Sodium lignin sulfonate-polyvinyl alcohol modified membrane-based biocompatible IPMC and preparation method thereof

Abstract

The invention discloses a biocompatible IPMC based on a sodium lignin sulfonate-polyvinyl alcohol modified membrane and a preparation method of the biocompatible IPMC. The biocompatible IPMC is composed of an electrolyte membrane, flexible electrodes fixed to the two sides of the electrolyte membrane and an external electric signal input system. The SLS-PVA film has high water solubility resistance and is not obviously dissolved in hot water at 90 DEG C; the modified membrane has ideal mechanical properties (the Young's modulus ranges from 23.20 MPa to 34.84 MPa, and the elongation at break ranges from 154.90% to 289.53%), adjustable ion exchange performance (0.44 mmol / g to 0.74 mmol / g) and high water storage performance (the water content is larger than 65.40%). The method can be used for preparing the low-price and environment-friendly ion exchange polymer / metal composite material electric driver.

Description

Technical Field

[0001] The present invention belongs to the cross-research field of hybrid material technology and biomimetic machinery, relates to a method for preparing a novel metal / polymer electric actuator, and its application in the field of biomimetic machinery, and specifically relates to a method for preparing an IPMC driver based on polyvinyl alcohol grafted sodium lignin sulfonate film and its application. Background Art

[0002] Ionic polymer-metal composites (IPMCs) are ionic electroactive polymers with broad application prospects in biomimetic mechanisms, biomedicine, aerospace, and other fields due to their lightweight, low driving voltage, and high energy conversion efficiency. IPMCs consist of an ion-exchange polymer (such as Nafion) and inert metal nanoelectrodes (such as Pt) adsorbed on either side of the polymer. Nafion's structural characteristics include a hydrophobic carbon-fluorocarbon backbone and hydrophilic acid side chains. Due to the presence of both hydrophilic and hydrophobic groups, microchannels with diameters of 0.5 to 5 nm form within the ion-exchange membrane after crystallization. Under the influence of an electric field, cations within the Nafion membrane carry a limited amount of water molecules through the microchannels toward the cathode, causing the anode to contract and the cathode to expand, resulting in bending of the material.

[0003] However, these rather expensive actuators suffer from serious drawbacks, including early dehydration due to leakage of internal electrolytes and hydrated cations under long-term actuation, rapid reverse relaxation behavior, limited operation under ambient conditions, and poor durability due to crack formation in the metal electrodes. Many researchers have attempted to overcome the above limitations by (1) designing new ion exchange membranes or modifying existing membranes, (2) replacing water with non-volatile solvents, and (3) using flexible non-metallic conductive materials instead of metal electrodes. In this regard, the search for naturally derived and biodegradable ion-conducting polymers and durable electrodes provides a solution for the development of innovative green and biocompatible ion actuators.

[0004] Polyvinyl alcohol (PVA) is often considered a promising polymer matrix for the preparation of novel biocompatible ionomers due to its excellent water solubility, outstanding film-forming ability, compatibility, toughness, transparency, nontoxicity, and biodegradability. However, due to the large number of hydroxyl groups on the PVA molecular chain, its films are highly unstable and easily dissolve in water. Furthermore, PVA's simple molecular structure and poor ion exchange capacity prevent the rapid migration of hydrated cations.

[0005] Sodium lignosulfonate (SLS), derived from the reaction of wood pulp with an aqueous solution of sulfur dichloride and sulfite, is a chemically stable and biodegradable compound. As a lignin derivative, it possesses hydrophilic sulfonic acid groups on its hydrophobic backbone. Blending with PVA can improve the ion exchange capacity of PVA. However, the hydrophilic sulfonic acid groups of SLS and the hydroxyl groups of PVA still cause the composite polymer membrane to swell in water and lose strength. Summary of the Invention

[0006] The present invention relates to sulfonated polyvinyl alcohol (PVA) and an ion exchange polymer / metal composite electric actuator prepared using it. The present invention utilizes glutaraldehyde (GA) as a crosslinking agent, effectively promoting crosslinking between PVA molecules and significantly improving the water resistance of the PVA matrix. Furthermore, the aldehyde groups of glutaraldehyde react with the hydroxyl groups on PVA and SLS to introduce sulfonic acid groups into the PVA molecular chains, thereby enhancing the ion exchange performance of the ion exchange membrane. A MWCNTs-PEDOT:PSS electrode slurry is sprayed on the surface of the actuator and a signal is introduced to produce a biocompatible soft actuator.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions: An IPMC electric actuator based on polyvinyl alcohol grafted sodium lignin sulfonate membrane (SLS-PVA) consists of an electrolyte membrane, flexible electrodes fixed on both sides of the electrolyte membrane, and an external electrical signal input system. The electrolyte membrane is a modified membrane of polyvinyl alcohol grafted with sodium lignin sulfonate using glutaraldehyde as a cross-linking agent, and the electrodes are made by spraying MWCNT / PEDOT:PSS composite electrode slurry.

[0008] Furthermore, the SLS-PVA modified membrane has a thickness of 270-280 μm, a water absorption of 65.4-85.5%, an ion exchange equivalent of 0.44-0.74 mmol / g, an elastic modulus of 23.20-34.84 MPa, and an elongation at break of 154.90-289.53%. The MWCNT / PEDOT:PSS composite electrode has a thickness of approximately 10 μm and a surface resistance of 150 Ω.

[0009] Furthermore, the electric signal of the electric signal input system is a sine wave with a frequency of 0.1-1 Hz and a voltage of 6-12 V. The working displacement of the IPMC electric actuator is 3.54-8.39 mm, and the total deflection angle is about 72°.

[0010] 1. A biocompatible IPMC based on a sodium lignin sulfonate-polyvinyl alcohol modified membrane, characterized by comprising an electrolyte membrane, flexible electrodes fixed on both sides of the electrolyte membrane, and an external electrical signal input system. The electrolyte membrane is a SLS-PVA modified membrane in which sodium lignin sulfonate (SLS) is grafted onto polyvinyl alcohol (PVA) using glutaraldehyde as a crosslinker.

[0011] 2. The biocompatible IPMC based on sodium lignin sulfonate-polyvinyl alcohol modified membrane according to claim 1, characterized in that: the SLS-PVA modified membrane has a thickness of 270-280 μm, a water absorption rate of 65.40%-85.50%, an ion exchange equivalent of 0.44-0.74 mmol / g, an elastic modulus of 23.20-34.84 MPa, an elongation at break of 154.90-289.53%, a working displacement of the IPMC of 3.54-8.39 mm, and a total deflection angle of 72°.

[0012] 3. The biocompatible IPMC based on sodium lignin sulfonate-polyvinyl alcohol modified membrane according to claim 1, wherein the flexible electrode is made by spraying a MWCNT / PEDOT:PSS composite electrode slurry; the flexible electrode has a thickness of 10 μm and a surface resistance of 150 Ω.

[0013] 4. The biocompatible IPMC based on sodium lignin sulfonate-polyvinyl alcohol modified membrane according to claim 1, wherein the electrical signal of the external electrical signal input system is a sine wave with a frequency of 0.1-1 Hz and a voltage of 6-12 V.

[0014] 5. The method for preparing a biocompatible IPMC based on a sodium lignin sulfonate-polyvinyl alcohol modified membrane according to any one of claims 1 to 4, characterized in that the steps are as follows: (1) Preparation of SLS-PVA modified membrane: Sodium lignosulfonate (SLS) powder, glutaraldehyde, and glycerol were added to a heated PVA solution under stirring until SLS was completely dissolved to obtain a mixed solution. The mixed solution was poured into a glass Petri dish and heated in an oven to evaporate the water in the mixed solution to obtain an SLS-PVA modified membrane. (2) Preparation of MWCNT / PEDOT:PSS composite electrode slurry; (3) Preparation of IPMC: Take an appropriate amount of electrode slurry in a spray gun, spray it evenly on both sides of the SLS-PVA modified membrane, and then put it in an oven to dry to obtain a biocompatible IPMC based on sodium lignin sulfonate-polyvinyl alcohol modified membrane.

[0015] Furthermore, in step (1), the amount of SLS powder used is 2.5 wt%-10 wt% of the dry weight of PVA, the amount of glutaraldehyde used is 5 wt% of the dry weight of PVA, the amount of glycerol used is 50 wt% of the dry weight of PVA, and the concentration of PVA in the mixed solution is 4 wt%.

[0016] Furthermore, the preparation method of the MWCNT / PEDOT:PSS composite electrode slurry in step (2) is as follows: 10 ml of PVA / SLS mixed solution, 10 ml of deionized water, 3 ml of PEDOT:PSS and 0.15 g of multi-walled carbon nanotubes are taken in a 50 ml beaker and ultrasonically mixed for 1 h to obtain a uniformly dispersed electrode slurry.

[0017] Furthermore, the concentration of PVA in the PVA / SLS mixed solution was 4 wt %, and the content of SLS was 2.5 wt % of the dry weight of PVA.

[0018] Furthermore, before spraying the electrode slurry in step (3), both sides of the SLS-PVA modified membrane obtained in step (1) are evenly polished with 800-mesh sandpaper to roughen the surface, and then the membrane is placed in a fixture to ensure the flatness of the membrane; an appropriate amount of electrode slurry is taken from a spray gun and evenly sprayed on both sides of the SLS-PVA modified membrane, and then placed in an oven at 60°C for drying for 20 minutes and then taken out, and this operation is repeated 5-8 times, and finally dried in an oven at 60°C for 12 hours.

[0019] Furthermore, in step (3), in order to ensure good bonding between the electrode layer and the PVA composite film, a flat-plate vulcanizer is used to perform hot pressing at 40°C and 2.5 MPa for 2 minutes.

[0020] The typical preparation method of the IPMC electric actuator based on SLS-PVA film of the present invention is as follows: (1) Preparation of SLS-PVA modified membrane: PVA powder was dissolved in deionized water at 90 °C for 2 h, and a uniform solution with a mass fraction of 5 wt% was prepared under continuous stirring. Different masses of SLS powder (2.5, 5, 7.5, 10 wt% relative to the dry weight of PVA), constant glutaraldehyde (5 wt% relative to the dry weight of PVA), and constant glycerol (50 wt% relative to the dry weight of PVA) were added to the heated PVA solution under stirring until SLS was completely dissolved. The final mixed solution was obtained by adding some deionized water to the PVA / SLS solution to maintain the PVA concentration at 4 wt%. An appropriate amount of the mixed solution was poured into a glass Petri dish with a diameter of 90 mm and heated in an oven at 70 °C for 12 h to evaporate the water of the mixed solution to obtain an SLS-PVA film.

[0021] (2) Preparation of MWCNT / PEDOT:PSS composite electrode slurry: 10 ml of a PVA / SLS mixed solution with an SLS concentration of 2.5 wt% (2.5 wt% of the dry weight of PVA), 10 ml of deionized water, 3 ml of PEDOT:PSS and 0.15 g of multi-walled carbon nanotubes were placed in a 50 ml beaker and ultrasonically mixed for 1 h to obtain a uniformly dispersed electrode slurry.

[0022] (3) Preparation of SLS-PVA membrane IPMC: Use 800-grit sandpaper to evenly polish both sides of the SLS-PVA modified membrane to roughen the surface, and then place the membrane in a homemade fixture to ensure the flatness of the membrane. Take an appropriate amount of electrode slurry in a spray gun and evenly spray it on both sides of the SLS-PVA modified membrane. Place it in an oven at 60°C and dry it for 20 minutes before taking it out. Repeat this operation seven times, and finally dry it in an oven at 60°C for 12 hours. In order to ensure good bonding between the electrode layer and the PVA composite membrane, a flat vulcanizer is used to hot press at 40°C and 2.5 MPa for 2 minutes. Cut it into 30mm×5mm strips to obtain SLS-PVA membrane IPMC.

[0023] This paper proposes for the first time that glutaraldehyde (GA) plays an important role in the chemical reaction between PVA and SLS. On the one hand, it acts as a bridge to introduce sulfonic acid groups into the PVA matrix, effectively solving the problem of insufficient ion exchange capacity of PVA. On the other hand, GA acts as a cross-linking agent, promoting cross-linking between PVA molecules and significantly enhancing the water resistance of the PVA matrix, making it suitable for use as an ion-conducting matrix for IPMC. The chemical reaction formula is as follows: Figure 5 A novel highly biocompatible IPMC based on SLS-PVA membrane was prepared by spraying MWCNTs-PEDOT:PSS / PVA electrodes, thus developing a low-cost, highly biocompatible IPMC actuator.

[0024] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention obtains a cheap and environmentally friendly ion exchange membrane by grafting sodium lignin sulfonate onto polyvinyl alcohol with glutaraldehyde, which can replace Nafion.

[0025] (2) Compared with pure PVA membrane, the water resistance of SLS-PVA modified membrane is improved and it can exist stably in deionized water at 90 °C for a long time without dissolving.

[0026] (3) The SLS-PVA modified membrane has ultra-high water storage capacity (water content greater than 65.4%), ideal mechanical properties (Young's modulus between 23.20-34.84 MPa, elongation at break between 154.90-289.53%) and adjustable ion exchange performance (0.44-0.74 mmol / g).

[0027] (4) The SLS-PVA-based IPMC electric actuator prepared by the present invention has broad application fields, such as biomedicine, due to its good biocompatibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 FTIR spectra of GA solution, SLS powder, PVA and SLS-PVA-10.0 film.

[0030] Figure 2 Water resistance test of PVA-related membranes, (a) Changes of PVA membrane in 90 ℃ aqueous solution; (b) Changes of SLS-PVA modified membrane in 90 ℃ aqueous solution; (c) Changes of SLS / PVA blend membrane without glutaraldehyde.

[0031] Figure 3 Scanning electron microscopy images of SLS-PVA-10.0 membrane IPMC, (a) cross-section of IPMC; (b) interface between electrode and electrolyte; (c) cross-sectional morphology of SLS-PVA-10.0 modified membrane; (d) magnified cross-sectional view of SLS-PVA-10.0 membrane; (e) electrode surface.

[0032] Figure 4 Screenshot of the SLS-PVA-10.0 membrane IPMC drive video.

[0033] Figure 5 Schematic diagram of the chemical reaction between PVA, GA and SLS. DETAILED DESCRIPTION

[0034] The present invention will be further described below with reference to specific examples. It should be understood that the following examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention, and that those skilled in the art may make non-essential improvements and adjustments based on the contents of the above invention.

[0035] (1) Preparation of SLS-PVA modified membrane: PVA powder was dissolved in deionized water at 90 °C for 2 h, and a uniform solution with a mass fraction of 5 wt% was prepared under continuous stirring. Different masses of SLS powder (2.5, 5, 7.5, 10 wt% relative to the dry weight of PVA), constant glutaraldehyde (5 wt% relative to the dry weight of PVA), and constant glycerol (50 wt% relative to the dry weight of PVA) were added to the heated PVA solution under stirring until SLS was completely dissolved. The final mixed solution was obtained by adding some deionized water to the PVA / SLS solution to maintain the PVA concentration at 4 wt%. An appropriate amount of the mixed solution was poured into a glass Petri dish with a diameter of 90 mm and heated in an oven at 70 °C for 12 h to evaporate the water of the mixed solution to obtain an SLS-PVA film.

[0036] (2) Preparation of MWCNT / PEDOT:PSS composite electrode slurry: 10 ml of a PVA / SLS mixed solution with an SLS concentration of 2.5 wt% (2.5 wt% of the dry weight of PVA), 10 ml of deionized water, 3 ml of PEDOT:PSS and 0.15 g of multi-walled carbon nanotubes were placed in a 50 ml beaker and ultrasonically mixed for 1 h to obtain a uniformly dispersed electrode slurry.

[0037] (3) Preparation of SLS-PVA membrane IPMC: Use 800-grit sandpaper to evenly polish both sides of the SLS-PVA modified membrane to roughen the surface, and then place the membrane in a homemade fixture to ensure the flatness of the membrane. Take an appropriate amount of electrode slurry in a spray gun and evenly spray it on both sides of the SLS-PVA modified membrane. Place it in an oven at 60°C and dry it for 20 minutes before taking it out. Repeat this operation seven times, and finally dry it in an oven at 60°C for 12 hours. In order to ensure good bonding between the electrode layer and the PVA composite membrane, a flat vulcanizer is used to hot press at 40°C and 2.5 MPa for 2 minutes. Cut it into 30mm×5mm strips to obtain SLS-PVA membrane IPMC.

[0038] The present invention prepared a PVA film without SLS and glutaraldehyde as a control group. PVA / SLS films with different SLS concentrations were distinguished by SLS-PVA-X, where X = 2.5, 5.0, 7.5, and 10.0, indicating SLS concentrations of 2.5, 5.0, 7.5, and 10.0 wt%, respectively.

[0039] Example 1 This embodiment is the preparation of PVA film, and the specific method is as follows: PVA powder was dissolved in deionized water at 90°C for 2 hours with continuous stirring to prepare a homogeneous solution with a mass fraction of 5 wt%. Glutaraldehyde (5 wt% of the PVA dry weight) and glycerol (50 wt% of the PVA dry weight) were added to the heated PVA solution with stirring until uniform. The final mixed solution was obtained by adding some deionized water to the PVA solution to maintain a PVA concentration of 4 wt%. An appropriate amount of the mixed solution was poured into a 90 mm diameter glass Petri dish and heated in an oven at 70°C for 12 hours to evaporate the water from the mixed solution, resulting in a PVA film.

[0040] Example 2 This example is the preparation of SLS-PVA-2.5 modified membrane, and the specific method is as follows: PVA powder was dissolved in deionized water at 90°C for 2 hours with continuous stirring to prepare a homogeneous solution with a mass fraction of 5 wt%. 30 mg of SLS powder (2.5 wt% of the dry weight of PVA), glutaraldehyde (5 wt% of the dry weight of PVA), and glycerol (50 wt% of the dry weight of PVA) were added to the heated PVA solution with stirring until the SLS was completely dissolved. The final mixed solution was obtained by adding some deionized water to the PVA / SLS solution to maintain a PVA concentration of 4 wt%. An appropriate amount of the mixed solution was poured into a 90 mm diameter glass Petri dish and heated in an oven at 70°C for 12 hours to evaporate the water from the mixed solution, resulting in an SLS-PVA-2.5 film.

[0041] Example 3 This example is the preparation of SLS-PVA-5.0 modified membrane, and the specific method is as follows: PVA powder was dissolved in deionized water at 90°C for 2 hours with continuous stirring to prepare a homogeneous solution with a mass fraction of 5 wt%. 60 mg of SLS powder (5 wt% of the dry weight of PVA), glutaraldehyde (5 wt% of the dry weight of PVA), and glycerol (50 wt% of the dry weight of PVA) were added to the heated PVA solution with stirring until the SLS was completely dissolved. The final mixed solution was obtained by adding some deionized water to the PVA / SLS solution to maintain a PVA concentration of 4 wt%. An appropriate amount of the mixed solution was poured into a 90 mm diameter glass Petri dish and heated in an oven at 70°C for 12 hours to evaporate the water from the mixed solution, resulting in an SLS-PVA-5.0 film.

[0042] Example 4 This example is the preparation of SLS-PVA-7.5 modified membrane, and the specific method is as follows: PVA powder was dissolved in deionized water at 90°C for 2 hours with continuous stirring to prepare a homogeneous solution with a mass fraction of 5 wt%. 90 mg of SLS powder (7.5 wt% of the PVA dry weight), glutaraldehyde (5 wt% of the PVA dry weight), and a constant amount of glycerol (50 wt% of the PVA dry weight) were added to the heated PVA solution with stirring until the SLS was completely dissolved. The final mixed solution was obtained by adding some deionized water to the PVA / SLS solution to maintain a PVA concentration of 4 wt%. An appropriate amount of the mixed solution was poured into a 90 mm diameter glass Petri dish and heated in an oven at 70°C for 12 hours to evaporate the water from the mixed solution, resulting in an SLS-PVA-7.5 film.

[0043] Example 5 This example is the preparation of SLS-PVA-10.0 modified membrane, and the specific method is as follows: PVA powder was dissolved in deionized water at 90°C for 2 hours with continuous stirring to prepare a homogeneous solution with a mass fraction of 5 wt%. 120 mg of SLS powder (10 wt% of the dry weight of PVA), glutaraldehyde (5 wt% of the dry weight of PVA), and glycerol (50 wt% of the dry weight of PVA) were added to the heated PVA solution with stirring until the SLS was completely dissolved. The final mixed solution was obtained by adding some deionized water to the PVA / SLS solution to maintain a PVA concentration of 4 wt%. An appropriate amount of the mixed solution was poured into a 90 mm diameter glass Petri dish and heated in an oven at 70°C for 12 hours to evaporate the water from the mixed solution, resulting in an SLS-PVA-10.0 film.

[0044] Example 6 Preparation of MWCNT / PEDOT:PSS composite electrode slurry: Take 10 ml of PVA / SLS mixed solution with an SLS concentration of 2.5 wt% (2.5 wt% of the dry weight of PVA) (the concentration of PVA in the PVA / SLS mixed solution is 4 wt%), 10 ml of deionized water, 3 ml of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and 0.15 g of multi-walled carbon nanotubes in a 50 ml beaker and ultrasonically mix for 1 h to obtain a uniformly dispersed electrode slurry.

[0045] Example 7 Use 800-mesh sandpaper to evenly polish both sides of the SLS-PVA modified membrane obtained in Example 2-5 to roughen the surface, and then place the membrane in a homemade fixture to ensure the flatness of the membrane. Take an appropriate amount of electrode slurry in the spray gun, spray it evenly on both sides of the SLS-PVA modified membrane, put it in an oven at 60°C and dry it for 20 minutes before taking it out. Repeat this operation seven times, and finally dry it in an oven at 60°C for 12 hours. In order to ensure a good bond between the electrode layer and the PVA composite membrane, a flat-plate vulcanizing machine is used to hot press at 40°C and 2.5 MPa for 2 minutes. Cut it into 30mm×5mm strips to obtain SLS-PVA-2.5 membrane IPMC, SLS-PVA-5.0 membrane IPMC, SLS-PVA-7.5 membrane IPMC, and SLS-PVA-10.0 membrane IPMC respectively. As Figure 3 This is a scanning electron micrograph of the IPMC of the SLS-PVA-10.0 membrane.

[0046] 1. Infrared spectroscopy analysis GA (glutaraldehyde) solution, SLS powder, PVA and SLS-PVA-10.0 modified film were tested by infrared ray. The results are as follows: Figure 1 For GA, 1720 cm -1 Its C=O stretching vibration absorption peak, 2950 cm -1 The characteristic peak at 1040 cm is the CH stretching vibration of the methylene group. -1 The characteristic peak at 3400 cm is the stretching vibration peak of the sulfonic acid group S=O on SLS. -1 The broad absorption peak near 1640 cm is attributed to OH stretching vibration, which comes from the large number of hydroxyl groups on the PVA molecular chain and the water contained in the PVA film. -1 is the bending vibration absorption peak of OH in adsorbed water molecules, 1050 cm -1 The stretching vibration absorption peak of CO on its molecular chain is 1040 cm -1 The stretching vibration peak attributed to S=O appeared at 1720 cm -1 The absorption peak representing the C=O stretching vibration disappeared, indicating that polyvinyl alcohol and sodium lignin sulfonate underwent aldol condensation reaction through glutaraldehyde.

[0047] 2. SLS-PVA modified film performance test Water resistance test: Place the sample film in deionized water and heat it in a water bath at 90°C. Figure 2 shown.

[0048] Swelling rate and water absorption test: The prepared sample film was cut into 20mm×20mm size, dried in an oven to constant weight, and then the sample was weighed (Mdry ) and measure its thickness (H dry ), then soak it in deionized water at room temperature for 24 h, take it out and dry the surface water with a paper towel and weigh it again (M wet ) and measure thickness (H wet ), through (M wet -M dry ) / M dry and (H wet -H dry ) / H dry Calculate the water absorption and swelling rate of the sample film.

[0049] Ion exchange equivalent test: The cut sample membrane is immersed in dilute hydrochloric acid for 24 hours, then washed with deionized water several times until the membrane is neutral, and then placed in NaOH solution, with methyl red and methylphenol green added as mixed indicators. After titration with HCl solution, the dry weight (M) of the membrane is weighed, and the formula IEC=(C HCl V HCl -C NaOH V NaOH ) / M to calculate the ion exchange equivalent of the membrane.

[0050] Mechanical properties testing: The SLS-PVA modified film was formed into a dumbbell shape and tested using an electronic universal testing machine. The test temperature was 25°C and the tensile rate was 50 mm / min.

[0051] Table 1 Related performance results of modified membrane The data in Table 1 show that the water absorption and swelling ratio of the SLS-PVA composite membrane are significantly lower than those of pure PVA membrane, and the decrease in water absorption becomes more pronounced with increasing SLS dosage. The lower water absorption and swelling ratio of the SLS-PVA composite membrane compared to pure PVA membranes is due to the large number of hydrophilic hydroxyl groups on the PVA molecular chains, allowing water molecules to quickly penetrate the polymer interstitial space. This reduces interactions between polymer macromolecules and further enhances the ability of water molecules to penetrate the membrane. Increasing the SLS dosage introduces more hydrophobic groups into the system. At the same time, chemical reactions consume some of the hydroxyl groups on the PVA molecular chains, forming a cross-linked network that increases intermolecular forces and makes it difficult for water molecules to penetrate the polymer interstitial space. Water absorption is a key factor affecting the driving performance of IPMC. Under the action of an electric field, hydrated cations within the IPMC membrane migrate, causing the anode to shrink and the cathode to expand. However, excessive water absorption and swelling ratios can lead to excessive swelling of the IPMC membrane, compromising its mechanical stability. In this work, the water absorption and swelling rate of PVA composite films were significantly reduced by adding SLS and glutaraldehyde, making it possible to use it as a polymer matrix for stable IPMC actuators.

[0052] The IEC values ​​for pure PVA membrane and SLS-PVA composite membrane are approximately 0.32, 0.44, 0.55, 0.68, and 0.74 mmol / g, respectively. This is because the addition of SLS introduces sulfonic acid groups into the PVA molecular chains, thereby enhancing the ion exchange properties of the composite membrane and increasing the IEC value. Furthermore, the IEC value of the composite membrane continues to increase with increasing SLS content. While the IEC value of the SLS-PVA-10.0 membrane still lags behind that of Nafion membrane (0.95 mmol / g), it is 1.31 times higher than that of pure PVA membrane. This indicates that the SLS-PVA-10.0 membrane contains a higher level of ion exchange sites, supporting its higher hydrophilicity and higher ion content. Furthermore, the membrane's higher IEC facilitates the uniform deposition of a larger number of electrodes on both sides of the membrane, thereby fabricating actuators with more suitable actuation performance.

[0053] Compared to pure PVA films, the tensile strength and Young's modulus of the SLS-PVA composite films were significantly improved. The tensile strength increased from 21.93 MPa for pure PVA films to 32.01 MPa for the SLS-PVA-10.0 composite film. Similarly, the Young's modulus of the films steadily increased, reaching a maximum of 34.84 MPa in the SLS-PVA-10.0 composite film. This indicates that the cross-linking reaction between PVA molecules improves the mechanical properties of the PVA film, which is crucial for the fabrication of high-performance actuators.

[0054] 3. IPMC electric drive performance test The experimental setup mainly consists of a signal generation unit, a signal amplification unit, and a force sensor. The signal generation unit's hardware is based on a NI 6024E multifunction data acquisition card; the software is programmed using LabVIEW; and the signal amplification unit is based on a TI OPA548 power amplifier chip.

[0055] Electric drive performance test: The IPMC was placed at the two poles of the power supply, the control voltage was between 6 and 12 V, the operating frequency was 0.1 to 1 Hz, and the displacement of the electric drive was observed and collected using a high-speed camera and a laser displacement sensor. The results are listed in Table 2 and Figure 4 .

[0056] Table 2 Electric drive displacement results of IPMC The data in Table 2 show that the actuator tip displacement increases with increasing SLS dosage and voltage. This is because increasing SLS dosage improves the mechanical properties and IEC of the SLS-PVA composite film, leading to an increase in the actuated displacement. Furthermore, since hydrated cations migrate under voltage, when the voltage is low, the force acting on them is small, their migration speed is slow, and a relatively small number of them reach the cathode, resulting in relatively small cathode expansion and anode contraction. As the voltage gradually increases, the electric field force acting on the hydrated cations gradually intensifies, increasing their migration speed and the number of hydrated cations reaching the cathode, leading to greater cathode expansion and anode contraction. Therefore, the actuated displacement of the IPMC increases with increasing voltage. However, as the test frequency increases, the detected actuated displacement shows a decreasing trend. This is because when the voltage remains constant but the frequency increases, the electric field changes too rapidly, and the inertia of the hydrated cations is much greater than that of the electrons. Consequently, the hydrated cations' movement speed is slower than the electric field's speed, preventing them from fully migrating from one electrode end to the other. This results in incomplete cathode expansion and anode contraction, ultimately leading to a gradual decrease in the deformation displacement. As the amount of SLS increases, the trend of the driver's test displacement decreasing as the test frequency increases becomes more obvious.

[0057] The above illustrates and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the foregoing embodiments. The foregoing embodiments and descriptions merely illustrate the principles of the present invention. Various modifications and improvements are possible without departing from the spirit and scope of the present invention. These modifications and improvements are intended to fall within the scope of the claimed invention. The scope of the claimed invention is defined by the appended claims and their equivalents.

Claims

1. A biocompatible IPMC based on sodium lignin sulfonate-polyvinyl alcohol modified membrane, characterized by: The invention consists of an electrolyte membrane, flexible electrodes fixed on both sides of the electrolyte membrane and an external electrical signal input system. The electrolyte membrane is a SLS-PVA modified membrane in which polyvinyl alcohol (PVA) is grafted with sodium lignin sulfonate (SLS) using glutaraldehyde as a cross-linking agent.

2. The biocompatible IPMC based on sodium lignin sulfonate-polyvinyl alcohol modified membrane according to claim 1, characterized in that: The thickness of the SLS-PVA modified membrane is 270-280 μm, the water absorption is 65.40%-85.50%, the ion exchange equivalent is 0.44-0.74 mmol / g, the elastic modulus is 23.20-34.84 MPa, the elongation at break is 154.90-289.53%, the working displacement of the IPMC is 3.54-8.39 mm, and the total deflection angle is 72°.

3. The biocompatible IPMC based on sodium lignin sulfonate-polyvinyl alcohol modified membrane according to claim 1, characterized in that: The flexible electrode is made by spraying MWCNT / PEDOT:PSS composite electrode slurry; the thickness of the flexible electrode is 10 μm and the surface resistance is 150 Ω.

4. The biocompatible IPMC based on sodium lignin sulfonate-polyvinyl alcohol modified membrane according to claim 1, characterized in that: The electric signal of the external electric signal input system is a sine wave with a frequency of 0.1-1 Hz and a voltage of 6-12V.

5. The method for preparing the biocompatible IPMC based on sodium lignin sulfonate-polyvinyl alcohol modified membrane according to any one of claims 1 to 4, characterized in that Here are the steps: (1) Preparation of SLS-PVA modified membrane: Sodium lignosulfonate (SLS) powder, glutaraldehyde, and glycerol were added to a heated PVA solution under stirring until SLS was completely dissolved to obtain a mixed solution. The mixed solution was poured into a glass Petri dish and heated in an oven to evaporate the water in the mixed solution to obtain an SLS-PVA modified membrane. (2) Preparation of MWCNT / PEDOT:PSS composite electrode slurry; (3) Preparation of IPMC: Take an appropriate amount of electrode slurry in a spray gun, spray it evenly on both sides of the SLS-PVA modified membrane, and then put it in an oven to dry to obtain a biocompatible IPMC based on sodium lignin sulfonate-polyvinyl alcohol modified membrane.

6. The method for preparing the biocompatible IPMC based on the sodium lignin sulfonate-polyvinyl alcohol modified membrane according to claim 5, characterized in that: In step (1), the amount of SLS powder used is 2.5 wt%-10 wt% of the dry weight of PVA, the amount of glutaraldehyde used is 5 wt% of the dry weight of PVA, the amount of glycerol used is 50 wt% of the dry weight of PVA, and the concentration of PVA in the mixed solution is 4 wt%.

7. The method for preparing the biocompatible IPMC based on the sodium lignin sulfonate-polyvinyl alcohol modified membrane according to claim 5, characterized in that: The preparation method of the MWCNT / PEDOT:PSS composite electrode slurry in step (2) is as follows: 10 ml of PVA / SLS mixed solution, 10 ml of deionized water, 3 ml of PEDOT:PSS and 0.15 g of multi-walled carbon nanotubes are taken in a 50 ml beaker and ultrasonically mixed for 1 h to obtain a uniformly dispersed electrode slurry.

8. The method for preparing biocompatible IPMC based on sodium lignin sulfonate-polyvinyl alcohol modified membrane according to claim 7, characterized in that: The concentration of PVA in the PVA / SLS mixed solution was 4 wt %, and the content of SLS was 2.5 wt % of the dry weight of PVA.

9. The method for preparing biocompatible IPMC based on sodium lignin sulfonate-polyvinyl alcohol modified membrane according to claim 5, characterized in that: Before spraying the electrode slurry in step (3), the SLS-PVA modified membrane obtained in step (1) is evenly polished on both sides with 800-mesh sandpaper to roughen the surface, and then the membrane is placed in a fixture to ensure the flatness of the membrane; an appropriate amount of electrode slurry is taken from the spray gun and evenly sprayed on both sides of the SLS-PVA modified membrane, and then placed in an oven at 60°C for drying for 20 minutes and then taken out, and the operation is repeated 5-8 times, and finally dried in an oven at 60°C for 12 hours.

10. The method for preparing biocompatible IPMC based on sodium lignin sulfonate-polyvinyl alcohol modified membrane according to claim 5, characterized in that: In step (3), in order to ensure good bonding between the electrode layer and the PVA composite film, a flat-plate vulcanizer is used to hot-press for 2 minutes at 40°C and 2.5 MPa.

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