Multi-responsive soft actuators based on silk fibroin, methods of preparation and regulation

Abstract

This invention discloses a multi-responsive soft actuator based on silk fibroin and its preparation method. The soft actuator includes a silk fibroin membrane and a flexible substrate. The silk fibroin membrane is placed on the flexible substrate and tightly bonded to form a bilayer membrane structure. The thermal expansion coefficients of the silk fibroin membrane and the flexible substrate are different. The preparation method of the soft actuator is as follows: the flexible substrate is plasma-treated, then a wet silk fibroin membrane is coated on the flexible substrate and dried to obtain the silk fibroin membrane, which forms a bilayer membrane with the flexible substrate. The bilayer membrane is immersed in water and then dried. After drying, the silk fibroin membrane in the bilayer membrane is immersed in calcium chloride aqueous solution, then removed and dried again. The soft actuator of this invention can be driven by a small energy input, has low energy consumption, better reversibility, a larger deformation angle, reprogrammable deformation of different regions, and multi-stimulus responsiveness.

Description

Technical Field

[0001] This invention relates to the design and fabrication of a soft actuator, specifically to a multi-responsive soft actuator based on silk fibroin and its fabrication method. Background Technology

[0002] Soft actuators, which can convert external stimuli into mechanical motion, hold immense potential in many cutting-edge applications, such as soft robotics, artificial muscles, biomimetic motion, and object grasping. Various soft actuators driven by different stimuli, including light, electricity, magnetism, heat, and humidity, have been widely reported. The key to developing high-performance soft actuators lies in the development of stimulus-responsive materials. Efficient stimulus-responsive materials require reversible, large-amplitude deformation capabilities, high power density, and sensitive response to minute energy inputs, which remains a significant challenge and necessitates targeted design of the material structure based on its intrinsic mechanisms.

[0003] Biomaterials, with their tunable multilayered assembly structures, offer abundant sites for large-scale programmable deformation, providing a significant advantage in constructing high-performance soft actuators, such as the super-contraction of spider silk under high humidity stimulation. This characteristic has inspired the design of stimulus-responsive materials and soft actuators; however, this contraction is irreversible, and fibrous materials face significant limitations in certain applications. Therefore, the development of efficient two-dimensional thin-film stimulus-responsive materials and soft actuators with reversible deformation capabilities based on biomimetic principles is of greater significance for practical applications, yet this aspect has been largely overlooked. Summary of the Invention

[0004] To address the problems existing in the background art, the purpose of this invention is to provide a multi-responsive soft actuator based on silk fibroin and its preparation method.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] I. A multi-responsive soft actuator based on silk fibroin:

[0007] The soft actuator includes a silk fibroin membrane and a flexible substrate, with the silk fibroin membrane placed on the flexible substrate and tightly bonded to form a double-layer membrane structure.

[0008] The thermal expansion coefficients of the silk fibroin membrane and the flexible substrate are significantly different.

[0009] The thermal expansion coefficient of the silk fibroin film is negative and differs significantly from that of the flexible substrate.

[0010] If the difference allows the actuator to function, that's fine; however, the greater the difference, the greater the deformation of the actuator. In the embodiments listed in this invention, the material system actually used has a thermal expansion coefficient of silk fibroin film of -800 to -1200 ppm K. -1 The coefficient of thermal expansion of the flexible substrate is 40-200 ppm K. -1 That is, the difference in the coefficient of thermal expansion is within 800 ppm K. -1 above.

[0011] II. A method for fabricating a multi-responsive soft actuator:

[0012] The soft actuator is fabricated in the following manner:

[0013] The flexible substrate is treated with plasma, and then a silk fibroin wet film is coated on the flexible substrate. After drying, a silk fibroin film is obtained, which forms a double film with the flexible substrate.

[0014] Soak the double-layer membrane in water for 0.1-20 minutes and then dry it;

[0015] After drying, the silk fibroin membrane in the double-layer membrane is immersed in a 0.5-3wt% calcium chloride aqueous solution for a period of 0.1-20 minutes, then removed and dried to obtain a soft actuator.

[0016] The silk fibroin wet film contains silk fibroin and formic acid.

[0017] Furthermore, the silk fibroin wet film of the present invention also contains calcium chloride.

[0018] The silk fibroin wet film is formed by dissolving 1.3g of degummed silk in a 3-5wt% calcium chloride-formic acid solution, then placing it in an ultrasonic cleaner to vibrate and obtain a silk fibroin solution, and finally coating the silk fibroin solution onto a flexible substrate.

[0019] Furthermore, the silk fibroin wet film of the present invention also contains photothermal conversion materials.

[0020] Specifically, the calcium chloride-formic acid solution contains a photothermal conversion dye, which is Rhodamine B, but not limited to this.

[0021] Furthermore, the soft actuator of the present invention has a heating electrode on a silk fibroin membrane or a flexible substrate for electrothermal actuation.

[0022] Furthermore, the flexible substrate of the present invention is made of PET, PI, or PE.

[0023] Furthermore, the thickness of the silk fibroin wet film of the present invention is 0.1-200 μm.

[0024] Furthermore, the thickness of the flexible substrate described in this invention is 10-100 μm.

[0025] III. Control methods for multi-response soft actuators:

[0026] Heating the soft actuator causes the silk fibroin membrane and the flexible substrate to undergo different thermal deformations, causing the bilayer membrane structure to bend and deform towards the side where the silk fibroin membrane is located.

[0027] The deformation angle, amplitude, and shape of the multi-responsive soft actuator can be controlled by adjusting whether the silk fibroin membrane in the dried bilayer membrane is immersed in a calcium chloride aqueous solution or the concentration of the calcium chloride aqueous solution.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] (1) The silk fibroin membrane has a huge negative thermal expansion property, which can shrink when the temperature rises, causing the actuator to bend towards the side of the silk fibroin membrane, with a larger deformation angle;

[0030] (2) The deformation mechanism of the soft actuator is a reversible change in the molecular chain conformation of the amorphous region, which does not involve the transformation between crystal form and secondary structure. It can be driven by a small energy input, has low energy consumption, and has better reversibility.

[0031] (3) The deformation capability of the soft actuator can be adjusted by the calcium chloride concentration to achieve reprogrammable deformation of different regions.

[0032] (4) The soft actuator described above has multi-stimulus responsiveness and can be driven by light, electricity, heat and humidity fields. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of a soft actuator with a double-layer membrane structure.

[0034] Figure 2 This is a diagram showing the deformed state of the soft actuator of the present invention.

[0035] Figure 3 The deformation curvature of soft actuators obtained by immersion in calcium chloride aqueous solutions of different concentrations at different temperatures.

[0036] Figure 4 This is a schematic diagram of a soft actuator with heating electrodes on a silk fibroin membrane.

[0037] Figure 5 This is a schematic diagram of a soft actuator with heating electrodes on a flexible substrate.

[0038] Figure 6This is a curve diagram showing the deformation curvature of different regions of a soft actuator under different electric heating powers.

[0039] Figure 7 This is a deformation diagram of a soft actuator under light stimulation.

[0040] In the figure, 1-silk fibroin membrane, 2-flexible substrate, 3-heating electrode. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0042] The embodiments of the present invention are as follows:

[0043] Example 1:

[0044] Prepare a 3wt% calcium chloride-formic acid solution. Dissolve 1.3g of degummed silk in 6.8ml of the above solution and place it in an ultrasonic cleaner and vibrate for 1h to obtain a silk fibroin solution.

[0045] A clean PI substrate with a thickness of 30 μm was used as the flexible substrate 2, and plasma treatment was performed for 2 min. A 200 μm thick four-sided coating tool was used to coat a wet silk fibroin film. After drying, a bilayer film consisting of silk fibroin film 1 and flexible substrate 2 was obtained, as shown below. Figure 1 As shown, the double-layer membrane was not soaked, completely soaked in a 1 wt% calcium chloride aqueous solution for 1 min and dried with nitrogen, completely soaked in a 2 wt% calcium chloride aqueous solution for 1 min and dried with nitrogen, and completely soaked in a 3 wt% calcium chloride aqueous solution for 1 min and dried with nitrogen to obtain soft actuators with different deformability.

[0046] When the actuator is in operation, the entire soft actuator is placed on a hot plate at 100°C. Because the coefficient of thermal expansion of the silk fibroin membrane 1 is negative, it undergoes thermal contraction as the temperature rises. Conversely, the coefficient of thermal expansion of the PI flexible substrate 2 is positive, causing it to expand as the temperature rises. This results in the double-layer membrane structure of the soft actuator bending towards the silk fibroin membrane 1 side. Figure 2 As shown. After the heating stage is turned off, the actuator temperature slowly decreases and returns to its initial shape. The bending curvature can be controlled by the heating stage temperature, and the soft actuators obtained after being immersed in calcium chloride aqueous solutions of different concentrations exhibit different bending curvatures, such as... Figure 3 As shown, the higher the concentration of the calcium chloride aqueous solution used for soaking, the greater the bending curvature of the soft actuator, indicating that the deformability of the silk fibroin-based soft actuator described in this invention can be effectively adjusted by the calcium chloride concentration.

[0047] Example 2:

[0048] Prepare a 4.8 wt% calcium chloride-formic acid solution. Dissolve 1.3 g of degummed silk in 6.8 ml of the above solution and place it in an ultrasonic cleaner and vibrate for 1 h to obtain a silk fibroin solution.

[0049] A clean PET film with a thickness of 50 μm was used as the flexible substrate 2 and plasma-treated for 2 min. A 100 μm thick four-sided coating tool was used to coat a wet silk fibroin film. The dried film was rinsed in water for 5 min, and after drying, a bilayer film consisting of silk fibroin film 1 and flexible substrate 2 was obtained. Figure 1 As shown. The entire bilayer membrane was immersed in a 2wt% calcium chloride aqueous solution for 1 minute and then dried with nitrogen gas. A silver heating electrode 3 was screen-printed on one side of the silk fibroin membrane 1 of the bilayer membrane and cut to the required size to obtain the soft actuator, as shown. Figure 4 As shown.

[0050] When the actuator is working, heating electrode 3 is connected to a DC power supply. Under a certain power, heating electrode 3 generates Joule heat, causing the overall temperature of the soft actuator to rise. Since the coefficient of thermal expansion of silk fibroin film 1 is negative, it undergoes thermal contraction when the temperature rises, while the coefficient of thermal expansion of PET flexible substrate 2 is positive, causing it to undergo thermal expansion when the temperature rises. This causes the double-layer film structure of the soft actuator to bend towards the silk fibroin film 1 side, and the bending curvature can be controlled by the electrical power. After the power is turned off, the actuator returns to its initial shape.

[0051] Example 3:

[0052] Prepare a 4.8 wt% calcium chloride-formic acid solution. Dissolve 1.3 g of degummed silk in 6.8 ml of the above solution and place it in an ultrasonic cleaner and vibrate for 1 h to obtain a silk fibroin solution.

[0053] A clean PE film with a thickness of 100 μm was used as the flexible substrate 2, and plasma-treated for 2 min. A 200 μm thick four-sided coating tool was used to coat a wet silk fibroin film. The dried film was rinsed in water for 5 min, and after drying, a bilayer film consisting of silk fibroin film 1 and flexible substrate 2 was obtained. Figure 1 As shown. Half of the bilayer membrane was immersed in a 2wt% calcium chloride aqueous solution for 1 minute and then dried with nitrogen gas. A silver heating electrode 3 was then screen-printed onto one side of the flexible substrate 2 of the bilayer membrane and cut to the required size to obtain the soft actuator, as shown. Figure 5 As shown.

[0054] When the actuator is working, heating electrode 3 is connected to a DC power supply. Under a certain power, heating electrode 3 generates Joule heat, causing the overall temperature of the soft actuator to rise. Since the thermal expansion coefficient of silk fibroin film 1 is negative, it undergoes thermal contraction when the temperature rises, while the thermal expansion coefficient of PE flexible substrate 2 is positive, causing it to expand when the temperature rises. This results in the double-layer membrane structure of the soft actuator bending towards the silk fibroin film 1. After the power is turned off, the actuator returns to its initial shape. Because silk fibroin films 1 with different calcium chloride contents have different thermal expansion coefficients, the curvature of the area soaked in 2wt% calcium chloride solution is greater than that of the area not soaked in calcium chloride solution, and the curvature of different areas can be controlled by the electrical power. A 55m diameter can be generated even with a heating power as low as 0.02W. -1 The curvature of the bend, such as Figure 6 As shown. This result indicates that the described soft actuator has very low energy consumption, and its deformation capability can be adjusted by the calcium chloride concentration, enabling programmability of deformation in different regions.

[0055] Example 4:

[0056] Prepare a 3 wt% calcium chloride-formic acid solution and add the dye Rhodamine B at a concentration of 100 mg / L. Dissolve 1.3 g of degummed silk in 6.8 ml of the above solution and place it in an ultrasonic cleaner and vibrate for 1 hour to obtain a silk fibroin solution containing photothermal conversion dye.

[0057] A clean PET substrate with a thickness of 50 μm was used as the flexible substrate 2 and plasma-treated for 2 min. A 100 μm thick four-sided fabricator was used to coat a wet silk fibroin film, which was then dried to obtain a bilayer membrane consisting of a silk fibroin membrane 1 and the flexible substrate 2. The bilayer membrane samples were then subjected to different methods: no soaking, complete immersion in a 2 wt% calcium chloride aqueous solution for 1 min followed by nitrogen drying, and half immersion in a 2 wt% calcium chloride aqueous solution for 1 min followed by nitrogen drying, resulting in soft actuators with different deformability.

[0058] When the actuator is working, an infrared lamp illuminates the soft actuator. Under the photothermal effect of Rhodamine B, the overall temperature of the soft actuator rises. Since the thermal expansion coefficient of silk fibroin film 1 is negative, it undergoes thermal contraction upon temperature rise, while the thermal expansion coefficient of the PET flexible substrate 2 is positive, causing thermal expansion. This results in the double-layer film structure of the soft actuator bending towards the silk fibroin film 1 side. After the light source is turned off, the actuator slowly returns to its initial shape. The curvature of the actuator or actuator area immersed in 2wt% calcium chloride solution is greater than that of the sample or area not immersed in calcium chloride solution. Figure 7 As shown. This result indicates that the deformability of the soft actuator can be adjusted by the calcium chloride concentration, and the programmability of deformation in different regions can be achieved.

[0059] Example 5:

[0060] Prepare a 3wt% calcium chloride-formic acid solution. Dissolve 1.3g of degummed silk in 6.8ml of the above solution and place it in an ultrasonic cleaner and vibrate for 1h to obtain a silk fibroin solution.

[0061] A clean PET substrate with a thickness of 30 μm was used as the flexible substrate 2, and plasma-treated for 2 min. A wet silk fibroin film was coated using an 80 μm thick four-sided fabricator, and after drying, a bilayer membrane structure soft actuator comprising a silk fibroin membrane 1 and a flexible substrate 2 was obtained, such as... Figure 1 As shown.

[0062] When the actuator is in operation, the entire soft actuator is placed on a nylon screen, and a water tank filled with water is placed under the nylon screen to place the soft actuator in a high humidity environment. Because the silk fibroin membrane 1 absorbs water and swells, while the PET flexible substrate 2 absorbs almost no water, the double-layer membrane structure of the soft actuator bends towards the flexible substrate 2. After being moved away from the humidity source, the actuator returns to its initial shape.

Claims

1. A method for fabricating a multi-responsive soft actuator, characterized in that: The soft actuator comprises a silk fibroin membrane and a flexible substrate. The silk fibroin membrane is placed on the flexible substrate and tightly bonded to form a double-layer membrane structure. The soft actuator is fabricated in the following manner: The flexible substrate is treated with plasma, and then a silk fibroin wet film is coated on the flexible substrate. After drying, a silk fibroin film is obtained, which forms a double film with the flexible substrate. Soak the double-layer membrane in water and then dry it; After drying, the silk fibroin membrane in the double-layer membrane is immersed in calcium chloride aqueous solution for a period of time, then removed and dried to obtain a soft actuator. By adjusting whether the silk fibroin membrane in the dried bilayer membrane is immersed in a calcium chloride aqueous solution or the concentration of the calcium chloride aqueous solution during the preparation process, the deformation angle, amplitude, and shape of the multi-responsive soft actuator can be controlled.

2. The preparation method according to claim 1, characterized in that: The silk fibroin wet film contains silk fibroin and formic acid.

3. The preparation method according to claim 1, characterized in that: The silk fibroin wet film also contains calcium chloride.

4. The preparation method according to claim 1, characterized in that: The silk fibroin wet film also contains photothermal conversion materials.

5. The preparation method according to claim 1, characterized in that: The soft actuator has heating electrodes on a silk fibroin membrane or flexible substrate for electrothermal actuation.

6. The preparation method according to claim 1, characterized in that: The thermal expansion coefficients of the silk fibroin membrane and the flexible substrate are different.

7. The preparation method according to claim 1, characterized in that: The coefficient of thermal expansion of the silk fibroin film is negative.

8. A method for controlling a multi-responsive soft actuator fabricated using any one of the preparation methods described in claims 1-7, characterized in that: Heating the soft actuator causes the silk fibroin membrane and the flexible substrate to undergo different thermal deformations, causing the bilayer membrane structure to bend and deform towards the side where the silk fibroin membrane is located.

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