Environment-friendly degradable green material and preparation process thereof

Abstract

The invention relates to the technical field of degradable materials, and discloses an environment-friendly degradable green material and a preparation process thereof, and the preparation process comprises the steps of raw material pretreatment, thermal response unit preparation, magnetic material biological extraction, thermal memory unit construction, multi-layer composite molding, thermal history accumulation trigger system construction, surface patterning treatment and the like. By constructing a three-stage linkage structure of heat energy capture, storage and slow release, the function that the material can still be degraded continuously in the intermittent period of a magnetic field is achieved, the dependence of a traditional thermal response material on the environment temperature is broken through, the degradation process can be remotely and actively controlled, and the degradation period can be accurately adjusted within the range of 15-120 days; the applicability and the energy utilization efficiency of the magnetic thermal response system in a complex environment are obviously improved.

Description

Technical Field

[0001] The present invention relates to the technical field of degradable materials, and more specifically, it relates to an environment-friendly degradable green material and its preparation process. Background Art

[0002] With the improvement of environmental protection awareness, the application of degradable biofilm materials in fields such as agricultural mulch films and drug sustained-release carriers has become increasingly widespread. However, the current degradable biofilms have the following technical problems: The degradation rate of existing degradable biofilms is difficult to precisely control, resulting in the inability to meet the diverse requirements of different application scenarios for the degradation time of materials in practical applications. For example, agricultural mulch films need to remain intact during the growth period of crops and rapidly degrade after harvest; drug sustained-release carriers need to degrade and release drugs at corresponding time points according to the treatment plan; Traditional thermoresponsive degradable materials rely entirely on the natural change of environmental temperature for passive degradation, and cannot achieve artificial intervention and remote active control, resulting in the degradation process being difficult to adapt to complex and changeable usage environments; Although some magnetothermal composite responsive materials have been developed in recent years, the internal temperature of such materials rapidly returns to the environmental temperature after the magnetic field is removed, and the thermoresponsive degradation unit cannot record the cumulative amount of received thermal stimuli, resulting in the degradation process stagnating during the magnetic field intermittent period, and continuous application of the magnetic field is required to maintain the degradation, which severely limits its practical application and causes energy waste. Summary of the Invention

[0003] The present invention provides an environment-friendly degradable green material and its preparation process, aiming to solve the above technical problems, achieve precise control and remote adjustment of the degradation behavior of degradable biofilms, and still maintain a continuous degradation process under intermittent magnetic field stimulation conditions.

[0004] The present invention provides an environment-friendly degradable green material, which includes a basic thermoresponsive layer, a magnetothermal conversion layer, and a thermosensitive memory layer stacked in sequence from bottom to top; Among them, the basic thermoresponsive layer contains thermoresponsive degradation units, the magnetothermal conversion layer contains magnetic particles that generate heat under the action of an alternating magnetic field, the thermosensitive memory layer contains a thermal history recording unit and a phase change material, the thermal history recording unit can record the cumulative effect of multiple short-term magnetothermal stimuli and trigger the degradation process when the cumulative heat reaches a preset threshold, and the phase change material stores thermal energy when heated and slowly releases heat after the magnetic field is removed to maintain the continuous progress of the degradation process, thereby realizing that the biofilm can continue to degrade during the magnetic field intermittent period.

[0005] Preferably: the thickness ratio of the thermosensitive memory layer, the magnetothermal conversion layer, and the basic thermoresponsive layer is 3:2:4.

[0006] Preferably, the basic thermal response layer is composed of modified starch, chitosan and thermal response degradation units, and their mass percentages are 50-70%, 20-30% and 10-20% respectively.

[0007] Preferably, the magnetic particles in the magnetothermal conversion layer are magnetite particles of biological origin, with a particle size of 50-100 nm, and are distributed in an ordered arrangement in the magnetothermal conversion layer.

[0008] Preferably, the phase change material in the thermosensitive memory layer is a plant wax microcapsule coated with chitosan, and its phase change temperature is 35-40 °C.

[0009] A preparation process of an environmentally friendly degradable green material, comprising the following steps: Step 1: Preparation of the thermal response degradation unit: Mix fatty acid ester and modified polyethylene glycol in a mass ratio of 3:1 and melt, add epoxidized triglyceride to react, cool and grind, and then mix with citric acid for treatment to obtain a thermal response degradation unit with a carboxyl group on the surface; Step 2: Biological extraction and modification of magnetic materials: Extract magnetite from iron-rich biomass and perform surface modification with chitosan; Step 3: Construction of the thermosensitive memory unit: Prepare phase change microcapsules, synthesize a thermal history recording unit, and mix the two to obtain a thermosensitive memory unit; Step 4: Multilayer composite molding: Sequentially prepare mixtures of the basic thermal response layer, the magnetothermal conversion layer and the thermosensitive memory layer, and stack the three layers into a composite film using a continuous casting technique; Step 5: Construction of the thermal history accumulation triggering system: Perform gradient cross-linking treatment on the composite film to form a gradient structure with a gradually decreasing cross-linking density from the surface to the inside, and perform surface patterning treatment.

[0010] Preferably, the biological extraction of magnetic materials in Step 2 includes: collecting iron-rich plant materials or iron bacteria cultures, drying and grinding, soaking in a citric acid solution, filtering and adding sodium hydroxide solution to adjust the pH to 10-11 to form a precipitate, and heat-treating the precipitate under nitrogen protection to obtain a powder of magnetite of biological origin.

[0011] Preferably, the preparation of the phase change microcapsules in Step 3 includes: mixing natural plant wax and modified vegetable oil in a mass ratio of 2:1 and melting, adding modified starch as a skeleton material, preparing into micron-sized droplets by high-speed shear homogenization treatment, and adding a chitosan solution for coating.

[0012] Preferably, the synthesis of the thermal history recording unit in Step 3 includes: mixing epoxidized triglyceride and polyol in a molar ratio of 1:2 to react to obtain a polyhydroxy prepolymer, and adding a thermal response degradation unit and methyl cellulose to form a thermal history recording composite system.

[0013] Preferably, the preparation of the magnetothermal conversion layer in step 4 includes: mixing modified starch, chitosan solution and surface-modified magnetic particles, placing them in a magnetic field of 300-500 Gauss and standing still to make the magnetic particles form an ordered arrangement, and adding a crosslinking agent to fix the spatial distribution of the magnetic particles.

[0014] Preferably, the gradient crosslinking treatment in step 5 includes: spraying a crosslinking agent solution with a concentration increasing from 0.5% to 2% on the composite membrane, while applying a pulsed magnetic field with a frequency of 1 Hz, a duration of 10 seconds, an interval of 20 seconds, and repeating 10-15 times.

[0015] The beneficial effects of the present invention are as follows: It breaks through the limitation of the passive dependence of traditional thermoresponsive degradable materials on environmental temperature and realizes the remote active control of the degradation process. By triggering the material degradation with an external magnetic field, the degradation process is no longer limited by the natural change of environmental temperature, greatly expanding the application scenarios of the material; It creatively solves the technical problem of degradation stagnation of magnetothermal-responsive materials under intermittent stimulation conditions, enabling the material to continue to degrade after the magnetic field is removed. Through the "thermal history cumulative trigger" effect of the thermosensitive memory unit, the material can record the cumulative effect of multiple short-term magnetothermal stimulations. When the cumulative heat reaches the preset threshold, the degradation process is automatically started, and the degradation can be maintained even during the magnetic field intermittent period; It realizes the precise control of the degradation rate of the degradable biofilm, and the degradation period can be accurately adjusted within the range of 15-120 days. By adjusting the composition and content of the thermoresponsive unit in the material, the distribution density of magnetic particles, and the gradient structure of the crosslinking network, the degradation period can be customized for different application scenarios to meet different application requirements; It significantly improves the energy utilization efficiency of the magnetothermal-responsive system. Through the capture and slow release of thermal energy by the phase change material, the material only needs to receive multiple short-term magnetic field stimulations to complete the entire degradation process. Compared with the traditional technology that requires continuous application of magnetic field, the energy utilization efficiency is increased by more than 65%; It realizes a magnetothermal-responsive degradable material system derived entirely from biological sources. By using magnetic materials, renewable resource-based materials and natural phase change materials of biological origin, the entire material system is more environmentally friendly and sustainable; The material system has excellent processability and formability, can be mass-produced by continuous casting technology, and has the potential for industrial-scale application.

[0016] These technical effects make the materials of the present invention particularly suitable for precision agriculture and drug targeted delivery systems that require remote control of the release process. For example, in precision agriculture, it can be used as an intelligent ground film, and the degradation time of the ground film can be triggered and controlled by an external magnetic field to precisely match the crop growth cycle. In the application of drug sustained-release carriers, the remote and precise control of the drug release process can be achieved through an external magnetic field, improving the treatment effect. At the same time, this material also has broad application prospects in the fields of environmental remediation, packaging materials, etc. Brief Description of the Drawings

[0017] Figure 1 is the degradation performance of the present invention under continuous magnetic field conditions; Figure 2 is the degradation performance of the present invention under intermittent magnetic field conditions; Figure 3 is the comparison of the expected and actual degradation cycles of different samples of the present invention; Figure 4 is the degradation cycles of different samples of the present invention under different environmental conditions; Figure 5 is the dynamic change of the degradation process of sample D3 of the present invention; Figure 6 is the comparison of the degradation rates of different samples of the present invention; Figure 7 is the comparison of the degradation times under different magnetic field application schemes of the present invention; Figure 8 is the comparison of the energy consumption required to reach 50% degradation of the present invention; Figure 9 is the energy saving ratio under the intermittent magnetic field scheme of the present invention; Figure 10 is the temperature change of the sample under the magnetic field of the present invention; Figure 11 is the comparison of the complete degradation time and degradation rate of the present invention; Figure 12 is the change of the microbial diversity index of the present invention; Figure 13 is the toxicity assessment of the degradation products of the present invention. Detailed Embodiments

[0018] Now, the subject matter described herein will be discussed with reference to exemplary embodiments. It should be understood that discussing these embodiments is only to enable those skilled in the art to better understand and thus implement the subject matter described herein. Without departing from the scope of protection of the content of this specification, changes can be made to the functions and arrangements of the elements discussed. Each example can omit, substitute, or add various processes or components as needed. Additionally, the features described in some examples can also be combined in other examples.

[0019] In at least one embodiment of the present invention, an environmentally friendly degradable green material is disclosed, which includes a basic thermoresponsive layer, a magnetothermal conversion layer, and a thermosensitive memory layer stacked in sequence from bottom to top; Among them, the basic thermoresponsive layer contains thermoresponsive degradation units, the magnetothermal conversion layer contains magnetic particles that generate heat under the action of an alternating magnetic field, and the thermosensitive memory layer contains a thermal history recording unit and a phase change material. The thermal history recording unit can record the cumulative effect of multiple short-term magnetothermal stimulations and trigger the degradation process when the cumulative heat reaches a preset threshold. The phase change material stores thermal energy when heated and slowly releases heat after the magnetic field is removed to maintain the continuous progress of the degradation process, so as to realize that the biofilm can continue to degrade during the magnetic field intermittent period.

[0020] Among them: The thickness ratio of the thermosensitive memory layer, the magnetothermal conversion layer, and the basic thermoresponsive layer is 3:2:4.

[0021] In at least one embodiment of the present invention, it is disclosed that the basic thermoresponsive layer is composed of modified starch, chitosan, and thermoresponsive degradation units, and their mass percentages are 50%, 30%, and 20% respectively.

[0022] In at least one embodiment of the present invention, it is disclosed that the basic thermoresponsive layer is composed of modified starch, chitosan, and thermoresponsive degradation units, and their mass percentages are 60%, 20%, and 20% respectively.

[0023] In at least one embodiment of the present invention, it is disclosed that the basic thermoresponsive layer is composed of modified starch, chitosan, and thermoresponsive degradation units, and their mass percentages are 70%, 20%, and 10% respectively.

[0024] In at least one embodiment of the present invention, it is disclosed that the basic thermoresponsive layer is composed of modified starch, chitosan, and thermoresponsive degradation units, and their mass percentages are 60%, 25%, and 15% respectively. In at least one embodiment of the present invention, it is disclosed that the magnetic particles in the magnetothermal conversion layer are magnetic iron oxide particles of biological origin, with a particle size of 50 nm, and are distributed in an ordered arrangement in the magnetothermal conversion layer.

[0025] In at least one embodiment of the present invention, it is disclosed that the magnetic particles in the magnetothermal conversion layer are magnetic iron oxide particles of biological origin, with a particle size of 80 nm, and are distributed in an ordered arrangement in the magnetothermal conversion layer.

[0026] In at least one embodiment of the present invention, it is disclosed that the magnetic particles in the magnetothermal conversion layer are magnetic iron oxide particles of biological origin, with a particle size of 100 nm, and are distributed in an ordered arrangement in the magnetothermal conversion layer.

[0027] In at least one embodiment of the present invention, the phase change material in the thermosensitive memory layer is a plant wax microcapsule coated with chitosan, and its phase change temperature is 35°C.

[0028] In at least one embodiment of the present invention, the phase change material in the thermosensitive memory layer is a plant wax microcapsule coated with chitosan, and its phase change temperature is 38°C.

[0029] In at least one embodiment of the present invention, the phase change material in the thermosensitive memory layer is a plant wax microcapsule coated with chitosan, and its phase change temperature is 40°C.

[0030] In at least one embodiment of the present invention, a preparation process of an environment-friendly and degradable green material is disclosed, including the following steps: Step 1: Preparation of the thermoresponsive degradation unit: Mix fatty acid ester and modified polyethylene glycol in a mass ratio of 3:1 and melt them, add epoxidized triglyceride for reaction, cool and grind, and then mix with citric acid for treatment to obtain a thermoresponsive degradation unit with carboxyl groups on the surface; Step 2: Biological extraction and modification of magnetic materials: Extract magnetic iron oxide from iron-rich biomass and perform surface modification with chitosan; Step 3: Construction of the thermosensitive memory unit: Prepare phase change microcapsules, synthesize a thermal history recording unit, and mix the two to obtain a thermosensitive memory unit; Step 4: Multilayer composite molding: Prepare mixtures of the base thermoresponsive layer, the magnetothermal conversion layer, and the thermosensitive memory layer in sequence, and stack the three layers into a composite film using the continuous casting technique; Step 5: Construction of the thermal history accumulation triggering system: Perform gradient crosslinking treatment on the composite film to form a gradient structure with a gradually decreasing crosslinking density from the surface to the inside, and perform surface patterning treatment.

[0031] Wherein: The biological extraction of magnetic materials in Step 2 includes: Collecting iron-rich plant materials or iron bacteria cultures, drying and grinding them, soaking them in a citric acid solution, filtering and adding sodium hydroxide solution to adjust the pH to 10 or 10.5 or 11 (adjusting the pH to 10 in this embodiment) to form a precipitate, and heat-treating the precipitate under nitrogen protection to obtain bio-derived magnetic iron oxide powder.

[0032] The preparation of phase change microcapsules in Step 3 includes: Mixing natural plant wax and modified vegetable oil in a mass ratio of 2:1 and melting them, adding modified starch as a skeleton material, preparing micron-sized droplets through high-speed shear homogenization treatment, and coating them with chitosan solution.

[0033] The synthesis of the thermal history recording unit in Step 3 includes: Mixing epoxidized triglyceride and polyol in a molar ratio of 1:2 for reaction to obtain a polyhydroxy prepolymer, and adding the thermoresponsive degradation unit and methyl cellulose to form a thermal history recording composite system.

[0034] The preparation of the magnetothermal conversion layer in step 4 includes: mixing modified starch, chitosan solution and surface-modified magnetic particles, placing them in a magnetic field of 300 or 400 or 500 (400 is selected in this embodiment) Gauss and standing still to make the magnetic particles form an orderly arrangement, and adding a crosslinking agent to fix the spatial distribution of the magnetic particles.

[0035] The gradient crosslinking treatment in step 5 includes: spraying a crosslinking agent solution with a concentration increasing from 0.5% to 2% on the composite membrane, while applying a pulsed magnetic field with a frequency of 1 Hz, a duration of 10 seconds, an interval of 20 seconds, and repeating 10 or 12 or 15 times (12 times are repeated in this embodiment).

[0036] Specific implementation examples: A preparation process of an environment-friendly and degradable green material includes the following steps: 1. Raw material preparation The main raw materials used in this embodiment include: Base materials: modified starch (such as hydroxypropyl starch, oxidized starch, etc.), chitosan (deacetylation degree ≥ 85%); Thermal response materials: fatty acid esters with specific melting points, modified polyethylene glycol (PEG); Sources of magnetic materials: iron methyl ferns (such as Adiantum capillus-veneris), iron bacteria cultures; Thermal memory materials: natural phase change waxes, modified vegetable oils; Crosslinking agents: epoxidized triglycerides, citric acid; Auxiliary materials: glycerol, vegetable oils, natural plasticizers.

[0037] The above materials are all renewable resources or biodegradable materials, meeting environmental protection requirements.

[0038] 2. Raw material pretreatment Step 2.1. Starch modification treatment The starch is gelatinized in a water bath at 50 - 60 °C for 15 - 30 minutes, citric acid (5 - 10% of the starch mass) is added for an esterification reaction, the pH is adjusted to 8.0 - 8.5, after reacting for 2 - 4 hours, it is cooled to room temperature, washed with water until neutral, and vacuum dried to obtain modified starch.

[0039] Step 2.2. Chitosan activation treatment The chitosan is dissolved in a 2% acetic acid solution, stirred until completely dissolved, sodium hydroxide solution is added to adjust the pH to 5.0 - 5.5, ultrasonic treatment is carried out for 30 minutes, and it is left standing overnight to obtain an activated chitosan solution.

[0040] 3. Preparation of the thermal response unit Step 3.1. Synthesis of the thermal response degradation unit The key to this step lies in synthesizing a degradation unit with a controllable thermal response threshold. The specific operations are as follows: Mix fatty acid esters (such as stearic acid esters) and modified polyethylene glycol in a mass ratio of 3:1, and melt them evenly at 60 °C; Add epoxidized triglyceride (5% of the mixture mass), and react at 65 - 70 °C for 4 hours to form a thermal response unit with a stable melting point; Cool down to room temperature, and grind the reaction product into fine powder with a particle size of 100 - 200 mesh; Mix the above fine powder with citric acid (weight ratio 10:1), and treat it at 55 °C for 1 hour to obtain a thermal response degradation unit with carboxyl groups on its surface.

[0041] The thermal response degradation unit prepared in this step has a clear thermal response threshold (35 - 45 °C). When the internal temperature of the material reaches this threshold, the thermal response unit melts and releases citric acid, triggering the degradation reaction of the surrounding matrix material. Compared with the prior art, the innovation of this thermal response unit lies in that the carboxyl groups introduced on its surface can interact with the thermal history recording unit in the subsequent step to achieve the cumulative recording of thermal history.

[0042] 4. Magnetic material bio - extraction and modification Step 4.1. Extraction of magnetic materials from biological sources (innovative step) The innovation of this step lies in extracting magnetic iron oxide materials from natural biomass, avoiding the use of chemically synthesized magnetic particles, and improving the environmental friendliness and biocompatibility of the materials. The specific operations are as follows: Collect iron - rich plant materials (such as Adiantum capillus - veneris) or iron - bacteria cultures, wash them, and dry them at 60 °C for 24 hours; After grinding the dried materials, soak them in a citric acid solution (0.5 mol / L) for 12 hours to promote the release of iron elements; After filtration, add sodium hydroxide solution to the filtrate to adjust the pH to 10 - 11, and stir at room temperature for 2 hours to form iron hydroxide precipitate; Collect the precipitate and heat - treat it under nitrogen protection at 300 - 400 °C for 1 hour to obtain magnetic iron oxide powder from biological sources; Disperse the obtained powder in deionized water by ultrasonic waves to prepare a suspension with a concentration of 5 - 10 mg / mL.

[0043] The magnetic iron oxide powder produced in this step has a particle size of 50 - 100 nm and excellent magnetothermal conversion performance, and can efficiently generate heat under the action of an alternating magnetic field.

[0044] Step 4.2. Surface modification of magnetic materials Mix the magnetic iron oxide suspension obtained in the previous step with a chitosan solution (1% concentration), and ultrasonically treat for 30 minutes to form chitosan-coated magnetic particles. Add glyceryl diacetate (5% of the weight of chitosan) as a crosslinking agent, stir at room temperature for 4 hours, obtain surface-modified magnetic particles by centrifugal separation, and finally freeze-dry to obtain the final product.

[0045] Surface modification endows the magnetic particles with better dispersibility and compatibility with the matrix material, preventing agglomeration during subsequent processing.

[0046] 5. Construction of Thermosensitive Memory Unit Step 5.1. Preparation of Phase Change Material The innovation of this step lies in preparing a material with appropriate phase change temperature and energy storage capacity for capturing and slowly releasing heat energy. The specific operations are as follows: Mix natural plant wax (such as beeswax) and modified vegetable oil (such as epoxidized soybean oil) in a mass ratio of 2:1; Melt and homogenize at 75 - 80 °C, and add vitamin E (0.5% of the total mass) as an antioxidant; Add modified starch (10 - 15% of the total mass) as a skeleton material, and continue stirring for 30 minutes to form a homogeneous mixture; Process the mixture through high-speed shear homogenization to prepare micron-sized droplets; Add a chitosan solution (2% concentration), and cool to room temperature under stirring to form chitosan-coated phase change microcapsules.

[0047] This phase change material can absorb heat and undergo a phase change at 35 - 40 °C, and slowly release the stored heat energy when the temperature decreases, realizing the functions of capturing and slowly releasing heat energy.

[0048] Step 5.2. Synthesis of Thermal History Recording Unit This step is the core innovative part of the entire technical solution. By optimizing the chemical structure combination, the material is endowed with the function of thermal history memory. The specific operations are as follows: Mix epoxidized triglyceride and polyol (such as sorbitol) in a molar ratio of 1:2, add an appropriate amount of catalyst, and react at 60 °C for 6 hours to obtain a prepolymer with multiple hydroxyl groups; Add the thermal response degradation unit prepared in Step 3.1 (mass ratio 3:1) to the prepolymer, and react at 55 °C for 2 hours; Add methyl cellulose (5 - 8% of the mass of the prepolymer), and continue stirring for 1 hour to form a thermal history recording composite system; Mix the above composite system with the phase change microcapsules prepared in Step 5.1 in a mass ratio of 1:1, and ultrasonically treat for 10 minutes to obtain the thermosensitive memory unit.

[0049] The thermosensitive memory unit prepared by this innovative step has the following structure and functions: When subjected to thermal stimulation, a chemical bond is formed between the thermoresponsive degradation unit and the prepolymer to record the cumulative effect of the thermal stimulation; at the same time, the phase change microcapsules absorb and store part of the heat; when the cumulative thermal stimulation reaches the threshold, the structure of the prepolymer changes, triggering the degradation process, and the phase change microcapsules slowly release heat to maintain the continuation of the degradation. This structure realizes the "memory" of the thermal stimulation history and the continuous maintenance of the degradation process, solving the problem of degradation stagnation under intermittent magnetic field stimulation conditions.

[0050] 6. Multilayer composite molding Step 6.1 Preparation of the basic thermoresponsive layer Mix the modified starch (70%) prepared in Step 2.1 and the activated chitosan solution (30%) prepared in Step 2.2, add glycerol as a plasticizer (15% of the total solid mass), and stir well until uniform. Add the thermoresponsive degradation unit prepared in Step 3.1 (10 - 15% of the total mass of the matrix), and continue to mix for 30 minutes to obtain the basic thermoresponsive layer mixture.

[0051] Step 6.2 Preparation of the magnetothermal conversion layer The innovation of this step lies in achieving the precise distribution of magnetic particles in the material through the field-induced orientation technology. The specific operations are as follows: Mix the modified starch (40%) prepared in Step 2.1 and the activated chitosan solution (60%) prepared in Step 2.2, add glycerol (20% of the total solid mass), and stir well until uniform; Add the surface-modified magnetic particles prepared in Step 4.2 (3 - 5% of the total mass of the matrix), and ultrasonically disperse for 20 minutes; Place the mixture in a uniform magnetic field (300 - 500 Gauss), and let it stand for 30 minutes under the action of the magnetic field to make the magnetic particles form an ordered arrangement; Under the condition of maintaining the magnetic field, add a crosslinking agent (epoxidized triglyceride, 2% of the total mass) to the mixture, and gently stir to evenly disperse the crosslinking agent while maintaining the ordered arrangement of the magnetic particles; Continue to let it stand for 2 hours under the action of the magnetic field to allow the crosslinking reaction to proceed fully and fix the spatial distribution of the magnetic particles, obtaining a magnetothermal conversion layer with directionally distributed magnetic particles.

[0052] This field-induced orientation technology enables the magnetic particles to form an ordered spatial arrangement in the material, significantly improving the magnetothermal conversion efficiency, reducing the usage amount of magnetic materials, and at the same time ensuring the uniform generation and conduction of heat.

[0053] Step 6.3 Preparation of the thermosensitive memory layer Mix the thermosensitive memory unit (70%) prepared in Step 5.2 with modified starch (20%) and chitosan solution (10%), add epoxidized triglyceride (3% of the total solid mass) as a crosslinking agent, and stir gently until homogeneous to obtain a thermosensitive memory layer mixture.

[0054] Step 6.4. Preparation of multi-layer composite film The innovation of this step lies in achieving precise superposition and interface control of three functional materials through the continuous casting technology. The specific operations are as follows: On a casting table at a temperature of 45 - 50 °C, first evenly spread the base thermoresponsive layer mixture with a thickness controlled at 200 - 300 microns; Wait until the surface of the base layer reaches a semi-dry state (about 2 - 3 minutes), and then evenly cast the magnetothermal conversion layer mixture on it with a thickness controlled at 100 - 150 microns; Continue to wait for 2 - 3 minutes, and then cast the thermosensitive memory layer mixture on the surface of the magnetothermal conversion layer with a thickness controlled at 150 - 200 microns; Dry the three-layer composite structure at 45 - 50 °C for 30 minutes to initially form a composite film; Under the action of a magnetic field (the same as in Step 6.2, 300 - 500 Gauss), perform heat treatment on the composite film at a temperature of 60 °C for 1 hour to promote interlayer interface bonding and fix the distribution of functional components.

[0055] Through this continuous casting and interface control technology, a tightly bonded but functionally independent interface structure is formed between the three functional layers, realizing a composite material system of "multi-layer cooperation and function integration".

[0056] 7. Construction of thermal history cumulative trigger system Step 7.1. Construction of gradient crosslinking network This step is the core process for realizing the thermal history cumulative trigger system. By creating a gradient-changing crosslinking network structure, the material shows different responses under different thermal history conditions. The specific operations are as follows: Place the composite film prepared in Step 6.4 in a light environment (wavelength 350 - 450 nm, light intensity 5 - 10 mW / cm²); Prepare a series of crosslinking agent solutions with different concentrations (epoxidized triglyceride, with concentrations increasing from 0.5% to 2%), and spray them evenly from both sides of the composite film in turn to form a gradient structure with gradually decreasing crosslinking density from the surface to the inside; During the spraying of the crosslinking agent, simultaneously apply a pulsed magnetic field (intensity 300 - 500 Gauss, frequency 1 Hz, duration 10 seconds, interval 20 seconds), and repeat 10 - 15 times; Dry the treated composite film at 50 °C for 2 hours to fully complete the crosslinking reaction.

[0057] This step realizes the thermal history accumulation triggering mode by creating a gradient cross-linked network structure: when an external magnetic field is applied, the magnetic particles generate heat, part of the heat is stored by the phase change material, and at the same time, it causes local structural changes in the thermoresponsive degradation unit; when the thermal stimulus accumulates to a certain extent, the preset chemical bonds begin to break, triggering the degradation reaction; at the same time, the stored heat begins to be slowly released to maintain the degradation process to continue after the magnetic field is removed. This structure realizes the "memory" function of the material for the thermal stimulus history.

[0058] Step 7.2, Surface patterning The surface of the composite film prepared in Step 7.1 is patterned to regulate the interaction between the material and the external environment. The specific operation is as follows: Use a mold to imprint a micron-scale pattern structure on the surface of the composite film, such as regularly arranged grooves or protrusions. These microstructures can increase the surface area of the material, improve the contact efficiency with the environment, and at the same time provide a diffusion channel for the degradation products.

[0059] Experimental example Experiment 1: Remote active control and continuous degradation performance test under intermittent magnetic field Experimental purpose Verify the remote active control degradation ability of the material of the present invention under an applied magnetic field condition, and the function of being able to continue to degrade during the magnetic field intermittent period.

[0060] Experimental materials An environmentally friendly degradable green material (Sample A) prepared according to the preparation process of the present invention; An ordinary magnetothermal-responsive degradable biofilm without a thermosensitive memory unit (control sample B); A degradable biofilm containing only a thermoresponsive degradation unit (control sample C); An alternating magnetic field generating device with adjustable frequency (frequency range: 0 - 100 Hz, magnetic field strength range: 0 - 1000 gauss); A constant temperature water bath with an accuracy of ±0.1 °C; An electronic balance with an accuracy of 0.0001 g; A digital observation and recording system.

[0061] Experimental method Cut test pieces of 10 cm × 10 cm in size from samples A, B, and C respectively, and record the initial mass m0.

[0062] Experimental condition settings: room temperature 25 °C, relative humidity 60%, magnetic field strength 400 gauss, frequency 10 Hz.

[0063] The following treatments are performed on samples A, B, and C respectively: Continuous magnetic field group: Apply an alternating magnetic field continuously for 30 minutes Intermittent magnetic field group: Apply an alternating magnetic field for 10 minutes and then remove it for 20 minutes, and repeat this cycle three times (the total magnetic field action time is also 30 minutes) After the treatment, place the samples in a simulated soil environment (humidity 70%), measure the mass of the samples every 6 hours until 72 hours, and calculate the percentage of mass loss

[0064] Observe the change of the surface morphology of the samples through an optical microscope

[0065] Experimental results Table 1. Percentage of mass loss of each sample under continuous magnetic field action (%) Table 2. Percentage of mass loss of each sample under intermittent magnetic field action (%) Figure 1 : Degradation performance under continuous magnetic field conditions

[0066] Figure 2 : Degradation performance under intermittent magnetic field conditions

[0067] Result analysis Under continuous magnetic field conditions, the degradation rates of sample A and sample B are similar and both are significantly higher than that of sample C, indicating that the magnetothermal response effect can effectively promote the degradation of materials

[0068] Under intermittent magnetic field conditions, the degradation rate of sample A still remains at a relatively high level, and the mass loss reaches 79.5% after 72 hours, while the degradation rate of sample B decreases significantly, and the mass loss is only 15.7% after 72 hours

[0069] The results prove that the thermosensitive memory function of the present invention enables the material to continue to degrade during the magnetic field intermittent period, effectively solving the limitation that traditional magnetothermal response materials need to apply a magnetic field continuously

[0070] Experiment 2: Test on the ability to precisely control the degradation rate Experimental purpose Verify the ability of the material of the present invention to precisely control the degradation period within the range of 15 - 120 days by adjusting the composition ratio and processing technology parameters

[0071] Experimental materials According to this embodiment, adjust the content of the thermoresponsive degradation unit, the distribution density of magnetic particles and the crosslinking network gradient structure parameters to prepare five samples (D1 - D5) with different degradation rates D1: The content of the thermoresponsive degradation unit is 20%, the content of magnetic particles is 5%, and the crosslinking density is high D2: The content of the thermoresponsive degradation unit is 15%, the content of magnetic particles is 4%, and it has a medium to high crosslinking density; D3: The content of the thermoresponsive degradation unit is 10%, the content of magnetic particles is 3%, and it has a medium crosslinking density; D4: The content of the thermoresponsive degradation unit is 8%, the content of magnetic particles is 2%, and it has a medium to low crosslinking density; D5: The content of the thermoresponsive degradation unit is 5%, the content of magnetic particles is 1%, and it has a low crosslinking density; Test devices (farmland soil, forest soil, water environment) for simulating different environmental conditions; Mass determination system and morphological observation system; Experimental method Prepare test pieces of samples D1 - D5 into sizes of 10 cm × 10 cm, and record the initial mass m0 and thickness.

[0072] Respectively place them under three typical application environmental conditions: Farmland soil environment: Temperature 25 ± 3°C, humidity 65 ± 5% Forest soil environment: Temperature 22 ± 2°C, humidity 80 ± 5% Water environment: Temperature 23 ± 1°C, pH = 7.0 ± 0.2 Apply the same intermittent magnetic field stimulation to each group of samples: Apply an alternating magnetic field (400 Gauss, 10 Hz) for 10 minutes once every 7 days.

[0073] Measure the mass loss and mechanical properties (tensile strength) of the samples once every 7 days until the samples are completely degraded (mass loss ≥ 90% or the material cannot maintain its complete form).

[0074] Record the time required for each sample to be completely degraded under different environmental conditions.

[0075] Experimental results Table 3. Complete degradation time (days) of different samples in the farmland soil environment Table 4. Degradation cycle (days) of different samples under three environmental conditions Table 5. Degradation process data of sample D3 in the farmland soil environment Figure 3 : Comparison of the expected and actual degradation cycles of different samples.

[0076] Figure 4 : Degradation cycles of different samples under different environmental conditions.

[0077] Figure 5: Dynamic changes during the degradation process of Sample D3.

[0078] Figure 6 : Comparison of the degradation rates of different samples.

[0079] Result Analysis The data shows that by adjusting the material component ratio and processing parameters, the precise control of the degradation period within the range of 15 - 120 days has been successfully achieved, and the actual degradation period highly coincides with the expected value.

[0080] The results show that there are differences in the degradation rates of the same sample under different environmental conditions. Among them, the degradation is the fastest in the forest soil environment and the slowest in the water environment, but the relative degradation rate relationship of each sample remains consistent.

[0081] The degradation process of the material presents a typical S-shaped curve. The mass loss rate is the fastest in the middle stage of degradation (28 - 42 days), and the tensile strength decreases significantly with the progress of degradation.

[0082] The results prove that by adjusting the content of the thermoresponsive degradation unit, the distribution density of magnetic particles, and the crosslinked network gradient structure parameters of the present invention, the degradation period of the material can be precisely controlled to meet the requirements of different application scenarios.

[0083] Experiment Three: Energy Utilization Efficiency Test Experiment Purpose Verify the energy utilization efficiency of the material of the present invention under the action of an intermittent magnetic field and its energy consumption advantage compared with traditional magnetothermal response materials.

[0084] Experiment Materials Environmentally friendly degradable green material (Sample E1) prepared according to the preparation process of the present invention; Traditional magnetothermal response degradable biofilm without a thermosensitive memory unit (control sample E2); Precisely controllable alternating magnetic field generating device equipped with a power measurement system; Infrared thermal imager (resolution 0.05°C); Rapid determination system for degradation degree; Experiment Method Design four different magnetic field application schemes: Scheme 1: Continuous magnetic field, applied continuously for 10 hours; Scheme 2: Intermittent magnetic field A, applied for 2 hours per day for 5 days (total application time 10 hours); Scheme 3: Intermittent magnetic field B, applied for 1 hour per day for 10 days (total application time 10 hours); Scheme 4: Intermittent magnetic field C, applied for 30 minutes every two days for 20 times (total application time 10 hours); Apply the above four magnetic field application schemes to samples E1 and E2 respectively, and uniformly set the magnetic field parameters to: 400 Gauss, 10 Hz.

[0085] Record the power consumption of the magnetic field generating device for each scheme and the total time required for the sample to reach 50% degradation.

[0086] Use an infrared thermal imager to monitor the temperature change of the sample under each scheme.

[0087] Calculate the energy utilization efficiency indicators: Degradation efficiency (DE) = Degree of degradation (%) ÷ Total applied magnetic field time (hours) Energy consumption efficiency (EE) = Degree of degradation (%) ÷ Total power consumption (kWh) Comprehensive energy efficiency index (CEI) = DE × EE ÷ 100 Experimental results Table 6. Comparison of energy utilization efficiency under different magnetic field application schemes Table 7. Comparison of actual power consumption required to reach 50% degradation Table 8. Temperature change of the sample surface under the magnetic field (°C) Figure 7 : Comparison of degradation time under different magnetic field application schemes.

[0088] Figure 8 : Energy consumption comparison required to reach 50% degradation.

[0089] Figure 9 : Energy saving ratio under the intermittent magnetic field scheme.

[0090] Figure 10 : Temperature change of the sample under the magnetic field.

[0091] Result analysis Data shows that under the continuous magnetic field scheme, the energy consumption of the thermosensitive memory sample E1 is close to that of the traditional magnetothermal sample E2; but under various intermittent magnetic field schemes, E1 shows a significant energy advantage.

[0092] Under the intermittent magnetic field scheme C (30 minutes every two days), to reach the same degree of degradation, the thermosensitive memory sample E1 only consumes 21.6% of the energy required by the traditional magnetothermal sample E2, and the energy saving ratio reaches 78.4%.

[0093] The temperature change data shows that after the magnetic field is removed, the thermosensitive memory sample E1 can maintain a relatively high temperature level, while the temperature of the traditional magnetothermal sample E2 drops rapidly. This confirms that the phase change material in the thermosensitive memory sample can effectively store and slowly release thermal energy.

[0094] With the increase of the interval time of magnetic field application, the degradation time gap between the two materials also increases, indicating that the thermosensitive memory function has more obvious advantages in the application scenario of long-period intermittent magnetic field.

[0095] The experimental results prove that the present invention significantly improves the energy utilization efficiency of the magnetothermal response system under the action of intermittent magnetic field through the "thermal energy capture - storage - slow release" three - level linkage structure and the "thermal history accumulation trigger" action mode. Compared with the traditional technology, the energy utilization efficiency is increased by more than 65% on average.

[0096] Experiment 4: Biological safety and environmental protection testing Experimental purpose Verify the biological safety and environmental friendliness of the materials of the present invention, and evaluate the impact of its degradation products on the environment and the complete degradation characteristics in the natural environment.

[0097] Experimental materials Environmentally friendly degradable green materials (sample F) prepared according to the preparation process of the present invention; Traditional petroleum - based plastic film (polyethylene, control sample G1); Commercially available ordinary degradable film (control sample G2); Standard soil environment simulation device (compliant with ISO 17556 standard); Wheat and corn seedling growth test system; Microbial diversity analysis equipment; Biotoxicity test reagents and instruments; Experimental methods Test for complete degradability of materials: Place the three material samples in the standard soil environment, and regularly monitor the mass change, morphological change and CO2 release amount of the materials Test period: 6 months for sample F, 2 years for sample G1, 1 year for sample G2; Take samples every 30 days to analyze the chemical composition of the residues; Assessment of the impact on soil microorganisms: Collect soil samples before, during and after the degradation of the materials; Analyze the change of microbial diversity index through high - throughput sequencing technology; Monitor the soil enzyme activities (urease, catalase, sucrase, etc.); Test for the impact on plant growth: Plant wheat and corn seeds in soil containing materials after complete degradation; Monitor the germination rate, seedling height, root development, and biomass; Compare the growth of plants in the three groups of experimental soils; Toxicity assessment of degradation products: Collect the leachate during the degradation process of the three materials; Use the luminescent bacteria method (GB / T 15441) to evaluate acute toxicity; Adopt the earthworm avoidance experiment (ISO 17512-1) to evaluate the impact of materials on soil organisms.

[0098] Experimental results Table 9. Comparison of the complete degradation cycles and degradation characteristics of the three materials Table 10. Changes in soil microbial diversity index during material degradation Table 11. Test results of the impact on plant growth (relative percentage compared with the control group) Table 12. Toxicity assessment results of degradation products Figure 11 : Comparison of the complete degradation time and degradation rate.

[0099] Figure 12 : Changes in microbial diversity index.

[0100] Figure 13 : Toxicity assessment of degradation products.

[0101] Result analysis Table 9 shows that the material of the present invention (sample F) achieved 99.3% complete degradation within 178 days, and the CO2 conversion rate reached 95.7%, far superior to traditional petroleum-based plastics and ordinary degradable materials. Moreover, the final degradation residue is plant-absorbable minerals and organic matter, without harmful residues.

[0102] The data in Table 10 indicate that as the degradation process progresses, the microbial diversity index of the soil where sample F is located shows a trend of first increasing and then returning to normal, indicating that during the material degradation process, not only does it not inhibit the growth of microorganisms, but it also promotes microbial diversity in the short term; while the traditional petroleum-based plastic G1 significantly reduces soil microbial diversity.

[0103] The plant growth test results in Table 11 further confirm that the soil environment after the degradation of the materials of the present invention has a slight promoting effect on plant growth, indicating that its degradation products can be absorbed and utilized as plant nutrients; while the degradation products of traditional petroleum-based plastics significantly inhibit plant growth.

[0104] The toxicity assessment results in Table 12 show that the degradation products of the materials of the present invention are lower than the safety standards in all test indicators, proving its excellent biosafety; while the degradation products of traditional petroleum-based plastics show obvious biotoxicity.

[0105] The comprehensive experimental results show that by using all-bio-based raw materials and green preparation processes, the present invention has successfully achieved the environmental protection and biosafety of degradable materials. The degradation products are harmless to the environment and even have a promoting effect on soil microorganisms and plant growth, reflecting the green environmental protection characteristics of the whole life cycle of the materials.

[0106] Experimental Summary and Conclusions Through the above four groups of systematic experiments, we have comprehensively evaluated the technical characteristics of the materials of the present invention. The experimental results have confirmed the various technical effects described in the patent specification of the present invention, specifically including: Verification of the effectiveness of the thermosensitive memory function: The results of Experiment 1 show that the materials of the present invention can still maintain efficient degradation (mass loss of 79.5% within 72 hours) under intermittent magnetic field conditions, while the degradation of traditional magnetothermal materials is significantly slowed down under the same conditions (mass loss is only 15.7%). This confirms that the thermosensitive memory unit can effectively record the cumulative effect of multiple short-term magnetothermal stimuli and achieve intermittent degradation control.

[0107] Verification of the ability to precisely control the degradation rate: The results of Experiment 2 show that by adjusting the material component ratio and processing parameters, the degradation period has been successfully and precisely controlled within the range of 15 - 120 days. The actual degradation period is highly consistent with the expected value, and the deviation rate is within ±10%. This confirms that the present invention can customize the degradation period according to the requirements of different application scenarios.

[0108] Verification of the improvement of energy utilization efficiency: The data of Experiment 3 prove that under intermittent magnetic field conditions (especially long-period intermittent magnetic field), the energy utilization efficiency of the materials of the present invention is significantly higher than that of traditional magnetothermal response materials, saving an average of more than 65% of energy, and up to 78.4% at most. This verifies the high efficiency of the "thermal energy capture - storage - slow release" three-level linkage structure.

[0109] Verification of biosafety and environmental protection: The results of Experiment 4 show that the materials of the present invention have excellent biodegradability (complete degradation rate of 99.3% within 178 days) and biosafety (all biotoxicity indicators are lower than the safety standards), and its degradation products even have a slight promoting effect on soil microorganisms and plant growth.

[0110] Combined with the analysis of experimental data and material properties, the core technological innovation and value of the present invention can be summarized as follows: Material structure innovation: Through a three-layer functional integration structure (basic thermal response layer, magnetothermal conversion layer, and thermosensitive memory layer), multiple functions are coordinated to form a complete degradation control system.

[0111] Mechanism of action innovation: The "thermal energy capture - storage - slow release" three-level linkage structure and the "thermal history accumulation trigger" mode of action enable the material to have a "memory" function, and it can automatically start and maintain the degradation process based on the cumulative heat threshold.

[0112] Energy efficiency advantage: Compared with traditional technologies, through the design of the thermosensitive memory unit, continuous degradation under intermittent magnetic field conditions is achieved, avoiding energy waste and significantly improving the practicality of the magnetothermal response system.

[0113] Environmental friendliness advantage: Using all bio-based raw materials and green preparation processes, the degradation products are harmless to the environment and even have a slight positive impact on the ecosystem, reflecting the ecological friendliness of the material throughout its life cycle.

[0114] Expansion of application scenarios: The ability of remote active control and precise regulation of the degradation rate makes the material particularly suitable for high-demand application fields such as precision agriculture, drug release control, and environmental remediation.

[0115] Summary of comparison with existing technologies Based on the experimental results, the present invention is compared and analyzed with existing technologies: Table 13. Comprehensive performance comparison between the present invention and existing technologies According to the analysis of experimental results, the materials of the present invention have the following potential application prospects: Intelligent agriculture application: Magnetically controlled degradable intelligent mulch films can be developed to achieve rapid degradation after crop harvest and solve the problem of agricultural film residue pollution. Experimental data show that complete degradation can be achieved within 178 days in the farmland environment, and it has a positive impact on soil microbial diversity and subsequent crop growth.

[0116] Controlled drug release carrier: Utilizing remote magnetic field control and thermosensitive memory functions to achieve precise spatio-temporal control of drug release and improve the treatment effect. Experimental data show that the thermal history memory function of the material can achieve complex release kinetic control.

[0117] Environmental remediation materials: Used to prepare environmentally friendly materials with controlled release, which can degrade by themselves after pollutant treatment is completed, avoiding secondary pollution. Biosecurity tests prove that the degradation products of the materials are harmless to the environment.

[0118] Intelligent packaging materials: Develop packaging materials with shelf-life indication and self-degradation functions to achieve rapid degradation after product use. Energy efficiency tests show that the materials can achieve efficient degradation with minimal energy input.

[0119] The above embodiments of the present invention have been described, but these embodiments are not limited to the above specific implementation manners. The above specific implementation manners are merely illustrative rather than restrictive. Under the inspiration of this embodiment, those of ordinary skill in the art can also make more equivalent embodiments in various forms, all of which fall within the protection scope of this embodiment.

Claims

1. An environmentally friendly and degradable green material, characterized in that, It includes a basic thermal response layer, a magnetothermal conversion layer, and a thermosensitive memory layer stacked in sequence from bottom to top; Among them, the basic thermal response layer contains a thermal response degradation unit, the magnetothermal conversion layer contains magnetic particles that generate heat under the action of an alternating magnetic field, and the thermosensitive memory layer contains a thermal history recording unit and a phase change material. The thermal history recording unit can record the cumulative effect of multiple short-term magnetothermal stimulations and trigger the degradation process when the cumulative heat reaches a preset threshold. The phase change material stores thermal energy when heated and slowly releases heat after the magnetic field is removed to maintain the continuous progress of the degradation process.

2. An environmentally friendly degradable green material according to claim 1, characterized in that, The thickness ratio of the thermosensitive memory layer, the magnetothermal conversion layer, and the basic thermal response layer is 3:2:

4.

3. An environmentally friendly degradable green material according to claim 1, characterized in that, The basic thermal response layer is composed of modified starch, chitosan, and a thermal response degradation unit, and their mass percentages are 50 - 70%, 20 - 30%, and 10 - 20% respectively.

4. An environmentally friendly degradable green material according to claim 1, characterized in that, The magnetic particles in the magnetothermal conversion layer are magnetic iron oxide particles of biological origin, with a particle size of 50 - 100 nm, and are distributed in an ordered arrangement in the magnetothermal conversion layer.

5. An environment-friendly degradable green material according to claim 1, characterized in that, The phase change material in the thermosensitive memory layer is a plant wax microcapsule coated with chitosan, and its phase change temperature is 35 - 40 °C.

6. A process for preparing the environmentally friendly degradable green material according to any one of claims 1-5, characterized in that, It includes the following steps: Step 1: Preparation of the thermal response degradation unit: Mix fatty acid ester and modified polyethylene glycol in a mass ratio of 3:1 and melt them, add epoxidized triglyceride for reaction, grind after cooling, and then mix with citric acid for treatment to obtain a thermal response degradation unit with carboxyl groups on the surface; Step 2: Biological extraction and modification of magnetic materials: Extract magnetic iron oxide from iron-rich biomass and perform surface modification with chitosan; Step 3: Construction of the thermosensitive memory unit: Prepare phase change microcapsules, synthesize the thermal history recording unit, and mix the two to obtain the thermosensitive memory unit; Step 4: Multilayer composite molding: Prepare mixtures of the basic thermal response layer, the magnetothermal conversion layer, and the thermosensitive memory layer in sequence, and use the continuous casting technology to stack the three layers into a composite film; Step 5: Construction of the thermal history accumulation trigger system: Perform gradient cross-linking treatment on the composite film to form a gradient structure with a gradually decreasing cross-linking density from the surface to the inside, and perform surface patterning treatment.

7. The preparation process according to claim 6, characterized in that, The biological extraction of magnetic materials in Step 2 includes: Collect iron-rich plant materials or iron bacteria cultures, dry and grind them, soak them in a citric acid solution, filter and add sodium hydroxide solution to adjust the pH to 10 - 11 to form a precipitate, and heat-treat the precipitate under nitrogen protection to obtain magnetic iron oxide powder of biological origin.

8. The preparation process according to claim 6, characterized in that, The preparation of phase change microcapsules in Step 3 includes: Mix natural plant wax and modified vegetable oil in a mass ratio of 2:1 and melt them, add modified starch as a skeleton material, prepare micron-sized droplets through high-speed shear homogenization treatment, and add chitosan solution for coating.

9. The preparation process according to claim 6, characterized in that, The synthesis of the thermal history recording unit in Step 3 includes: Mix epoxidized triglyceride and polyol in a molar ratio of 1:2 for reaction to obtain a polyhydroxy prepolymer, and add the thermal response degradation unit and methyl cellulose to form a thermal history recording composite system.

10. The preparation process according to claim 6, characterized in that, The preparation of the magnetothermal conversion layer in Step 4 includes: mixing modified starch, chitosan solution and surface-modified magnetic particles, placing them in a magnetic field of 300-500 Gauss and standing still to make the magnetic particles form an ordered arrangement, and adding a crosslinking agent to fix the spatial distribution of the magnetic particles.

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