A bio-based composite material and a flexible acupoint patch prepared therefrom

Abstract

This invention discloses a bio-based composite material and a flexible acupoint patch prepared therefrom, belonging to the field of bio-based membrane material technology. It primarily addresses the technical problem that the flexible mechanical properties, sweat absorption and moisture regulation properties, and wet stability of bio-based polymer film materials used in acupoint patches need further improvement. Specifically, it includes a bio-based elastic base membrane and an ion-gated grafting layer disposed on the bio-based elastic base membrane. The skin contact surface of the bio-based elastic base membrane has a microcavity array and lateral microchannels communicating with the microcavity array. This invention uses castor oil-based polyurethane prepolymer, sweat-responsive hydrophilic microgel, and an ion-gated grafting layer to enable the bio-based composite material to possess mechanical support, sweat absorption and moisture regulation, wetting and fluid conduction, and wet stability properties, preventing overall membrane swelling, softening, or microstructural collapse, thus improving the stability and comfort of the acupoint patch in dynamic skin environments.

Description

Technical Field

[0001] This invention relates to the field of bio-based membrane materials technology, specifically to a bio-based composite material and a flexible acupoint patch prepared therefrom. Background Technology

[0002] Acupoint patches are a type of external patch product that is applied to specific acupoints on the human body to achieve drug release, physical stimulation, health care, or auxiliary conditioning effects. Compared with oral administration or invasive treatment methods, acupoint patches have the advantages of convenient use, clear target location, and better patient compliance. Therefore, they have a wide range of applications in the fields of traditional Chinese medicine physiotherapy, sports rehabilitation, daily health care, and auxiliary conditioning of chronic symptoms.

[0003] Acupoint patches typically use bio-based polymer films as carriers, which are characterized by good flexibility, strong designability, and relatively renewable sources. However, bio-based polymer films are usually highly hydrophobic, making it difficult to absorb and conduct sweat from the skin surface in a timely manner, affecting wearing comfort and application stability. Moreover, the surface of human skin is not a flat and rigid interface, and it will undergo continuous deformation during exercise, sweating, bending, and stretching. If the substrate of the acupoint patch is not flexible enough, it is easy to cause edge lifting, falling off, or local pressure. If the sweat absorption capacity is too strong but there is no structural confinement, it may damage the application interface due to significant expansion. Especially in summer, high humidity environments, or during exercise, sweat will remain between the acupoint patch and the skin, which will significantly reduce skin comfort and continuous use stability.

[0004] Therefore, how to achieve controllable absorption, rapid wetting, and directional expulsion of sweat while ensuring the flexible mechanical properties of bio-based polymer film materials is a technical problem that flexible acupoint patch materials urgently need to solve. To this end, a solution is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a bio-based composite material and a flexible acupoint patch prepared therefrom, in order to solve the technical problem that the flexible mechanical properties, sweat absorption and moisture regulation properties, and wet stability of bio-based polymer film materials used in acupoint patches in the prior art need to be further improved.

[0006] The objective of this invention can be achieved through the following technical solution: a bio-based composite material, comprising a bio-based elastic base membrane and an ion-gated graft layer disposed on the bio-based elastic base membrane; The skin contact surface of the bio-based elastic base membrane has a microcavity array and lateral microchannels communicating with the microcavity array; The bio-based elastic membrane is formed by template molding and ultraviolet curing of a photocurable elastic membrane slurry. The photocurable elastic membrane slurry includes castor oil-based polyurethane prepolymer, lauryl acrylate, pentaerythritol diacrylate, sweat-responsive hydrophilic microgel, and photoinitiator. The ion-gated graft layer is formed by in-situ photocuring of an ion-gated grafting solution on the surface of the microchannels on the side of the microcavity array. The ion-gated grafting solution includes methacryloyl ethyl sulfobetaine, acrylic acid, methacrylamide, polyethylene glycol diacrylate, glycerol, ethanol solution and photoinitiator.

[0007] Furthermore, the preparation method of the castor oil-based polyurethane prepolymer is as follows: castor oil and dimer polyester diol are mixed, the reaction system is heated to 90-100℃, the reaction system is vacuum dehydrated to -0.09~-0.095MPa for 2-3 hours under vacuum protection, the reaction system is cooled to 70-75℃ under inert gas protection, isophorone diisocyanate and catalyst are added to the reaction system, the reaction is kept at the temperature for 3-4 hours, the reaction system is cooled to 55-60℃, hydroxyethyl acrylate is added to the reaction system, and the reaction system is allowed to cool naturally to room temperature to obtain the castor oil-based polyurethane prepolymer.

[0008] Furthermore, the weight ratio of castor oil, dimer polyester diol, catalyst, and hydroxyethyl acrylate is 60-70:38-42:0.05:2-3, the molar amount of isophorone diisocyanate is 1.5 times the molar amount of hydroxyl groups in the reaction system, and the catalyst is dibutyltin dilaurate.

[0009] Furthermore, the preparation method of sweat-responsive hydrophilic microgel is as follows: alginate composite microgel and acetate buffer are mixed and stirred, then methacrylated chitosan is added to the reaction system and stirred for 60-80 min, tannic acid is added to the reaction system and stirred for another 30-50 min, and then post-processed to obtain sweat-responsive hydrophilic microgel.

[0010] Furthermore, the ratio of the alginate composite microgel, acetate buffer, methacrylamide chitosan, and tannic acid is 50g:500mL:0.2-0.3g:0.08-0.1g. The acetate buffer is a 2-3wt% sodium acetate aqueous solution with pH=5.5. The post-treatment includes: after the reaction is complete, centrifugation is performed, the precipitate is collected, the precipitate is replaced with anhydrous ethanol, and dried in a drying oven at 60-70℃ to constant weight to obtain a sweat-responsive hydrophilic microgel.

[0011] Furthermore, the alginate composite microgel is obtained by the following steps: B1. Mix sodium alginate and deionized water, and stir at room temperature until the system dissolves. Add sodium carboxymethyl cellulose, betaine and glycerol to the reaction system, and stir for 60-80 min. Add nano calcium carbonate to the reaction system and sonicate for 20-30 min to obtain a microgel aqueous phase. B2. Mix ethyl oleate, Span 80 and lecithin, and stir at room temperature for 30-50 minutes to obtain the oil phase; B3. Add the aqueous phase of the microgel to the oil phase, emulsify and disperse for 15-20 min to form an oil-in-water reverse emulsion, add gluconate-δ-lactone aqueous solution to the reaction system, stir for 90-120 min, and then perform post-treatment to obtain alginate composite microgel.

[0012] Furthermore, in step B1, the ratio of sodium alginate, deionized water, sodium carboxymethyl cellulose, betaine, glycerol, and nano-calcium carbonate is 1.8-2g:100mL:0.5-0.6g:0.9-1.1g:1-1.2g:0.4-0.5g.

[0013] Furthermore, in step B2, the ratio of ethyl oleate, Span 80, and lecithin is 300mL:9-10g:1-2g.

[0014] Further, in step B3, the volume ratio of the aqueous phase to the oil phase of the microgel is 1:1, the mass fraction of the gluconate-δ-lactone aqueous solution is 20%, the volume ratio of the gluconate-δ-lactone aqueous solution to the aqueous phase of the microgel is 10:1, the rotation speed of the emulsification dispersion is 7000-8000 rpm, and the post-treatment includes: after the reaction is completed, adding 3 times the volume of anhydrous ethanol to the reaction system, stirring and dispersing for 20-30 min, centrifuging, collecting the precipitate, replacing the precipitate with anhydrous ethanol, and drying it to constant weight in a drying oven at 60-70℃ to obtain the alginate composite microgel.

[0015] Furthermore, the bio-based composite material is obtained through the following steps: S1. Under a light-shielding environment, castor oil-based polyurethane prepolymer, lauryl acrylate, pentaerythritol diacrylate, sweat-responsive hydrophilic microgel, and photoinitiator are mixed and stirred. The reaction system is heated to 70-80℃ and stirred for 50-70 minutes to obtain a photocurable elastic film slurry. S2. The photocurable elastic film slurry is poured onto the surface of a fluorinated PDMS template with a microcavity array and lateral microgrooves. The template is vacuumed for 3-5 minutes under a vacuum environment of -0.08~-0.09MPa to fill the microcavities and lateral microgrooves with the photocurable elastic film slurry. Then, the film thickness is controlled to be 1.0±0.1mm using a doctor blade to remove excess slurry. Finally, a transparent PET film is covered on top and UV cured to obtain a bio-based elastic film. S3. Mix and stir methacryloyl ethyl sulfobetaine, acrylic acid, methacrylamide, polyethylene glycol diacrylate, glycerol, ethanol solution and photoinitiator evenly. Add acetic acid to the reaction system and adjust the pH of the system to 5.5-6 to obtain ion-gated grafting solution. S4. Place the bio-based elastic membrane in an ion-gated grafting solution and vacuum it for 3-5 minutes under a vacuum environment of -0.08~-0.09MPa. Then, remove the bio-based elastic membrane blank from the ion-gated grafting solution, remove excess solution from the surface of the bio-based elastic membrane blank with a scraper, and cure it with ultraviolet light to obtain the bio-based composite material.

[0016] Furthermore, in step S1, the weight ratio of the castor oil-based polyurethane prepolymer, lauryl acrylate, pentaerythritol diacrylate, sweat-responsive hydrophilic microgel, and photoinitiator is 80-90:15-18:3-6:30-36:1.8-2.2, and the photoinitiator is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide.

[0017] Further, in step S2, the ultraviolet curing treatment includes: irradiating the sample with ultraviolet light at a wavelength of 365nm and a light intensity of 12mW / cm2 for 3-5 minutes to cure the slurry into a film; peeling the cured film off the PET film after curing; post-curing at 60°C for 120-150 minutes; then placing it in a 50% vol ethanol aqueous solution at room temperature to replace the solvent; and then drying it in a vacuum environment at 50-60°C for 8-10 hours to obtain a bio-based elastic film.

[0018] Furthermore, in step S3, the ratio of the amount of methacryloylethyl sulfobetaine, acrylic acid, methacrylamide, polyethylene glycol diacrylate, glycerol, ethanol solution and photoinitiator is 6-7g:0.8-1.2g:0.2-0.3g:0.6-0.8g:0.1-0.2g:80mL:2-3g, and the photoinitiator is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide.

[0019] Further, in step S4, the ultraviolet curing treatment includes: irradiating the sample with ultraviolet light at a wavelength of 365nm and a light intensity of 12mW / cm2 for 3-5 minutes, then placing it in a 50% vol ethanol aqueous solution, replacing the solvent at room temperature, and then drying it in a vacuum environment at 50-60℃ for 8-10 hours to obtain a bio-based composite material.

[0020] The present invention also proposes a flexible acupoint patch, which is prepared using the above-mentioned bio-based composite material.

[0021] The present invention has the following beneficial effects: 1. This invention uses a bio-based polyurethane acrylate network formed from castor oil and dimer polyester diol as a hydrophobic elastic continuous phase, providing flexible segments, urethane hard segments, and photocurable crosslinking points, enabling the material to possess basic strength, tensile deformation capacity, and elastic recovery capacity. Simultaneously, the sweat-responsive hydrophilic microgel, after surface modification with methacryloylchitosan and tannic acid, forms hydrogen bonds, electrostatic interactions, physical entanglements, and possible photocurable interface anchoring with the polyurethane acrylate matrix. This reduces interfacial debonding and stress concentration caused by the hydrophilic microgel as a filler, endowing the material with sweat-absorbing properties while avoiding the disruption of the continuity of the elastic matrix, enabling the material to simultaneously obtain high tensile strength, large elongation at break, and good cyclic elastic recovery performance.

[0022] 2. This invention also utilizes the calcium alginate ion crosslinking network, sodium carboxymethyl cellulose, betaine, and glycerol in the alginate composite microgel to form a hydrophilic liquid-absorbing structure, enabling the microgel to respond to sweat and undergo moderate hydration. An ion-gated grafting layer formed by methacryloyl ethyl sulfobetaine, acrylic acid, methacrylamide, and polyethylene glycol diacrylate introduces sulfobetaine groups, carboxyl groups, amide groups, and polyether segments onto the surfaces of the microcavity walls and lateral microchannel walls. This reduces the water contact angle of the material surface, improves the wetting and penetration ability of sweat onto the microstructure surface, allows the hydrophilic microgel to absorb and temporarily store sweat, the ion-gated grafting layer to reduce interfacial wetting resistance, and the microcavity array and lateral microchannels to provide sweat-accommodating space and directional migration paths. The synergistic effect of these three elements results in a material exhibiting suitable non-swelling absorption capacity and high sweat permeability.

[0023] 3. This invention also adapts to the microscopic undulations of the skin surface through a microcavity array to form a localized fitting space. The lateral microchannels can guide the sweat generated in the central area of ​​the acupoint patch to the surrounding area, avoiding excessive sweat retention at the application interface. At the same time, the sweat-responsive hydrophilic microgel, after absorbing liquid, is confined by the calcium alginate cross-linked network, chitosan, tannic acid surface layer, and polyurethane elastic matrix. The elastic matrix support, microcavity fitting, sweat absorption, and lateral moisture guidance work together to reduce the risk of stuffiness, edge lifting, and detachment caused by sweating. It also ensures that the membrane material only expands moderately, avoiding overall membrane swelling, softening, or microstructural collapse, thus improving the stability and comfort of the acupoint patch in dynamic skin environments. Detailed Implementation

[0024] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] In this invention, the lecithin is food-grade soybean lecithin with a content of 99%; In this invention, the glycerol is food-grade glycerol with a content of 99%; In this invention, the castor oil has a hydroxyl content of 4.94%. In this invention, the dimer polyester diol is PEGDA 600, with a content of 98%; In this invention, the content of polyethylene glycol diacrylate is 99%, and the type of polyethylene glycol in the molecular formula is PEG-400.

[0026] Example 1 This embodiment provides a method for preparing sweat-responsive hydrophilic microgels, specifically including the following steps: Step 1: Preparation of alginate composite microgels Weigh out 9g of sodium alginate and 500mL of deionized water and add them to the reaction flask. Stir at room temperature until the system dissolves. Add 2.5g of sodium carboxymethyl cellulose, 4.5g of betaine and 5g of glycerol to the reaction flask and stir for 60min. Add 2g of nano-calcium carbonate to the reaction flask and sonicate for 20min to obtain a microgel aqueous phase. Ethyl oleate, Span 80 and lecithin were added to a reaction flask at a ratio of 300 mL: 9 g: 1 g and stirred at room temperature for 30-50 min to obtain the oil phase. Weigh 500 mL of the oil phase and add it to a high-speed disperser containing 500 mL of the microgel aqueous phase. Set the emulsification and dispersion speed to 7000 rpm and emulsify and disperse for 15 min to form an oil-in-water reverse emulsion. Add 50 mL of 20 wt% gluconate-δ-lactone aqueous solution to the high-speed disperser and stir for 90 min. Add 1500 mL of anhydrous ethanol to the high-speed disperser and stir and disperse for 20 min. Centrifuge and collect the sediment. Replace the sediment with anhydrous ethanol and dry it in a drying oven at 60 °C to constant weight to obtain the alginate composite microgel.

[0027] In the preparation of alginate composite microgels, sodium alginate, sodium carboxymethyl cellulose, betaine, and glycerol first form a homogeneous hydrophilic polymer system in an aqueous phase. Sodium alginate contains a large number of carboxyl groups, which can serve as the main gel backbone; sodium carboxymethyl cellulose also contains carboxyl and hydroxyl groups, which can form hydrogen bond entanglements and semi-interpenetrating networks with sodium alginate; betaine has a zwitterionic structure, which can enhance the microgel's responsiveness to moisture and ions in sweat; glycerol plays a role in moisturizing, plasticizing, and reducing brittleness after drying. Subsequently, nano-calcium carbonate is added and ultrasonically dispersed to ensure that calcium carbonate is uniformly distributed in the aqueous droplets.

[0028] In the reverse emulsification system, the microgel aqueous phase is dispersed into fine droplets, with ethyl oleate serving as the continuous phase, and Span80 and lecithin acting as emulsifying stabilizers to ensure the stable existence of the aqueous droplets. Upon addition of gluconate-δ-lactone, it slowly hydrolyzes in the aqueous phase, releasing acidic substances, which gradually dissolves the nano-calcium carbonate and releases Ca. 2+ Ca 2+ Ionic crosslinking occurs between the sodium alginate and the carboxylate groups on the molecular chain, resulting in in-situ gelation within the dispersed droplets to obtain alginate composite microgels. The addition of anhydrous ethanol disrupts the emulsion system and facilitates dehydration, sedimentation, and preliminary solvent replacement. Subsequent drying yields microgels with stable particle morphology, endowing the material with excellent subsequent sweat absorption, water retention, and non-swelling absorption properties.

[0029] Step 2: Preparation of sweat-responsive hydrophilic microgels Sodium acetate and deionized water were mixed and stirred until the system was dissolved. Acetic acid was added dropwise to the reaction system to adjust the pH of the system to 5.5, resulting in a 2 wt% acetate buffer solution. Weigh 100g of alginate composite microgel and 1000mL of acetate buffer into a reaction flask and stir. Stir for 15min at room temperature. Add 0.4g of methacrylamide chitosan to the reaction flask and stir for 60min. Add 0.16g of tannic acid to the reaction flask and continue stirring for 30min. Centrifuge and collect the precipitate. Replace the precipitate with anhydrous ethanol and dry it to constant weight in a drying oven at 60℃ to obtain sweat-responsive hydrophilic microgel.

[0030] During the preparation of sweat-responsive hydrophilic microgels, the amino groups in methacrylamide chitosan are protonated to form a positively charged ammonium salt structure. This structure undergoes electrostatic adsorption and hydrogen bonding with the carboxyl groups on the surface of the alginate microgel and the carboxyl groups in sodium carboxymethyl cellulose, thereby forming a chitosan-modified layer on the microgel surface. The methacrylamide chitosan molecule contains photopolymerizable carbon-carbon double bonds, which not only improve the surface properties of the microgel but also provide reaction sites for copolymerization or grafting with the acrylate matrix during subsequent UV curing.

[0031] Subsequently, tannic acid was added. Tannic acid contains a large number of phenolic hydroxyl groups, which can form multiple hydrogen bonds with chitosan, alginate, and sodium carboxymethyl cellulose. It can also enhance the surface layer stability through hydrophobic association and physical cross-linking. The resulting sweat-responsive hydrophilic microgel has reactive and interfacial bonding capabilities. This modification improves the dispersibility and interfacial bonding of the microgel in a castor oil-based polyurethane acrylate matrix, reducing particle aggregation, interfacial debonding, and stress concentration.

[0032] Example 2 This embodiment provides a method for preparing sweat-responsive hydrophilic microgels, specifically including the following steps: Step 1: Preparation of alginate composite microgels Weigh out 9.5g of sodium alginate and 500mL of deionized water and add them to the reaction flask. Stir at room temperature until the system dissolves. Add 2.75g of sodium carboxymethyl cellulose, 5.0g of betaine and 5.5g of glycerol to the reaction flask and stir for 70min. Add 2.3g of nano-calcium carbonate to the reaction flask and sonicate for 25min to obtain a microgel aqueous phase. Ethyl oleate, Span 80 and lecithin were added to a reaction flask at a ratio of 300 mL: 9.5 g: 1.5 g and stirred at room temperature for 40 min to obtain the oil phase. Weigh 500 mL of the oil phase and add it to a high-speed disperser containing 500 mL of the microgel aqueous phase. Set the emulsification and dispersion speed to 7500 rpm and emulsify and disperse for 17 min to form an oil-in-water reverse emulsion. Add 50 mL of 20 wt% gluconate-δ-lactone aqueous solution to the high-speed disperser and stir for 105 min. Add 1500 mL of anhydrous ethanol to the high-speed disperser and stir and disperse for 25 min. Centrifuge and collect the sediment. Replace the sediment with anhydrous ethanol and dry it in a drying oven at 65 °C to constant weight to obtain the alginate composite microgel.

[0033] Step 2: Preparation of sweat-responsive hydrophilic microgels Sodium acetate and deionized water were mixed and stirred until the system was dissolved. Acetic acid was added dropwise to the reaction system to adjust the pH of the system to 5.5, resulting in a 2.5 wt% acetate buffer solution. Weigh 100g of alginate composite microgel and 1000mL of acetate buffer into a reaction flask and stir. Stir for 20min at room temperature. Add 0.5g of methacrylamide chitosan to the reaction flask and stir for 70min. Add 0.18g of tannic acid to the reaction flask and continue stirring for 40min. Centrifuge and collect the precipitate. Replace the precipitate with anhydrous ethanol and dry it to constant weight in a drying oven at 65℃ to obtain sweat-responsive hydrophilic microgel.

[0034] Example 3 This embodiment provides a method for preparing sweat-responsive hydrophilic microgels, specifically including the following steps: Step 1: Preparation of alginate composite microgels Weigh out 10g of sodium alginate and 500mL of deionized water and add them to the reaction flask. Stir at room temperature until the system dissolves. Add 3.0g of sodium carboxymethyl cellulose, 5.5g of betaine and 6g of glycerol to the reaction flask and stir for 80min. Add 2.5g of nano calcium carbonate to the reaction flask and sonicate for 30min to obtain a microgel aqueous phase. Ethyl oleate, Span 80 and lecithin were added to a reaction flask at a ratio of 300 mL: 10 g: 2 g and stirred for 50 min at room temperature to obtain the oil phase. Weigh 500 mL of the oil phase and add it to a high-speed disperser containing 500 mL of the microgel aqueous phase. Set the emulsification and dispersion speed to 8000 rpm and emulsify and disperse for 20 min to form an oil-in-water reverse emulsion. Add 50 mL of 20 wt% gluconate-δ-lactone aqueous solution to the high-speed disperser and stir for 120 min. Add 1500 mL of anhydrous ethanol to the high-speed disperser and stir and disperse for 30 min. Centrifuge and collect the sediment. Replace the sediment with anhydrous ethanol and dry it in a drying oven at 70 °C to constant weight to obtain the alginate composite microgel.

[0035] Step 2: Preparation of sweat-responsive hydrophilic microgels Sodium acetate and deionized water were mixed and stirred until the system was dissolved. Acetic acid was added dropwise to the reaction system to adjust the pH of the system to 5.5, resulting in a 3 wt% acetate buffer solution. Weigh 100g of alginate composite microgel and 1000mL of acetate buffer into a reaction flask and stir. Stir for 25min at room temperature. Add 0.6g of methacrylamide chitosan to the reaction flask and stir for 80min. Add 0.2g of tannic acid to the reaction flask and continue stirring for 50min. Centrifuge and collect the precipitate. Replace the precipitate with anhydrous ethanol and dry it to constant weight in a drying oven at 70℃ to obtain sweat-responsive hydrophilic microgel.

[0036] Example 4 This embodiment provides a method for preparing a bio-based composite material, specifically including the following steps: Step I: Preparation of castor oil-based polyurethane prepolymer Weigh out 600g of castor oil and 380g of dimer polyester diol and add them to the reaction flask. Stir the mixture and heat the reaction flask to 90℃. Then, apply a negative pressure of -0.09MPa to the reaction flask and dehydrate it under vacuum for 2 hours. Nitrogen gas was introduced into the reaction flask, and the reaction flask was restored to normal pressure. Then the reaction flask was cooled to 70°C, and 0.5g of isophorone diisocyanate and dibutyltin dilaurate were added to the reaction flask. The reaction was kept at this temperature for 3 hours. The reaction flask was then cooled to 55°C, and 20g of hydroxyethyl acrylate was added to the reaction flask. The reaction flask was then allowed to cool naturally to room temperature to obtain castor oil-based polyurethane prepolymer, wherein the molar amount of isophorone diisocyanate was 1.5 times the molar amount of hydroxyl groups in the reaction system.

[0037] In the preparation of castor oil-based polyurethane prepolymer, water is removed from castor oil and dimer polyester diol through vacuum dehydration to avoid side reactions between water and isocyanate, which would generate urea bonds and carbon dioxide bubbles, thus ensuring a uniform prepolymer structure. Then, under the catalysis of dibutyltin dilaurate, the isocyanate groups undergo an addition reaction with the hydroxyl groups in castor oil and dimer polyester diol to form urethane bonds, yielding polyurethane segments. Since the amount of isophorone diisocyanate is in excess relative to the hydroxyl groups, a certain amount of terminal isocyanate groups remains in the system after the reaction. Subsequently, hydroxyethyl acrylate is added, and the hydroxyl groups in hydroxyethyl acrylate continue to react with the terminal isocyanate groups, introducing acrylate double bonds into the polyurethane prepolymer chain ends, resulting in a photocurable castor oil-based polyurethane prepolymer.

[0038] In castor oil-based polyurethane prepolymers, the long chains of castor oil and the dimer polyester segments provide flexibility and ductility, the polyurethane bonds provide hydrogen bonding and a certain mechanical strength, and the acrylate double bonds provide sites for subsequent ultraviolet crosslinking reactions, giving the material strength, flexibility, and elastic recovery capabilities.

[0039] Step II: Preparation of photocurable elastic film slurry Weigh out 800g of castor oil-based polyurethane prepolymer, 150g of lauryl acrylate, 30g of pentaerythritol diacrylate, 300g of sweat-responsive hydrophilic microgel prepared in Example 1, and 18g of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide. Add these ingredients to a light-shielded reaction flask and stir. Heat the reaction system to 70°C and stir for 50 minutes to obtain a photocurable elastic film slurry.

[0040] By using castor oil-based polyurethane prepolymer as the main film-forming resin and lauryl acrylate as a reactive diluent, the viscosity of the system is reduced and long alkyl flexible segments are introduced, improving the flexibility and tensile deformation capacity of the membrane material. Pentaerythritol diacrylate, as a multifunctional crosslinking monomer, can increase crosslinking points during UV curing, improving the network integrity, strength, and elastic recovery of the material. Sweat-responsive hydrophilic microgels are dispersed in the slurry as the liquid-absorbing functional phase. Due to the double bond structure provided by methacryloyl chitosan on its surface, it can copolymerize or graft with the acrylate system to a certain extent during subsequent photocuring, thereby improving the interfacial bonding between the microgel and the elastic matrix.

[0041] 2,4,6-Trimethylbenzoyl-diphenylphosphine oxide, acting as a photoinitiator, generates free radicals under 365nm ultraviolet light irradiation, initiating the polymerization of acrylate double bonds. Light-shielding treatment prevents premature curing of the slurry during mixing. By controlling the proportions of elastic resin, flexible diluent, crosslinking agent, and hydrophilic microgel, the material possesses both a continuous elastic network and dispersed sweat-absorbing microregions, thus providing a foundation for achieving higher tensile strength, greater elongation at break, and higher non-swelling absorption.

[0042] Step III: Preparation of bio-based elastic membrane A photocurable elastic film slurry was poured onto the surface of a fluorinated PDMS template with a microcavity array and lateral microgrooves. The template was then vacuumed for 3 minutes at -0.08 MPa to ensure the slurry filled the microcavities and lateral microgrooves. The film thickness was then controlled to 1.0 ± 0.1 mm using a doctor blade, and excess slurry was removed. A transparent PET film was then placed on top. The sample was then exposed to light at a wavelength of 365 nm and an intensity of 12 mW / cm². 2 Under the condition of UV irradiation for 3 min, the slurry is cured into a film. After curing, the cured film is peeled off from the PET film and cured at 60℃ for 120 min. Then it is placed in 50% vol ethanol aqueous solution, and the solvent is replaced at room temperature. Then it is placed in a vacuum environment at 50℃ for 8 h to obtain a bio-based elastic film.

[0043] By applying a photocurable elastic film slurry onto the surface of a fluorinated PDMS template with a microcavity array and lateral microgrooves, vacuum treatment allows the slurry to fully penetrate the microcavities and lateral microgrooves. The microcavity structure forms a temporary sweat storage space on the material surface, while the lateral microgrooves form a channel for the directional migration of sweat. Using a doctor blade to control the film thickness ensures uniform material thickness, thereby reducing performance fluctuations during testing. Covering with a transparent PET film makes the film surface smooth and reduces the inhibition of free radical polymerization by oxygen.

[0044] During ultraviolet irradiation, the photoinitiator generates free radicals, which initiate free radical polymerization between the castor oil-based polyurethane prepolymer, lauryl acrylate, pentaerythritol diacrylate, and double bonds on the microgel surface, forming a cross-linked elastic network. Ethanol-water displacement and vacuum drying help remove residual small molecules, emulsifiers, or unreacted monomers, and stabilize the microgel and elastic membrane structure.

[0045] Step IV: Preparation of ion-gated grafting solution Anhydrous ethanol and deionized water were mixed evenly at a volume ratio of 7:3 to obtain an ethanol solution. Weigh out 60g of methacryloylethyl sulfobetaine, 8g of acrylic acid, 2g of methacrylamide, 6g of polyethylene glycol diacrylate, 1g of glycerol, 800mL of ethanol solution, and 6g of photoinitiator 2,4,6-trimethylbenzoyl-diphenylphosphine oxide. Add these ingredients to a reaction flask and stir until homogeneous. Add acetic acid to the reaction flask to adjust the pH of the system to 5.5, thus obtaining the ion-gated grafting solution.

[0046] The ion-gated grafting solution contains methacrylethyl sulfobetaine, which has zwitterionic groups and can form a strong hydration layer with water molecules, improving the hydrophilicity and sweat stain resistance of the material surface. Acrylic acid contains carboxyl groups, which undergo protonation and deprotonation changes under different pH and ionic environments, exhibiting certain sweat response characteristics. Methacrylamide contains amide groups, which enhance surface hydrophilicity through hydrogen bonding. Polyethylene glycol diacrylate contains both hydrophilic polyether segments and can act as a crosslinking agent to form a stable grafting network. Glycerin further improves surface moisturizing and flexibility, adjusts the pH to slightly acidic, which is beneficial for simulating a slightly acidic sweat environment, and keeps the hydrophilic monomers such as acrylic acid and betaine in a suitable ionic state. The ion-gated grafting solution coating forms a photocurable hydrophilic ionic network on the material surface and within the microstructure, which can significantly reduce the water contact angle of the material surface and provide wetting conditions for sweat to quickly enter the microcavities and lateral microchannels.

[0047] Step V: Preparation of bio-based composite materials The bio-based elastic membrane was placed in an ion-gated grafting solution and vacuumed for 3 minutes at -0.08 MPa. The bio-based elastic membrane preform was then removed from the ion-gated grafting solution, and excess solution was removed from its surface using a scraper. The sample was then subjected to light at a wavelength of 365 nm and an intensity of 12 mW / cm². 2 Under the condition of UV irradiation for 3 min, it was then placed in a 50% vol ethanol aqueous solution, the solvent was replaced at room temperature, and then it was dried in a vacuum environment at 50℃ for 8 h to obtain the bio-based composite material.

[0048] The bio-based elastic membrane was placed in an ion-gated grafting solution and subjected to vacuum treatment, allowing the grafting solution to penetrate the microcavities, lateral microgrooves, and near-surface pores on the membrane surface. Excess solution was then scraped off to prevent the formation of an excessively thick hydrophilic coating, thus preventing surface stickiness, decreased mechanical properties, or microchannel blockage. Upon subsequent UV irradiation, the methacryloxyethyl sulfobetaine, acrylic acid, methacrylamide, and polyethylene glycol diacrylate in the grafting solution underwent free radical polymerization, forming a cross-linked ion-gated grafted layer on the surface and within the microstructure of the elastic membrane.

[0049] This ion-gated grafted layer rapidly hydrates upon contact with sweat. After water and ions from the sweat enter, the zwitterionic groups, carboxyl groups, amide groups, and polyether segments work together to reduce the interfacial resistance of the liquid entering the microstructure, allowing sweat to quickly wet the microcavity walls and lateral channel walls. Simultaneously, the hydrophilic microgel absorbs and temporarily stores some sweat, the lateral microgrooves guide localized sweat outwards, and the ion-gated grafted layer enhances the continuity of the liquid-conducting interface.

[0050] Example 5 This embodiment provides a method for preparing a bio-based composite material, specifically including the following steps: Step I: Preparation of castor oil-based polyurethane prepolymer Weigh out 650g of castor oil and 400g of dimer polyester diol and add them to the reaction flask. Stir the mixture and heat the reaction flask to 95℃. Then, apply a negative pressure of -0.093MPa to the reaction flask and dehydrate it under vacuum for 2.5 hours. Nitrogen gas was introduced into the reaction flask, and the flask was restored to atmospheric pressure. Then, the reaction flask was cooled to 73°C. 0.5 g of isophorone diisocyanate and dibutyltin dilaurate were added to the reaction flask, and the reaction was maintained at this temperature for 3.5 h. The reaction flask was then cooled to 57°C, and 25 g of hydroxyethyl acrylate was added to the reaction flask. The reaction flask was then allowed to cool naturally to room temperature to obtain a castor oil-based polyurethane prepolymer, wherein the molar amount of isophorone diisocyanate was 1.5 times the molar amount of hydroxyl groups in the reaction system.

[0051] Step II: Preparation of photocurable elastic film slurry Weigh out 850g of castor oil-based polyurethane prepolymer, 165g of lauryl acrylate, 45g of pentaerythritol diacrylate, 330g of sweat-responsive hydrophilic microgel prepared in Example 2, and 20g of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide. Add these ingredients to a light-shielded reaction flask and stir. Heat the reaction system to 75°C and stir for 60 minutes to obtain a photocurable elastic film slurry.

[0052] Step III: Preparation of bio-based elastic membrane A photocurable elastic film slurry was poured onto the surface of a fluorinated PDMS template with a microcavity array and lateral microgrooves. The template was then vacuumed for 4 minutes at -0.085 MPa to ensure the slurry filled the microcavities and lateral microgrooves. The film thickness was then controlled to 1.0 ± 0.1 mm using a doctor blade, and excess slurry was removed. A transparent PET film was then placed on top. The sample was then exposed to light at a wavelength of 365 nm and an intensity of 12 mW / cm². 2 Under the condition of UV irradiation for 4 min, the slurry is cured into a film. After curing, the cured film is peeled off from the PET film and cured at 60℃ for 135 min. Then it is placed in 50% vol ethanol aqueous solution, and the solvent is replaced at room temperature. Then it is dried in a vacuum environment at 55℃ for 9 h to obtain a bio-based elastic film.

[0053] Step IV: Preparation of ion-gated grafting solution Anhydrous ethanol and deionized water were mixed evenly at a volume ratio of 7:3 to obtain an ethanol solution. Weigh out 65g of methacryloylethyl sulfobetaine, 10g of acrylic acid, 2.5g of methacrylamide, 7g of polyethylene glycol diacrylate, 1.5g of glycerol, 800mL of ethanol solution, and 7g of photoinitiator 2,4,6-trimethylbenzoyl-diphenylphosphine oxide. Add these ingredients to a reaction flask and stir until homogeneous. Add acetic acid to the reaction flask to adjust the pH of the system to 5.7, thus obtaining the ion-gated grafting solution.

[0054] Step V: Preparation of bio-based composite materials The bio-based elastic membrane was placed in an ion-gated grafting solution and vacuumed for 4 minutes at -0.085 MPa. The bio-based elastic membrane preform was then removed from the ion-gated grafting solution, and excess solution was removed from its surface using a scraper. The sample was then subjected to light at a wavelength of 365 nm and an intensity of 12 mW / cm². 2 Under the condition of UV irradiation for 4 min, it was then placed in a 50% vol ethanol aqueous solution, and the solvent was replaced at room temperature. Then it was dried in a vacuum environment at 55℃ for 9 h to obtain the bio-based composite material.

[0055] Example 6 This embodiment provides a method for preparing a bio-based composite material, specifically including the following steps: Step I: Preparation of castor oil-based polyurethane prepolymer Weigh out 700g of castor oil and 420g of dimer polyester diol and add them to the reaction flask. Stir the mixture and heat the reaction flask to 100℃. Then, apply a negative pressure of -0.095MPa to the reaction flask and dehydrate it under vacuum for 3 hours. Nitrogen gas was introduced into the reaction flask, and the reaction flask was restored to normal pressure. Then the reaction flask was cooled to 75°C, and 0.5g of isophorone diisocyanate and dibutyltin dilaurate were added to the reaction flask. The reaction was kept at this temperature for 4 hours, and then the reaction flask was cooled to 60°C. 30g of hydroxyethyl acrylate was added to the reaction flask, and the reaction flask was allowed to cool naturally to room temperature to obtain castor oil-based polyurethane prepolymer, wherein the molar amount of isophorone diisocyanate was 1.5 times the molar amount of hydroxyl groups in the reaction system.

[0056] Step II: Preparation of photocurable elastic film slurry Weigh out 900g of castor oil-based polyurethane prepolymer, 180g of lauryl acrylate, 60g of pentaerythritol diacrylate, 360g of sweat-responsive hydrophilic microgel prepared in Example 3, and 22g of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide. Add these ingredients to a light-shielded reaction flask and stir. Heat the reaction system to 80°C and stir for 70 minutes to obtain a photocurable elastic film slurry.

[0057] Step III: Preparation of bio-based elastic membrane A photocurable elastic film slurry was poured onto the surface of a fluorinated PDMS template with a microcavity array and lateral microgrooves. The template was then vacuumed for 5 minutes at -0.09 MPa to ensure the slurry filled the microcavities and lateral microgrooves. The film thickness was then controlled to 1.0 ± 0.1 mm using a doctor blade, and excess slurry was removed. A transparent PET film was then placed on top. The sample was then exposed to light at a wavelength of 365 nm and an intensity of 12 mW / cm². 2 Under the condition of UV irradiation for 5 min, the slurry is cured into a film. After curing, the cured film is peeled off from the PET film and cured at 60℃ for 150 min. Then it is placed in 50% vol ethanol aqueous solution, and the solvent is replaced at room temperature. Then it is dried in a vacuum environment at 60℃ for 10 h to obtain a bio-based elastic film.

[0058] Step IV: Preparation of ion-gated grafting solution Anhydrous ethanol and deionized water were mixed evenly at a volume ratio of 7:3 to obtain an ethanol solution. Weigh out 70g of methacryloylethyl sulfobetaine, 12g of acrylic acid, 3g of methacrylamide, 8g of polyethylene glycol diacrylate, 2g of glycerol, 800mL of ethanol solution, and 8g of photoinitiator 2,4,6-trimethylbenzoyl-diphenylphosphine oxide. Add these ingredients to a reaction flask and stir until homogeneous. Add acetic acid to the reaction flask to adjust the pH of the system to 6, thus obtaining the ion-gated grafting solution.

[0059] Step V: Preparation of bio-based composite materials The bio-based elastic membrane was placed in an ion-gated grafting solution and vacuumed for 5 minutes at -0.09 MPa. The bio-based elastic membrane preform was then removed from the ion-gated grafting solution, and excess solution was removed from its surface using a scraper. The sample was then subjected to light at a wavelength of 365 nm and an intensity of 12 mW / cm². 2 Under the condition of UV irradiation for 5 min, it was then placed in a 50% vol ethanol aqueous solution, and the solvent was replaced at room temperature. Then it was dried in a vacuum environment at 60℃ for 10 h to obtain the bio-based composite material.

[0060] Comparative Example 1 The difference between this comparative example and Example 6 is that the sweat-responsive hydrophilic microgel used in step II is replaced by the alginate composite microgel prepared in step 1.

[0061] Comparative Example 2 The difference between this comparative example and Example 6 is that sweat-responsive hydrophilic microgels were not added in step II.

[0062] Comparative Example 3 The difference between this comparative example and Example 6 is that steps IV and V are omitted, and a bio-based elastic membrane is used as the bio-based composite material.

[0063] Performance testing: The tensile strength, elongation at break, and elastic recovery rate of the bio-based composite materials prepared in Examples 4-6 and Comparative Examples 1-3 were determined according to standard GB / T 528-2009 "Determination of Tensile Stress-Strain Properties of Vulcanized Rubber or Thermoplastic Rubber". The elastic recovery rate was determined using the formula... Calculate the elastic recovery retention rate of the specimen after 50 cyclic stretching cycles at 100% elongation, where L is the elastic recovery retention rate. 50 L1 is the length of the specimen after the 50th stretch, L2 is the length of the specimen after the 1st stretch, and L0 is the length of the specimen before stretching. The water contact angles of the bio-based composite materials prepared in Examples 4-6 and Comparative Examples 1-3 were determined according to the standard GB / T 30693-2014 "Measurement of the contact angle between plastic films and water". The permeation flux of the bio-based composite materials prepared in Examples 4-6 and Comparative Examples 1-3 to the acidic test solution in standard GB / T 3922-2013 was determined according to standard GB / T 34243-2017 "Permeable vaporization water-permeable membrane performance test method". The non-swelling absorption of deionized water by the bio-based composite materials prepared in Examples 4-6 and Comparative Examples 1-3 was determined according to standard YY / T 0471.1-2004 "Test methods for contact wound dressings - Part 1: Liquid absorbability". The specific test data are shown in Table 1 below.

[0064] Table 1 - Performance Test Data of Samples Data Analysis: Comparative analysis of the data in the table above shows that the bio-based composite material prepared in this invention exhibits a tensile strength of 2.15-2.21 MPa, an elongation at break of 355-360%, an elastic recovery rate of 88.4-89.2%, a water contact angle of 50.0-51.4°, and a permeation flux of 0.43-0.46 kg / (m²). 2 (·h), with a non-swelling absorption capacity of 0.20-0.22 g / cm³. 2 The performance test data of the present invention are all superior to those of the comparative example, indicating that the present invention provides mechanical strength and elastic recovery by using castor oil-based polyurethane prepolymer, provides stable sweat absorption capacity by using sweat-responsive hydrophilic microgel, provides temporary storage and directional transport path for sweat by using microchannels, and reduces the surface water contact angle and promotes sweat wetting and diffusion by using ion-gated grafted layers; thus, the bio-based composite material has the properties of mechanical support, sweat absorption and moisture regulation, wetting and liquid conduction and wet stability, avoiding overall swelling, softening or microstructure collapse of the membrane, and improving the stability and comfort of acupoint patch in dynamic skin environment.

[0065] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A bio-based composite material, characterized in that, This includes a bio-based elastic base membrane and an ion-gated graft layer disposed on the bio-based elastic base membrane; The skin contact surface of the bio-based elastic base membrane has a microcavity array and lateral microchannels communicating with the microcavity array; The bio-based elastic membrane is formed by template molding and ultraviolet curing of a photocurable elastic membrane slurry. The photocurable elastic membrane slurry includes castor oil-based polyurethane prepolymer, lauryl acrylate, pentaerythritol diacrylate, sweat-responsive hydrophilic microgel, and photoinitiator. The ion-gated graft layer is formed by in-situ photocuring of ion-gated grafting liquid on the surface of the microchannels on the side of the microcavity array.

2. The bio-based composite material according to claim 1, characterized in that, The method for preparing the castor oil-based polyurethane prepolymer is as follows: castor oil and dimer polyester diol are mixed, the reaction system is heated to 90-100℃, the reaction system is vacuum dehydrated for 2-3 hours under negative pressure, the reaction system is cooled to 70-75℃ under inert gas protection, isophorone diisocyanate and catalyst are added to the reaction system, the reaction is kept at this temperature for 3-4 hours, the reaction system is cooled to 55-60℃, hydroxyethyl acrylate is added to the reaction system, and the reaction system is allowed to cool naturally to room temperature to obtain the castor oil-based polyurethane prepolymer.

3. The bio-based composite material according to claim 2, characterized in that, The weight ratio of castor oil, dimer polyester diol, catalyst, and hydroxyethyl acrylate is 60-70:38-42. 0.05:2-3, wherein the molar amount of isophorone diisocyanate is 1.5 times the molar amount of hydroxyl groups in the reaction system, and the catalyst is dibutyltin dilaurate.

4. The bio-based composite material according to claim 1, characterized in that, The preparation method of sweat-responsive hydrophilic microgel is as follows: alginate composite microgel and acetate buffer are mixed and stirred, then methacrylated chitosan is added to the reaction system and stirred for 60-80 min. Tannic acid is added to the reaction system and stirred for another 30-50 min. After post-treatment, sweat-responsive hydrophilic microgel is obtained.

5. A bio-based composite material according to claim 4, characterized in that, The ratio of alginate composite microgel, acetate buffer, methacrylamide chitosan and tannic acid is 50g:500mL:0.2-0.3g:0.08-0.1g, and the acetate buffer is a 2-3wt% sodium acetate aqueous solution with pH=5.

5.

6. The bio-based composite material according to claim 4, characterized in that, Alginate composite microgels are obtained by the following steps: B1. Mix sodium alginate and deionized water, and stir at room temperature until the system dissolves. Add sodium carboxymethyl cellulose, betaine and glycerol to the reaction system, and stir for 60-80 min. Add nano calcium carbonate to the reaction system and sonicate for 20-30 min to obtain a microgel aqueous phase. B2. Mix ethyl oleate, Span 80 and lecithin, and stir at room temperature for 30-50 minutes to obtain the oil phase; B3. Add the aqueous phase of the microgel to the oil phase, emulsify and disperse for 15-20 min to form an oil-in-water reverse emulsion, add gluconate-δ-lactone aqueous solution to the reaction system, stir for 90-120 min, and then perform post-treatment to obtain alginate composite microgel.

7. A bio-based composite material according to claim 6, characterized in that, In step B1, the ratio of sodium alginate, deionized water, sodium carboxymethyl cellulose, betaine, glycerol, and nano-calcium carbonate is 1.8-2g:100mL:0.5-0.6g:0.9-1.1g:1-1.2g:0.4-0.5g; in step B2, the ratio of ethyl oleate, Span 80, and lecithin is 300mL:9-10g:1-2g; in step B3, the volume ratio of the microgel aqueous phase to the oil phase is 1:1, the mass fraction of the glucono-δ-lactone aqueous solution is 20%, and the volume ratio of the glucono-δ-lactone aqueous solution to the microgel aqueous phase is 10:

1.

8. A bio-based composite material according to claim 1, characterized in that, It is obtained by the following steps: S1. Under a light-shielding environment, castor oil-based polyurethane prepolymer, lauryl acrylate, pentaerythritol diacrylate, sweat-responsive hydrophilic microgel, and photoinitiator are mixed and stirred. The reaction system is heated to 70-80℃ and stirred for 50-70 minutes to obtain a photocurable elastic film slurry. S2. Apply the photocurable elastic film slurry onto the surface of a fluorinated PDMS template with a microcavity array and lateral microgrooves. Vacuum the template for 3-5 minutes to fill the microcavities and lateral microgrooves with the photocurable elastic film slurry. Then, use a scraper to control the film thickness to 1.0±0.1mm and scrape off the excess slurry. Finally, cover the top with a transparent PET film and cure it with ultraviolet light to obtain a bio-based elastic film. S3. Mix and stir methacryloyl ethyl sulfobetaine, acrylic acid, methacrylamide, polyethylene glycol diacrylate, glycerol, ethanol solution and photoinitiator evenly. Add acetic acid to the reaction system and adjust the pH of the system to 5.5-6 to obtain ion-gated grafting solution. S4. Place the bio-based elastic membrane in an ion-gated grafting solution and vacuum it for 3-5 minutes. Then, remove the bio-based elastic membrane blank from the ion-gated grafting solution, remove excess solution from the surface of the bio-based elastic membrane blank with a scraper, and cure it with ultraviolet light to obtain the bio-based composite material.

9. A bio-based composite material according to claim 8, characterized in that, In step S1, the weight ratio of the castor oil-based polyurethane prepolymer, lauryl acrylate, pentaerythritol diacrylate, sweat-responsive hydrophilic microgel, and photoinitiator is 80-90:15-18:3-6:30-36:1.8-2.2; in step S3, the dosage ratio of the methacryloyl ethyl sulfobetaine, acrylic acid, methacrylamide, polyethylene glycol diacrylate, glycerol, ethanol solution, and photoinitiator is 6-7g:0.8-1.2g:0.2-0.3g:0.6-0.8g:0.1-0.2g:80mL:2-3g.

10. A flexible acupoint patch, characterized in that, It is prepared using the bio-based composite material as described in any one of claims 1-9.

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