Preparation method and application of dynamic-based pH / light dual-response double-layer programmable hydrogel

Abstract

This invention discloses a method for preparing and applying a dynamic pH / light-responsive bilayer programmable hydrogel, belonging to the field of hydrogel materials technology. The purpose of this invention is to address the problems of existing hydrogel materials, such as single crosslinking structure, irreversible crosslinking, difficulty in simultaneously achieving mechanical and responsive properties, single response mode, and insufficient programmable controllability. The method involves: 1. Preparing a borate ester crosslinked PVA-B-O-PVA hydrogel; 2. Preparing a pH / light-responsive bilayer hydrogel. This hydrogel can achieve swelling regulation through reversible breaking and recombination of borate ester bonds under varying acidic and alkaline conditions. Under light irradiation, it achieves photochromism and deformation response through the SP / MC structural transformation of spiropyran molecules. Furthermore, it achieves bending, folding, and programmable motion behavior through the synergistic effect of different functional layers in the bilayer structure. It can be applied to flexible actuators, programmable soft actuators, and environmental response sensors in complex environments.

Description

Technical Field

[0001] This invention belongs to the field of hydrogel materials technology, specifically relating to a method for preparing and applying a dynamic pH / light dual-response bilayer programmable hydrogel. Background Technology

[0002] With the rapid development of smart materials and flexible actuation devices, the application of traditional rigid materials in soft robots, biomimetic devices, and flexible actuators is limited due to their high elastic modulus, limited deformability, and mismatch with the mechanical properties of biological tissues. In contrast, hydrogel materials have attracted widespread attention in the field of smart actuation materials due to their high water content, good flexibility, and excellent biocompatibility. Hydrogels can undergo volume or morphological changes under external stimuli such as temperature, light, pH, electric fields, and chemical environments, making them an important material basis for constructing flexible robots and programmable actuation systems.

[0003] The cross-linking mechanisms of hydrogels mainly include physical cross-linking, permanent covalent cross-linking, and dynamic reversible covalent cross-linking. Although physical cross-linking methods (such as hydrogen bonding, crystalline regions, and molecular chain entanglement) have mild preparation conditions, the cross-linking strength is limited, and structural damage is prone to occur during long-term cyclic deformation. Although traditional permanent covalent cross-linking methods can improve the mechanical strength of hydrogels, once the cross-linked structure is formed, it is difficult to recombine, and the material is prone to irreversible damage after repeated deformation.

[0004] Dynamically covalently crosslinked hydrogels can undergo reversible breakage and recombination under external stimuli, thus exhibiting both high structural stability and tunability. Among them, the borate ester bond, as a typical dynamic covalent bond, can be formed by the condensation reaction of borate groups and vicinal diol structures under alkaline conditions and can dissociate in acidic environments, thus exhibiting excellent pH-responsive properties. Furthermore, by introducing photoresponsive molecules (such as spiropyran) into the hydrogel system, photochromic and photoresponsive deformation capabilities can be acquired, enabling the material to possess multi-stimulus synergistic response characteristics.

[0005] However, existing dynamic borate ester hydrogels still suffer from problems such as simple structure, limited deformation modes, and insufficient functional integration, making it difficult to achieve programmable motion control in complex environments. Therefore, it is necessary to construct a multilayered dynamic borate ester hydrogel system to achieve synergistic regulation of multi-stimulus response behavior. Summary of the Invention

[0006] The purpose of this invention is to address the problems of existing hydrogel materials, such as single crosslinking structure, irreversible crosslinking structure, difficulty in balancing mechanical and responsive properties, single response mode, and insufficient programmable control capability, and to provide a method for preparing and applying a dynamic pH / light dual-response bilayer programmable hydrogel.

[0007] A method for preparing a dynamic pH / light-responsive bilayer programmable hydrogel is specifically carried out according to the following steps:

[0008] I. Preparation of PVA-BO-PVA hydrogel layer crosslinked with borate ester bonds:

[0009] ① Add polyvinyl alcohol to deionized water and stir magnetically until completely dissolved to obtain a uniform and transparent PVA aqueous solution;

[0010] ② Dissolve 4-formylphenylboronic acid in anhydrous ethanol to obtain a 4-formylphenylboronic acid solution;

[0011] ③ Add 4-formylphenylboronic acid solution dropwise to PVA aqueous solution, adjust the pH of the system to 8~10, stir magnetically to cause the boric acid group to undergo a condensation reaction with the vicinal diol structure on the PVA molecular chain, forming a dynamic boric acid ester bond cross-linking network, and obtain mixed solution I;

[0012] ④ The mixed solution I is poured into a mold and subjected to freezing and thawing cycles to form a stable three-dimensional network structure, thus obtaining the first PVA-BO-PVA hydrogel layer;

[0013] II. Preparation of photoresponsive hydrogel layers containing spiropyran structures:

[0014] ① Add polyvinyl alcohol to deionized water and stir magnetically until completely dissolved to obtain a uniform and transparent PVA aqueous solution;

[0015] ② Add hydroxyspiropyran to the PVA aqueous solution and stir under light-protected conditions to make the spiropyran molecules uniformly dispersed in the solution system, thus obtaining mixed solution II;

[0016] ③ Dissolve 4-formylphenylboronic acid in anhydrous ethanol to obtain a 4-formylphenylboronic acid solution;

[0017] ④ Add 4-formylphenylboronic acid solution dropwise to mixed solution II, adjust the pH of the system to 8-10, and stir magnetically to form a dynamic borate ester crosslinking network between the boric acid groups and PVA segments to obtain mixed solution III;

[0018] ⑤ The mixed solution Ⅲ is cast onto the surface of the first PVA-BO-PVA hydrogel layer and subjected to freezing and thawing cycles to form a second PVA-BO-SP functional hydrogel layer on the surface of the first PVA-BO-PVA hydrogel layer, thus obtaining a double-layer hydrogel.

[0019] ⑥ The bilayer hydrogel is washed to obtain a dynamic pH / light dual-response bilayer programmable hydrogel.

[0020] Advantages of this invention:

[0021] I. This invention introduces dynamic borate ester bonds as a crosslinking structure, enabling the hydrogel to undergo reversible fracture and recombination under varying acid and alkaline conditions, thereby improving the material's self-adaptability and cycle stability.

[0022] II. This invention constructs a two-layer hydrogel system, and through the differences in swelling behavior of different functional layers, it achieves controllable bending deformation and improves the motion programmability of hydrogel robots.

[0023] Third, by introducing a spiropyran photoresponsive structure, this invention enables the hydrogel to possess photochromic and photoresponsive deformation capabilities, thereby improving the diversity of the material's stimulus response.

[0024] IV. The preparation method of the present invention has mild conditions, requires no complex equipment, and is easy to scale up.

[0025] V. The hydrogel robot of this invention can generate reversible deformation under pH value changes or light stimulation conditions, and can be applied to programmable motion drive and software execution and manipulation in complex scenarios. It can also be applied to the fields of flexible actuators, bionic actuators and environmental response sensors. Attached Figure Description

[0026] Figure 1 This is a reaction mechanism diagram of the formation of the first PVA-BO-PVA hydrogel layer in step one of Example 1;

[0027] Figure 2 This is a reaction mechanism diagram of the formation of the second PVA-BO-SP functional hydrogel layer in step two of Example 1;

[0028] Figure 3 This is a reaction mechanism diagram of the formation of the bilayer hydrogel in step two of Example 1;

[0029] Figure 4 This is the UV spectrum of SP-OH;

[0030] Figure 5 This is a photograph of the mixed solution III prepared in step two of Example 1, before gelation;

[0031] Figure 6 This is a photograph of the actual product of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1;

[0032] Figure 7The figures show infrared spectra. In the figure, a represents the infrared spectrum of SP-OH, b represents the infrared spectrum of 4-FPBA, c represents the blank PVA hydrogel, d represents the first PVA-BO-PVA hydrogel layer obtained in step one of Example 1, e represents the second PVA-BO-SP functional hydrogel layer obtained in step two of Example 1, and f represents the PVA-BO-PVA / PVA-BO-SP hydrogel obtained in Example 1.

[0033] Figure 8 The figures show X-ray diffraction patterns. In the figure, a represents the X-ray diffraction pattern of the blank PVA hydrogel, b represents the X-ray diffraction pattern of the first PVA-BO-PVA hydrogel layer obtained in step one of Example 1, c represents the X-ray diffraction pattern of the second PVA-BO-SP functional hydrogel layer obtained in step two of Example 1, and d represents the PVA-BO-PVA / PVA-BO-SP hydrogel.

[0034] Figure 9 This is a thermogravimetric analysis diagram of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1;

[0035] Figure 10 The differential scanning calorimetry spectrum of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1 is shown.

[0036] Figure 11 This is a scanning electron microscope image (SEM) image, magnified 50x, of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1.

[0037] Figure 12 This is a scanning electron microscope image of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1, magnified 100 times.

[0038] Figure 13 This is a scanning electron microscope image of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1, magnified 400 times.

[0039] Figure 14 The graph shows the swelling rate of PVA-BO-PVA / PVA-BO-SP bilayer hydrogels over time under different mass ratios of 4-formylphenylboronic acid to polyvinyl alcohol, obtained by preparing the hydrogels according to the method of Example 1, except for changing the amount of 4-formylphenylboronic acid added in steps 1 ② and 2 ③. The mass ratios of 4-formylphenylboronic acid to polyvinyl alcohol are 0.02:1, 0.04:1, 0.06:1, 0.08:1, and 0.10:1, respectively.

[0040] Figure 15This is a graph showing the weight change over time of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1 during a degradation test;

[0041] Figure 16 The figures are tensile stress-strain curves. Figure a represents the tensile stress-strain curve of PVA, and figure b represents the tensile stress-strain curve of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1.

[0042] Figure 17 The figures are compressive stress-strain curves. Figure a represents the compressive stress-strain curve of PVA, and figure b represents the compressive stress-strain curve of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1.

[0043] Figure 18 This is a color change comparison diagram of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1 before and after ultraviolet light irradiation;

[0044] Figure 19 This is the photoresponse color change diagram of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1 under local shading conditions;

[0045] Figure 20 This is a graph showing the color-changing cycling performance of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1 under UV / Vis cyclic irradiation conditions.

[0046] Figure 21 This is a photoresponse rate test diagram of a dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1;

[0047] Figure 22 This is a graph showing the color change of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1 under different light exposure conditions.

[0048] Figure 23 This is a schematic diagram of the patterned color change of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1;

[0049] Figure 24 This is a schematic diagram of the local photoresponse resolution of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1;

[0050] Figure 25 This is a diagram showing the deformation process of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1 under ultraviolet light irradiation.

[0051] Figure 26The graph shows the deformation angle of a bilayer hydrogel prepared according to the method of Example 1, except for the amount of hydroxyspiropyran added in step 2②, as a function of time under ultraviolet light irradiation. SP-0.0 is the control sample without added hydroxyspiropyran, and SP-0.1, SP-0.3, and SP-0.8 are samples with added amounts of 0.10g, 0.30g, and 0.80g of hydroxyspiropyran, respectively.

[0052] Figure 27 This is a test diagram of the deformation stability of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1 under multiple light stimulation cycles.

[0053] Figure 28 This is a diagram of the dynamic continuous deformation process of the pH / light dual-response bilayer programmable hydrogel obtained in Example 1;

[0054] Figure 29 This is a schematic diagram of the loading capacity of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1 under light-driven conditions.

[0055] Figure 30 This is a schematic diagram of motion control of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1 under multi-point light-driven conditions. Detailed Implementation

[0056] Specific Implementation Method 1: This implementation method is a preparation method for a dynamic pH / light dual-response bilayer programmable hydrogel, specifically completed according to the following steps:

[0057] I. Preparation of PVA-BO-PVA hydrogel layer crosslinked with borate ester bonds:

[0058] ① Add polyvinyl alcohol to deionized water and stir magnetically until completely dissolved to obtain a uniform and transparent PVA aqueous solution;

[0059] ② Dissolve 4-formylphenylboronic acid in anhydrous ethanol to obtain a 4-formylphenylboronic acid solution;

[0060] ③ Add 4-formylphenylboronic acid solution dropwise to PVA aqueous solution, adjust the pH of the system to 8~10, stir magnetically to cause the boric acid group to undergo a condensation reaction with the vicinal diol structure on the PVA molecular chain, forming a dynamic boric acid ester bond cross-linking network, and obtain mixed solution I;

[0061] ④ The mixed solution I is poured into a mold and subjected to freezing and thawing cycles to form a stable three-dimensional network structure, thus obtaining the first PVA-BO-PVA hydrogel layer;

[0062] II. Preparation of photoresponsive hydrogel layers containing spiropyran structures:

[0063] ① Add polyvinyl alcohol to deionized water and stir magnetically until completely dissolved to obtain a uniform and transparent PVA aqueous solution;

[0064] ② Add hydroxyspiropyran to the PVA aqueous solution and stir under light-protected conditions to make the spiropyran molecules uniformly dispersed in the solution system, thus obtaining mixed solution II;

[0065] ③ Dissolve 4-formylphenylboronic acid in anhydrous ethanol to obtain a 4-formylphenylboronic acid solution;

[0066] ④ Add 4-formylphenylboronic acid solution dropwise to mixed solution II, adjust the pH of the system to 8-10, and stir magnetically to form a dynamic borate ester crosslinking network between the boric acid groups and PVA segments to obtain mixed solution III;

[0067] ⑤ The mixed solution Ⅲ is cast onto the surface of the first PVA-BO-PVA hydrogel layer and subjected to freezing and thawing cycles to form a second PVA-BO-SP functional hydrogel layer on the surface of the first PVA-BO-PVA hydrogel layer, thus obtaining a double-layer hydrogel.

[0068] ⑥ The bilayer hydrogel is washed to obtain a dynamic pH / light dual-response bilayer programmable hydrogel.

[0069] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the temperature for magnetic stirring in steps one ① and two ① is 85℃~90℃, and the stirring time is 2h~3h. Other steps are the same as in Specific Implementation Method One.

[0070] Specific Implementation Method 3: The difference between this implementation method and Specific Implementation Method 1 or 2 is that the concentration of the PVA aqueous solution mentioned in Step 1 ① and Step 2 ① is 6g / 100mL to 10g / 100mL; the concentration of the 4-formylphenylboronic acid solution mentioned in Step 1 ② and Step 2 ③ is 2% to 10%. The other steps are the same as in Specific Implementation Method 1 or 2.

[0071] Specific Implementation Method Four: The difference between this implementation method and one of Specific Implementation Methods One to Three is that: in step one ③, the mass ratio of 4-formylphenylboronic acid to polyvinyl alcohol in the mixed solution I is (0.02~0.10):1; the magnetic stirring temperature in steps one ③ and two ④ is 85℃~90℃, and the magnetic stirring time is 30min~45min. Other steps are the same as in Specific Implementation Methods One to Three.

[0072] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that: the number of freezing and thawing cycles in steps One (④) and Two (⑤) is 2 to 4 times; the freezing temperature in each freezing and thawing cycle is -20°C, the freezing time is 6 to 10 hours, and the thawing temperature is 25°C, the thawing time is 20 to 40 minutes. Other steps are the same as in Specific Implementation Methods One to Four.

[0073] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that: the stirring time in step two ② is 30 min to 40 min; the hydroxyspiropyran mentioned in step two ② is commercially available hydroxyspiropyran purchased from Maclean; the amount of hydroxyspiropyran added in step two ② is 1% to 10% of the mass of polyvinyl alcohol. Other steps are the same as in Specific Implementation Methods One to Five.

[0074] Specific Implementation Method Seven: The difference between this implementation method and Specific Implementation Methods One to Six is ​​that the mass ratio of 4-formylphenylboronic acid to polyvinyl alcohol in the mixed solution III described in step two, fourth step is (0.02~0.10):1. The other steps are the same as in Specific Implementation Methods One to Six.

[0075] Specific Implementation Method Eight: The difference between this implementation method and Specific Implementation Methods One to Seven is that the cleaning method described in step two (⑥) is as follows: the bilayer hydrogel is immersed in deionized water, and the deionized water is replaced every 12 hours for a total of 48 hours to remove unreacted monomers and residual solvents. The other steps are the same as in Specific Implementation Methods One to Seven.

[0076] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One through Eight in that the dynamic pH / light dual-response bilayer programmable hydrogel described in step two (⑥) is a bilayer heterogeneous structure, wherein: the upper layer is a light-responsive functional layer; the lower layer is a pH-responsive structural layer; and the two layers are bonded to a stable interface through hydrogen bonding and dynamic covalent bonding of borate esters. Other steps are the same as in Specific Implementation Methods One through Eight.

[0077] Specific Implementation Method 10: This implementation method is based on the application of dynamic pH / light dual-response bilayer programmable hydrogel in light-responsive deformation-driven sensors and environmental stimulus-response sensors to achieve programmable motion control in complex scenarios.

[0078] The beneficial effects of the present invention are verified using the following embodiments:

[0079] Example 1: A method for preparing a dynamic pH / light-responsive bilayer programmable hydrogel. In this example, the mass ratio of 4-formylphenylboronic acid to polyvinyl alcohol in the monolayer hydrogel is 0.02:1. Figure 14The 4-FPBA-0.02 sample was used; 0.10 g of hydroxyspiropyran (SP-OH) was used, corresponding to Figure 26 The SP-0.1 sample was prepared using the following steps:

[0080] I. Preparation of PVA-BO-PVA hydrogel layer crosslinked with borate ester bonds:

[0081] ① Add 8g of polyvinyl alcohol (PVA) to 100mL of deionized water, and stir magnetically for 2h at 85℃ water bath and 1000r / min until completely dissolved. Use deionized water to make up to 100mL to obtain a uniform and transparent PVA aqueous solution.

[0082] ② Dissolve 0.16g of 4-formylphenylboronic acid (4-FPBA) in 8mL of anhydrous ethanol and stir at room temperature for 10min to ensure complete dissolution, thus obtaining a 4-formylphenylboronic acid solution.

[0083] ③ Add 4-formylphenylboronic acid solution dropwise to PVA aqueous solution and adjust the pH of the system to 9. Stir magnetically at 85℃ for 30 min to allow the boric acid group to undergo a condensation reaction with the vicinal diol structure on the PVA molecular chain, forming a dynamic boric acid ester bond cross-linking network, and obtain mixed solution I.

[0084] ④ The mixed solution I is poured into a PDMS mold and subjected to freezing and thawing cycles to form a stable three-dimensional network structure, thus obtaining the first PVA-BO-PVA hydrogel layer;

[0085] The freezing and thawing cycle described in step 1, ④, is repeated 3 times; in each freezing and thawing cycle, the freezing temperature is -20℃, the freezing time is 8 hours, the thawing temperature is 25℃, and the thawing time is 30 minutes.

[0086] II. Preparation of photoresponsive hydrogel layers containing spiropyran structures:

[0087] ① Add 8g of polyvinyl alcohol to 100mL of deionized water and stir magnetically at 85℃ for 2 hours until completely dissolved. Use deionized water to bring the solution to a final volume of 100mL to obtain a uniform and transparent PVA aqueous solution.

[0088] ② Add 0.10 g of hydroxyspiropyran (SP-OH) to the PVA aqueous solution and stir magnetically for 30 min under light-protected conditions to uniformly disperse the spiropyran molecules in the solution system, thus obtaining mixed solution II;

[0089] ③ Dissolve 0.16g of 4-formylphenylboronic acid in 8mL of anhydrous ethanol and stir at room temperature for 10min to ensure complete dissolution, thus obtaining a 4-formylphenylboronic acid solution.

[0090] ④ Add 4-formylphenylboronic acid solution dropwise to mixed solution II, adjust the pH of the system to 9, and stir magnetically at 85℃ for 30 min to form a dynamic borate ester crosslinking network between the boric acid groups and PVA segments, thus obtaining mixed solution III;

[0091] ⑤ The mixed solution Ⅲ is cast onto the surface of the first PVA-BO-PVA hydrogel layer and subjected to freezing and thawing cycles to form a second PVA-BO-SP functional hydrogel layer on the surface of the first PVA-BO-PVA hydrogel layer, thus obtaining a double-layer hydrogel.

[0092] The hydroxyspiropyran (SP-OH) mentioned in step 2② was purchased from Maclean's.

[0093] The freezing and thawing cycle described in step 2.⑤ is repeated 3 times; in each freezing and thawing cycle, the freezing temperature is -20℃, the freezing time is 8 hours, the thawing temperature is 25℃, and the thawing time is 30 minutes.

[0094] ⑥ The bilayer hydrogel is washed to obtain a dynamic pH / light dual-response bilayer programmable hydrogel (PVA-BO-PVA / PVA-BO-SP).

[0095] The cleaning method described in step 2⑥ is as follows: Immerse the bilayer hydrogel in deionized water, change the deionized water every 12 hours, and soak continuously for 48 hours to remove unreacted monomers and residual solvents.

[0096] The dynamic pH / light dual-response bilayer programmable hydrogel described in step 2⑥ is a bilayer heterostructure, wherein: the upper layer is a light-responsive functional layer; the lower layer is a pH-responsive structural layer; and the two layers are bonded to a stable interface through hydrogen bonding and dynamic covalent bonding of borate esters.

[0097] Figure 1 This is a reaction mechanism diagram of the formation of the first PVA-BO-PVA hydrogel layer in step one of Example 1;

[0098] pass Figure 1 It is known that under alkaline conditions, the boric acid group in 4-formylphenylboronic acid undergoes a reversible condensation reaction with the vicinal diol structure on the PVA molecular chain to form dynamic borate ester bonds (BO bonds), thereby constructing a cross-linked network structure with reversible breaking and recombination capabilities.

[0099] Figure 2 This is a reaction mechanism diagram of the formation of the second PVA-BO-SP functional hydrogel layer in step two of Example 1;

[0100] pass Figure 2It is known that after introducing hydroxyspiropyran (SP-OH) into the PVA system, it participates in hydrogen bonding to stabilize the network structure on the one hand, and as a photoresponsive unit, it undergoes SP→MC structural transformation under ultraviolet light irradiation, enabling the system to have photochromic and photoresponsive capabilities. At the same time, the borate ester bond continues to serve as a dynamic crosslinking point to maintain network stability.

[0101] Figure 3 This is a reaction mechanism diagram of the formation of the bilayer hydrogel in step two of Example 1;

[0102] Mixed solution III is poured onto the formed PVA-BO-PVA layer, and a double-layer structure is formed through freeze-thaw cycles. Due to the difference in crosslinking density and function, the two layers exhibit different swelling behaviors under external stimuli, thereby driving the whole to bend or deform.

[0103] Figure 4 This is the UV spectrum of SP-OH;

[0104] Depend on Figure 4 It can be seen that SP-OH mainly exhibits a closed-ring state (SP) when not exposed to ultraviolet light, with its absorption peak located in the range of 200-300 nm. Under the action of ultraviolet light, the molecule undergoes a ring-opening reaction to form an MC structure, which will generate a new absorption band in the visible light region, proving that it has typical photochromic properties.

[0105] Figure 5 This is a photograph of the mixed solution III prepared in step two of Example 1, before gelation;

[0106] Figure 6 This is a photograph of the actual product of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1;

[0107] pass Figure 5 and Figure 6 The comparison shows that the system transforms from a flowing solution into a gel with a certain shape retention capability, proving the successful formation of a three-dimensional network structure.

[0108] Figure 7 The figures show infrared spectra. In the figure, a represents the infrared spectrum of SP-OH, b represents the infrared spectrum of 4-FPBA, c represents the blank PVA hydrogel, d represents the first PVA-BO-PVA hydrogel layer obtained in step one of Example 1, e represents the second PVA-BO-SP functional hydrogel layer obtained in step two of Example 1, and f represents the PVA-BO-PVA / PVA-BO-SP hydrogel obtained in Example 1.

[0109] Depend on Figure 7 It can be determined that: 1200-1400cm -1 A characteristic absorption peak for BO bonds appears at 1550 cm⁻¹.-1 With 1250cm -1 The presence of a spiropyran characteristic peak at the location proves that the boronic ester bond was successfully formed and the photoresponsive molecule was successfully introduced.

[0110] Figure 8 The figures show X-ray diffraction patterns. In the figure, a represents the X-ray diffraction pattern of the blank PVA hydrogel, b represents the X-ray diffraction pattern of the first PVA-BO-PVA hydrogel layer obtained in step one of Example 1, c represents the X-ray diffraction pattern of the second PVA-BO-SP functional hydrogel layer obtained in step two of Example 1, and d represents the PVA-BO-PVA / PVA-BO-SP hydrogel.

[0111] Depend on Figure 8 It can be seen that pure PVA exhibits a broad peak at 2θ≈20°, indicating an amorphous structure. After introducing borate ester bonds and spiropyran, the diffraction peak intensity decreases and broadens, proving that the cross-linking structure disrupts the regular stacking of chain segments, increasing the amorphous degree of the system.

[0112] Figure 9 This is a thermogravimetric analysis diagram of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1;

[0113] Depend on Figure 9 It can be seen that the hydrogel decomposition process is mainly divided into three stages: the low temperature zone is the volatilization of bound water, the medium temperature zone is the breakage of borate ester bonds and the decomposition of the main chain, and the high temperature zone is the degradation of the carbon skeleton; the thermal stability of the system containing BO bonds is significantly better than that of pure PVA.

[0114] Figure 10 The differential scanning calorimetry spectrum of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1 is shown.

[0115] Depend on Figure 10 It can be seen that after the introduction of borate ester bonds, the hydrogel backbone decomposition peak shifts to the high-temperature region, proving that the dynamic cross-linking structure enhances the thermal stability of the system.

[0116] Figure 11 This is a scanning electron microscope image (SEM) image, magnified 50x, of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1.

[0117] Figure 12 This is a scanning electron microscope image of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1, magnified 100 times.

[0118] Figure 13 This is a scanning electron microscope image of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1, magnified 400 times.

[0119] Depend on Figure 11-13It can be seen that the borate ester bond hydrogel exhibits a typical hydrogel microstructure, with continuous and densely connected pores of varying sizes.

[0120] The dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1 was immersed in deionized water at room temperature. The water was removed at different time points, and the surface moisture was blotted dry with filter paper before weighing. The process continued until the gel weight no longer changed. The results are shown in [Figure 1]. Figure 14 ;

[0121] Figure 14 The graph shows the swelling rate of PVA-BO-PVA / PVA-BO-SP bilayer hydrogels over time under different mass ratios of 4-formylphenylboronic acid to polyvinyl alcohol, obtained by preparing the hydrogels according to the method of Example 1, except for changing the amount of 4-formylphenylboronic acid added in steps 1 ② and 2 ③. The mass ratios of 4-formylphenylboronic acid to polyvinyl alcohol are 0.02:1, 0.04:1, 0.06:1, 0.08:1, and 0.10:1, respectively.

[0122] Depend on Figure 14 It can be seen that the dynamic pH / light dual-response bilayer programmable hydrogel obtained in this invention, after being soaked in deionized water for 12 hours, showed a swelling rate that increased to 712.06% and then tended to stabilize, exhibiting good swelling performance.

[0123] Figure 15 This is a graph showing the weight change over time of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1 during a degradation test;

[0124] Depend on Figure 15 It can be seen that the borate ester bond gel did not undergo significant degradation in phosphate buffer solution, indicating that the hydrogel has good stability and is suitable for long-term use in in vitro environments.

[0125] Figure 16 The figures are tensile stress-strain curves. Figure a represents the tensile stress-strain curve of PVA, and figure b represents the tensile stress-strain curve of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1.

[0126] Figure 17 The figures are compressive stress-strain curves. Figure a represents the compressive stress-strain curve of PVA, and figure b represents the compressive stress-strain curve of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1.

[0127] Depend on Figure 16 and 17 It can be seen that the improved mechanical properties and toughness of the gel, and the required stress for the same tensile / compressive deformation, are significantly increased.

[0128] Figure 18This is a color change comparison diagram of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1 before and after ultraviolet light irradiation;

[0129] Depend on Figure 18 It can be seen that under ultraviolet light irradiation, the hydrogel gradually changes from colorless to colored, proving that the hydroxyspiropyran in the system undergoes a transformation from a closed-ring structure (SP) to an open-ring structure (MC), thereby endowing the hydrogel with good photochromic properties.

[0130] Figure 19 This is the photoresponse color change diagram of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1 under local shading conditions;

[0131] Depend on Figure 19 It can be seen that only the ultraviolet light irradiated area shows a significant color change, while the unirradiated area remains unchanged, proving that the hydrogel has good spatially selective light response capability.

[0132] Figure 20 This is a graph showing the color-changing cycling performance of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1 under UV / Vis cyclic irradiation conditions.

[0133] from Figure 20 It can be seen that the hydrogel can still achieve stable color change and recovery during multiple cycles, proving that it has good photoresponse reversibility and cycle stability.

[0134] Figure 21 This is a photoresponse rate test diagram of a dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1;

[0135] from Figure 21 It can be seen that under ultraviolet light irradiation, the hydrogel can complete the color change in a short time and can gradually recover under visible light or light-protected conditions, proving that the system has a fast response rate.

[0136] Figure 22 This is a graph showing the color change of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1 under different light exposure conditions.

[0137] from Figure 22 It can be seen that as the illumination time increases or the light intensity increases, the color of the hydrogel gradually deepens, proving that the photoresponse degree is positively correlated with the light energy input. The mechanism is that more SP molecules are converted into MC structures, resulting in an increase in the proportion of conjugated structures in the system.

[0138] Figure 23 This is a schematic diagram of the patterned color change of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1;

[0139] from Figure 23 It can be seen that by designing the illumination area, a specific pattern of color change can be formed on the surface of the hydrogel, proving that the system has good patterning response capability and can realize spatial encoding of light information. Its essence is that the light field distribution controls the molecular structure transformation region.

[0140] Figure 24 This is a schematic diagram of the local photoresponse resolution of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1;

[0141] from Figure 24 It can be seen that a high-resolution color response can be achieved under local illumination, proving that the hydrogel system has the ability to finely regulate space and can achieve precise control of molecular structure response within the microscale range.

[0142] Figure 25 This is a diagram showing the deformation process of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1 under ultraviolet light irradiation.

[0143] from Figure 25 It can be seen that the hydrogel undergoes bending deformation under light, proving that light stimulation not only induces changes in molecular configuration, but also causes swelling differences in different regions of the gel by changing local hydrophilicity and network structure, thereby forming internal stress and driving macroscopic deformation.

[0144] Figure 26 The graph shows the deformation angle of a bilayer hydrogel prepared according to the method of Example 1, except for the amount of hydroxyspiropyran added in step 2②, as a function of time under ultraviolet light irradiation. SP-0.0 is the control sample without added hydroxyspiropyran, and SP-0.1, SP-0.3, and SP-0.8 are samples with added amounts of 0.10g, 0.30g, and 0.80g of hydroxyspiropyran, respectively.

[0145] from Figure 26 It can be seen that as the illumination time increases, the bending angle of the hydrogel gradually increases, proving that the deformation behavior is time-dependent. The mechanism is that the molecular structure transformation in the light-response region gradually accumulates, leading to a continuous increase in the swelling difference.

[0146] Figure 27 This is a test diagram of the deformation stability of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1 under multiple light stimulation cycles.

[0147] from Figure 27 It can be seen that the system maintains stable deformation capacity after multiple light exposure and recovery cycles, which proves that the dynamic reversibility of borate ester bonds in the system can effectively alleviate stress concentration and maintain network integrity, thereby improving cycle stability.

[0148] Figure 28 This is a diagram of the dynamic continuous deformation process of the pH / light dual-response bilayer programmable hydrogel obtained in Example 1;

[0149] from Figure 28 It can be seen that hydrogels can achieve continuous deformation or motion behavior under continuous or changing light conditions, proving that the system has good dynamic response capability, which is essentially due to the synergistic effect between the photoresponsive unit and the dynamic cross-linking network.

[0150] Figure 29 This is a schematic diagram of the loading capacity of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1 under light-driven conditions.

[0151] from Figure 29 It can be seen that the hydrogel can still bear a certain external load during the deformation process, which proves that the hydrogel maintains a certain mechanical strength while having responsive properties. The mechanism lies in the multi-crosslinked network structure jointly constructed by borate ester bonds and hydrogen bonds.

[0152] Figure 30 This is a schematic diagram of motion control of the dynamic pH / light dual-response bilayer programmable hydrogel obtained in Example 1 under multi-point light-driven conditions;

[0153] from Figure 30 It can be seen that bending and movement in different directions can be achieved by changing the position and method of illumination, which proves that the hydrogel system has good programmable driving capability. Its essence is the result of the combined effect of local structural changes induced by light stimulation and the overall network synergistic response.

Claims

1. A method for preparing a dynamic pH / light-responsive bilayer programmable hydrogel, characterized in that... The preparation method is specifically carried out according to the following steps: I. Preparation of PVA-BO-PVA hydrogel layer crosslinked with borate ester bonds: ① Add polyvinyl alcohol to deionized water and stir magnetically until completely dissolved to obtain a uniform and transparent PVA aqueous solution; ② Dissolve 4-formylphenylboronic acid in anhydrous ethanol to obtain a 4-formylphenylboronic acid solution; ③ Add 4-formylphenylboronic acid solution dropwise to PVA aqueous solution, adjust the pH of the system to 8~10, stir magnetically to cause the boric acid group to undergo a condensation reaction with the vicinal diol structure on the PVA molecular chain, forming a dynamic boric acid ester bond cross-linking network, and obtain mixed solution I; ④ The mixed solution I is poured into a mold and subjected to freezing and thawing cycles to form a stable three-dimensional network structure, thus obtaining the first PVA-BO-PVA hydrogel layer; II. Preparation of photoresponsive hydrogel layers containing spiropyran structures: ① Add polyvinyl alcohol to deionized water and stir magnetically until completely dissolved to obtain a uniform and transparent PVA aqueous solution; ② Add hydroxyspiropyran to the PVA aqueous solution and stir under light-protected conditions to make the spiropyran molecules uniformly dispersed in the solution system, thus obtaining mixed solution II; ③ Dissolve 4-formylphenylboronic acid in anhydrous ethanol to obtain a 4-formylphenylboronic acid solution; ④ Add 4-formylphenylboronic acid solution dropwise to mixed solution II, adjust the pH of the system to 8-10, and stir magnetically to form a dynamic borate ester crosslinking network between the boric acid groups and PVA segments to obtain mixed solution III; ⑤ The mixed solution Ⅲ is cast onto the surface of the first PVA-BO-PVA hydrogel layer and subjected to freezing and thawing cycles to form a second PVA-BO-SP functional hydrogel layer on the surface of the first PVA-BO-PVA hydrogel layer, thus obtaining a double-layer hydrogel. ⑥ The bilayer hydrogel is washed to obtain a dynamic pH / light dual-response bilayer programmable hydrogel.

2. The method for preparing a dynamic pH / light-responsive bilayer programmable hydrogel according to claim 1, characterized in that... The temperature for magnetic stirring in steps 1① and 2① is 85℃~90℃, and the stirring time is 2h~3h.

3. The method for preparing a dynamic pH / light-responsive bilayer programmable hydrogel according to claim 1, characterized in that... The concentration of the PVA aqueous solution mentioned in Step 1① and Step 2① is 6g / 100mL to 10g / 100mL; the concentration of the 4-formylphenylboronic acid solution mentioned in Step 1② and Step 2③ is 2% to 10%.

4. The method for preparing a dynamic pH / light-responsive bilayer programmable hydrogel according to claim 1, characterized in that... In step 1, ③, the mass ratio of 4-formylphenylboronic acid to polyvinyl alcohol in the mixed solution I is (0.02~0.10):1; the magnetic stirring temperature in steps 1, ③ and 2, ④ is 85℃~90℃, and the magnetic stirring time is 30min~45min.

5. The method for preparing a dynamic pH / light-responsive bilayer programmable hydrogel according to claim 1, characterized in that... The freezing and thawing cycle described in Step 1, ④ and Step 2, ⑤ is repeated 2 to 4 times. During each freezing and thawing cycle, the freezing temperature is -20℃, the freezing time is 6 to 10 hours, the thawing temperature is 25℃, and the thawing time is 20 to 40 minutes.

6. The method for preparing a dynamic pH / light-responsive bilayer programmable hydrogel according to claim 1, characterized in that... The stirring time in step 2② is 30 min to 40 min; the hydroxyspiropyran mentioned in step 2② is commercially available hydroxyspiropyran purchased from Maclean; the amount of hydroxyspiropyran added in step 2② is 1% to 10% of the mass of polyvinyl alcohol.

7. The method for preparing a dynamic pH / light-responsive bilayer programmable hydrogel according to claim 1, characterized in that... In step 2, the mass ratio of 4-formylphenylboronic acid to polyvinyl alcohol in the mixed solution III is (0.02~0.10):

1.

8. The method for preparing a dynamic pH / light-responsive bilayer programmable hydrogel according to claim 1, characterized in that... The cleaning method described in step 2⑥ is as follows: immerse the bilayer hydrogel in deionized water, changing the deionized water every 12 hours, and continue immersion for 48 hours to remove unreacted monomers and residual solvents.

9. The method for preparing a dynamic pH / light-responsive bilayer programmable hydrogel according to claim 1, characterized in that... The dynamic pH / light dual-response bilayer programmable hydrogel described in step 2⑥ is a bilayer heterostructure, wherein: the upper layer is a light-responsive functional layer; the lower layer is a pH-responsive structural layer; and the two layers are bonded to a stable interface through hydrogen bonding and dynamic covalent bonding of borate esters.

10. The application of the dynamic pH / light dual-response bilayer programmable hydrogel prepared by the preparation method according to any one of claims 1 to 9, characterized in that... The application of dynamic pH / light dual-response bilayer programmable hydrogels in light-responsive deformation-driven sensors and environmental stimulus-responsive sensors enables programmable motion control in complex scenarios.

Images