capable of generating greater driving force and working capacity. Finally, it achieves actuation through contraction in the dry state and stretching in the hydrogel state, realizing antagonistic movement. The hydrated, programmable shape memory artificial muscle of this invention can be shape-programmed at low modulus and driven at high modulus, simulating the movement of antagonistic muscles—something ordinary hydrogel artificial muscles cannot achieve.

[0026] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0027] This invention provides a method for preparing shape memory artificial muscles, using widely available raw materials and a simple and quick process.

[0028] This invention provides a shape memory artificial muscle with ultra-high elongation at break and toughness, which can realize the shape programming and recovery process under high pre-stretch ratio and constant stress.

[0029] This invention also provides an application of shape memory artificial muscles, realizing antagonistic movement of artificial bionic structures. Attached Figure Description

[0030] Figure 1This is the hydration programming process of the shape memory artificial muscle in Example 1 and a physical image of its contraction under temperature response;

[0031] Figure 2 This is a scanning electron microscope (SEM) image of the shape memory artificial muscle in Example 1 during the contraction process;

[0032] Figure 3 This is a flowchart of the actual process of antagonistic movement of the artificial arm assembled with shape memory artificial muscles in Example 3. Detailed Implementation

[0033] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0034] Example 1

[0035] The preparation method of shape memory artificial muscles involves the following steps:

[0036] (1) Dissolve 0.25g polyvinyl alcohol, 1.917g acrylamide, 0.583g acrylic acid and 0.0025g N,N'-methylenebisacrylamide in 1% aqueous dispersion of sea squirt cellulose nanocrystals, add 0.01g ammonium persulfate as an initiator, and incubate at 55℃ for 2h to obtain a polymerization precursor dispersion;

[0037] (2) The polymerization precursor dispersion was cooled in an ice-water bath, then ammonium persulfate was added and injected into a polytetrafluoroethylene pipe mold with a diameter of 1.5 mm. The polymerization reaction was carried out at 60°C for 5 h to form a fibrous hydrogel material, thus obtaining shape memory artificial muscle (HP-SMP).

[0038] like Figure 1 As shown in the physical diagram, the shape memory artificial muscle of this embodiment was pre-stretched by 800% and then air-dried, transforming from a hydrogel state to a fixed shape memory state. Upon heating, the shape memory artificial muscle contracted in response to temperature. The mechanical properties of the shape memory artificial muscle were reflected by strain and working capacity. Strain was calculated as the ratio of the contracted length of the fiber to its original length, while working capacity was the ratio of the increase in gravitational potential energy during fiber contraction and lifting of a heavy object to the mass of the object. The shape memory artificial muscle in its shape memory state contracted by -60% strain within 3 seconds when heated to 120°C, and its maximum working capacity under 3MPa stress reached 751J / kg, more than 18 times that of human skeletal muscle.

[0039] The microstructure of shape memory artificial muscles during temperature-responsive contraction was observed using scanning electron microscopy. Figure 2This reflects the morphology of the shape memory artificial muscle under a fixed shape memory state and at contraction strains of -20%, -40%, and -60%. Figure 2 As can be seen, the surface of the shape memory artificial muscle exhibits periodic wrinkles due to the addition of sea squirt cellulose nanocrystals. These wrinkles facilitate further contraction of the shape memory artificial muscle in response to temperature. Therefore, this invention achieves the desired function without requiring processing into a specific spring-like helical structure.

[0040] Example 2

[0041] The shape memory artificial muscle prepared in Example 1 was pre-stretched under a 20g weight and then air-dried to obtain shape memory fibers. These fibers were then assembled into an artificial arm as the biceps brachii muscle to simulate muscle contraction and to measure its lifting capacity. In this test, it could lift a 10g weight within 10 seconds, with the arm flexion angle increasing from 0° to 76°, and the fiber contraction strain being -24%. The arm returned to its initial position after being immersed in water for 6 minutes.

[0042] Example 3

[0043] The shape memory artificial muscle prepared in Example 1 was hydrated and programmed, pre-stretched under a 20g weight, and then air-dried to obtain shape memory fibers (stretched to a predetermined stretch ratio in a hydrogel state and then dried and fixed). These fibers were then assembled into the artificial arm as the biceps brachii muscle, simulating an antagonist muscle pair composed of an agonist and an antagonist muscle, and applied to the antagonist movement of the artificial arm. Specifically, the shape memory artificial muscle capable of contracting under heat served as the agonist muscle, while the shape memory artificial muscle stretched in a hydrated state served as the antagonist muscle.

[0044] The demonstration process of the artificial arm is as follows: Figure 3 As shown, the agonist and antagonist muscles are used as the biceps and triceps brachii muscles of the artificial arm, respectively, and assembled on both sides. Hydration and heating are used to alter the stretching and contraction patterns of the muscles. When the arm needs to be bent, the triceps fibers are first hydrated, and then the biceps are heated to cause contraction, resulting in a bent arm. When the arm needs to be straightened, the biceps are hydrated, and then the triceps are heated to cause contraction. In simulated motion, the bending angle of the artificial arm during antagonistic movements was measured. The artificial arm in this embodiment can cyclically bend up to 72°, with a muscle fiber contraction strain of -21%.

[0045] The physical demonstrations and test results of the above embodiments show that the shape memory artificial muscle with a semi-interpenetrating network prepared by this invention has ultra-high elongation at break and toughness, and can achieve a high pre-stretch ratio (800%) shape programming process, providing a basis for the high contractile strain of shape memory fibers. This shape memory artificial muscle has good mechanical properties and working capacity, can contract by -60% strain within 3 seconds, and its maximum working capacity under 3MPa stress reaches 751J / kg, which is more than 18 times that of human skeletal muscle.

[0046] This invention relates to shape memory artificial muscles capable of shape programming and recovery under constant stress, a capability unattainable by traditional shape memory polymer materials due to their smaller modulus difference between the programmed and recovered states. The shape memory artificial muscles of this invention can be stretched under constant stress in a low-modulus hydrated state, transforming into high-modulus glassy fibers after air drying, and then contracting under constant stress upon heating. Based on this characteristic, shape memory artificial muscles can be assembled into antagonistic muscle pairs to achieve antagonistic movements. By stretching and contracting under constant stress, shape memory fibers can simulate agonist and antagonist muscles, including the biceps and triceps, assembling into antagonist muscle pairs on an artificial arm. The antagonist muscle is first hydrated to reduce its modulus; the agonist muscle contracts upon heating, simultaneously stretching the antagonist muscle; and the antagonist muscle's shape is fixed after drying, completing one antagonistic movement. By simulating the antagonistic movement between the biceps and triceps, reversible bending and straightening of the artificial arm is achieved, accompanied by the role reversal between the antagonist and agonist muscles.

[0047] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for preparing shape memory artificial muscles, characterized in that, Includes the following steps: (1) In a solution environment, polyvinyl alcohol, sea squirt cellulose nanocrystals and polymer monomers composed of acrylamide, acrylic acid and N,N'-methylenebisacrylamide were mixed and incubated to obtain a polymerization precursor dispersion; (2) An initiator is added to the polymerization precursor dispersion, and the mixture is processed by polymerization to form a fibrous hydrogel material, thereby obtaining shape memory artificial muscle.

2. The method according to claim 1, characterized in that: In step (1), the total content of polyvinyl alcohol accounts for 0.1 wt.% to 10.0 wt.% of the polymerization precursor dispersion; the total content of the polymeric monomers accounts for 20 wt.% to 30 wt.% of the polymerization precursor dispersion.

3. The method according to claim 1, characterized in that: In step (1), the mass ratio of acrylamide, acrylic acid and N,N'-methylenebisacrylamide in the polymer monomers is 1-9:1-9:0.0001-0.

1.

4. The method according to claim 1, characterized in that: In step (1), the polymerization precursor dispersion is formed by mixing polyvinyl alcohol and polymer monomer dissolved in an aqueous dispersion of sea squirt cellulose nanocrystals and incubating them.

5. The method according to claim 4, characterized in that: The content of sea squirt cellulose nanocrystals in the aqueous dispersion of sea squirt cellulose nanocrystals is 0.1 wt.% to 5.0 wt.%.

6. The method according to claim 1, characterized in that: In step (1), the incubation temperature is 50-90°C and the incubation time is 1-5 hours.

7. The method according to claim 1, characterized in that: In step (2), the polymerization reaction is carried out at a temperature of 40–80°C for 1–8 hours.

8. A shape memory artificial muscle, characterized in that: It is made by means of any one of claims 1 to 7.

9. An application of the shape memory artificial muscle as described in claim 8, characterized in that: Application of shape memory materials in antagonistic motion of biomimetic structures.

10. The application according to claim 9, characterized in that, The method is as follows: Shape memory artificial muscles are stretched and dried under strain and stress control to form antagonistic muscle pairs that simulate agonist and antagonist muscles. The antagonist muscle pairs are assembled on both sides of the bionic arm as the biceps and triceps muscles of the arm. Under temperature response, the agonist muscles contract and drive the antagonist muscles to extend, thereby realizing the cyclic antagonistic movement of the arm.

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