BACKGROUND OF THE INVENTION

1. FIELD OF THE INVENTION

The present invention relates to a method and apparatus to im prove the handling of photoresponsive materials in volumetric printers for the volumetric fabrication of three-dimensional ob jects or articles from photoresponsive materials, by use of sterilizable, precise and transparent resin containers, option ally coupled to a precise holder which is a significant improve ment over prior art. In particular, the present invention is re lated to volumetric manufacturing systems wherein the photore sponsive material demands precise, sterile and user-friendly handling.

2. BACKGROUND ART

The working principle of volumetric printing, for instance volu metric tomographic printing (WO 2019/043529 A1), is different than the traditional layer-by-layer approach (i.e. 3D printing with the formation of one layer over the other) in conventional additive manufacturing (AM).

In conventional additive manufacturing, a three-dimensional ob ject is fabricated either by pointwise scanning of the object volume or in a layer-by-layer fashion. An example is stereo lithography (SLA) (see for example US-5,344,298), where the ob ject is formed one layer at a time by the solidification of a photocurable resist under light irradiation before application of a subsequent layer. The successive layers of the object can be defined for example by scanning a laser beam point-by-point, as suggested in US-5,344,29, or by digital light processing (DLP) technology, as described in US-6,500,378.

On the other hand, in volumetric AM, the entire volume of the article to build is formed at once without any mechanical motion within the build volume.

In volumetric and light-based additive manufacturing techniques, a precise positioning of the photoresponsive material with re spect to the illumination source is required to achieve a cor rect and accurate projection of the light patterns onto the pho toresponsive material, which subsequently lead to the formation of three-dimensional objects.

Furthermore, sterility of the photoresponsive material and the build volume must be ensured in certain applications of AM such as bioprinting, in which sensitive cells are either loaded in the resin during the AM process or onto the formed object. Sur gery, another domain in which the use of AM is growing, also re quires the production of sterile parts since the formed objects will be put within a patient's body. In addition, dentistry and audiology, in which AM is used to create custom three- dimensional objects, also have high cleanliness standards for the objects that will be in contact with the body of patients.

Current AM devices either integrate a static sterilizable print ing chamber (W02019106606A1, US 2015/0217514 Al, US 2017/0128601 A1) or are placed under a laminar flow cabinet to ensure steril ity of the manufacturing process, such technical solutions are expensive and take space.

Finally, a fast and smooth handling of the photoresponsive mate rial by operators of AM devices is required to ensure a fast production of three-dimensional objects. Fast production of ob jects is of paramount importance in applications such as bi oprinting, in which cells survive only a short time outside of their culture medium. In any kind of AM device, a fast and smooth handling of the photoresponsive material and its build volume facilitates the subsequent production steps of the formed object, such as post-processing steps (for instance rinsing and post-curing), which allows to dramatically reduce production costs.

Currently, light-based 3D printers such as DLP or SLA use car tridges to fill a static, open-air photoresponsive material bath (US 2015/0352788 A1, WO 2017/194151 A1), namely a build region. An open-air bath does not protect the photoresponsive material from environmental contaminants. Furthermore, changing the con tent of such bath is not straightforward and demands several manual steps. In addition, in most light-based additive manufac turing devices, the resin is in contact with a support platform and a recoater (EP1769902B1). Moreover, in current volumetric printers, a rotation (WO 2019/043529 A1) or a translation (https://www.linkedin.com/posts/xolo3d_xolography-volumetric - printing-3dprinting-activity-6729069548449878016-24rT, retrieved on 05-11-2020) of the build region occurs, thus a precise posi tioning of the build region is needed to achieve the best print ing resolution of the three-dimensional object.

As a consequence, there is a need for an industrially applicable system to offer a sterile, user-friendly and precise handling of photoresponsive material used to manufacture three-dimensional objects via volumetric additive manufacturing. SUMMARY OF THE INVENTION

The present invention circumvents all of the previous shortcom ings of sterility, positioning and practicability encountered when forming 3D objects with a volumetric approach such as with tomographic back-projection or dual-wavelength photopolymeriza tion.

The invention herein disclosed provides a way to maintain ste rility of the manufacturing throughout the entire volumetric production process. In addition, the present invention provides a way for operators of additive manufacturing devices to posi tion both easily and precisely resin containers into the devic es.

According to a preferred embodiment, the present invention is related to a system for sterile, precise and user-friendly han dling of photoresponsive materials in a volumetric additive man ufacturing device, the system comprising:

- A resin container for providing a photoresponsive materi al to be polymerized;

- A holder for precisely inserting or placing said resin container;

- A volumetric additive manufacturing device;

- A lid or cap that can be inserted into said resin con tainer to make the assembly of said lid or cap and resin container water-tight and air-tight.

In another preferred embodiment, said resin container and said lid or cap can be sterilized.

In another preferred embodiment a cap, or preferably a screw cap is used to make said resin container water-tight and air-tight. Preferably, said resin container, said lid or said cap can be sterilized by sterilization means selected from the group con sisting of steam sterilization, dry heat sterilization, chemical sterilization and radiation sterilization.

Most preferably, said resin container, said lid or said cap are sterilized by steam sterilization.

Preferably, said resin container is transparent to wavelengths of light between 365 nm and 800 nm, and preferably between 390 nm and 600 nm.

Preferably, said resin container has a flat bottom.

In another preferred embodiment, to provide a precise and user- friendly positioning of said resin container into said holder, at least one of the nominal dimensions of said resin container has manufacturing tolerances of preferably -10 pm to -22 pm and most preferably -4 to -12 pm if said nominal dimension of said resin container is below 6 mm, -16 pm to -34 pm and most pref erably -6 to -17 pm if said nominal dimension of said resin con tainer is between 6 and 18 mm, -25 pm to -50 pm and most prefer ably -9 to -25 pm if said nominal dimension of said resin con tainer is between 18 and 50 mm, -36 pm to -71 pm and most pref erably -12 to -34 pm if said nominal dimension of said resin container is between 50 and 120 mm, -50 pm to -96 pm and most preferably -15 to -44 pm if said nominal dimension of said resin container is between 120 and 250 mm; wherein at least one of the nominal dimensions of said holder has manufacturing tolerances of preferably +18 pm to 0 pm and most preferably +12 to 0 pm if said nominal dimension of said holder is below 6 mm, preferably +27 pm to 0 pm and most prefer ably +18 to 0 pm if said nominal dimension of said holder is be- tween 6 mm and 18 mm, preferably +39 pm to 0 pm and most prefer ably +25 to 0 pm if said nominal dimension of said holder is be tween 18 mm and 50 mm, preferably +63 pm to 0 pm and most pref erably +35 to 0 pm if said nominal dimension of said holder is between 50 mm and 120 mm, preferably +72 pm to 0 pm and most preferably +56 to 0 pm if said nominal dimension of said holder is between 120 mm and 250 mm.

In another embodiment, the resin container has two faces that are arranged such that an angle between 60° and 120°, preferably of 90°, is formed between said faces. For instance the resin container can be, but is not limited to, a hollow glass or plas tic cube.

Preferably, said resin container is a hollow cylinder, wherein the wall thickness of said hollow cylinder is larger than, but not limited to, 10% of the outer diameter of said hollow cylin der.

Preferably, said hollow cylindrical resin container has a lack of circularity on its outer diameter lower than 1%, and most preferably lower than 0.2%.

Preferably, said resin container is made of glass, and most preferably of borosilicate glass.

Preferably, said lid or said cap is made of a material selected from the group consisting of inert phenolic plastic, PTFE, poly propylene, polycarbonate and silicone.

Most preferably, said holder is a clamping system comprised of a toolholder, a clamping collet and clamping nut, wherein said toolholder can fit clamping collets of various sizes. Preferably, said clamping system is a DIN6499 clamping system.

Preferably, said holder is a self-centering chuck.

Preferably, said holder can fit different resin container sizes.

Preferably, said holder is fastened onto a part of said volumet ric additive manufacturing device.

Preferably, said resin container and said holder are rotated or translated during the volumetric fabrication of a three- dimensional object by said volumetric additive manufacturing de vice.

In another preferred embodiment, said holder and said resin con tainer are static during the volumetric fabrication of a three- dimensional object by said volumetric additive manufacturing de vice.

Most preferably, said volumetric additive manufacturing device operates by tomographic back-projections.

Preferably, said volumetric additive manufacturing device oper ates by forming the objects with two or more different light beams of different wavelengths.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the present invention will become better understood with regard to the fol lowing non-limiting description and drawings where: Figure 1: is a schematic illustration of a first embodiment of the handling system and the volumetric additive manufacturing device according to the present in vention.

Figure 2: is a schematic illustration of one alternative to a first embodiment of the handling system and the volumetric additive manufacturing device according to the present invention.

Figure 3: is a schematic illustration of one alternative to a first embodiment of the handling system and the volumetric additive manufacturing device according to the present invention, wherein multiple light beams are used to form a three-dimensional object,

Figure 4: is a graph describing inner volume usage of a cy lindrical resin container as a function of its relative thickness when illuminated with a colli mated incident light beam covering the entire con tainer diameter.

Figure 5: is a schematic illustration of another embodiment of the present invention wherein a holder can fit resin containers of different sizes,

Figure 6: is a schematic illustration of another embodiment of the present invention wherein a holder can fit resin containers of different sizes,

Figure 7: is a schematic illustration of an alternative em bodiment of the present invention wherein the vol umetric printing process takes place in a light- sealed enclosure protected by a safety interlock and a door.

Figure 8: is a flowchart describing a method for precise, sterile and user-friendly handling of resin con tainers and photoresponsive materials in volumet ric additive manufacturing. Figure 9: is a picture of an experimental clamping system, holding an autoclavable glass resin container, as implemented onto a volumetric additive manufactur ing device.

Figure 10: is another picture of the experimental clamping system shown in Figure 9, in which the various components of the clamping system are disassem bled.

DETAILED DESCRIPTION

In the figures, same reference numbers denote the same compo nents.

The present invention is related to volumetric additive manufac turing systems, with one or more wavelengths projected through one or more light beams, wherein the photoresponsive materials are handled using resin containers that allow to maintain ste rility of the build region throughout the production process as well as ensuring a precise and easy handling of the resin con tainers by the operators of the volumetric additive manufactur ing devices. According to the present invention, the term "build region" designates the volume formed by the resin container, the lid or cap sealing said resin container and the photoresponsive material provided within said resin container.

In volumetric additive manufacturing, and more generally in ad ditive manufacturing, ensuring sterility of the build region is critical for bioprinting applications as it prevents contamina tion of the fabricated cell-laden three-dimensional objects (that may be be prepared by e.g. pipetting cells within a bi opolymer material by unwanted biologicals or organisms such as, but not limited to, germs, bacteria, viruses, fungi. Keeping the build region sterile also maximizes the viability and reproduci- bility of the volumetric fabrication of cell-laden three- dimensional objects. Sterility of the build region is also crit ical to prevent any risk of infection for other applications of volumetric additive manufacturing in which the formed three- dimensional object is later put in contact with human beings such as in dentistry or audiology.

Furthermore, in light-based additive manufacturing devices, a precise and repeatable positioning of the photoresponsive mate rial with respect to the single or multiple light beams is crit ical to achieve a high manufacturing resolution of the three- dimensional object.

The present invention thus provides a way for operators of addi tive manufacturing devices to position both easily and precisely resin containers and hence the build region into the volumetric devices. Combining the ease of handling of resin containers with their precise positioning into a volumetric additive manufactur ing provides a tool for fast, cost-saving and repeatable volu metric fabrication of three-dimensional objects, thus circum venting shortcomings of state-of-the-art volumetric additive manufacturing devices and leading to a wider range of industrial applications of volumetric additive manufacturing.

According to the present invention, it was found that placing a sterilizable resin container with tight manufacturing tolerances into a holder fitting said resin container can be used for es tablishing a robust, industrially applicable system to print high-resolution three-dimensional object with volumetric addi tive manufacturing.

A first embodiment of the present invention is described in Fig ure 1. In detail, the system according to the first embodiment for sterile, precise and user-friendly handling and positioning of a photoresponsive material 10 in a volumetric additive manu facturing device 11 comprises:

- A resin container 12 for providing the photoresponsive material 10 to be polymerized,

- A holder 13 for precisely inserting or placing said resin container 12 into said volumetric additive manufacturing device 11;

- A lid 14 that can be inserted onto said resin container 12 to make the assembly of said lid 14 and resin contain er 12 water-tight and air-tight.

In another preferred embodiment, a cap 14, or preferably a screw cap is used instead of a lid 14 to make said resin container 12 water-tight and air-tight. Said cap or screw cap can be steri lized.

In another alternative of said first embodiment, said resin con tainer 12 and said lid or cap 14 can be sterilized.

In a preferred embodiment, said resin container 12, said lid or said cap 14 are sterilized before use by sterilization means se lected from the group consisting of steam sterilization, dry heat sterilization, chemical sterilization and radiation steri lization .

Most preferably, said resin container 12, said lid or said cap 14 are sterilized by steam sterilization. Autoclaves are stand ard laboratory equipment in biology facilities, thus making a steam sterilized resin container 12 and lid 14 readily applica ble to the life sciences industry. In another preferred embodiment, said resin container 12 is transparent to wavelengths of light between 365 nm and 800 nm, and preferably between 390 nm and 600 nm, so that the photore- sponsive material 10 it contains can be irradiated with one or more beams of light 15 of one or more wavelengths to selectively trigger photopolymerization of said photoresponsive material 12. In addition, in a preferred embodiment said volumetric additive manufacturing device 11 is setting into rotation or translation said holder 13, thereby setting said resin container 12, said lid or cap 14 and said photoresponsive material 10 into rotation while concurrently irradiating said photoresponsive material 10 with one or more beams of light 15 of one or more wavelengths.

In another preferred embodiment, said resin container 12, said lid or cap 14 and said photoresponsive material 12 remain static during the volumetric printing of a three-dimensional object.

In a preferred embodiment, said resin container 12 has a flat bottom. Such feature is advantageous to prevent any photorespon sive material 10 from not being properly irradiated by said light beams 15 during the volumetric additive manufacturing pro cess, thus saving photoresponsive material 10, thereby saving cost for the users of the volumetric device since the photore sponsive material 10 might contain expensive chemicals or cells.

In a preferred embodiment, at least one of the nominal dimen sions 16 of said resin container 12 has manufacturing tolerances of preferably -10 pm to -22 pm and most preferably -4 to -12 pm if said nominal dimension 16 is below 6 mm, -16 pm to -34 pm and most preferably -6 to -17 pm if said nominal dimension 16 of said resin container 12 is between 6 and 18 mm, -25 pm to -50 pm and most preferably -9 to -25 pm if said nominal dimension 16 of said resin container 12 is between 18 and 50 mm, -36 pm to -71 mpi and most preferably -12 to -34 m if said dimension 16 of said resin container 12 is between 50 and 120 mm, -50 pm to -96 pm and most preferably -15 to -44 pm if said nominal dimension

16 of said resin container 12 is between 120 and 250 mm; wherein at least one of the nominal dimensions 17 of said holder 13 has manufacturing tolerances of preferably +18 pm to 0 pm and most preferably +12 to 0 pm if said nominal dimension 17 of said holder 13 is below 6 mm, preferably +27 pm to 0 pm and most preferably +18 to 0 pm if said nominal dimension 17 of said holder 13 is between 6 mm and 18 mm, preferably +39 pm to 0 pm and most preferably +25 to 0 pm if said nominal dimension 17 of said holder 13 is between 18 mm and 50 mm, preferably +63 pm to

0 pm and most preferably +35 to 0 pm if said nominal dimension

17 of said holder 13 is between 50 mm and 120 mm, preferably +72 pm to 0 pm and most preferably +56 to 0 pm if said nominal di mension 17 of said holder 13 is between 120 mm and 250 mm.

It was found that said manufacturing tolerances of both said resin container 12 and said holder 13 allow for an effortless precise positioning and removal of said resin container 12 into said holder 13, thus making the handling of photoresponsive ma terial 10 in volumetric additive manufacturing devices 14 fast er, more precise and more user-friendly for operators.

Figure 2 shows another preferred embodiment of the present in vention, in which said resin container 12 is inserted within a hollow holder 13 fastened onto a part of a volumetric additive manufacturing device 11, thus allowing the bottom part of said resin container 12 to be irradiated with one or more light beams 15 of one or more wavelengths.

In a preferred embodiment, said volumetric additive manufactur ing device 11 operates by tomographic back-projections as fur- ther described in Loterie, D., Delrot, P. & Moser, C. High- resolution tomographic volumetric additive manufacturing. Nat Commun 11 , 852 (2020). https://doi.org/10.1038/s41467-020-14630-

4 or in WO 2019/043529 A1.

Figure 3 describes another embodiment of the present invention, wherein said volumetric additive manufacturing device 11 oper ates by forming three-dimensional objects via the concurrent ir radiation of said photoresponsive material 10 with at least two different light beams 30 and 31 of at least two different wave lengths. For instance, but not limited to, said photoresponsive material 10 can be crosslinked only upon concurrent irradiation with two light beams 30 and 31 of different wavelengths, and not crosslinked when a single beam of light of said first wavelength 30 or said second wavelength 31 irradiates said photoresponsive material 10. In another non-limiting example, said photorespon sive material 10 is photopolymerized by the irradiation of a light beam of said first wavelength 30 whereas its crosslinking process is photo-inhibited by the irradiation of a light beam of said second wavelength 31.

In a preferred embodiment of the present invention, as described in Figure 2 and 3, said resin container 12 is a hollow cylinder with a flat bottom, wherein the wall thickness 18 of said hollow cylinder is larger than, but not limited to, 10% of the outer diameter 16 of said hollow cylinder. In this embodiment the out er diameter 16 of said resin container 12 is the dimension 16 over which manufacturing tolerances apply. Similarly, in this embodiment, the part of said holder 13 fitting said resin con tainer 12 is a hollow cylinder whose inner diameter 17 is the dimension 17 over which manufacturing tolerances apply. This em bodiment is advantageous as it allows to maximize the volume of photoresponsive material irradiated by said light beam 15 (or light beams 30, 31), thus saving potentially expensive photore- sponsive material 10. This advantage is better understood using the graph in Figure 4, which shows the volume usage of a cylin drical resin container filled with a resin of a selected refrac tive index n _res in as a function of the relative container thick ness of refractive index n _giass =1.47. The graph in Figure 4 is better understood by picturing a collimated beam of light inci dent onto said cylindrical resin container 12, said beam of light is first refracted by a convex air-glass interface and then refracted by a second glass-resin interface to irradiate only part of the photoresponsive material of refractive index n _resin 10 provided into said resin container 12 of refractive in dex n _giass =1.47. Preferably, said hollow cylindrical resin con tainer 12 further has a lack of circularity on its outer diame ter lower than 1% on the entire cylinder, and most preferably lower than 0.2% on the entire cylinder. A 0.2% lack of circular ity limits a potential nutation of said resin container 12 and said photoresponsive material 10 to about 0.15° around the cyl inder revolution axis, which only degrades the manufacturing resolution of 12.5 pm during a volumetric tomographic fabrica tion of a three-dimensional object.

In a preferred embodiment, said resin container 12 is made of glass, and most preferably of borosilicate glass. These materi als can withstand steam sterilization, thus providing a sterile means for handling a photoresponsive material 10.

In a preferred embodiment, said lid or said cap 14 are made of a material selected from the group consisting of inert phenolic plastic, PTFE, polypropylene, polycarbonate and silicone. These materials can withstand steam sterilization, thus providing a sterile means for a sealing of said resin containers. In another embodiment of the present invention, said resin con tainer 12 has at least two faces that are arranged such that an angle between 60° and 120°, preferably of 90°, is formed between said faces. For instance the resin container 12 can be, but is not limited to, a hollow glass or plastic cube. This embodiment is advantageous in volumetric additive manufacturing devices 11 wherein multiple beams of light are irradiating said resin con tainer and said photoresponsive material from various direc tions, as described in Figure 3. In this embodiment, the bottom width and length of said resin container 12 can be the dimen sions 16 (not shown here) over which manufacturing tolerances apply. Similarly, in this embodiment, said holder 13 can be a rectangular groove whose width and length fit said resin con tainer 12 bottom width and length up to a manufacturing toler ance 17 (not shown here).

Figures 5 and 6 describe another embodiment of the present in vention wherein said holder 13 can fit resin containers 12 of different sizes.

The schematic illustration of Fig. 7 and the flowchart of Figure 8 describe a method of the present invention for sterile, pre cise and user-friendly handling of photoresponsive material 10 in a volumetric additive manufacturing device 11. The method comprises the steps of:

- Opening a door 70 of said volumetric additive manufacturing device 11, thus activating a safety interlock and prevent ing a light beam 15 from being emitted towards an operator (step 81). What is meant by safety interlock according to the present invention is a device or means that places said volumetric additive manufacturing device into a zero, or substantially reduced, danger-mode upon intent to access.

- Providing in a resin container 12 sealed with a lid or cap 14, of an apparatus for volumetric additive manufacturing 11, a photoresponsive material 10 (step 82). Said resin container 12 and lid or cap 14 are preferably sterilized beforehand .

Inserting said precise resin container 12 into said holder 13 (step 83).

- Closing said door 70, thus activating said safety interlock and allowing said light beam 15 to be emitted towards said resin container 12 and said photoresponsive material 10 (step 84).

- Fabricating via volumetric additive manufacturing process a three-dimensional object 71 (step 85).

- Once the volumetric fabrication process is complete, open ing said door 70, thus activating said safety interlock and preventing said light beam 15 from being emitted towards an operator (step 86).

- Collecting said resin container 12, said lid or cap 14 and said photoresponsive material 10 and formed three- dimensional object 71 from said holder 13 (step 87), thus allowing for a new volumetric manufacturing process by re peating steps 82 to 87.

- Collecting said three-dimensional object 71 from said pho toresponsive material 10 (step 88).

In a preferred embodiment shown in Fig. 9, said holder 13 is a clamping system comprised of a toolholder 90, a clamping collet 91 and a clamping nut 92, wherein said toolholder 90 can fit clamping collets 91 of various sizes. Clamping systems are for instance used in drilling systems to precisely center drilling bits onto a rotation axis. In the present invention, a clamping system offers a precise, fast and user-friendly positioning of a cylindrical resin container 12 onto a rotation axis of a volu metric additive manufacturing device 11. In this way, said pho- toresponsive material 10 contained in said resin container is handled precisely and without difficulty by operators, thus al lowing for both fast and high-resolution volumetric additive manufacturing of three-dimensional objects.

In another preferred embodiment, said clamping system is a DIN6499 clamping system. As described in the experimental setup pictured in Figures 9 and 10, an embodiment with a DIN6499 clamping system offers the advantage to precisely center a cy lindrical resin container 12 with its cap 14 (or lid 14) and the contained photoresponsive material 10 onto a holder 13 that is comprised of a toolholder 90, a clamping collet 91 and a clamp ing nut 92, wherein the toolholder is fastened onto a volumetric additive manufacturing device 11. The clamping system shown in Figures 9 and 10 offers an experimental centering precision of 10 pm of cylindrical autoclavable glass resin containers 11. It can also fit resin containers that are manufactured with a loose tolerance, thus offering a precise positioning of off-the-shelf glass resin containers 11 such as the autoclavable cylindrical glass resin containers showed Figures 9 and 10. A non-limiting experimental clamping system as shown in Figures 9 and 10, can precisely center cylindrical autoclavable glass resin containers of nominal diameter of 18 mm with a 150 micrometer diameter de viation over a batch of 40 resin containers (SciLabware, 1636/32MP) . A non-limiting example of components composing a clamping system, as shown in Figures 9 and 10, can be an ER clamping nut 92 Hi-Q/ERAX 32 from Regofix AG, a norm 32 clamping collet 91 ER (ER 32 DM D 18.0-17.5 from Regofix AG) and a cus tom-made toolholder 90. Interestingly, a norm 32 toolholder, like the one depicted in Figures 9 and 10, can fit every norm 32 clamping collet, thus an operator can easily change the clamping collet to fit resin containers of a different size. Then, the operator insert a resin container filled with a photoresponsive material into the clamping collet, tightens the clamping nut to fasten the resin container onto a precise and centered position.

In another preferred embodiment, said holder is a self-centering chuck. A self-centering chuck is also useful to precisely center a cylindrical resin container onto a rotation axis of a volumet ric additive manufacturing device 11.