Preparation method of edible and degradable starch-based elastic hydrogel

Abstract

The present invention discloses a method for preparing an edible and degradable starch-based elastic hydrogel. The method comprises the following steps: (1) preparing a starch suspension: dispersing starch in an aqueous solution of a polyol to obtain a starch suspension; (2) thermal gelatinization: gelatinizing the starch suspension in a boiling water bath to obtain solution A; (3) mixing an organic solvent: mixing an organic solvent into solution A and stirring uniformly to obtain solution B; (4) centrifugation: removing the supernatant from solution B by centrifugation to obtain a precipitate; (5) phase separation: drying the precipitate in an oven at a certain temperature for 2 days to obtain a starch-based hydrogel. The present invention utilizes a phase separation strategy, utilizing the different affinities of polyols / organic solvents with starch to construct a phase separation strategy to prepare an edible and degradable starch-based elastic hydrogel.

Description

Technical Field

[0001] The invention relates to a starch-based hydrogel, in particular to a method for preparing an edible and degradable starch-based elastic hydrogel. Background Art

[0002] Elastomers, such as polydimethylsiloxane (PDMS), polyethylene terephthalate (PET), polypropylene (PP), thermoplastic polyurethane (TPU), and rubber, are widely used in soft robotics, tissue engineering, and flexible electronics due to their exceptional toughness. However, the widespread use of these non-degradable materials poses a challenge to the sustainable and green production and development of engineering materials. Therefore, the development of green, environmentally friendly, safe, and biodegradable materials is crucial. Natural, edible biomaterials, due to their inherent biodegradability, are ideal candidates for flexible electronics. Their edibility further drives innovative applications such as in vivo delivery robots and medical-grade food manipulation devices. However, most bio-based hydrogels typically exhibit soft and brittle mechanical properties, such as low stiffness, low fracture strength, and low fracture toughness, making them difficult to meet the mechanical performance requirements of various practical applications. Therefore, improving the mechanical properties of green, degradable, and edible hydrogels has become a key research frontier, aiming to reconcile environmental sustainability with the performance requirements of modern engineering applications.

[0003] Starch is a biodegradable polysaccharide widely used in food and non-food industries, including fermentation, adhesives, chemical production, and textiles. Its numerous advantages make it a promising candidate for sustainable materials: 1) low cost and widespread availability; 2) natural biodegradation through environmental microbial activity and non-toxicity; 3) edibility and high biocompatibility (suitable for biomedical applications); and 4) lightweight, enhancing product portability. In recent years, researchers have combined starch with other polymers to create starch-based hydrogels. For example, polyvinyl alcohol (PVA) has been combined with starch to create flexible gripper devices, and polyacrylamide has been combined with starch to create hydrogels for use as body sensors. The addition of these polymers enhances the hydrogel's mechanical properties, such as stretchability and toughness, but at the expense of complete biodegradability and eco-friendliness. Currently, no starch-based hydrogels have been reported that combine outstanding mechanical properties with edible / degradable properties. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides a method for preparing an edible and degradable starch-based elastic hydrogel.

[0005] The present invention provides the following technical solution: a method for preparing an edible and degradable starch-based elastic hydrogel, comprising the following steps:

[0006] (1) Preparation of starch suspension: Dispersing starch in an aqueous solution of a polyol to obtain a starch suspension;

[0007] (2) Thermal gelatinization: The starch suspension is gelatinized in a boiling water bath to obtain solution A;

[0008] (3) Mixing organic solvent: Mix the organic solvent into solution A and stir evenly to obtain solution B;

[0009] (4) Centrifugation: Remove the supernatant from solution B by centrifugation to obtain the precipitate;

[0010] (5) Phase separation: The precipitate was placed in an oven at a certain temperature and dried for 2 days to obtain a starch-based hydrogel.

[0011] Furthermore, the starch is one or more of corn starch, potato starch, barley starch, rice starch, wheat starch, and tapioca starch.

[0012] Furthermore, the polyol is one or more of glycerol, erythritol, xylitol, mannitol, and sorbitol.

[0013] Furthermore, the volume ratio of the polyol to water in the polyol aqueous solution is 2:8-9:1; and the mass ratio of the starch to the polyol aqueous solution in the starch suspension is 1:50-1:2.

[0014] Furthermore, the boiling water bath gelatinization process is as follows: in a 100° C. water bath, magnetic stirring is performed at a speed of 800 rpm for 30 minutes.

[0015] Furthermore, the mixed organic solvent treatment conditions are: magnetic stirring at 800 rpm for 1 hour; the organic solvent is one or more of ethanol, acetone, and n-hexane; and the volume ratio of the organic solvent to the polyol aqueous solution is 1:2 to 2:1.

[0016] Furthermore, the centrifugation condition is: centrifugation at 8000 rpm for 10 min.

[0017] Furthermore, the phase separation temperature is 20-80°C.

[0018] The beneficial effects of the present invention are as follows:

[0019] This invention utilizes a phase separation strategy, leveraging the varying affinities of polyols / organic solvents with starch, to prepare edible and biodegradable starch-based elastic hydrogels. The organic solvent (a poor solvent) drives the starch chains to reorganize into V+B-type crystals, generating an energy-dissipating phase through localized chain contraction. The polyol (a good solvent) synergistically interacts with bound water to form a hydrogen-bonded soft matrix, thereby enhancing the mechanical properties of the starch-based hydrogel. This successful combination of edible and biodegradable properties with excellent mechanical properties can be used to manufacture pneumatically actuated soft grippers, medical food devices, and more. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a flow chart for preparing the edible, degradable starch-based elastic hydrogel of the present invention;

[0021] Figure 2 (a) is a cryo-scanning electron microscope (cryo-EM) image of Example 1, (b) is a cryo-EM image of Example 2, (c) is a cryo-EM image of Example 3, (d) is a cryo-EM image of Comparative Example 1, (e) is a cryo-EM image of Comparative Example 2, (f) is a cryo-EM image of Comparative Example 3, (g) is a cryo-EM image of Comparative Example 4, and (h) is a cryo-EM image of Comparative Example 5;

[0022] Figure 3 (a) is a moisture content graph of Example 1, (b) is a moisture content graph of Example 2, (c) is a moisture content graph of Example 3, (d) is a moisture content graph of Comparative Example 1, (e) is a moisture content graph of Comparative Example 2, (f) is a moisture content graph of Comparative Example 3, (g) is a moisture content graph of Comparative Example 4, and (h) is a moisture content graph of Comparative Example 5;

[0023] Figure 4 (a) is the strain-stress curve of Example 1, (b) is the strain-stress curve of Example 2, (c) is the strain-stress curve of Example 3, (d) is the strain-stress curve of Comparative Example 1, (e) is the strain-stress curve of Comparative Example 2, (f) is the strain-stress curve of Comparative Example 3, (g) is the strain-stress curve of Comparative Example 4, and (h) is the strain-stress curve of Comparative Example 5;

[0024] Figure 5 (a) is a rebound curve diagram of Example 1, (b) is a rebound curve diagram of Example 2, and (c) is a rebound curve diagram of Example 3;

[0025] Figure 6 (a) is the XRD pattern of Example 1, (b) is the XRD pattern of Example 2, (c) is the XRD pattern of Example 3, (d) is the XRD pattern of Comparative Example 1, (e) is the XRD pattern of Comparative Example 2, (f) is the XRD pattern of Comparative Example 3, (g) is the XRD pattern of Comparative Example 4, and (h) is the XRD pattern of Comparative Example 5;

[0026] Figure 7 (a) is the Fourier transform infrared (FTIR) spectrum of Example 1, and (b) is the FTIR spectrum of Comparative Example 1;

[0027] Figure 8 (a) is the soil degradation diagram of Example 1, (b) is the soil degradation diagram of Example 2, and (c) is the soil degradation diagram of Example 3. DETAILED DESCRIPTION

[0028] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the specific implementation methods, structures, features and effects of the present invention are described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0029] This invention utilizes a phase separation strategy, leveraging the varying affinities of polyols / organic solvents with starch, to prepare edible, biodegradable starch-based elastic hydrogels. The organic solvent (a poor solvent) drives the starch chains to reorganize into V+B-type crystals, generating an energy-dissipating phase through localized chain contraction. The polyol (a good solvent) synergistically interacts with bound water to form a hydrogen-bonded soft matrix, thereby enhancing the mechanical properties of the starch-based hydrogel.

[0030] The embodiments of the present invention are further described below with reference to a number of embodiments.

[0031] Example 1

[0032] A method for preparing an edible and degradable starch-based elastic hydrogel comprises the following steps:

[0033] (1) Preparation of starch suspension: starch is dispersed in an aqueous solution of a polyol to obtain a starch suspension; the starch is 100 g corn starch; the polyol is glycerol; the volume ratio of the polyol to water in the aqueous solution of the polyol is 1:1; the mass ratio of the starch to the aqueous solution of the polyol in the starch suspension is 1:10;

[0034] (2) Thermal gelatinization: The starch suspension was gelatinized in a boiling water bath to obtain solution A. The boiling water bath gelatinization process was as follows: in a 100°C water bath, magnetically stirred at 800 rpm for 30 min.

[0035] (3) Mixing organic solvents: The organic solvent is mixed into solution A and stirred evenly to obtain solution B; the treatment conditions for the mixed organic solvent are: magnetic stirring at 800 rpm for 1 h; the organic solvent is ethanol; the volume ratio of the organic solvent to the aqueous solution of the polyol is 1:1;

[0036] (4) Centrifugation: Centrifuge Solution B at 8000 rpm for 10 min to remove the supernatant and obtain the precipitate;

[0037] (5) Phase separation: The precipitate was dried in an oven at 50 °C for 2 days to obtain a starch-based hydrogel.

[0038] The morphology, structure and mechanical properties of the prepared samples are characterized as follows:

[0039] Morphological observation: Figure 2In (a), the sample was frozen to sublime the water, then coated on a conductive adhesive and sprayed with gold for cryo-electron microscopy (cryo-EM) observation.

[0040] Moisture content: Figure 3 In (a), cut the sample into pieces and use a moisture tester to measure the moisture content of the sample.

[0041] Mechanical properties: such as Figure 4 (a) and Figure 5 In (a), the sample is tested for strain-stress curve and rebound curve.

[0042] Structural observation: Figure 6 (a) in Figure 7 (a) X-ray diffraction pattern (XRD) and Fourier transform infrared spectrum (FTIR) of the test sample.

[0043] Degradability: Figure 8 In (a), the sample was placed in soil to test its degradability.

[0044] From cryo-EM, XRD, and FTIR, this example successfully produced a porous cross-linked starch-based elastic hydrogel with a moisture content of 28.19%, a maximum tensile strain and a maximum tensile stress of 263.0% and 104 kPa, respectively. It has excellent resilience and can be completely degraded in soil within 27 days.

[0045] Example 2

[0046] A method for preparing an edible and degradable starch-based elastic hydrogel comprises the following steps:

[0047] (1) Preparation of starch suspension: starch is dispersed in an aqueous solution of a polyol to obtain a starch suspension; the starch is 50 g of potato starch and 50 g of highland barley starch; the polyol is erythritol and xylitol in a mass ratio of 1:1; the volume ratio of the polyol to water in the aqueous solution of the polyol is 2:8; the mass ratio of the starch to the aqueous solution of the polyol in the starch suspension is 1:2;

[0048] (2) Thermal gelatinization: The starch suspension was gelatinized in a boiling water bath to obtain solution A. The boiling water bath gelatinization process was as follows: in a 100°C water bath, magnetically stirred at 800 rpm for 30 min.

[0049] (3) Mixing organic solvents: The organic solvent is mixed into solution A and stirred evenly to obtain solution B; the treatment conditions for the mixed organic solvent are: magnetic stirring at 800 rpm for 1 h; the organic solvent is ethanol; the volume ratio of the organic solvent to the aqueous solution of the polyol is 2:1;

[0050] (4) Centrifugation: Centrifuge Solution B at 8000 rpm for 10 min to remove the supernatant and obtain the precipitate;

[0051] (5) Phase separation: The precipitate was dried in an oven at 20 °C for 2 days to obtain a starch-based hydrogel.

[0052] The morphology, structure and mechanical properties of the prepared samples are characterized as follows:

[0053] Morphological observation: Figure 2 In (b), the sample was frozen to sublime the water, then coated on a conductive adhesive and sprayed with gold for cryo-electron microscopy (cryo-EM) observation.

[0054] Moisture content: Figure 3 In (b), the sample is cut into pieces and the moisture content of the sample is measured using a moisture tester.

[0055] Mechanical properties: such as Figure 4 (b) and Figure 5 In (b), the sample is tested for strain-stress curve and rebound curve.

[0056] Structural observation: Figure 6 (b) Figure 7 (b) X-ray diffraction pattern (XRD) and Fourier transform infrared spectrum (FTIR) of the test sample.

[0057] Degradability: Figure 8 In (b), the samples were placed in soil to test their degradability.

[0058] From cryo-EM, XRD and FTIR, this example successfully produced a porous cross-linked starch-based elastic hydrogel with a moisture content of 20.58%, a maximum tensile strain and stress of 256.5% and 318 kPa, respectively. It has excellent rebound ability and can be completely degraded in soil within 27 days.

[0059] Example 3

[0060] A method for preparing an edible and degradable starch-based elastic hydrogel comprises the following steps:

[0061] (1) Preparation of starch suspension: starch was dispersed in an aqueous solution of a polyol to obtain a starch suspension; the starch was 33 g rice starch, 33 g wheat starch, and 33 g cassava starch in a mass ratio; the polyol was mannitol and sorbitol in a mass ratio of 1:1; the volume ratio of the polyol to water in the aqueous solution of the polyol was 9:1; the mass ratio of the starch to the aqueous solution of the polyol in the starch suspension was 1:50;

[0062] (2) Thermal gelatinization: The starch suspension was gelatinized in a boiling water bath to obtain solution A. The boiling water bath gelatinization process was as follows: in a 100°C water bath, magnetically stirred at 800 rpm for 30 min.

[0063] (3) Mixing organic solvents: The organic solvent is mixed into solution A and stirred evenly to obtain solution B; the treatment conditions for the mixed organic solvent are: magnetic stirring at 800 rpm for 1 h; the organic solvent is a mixed solution of acetone and n-hexane, and the volume ratio of acetone to n-hexane is 1:1; the volume ratio of the organic solvent to the aqueous solution of the polyol is 1:2;

[0064] (4) Centrifugation: Centrifuge Solution B at 8000 rpm for 10 min to remove the supernatant and obtain the precipitate;

[0065] (5) Phase separation: The precipitate was dried in an oven at 80 °C for 2 days to obtain a starch-based hydrogel.

[0066] The morphology, structure and mechanical properties of the prepared samples are characterized as follows:

[0067] Morphological observation: Figure 2 In (c), the sample was frozen to sublime the water, then coated on a conductive adhesive and sprayed with gold for cryo-electron microscopy (cryo-EM) observation.

[0068] Moisture content: Figure 3 In (c), the sample is cut into pieces and the moisture content of the sample is measured using a moisture tester.

[0069] Mechanical properties: such as Figure 4 (c) and Figure 5 In (c), the sample is tested for strain-stress curve and rebound curve.

[0070] Structural observation: Figure 6 (c) Figure 7 (c) X-ray diffraction pattern (XRD) and Fourier transform infrared spectrum (FTIR) of the test sample.

[0071] Degradability: Figure 8 In (c), the samples were placed in soil to test their degradability.

[0072] From cryo-EM, XRD and FTIR, this example successfully produced a porous starch-based elastic hydrogel with a moisture content of 58.32%, a maximum tensile strain and stress of 329.5% and 60 kPa, respectively. It has excellent resilience and can be completely degraded in soil within 24 days.

[0073] Comparative Example 1

[0074] The difference between this comparative example and Example 1 is that no polyol is used, and the preparation steps are as follows:

[0075] (1) Preparation of starch suspension: Disperse 100 g corn starch in aqueous solution to obtain starch suspension; the mass ratio of starch to water is 1:10;

[0076] (2) Thermal gelatinization: The starch suspension was gelatinized in a boiling water bath to obtain solution A. The boiling water bath gelatinization process was as follows: in a 100°C water bath, magnetically stirred at 800 rpm for 30 min.

[0077] (3) Mixing organic solvents: The organic solvent is mixed into solution A and stirred evenly to obtain solution B; the treatment conditions for the mixed organic solvent are: magnetic stirring at 800 rpm for 1 h; the organic solvent is ethanol; the volume ratio of the organic solvent to the aqueous solution of the polyol is 1:1;

[0078] (4) Centrifugation: Centrifuge Solution B at 8000 rpm for 10 min to remove the supernatant and obtain the precipitate;

[0079] (5) Phase separation: The precipitate was dried in an oven at 50 °C for 2 days to obtain a starch-based hydrogel.

[0080] The morphology, structure and mechanical properties of the prepared samples are characterized as follows:

[0081] Morphological observation: Figure 2 In (d), the sample was frozen to sublime the water, then coated on a conductive adhesive and sprayed with gold for cryo-electron microscopy (cryo-EM) observation.

[0082] Moisture content: Figure 3 In (d), cut the sample into pieces and use a moisture tester to measure the moisture content of the sample.

[0083] Mechanical properties: such as Figure 4 In (d), the sample is tested for strain-stress curve.

[0084] Structural observation: Figure 6 (d) X-ray diffraction pattern (XRD) of the test sample.

[0085] Cryo-EM and XRD analysis revealed that this example failed to successfully produce a porous, cross-linked starch-based elastic hydrogel. Its moisture content was 5.68%, and its maximum tensile strain and maximum tensile stress were 23.5% and 328 kPa, respectively, indicating poor mechanical properties. This comparison with Example 1 demonstrates the importance of polyols in forming dynamic hydrogen bonds to improve the mechanical properties of starch-based hydrogels.

[0086] Comparative Example 2

[0087] The difference between this comparative example and Example 1 is that the phase separation temperature is too low, and the preparation steps are as follows:

[0088] (1) Preparation of starch suspension: starch is dispersed in an aqueous solution of a polyol to obtain a starch suspension; the starch is 100 g corn starch; the polyol is glycerol; the volume ratio of the polyol to water in the aqueous solution of the polyol is 1:1; the mass ratio of the starch to the aqueous solution of the polyol in the starch suspension is 1:10;

[0089] (2) Thermal gelatinization: The starch suspension was gelatinized in a boiling water bath to obtain solution A. The boiling water bath gelatinization process was as follows: in a 100°C water bath, magnetically stirred at 800 rpm for 30 min.

[0090] (3) Mixing organic solvents: The organic solvent is mixed into solution A and stirred evenly to obtain solution B; the treatment conditions for the mixed organic solvent are: magnetic stirring at 800 rpm for 1 h; the organic solvent is ethanol; the volume ratio of the organic solvent to the aqueous solution of the polyol is 1:1;

[0091] (4) Centrifugation: Centrifuge Solution B at 8000 rpm for 10 min to remove the supernatant and obtain the precipitate;

[0092] (5) Phase separation: The precipitate was dried in an oven at 10°C for 2 days to obtain a starch-based hydrogel.

[0093] The morphology, structure and mechanical properties of the prepared samples are characterized as follows:

[0094] Morphological observation: Figure 2 In (e), the sample was frozen to sublime the water, then coated on a conductive adhesive and sprayed with gold for cryo-electron microscopy (cryo-EM) observation.

[0095] Moisture content: Figure 3 In (e), cut the sample into pieces and use a moisture tester to measure the moisture content of the sample.

[0096] Mechanical properties: such as Figure 4 In (e), the sample is tested for strain-stress curve.

[0097] Structural observation: Figure 6 (e) X-ray diffraction pattern (XRD) of the test sample.

[0098] From cryo-EM and XRD, this comparative example successfully prepared a starch-based elastic hydrogel, but the pore distribution was uneven, its water content was 16.4%, and its maximum tensile strain and maximum tensile stress were 11.3% and 81 kPa respectively, and the mechanical properties were poor. Comparative Example 1 shows the importance of phase separation temperature to the mechanical properties of starch-based hydrogels. The lower phase separation temperature causes the starch chain to have insufficient thermal driving force in the phase separation stage, resulting in reduced starch chain mobility and insufficient cross-linking, which leads to poor mechanical properties of the sample.

[0099] Comparative Example 3

[0100] The difference between this comparative example and Example 1 is that the phase separation temperature is too high, and the preparation steps are as follows:

[0101] (1) Preparation of starch suspension: starch is dispersed in an aqueous solution of a polyol to obtain a starch suspension; the starch is 100 g corn starch; the polyol is glycerol; the volume ratio of the polyol to water in the aqueous solution of the polyol is 1:1; the mass ratio of the starch to the aqueous solution of the polyol in the starch suspension is 1:10;

[0102] (2) Thermal gelatinization: The starch suspension was gelatinized in a boiling water bath to obtain solution A. The boiling water bath gelatinization process was as follows: in a 100°C water bath, magnetically stirred at 800 rpm for 30 min.

[0103] (3) Mixing organic solvents: The organic solvent is mixed into solution A and stirred evenly to obtain solution B; the treatment conditions for the mixed organic solvent are: magnetic stirring at 800 rpm for 1 h; the organic solvent is ethanol; the volume ratio of the organic solvent to the aqueous solution of the polyol is 1:1;

[0104] (4) Centrifugation: Centrifuge Solution B at 8000 rpm for 10 min to remove the supernatant and obtain the precipitate;

[0105] (5) Phase separation: The precipitate was dried in an oven at 90 °C for 2 days to obtain a starch-based hydrogel.

[0106] The morphology, structure and mechanical properties of the prepared samples are characterized as follows:

[0107] Morphological observation: Figure 2 In (f), the sample was frozen to sublime the water, then coated on a conductive adhesive and sprayed with gold for cryo-electron microscopy (cryo-EM) observation.

[0108] Moisture content: Figure 3 In (f), cut the sample into pieces and use a moisture tester to measure the moisture content of the sample.

[0109] Mechanical properties: such as Figure 4 In (f), the sample is tested for strain-stress curve.

[0110] Structural observation: Figure 6 (f) X-ray diffraction pattern (XRD) of the tested sample.

[0111] From cryo-EM and XRD, this comparative example failed to successfully produce a starch-based elastic hydrogel with a non-porous structure, a water content of 10.68%, a maximum tensile strain and stress of 23.2% and 261 kPa, respectively, and poor mechanical properties. Comparative Example 1 shows the importance of phase separation temperature to the formation of starch-based hydrogels. Excessively high phase separation temperatures prevent organic solvents and water from reacting with starch chains, leading to rapid volatilization and removal, which weakens the phase separation effect and prevents the formation of dense and loose regions, resulting in the inability to form a hydrogel with strong mechanical properties.

[0112] Comparative Example 4

[0113] The difference between this comparative example and Example 1 is that the organic solvent is too little, and the preparation steps are as follows:

[0114] (1) Preparation of starch suspension: starch is dispersed in an aqueous solution of a polyol to obtain a starch suspension; the starch is 100 g corn starch; the polyol is glycerol; the volume ratio of the polyol to water in the aqueous solution of the polyol is 1:1; the mass ratio of the starch to the aqueous solution of the polyol in the starch suspension is 1:10;

[0115] (2) Thermal gelatinization: The starch suspension was gelatinized in a boiling water bath to obtain solution A. The boiling water bath gelatinization process was as follows: in a 100°C water bath, magnetically stirred at 800 rpm for 30 min.

[0116] (3) Mixing organic solvents: The organic solvent is mixed into solution A and stirred evenly to obtain solution B; the treatment conditions for the mixed organic solvent are: magnetic stirring at 800 rpm for 1 h; the organic solvent is ethanol; the volume ratio of the organic solvent to the aqueous solution of the polyol is 2:8;

[0117] (4) Centrifugation: Centrifuge Solution B at 8000 rpm for 10 min to remove the supernatant and obtain the precipitate;

[0118] (5) Phase separation: The precipitate was dried in an oven at 50 °C for 2 days to obtain a starch-based hydrogel.

[0119] The morphology, structure and mechanical properties of the prepared samples are characterized as follows:

[0120] Morphological observation: Figure 2 In (g), the sample was frozen to sublime the water and then coated on a conductive adhesive and sprayed with gold for cryo-electron microscopy (cryo-EM) observation.

[0121] Moisture content: Figure 3After the sample is cut into pieces, the moisture content of the sample is measured using a moisture tester.

[0122] Mechanical properties: such as Figure 4 In (g), the sample was tested for strain-stress curve.

[0123] Structural observation: Figure 6 (g) X-ray diffraction pattern (XRD) of the test sample.

[0124] From cryo-EM and XRD, this comparative example successfully prepared a starch-based elastic hydrogel with a moisture content of 47.30%, a maximum tensile strain and a stress of 5.1% and 60 kPa, respectively, and poor mechanical properties. Comparative Example 1 shows the importance of mixed organic solvents in the phase separation process. Due to the different affinities of starch in organic solvents and polyol solutions, starch chains can be separated. Organic solvents mainly cause the rearrangement of starch chains to form V-shaped single helical crystals, promote hydrogel cross-linking, and improve the mechanical properties of the hydrogel. Therefore, the proportion of organic solvent is low, and the phase separation step cannot be carried out, resulting in the poor mechanical properties of the starch-based hydrogel formed.

[0125] Comparative Example 5

[0126] The difference between this comparative example and Example 1 is that there is too much organic solvent, and the preparation steps are as follows:

[0127] (1) Preparation of starch suspension: starch is dispersed in an aqueous solution of a polyol to obtain a starch suspension; the starch is 100 g corn starch; the polyol is glycerol; the volume ratio of the polyol to water in the aqueous solution of the polyol is 1:1; the mass ratio of the starch to the aqueous solution of the polyol in the starch suspension is 1:10;

[0128] (2) Thermal gelatinization: The starch suspension was gelatinized in a boiling water bath to obtain solution A. The boiling water bath gelatinization process was as follows: in a 100°C water bath, magnetically stirred at 800 rpm for 30 min.

[0129] (3) Mixing organic solvents: The organic solvent is mixed into solution A and stirred evenly to obtain solution B; the treatment conditions for the mixed organic solvent are: magnetic stirring at 800 rpm for 1 h; the organic solvent is ethanol; the volume ratio of the organic solvent to the aqueous solution of the polyol is 3:1;

[0130] (4) Centrifugation: Centrifuge Solution B at 8000 rpm for 10 min to remove the supernatant and obtain the precipitate;

[0131] (5) Phase separation: The precipitate was dried in an oven at 50 °C for 2 days to obtain a starch-based hydrogel.

[0132] The morphology, structure and mechanical properties of the prepared samples are characterized as follows:

[0133] Morphological observation: Figure 2 In (f), the sample was frozen to sublime the water, then coated on a conductive adhesive and sprayed with gold for cryo-electron microscopy (cryo-EM) observation.

[0134] Moisture content: Figure 3 In (f), cut the sample into pieces and use a moisture tester to measure the moisture content of the sample.

[0135] Mechanical properties: such as Figure 4 In (f), the sample is tested for strain-stress curve.

[0136] Structural observation: Figure 6 (f) X-ray diffraction pattern (XRD) of the tested sample.

[0137] From cryo-EM and XRD, this comparative example failed to successfully produce a starch-based elastic hydrogel, with a moisture content of 6.89%, a maximum tensile strain and a stress of 34.8% and 362 kPa, respectively, and poor mechanical properties. Comparative Example 1 shows the importance of the ratio of organic solvent to polyol in improving the mechanical properties of the hydrogel. A higher ratio of organic solvent to polyol results in severe dehydration of the sample, which limits the activity space of the starch chain and causes the sample's mechanical properties to deteriorate.

[0138] Comparative Example 6

[0139] The difference between this comparative example and Example 1 is that the polyol and the organic solvent are added simultaneously, and the preparation steps are as follows:

[0140] (1) Mixing starch with other solutions: Starch, polyol aqueous solution, and organic solvent are mixed together to obtain a mixed suspension A. The starch is 100 g corn starch; the polyol is glycerol; the organic solvent is ethanol; the volume ratio of the polyol to water in the polyol aqueous solution is 1:1; the mass ratio of starch to the polyol aqueous solution is 1:10; and the volume ratio of the organic solvent to the polyol aqueous solution is 1:1.

[0141] (2) Thermal gelatinization: The mixed suspension A obtained in step (1) was gelatinized in a boiling water bath to obtain solution B. The gelatinization process was as follows: in a 100°C water bath, magnetically stirred at 800 rpm for 30 min;

[0142] (3) Centrifugation: Centrifuge Solution B at 8000 rpm for 10 min to remove the supernatant and obtain the precipitate;

[0143] (5) Phase separation: The precipitate was dried in an oven at 50 °C for 2 days to obtain a starch-based hydrogel.

[0144] The sample prepared in this comparative example was difficult to form, the starch-based elastic hydrogel was not successfully prepared, and the strain-stress curve could not be tested. Comparative Example 1 shows the importance of the order in which the polyol and the organic solvent act on starch.

[0145] Comparative Example 7

[0146] The difference between this comparative example and Example 1 is that no phase separation is performed, and the preparation steps are as follows:

[0147] (1) Preparation of starch suspension: starch is dispersed in an aqueous solution of a polyol to obtain a starch suspension; the starch is 100 g corn starch; the polyol is glycerol; the volume ratio of the polyol to water in the aqueous solution of the polyol is 1:1; the mass ratio of the starch to the aqueous solution of the polyol in the starch suspension is 1:10;

[0148] (2) Thermal gelatinization: The starch suspension was gelatinized in a boiling water bath to obtain solution A. The boiling water bath gelatinization process was as follows: in a 100°C water bath, magnetically stirred at 800 rpm for 30 min.

[0149] (3) Mixing organic solvents: The organic solvent is mixed into solution A and stirred evenly to obtain solution B; the treatment conditions for the mixed organic solvent are: magnetic stirring at 800 rpm for 1 h; the organic solvent is ethanol; the volume ratio of the organic solvent to the aqueous solution of the polyol is 1:1;

[0150] (4) Centrifugation: Centrifuge solution B at 8000 rpm for 10 min to remove the supernatant and obtain the precipitate.

[0151] The sample prepared in this comparative example was fragile and difficult to form, and the starch-based elastic hydrogel was not successfully prepared, and the strain-stress curve could not be tested. Comparative Example 1 shows the importance of the phase separation step for the formation of starch-based elastic hydrogel.

[0152] The above examples and comparative examples demonstrate the importance of polyols, organic solvents, their ratio, and phase separation temperature for the formation of edible and stretchable starch-based hydrogels. Starch granules undergo thermal gelation in a polyol aqueous solution (i.e., a good solvent) at 100°C, forming a near-equilibrium network. Subsequently, gradual replacement of the organic solvent triggers controlled phase separation, inducing the evolution of a biphasic structure: (i) localized aggregation of starch chains into dense sacrificial domains and (ii) the overall formation of an interconnected dilute phase network. This unique structure creates a stress redistribution mechanism, in which the continuous dilute phase promotes stress transfer, while the dense domains act as energy dissipation motifs through sacrificial bond cleavage, synergistically improving the mechanical properties of the starch hydrogel. The polyol forms dynamic hydrogen bonds with starch and water, facilitating the stretching and rebound of the hydrogel. However, the lack of polyol interaction results in a decrease in bound water content, hindering hydrogel formation. Organic solvents can induce supramolecular reorganization of starch chains, triggering chain entanglement and densification, promoting an increase in cross-linking density, thereby improving mechanical strength, and increasing the effective chain length within the same distance, thereby amplifying the macroscopic strain, which is beneficial to improving the strength and toughness of the hydrogel. When the volume ratio of organic solvent to polyol is too high, the sample will be severely dehydrated, the starch chain cross-linking will be restricted, and the mechanical properties of the sample will deteriorate. The mechanical properties of starch-based hydrogels are also affected by the phase separation temperature. Excessively high phase separation temperatures cause the organic solvent and water to evaporate and be removed too quickly before they have time to react with the starch chains, resulting in a weakened phase separation effect and the inability to form dense and loose areas, resulting in the inability to form a hydrogel with strong mechanical properties. A lower phase separation temperature results in insufficient thermal driving force for the starch chains during the phase separation stage, resulting in reduced starch chain activity and insufficient cross-linking, which in turn leads to poor mechanical properties of the sample.

[0153] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, make some changes or modifications to equivalent embodiments using the technical contents disclosed above. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing an edible and degradable starch-based elastic hydrogel, characterized in that: The steps include: (1) Preparing a starch suspension: dispersing starch in an aqueous solution of a polyol to obtain a starch suspension; the volume ratio of the polyol to water in the aqueous solution of the polyol is 2:8 to 9:1; the mass ratio of starch to the aqueous solution of the polyol in the starch suspension is 1:50 to 1:2; the polyol is one or more of glycerol, erythritol, xylitol, mannitol, and sorbitol; (2) Thermal gelatinization: The starch suspension is gelatinized in a boiling water bath to obtain solution A; (3) Mixing organic solvents: mixing an organic solvent into solution A and stirring evenly to obtain solution B; the treatment conditions for the mixed organic solvents are: magnetic stirring at 800 rpm for 1 hour; the organic solvent is one or more of ethanol, acetone, and n-hexane; the volume ratio of the organic solvent to the aqueous solution of the polyol is 1:2 to 2:1; (4) Centrifugation: Remove the supernatant from solution B by centrifugation to obtain the precipitate; (5) Phase separation: The precipitate is placed in an oven at a certain temperature and dried for 2 days to obtain a starch-based hydrogel; the phase separation temperature is 20-80°C.

2. The preparation method according to claim 1, characterized in that The starch is one or more of corn starch, potato starch, highland barley starch, rice starch, wheat starch and tapioca starch.

3. The preparation method according to claim 1, characterized in that The boiling water bath gelatinization process is as follows: in a 100° C. water bath, magnetic stirring is performed at a speed of 800 rpm for 30 minutes.

4. The preparation method according to claim 1, characterized in that The centrifugation condition is: 8000 rpm for 10 min.

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