High-transparency, antibacterial and tough dual-network hydrogel coating as well as preparation method and application of high-transparency, antibacterial and tough dual-network hydrogel coating

Abstract

The invention belongs to the technical field of biomedical materials, and particularly relates to a high-transparency, antibacterial and tough dual-network hydrogel coating as well as a preparation method and application thereof. Through a dynamic interpenetrating structure of the SA / PAM double-network hydrogel, the mechanical strength (the elongation at break is greater than 600%), the high light transmittance (gt, 88%), the super-hydrophilicity (the contact angle is less than 10 degrees), the long-acting antibacterial property (the antibacterial rate is greater than 90%) and the biological safety (the cell survival rate is gt, 95%, and the hemolysis rate is less than 4%) are synergistically optimized. The coating is prepared through plasma activation-silane coupling synergistic modification, gradient spin-coating and secondary cross-linking processes, meets the biological safety standard of medical instruments, can effectively prevent enamel demineralization and decayed teeth in the orthodontic process, and is suitable for invisible orthodontic devices made of PETG / TPU (polyethylene terephthalate / thermoplastic polyurethane) materials.

Description

Technical Field

[0001] This invention belongs to the field of biomedical materials technology, specifically relating to a dual-network hydrogel coating that combines high transparency, antibacterial properties, and toughness, as well as its preparation method and application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Invisible aligner technology is based on three-dimensional oral scanning and thermoforming processes using thermoplastic polymer materials (such as TPU / PETG). However, clinical studies have confirmed the following problems with invisible aligners during orthodontic treatment: (1) Risk of plaque buildup: The braces cover the tooth surface and form a closed microenvironment. The corrugated groove structure on the surface easily traps food debris, leading to the proliferation of cariogenic bacteria such as Streptococcus mutans. Furthermore, long-term wear accelerates material aging, further promoting bacterial adhesion. (2) Enamel demineralization mechanism: Cariogenic bacteria metabolize carbohydrates to produce organic acids, which destroy the mineral structure of tooth enamel, leading to demineralization and even the formation of cavities.

[0004] Therefore, there is an urgent need to improve the currently used invisible aligners so that they have antibacterial functions, can inhibit cariogenic bacteria, thereby preventing enamel demineralization and tooth decay, and thus improving the aesthetic effect of orthodontics and maintaining the oral health of patients.

[0005] However, existing antibacterial modification schemes have the following limitations: (1) Inorganic antibacterial agents, such as metal nanoparticles, can lead to a decrease in light transmittance; (2) Organic antibacterial agents, such as quaternary ammonium salt polymers, have problems with poor sustained release and easy dissolution and failure; (3) Hydrogel structures, such as single-network SA or PAM, have problems such as low strength and high swelling rate.

[0006] Therefore, existing coatings cannot simultaneously meet the requirements of high transparency, strong mechanical properties, and long-lasting antibacterial properties for invisible orthodontic appliances, which is a direction that needs to be explored by those skilled in the art. Summary of the Invention

[0007] To address the aforementioned problems, the present invention aims to provide a dual-network hydrogel coating with high transparency, antibacterial properties, and strong toughness, along with its preparation method and applications. This invention utilizes the dynamic interpenetrating structure of the SA / PAM dual-network hydrogel to synergistically optimize mechanical strength (elongation at break > 600%), high light transmittance (> 88%), superhydrophilicity (contact angle < 10°), long-lasting antibacterial properties (bacteriostatic rate > 90%), and biocompatibility (cell viability > 95%, hemolysis rate < 4%). This coating is prepared through plasma activation-silane coupling synergistic modification, gradient spin coating, and secondary cross-linking processes. It meets medical device biocompatibility standards and can effectively prevent enamel demineralization and tooth decay during orthodontic treatment. It is suitable for PETG / TPU invisible aligners.

[0008] Specifically, the present invention provides the following technical solution: In a first aspect, the present invention provides a dual-network hydrogel coating that combines high transparency, antibacterial properties, and toughness. The dual-network hydrogel coating sequentially comprises: a plasma-activated substrate layer, a silane coupling interface layer, and a dual-network hydrogel functional layer. The silane coupling interface layer is formed by covalent bonding of a silane coupling agent to the substrate layer. The dual-network hydrogel functional layer includes a first network and a second network. The first network is a polymer backbone network formed by free radical covalent crosslinking of polyacrylamide, and the second network is formed by sodium alginate covalently crosslinking with Zn. 2+ Ca 2+ The ion-crosslinked network formed by ion crosslinking, wherein the first network and the second network interpenetrate each other to form a double-network hydrogel structure.

[0009] Preferably, the substrate component in the plasma-activated substrate layer is made of polyester and / or polyurethane material; more preferably, the substrate in the plasma-activated substrate layer is selected from one or more of polyethylene terephthalate-1,4-cyclohexanediol ester and thermoplastic polyurethane elastomer.

[0010] Preferably, the silane coupling agent is an organosilicon coupling agent. More preferably, the organosilicon coupling agent is selected from one or more of γ-methacryloxypropyltrimethoxysilane (γ-MPS), γ-aminopropyltriethoxysilane (APTES), γ-glycidoxypropyltrimethoxysilane (GPTMS), vinyltrimethoxysilane (VTMS), and γ-mercaptopropyltrimethoxysilane (MPTMS).

[0011] Preferably, the Zn in the dual-network hydrogel functional layer 2+ Selected from one or more of basic zinc carbonate, zinc acetate, zinc sulfate, and zinc chloride, wherein Ca 2+ The Zn is selected from one or more of calcium chloride, calcium sulfate, calcium lactate, and calcium nitrate. 2+The mass of sodium alginate is (26~53) wt%; the Ca 2+ The mass concentration is 0.8%~1.2%.

[0012] Preferably, the Zn in the dual-network hydrogel functional layer 2+ The loading rate is (7.2~8.5) wt%, Ca 2+ The load is (6.5~7.8) wt%.

[0013] Preferably, the dual-network hydrogel coating has a light transmittance > 88% and a water contact angle < 10°.

[0014] Preferably, the dual-network hydrogel coating is effective against Streptococcus mutans (Streptococcus mutans). Streptococcus mutans The antibacterial rate of UA159 is >90%, and the hemolysis rate is <4%.

[0015] Preferably, the dual-network hydrogel coating enables HGF-1 human gingival fibroblasts to survive at a rate >95%.

[0016] A second aspect of the present invention provides a method for preparing the above-mentioned dual-network hydrogel coating that combines high transparency, antibacterial properties, and toughness, comprising the following steps: S1. The substrate is pretreated by plasma activation. The activated substrate is then immersed in a silane coupling agent solution and reacted by shaking to form a silane coupling interface layer. S2, a mixture of acrylamide, sodium alginate, crosslinking agent, initiator, accelerator and zinc salt, the resulting mixed prepolymer is coated on the surface of the silane coupling interface layer, and after static curing, it is immersed in calcium salt solution for secondary crosslinking treatment, and the post-treatment is obtained.

[0017] Preferably, in step S1, the plasma pretreatment is performed by placing the substrate in an oxygen plasma treatment system and treating it for 3 to 8 minutes at a pressure of 50 to 100 Pa and a power of 150 to 250 W, so as to generate -OH and -COOH active groups on the surface of the substrate.

[0018] Preferably, in step S1, the silane coupling agent solution is an anhydrous ethanol solution of silane coupling agent, wherein the mass concentration of silane coupling agent is 18%~25%.

[0019] Preferably, in step S2, the crosslinking agent is selected from one or more of N,N'-methylenebisacrylamide (MBAA), polyethylene glycol diacrylate (PEGDA), N,N'-(1,2-dihydroxyethylidene)bisacrylamide (DHEBA), and diacrylate crosslinking agents; more preferably, the diacrylate crosslinking agent is selected from one or more of 1,4-butanediol diacrylate (BDDA) and ethylene glycol dimethacrylate (EGDMA).

[0020] Preferably, in step S2, the initiator is selected from one or more of D-(+)-gluconolactone (GDL), potassium persulfate, and ammonium persulfate.

[0021] Preferably, in step S2, the accelerator is selected from one or more of tetramethylethylenediamine (TEMED), dimethylaminoacetonitrile (DMAPN), N,N-dimethylaniline (DMA), β-dimethylaminopropionitrile, and triethanolamine (TEA).

[0022] Preferably, in step S2, the mass ratio of acrylamide to sodium alginate is 8~11:1; the mass ratio of acrylamide to crosslinking agent is 10%~75%; and the mass ratio of sodium alginate to zinc salt is 30%~45%.

[0023] More preferably, the mass ratio of acrylamide to sodium alginate is 10:1; the mass ratio of acrylamide to crosslinking agent is 10%~75%; and the mass ratio of zinc salt to sodium alginate is 40%.

[0024] Preferably, in step S2, the coating method is gradient spin coating, specifically: the mixed prepolymer liquid is applied at a rate of 3 mL / 78.75 cm⁻¹. 2 Apply a quantitative amount of coating to the substrate surface. First, rotate at 35-60 rpm for 25-35 seconds to spread it evenly, and then rotate at 80-120 rpm for 15-25 seconds to control the coating thickness to 40-60 μm.

[0025] Preferably, in step S2, the static curing temperature is room temperature and constant humidity environment (RH 60±5%), and the time is 36~50 h; the secondary crosslinking time is 10~20 min.

[0026] Preferably, in step S2, the post-treatment includes washing three times with deionized water to remove unreacted substances.

[0027] A third aspect of the present invention provides the application of the dual-network hydrogel coating described in the first aspect, which combines high transparency, antibacterial properties, and toughness, in invisible orthodontic appliances.

[0028] One or more embodiments of the present invention have at least the following beneficial effects: (1) This invention introduces antibacterial components into the SA / PAM system for the first time. Through the enhancement mechanism of double network interpenetration, it not only solves the problem of weak mechanical properties of single-network hydrogels, but also gives the material excellent optical properties. At the same time, the hydrogel system has a good inhibitory effect on Streptococcus mutans, providing a new idea for the design of functionalized hydrogels. Specifically, this invention uses the dynamic interpenetration of the covalent cross-linked network of polyacrylamide and the ionic cross-linked network of sodium alginate to synergistically optimize the mechanical strength, swelling rate (only 38%) and structural stability of the coating, avoiding the limitations of a single network. At the same time, by adopting plasma activation-silane coupling synergistic modification and gradient spin coating process, it ensures a firm bond between the coating and the substrate (such as PETG / TPU), uniform thickness, and almost no loss of light transmittance, meeting the clinical requirements for transparency.

[0029] (2) Compared with single-component SA hydrogel (tensile strength 3.0±1.0 kPa) and PAM hydrogel (tensile strength 11.1±2.0 kPa), the composite hydrogel prepared in this invention has significantly improved mechanical properties of the SA / PAM dual-network system (tensile strength 68.4±4.0 kPa, toughness 346.6±15.0 kJ / m). 3 Meanwhile, the transmittance remains above 85% (wavelength 550 nm), overcoming the limitation of low transparency (<70%) in single-component SA hydrogels; furthermore, the SA / PAM hydrogel releases Zn in a controlled manner. 2+ It disrupts bacterial biofilm formation and exhibits good antibacterial activity against Streptococcus mutans, with the antibacterial effect correlated with ZCB concentration. In vitro cell experiments show that the SA / PAM hydrogel exhibits good biocompatibility after immersion in CaCl2 solution.

[0030] (3) This invention innovatively introduces the SA / PAM dual-network antibacterial hydrogel coating into the field of orthodontic invisible aligners, providing an active protection strategy for preventing complications such as demineralization and tooth decay during orthodontic treatment. Attached Figure Description

[0031] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0032] Figure 1 These are scanning electron microscope images of the polyacrylamide hydrogel, sodium alginate hydrogel, and composite hydrogel in Experimental Example 1 of this invention; Figure 2 This is a schematic diagram illustrating the principles of sodium alginate hydrogel, polyacrylamide hydrogel, and composite hydrogel in Experimental Example 1 of the present invention. Figure 3The infrared spectra of the polyacrylamide hydrogel, sodium alginate hydrogel, and composite hydrogel in Experimental Example 1 of this invention are shown. Figure 4 The final gel macromorphology of the polyacrylamide hydrogel, sodium alginate hydrogel and composite hydrogel in Experimental Example 2 of the present invention; Figure 5 Ultraviolet spectral analysis of polyacrylamide hydrogel, sodium alginate hydrogel and composite hydrogel in Experimental Example 2 of the present invention; Figure 6 The mechanical properties of polyacrylamide hydrogel, sodium alginate hydrogel and composite hydrogel in Experimental Example 2 of the present invention are analyzed, wherein (a) is the stress-strain curve of polyacrylamide hydrogel, sodium alginate hydrogel and composite hydrogel, and (b) is the Young's modulus, tensile strength and toughness test of polyacrylamide hydrogel, sodium alginate hydrogel and composite hydrogel. Figure 7 The mechanical properties of the composite hydrogels with different monomer ratios in Experimental Example 2 of the present invention are analyzed, wherein (a) is the stress-strain curve of the composite hydrogel with different monomer ratios, and (b) is the Young's modulus, tensile strength and toughness test of the composite hydrogel with different monomer ratios. Figure 8 The mechanical properties of composite hydrogels with different concentrations of MBAA in Experimental Example 2 of the present invention are analyzed, wherein (a) is the stress-strain curve of composite hydrogels with different concentrations of MBAA, and (b) is the Young's modulus, tensile strength and toughness test of composite hydrogels with different concentrations of MBAA. Figure 9 The mechanical properties of composite hydrogels with different concentrations of ZBC in Experimental Example 2 of the present invention are shown. (a) shows the stress-strain curves of composite hydrogels with different concentrations of ZBC, and (b) shows the Young's modulus, tensile strength and toughness of composite hydrogels with different concentrations of ZBC. Figure 10 This is an analysis of the mechanical properties of the composite hydrogel after CaCl2 immersion treatment in Experimental Example 2 of the present invention. (a) is the stress-strain curve of the composite hydrogel after CaCl2 immersion, and (b) is the Young's modulus, tensile strength and toughness test of the composite hydrogel after CaCl2 immersion. Figure 11 The swelling rate of polyacrylamide hydrogel, sodium alginate hydrogel and composite hydrogel in Experimental Example 2 of this invention was tested. Figure 12 This is a swelling rate test for different ZnCO3 / SA mass ratios in Experimental Example 2 of the present invention; Figure 13 These are scanning electron microscope images of TPU, TPU coating, PETG, and PETG coating in Experimental Example 3 of this invention. Figure 14The EDS spectra of TPU, TPU coating, PETG, and PETG coating in Experimental Example 3 of this invention are shown. Figure 15 XPS analysis images of TPU, TPU coating, PETG, and PETG coating in Experimental Example 3 of the present invention are shown. (a) is a broadband scan image of TPU, TPU coating, PETG, and PETG coating, and (b) is a high-resolution spectrum of characteristic elements of TPU, TPU coating, PETG, and PETG coating. Figure 16 The Fourier transform infrared spectra of TPU, TPU coating, PETG, and PETG coating in Experimental Example 3 of this invention are shown below. Figure 17 The optical properties of the SA / PAM composite hydrogel coating in Experimental Example 4 of this invention are characterized, wherein (a) is a macroscopic image of the orthodontic appliance and the orthodontic appliance coating, and (b) is an ultraviolet analysis diagram of TPU, PETG, TPU coating and PETG coating. Figure 18 Contact angle tests were conducted on TPU, TPU coating, PETG, and PETG coating in Experimental Example 4 of this invention. Figure 19 The CCK8 results for TPU, PETG, TPU coating, and PETG coating in Experimental Example 4 of this invention are shown. Figure 20 The results of live / dead cell staining (×40) of TPU, PETG, TPU coating, and PETG coating in Experimental Example 4 of this invention. Figure 21 The results of blood compatibility tests for TPU, PETG, TPU coating, and PETG coating in Experimental Example 4 of this invention; Figure 22 The bacterial plate count results for TPU, PETG, TPU coating, and PETG coating in Experimental Example 4 of this invention; Figure 23 The results of bacterial live / dead staining of TPU, PETG, TPU coating, and PETG coating in Experimental Example 4 of this invention; Figure 24 The results of scanning electron microscopy of bacteria in Experimental Example 4 of this invention are shown. Detailed Implementation

[0033] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0034] The protection scheme of the present invention will be described below through specific embodiments. It should be noted that these embodiments are only used to facilitate understanding by those skilled in the art and should not be considered as limiting the scope of protection of the present invention. Unless otherwise stated, the reagents used in the embodiments are all commercially available.

[0035] Example 1 This embodiment provides a dual-network hydrogel coating with high transparency, antibacterial properties, and toughness, and its preparation method. Step 1: Substrate Pretreatment (1) Plasma activation treatment: The substrate (polyethylene terephthalate-1,4-cyclohexanediethanol ester (PETG)) was placed in a vacuum plasma treatment system (power 200 W, vacuum degree 10 Pa), and high-purity oxygen was introduced as the working gas. Low-temperature plasma treatment was carried out for 5 minutes at a pressure of 50 Pa. High-energy particle bombardment generated a large number of active sites (such as -OH, -COOH, etc.) on the surface of the material, providing reaction sites for subsequent silane coupling.

[0036] (2) Silane coupling agent modification: The activated substrate was rapidly transferred to an anhydrous ethanol solution containing 20% ​​(v / v) 3-(isobutyryloxy)propyltrimethoxysilane (γ-MPS) and reacted under nitrogen protection at 25°C with constant temperature shaking (120 rpm) for 12 hours. After hydrolysis, the methoxy group in the γ-MPS molecule condenses with the hydroxyl groups on the substrate surface to form a covalent bond, while the retained methacryloxy group provides an active site for subsequent hydrogel polymerization.

[0037] (3) Post-processing and storage: After the reaction, the sample was ultrasonically cleaned three times with anhydrous ethanol (10 minutes each time, 100 W power) to remove the physically adsorbed coupling agent. The cleaned sample was stored in a vacuum drying oven at 40℃ for later use to ensure the stability of the surface active groups.

[0038] Step 2: Preparation of the dual-network hydrogel (prepolymer solution) (a) Take 1.21 g of acrylamide powder (AM) and 121 mg of sodium alginate (SA) (AM / SA mass ratio is 10:1, acrylamide / (sodium alginate + acrylamide) mass ratio is 90.9%), dissolve them together in ultrapure water to form a homogeneous solution, add 48 mg of basic zinc carbonate powder and 156 mg of D-(+)-glucono-δ-lactone (GDL) to it, and ultrasonically disperse for 10 min to achieve uniform distribution; then add 730 mg of MABA crosslinking agent, 10 mg of ammonium persulfate (APS) initiator and 5 μL of tetramethylethylenediamine (TEMED) accelerator to construct a free radical polymerization network; (b) The mixed solution was injected into a 20.0 mm*20.0 mm*1.0 mm acrylic plate mold and cured in a constant temperature and humidity chamber at 25℃ for 48 h to form a double network structure.

[0039] Step 3: Spin coating and crosslinking of dual-network hydrogel (1) Spin coating: Apply a quantitative amount of prepolymer solution (3 mL / 78.75 cm⁻¹) to a film. 2 The prepolymer solution is dropped onto the pretreated substrate surface and immediately subjected to gradient spin coating using a benchtop spin coater (LEBO SCIENCE, EZ4-S): initially, the spin coater is operated at a low speed of 50 rpm for 30 seconds to spread the prepolymer solution evenly; then the spin coater is operated at 100 rpm for 20 seconds to control the coating thickness within the range of 40-60 μm.

[0040] (2) Free radical polymerization and ionic crosslinking: The coated sample was transferred to a constant temperature and humidity chamber (25±1℃, RH 60±5%) and left to stand for 48 hours to complete the free radical polymerization reaction of acrylamide (AM) monomer and the crosslinking reaction of sodium alginate (SA) with zinc ions, forming a stable covalent crosslinking-ionic crosslinking dual network.

[0041] (3) Ion crosslinking enhancement: Immerse the sample in 50 mL of 1% (w / v) CaCl2 crosslinking solution for 15 minutes to allow the sodium alginate (SA) molecular chains to crosslink with Ca. 2+ The bridging process forms an "egg-box" structure, constructing a second cross-linked network. The cross-linked sample is washed three times with deionized water to remove unreacted CaCl2, ultimately yielding a composite coating material with stable interfacial bonding.

[0042] Example 2 This embodiment provides a dual-network hydrogel coating with high transparency, antibacterial properties, and toughness, and its preparation method. The difference between this comparative example and Example 1 is that the substrate type is different; the substrate in this example is thermoplastic polyurethane elastomer (TPU).

[0043] Comparative Example 1 This comparative example provides a sodium alginate hydrogel coating and its preparation method. The difference between this comparative example and Example 1 is that in step two, only a single hydrogel structure (sodium alginate hydrogel) is involved, while the other preparation methods are the same as in Example 1.

[0044] (a) Dissolve 121 mg of sodium alginate powder in ultrapure water and stir magnetically until completely dissolved; (b) Add 48 mg of basic zinc carbonate powder and disperse ultrasonically for 10 min to form a uniform suspension; (c) Add 156 mg of D-(+)-gluconic acid δ-lactone (GDL), maintaining the molar percentage of GDL to zinc carbonate at 10% throughout, and then transfer the mixed solution to a polytetrafluoroethylene (PTFE) mold; (d) Allow to cure in a constant temperature and humidity chamber at 25°C for 48 h; (e) Immerse the molded gel in 50 mL of 1% w / v CaCl2 aqueous solution for secondary crosslinking for 10-15 min; (f) Finally, rinse three times with ultrapure water to remove unreacted substances and store in a sealed container with humidity >95%.

[0045] Comparative Example 2 This comparative example provides a polyacrylamide hydrogel coating and its preparation method. The difference between this comparative example and Example 1 is that in step two, only a single hydrogel structure (polyacrylamide hydrogel) is involved, while the other preparation methods are the same as in Example 1.

[0046] (a) Dissolve 1.21 g of acrylamide monomer in ultrapure water and stir magnetically to form a homogeneous solution; (b) Add 5 μL of tetramethylethylenediamine (TEMED), 730 mg of N,N'-methylenebisacrylamide (MBAA) crosslinking agent and 10 mg of ammonium persulfate (APS) initiator sequentially; (c) Pour the mixed solution into a 20.0 mm*20.0 mm*1.0 mm acrylic plate mold and cover the surface with an acrylic plate of the same specification to control the thickness; (d) Polymerize at 25°C and constant humidity for 24 h; (e) Take out the gel, wash it with ultrapure water, and store it three times in a constant temperature and humidity environment.

[0047] Comparative Example 3 This comparative example provides a dual-network hydrogel coating and its preparation method. The difference between this comparative example and Example 1 is that in step two, the mass ratio of acrylamide / (sodium alginate + acrylamide) is 85.7% (AM / SA mass ratio is 6:1), while the contents of other components and the preparation methods are the same as in Example 1.

[0048] Comparative Example 4 This comparative example provides a dual-network hydrogel coating and its preparation method. The difference between this comparative example and Example 1 is that in step two, the mass ratio of acrylamide / (sodium alginate + acrylamide) is 80% (AM / SA mass ratio is 4:1), while the content of other components and the preparation method are the same as in Example 1.

[0049] Comparative Example 5This comparative example provides a dual-network hydrogel coating and its preparation method. The difference between this comparative example and Example 1 is that in step two, the mass ratio of acrylamide / (sodium alginate + acrylamide) is 92.3% (AM / SA mass ratio is 12:1), while the contents of other components and the preparation methods are the same as in Example 1.

[0050] Comparative Example 6 This comparative example provides a dual-network hydrogel coating and its preparation method. The difference between this comparative example and Example 1 is that in step two, the mass ratio of basic zinc carbonate to sodium alginate is 13%, while the content of other components and the preparation method are the same as in Example 1.

[0051] Comparative Example 7 This comparative example provides a dual-network hydrogel coating and its preparation method. The difference between this comparative example and Example 1 is that in step two, the mass ratio of basic zinc carbonate to sodium alginate is 26%, while the content of other components and the preparation method are the same as in Example 1.

[0052] Comparative Example 8 This comparative example provides a dual-network hydrogel coating and its preparation method. The difference between this comparative example and Example 1 is that in step two, the mass ratio of basic zinc carbonate to sodium alginate is 53%, while the content of other components and the preparation method are the same as in Example 1.

[0053] Comparative Example 9 This comparative example provides a dual-network hydrogel coating and its preparation method. The difference between this comparative example and Example 1 is that in step two, the mass ratio of MBAA crosslinking agent to acrylamide is 0.6%, while the content of other components and the preparation method are the same as in Example 1.

[0054] Comparative Example 10 This comparative example provides a dual-network hydrogel coating and its preparation method. The difference between this comparative example and Example 1 is that in step two, the mass ratio of MBAA crosslinking agent to acrylamide is 6%, while the content of other components and the preparation method are the same as in Example 1.

[0055] Comparative Example 11 This comparative example provides a dual-network hydrogel coating and its preparation method. The difference between this comparative example and Example 1 is that in step two, the mass ratio of MBAA crosslinking agent to acrylamide is 80%, while the content of other components and the preparation method are the same as in Example 1.

[0056] Experimental Example 1In this experiment, the structures of the double-network hydrogel structure prepared in Example 1 and the single hydrogel structures prepared in Comparative Examples 1 and 2 were determined. (1) Testing Procedure: The hydrogel was rapidly immersed in liquid nitrogen and freeze-dried. The freeze-dried hydrogel was then fractured to obtain a complete cross-section. The cross-sectional structure of the hydrogel was characterized using field emission scanning electron microscopy. Before testing, the sample was sputtered in an ion sputtering instrument at a current of 2.5 mA and a speed of 1 × 10⁻⁶. -3 Platinum sputtering was performed for 30 seconds under Torr vacuum conditions to improve surface conductivity. Microscopic observations were conducted at an accelerating voltage of 15 kV, with the working distance maintained within the range of 8–10 mm to ensure optimal imaging. Chemical structure analysis of the samples was performed using attenuated total reflectance Fourier transform infrared spectroscopy, with the test parameters set to a wavenumber range of 400–4000 cm⁻¹. -1 .

[0057] Test results: such as Figure 1 As shown in Figure 1(b), the single-component sodium alginate hydrogel has a very large and non-uniform pore size, while the polyacrylamide hydrogel is very dense and uniform with a smaller cross-sectional pore size (as shown in Figure 1(a)). The composite hydrogel has a pore size range of 15~35 μm, falling between the two, and the pore size is relatively uniform (as shown in Figure 1(a)). Figure 1 As shown in (c), Alginate-polyacrylamide.

[0058] Figure 2 The cross-linking mechanism of the three-component hydrogel is demonstrated. The alginate chains are composed of mannuronic acid (M units) and guluronic acid (G units), which exist in the form of blocks rich in G units, rich in M ​​units, and alternating G and M units. In aqueous solution, the G blocks in different alginate chains are cross-linked by divalent cations (e.g., Zn). 2+ ) forms ionic crosslinks (yellow circles), thereby forming a network structure in water—that is, alginate hydrogels (such as... Figure 2 (as shown in (a)). In contrast, in polyacrylamide monocomponent hydrogels, the acrylamide chains are covalently crosslinked (as shown in (a)). Figure 2 (The purple polygonal markings in (b)) form a network. In the sodium alginate and polyacrylamide composite gel, the two polymer networks intertwine and are cross-linked (e.g., through covalent cross-linking between the amino groups on the polyacrylamide chains and the carboxyl groups on the alginate chains) Figure 2 The green quadrilateral markers in (c) are connected together.

[0059] (2) Infrared spectrum: such as Figure 3 As shown, at 1346 cm -1A new CN stretching peak was generated at this point, along with absorption bands associated with primary amides (1606, 1446, 1107 cm⁻¹). -1 The intensity of ) decreased, and the OH stretching peak (3199 cm⁻¹) was reduced. -1 CO2 stretching vibration (1015 cm) -1 The strength of the polyacrylamide decreased. This result indicates that a new bond was formed between the -NH2 group of the polyacrylamide and the -COOH group of the alginate.

[0060] Experiment Example 2 This experiment measured the properties of the hydrogel structures prepared in Example 1 and the comparative example. (1) Optical performance: Testing Procedure: The hydrogel was clamped in a fixture. Baseline calibration was performed using a blank substrate as a reference before testing. Transmittance (%T) and absorbance (Abs) spectra were collected within the 300-900 nm spectral range. Key Parameter Settings: Measurement method: transmittance; slit width: 2.0 nm; external dual detector unit. Each sample was measured in triplicate to evaluate the material's optical properties.

[0061] Test result analysis: such as Figure 4 As shown, the final gel macromorphology of polyacrylamide hydrogel, sodium alginate hydrogel and composite hydrogel showed significant differences, namely, polyacrylamide hydrogel has high transparency, sodium alginate hydrogel has low transparency, and composite hydrogel has transparency in between.

[0062] like Figure 5 As shown, ultraviolet spectroscopy reveals that both the polyacrylamide hydrogel and the composite hydrogel exhibit transmittance exceeding 85% across the entire 400-900 nm wavelength range, displaying glass-like optical properties. In contrast, the sodium alginate hydrogel exhibits lower transmittance (65.4%, 550 nm), which may stem from the heterogeneity of its ionic crosslinking network. When the size of the crosslinked clusters approaches the visible light wavelength (400-700 nm), Mie scattering occurs, leading to multiple scattering and transmission loss of incident light. Notably, the composite hydrogel, through a synergistic effect of dual-network optimization, maintains the ordered covalent network of the polyacrylamide while potentially forming nanoscale zinc alginate crosslinking domains, thereby reducing light scattering effects and achieving higher transmittance. This demonstrates the superiority of the material design in terms of optical performance.

[0063] (2) Mechanical properties: Mechanical tests were conducted under different conditions using a mechanical testing machine (Sansi TaiJie, CMT-1000I, 500N). Three hydrogels were stretched from a static state until fracture. Stress was defined as the force applied to the deformed gel divided by the initial cross-sectional area of ​​the gel. Strain was defined as the length of the stretched deformed gel divided by the initial length of the gel. This definition does not consider the change in cross-sectional area due to material thinning during stretching. To optimize the mechanical properties of the composite hydrogel and improve the mechanical properties of the polymer coating, a series of tensile stress-strain tests were performed, with each experiment repeated five times, and the mean ± standard deviation was taken. Through optimization of mechanical properties, the most suitable hydrogel ratio with good stiffness and toughness was selected.

[0064] like Figure 6 As shown in (a), the elongation of polyacrylamide can reach 2500%, while that of sodium alginate is only 30%, and the elongation of the composite hydrogel is in between at 625%. Figure 6 As shown in (b), the Young's modulus and tensile strength of sodium alginate and polyacrylamide hydrogels are extremely low, while the Young's modulus and tensile strength of the composite hydrogel are greatly improved. In comparison, the toughness of the composite hydrogel is also greatly improved.

[0065] like Figure 7 As shown, with the decrease in the proportion of acrylamide monomer, the tensile strength of the composite hydrogel increases significantly, but the toughness decreases drastically. The composite hydrogel reaches its strongest toughness when the acrylamide mass percentage is 90.9% (e.g., ...). Figure 7 As shown in (b), the toughness of the composite hydrogel decreased when the mass percentage of acrylamide exceeded or fell below 90.9%. After comprehensively considering the various mechanical properties of the hydrogel, the next experiment determined the ratio of acrylamide to sodium alginate to be 10:1, and then further optimized the ratio of various components based on this.

[0066] like Figure 8 As shown, with increasing MBAA concentration (0.6%, 6%, 60%, and 80% of the acrylamide monomer mass), the crosslinking density of the polyacrylamide network increases, and the stiffness and toughness of the composite gel reach their maximum at 60% (e.g., ...). Figure 8 As shown in (b), based on this, the concentration of MBAA is determined to be 60 wt%.

[0067] like Figure 9 As shown, with the increase of ZCB concentration (13%, 26%, 40%, and 53% of sodium alginate monomer mass), the tensile strength exhibits a trend of first increasing and then decreasing. Figure 9 As shown in Figure (b), the stiffness and toughness of the composite hydrogel reach their maximum when the mass of ZCB is 26% and 40% of the mass of sodium alginate.

[0068] like Figure 10 As shown, after being soaked in CaCl2, the mechanical properties of the hydrogel in Example 1 of the present invention decreased slightly, mainly due to a decrease in toughness. This may be because the initial gel undergoes further cross-linking when immersed in CaCl2 solution, resulting in an increase in cross-linking density.

[0069] (3) Swelling properties: The water absorption capacity of the hydrogel was evaluated by conducting a swelling test. Before swelling, the hydrogel was cut into sheets with an initial diameter of 10.5 mm and a thickness of 1 mm. The samples were then immersed in deionized water at room temperature for specific durations t (0, 4, 8, 12, 16, 20, 24, 28, 32, and 36 hours). After immersion, the hydrogels were removed, thoroughly dried, and their weight was recorded. The swelling ratio (Qs) of the hydrogel was defined by the equation:

[0070] in, W s and W i These are the weight of the swollen hydrogel at immersion time t and the initial weight of the hydrogel, respectively.

[0071] like Figure 11 As shown, the swelling ratio of polyacrylamide hydrogel reaches 160%. In contrast, sodium alginate hydrogel has a non-uniform pore size and an average swelling ratio of 28%, which is much lower than that of polyacrylamide hydrogel. The composite hydrogel has a pore size between the two, with a more uniform pore size, and a slightly higher swelling ratio of 38% than sodium alginate hydrogel. Therefore, the composite hydrogel modifies the high water absorption physical properties of polyacrylamide hydrogel, exhibiting a smaller swelling volume and swelling ratio, making it more suitable for clinical applications in the dental field.

[0072] like Figure 12 As shown in Figure (b), the swelling ratio of the composite hydrogel did not exhibit a linear change with increasing ZnCO3 mass. The minimum swelling ratio (35%) was observed when the ZnCO3 / SA mass ratio was 26%; the swelling ratio slightly increased to 38% at a ZnCO3 / SA mass ratio of 40%; and reached 52% at a ZnCO3 / SA mass ratio of 53%. It is noteworthy that the volume change of the hydrogel before and after swelling was not significant, with diameter changes all within 3 mm (e.g., ...). Figure 12 (as shown in (a)).

[0073] Experimental Example 3 This experimental example demonstrates the structural determination of the dual-network hydrogel coatings prepared in Examples 1 and 2. like Figure 13As shown in (a), SEM analysis revealed that the original TPU and PETG surfaces exhibited a grooved structure and micron-sized depressions. After hydrogel coating, the coating material effectively filled the surface defects of the substrate, forming a smooth and continuous interface, and no structural defects such as cracks were observed, confirming that the spin coating process parameters were set reasonably. Figure 13 As shown in (b), the coating thickness reaches 42 μm.

[0074] like Figure 14 As shown, EDS surface scan analysis revealed that only basic elements such as C and O were detected on the original TPU / PETG surface. The coated sample surface showed significant presence of Ca. 2+ Characteristic peak (7.18 wt%) and Zn 2+ Characteristic peak (7.81 wt%), with atomic percentages of 2.41 at% and 1.90 at%, respectively. The uniform distribution of zinc confirms that the antibacterial component achieved stable loading in the coating.

[0075] In-depth analysis of the chemical composition of the coating surface was performed using X-ray photoelectron spectroscopy (XPS). For example... Figure 15 As shown in (a), the broad scan spectrum reveals that the original TPU and PETG substrates mainly exhibit characteristic peaks of carbon (C 1s, 284.8 eV) and oxygen (O 1s, 532.3 eV), with a peak intensity ratio (C / O = 3.2) consistent with the ester group structure characteristics in the polymer molecular chain. After hydrogel coating, characteristic double peaks of Zn 2p (1021.6 eV) and Ca 2p (347.1 eV) appear significantly in the full spectrum.

[0076] like Figure 15 As shown in Figure (b), high-resolution spectral analysis of the characteristic elements shows that, compared with the original membrane, the hydrogel coating group exhibits a significant Zn 2p signal at a binding energy of 1200 eV and a significant Ca 2p signal at a binding energy of 346 eV, indicating that the hydrogel coating was successfully formed on the TPU and PETG surfaces.

[0077] like Figure 16As shown, both TPU and PETG exhibited enhanced peak intensity after being treated with a sodium alginate and polyacrylamide copolymer coating. This can be analyzed from the following aspects: (1) Optical properties of the coating: The sodium alginate and polyacrylamide coating has good optical transparency, which means that it absorbs less light, thereby improving the overall transmittance. The refractive index of these polymers is similar to that of TPU and PETG, which can reduce light scattering and reflection, and improve light transmittance. (2) Improvement of surface smoothness: The coating improves the smoothness of the TPU and PETG surfaces and reduces the micro-roughness of the surfaces. This can lead to a reduction in light scattering, thereby improving transmittance. A smooth surface can reduce light scattering loss, allowing more light to pass through the material. (3) Chemical compatibility: The good compatibility of the sodium alginate and polyacrylamide coating with TPU and PETG helps to form a uniform coating, further improving the transparency and stability of the coating. This compatibility also reduces bubbles or defects in the coating, reducing light scattering. (4) Adjustment of optical properties: The coating material has specific optical functions, such as UV resistance and anti-reflection, thereby improving transmittance. By adjusting the thickness and composition of the coating, the light transmittance can be optimized. (5) Influence of functional groups: The functional groups of sodium alginate and polyacrylamide interact with the functional groups on the surface of TPU and PETG, changing the surface chemical environment and thus affecting the light absorption and scattering characteristics. In summary, the sodium alginate and polyacrylamide copolymer coating improves the infrared peak intensity of TPU and PETG through multiple mechanisms, including improving optical properties, surface smoothness, chemical compatibility, and adjusting optical properties.

[0078] Experiment Example 4 This experimental example measures the performance of the dual-network hydrogel coatings prepared in Examples 1 and 2. (1) Optical performance: Testing Procedure: Tests were conducted according to GB / T 2410-2008 standard. The optical properties of the hydrogel coating were evaluated using a UV spectrophotometer system: uncoated and hydrogel-coated orthodontic appliances were clamped in a fixture. Baseline calibration was performed using a blank substrate as a reference before testing. Transmittance (%T) and absorbance (Abs) spectra were collected in the 300-900 nm spectral range. Key parameter settings: Measurement method: transmittance; slit width: 2.0 nm; external dual detector unit. Each sample was measured in triplicate to evaluate the material's light modulation performance.

[0079] To visually demonstrate the coating distribution, a trace amount of yellow food coloring (0.01 wt%) was added to the hydrogel prepolymer solution for tracer observation. The coating completely covered the surface of the orthodontic appliance without any edge curling (e.g., Figure 17 As shown in (a). Figure 17As shown in Figure (b), both the original TPU and PETG substrates exhibit excellent optical transparency. After coating with a dual-network hydrogel, a uniform and continuous composite coating is formed on the surface of the clear aligner (COA), and the coating system maintains high transparency (transmittance 88.3 ± 1.2%). The transmittance of both the original TPU substrate and the coated TPU is above 85% (400 nm ~ 800 nm), while the transmittance of both the original PETG substrate and the coated TPU is above 90%.

[0080] (2) Hydrophilic and hydrophobic properties: The wettability of the substrate was determined using a seated drop contact angle meter under standard environmental conditions (25±1℃, RH 50-60%). Figure 18 As shown in (a), the original TPU surface exhibits hydrophobic properties (water contact angle 86.2°); while the PETG substrate, due to the presence of polar ester groups, exhibits moderate hydrophilicity (contact angle 68.1°). After plasma treatment (as shown in Figure (a)...), the surface of the PETG substrate... Figure 18 As shown in (b), the contact angle of the TPU surface decreased significantly to 61.75° (a reduction of 28.4%). This is attributed to the surface oxidation reaction induced by high-energy particle bombardment, which successfully introduced polar functional groups such as hydroxyl (-OH) and carboxyl (-COOH) groups. Notably, the contact angle of the PETG substrate did not change significantly (difference < 5°), suggesting that its ester-dominated surface chemistry is less sensitive to plasma treatment.

[0081] After applying a dual-network hydrogel coating to the orthodontic appliance (such as...) Figure 17 As shown in (c), both TPU and PETG substrates achieved superhydrophilic surface construction (contact angle < 10°), and the droplets spread completely within 1 second during the test. Specifically, the contact angle of the TPU system decreased to 7.3°, while that of the PETG system reached 7.86°, with no statistical difference between the two (p > 0.05). This significant change is due to: (1) the hydration of a large number of carboxylic acid groups in the sodium alginate molecular chain; (2) the three-dimensional hydrophilic channels formed by the acrylamide network; and (3) the effective transfer of hydrophilic properties by the stable interface layer constructed by the silane coupling agent.

[0082] (3) Biocompatibility: The in vitro cell compatibility of the coated orthodontic device was assessed using CCK-8 and live / dead cell staining, such as... Figure 19 As shown, HGF cultured in uncoated TPU and PETG was set as the control group. Compared with the control group, both the TPU-coated group and the PETG-coated group had good cell viability. One-way ANOVA showed no statistically significant difference from the control group (p>0.05).

[0083] like Figure 20As shown, the live / dead cell staining results visually demonstrate that the live cell density in the coated group (>95% Calcein-AM positive) is comparable to that in the Control group.

[0084] like Figure 21 As shown, the hemolysis results indicate that the hemolysis rates of both the TPU-coated group and the PETG-coated group are less than 4%, which meets the medical device standards.

[0085] (4) Antibacterial properties: like Figure 22 As shown, the bacterial plate count results were obtained, and the antibacterial effect was quantified using the colony counting method. The results after co-culturing the coating with bacteria showed a significant decrease in colony count in the coated group (an average of 256 colonies in the uncoated group and 93 colonies in the coated group).

[0086] like Figure 23 As shown, the bacterial viability results visually indicate that bacteria incubated with the hydrogel-coated extract showed a large amount of red fluorescence, while the uncoated group only showed sporadic red fluorescence, which is consistent with the antibacterial trend of plate counting.

[0087] like Figure 24 As shown, scanning electron microscopy results revealed that *Streptococcus mutans* treated with TPU and PETG exhibited intact and smooth cell membranes, and their morphology was a rounded, plump oval shape, indicating that the damage to bacteria from the transparent orthodontic appliance substrate was negligible. In contrast, the bacterial surface of the hydrogel-coated group showed wrinkling and became uneven, and the bacterial morphology was no longer a rounded oval, indicating that the coated orthodontic appliance prepared in this embodiment of the invention possesses special antibacterial capabilities.

[0088] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A dual-network hydrogel coating with high transparency, antibacterial, and toughness, characterized in that, The double network hydrogel coating comprises, in sequence, a plasma-activated substrate layer, a silane coupling interface layer, and a double network hydrogel functional layer; the silane coupling interface layer is formed by covalent bonding of a silane coupling agent and the substrate layer; the double network hydrogel functional layer comprises a first network and a second network, the first network is a polymer skeleton network formed by covalent crosslinking of polyacrylamide through free radicals, and the second network is an ionic crosslinking network formed by crosslinking of sodium alginate with Zn 2+ , Ca 2+ ions, the first network and the second network are interpenetrated to form a double network hydrogel structure.

2. The dual-network hydrogel coating of claim 1, wherein, The substrate component in the plasma-activated substrate layer is made of polyester and / or polyurethane material; preferably, the substrate in the plasma-activated substrate layer is selected from one or more of polyethylene terephthalate-1,4-cyclohexane dimethanol, thermoplastic polyurethane elastomer; Preferably, the silane coupling agent is an organosilicon coupling agent, and further preferably, the organosilicon coupling agent is selected from one or more of γ-methacryloxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-glycidyl ether propyltrimethoxysilane, vinyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane.

3. The dual-network hydrogel coating of claim 1, wherein, Zn in the double network hydrogel functional layer 2 + one or more selected from the group consisting of basic zinc carbonate, zinc acetate, zinc sulfate, zinc chloride, the Ca 2+ one or more selected from the group consisting of calcium chloride, calcium sulfate, calcium lactate, calcium nitrate, the Zn 2+ the mass of the sodium alginate is (26~53) wt%; the Ca 2+ the mass concentration of the Ca is 0.8%~1.2%; Preferably, Zn 2+ Ca loading is (7.2-8.5) wt% 2+ Ca loading is (6.5-7.8) wt%.

4. The dual-network hydrogel coating of claim 1, wherein, The light transmittance of the double-network hydrogel coating is > 88%, and the water contact angle is < 10°. Preferably, the dual-network hydrogel coating is effective against Streptococcus mutans (Streptococcus mutans). Streptococcus mutans The antibacterial rate of UA159 is >90%, and the hemolysis rate is <4%. Preferably, the double-network hydrogel coating has a HGF-1 human gingival fibroblast survival rate of > 95%.

5. A method for preparing the dual-network hydrogel coating with high transparency, antibacterial and strong toughness according to any one of claims 1-4, characterized in that, The method comprises the following steps: S1, the substrate is subjected to plasma activation pretreatment, and the activated substrate is immersed in a silane coupling agent solution, and a silane coupling interface layer is formed after oscillation reaction; S2, acrylamide, sodium alginate, crosslinking agent, initiator, accelerator and zinc salt are mixed, the obtained mixed prepolymer solution is coated on the surface of the silane coupling interface layer, and after standing and curing, it is immersed in a calcium salt solution for secondary crosslinking treatment, and after post-treatment, the double-network hydrogel coating is obtained.

6. The production method according to claim 5, wherein In step S1, the plasma pretreatment is to place the substrate in an oxygen plasma treatment system and treat it at a gas pressure of 50-100 Pa and a power of 150-250 W for 3-8 min. Preferably, the silane coupling agent solution is anhydrous ethanol solution of silane coupling agent, and the mass concentration of the silane coupling agent is 18%-25%.

7. The production method according to claim 5, wherein In step S2, the crosslinking agent is selected from one or more of N,N'-methylenebisacrylamide, polyethylene glycol diacrylate, N,N'-(1,2-dihydroxyethyl) bisacrylamide, and a bisacrylate crosslinking agent; further preferably, the bisacrylate crosslinking agent is selected from one or more of 1,4-butanediol diacrylate and ethylene glycol dimethyl acrylate; Preferably, the initiator is selected from one or more of D-(+)-gluconic acid δ-lactone, potassium persulfate, and ammonium persulfate; Preferably, the accelerator is selected from one or more of tetramethylethylenediamine, dimethylaminoacetonitrile, N,N-dimethylaniline, β-dimethylaminopropionitrile, and triethanolamine; Preferably, the mass ratio of acrylamide to sodium alginate is 8-11:1, the mass ratio of acrylamide to crosslinking agent is 10%-75%, and the mass ratio of sodium alginate to zinc salt is 30%-45%. Further preferably, the mass ratio of acrylamide to sodium alginate is 10:1, the mass ratio of acrylamide to crosslinking agent is 10%-75%, and the mass ratio of zinc salt to sodium alginate is 40%.

8. The production method according to claim 5, wherein In step S2, the coating method is gradient spin coating, specifically: the mixed prepolymer solution is coated on the substrate surface at 3 mL / 78.75 cm 2 Quantitative coating on the substrate surface, first spread evenly at 35-60 rpm for 25-35 seconds, and then control the coating thickness to 40-60 μm at 80-120 rpm for 15-25 seconds.

9. The production method according to claim 5, wherein In step S2, the standing and curing is carried out in a room temperature and humidity environment, and the time is 36-50 h; the post-treatment includes washing with deionized water for 3 times.

10. Use of the dual-network hydrogel coating with high transparency, antibacterial and high toughness according to any one of claims 1-5 in an invisible aligner.

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