Hydrogel with programmable reversible shape movement and pH dual stimulation response and preparation method thereof

Abstract

The invention relates to a dual-stimulus-responsive hydrogel with programmable reversible shape movement (namely bidirectional shape memory) and pH (Potential of Hydrogen). The invention belongs to the field of organic polymer materials. According to the method, stearyl acrylate, acrylic acid and N-isopropylacrylamide are copolymerized through free radical copolymerization, the method is wide in raw material source, simple to operate and easy for industrial production, and the dual-stimulus-responsive hydrogel prepared by the method is a brand new material which is never reported and has wide application prospects. The shape memory characteristic is good, the pH sensitivity is high (the whole period of pH softening / enhancing only needs 5 minutes), and the pH range is wide (1-14). The hydrogel with dual effects (good shape memory characteristic and high pH sensitivity) has wide positive effects on drug delivery, control and release in the biomedical field.

Description

Technical Field

[0001] The present invention belongs to the field of polymer materials, and relates to a hydrogel with programmable reversible shape movement (i.e., two-way shape memory) and pH dual stimulus responsiveness and a preparation method thereof, in particular to a method for preparing a hydrogel with two-way shape memory and pH dual stimulus responsiveness based on the combination of N-isopropylacrylamide with stearyl acrylate and acrylic acid. Background Art

[0002] Hydrogel is a soft material composed of a three-dimensional polymer network containing a large amount of water. It has a medium composition similar to that of an organism and good 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, and when the temperature is below the lower critical transition temperature, the gel expands. Based on this property, poly(N-isopropylacrylamide) hydrogel can be used as a temperature-sensitive smart response material. In many application scenarios, it is necessary for the material to respond to changes in external temperature. However, hydrogels that are only temperature-sensitive are limited in practical application scenarios. The current pursuit of smart materials, including double-layer hydrogel actuators, requires feedback to a variety of environmental stimuli. Temperature changes are the most commonly used environmental conditions. Therefore, it is meaningful to use temperature-sensitive materials such as poly(N-isopropylacrylamide) as substrates to produce materials that are sensitive to a variety of environmental stimuli.

[0003] Solid polymers that can perform programmable reversible shape movement (i.e., two-way shape memory) have been discovered. Most typically, such materials have two separate (or wide) crystalline melting transitions. The network anisotropy is introduced for programming using the high melting point transition stage, while heating and cooling through the low melting point transition leads to reversible shape transformation through crystallization-induced elongation and melt-induced contraction. The responsiveness to the pH of the material comes from the ionization of functional side groups on the polymer backbone. When the side functional groups are ionized, the charge density of the hydrogel is redistributed. Due to electrostatic repulsion, two hydrogel backbones with the same charge will separate from each other, making the polymer network looser, ultimately causing the gel to absorb water and swell. Typical representatives of pH-responsive materials include polyacrylic acid, polyacrylamide, and polymethacrylic acid. Summary of the invention

[0004] The present invention is a hydrogel with simple and controllable synthesis and programmable reversible shape movement (i.e., two-way shape memory) and pH dual stimulus responsiveness and a preparation method thereof. The method has a wide source of raw materials, is simple to operate, and is easy to industrialize. The dual stimulus responsiveness 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 (it only takes 5 minutes to complete the entire cycle of pH softening / enhancing) and a wide pH range (1-14). This hydrogel with dual effects (good shape memory characteristics and high pH sensitivity) has a wide range of positive effects on the delivery, control and release of drugs in the biomedical field.

[0005] To achieve the above object, the present invention adopts the following technical solution: a hydrogel having both programmable reversible shape movement (i.e., two-way shape memory) and pH dual stimulus responsiveness is prepared from the following components by mass fraction:

[0006]

[0007]

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

[0009] Preferably, it is a free radical polymerization, the initiator is benzophenone or α-ketoglutaric acid, and the synthesis condition is polymerization under ultraviolet light.

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

[0011] Preferably, instead of a single programmable reversible shape movement (ie, two-way shape memory) or a single pH responsive hydrogel, a dual response of programmable reversible shape movement (ie, two-way shape memory) and pH responsiveness is combined into the same hydrogel.

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

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

[0014] To achieve the above object, the present invention adopts the following technical scheme to achieve it: 1. The preparation method of the responsive hydrogel having both programmable reversible shape movement and pH dual stimulus response comprises the following steps:

[0015] (1) By mass fraction, take 20 parts of N-isopropylacrylamide, 7 parts of shape memory molecules, 3 parts of pH response molecules, 1 part of initiator, 1 part of cross-linking agent, and 165-220 parts of dimethyl sulfoxide;

[0016] (2) N-isopropylacrylamide, shape memory molecules, pH responsive molecules and cross-linking agents were dissolved in dimethyl sulfoxide. After adding the initiator, the solution was quickly transferred into a polytetrafluoroethylene reaction tank. The reaction was irradiated with ultraviolet light for 8-12 hours. After polymerization, the prepared hydrogel was immersed in deionized water for solvent exchange. The water of the hydrogel was then 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, the method comprises the following steps:

[0019] (1) 20 parts of N-isopropyl acrylamide, 7 parts of stearyl acrylate, 3 parts of acrylic acid, 1 part of N,N'-methylenebisacrylamide, and 1 part of benzophenone were dissolved in 220 parts of dimethyl sulfoxide, and the mass fraction ratio of stearyl acrylate to acrylic acid was 7:3;

[0020] (2) The above obtained solutions are quickly mixed, and after being fully stirred, the solutions are quickly transferred to a polytetrafluoroethylene reaction tank;

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

[0022] The solvent is dimethyl sulfoxide, which is a colorless, odorless, transparent liquid at room temperature. It is a hygroscopic flammable liquid with the characteristics of high polarity, high boiling point, non-proton and miscible with water. It has extremely low toxicity, good thermal stability, is not miscible with alkanes, and is soluble in most organic substances such as water, ethanol, propanol, ether, benzene and chloroform. It is known as the "universal solvent" and is one of the commonly used organic solvents with the strongest dissolving ability.

[0023] The present invention also discloses a method for preparing the dual-responsive hydrogel. By free radical copolymerization, stearyl acrylate, acrylic acid and N-isopropylacrylamide are copolymerized. The reversible shape movement of the hydrogel is achieved by combining the melting transition of the stearyl acrylate crystal region with the thermal response volume phase transition of the poly-N-isopropylacrylamide polymer chain. The response to different pH values ​​is achieved by the ionization equilibrium of the carboxyl group in the acrylic acid.

[0024] The low-cost and easy-to-synthesize N-isopropylacrylamide is used as the hydrogel matrix, and poly(N-isopropylacrylamide) is a typical temperature-responsive hydrogel. When the temperature is higher than the lower critical transition temperature (LCST), the gel shrinks, and when the temperature is lower than the lower critical transition temperature (LCST), the gel expands. Based on this property, poly(N-isopropylacrylamide) hydrogel can be used as a temperature-sensitive smart response material.

[0025] Beneficial effects of the present invention:

[0026] 1. The present invention discloses a hydrogel with programmable reversible shape movement (i.e., two-way shape memory) and pH dual stimulus responsiveness. The dual stimulus responsiveness hydrogel prepared by the method is a brand-new material that has never been reported before, and has good shape memory characteristics and high pH sensitivity (it only takes 5 minutes to complete the entire cycle of pH softening / enhancement) and a wide pH range (1-14). This hydrogel with dual effects (good shape memory characteristics and high pH sensitivity) has a wide range of positive effects on the delivery, control and release of drugs in the biomedical field.

[0027] 2. The dual-responsive hydrogels in the present invention exhibit transient structural anisotropy, which is caused by the deformed hydrophobic domains of the stearyl group after thermomechanical programming, which provides a template for the reversible ball-in-loop transformation of the poly(N-isopropylacrylamide) chains. The structural anisotropy is transient and can be eliminated after cooling, allowing repeated programming of reversible shape transformations.

[0028] 3. Use acrylic acid as pH-responsive material to introduce carboxyl groups into hydrogel. Under acidic environmental conditions, due to the hydrogen bonding between carboxyl groups, the distance between chain segments in the network is close, so the swelling rate of the hydrogel is low. As the pH increases, the carboxyl group (-COOH) ionizes into carboxyl anions (-COO - ), which causes the hydrogen bonds between the macromolecular chains in the gel network to dissociate, the electrostatic repulsion between ions to increase, the network structure to become looser, the volume to increase, and then the swelling rate to increase.

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

[0030] 5. Comparing Example 1 with Example 3, when other conditions are the same, increasing the content of the initiator will lead to a decrease in the time of hydrogel polymerization, but the texture of the formed hydrogel is less uniform.

[0031] 6. Comparing Example 1 with Example 4, when other conditions are the same, increasing the content of dimethyl sulfoxide will make the hydrogel stock solution more evenly dispersed, so that the texture of the hydrogel polymerized in Example 1 is more uniform.

[0032] 7. By comparing Example 1 with Comparative Examples 1-6, it can be seen that in Comparative Examples 1-6, the hydrogels prepared do not have a programmable reversible shape movement (i.e., two-way shape memory) function, but only a pH response function, and with the increase of the mass fraction ratio of stearyl acrylate to acrylic acid, the time for the hydrogel to swell when immersed in an alkaline solution tends to first decrease and then increase, and the time for the hydrogel to recover to its original size when immersed in an acid solution again tends to increase; the hydrogel prepared in Example 1 has a dual response of programmable reversible shape movement (i.e., two-way shape memory) and pH response, and has the best performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a SEM image of the network structure of the dual-responsive hydrogel with programmable reversible shape movement (i.e., two-way shape memory) and pH response (Example 1) prepared in the present invention;

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

[0035] Figure 3 Shown in the figure is the swelling kinetics measurement of the dual-responsive hydrogel (Example 1) having programmable reversible shape movement (i.e., two-way shape memory) and pH response prepared by the present invention;

[0036] Figure 4 Shown is the equilibrium swelling curve of the dual-responsive hydrogel with programmable reversible shape movement (i.e., two-way shape memory) and pH response (Example 1) prepared by the present invention in deionized water as the temperature changes;

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

[0038] Figure 6 The equilibrium swelling curves of the prepared dual-responsive hydrogel with programmable reversible shape movement (i.e., two-way shape memory) and pH response (Example 1) at different pH values;

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

[0040] Figure 8 This is a diagram showing the shape memory function of the hydrogel prepared in Comparative Example 1.

[0041] Fig. 9 This is a diagram showing the shape memory function of the hydrogel prepared in Comparative Example 2. DETAILED DESCRIPTION

[0042] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0043] Example 1

[0044] A method for preparing a hydrogel having programmable reversible shape movement (i.e., two-way shape memory) and pH response dual response, comprising 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] The mass fraction ratio of stearyl acrylate to acrylic acid is 7:3;

[0047] 2) The above obtained solutions are quickly mixed, and after sufficient stirring, the solutions are quickly transferred to a 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 also Figure 1 , is a scanning electron microscope photograph of the hydrogel with programmable reversible shape movement (i.e., two-way shape memory) and pH response prepared in Example 1. Figure 1 It can be seen that the hydrogels all show an interconnected porous structure with abundant pores and water transport channels and an average pore size of about 20 μm.

[0050] Figure 2 The infrared spectra of the hydrogel without acrylic acid and the hydrogel with programmable reversible shape movement (i.e., two-way shape memory) and pH response prepared in Example 1 of the present invention are shown in FIG. The hydrogel containing acrylic acid (AA) has an infrared spectrum at 1723 cm -1 The C=O double bond stretching vibration peak appeared at , proving that acrylic acid has been successfully polymerized on the hydrogel.

[0051] Figure 3 The swelling kinetics of the hydrogel with programmable reversible shape movement (i.e., bidirectional shape memory) and pH response prepared in Example 1 of the present invention are shown in the figure. A certain amount of dry gel is immersed in deionized water, removed at regular intervals, and the surface moisture is absorbed with filter paper and weighed until the swelling equilibrium is reached. The swelling rate (SR) of the hydrogel is calculated as follows: SR = ((W t –W d ) / W d ), where W t is the mass of the swollen sample at time t, W d is the mass of the dry sample. Figure 3 The curve of the swelling rate of the hydrogel dry sample immersed in distilled water at 25°C shows that the water absorption rate of the hydrogel is high in the early stage, and decreases in the later stage. After reaching a certain level, the water absorption rate remains basically unchanged, that is, it reaches water absorption saturation. The maximum swelling rate of the hydrogel in distilled water is about 24 mg / mg.

[0052] Figure 4 The temperature response of the hydrogel with programmable reversible shape movement (i.e., two-way shape memory) and pH response prepared in Example 1 of the present invention is shown in the figure. A certain amount of dry gel is immersed in deionized water at different temperatures until swelling equilibrium is reached, and the equilibrium swelling rate at different temperatures is measured respectively. The equilibrium swelling rate (ESR) of the hydrogel is calculated as follows: ESR = ((W s –W d ) / W d ), where W s To balance the mass of the swollen sample, W d is the mass of the dry sample.

[0053] Depend on Figure 4The equilibrium swelling curve of the hydrogel in deionized water with temperature shows that the equilibrium swelling rate of the hydrogel shows a downward trend with the increase of temperature. The hydrogel shows a heat-shrinkage-sensitive property, which is due to the amphiphilicity of the hydrogel. The swelling process of the hydrogel is the process of water molecules diffusing into the gel and forming hydrogen bonds with the hydrophilic groups on the side chains of the gel. When the temperature rises, the vibration energy of the hydrogen bond increases, destroying the restraint of the hydrogen bond and breaking it, and the swelling rate of the hydrogel decreases. When the temperature is lower than the lower critical phase transition temperature (LCST), the hydrogel shows hydrophilicity and swells with water; when the temperature is higher than the LCST, the hydrogel shrinks and forms a collapsed, dehydrated hydrophobic state.

[0054] Figure 5 Shown in the figure is the shape memory function of the hydrogel with programmable reversible shape movement (i.e., two-way shape memory) and pH response dual response prepared by the present invention. In the starting hydrogel in cold water (shape 1, original shape), the poly(N-isopropylacrylamide) chain is in a relaxed random coil state, and the network is isotropic. During hot water programming, the hydrophobic stearyl domain is stretched, and due to hydrophobic interactions, the spherical collapsed poly(N-isopropylacrylamide) will gather around the stearyl domain, thereby temporarily fixing the deformed stearyl domain and the macroscopic shape (shape 2, shape fixed). In this state, poly(N-isopropylacrylamide) also exhibits anisotropy due to the stretching of the chain, and poly(N-isopropylacrylamide) repels water molecules, forming a surrounding water-rich area. After cooling, poly(N-isopropylacrylamide) absorbs more water and slowly relaxes to a hydrophilic coil. This transition behavior cannot be recovered in a short time, which is probably because the hydrophobic stearyl domain slows down this conformational transition. Therefore, there is a transient state in which the orientation of the residual poly(N-isopropylacrylamide) and stearyl domains is kinetically trapped (shape 3). When the kinetically trapped transient hydrogel is immersed in hot water again, the coiling transition process of the poly(N-isopropylacrylamide) chain tends to occur along the direction of the residual poly(N-isopropylacrylamide). Therefore, the hydrogel anisotropically changes toward the programmed shape (shape 4), showing programmable reversible actuation.

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

[0056] Figure 6The following is a diagram showing the equilibrium swelling curves of the hydrogel with programmable reversible shape movement (i.e., two-way shape memory) and pH response at different pH values ​​prepared in Example 1 of the present invention. Different pH aqueous solutions were prepared with hydrochloric acid and sodium hydroxide, and a certain mass of dry gel was weighed and placed in the solution. After being fully soaked, the dry gel was taken out and the surface moisture was wiped off with dry filter paper and weighed. The equilibrium swelling rate at different pH values ​​was measured, and the swelling rate (ESR) of the hydrogel was calculated according to the following formula: ESR = (W s –W d ) / W d , where W s To balance the mass of the swollen sample, W d is the mass of the dry sample. Figure 7 It can be seen that with the increase of pH, the swelling rate of the hydrogel shows a trend of first increasing and then decreasing. This is because the ionization balance of the carboxyl group of the hydrogel, the electrostatic repulsion of ions on the polymer chain, and the balance inside and outside the gel are all related to pH, and the main influencing factor is the electrostatic balance between ions. Under acidic environmental conditions, due to the hydrogen bonding between carboxyl groups, the distance between chain segments in the network is relatively close, so the swelling rate of the hydrogel is low. With the increase of pH, the carboxyl group (-COOH) is charged to the carboxyl group (-COO - ), the hydrogen bonds between the macromolecular chains in the gel network dissociate, the electrostatic repulsion between ions increases, the network structure becomes looser, the volume increases, and the swelling rate increases. However, when the swelling rate reaches a certain value, the pH value increases and the gel no longer swells. The reason is that at this time, the weak acidic groups of the macromolecules are completely dissociated, and the ion concentrations in the gel and the environment tend to be equal.

[0057] Figure 7 What is shown is a pH response demonstration diagram of a hydrogel with programmable reversible shape movement (i.e., two-way shape memory) and pH response dual response prepared by Example 1 of the present invention. The original size of the hydrogel is 6.5 cm. After being immersed in a solution with a pH value of > 7 for 4.5 minutes, it absorbs water, swells, and softens, and its size becomes 8 cm. After being immersed in a solution with a pH value of < 7 for 0.5 minutes, it loses water and shrinks, and its hardness is restored, and its size becomes the original 6.5 cm. It only takes 5 minutes to complete this cycle, and it can be repeated many times.

[0058] Example 2

[0059] A method for preparing a hydrogel having programmable reversible shape movement (i.e., two-way shape memory) and pH response dual response, comprising 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, and the mass fraction ratio of stearyl acrylate to acrylic acid is 7:3; 2) Quickly mix the above obtained solution, and after sufficient stirring, quickly transfer the solution to 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 having programmable reversible shape movement (i.e., two-way shape memory) and pH response dual response, comprising the following steps:

[0064] 1) 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 are dissolved in 220 parts of dimethyl sulfoxide, and the mass fraction ratio of stearyl acrylate to acrylic acid is 7:3; 2) The above obtained solution is quickly mixed, and after sufficient stirring, the solution is quickly transferred to 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 having programmable reversible shape movement (i.e., two-way shape memory) and pH response dual response, comprising the following steps:

[0068] 1) 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 are dissolved in 165 parts of dimethyl sulfoxide, and the mass fraction ratio of stearyl acrylate to acrylic acid is 7:3;

[0069] 2) The above obtained solutions are quickly mixed, and after sufficient stirring, the solutions are quickly transferred to a 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) 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 were dissolved in 220 parts of dimethyl sulfoxide, and the mass fraction ratio of stearyl acrylate to acrylic acid was 7:4;

[0073] 2) The above obtained solutions are quickly mixed, and after sufficient stirring, the solutions are quickly transferred to a 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) 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 were dissolved in 220 parts of dimethyl sulfoxide, and the mass fraction ratio of stearyl acrylate to acrylic acid was 7:5;

[0077] 2) The above obtained solutions are quickly mixed, and after sufficient stirring, the solutions are quickly transferred to a 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) 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 were dissolved in 220 parts of dimethyl sulfoxide, and the mass fraction ratio of stearyl acrylate to acrylic acid was 7:6;

[0081] 2) The above obtained solutions are quickly mixed, and after sufficient stirring, the solutions are quickly transferred to a 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) 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 were dissolved in 220 parts of dimethyl sulfoxide, and the mass fraction ratio of stearyl acrylate to acrylic acid was 7:7;

[0085] 2) The above obtained solutions are quickly mixed, and after sufficient stirring, the solutions are quickly transferred to a 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) 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 were dissolved in 220 parts of dimethyl sulfoxide, and the mass fraction ratio of stearyl acrylate to acrylic acid was 7:8;

[0089] 2) The above obtained solutions are quickly mixed, and after sufficient stirring, the solutions are quickly transferred to a 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, and the mass fraction ratio of stearyl acrylate to acrylic acid is 7:9; 2) Quickly mix the above obtained solution, stir it thoroughly and then quickly transfer the solution to 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 with Example 3, when other conditions are the same, increasing the content of the initiator will shorten the polymerization time of the hydrogel, but the texture of the formed hydrogel is less uniform.

[0096] Comparing Example 1 with Example 4, when other conditions are the same, increasing the content of dimethyl sulfoxide will make the hydrogel stock solution more evenly dispersed, so that the texture of the hydrogel polymerized in Example 1 is more uniform.

[0097] In Comparative Example 1, the original size of the hydrogel was 5.7 cm. After being immersed in a solution with a pH value of more than 7 for 15 minutes, it absorbed water, swelled, and softened, and its size became 6.8 cm. After being immersed in a solution with a pH value of less than 7 for 1 minute, it lost water and shrank, and its hardness recovered, and its size became the original 5.7 cm. It took 16 minutes to complete this cycle, and it could be repeated many times.

[0098] In Comparative Example 2, the original size of the hydrogel was 5.5 cm. After being immersed in a solution with a pH value of more than 7 for 3 minutes, it absorbed water, swelled, and softened, and its size became 7.7 cm. After being immersed in a solution with a pH value of less than 7 for 4 minutes, it lost water and shrank, and its hardness recovered, and its size became the original 5.5 cm. It took 7 minutes to complete this cycle, and it could be repeated many times.

[0099] In Comparative Example 3, the original size of the hydrogel was 5.5 cm. After being immersed in a solution with a pH value of more than 7 for 15 minutes, it absorbed water, swelled, and softened, and its size became 6.7 cm. After being immersed in a solution with a pH value of less than 7 for 15 minutes, it lost water and shrank, and its hardness recovered, and its size became the original 5.5 cm. It took 30 minutes to complete this cycle, and it could be repeated many times.

[0100] In Comparative Example 4, the original size of the hydrogel was 4.8 cm. After being immersed in a solution with a pH value of more than 7 for 15 minutes, it absorbed water, swelled, and softened, and its size became 6.0 cm. After being immersed in a solution with a pH value of less than 7 for 15 minutes, it lost water and shrank, and its hardness was restored, and its size became the original 4.8 cm. It took 30 minutes to complete this cycle, and it could be repeated many times.

[0101] In Comparative Example 5, the original size of the hydrogel was 4.5 cm. After being immersed in a solution with a pH value of more than 7 for 10 minutes, it absorbed water, swelled, and softened, and its size became 6.0 cm. After being immersed in a solution with a pH value of less than 7 for 15 minutes, it lost water and shrank, and its hardness was restored, and its size became the original 4.5 cm. It took 25 minutes to complete this cycle, and it could be repeated many times.

[0102] In Comparative Example 6, the original size of the hydrogel was 4.0 cm. After being immersed in a solution with a pH value of more than 7 for 25 minutes, it absorbed water, swelled, and softened, and its size became 4.9 cm. After being immersed in a solution with a pH value of less than 7 for 31 minutes, it lost water and shrank, and its hardness was restored, and its size became the original 4.0 cm. It took 56 minutes to complete this cycle, and it could be repeated many times.

[0103] Figure 8 , 9What is shown in the figure is the shape memory function of the hydrogel prepared in the test comparative examples 1 and 2. It can be seen from the figure that with the increase of the mass fraction ratio of stearyl acrylate and acrylic acid, the hydrogel does not have the programmable reversible shape movement (i.e., two-way shape memory) function.

[0104] In Comparative Examples 1-6, the prepared hydrogels do not have a programmable reversible shape movement (i.e., two-way shape memory) function, but only a pH response function. Moreover, as the mass fraction ratio of stearyl acrylate to acrylic acid increases, the time for the hydrogel to swell when immersed in an alkaline solution first decreases and then increases, and the time for the hydrogel to recover to its original size when immersed in an acid solution again tends to increase.

[0105] The present invention is not limited to the specific technical solutions described in the above embodiments, and all technical solutions formed by equivalent replacement are within the protection scope required by the present invention.

Claims

1. A hydrogel having both programmable reversible shape movement and pH dual stimulus responsiveness, characterized in that: It is prepared from the following components by mass fraction:

2. The hydrogel having both programmable reversible shape movement and pH dual stimulus responsiveness according to claim 1, characterized in that: It is a free radical polymerization, and it is simple and easy to initiate free radical polymerization using an initiator.

3. The hydrogel having both 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 or α-ketoglutaric acid, and the synthesis condition is polymerization under ultraviolet light.

4. The hydrogel having both programmable reversible shape movement and pH dual stimulus responsiveness according to claim 1, characterized in that: The hydrogels were synthesized by free radical copolymerization of N-isopropylacrylamide (NIPAM), acrylic acid (AA), stearyl acrylate (SA) and N,N'-methylenebisacrylamide (MBA) in dimethyl sulfoxide (DMSO).

5. The hydrogel having both programmable reversible shape movement and pH dual stimulus responsiveness according to claim 1, characterized in that: It is not a single programmable reversible shape movement, i.e., two-way shape memory, or a single pH-responsive hydrogel, but a combination of programmable reversible shape movement, i.e., two-way shape memory, and pH-responsive dual response into the same hydrogel.

6. The hydrogel having both programmable reversible shape movement and pH dual stimulus responsiveness according to claim 1, characterized in that: 1) The melting transition of the stearyl chain segment; 2) The thermal responsiveness of the poly(N-isopropylacrylamide) chain, which corresponds to the volume phase transition (VPT) of the hydrogel. The melting transition is the basis of cooling-induced shape fixation and heating-induced recovery. The VPT is consistent with its lower critical phase transition temperature (LCST), forming the opposite shape memory behavior, namely heating-induced shape fixation and cooling-induced recovery.

7. The hydrogel having both programmable reversible shape movement and pH dual stimulus responsiveness according to claim 1, characterized in that: The responsiveness to the pH of the material comes from the ionization of the functional side groups on the polymer backbone.

8. The method for preparing a hydrogel having both programmable reversible shape movement and pH dual stimulus responsiveness according to claim 1, characterized in that: The following steps are involved: (1) By mass fraction, take 20 parts of N-isopropylacrylamide, 7 parts of shape memory molecules, 3 parts of pH response molecules, 1 part of initiator, 1 part of cross-linking agent, and 165-220 parts of dimethyl sulfoxide; (2) N-isopropylacrylamide, shape memory molecules, pH responsive molecules and cross-linking agents were dissolved in dimethyl sulfoxide. After adding the initiator, the solution was quickly transferred into a polytetrafluoroethylene reaction tank. The reaction was irradiated with ultraviolet light for 8-12 hours. After polymerization, the prepared hydrogel was immersed in deionized water for solvent exchange. The water of the hydrogel was then changed every 12 hours. After 3 days, a hydrogel with a thickness of 1.0±0.1 mm was obtained.

9. The method for preparing a hydrogel having both programmable reversible shape movement and pH dual stimulus responsiveness according to claim 1, characterized in that: The preparation method is simple, the reaction does not require heating, and the risk factor is low.

10. The method for preparing a hydrogel having both programmable reversible shape movement and pH dual stimulus responsiveness according to claim 1, characterized in that: The following steps are involved: (1) 20 parts of N-isopropyl acrylamide, 7 parts of stearyl acrylate, 3 parts of acrylic acid, 1 part of N,N'-methylenebisacrylamide, and 1 part of benzophenone were dissolved in 220 parts of dimethyl sulfoxide, and the mass fraction ratio of stearyl acrylate to acrylic acid was 7:3; (2) The above obtained solutions are quickly mixed, and after being fully stirred, the solutions are quickly transferred to a polytetrafluoroethylene reaction tank; (3) The reaction was maintained under UV light for 10 hours. After polymerization, the prepared gel was immersed in deionized water for solvent exchange. The water was changed every 12 hours, and after three days, an equilibrium hydrogel with a thickness of 1.0±0.1 mm was obtained.

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