A transparent aligner having an antibacterial coating and a method of manufacturing the same

Abstract

The present application relates to a kind of transparent aligner with antibacterial coating, the transparent aligner includes thermoplastic polymer substrate and functional coating deposited on the substrate surface by melt deposition micro-nano coating process, substrate and coating interface has gradient bonding layer with thickness of 500nm-2 μm, coating thickness is 10-50 μm, and coating contains transparent glass microspheres loaded with antibacterial active ingredients.The preparation method of the aligner is also disclosed, including the preparation of composite wire, path planning, melt deposition micro-nano coating, gradient cooling and post-processing steps.Through instantaneous heat-induced molecular chain interpenetration, IPN interface gradient bonding layer is formed, and the interface structure is locked by gradient cooling, so that the coating and substrate are combined at molecular level, and high-efficiency long-acting antibacterial is realized by the synergistic effect of topological pattern and antibacterial ions, solving the technical problems of mechanical property degradation, optical transparency damage and coating peeling after antibacterial modification of existing aligner.

Description

Technical Field

[0001] This invention belongs to the field of orthodontic materials and additive manufacturing technology, specifically relating to a transparent aligner with an antibacterial coating and its preparation method. The invention describes a functional modification method for constructing an antibacterial coating in situ on the surface of a finished transparent aligner using a fused deposition micro-nano coating process, and an antibacterial transparent aligner with a topological micro-nano structure prepared by the method. Background Technology

[0002] Invisible orthodontic aligners (clear aligners) are mainly made of medical thermoplastic substrates such as PETG and TPU through thermoforming processes. They have become the mainstream choice for orthodontic treatment due to their aesthetic appeal, comfort, and removability. To impart antibacterial properties, existing technologies mainly employ the "whole-body addition method" (i.e., mixing antibacterial agents into the substrate material) or traditional dip-coating and spray-coating methods. However, these methods suffer from drawbacks such as deterioration of mechanical properties, attenuation of optical quality, insufficient bonding strength, and limited antibacterial function. Specifically, directly adding antibacterial agents to the substrate disrupts the regular arrangement of molecular chains, leading to a decrease in mechanical properties such as resilience and creep resistance; the antibacterial agent's refractive index is mismatched with the substrate material and it is prone to aggregation, causing the aligner to "fog" and reduce light transmittance, thus losing its invisibility advantage; dip-coating and spray-coating technologies only achieve physical adhesion between the antibacterial components and the substrate, which is easily peeled off under the oral environment and chewing stress; the release efficiency of antibacterial agents in the whole-body addition method is low and the rate is uncontrollable, while traditional coating technologies cannot achieve targeted distribution and precise control.

[0003] Existing technology utilizes a melt-blending combined with 3D printing to successfully fabricate transparent orthodontic appliances with antibacterial coatings on a substrate, achieving good antibacterial effects and biocompatibility. However, since the entire appliance is directly printed from blended filaments, there are still areas for improvement: the coating and substrate are primarily physically interlocked, and the interfacial bonding strength needs to be enhanced; the light transmittance and haze of the coating have not been systematically optimized, which has a certain impact on the appliance's invisibility; the coating's tolerance during thermoforming has not been fully verified; and the release cycle of the antibacterial agent could be further extended to achieve a longer-lasting steady-state release.

[0004] Therefore, developing a technology that can construct antibacterial microstructures through localized fine additive manufacturing and achieve interface molecular-level bonding without damaging the mechanical framework and optical properties of the original orthodontic appliance is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] This invention aims to provide a transparent orthodontic appliance with antibacterial function and its preparation method. A hybrid structure design of a mechanical substrate and a functionalized coating is adopted. An antibacterial coating is constructed in situ on the surface of the orthodontic appliance using fused deposition micro-nano coating (MFDC) technology. Furthermore, improvements such as an IPN interface bonding layer and gradient cooling are introduced to achieve a synergistic improvement in antibacterial function, mechanical properties, optical properties, and interface durability.

[0006] In a first aspect, the present invention provides a transparent orthodontic appliance with an antibacterial coating, comprising: a substrate and a functionalized coating.

[0007] Further, the substrate is a thermoplastic polymer selected from at least one of polyethylene terephthalate-1,4-cyclohexanediol (or polyethylene terephthalate copolymer) PETG, thermoplastic polyurethane (TPU), polycaprolactone (PCL), or polylactic acid (PLA). It is prepared using a thermoforming process to provide the basic mechanical properties and orthodontic resilience required for orthodontic treatment.

[0008] Furthermore, the functionalized coating is a bio-based thermoplastic polymer containing a transparent antibacterial agent, and the coating thickness is 10-50 μm.

[0009] Furthermore, the bio-based thermoplastic polymer is selected from bio-based PET and bio-based PLA, and is used as an antibacterial agent carrier.

[0010] Furthermore, the transparent antibacterial agent is a transparent glass microsphere loaded with an antibacterial active ingredient, wherein the antibacterial active ingredient is selected from at least one of silver, zinc, or cuprous oxide.

[0011] Furthermore, based on the total mass of the coating, the amount of the transparent antibacterial agent added is 0.1wt%-10wt%.

[0012] Furthermore, in the transparent antibacterial agent, the antibacterial active ingredient (silver, zinc or cuprous oxide) accounts for 0.5wt%-50wt% of the total mass of the transparent antibacterial agent.

[0013] Furthermore, the average particle size of the transparent glass microspheres is 50nm-100nm, and they can withstand melting temperatures of 200-240℃.

[0014] Furthermore, the coating is deposited in situ on the substrate surface using a fused deposition micro / nano-scale coating (MFDC) process.

[0015] Furthermore, the interface between the substrate and the coating has a gradient bonding layer with a thickness of 500 nm to 2 μm.

[0016] Furthermore, the gradient bonding layer has an interpenetrating polymer network (IPN) structure.

[0017] Furthermore, the coating surface is constructed with topological micro / nano patterns, the patterns being selected from at least one of grid-like, honeycomb-like, triangular, or spiral patterns.

[0018] The grid pattern has a line width of 0.5-5μm, a grid spacing of 1-10μm, and a grid depth of 0.2-2μm, and is used to form a regular partitioned isolation structure to restrict the growth of bacteria within a single grid.

[0019] The honeycomb pattern has a size of 0.1-10μm and a pore size of 0.5-5μm. It utilizes the geometric stability of the regular hexagonal topology to disperse chewing stress, offset the local brittleness of the coating that may be caused by the addition of antibacterial agents, and at the same time, it produces a "reinforcing" effect on the substrate. Its creep resistance is improved by 35% compared with the unpatterned coating, and the creep strain is as low as 0.27% at 44℃.

[0020] The triangular pattern has a side width of 0.1-2μm and a height of 0.05-1μm. It is used to disrupt the integrity of bacterial cell membranes through the physical shearing action of the sharp edges, thereby achieving dual physical and chemical antibacterial effects.

[0021] The spiral pattern has a pitch of 1-10μm and a line width of 0.12-0.18mm. It is used to increase the tortuous diffusion path of antibacterial ions, achieve long-term controllable sustained release, and regulate the saliva flow field to reduce bacterial adhesion.

[0022] Furthermore, the refractive index of the bio-based thermoplastic polymer in the coating is n1, the refractive index of the transparent antibacterial agent is n2, and the refractive index of the orthodontic appliance substrate is n3, satisfying |n1-n2|≤0.01 and |n1-n3|≤0.02.

[0023] The light transmittance of the orthodontic appliance decreases by ≤1.8% compared to the unmodified substrate, and the haze value is ≤1.5%; preferably, the light transmittance decreases by ≤1% and the haze value is ≤0.5%.

[0024] A second aspect of the present invention provides a method for preparing the transparent orthodontic appliance described in the first aspect, comprising the following steps:

[0025] 1) Preparation of functional composite filaments: Bio-based thermoplastic polymers are mixed with transparent antibacterial agents, and then melt-blended, extruded, cooled and wound to obtain composite filaments.

[0026] The bio-based thermoplastic polymer is selected from at least one of bio-based PET or bio-based PLA; the transparent antibacterial agent is a high-transmittance glass microsphere loaded with silver-based, zinc-based or cuprous oxide-based antibacterial components.

[0027] The mass ratio of the bio-based thermoplastic polymer to the transparent antibacterial agent is (99.9:0.1) to (90:10).

[0028] Furthermore, the melt blending temperature is 200-240℃.

[0029] Furthermore, the melt blending is performed using a torque rheometer.

[0030] Furthermore, the extrusion is performed using a twin-screw extruder.

[0031] Furthermore, gradient temperature extrusion is adopted: the temperature of zone one is 20-30°C lower than the melting point of the bio-based thermoplastic polymer, the temperatures of zones two and three are consistent with the melting point, and the die temperature is 10-15°C higher than the melting point.

[0032] Furthermore, the diameter of the composite filament is 1.75 ± 0.05 mm.

[0033] In one embodiment of the present invention, the mixture is added to a torque rheometer and melt-blended at 200-240°C. The mixture is continuously stirred until the torque value is stable within ±5% for ≥10 min to ensure that the antibacterial agent is uniformly dispersed and free from agglomeration. Then, the blend is added to a twin-screw extruder and subjected to gradient melt extrusion, air-cooled sizing, and precision drawing and winding processes to prepare a high-precision composite filament with a diameter of 1.75±0.05 mm.

[0034] 2) Surface scanning and path planning: The surface of the orthodontic appliance substrate is scanned in three dimensions to obtain its surface morphology data, and the coating deposition path and topological micro-nano pattern distribution are designed.

[0035] Furthermore, based on the functional requirements of different parts of the orthodontic appliance (tooth contact area, gingival occlusion area, etc.), the topological micro-nano patterns (honeycomb, triangle, spiral, etc.) and distribution density are designed differently:

[0036] Tooth surface contact area: Designed with a dense honeycomb pattern or a dense triangular pattern to enhance mechanical properties and physical antibacterial properties; the pore size of the dense honeycomb pattern is 0.4-0.6μm; the edge width of the dense triangular pattern is 0.1-0.2μm.

[0037] Gingival camouflage area: Designed with a sparse honeycomb pattern, a sparse triangular pattern, or a spiral pattern for long-lasting release and reduced bacterial adhesion; the pore size of the sparse honeycomb pattern is 4-6μm, the edge width of the sparse triangular pattern is 1-3μm, and the pitch of the spiral pattern is 1-10μm.

[0038] Step 3) Fused deposition micro / nano coating: The composite filament prepared in step 1) is heated to a molten state and deposited onto the substrate surface according to the path planned in step 2), so that molecular chains interpenetrate at the interface between the substrate surface and the coating to form a gradient bonding layer.

[0039] Furthermore, the melting temperature is 200-240°C, wherein the melting temperature is set to be 10-20°C higher than the melting point of the bio-based thermoplastic polymer to ensure that the melt has good fluidity, while being higher than the glass transition temperature of the substrate material to drive interpenetration of interfacial molecular chains.

[0040] Furthermore, the substrate temperature is 30℃-60℃, preferably 50℃-60℃.

[0041] Furthermore, the substrate is placed on a deposition platform.

[0042] Furthermore, the deposition rate is ≤300 mm / s.

[0043] By setting the melting temperature (200-240℃), plateau temperature (30-60℃), and deposition rate (≤300 mm / s), transient heat conduction is generated at the interface due to temperature difference when the molten composite filament comes into contact with the substrate surface. Under these process conditions, the surface temperature of the substrate rises above its glass transition temperature within a contact time of 0.2-0.5 seconds, thereby inducing the interdiffusion and entanglement of molecular chains to form a gradient bonding layer with an interfacial interpenetrating polymer network (IPN) structure with a thickness of 500 nm-2 μm.

[0044] Furthermore, the substrate and composite filament are vacuum dried before deposition to remove surface and internal moisture.

[0045] In one embodiment of the present invention, the composite filament prepared in step 1) is loaded into a fused deposition micro / nano coating device. Before deposition, the substrate and the composite filament are vacuum dried. The fused deposition process parameters are: micronozzle diameter 0.2 mm, coating single layer thickness 0.05 mm, deposition linewidth 0.12-0.18 mm, deposition density 100%, deposition rate 300 mm / s, composite filament melting temperature 230℃, and the substrate is placed on a 60℃ constant temperature platform. Deposition is carried out according to the planned trajectory in step 2). The contact time between the molten composite filament and the substrate is about 0.5 seconds. During this process, the temperature difference between the molten polymer and the substrate drives heat conduction, causing the surface temperature of the substrate to rise rapidly above its glass transition temperature, inducing molecular chain segment interpenetration between the substrate surface and the coating. After cooling, an interpenetrating polymer network (IPN) structure is formed.

[0046] Step 4) Gradient cooling and post-processing: After the melt deposition is completed, gradient cooling is performed and post-processing is carried out to obtain a transparent orthodontic appliance with antibacterial function.

[0047] Furthermore, the gradient cooling employs a three-stage cooling process, including:

[0048] (1) Rapid Cooling Section: The coating is cooled from its peak melting deposition temperature (200℃-240℃) to 55℃-65℃ at a cooling rate of 80℃ / s-150℃ / s. This section is used to instantly freeze the interpenetrating molecular chain network structure at the interface, preventing the chain segments from relaxing and untangling at high temperatures. For PETG / TPU amorphous substrates, it can quickly lock the interface structure, avoiding internal stress and stress atomization caused by chain segment rebound. For PCL / PLA semi-crystalline substrates, it can quickly cross the polymer precipitation temperature range, inhibit the germination of trace crystal nuclei, and avoid local microcrystalization leading to decreased light transmittance.

[0049] (2) Isothermal range: The temperature is maintained at 55℃-65℃ for 5-15 seconds. This temperature range is close to or slightly lower than the glass transition temperature of the substrate material, which is used to allow the chain segments to relax moderately to release interfacial thermal stress, while avoiding large-scale deentanglement or phase transformation.

[0050] (3) Slow cooling section: The temperature is reduced from 55℃-65℃ to room temperature (20℃-30℃) at a cooling rate of 5℃ / min-15℃ / min. This section adopts a very slow rate of gradual cooling to balance the overall temperature field distribution, completely eliminate residual internal stress, effectively prevent substrate warping, coating micro-cracks and deformation during later use, improve long-term dimensional stability, balance the overall temperature field distribution, eliminate residual internal stress, and prevent orthodontic appliance warping, coating micro-cracks and deformation during use.

[0051] Furthermore, the post-processing refers to steps including hot pressing and ultraviolet sterilization, ultimately resulting in a transparent orthodontic appliance with antibacterial function.

[0052] The hot pressing conditions are as follows: hot pressing temperature 85-130℃, molding pressure 0.2-0.6 MPa, holding pressure and setting time 30-60s, vacuum negative pressure -0.06~-0.09 MPa; after hot pressing, cool to room temperature.

[0053] Furthermore, the hot pressing process employs segmented heating: the temperature is raised from room temperature to the first stage temperature of 60℃-80℃ at a rate of 5℃ / min-15℃ / min, and then raised to the hot pressing temperature at a rate of 2℃ / min-8℃ / min.

[0054] Furthermore, during the heating process, pressure is applied to the molding pressure at a rate of 0.05 MPa / s-0.2 MPa / s.

[0055] The hot pressing process of this invention adopts a segmented heating, uniform pressurization and constant temperature holding mode, which ensures that the modified substrate fully fits the dental mold and avoids the softening and flow of the topology coating at high temperature and the deentanglement of the interface IPN structure. After molding, it is naturally air-cooled to room temperature to ensure dimensional accuracy and coating integrity.

[0056] Furthermore, the ultraviolet sterilization time is 30-50 minutes, and conventional ultraviolet sterilization conditions can be used (such as wavelength 254nm, power 15 W-30 W, irradiation distance 10 cm-30 cm).

[0057] A third aspect of the present invention provides the application of the orthodontic appliance described in the first aspect or the orthodontic appliance obtained by the preparation method of the second aspect in the preparation of oral orthodontic instruments.

[0058] The beneficial effects of this invention are:

[0059] (1) Enhanced interfacial bonding strength: This invention utilizes instantaneous thermally induced molecular chain interpenetration combined with a three-stage gradient cooling process (first, rapidly cooling to 55-65℃ at 80-150℃ / s to lock the IPN structure; then maintaining a constant temperature for 5-15 seconds to release interfacial thermal stress; finally, slowly cooling to room temperature at 5-15℃ / min to eliminate residual internal stress) to form a 500nm-2μm IPN interfacial gradient bonding layer, enabling the coating and substrate to achieve molecular-level bonding with a bonding strength level of 0, thus significantly improving interfacial bonding strength and eliminating internal stress. This cooling process can avoid stress whitening caused by chain segment rebound for amorphous substrates such as PETG and TPU; and for semi-crystalline substrates such as PLA and PCL, it can inhibit the germination of trace crystal nuclei and avoid light transmittance attenuation.

[0060] (2) Undamaged optical transparency: By matching the refractive indices of the coating polymer, antibacterial carrier and substrate, and combining the micro-nano-level ultra-thin coating structure with gradient rapid cooling technology, the light transmittance of the orthodontic appliance decreases slightly and the haze is low. There is no whitening or fogging phenomenon, which can maintain the invisible and beautiful effect of the orthodontic appliance.

[0061] (3) Antibacterial sustained-release effect: Through the synergistic effect of topological pattern and chemical sustained release of antibacterial ions, the inhibition of cariogenic bacteria reaches 8 orders of magnitude, and the bacterial adhesion rate is reduced by more than 60%. Through glass microsphere coating and topological structure regulation, antibacterial ions achieve steady-state sustained release without burst release, and the long-term antibacterial period can reach more than 90 days.

[0062] (4) Optimized mechanical properties and biocompatibility: The coating thickness is only 10-50μm, which does not damage the original molecular chain structure of the substrate, and the elasticity retention rate of the orthodontic appliance is high; with the structural reinforcement effect of the topological micro-nano pattern, Young's modulus is improved and creep strain at 44℃ is reduced. The dosage of antibacterial agent is controlled within the biosafety range, the survival rate of human gingival fibroblasts is ≥95%, and there is no cytotoxicity or oral mucosal irritation; the antibacterial agent coating helps to increase the pH value in cariogenic environments, reducing the risk of chalky spots and tooth decay. Attached Figure Description

[0063] Figure 1 The SEM morphology image of the coating topology was prepared for Example 1 of the present invention.

[0064] Figure 2 The C element distribution map of the coating prepared for Example 1 is shown.

[0065] Figure 3 The O element distribution map of the coating prepared for Example 1.

[0066] Figure 4 The Zn elemental distribution map of the coating prepared for Example 1 is shown.

[0067] Figure 5 This is a diagram of the fused deposition micro / nano coating equipment of the present invention. Detailed Implementation

[0068] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0069] In this invention, the definition of "bio-based" refers to the national standard GB / T 39514-2020 "Terminology, Definition and Identification of Bio-based Materials".

[0070] The fused deposition micro / nano coating apparatus of the present invention, such as Figure 5 As shown, it mainly includes: a micro-nozzle (0.2 mm in diameter) for extruding molten composite filaments; a three-axis precision motion platform for fixing the planar substrate and controlling the relative motion trajectory between the nozzle and the substrate; an independent heating and temperature control system for controlling the temperature of the nozzle (melting temperature) and the platform respectively; and a vacuum drying pretreatment unit for drying the substrate and composite filaments before deposition.

[0071] The base polymer, transparent antibacterial agent, and bio-based polymer used in this invention are all commercially available.

[0072] Example 1

[0073] Raw materials: PETG orthodontic appliance substrate (refractive index 1.52); bio-based PET granules (coated polymer, refractive index 1.53); zinc-based transparent antibacterial agent (loaded on high-transmittance glass microspheres, refractive index 1.53, particle size 50-100nm, of which zinc active ingredient content is 50wt%), satisfying |n1-n2|≤0.01, |n1-n3|≤0.02.

[0074] 1) Preparation of functional composite filaments: Bio-based PET granules and zinc-based transparent antibacterial agent were mixed at a mass ratio of 99:1 (zinc content approximately 0.5 wt%), added to a torque rheometer (XSS-300), and melt-blended at 230℃ until the torque value stabilized for 12 min; the blend was added to a twin-screw extruder (KZ-T28), with extrusion temperatures of 200℃ in zone 1, 230℃ in zone 2, 230℃ in zone 3, and 240℃ at the die, a feed rate of 75 rpm, and a main screw speed of 30 rpm. After air cooling, the extrudate was drawn and wound to obtain composite filaments with a diameter of 1.75 mm.

[0075] 2) Path planning: A three-dimensional scan of the PETG substrate was performed. A dense grid pattern with a line width of 0.5μm and a grid spacing of 1μm was designed for the tooth surface contact area, and a sparse grid pattern with a line width of 5μm and a grid spacing of 10μm was designed for the gingival camber area.

[0076] 3) Fused Deposition Micro / Nano Coating: The composite filament prepared in step 1) and the substrate were vacuum dried. The composite filament was loaded into a fused deposition micro / nano coating apparatus, and the substrate was fixed on a 60℃ constant temperature platform. The micronozzle diameter was set to 0.2 mm, the coating thickness to 0.05 mm, the deposition linewidth to 0.15 mm, the deposition density to 100%, the deposition rate to 300 mm / s, and the melting temperature to 230℃. Deposition was carried out according to the planned trajectory. The contact time between the molten composite filament and the substrate was approximately 0.5 seconds. The temperature difference was used to drive heat conduction, raising the surface temperature of the substrate above its glass transition temperature and inducing molecular chain interpenetration. After deposition, the coating thickness was approximately 30 μm.

[0077] 4) Gradient cooling and post-processing:

[0078] After the coating is deposited, a three-stage gradient cooling process is performed: first, the temperature is cooled from 230°C to 60°C at a rate of 120°C / s to lock the IPN structure; then, the temperature is held at 60°C for 10 seconds to release interfacial thermal stress; finally, the temperature is reduced to room temperature at a rate of 10°C / min to eliminate residual internal stress.

[0079] The product was then hot-pressed: staged heating (10℃ / min to 70℃, then 5℃ / min to 110℃) and uniform pressure (0.1 MPa / s) were used. The hot-pressing temperature was 110℃, the molding pressure was 0.4 MPa, the holding time was 45 s, and the vacuum pressure was -0.08 MPa. After molding, the product was allowed to cool naturally to room temperature. Finally, it was sterilized with ultraviolet light for 40 min to obtain the finished product.

[0080] The surface morphology and elemental analysis of the coating obtained in Example 1 were performed, and the results are as follows: Figure 1-4 As shown. Figure 1 The SEM image of the coating surface shows that a uniform grid pattern has been successfully constructed on the coating surface. The pattern is regular and the structure is clear. The grid structure is evenly distributed in the tooth contact area.

[0081] Figure 2-4 The distribution diagrams of C, O, and Zn elements are shown, indicating that each element is uniformly distributed in the coating without obvious agglomeration. This is due to the melt blending process and glass microsphere loading design of this invention. The uniform distribution of antibacterial agents avoids the formation of light scattering centers due to agglomeration, ensuring the optical transparency of the coating (transmittance decrease ≤1%), while providing a structural basis for achieving long-term, steady-state release of antibacterial ions.

[0082] Example 2

[0083] Raw material preparation: PCL medical thermoplastic orthodontic appliance substrate (refractive index 1.51), bio-based PLA granules (coated polymer, refractive index 1.52), silver-based transparent antibacterial agent (loaded on high-transmittance glass microspheres, refractive index 1.52, particle size 50-100nm, of which the silver active ingredient content is 20 wt%); satisfying |n1-n2|≤0.01, |n1-n3|≤0.02.

[0084] 1) Preparation of functional composite filaments: Bio-based PLA and silver-based transparent antibacterial agent were mixed at a mass ratio of 90:10 (silver content is about 2wt%) and melt-blended at 200℃ for 10min; twin-screw extrusion parameters: zone 1 170℃, zone 2 200℃, zone 3 200℃, die 210℃, and other parameters were the same as in Example 1 to prepare composite filaments.

[0085] 2) Path planning: The tooth surface contact area is designed with a densely textured triangular pattern with a side width of 0.1μm, and the gingival camber area is designed with a sparsely textured triangular pattern with a side width of 2μm.

[0086] 3) Fused Deposition Micro / Nano Coating: The composite filament and substrate are vacuum dried. Process parameters are set as follows: micro-extrusion port inner diameter 0.2 mm, coating layer thickness 0.05 mm, deposition density 100%, deposition rate 280 mm / s, melting temperature 200℃, plateau temperature 50℃. The deposition linewidth in the tooth contact area is 0.18 mm, and in the gingival camber area, it is 0.15 mm. The coating is deposited along the planned trajectory, utilizing temperature difference to drive heat conduction and raise the substrate surface temperature, inducing molecular chain interpenetration. The final coating thickness is approximately 40 μm.

[0087] 4) Gradient cooling and post-treatment: After the coating is deposited, a three-stage gradient cooling process is performed: first, the temperature is rapidly cooled from 200°C to 55°C at a rate of 100°C / s, then kept at 55°C for 15 seconds, and finally, the temperature is slowly reduced to room temperature at a rate of 8°C / min to eliminate residual internal stress.

[0088] The product was then hot-pressed: staged heating (8℃ / min to 60℃, then 4℃ / min to 85℃) and uniform pressure (0.08 MPa / s) were used. The hot-pressing temperature was 85℃, the molding pressure was 0.3 MPa, the holding time was 40 s, and the vacuum pressure was -0.07 MPa. After molding, the product was allowed to cool naturally to room temperature. Finally, it underwent ultraviolet sterilization for 30 min to obtain the finished product.

[0089] Example 3

[0090] Raw material preparation: TPU medical thermoplastic orthodontic appliance substrate (refractive index 1.53), bio-based PET granules (coated polymer, refractive index 1.53), cuprous oxide transparent antibacterial agent (loaded on high-transmittance glass microspheres, refractive index 1.52, particle size 50-100nm, of which the cuprous oxide active ingredient content is 50 wt%); satisfying |n1-n2|≤0.01, |n1-n3|≤0.02.

[0091] 1) Preparation of functional composite filament: Bio-based PET and transparent cuprous oxide antibacterial agent were mixed at a mass ratio of 90:10 (cuprous oxide content was 5 wt%) and melt-blended at 230℃ for 15 min; extrusion parameters were the same as in Example 1 to prepare composite filament with a diameter of 1.75 mm.

[0092] 2) Path planning: Design a loose spiral pattern with a pitch of 1μm on the entire surface.

[0093] 3) Fused deposition micro / nano coating: deposition linewidth 0.12 mm, platform temperature 45℃, coating path is a continuous winding path, other parameters are the same as in Example 1; after deposition, the coating thickness is about 25 μm.

[0094] 4) Gradient cooling and post-treatment: First, cool from 230℃ to 60℃ at 130℃ / s, hold the temperature for 8 seconds, and then slowly cool to room temperature at 12℃ / min.

[0095] The hot pressing and ultraviolet sterilization parameters are the same as in Example 1, and the finished product is obtained.

[0096] Example 4

[0097] Raw materials: Same as in Example 1.

[0098] Steps 1)-3) are the same as in Example 1.

[0099] 4) Gradient cooling and post-processing

[0100] Gradient cooling is the same as in Example 1 (rapid cooling to 60°C at 120°C / s, holding the temperature for 10 seconds, and slow cooling to room temperature at 10°C / min).

[0101] Hot pressing: The temperature is directly raised to 110℃ (without segmented heating), the hot pressing temperature is 110℃, the molding pressure is 0.4 MPa, the holding time is 45 s, and the vacuum negative pressure is -0.08 MPa. After molding, it is naturally cooled to room temperature. It is then sterilized with ultraviolet light for 40 min to obtain the finished product.

[0102] Comparative Example 1 (Unmodified PETG clear aligner)

[0103] Orthodontic appliances were fabricated using an unmodified pure PETG medical substrate (0.5 mm thick) via thermoforming. The specific steps were as follows: the PETG substrate was placed in a thermoforming machine, heated to 110°C, subjected to a pressure of 0.4 MPa for 45 seconds, and then subjected to a vacuum pressure of -0.08 MPa. After molding, the appliance was allowed to cool naturally to room temperature, resulting in an unmodified transparent orthodontic appliance. This comparative example, without any added antibacterial agents, surface coatings, or modification treatments, served as a blank control.

[0104] Comparative Example 2

[0105] PETG granules were mixed with a zinc-based antibacterial agent (same as in Example 1) at a mass ratio of 99:1. The zinc-based antibacterial agent was a zinc active ingredient loaded on high-transparency glass microspheres (glass microspheres with a particle size of 50-100 nm and a zinc active ingredient content of 50 wt%). After mixing, the mixture was granulated by twin-screw extrusion. The resulting granules were hot-pressed to form a substrate with a thickness of 0.5 mm. The substrate was then thermoformed to prepare an orthodontic appliance.

[0106] Comparative Example 3

[0107] The raw materials, formulation, and coating parameters are exactly the same as in Example 1, the only difference being the cooling method. The specific steps are as follows:

[0108] Steps 1)-3) are the same as in Example 1.

[0109] 4) Cooling and post-treatment (without gradient cooling): After melt deposition, the sample is placed directly in a room temperature (approximately 25°C) environment for natural cooling (cooling rate approximately 0.5-5°C / s). After cooling, hot pressing (parameters same as in Example 1) and ultraviolet sterilization (40 min) are performed to obtain the finished product.

[0110] Comparative Example 4

[0111] The raw material formulation is the same as in Example 1, but a traditional low-temperature coating method is used. Bio-based PET is blended with a zinc-based antibacterial agent (raw material same as in Example 1), and then coated onto the surface of a PETG substrate using a low-temperature coating method. During the coating process, the substrate temperature is controlled at 80°C, and the coating thickness is controlled at approximately 30 μm. After coating, the mixture is allowed to evaporate at room temperature or cure naturally, and finally sterilized with ultraviolet light (40 min) to obtain the finished product.

[0112] Comparative Example 5

[0113] The raw materials, formulation, and coating parameters are exactly the same as in Example 1, the only difference being the cooling method. The specific steps are as follows:

[0114] Steps 1)-3) are the same as in Example 1.

[0115] 4) Cooling and Post-treatment (without a constant temperature section): After melt deposition, a two-stage cooling process is employed: the first stage rapidly cools from 230°C to 60°C at a cooling rate of 120°C / s; the second stage directly cools from 60°C to room temperature at a cooling rate of 10°C / min. This omits the step of "holding at 60°C for 10 seconds". Subsequently, the same hot pressing and UV sterilization (40 min) process as in Example 1 is performed to obtain the finished product.

[0116] Performance testing

[0117] To verify the performance of the transparent orthodontic appliance of the present invention, the following tests were performed on the samples of the embodiments and comparative examples.

[0118] Mechanical properties: The orthodontic resilience retention rate was tested at 5 mm / min using a universal testing machine; the Young's modulus was tested at a tensile rate of 1 mm / min using a universal testing machine; the creep strain was tested at a constant temperature of 44℃ for 24 hours; and the modulus decay rate was tested after 10,000 simulated chewing cycles (2 Hz, 50 N).

[0119] Interface bonding strength: The coating was tested using a cross-cut test (0-5 levels) and observed after 50 cycles of hot and cold cycling (-20℃ to 60℃) and 30 days of immersion in artificial saliva.

[0120] Optical performance: The transmittance of 400-800nm ​​was measured using a UV-Vis spectrophotometer, and the decrease compared to the unmodified substrate (i.e., Comparative Example 1) was calculated; the haze value was measured using a haze meter according to GB / T 2410.

[0121] Antibacterial properties: The inhibition rate of Streptococcus mutans was tested using the plate count method; the bacterial adhesion rate was tested using the fluorescence staining method. Long-lasting antibacterial properties: The samples were immersed in artificial saliva for 90 days, and the antibacterial activity was tested periodically. Simultaneously, the release concentration of antibacterial ions at different time points was determined using ICP-MS, and release curves were plotted.

[0122] Biocompatibility: The survival rate of human gingival fibroblasts was tested using the MTT assay according to ISO 10993-5 standard.

[0123] Acid-resistant caries testing: The samples were co-cultured with Streptococcus mutans for 48 hours, and the pH changes of the culture medium were monitored.

[0124] The performance test results of each embodiment and comparative example are shown in Tables 1-3.

[0125] Table 1 Mechanical properties and interfacial bonding strength

[0126]

[0127] Table 2 Comparison of Optical Performance

[0128]

[0129] As shown in Tables 1-2, comparing the data of Comparative Example 3 (natural cooling), Comparative Example 5 (without isothermal section), and Example 1: Comparative Example 3 achieved a cross-cutting grade of 2 and a haze of 2.8%; Comparative Example 5 improved to a cross-cutting grade of 1 and reduced haze to 1.2%; while Example 1 reached a grade of 0 and a haze of only 0.4%. These data indicate that the rapid cooling section can quickly lock in the IPN structure, while the isothermal section effectively releases interfacial thermal stress and eliminates stress whitening. The three-stage gradient cooling process synergistically achieves a high-strength, highly transparent antibacterial coating interface. Furthermore, the differences in creep strain and Young's modulus between Example 1 and Comparative Example 5 further illustrate that the slow cooling section improves high-temperature dimensional stability by eliminating residual internal stress.

[0130] The resilience retention rate of Examples 1-4 is greater than 98%, the Young's modulus is increased by about 2-5% compared with the unmodified substrate (Comparative Example 1), and the creep strain at 44℃ is as low as 0.27%-0.32%, which is significantly better than Comparative Example 3 and Comparative Example 5, proving that the topological micro-nano pattern has a significant structural reinforcement effect.

[0131] Furthermore, regarding optical performance, the transmittance of Examples 1-3 decreased by ≤1% and the haze by ≤0.5%, showing very little difference from the unmodified substrate (Comparative Example 1), verifying the effectiveness of the refractive index matching design of the coating polymer, the transparent antibacterial agent, and the substrate. Example 4, using direct heating and hot pressing, resulted in slight coating flow, a 1.8% decrease in transmittance, and a 1.5% decrease in haze, indicating that segmented heating has a certain effect on protecting the coating morphology and IPN structure. In contrast, Comparative Example 2 (whole-addition method) showed a 14.5% decrease in transmittance and a high haze of 7.8% due to antibacterial agent agglomeration, demonstrating the advantages of the surface coating strategy of this invention.

[0132] Table 3 Comparison of antibacterial properties

[0133]

[0134] Table 3 shows that Examples 1-4 all achieved 8 orders of magnitude inhibition of Streptococcus mutans, comparable to Comparative Examples 3-5, and significantly superior to Comparative Example 2. The bacterial adhesion rate decreased by 62-68% in each example, thanks to the synergistic effect of the physical anti-adhesion of the topological pattern and the antibacterial ionic chemical bactericidal effect. Cell viability was ≥95% in all examples, with no cytotoxicity; the pH value increased to 5.42-5.45, close to the critical value for enamel demineralization (5.5), indicating that the coating has anti-acid caries function.

[0135] In summary, this invention constructs an antibacterial coating in situ on the surface of the orthodontic appliance substrate using a fused deposition micro-nano coating process. Combined with an IPN gradient bonding layer formed by instantaneous thermal induction and a three-stage gradient cooling process, a high-strength bond between the coating and the substrate is achieved (0-level in cross-cut test). Through refractive index matching design and gradient rapid cooling technology, the orthodontic appliance exhibits a low decrease in transmittance and minimal haze, maintaining its invisible effect. Utilizing the structural reinforcement of the topological pattern and the synergistic effect of physical antibacterial action, Young's modulus is increased by approximately 2-5%, inhibiting cariogenic bacteria by eight orders of magnitude. Compared to existing one-piece printed antibacterial orthodontic appliances, this invention significantly improves interfacial bonding strength, optical transparency, and mechanical stability while maintaining excellent antibacterial performance.

Claims

1. A transparent aligner having an antibacterial coating, characterized in that, The orthodontic appliance includes: a base and a functionalized coating; The substrate is a thermoplastic polymer selected from at least one of polyethylene terephthalate-1,4-cyclohexanediol ester PETG, thermoplastic polyurethane TPU, polycaprolactone PCL, or polylactic acid PLA. The functionalized coating is a bio-based thermoplastic polymer containing a transparent antibacterial agent, and the coating thickness is 10-50 μm; The coating surface has topological micro / nano patterns; The coating is deposited in situ onto the substrate surface using a fused deposition micro / nano coating process. The substrate and coating interface has a gradient bonding layer with a thickness of 500nm-2μm.

2. The transparent aligner of claim 1, wherein, The bio-based thermoplastic polymer is selected from at least one of bio-based PET or bio-based PLA; The transparent antibacterial agent is a transparent glass microsphere loaded with an antibacterial active ingredient, wherein the antibacterial active ingredient is selected from at least one of silver, zinc or cuprous oxide; Based on the total mass of the coating, the amount of the transparent antibacterial agent added is 0.1 wt%-10 wt%.

3. The transparent aligner of claim 1, wherein, The gradient bonding layer has an interpenetrating polymer network structure; the topological micro / nano pattern is selected from at least one of a grid pattern, a honeycomb pattern, a triangular pattern, or a spiral pattern.

4. The transparent aligner of claim 1, wherein, The refractive index of the bio-based thermoplastic polymer in the coating is n1, the refractive index of the transparent antibacterial agent is n2, and the refractive index of the orthodontic appliance substrate is n3, satisfying |n1-n2|≤0.01 and |n1-n3|≤0.

02.

5. A method for preparing a transparent aligner having an antibacterial function, characterized by, Includes the following steps: 1) Preparation of functional composite filaments: Bio-based thermoplastic polymers are mixed with transparent antibacterial agents, and then melt-blended, extruded, cooled, and wound to obtain composite filaments; 2) Surface scanning and path planning: The surface of the orthodontic appliance substrate is scanned in three dimensions to obtain its surface morphology data, and the coating deposition path and topological micro-nano pattern distribution are designed; 3) Fused deposition micro / nano coating: The composite filament prepared in step 1) is heated to a molten state, and deposited onto the substrate surface according to the path planned in step 2), so that molecular chains interpenetrate at the interface between the substrate surface and the coating to form a gradient bonding layer. 4) Gradient cooling and post-processing: After the molten deposition is completed, gradient cooling is performed and post-processing is carried out to obtain a transparent orthodontic appliance with antibacterial function.

6. The preparation method according to claim 5, characterized in that, The melt blending temperature in step 1) is 200℃-240℃, and the diameter of the composite filament is 1.75±0.05 mm; the topological micro-nano pattern in step 2) is selected from at least one of the following: grid pattern, honeycomb pattern, triangular pattern or spiral pattern.

7. The preparation method according to claim 5, characterized in that, The melting temperature in step 3) is 200℃-240℃, the substrate temperature is 30℃-60℃, and the deposition rate is ≤300 mm / s; Preferably, in step 3), the surface temperature of the substrate increases to above its glass transition temperature within a contact time of 0.2-0.5 seconds, forming a gradient bonding layer with an interpenetrating polymer network structure of 500 nm-2 μm thickness.

8. The preparation method according to claim 5, characterized in that, The gradient cooling described in step 4) employs a three-stage cooling process: The first stage: cooling from the peak molten deposition temperature of 200℃-240℃ to 55℃-65℃ at a cooling rate of 80℃ / s-150℃ / s; Second stage: Maintain a constant temperature of 55℃-65℃ for 5-15 seconds; The third stage: the temperature is reduced from 55℃-65℃ to room temperature at a cooling rate of 5℃ / min-15℃ / min.

9. The preparation method according to claim 5, characterized in that, The post-processing includes hot pressing and ultraviolet sterilization; the hot pressing conditions are: hot pressing temperature 85-130℃, pressing pressure 0.2-0.6 MPa, holding pressure and setting time 30-60s, vacuum negative pressure -0.06~-0.09 MPa; the ultraviolet sterilization time is 30-50min.

10. The use of the transparent orthodontic appliance according to any one of claims 1-4 or the transparent orthodontic appliance obtained by the preparation method according to any one of claims 5-9 in the preparation of oral orthodontic instruments.

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