A hydrogel with programmable reversible shape movement and pH dual stimuli response and a preparation method thereof

Abstract

The present application relates to a kind of both programmable reversible shape movement (i.e. bidirectional shape memory) and pH dual-stimuli responsive hydrogel.The present application belongs to the field of organic polymer materials.By free radical copolymerization, stearyl acrylate, acrylic acid and N-isopropyl acrylamide are copolymerized, the method is widely available, easy to operate, easy to industrial production, and the dual-stimuli responsive hydrogel prepared by the method is a brand new material that has never been reported, and has good shape memory characteristics and high pH sensitivity (only 5 minutes are needed to complete the pH softening / strengthening whole cycle) and wide pH range (1-14). This dual-acting (with good shape memory characteristics and high pH sensitivity) hydrogel has a wide range of positive effects on drug delivery, control and release in the field of biological medicine.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials and relates to a hydrogel with programmable and reversible shape movement (i.e., bidirectional shape memory) and pH dual stimulation response, and its preparation method. In particular, it relates to a method for preparing a hydrogel with bidirectional shape memory and pH dual stimulation response based on the combined use of N-isopropylacrylamide, stearyl acrylate, and acrylic acid. Background Technology

[0002] Hydrogels are soft materials composed of a three-dimensional network of polymers containing a large amount of water. They possess a composition similar to that of biological media and exhibit excellent flexibility, unique properties, and broad application prospects. Poly(N-isopropylacrylamide) is a typical temperature-responsive hydrogel. When the temperature is above the lower critical transition temperature (LCST), the gel shrinks; when the temperature is below the LCST, the gel expands. Based on this property, poly(N-isopropylacrylamide) hydrogels can be used as temperature-sensitive smart responsive materials. In many applications, materials need to respond to changes in external temperature. However, hydrogels that are only temperature-sensitive have limitations in practical applications. Current pursuits of smart materials, including bilayer hydrogel actuators, require feedback to a variety of environmental stimuli. Temperature changes are the most common environmental condition. Therefore, using temperature-sensitive materials such as poly(N-isopropylacrylamide) as a substrate to produce materials sensitive to multiple environmental stimuli is meaningful.

[0003] Solid polymers capable of programmable and reversible shape movement (i.e., bidirectional shape memory) have been discovered. Most typically, such materials exhibit two separate (or broad) crystalline melt transitions. Programming is achieved by introducing network anisotropy through the high-melting-point transition stage, while heating and cooling through the low-melting-point transition result in reversible shape transitions via crystallization-induced elongation and melt-induced contraction. The pH responsiveness of the material arises from the ionization of functional side groups on the polymer backbone. When these side functional groups are ionized, the charge density of the hydrogel is redistributed. Due to electrostatic repulsion, two hydrogel backbones with the same charge separate from each other, making the polymer network looser and ultimately causing the gel to absorb water and swell. Typical examples of pH-responsive materials include polyacrylic acid, polyacrylamide, and polymethacrylic acid. Summary of the Invention

[0004] This invention relates to a simple and controllable hydrogel with both programmable and reversible shape movement (i.e., bidirectional shape memory) and pH-responsive properties, as well as its preparation method. The method utilizes readily available raw materials, is simple to operate, and is easily industrialized. The resulting bidirectional responsive hydrogel is a novel material never before reported, exhibiting excellent shape memory characteristics, high pH sensitivity (the entire pH softening / enhancing cycle takes only 5 minutes), and a wide pH range (1-14). This hydrogel with dual functions (excellent shape memory and high pH sensitivity) has broad positive applications in the biomedical field for drug delivery, control, and release.

[0005] To achieve the above objectives, the present invention employs the following technical solution: a hydrogel possessing both programmable and reversible shape movement (i.e., bidirectional shape memory) and pH dual-stimulus responsiveness, prepared by mass fraction from the following components:

[0006]

[0007]

[0008] Preferably, it belongs to free radical polymerization, and using a photoinitiator to initiate free radical polymerization is simple and easy.

[0009] Preferably, it belongs to free radical polymerization, the initiator is benzophenone or α-ketoglutaric acid, and the polymerization is carried out under ultraviolet light irradiation.

[0010] Preferably, the hydrogel is synthesized by free radical copolymerization of N-isopropylacrylamide (NIPAM), acrylic acid (AA), stearate acrylate (SA), and N,N'-methylenebisacrylamide (MBA) in dimethyl sulfoxide (DMSO).

[0011] Preferably, it is not a single programmable reversible shape movement (i.e., bidirectional shape memory) or a single pH-responsive hydrogel, but rather a combination of programmable reversible shape movement (i.e., bidirectional shape memory) and pH response in the same hydrogel.

[0012] Preferably, 1) the melt transition of stearyl segments; 2) the thermal responsiveness of poly(N-isopropylacrylamide) chains, which corresponds to the volume phase transition (VPT) of hydrogels. The melt transition is the basis for cooling-induced shape fixation and heating-induced recovery. The VPT is consistent with its lower critical phase transition temperature (LCST), forming opposite shape memory behaviors, namely heating-induced shape fixation and cooling-induced recovery.

[0013] Preferably, the pH responsiveness of the material originates from the ionization of functional side groups on the polymer backbone.

[0014] To achieve the above objectives, the present invention employs the following technical solution: 1. The preparation method of the responsive hydrogel possessing both programmable and reversible shape movement and pH dual stimulation response includes the following steps:

[0015] (1) By mass fraction, take 20 parts of N-isopropylacrylamide, 7 parts of shape memory molecule, 3 parts of pH-responsive molecule, 1 part of initiator, 1 part of crosslinking agent, and 165-220 parts of dimethyl sulfoxide.

[0016] (2) N-isopropylacrylamide, shape memory molecules, pH-responsive molecules and crosslinking agents were dissolved in dimethyl sulfoxide. After adding the initiator, the solution was quickly transferred into a polytetrafluoroethylene reaction tank. The reaction was carried out under ultraviolet irradiation for 8-12 hours. After polymerization, the prepared hydrogel was soaked in deionized water for solvent exchange. The water in the hydrogel was changed every 12 hours. After 3 days, a hydrogel with a thickness of 1.0±0.1 mm was obtained.

[0017] Preferably, the preparation method is simple, the reaction does not require heating, and the risk factor is low.

[0018] Preferably, it includes the following steps:

[0019] (1) Dissolve 20 parts of N-isopropylacrylamide, 7 parts of stearyl acrylate, 3 parts of acrylic acid, 1 part of N,N'-methylenebisacrylamide, and 1 part of benzophenone in 220 parts of dimethyl sulfoxide, and the mass fraction ratio of stearyl acrylate to acrylic acid is 7:3.

[0020] (2) The solutions obtained above are quickly mixed and stirred thoroughly. The solutions are then quickly transferred to the polytetrafluoroethylene reaction tank.

[0021] (3) The reaction was kept under UV light for 10 hours. After polymerization, the prepared gel was soaked in deionized water for solvent exchange. The water was changed every 12 hours. After three days, an equilibrium hydrogel with a thickness of 1.0±0.1 mm was obtained.

[0022] The solvent is dimethyl sulfoxide, a colorless and odorless transparent liquid at room temperature. It is a hygroscopic and flammable liquid with high polarity, high boiling point, aprotic properties, and water miscibility. It has extremely low toxicity, good thermal stability, is immiscible with alkanes, and is soluble in most organic compounds such as water, ethanol, propanol, diethyl ether, benzene, and chloroform. It is known as a "universal solvent" and is one of the most powerful dissolving agents among commonly used organic solvents.

[0023] This invention also discloses a method for preparing the above-mentioned dual-response hydrogel. By free radical copolymerization, stearyl acrylate, acrylic acid and N-isopropylacrylamide are copolymerized. By combining the melt transformation of the stearyl acrylate crystal region with the thermal response volume phase transformation of the poly(N-isopropylacrylamide) polymer chain, the reversible shape movement of the hydrogel is achieved. The ionization equilibrium of the carboxyl groups in acrylic acid is used to achieve the response to different pH values.

[0024] Using inexpensive and easily synthesized N-isopropylacrylamide as the hydrogel matrix, and considering that poly(N-isopropylacrylamide) is a typical temperature-responsive hydrogel, the gel shrinks when the temperature is above the lower critical transition temperature (LCST) and expands when the temperature is below the LCST. Based on this property, poly(N-isopropylacrylamide) hydrogels can be used as temperature-sensitive smart responsive materials.

[0025] The beneficial effects of this invention are:

[0026] 1. This invention discloses a hydrogel with programmable and reversible shape movement (i.e., bidirectional shape memory) and dual pH stimulation responsiveness. The dual stimulation-responsive hydrogel prepared by this method is a novel material never before reported, exhibiting excellent shape memory characteristics, high pH sensitivity (completing the entire pH softening / enhancing cycle takes only 5 minutes), and a wide pH range (1-14). This hydrogel with dual functions (excellent shape memory characteristics and high pH sensitivity) has broad positive applications in the biomedical field for drug delivery, control, and release.

[0027] 2. The dual-response hydrogel in this invention exhibits transient structural anisotropy, which is caused by the deformation of the hydrophobic domains of the stearyl group after thermomechanical programming. This provides a template for the reversible spheroidal transformation of the poly(N-isopropylacrylamide) chain. The structural anisotropy is transient and can be eliminated upon cooling, thus allowing for repeated programming of reversible shape transformations.

[0028] 3. Using acrylic acid as a pH-responsive material to introduce carboxyl groups into the hydrogel, under acidic conditions, due to the hydrogen bonding between carboxyl groups, the intersegments in the network are relatively close, resulting in a lower swelling ratio of the hydrogel. As the pH increases, the carboxyl group (-COOH) ionizes into a carboxyl anion (-COO). - This causes the hydrogen bonds between the macromolecular chains in the gel network to dissociate, increases the electrostatic repulsion between ions, makes the network structure looser, increases the volume, and thus exhibits an increased swelling rate.

[0029] 4. The initiators used are benzophenone and α-ketoglutaric acid. The synthesis is carried out under ultraviolet light irradiation, which is simple, safe and reliable. Therefore, the dual-stimulus responsive hydrogel of the present invention combines programmable reversible shape movement (i.e., bidirectional shape memory) and pH response into the same hydrogel, thereby achieving dual stimulation response of shape memory and pH response.

[0030] 5. Comparing Example 1 and Example 3, under the same conditions, increasing the initiator content leads to a decrease in the hydrogel polymerization time, but the resulting hydrogel has a less uniform texture.

[0031] 6. Comparing Example 1 and Example 4, under the same conditions, increasing the content of dimethyl sulfoxide will make the hydrogel stock solution more uniformly dispersed, thus making the hydrogel polymerized in Example 1 more uniform in texture.

[0032] 7. Comparison of Example 1 and Comparative Examples 1-6 shows that the hydrogels prepared in Comparative Examples 1-6 do not have programmable reversible shape movement (i.e., bidirectional shape memory) function, but only pH response function. Furthermore, as the mass fraction ratio of stearyl acrylate and acrylic acid increases, the swelling time of the hydrogel after immersion in alkaline solution shows a trend of first decreasing and then increasing, while the time to recover to the original size after immersion in acid solution shows an increasing trend. The hydrogel prepared in Example 1 has both programmable reversible shape movement (i.e., bidirectional shape memory) and pH response, and its performance is optimal. Attached Figure Description

[0033] Figure 1 SEM image of the network structure of the hydrogel (Example 1) with programmable and reversible shape movement (i.e., bidirectional shape memory) and pH response obtained in this invention;

[0034] Figure 2 Infrared absorption spectra of the hydrogel before and after the introduction of acrylic acid (AA);

[0035] Figure 3 The swelling kinetics of the hydrogel (Example 1) prepared by the present invention, which has programmable reversible shape movement (i.e., bidirectional shape memory) and pH response, are shown in the figure.

[0036] Figure 4 The diagram shows the equilibrium swelling curve of the hydrogel (Example 1) prepared by the present invention, which has programmable and reversible shape movement (i.e., bidirectional shape memory) and pH response, in deionized water as a function of temperature.

[0037] Figure 5 A demonstration diagram of the bidirectional shape memory of the hydrogel (Example 1) with programmable and reversible shape movement (i.e., bidirectional shape memory) and pH response.

[0038] Figure 6 The equilibrium swelling curves of the prepared hydrogel (Example 1) with programmable and reversible shape movement (i.e., bidirectional shape memory) and pH response at different pH values ​​are shown.

[0039] Figure 7 A pH response demonstration diagram of the prepared hydrogel with programmable reversible shape movement (i.e., bidirectional shape memory) and pH response (Example 1).

[0040] Figure 8 To test the shape memory function of the hydrogel prepared in Comparative Example 1.

[0041] Figure 9 To test the shape memory function of the hydrogel prepared in Comparative Example 2. Detailed Implementation

[0042] The present invention will now be described in further detail with reference to the accompanying drawings:

[0043] Example 1

[0044] A method for preparing a hydrogel with programmable and reversible shape movement (i.e., bidirectional shape memory) and pH-responsive dual properties includes the following steps:

[0045] 1) Dissolve 20 parts of N-isopropylacrylamide (200 mg), 7 parts of stearyl acrylate (70 mg), 3 parts of acrylic acid (30 mg), 1 part of N,N'-methylenebisacrylamide (10 mg), and 1 part of benzophenone (10 mg) in 220 parts of dimethyl sulfoxide (2 mL).

[0046] In this mixture, the mass fraction ratio of stearyl acrylate to acrylic acid is 7:3;

[0047] 2) Quickly mix the solutions obtained above, stir thoroughly, and then quickly transfer the solutions into the polytetrafluoroethylene reaction tank;

[0048] 3) The reaction was maintained under UV light for 10 hours. After polymerization, the prepared gel was immersed in deionized water for solvent exchange. By changing the water every 12 hours, an equilibrium hydrogel with a thickness of 1.0 ± 0.1 mm was obtained after three days.

[0049] See Figure 1 The image shown is a scanning electron microscope (SEM) image of the hydrogel prepared in Example 1, which exhibits both programmable reversible shape movement (i.e., bidirectional shape memory) and pH-responsive dual-reaction. Figure 1 As can be seen, the hydrogels all exhibit interconnected porous structures with abundant pores and water transport channels, and the average pore size is around 20 μm.

[0050] Figure 2 The image shows the infrared spectra of a hydrogel without acrylic acid and a hydrogel with programmable reversible shape movement (i.e., bidirectional shape memory) and pH response prepared according to Example 1 of this invention. The hydrogel containing acrylic acid (AA) has an infrared spectrum at 1723 cm⁻¹. -1 The presence of a C=O double bond stretching vibration peak at the point proves that acrylic acid has been successfully polymerized on the hydrogel.

[0051] Figure 3 The diagram illustrates the swelling kinetics of a hydrogel with programmable and reversible shape movement (i.e., bidirectional shape memory) and pH-responsive dual response, prepared according to Example 1 of this invention. A certain amount of dry gel was weighed and immersed in deionized water. The gel was removed periodically, and the surface moisture was blotted dry with filter paper before weighing again until swelling equilibrium was reached. The swelling ratio (SR) of the hydrogel was calculated using the following formula: SR = ((W t –W d ) / W d ), where W t Let W be the mass of the swollen sample at time t. d This refers to the mass of the dry sample. Figure 3 The swelling rate of the hydrogel sample after immersion in distilled water at 25℃ over time shows that the hydrogel has a high water absorption rate initially, decreases later, and then remains essentially constant after reaching a certain point, indicating that it has reached water saturation. The maximum swelling rate of the hydrogel in distilled water is approximately 24 mg / mg.

[0052] Figure 4 This paper demonstrates the temperature response of a hydrogel prepared according to Example 1 of the present invention, which exhibits programmable and reversible shape movement (i.e., bidirectional shape memory) and pH response. A certain amount of dry gel was immersed in deionized water at different temperatures until swelling equilibrium was reached, and its equilibrium swelling ratio at different temperatures was measured. The equilibrium swelling ratio (ESR) of the hydrogel was calculated using the following formula: ESR = ((W s –W d ) / W d ), where W s To balance the mass of the swollen sample, W d This refers to the mass of the dry sample.

[0053] Depend on Figure 4The equilibrium swelling curves of hydrogels in deionized water as a function of temperature show that the equilibrium swelling ratio of hydrogels decreases with increasing temperature, indicating that hydrogels exhibit heat-shrinkage susceptibility due to their amphiphilic nature. The swelling process of hydrogels involves the diffusion of water molecules into the gel interior and the formation of hydrogen bonds with hydrophilic groups on the gel side chains. As temperature increases, the vibrational energy of hydrogen bonds increases, breaking the bonds and reducing the swelling ratio. When the temperature is below the lower critical phase transition temperature (LCST), the hydrogel exhibits hydrophilicity and absorbs water to swell; however, when the temperature is above the LCST, the hydrogel shrinks, forming a collapsed, dehydrated, hydrophobic state.

[0054] Figure 5 This invention demonstrates the shape memory function of a hydrogel with programmable and reversible shape movement (i.e., bidirectional shape memory) and dual pH-responsiveness, prepared according to this invention. In the initial hydrogel in cold water (shape 1, original shape), the poly(N-isopropylacrylamide) chains are in a relaxed, random coil state, and the network is isotropic. During hot water programming, the hydrophobic stearyl domains are stretched, and due to hydrophobic interactions, the spherically collapsed poly(N-isopropylacrylamide) aggregates around the stearyl domains, temporarily fixing the deformed stearyl domains and macroscopic shape (shape 2, shape fixed). In this state, the poly(N-isopropylacrylamide) also exhibits anisotropy due to chain stretching, and it repels water molecules, forming a surrounding water-rich area. Upon cooling, the poly(N-isopropylacrylamide) absorbs more water and slowly relaxes into a hydrophilic coil. This transition behavior cannot be recovered in a short time, likely because the hydrophobic stearyl domains slow down this conformational transition. Therefore, a transient state exists in which the orientation of the residual poly(N-isopropylacrylamide) and stearyl domains is kinetically captured (shape 3). When this kinetically captured transient hydrogel is then re-immersed in hot water, the coiling transition of the poly(N-isopropylacrylamide) chains tends to occur along the direction of the residual poly(N-isopropylacrylamide). Thus, the hydrogel anisotropically changes towards a programmed shape (shape 4), demonstrating programmable and reversible actuation.

[0055] If the hydrogel is immersed in cold water for a sufficiently long time, the isotropic and fully relaxed chain structure reaches an equilibrium state, which will eliminate previously programmed reversible actuation and enable reprogrammability. The reversible actuation is mainly caused by the thermally responsive conformational change of the poly(N-isopropylacrylamide) chains.

[0056] Figure 6This document displays the equilibrium swelling curves of a hydrogel with programmable and reversible shape movement (i.e., bidirectional shape memory) and dual pH response, prepared according to Example 1 of this invention, at different pH values. Aqueous solutions of different pH values ​​were prepared using hydrochloric acid and sodium hydroxide, respectively. A certain mass of dry gel was weighed and immersed in the solutions, then removed, the surface moisture was wiped off with dry filter paper, and the weight was measured. The equilibrium swelling ratio (ESR) of the hydrogel at different pH values ​​was measured, and the hydrogel swelling ratio (ESR) was calculated using the following formula: ESR = (W s –W d ) / W d W s To balance the mass of the swollen sample, W d This refers to the mass of the dry sample. Figure 7 It can be seen that the swelling ratio of the hydrogel first increases and then decreases with increasing pH. This is because the ionization equilibrium of the carboxylic acid groups in the hydrogel, the electrostatic repulsion of ions on the polymer chains, and the internal and external equilibrium of the gel are all related to pH, with the electrostatic equilibrium between ions being the main influencing factor. Under acidic conditions, due to the hydrogen bonding between carboxyl groups, the distance between chain segments in the network is relatively short, so the swelling ratio of the hydrogel is low. As the pH increases, the carboxyl group (-COOH) is converted to a carboxyl anion (-COO). - This process causes the hydrogen bonds between the macromolecular chains in the gel network to dissociate, increasing the electrostatic repulsion between ions, making the network structure looser, increasing its volume, and consequently increasing its swelling rate. However, once the swelling rate reaches a certain value, as the pH increases (around 13), the gel will no longer swell. This is because at this point, the weakly acidic groups of the polymer are completely dissociated, and the ion concentration in the gel tends to be equal to that in the environment.

[0057] Figure 7 The diagram shows the pH response of a hydrogel with programmable reversible shape movement (i.e., bidirectional shape memory) and dual pH response, prepared according to Example 1 of this invention. The hydrogel has an original size of 6.5 cm. After being immersed in a solution with pH > 7, it absorbs water, swells, and softens in 4.5 minutes, changing its size to 8 cm. After being immersed in a solution with pH < 7, it loses water, shrinks, and recovers its hardness in 0.5 minutes, changing its size back to the original 6.5 cm. This cycle can be completed in just 5 minutes and can be repeated multiple times.

[0058] Example 2

[0059] A method for preparing a hydrogel with programmable and reversible shape movement (i.e., bidirectional shape memory) and pH-responsive dual properties includes the following steps:

[0060] 1) Dissolve 20 parts of N-isopropylacrylamide, 7 parts of stearyl acrylate, 3 parts of acrylic acid, 1 part of N,N'-methylenebisacrylamide, and 1 part of α-ketoglutaric acid in 220 parts of dimethyl sulfoxide, with the mass fraction ratio of stearyl acrylate to acrylic acid being 7:3; 2) Quickly mix the above solutions, stir thoroughly, and then quickly transfer the solution into a polytetrafluoroethylene reaction tank;

[0061] 3) The reaction was maintained under UV light for 10 hours. After polymerization, the prepared gel was immersed in deionized water for solvent exchange. By changing the water every 12 hours, an equilibrium hydrogel with a thickness of 1.0 ± 0.1 mm was obtained after three days.

[0062] Example 3

[0063] A method for preparing a hydrogel with programmable and reversible shape movement (i.e., bidirectional shape memory) and pH-responsive dual properties includes the following steps:

[0064] 1) Dissolve 20 parts of N-isopropylacrylamide, 7 parts of stearyl acrylate, 3 parts of acrylic acid, 1 part of N,N'-methylenebisacrylamide, and 1.5 parts of benzophenone in 220 parts of dimethyl sulfoxide, with a mass ratio of stearyl acrylate to acrylic acid of 7:3; 2) Quickly mix the above solutions, stir thoroughly, and then quickly transfer the solution into a polytetrafluoroethylene reaction tank;

[0065] 3) The reaction was maintained under UV light for 8 hours. After polymerization, the prepared gel was immersed in deionized water for solvent exchange. By changing the water every 12 hours, an equilibrium hydrogel with a thickness of 1.0 ± 0.1 mm was obtained after three days.

[0066] Example 4

[0067] A method for preparing a hydrogel with programmable and reversible shape movement (i.e., bidirectional shape memory) and pH-responsive dual properties includes the following steps:

[0068] 1) Dissolve 20 parts of N-isopropylacrylamide, 7 parts of stearyl acrylate, 3 parts of acrylic acid, 1 part of N,N'-methylenebisacrylamide, and 1 part of benzophenone in 165 parts of dimethyl sulfoxide, and the mass fraction ratio of stearyl acrylate to acrylic acid is 7:3.

[0069] 2) Quickly mix the solutions obtained above, stir thoroughly, and then quickly transfer the solutions into the polytetrafluoroethylene reaction tank;

[0070] 3) The reaction was maintained under UV light for 10 hours. After polymerization, the prepared gel was immersed in deionized water for solvent exchange. By changing the water every 12 hours, an equilibrium hydrogel with a thickness of 1.0 ± 0.1 mm was obtained after three days.

[0071] Comparative Example 1

[0072] 1) Dissolve 20 parts of N-isopropylacrylamide, 7 parts of stearyl acrylate, 4 parts of acrylic acid, 1 part of N,N'-methylenebisacrylamide, and 1 part of benzophenone in 220 parts of dimethyl sulfoxide, and the mass fraction ratio of stearyl acrylate to acrylic acid is 7:4.

[0073] 2) Quickly mix the solutions obtained above, stir thoroughly, and then quickly transfer the solutions into the polytetrafluoroethylene reaction tank;

[0074] 3) The reaction was maintained under UV light for 10 hours. After polymerization, the prepared gel was immersed in deionized water for solvent exchange. By changing the water every 12 hours, an equilibrium hydrogel with a thickness of 1.0 ± 0.1 mm was obtained after three days.

[0075] Comparative Example 2

[0076] 1) Dissolve 20 parts of N-isopropylacrylamide, 7 parts of stearyl acrylate, 5 parts of acrylic acid, 1 part of N,N'-methylenebisacrylamide, and 1 part of benzophenone in 220 parts of dimethyl sulfoxide, and the mass fraction ratio of stearyl acrylate to acrylic acid is 7:5;

[0077] 2) Quickly mix the solutions obtained above, stir thoroughly, and then quickly transfer the solutions into the polytetrafluoroethylene reaction tank;

[0078] 3) The reaction was maintained under UV light for 10 hours. After polymerization, the prepared gel was immersed in deionized water for solvent exchange. By changing the water every 12 hours, an equilibrium hydrogel with a thickness of 1.0 ± 0.1 mm was obtained after three days.

[0079] Comparative Example 3

[0080] 1) Dissolve 20 parts of N-isopropylacrylamide, 7 parts of stearyl acrylate, 6 parts of acrylic acid, 1 part of N,N'-methylenebisacrylamide, and 1 part of benzophenone in 220 parts of dimethyl sulfoxide, and the mass fraction ratio of stearyl acrylate to acrylic acid is 7:6.

[0081] 2) Quickly mix the solutions obtained above, stir thoroughly, and then quickly transfer the solutions into the polytetrafluoroethylene reaction tank;

[0082] 3) The reaction was maintained under UV light for 10 hours. After polymerization, the prepared gel was immersed in deionized water for solvent exchange. By changing the water every 12 hours, an equilibrium hydrogel with a thickness of 1.0 ± 0.1 mm was obtained after three days.

[0083] Comparative Example 4

[0084] 1) Dissolve 20 parts of N-isopropylacrylamide, 7 parts of stearyl acrylate, 7 parts of acrylic acid, 1 part of N,N'-methylenebisacrylamide, and 1 part of benzophenone in 220 parts of dimethyl sulfoxide, and the mass fraction ratio of stearyl acrylate to acrylic acid is 7:7.

[0085] 2) Quickly mix the solutions obtained above, stir thoroughly, and then quickly transfer the solutions into the polytetrafluoroethylene reaction tank;

[0086] 3) The reaction was maintained under UV light for 10 hours. After polymerization, the prepared gel was immersed in deionized water for solvent exchange. By changing the water every 12 hours, an equilibrium hydrogel with a thickness of 1.0 ± 0.1 mm was obtained after three days.

[0087] Comparative Example 5

[0088] 1) Dissolve 20 parts of N-isopropylacrylamide, 7 parts of stearyl acrylate, 8 parts of acrylic acid, 1 part of N,N'-methylenebisacrylamide, and 1 part of benzophenone in 220 parts of dimethyl sulfoxide, and the mass fraction ratio of stearyl acrylate to acrylic acid is 7:8.

[0089] 2) Quickly mix the solutions obtained above, stir thoroughly, and then quickly transfer the solutions into the polytetrafluoroethylene reaction tank;

[0090] 3) The reaction was maintained under UV light for 10 hours. After polymerization, the prepared gel was immersed in deionized water for solvent exchange. By changing the water every 12 hours, an equilibrium hydrogel with a thickness of 1.0 ± 0.1 mm was obtained after three days.

[0091] Comparative Example 6

[0092] 1) Dissolve 20 parts of N-isopropylacrylamide, 7 parts of stearyl acrylate, 9 parts of acrylic acid, 1 part of N,N'-methylenebisacrylamide, and 1 part of benzophenone in 220 parts of dimethyl sulfoxide, with the mass fraction ratio of stearyl acrylate to acrylic acid being 7:9; 2) Quickly mix the above solutions, stir thoroughly, and then quickly transfer the solution into a polytetrafluoroethylene reaction tank;

[0093] 3) The reaction was maintained under UV light for 10 hours. After polymerization, the prepared gel was immersed in deionized water for solvent exchange. By changing the water every 12 hours, an equilibrium hydrogel with a thickness of 1.0 ± 0.1 mm was obtained after three days.

[0094] summary:

[0095] Comparing Example 1 and Example 3, under the same conditions, increasing the initiator content leads to a shorter hydrogel polymerization time, but the resulting hydrogel has a less uniform texture.

[0096] Comparing Example 1 and Example 4, under the same conditions, increasing the content of dimethyl sulfoxide makes the hydrogel stock solution more uniformly dispersed, thus making the hydrogel polymerized in Example 1 more uniform in texture.

[0097] In Comparative Example 1, the hydrogel's original size was 5.7 cm. After being immersed in a solution with pH > 7 for 15 minutes, it absorbed water, swelled, and softened, changing its size to 6.8 cm. After being immersed in a solution with pH < 7 for 1 minute, it lost water, shrank, and regained its hardness, returning to its original size of 5.7 cm. This cycle took 16 minutes to complete and could be repeated multiple times.

[0098] In Comparative Example 2, the hydrogel originally had a size of 5.5 cm. After being immersed in a solution with pH > 7, it absorbed water, swelled, and softened for 3 minutes, changing its size to 7.7 cm. After being immersed in a solution with pH < 7, it lost water, shrank, and regained its hardness for 4 minutes, changing its size back to the original 5.5 cm. This cycle takes 7 minutes to complete and can be repeated multiple times.

[0099] In Comparative Example 3, the hydrogel's original size was 5.5 cm. After being immersed in a solution with pH > 7 for 15 minutes, it absorbed water, swelled, and softened, changing its size to 6.7 cm. After being immersed in a solution with pH < 7 for 15 minutes, it lost water, shrank, and regained its hardness, returning to its original size of 5.5 cm. This cycle takes 30 minutes to complete and can be repeated multiple times.

[0100] In Comparative Example 4, the hydrogel's original size was 4.8 cm. After being immersed in a solution with pH > 7 for 15 minutes, it absorbed water, swelled, and softened, changing its size to 6.0 cm. After being immersed in a solution with pH < 7 for 15 minutes, it lost water, shrank, and regained its hardness, changing its size back to the original 4.8 cm. This cycle takes 30 minutes to complete and can be repeated multiple times.

[0101] In Comparative Example 5, the hydrogel originally had a size of 4.5 cm. After being immersed in a solution with pH > 7, it absorbed water, swelled, and softened for 10 minutes, changing its size to 6.0 cm. After being immersed in a solution with pH < 7, it lost water, shrank, and regained its hardness for 15 minutes, changing its size back to the original 4.5 cm. This cycle took 25 minutes to complete and could be repeated multiple times.

[0102] In Comparative Example 6, the hydrogel originally had a size of 4.0 cm. After being immersed in a solution with pH > 7 for 25 minutes, it absorbed water, swelled, and softened, changing its size to 4.9 cm. After being immersed in a solution with pH < 7 for 31 minutes, it lost water, shrank, and regained its hardness, returning to its original size of 4.0 cm. This cycle took 56 minutes to complete and could be repeated multiple times.

[0103] Figure 8 , 9The figure shows the shape memory function of the hydrogels prepared in Comparative Examples 1 and 2. As can be seen from the figure, as the mass fraction ratio of stearyl acrylate and acrylic acid increases, the hydrogel does not have a programmable reversible shape movement (i.e., bidirectional shape memory) function.

[0104] In Comparative Examples 1-6, the prepared hydrogels do not have programmable reversible shape movement (i.e., bidirectional shape memory) function, but only pH response function. Furthermore, as the mass fraction ratio of stearyl acrylate to acrylic acid increases, the time for the hydrogel to swell after immersion in alkaline solution shows a trend of first decreasing and then increasing, while the time for it to recover to its original size after immersion in acid solution shows a trend of increasing.

[0105] The present invention is not limited to the specific technical solutions described in the above embodiments. All technical solutions formed by equivalent substitutions are within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a hydrogel with programmable and reversible shape movement and pH dual stimulation responsiveness, characterized in that: Includes the following steps: (1) Dissolve 20 parts of N-isopropylacrylamide 200 mg, 7 parts of stearyl acrylate 70 mg, 3 parts of acrylic acid 30 mg, 1 part of N,N'-methylenebisacrylamide 10 mg, and 1 part of benzophenone 10 mg in 220 parts of dimethyl sulfoxide, and the mass fraction ratio of stearyl acrylate to acrylic acid is 7:

3. (2) Quickly mix the solutions obtained above, stir thoroughly, and then quickly transfer the solutions into the polytetrafluoroethylene reaction tank; (3) The reaction was kept under UV light for 10 hours; after polymerization, the prepared gel was soaked in deionized water for solvent exchange; by changing the water every 12 hours, a balanced hydrogel with a thickness of 1.0 ± 0.1 mm was obtained after three days.

2. The method for preparing a hydrogel with programmable reversible shape movement and pH dual-stimulus responsiveness according to claim 1, characterized in that: It belongs to free radical polymerization, the initiator is benzophenone, and the synthesis is carried out under ultraviolet light irradiation.

3. The method for preparing a hydrogel with programmable reversible shape movement and pH dual-stimulus responsiveness according to claim 1, characterized in that, Hydrogels were synthesized by free radical copolymerization of N-isopropylacrylamide (NIPAM), acrylic acid (AA), stearate acrylate (SA), and N,N'-methylenebisacrylamide (MBA) in dimethyl sulfoxide (DMSO).

4. The hydrogel with programmable reversible shape movement and pH dual-stimulus responsiveness prepared by the method according to claim 1, characterized in that, It is not a single programmable reversible shape movement, i.e., bidirectional shape memory, or a single pH-responsive hydrogel, but rather a combination of programmable reversible shape movement, i.e., bidirectional shape memory, and pH response, in the same hydrogel.

5. The hydrogel with programmable reversible shape movement and pH dual-stimulus responsiveness prepared by the method according to claim 4, characterized in that, The prepared hydrogel has programmable and reversible shape movement, i.e., bidirectional shape memory and pH response. The original size of the hydrogel is 6.5 cm. After being immersed in a solution with pH > 7, it absorbs water, swells and softens in 4.5 min, and its size becomes 8 cm. After being immersed in a solution with pH < 7, it loses water, shrinks and recovers its hardness in 0.5 min, and its size becomes the original 6.5 cm. This cycle can be completed in only 5 minutes and can be repeated multiple times.

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