Biodegradable dental aligners and manufacturing methods

Abstract

The present invention is in the field of additive manufacturing. Positive models of one or more teeth and / or gums suitable for manufacturing dental aligners are provided, the models comprising polyhydroxyalkanoates (PHAs). Such models are also provided by sintering or fusing powders comprising polyhydroxyalkanoates (PHAs).

Description

[Technical Field]

[0001] The present invention is in the field of additive manufacturing. In particular, the present invention is directed to models of one or more teeth and / or gums, and additive manufacturing methods for producing such models. [Background technology]

[0002] Additive manufacturing processes, such as stereolithography, have been employed in dental applications for many years. In one common application, a liquid radiation-curable resin composition is selectively cured via an additive manufacturing process to produce a three-dimensional mold. After production using additive manufacturing, the mold is post-cured, heat-treated, and cooled. Finally, a thermoplastic sheet is molded onto the mold using thermoforming or vacuum forming to create an aligner, which is inserted into the patient's mouth for use in orthodontics. Typically, a series of molds is produced, with each successive mold representing an increasingly improved realignment position of the patient's teeth.

[0003] As used herein, "aligner" or "dental aligner," also known as "clear aligner" or "invisible aligner" or "plastic orthodontic appliance," refers to an orthodontic appliance typically made of clear plastic that may be used, for example, as a form of dental braces used to adjust teeth or as a mouthguard to prevent teeth grinding.

[0004] Aligners are described, for example, in US-B-8 019 465 to Align Technology, Inc. Vacuum forming of dental aligners onto dental aligner forms involving the application of significant force and heat is described, for example, in US-B-5 242 304 to Tru-Train, Inc.

[0005] It is important that the dental aligner mold on which the dental aligner is formed has good mechanical properties. These mechanical properties are determined, for example, by the glass transition temperature (T g), heat deflection temperature, and Young's modulus.

[0006] Disadvantages of manufacturing dental aligner molds using selective curing of liquid radiation-curable resins include the fact that the process can be relatively slow and / or expensive compared to other additive manufacturing processes, and the printed parts tend to be brittle. Additionally, the selection of materials suitable for selective curing is limited compared to the selection of materials for other manufacturing techniques. Another disadvantage is that articles made by selective curing of liquid radiation-curable resins are typically not easily recyclable. Particularly when a series of molds are produced to incrementally improve the realignment position of a patient's teeth, many molds are produced that are used only once and then become non-recyclable waste.

[0007] For dental aligners to be effective and comfortable, the dimensions of the dental aligner molds need to be very precise, meaning the 3D printing process and materials used need to be suitable for printing with high dimensional and / or surface accuracy.

[0008] WO 2020 / 163433 A1 describes powder bed fusion bonding of dental aligner molds from nylon. However, producing dental aligner molds from nylon, such as polyamide 12 (PA12), also results in the generation of significant undesirable waste.

[0009] Given the increasing use of plastics worldwide, there is a strong and growing demand to provide more sustainable solutions. This can be facilitated by additive manufacturing technologies, which result in higher levels of customization and less waste than traditional manufacturing techniques. Furthermore, some plastics are easily recyclable, which facilitates multiple functional uses from a given unit of starting material. Furthermore, an increasing number of manufacturers are offering thermoplastic materials from bio-based sources rather than petroleum-based sources. "Bio-based" means that the material is synthesized in whole or in part from living sources, such as plants, animals, or microorganisms.

[0010] It would also be desirable to use biodegradable or at least compostable plastics in the manufacture of dental aligner molds. As is widely known, most plastics used today, such as UV-cured resins, do not readily decompose or decay at the end of their useful life, and they are typically disposed of by either incineration or deposition in landfills. Unfortunately, much of the used plastic is increasingly finding its way into the world's waterways and oceans. This accumulation of plastic is not only unsightly, but also harmful to certain marine organisms. Therefore, it is particularly desirable to utilize more plastics that are "biodegradable," i.e., plastics that can be easily broken down by living organisms into natural by-products such as water, carbon dioxide, and biomass.

[0011] Many types of biodegradable plastics are known. Biodegradable plastics can come from biological or petroleum-derived sources. From a sustainability perspective, bio-based plastics are typically preferred.

[0012] WO 2019 / 043137 A1, assigned to Evonik Rohm GmbH, is directed to biocompatible polymer powders for use in 3D printing applications, with examples based on polylactic acid (PLA, PLLA) and polycaprolactone (PCL).

[0013] However, articles made from such biodegradable and / or bio-derived powders typically have poor mechanical properties and are often not highly heat resistant, making them unsuitable for use as dental aligner molds due to the heat involved in thermoforming a dental aligner onto the dental aligner mold.

[0014] Despite the aforementioned attempts, there remains an unmet need to provide dental aligner forms that are biodegradable while still providing desired dimensional accuracy, surface accuracy, and / or dimensional stability.

[0015] It is an object of the present invention to provide materials and / or methods that can be used to provide dental aligner forms that are biodegradable and / or compostable. Summary of the Invention

[0016] The inventors have surprisingly discovered that this objective can be met, at least in part, by fabricating dental aligner forms from polyhydroxyalkanoate (PHA) materials.

[0017] Thus, according to a first aspect of the present invention, there is provided a positive model of one or more teeth and / or gums suitable for the manufacture of dental aligners, the model comprising polyhydroxyalkanoate (PHA).

[0018] According to a second aspect of the present invention, there is provided an additive manufacturing method for producing such models, comprising sintering or fusing a powder comprising polyhydroxyalkanoate (PHA).

[0019] The inventors have discovered that articles with high dimensional accuracy and dimensional stability can be produced by powder bed fusion bonding of powders containing polyhydroxyalkanoates (PHAs). Surprisingly, despite the fact that PHA materials have a low melting temperature and are not as strong as PA12, a material typically used for powder bed fusion bonding, models according to the present invention have sufficient dimensional accuracy to be used as dental aligner molds. Additionally, despite the temperatures used for thermoforming being very close to, or in some cases even higher than, the melting temperature of the PHA material, the models can withstand the conditions for thermoforming dental aligners. Under the same conditions, other biodegradable materials, such as polylactic acid (PLA), have been found to be unsuitable for dental aligner molds, despite having higher melting points than certain suitable PHA materials. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 shows photographs of dental aligner molds made from PHBx and test materials. DETAILED DESCRIPTION OF THE INVENTION

[0021] According to a first aspect of the present invention, there is provided a positive model of one or more teeth and / or gums suitable for manufacturing dental aligners, the model comprising polyhydroxyalkanoate (PHA).

[0022] While PHA polymers encompass a larger number of species than the PHBx polymers described elsewhere herein, a preferred subset of PHAs includes species from the PHBx group. Particularly preferred PHAs useful as powders include poly-3-hydroxybutyrate (P3HB), poly-4-hydroxybutyrate (P4HB), polyhydroxyvalerate (PHV), polyhydroxyhexanoate (PHH), polyhydroxyoctanoate (PHO), polyhydroxydecanoate (PHD), polyhydroxydodecanoate (PHDD), or copolymers thereof. Thus, in one embodiment, the PHA powder comprises, consists of, or consists essentially of P3HB, P4HB, PHV, PHH, PHO, PHD, PHDD, or any combination thereof. In particularly preferred embodiments, the PHA powder comprises, consists of, or consists essentially of P3HB.

[0023] In a preferred embodiment, the PHA comprises, consists essentially of, or consists of a homopolymer or copolymer of 3-hydroxybutyric acid. 3-Hydroxybutyric acid, also known as β-hydroxybutyric acid, is an organic compound and a beta-hydroxy acid with the chemical formula CH3CH(OH)CH2CO2H, and its conjugate base is β-hydroxybutyrate, also known as 3-hydroxybutyrate. β-Hydroxybutyric acid is a chiral compound with two enantiomers, D-β-hydroxybutyric acid and L-β-hydroxybutyric acid. Its oxidized polymeric derivatives occur widely in nature. 3-Hydroxybutyric acid is a precursor to the biodegradable polyester poly(3-hydroxybutyrate) (P3HB). The chemical structure of P3HB is shown below.

[0024] [ka]

[0025] In embodiments, the powder composition comprises a homopolymer or copolymer of 3-hydroxybutyric acid. In various embodiments, the powder composition comprises a (co)polymer of 3-hydroxybutyric acid and an additional acid. The additional acid can be of any suitable type that ensures compatibility and biodegradability of the resulting polymer, but particularly preferred additional acids include 3-hydroxyhexanoic acid, 3-hydroxyvaleric acid, and 4-hydroxybutyric acid. As used herein, a copolymer of 3-hydroxybutyric acid and 3-hydroxyhexanoic acid is referred to as "PHBH," while a copolymer of 3-hydroxybutyric acid and 3-hydroxyvaleric acid is referred to as "PHBV." A copolymer of 3-hydroxybutyric acid and 4-hydroxybutyric acid is referred to as "P3HB4HB." Furthermore, as used herein, the general designation for a homopolymer of 3-hydroxybutyric acid or a copolymer of 3-hydroxybutyric acid and any additional acid is referred to herein according to the general designation "PHBx."

[0026] When used, the comonomers can be incorporated into the 3-hydroxybutyric acid in any amount relative to each other as desired, such as in an amount of 1 to 50 mol %, preferably 1 to 15 mol %, and more preferably 5 to 12 mol %.

[0027] To withstand the conditions of dental aligners or other orthodontic appliances, the model PHA preferably has a peak melting temperature of 130° C. or higher, more preferably 135° C. or higher, and even more preferably 140° C. or higher. The melting temperature of the PHA may be as high as 190° C., such as 140-180° C., or 145-175° C.

[0028] As used herein, the melting behavior of a material, such as peak melting temperature, onset melting temperature, and onset crystallization temperature, is preferably measured in accordance with ISO 11357-1 / 3. Unless otherwise indicated, the terms melting point and melting temperature refer to the peak melting temperature of a material.

[0029] In embodiments, the peak melting temperature of the PHA in the model is higher than the temperature used in the thermoforming process used to make dental aligners. Surprisingly, the model may also be suitable for use as a dental aligner mold when the peak melting temperature of the PHA is close to or lower than the temperature used in the thermoforming process. This can be explained, at least in part, by the fact that dental aligner molds are typically subjected to thermoforming conditions for only short periods of time, such as for durations of 30 seconds to 2 minutes.

[0030] Other biodegradable materials, particularly polylactic acid (PLA), do not exhibit the same stability as PHA at temperatures close to their peak melting temperatures. To predict the stability of a material at high temperatures, parameters or measurements such as heat deflection temperature (HDT) and / or dynamic mechanical thermal analysis (DMTA) may be applied. Apart from the preferred PHA materials mentioned above, those skilled in the art may select other suitable PHA materials for the model based on these parameters and the conditions used for thermoforming the dental aligner.

[0031] In one embodiment, the model may further include one or more additive components. Such additives may be any suitable additive used in 3D printing, such as, but not limited to, flame retardants, flow aids, fillers, pigments, and stabilizers. Suitable flow aids include fumed silica and precipitated silica. Suitable fillers include glass particles and glass fibers (having lengths up to, but preferably less than, 100 microns), glass beads, metal particles, and ceramic particles. Suitable pigments include titanium dioxide, rutile particles, anatase particles, carbon black particles, carbon fibers, and stabilizers such as thermal stabilizers and UV stabilizers. If used, in one embodiment, one or more flow aids may be included in an amount of 0.05 to 20% by weight of the total model.

[0032] Various additional additives are known that can be incorporated into the models according to the present invention. Additives that may be present in the mold include additives for additive manufacturing, including, for example, flow aids (other than the monomeric, oligomeric, or polymeric flow aids described elsewhere herein), fillers (chopped or crushed glass fiber, chopped or crushed carbon fiber, nanofillers, dispersed reinforcing materials such as clay, wollastonite, and mica, and continuous reinforcing materials), pigments, processing aids (such as mold release agents), leveling agents, degassing agents, stabilizers (such as antioxidants and UV stabilizers), plasticizers, impact modifiers (core-shell rubber particles), and carrier polymers.

[0033] Other examples of fillers that are known and commonly used in thermoplastic resin compositions include inorganic fillers such as clay, mica, talc, and glass spheres or beads. Reinforcing fibers are, for example, glass fibers. An advantage of resin compositions containing glass fibers is their high strength and stiffness, especially at elevated temperatures, which allows them to be used at temperatures up to the melting point of the polymer in the relevant composition.

[0034] Inorganic materials are particularly suitable as fillers because they tend to impart water resistance, heat resistance, and robust mechanical properties to the composition. In one embodiment of the present invention, the filler is inorganic and includes ceramics such as silica (SiO2) nanoparticles, i.e., particles with an average particle size of 1 nanometer (nm) to 999 nm or 5 nm to 800 nm, or microparticles, i.e., particles with an average particle size of 1 micrometer (μm) to 999 μm or 1 to 100 μm. Average particle size can be measured using various techniques, such as scanning electron microscopy or laser diffraction particle size analysis according to ISO 13320-1. For further examples of silica nanoparticles, see U.S. Patent No. 6,013,714.

[0035] In other embodiments of the present invention, alternative inorganic filler materials may be present, such as those containing glass or metal particles. Specific, non-limiting examples of such materials include glass powder, alumina, alumina hydrate, magnesium oxide, magnesium hydroxide, barium sulfate, calcium sulfate, calcium carbonate, magnesium carbonate, silicate minerals, diatomaceous earth, silica sand, silica powder, titanium oxide, aluminum powder, bronze, zinc powder, copper powder, lead powder, gold powder, silver dust, glass fiber, cellulose fiber, cellulose nanocrystals, potassium titanate whiskers, carbon whiskers, sapphire whiskers, verification rear whiskers, boron carbide whiskers, silicon carbide whiskers, and silicon nitride whiskers.

[0036] However, in one embodiment, the model according to the present invention is substantially free of any fillers, which may be beneficial as it ensures improved workability (i.e., flowability, surface finish) of the model.

[0037] Suitable impact modifiers are rubbery polymers containing polar or reactive monomers, such as olefins, as well as acrylates and epoxides, acid- or anhydride-containing monomers, among others. Examples include copolymers of ethylene and (meth)acrylic acid, or ethylene / propylene copolymers functionalized with anhydride groups. The advantage of impact modifiers is that they not only improve the impact strength of the resin composition, but also contribute to increasing the viscosity. An example of a suitable impact modifier is maleic anhydride-functionalized polyolefin.

[0038] Colorants, such as pigments or dyes, may also be optionally present in various embodiments. Examples of colorants include carbon black or nigrosine. EP 2935430 describes a variety of other common pigments that may be suitably used herein, including titanium dioxide in one or more of the three crystalline forms (rutile, anatase, and titanate), ultramarine, iron oxide, bismuth vanadate, metallic pigments such as aluminum flake, and pearlescent pigments such as mica, as well as organic pigments such as phthalocyanines, perylenes, azo compounds, isoindolines, quinophthalones, diketopyrrolopyrroles, quinacridones, dioxazines, and indanthrones.

[0039] The model may additionally contain one or more stabilizers. The presence of a stabilizer is optional. Stabilizers are known per se and are intended to combat degradation as a result of, for example, the effects of heat, light, and radicals. Known stabilizers that may be present in the model include, for example, hindered amine stabilizers, hindered phenols, phenolic antioxidants, copper salts and halides, preferably bromides and iodides, and mixtures of copper salts and halides, such as copper iodide / potassium iodide compositions, as well as phosphites, phosphonites, thioethers, substituted reorcinols, salicylates, benzotriazoles, hindered benzoates, and benzophenones. Preferably, the stabilizer is selected from the group consisting of inorganic hindered phenol stabilizers, hindered amine stabilizers, and combinations thereof. More preferably, the stabilizer is a combination of inorganic stabilizers, phenolic antioxidants, and hindered amines. In one embodiment, when the model includes a stabilizer component, such component is present in an amount of about 0.05% to about 2.0% by weight, or about 0.1 to 1.5% by weight, or 0.3 to 1.2% by weight, based on the total composition.

[0040] In one embodiment, the model also includes one or more lubricants. Such materials include long-chain fatty acids, particularly stearic acid or behenic acid, their salts, particularly calcium stearate or zinc stearate, and their ester or amide derivatives, particularly ethylene bis-stearylamide, montan wax, and low molecular weight polyethylene or polypropylene waxes. In one embodiment, suitable lubricants include esters or amides of saturated or unsaturated aliphatic carboxylic acids of 8 to 40 carbon atoms with saturated aliphatic alcohols, or amines of 2 to 40 carbon atoms, as well as metal salts of saturated or unsaturated aliphatic carboxylic acids of 8 to 40 carbon atoms used with ethylene bis-stearylamide, and calcium stearate.

[0041] The foregoing list of additives is not intended to be limiting, and any other suitable additives may be employed as would be commonly known to one skilled in the art to which the present invention applies. Further such examples include UV stabilizers, gamma stabilizers, hydrolysis stabilizers, heat stabilizers, antistatic agents, emulsifiers, nucleating agents, drip agents (such as polytetrafluoroethylene or polyvinylpyrrolidone), and plasticizers.

[0042] When included, the additives described herein may be used alone or in combination of two or more. When any additive is present, the model may contain 0.001% to 80% by weight, or 0.1% to 60% by weight, or 0.5% to 25% by weight of the additive, based on the total weight of the model.

[0043] Considering the biodegradability of the model powder composition and articles made therefrom, it may be preferable for the amount of pigments and / or other additives to be low relative to the amount of PHA. Therefore, the amount of PHA relative to the total weight of the model is preferably 80% by weight or more, more preferably 90% by weight or more, and even more preferably 95% by weight or more. The amount of PHA may be as high as 99.95% by weight. For example, the amount of PHA in the model may be 92-99% by weight or 94-97% by weight. In an embodiment, the amount of PHA by weight relative to the total weight of the entire model is 80-99.9%.

[0044] For example, to withstand the heat applied when thermoforming a dental aligner around a dental aligner mold, the model preferably has a heat deflection temperature of 70°C or greater, preferably 100°C or greater, more preferably 120°C or greater, e.g., 80-175°C, at 1.8 MPa, as measured according to ASTM D648.

[0045] Alternatively or additionally, the model preferably has a tensile modulus, measured according to ASTM D638, of 800 MPa or more, preferably 1500 MPa or more, more preferably 2000 MPa or more, for example 1200 to 3000 MPa.

[0046] Alternatively or additionally, the model preferably has an elongation at break, as measured according to ASTM D638, of 2% or more, more preferably 4% or more, even more preferably 5% or more, or may generally be in the range of 3 to 20%.

[0047] Alternatively or additionally, the model preferably has an ultimate tensile strength of 10 MPa or greater, more preferably 15 MPa or greater, and even more preferably 20 MPa or greater, according to ISO 527-1 / 2. The ultimate tensile strength may be 150 MPa or greater. For example, the ultimate tensile strength may be between 10 and 50 MPa.

[0048] According to a second aspect of the present invention, there is provided an additive manufacturing method for producing a positive model of one or more teeth and / or gums as described herein, comprising sintering or fusing a powder comprising polyhydroxyalkanoate (PHA).

[0049] The additive manufacturing methods described herein include the steps of: (a) providing a layer of powder comprising polyhydroxyalkanoate (PHA) and having a D50 particle size value of 20 to 150 μm, wherein the powder has a crystallization onset temperature T measured according to ISO 11357-1 / 3; c,開始 , and the melting peak temperature T m,ピーク and (b) fusing regions in the layer of powder by applying fusion radiation to the regions, thereby forming a cross-section of the positive model, wherein the temperature of the powder bed is between a crystallization onset temperature and a melting peak temperature, and steps (a) and (b) are repeated until the positive model is completed.

[0050] Suitable powder bed fusion techniques include selective laser sintering (SLS), high speed sintering (HSS), SAF, or multi-jet fusion (MJF). Preferably, SLS and / or SAF are used.

[0051] The PHA is preferably a homopolymer or copolymer of 3-hydroxybutyric acid, preferably a copolymer of 3-hydroxybutyric acid with 3-hydroxyhexanoic acid and / or 3-hydroxyvaleric acid as comonomers.

[0052] When SLS is used as a powder bed fusion technique, a high-density, high-energy radiation source, such as a laser, is used to selectively melt or fuse portions of particles into a desired shape. A control mechanism directs both the path and intensity of the laser to fuse the powder within specified boundaries, often in layers. Each layer, or "slice," represents a cross-section of the final component to be produced at a specified thickness. A machine control selectively operates to sinter successive layers of powder, producing a finished part that includes multiple slices sintered together. The machine control mechanism is computer-directed, preferably utilizing CAD files in various formats to determine the boundaries defined for each slice.

[0053] A part can be fabricated by depositing a first portion of a sinterable powder on a target surface of a part bed, scanning a laser directed over the target surface, and fusing by sintering or melting a first layer of the first portion of powder on the target surface to form a first slice. The powder is thus sintered or fused by operating a laser beam directed within a boundary defining the first slice with sufficient energy or fluence to sinter or fuse the powder. The first slice corresponds to a first cross-sectional area of ​​the part.

[0054] A second portion of powder may then be deposited on the part bed and the surface of the first sintered slice placed thereon, and a directed laser beam may be scanned across the powder covering the first sintered slice. A second layer of the second portion of powder is then sintered by operating the laser beam within a boundary, thereby defining a second slice. The sintered second slice is formed at a temperature sufficient to sinter it to the first slice, fusing the two slices together into a single portion of the object to be built. Subsequent layers of powder are deposited on the previously sintered slice, each layer being sintered in turn to form additional slices.

[0055] Different types of directional lasers can be used as high-density, high-energy radiation sources to selectively melt or fuse portions of particles into desired shapes. To melt or fuse portions of particles, the particles must absorb at least a portion of the radiation emitted by the laser. If the particles do not absorb enough of the laser's radiation to melt, pigments or dyes can be added to increase absorption of the laser radiation. Gas lasers, such as CO2 lasers, are often used in powder bed fusion processes due to their high power and efficiency. CO2 lasers typically emit light with wavelengths between 9.6 and 10.6 microns and can have output powers of up to 100 watts or more. Polyamide and polyester materials typically used in powder bed fusion processes, including bio-based and / or biodegradable materials, absorb a portion of the light emitted by CO2 lasers. However, CO2 lasers are typically large, complex, and expensive. CO2 lasers are also very sensitive to proper alignment. This makes CO2 lasers less suitable for small businesses and home users who may wish to use powder bed fusion processes, for example. Therefore, small powder-bed fusion printers using other types of lasers have recently gained attention. For example, laser diodes with wavelengths in the near-infrared (NIR) range, such as around 800 nm, are also available for use in powder-bed fusion. Common wavelengths for these diode lasers are 808 nm, 976 nm, or 1065 nm. These laser diodes typically have much lower output power than CO2 lasers, for example, around 5-30 W. Polyamide and polyester materials typically do not absorb enough radiation in the NIR range to undergo melting. Therefore, to be suitable for powder-bed fusion using NIR lasers, material particles are often mixed with pigments or dyes that absorb radiation in the NIR range. However, adding excessive pigments can adversely affect other properties of the powder, such as the mechanical properties of the printed part. Additionally, adding excessive pigments can adversely affect biodegradability, especially when biodegradable parts are being produced.

[0056] Taking the above into consideration and depending on the type of laser that may be used in the powder bed fusion process, the powder may further include a pigment, e.g., a pigment that absorbs laser radiation in the near-infrared region, and / or other additives, e.g., in amounts as described above for the model. In embodiments, the powder includes a pigment, and the weight of the pigment relative to the total weight of the powder is 2.0 wt.% or less, preferably 1.5 wt.% or less, more preferably 1.0 wt.% or less, even more preferably 0.5 wt.% or less, e.g., 0.4 wt.% or less, or even 0.3 wt.% or less, or 0.25 wt.% or less. The amount of pigment may be as low as 0.05 wt.%, but is typically higher. Taking the above into consideration, the model may include one or more pigments, and the total weight of the pigment relative to the total weight of the entire model is preferably 5.0 wt.% or less, more preferably 2.0 wt.% or less, e.g., 0.05-0.5%, 0.05-0.4%, or 0.05-0.25%. Preferably, the total weight of pigments that absorb radiation in the near-infrared region (e.g., carbon black) relative to the total weight of the entire model is 2.0% or less, more preferably 0.5% or less, for example, 0.05 to 0.5%, or 0.05 to 0.4%, or 0.05 to 0.25%.

[0057] Preferably, the pigment absorbs radiation in the near-infrared region of the electromagnetic spectrum, especially when low-power laser diodes are used. This means that the powder composition can be effectively heated by irradiation with an NIR laser. The pigment preferably has a reflectance of 20% or less, preferably 10% or less, at 800 nm. The pigment is preferably biodegradable, compostable, and / or environmentally friendly when the powder composition or article is decomposed.

[0058] Alternatively or additionally, in a so-called print-and-fuse powder bed fusion process, an absorber may be selectively printed onto a layer of powder to define the areas to be fused, in order to selectively apply radiation to those areas. Radiation may then be applied non-selectively to the layer, e.g., emitted by an elongated lamp spanning the width of the build bed and passing through the layer, where it is preferentially absorbed by the absorber, melting and fusing the powder in those areas. Thus, instead of being present throughout the powder composition, the absorber may be selectively applied to the layer, e.g., in the form of a pigment (e.g., a pigment described herein) suspended in a fluid or in the form of a dye, which may be applied by a fluid deposition device, e.g., one or more inkjet printheads.

[0059] The fusion radiation may be provided by a radiation source emitting near-infrared radiation, optionally at a wavelength between 750 nm and 1500 nm. The radiation source may be a laser, optionally emitting near-infrared radiation at a wavelength between 750 nm and 850 nm.

[0060] The powder preferably has a reflectance of 50% or less, preferably 30% or less, more preferably 25% or less at a wavelength of 800 nm.

[0061] Dimensional accuracy can be an important factor for using the model as a dental aligner mold. Therefore, the additive manufacturing method may further include providing a digital 3D model of one or more teeth and / or gums according to which a physical positive model is created, and parameters are preferably selected so that the 80% quantile of the model formed in step (b) is 0.5 mm or less, preferably 0.3 mm or less, and more preferably 0.2 mm or less, compared to the digital 3D model. The exact parameters of the equipment used to perform the powder bed fusion step of the additive manufacturing method, i.e., the 3D printer, depend on the powder material properties and the equipment and process settings used. Thus, a physical positive model may be created on the printer based on the digital 3D model of one or more teeth and / or gums, and the 80% quantile of the completed physical positive model is 0.5 mm or less, preferably 0.3 mm or less, and more preferably 0.2 mm or less, compared to the digital 3D model. The digital 3D model may be dimensionally modified to account for shrinkage upon cooling, for example, based on 3D printer parameters and / or parameters obtained from a test object formed on the 3D printer, and a physical positive model may then be formed based on the dimensionally modified digital 3D model. In other words, the printing instructions provided to the printer are based on the dimensionally modified digital 3D model for further accuracy.

[0062] The temperature of the powder bed during powder bed fusion is preferably 50°C or less below the peak melting temperature of the powder composition, more preferably 40°C or less below the peak melting temperature of the powder composition, e.g., 30-5°C, or 25-10°C below the peak melting temperature of the powder composition. The temperature of the powder bed can be expressed in terms of the temperature of each layer as it is processed. Each layer may be heated to a target temperature between the crystallization onset temperature and the peak melting temperature by one or more non-fusion heat sources without causing fusion, optionally operated based on the temperature measurements of each layer. This preheating is applied before the fusion step and before the optional application of an absorbent by a fluid deposition device.

[0063] The temperature of the powder bed, or target bed temperature, may be between the crystallization onset temperature and the peak melting onset temperature of the powder. The temperature measurements may be provided by a thermal camera configured to measure the temperature of the bed one or more times while the bed is being processed. The additional heat source may be one or more of a scanning infrared lamp and a static overhead heater. The static overhead heater may be operated based on measurements by the thermal camera.

[0064] The peak melting temperature of the PHA depends on the type of monomer and comonomer used. For example, when using PHBV powder containing approximately 2 wt. % valerate, which has a peak melting temperature of 175°C, the temperature of the powder bed during additive manufacturing may be preheated to a target temperature of, for example, 140-170°C. For example, when using PHBH powder containing approximately 6 wt. % hexanoate, which has a peak melting temperature of 145°C, the target temperature of the powder bed during additive manufacturing may be, for example, 110-140°C.

[0065] In an embodiment, to obtain a powder particularly suitable for powder bed fusion, the method comprises the steps of providing a particulate starting material comprising a homopolymer or copolymer of 3-hydroxybutyric acid, applying a pressure of >5 kN / cm 2 the starting material, the compacted material, and / or the size-reduced material to a sufficiently high temperature to prevent sticking of the starting material, the compacted material, and / or the size-reduced material, thereby obtaining an annealed material; mixing the starting material, the compacted material, the size-reduced material, or the annealed material with a pigment, preferably using high shear mixing; and size fractionating the starting material, the compacted material, the size-reduced material, the annealed material, and / or the mixed material.

[0066] In embodiments, the starting material consists of or consists essentially of P3HB polymer. At standard temperature and pressure, the P3HB polymer can be in any suitable form, such as powder, flakes, or granules. Of these, powder is preferred.

[0067] In one embodiment, the method according to the first aspect of the invention includes the optional step of sizing the starting material to form a size-reduced material having, inter alia, a desired average particle size or particle size distribution. This step is necessary when the starting material is in the form of flakes, granules or another powder having an average particle size larger than the desired final average particle size of the final build material for a given additive manufacturing process.

[0068] Size reduction can involve a grinding or micronization process to provide a particle size suitable for the intended printing process. Grinding can occur at or near room temperature (e.g., 10-30°C), but can be lower with other methods such as cryogenic grinding. In cryogenic grinding, or cryo-grinding, the polymer is cooled with liquid nitrogen (alternatives to N2 include solid or liquid carbon dioxide) to prevent softening and clogging of the equipment during grinding.

[0069] Other well-known milling techniques include jet milling and mechanical milling. Jet milling processes, for example, use high-velocity jets of compressed air or inert gas to crush materials by colliding particles with each other. Jet mills can be designed or used to output particles below a certain size, and continuously crush particles above that size, resulting in a narrow particle size distribution of the resulting product. Particles exiting the mill can be separated from the gas stream by cyclone separation.

[0070] Milling techniques, particularly mechanical milling, can be carried out in a pinned-disk mill, a fluidized-bed opposed-jet mill, or a baffle-plate impact mill. Regardless of the milling technique and equipment used (all of which are well known in the art), the process should be carried out so that the resulting particle size distribution has a median particle diameter D50 in the range of 1 to 650 microns, or more preferably 1 to 400 microns, or, for example, 10 to 200 microns, 20 to 100 microns, or 40 to 50 microns. The median particle diameter D50 can be determined via various methods, including TEM, SEM, dynamic light scattering, and static light scattering. Non-limiting examples of suitable devices for measuring particle size include the LB-550, available from Horiba Instruments, Inc., which measures particle size by dynamic light scattering. A preferred method for determining the D50 median particle diameter is by laser diffraction particle size analysis in accordance with ISO 13320-1. In particular, particle size analysis using a SYMPATEC HELOS / H3982 can be used to determine the particle size distribution.

[0071] In preferred embodiments, the starting material or size-reduced starting material has a particle size distribution with a D50 particle size in the range of 20-100 microns, or 30-90 microns, or 30-80 microns, or 40-90 microns, or 40-80 microns, or 40-50 microns. A narrow particle size distribution with average particles of the recited size is desirable because it tends to improve the flowability of the final powder made therefrom. This ensures good processability and reduced agglomeration when the powder is used in powder-based additive manufacturing processes such as multi-jet fusion or selective laser sintering.

[0072] In a preferred embodiment, the size reduction step comprises a jet milling or mechanical milling process, wherein the jet milling or mechanical milling process is carried out at a temperature of 15 to 35°C, or 15 to 30°C.

[0073] If the particle size distribution of the starting material, size-reduced material, or blended material is too broad, or if a narrower particle size distribution is desired, a size fractionation step can be performed to obtain a narrower particle size distribution. Size fractionation may be performed one or more times to select a subset of particles, flakes, or granules contained in the material for further processing or use. This is typically achieved via sieving or screening, and the screening and / or screening equipment can be selected with one or more sieves or sieves to select and remove particles above and / or below any specified size. In one embodiment, the starting material is sieved to ensure that particles below 30 microns and above 100 microns are not retained to any substantial extent. Size fractionation may be performed at any point or points along the process, but is typically performed on the starting material, after the size reduction step, or not at all. In an alternative embodiment, a size fractionation step is performed before or after multiple steps of the process, or even before or after each step of the process. Size fractionation is preferably performed as a final step to ensure that the resulting powder composition is optimized for suitability as a powder build material for use in additive manufacturing processes.

[0074] The starting material or size-reduced material may be mixed with the pigment, for example, using high-shear mixing. High-shear mixing refers to any mixing in which solid materials are subjected to a significant amount of shear. This can be achieved using a wide variety of different types of mixers. Mixers suitable for high-shear mixing include conical screw mixers, also known as Nauta® mixers, conical paddle mixers, and cyclomixers. A suitable method for determining the amount of shear provided by mixers with rotating elements, such as paddle mixers, blade mixers, or screw mixers, is the tip speed of the rotating elements. High-shear mixing preferably involves mixing using rotating elements with tip speeds of at least 1.0 m / s, more preferably 3.0 m / s, and even more preferably 5.0 m / s or greater. Tip speeds can be as high as 200 m / s, but are typically lower, e.g., 50 m / s or less, such as 10-40 m / s, or 15-30 m / s. Apart from mixers with rotating elements, other types of equipment, such as shakers, can also be used for high-shear mixing. To determine whether mixing using a different type of mixer than a mixer with rotating elements qualifies as high shear mixing in the context of the present invention, the performance of such a non-rotating mixer can be compared to a mixer with rotating elements (e.g., a conical paddle mixer manufactured by HosoLNG Micro) by comparing the NIR reflectance over time when mixing the starting material or the size-reduced material with the pigment.

[0075] High shear mixing can include one or more mixing steps, for example, high shear mixing can include mixing the starting material or size-reduced material with the pigment in a low shear mixer (e.g., a Loedige mixer), followed by shaking using high shear.

[0076] High shear mixing can produce powder compositions with lower NIR reflectance and / or achieve minimum NIR reflectance in a shorter time than low shear mixing, using the same materials. Long mixing times are undesirable for economic reasons and because they slow the production of the powder composition. Therefore, the high shear mixing step is preferably carried out for 90 minutes or less, more preferably 60 minutes or less, and even more preferably 30 minutes or less. For example, the high shear mixing step is carried out for 0.5 to 15 minutes, or 1 to 10 minutes.

[0077] In some embodiments according to the first aspect, the starting material is first subjected to a compaction step to increase the free bulk density (FBD) of the starting material. In preferred embodiments, compaction is carried out by any suitable apparatus for compacting such materials, including, for example, a Bepex Labor Kompaktor. The force and / or pressure applied to the starting material may be varied as desired, but in preferred embodiments, compaction is carried out at a pressure of 5 kN / cm on the material. 2 More preferably, greater than 25 kN / cm 2 More preferably, more than 40 kN / cm 2 or 5 to 400 kN / cm 2 , or 25 to 300 kN / cm 2 , or 40 to 200 kN / cm 2 The consolidation step is carried out to apply a pressure of 0.5 to 1.5 mm. The inventors have surprisingly discovered that the beneficial effects of this consolidation step remain in the starting material even after subsequent downstream processing described elsewhere herein, such that the resulting processed material retains improved suitability for use in additive manufacturing applications. If a consolidation step is carried out, it is preferably carried out prior to size reduction and / or mixing the starting or size-reduced material with a pigment.

[0078] For example, if the starting material contains low-density PHBx, consolidation of the starting material can be carried out to obtain PHBx having a density of 0.4 g / mL or more, preferably 0.5 g / mL or more, for example, 0.5 to 0.8 g / mL.

[0079] According to some embodiments of the first aspect, the starting material is heated to produce an annealed material. In such a heating step, the material is preferably heated to a temperature sufficient to prevent sticking of the consolidated material. The heating process preferably includes annealing, in the sense that the material is heated for a moderate period to a temperature below its glass transition temperature or peak melting temperature, and then cooled again to reduce its internal stress and increase the melting onset temperature. If performed, the heating step is preferably performed before the mixing step. If a consolidation step is also performed, the heating step is preferably performed after the consolidation step. The heating step can be performed before the size reduction step (e.g., on the granules) and / or after the size reduction step, i.e., on the powder.

[0080] The heating method will vary depending on several factors that will be understood by those skilled in the art to which this invention pertains, including, but not limited to, the desired amount of material to be heat-treated. General common techniques include batch heating and continuous heating. Batch heating typically involves forced convection in an oven, although for laboratory-scale quantities, other methods can be used, such as inserting a flask containing the material into a high-temperature oil bath or tumble dryer under vacuum while purging with an inert gas. Continuous heating, on the other hand, typically involves passing the material along a conveyor through a heated tube or chamber. This method is more suitable for industrial-scale heating processes because it allows for less restriction of airflow. Regardless of whether a batch or continuous heating process is utilized, other heating methods, such as through the application of infrared radiation, may be employed as an alternative to the aforementioned convection heating.

[0081] Regardless of the overall technique, the process typically involves (i) heating the material to a desired temperature (ii) at a controlled rate, (iii) maintaining this desired temperature for a specified period of time, and then (iv) cooling the material at a controlled rate to (v) a final temperature. Any of (i)-(v) can be varied as desired, as will be understood by those skilled in the art, and it is further understood that different PHBx polymers will require different conditions because they will have inherently different material properties.

[0082] However, in various embodiments, (i) is selected to be at most 120° C., or 130° C., or 135° C., or 140° C., or 150° C., or 160° C., or 170° C. The final desired temperature (i) should be selected so as not to exceed the peak melting temperature of the material utilized, but not the melting point onset temperature (T m , onset) for at least a short time. For example, (i) may be 1 to 100°C below the peak melting temperature of the material, preferably 5 to 80°C below the peak melting temperature, and more preferably 10 to 60°C below the peak melting temperature. In other embodiments, (i) may vary depending on the material, such as 100 to 200°C, or 120 to 180°C, or 130 to 160°C.

[0083] Regardless of the final heating temperature, various heating rates (ii) may be selected, for example, 1°C / hr to 100°C / hr, or 2°C / hr to 25°C / hr, more preferably 5°C / hr to 10°C / hr, although other rates may be suitably used. The heating rate (ii) is not necessarily as critical as (i) or (iii), provided that the material is heated uniformly and does not locally exceed the peak melting temperature. It will, of course, be understood that rapid heating is desirable to minimize overall processing time.

[0084] It is further understood that heating can occur continuously or in a stepwise process, i.e., the material can be heated to a particular intermediate value below the final desired peak temperature (i), maintained for a specified period of time, and then further increased as needed. This stepwise process can occur in the presence of two or more so-called intermediate desired temperatures with one, two, or more than two intermediate maintenance periods in between.

[0085] Once the final desired temperature (i) is achieved, the material may be maintained at such temperature for any specified length of time (iii), which in one embodiment is from 1 minute to 4 hours, or from 30 minutes to 2 hours.

[0086] Finally, the material is preferably cooled from the desired temperature to return to an equilibrium temperature for use in further processing of the material. It is understood that this cooling can occur at any rate (iv), and that the cooling can be continuous or stepwise, and can be under N2 atmosphere and / or reduced pressure. However, the final equilibrium temperature (v) is preferably at or near ambient or room temperature.

[0087] [Example] Example 1: Preparation of PHBV powder PHBV containing approximately 2 wt.% valeric acid (Enmat Y1000P, Helian Polymers, The Netherlands) granules was cryogenically ground to a fine powder. After sieving through a 100 μm sieve, a powder with a particle size D50 of 46 μm was obtained. The powder was then mixed with 0.25 wt.% carbon black in a cluster blender at speed 12 for 3 minutes.

[0088] Example 2: Preparation of PHBH powder PHBH containing approximately 6 wt. % hexanoic acid (Kaneka Belgium, X131A) granules was first dried for 1 hour, then heated to 110°C and maintained at that temperature for another 1 hour. The temperature was then increased stepwise to 115°C, 120°C, and 125°C, thereby maintaining the temperature at each of the preceding steps for 1 hour before further increasing the temperature. The temperature was then increased once more to 130°C and maintained at this temperature for 1 hour. After the last step, the granules were cooled. The granules were ground to a fine powder in a cryogenic mill. Sieving through a 100 μm sieve yielded a powder with a particle size D50 of 58 μm. The powder was then mixed with 0.25 wt. % carbon black in a cluster blender at speed 12 for 3 minutes.

[0089] Example 3: Fabrication of a dental aligner mold The black powders produced in Examples 1 and 2 were used to print dental molds on a Lisa Pro (Sinterit, Poland) SLS printer.

[0090] As a comparative example, parts were made by pressure molding PHBH 151C granulation (Kaneka, Belgium) at 155°C for 5 minutes, followed by slow cooling. A bar (5 x 1 x 1 cm) was cut out of the molded part and placed in fresh plaster. After the plaster hardened, the PHBH bar could be removed and easily placed back into the plaster mold. The PHBH bar was then subjected to thermoforming using CA® foil. After thermoforming, the bar began to melt and changed shape, so it no longer fit the plaster mold. For the production of dental aligners, such melting of the mold edges is unacceptable because the resulting aligner would not fit the teeth.

[0091] As a comparative example, dental aligner molds were fabricated by fused filament fabrication (FFF) printing of PLA filament. A 1.75 mm diameter PLA filament from Makerspoint was used in a RepRap X500 FFF printer with a 0.2 mm nozzle diameter. The print bed was set at 40°C, and the nozzle temperature was set at 200°C. The filament spool was clamped and transported through the printhead. The layer height was set at 0.2 mm, and the layer width was set at 0.4 mm. The molds were printed at a print speed of 12 mm / s. Similar to the PHBH bars, the PLA dental aligner molds began to melt and deform when subjected to the thermoforming conditions used to manufacture dental aligners.

[0092] Example 4: Fabrication of dental aligners by thermoforming The dental aligner molds prepared in Example 3 were used to prepare dental aligners by thermoforming 0.625 mm thick CA clear aligner medium (PET-G) foil (Scheu-dental, Germany) using a Biostar thermoforming machine. The process guidelines provided by the supplier were followed. The dental aligner molds were inspected by visual observation before and after the thermoforming process. The results are shown in Table 1.

[0093] [Table 1]

[0094] It was observed that Sample 1, PHBV Y1000P, with a melting point of 175°C, withstood the thermoforming process without any visible change in geometry. Sample 2, PHBH X131A, with a melting point of 145°C, withstood the thermoforming process. In contrast, PLA, with a melting point of 160°C, began to melt during the thermoforming process and was therefore not suitable for use as a dental aligner mold. PHBH 151C, with a melting point of 130°C, also began to melt during the thermoforming process and was therefore not a suitable material.

[0095] Example 5: Dimensional Accuracy of Dental Aligner Molds Dental aligner molds were produced using different SLS printers using the black PHBx powders prepared according to Examples 1 and 2. The printing conditions are listed in Table 2.

[0096] In experiments 3a, 3b, and 3c, dental aligner molds were produced from the PHBV powder prepared according to Example 1 using a Lisa X printer (Sinterit, Poland). To study the effect of print position on the build, aligner molds were printed on the top, center, and bottom of the powder bed, respectively. In experiment 4, dental aligner molds were produced from the PMTX powder prepared according to Example 1 using a Prodways P2000ST 3D printer equipped with a 100W CO2 laser and counter-rotating rollers as a recoating system. In experiment 5, dental aligner molds were produced from the PHBH powder prepared according to Example 2 using a Lisa Pro printer (Sinterit, Poland). After printing, the dental aligner molds were used to produce dental aligners by thermoforming 0.625 mm thick CA clear aligner media (PET-G) foil (Scheu-dental, Germany) using a Biostar thermoforming machine. The process guidelines provided by the supplier were followed. Before and after the thermoforming process, the mold dimensions were determined with a scanner and compared with the STL file dimensions, and the 80% quantile (the deviation distance from the STL file covering 80% of the measured points) was calculated. Only small deviations were observed before and after thermoforming, indicating that the dental aligner molds were stable enough to withstand the thermoforming process without losing dimensional accuracy. Table 2 shows a summary of the results.

[0097] [Table 2]

Claims

1. A positive model of one or more teeth and / or gums suitable for the manufacture of dental aligners, the positive model comprising polyhydroxyalkanoate (PHA).

2. The PHA comprises or consists essentially of poly-3-hydroxybutyrate (P3HB), poly-4-hydroxybutyrate (P4HB), polyhydroxyvalerate (PHV), polyhydroxyhexanoate (PHH), polyhydroxyoctanoate (PHO), polyhydroxydecanoate (PHD), polyhydroxydodecanoate (PHDD), or copolymers thereof.

2. The model according to claim 1, which is made of polyhydroxyoctanoate (PHO), polyhydroxydecanoate (PHD), polyhydroxydodecanoate (PHDD), or copolymers thereof, or made of poly-3-hydroxybutyrate (P3HB), poly-4-hydroxybutyrate (P4HB), polyhydroxyvalerate (PHV), polyhydroxyhexanoate (PHH), polyhydroxyoctanoate (PHO), polyhydroxydecanoate (PHD), polyhydroxydodecanoate (PHDD), or copolymers thereof.

3. 3. A model according to claim 1 or claim 2, wherein the PHA comprises a homopolymer or copolymer of 3-hydroxybutyric acid, preferably a copolymer of 3-hydroxybutyric acid with 3-hydroxyhexanoic acid and / or 3-hydroxyvaleric acid as comonomers, or consists essentially of a homopolymer or copolymer of 3-hydroxybutyric acid, preferably a copolymer of 3-hydroxybutyric acid with 3-hydroxyhexanoic acid and / or 3-hydroxyvaleric acid as comonomers, or consists of a homopolymer or copolymer of 3-hydroxybutyric acid, preferably a copolymer of 3-hydroxybutyric acid with 3-hydroxyhexanoic acid and / or 3-hydroxyvaleric acid as comonomers.

4. The model according to any one of claims 1 to 3, wherein the PHA has a peak melting temperature of 130°C or higher.

5. The model according to any one of claims 1 to 4, wherein the PHA has a peak melting temperature of 135°C or higher.

6. The model according to any one of claims 1 to 5, wherein the PHA has a peak melting temperature of 140°C or higher.

7. A model according to any one of claims 1 to 6, further comprising one or more additives preferably selected from flow aids, fillers, pigments and / or stabilizers.

8. 8. The model of claim 7, wherein the one or more additives are present in an amount of 0.05 to 20% by weight based on the total weight of the entire model.

9. 9. The model of claim 8, wherein the one or more additives include one or more pigments, and the total weight of the pigments relative to the total weight of the entire model is 0.05 to 0.5%, or 0.05 to 0.4%, or 0.05 to 0.25%.

10. The model of claim 9 , wherein the one or more pigments include carbon black.

11. 11. The model according to claim 1, wherein the weight of the PHA is 80 to 99.9% of the total weight of the entire model.

12. 12. An additive manufacturing method for producing a positive model of the one or more teeth and / or gums according to any one of claims 1 to 11, comprising fusing a powder comprising polyhydroxyalkanoate (PHA).

13. (a) providing a layer of powder comprising polyhydroxyalkanoate (PHA) and having a D50 particle size value of 20 to 150 μm, wherein the powder has a crystallization onset temperature T ｃ、開始 and melting peak temperature T ｍ、ピーク and 13. The additive manufacturing method of claim 12, further comprising: (b) fusing regions within the layer of powder by applying fusion radiation to the regions, thereby forming a cross section of the positive model, wherein the temperature of the powder bed is between the crystallization onset temperature and the melting peak temperature; and wherein steps (a) and (b) are repeated until the positive model is completed.

14. 14. The additive manufacturing method according to claim 12 or 13, wherein the PHA is a homopolymer or copolymer of 3-hydroxybutyric acid, preferably a copolymer of 3-hydroxybutyric acid with 3-hydroxyhexanoic acid and / or 3-hydroxyvaleric acid as comonomers.

15. The additive manufacturing method according to any one of claims 12 to 14, wherein the PHA has a peak melting temperature of 130°C or higher.

16. The additive manufacturing method according to any one of claims 12 to 15, wherein the PHA has a peak melting temperature of 135°C or higher.

17. The additive manufacturing method according to any one of claims 12 to 16, wherein the PHA has a peak melting temperature of 140°C or higher.

18. 18. The additive manufacturing method of any one of claims 12 to 17, wherein the positive model is formed based on a digital 3D model of one or more teeth and / or gums, and wherein an 80% quantile of the completed positive model compared to the digital 3D model is 0.5 mm or less, preferably 0.3 mm or less, more preferably 0.2 mm or less.

19. 20. The additive manufacturing method of claim 18, wherein the digital 3D model is dimensionally modified to account for shrinkage upon cooling, and the positive model is formed based on the dimensionally modified digital 3D model.

20. The additive manufacturing method according to any one of claims 12 to 19, wherein the powder has a reflectance of 50% or less, preferably 30% or less, and more preferably 25% or less at a wavelength of 800 nm.

21. 21. The additive manufacturing method of any one of claims 12 to 20, wherein the fusion radiation in step (b) is provided by a radiation source emitting near-infrared radiation, optionally at a wavelength of 750 nm to 1500 nm.

22. 22. The additive manufacturing method of any one of claims 12 to 21, wherein the radiation source is a laser, optionally emitting near infrared radiation at a wavelength of 750 nm to 850 nm.

23. 23. The additive manufacturing method of any one of claims 12 to 22, wherein the powder composition further comprises a pigment, and wherein the amount of the pigment relative to the total weight of the powder is 2.0% or less, preferably 1.0% or less, more preferably 0.4% or less, and optionally the amount of the pigment is at least 0.05%.

24. 24. The additive manufacturing method of any one of claims 12 to 23, wherein applying fusion radiation comprises passing a lamp over the layer, and wherein between steps (a) and (b) a near-infrared absorber is selectively applied to the areas to be fused, optionally the absorber being provided in the form of a pigment suspended in a fluid, the fluid being selectively applied onto the areas by a fluid deposition device.

25. 25. The additive manufacturing method of any one of claims 12 to 24, wherein each layer is heated to a target temperature between the crystallization onset temperature and the peak melting temperature of the PHA by one or more non-fusion heat sources, and optionally the one or more non-fusion heat sources are operated based on temperature measurements of each layer.

26. The additive manufacturing method of any one of claims 12 to 25, wherein the temperature of the powder bed is between the crystallization onset temperature and the peak melting onset temperature of the PHA.

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