Systems and methods for tomographic bath photopolymerization

Abstract

The present invention relates to a method for fabricating a three-dimensional object by tomographic vat photopolymerization, the method including: calculating a number of primary projections describing the three-dimensional object, the primary projections including positive and negative intensity values; deriving positive and negative projections from each primary projection, respectively, corresponding to the positive and negative intensity values; providing a build volume (24), the build volume including a monomer; a precursor to a stable radical scavenger inducible by light at a first wavelength, the stable radical scavenger being sensitive to light at a second wavelength; and a photosensitive component capable of initiating polymerization of the monomer by light at the second wavelength; and irradiating the build volume with light at the first wavelength in a first series of light patterns and light at the second wavelength in a second series of light patterns in respective corresponding orientations.

Description

[Technical Field]

[0001] SUMMARY The present disclosure relates to a system for tomographic bath photopolymerization and a method of using the system. [Background technology]

[0002] Additive manufacturing (AM) is a technique for producing a wide range of structures and complex geometric shapes based on three-dimensional model data. The process relies on printing successive layers of material on top of each other. The technology was originally developed in a process known as stereolithography (SLA).

[0003] SLA typically uses UV light to initiate a chain reaction on a layer of resin or monomer solution, such as an acrylic or epoxy system. The monomers are UV-active and are converted into polymer chains after activation (radicalization). Polymerization creates a pattern within the resin layer, which solidifies and can hold subsequent layers. After printing, unreacted resin is removed. Additionally, post-processing treatments such as heating or light curing can be applied to the printed object, depending on the material and desired mechanical properties.

[0004] SLA is a versatile method and is widely used, largely due to its success in rapid and inexpensive prototyping. However, it suffers from a slow printing speed. This is inherent to SLA, as it is a layer-by-layer process. Once a layer is irradiated and cured, a new layer of uncured material must be applied above or below the solid layer, depending on the build direction. Most commonly, uncured material is applied by mechanically recoating the surface, which increases printing times and can distort the molded part.

[0005] Another, more recent technique is tomographic vat photopolymerization, in which a build volume containing a photosensitive component is irradiated from multiple angles to rapidly fabricate complex materials. This technique therefore relies on a completely different approach compared to layer-by-layer techniques, physically reversing the principles of computed tomography (CT) to achieve fast, tool-free 3D printing.

[0006] WO 2018 / 208378 discloses a method of forming an object, the method including providing a volume of photocurable resin contained within an optically transparent resin container, and simultaneously directing light projections from multiple angles about a z-axis extending through the volume of photocurable resin, the projections acting for an exposure period of predetermined time, during which the net light exposure is sufficient to cure selected portions of the volume of photocurable resin and leave other portions uncured.

[0007] WO2021 / 116501A1 discloses a conventional layer-by-layer method for volumetric microlithography, in which individual planes of a build volume are exposed and polymerized successively.

[0008] Tomographic bath photopolymerization is still in its early stages and shows great promise for the future. However, a significant drawback is the limited achievable printing precision combined with the typical short time span over which maximum printing accuracy is achieved.

[0009] Therefore, there is a need to improve the printing accuracy of tomographic bath polymerization and the time span over which high printing accuracy can be achieved. Summary of the Invention

[0010] The inventors believe that the technical field of tomographic vat photopolymerization builds on knowledge gained from computed tomography (CT) in that tomographic vat photopolymerization physically reverses the principles of CT, but tomographic vat polymerization is limited by non-negativity constraints.

[0011] While CT relies on techniques to generate negative values ​​in the sinogram to improve the quality of the geometric reconstruction, the light source for tomographic vat polymerization cannot deliver negative illumination. As a result, tomographic vat polymerization has limited printing accuracy.

[0012] To overcome the non-negativity constraints associated with tomographic bath polymerization, the inventors further recognized that sigma containing negative values ​​may be used in tomographic bath photopolymerization by relying on a combination of multiple wavelengths, where at least one first wavelength is associated with the induction of a stable radical scavenger and at least one second wavelength is associated with the initiation of polymerization of a monomer, and the stable radical scavenger is sensitive to at least one of the second wavelength(s).

[0013] Thus, in a first aspect, the present disclosure relates to a method of manufacturing a three-dimensional object, such as by tomographic vat photopolymerization, the method comprising: calculating a number of primary projections describing the three-dimensional object formed from different orientation angles of the three-dimensional object, the primary projections including positive and negative intensity values; deriving from each primary projection a positive projection corresponding to positive intensity values ​​and a negative projection corresponding to negative intensity values; Providing a build volume, the build volume comprising: A monomer, a precursor to a stable radical scavenger, wherein the stable radical scavenger is inducible by light of a first wavelength and the stable radical scavenger is sensitive to light of a second wavelength; a photosensitive component capable of initiating polymerization of the monomer upon receiving light of a second wavelength; For example, to generate a 3D energy distribution, light of a first wavelength in a first series of light patterns defined by the negative projection; and light of a second wavelength in a second series of light patterns defined by positive projection; and irradiating the build volume at different orientation angles.

[0014] Thus, light at a first wavelength can produce a first 3D energy distribution, while light at a second wavelength can produce a second 3D energy distribution. Thus, fabrication of three-dimensional objects relies on generating a first energy distribution of light that inhibits and / or prevents polymerization and a second energy distribution of light that activates the photosensitive component.

[0015] The stable radical scavenger can be configured such that it absorbs light at the second wavelength. Further, polymerization of the voxels can be inhibited and / or prevented by irradiating the voxels with light at the first wavelength.

[0016] The present methods may be configured such that the focal length is set so that the focal plane intersects the center of the build volume. Thus, the presently disclosed methods may differ from other additive manufacturing methods that rely on varying the focal length. Furthermore, the presently disclosed methods are typically arranged to provide irradiation from multiple angles relative to the build volume, for example, by rotating the build volume around the center of the build volume, which may correspond to the focal plane of the irradiation. Alternatively, or additionally, the irradiation source may be arranged to rotate around the build volume.

[0017] Advantageously, the method allows for individually controllable stability for each voxel of the build volume and can be utilized to remove non-negativity constraints for tomographic bath polymerization; therefore, the method may enable improved printing accuracy, wider process window, faster printing speed, and enhanced feature modulation through grayscale printing, and may even be used to fabricate more complex shapes that were previously impossible.

[0018] As used herein, a voxel (volumetric image element) refers to a volume element, usually a cube, that represents a value on a structured grid in three-dimensional space.

[0019] The build volume is divided into a number of voxels, each of which is a liquid voxel, as used herein, which is a voxel that remains liquid to accurately reproduce the three-dimensional object. Alternatively, a voxel may be a solid voxel, as used herein, which is a voxel that becomes solid (e.g., polymerized) to accurately reproduce the three-dimensional object.

[0020] The voxels can therefore be said to be a 3D binary grid array, with each voxel having a binary value that is either liquid or solid, as dictated by the three-dimensional object being reproduced.

[0021] The size of the voxels affects the precision with which a three-dimensional object can be produced. Typically, the voxel size is determined by the printing resolution. Smaller voxels (i.e., higher printing resolution) typically allow for a higher degree of detail to be reproduced and greater precision in printing.

[0022] The primary projections represent the three-dimensional object formed from various orientation angles of said object and are used to derive the positive and negative projections.

[0023] Illumination of the build volume induces polymerization of voxels that will polymerize while inhibiting polymerization of voxels that will not polymerize, which is advantageously achieved by illuminating the build volume at different orientation angles with a first projection, such that light of a first wavelength in a first series of light patterns is defined by a negative projection and light of a second wavelength in a second series of light patterns is defined by a positive projection.

[0024] Typically, the energy deposited in the first series of light patterns acts to induce stable radical scavengers, thus preventing polymerization of voxels that receive said energy, while the energy deposited in the second series of light patterns acts to induce polymerization of voxels that receive this energy, typically by activating photosensitive components and / or by acting to deplete the stable radical scavengers of the voxels.

[0025] Preferably, the build volume, as defined by a positive projection, is: light at a first wavelength in a first series of light patterns; and a second wavelength of light in a second series of light patterns; They are usually illuminated in their respective orientations simultaneously.

[0026] The precursor to the stable radical scavenger can vary depending on the polymerization system used, and various chain-growth polymerization methods are known. Preferably, the precursor to the stable radical scavenger is selected such that the stable scavenger is a species that: i) can be generated via an external stimulus (e.g., UV irradiation), ii) absorbs incident light having a second wavelength, iii) has a long lifespan, and / or iv) inhibits polymerization.

[0027] Preferably, the stable radical scavenger is configured to be generated from or by a stable radical scavenger precursor upon induction with light of the first wavelength. Once generated, the stable radical scavenger is preferably configured to inhibit polymerization by absorbing light of the second wavelength. In this manner, the light can be prevented from activating initiation of polymerization of the photosensitive component. Typically, the concentration of the stable radical scavenger can be reduced by providing light of the second wavelength. Thus, light of the first wavelength can be used to induce the stable radical scavenger from the precursor, while light of the second wavelength can be used to remove the stable radical scavenger.

[0028] In this way, the rate of polymerization can be controlled by controlling the relative energy dose between the first and second wavelengths delivered to each voxel in the build volume, thereby improving printing accuracy, widening the process window, and increasing overall printing speed.

[0029] Typically, the primary projections are one or more sinograms containing positive and negative values. Furthermore, it is preferred that one or more primary projections are divided into one or more positive projections and one or more negative projections. Preferably, all negative pixel values ​​form part of one or more negative projections, and all positive pixel values ​​form part of one or more positive projections. Most preferably, the primary projections are obtained by aggregating the positive and negative projections for each pixel.

[0030] Therefore, negative intensity values ​​are typically used to project negative pixels into the build volume to accurately reproduce the three-dimensional object. Because negative intensity values ​​cannot be illuminated into the build volume, the resulting energy distribution of the negative pattern of illumination with the first wavelength of light is instead used to create the negative illumination effect, as the first wavelength of light can induce stable radical scavengers. In this way, methods used in computed tomography, such as sinogram calculations, can also be directly applied to graphical vat photopolymerization.

[0031] In a second aspect, the present disclosure relates to a system for manufacturing a three-dimensional object from a build volume, the system comprising: A processing unit, calculating multiple primary projections describing the multi-material three-dimensional object formed from different orientation angles of the three-dimensional object, the primary projections including positive and negative intensity values; and a processing unit configured to derive from each primary projection a positive projection corresponding to a positive intensity value and a negative projection corresponding to a negative intensity value; 1. A projection system comprising: light of a first wavelength in a first series of light patterns defined by the negative projection; and light of a second wavelength in a first series of light patterns defined by positive projection; a projection system configured for illuminating the build volume at different orientation angles; Includes.

[0032] The system is preferably configured to perform a method for manufacturing a three-dimensional object, as disclosed elsewhere herein. The system may be configured to perform a method for manufacturing a three-dimensional object, for example, by tomographic bath photopolymerization. For example, the system may be arranged to irradiate a build volume with a series of projections, e.g., primary projections, at a fixed focal length and at different orientation angles. The focal length may be set, for example, so that the focal plane intersects the center of the build volume.

[0033] The system is typically configured to fabricate a three-dimensional object based on a build volume. In certain embodiments, the build volume can form part of the system. In such embodiments, the system can include a build volume, which can include: A monomer, a precursor to a stable radical scavenger, wherein the stable radical scavenger is inducible by light of a first wavelength, and the stable radical scavenger is sensitive to light of a second wavelength; a photosensitive component capable of initiating polymerization of the monomer upon receiving light at a second wavelength; may include:

[0034] Typically, the system is arranged to irradiate the build volume with light of a first wavelength in a first series of light patterns at respective corresponding orientations such that a first energy distribution is provided to the build volume, wherein the energy provided to non-polymerized voxels (non-polymerized, i.e., voxels that remain non-polymerized to accurately reproduce the three-dimensional object) is higher than the energy provided to polymerized voxels, and the polymerized voxels and non-polymerized voxels are voxels of the build volume that either polymerize or remain non-polymerized to accurately reproduce the three-dimensional object.

[0035] The following embodiments and examples will be described in more detail with reference to the accompanying drawings. [Brief explanation of the drawings]

[0036] [Figure 1] 1 shows the change in concentration of a radical scavenger species in a build volume during irradiation of the build volume with light at a first wavelength and light at a second wavelength in accordance with a method of fabricating a three-dimensional object disclosed herein. [Figure 2] 1 shows a schematic diagram of an embodiment of a system for two-color tomographic volumetric printing (DC tomography bath polymerization) as disclosed herein. [Figure 3] 1 shows a comparison of the generation of three-dimensional objects at different exposure times based on single-color and two-color tomographic bath polymerization according to embodiments disclosed herein. [Figure 4] A square projection pattern and the corresponding sinogram and histogram are shown. [Figure 5] The effect of non-negative constraints on conventional tomographic bath photopolymerization is shown using the sinogram of FIG. [Figure 6] 10 shows the resulting sinogram and histogram according to one embodiment of the disclosed method. [Figure 7] 1 illustrates the generation of a three-dimensional object according to an embodiment of the disclosed method. DETAILED DESCRIPTION OF THE INVENTION

[0037] Tomographic volumetric printing (or computational axial lithography) can be thought of as a physical inversion of the principles of computed tomography (CT) to achieve fast, tool-free 3D printing. In tomographic bath polymerization, all points of a 3D object are typically cured in parallel, and print times can become independent of the number of voxels.

[0038] While CT allows for negative values ​​in the sinogram to improve the quality of geometric reconstruction (e.g., filtered backprojection), the projector for tomographic bath polymerization cannot provide negative illumination. Tomographic bath polymerization instead relies on sophisticated algorithms for sinogram calculation, resulting in reduced printing accuracy.

[0039] The use of stable radical scavengers allows us to redefine the behavior of photopolymerizable systems. Tomographic bath polymerization without stable radical scavengers proceeds unidirectionally along the abscissa (Figure 1). The concentration of the secondary radical scavenger is zero in such systems, i.e., the concentration at each voxel is (C A0, For example, irradiation with light at a second wavelength pushes the state of the voxel towards the origin (0,0), where polymerization occurs. The system for this implementation is typically a monochromatic tomographic bath polymerization system.

[0040] FIG. 1 shows the change in concentration of radical scavenger species in a build volume during irradiation of the build volume with light at a first wavelength and light at a second wavelength according to a method of fabricating a three-dimensional object disclosed herein.

[0041] In conventional monochromatic tomographic bath polymerization (1), the entire build volume is illuminated from multiple angles, and voxels inevitably undergo illumination aimed at shadowing voxels, as shown in Figure 1. Ultimately, all voxels move toward the origin (5) (only in stationary systems for monochromatic tomographic bath polymerization).

[0042] If two voxels are adjacent in the build volume and one of the voxels is cured but the other is not, a dose contrast must be created such that the exposure can be terminated when the exposure received by the former exceeds the cure threshold while the exposure received by the latter does not. The period of time that satisfies this requirement is referred to herein as the process window.

[0043] By using a two-color system for tomographic bath polymerization in combination with a stable radical scavenger, a binary photoinhibition system (BPS) can be formed, which can be utilized to create steady states (SS) with individually controllable stability for each voxel and remove the non-negativity constraint (NNC) of tomographic bath polymerization. Thus, negative projections (e.g., sinograms) with negative intensity values, which are typically required for accurate reconstruction of three-dimensional objects, are possible.

[0044] The ideal BPS is usually expressed as follows:

number

number

[0045] The build volume containing the stable radical scavenger allows for the creation of a new rest system on the vertical axis (Figure 1).

number

[0046] Therefore, the sinogram calculation is preferably configured such that all overlapping voxels (2) move rapidly towards the origin, while non-overlapping voxels (3) move slowly towards an alternative rest state (4).

[0047] Thus, in a first aspect, the present disclosure relates to a method of manufacturing a three-dimensional object.

[0048] The method typically includes calculating multiple primary projections, which may describe a three-dimensional object formed from different orientation angles of the object, and which typically include positive and negative intensity values.

[0049] The method may include deriving from each primary projection a positive projection corresponding to positive intensity values ​​and a negative projection corresponding to negative intensity values. The positive projection and / or negative projection are preferably one or more sinograms. Typically, the positive projection of the original primary projection and / or sinogram(s) is a sinogram that includes all positive values, and the negative projection is a sinogram that includes all negative values.

[0050] The method may further include irradiating the build volume with light of a first wavelength in a first series of light patterns defined by negative projections and light of a second wavelength in a second series of light patterns defined by positive projections at respective corresponding orientations.

[0051] In one example, the illuminating step includes illuminating the build volume with primary projections at different orientation angles, such that light of a first wavelength in a first series of light patterns is defined by a negative projection and light of a second wavelength in a second series of light patterns is defined by a positive projection.

[0052] Preferably, the build volume is irradiated with light of a first wavelength in a first series of light patterns, each in a corresponding direction, such that a first energy distribution is provided in the build volume, wherein the energy provided to non-polymerized voxels is higher than the energy provided to polymerized voxels, wherein polymerized voxels are voxels of the build volume that are to be polymerized to accurately reproduce the three-dimensional object or that remain non-polymerized, and wherein non-polymerized voxels are voxels of the build volume that remain non-polymerized to accurately reproduce the three-dimensional object.

[0053] Alternatively or additionally, the build volume is preferably irradiated with light of a second wavelength in a second series of light patterns at respective corresponding orientations, thereby providing a second energy distribution to the build volume, wherein the energy provided to polymerize voxels is higher than the energy provided to not polymerize voxels, and the voxels of the build volume to polymerize and to remain not polymerized are polymerized voxels and non-polymerized voxels, respectively, to accurately reproduce the three-dimensional object.

[0054] Preferably, the method is configured such that the first energy distribution provides an energy contrast between non-polymerizing and polymerizing voxels of at least 1.5, more preferably at least 2, even more preferably at least 5, and most preferably at least 10.

[0055] Typically, the first energy distribution is configured such that higher energy is provided to non-polymerizing voxels adjacent to polymerizing voxels than to non-polymerizing voxels adjacent to other non-polymerizing voxels.

[0056] Preferably, the primary projection, the negative projection, and / or the positive projection are sinograms.

[0057] More preferably, the primary projection is a sinogram comprising positive and negative values, with positive and negative projections being derived from said primary projection, such that the positive projection comprises the positive intensity values ​​of the primary projection and the negative projection comprises the negative intensity values ​​of the primary projection.

[0058] Additionally, the method can include use of a build volume, which upon irradiation of said build volume is used to form the three-dimensional object. and / or a precursor to a stable radical scavenger, wherein the stable radical scavenger is inducible by light of a first wavelength and the stable radical scavenger is sensitive to light of a second wavelength; and / or a photosensitive component capable of initiating polymerization of the monomer upon receiving light at a second wavelength; may include:

[0059] Thus, the precursor of the stable radical scavenger is typically configured to be sensitive to light of the first wavelength. The precursor may be configured to generate the stable radical scavenger upon receiving light of the first wavelength. The precursor may, for example, be configured to convert to the stable radical scavenger upon receiving light of the first wavelength; for example, the precursor may be configured to convert to the stable radical scavenger by, for example, a photolytic reaction. Preferably, the stable radical scavenger is inducible by photolysis of the precursor by light of the first wavelength.

[0060] Preferably, the stable radical scavenger is configured to prevent polymerization, i.e., polymerization of voxels containing the stable radical scavenger. Typically, the stable radical scavenger is configured to absorb light of the second wavelength. Thus, by absorbing light of the second wavelength, the stable radical scavenger can prevent polymerization. Preferably, the stable radical scavenger is configured such that light of the second wavelength consumes the stable radical scavenger; for example, the stable radical scavenger can be decomposed by photolysis. Thus, the concentration of the stable radical scavenger can be controlled by the energy distribution of light of the first and / or second wavelengths.

[0061] In one example, a stable radical scavenger can be formed in a voxel by providing light at a first wavelength to the voxel. This can lead to a precursor of the stable radical scavenger forming the stable radical scavenger. Increasing the amount of light at the first wavelength provided to the voxel typically results in an increase in the concentration of the stable radical scavenger in the voxel.

[0062] Similarly, by providing a voxel with light of a second wavelength, the stable radical scavenger can be removed from the voxel, e.g., by a photolysis event, i.e., the concentration of the stable radical scavenger decreases. The photolysis event can, for example, act to cleave and / or decompose the stable radical scavenger. The stable radical scavenger depends on the build volume / resin, i.e., the photopolymerization system. The stable radical scavenger can be, for example, bis[2-(o-chlorophenyl)-4,5-diphenylimidazole] (o-Cl-HABI). This molecule generates two propyl radicals upon photolysis, and its ability to generate photonegativity scales stoichiometrically with its concentration ([o-Cl-HABI]).

[0063] Furthermore, in contrast to the photoinhibitors used in conventional light-based additive manufacturing methods, stable radical scavengers are preferred in systems designed for tomographic printing due to their cumulative nature.

[0064] In one embodiment of the present disclosure, the rate of polymerization is a function of the ratio of the intensity of light of the first wavelength to the intensity of light of the second wavelength. Since light having a first wavelength can be used to inhibit polymerization of voxels illuminated by said light, i.e., voxels that absorb said light, polymerization of these voxels can be controlled by selecting the provided doses of light having the first and second wavelengths.

[0065] Controlling the light at the first and second wavelengths typically also involves controlling the temporal delivery of the light dose based on the nonlinear photosensitivity of the components of the build volume. Therefore, it can be advantageous to ensure that voxels of the build volume that remain continuously unpolymerized (i.e., remain as liquid voxels) during the curing process have components that act to inhibit polymerization (typically by having a non-zero concentration of a stable radical scavenger). Typically, the energy distribution of the light at the first wavelength is such that voxels that remain unpolymerized (liquid voxels) adjacent to and / or close to polymerized voxels (solid voxels) receive a higher dose of said light having the first wavelength compared to the liquid voxels to accurately reproduce the three-dimensional object.

[0066] In one embodiment of the present disclosure, the build volume can include a secondary radical scavenger. A secondary radical scavenger is typically a chemical compound configured to prevent polymerization of the build volume, e.g., monomers. The secondary radical scavenger can be sensitive to light of a second wavelength, e.g., the secondary radical scavenger can be configured to absorb light of a second wavelength. In this manner, the secondary radical scavenger can be said to compete with the photoinitiator for light of the second wavelength. The secondary radical scavenger can be configured to prevent polymerization by absorbing light of the second wavelength.

[0067] The secondary radical scavenger may be uniformly dispersed within the build volume, and / or in certain embodiments, the build volume may be provided with a secondary radical scavenger. Typically, the secondary radical scavenger is stable in the absence of irradiation (e.g., oxygen during free radical polymerization). Thus, in one embodiment of the present disclosure, the secondary radical scavenger is selected from the list including oxygen and / or 2,2,6,6-tetramethylpiperidinoxyl.

[0068] Preferably, the stable radical scavenger is selected so that it is stable for an extended period of time, preferably the entire time that the build volume is irradiated with light having the secondary wavelength. Typically, the stable radical scavenger is stable for at least 1 second, more preferably at least 3 seconds, even more preferably at least 5 seconds, and most preferably at least 10 seconds, and most preferably, the stable radical scavenger is stable in the absence of light having the secondary wavelength.

[0069] Those skilled in the art are familiar with various setups for performing tomographic bath photopolymerization. Light may be provided, for example, from one or more fixed light sources (e.g., projectors), while the build volume is rotated to receive light from the light sources at multiple angles. Typically, the build volume is provided in, for example, a cylindrical beaker placed within a rectangular outer container containing a refractive index-matched liquid. The build volume may be provided in, for example, a cylindrical beaker placed within a rectangular outer container containing an index-matched liquid. However, in other embodiments, the build volume is stationary, while one or more light sources are arranged to rotate about a central vertical axis of the build volume to provide light onto the build volume from multiple angles. In other embodiments, there may be multiple light sources providing light from different angles, typically within the same plane as the plane of rotation of the build volume. However, one or more light sources may be provided in other planes. Typically, the relative rotation between the build volume and the illumination(s) / light source(s) is at least 180 degrees. Therefore, if the light source(s) are stationary, the build volume must rotate at least 180 degrees. Alternatively, the build volume may be stationary and the light source(s) may be positioned to rotate at least 180 degrees around the build volume so that the build volume is illuminated by light from a 180-degree sector. However, as noted above, the build volume may be positioned to rotate while the light source is moved relative to the build volume; therefore, in such cases, a relative rotation may be referred to, which is typically at least 180 degrees, i.e., the build volume is illuminated from a 180-degree sector. However, the sector may be at least 360 degrees or more. Preferably, the sector is at least 360 degrees, e.g., at least 720 degrees, or even 1080 degrees. The sector may be, for example, between 360 degrees and 3600 degrees.

[0070] The system may be configured, for example, such that the system simultaneously illuminates the build volume with light at the first and second wavelengths, which may be merged, for example, by a dichroic mirror, such that they are provided to the build volume from the same angle.

[0071] In TVP, the light dose delivered to voxels in the build volume is gradually increased so that voxels that polymerize, i.e., voxels that should be solid, polymerize substantially simultaneously. This contrasts with other additive manufacturing (AM) methods, such as layer-by-layer approaches in which voxels are sequentially polymerized to fabricate a three-dimensional object, e.g., in which planes are polymerized individually. In TVP, polymerization of a voxel typically requires that said voxel receive a light dose that is the result of irradiation with a series of light patterns from multiple orientation angles. For example, polymerization may occur after receiving light from a larger portion of the illumination sector, e.g., 180 degrees of the sector. Thus, polymerization typically results from a three-dimensional energy distribution, not a dose distribution delivered to a single plane, as in the case of delivering a dose distribution to another plane.

[0072] However, preferentially, the build volume is simultaneously irradiated with light having a first wavelength and light having a second wavelength. Preferably, the build volume is irradiated with light having the first wavelength following completion of irradiation with light having the second wavelength. Light having the second wavelength may be an initiator of reactive species (e.g., radicals) in the build volume, and continuing to irradiate the build volume with light having the first wavelength after terminating irradiation of the build volume with light having the second wavelength may prevent polymerization of voxels that remain unpolymerized (e.g., liquid voxels), and may improve printing accuracy.

[0073] Typically, the build volume is provided with light of a first wavelength and light of a second wavelength in respective orientations defined by the negative and positive projections. Typically, the build volume is provided with light of the first wavelength in a first series of light patterns defined by the negative projections and light of the second wavelength in a second series of light patterns defined by the positive projections.

[0074] Those skilled in the art are familiar with many different systems for photopolymerization of a build volume, i.e., many different components of a build volume that can be used for photopolymerization.

[0075] Generally, systems for photopolymerization rely on free radical polymerization (FRP), a polymerization method that forms polymers by the sequential addition of free radical building blocks. Free radicals can be formed by several different mechanisms, usually involving separate initiator molecules. Following their generation, the initiating free radicals add (non-radical) monomer units, thereby growing a polymer chain. The build volume may contain, for example, acrylate, epoxy, or vinyl monomers to be polymerized. Those skilled in the art are familiar with various photoinitiators and their sensitivity to different wavelengths of light.

[0076] Typically, one of the first and second wavelengths is in the UV region, with a wavelength range of 10 nm to 400 nm, and the other of the wavelengths is in the visible light region, with a wavelength range of 400 nm to 700 nm. For example, the first wavelength may be in the range of 365 nm to 385 nm, and the second wavelength may be in the range of 400 nm to 500 nm. Alternatively, the first wavelength may be in the range of 400 nm to 500 nm, while the second wavelength may be in the range of 365 nm to 385 nm.

[0077] The stable radical scavenger may be selected based on the photosystem used. However, as discussed elsewhere herein, the stable radical scavenger is typically inducible by light of a first wavelength and sensitive to light of a second wavelength. Therefore, the stable radical scavenger may be configured to absorb light of a second wavelength, for example, to prevent the photoinitiator from being activated.

[0078] In one embodiment of the present disclosure, the stable radical scavenger is selected from the list comprising propyl radical and / or tetraethylthiuram disulfide.

[0079] Similarly, various monomers are known to be suitable for different photochemical polymerization systems. In one example, the monomers are selected from the group including TEGDMA and / or BisGMA.

[0080] The photoinitiator may be selected from the group comprising camphorquinone and / or ethyl 4-(dimethylamino)benzoate. Ethyl 4-(dimethylamino)benzoate (Et-PABA) is a hydrophilic polymer and may also be used as a derivative of 4-aminobenzoic acid.

[0081] Camphorquinone, also known as 2,3-bornanedione, is a photoinitiator that generally induces polymerization slowly, so amines such as N,N-dimethyl-p-toluidine, 2-ethyl-dimethylbenzoate, and N-phenylglycine are usually added to increase the rate of cure. It has very weak absorption at 468 nm and is pale yellow in color.

[0082] In a further aspect, the present disclosure relates to a system for fabricating a three-dimensional object from a build volume. The system typically includes a processing unit and / or memory. The system and / or memory typically includes a computer program that, when executed (e.g., by the system or computer), includes instructions that cause the program to calculate multiple primary projections describing the three-dimensional object formed from different orientations of the object, the primary projections including positive and negative intensity values. The system can thus be configured to derive from each primary projection a positive projection corresponding to a positive intensity value and a negative projection corresponding to a negative intensity value.

[0083] Typically, a positive projection may be provided as a positive sinogram or may be used to form a positive sinogram. Similarly, a negative projection may be provided as a negative sinogram or may be used to form a negative sinogram. Typically, addition (e.g., pixel-by-pixel addition) is performed.

[0084] The system typically further comprises a projection system configured to illuminate the build volume at each corresponding orientation. The projection system may include one or more light sources, e.g., projectors. The light sources may be positioned in the same plane as the plane of rotation of the build volume. Alternatively, the light sources may be in one or more planes. In other embodiments, the light sources rotate around the build volume.

[0085] In a preferred embodiment of the present disclosure, the system includes a processor adapted to execute the methods for manufacturing a three-dimensional object disclosed elsewhere herein.

[0086] The system can include a build volume containing a monomer, a precursor to a stable radical scavenger, and a photosensitive component, wherein the stable radical scavenger is inducible by light at a first wavelength and the stable radical scavenger is sensitive to light at a second wavelength and capable of initiating polymerization of the monomer upon receiving light at the second wavelength. The monomer, precursor, and / or stable radical scavenger can be configured as disclosed elsewhere herein, i.e., configured to perform a method disclosed elsewhere herein. Thus, the precursor can be bis[2-(o-chlorophenyl)-4,5-diphenylimidazole] (o-Cl-HABI) and / or configured to generate two propyl radicals upon photolysis and capable of stoichiometrically creating a photonegativity scale using its concentration ([o-Cl-HABI]).

[0087] In one embodiment of the present disclosure, the system is arranged to irradiate the build volume with light of a first wavelength in a first series of light patterns, and to provide a first energy distribution to the build volume at each corresponding orientation, where the energy provided to non-polymerized voxels is higher than the energy provided to polymerized voxels, and the polymerized voxels and non-polymerized voxels are voxels of the build volume that either polymerize or remain non-polymerized to accurately reproduce the three-dimensional object.

[0088] In one embodiment of the present disclosure, the first energy distribution is configured to provide an energy contrast between non-polymerizing and polymerizing voxels of at least 1.5, more preferably at least 2, even more preferably at least 5, and most preferably at least 10.

[0089] In one embodiment of the present disclosure, the first energy distribution is configured to provide a higher energy to non-polymerizing voxels adjacent to polymerizing voxels than to non-polymerizing voxels adjacent to other non-polymerizing voxels.

[0090] In one embodiment of the present disclosure, the primary projection, the negative projection and / or the positive projection is a sinogram.

[0091] In one embodiment of the present disclosure, a positive projection includes positive pixel values ​​of the corresponding primary projection, and a negative projection includes negative pixel values ​​of the corresponding primary projection.

[0092] In one embodiment of the present disclosure, each primary projection includes intensity values ​​of the corresponding positive and negative projections.

[0093] In one embodiment of the present disclosure, the build volume is light at a first wavelength in a first series of light patterns; and with light of a second wavelength in a second series of light patterns They are usually illuminated in their respective orientations simultaneously.

[0094] For example, the methods disclosed herein can be implemented using a system for two-color tomographic volumetric printing (DCTVP) (FIG. 2). Such a system can include a means for visualizing the polymerization process as it occurs. The visualization means can include a visible light source and a camera. In either case, the system typically includes at least one light source, preferably two. As shown in FIG. 2, the light source can be one or more projectors. Preferably, one light source is a UV light source (21) and the other is a visible light source (22). The UV and visible light paths can be configured orthogonal to each other, and illumination for in situ imaging can be merged into the visible light path via a dichroic mirror. For example, a dichroic mirror can typically reflect longer visible light below a specific wavelength, such as 490 nm, from the visible light path if the system includes a visualization means.

[0095] The visible light source (22) may be, for example, a DLP projector. The visible light source may be used in conjunction with an optical lens (23, e.g., f=200 mm) to project visible light into the curing volume (24). The UV light source (21) may be a UV DMD projector. The UV light source may be focused through a 4f lens system (25, e.g., L2: f=200 mm and L3: f=300 mm), and an aperture may be used on its Fourier plane to block unwanted diffraction orders from the DMD and improve intensity uniformity. The two projection centerlines are typically aligned to intersect at the axis of rotation of the curing volume. An imaging light source, such as an LED light source, may be used. The imaging light source may be collimated through two 4f lens systems (27) and used as a visualization means in conjunction with a camera (28).

[0096] Figure 4 illustrates the effect of the non-negativity constraint (NNC). A square and its sinogram and histogram are calculated using an iterative method and are shown in Figures 4A-4C. As shown in the histogram (Figure 4C), the sinogram (Figure 4B) contains negative intensity values ​​that eliminate the accumulation of unwanted energy. (B) Two methods for handling negatives in monochromatic printing are: 1) setting all negatives to zero (Figure 5A); and 2) a non-negativity constraint applied at each iteration during sinogram calculation (Figure 5B).

[0097] Example 1: Removing the Non-Negative Polarity Constraint in Tomographic Volumetric Printing by Using Radical-Stable Scavengers

[0098] Materials and Methods A cylindrical test tube (Φ2.4 mm) containing photoresin was mounted on a motorized rotation stage (PRM1 / MZ8, Thorlabs) positioned at the intersection of the two optical paths, as shown in Figure 1. A rectangular fluid tank containing index-matching fluid was placed outside the test tube with its walls perpendicular to the incident beam.

[0099] A methacrylate-based photoresin was prepared by mixing triethylene glycol dimethacrylate (TEGDMA, CAS#109-16-0, Sigma-Aldrich) and bisphenol A glycerolate dimethacrylate (bisGMA, CAS#1565-94-2, Sigma-Aldrich) in a 1:1 weight ratio, and adding 0.2 wt % camphorquinone (CQ, CAS#10373-78-1, ≥96.5% purity, Sigma-Aldrich) and 0.5 wt % ethyl 4-dimethylaminobenzoate (EDAB, CAS#10287-53-3, Sigma-Aldrich) as a photoinitiator and co-initiator, respectively. 2,2'-Bis(2-chlorophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole (o-Cl-HABI, CAS# 7189-82-4, TCI Europe) was first dissolved in tetrahydrofuran (THF, CAS# 109-99-9, Fisher Scientific) at 28 wt% and then added to the photoresin at 1 wt%. As disclosed herein, other concentrations (e.g., 3 wt%) are possible.

[0100] Resin response calibration The irradiance was measured as a function of the grayscale intensity of both light sources. Next, a ball series (Figure 3A) at the center of rotation was printed at various UV intensities for photoresponse calibration. Six filled circles (Φ3 mm) were projected at maximum intensity (grayscale 255) by the visible light source (31) and at increasing intensities from 0 to 255 by the UV light source (32). The rotation period was set to 24 seconds. Figure 3B shows the monochromatic mode (e.g., visible light source only) at t = 0 (33), t = 37 s (34), t = 40 s (35), and t = 43 s (36), while Figure 3C shows the bichromatic mode (e.g., visible light source and UV light source) at t = 0 s (37), t = 37 s (38), t = 43 s (39), t = 49 s (40), t = 53 s (41), t = 57 s (42), and t = 62 s (43). The delay in the appearance of the workpiece reflected the efficiency of negative generation as a function of UV irradiance.

[0101] The visible intensity was set to 255 for all six filled circles. The UV intensities were (from top to bottom) 255, 205, 155, 105, 55, and 0. For the single-color print (Figure 3B), the workpiece emerged after 37 seconds. For the two-color print (Figure 3C), all workpieces emerged by 62 seconds, suggesting W ≤ 0.68 at the center of rotation.

[0102] Sinogram Calculation The sinogram calculation relied on iterative sinogram calculation. ChiTuBox (CBD-Tech, SZX) was used to slice the STL files and adjust the pixel gray values ​​of the resulting TIFF stack according to the desired target dose distribution. The primary projections were sinograms calculated using a naive forward projection, i.e., for each projection angle θ, the position D(d) of the projection of a point P(x,y) on the 1D detector is given by

number

[0103] The workpiece was then compared to the original design and the difference was forward projected to generate a correction to the primary projection (i.e., the previous sinogram) to become an updated primary projection (sinogram).

[0104] The corrections can be negative, and if these negativity are kept until the last iteration and then set to zero, the resulting projections (sinograms and projections) will look like those shown in Figures 5A-5B.

[0105] If these are set to zero at each iteration, the resulting projections (sinogram and projections) will look like those shown in Figures 5C-5D. This method of negativity removal prevents the sinogram from perfectly reconstructing the desired geometry, and therefore heuristic thresholding has become essential in generating sinograms for satisfactory print quality.

[0106] If the negativity is left unprocessed, the resulting sinogram can be divided according to the sign and directly used in a two-color binary photoinhibition system along with the respective sinograms (Figures 6A and 6B), as shown in Figures 6B (visible light ~ 455 nm) and 6D (UV light ~ 365 nm). Thus, in this example, positive and negative projections were formed using two rectangles, as shown in Figures 7A-7B.

[0107] In general, the goal is to minimize the number of error voxels, which are intended solid voxels that did not receive enough light dose and consequently remain unpolymerized (negative error voxels, or NEVs), or voxels that remain unpolymerized but are over-dosed due to solidification (PEVs). When there is a non-negativity constraint (NNC), the print time is determined by the minimum number of full rotations required to eliminate NEVs, and print quality decreases as the number of PEVs generated during these rotations increases. Setting a negative zero (e.g., as in Figures 5A-5B) typically corresponds to intentionally switching voxels most susceptible to overexposure (e.g., square corners) into PEVs, thus limiting the achievable print accuracy. Nevertheless, when NNC is considered during iterative sinogram calculations, the additional dose to the most susceptible voxels is typically distributed throughout the cured volume; i.e., the high tendency of a few voxels to become PEVs is reduced at the expense of repeated undesired dose buildup in many other voxels. The resulting calculated projection provides high accuracy, but print quality quickly degrades due to the increase in PEV when the optimal endpoint is removed. Removing the NNC significantly extends the process window without sacrificing accuracy. The original sinogram was divided into two parts according to the sign of pixel intensity. Positive pixels were projected by the visible light source, and negative pixels were projected by the UV light. Therefore, the information conveyed by negativity was preserved by taking the absolute values ​​of the corresponding pixels and converting them into a positive grayscale UV pattern. UV stabilizes voxels in a nonpolymerizing steady state (SS), preventing the increase in PEV after all NEV has been removed. Before NEV completely disappears, the workpiece shape is sensitive to the rotation period. With a rotation period of 24 seconds, this sensitivity persisted for the first three full rotations of our test.

[0108] irradiation Resin (M-1) was irradiated with visible light for 48 seconds and UV light for 54 seconds during a 24-second rotation period. To form the tube, the positive projection was defined by the visible light pattern (71) and used two rectangular shapes. At the same time, the negative projection was defined by the UV light pattern (70) and narrowed to prevent polymerization of the inner part of the tube (22, Figure 7B).

[0109] Results and Conclusions Three-dimensional tubes were successfully reproduced with unpolymerized inner portions. The non-negativity constraint of tomographic volumetric printing was overcome by the use of radical-stable scavengers.

[0110] With NNC, the SC mode was unable to prevent overexposure at the four corners. Without NNC, the DCTVP not only produced more accurate workpieces, but also continued to improve print quality after three full revolutions.

[0111] Terms 1. A method for manufacturing a three-dimensional object, comprising: calculating a number of primary projections describing the three-dimensional object formed from different orientation angles of the three-dimensional object, the primary projections including positive and negative intensity values; deriving from each primary projection a positive projection corresponding to said positive intensity values ​​and a negative projection corresponding to said negative intensity values; Providing a build volume, the build volume comprising: A monomer, a precursor to a stable radical scavenger, said stable radical scavenger being inducible by light of a first wavelength and said stable radical scavenger being sensitive to light of a second wavelength; a photosensitive component capable of initiating polymerization of the monomer upon receiving light of the second wavelength; light at the first wavelength in a first series of light patterns defined by the negative projection; and illuminating the build volume at the respective corresponding orientations with light at the second wavelength in a second series of light patterns defined by the positive projections; The method comprising:

[0112] 2. The method of clause 1, wherein the build volume is illuminated with light of the first wavelength in the first series of light patterns, and a first energy distribution is provided to the build volume in each corresponding orientation, the energy provided to non-polymerized voxels is higher than the energy provided to polymerized voxels, and the polymerized voxels and non-polymerized voxels are voxels of the build volume that polymerize or remain non-polymerized, respectively, to accurately reproduce the three-dimensional object.

[0113] 3. The method of clause 2, wherein the first energy distribution is configured to provide an energy contrast between non-polymerizing and polymerizing voxels of at least 1.5, more preferably at least 2, even more preferably at least 5, and most preferably at least 10.

[0114] 4. The system of any one of clauses 2-3, wherein the first energy distribution is configured to provide higher energy to non-polymerized voxels adjacent to polymerized voxels than to non-polymerized voxels adjacent to other non-polymerized voxels.

[0115] 5. The method of any one of the preceding clauses, wherein the primary projection, the negative projection, and / or the positive projection are sinograms.

[0116] 6. A method according to any one of the preceding clauses, wherein the positive projections of each corresponding primary projection contain the positive pixel values ​​and the negative projections contain the negative pixel values.

[0117] 7. A method according to any one of the preceding clauses, wherein each primary projection comprises the intensity values ​​of the corresponding positive and negative projections.

[0118] 8. The method of any one of the preceding clauses, wherein the stable radical scavenger is inducible by photolysis of the precursor with light at the first wavelength.

[0119] 9. The method of any one of the preceding clauses, wherein the stable radical scavenger absorbs light at the second wavelength.

[0120] 10. The method of any one of the preceding clauses, wherein the concentration of the stable radical scavenger is reduced by providing light of the second wavelength.

[0121] 11. A method according to any one of the preceding clauses, wherein the polymerization of voxels is inhibited and / or prevented by irradiating the voxels with light of the first wavelength.

[0122] 12. The method of any one of the preceding clauses, wherein the rate of polymerization is a function of the ratio between the intensities of the light at the first wavelength and the light at the second wavelength.

[0123] 13. The method of any one of the preceding clauses, wherein the stable radical scavenger acts to inhibit and / or prevent polymerization of the monomer.

[0124] 14. The method of any one of the preceding clauses, wherein the build volume comprises a secondary radical scavenger that is sensitive to light at a second wavelength.

[0125] 15. The method of clause 14, wherein the secondary radical scavenger is configured to absorb light at the second wavelength.

[0126] 16. The method of any one of clauses 14-15, wherein the secondary radical scavenger is configured to inhibit and / or prevent polymerization of the monomer.

[0127] 17. The method of any one of the preceding clauses, wherein the stable radical scavenger is configured to be stable in the build volume in the absence of light at the second wavelength for at least 1 second, more preferably at least 3 seconds, even more preferably at least 5 seconds, and most preferably at least 10 seconds.

[0128] 18. The build volume is: light of the first wavelength in the first series of light patterns as defined by the negative projection; and light at the second wavelength in the second series of light patterns as defined by the positive projection; 10. The method of any one of the preceding clauses, wherein the light sources are simultaneously illuminated in their respective corresponding orientations.

[0129] 19. The method of any one of the preceding clauses, wherein one of the first and second wavelengths is within the UV range of wavelengths from 10 nm to 400 nm, and the other of the wavelengths is within the visible range of wavelengths from 400 nm to 700 nm.

[0130] 20. The method of any one of the preceding clauses, wherein the precursor of the stable radical scavenger is o-Cl-HABI.

[0131] 21. The method according to any one of the preceding clauses, wherein the stable radical scavenger is selected from the group comprising propyl radical and / or tetraethylthiuram disulfide.

[0132] 22. The method according to any one of the preceding clauses, wherein the secondary radical scavenger is selected from the list comprising oxygen and / or 2,2,6,6-tetramethylpiperidinoxyl.

[0133] 23. The method according to any one of the preceding clauses, wherein the monomer is selected from the group comprising TEGDMA and / or bisGMA.

[0134] 24. The method of any one of the preceding clauses, wherein the build volume comprises a photoinitiator selected from the group comprising camphorquinone and / or ethyl 4-dimethylaminobenzoate.

[0135] 25. A system for fabricating a three-dimensional object from a build volume, comprising: A processing unit, calculating a number of primary projections describing the three-dimensional object formed from different orientation angles of the three-dimensional object, the primary projections including positive and negative intensity values; deriving from each primary projection a positive projection corresponding to the positive intensity values ​​and a negative projection corresponding to the negative intensity values; 1. A projection system comprising: light of a first wavelength in a first series of light patterns as defined by said negative projection; and and (preferably simultaneously) projecting light of a second wavelength in a second series of light patterns as defined by said positive projection. the projection system configured for illuminating the build volume at each corresponding orientation; The system comprising:

[0136] 26. A system according to clause 25, wherein the system is configured to carry out a method according to any one of clauses 1 to 24.

[0137] 27. The system includes a build volume, the build volume comprising: A monomer, a precursor to a stable radical scavenger, said stable radical scavenger being inducible by light of said first wavelength and said stable radical scavenger being sensitive to light of said second wavelength; a photosensitive component capable of initiating polymerization of the monomer upon receiving light at the second wavelength; 27. The system of any one of clauses 25-26, comprising:

[0138] 28. The system is configured to illuminate the build volume, and the energy of the light at the first wavelength provided to voxels that do not polymerize is higher than the energy provided to voxels that do polymerize; and / or the energy of the light at the second wavelength provided to voxels that polymerize is higher than the energy provided to voxels that do not polymerize. A system according to any one of clauses 25 to 27.

[0139] 29. A system described in any one of clauses 25 to 28, wherein the first energy distribution is configured to provide an energy contrast between non-polymerizing and polymerizing voxels of at least 1.5, more preferably at least 2, even more preferably at least 5, and most preferably at least 10.

[0140] 30. A system described in any one of clauses 25 to 29, wherein the first energy distribution is configured to provide higher energy to non-polymerizing voxels adjacent to polymerizing voxels than to non-polymerizing voxels adjacent to other non-polymerizing voxels.

[0141] 31. The system of any one of clauses 25 to 30, wherein the primary projection, the negative projection, and / or the positive projection are sinograms.

[0142] 32. A system according to any one of clauses 25 to 31, wherein the positive projections of each corresponding primary projection include the positive pixel values ​​and the negative projections include the negative pixel values.

[0143] 33. A system according to any one of clauses 25 to 32, wherein each primary projection comprises the intensity values ​​of the corresponding positive and negative projections.

[0144] 34. The build volume is: light of the first wavelength in the first series of light patterns as defined by the negative projection; and the second wavelength of light in the second series of light patterns as defined by the positive projection. 34. The system of any one of clauses 25 to 33, wherein the light sources are simultaneously illuminated in the respective corresponding orientations.

Claims

1. 1. A method for producing a three-dimensional object by tomographic vat photopolymerization, comprising: calculating a number of primary projections describing the three-dimensional object formed from different orientation angles of the three-dimensional object, the primary projections including positive and negative intensity values; deriving from each primary projection a positive projection corresponding to said positive intensity values ​​and a negative projection corresponding to said negative intensity values; Providing a build volume, the build volume comprising: A monomer, a precursor to a stable radical scavenger, said stable radical scavenger being inducible by light of a first wavelength and said stable radical scavenger being sensitive to light of a second wavelength; a photosensitive component capable of initiating polymerization of the monomer upon receiving light of the second wavelength; the steps including: light at the first wavelength in a first series of light patterns defined by the negative projection; and light at the second wavelength in a second series of light patterns defined by the positive projection; irradiating the build volume at the different orientation angles; The method comprising:

2. 10. The method of any one of the preceding claims, wherein the build volume is illuminated with light at the first wavelength in the first series of light patterns, and wherein a first energy distribution is provided in the build volume at the respective corresponding orientations, wherein the energy provided to non-polymerized voxels is higher than the energy provided to polymerized voxels, and wherein the polymerized voxels and the non-polymerized voxels are voxels of the build volume that polymerize or remain non-polymerized, respectively, to accurately reproduce the three-dimensional object.

3. 4. The method of claim 3, wherein the first energy distribution is configured to provide an energy contrast between non-polymerizing and polymerizing voxels of at least 1.5, more preferably at least 2, even more preferably at least 5, and most preferably at least 10.

4. 5. The system of claim 3, wherein the first energy distribution is configured to provide a higher energy to non-polymerizing voxels adjacent to polymerizing voxels than to non-polymerizing voxels adjacent to other non-polymerizing voxels.

5. 10. The method according to any of the preceding claims, wherein the primary projection, the negative projection and / or the positive projection are sinograms.

6. 10. A method according to any one of the preceding claims, wherein the positive projections of each corresponding primary projection comprise the positive pixel values ​​and the negative projections comprise the negative pixel values.

7. 10. A method according to any one of the preceding claims, wherein each primary projection comprises the intensity values ​​of the corresponding positive and negative projections.

8. 10. The method of any one of the preceding claims, wherein the stable radical scavenger is inducible by photolysis of the precursor by light of the first wavelength.

9. 10. The method of any one of the preceding claims, wherein the stable radical scavenger absorbs light at the second wavelength.

10. 10. The method of any one of the preceding claims, wherein the concentration of the stable radical scavenger is reduced by providing light at the second wavelength.

11. 10. The method of any one of the preceding claims, wherein the rate of polymerization is a function of the ratio between the intensities of the light at the first wavelength and the light at the second wavelength.

12. 10. The method of any one of the preceding claims, wherein the build volume comprises a secondary radical scavenger that is sensitive to light of the second wavelength.

13. 13. The method of claim 12, wherein the secondary radical scavenger is configured to absorb light at the second wavelength.

14. The method of any one of claims 12 to 13, wherein the secondary radical scavenger is configured to inhibit and / or prevent polymerization of the monomer.

15. 10. The method of any one of the preceding claims, wherein the stable radical scavenger is configured to be stable in the build volume in the absence of light at the second wavelength for at least 1 second, more preferably at least 3 seconds, even more preferably at least 5 seconds, and most preferably at least 10 seconds.

16. the build volume: light at a first wavelength in a first series of light patterns; and light at a second wavelength in a second series of light patterns; 10. A method according to any one of the preceding claims, wherein the light is irradiated simultaneously in each of the corresponding orientations.

17. 10. A method according to any one of the preceding claims, wherein one of the first and second wavelengths is in the UV range, in the wavelength range of 10 nm to 400 nm, and the other of the wavelengths is in the visible range, in the wavelength range of 400 nm to 700 nm.

18. 10. The method of any one of the preceding claims, wherein the precursor of the stable radical scavenger is o-Cl-HABI.

19. 10. The method of any one of the preceding claims, wherein the stable radical scavenger is selected from the group comprising propyl radical and / or tetraethylthiuram disulfide.

20. 10. A method according to any one of the preceding claims, wherein the secondary radical scavenger is selected from the list comprising oxygen and / or 2,2,6,6-tetramethylpiperidinoxyl.

21. 10. The method of any one of the preceding claims, wherein the monomer is selected from the group comprising TEGDMA and / or bisGMA.

22. 10. The method of any one of the preceding claims, wherein the build volume comprises a photoinitiator selected from the group comprising camphorquinone and / or ethyl 4-dimethylaminobenzoate.

23. 1. A system for fabricating a three-dimensional object from a build volume by tomographic vat photopolymerization, comprising: A processing unit, calculating a number of primary projections describing the three-dimensional object from different orientation angles of the three-dimensional object, the primary projections including positive and negative intensity values; deriving from each primary projection a positive projection corresponding to the positive intensity values ​​and a negative projection corresponding to the negative intensity values; 1. A projection system comprising: light of a first wavelength in a first series of light patterns as defined by the negative projection; and the projection system configured for illuminating the build volume with light of a second wavelength in a second series of light patterns at the respective corresponding orientations as defined by the positive projections; The system comprising:

24. The system of claim 23, wherein the system is configured to perform the method of any one of claims 1 to 22.

25. The system includes a build volume, the build volume comprising: A monomer, a precursor to a stable radical scavenger, said stable radical scavenger being inducible by light of said first wavelength and said stable radical scavenger being sensitive to light of said second wavelength; a photosensitive component capable of initiating polymerization of the monomer upon receiving light of the second wavelength; The system according to any one of claims 23 to 24, comprising:

26. the system is configured to illuminate the build volume, and the energy of the light at the first wavelength provided to voxels that do not polymerize is higher than the energy provided to voxels that do polymerize; and / or 26. The system of claim 23, wherein the energy of the light at the second wavelength provided to voxels that polymerize is higher than the energy provided to voxels that do not polymerize.

27. 27. The system of any one of claims 23 to 26, wherein the first energy distribution is configured to provide an energy contrast between non-polymerizing and polymerizing voxels of at least 1.5, more preferably at least 2, even more preferably at least 5, and most preferably at least 10.

28. 28. The system of claim 23, wherein the first energy distribution is configured to provide a higher energy to non-polymerizing voxels adjacent to polymerizing voxels than to non-polymerizing voxels adjacent to other non-polymerizing voxels.

29. The system according to any one of claims 23 to 28, wherein the primary projection, the negative projection and / or the positive projection are sinograms.

30. The system of any one of claims 23 to 29, wherein the positive projections of each corresponding primary projection comprise the positive pixel values ​​and the negative projections comprise the negative pixel values.

31. A system according to any one of claims 23 to 30, wherein each primary projection comprises the intensity values ​​of the corresponding positive and negative projections.

32. the build volume: light of the first wavelength in the first series of light patterns as defined by the negative projection; and with light at the second wavelength in the second series of light patterns as defined by the positive projection; A system according to any one of claims 23 to 31, wherein the light sources are illuminated simultaneously in each of the corresponding orientations.

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