Food colorant-enhanced HPC photonic gels, food colorant-enhanced HPC photonic gel films, and preparation thereof

Abstract

The invention discloses an edible pigment reinforced HPC photon gel, an edible pigment reinforced HPC photon gel film and preparation of the edible pigment reinforced HPC photon gel and the edible pigment reinforced HPC photon gel film. The HPC photon gel contains a food colorant as a background color material, the food colorant is uniformly dispersed in the HPC photon gel, the food colorant is a hydrophilic food colorant or a hydrophobic food colorant, and when the food colorant is the hydrophilic food colorant, the dispersion medium is water; when the food coloring is a hydrophobic food coloring, the dispersion medium is a combination of water and a cosolvent, and the mass of the cosolvent does not exceed 30% of the mass of the water. The invention further provides an edible pigment reinforced HPC photon hydrogel film prepared from the edible pigment reinforced HPC photon hydrogel. The food coloring is introduced as the background color, so that the material is endowed with antioxidant activity and a pH response function while the visual recognition degree of the HPC photon hydrogel structural color is improved.

Description

Technical Field

[0001] This invention relates to the field of functional materials technology, specifically to an edible pigment-enhanced HPC (hydroxypropyl cellulose) photonic gel and its preparation method, and an edible pigment-enhanced HPC (hydroxypropyl cellulose) photonic gel film and its preparation method. Background Technology

[0002] Structural color is a color produced by the interaction of the ordered structure of a material at the microscopic or nanoscale with light. It possesses advantages such as high color saturation, resistance to fading, and environmental friendliness, showing broad application prospects in optical displays, anti-counterfeiting packaging, intelligent sensing, and food materials. Hydroxypropyl cellulose (HPC) is an abundant and easily degradable polymer material that can form a chiral nematic liquid crystal phase and produce structural color in high-concentration aqueous solutions (60–70 wt%). However, to ensure clear display of its structural color, a background color is often needed to enhance its contrast with the environment, thereby improving visual recognition. Furthermore, the structural color of HPC gels can be flexibly controlled by adjusting the water content (30–40 wt%), applying external stimuli (such as temperature, pressure, tension, etc.), or regulating intermolecular interactions (such as hydrogen bonding, covalent crosslinking, electrostatic interactions, etc.). This tunable characteristic significantly broadens the application range of HPC in advanced photonic materials. Therefore, how to improve the visual recognition of structural color in HPC systems and achieve controllable adjustment has become a key issue in promoting the expansion of photonic gel applications.

[0003] In the application of photonic gels, a background material with high absorbency is usually introduced to enhance the contrast of the structural color of HPC photonic gels. However, existing background color materials suffer from problems such as biotoxicity, limited functionality, and lack of responsiveness, which seriously restricts the expansion of HPC photonic gel applications. For example, patent CN117050250A uses carbon black as the gel background color, which can improve the visual recognition of the structural color, but carbon black itself has limited functionality and lacks bioactivity and responsiveness, which is not conducive to the development of multifunctional materials. Patent CN119220242A utilizes MXene two-dimensional nanosheets as a broadband absorber and a black substrate, which not only significantly improves the color saturation of nanocellulose liquid crystals but also endows the material with flexible and tunable initial color and dynamic color-changing response capabilities; however, MXene is prone to oxidative degradation in humid environments, exhibiting insufficient stability. Another patent, CN116607227A, uses more stable carbon nanotubes as the background color, leveraging their excellent conductivity to introduce electronic sensing functions into the material; however, studies have shown that carbon nanotubes may induce lung inflammation, posing a potential biosafety risk.

[0004] Besides background color selection, the structural color regulation and performance improvement of HPC gels also rely on the introduction of functional additives. However, existing additives generally have limitations such as health risks or limited functionality. For example, patent CN116731357A uses glutaraldehyde for covalent cross-linking, which enhances the flexibility and durability of the material while adjusting the structural color. However, glutaraldehyde is highly irritating and toxic to the skin, eyes, and respiratory tract, and long-term exposure may cause allergic reactions, posing a safety hazard. Patent CN119350720A uses small-molecule carboxylic acids as additives, which can adjust the structural color and improve the flexibility and strength of HPC films to a certain extent, and has relatively high safety. However, its effect is mainly limited to enhancing mechanical properties, and it is difficult to impart additional functions such as antibacterial or antioxidant properties. These problems restrict the further promotion and application of HPC structural color materials in the field of photonic functional materials technology.

[0005] Therefore, this invention proposes and constructs an HPC photonic gel reinforced with food coloring and natural eutectic solvent (NADES) and its preparation method. This system, by introducing food coloring as a background color, enhances the visual recognition of the structural color while also endowing the material with multiple functional properties such as antioxidant activity and pH response. Furthermore, this invention further combines the food coloring-reinforced HPC photonic gel with NADES, simultaneously enhancing the material's mechanical properties. In summary, the food coloring and NADES synergistically reinforced HPC photonic gel constructed in this invention possesses high visual recognition, multiple responsiveness, antioxidant properties, antibacterial properties, and good biocompatibility, providing a new strategy for developing green and efficient photonic functional materials. Summary of the Invention

[0006] To overcome the limitations and shortcomings of the existing technology, the first technical problem to be solved by the present invention is to provide an HPC photonic gel enhanced with food coloring. By introducing food coloring as a background color, the visual recognition of the structural color of the HPC photonic gel is improved, while the material is endowed with antioxidant activity and pH response function.

[0007] The second technical problem to be solved by the present invention is to provide a method for preparing HPC photonic gel enhanced with food coloring.

[0008] The third technical problem to be solved by the present invention is to provide an HPC photonic gel membrane enhanced with food coloring.

[0009] The fourth technical problem to be solved by the present invention is to provide a method for preparing an HPC photonic gel film enhanced with food coloring.

[0010] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides an HPC photonic gel reinforced with food coloring. The HPC photonic gel comprises an HPC gel framework and a dispersion medium, and further contains food coloring as a background color material. The food coloring is uniformly dispersed in the HPC photonic gel. The food coloring is either hydrophilic or hydrophobic. When the food coloring is hydrophilic, the dispersion medium is water; when the food coloring is hydrophobic, the dispersion medium is a combination of water and a cosolvent, wherein the cosolvent is capable of dissolving the hydrophobic food coloring, and the mass of the cosolvent does not exceed 30% of the mass of water. In the HPC photonic gel, the dispersion medium content is 32-38 wt%, and the food coloring content is 0.001-0.06 wt%.

[0011] In some embodiments, the hydrophilic food coloring is anthocyanin or sodium copper chlorophyllin. In a preferred embodiment, in the anthocyanin (C3G) or sodium copper chlorophyllin (SCC)-reinforced HPC photonic gel, the dispersion medium is water, with a water content of 32-38 wt% and anthocyanin or sodium copper chlorophyllin content of 0.01-0.06 wt%. In some preferred embodiments, the anthocyanin or sodium copper chlorophyllin content is 0.03-0.04%. Further, the anthocyanin (C3G) or sodium copper chlorophyllin (SCC)-reinforced HPC photonic gel is composed of an HPC gel framework, a dispersion medium, and a food coloring.

[0012] In some embodiments, the hydrophobic food coloring is curcumin (CUR) or lutein (Lut), and the dispersion medium is a combination of water and ethanol, wherein the mass of ethanol is 15-25% of the mass of water. In a preferred embodiment, in the curcumin or lutein-enhanced HPC photonic gel, the dispersion medium is a combination of water and ethanol, wherein the mass of ethanol is 15-25% of the mass of water, the dispersion medium content in the HPC photonic gel is 32-38 wt%, and the content of anthocyanin or sodium copper chlorophyllin is 0.001-0.005 wt%. In some preferred embodiments, the mass of ethanol is 20% of the mass of water, and the content of anthocyanin or sodium copper chlorophyllin is 0.002-0.003 wt%. Further, the curcumin or lutein-enhanced HPC photonic gel is composed of an HPC gel framework, a dispersion medium, and a food coloring.

[0013] In a preferred embodiment, the HPC photonic gel further contains a natural eutectic solvent (NADES), which is selected from one of the following: ① Choline chloride-citric acid-pure water system (Ch-CA), wherein the molar ratio of choline chloride to citric acid is 2:1, and the pure water content is 20wt% (Chcl:CA, molar ratio 2:1, with 20wt% pure water added). ② Fructose-citric acid-pure water system (Fru-CA), wherein the molar ratio of fructose, citric acid and pure water is 1:1:5; The HPC photonic gel contains 5-10 wt% natural eutectic solvent and 32-35 wt% dispersion medium. This invention further introduces NADES into the HPC photonic gel, utilizing its charge interaction and hydrogen bond network to achieve precise control of the HPC structural color; the plasticizing effect of NADES also enhances the gel's mechanical properties (flexibility) and imparts additional antibacterial properties to the material. Furthermore, the HPC photonic gel is composed of an HPC gel framework, dispersion medium, natural eutectic solvent, and food coloring.

[0014] In a second aspect, the present invention provides a method for preparing the food coloring-enhanced HPC photonic gel described in the first aspect, comprising the following steps: Step 1: Mix the food coloring, dispersion medium and HPC to obtain a mixed solution containing food coloring and HPC; Step 2: The mixed solution containing food coloring and HPC obtained in step (1) is placed in a water bath at 25-35℃ for 1.5-2 hours. The mixed solution after water bath is stirred thoroughly to make the components evenly distributed. Then, the air bubbles are removed by centrifugation at room temperature. The centrifuged gel is stored at 4-25℃ until the structural color is uniform to obtain the food coloring-enhanced HPC photonic gel.

[0015] Preferably, the preparation method further includes: in step 2, adding a natural eutectic solvent to the mixed solution after water bath, and then continuing the subsequent operations of step 2, that is, stirring thoroughly to make the water evenly distributed, and then removing air bubbles by centrifugation at room temperature. The centrifuged gel is stored at 4-25℃ until the structural color is uniform to obtain the food coloring-enhanced HPC photonic gel.

[0016] Preferably, in step 2, the water bath temperature is 30-35℃, more preferably 33℃; and the water bath time is 1.5-2 hours, more preferably 2 hours.

[0017] Preferably, in step 2, the stirring conditions are 50-70 minutes, more preferably 60 minutes.

[0018] Preferably, in step 2, the centrifugation conditions are 10,000-12,000 rpm for 25-45 minutes, and more preferably, 12,000 rpm for 45 minutes.

[0019] Preferably, in step 2, the storage condition is 4°C.

[0020] Thirdly, the present invention provides an edible pigment-enhanced HPC photonic gel membrane made from the edible pigment-enhanced HPC photonic gel described in the first aspect.

[0021] Fourthly, the present invention provides a method for preparing the food coloring-enhanced HPC photonic gel film described in the third aspect, comprising the following steps: Step 1: The food coloring-enhanced HPC photonic gel described in the first aspect is uniformly coated onto a glass slide, and then the glass slide containing the gel layer is sealed and stored in an environment of 4-25°C until the structural color of the gel is uniform. Step 2: Place the glass slide containing the gel layer, which was stored in Step 1, in an oven at 60-100℃ and dry it to constant weight. Peel the gel layer off the glass slide to obtain the HPC photonic gel film reinforced with food coloring.

[0022] Preferably, the gel storage temperature in step 1 is 4°C.

[0023] Preferably, the drying temperature in step 2 is 70°C, and the product is dried to a constant weight.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. In the HPC photonic gel system described in this invention, edible pigments are innovatively introduced as a background color to replace the traditional black substrate material. These pigments are safe, non-toxic, and environmentally friendly, improving the visual recognition of HPC structural colors. Simultaneously, edible pigments also possess physiologically beneficial properties. For hydrophilic pigments, such as anthocyanins and chlorophyll derivatives, they not only exhibit excellent antioxidant activity (chlorophyll derivatives demonstrate good light / thermal stability), but anthocyanins are also highly sensitive to pH values, providing the photonic gel with additional environmental pH responsiveness. For hydrophobic pigments, such as curcumin and lutein, they possess anti-inflammatory effects, further broadening the application of photonic gels in functional food packaging and biomedical fields. For these pigments, this invention introduces ethanol as a co-solvent, not only solving the dissolution problem of hydrophobic pigments in aqueous HPC systems, but also achieving synergistic control of the photonic crystal pitch through the swelling effect of ethanol.

[0025] 2. This invention introduces NADES into a food coloring-enhanced HPC gel system. NADES, a green solvent system formed by natural small molecules through hydrogen bonding, can regulate the intermolecular interactions of HPC through electrostatic interactions and hydrogen bonding. This suppresses the blue shift of the structural color during the heating and drying process, improving its structural color stability and thus enabling more precise control of the target color. Simultaneously, NADES possesses excellent plasticizing ability, effectively improving the mechanical properties of the HPC gel. Ch-CA enhances toughness, while Fru-CA simultaneously strengthens both strength and extensibility. Furthermore, the antibacterial and antioxidant properties of NADES add additional functional value to the material. Therefore, the addition of NADES achieves a multi-functional integration of controllable structural color, improved mechanical properties, and antibacterial properties.

[0026] 3. This invention integrates multiple functions by introducing food coloring and NADES into the HPC gel system, thus constructing a multifunctional gel system with high recognition, adjustable structural color, enhanced mechanical properties, antibacterial and antioxidant properties. This design has significant application potential in the fields of food coloring agents, smart food packaging, smart sensing, and multifunctional photonic materials. Attached Figure Description

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0028] Figure 1 A typical preparation flow chart of food coloring and NADES-enhanced HPC photonic gel.

[0029] Figure 2 Images and reflection spectra of HPC photonic gels prepared in Examples 1-6 and food coloring-enhanced HPC photonic gels prepared in Examples 1-14 of Product 1.

[0030] Figure 3 Schematic diagram of structural color changes at different temperatures for aniline black-enhanced HPC photonic gels prepared in Comparative Examples 1-4 and food coloring-enhanced HPC photonic gels prepared in Examples 1-8 of Product 1.

[0031] Figure 4 Schematic diagram of structural color changes before and after pressing of aniline black-enhanced HPC photonic gel prepared in Examples 1-4 of Product 1 and food coloring-enhanced HPC photonic gel prepared in Examples 1-8 of Product 1.

[0032] Figure 5 : Schematic diagram of structural color changes before and after stretching of aniline black-reinforced HPC photonic gels prepared in Comparative Examples 1-4 and food coloring-reinforced HPC photonic gels prepared in Examples 1-8 of Product 1.

[0033] Figure 6 pH response of the aniline black-enhanced HPC photonic gel prepared in Example 3 of Product 1 and the anthocyanin-enhanced HPC photonic gel prepared in Example 3 of Product 1.

[0034] Figure 7 The antioxidant activity of the aniline black-enhanced HPC photonic gel prepared in Example 3 of Product 1 and the food coloring-enhanced HPC photonic gel prepared in Examples 3 and 7 of Product 1 was compared. Among them, HPC / No-BC: HPC photonic gel with no background color and a water content of 36%; HPC / Nig-36%: HPC photonic gel with aniline black as the background color and a water content of 36%; HPC / C3G-36%: HPC photonic gel with anthocyanin as the background color and a water content of 36%; HPC / SCC-36%: HPC photonic gel with sodium copper chlorophyllin as the background color and a water content of 36%.

[0035] Figure 8 Product 2 Examples 1-7: Physical images and reflection spectra of the food coloring and NADES-enhanced HPC photonic gel prepared.

[0036] Figure 9 : Schematic diagram of the structural color changes of food coloring and NADES-enhanced HPC photonic gel prepared in Examples 1-4 of Product 2 at different temperatures.

[0037] Figure 10 Product 2 Examples 1-4: Schematic diagram of structural color changes before and after pressing of food coloring and NADES-enhanced HPC photonic gel.

[0038] Figure 11 : Schematic diagram of structural color changes before and after stretching of food coloring and NADES-reinforced HPC photonic gel prepared in Examples 1-4 of Product 2.

[0039] Figure 12 Product 3: Physical images and reflection spectra of the food coloring and NADES-reinforced HPC photonic gel film prepared in Examples 1-2.

[0040] Figure 13 : Schematic diagram of the structural color stability of food coloring and NADES-reinforced HPC photonic gel film prepared in Examples 1-2 of Product 3 at different temperatures.

[0041] Figure 14 Product 3 Example 1-2: Schematic diagram of structural color stability of food coloring and NADES-enhanced HPC photonic gel film before and after pressing.

[0042] Figure 15Product 3 Example 1-2: Schematic diagram of structural color stability of food coloring and NADES-reinforced HPC photonic gel film before and after stretching.

[0043] Figure 16 : Schematic diagram of structural color recovery after water absorption of food coloring prepared in Examples 1-2 of Product 3 and NADES-enhanced HPC photonic gel film.

[0044] Figure 17 : Mechanical property data of food coloring and NADES-enhanced HPC photonic gel film prepared in Examples 1-2 of Product 3.

[0045] Figure 18 Product 3: Data graphs showing the antibacterial properties of food coloring and NADES-enhanced HPC photonic gel membranes prepared in Examples 1-2. Detailed Implementation

[0046] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be noted that any processes not specifically described in detail below are those that can be implemented or understood by those skilled in the art by referring to the prior art. Reagents or instruments whose manufacturers are not specified are considered to be conventional products that can be purchased commercially.

[0047] The materials involved in this invention are HPC with a molecular weight of 100,000. Lactic acid, citric acid, choline chloride, curcumin, and lutein were purchased from China National Pharmaceutical Group Corporation. Betaine, fructose, glucose, anthocyanins, and sodium copper chlorophyllin were purchased from Shanghai Yuanye Biotechnology Co., Ltd. All chemical substances are analytical grade and can be used without further purification.

[0048] In some embodiments, the natural eutectic solvent is selected from one of the following: ① Choline chloride-citric acid-pure water system (Ch-CA), wherein the molar ratio of choline chloride to citric acid is 2:1, and the pure water content is 20wt%; ② Fructose-citric acid-pure water system (Fru-CA), wherein the molar ratio of fructose, citric acid and pure water is 1:1:5; ③ Betaine-fructose-pure water system (Bet-Fru), wherein (Bet:Fru:H2O, Beet:Fru molar ratio 1:1, 30wt% pure water added). ④ Choline chloride-glucose-pure water system (Ch-Glu), in which the molar ratio of choline chloride, glucose and pure water is 5:2:5; ⑤ The choline chloride-lactic acid system (Ch-LA) has a molar ratio of choline chloride to lactic acid of 1:7.

[0049] Taking the choline chloride-citric acid-pure water system (Ch-CA) as an example, it can be prepared by the following method: choline chloride and citric acid are mixed in a specified molar ratio (2:1), and 20 wt% water is added to obtain a Ch-CA mixed solution. The prepared solution is placed in a sealed reagent bottle and stirred at 450 rpm using a magnetic stirrer; the temperature is maintained at 80°C until a transparent, homogeneous liquid is obtained. Several other natural eutectic solvents can also be prepared using similar methods.

[0050] This invention provides three products: Product 1: HPC photonic gel reinforced with food coloring; Product 2: HPC photonic gel reinforced with food coloring and NADES; and Product 3: HPC photonic gel membrane reinforced with food coloring and NADES. The following implementation process describes each of the three products separately.

[0051] Product 1: Food coloring-enhanced HPC photonic gel

[0052] Product 1: Comparative Examples 1-4: Preparation of HPC photonic gels with added aniline black

[0053] Product 1 Comparative Example 1: Aniline black (0.5 mg, 0.005 wt%) was dissolved in pure water (3.2 g, 32 wt%), and then HPC (6.8 g, 68 wt%) was added to the water. The mixture was incubated in a water bath at 33°C for 2 hours. The mixture was then stirred for 60 min using a cantilever electric stirrer. After stirring, the mixture was centrifuged at 12000 rpm for 45 min to remove air bubbles. The well-mixed gel was stored in a refrigerator at 4°C until the structural color became uniform, resulting in a blue HPC photonic gel with a water content of 32%.

[0054] Product 1 compared to Example 2: Aniline black (0.5 mg, 0.005 wt%) was dissolved in pure water (3.4 g, 34 wt%), and then HPC (6.6 g, 66 wt%) was added to the water. The mixture was incubated in a water bath at 33°C for 2 hours. The mixture was then stirred for 60 minutes using a cantilever electric stirrer. After stirring, the mixture was centrifuged at 12,000 rpm for 45 minutes to remove air bubbles. The well-mixed gel was stored in a refrigerator at 4°C until the structural color became uniform, resulting in a green HPC photonic gel with a water content of 34%.

[0055] Product 1 Comparative Example 3: Aniline black (0.5 mg, 0.005 wt%) was dissolved in pure water (3.6 g, 36 wt%), and then HPC (6.4 g, 64 wt%) was added to the water. The mixture was incubated in a water bath at 33°C for 2 hours. The mixture was then stirred for 60 minutes using a cantilever electric stirrer. After stirring, the mixture was centrifuged at 12,000 rpm for 45 minutes to remove air bubbles. The well-mixed gel was stored in a refrigerator at 4°C until the structural color became uniform, resulting in an orange HPC photonic gel with a water content of 36%.

[0056] Product 1 Comparative Example 4: Aniline black (0.5 mg, 0.005 wt%) was dissolved in pure water (3.8 g, 38 wt%), and then HPC (6.2 g, 62 wt%) was added to the water. The mixture was incubated in a water bath at 33°C for 2 hours. The mixture was then stirred for 60 minutes using a cantilever electric stirrer. After stirring, the mixture was centrifuged at 12,000 rpm for 45 minutes to remove air bubbles. The well-mixed gel was stored in a refrigerator at 4°C until the structural color became uniform, resulting in a red HPC photonic gel with a water content of 38%.

[0057] Product 1 Comparative Example 5: Lutein (0.225 mg, 0.00225 wt%) was added to pure water (3.2 g, 32 wt%), followed by the addition of HPC (6.8 g, 68 wt%). The mixture was incubated in a 33°C water bath for 2 hours, then stirred for 60 minutes using a cantilever electric stirrer. After stirring, the mixture was centrifuged at 12000 rpm for 45 minutes to remove air bubbles. The well-mixed gel was then stored at 4°C until the structural color became uniform, yielding a blue HPC photonic gel with a water content of 32%. Figure 2 As shown, the pigment distribution in the gel is uneven.

[0058] Product 1 Comparative Example 6: Curcumin (0.225 mg, 0.005 wt%) was added to pure water (3.2 g, 32 wt%), followed by the addition of HPC (6.8 g, 68 wt%). The mixture was incubated in a 33°C water bath for 2 hours, then stirred for 60 minutes using a cantilever electric stirrer. After stirring, the mixture was centrifuged at 12000 rpm for 45 minutes to remove air bubbles. The well-mixed gel was then stored at 4°C until the structural color became uniform, yielding a blue HPC photonic gel with a water content of 32%. Figure 2 As shown, the pigment distribution in the gel is uneven.

[0059] Product 1 Examples 1-4: Preparation of HPC photonic gels with added anthocyanins

[0060] Example 1 of Product 1: Anthocyanins (3 mg, 0.03 wt%) were dissolved in pure water (3.2 g, 32 wt%) and sonicated at 500 W for 1 hour. Then HPC (6.8 g, 68 wt%) was added to the water. The mixture was incubated in a water bath at 33 °C for 2 hours. The mixture was then stirred with a cantilever electric stirrer for 60 min. After stirring, the mixture was centrifuged at 12000 rpm for 45 min to remove air bubbles. The well-mixed gel was stored in a refrigerator at 4 °C until the structural color became uniform, resulting in a blue HPC photonic gel with an anthocyanin-enhanced structure containing 32% water.

[0061] Example 2 of Product 1: Anthocyanins (3 mg, 0.03 wt%) were dissolved in pure water (3.4 g, 34 wt%) and sonicated at 500 W for 1 hour. Then HPC (6.6 g, 66 wt%) was added to the water. The mixture was incubated in a water bath at 33 °C for 2 hours. The mixture was then stirred with a cantilever electric stirrer for 60 min. After stirring, the mixture was centrifuged at 12000 rpm for 45 min to remove air bubbles. The well-mixed gel was stored in a refrigerator at 4 °C until the structural color became uniform, resulting in a green HPC photonic gel with an anthocyanin-enhanced structure containing 34% water.

[0062] Example 3 of Product 1: Anthocyanins (3 mg, 0.03 wt%) were dissolved in pure water (3.6 g, 36 wt%) and sonicated at 500 W for 1 hour. Then HPC (6.4 g, 64 wt%) was added to the water, and the mixture was incubated in a water bath at 33 °C for 2 hours. After that, the mixture was stirred with a cantilever electric stirrer for 60 min. After stirring, it was centrifuged at 12000 rpm for 45 min to remove air bubbles. The well-mixed gel was stored in a refrigerator at 4 °C until the structural color was uniform, resulting in an anthocyanin-enhanced orange HPC photonic gel with a water content of 36%.

[0063] Example 4 of Product 1: Anthocyanins (3 mg, 0.03 wt%) were dissolved in pure water (3.8 g, 38 wt%) and sonicated at 500 W for 1 hour. Then HPC (6.2 g, 62 wt%) was added to the water, and the mixture was incubated in a water bath at 33 °C for 2 hours. The mixture was then stirred with a cantilever electric stirrer for 60 min. After stirring, the mixture was centrifuged at 12000 rpm for 45 min to remove air bubbles. The well-mixed gel was stored in a refrigerator at 4 °C until the structural color became uniform, resulting in a red HPC photonic gel with anthocyanin enhanced by 38% water content.

[0064] Product 1 Examples 5-8: Preparation of HPC photonic gels with added sodium copper chlorophyllin

[0065] Example 5 of Product 1: Referring to Example 1 of Product 1, the only difference is that anthocyanins are replaced with sodium copper chlorophyllin.

[0066] Example 6 of Product 1: Referring to Example 2 of Product 1, the only difference is that anthocyanins are replaced with sodium copper chlorophyllin.

[0067] Example 7 of Product 1: Referring to Example 3 of Product 1, the only difference is that anthocyanins are replaced with sodium copper chlorophyllin.

[0068] Example 8 of Product 1: Referring to Example 4 of Product 1, the only difference is that anthocyanins are replaced with sodium copper chlorophyllin.

[0069] Example 9 of Product 1: Aniline black (0.5 mg, 0.005 wt%) was dissolved in pure water (2.8 g, 28 wt%). Then, 0.56 g of ethanol (20% of the mass of pure water) and HPC (7.2 g, 72 wt%) were added to the water. The mixture was incubated in a water bath at 33°C for 2 hours. After that, the mixture was stirred for 60 min using a cantilever electric stirrer. After stirring, the mixture was centrifuged at 12000 rpm for 45 min to remove air bubbles. The well-mixed gel was stored in a refrigerator at 4°C until the structural color became uniform, resulting in a blue HPC photonic gel with a water content of 28%.

[0070] Example 10 of Product 1: Aniline black (0.5 mg, 0.005 wt%) was dissolved in pure water (3.2 g, 32 wt%). Then, 0.64 g of ethanol (20% of the mass of pure water) and HPC (6.8 g, 68 wt%) were added to the water. The mixture was incubated in a water bath at 33°C for 2 hours. After that, the mixture was stirred for 60 min using a cantilever electric stirrer. After stirring, the mixture was centrifuged at 12000 rpm for 45 min to remove air bubbles. The well-mixed gel was stored in a refrigerator at 4°C until the structural color was uniform, resulting in a red HPC photonic gel with a water content of 32%.

[0071] Example 11 of Product 1: Lutein (0.225 mg, 0.00225 wt%) was dissolved in ethanol (0.56 g). The lutein ethanol solution was then added to pure water (2.8 g, 28 wt%). HPC (7.2 g, 72 wt%) was then added to the water. The mixture was incubated in a water bath at 33°C for 2 hours, and then stirred for 60 min. After stirring, the mixture was centrifuged at 12000 rpm for 45 min to remove air bubbles. The well-mixed gel was stored in a refrigerator at 4°C until the structural color became uniform, resulting in a blue HPC photonic gel with 28% water content and enhanced lutein.

[0072] Example 12 of Product 1: Lutein (0.225 mg, 0.00225 wt%) was dissolved in ethanol (0.64 g), and then the lutein ethanol solution was added to pure water (3.2 g, 32 wt%). HPC (6.8 g, 68 wt%) was then added to the water. The mixture was incubated in a water bath at 33°C for 2 hours, and then stirred for 60 min. After stirring, the mixture was centrifuged at 12000 rpm for 45 min to remove air bubbles. The well-mixed gel was stored in a refrigerator at 4°C until the structural color became uniform, resulting in a red HPC photonic gel with 32% water content and enhanced lutein.

[0073] Example 13 of Product 1: Referring to Example 11 of Product 1, the only difference is that lutein is replaced with curcumin.

[0074] Example 14 of Product 1: Referring to Example 12 of Product 1, the only difference is that lutein is replaced with curcumin.

[0075] Product 2: Food coloring and NADES-enhanced HPC photonic gel

[0076] Product 2 Examples 1-4: Preparation of HPC photonic gels with added sodium copper chlorophyllin and NADES

[0077] Example 1 of Product 2: Step 1: Preparation of NADES: Mix choline chloride and citric acid in a specified molar ratio (2:1) and add 20wt% water to obtain a Ch-CA mixed solution. Place the prepared mixed solution in a sealed reagent bottle and stir it at 450 rpm using a magnetic stirrer. Keep the temperature at 80℃ until a transparent and homogeneous liquid is obtained.

[0078] Step 2: Dissolve sodium copper chlorophyllin (3 mg, 0.03 wt%) in pure water (3.42 g, 34.2 wt%); add HPC (6.08 g, 60.8 wt%) to the sodium copper chlorophyllin aqueous solution, and incubate the mixed solution in a water bath at 33°C for 2 hours. Add Ch-CA (0.5 g, 5 wt%) obtained in Step 1 to the solution after the water bath to obtain a mixed solution.

[0079] Step 3: Stir the mixture obtained in Step 2 at room temperature for 60 min. After stirring, centrifuge at 12000 rpm for 45 min to remove air bubbles. Store the well-mixed gel at 4℃ until the structural color is uniform. This yields a sodium copper chlorophyllin and NADES-enhanced HPC photonic gel.

[0080] Product 2 Example 2: Step 1: Preparation of NADES: Mix choline chloride and citric acid in a specified molar ratio (2:1) and add 20wt% water to obtain a Ch-CA mixed solution. Place the prepared mixed solution in a sealed reagent bottle and stir it at 450 rpm using a magnetic stirrer. Keep the temperature at 80℃ until a transparent and homogeneous liquid is obtained.

[0081] Step 2: Dissolve sodium copper chlorophyllin (3 mg, 0.03 wt%) in pure water (3.24 g, 32.4 wt%); add HPC (5.76 g, 57.6 wt%) to the sodium copper chlorophyllin aqueous solution, and incubate the mixed solution in a water bath at 33°C for 2 hours. Add Ch-CA (1.0 g, 10 wt%) obtained in Step 1 to the solution after the water bath to obtain a mixed solution.

[0082] Step 3: Stir the mixture obtained in Step 2 at room temperature for 60 min. After stirring, centrifuge at 12000 rpm for 45 min to remove air bubbles. Store the well-mixed gel at 4℃ until the structural color is uniform. This yields a sodium copper chlorophyllin and NADES-enhanced HPC photonic gel.

[0083] Product 2 Example 3: Refer to Example 1 of Product 2, the only difference being that NADES is replaced by Fru-CA instead of Ch-CA.

[0084] Example 4 of Product 2: Refer to Example 2 of Product 2, the only difference being that NADES is replaced by Fru-CA instead of Ch-CA.

[0085] Example 5 of Product 2: Refer to Example 2 of Product 2, the only difference being that NADES is replaced by Bet-Fru instead of Ch-CA.

[0086] Example 6 of Product 2: Refer to Example 2 of Product 2, the only difference being that NADES is replaced by Ch-Glu instead of Ch-CA.

[0087] Example 7 of Product 2: Refer to Example 2 of Product 2, the only difference being that NADES is replaced by Ch-LA instead of Ch-CA.

[0088] Product 3: Food coloring and NADES-enhanced HPC photonic gel membrane

[0089] Example 1 of Product 3: Preparation of HPC photonic gel film with added sodium copper chlorophyllin

[0090] Step 1: The photonic gel prepared in Example 7 of Product 1 is uniformly coated onto a glass slide, and then the glass slide containing the gel layer is sealed and stored in an environment of 4°C until the structural color of the gel is uniform. Step 2: Place the glass slide containing the gel layer, which was stored in Step 1, in a 70°C oven and dry it to constant weight. Peel the gel layer off the glass slide to obtain the chlorophyll copper sodium-reinforced HPC photonic gel film.

[0091] Example 2 of Product 3: Preparation of HPC photonic gel film with added sodium copper chlorophyllin and NADES

[0092] Step 1: The photonic gel prepared in Examples 2 and 4 is uniformly coated onto a glass slide, and the slide containing the gel layer is sealed and stored in an environment of 4°C until the structural color of the gel is uniform. Step 2: Place the glass slide containing the gel layer, which was stored in Step 1, in a 70°C oven and dry it to constant weight. Peel the gel layer off the glass slide to obtain the HPC photonic gel membrane reinforced with sodium copper chlorophyllin and NADES.

[0093] The photonic gels and photonic gel films prepared in the above embodiments and comparative examples were subjected to the following performance tests: 1. Photonic gel reflectance spectroscopy test: The photonic gel was transferred between two glass slides separated by a circular spacer, and the slides were sealed with sealing film. The slides were then stored at 4°C for 24 hours to allow the structural color to uniformize. Testing was performed using the Shimadzu UV-3600i Plus diffuse mode. The sealing film wrapped around the outside was removed before testing, and the test was conducted at 4°C.

[0094] 2. Photon gel responsiveness test: (1) Moisture content: Select photonic gels with uniform structural color and different moisture contents (32-38wt%). Transfer the photonic gels between two glass slides, separated by a circular spacer (19mm in diameter and 1mm in thickness). Seal the glass slides with sealing film and store them in a refrigerator at 4℃ for 24 hours to allow the structural color to become uniform. Remove the sealing film when taking photos and record the changes in structural color of gels with different moisture contents.

[0095] (2) Temperature response: The photonic gel was transferred between two glass slides, separated by a circular spacer (19 mm in diameter and 1 mm in thickness), and the slides were sealed with a sealing film and stored in a 4°C refrigerator for 24 hours to allow the structural color to become uniform. Before taking the photographs, the slides were stored at different temperatures (4°C, 25°C, 37°C) for 24 hours, and the sealing film was removed before taking the photographs.

[0096] (3) Tensile response: The photonic gel (1g) was transferred between two pieces of transparent rubber (50mm×50mm), and gently pressed until flat. The sample was stored in a 4℃ refrigerator for 24 hours to allow the structural color to become uniform. During the experiment, the rubber was stretched to 10cm, and the color change of the sample before and after stretching was recorded by taking pictures.

[0097] (4) Pressure response: The photonic gel was transferred between two glass slides, with spacers (length × width × height, 20mm × 5mm × 1mm) separating the two sides of the gap between the slides. The slides were then sealed with sealing film and stored in a refrigerator at 4°C for 24 hours to allow the structural color to become uniform. Before the experiment, the spacers and sealing film were removed, and a pressure gauge (20N) was used to press the gel. The changes in structural color before and after pressing were recorded.

[0098] (5) pH response: The photonic gel (1g) was transferred to a six-well plate, the plate was sealed with sealing film, and stored in a 4°C refrigerator for 24 hours to allow the structural color to become uniform. After storage, buffer solutions with different pH values ​​(pH=1, 11) were added to the plate, and the color change of the gel was recorded by taking pictures.

[0099] 3. Reflectance test of photonic gel film: Before testing, the gel was cut into squares (20mm×20mm) and tested using the Shimadzu UV-3600i Plus diffuse mode.

[0100] 4. Photonic gel film responsiveness test: (1) Temperature response: The photon gel film was cut into squares (20mm×20mm) and stored at different temperatures (4℃, 25℃, 37℃) for 24 hours. The gel color before and after storage was recorded.

[0101] (2) Tensile response: The photonic gel film was cut into a rectangle (20mm×20mm), and a tensile force of 20N was applied using a tensile tester. The color change of the sample before and after stretching was recorded by taking pictures.

[0102] (3) Pressure response: The photonic gel film was cut into a rectangle (50mm×10mm), and a pressure of 20N was applied using a pressure gauge. The color change of the sample before and after stretching was recorded by taking pictures.

[0103] 5. Reversible swelling test of photonic gel film structure color: The photon gel membrane was cut into a rectangle (30mm×10mm) and placed in a glass dish filled with water. A photograph was taken every 1 minute to record the changes in the gel structure color in the water.

[0104] 6. Mechanical property testing of photon gel membrane: The photonic gel film was cut into rectangular strips 45 mm long and 10 mm wide, and subjected to tensile tests at a strain rate of 50 mm / min on a universal testing machine (Instron 5966 dual-column test system).

[0105] 7. Antioxidant performance test of photonic gel: Antioxidant activity was assessed using DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) assays. The free radical scavenging ability of the antioxidants was quantified by the decrease in absorbance of the DPPH or ABTS solution. The DPPH stock solution was prepared by dissolving 5 mg of DPPH in 100 mL of ethanol. The ABTS stock solution was prepared by mixing 7.4 mM ABTS and 2.6 mM potassium persulfate in a 1:1 ratio and incubating at room temperature in the dark for 12–16 hours. Before testing, the ABTS stock solution was diluted with water to obtain a working solution with an absorbance of 0.7 ± 0.05 at 734 nm. For measurement, 20 mg of gel was added to a disposable cuvette containing 2 mL of DPPH or ABTS solution. The cuvette was incubated in the dark for 1 hour. Absorbance was measured at 517 nm (DPPH) and 734 nm (ABTS) using a UV-Vis spectrophotometer. Absorbance of the control sample (without gel) was recorded before and after incubation. Antioxidant activity was calculated using the following formula:

[0106] 8. Antibacterial performance test of photonic gel membrane: The photonic films were sterilized by UV irradiation for 30 minutes, and then placed in 15 ml of Luria-Bertani (LB) medium inoculated with single colonies of *E. coli* and *S. aureus*. LB medium without the film, inoculated only with single colonies of *E. coli* and *S. aureus*, served as a control. The initial numbers of *E. coli* and *S. aureus* were 1.21 x 10⁻⁶. 7 The samples were then incubated with shaking at 200 rpm and 37°C for 15 hours. 5 mL of the bacterial culture was transferred to an agar plate and evenly spread, then incubated at 37°C for 24 hours. The antibacterial activity of the photonic film was evaluated by recording the growth of colonies on the agar plate.

[0107] The test results are as follows: 1. Reflectance spectrum and responsiveness of food coloring-enhanced HPC photonic gel of Product 1 1.1 Effect of adding different food colorings on the structural color of HPC photonic gel (Product 1) The photonic gels prepared by Product 1 in Examples 1-4 and Examples 1-14 were subjected to reflectance spectroscopy tests, and the results are as follows: Figure 2As shown in the figure. The results indicate that both moisture content and background color affect the photon reflection properties and visual color of HPC gels, but their mechanisms of action differ. In the same background color system, with increasing moisture content, the reflection peak exhibits a red shift, and the macroscopic color of the sample transitions sequentially from blue through green and orange to red. This red shift phenomenon can be attributed to the expansion of the helical pitch in the HPC gel with increasing moisture content. According to Bragg's law of selective reflection, an increase in pitch will cause the reflected wavelength to shift towards longer wavelengths, thus resulting in a significant red shift. When C3G or SCC is introduced into the HPC system as a background color under fixed moisture content conditions, its reflection peak position does not shift significantly compared to the Nig background, indicating that the background color mainly affects the visual contrast and color saturation of the gel, without significantly altering the liquid crystal helical pitch structure. Therefore, the background color mainly plays a role in enhancing the visualization effect of structural color in the system, rather than being a key factor determining the structural color itself. It is noteworthy that in HPC gel with a moisture content of 36%, the reflectance spectrum shows a double peak (600 nm and 668 nm) when SCC is used as the background color. This phenomenon may be due to the optical interference enhancement effect between the absorption band of chlorophyll molecules and the reflectance band of HPC liquid crystal, indicating that natural pigments may synergize with the photonic structure of HPC under specific conditions to form new optical features.

[0108] To clarify the effect of ethanol on the structural color of HPC gel, a gel with Nig as the background color was first used as a control group to investigate the effect of ethanol on the structural color of HPC. The experimental results showed that after adding ethanol at 20% relative to the mass of pure water, the reflectance spectrum of the gel underwent a significant red shift, with the reflectance peak shifting from 489 nm (blue) in the ethanol-free state to 593 nm (red). This was attributed to the swelling effect caused by the change in solvent environment after the introduction of ethanol and the change in pitch of the cholesteric phase liquid crystal. In order to eliminate the interference of wavelength shift on lateral contrast, the red shift effect caused by ethanol was offset by reducing the water content from 32% to 28%. Based on this, the modulation effects of Nig and CUR / Lut as background colors on the gel reflectance spectrum were compared. The results showed that, compared to the Nig background, the gel system using CUR and Lut as background colors exhibited significantly differentiated reflectance characteristics. Specifically, in the short-wavelength blue region, since the characteristic absorption peaks of CUR and Lut are mainly concentrated in the 400-500 nm band, they strongly compete with the scattered light generated by the gel structure, resulting in a significantly lower reflectance intensity in this band than the Nig background. In the long-wavelength red region, since CUR and Lut have weak absorption in the 600 nm band, the reflectance signal intensity is higher than the fully absorbed Nig background. This confirms that the system constructed in this invention achieves spectral coupling of physical structural color and chemical absorption color. It can not only achieve precise control of the structural color wavelength through the synergistic adjustment of solvent and water content, but also achieve selective filtering and enhancement of reflected light in specific bands by utilizing the specific absorption spectra of active pigments. However, when lutein and curcumin are added to the HPC pure hydrogel system, the visibility of the structural color is significantly reduced due to the dominant yellow absorption characteristics of these pigments. This phenomenon can be attributed to the spectral overlap and optical competition between pigment absorption and cholesteric phase structural photon reflection. Structural color originates from coherent Bragg reflection at a specific wavelength determined by the pitch of the cholesteric liquid crystal helices. However, lutein and curcumin have strong and broad absorption bands in the blue-green spectral region (400-520 nm), and most of the reflected light is absorbed by the pigments before reaching the observer, thus reducing the intensity of reflected light and visual recognition.

[0109] 1.2 Effects of different food colorings on the responsiveness and antioxidant activity of HPC photonic gel (Product 1)

[0110] The photonic gels prepared by Product 1 in Examples 1-4 and Examples 1-8 were subjected to temperature, pressure, and tensile response tests. The results are as follows: Figure 3 , 4As shown in Figure 5, the results indicate that, in terms of temperature response, under the same background color and different moisture contents, the photonic gel exhibits a structural color redshift with increasing temperature (4℃–37℃), mainly due to the expansion of the helical pitch in the HPC gel system as temperature rises. When the moisture content is constant, photonic gels with different background colors also exhibit a redshift with increasing temperature, indicating that the introduction of the background color does not disrupt the inherent temperature response characteristics of the HPC gel. However, the redshift amplitude varies among samples with different background colors: taking the gel with a water content of 34wt% as an example, the gel with added Nig and SCC shows a redshift with increasing temperature, while the gel with added C3G shows a significantly smaller redshift. This difference is consistent with the aforementioned mechanism of anthocyanin's influence on structural color: when the temperature rises and causes the helical structure to expand, the hydrogen bond interaction between C3G and the HPC chain inhibits the expansion of the helical pitch to some extent, resulting in a smaller redshift amplitude. Regarding tensile and compressive responses, for gels with the same background color but different moisture contents, a blue shift in structural color was observed under applied tensile or compressive force. This mechanism can be attributed to the compression of the HPC gel helical spacing caused by the external force. In gels with the same moisture content but different background colors, the external force also induced a blue shift, and the magnitude of the blue shift was basically consistent across samples with different background colors, indicating that the background color type has no significant effect on the tensile-compressive response behavior of the HPC gel. Regarding pH response, due to the inherent pH response of C3G, gels with added C3G as a background color exhibited a significant pH response. A buffer solution at pH=1 changed the gel color from yellow to red, while a buffer solution at pH=11 changed the gel color from yellow to yellowish-green. Regarding antioxidant activity, HPC gels, which inherently lack antioxidant activity, benefited from the inherent antioxidant activity of C3G and SCC, exhibiting significant scavenging abilities against DPPH and ABTS.

[0111] 2. Reflectance spectrum and responsiveness of product 2, food coloring and NADES-enhanced HPC photonic gel.

[0112] 2.1 Effect of NADES on the structural color of food coloring-enhanced HPC photonic gel (Product 2)

[0113] The photonic gels prepared in Examples 1-7 of Product 2 were subjected to reflectance spectroscopy testing, and the experimental results are as follows: Figure 8As shown. Since HPC gels with added Bet-Fru, Ch-Glu, and Ch-LA undergo phase separation and lack structural color, this invention focuses on the effects of two NADES types, Ch-CA and Fru-CA, on structural color. Under the same background color and NADES addition levels, different NADES types have drastically different effects on structural color: Ch-CA induces a blue shift in structural color, while Fru-CA causes a red shift. From a molecular mechanism perspective, the positive charge of ChCl in the Ch-CA system generates electrostatic attraction with the negatively charged HPC chains. Simultaneously, the hydrogen bonds in Ch-CA form strong intermolecular interactions with HPC, both contributing to gel pitch compression and thus a blue shift in reflection wavelength. In contrast, the citric acid in the Fru-CA system is acidic and can dissociate into negative ions in aqueous solution, generating charge repulsion with the similarly negatively charged HPC chains, promoting pitch expansion and resulting in a red shift in reflection wavelength. Under the same NADES type and background color but different addition levels, the gel structural color remained unchanged with increasing NADES addition. This may be because even the minimum addition amount (5 wt%) has reached its saturation threshold for structural color modulation, so further increases in dosage no longer cause changes in optical response, also indicating that higher addition amounts do not disrupt the structural color stability of the gel. In systems with fixed NADES types and amounts but different background colors, the structural colors exhibit significant differences. Taking the addition of 5 wt% Ch-CA as an example, the reflectance peak of the gel with anthocyanin as the background color differs from that of the aniline black background sample; the former is red, while the latter is blue. This difference likely stems from the pH change caused by the introduction of NADES, leading to a change in the anthocyanin molecule configuration. As previously mentioned, the hydrogen bonding between anthocyanin and HPC can promote a blue shift in structural color; therefore, it is speculated that pH changes may modulate the strength of the hydrogen bonding interaction between anthocyanin and HPC, ultimately affecting the overall color development. The effect on the reflectance behavior of the anthocyanin-background gel in the Fru-CA system is relatively consistent, all leading to a red shift. Furthermore, a dual reflection peak phenomenon was observed in samples with anthocyanin and sodium copper chlorophyll as the background. This may stem from the non-uniformity of the pitch distribution: different components (Chcl, CA) in NADES influence the structural color of HPC through different mechanisms, inducing different pitch regions during gel formation, thus resulting in the simultaneous appearance of two reflection peaks: blue (approximately 416 nm) and orange (approximately 623 nm). In summary, there is a complex interaction between the chemical properties of the background pigments themselves and the type and amount of NADES added, which together determine the final optical response behavior of the HPC-NADES photonic gel.

[0114] 2.2 Effect of NADES on the responsiveness of food coloring-enhanced HPC photonic gel (Product 2)

[0115] The photonic gels prepared in Examples 1-4 of Product 2 were subjected to temperature, pressure, and tensile response tests. The experimental results are as follows: Figure 9 , 10 As shown in Figure 11. First, under the same background color conditions, comparing the gel response behavior with and without NADES revealed that, in terms of temperature response, the introduction of NADES altered the gel's temperature response behavior. Specifically, the blue gel with added Ch-CA did not undergo a red shift in its structural color with increasing temperature; instead, it gradually changed from blue to light blue. The red gel with added Fru-CA, during temperature rise, showed a structural color shift from orange to red, and gradually faded at 37°C due to color lightening. This phenomenon can be attributed to the combined effect of temperature rise and Fru-CA causing a red shift in the structural color, leading to excessive pitch expansion and ultimately causing phase separation of the gel, thus affecting the stability of the structural color. In terms of pressure and tension response, since the Ch-CA gel was initially blue and already in the short wavelength region, it could not undergo further blue shift; therefore, its color changed from blue to light blue during pressing and stretching. The gel with added Fru-CA, however, showed the same color change under external force as the gel without NADES, i.e., a change from red to blue. Secondly, comparing gels with the same amount of NADES added but different background colors, the results showed that the difference in background color did not affect the response behavior of HPC gels under temperature, pressure, and tensile stress. The structural color changes of NADES gels with different background colors under various stimuli were consistent with the above conclusions.

[0116] Product 3: Reflectance spectrum, responsiveness and mechanical properties of HPC photonic gel film reinforced with food coloring and NADES.

[0117] 3.1 Reflectance spectrum of HPC photonic gel film reinforced with food coloring and NADES (Product 3)

[0118] The photonic gel films prepared in Examples 1 and 2 of Product 3 were subjected to reflectance spectroscopy testing, and the experimental results are as follows: Figure 12In systems containing NADES under the same background color, the position of the reflection peak can be effectively controlled. Specifically, the Ch-CA system, due to its initial short-pitch blue structural color, has limited space for further pitch shrinkage during drying, resulting in a smaller blue shift. The Fru-CA system, with its initial red structural color corresponding to a larger pitch, still exhibits a blue shift after drying, but the reflection peak, originally located in the long-wavelength region, remains in the orange-red range after film formation. The reflection peak of the gel without NADES shifted from 605 nm (orange) to 495 nm (green) after drying, a shift of 110 nm. The gel with Ch-CA (choline-citric acid) NADES, initially blue, shifted only from 416 nm to 382 nm after drying, a shift of 34 nm. The gel with Fru-CA (fructose-citric acid) NADES shifted from 665 nm (red) to 582 nm (yellow), a shift of 83 nm. These results indicate that NADES can achieve pre-control of structural color during photonic thin film fabrication. Given that drying-induced blue shift is a common phenomenon in HPC photonic gels, the target hue (especially orange or red) can be pre-adjusted by controlling the type and concentration of NADES during the gelation stage, causing a red shift in the reflection peak. Thus, even after pitch compression during the drying process, the final film can still maintain the desired reflection wavelength, achieving more accurate color reproduction. In the reflection spectra of gel films using the same NADES on different background colors, only the Ch-CA system showed significant differences, exhibiting a double reflection peak. This may be due to the influence of NADES composition on the structural color, resulting in significant pitch inhomogeneity.

[0119] 3.2 Stimulation response and swelling behavior of HPC photonic gel membrane reinforced with food coloring and NADES (Product 3)

[0120] The photonic gel films prepared in Examples 1 and 2 of Product 3 were subjected to stimulation-responsiveness and swelling behavior tests. The experimental results are as follows: Figure 13 , 14 As shown in Figures 15 and 16, the results show that the structural color of the gel film remains unchanged under various heating, pressing, and stretching conditions, indicating that its optical structure has good mechanical and thermal stability. However, when placed in water, the structural color can be restored to its pre-drying state, and this behavior is reversible under different NADES and background color conditions. The mechanism stems from the difference in the mobility of polymer molecular chains in the dry and swollen states: during drying, water loss leads to enhanced hydrogen bonds between molecular chains, freezing of chain segments, and formation of a glassy solid, which macroscopically manifests as a fixed structural color; while after absorbing water, the plasticizing effect of water molecules restores the system to a rubbery state, allowing the molecular chains to regain mobility and spontaneously recover to a thermodynamically stable helical arrangement, thus restoring the structural color.

[0121] 3.3 Mechanical and antibacterial properties of HPC photonic gel membranes reinforced with food coloring and NADES (Product 3)

[0122] The photonic gel films prepared in Examples 1 and 2 of Product 3 were subjected to mechanical and antibacterial property tests. The experimental results are as follows: Figure 17 , 18 As shown in the figure, the mechanical results indicate that the addition of NADES significantly modulates the mechanical behavior. The ultimate tensile strength of the gel film without NADES is 26 MPa, and the strain is 11%. After adding Ch-CA, the strength of the HPC gel decreases to 20 MPa (a decrease of 6 MPa), while the strain increases to 20% (an increase of 9%). With Ch-CA, the strength of the HPC gel increases to 32 MPa (an increase of 6 MPa), while the fracture strain increases to 17% (an increase of 8%). These results demonstrate that both Ch-CA and Fru-CA can improve the toughness of the material, but Ch-CA comes at the cost of strength, while Fru-CA can simultaneously enhance both strength and toughness. Based on the previous research on the interaction between NADES and HPC molecules, this phenomenon can be attributed to the following mechanism: Ch-CA forms a rigid network through multi-site hydrogen bonds and electrostatic interactions. This structure is prone to brittle instability under strain, leading to decreased strength but increased ductility. Fru-CA, on the other hand, constructs a dynamic reversible network through multi-site hydrogen bonds between fructose and citric acid, endowing the system with higher chain segment mobility. This allows it to effectively disperse stress through chain segment slippage and orientation during deformation, thereby achieving both higher load-bearing capacity and ductility. Antibacterial test results show that the photonic film acquires significant antibacterial ability after introducing different types of NADES components. Compared with the blank control group, the SCC / ND-0% photonic film showed consistent bacterial growth trends, with a higher colony count (Log) against Escherichia coli and Staphylococcus aureus. 10 The CFU group showed no significant difference compared to the control group, indicating that the photonic film with SCC alone did not possess significant antibacterial activity. However, upon further addition of NADES, the photonic film exhibited significant antibacterial activity, with a significant decrease in the number of Staphylococcus aureus and Escherichia coli colonies compared to the control group. The introduction of Ch-CA and Fru-CA both conferred significant antibacterial properties upon the material. This phenomenon can be attributed to the inherent antibacterial ability of NADES itself: the organic acids in NADES lower the pH of the environment, thereby damaging the cell membrane and its proteins. The choline cations in NADES interact with the polysaccharide chains through hydrogen bonds or electrostatic interactions, leading to cell wall rupture and bacterial inactivation.

[0123] In summary, the HPC-based photonic gel smart material system developed in this invention fully leverages the synergistic regulatory advantages of food coloring and NADES. By combining food coloring with HPC, not only is the visual recognition of HPC structural color enhanced by the absorption of visible light by the pigments, but the antioxidant properties of the pigments themselves are also preserved. Subsequently, combining the pigments with NADES and HPC not only preserves the inherent chiral nematic liquid crystal structure of HPC, but also constructs a smart gel system with stimulus responsiveness and enhanced mechanical properties through molecular interactions. This system achieves enhanced visual recognition and precise control of structural color through multiple mechanisms: first, the visual recognition of HPC gel structural color is improved by utilizing the absorption of visible light by different pigments; second, the antioxidant properties of different pigments endow the material with multiple functional characteristics; finally, the introduction of NADES achieves precise adjustment of structural color through electrostatic interactions and hydrogen bonding, enhancing the mechanical properties of the HPC gel. Specifically, Ch-CA can improve toughness, while Fru-CA can simultaneously enhance strength and ductility. This dual reinforcement of "pigment-NADES" gives the material broad application potential in numerous fields. It should be noted that the above embodiments are only preferred embodiments of the present invention, and the scope of protection of the present invention should be determined by the claims. Any equivalent substitutions or improvements based on the core concept of the present invention should be considered to fall within the scope of protection of the present invention.

Claims

1. An HPC photonic gel enhanced with food coloring, characterized in that: The HPC photonic gel comprises an HPC gel framework and a dispersion medium, and also contains edible pigment as a background color material. The edible pigment is uniformly dispersed in the HPC photonic gel. The edible pigment is either hydrophilic or hydrophobic. When the edible pigment is hydrophilic, the dispersion medium is water; when the edible pigment is hydrophobic, the dispersion medium is a combination of water and a cosolvent. The cosolvent is capable of dissolving the hydrophobic edible pigment, and the mass of the cosolvent does not exceed 30% of the mass of water. In the HPC photonic gel, the dispersion medium content is 32-38 wt%, and the edible pigment content is 0.001-0.06 wt%.

2. The food coloring-enhanced HPC photonic gel as described in claim 1, characterized in that: The hydrophilic food coloring is anthocyanin or sodium copper chlorophyllin. In the HPC photonic gel reinforced with anthocyanin or sodium copper chlorophyllin, the dispersion medium is water, with a water content of 32-38 wt% and anthocyanin or sodium copper chlorophyllin content of 0.01-0.06 wt%.

3. The food coloring-enhanced HPC photonic gel as described in claim 1, characterized in that: The hydrophobic food coloring is curcumin or lutein, and the dispersion medium is a combination of water and ethanol, wherein the mass of ethanol is 15-25% of the mass of water.

4. The food coloring-enhanced HPC photonic gel as described in claim 3, characterized in that: In HPC photonic gels enhanced with curcumin or lutein, the dispersion medium content is 32-38 wt%, and the anthocyanin or sodium copper chlorophyllin content is 0.001-0.005 wt%.

5. The HPC photonic gel enhanced with food coloring as described in any one of claims 1-4, characterized in that: The HPC photonic gel also contains a natural eutectic solvent, which is selected from one of the following: ①A choline chloride-citric acid-pure water system, wherein the molar ratio of choline chloride to citric acid is 2:1, and the pure water content is 20 wt%; ② Fructose-citric acid-pure water system, wherein the molar ratio of fructose, citric acid and pure water is 1:1:5; The HPC photonic gel contains 5-10 wt% natural eutectic solvent and 32-35 wt% dispersion medium.

6. A method for preparing an HPC photonic gel enhanced with food coloring as described in any one of claims 1-4, comprising the following steps: Step 1: Mix the food coloring, dispersion medium and HPC to obtain a mixed solution containing food coloring and HPC; Step 2: The mixed solution containing food coloring and HPC obtained in step (1) is placed in a water bath at 25-35℃ for 1.5-2 hours. The mixed solution after water bath is stirred thoroughly to make the components evenly distributed. Then, the air bubbles are removed by centrifugation at room temperature. The centrifuged gel is stored at 4-25℃ until the structural color is uniform to obtain the food coloring-enhanced HPC photonic gel.

7. The preparation method according to claim 6, characterized in that: The preparation method further includes: in step 2, adding a natural eutectic solvent to the mixed solution after water bath, and then continuing the subsequent operations of step 2, that is, stirring thoroughly to make the components evenly distributed, and then removing air bubbles by centrifugation at room temperature. The centrifuged gel is stored at 4-25℃ until the structural color is uniform to obtain the food coloring-enhanced HPC photonic gel. The natural eutectic solvent is selected from one of the following: ①A choline chloride-citric acid-pure water system, wherein the molar ratio of choline chloride to citric acid is 2:1, and the pure water content is 20 wt%; ② Fructose-citric acid-pure water system, wherein the molar ratio of fructose, citric acid and pure water is 1:1:5; The HPC photonic gel contains 5-10 wt% natural eutectic solvent and 32-35 wt% dispersion medium.

8. The preparation method according to claim 6, characterized in that: In step 2, the water bath temperature is 30-35℃, more preferably 33℃; the water bath time is 1.5-2 hours, more preferably 2 hours; the stirring conditions are stirring for 50-70 minutes, more preferably 60 minutes; and the storage conditions are storage at 4℃.

9. An edible-color-enhanced HPC photonic gel membrane made from the edible-color-enhanced HPC photonic gel according to any one of claims 1-5.

10. A method for preparing an HPC photonic gel film enhanced with food coloring as described in claim 9, characterized in that: The preparation method includes the following steps: Step 1: The food coloring-enhanced HPC photonic gel is uniformly coated onto a glass slide, and the slide containing the gel layer is sealed and stored in an environment of 4-25°C until the structural color of the gel is uniform. Step 2: Place the glass slide containing the gel layer, which was stored in Step 1, in an oven at 60-100℃ and dry it to constant weight. Peel the gel layer off the glass slide to obtain the HPC photonic gel film reinforced with food coloring.

Images