Soft actuator driven by humidity and preparation method thereof

Abstract

The invention discloses a humidity-driven soft actuator and a preparation method thereof, the actuator takes a patterned black polyimide (PI) film as a substrate, and the substrate is compounded with two-dimensional transition metal carbide Ti3C2Tx (MXene) / amylopectin amp; a functional layer is formed by Amylose / carbon nanotubes (CNTs), when the functional layer absorbs moisture and expands, the actuator is bent towards the PI side, and when the functional layer is dehumidified and contracts, the actuator is bent reversely; the bending response direction is defined through the substrate gap direction of nanosecond laser machining, and the initial curvature and the bending degree are regulated and controlled through vacuum hot pressing treatment. The components cooperate to endow the actuator with rapid humidity response capability and excellent mechanical stability. The technical problems that an existing humidity driving actuator is poor in programmability and an interface is prone to stripping are solved, an external driving source is not needed, the technology is simple, convenient and controllable, and the potential application value in the fields of soft robots, flexible intelligent equipment and the like is shown.

Description

Technical Field

[0001] This invention relates to the field of soft robots, and more particularly to a programmable soft actuator driven by humidity that responds to bending direction and degree of bending and has excellent mechanical properties, as well as a method for its fabrication. Background Technology

[0002] As the core execution component of intelligent robots, micro-manipulation platforms, and flexible electronic devices, soft actuators have shown broad application prospects in fields such as biomedicine, precision manufacturing, and environmental monitoring due to their excellent compliance, adaptability, and controllable deformation.

[0003] Among them, humidity-driven soft actuators use changes in ambient humidity as the driving source, requiring no external power supply, high-pressure gas, or chemical reagents. They have unique advantages such as being green and environmentally friendly, having low energy consumption, and being lightweight, making them one of the research hotspots in the field of flexible actuators in recent years.

[0004] Despite the advantages mentioned above, existing humidity-driven soft actuators still face several critical bottlenecks that hinder their industrial application. Most current actuators have a fixed bending direction, making it difficult to achieve multi-directional, customizable deformation responses through simple structural adjustments, thus failing to meet the precise operational requirements of complex scenarios. Even when directional control is achieved through methods such as stress unloading, there is no further control over the actuator's initial curvature and degree of bending. The actuator's functional layer (hygroscopic expansion layer) and substrate (support layer) are often achieved through simple coating or physical composite methods. Under repeated moisture absorption-dehydration cycles and external loads, interface delamination and separation easily occur, leading to performance degradation or even failure. Furthermore, traditional humidity-responsive materials (such as single polymers and natural polymers) have low moisture absorption and dehydration rates, resulting in excessively long deformation start-up and recovery times for the actuators, failing to meet real-time control requirements. During cyclic use, irreversible deformation easily occurs under varying loads such as tension and bending, resulting in a short service life, which places higher demands on the actuator's mechanical performance.

[0005] To address the shortcomings of the existing technologies, the key to promoting humidity-driven applications lies in developing a humidity-driven software actuator with high programmability, strong interface bonding, fast humidity response, and excellent mechanical stability. Summary of the Invention

[0006] Purpose of the invention: The purpose of this invention is to address the shortcomings of existing humidity-driven actuators, such as weak programmability, easy interface peeling, and easy interface failure. It provides a humidity-driven soft actuator and its fabrication method, which enhances the programmability of the soft actuator in response direction, especially in response degree, and improves the mechanical performance required to handle varying loads during cyclic use. The overall structure requires no external drive source, the fabrication process is simple and the parameters are controllable, making it suitable for applications such as soft actuators and flexible intelligent devices.

[0007] Technical solution: The present invention uses a humidity-driven soft actuator made of a double-layer composite film. A black polyimide (PI) film is processed using a patterned editing method to respond to the bending direction as the base film layer, and a two-dimensional transition metal carbide Ti3C2T is laminated on it. x A functional layer is formed by combining MXene, amylopectin, amylose, and carbon nanotubes (CNTs). The difference in the coefficient of swelling between the functional layer and the substrate enables humidity-driven bending deformation.

[0008] The soft actuator obtains its initial curvature through vacuum hot pressing; the bending response direction of the actuator is determined by the patterned gap direction, and the difference in the coefficient of hygroscopic expansion between the functional layer and the base layer causes the soft actuator to bend under humidity-driven conditions.

[0009] This invention relates to a method for preparing a humidity-driven soft actuator, which involves patterning a 10–15 μm thick PI film; immersing the patterned PI film in a 0.4–1 mol / L NaOH solution, rinsing it with deionized water until neutral, and then air-drying the PI film before plasma cleaning; vacuum-adsorbing the cleaned PI film onto a horizontal silicone pad; cutting a hydrophobic silicone film with a thickness greater than 1 mm into a mold and placing it on the PI film; dripping a mixed solution of MXene / Amylopectin & Amylose / CNT into the mold using a drop casting method, and air-drying it to form an MXene / Amylopectin & Amylose / CNT-PI composite film based on PI; and hot-pressing the MXene / Amylopectin & Amylose / CNT-PI composite film to shape its initial curvature.

[0010] The method for preparing the humidity-driven soft actuator of the present invention includes the following steps:

[0011] Step 1), PI substrate patterning: A rectangular black PI film with a thickness of 10–15 μm is fixed on a laser processing platform. A nanosecond laser is used to process parallel strip-shaped gaps or segmented strip-shaped gaps along a predetermined direction on the PI film surface. The direction angle of the gaps can be any angle within the range of 0°–180°. The laser parameters are set as follows: power 200–300 W, laser frequency 15–25 kHz, scanning speed 250–500 mm / s, and 1–3 scans. The processed gaps have a width of 0.5–1 mm, a length <15 mm, and an interval of 1.5–3 mm. Simultaneously, a certain width of unprocessed area is maintained between the edge of the gap matrix and the boundary of the PI film. If the gap direction is not parallel to the film edge, the gap length along the matrix edge gradually decreases.

[0012] Step 2), Preparation of CNT aqueous solution: Take multi-walled carbon nanotube powder and spread it evenly in a petri dish, with the powder layer thickness not exceeding 0.1 mm. Place the petri dish into the plasma reaction chamber for plasma cleaning. After taking it out, turn the powder over and clean it again. Repeat this process 5 to 7 times, with each cleaning time being 3 to 5 minutes. After the treatment is completed, take out the powder and dry it in a vacuum drying oven at 60 to 80°C for 0.5 to 1 hour to obtain hydroxylated multi-walled carbon nanotube powder.

[0013] Step 3): Dissolve 1–2 g of multi-walled carbon nanotube (MWC) aqueous dispersant in 250–500 mL of deionized water. Heat and stir in a water bath at 40–50 °C for 10–15 min until completely dissolved. Add 10–20 g of hydroxylated MWC powder and continue stirring for 15–30 min. Observe that no obvious insoluble large particles are observed. Transfer the solution to an ultrasonic cell disruptor and sonicate at 500–650 W for 1–2 h. Use a dropper to collect the ultrasonically dispersed dispersion and add it to distilled water. After observing complete diffusion and no suspended large particles, dispense the ultrasonically dispersed dispersion into centrifuge tubes and centrifuge at 2000–3000 rpm for 20–40 min. Take the supernatant as the final CNT aqueous solution. Take 3–5 mL of the CNT aqueous solution, vacuum filter, air dry, and weigh. Calculate the mass concentration of the CNT aqueous solution.

[0014] Step 4) Preparation of Amylopectin & Amylose aqueous solution: Weigh Amylopectin and Amylose powders at a mass ratio of 8:2 to 8:3, mix them, and sieve them through a 200-300 mesh sieve 3-5 times to ensure uniformity. Dissolve 10-15g of the Amylopectin & Amylose mixed powder in 200-250mL of deionized water, place it on a magnetic stirrer and stir for 10-20min to form a white turbid solution. Transfer it to a water bath and gradually heat it from room temperature to 85-100℃. During the heating process, gradually increase the stirring speed from 800-1000rpm to 2000-3000rpm, and keep stirring for 2-3min until the solution changes from a white turbid state to a colorless, transparent, and viscous state. After turning off the heating, let it stand and cool to room temperature. The viscosity of the solution will further increase. Then, sonicate the cooled solution with 80-100W power for 5-10min to obtain the Amylopectin & Amylose aqueous solution.

[0015] Step 5): Perform hydrophilication pretreatment on the patterned PI film from Step 1): Immerse the patterned PI film in a 0.4–1 mol / L NaOH solution and let it stand for 12–24 hours. Remove the film and rinse it repeatedly with deionized water until the rinsing solution is neutral. Place it in a ventilated area to air dry naturally. Then, place the dried PI film in a plasma cleaner for 10–20 minutes to enhance the hydrophilicity of the substrate surface and thus improve the interfacial adhesion. To ensure the interfacial adhesion effect, drop casting should be completed within 1 hour after cleaning.

[0016] Step 6) Preparation of MXene / Amylopectin & Amylose / CNT-PI composite membrane: Take 10-15 mL of MXene aqueous solution with a concentration of 10-15 mg / mL and 2-3 mL of CNT aqueous solution with a concentration of 3-6 mg / mL and add them to a beaker. Stir for 20-30 min, then sonicate at 50-70 W power for 15-30 min to obtain MXene / CNT mixture. Heat the Amylopectin & Amylose aqueous solution to above 85°C using a water bath method, maintain and stir for 2-3 min, and then cool to room temperature. Add 3-7 mL of cooled Amylopectin & Amylose aqueous solution to the MXene / CNT mixture while stirring for 15-30 min, then sonicate at 30-60 W power for 0.5-1 h, and then refrigerate at below 4°C for later use.

[0017] A patterned PI substrate is attached to a horizontal silicone pad. A rectangular mold matching the pretreated PI film is cut from a hydrophobic silicone film with a thickness greater than 1 mm and placed on the surface of the PI film to ensure a bubble-free fit. The mixed solution is evenly dripped into the mold and placed in a ventilated place to air dry naturally for 18–36 hours. After the mixed solution is completely dry, the silicone mold is removed to obtain the MXene / Amylopectin & Amylose / CNT-PI composite film.

[0018] Step 7) Hot-pressing the MXene / Amylopectin & Amylose / CNT-PI composite film to shape the initial curvature: Cut a rectangular sheet encompassing several patterned matrix units from the MXene / Amylopectin & Amylose / CNT-PI composite film. Lay the rectangular sheet flat between two clean glass plates, symmetrically clamp the glass plates with long-tail clamps to apply uniform pressure, and place the glass plate assembly into a vacuum drying oven. After evacuating to a pressure ≤10Pa, set the heating temperature to 75-105℃ and the heating time to 3-5 minutes. After heating, turn off the power and cool to room temperature. Open the oven door, remove the assembly, and remove the long-tail clamps and glass plates to obtain a humidity-driven soft actuator with a preset initial curvature. The initial curvature and degree of bending can be adjusted by adjusting the heating temperature and time.

[0019] In step 2), the steps for preparing hydroxylated multi-walled carbon nanotube powder are as follows:

[0020] (1) Spread multi-walled carbon nanotube powder in a shallow layer on a culture dish and place it in a plasma reaction chamber.

[0021] (2) After vacuuming, perform air plasma treatment for 3 to 5 minutes, take it out and turn the multi-walled carbon nanotube powder over, and wash it again. Repeat the cycle 5 to 7 times in total.

[0022] (3) After the treatment is completed, the multi-walled carbon nanotube powder is taken out and vacuum dried at 60-80℃ for 0.5-1h to obtain hydroxylated multi-walled carbon nanotube powder.

[0023] Working principle: The humidity-driven soft actuator of this invention is a double-layer composite film. The base layer is a patterned black polyimide (PI) film, and the functional layer is a two-dimensional transition metal carbide Ti3C2T. x (MXene) / amylopectin & amylose / carbon nanotubes (CNT) film. Initial curvature is obtained through vacuum hot pressing; the patterned gap direction defines the bending response direction of the actuator, and the difference in the coefficients of hygroscopic expansion between the functional layer and the substrate enables humidity-driven bending deformation.

[0024] The soft actuator of this invention uses a patterned black PI film as a substrate, and constructs an MXene / Amylopectin & Amylose / CNT composite functional layer on the surface of the PI film. Due to the significant difference in the coefficients of hygroscopic expansion between the substrate and the functional layer, when the ambient humidity increases and the functional layer absorbs moisture and expands, the actuator undergoes bending deformation towards the PI side; when the humidity decreases and the functional layer dehydrates and shrinks, the actuator bends in the opposite direction. The substrate gap structure formed by nanosecond lasers defines the dominant direction of the bending response, and a vacuum hot pressing process is further used to adjust and control the initial curvature and bending amplitude. The synergistic effect of the MXene, starch system, and CNTs enables the actuator to possess both rapid humidity response characteristics and good mechanical stability.

[0025] The patterning method employs nanosecond laser processing to create parallel strip-shaped gaps along a predetermined direction on a rectangular black PI film of a fixed size. The direction of these gaps determines the direction of the actuator's response bending. Finally, quantitative hot pressing is used to determine the initial curvature and the degree of response bending.

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

[0027] (1) This invention utilizes a comprehensive process combining nanosecond laser patterning with composite functional layer fabrication and vacuum hot pressing to process parallel strip-shaped gaps in a predetermined direction on the surface of a black PI film substrate, and then composites them to form an MXene / Amylopectin & Amylose / CNT functional layer, thereby producing a humidity-driven soft actuator. The gap structure processed by nanosecond laser not only provides a stable supporting substrate for the functional layer, but also adjusts the anisotropy of the substrate response through the gap direction, directly defining the bending response direction of the actuator.

[0028] (2) Amylopectin readily forms a network structure, enhancing flexibility, while Amylose exhibits stronger tensile strength. Amylopectin & Amylose solution, prepared by adjusting their ratio, possesses excellent film-forming properties and water absorption. Combined with the integral network structure constructed from MXene and hydroxylated multi-walled carbon nanotubes, it exhibits very stable adhesion to the substrate, enabling rapid sensing of changes in ambient humidity and thus driving the actuator to achieve flexible deformation. Furthermore, the synergistic effect of MXene and carbon nanotubes enhances the mechanical support of the composite functional layer, avoiding the structural relaxation issues that easily occur with single hydrophilic materials during deformation. Simultaneously, the NaOH immersion and plasma cleaning treatment of the patterned PI film further strengthens the interfacial bonding between the substrate and the functional layer, reducing the risk of functional layer delamination during long-term cyclic deformation and improving the structural stability of the actuator.

[0029] (3) During the vacuum hot-pressing treatment of the composite membrane, under constrained conditions, the significant difference in the coefficients of thermal expansion between the PI substrate layer and the MXene / Amylopectin & Amylose / CNT functional layers causes shear stress on the functional layers from the substrate layer, resulting in relative sliding. As the temperature decreases, although the substrate layer contracts, the functional layers have already undergone irreversible sliding, preventing the entire membrane from fully returning to its initial state. This imparts the initial curvature to the actuator and further determines the degree of bending. This drive method, powered by changes in ambient humidity, requires no external power supply or additional driving medium. The drive process is gentle and adaptable to various complex working scenarios, making it particularly suitable for fields requiring energy consumption control and biocompatibility.

[0030] (4) In addition, the synergistic cooperation of the components in the composite functional layer not only ensures the actuator’s sensitivity to humidity changes, but also improves its durability during repeated use; and the entire manufacturing process does not require complex and precision equipment, making it easy to adjust the structural parameters according to actual needs and expanding the actuator’s applicable scenarios.

[0031] (5) The synergistic effect of patterned substrate, composite functional layer and hot pressing process effectively improves the response controllability, structural stability and scene adaptability of humidity driven soft actuator, and further expands its application space in the field of flexible intelligent devices.

[0032] (6) The laser processing method offers high precision and minimal damage, reducing fabrication difficulty and improving pattern consistency. The functional layer, through multi-component synergy, increases the difference in the coefficient of thermal expansion between the functional layer and the PI substrate, enabling rapid humidity-driven deformation. Starch enhances interfacial bonding, reducing the risk of interlayer delamination and improving actuator stability and lifespan. The hot-pressing process is simple, allowing for adjustment of the actuator's bending displacement stroke without complex equipment. Attached Figure Description

[0033] Figure 1 This is a flowchart illustrating the preparation and processing of the actuator composite membrane in Embodiment 1 of the present invention;

[0034] Figure 2 This is a partial schematic diagram of the patterned regions of the laser-processed PI film in Embodiment 1 of the present invention, including a transverse gap group in region I, a longitudinal gap group in region II, an oblique gap group in region III, and a mixed gap group in region IV.

[0035] Figure 3 shows a comparison of the bending direction of the actuator under different gap orientations in Embodiment 1 of the present invention;

[0036] Figure 3(a) shows the bending response of the actuator under 0° gap orientation;

[0037] Figure 3(b) shows the bending response of the actuator under a 90° gap orientation;

[0038] Figure 3(c) shows the bending response of the actuator under a 45° gap orientation;

[0039] Figure 4 This is a flowchart illustrating the preparation of the MXene / Amylopectin & Amylose / CNT solution in Example 1 of the present invention.

[0040] Figure 5 The Raman spectra of the MXene / Amylopectin & Amylose / CNT membrane and its component membranes in Example 1 of this invention are shown below.

[0041] Figure 6 This is a schematic diagram of the drop casting film formation in Embodiment 1 of the present invention, including a horizontal substrate 1, a silicone pad 2, a patterned PI substrate 3, and a silicone mold 4;

[0042] Figure 7 This is a comparison chart of the ultrasonic stability test results of the MXene / Amylopectin&Amylose / CNT-PI composite membrane and the MXene-PI composite membrane in Example 1 of the present invention;

[0043] Figure 8 This is a diagram showing the response of the actuator to wet vapor and near-infrared light in Embodiment 1 of the present invention. Detailed Implementation

[0044] Example:

[0045] The substrate of the humidity-driven soft actuator of this invention is a patterned black PI film, and the functional layer is an MXene / Amylopectin & Amylose / CNT composite material layer. The bending response direction is controlled by the substrate gap direction.

[0046] Example 1

[0047] The method for preparing the humidity-driven soft actuator that bends in a single direction within the range of 0° to 90° according to the present invention is as follows:

[0048] Step 1), the complete preparation process of this embodiment strictly follows Figure 1 The actuator composite film preparation and processing flow shown first involves processing the PI film gap structure: using a nanosecond laser to process parallel strip-shaped gaps on the pretreated PI film surface, with the processing direction forming an angle of 0° to 90° with the long side direction; as shown... Figure 2The processing areas I, II, and III are shown. The laser parameters used were a scanning speed of 500 mm / s, a laser power of 250 W, a laser frequency of 20 kHz, and one scan. The resulting gap width was 0.5 mm, the length was 6 mm, and the interval was 1.5 mm. A 2 cm unprocessed area was left between the edge of the gap matrix and the boundary of the PI film. The correspondence between the processing gap direction and the actuator response bending direction is shown in Figure 3. The comparison of the actuator bending direction under different gap orientations is shown. When the processing gap is oriented at 0° (Figure 3(a)), 90° (Figure 3(b)), and 45° (Figure 3(c)), the actuator bending response direction is consistent with the gap direction, indicating that the gap direction has a guiding effect on the actuator bending response direction.

[0049] Step 2), Preparation of hydroxylated multi-walled carbon nanotubes: as follows Figure 4 As shown, to prepare the MXene / Amylopectin & Amylose / CNT solution, 20g of multi-walled carbon nanotube powder is first spread in a shallow layer in a petri dish and placed in a plasma reaction chamber. After evacuation, air is introduced and plasma treatment is performed for 3 minutes. The powder is then removed, turned over, and washed again, and this process is repeated 7 times. After the treatment is completed, the powder is removed and vacuum dried at 60℃ for 1 hour to obtain hydroxylated multi-walled carbon nanotube powder.

[0050] Step 3), Preparation of CNT aqueous solution: Weigh 1g of multi-walled carbon nanotube water dispersant and dissolve it in 250mL of deionized water. Heat in a 50℃ water bath to aid dissolution. Add 10g of the above-mentioned hydroxylated multi-walled carbon nanotube powder and stir until initially dispersed. Use an ultrasonic cell disruptor to sonicate the solution at a power of 600W for 1h. Divide the dispersion into centrifuge tubes and centrifuge at 2000rpm for 30min. Take the supernatant as the CNT aqueous solution.

[0051] Step 4), Preparation of Amylopectin & Amylose aqueous solution: Weigh Amylopectin powder and Amylose powder at a mass ratio of 8:2, mix and sieve through a 300-mesh sieve; dissolve 10g of the mixed powder in 200mL of deionized water and stir until initially dispersed; transfer the solution to a water bath and gradually heat from room temperature to 85℃, gradually increasing the stirring speed during heating until the solution changes from white turbidity to a colorless, transparent, and viscous state, and maintain this temperature while stirring for 1min; remove the solution and let it stand and cool to room temperature, then sonicate at 80W power for 10min to obtain Amylopectin & Amylose aqueous solution.

[0052] Step 5), hydrophilic treatment of patterned substrate: After laser patterning, the PI substrate film is placed in 0.4 mol / L NaOH solution for 24 hours, then taken out, rinsed with deionized water and air-dried. It is then placed in a plasma cleaning chamber for 15 minutes of plasma cleaning.

[0053] Step 6), Composite membrane forming and hot pressing: Mix 10 ml of MXene aqueous solution and 2 ml of CNT aqueous solution, stir evenly, and then sonicate at 60 W power for 30 min to obtain an MXene / CNT mixture; add 5 ml of Amylopectin & Amylose aqueous solution to the MXene / CNT mixture, stir thoroughly, and then sonicate at 60 W power for 1 h to obtain a composite functional solution. Figure 5 The Raman spectra of the films with different components shown indicate that each component was successfully composited into the functional layer, with no component omission or decomposition occurring; as shown Figure 6 As shown, a silicone pad 2 is laid flat on a horizontal platform 1 to ensure the uniformity of the functional layer distribution on the substrate after the solution air-dries. A patterned and hydrophilicated PI substrate 3 is vacuum-adheded onto the flat silicone pad 2. A 1mm thick hydrophobic silicone film is cut into a silicone mold 4 that matches the substrate, covering its surface and encompassing the entire patterned area. The composite functional solution is uniformly dripped into the silicone mold 4 using a drop casting method. After air-drying in a well-ventilated area without direct sunlight for 18–36 hours, an MXene / Amylopectin & Amylose / CNT-PI composite film is formed. Figure 7 As shown, the composite membrane with Amylopectin & Amylose and CNT components added to the functional layer exhibits stronger interfacial bonding compared to the composite membrane with a single MXene functional layer. After 30 minutes of ultrasonication at 100W, the MXene layer of the MXene-PI composite membrane was completely peeled off and dissolved in water, while only a very small area of ​​the functional layer of the MXene / Amylopectin & Amylose / CNT-PI composite membrane was detached. Rectangular strips comprising 7×1 patterned matrix units (each unit containing 4 gaps) were cut from the MXene / Amylopectin & Amylose / CNT-PI composite membrane, as shown... Figure 8 As shown, the actuator driven by moisture quickly flattens out from its initial circular shape within 1.5s, and then quickly curls back to its initial state within 1.5s under the action of near-infrared light. The rectangular sheet is laid flat between two glass plates and clamped and fixed with a long tail clamp. It is then transferred to a vacuum drying oven, evacuated, and heated to 80°C, and kept at this temperature for 5 minutes. After being taken out, it is allowed to cool to room temperature, and the glass plates and fixing device are removed to obtain a moisture-driven soft actuator that bends along the 0° direction.

[0054] Example 2

[0055] The method for fabricating a segmented humidity-driven soft actuator with different bending response directions according to the present invention is as follows:

[0056] Step (1) Processing the gap structure on the PI film surface: Using a nanosecond laser, segmented strip gaps are processed on the pre-treated PI film surface, such as... Figure 2 As shown in area IV of the local processing area, the angle between the direction of each gap and the long side is 0° to 180°. The laser parameters used are: scanning speed 500mm / s, laser power 250W, laser frequency 20kHz, and 1 scan. The width of the processed gap is 0.5mm, the length in the middle is 15mm, and the gap length along the edge of the matrix gradually decreases from 15mm to 2mm with an interval of 1.5mm. A 2cm unprocessed area is left between the edge of the gap matrix and the boundary of the PI film.

[0057] Steps (2) to (6): are consistent with steps (2) to (6) in Example 1.

Claims

1. A humidity-driven soft actuator, characterized in that: The soft actuator employs a double-layer composite membrane, with a patterned black polyimide (PI) membrane as the base layer and a two-dimensional transition metal carbide (Ti3C2T) as the functional layer. x (MXene) / Amylopectin & Amylose / Carbon Nanotube (CNT) film; the soft actuator obtains its initial curvature through vacuum hot pressing. The bending response direction of the actuator is determined by the patterned gap direction, and the difference in the coefficient of hygroscopic expansion between the functional layer and the base layer causes the soft actuator to bend under humidity-driven conditions.

2. A method for fabricating a humidity-driven soft actuator as described in claim 1, characterized in that: A 10–15 μm thick PI film is patterned; the patterned PI film is immersed in a 0.4–1 mol / L NaOH solution, rinsed with deionized water until neutral, and then air-dried before plasma cleaning; the cleaned PI film is vacuum-adsorbed onto a horizontal silicone pad; a hydrophobic silicone film with a thickness greater than 1 mm is cut into a mold and placed on the PI film; a mixed solution of MXene / Amylopectin & Amylose / CNT is dripped into the mold using a drop casting method, and after air drying, an MXene / Amylopectin & Amylose / CNT-PI composite film with PI as the substrate is formed; the initial curvature of the MXene / Amylopectin & Amylose / CNT-PI composite film is shaped by hot pressing.

3. A method for preparing a humidity-driven soft actuator as described in claim 1, characterized in that: Includes the following steps: 1) Nanosecond lasers are used to pattern parallel strip gaps or segmented strip gaps on the surface of 10-15μm thick PI films; the laser power is 200-300W, the frequency is 15-25kHz, the scanning speed is 250-500mm / s, and the number of scans is 1-3; the width of the processed gaps is 0.5-1mm, the length is <15mm, and the interval is 1.5-3mm. 2) Spread the multi-walled carbon nanotube powder evenly on a petri dish, place it in a plasma reaction chamber and evacuate it. After 3-5 minutes of air plasma cleaning, take it out and clean it again. Repeat the cycle 5-7 times and vacuum dry it at 60-80℃ for 0.5-1 hours to obtain hydroxylated multi-walled carbon nanotube powder. 3) Dissolve 1-2 g of multi-walled carbon nanotube (CNT) aqueous dispersant in 250-500 mL of deionized water, heat and stir in a water bath at 40-50°C until dissolved, add 10-20 g of hydroxylated CNT powder and stir for 15-30 min, then sonicate at 500-650 W for 1-2 h to obtain a dispersion. After the ultrasonically dispersed dispersion is dropped into clean water and diffused without any suspended particles, dispense the ultrasonically dispersed dispersion into centrifuge tubes and centrifuge at 2000-3000 rpm for 20-40 min. Take the supernatant as the CNT aqueous solution; take 3-5 mL of the CNT aqueous solution, vacuum filter, air dry, weigh, and calculate the mass concentration of the CNT aqueous solution. 4) Weigh Amylopectin and Amylose powders in a mass ratio of 8:2 to 8:3, mix them, and sieve them through a 200-300 mesh sieve 3 to 5 times to obtain a mixed powder. Take 10-15g of the mixed powder and dissolve it in 200-250mL of deionized water. Heat the white turbid solution formed by stirring for 10-20min to 85-100℃, stir for 2-3min until the solution becomes colorless, transparent and viscous, then cool it to room temperature, and then sonicate it at 80-100W for 5-10min to obtain an Amylopectin & Amylose aqueous solution. 5) Immerse the patterned PI film from step 1) in a 0.4-1 mol / L NaOH solution and let it stand for 12-24 hours. Then rinse it with deionized water until the rinsing solution is neutral. Finally, perform plasma cleaning on the dried PI film for 10-20 minutes. 6) Take 10-15 mL of MXene aqueous solution with a concentration of 10-15 mg / mL and 2-3 mL of CNT aqueous solution with a concentration of 3-6 mg / mL, mix and stir for 20-30 min, then sonicate at 50-70 W for 15-30 min to obtain MXene / CNT mixture; add 3-7 mL of Amylopectin & Amylose aqueous solution to MXene / CNT mixture, stir for 15-30 min, sonicate at 30-60 W for 0.5-1 h, and refrigerate below 4℃ to obtain mixed solution; attach patterned PI film to horizontal silicone pad, cut a mold matching the PI film with a hydrophobic silicone film with a thickness greater than 1 mm, cover the surface of PI film, drop the mixed solution into the mold, air dry for 18-36 h, remove the mold after the solution is dry to obtain MXene / Amylopectin & Amylose / CNT-PI composite film; 7) Cut a rectangular sheet containing multiple patterned matrix units from the composite film and lay it flat between two glass plates. Clamp the glass plates, apply pressure, and place it in a vacuum drying oven. After evacuating to a pressure ≤10Pa, heat it to 75~105℃ for 3~5min and then cool it to room temperature to obtain a humidity-driven soft actuator with a preset initial curvature.

4. The method for preparing a humidity-driven soft actuator according to claim 3, characterized in that: In step 1), when using a nanosecond laser to process parallel strip-shaped gaps on the surface of a 10-15 μm thick PI film, the angle between the processing direction and the long side of the PI film is 0° to 90°.

5. The method for preparing a humidity-driven soft actuator according to claim 3, characterized in that: In step 1), when using a nanosecond laser to process strip-shaped gaps on the surface of a 10-15 μm thick PI film, the angle between the direction of each gap and the long side of the PI film is 0° to 180°.

6. The method for preparing a humidity-driven soft actuator according to claim 3, characterized in that: In step 1), when the gap direction is not parallel to the edge of the PI film, the gap processing length gradually decreases from the middle to both sides.

7. The method for preparing a humidity-driven soft actuator according to claim 3, characterized in that: In step 2), multi-walled carbon nanotube powder is spread evenly in a petri dish, with the thickness of the multi-walled carbon nanotube powder layer being ≤0.1mm.

8. The method for preparing a humidity-driven soft actuator according to claim 3, characterized in that: In step 7), the initial curvature and bending degree of the soft actuator are controlled by adjusting the heating temperature and duration.

9. The method for preparing a humidity-driven soft actuator according to claim 3, characterized in that: In step 1), the gap edge and the PI film boundary retain an unprocessed area.

10. The method for preparing a humidity-driven soft actuator according to claim 3, characterized in that: In step 4), the white turbid solution formed by stirring for 10 to 20 minutes is transferred to a water bath and heated to 85 to 100°C. During heating, the stirring speed is increased from 800 to 1000 rpm to 2000 to 3000 rpm.

Images