A light-driven hydrogel actuator with piezoresistive / piezoelectric dual-mode sensing and its preparation method

Abstract

The present invention relates to an optically driven hydrogel actuator with integrated piezoresistive / piezoelectric dual-mode sensing function, a preparation method thereof, and an application thereof. The preparation method of the optically driven hydrogel actuator comprises: (1) preparing a (PVA) PNIPAM / PANI hydrogel actuator; (2) preparing a P(VDF-TrFE) flexible piezoelectric film; and (3) preparing a double-layer optically driven hydrogel for piezoresistive / piezoelectric dual-mode sensing: using the (PVA) PNIPAM / PANI hydrogel as a substrate, casting a PVA prepolymer solution and laying a P(VDF-TrFE) piezoelectric film, and performing repeated freeze-thaw processes (low-temperature curing-room-temperature melting) followed by chemical cross-linking by soaking in a glutaraldehyde solution to obtain the double-layer optically driven hydrogel actuator. The optically driven hydrogel actuator prepared by the present invention has piezoresistive / piezoelectric dual-mode sensing performance and excellent optical driving capability, and can be applied to underwater intelligent robots, manipulator grasping, and other aspects.

Description

Technical Field

[0001] The present invention belongs to the field of hydrogel driven sensing, and in particular relates to a preparation method and application of a light-driven hydrogel actuator for piezoresistive / piezoelectric dual-mode sensing. Background Art

[0002] Biological systems have evolved a variety of complex regulatory mechanisms to sense and respond to changes in the external environment. Take pine cones, for example. Due to the hygroscopic properties of individual cone scales, they can open when dry to release seeds and close when wet. Mimosa pudica is able to change the orientation of its leaves in response to mechanical stimulation (touch). Cephalopods (such as octopuses) exhibit a distributed sensory neuromotor control system with non-segmented arms that can sense their own movement (proprioception) and external tactile stimuli. The ability of these organisms to sense external stimuli and manage their movement to adapt to the environment has inspired the next paradigm of biological sensing and actuation devices. However, mimicking this biological somatosensory system to achieve active movement and perception requires the integration of sensors and actuators.

[0003] Currently, several representative sensing technologies are expected to be used in the development of new soft actuation-sensing integration, including piezoresistive, capacitive, piezoelectric, and triboelectric. Among these sensing technologies, resistor-based sensors are the most common for detecting applied external stimuli and deformation of soft actuators. However, resistive sensors often suffer from issues such as nonlinearity and hysteresis and are easily affected by their surrounding environmental conditions (such as temperature and humidity). Capacitive sensors offer high sensitivity and stable sensing signals, but their complex device structure and circuits limit their applications. Piezoelectric and triboelectric sensors have the advantage of being self-powered, but they are only suitable for dynamic mechanical sensing. However, complex signal conditioning electronics and limited stretchability restrict their further application in soft actuators. Therefore, developing an ideal hydrogel actuator with integrated actuation / sensing technology that meets requirements and balances various trade-offs, including compliant materials, sensory feedback, ease of fabrication, and application scenarios, will be challenging. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a method for preparing a piezoresistive / piezoelectric dual-mode sensing optically driven hydrogel actuator, the method comprising the following steps:

[0005] (1) preparing ammonium persulfate solution (APS) for use: adding ammonium persulfate to deionized water and stirring until completely dissolved, then adding deionized water to prepare ammonium persulfate solution, and then pre-cooling for use;

[0006] (2) Preparation of hydrogel precursor solution: N,N'-methylenebisacrylamide (BIS), N-isopropylacrylamide (NIPAM), and 2-hydroxy-2-methyl-1-phenyl-1-propanone (1173) were added to a mixed solvent of dimethyl sulfoxide (DMSO) and deionized water and stirred to obtain a clear and transparent solution. Subsequently, ANI, HCl (37%), and PVA solution were added in an ice-water bath. After all components were completely dissolved, pre-cooled ammonium persulfate solution (APS) was added and stirred rapidly.

[0007] (3) Injection molding: Inject the prepared hydrogel precursor solution into the mold, avoiding the generation of bubbles during the injection process;

[0008] (4) Cross-linking: Place the mold after injection molding in an ice water bath under a UV lamp for light curing;

[0009] (5) Polymerization: The mold is then placed at a low temperature to polymerize aniline. After the reaction is complete, the mold is removed and repeatedly rinsed with deionized water to obtain a light-driven / piezoresistive sensing (PVA) PNIPAM / PANI hydrogel actuator.

[0010] (6) Preparation of P(VDF-TrFE) flexible piezoelectric film: P(VDF-TrFE) powder was dissolved in N,N-dimethylformamide (DMF), and then heated and stirred until completely dissolved to obtain a colorless and transparent uniform solution. The uniform solution was then dropped onto a glass mold, scraped flat with a spatula, and placed in an oven to dry into a thin film. The film was then annealed, cooled to room temperature, and demolded. The film was then placed in a silicone oil bath and polarized under an electric field. Finally, it was washed several times to remove the residual silicone oil on the film surface to obtain the P(VDF-TrFE) piezoelectric film.

[0011] (7) Preparation of piezoresistive / piezoelectric dual-mode double-layer light-driven hydrogel: PVA is added to deionized water, heated in a water bath and stirred until completely dissolved to obtain a PVA solution. The (PVA)PNIPAM / PANI hydrogel obtained in step (5) is taken and a mold is made with a silicone pad, tape and a glass slide. The PVA solution is cast on the mold and cooled and solidified to form a gel. After the PVA layer is formed, the P(VDF-TrFE) piezoelectric film prepared in step (6) is laid on it, and then the PVA solution is cast again and the cooling and solidification-room temperature thawing process is repeated. The freeze-thaw process is repeated 3 times to obtain a double-layer hydrogel. The double-layer hydrogel is then placed in a glutaraldehyde solution for immersion to complete chemical crosslinking. After being taken out, it is washed with excess deionized water to obtain a piezoresistive / piezoelectric dual-mode sensing light-driven hydrogel actuator.

[0012] Furthermore, the concentration of the ammonium persulfate solution (APS) in step (1) is 1.5-2.5 mol / L, and the pre-cooling temperature is 0-4°C.

[0013] Furthermore, the DMSO in step (2) accounts for 40% to 80% of the total volume.

[0014] Furthermore, the mass concentration of the PVA solution in step (2) is 2 to 10%.

[0015] Furthermore, in step (4), the distance between the ultraviolet lamp and the mold is 12 to 18 cm, the wavelength of the ultraviolet lamp is 350 to 380 nm, the power is 250 W, and the ultraviolet lamp irradiation cross-linking time is 6 to 8 minutes.

[0016] Furthermore, the concentration of the glutaraldehyde solution in step (7) is 0.8-1.2 wt %, and the soaking and cross-linking time is 9-12 h.

[0017] The present invention also provides a piezoresistive / piezoelectric dual-mode sensing optically driven hydrogel actuator prepared according to the above preparation method.

[0018] The present invention also provides an application of the above-mentioned light-driven hydrogel actuator, which is assembled on an octopus tentacle to grasp objects, achieving rapid grasping under light while providing real-time feedback of piezoresistive and piezoelectric signals.

[0019] The present invention has the following advantages:

[0020] 1. Due to the efficient photothermal effect of polyaniline and the high responsiveness of its open-pore structure, the (PVA)PNIPAM / PANI composite hydrogel exhibits omnidirectional light-driven capabilities, bending to more than 90° within 4 seconds under UV light irradiation, and the recovery time is shortened to less than 10 seconds.

[0021] 2. The dual-mode sensor can collect information on bending angle, bending rate and bending direction during the bending process and simulate the actual bending process, demonstrating excellent in vitro sensing capabilities.

[0022] 3. Since sensing and actuation are integrated into a single material, when the hydrogel bends under photothermal actuation, motion feedback can be obtained through real-time resistance changes, thereby realizing the dual functions of remote-controlled actuation and self-sensing of the hydrogel system. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a diagram of the underwater driving and recovery process and angle change of the hydrogel under near-infrared light irradiation.

[0024] Figure 2 The bending deformation of the hydrogel in water under near-infrared light has synchronously fed back the bending angle and real-time self-sensing resistance change diagram.

[0025] Figure 3 Signal diagram for piezoelectric sensing to dynamically identify the bending of hydrogel in different directions.

[0026] Figure 4 The hydrogel is assembled on the octopus arm and realizes the process of grasping objects and synchronously feedback piezoresistive / piezoelectric signals.

[0027] Figure 5 It is the real-time sensing signal of the optical drive grabbing process. DETAILED DESCRIPTION

[0028] The present invention is described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several variations and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0029] Example 1

[0030] (1) Preparation steps of optically driven hydrogel actuator with piezoresistive / piezoelectric dual-mode sensing:

[0031] a) Prepare ammonium persulfate solution (APS): Add 4.564 g of ammonium persulfate to a certain amount of deionized water and stir until completely dissolved. Then, add more deionized water to make the solution 10 mL, to prepare a 2 mol / L ammonium persulfate solution. Precool the solution in the upper rack of a refrigerator (4°C) until ready to use.

[0032] b) Preparation of hydrogel precursor solution: 20 mg N,N'-methylenebisacrylamide (BIS), 1 g N-isopropylacrylamide (NIPAM), and 25 μL 2-hydroxy-2-methyl-1-phenyl-1-propanone (1173) were added to 3 mL of dimethyl sulfoxide (DMSO) / deionized water mixed solvent and stirred to obtain a clear and transparent solution. Subsequently, 138 μL ANI, 0.42 mL HCl (37%), and 1 mL PVA (10%) were added in an ice-water bath. After all components were completely dissolved, 0.5 mL of pre-cooled APS solution was added and stirred rapidly for 1 min.

[0033] c) Injection Molding: The prepared hydrogel precursor solution is injected into a mold consisting of two glass slides (60 mm × 25 mm) sandwiched with a 40 mm × 10 mm hollowed-out silicone gasket. The thickness of the silicone gasket is controllable and is generally 1.5 mm thick unless otherwise specified. The hydrogel precursor solution is carefully injected into the mold to avoid creating bubbles during the injection process.

[0034] d) Cross-linking: The mold after injection molding was placed in an ice-water bath 15 cm below a UV lamp (λ = 365 nm, 250 W) and illuminated for 6 min. After curing, the mold was demolded to obtain the (PVA)PNIPAM composite hydrogel.

[0035] e) Polymerization: The mold was then placed at 4°C to polymerize aniline. After waiting for 72 hours, the mold was removed and demolded. The mold was then rinsed repeatedly with deionized water to obtain a light-driven / piezoresistive sensing (PVA) PNIPAM / PANI hydrogel actuator.

[0036] f) Preparation of P(VDF-TrFE) flexible piezoelectric film: P(VDF-TrFE) powder was dissolved in N,N-dimethylformamide (DMF) at a mass ratio of 1:20, and then the mixed solution was placed in a 60°C water bath and heated with stirring for 3 hours until completely dissolved to obtain a colorless, transparent, uniform solution. The solution was then dropped onto a glass mold, flattened with a scraper, and placed in an 80°C oven to dry for 30 minutes to form a film. Subsequently, annealing was performed at 120°C for 2 hours to increase the crystallinity of the film, and then the film was demolded after cooling to room temperature. The annealed film was placed in a silicone oil bath, polarized under a 1kV high-voltage electric field for 2 hours, and then taken out. Finally, it was washed several times to remove the residual silicone oil on the surface of the film to obtain the P(VDF-TrFE) piezoelectric film;

[0037] g) Preparation of piezoresistive / piezoelectric dual-mode double-layer light-driven hydrogel: 10g PVA was added to 90mL deionized water and stirred at 95°C for 5h until completely dissolved to obtain a 10% PVA solution. The (PVA)PNIPAM / PANI hydrogel obtained in step (5) was made into a mold with a silicone pad, tape and a glass slide, and the 10% PVA solution was cast on the mold. It was cooled at -20°C for 30min to solidify to form a gel. After the PVA layer was formed, the P(VDF-TrFE) piezoelectric film prepared in step (6) was placed on it, and then a 10% PVA solution was cast again and low-temperature solidified for 30min. After the PVA layer was solidified, it was taken out and thawed at room temperature for 30min, and then continued to be placed in a refrigerator for low-temperature solidification. The freeze-thaw process was repeated 3 times to obtain a double-layer hydrogel. The double-layer hydrogel was then placed in a 1wt% glutaraldehyde solution and soaked for 10h to complete chemical crosslinking. After being taken out, it was washed and soaked with excess deionized water to obtain the final piezoresistive / piezoelectric dual-mode sensing light-driven hydrogel actuator.

[0038] (2) Driving performance test: When near-infrared light is irradiated on the hydrogel strip at any angle, the hydrogel bends in the direction of the incident light and can accurately track the light source. When the light source is turned on, the hydrogel quickly bends to more than 90° within 4 seconds. When the light source is maintained, the hydrogel bends in the direction of the light source. When the light source is turned off, the hydrogel quickly returns to its original undeformed structure within 10 seconds. Figure 1 The underwater optical drive-recovery process of the hydrogel is shown, which shows that the optical drive performance of the composite hydrogel is excellent.

[0039] (3) Sensing performance test: In strain detection, the sensing modes of the piezoresistive layer and the piezoelectric layer each have their own shortcomings. The piezoresistive sensing mode has good static sensing characteristics and can sense the specific bending strain, but it cannot detect the bending direction. Figure 2 This provides real-time piezoresistive signal feedback during the hydrogel's optical actuation process. During underwater light actuation, the hydrogel bends due to localized contraction of the illuminated area. This compressed area causes the PANI network to contract, enhancing its conductivity. During underwater self-sensing actuation, the resistance decreases as the bending angle increases. Figure 3 This is the bending signal feedback from the hydrogel piezoelectric layer, where leftward bending angles are defined as positive and rightward bending angles as negative. During both bending recovery and reverse bending, the piezoelectric sensor outputs negative voltages. Because the piezoelectric peak value is only related to the strain rate at the moment of deformation, the piezoelectric output signal during both strain processes cannot distinguish between bending directions. This requires dual-mode sensing to address this issue.

[0040] (4) Dual-mode sensing: During bending strain detection, piezoresistive and piezoelectric sensing modes are used simultaneously. By leveraging the specific complementary properties of different sensing modes, more comprehensive bending strain information can be obtained. In actual testing, the dual-mode sensor can simultaneously sense the bending angle, strain rate, and bending direction of the sample. Figure 4 The real-time feedback signal of dual-mode sensing is demonstrated: when the piezoelectric signal is positive, the resistance increases, and the surface bends to the left. When the piezoelectric signal is negative, the resistance increases, and the surface bends to the right. When the piezoelectric signal is negative, the resistance decreases, and the surface bends back to the right.

[0041] Example 2

[0042] To further demonstrate real-time signal feedback during autonomous actuation, we assembled the hydrogel into a model octopus arm, acting as a soft proprioceptive arm to mimic the octopus's grasping motion in water. The octopus arm begins in a straight, inert state. When illuminated by near-infrared light, it begins to bend and wrap around a cylinder. After a period of time, the light is turned off, and the arm releases the cylinder and returns to its original position. During this process, we collected real-time resistance and voltage signals. When the near-infrared light is applied to the octopus arm, the hydrogel begins to bend, generating a positive voltage pulse and a decrease in relative resistance. When the resistance stabilizes, it indicates that the octopus arm has grasped the object. When the light is turned off, a negative voltage signal is generated, accompanied by an increase in resistance, indicating that the arm has released the object and begun to recover. After a period of time, the resistance stabilizes, and the hydrogel's bending has largely recovered. Figure 5 It is the real-time sensing signal of the optical drive grabbing process.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing a light-driven hydrogel actuator with piezoresistive / piezoelectric dual-mode sensing, comprising the following steps: (1) Prepare ammonium persulfate solution (APS) for use: add ammonium persulfate to deionized water and stir until completely dissolved, then add deionized water to prepare ammonium persulfate solution, and then pre-cool for use; (2) Preparation of hydrogel precursor solution: Add N,N'-methylenebisacrylamide (BIS), N-isopropylacrylamide (NIPAM), and 2-hydroxy-2-methyl-1-phenyl-1-propanone (1173) to a mixed solvent of dimethyl sulfoxide (DMSO) and deionized water and stir evenly to obtain a clear and transparent solution. Then, add ANI, 37% HCl, and PVA solution in an ice-water bath in sequence. After all components are completely dissolved, add pre-cooled ammonium persulfate solution (APS) and stir rapidly. (3) Injection molding: Inject the prepared hydrogel precursor solution into the mold, avoiding the generation of bubbles during the injection process; (4) Cross-linking: Place the mold after injection molding in an ice water bath under a UV lamp for light curing; (5) Polymerization: The mold is then placed at a low temperature to polymerize aniline. After the reaction is completed, the mold is removed and repeatedly rinsed with deionized water to obtain a light-driven / piezoresistive sensing (PVA) PNIPAM / PANI hydrogel actuator. (6) Preparation of P(VDF-TrFE) flexible piezoelectric film: P(VDF-TrFE) powder was dissolved in N,N-dimethylformamide (DMF), and then heated and stirred until completely dissolved to obtain a colorless and transparent uniform solution. The uniform solution was then dropped onto a glass mold, scraped flat with a scraper, and placed in an oven to dry into a thin film. The film was then annealed, cooled to room temperature, and demolded. The film was then placed in a silicone oil bath and polarized under an electric field. Finally, it was washed several times to remove the residual silicone oil on the surface of the film to obtain the P(VDF-TrFE) piezoelectric film. (7) Preparation of piezoresistive / piezoelectric dual-mode double-layer light-driven hydrogel: PVA is added to deionized water, heated in a water bath and stirred until completely dissolved to obtain a PVA solution. The (PVA)PNIPAM / PANI hydrogel obtained in step (5) is made into a mold with a silicone pad, tape and a glass slide. The PVA solution is cast on the mold and cooled and solidified to form a gel. After the PVA layer is formed, the P(VDF-TrFE) piezoelectric film prepared in step (6) is laid on it. Then, the PVA solution is cast again and the cooling and solidification-room temperature thawing process is repeated. The freeze-thaw process is repeated 3 times to obtain a double-layer hydrogel. The double-layer hydrogel is then placed in a glutaraldehyde solution for immersion to complete chemical crosslinking. After being taken out, it is washed with excess deionized water to obtain a piezoresistive / piezoelectric dual-mode sensing light-driven hydrogel actuator.

2. The method for preparing a piezoresistive / piezoelectric dual-mode sensing optically driven hydrogel actuator according to claim 1, characterized in that: The concentration of the ammonium persulfate solution (APS) in step (1) is 1.5-2.5 mol / L, and the pre-cooling temperature is 0-4°C.

3. The method for preparing a piezoresistive / piezoelectric dual-mode sensing optically driven hydrogel actuator according to claim 1, characterized in that: The DMSO in step (2) accounts for 40% to 80% of the total volume.

4. The method for preparing a piezoresistive / piezoelectric dual-mode sensing optically driven hydrogel actuator according to claim 1, characterized in that: The mass concentration of the PVA solution in step (2) is 2-10%.

5. The method for preparing a piezoresistive / piezoelectric dual-mode sensing optically driven hydrogel actuator according to claim 1, characterized in that: In step (4), the distance between the UV lamp and the mold is 12-18 cm, the wavelength of the UV lamp is 350-380 nm, the power is 250 W, and the UV lamp irradiation cross-linking time is 6-8 min.

6. The method for preparing a piezoresistive / piezoelectric dual-mode sensing optically driven hydrogel actuator according to claim 1, characterized in that: The concentration of the glutaraldehyde solution in step (7) is 0.8-1.2 wt %, and the soaking and cross-linking time is 9-12 h.

7. A light-driven hydrogel actuator with piezoresistive / piezoelectric dual-mode sensing prepared by the preparation method according to any one of claims 1 to 6.

8. An application of the optically driven hydrogel actuator according to claim 1, characterized in that: The light-driven hydrogel actuator is assembled on the octopus tentacles to grasp objects, achieving rapid grasping under light while providing real-time feedback of piezoresistive and piezoelectric signals.

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