METAL FILTER WITH MICROSTRUCTURED ARCHITECTURE WITH CONTROLLED POROSITY AND METHOD FOR MANUFACTURING SUCH A FILTER

Description

Technical field of the invention

[0001] The invention relates to metal filters with microstructured architecture.

[0002] An architecture is said to be microstructured to the extent that the main elements forming said architecture have micrometric dimensions, that is to say dimensions less than 1000 µm, in at least two spatial dimensions.

[0003] Such metal filters conventionally make it possible to filter a fluid, liquid or gaseous, while being sufficiently permeable to allow at least part of said fluid to circulate.

[0004] The invention also relates to methods of manufacturing metal filters with microstructured architecture.

[0005] The invention finds its application in systems requiring the filtration of a fluid. For example, the invention can be used in a sanitary filtration system such as a sanitary filter or a sanitary mask. For example, the invention can also be used in gas diffusion plates. The invention can also be used in air pollution control systems or radioactive waste filtration systems. WO 2018 / 005315 A1, US 2017 / 239726 A1 and US 2020 / 306674 A1 represent the relevant state of the art. Technical background

[0006] Since the spread of COVID-19, sanitary, surgical, or FFP1 or FFP2 standard masks have become everyday consumer products for billions of people around the world. Since these masks are inherently ephemeral and non-reusable, they currently represent a large source of potentially soiled waste. Washing surgical masks is not recommended by health authorities due to the loss of effectiveness that occurs when moisture builds up during use. Furthermore, even if washing these types of masks were considered, it would generate other environmental disadvantages, as evidenced by the analysis of wastewater, for example, carried out in the city of Paris. This analysis revealed the presence of traces of COVID-19 in these waters.Thus, the problem would be shifted since it would consist of managing the environmental consequences of washing millions of surgical masks.

[0007] One possible option to address these issues is to use sanitary masks with a longer lifespan.

[0008] In this respect, metal filters manufactured by powder sintering are already known. However, in addition to the complexity of the sintering processes, they are also very expensive. In addition, the resulting metal filters can only be produced in limited shapes and have heterogeneous porosity. Due to this heterogeneous porosity, it is more difficult to achieve low pressure drop, i.e., a low limitation of the speed at which the fluid passes through the filter, and at the same time efficient filtration. If we consider maximum filtration of small particles, i.e., grade 0.1 filtration in which more than 99% of particles larger than 100 nm are filtered, then the pressure drop is high. A compromise must therefore be found.

[0009] Homogeneous porosity filters with microstructured architecture manufactured by 3D printing have also been proposed ( Figure 1). However, such filters do not fully address the problem of pressure drop when filtration efficiency increases. Indeed, while it is easier to find a compromise between pressure drop and filtration efficiency, the pressure drop nevertheless remains high. Summary of the invention

[0010] The invention makes it possible to overcome the aforementioned drawbacks and proposes for this purpose a metallic filter comprising a microstructured architecture defined in a three-dimensional space having orthogonal axes X, Y, Z, the microstructured architecture comprising: a metal network formed from a plurality of longitudinal connecting strands, namely extending along a longitudinal axis direction (X axis), and a pore network formed from a plurality of longitudinal interstices located along longitudinal connecting strands, each longitudinal interstice corresponding to a subset of pores of said pore network, subset of pores for which the pores are aligned along the longitudinal axis X, the longitudinal interstices thus defining an axis of anisotropy of the microstructured architecture.

[0011] Thus, in practice, within the pore network, the pores are distributed so that an anisotropy of the microstructured architecture is obtained in the direction of the longitudinal axis X, with respect to the two other directions Y, Z.

[0012] The pores of a given gap are generally parallel to the pores of another gap and so on for all the gaps. The gaps in the pore network are therefore generally parallel to each other. Porosity is therefore controlled within the microstructured architecture. The metal filter according to the invention thus allows for low pressure drop while having high filtration efficiency.

[0013] According to different characteristics of the invention which may be taken together or separately: the pores have the same size; the porosity is between 10% and 70%; the connecting strands have a width between 10 µm and 500 µm, and the longitudinal interstices have a width between 1 µm and 100 µm; the metal filter has a thickness defined along the longitudinal axis between 250 µm and 300 mm; the metal network is made of a metal chosen from aluminum, nickel, cobalt, iron, copper, palladium, titanium, tungsten, silver or platinum, or an alloy of materials such as stainless steel, a metal alloy or a metal oxide; the metal filter further comprises two opposite main faces delimiting the microstructured architecture, said longitudinal faces being respectively covered with a virucidal or bactericidal thin layer.

[0014] The invention also relates to a functional part comprising a metal filter according to the invention and a peripheral border of zero porosity surrounding the microstructured architecture of the metal filter.

[0015] The invention further relates to a method for additively manufacturing a metal filter as described above, said additive manufacturing method comprising the following steps: depositing a layer of metal powder of a given material or an alloy of materials on a support, said layer of metal powder having a thickness of between 1 µm and 200 µm; performing localized laser melting of the metal grains of the powder, at a temperature higher than the melting temperature of the material or alloy of materials forming said metal powder deposited during the step of depositing the layer of metal powder and executing a computer program so as to create a predetermined pattern of a microstructured architecture defined in a three-dimensional space having orthogonal axes X, Y, Z, the microstructured architecture comprising: a metal network formed of a plurality of longitudinal connecting strands, namely extending in a direction of longitudinal axis X, and a network of pores formed of a plurality of longitudinal interstices located along longitudinal connecting strands,each longitudinal interstice corresponding to a subset of pores of said pore network, subset of pores for which the pores are aligned along the longitudinal axis X, the longitudinal interstices thus defining an axis of anisotropy of the microstructured architecture.

[0016] The method according to the invention may comprise at least one of the following steps, taken alone or in combination: the support is heated to a temperature strictly higher than ambient temperature and lower than or equal to 250°C; the support is heated to a temperature between 180°C and 220°C, advantageously between 190°C and 210°C; a volume energy density of the laser beam during the localized laser melting step corresponds to 30% to 90% of the value of the volume energy density of the laser beam necessary to form a non-porous block from said metal powder; the deposition step and the localized melting step are successively repeated. Brief description of the figures

[0017] Other objects and characteristics of the invention will appear more clearly in the following description, made with reference to the appended figures, in which: There figure 1 is a schematic overall perspective view of a metal filter according to an exemplary embodiment of the present invention; The figure 2is a schematic sectional view of a metal filter along a direction vector plane X And Y illustrating the microstructured architecture of a metal filter according to an embodiment of the present invention; The figure 3 is a schematic sectional view of a metal filter along a direction vector plane Y And Z illustrating the microstructured architecture of a metal filter according to an embodiment of the present invention; The figure 4 is an image of a microstructured architecture according to the prior art; The Figure 5 is an image of a microstructured architecture according to the invention. Detailed description of the invention

[0018] In reference to the figure 1 , the invention relates to a metallic filter 1 comprising a microstructured architecture defined in a three-dimensional space having orthogonal axes X, Y and Z.

[0019] The metal filter 1 allows the filtration of a liquid or gaseous fluid F. For example, if the metal filter is intended to be used as a sanitary mask, the fluid is the air exhaled and inhaled by an individual. This air can therefore be loaded with droplets. The metal filter 1 can have any shape; it can thus be parallelepiped as illustrated in the figure 1 but also prismatic or polyhedral. The shape will be adapted according to the need.

[0020] Whatever the geometric shape chosen, it will be considered in the remainder of this description that the fluid F moves in the direction of the thickness e of the metal filter 1. The thickness e of the metal filter corresponds to the smallest dimension of said metal filter. In this case, it is therefore the distance between a first main face 3 and a second main face 4 of the metal filter 1. In the embodiment illustrated in the figure 1, the thickness e is therefore defined in a longitudinal axis direction, this axis (X axis) being orthogonal to the main faces 3,4. Thus, when the fluid F moves in the direction of the thickness e of the metal filter 1, this means that it first passes through the first main face 3 of the metal filter, then enters the metal filter 1 and finally passes through the second main face 4 of said metal filter in this order. It should be noted that this does not define the actual trajectory or the dynamics of movement of the fluid F outside or inside the metal filter 1, but only the overall movement.

[0021] The metal filter 1 comprises a microstructured architecture 2. The architecture 2 is said to be microstructured insofar as the main elements forming said architecture have micrometric dimensions, that is to say dimensions less than 1000 µm, in at least two spatial dimensions. The main elements of the microstructured architecture are described below. First of all, let us specify that the microstructured architecture 2 extends from the first main face 3 to the second main face 4. It can also be emphasized that the metal filter can integrate a functional part comprising a peripheral border 32 surrounding the microstructured architecture 2. In other words, the functional part comprises the metal filter 1 surrounded by the peripheral border. The peripheral border 32 has zero porosity (in other words, equal to 0), that is to say that it is non-porous.This makes it possible to strengthen the mechanical strength of the metal filter 1 as a whole and to facilitate its integration into a manufacturing process for the functional part.

[0022] In reference to the figure 2 , the microstructured architecture 2 comprises a metal network 10 formed from a plurality of connecting strands 12 extending in a longitudinal axis direction (X axis). The section plane of the microstructured architecture 2 illustrated in figure 2 is orthogonal to the principal faces 3,4 of the metallic filter 1. This plane is a subspace of the previously introduced X, Y, Z space of direction vectors X And Y . It corresponds, for example, to the surface E in perspective which is delimited by dotted lines on the figure 1 . The sectional plan of the figure 2 is also illustrated by a dotted line E on the figure 3(it is normal on the page). Each connecting strand 12 is presented as an elongated structure having the appearance of a filament whose contours are not linear. As will be seen in more detail below, the connecting strands 12 are formed by localized laser fusion of the grains of a metal powder. The connecting strands 12 are of micrometric dimensions in at least two directions of space which implies, in practice, that they have substantially the shape of a disc of micrometric diameter in a plane of section transverse to their length.

[0023] The metal network 12 can advantageously comprise material bridges 14 ensuring the cohesion of the metal strands 12. The material bridges 14 allow the metal network 10 to form a solid assembly.

[0024] The microstructured architecture 2 also comprises a network 20 of pores 24 delimiting the connecting strands 12. The pores 24 have the usual meaning given to them in the state of the art and correspond to the empty spaces left within a porous material. It is recalled that the figure 2 is a schematic illustration of the microstructured architecture 2. Thus, contrary to what is illustrated, the pores 24 can have differentiated shapes with respect to each other even if, as will be explained below, their distribution and size are controlled. Indeed, the pores 24 also result from the localized fusion of the grains of the metal powder, except that they are the indirect consequence thereof.

[0025] The network 20 of pores 24 comprises a plurality of longitudinal interstices 22 (X axis) corresponding to subsets of pores 24. More precisely, these are subsets of pores 24 located along connecting strands 12. Incidentally, each longitudinal interstice 22 corresponds to a subset of pores 24 located between connecting strands 12 located side by side without being in direct contact with each other. If each pore 24, taken in isolation, has micrometric dimensions, the longitudinal interstices 22 have a dimension significantly larger than the other dimensions which gives them an elongated shape.

[0026] According to the invention, the longitudinal interstices 22 are all oriented in the same direction X, which is not the case in the other directions Y, Z, hence an anisotropy of the microstructured architecture. Incidentally, the longitudinal interstices 22 are parallel to each other in this longitudinal direction. This anisotropy is illustrated schematically in the figure 2 which shows the distribution of pores in the direction vector plane X And Y The longitudinal axis X may be called the anisotropy axis in the remainder of this description.

[0027] Of course, the direction of each longitudinal gap 22, considered in isolation, corresponds to the straight line parallel to the longitudinal axis passing through the centers of the pores 24 forming this longitudinal gap 22. The direction of a longitudinal gap 22 therefore necessarily depends on the arrangement of the subset of pores 24 forming it. It should nevertheless be specified that the pores 24 of a longitudinal gap 22 do not necessarily always respect a perfect alignment. This is for example illustrated for the longitudinal gap 22 framed in dotted lines on the right in the figure 2 The direction of the longitudinal gap 22 therefore corresponds to the direction line defined by the longitudinal axis X passing through a midpoint (x; y) whose ordinate y is the median of the ordinates of the centers of the pores 24.

[0028] This anisotropy makes it possible to obtain a microstructured architecture 2 having therefore a controlled porosity, the porosity being controlled by a controlled distribution of the pores 24 in longitudinal interstices 22 as defined above. When the fluid F passes through the metal filter 1, it is constrained by the microstructuring of the microstructured architecture 2 while having a circulation facilitated by the presence of the longitudinal interstices 22. The invention therefore makes it possible to obtain a high filtration efficiency while having a low pressure drop. The circulation of the fluid F within the microstructured architecture is thus improved.

[0029] Advantageously, the pores 24 of the pore network 20 have substantially the same size. Thus, in addition to the distribution of the pores 24, the porosity of the microstructured architecture 2 can also be controlled by means of a homogeneous pore size. It will be easily understood that, to the extent that the longitudinal interstices 22 define an anisotropy of the microstructured architecture along the longitudinal axis direction (X axis) and when the pores 24 all have the same size in the microstructured architecture 2, it is possible to very precisely control the filtration efficiency and at the same time the pressure drop, depending on the intended application, by varying only the size of the pores 24. It is nevertheless recalled that the pores 24 are of micrometric size.

[0030] There figure 3illustrates the microstructured architecture 2 according to a plane parallel to the main faces 3, 4 of the metallic filter 1. This plane is a subspace of the X, Y, Z space, previously introduced, of direction vectors Y And Z . As it appears better in this figure, each interstice 22, of which we only see one pore 24 on the figure 3 , is generally surrounded by four connecting strands 12, two by two located side by side. The same applies to each connecting strand 12 which is generally surrounded by four longitudinal interstices 22 according to the embodiment considered. However, the distribution of the pores 24 as illustrated in the figure 3 is not mandatory and other distributions may be considered subject to the following.

[0031] Within the pore network, the pores 24 are distributed so that anisotropy is obtained in the longitudinal axis direction X, with respect to the other two directions Y, Z. The distribution of the pores 24 promotes the movement of the fluid F through the longitudinal interstices 22 which are therefore configured to facilitate the movement of the fluid F with respect to the other directions.

[0032] Preferably, the porosity (or porosity rate) of the microstructured architecture 2 is between 10% and 70%. This makes it possible to obtain a permeability of between 11 and 200 lm -2< .s -1< for a pressure drop between the main faces 3, 4 of approximately 100 Pascals. The aforementioned porosity range is particularly suitable for sanitary filtration masks such as those described in the preamble to the present description. That being said, the higher the porosity, the lower the pressure drop and, vice versa. Other applications may be envisaged within the framework of the present invention.

[0033] Preferably, the connecting strands 12 have a width of between 10 µm and 500 µm while the longitudinal interstices 22 have a width of between 1 µm and 100 µm. In the attached diagrams, the width is taken along the Y axis, orthogonal to the longitudinal axis. This is not the largest dimension of the connecting strands 12 and the longitudinal interstices 22. Such parameters make it possible to obtain a microstructuring of the architecture 2 appropriate for the desired type of filtration.

[0034] Particularly advantageously, the thickness e of the metal filter 1, i.e. the smallest dimension of the metal filter 1, extends along the anisotropy axis X. When the metal filter 1 has this configuration, the fluid F moves in a preferential direction which is also the smallest dimension of the metal filter. There is therefore less friction within the microstructured architecture 2, which means that the dynamics of movement of the fluid F within the microstructure are mainly guided by the anisotropic distribution of the longitudinal interstices 22 and the size of the pores 24. The pressure drop experienced by the fluid F when passing through the metal filter 1 and the filtration efficiency are even better controlled.

[0035] The thickness e of the metal filter 1 is preferably between 250 µm and 300 mm. In practice, it will depend essentially on the application considered. For a sanitary filtration mask, a thickness of between 400 µm and 2 mm will be chosen, for example. If the metal filter 1 according to the invention is used in the manufacture of functional parts such as high-efficiency air filters generally used in an air treatment device or a pollution control device, its thickness may be much greater.

[0036] The metal network 10 is made of a metal in pure form, or in the form of an alloy of metals or metal oxides, the metal(s) being chosen from aluminum, stainless steel, nickel, cobalt, iron, copper, palladium, titanium, tungsten, silver, platinum. These metals are not only in solid form at room temperature, but they are also good candidates for microstructuring by laser melting. In addition, they have good mechanical properties and are suitable for receiving a deposition of thin layers.

[0037] In this regard, the metal filter 1 may further comprise a virucidal or bactericidal thin layer covering the main faces 3, 4 of the metal filter 1. Depending on the deposition technique envisaged, this thin layer may extend over a certain pore depth from the main faces 3, 4. This virucidal or bactericidal thin layer is a barrier layer for infectious microorganisms such as bacteria and viruses. For example, such a thin layer may be made of a pure metal, a metal alloy or metal oxides such as titanium, copper, zinc, nickel or silver.

[0038] Other practical features may be added to the metal filter 1 to enhance its properties by means of this thin layer or an additional thin layer. For example, the thin layer may make the microstructured architecture 2 hydrophilic on one of the main faces 3, 4 while it will be hydrophobic on the other of the main faces 3, 4. This may in particular make it possible to control the humidity of a functional part equipped with such a metal filter.

[0039] The invention also relates to a method for additive manufacturing of a metal filter 1 as previously described.

[0040] A first step 110 of the additive manufacturing method according to the invention consists of depositing at least one layer of metal powder of a given material, or of an alloy of materials, on a support. Each layer of metal powder has a thickness which may be between 1 µm and 200 µm. Advantageously, each layer of powder has a thickness of between 1 µm and 150 µm, between 1 µm and 120 µm or even more precisely between 10 µm and 120 µm. Typically, a layer with a thickness of approximately 30 µm, 50 µm or 100 µm may be used.

[0041] The support can be heated to a temperature strictly above room temperature and less than or equal to 250°C. Advantageously, the support can more precisely be heated to a temperature between 180°C and 220°C, and even more advantageously between 190°C and 210°C. This increases adhesion to the support and structurally stabilizes the layer thus formed. The finished product is therefore less fragile.

[0042] A second step of the additive manufacturing method according to the invention consists of carrying out a localized laser melting of the metal grains of the powder, at a temperature higher than the melting temperature of the given material, or of the given alloy of materials, forming said metal powder deposited during step 110. The laser melting carried out under these conditions allows a localized supply of energy under the action of a laser beam which allows the grains of the powder to be melted in a localized manner.

[0043] This localized, and therefore selective, fusion is carried out by means of a computer program which makes it possible to create a predetermined pattern M of the microstructured architecture 2 from a pre-established computer database.

[0044] There Figure 5 is an image of a microstructured architecture 2 according to the invention. The anisotropy of the longitudinal interstices 22 which are all parallel to each other in a given direction can be distinguished. On the contrary, in a microstructured architecture obtained by a method according to the prior art as illustrated in the figure 4 , the pores are distributed according to an isotropic distribution.

[0045] It may be necessary to repeat steps 110 and 120 several times to form connecting strands 12 of the appropriate dimensions.

[0046] At each laser melting step, the trajectory adopted by the laser beam comprises displacement vectors where the displacement vectors are spatially offset two by two according to an offset value and the porosity rate of the pores within the metal filter 1 is adjusted, for a given laser beam power and a given layer thickness, by adapting said offset value, the porosity rate increasing as the offset value increases. The offset value HD, this value having an impact on the manufactured metal filter 1.

[0047] In this respect, the volume energy density of the laser beam at each pass during the laser melting step, at the level of the microstructured architecture 2, is between 30% and 90% of a volume energy density value of the laser beam necessary to obtain a non-porous block from said metal powder. To adapt this volume energy density, it is possible, for example, to set a laser power by acting on the other parameters: HD, V and e C. Reference may be made to the mathematical formula (F1) below which defines these parameters.

[0048] The computer program, using the database, controls the movement of the laser beam relative to the metal powder deposited during step 110, according to at least one of the parameters chosen from: a relative trajectory between the laser beam and the previously deposited metallic material powder, a displacement speed “V” corresponding to a relative speed between the laser beam and the previously deposited metallic material powder, a power of the laser beam “P”, a volume energy density of the laser beam “E”.

[0049] The volumetric energy density E of the laser beam, expressed in J / mm 3< , is defined by the following mathematical formula (F1): E = P V . HD . e C

[0050] Where: P is the laser beam power, expressed in Watt (W), V is the laser beam displacement speed, expressed in mm / s, HD is a shift value between two adjacent laser beam application vectors, expressed in mm, and e C is the layer thickness, expressed in mm, E is the volume energy density of the laser beam.

[0051] This three-dimensional additive manufacturing solution by depositing successive layers then melting by laser according to pre-established and computer-controlled trajectories, is known under the technology called "SLM" which is the acronym for "Selective Laser Melting" according to Anglo-Saxon terminology, which can therefore be translated, as we will have understood, by "localized fusion by laser".

[0052] In an SLM additive method, operations are carried out in an environment under neutral gas (usually argon), where a thin layer of metal powder is spread on a metal substrate. The laser beam then provides the powder with the energy needed to melt it and adhere to the lower layers selectively depending on the geometry of the part. The repetition of these actions allows the manufacture of metal parts with complex geometry in three dimensions. To do this, it is necessary to prepare the "computer-aided control" type file of the part by cutting it into slices of the desired manufacturing layer thickness to create a set of two-dimensional plans. It is also necessary to create support supports and assign it a set of parameters that will define the trajectories of the laser beam on the powder.All of these operations produce a file which is transmitted and controls the manufacturing machine.

[0053] Other methods of additive manufacturing of materials could be considered, such as the technology called "SLS" which is the acronym for "Selective Laser Sintering" in English terminology which can be translated as "localized laser sintering". There are other techniques.

[0054] Finally, it is possible to provide, within the framework of the invention, a step of depositing a thin layer interposed between a step 120 of laser melting and the step 110 of depositing a layer of metal powder if a functionality requires it. Other modifications of the method can be provided in order to functionalize the successive layers thus formed. Practical implementation of the method according to the invention

[0055] According to a particular implementation example, the method comprises the following steps: during step 110 a metal powder with a thickness equal to 50 µm is deposited on the support; step 120 is implemented with a laser beam with a power equal to 275 W, an offset value HD set at 0.1 mm or 0.12 mm and a lower threshold for the speed of movement of the laser beam being (relative to the powder layer) between 1500 and 6000 mm / s.

[0056] In this implementation example, it was possible to highlight an increase in the porosity rate within the microstructured architecture, above a lower threshold of displacement speed, as the displacement speed increased.

[0057] It was also demonstrated that the porosity rate of the pores within the microstructured architecture 2 can be adjusted by adapting the volume energy density of the laser beam. Indeed, the porosity rate increases, below a higher volume energy density threshold, as the volume energy density decreases.

[0058] In this regard, according to a particular implementation example, the method comprises the following steps: during step 110 a metal powder with a thickness equal to 50 µm is deposited on the support; step 120 is implemented with a laser beam with a power equal to 275 W, an upper threshold of the volume energy density of the laser beam can vary between 7 J / mm 3< and 80 J / mm 3< and more specifically in this example between 7 J / mm 3< and 30 J / mm 3< (in particular depending on the offset value HD: 0.1 mm or 0.12 mm).

[0059] Tests were carried out using a 316L stainless steel powder marketed by SLM Solutions ®< . These are the results shown on the Figures 4 and 5 The metallic material can also be aluminum or an aluminum alloy, which have the advantage of being light and thermally stable at disinfection temperatures.

Claims

1. A metallic filter (1) comprising a microstructured architecture (2) defined in a three-dimensional space having orthogonal axes (X, Y, Z), the microstructured architecture (2) comprising a metallic network (10) formed of a plurality of longitudinal connecting strands (12), namely extending along a longitudinal axis (X) direction, the metallic filter being characterised in that: - the microstructured architecture (2) comprises a network (20) of pores formed of a plurality of longitudinal interstices (22) located along connecting strands (12), each longitudinal interstice corresponding to a subset of pores (24) of said network (20) of pores, subset of pores (24) for which the pores are aligned along the longitudinal axis (X), the longitudinal interstices (22) thereby defining an axis of anisotropy of the microstructured architecture.

2. The metallic filter according to claim 1, wherein the pores (24) have the same size.

3. The metallic filter according to any one of claims 1 or 2, wherein the porosity is between 10% and 70%.

4. The metallic filter (1) according to any one of claims 1 to 3, wherein the connecting strands (12) have a width of between 10 µm and 500 µm, and the longitudinal interstices (22) have a width of between 1 µm and 100 µm.

5. The metallic filter (1) according to any one of claims 1 to 4, having a thickness (e) defined along the longitudinal axis (X) of between 250 µm and 300 mm.

6. The metallic filter (1) according to any one of claims 1 to 5, wherein the metallic network (10) is made of a metal selected from aluminium, nickel, cobalt, iron, copper, palladium, titanium, tungsten, silver or platinum, or of an alloy of materials such as stainless steel, metal alloy or metal oxide.

7. The metallic filter (1) according to any one of claims 1 to 6, further comprising two opposite main faces (3, 4) delimiting the microstructured architecture (2), said longitudinal faces (3, 4) being respectively covered with a thin virucidal or bactericidal layer.

8. A functional part (30) comprising a metallic filter (1) according to any one of claims 1 to 7 and a peripheral edge (32) of zero porosity surrounding the microstructured architecture (2) of the metallic filter.

9. A method (100) of additive manufacturing of a metallic filter (1) according to any one of claims 1 to 7, said method (100) of additive manufacturing comprising the following steps: (110) depositing at least one layer of metallic powder of a given material or of a given alloy of materials on a support, said layer of metallic powder having a thickness of between 1 µm and 200 µm; (120) performing localised laser melting of the metal grains of the powder, at a temperature higher than the melting temperature of the given material or of the given alloy of materials forming said metallic powder deposited in the step (110), the method being characterised in that a computer program is run so as to create a predetermined pattern (M) of a microstructured architecture (2) defined in a three-dimensional space having orthogonal axes (X, Y, Z), the microstructured architecture (2) comprising: - a metallic network (10) formed of a plurality of longitudinal connecting strands (12), namely extending along a longitudinal axis direction (axis X), and - a network (20) of pores formed of a plurality of longitudinal interstices (22) along connecting strands, each longitudinal interstice (22) corresponding to a subset of pores (24) of the network (20) of pores, subset of pores for which the pores are aligned along the longitudinal axis (X), the longitudinal interstices (22) thereby defining an axis of anisotropy of the microstructured architecture.

10. The method (100) according to claim 9, wherein the support is heated to a temperature strictly above ambient temperature and less than or equal to 250°C.

11. The method (100) according to any one of claims 9 or 10, wherein the support (S) is heated to a temperature between 180°C and 220°C, advantageously between 190°C and 210°C.

12. The method (100) according to any one of claims 9 to 11, wherein a volume energy density of the laser beam during the step (120) of localized laser melting corresponds to 30% to 90% of the value of the volume energy density of the laser beam required to form a non-porous block from said metallic powder.

13. The method (100) according to any one of claims 9 to 12, wherein the step (110) of deposition and the step (120) of local laser melting are successively repeated several times.