Preparation method and application of microgel cross-linked photothermal response flexible double-layer hydrogel valve robot

Abstract

The application relates to a preparation method and application of a microgel crosslinked photothermal response flexible double-layer hydrogel valve control robot, and relates to a double-layer hydrogel preparation method and application. The application aims to solve the problem that existing valve controls cannot simultaneously consider high strength, excellent flexibility and multiple response functions, resulting in insufficient intelligent response capability of valve control robot materials. In the application, N-isopropyl acrylamide is used as raw material, and a poly(N-isopropyl acrylamide-co-styrene) microgel solution is obtained through a soap-free emulsion polymerization reaction under the action of styrene and divinylbenzene; then, the solution is crosslinked and polymerized with N-isopropyl acrylamide to prepare a hydrogel matrix I; then, a multi-walled carbon nanotube dispersion liquid is subjected to a free radical polymerization reaction with acrylamide to obtain a hydrogel matrix II; then, unreacted substances are removed to obtain a microgel crosslinked photothermal response flexible double-layer hydrogel valve control robot, which is used as a controller material for controlling and limiting fluid flow under the stimulation of environmental light and thermal information.

Description

Technical Field

[0001] This invention relates to a method for preparing a bilayer hydrogel and its application. Background Technology

[0002] Control valves are crucial in modern industrial production. Control systems in industries such as wastewater treatment, petrochemicals, and municipal water supply and drainage all require precise control of liquid flow rates. Intelligent shut-off valves can achieve responsive control based on the fluid's physicochemical properties such as temperature and pH. Currently, most intelligent shut-off valves use rigid mechanical valves or flexible pneumatic valves to intercept and discharge water, but these suffer from drawbacks such as high equipment cost, unsuitability for continuous humid environments, and difficult maintenance. Flexible intelligent robots show great potential in real-time and continuous monitoring of fluid discharge, possessing inherent advantages such as high flexibility, convenience, and low cost. Currently, combining photothermal materials such as carbon nanotubes and graphene with elastomer composite substrates has successfully produced flexible robots with excellent intelligent responsiveness. Traditional thermosensitive hydrogels, such as poly(N-isopropylacrylamide) loaded with photothermal multi-walled carbon nanotubes, can achieve infrared-induced deformation or shape memory properties, but this deformation is merely the swelling or contraction of the hydrogel and cannot achieve complex movements. Combining stimulus-responsive hydrogels with traditional hydrogels to prepare bilayer hydrogels allows for asymmetric deformation and motion under external stimuli, potentially serving as flexible robotic control valves. However, currently developed bilayer flexible hydrogel robotic materials cannot simultaneously achieve high strength, excellent flexibility, and multi-stimuli responsiveness, making it difficult to implement flow interception, discharge conduction, and monitoring under complex fluid conditions. Therefore, there is an urgent need to explore novel hydrogel synthesis strategies to prepare new flexible hydrogel robotic materials that possess high mechanical strength, sensitive signal response, and strong flexibility. Summary of the Invention

[0003] The purpose of this invention is to solve the problem that existing control valves cannot simultaneously achieve high strength, excellent flexibility, and multiple response functions, resulting in insufficient intelligent response capabilities of valve control robot materials. The invention provides a method for preparing and applying a microgel-crosslinked photothermal responsive flexible bilayer hydrogel valve control robot.

[0004] The microgel-crosslinked photothermal-responsive flexible bilayer hydrogel valve control robot prepared in this invention uses N-isopropylacrylamide as raw material. Under the action of styrene and divinylbenzene, a soap-free emulsion polymerization reaction is carried out to obtain a poly(N-isopropylacrylamide-co-styrene) microgel solution. Then, the poly(N-isopropylacrylamide-co-styrene) microgel solution is crosslinked and polymerized with N-isopropylacrylamide to prepare hydrogel matrix I. Multi-walled carbon nanotubes are then used as material, and under the action of hexadecyltrimethylammonium bromide, a multi-walled carbon nanotube dispersion is obtained through ultrasonic dispersion. The multi-walled carbon nanotube dispersion is then subjected to a free radical polymerization reaction with acrylamide to obtain hydrogel matrix II. Finally, a microgel-crosslinked photothermal-responsive flexible bilayer hydrogel valve control robot is obtained using a melt casting method.

[0005] A method for fabricating a microgel-crosslinked photothermal responsive flexible bilayer hydrogel valve-controlled robot is specifically carried out according to the following steps:

[0006] I. Preparation of poly(N-isopropylacrylamide-co-styrene) microgels:

[0007] ① Add N-isopropylacrylamide and N,N'-methylenebisacrylamide to deionized water and stir magnetically for a period of time at room temperature to obtain a homogeneous and transparent mixed solution I;

[0008] ② Add styrene and divinylbenzene dropwise to a homogeneous and transparent mixed solution I, mix well, and obtain mixed solution II;

[0009] ③ Puff nitrogen gas into mixed solution II for a period of time, then add ammonium persulfate aqueous solution, heat in a water bath at 80℃~90℃ and stir magnetically for a period of time to terminate the reaction and obtain a crude solution of poly(N-isopropylacrylamide-co-styrene) microgel;

[0010] ④ The crude solution of poly(N-isopropylacrylamide-co-styrene) microgel was dialyzed to obtain a pure solution of poly(N-isopropylacrylamide-co-styrene) microgel.

[0011] ⑤ Pre-freeze the pure solution of poly(N-isopropylacrylamide-co-styrene) microgel at -20℃ for a period of time, and then freeze-dry it under vacuum for a period of time to obtain poly(N-isopropylacrylamide-co-styrene) microgel.

[0012] II. Preparation of hydrogel matrix I:

[0013] ① Poly(N-isopropylacrylamide-co-styrene) microgel was dissolved in deionized water and dispersed by ultrasonication to obtain a poly(N-isopropylacrylamide-co-styrene) microgel dispersion;

[0014] ② Add the poly(N-isopropylacrylamide-co-styrene) microgel dispersion to the mold, dry it, and obtain a mold with the poly(N-isopropylacrylamide-co-styrene) microgel on the bottom surface;

[0015] ③ Add N-isopropylacrylamide and N',N'-methylenebisacrylamide to deionized water and stir for a period of time to obtain mixed solution III; place mixed solution III in an environment of -4℃ for a period of time to obtain pre-cooled mixed solution III;

[0016] ④ Dissolve ammonium persulfate powder in deionized water to obtain an ammonium persulfate aqueous solution; add N,N,N',N'-tetramethylethylenediamine and the ammonium persulfate aqueous solution to the pre-cooled mixed solution III in sequence, stir evenly to obtain reaction solution I;

[0017] ⑤ Place reaction solution I into the mold with the bottom surface of poly(N-isopropylacrylamide-co-styrene) microgel obtained in step 2 ②, and then transfer it to an environment of -4℃ to initiate the reaction for 24h to 48h to obtain a mold with hydrogel matrix I.

[0018] III. Fabrication of a bilayer hydrogel valve-controlled robot:

[0019] ① Dissolve multi-walled carbon nanotubes and hexadecyltrimethylsodium bromide in deionized water and ultrasonically disperse for a period of time to obtain a multi-walled carbon nanotube dispersion;

[0020] ② Dissolve acrylamide and N,N'-methylenebisacrylamide in deionized water, stir for a period of time, add multi-walled carbon nanotube dispersion, and continue stirring for a period of time to obtain mixed solution IV;

[0021] ③ Dissolve ammonium persulfate powder in deionized water to obtain an aqueous solution of ammonium persulfate; add N,N,N',N'-tetramethylethylenediamine and the aqueous solution of ammonium persulfate to mixed solution IV in sequence, stir evenly to obtain reaction solution II;

[0022] ④ Place the reaction solution II into the mold containing the hydrogel matrix I obtained in step 2 ⑤, and then transfer it to an environment of -4℃ to initiate the reaction for 24h to 48h. Hydrogel matrix II is obtained on the hydrogel matrix I, which is a colloidal mixture.

[0023] ⑤ Soak the colloidal mixture in deionized water, changing the water periodically to remove unreacted substances, and obtain a microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot.

[0024] Principle of this invention:

[0025] This invention prepares a microgel-enhanced photothermal responsive flexible bilayer hydrogel valve control robot. The responsive layer uses a thermosensitive hydrogel, poly(N-isopropylacrylamide). To improve the mechanical properties of this hydrogel layer, N-isopropylacrylamide and styrene are polymerized in a soap-free emulsion to obtain poly(N-isopropylacrylamide-co-styrene) microgel. The microgel is uniformly dispersed in the hydrogel matrix and dissipates energy during deformation. The stimulation layer uses a polyacrylamide hydrogel loaded with multi-walled carbon nanotubes. The multi-walled carbon nanotubes generate a photothermal effect and heat up under 808nm infrared light stimulation. The temperature is gradually conducted from the interface of the bilayer hydrogel, causing the temperature of the thermosensitive hydrogel in the responsive layer to rise and generate a temperature gradient, thereby causing the responsive layer to shrink and the bilayer hydrogel to bend and deform. Traditional thermosensitive hydrogels loaded with multi-walled carbon nanotubes only shrink under infrared stimulation. However, the present invention prepares a bilayer hydrogel valve-controlled robot that achieves various deformations such as bending of the hydrogel through an asymmetric structure. Furthermore, multi-walled carbon nanotubes are loaded into a stimulation layer without thermosensitive effect. The uneven temperature conduction in the thermosensitive hydrogel layer causes a temperature gradient inside the hydrogel, resulting in uneven shrinkage of the response layer, thereby improving the flexibility and sensitivity of the hydrogel robot.

[0026] Advantages of this invention:

[0027] I. The raw materials used in the microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot prepared by this invention are polyacrylamide and poly(N-isopropylacrylamide), both of which are biocompatible polymers.

[0028] II. The microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot prepared by the present invention uses N-isopropylacrylamide and styrene through soap-free emulsion polymerization to obtain micron-scale poly(N-isopropylacrylamide-co-styrene) microgel.

[0029] III. The microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot prepared in this invention, with the addition of multi-walled carbon nanotubes, exhibits excellent photothermal response characteristics.

[0030] IV. The microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot prepared by this invention adopts a melt-cast bilayer structure and exhibits excellent response anisotropy.

[0031] This invention provides a microgel-crosslinked photothermal responsive flexible bilayer hydrogel valve control robot. Attached Figure Description

[0032] Figure 1 This is a reaction mechanism diagram of step one in Example 1;

[0033] Figure 2 This is a reaction mechanism diagram for steps two and three of Example 1. In the diagram, a represents the reaction mechanism diagram for step two, and b represents the reaction mechanism diagram for step three.

[0034] Figure 3 This is a particle size distribution diagram of poly(N-isopropylacrylamide-co-styrene) microgels obtained in step one of Example 1;

[0035] Figure 4 The figures are infrared spectra. In the figure, a represents the infrared spectrum of polyacrylamide, b represents the infrared spectrum of hydrogel matrix I in step two ⑤, and c represents the infrared spectrum of the microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot obtained in step three ⑤ of example one.

[0036] Figure 5 The figures are X-ray diffraction patterns. In the figure, a represents the X-ray diffraction pattern of hydrogel matrix I in step two (⑤), and b represents the X-ray diffraction pattern of the microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot obtained in step three (⑤) of Example one.

[0037] Figure 6 This is the differential scanning calorimetry spectrum of the microgel crosslinked photothermal responsive flexible bilayer hydrogel valve-controlled robot obtained in step three of Example 1;

[0038] Figure 7 This is a thermogravimetric analysis diagram of the microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot obtained in step 3.5 of Example 1;

[0039] Figure 8 This is a scanning electron microscope image of the microgel crosslinked photothermal responsive flexible bilayer hydrogel valve-controlled robot obtained in step three of Example 1.

[0040] Figure 9 This is a rheological performance test diagram of the microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot obtained in step 3.5 of Example 1; in the figure, █ represents the storage modulus of the hydrogel, and ● represents the loss modulus of the hydrogel.

[0041] Figure 10 The figure shows the tensile stress-strain test results of the microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot obtained in step 3.5 of Example 1.

[0042] Figure 11 This is a graph showing the weight change over time of the microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot obtained in step 3.5 of Example 1 during a degradation test;

[0043] Figure 12 This is a graph showing the change of gel temperature with infrared irradiation time in the infrared response test of the microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot obtained in step 3⑤ of Example 1.

[0044] Figure 13Figure 1 shows the cyclic test results of the microgel-crosslinked photothermal responsive flexible bilayer hydrogel valve control robot obtained in step 3.5 of Example 1, in the temperature response test. Figure 1a shows the change in the curvature of the microgel-crosslinked photothermal responsive flexible bilayer hydrogel valve control robot obtained in step 3.5 as a function of infrared irradiation time, where ● represents the robot's heating process after infrared irradiation is turned on, and ▲ represents the robot's cooling process after infrared irradiation is turned off. Figure 1b shows the change in temperature and curvature of the microgel-crosslinked photothermal responsive flexible bilayer hydrogel valve control robot obtained in step 3.5 during the cyclic opening and closing of infrared irradiation, where ● represents temperature and ▲ represents curvature. Figure 1c shows the actual changes of the microgel-crosslinked photothermal responsive flexible bilayer hydrogel valve control robot obtained in step 3.5 under photothermal influence.

[0045] Figure 14 This is a schematic diagram of the fluid control of the microgel crosslinked photothermal responsive flexible bilayer hydrogel valve-controlled robot obtained in step three (⑤) of Example 1. Detailed Implementation

[0046] Specific Implementation Method 1: This implementation method describes a method for preparing a microgel-crosslinked photothermal-responsive flexible bilayer hydrogel valve-controlled robot, which is specifically completed according to the following steps:

[0047] I. Preparation of poly(N-isopropylacrylamide-co-styrene) microgels:

[0048] ① Add N-isopropylacrylamide and N,N'-methylenebisacrylamide to deionized water and stir magnetically for a period of time at room temperature to obtain a homogeneous and transparent mixed solution I;

[0049] ② Add styrene and divinylbenzene dropwise to a homogeneous and transparent mixed solution I, mix well, and obtain mixed solution II;

[0050] ③ Puff nitrogen gas into mixed solution II for a period of time, then add ammonium persulfate aqueous solution, heat in a water bath at 80℃~90℃ and stir magnetically for a period of time to terminate the reaction and obtain a crude solution of poly(N-isopropylacrylamide-co-styrene) microgel;

[0051] ④ The crude solution of poly(N-isopropylacrylamide-co-styrene) microgel was dialyzed to obtain a pure solution of poly(N-isopropylacrylamide-co-styrene) microgel.

[0052] ⑤ Pre-freeze the pure solution of poly(N-isopropylacrylamide-co-styrene) microgel at -20℃ for a period of time, and then freeze-dry it under vacuum for a period of time to obtain poly(N-isopropylacrylamide-co-styrene) microgel.

[0053] II. Preparation of hydrogel matrix I:

[0054] ① Poly(N-isopropylacrylamide-co-styrene) microgel was dissolved in deionized water and dispersed by ultrasonication to obtain a poly(N-isopropylacrylamide-co-styrene) microgel dispersion;

[0055] ② Add the poly(N-isopropylacrylamide-co-styrene) microgel dispersion to the mold, dry it, and obtain a mold with the poly(N-isopropylacrylamide-co-styrene) microgel on the bottom surface;

[0056] ③ Add N-isopropylacrylamide and N',N'-methylenebisacrylamide to deionized water and stir for a period of time to obtain mixed solution III; place mixed solution III in an environment of -4℃ for a period of time to obtain pre-cooled mixed solution III;

[0057] ④ Dissolve ammonium persulfate powder in deionized water to obtain an ammonium persulfate aqueous solution; add N,N,N',N'-tetramethylethylenediamine and the ammonium persulfate aqueous solution to the pre-cooled mixed solution III in sequence, stir evenly to obtain reaction solution I;

[0058] ⑤ Place reaction solution I into the mold with the bottom surface of poly(N-isopropylacrylamide-co-styrene) microgel obtained in step 2 ②, and then transfer it to an environment of -4℃ to initiate the reaction for 24h to 48h to obtain a mold with hydrogel matrix I.

[0059] III. Fabrication of a bilayer hydrogel valve-controlled robot:

[0060] ① Dissolve multi-walled carbon nanotubes and hexadecyltrimethylsodium bromide in deionized water and ultrasonically disperse for a period of time to obtain a multi-walled carbon nanotube dispersion;

[0061] ② Dissolve acrylamide and N,N'-methylenebisacrylamide in deionized water, stir for a period of time, add multi-walled carbon nanotube dispersion, and continue stirring for a period of time to obtain mixed solution IV;

[0062] ③ Dissolve ammonium persulfate powder in deionized water to obtain an aqueous solution of ammonium persulfate; add N,N,N',N'-tetramethylethylenediamine and the aqueous solution of ammonium persulfate to mixed solution IV in sequence, stir evenly to obtain reaction solution II;

[0063] ④ Place the reaction solution II into the mold containing the hydrogel matrix I obtained in step 2 ⑤, and then transfer it to an environment of -4℃ to initiate the reaction for 24h to 48h. Hydrogel matrix II is obtained on the hydrogel matrix I, which is a colloidal mixture.

[0064] ⑤ Soak the colloidal mixture in deionized water, changing the water periodically to remove unreacted substances, and obtain a microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot.

[0065] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in the following ways: In step one ①, the molar volume ratio of N-isopropylacrylamide, N,N'-methylenebisacrylamide, and deionized water is (2 mmol–4 mmol):(0.05 mmol–0.11 mmol):100 mL; the magnetic stirring time in step one ① is 10 min–30 min, and the magnetic stirring speed is 1000 r / min–2000 r / min; in step one ②, the molar volume ratio of N-isopropylacrylamide, styrene, and divinylbenzene in mixed solution II is (2 mmol–4 mmol):(1 mL–3 mL):(0.1 mL–0.3 mL). All other steps are the same as in Specific Implementation Method One.

[0066] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in the following ways: the heating and magnetic stirring speed in step 1.③ is 600 r / min to 1200 r / min, and the time is 5 h to 8 h; the nitrogen blowing time into mixed solution II in step 1.③ is 10 min to 15 min; the concentration of the ammonium persulfate aqueous solution in step 1.③ is 20 mg / mL to 40 mg / mL; and the volume ratio of the ammonium persulfate aqueous solution to the styrene in step 1.② is (2 mL to 5 mL):(1 mL to 3 mL). Other steps are the same as in Specific Implementation Method One or Two.

[0067] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in the following ways: the dialysis time in step one (④) is 72 hours, with water changed every 12 hours; the pre-freezing time in step one (⑤) is 8 to 12 hours; and the vacuum freeze-drying time in step one (⑤) is 24 to 48 hours. The other steps are the same as in Specific Implementation Methods One to Three.

[0068] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that: the mass ratio of poly(N-isopropylacrylamide-co-styrene) microgel to deionized water in step two① is 0.5g:(3mL~6mL); the ultrasonic dispersion power in step two① is 300W~500W, and the ultrasonic dispersion time is 30min~60min. Other steps are the same as in Specific Implementation Methods One to Four.

[0069] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in the following ways: the mold dimensions in step two ② are 5cm × 2cm × 2cm; the drying temperature in step two ② is 80℃~90℃; and the thickness of the poly(N-isopropylacrylamide-co-styrene) microgel bottom surface in step two ② is 0.5cm~1.5cm. The other steps are the same as in Specific Implementation Methods One to Five.

[0070] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One through Six in that: the mass-to-volume ratio of N-isopropylacrylamide, N,N'-methylenebisacrylamide, and deionized water in step two ③ is (1.31g~2.62g):(40mg~80mg):(20mL~40mL); the pre-cooling time in step two ③ is 30min~60min; the stirring speed in step two ③ is 1000r / min~2000r / min, and the stirring time is 5min~ 15 min; the concentration of the ammonium persulfate aqueous solution in step 2④ is 40 mg / mL to 60 mg / mL; the volume ratio of the ammonium persulfate aqueous solution, N,N,N',N'-tetramethylethylenediamine, and the pre-cooled mixed solution III in step 2④ is (3 mL to 6 mL):(30 μL to 60 μL):(20 mL to 40 mL); the stirring speed in step 2④ is 500 r / min to 800 r / min; the thickness of the hydrogel matrix I in step 2② is 0.5 cm to 1.5 cm. Other steps are the same as in specific embodiments one to six.

[0071] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in the following ways: In step three ①, the mass-to-volume ratio of multi-walled carbon nanotubes, hexadecyltrimethylsodium bromide, and deionized water is (30mg-60mg):(30mg-60mg):(10mL-20mL); the ultrasonic dispersion power in step three ① is 300W-500W, and the ultrasonic dispersion time is 30min-60min; in step three ②, the volume ratio of acrylamide, N,N'-methylenebisacrylamide, deionized water, and multi-walled carbon nanotube dispersion is (1g-2g):(20mg-40mg):(7mL-14mL):(3mL-6mL); and the stirring speed in step three ② is 1000r / min-2000r / min, and the stirring time is 5min-15min. Other steps are the same as in Specific Implementation Methods One to Seven.

[0072] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in the following ways: the concentration of the ammonium persulfate aqueous solution in step 3.③ is 40 mg / mL to 60 mg / mL; the volume ratio of the ammonium persulfate aqueous solution, N,N,N',N'-tetramethylethylenediamine, and mixed solution IV in step 3.③ is (1 mL to 2 mL):(20 μL to 40 μL):(5 mL to 10 mL); the stirring speed in step 3.③ is 500 r / min to 800 r / min; the thickness of the hydrogel matrix II in step 3.④ is 0.5 cm to 1.5 cm; and the water is changed every 12 hours in step 3.⑤, for a total of 5 to 7 water changes. The other steps are the same as in Specific Implementation Methods One to Eight.

[0073] Specific Implementation Method 10: This implementation method is a microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot used as a controller material to control and restrict fluid flow in response to environmental photothermal information stimulation.

[0074] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0075] Example 1: A method for preparing a microgel-crosslinked photothermal responsive flexible bilayer hydrogel valve-controlled robot, specifically completed according to the following steps:

[0076] I. Preparation of poly(N-isopropylacrylamide-co-styrene) microgels:

[0077] ① Add 4 mmol N-isopropylacrylamide and 0.11 mmol N,N'-methylenebisacrylamide to 100 mL of deionized water and stir magnetically for 10 min at room temperature and a stirring speed of 1000 r / min to obtain a homogeneous and transparent mixed solution I.

[0078] ② Add 3 mL of styrene and 0.3 mL of divinylbenzene to a homogeneous and transparent mixed solution I, mix well, and obtain mixed solution II;

[0079] ③ Purge nitrogen gas into mixed solution II for 15 min, then add 5 mL of ammonium persulfate aqueous solution with a concentration of 20 mg / mL. Stir magnetically for 8 h in a water bath at 80 °C and at a stirring speed of 1000 r / min to terminate the reaction and obtain a crude solution of poly(N-isopropylacrylamide-co-styrene) microgel.

[0080] ④ The crude solution of poly(N-isopropylacrylamide-co-styrene) microgel was subjected to dialysis for 72 hours, with water changed every 12 hours, to obtain a pure solution of poly(N-isopropylacrylamide-co-styrene) microgel.

[0081] ⑤ Pre-freeze the pure solution of poly(N-isopropylacrylamide-co-styrene) microgel at -20℃ for 8 hours, and then freeze-dry it under vacuum for 24 hours to obtain poly(N-isopropylacrylamide-co-styrene) microgel.

[0082] II. Preparation of hydrogel matrix I:

[0083] ① Dissolve 0.5g of poly(N-isopropylacrylamide-co-styrene) microgel in 3mL of deionized water and sonicate at 400W for 60min to obtain a poly(N-isopropylacrylamide-co-styrene) microgel dispersion.

[0084] ② Add 1 mL of poly(N-isopropylacrylamide-co-styrene) microgel dispersion to a mold with dimensions of 5 cm × 2 cm × 2 cm, and dry it in a forced-air drying oven at 80 °C to obtain a mold with the bottom surface of poly(N-isopropylacrylamide-co-styrene) microgel.

[0085] ③ Add 1.31g N-isopropylacrylamide and 40mg N',N'-methylenebisacrylamide to 20mL of deionized water and stir at 1000r / min for 15min to obtain mixed solution III; place mixed solution III in an environment of -4℃ for 60min to obtain pre-cooled mixed solution III.

[0086] ④ Dissolve ammonium persulfate powder in deionized water to obtain an ammonium persulfate aqueous solution with a concentration of 40 mg / mL; add 30 μL of N,N,N',N'-tetramethylethylenediamine and 3 mL of the 40 mg / mL ammonium persulfate aqueous solution to the pre-cooled mixed solution III, and stir evenly at a stirring speed of 800 r / min to obtain reaction solution I;

[0087] ⑤ Place 5 mL of reaction solution I into the mold with the bottom surface of poly(N-isopropylacrylamide-co-styrene) microgel obtained in step 2 ②, and then transfer it to an environment of -4℃ to initiate the reaction for 24 h to obtain a mold with hydrogel matrix I.

[0088] III. Fabrication of a bilayer hydrogel valve-controlled robot:

[0089] ① Dissolve 30 mg of multi-walled carbon nanotubes and 30 mg of cetyltrimethyl sodium bromide in 10 mL of deionized water and ultrasonically disperse them at an ultrasonic power of 400 W for 60 min to obtain a multi-walled carbon nanotube dispersion.

[0090] ② Dissolve 1g acrylamide and 20mg N,N'-methylenebisacrylamide in 7mL of deionized water, stir at 1000r / min for 15min, add 3mL of multi-walled carbon nanotube dispersion, and continue stirring for 15min to obtain mixed solution IV;

[0091] ③ Dissolve ammonium persulfate powder in deionized water to obtain an ammonium persulfate aqueous solution with a concentration of 40 mg / mL; add 30 μL of N,N,N',N'-tetramethylethylenediamine and 1 mL of the 40 mg / mL ammonium persulfate aqueous solution to mixed solution IV in sequence, and stir evenly at a stirring speed of 800 r / min to obtain reaction solution II;

[0092] ④ Place 5 mL of reaction solution II into the mold containing hydrogel matrix I obtained in step 2 ⑤, and then transfer it to an environment of -4℃ to initiate the reaction for 24 h. Hydrogel matrix II is obtained on hydrogel matrix I, which is a colloidal mixture.

[0093] ⑤ Soak the colloidal mixture in 200mL of deionized water, changing the water every 12 hours for a total of 6 times to remove unreacted substances and obtain a microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot.

[0094] Figure 1 This is a reaction mechanism diagram of step one in Example 1;

[0095] pass Figure 1 It can be seen that poly(N-isopropylacrylamide-co-styrene) microgels are obtained by soap-free emulsion polymerization under the action of styrene, divinylbenzene and initiator ammonium persulfate solution.

[0096] Figure 2 This is a reaction mechanism diagram for steps two and three of Example 1. In the diagram, a represents the reaction mechanism diagram for step two, and b represents the reaction mechanism diagram for step three.

[0097] pass Figure 2 From a, we know that the N-isopropylacrylamide carbon-carbon double bond opens, and through free radical polymerization with the microgel, it forms a stable carbon-carbon single bond, generating hydrogel matrix I; through Figure 2 As shown in b, acrylamide breaks down carbon-carbon double bonds through free radical polymerization to form stable carbon-carbon single bonds. After being mixed with ultrasonically dispersed multi-walled carbon nanotube dispersion, it is cast onto the hydrogel matrix I obtained in step two (⑤). Through hydrogen bonding, a microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot is obtained.

[0098] Figure 3 This is a particle size distribution diagram of poly(N-isopropylacrylamide-co-styrene) microgels obtained in step one of Example 1;

[0099] Depend on Figure 3 It can be seen that the particle size distribution range of poly(N-isopropylacrylamide-co-styrene) microgel is 141 nm to 29 nm, and the average particle size is 238.5 ± 2.784 nm, which is consistent with the defined scale range of microgels, indicating that poly(N-isopropylacrylamide-co-styrene) microgels were successfully prepared.

[0100] Figure 4 The figures are infrared spectra. In the figure, a represents the infrared spectrum of polyacrylamide, b represents the infrared spectrum of hydrogel matrix I in step two ⑤, and c represents the infrared spectrum of the microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot obtained in step three ⑤ of example one.

[0101] Depend on Figure 4 It can be seen that spectrum a belongs to 3330cm. -1 The characteristic absorption peak of free amino groups, 2920 cm⁻¹ -1 The methylene stretching vibration peak and 1460 cm⁻¹ -1 The carbonyl stretching vibration peaks in the amide bonds are all present in spectrum c, indicating that the two have similar molecular structures, and the flexible bilayer hydrogel valve-controlled robot material has a polyacrylamide framework. Furthermore, comparing spectrum b, a 2990 cm⁻¹ peak appears in hydrogel matrix I. -1 The peak at 1460 cm⁻¹ represents the stretching vibration of CH on the methyl group of N-isopropylacrylamide. -1 1180cm -1 The enhanced signal peak indicates the presence of a poly-N-isopropylacrylamide structure in the bilayer gel, signifying the successful preparation of a flexible bilayer hydrogel valve control robot material.

[0102] Figure 5 The figures are X-ray diffraction patterns. In the figure, a represents the X-ray diffraction pattern of hydrogel matrix I in step two (⑤), and b represents the X-ray diffraction pattern of the microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot obtained in step three (⑤) of Example one.

[0103] from Figure 5 It can be seen that two broad diffraction peaks appear near 7° and 20° in the X-ray diffraction pattern of hydrogel matrix I, indicating that the poly-N-isopropylacrylamide network has an amorphous structure. In addition, the X-ray diffraction patterns of all the materials measured show broad diffuse scattering peaks, that is, they have an amorphous structure.

[0104] Figure 6 This is the differential scanning calorimetry spectrum of the microgel crosslinked photothermal responsive flexible bilayer hydrogel valve-controlled robot obtained in step three of Example 1;

[0105] Figure 7 This is a thermogravimetric analysis diagram of the microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot obtained in step 3.5 of Example 1;

[0106] Depend on Figure 7It can be seen that the hydrogel material of the present invention experiences a mass loss of approximately 4% due to the evaporation of bound water between 25°C and 130°C. Further increasing the temperature, from 200°C to 280°C, a second mass loss occurs, which can be attributed to the breaking of hydrogen bonds in the gel network. Continuing to raise the temperature to 440°C, a third mass loss occurs, presumably due to the cracking of carbon-carbon single bonds in the main cross-linked backbone of the hydrogel, leading to the breakage and degradation of the gel molecular chain structure. Furthermore, differential scanning calorimetry (DSC) shows two endothermic peaks near 275°C and 400°C in the hydrogel material of the present invention. The weaker endothermic peak near 275°C is presumably due to the endothermic effect of hydrogen bond breaking, while the peak at 400°C involves the endothermic breaking of numerous C-C single bonds formed during free radical polymerization. These thermogravimetric analysis results corroborate the high endothermic peak temperatures of the hydrogel material of the present invention, indicating excellent thermal stability.

[0107] Figure 8 This is a scanning electron microscope image of the microgel crosslinked photothermal responsive flexible bilayer hydrogel valve-controlled robot obtained in step three of Example 1.

[0108] Depend on Figure 8 It can be seen from the comparative analysis of the microstructure of the microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot prepared by the present invention at magnifications of 30x, 100x, and 500x. It can be seen that the microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot prepared by the present invention has a multi-level pore size three-dimensional network structure with tightly connected pores, indicating that the target hydrogel material has been successfully prepared.

[0109] Figure 9 This is a rheological performance test diagram of the microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot obtained in step 3.5 of Example 1; in the figure, █ represents the storage modulus of the hydrogel, and ● represents the loss modulus of the hydrogel.

[0110] Depend on Figure 9 It can be seen that the hydrogel material of the present invention exhibits a storage modulus greater than a dissipation modulus within the scanning range, indicating that the samples all present a solid gel state, and its elastic behavior is greater than its viscous behavior, confirming the successful preparation of the hydrogel. The delocalized π bonds formed by carbon atoms in the cross-section of multi-walled carbon nanotubes and the surface hydrophilic groups are non-covalently bonded to the hydrogel framework, making the hydrogel chain network compact, thereby improving the mechanical strength of the robot material.

[0111] Figure 10 The figure shows the tensile stress-strain test results of the microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot obtained in step 3.5 of Example 1.

[0112] Depend on Figure 10It can be seen that the fracture stress of the microgel-crosslinked photothermal responsive flexible bilayer hydrogel valve-controlling robot of the present invention is 59 kPa, and the elongation at break is 72.52%. Integrating the stress-strain curve, the toughness of the microgel-crosslinked photothermal responsive flexible bilayer hydrogel valve-controlling robot is 2.689 MPa. The interaction between the delocalized π bonds in the multi-walled carbon nanotubes and the hydrogel chain skeleton effectively improves the mechanical strength of the bilayer hydrogel valve-controlling robot.

[0113] Figure 11 This is a graph showing the weight change over time of the microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot obtained in step 3.5 of Example 1 during a degradation test;

[0114] Depend on Figure 11 It can be seen that the microgel crosslinked photothermal responsive bilayer hydrogel valve control robot prepared in this invention, after being immersed in 10 mL of 0.01 M PBS solution for 30 days, still has a quality retention rate of more than 95%, indicating that the target flexible bilayer hydrogel valve control robot has not undergone significant degradation in the external environment, has good stability, and can be used as an in vitro intelligent robot for a long time.

[0115] Figure 12 This is a graph showing the change of gel temperature with infrared irradiation time in the infrared response test of the microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot obtained in step 3⑤ of Example 1.

[0116] Depend on Figure 12 It can be seen that the microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot prepared by the present invention exhibits significant temperature changes after infrared light irradiation. The temperature increases by 8.59℃ in the first 300s, with a relatively fast heating rate. The heating rate slows down from 300s to 600s, and after irradiation time continues to 600s, the gel temperature does not show significant changes, demonstrating good photothermal performance.

[0117] Figure 13 Figure 1 shows the cyclic test results of the microgel-crosslinked photothermal responsive flexible bilayer hydrogel valve control robot obtained in step 3.5 of Example 1, in the temperature response test. Figure 1a shows the change in the curvature of the microgel-crosslinked photothermal responsive flexible bilayer hydrogel valve control robot obtained in step 3.5 as a function of infrared irradiation time, where ● represents the robot's heating process after infrared irradiation is turned on, and ▲ represents the robot's cooling process after infrared irradiation is turned off. Figure 2b shows the change in temperature and curvature of the microgel-crosslinked photothermal responsive flexible bilayer hydrogel valve control robot obtained in step 3.5 during the cyclic opening and closing of infrared irradiation, where ● represents temperature and ▲ represents curvature. Figure 2c shows the actual changes of the microgel-crosslinked photothermal responsive flexible bilayer hydrogel valve control robot obtained in step 3.5 under photothermal influence.

[0118] Depend on Figure 13It can be seen that the microgel-crosslinked photothermal responsive flexible bilayer hydrogel valve control robot prepared by this invention shrinks and bends when heated in a 50°C water bath, and recovers after cooling in a 20°C water bath. Under high temperature conditions, the bending angle of the microgel-crosslinked photothermal responsive flexible bilayer hydrogel valve control robot increases from 190° to 323° within 10 minutes, and recovers from 323° to 185° after cooling in a 20°C water bath in about 20 minutes; it can achieve at least 5 cycles of reversible bending. In addition, after 50 cycles of infrared irradiation, the microgel-crosslinked photothermal responsive flexible bilayer hydrogel valve control robot prepared by this invention maintains good stability of gel photothermal responsive deformation performance, with a temperature rise error of about 2°C and a deformation error of about 10°C, which confirms that the microgel-crosslinked photothermal responsive flexible bilayer hydrogel valve control robot prepared by this invention can achieve undiminished cyclic bending deformation behavior.

[0119] Figure 14 This is a schematic diagram of the fluid control of the microgel crosslinked photothermal responsive flexible bilayer hydrogel valve-controlled robot obtained in step three (⑤) of Example 1.

[0120] The microgel-crosslinked photothermal responsive flexible bilayer hydrogel valve control robot prepared in this invention was cut into sample blocks of 2.0cm × 1.0cm × 0.1cm for later use. Waterproof tape was cut to an appropriate size and attached to the filter cake of a glass filter. A 1.0cm × 0.5cm square hole was then cut in the center of the tape. The cut valve control robot was placed above the hole, and one side of the gel was secured with tape. Without the valve control robot, liquid flowed out through the pre-drilled hole at a flow rate of approximately 15mL / s. After inserting the valve control robot material, no liquid flowed out of the hole when the water temperature was 20℃. When the water temperature rose to 40℃ or after infrared irradiation, the hydrogel material deformed under photothermal stimulation, creating a gap between the hydrogel and the hole to allow water flow. This indicates that the flexible bilayer hydrogel valve control robot material prepared in this invention possesses photothermal responsive valve control performance.

Claims

1. A method for fabricating a microgel-crosslinked photothermal-responsive flexible bilayer hydrogel valve-controlled robot, characterized in that... The preparation method is specifically carried out according to the following steps: I. Preparation of poly(N-isopropylacrylamide-co-styrene) microgels: ① Add N-isopropylacrylamide and N,N'-methylenebisacrylamide to deionized water and stir magnetically for a period of time at room temperature to obtain a homogeneous and transparent mixed solution I; ② Add styrene and divinylbenzene dropwise to a homogeneous and transparent mixed solution I, mix well, and obtain mixed solution II; ③ Puff nitrogen gas into mixed solution II for a period of time, then add ammonium persulfate aqueous solution, heat in a water bath at 80℃~90℃ and stir magnetically for a period of time to terminate the reaction and obtain a crude solution of poly(N-isopropylacrylamide-co-styrene) microgel; ④ The crude solution of poly(N-isopropylacrylamide-co-styrene) microgel was dialyzed to obtain a pure solution of poly(N-isopropylacrylamide-co-styrene) microgel. ⑤ Pre-freeze the pure solution of poly(N-isopropylacrylamide-co-styrene) microgel at -20℃ for a period of time, and then freeze-dry it under vacuum for a period of time to obtain poly(N-isopropylacrylamide-co-styrene) microgel. II. Preparation of hydrogel matrix I: ① Poly(N-isopropylacrylamide-co-styrene) microgel was dissolved in deionized water and dispersed by ultrasonication to obtain a poly(N-isopropylacrylamide-co-styrene) microgel dispersion; ② Add the poly(N-isopropylacrylamide-co-styrene) microgel dispersion to the mold, dry it, and obtain a mold with the poly(N-isopropylacrylamide-co-styrene) microgel on the bottom surface; ③ Add N-isopropylacrylamide and N',N'-methylenebisacrylamide to deionized water and stir for a period of time to obtain mixed solution III; place mixed solution III in an environment of -4℃ for a period of time to obtain pre-cooled mixed solution III; ④ Dissolve ammonium persulfate powder in deionized water to obtain an ammonium persulfate aqueous solution; add N,N,N',N'-tetramethylethylenediamine and the ammonium persulfate aqueous solution to the pre-cooled mixed solution III in sequence, stir evenly to obtain reaction solution I; ⑤ Place reaction solution I into the mold with the bottom surface of poly(N-isopropylacrylamide-co-styrene) microgel obtained in step 2 ②, and then transfer it to an environment of -4 ℃ to initiate the reaction for 24h~48h to obtain a mold with hydrogel matrix I. III. Fabrication of a bilayer hydrogel valve-controlled robot: ① Dissolve multi-walled carbon nanotubes and hexadecyltrimethylsodium bromide in deionized water and ultrasonically disperse for a period of time to obtain a multi-walled carbon nanotube dispersion; ② Dissolve acrylamide and N,N'-methylenebisacrylamide in deionized water, stir for a period of time, add multi-walled carbon nanotube dispersion, and continue stirring for a period of time to obtain mixed solution IV; ③ Dissolve ammonium persulfate powder in deionized water to obtain an aqueous solution of ammonium persulfate; add N,N,N',N'-tetramethylethylenediamine and the aqueous solution of ammonium persulfate to mixed solution IV in sequence, stir evenly to obtain reaction solution II; ④ Place the reaction solution II into the mold containing the hydrogel matrix I obtained in step 2 ⑤, and then transfer it to an environment of -4℃ to initiate the reaction for 24h~48h. Hydrogel matrix II is obtained on the hydrogel matrix I, which is a colloidal mixture. ⑤ Soak the colloidal mixture in deionized water, changing the water periodically to remove unreacted substances, and obtain a microgel crosslinked photothermal responsive flexible bilayer hydrogel valve control robot.

2. The method for preparing a microgel-crosslinked photothermal-responsive flexible bilayer hydrogel valve-controlled robot according to claim 1, characterized in that... The molar volume ratio of N-isopropylacrylamide, N,N'-methylenebisacrylamide and deionized water in step 1① is (2 mmol~4 mmol):(0.05 mmol~0.11 mmol):100 mL; the magnetic stirring time in step 1① is 10 min~30 min, and the magnetic stirring speed is 1000 r / min~2000 r / min; the molar volume ratio of N-isopropylacrylamide, styrene and divinylbenzene in mixed solution II in step 1② is (2 mmol~4 mmol):(1 mL~3 mL):(0.1 mL~0.3 mL).

3. The method for preparing a microgel-crosslinked photothermal-responsive flexible bilayer hydrogel valve-controlled robot according to claim 1, characterized in that... The heating and magnetic stirring speed in step 1③ is 600 r / min to 1200 r / min, and the time is 5 h to 8 h; the time for blowing nitrogen into mixed solution II in step 1③ is 10 min to 15 min; the concentration of the ammonium persulfate aqueous solution in step 1③ is 20 mg / mL to 40 mg / mL; the volume ratio of the ammonium persulfate aqueous solution to the styrene in step 1② is (2 mL to 5 mL): (1 mL to 3 mL).

4. The method for preparing a microgel-crosslinked photothermal-responsive flexible bilayer hydrogel valve-controlled robot according to claim 1, characterized in that... The dialysis time in step 1 ④ is 72 hours, with water changed every 12 hours; the pre-freezing time in step 1 ⑤ is 8 to 12 hours; and the vacuum freeze-drying time in step 1 ⑤ is 24 to 48 hours.

5. The method for preparing a microgel-crosslinked photothermal-responsive flexible bilayer hydrogel valve-controlled robot according to claim 1, characterized in that... The mass ratio of poly(N-isopropylacrylamide-co-styrene) microgel to deionized water in step 2① is 0.5 g:(3 mL~6 mL); the ultrasonic dispersion power in step 2① is 300 W~500 W, and the ultrasonic dispersion time is 30 min~60 min.

6. The method for preparing a microgel-crosslinked photothermal-responsive flexible bilayer hydrogel valve-controlled robot according to claim 1, characterized in that... The dimensions of the mold mentioned in step 2② are 5cm×2cm×2cm; the drying temperature mentioned in step 2② is 80℃~90℃; the thickness of the bottom surface of the poly(N-isopropylacrylamide-co-styrene) microgel mentioned in step 2② is 0.5cm~1.5cm.

7. The method for preparing a microgel-crosslinked photothermal-responsive flexible bilayer hydrogel valve-controlled robot according to claim 1, characterized in that... The mass-to-volume ratio of N-isopropylacrylamide, N,N'-methylenebisacrylamide, and deionized water mentioned in step 2③ is (1.31g~2.62g):( 40mg~80mg):(20mL~40mL); The pre-cooling time in step 2③ is 30min~60min; The stirring speed in step 2③ is 1000r / min~2000r / min, and the stirring time is 5min~15min; The concentration of the ammonium persulfate aqueous solution in step 2④ is 40mg / mL~60mg / mL; The volume ratio of the ammonium persulfate aqueous solution, N,N,N',N'-tetramethylethylenediamine and the pre-cooled mixed solution III in step 2④ is (3mL~6mL):(30µL~60µL):(20mL~40mL); The stirring speed in step 2④ is 500r / min~800r / min; The thickness of the hydrogel matrix I in step 2⑤ is 0.5cm~1.5cm.

8. The method for preparing a microgel-crosslinked photothermal-responsive flexible bilayer hydrogel valve-controlled robot according to claim 1, characterized in that... The mass-to-volume ratio of multi-walled carbon nanotubes, hexadecyltrimethylsodium bromide, and deionized water in step 3.① is (30mg~60mg):(30mg~60mg):(10mL~20mL); the ultrasonic dispersion power in step 3.① is 300W~500W, and the ultrasonic dispersion time is 30min~60min; the volume ratio of acrylamide, N,N'-methylenebisacrylamide, deionized water, and multi-walled carbon nanotube dispersion in step 3.② is (1g~2g):(20mg~40mg):(7mL~14mL):(3mL~6mL).

9. The method for preparing a microgel-crosslinked photothermal-responsive flexible bilayer hydrogel valve-controlled robot according to claim 1, characterized in that... The concentration of the ammonium persulfate aqueous solution in step 3.③ is 40 mg / mL to 60 mg / mL; the volume ratio of the ammonium persulfate aqueous solution, N,N,N',N'-tetramethylethylenediamine, and mixed solution IV in step 3.③ is (1 mL to 2 mL):(20 µL to 40 µL):(5 mL to 10 mL); the stirring speed in step 3.③ is 500 r / min to 800 r / min; the thickness of the hydrogel matrix II in step 3.④ is 0.5 cm to 1.5 cm; and the water is changed every 12 hours in step 3.⑤, for a total of 5 to 7 water changes.

10. The application of a microgel crosslinked photothermal responsive flexible bilayer hydrogel valve-controlled robot prepared by the preparation method described in claim 1, characterized in that... A microgel-crosslinked photothermal responsive flexible bilayer hydrogel valve-controlled robot is used as a controller material to control and restrict fluid flow in response to environmental photothermal information.

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