FILTRATION UNIT WITH A CURVED EDGE

Description

[0001] The invention relates to a unit for filtering a biological fluid such as blood or a blood component and to a bag system comprising such a filtration unit.

[0002] The invention applies to the field of filtration of biological fluids and in particular the filtration of blood or blood components.

[0003] In the field of transfusion, it is classic to treat blood to remove unwanted substances such as leukocytes, pathogens, certain proteins - for example prions - and / or substances used in processes of inactivation, reduction and / or elimination of pathogens.

[0004] To remove these unwanted substances by filtration, there are two main categories of filtration units: so-called flexible filtration units comprising a flexible outer casing, and so-called rigid filtration units comprising a rigid housing. A filtration medium capable of removing unwanted substances from the fluid is enclosed in these filtration units.

[0005] These filtration units are generally integrated into bag systems allowing blood and blood components to be treated in a closed circuit.

[0006] Thus, after collecting whole blood, such bag systems are placed in centrifugation devices in order to separate the different blood components according to their density, by subjecting them to centrifugal force.

[0007] However, during this centrifugation step, there is a risk not only that these rigid filtration units will be damaged but also that the rigid filtration units will damage adjacent bags, rendering the bag systems unusable and possibly contaminating the external environment and the user.

[0008] Indeed, as illustrated in document WO 2008 / 103142, the rigid filtration units comprise housings with edges forming substantially right angles and also have fluid inlet and / or outlet orifices projecting from the housing forming sharp edges. With the pressure generated by centrifugation, these angular parts can perforate the bags.

[0009] Although some rigid filtration units have rounded corners, such as those illustrated in EP 1 156 067 A2, these units still have angular parts that may damage the flexible bags during centrifugation.

[0010] To avoid the degradation of bag systems during centrifugation, flexible filtration units have been developed, for example like that of document EP-A-526 678. These flexible filtration units are however difficult to manufacture.

[0011] On the other hand, different solutions have been proposed in order to avoid damage related to rigid filtration units during centrifugation.

[0012] For example, in EP 0627 228 it is proposed to place the filtration units outside the centrifugation bucket on the centrifuge rotor.

[0013] In the same vein, in document US 5,100,564, the filtration unit is arranged above the centrifugation bucket using a suitable support.

[0014] On the other hand, it is known from document EP 0 679 490 A2, a method for manufacturing a rigid filtration unit comprising aligning a filtration medium between two housing elements and injection molding a rigid thermoplastic overmolded strip around the two housing elements so as to form a hermetic seal at the end of the filtration medium. The resulting filtration unit comprises protruding and angular parts unsuitable for centrifugation with flexible bags.

[0015] The invention provides a substantially rigid type filtration unit which can be centrifuged in a centrifuge bucket with flexible bags without damaging them.

[0016] Thus, and according to the first aspect, the invention proposes a filtration unit intended for the filtration of a fluid comprising a housing formed from a first housing element and a second housing element between which a filtration medium arranged so as to define an inlet compartment for the fluid to be filtered and an outlet compartment for the filtered fluid, said housing comprising an inlet conduit opening into the inlet compartment and an outlet conduit opening into the outlet compartment, each of said housing elements comprising a bottom extending in a median plane while being surrounded by a periphery, said housing elements being assembled together in a sealed manner at their periphery, the housing having a peripheral edge having a curved outer profile which extends between the median planes of the bottoms.

[0017] According to a second aspect, the invention relates to a bag system for filtering a fluid, comprising: a filtration unit according to the first aspect of the invention, and a filtrate collection bag, said collection bag being connected, via a first tube, to the outlet conduit of the filtration unit.

[0018] Other objects and advantages will appear during the description which follows in connection with the attached figures according to which: There figure 1 represents a schematic perspective view of the filtration unit according to one embodiment of the invention. The figures 2 à 4 represent schematic views of two different profiles of the filtration unit of the figure 1 . There figure 5 represents a schematic top view of the filtration unit of the figure 1 . There figure 6 represents a schematic sectional view of the filtration unit of the figure 1 . THE figures 7a et 7b represent a partial schematic and sectional view of a filtration unit according to two other embodiments. The figure 8 represents an exploded schematic and profile view of the first and second housing elements and the filtration medium of the filtration unit of the figure 1 . There figure 9 represents a schematic view of a bag system comprising the filtration unit of the figure 1 .

[0019] The invention relates to a filtration unit for filtering a fluid, in particular blood or a blood component such as plasma including platelet-rich plasma and platelet-poor plasma, red blood cell concentrate or blood platelet concentrate.

[0020] The filtration unit is intended to remove target components from the fluid, including leukocytes, prion proteins or pathogen-inactivating substances such as methylene blue.

[0021] In relation to the figures 1 à 8 , the filtration unit 1 comprises a rigid housing formed from a first housing element 2 and a second housing element 3 between which a filtration medium 4 is arranged so as to define an inlet compartment 5 for the fluid to be filtered and an outlet compartment 6 for the filtered fluid.

[0022] The housing elements are made of a thermoplastic polymer material such as polycarbonate, polyvinyl chloride, polypropylene or acrylonitrile-butadiene-styrene.

[0023] The inlet compartment 5 is limited by the first housing element 2 and the filter medium 4. The outlet compartment 6 is limited by the second housing element 3 and the filter medium 4.

[0024] This filtration unit 1 is intended to filter a biological fluid which is, for example, a biological fluid such as blood or a blood component.

[0025] In one embodiment, the filtration medium 4 is capable of removing leukocytes from the blood or a blood component. The filtration medium notably comprises one or more layers of a woven or non-woven material. For example, the filtration medium comprises an assembly of several layers of non-woven.

[0026] The material(s) forming the layer(s) of the leukocyte removal medium are chosen from the group comprising polymers or copolymers based on polypropylene, polyester, polyamide, high or low density polyethylene, polyurethane, polyvinylidene fluoride, polyvinylpyrrolidone and their derivatives. Advantageously, the material is polypropylene, polyethylene terephthalate or polybutylene terephthalate.

[0027] In relation to the figure 6 , the housing comprises an inlet duct 7 opening into the inlet compartment 5 and an outlet duct 8 opening into the outlet compartment 6.

[0028] According to one embodiment, the inlet duct 7 and the outlet duct 8 are arranged parallel to said filtration medium 4.

[0029] The inlet and outlet conduits 7,8 are in particular hollow and rigid tubular conduits. These conduits are capable of receiving flexible tubing in order to be able to integrate the filtration unit into a bag system such as that shown in the figure 8 .

[0030] In the embodiment shown, the first housing element 2 comprises the inlet conduit 7 for the fluid to be filtered and the second housing element 3 comprises the outlet conduit 8 for the filtrate.

[0031] As shown in the figures, each of the first and second housing elements 2, 3 comprises a bottom 9, 10 surrounded by a peripheral wall 25, 26, the bottom of at least one of said housing elements comprising a main portion 11, 12 and at least one domed portion 13, 14 which is delimited by a periphery by having an internal wall 15, 16 extending from said periphery towards an apex 17, 18 and an external wall 19, 20 extending from said apex 17, 18 towards said periphery.

[0032] In the description and in relation to the filtration unit, the adjective "internal" is to be understood in opposition to the adjective "external". A so-called "external" means a means which is turned away from the central part of the filtration unit.

[0033] The bottom 9, 10 of each of the housing elements extends in a median plane P5, P6 while being surrounded by a peripheral wall 25, 26.

[0034] The main portion 11, 12 of the bottom of the housing elements 2, 3 is notably substantially flat and defines a base plane.

[0035] The domed portion 13, 14 of the bottom of the housing elements 2, 3 advantageously does not include any angular part, so that the risk of perforating adjacent pockets during centrifugation is reduced.

[0036] In particular and according to the figure 4 , the internal 15 and external 19 walls of the domed portion 13 of one of the housing elements 2 extend respectively in a median plane P1, P2 forming between them an angle α1 strictly greater than 90°, particularly between 100° and 130°.

[0037] The internal 16 and external 20 walls of the domed portion 14 of the other housing element 3 extend respectively in a median plane P3, P4 forming between them an angle α2 strictly greater than 90°, particularly between 100° and 130°.

[0038] By "median plane" of a wall is meant the plane located in the middle of said wall.

[0039] Furthermore, the apex 17, 18 of the domed portion 13, 14 has a curved external profile which extends between said median planes P1, P2 and P3, P4 at the junction between the internal 15, 16 and external 19, 20 walls. The external contour of the domed portion 13, 14 thus does not have a straight or flat part.

[0040] According to one embodiment, the curved external profile has, seen in profile, a radius of curvature strictly greater than the height of the domed portion taken from the base plane P5, P6 of the main portion 11, 12 of the bottom of the housing element 2, 3.

[0041] As illustrated in the figure 4 , the median plane of the internal wall P1,P3 of the domed portion 13,14 forms an angle α3,α4 between 120° and 150° with the base plane P5,P6 of the main portion 11,12 of the bottom.

[0042] The median plane P2,P4 of the external wall 19,20 of the domed portion 13,14 forms an angle α5,α6 between 120° and 150° with a base plane P5,P6 of the main portion 11,12 of the bottom 9,10.

[0043] Thus, the domed portion 13, 14 is relatively low so that the dead volume of the housing of the filtration unit 1 is reduced.

[0044] More particularly and in relation to the figure 5 , the external wall 19,20 extends from the apex 17,18 towards a portion of the periphery which is adjacent to the peripheral wall 25,26 of the bottom 9,10.

[0045] The inner wall 15, 16 extends towards the apex 17, 18 from a substantially U-shaped portion of the periphery. Even more particularly, the ends of the branches of the U are adjacent to the peripheral wall 25, 26 of the bottom 9, 10.

[0046] In other words, the domed portion 13, 14 of the housing element 2, 3 is located in the vicinity of the peripheral wall 25, 26 of the bottom 9, 10 of the housing element 2, 3.

[0047] According to a particular embodiment, the bottom 9,10 has a dimension which extends along the main portion 11,12 and the domed portion 13,14, the internal wall 15,16 extending along said dimension over a distance of between 20% and 40% of said dimension.

[0048] As shown in the figure 6 , at least one of the inlet 7 and outlet 8 conduits opens through the external wall 19,20 of the domed portion 13,14 of a housing element 2,3.

[0049] More particularly, an external end of an inlet 7 and outlet 8 conduit opens into the external wall 19, 20 while being adjacent to the peripheral wall 25, 26 of the bottom 9, 10 of the housing element 2, 3.

[0050] Advantageously, the external wall 19, 20 has an orifice in which at least one external end 21, 22 of an inlet 7 and outlet 8 conduit is inscribed. The domed portion 13, 14 then completely covers the inlet 7 or outlet 8 conduit, so that no fragile projecting element extends from the domed portion 13, 14.

[0051] The raised parts of the housing thus have a curved shape so that, whatever the position of the housing in the centrifugation bucket, the risk of rupture of the inlet and outlet conduits 7,8 and the risk of damaging the surrounding bags are reduced or even eliminated.

[0052] And, in this embodiment, the external end 21, 22 of the inlet and / or outlet duct 7, 8 is not straight, that is to say it is not perpendicular to the longitudinal axis of the inlet and / or outlet duct 7, 8.

[0053] For example, as shown in the figure 5 , the external end of the inlet and / or outlet conduit 7,8 has a bevel. In the case of a tubular conduit, the orifice is then substantially oval.

[0054] According to a particular embodiment shown on the figure 6 , at least one of the inlet and outlet conduits 7,8 has at its internal end 23,24 an opening having a smaller section than the section of the opening of said conduit 7,8 at its external end 21,22 ( figure 6 ).

[0055] In order to allow better emptying of the filtration unit 1, the internal end 24 of the outlet duct 8 is provided with a flow restriction formed by a reduction in section compared to the section of this duct at its external end. By Venturi effect, the flow restriction creates an acceleration of the flow of filtered fluid which tends to suck the fluid out of the filtration unit 1.

[0056] In particular, the inner end 23 of the inlet duct 7 is also provided with a flow restriction. Even more particularly, the inlet duct 7 and the outlet duct 8 have substantially the same geometry and the same dimensions.

[0057] Advantageously, each of the housing elements 2, 3 has a domed portion 13, the inlet duct 7 opening into the external wall 19 of the domed portion 13 of said first housing element 2 and the outlet duct 8 opening into the external wall 20 of the domed portion 14 of said second housing element 3.

[0058] According to one embodiment, the domed portion 13 of the first housing element 2 and the domed portion 14 of the second housing element 3 have substantially the same geometry and the same dimensions.

[0059] In relation to the figures 6 , 7a et 7b , each of the first and second housing elements 2,3 comprises a cavity formed by the bottom 9,10 and a peripheral side wall 25,26, the domed portion 13,14 being arranged on the outer surface of the bottom 9,10 of one of the first or second housing elements 2,3.

[0060] The housing elements 2, 3 are assembled together in a sealed manner at their periphery, so as to form a fluid-tight housing.

[0061] For example, the first and second housing elements 2, 3 are joined together by high-frequency, radiofrequency or ultrasonic welding. Alternatively, the housing elements 2, 3 are joined by gluing.

[0062] In order to facilitate the assembly of the two housing elements 2,3, the housing elements 2,3 are adjusted together by form-fitting or snap-fitting.

[0063] In relation to the figures 6 , 7a et 7b , the peripheral side wall 25 of the first housing element 2 and the peripheral side wall 26 of the second housing element 3 are brought into contact on their extreme surface by shape matching.

[0064] In one embodiment, the housing of the filtration unit 1 has a peripheral edge 27 having a curved external profile which extends between the median planes P5, P6 of the bottoms 9, 10 of the first and second housing elements 2, 3.

[0065] The outer contour of the peripheral edge 27, that is to say the portion joining the substantially flat portions of the bottoms 9, 10 of the first and second housing elements 2, 3, thus does not have a straight or flat part.

[0066] This peripheral edge 27 with a curved outer profile helps to reduce the risk of damage to the flexible bags when the filtration unit and the flexible bags are centrifuged in the same bucket.

[0067] The profile of the peripheral edge 27 does not have a substantially flat part.

[0068] In particular, the curved outer profile of the peripheral edge 27 has a radius of curvature which is greater than half the distance between the two median planes P5, P6.

[0069] The radius of curvature is the radius of the circle tangent to the curved outer profile of the peripheral edge seen in cross section.

[0070] According to a first achievement represented in particular on the figures 6 And 7a , the filtration unit comprises an element 28 which is attached to the assembly of the peripheries of the housing elements 2, 3, the peripheral edge 27 having a curved external profile being formed on said attached element 28.

[0071] In addition, the insert 28 is arranged to ensure sealing of the assembly of the peripheries of the housing elements 2, 3.

[0072] In particular, the insert 28 is associated around the peripheries of the housing elements 2, 3.

[0073] Even more particularly, the element 28 is added by overmolding onto the assembly of the peripheries of the housing elements 2, 3.

[0074] Overmolding consists of placing, in the impression of a cavity of an injection mold, the housing of the filtration unit 1, and injecting the added element 28. Filling the impression makes it possible to overmold the housing with the added element 28.

[0075] By this overmolding technique, the insert 28 adheres to the housing elements 2, 3 by physicochemical bonding, the housing thus not allowing the fluid to pass to the outside.

[0076] Thus, the assembly of the case is carried out automatically at the time of overmolding.

[0077] Furthermore, it is also possible to carry out the injection of the housing elements, the integration of the filtration medium and the overmolding in a single cycle in a single injection molding machine using a special mold. It is then not necessary to design and / or provide an assembly machine adapted to the final housing. This reduces the total manufacturing time and therefore costs and thus provides higher quality to the filtration unit.

[0078] On the figure 6 , the element 28 is attached between the two housing elements 2, 3, without extending onto the outer surface of the housing elements 2, 3.

[0079] In this case, as illustrated in the figure 6 , the two peripheral side walls 25, 26 partly forming the peripheral edge 27 of the housing have a curved outer surface.

[0080] In relation to the figure 7a , the added element 28 has a U-shaped profile, each branch of which extends substantially in a median plane P5, P6 respectively to be arranged in the extension of a base 9, 10.

[0081] More specifically, the insert 28 extends partly over the first and second housing elements 2, 3. In this case, the insert 28 is advantageously made of an elastomeric thermoplastic material, so as to protect the filtration unit from possible impacts and to avoid damage to the bag system during centrifugation. The insert 28 thus has not only an assembly function but also a protective cushion function.

[0082] Furthermore, the peripheries of the housing elements 2, 3 have a complementary geometry which is arranged to form a peripheral recess 29 at their interface, the insert 28 being arranged in said recess.

[0083] In particular, the geometry and dimensions of the peripheral recess 29 are configured so that, during overmolding, the insert 28 and / or the housing elements 2, 3 do not melt at the level of the filtration medium 4.

[0084] The insert 28 is made of a material identical to or different from that of the housing elements 2, 3. Advantageously, for reasons of compatibility and chemical adhesion, the insert 28 is made of a thermoplastic polymer material of the same family as the material used for the housing elements 2, 3.

[0085] In particular, the added element 28 is made from a thermoplastic material, in particular a thermoplastic elastomer material.

[0086] For example, the insert 28 is made of a thermoplastic polymer material such as polycarbonate, polyvinyl chloride, polypropylene or acrylonitrile-butadiene-styrene.

[0087] Alternatively, the insert 28 is made of a thermoplastic elastomer material, in particular based on polyurethane or based on styrenic polymers. Examples of overmolding material are the Dryflex products from the company Hexpol or Hytrel from the company DuPont.

[0088] In particular, the insert 28 has a hardness of between 50 and 100 Shore A, less than the hardness of at least one of the housing elements 2, 3. For example, the sealing element has a hardness of approximately 70 Shore A.

[0089] According to a second embodiment, the peripheries of the housing elements 2, 3 have a complementary geometry which is arranged to form the peripheral edge 27 having a curved external profile.

[0090] In particular, in relation to the figure 7b , each of the housing elements 2,3 comprises an inner mating element 49,50 substantially parallel to the side wall 25,26. The two inner mating elements 49,50 of each of the housing elements 2,3 cooperate by form mating, so that once the housing elements 2,3 are assembled together, a hollow portion 51 is formed between the side walls 25,26 and the inner mating elements 49,50.

[0091] In a variant not shown, the housing of the filtration unit 1 further comprises one or more protective elements added by overmolding a thermoplastic elastomer material configured to protect the housing from impacts and / or prevent damage to the flexible bags.

[0092] The filter medium 4 is arranged between the two housing elements 2, 3 and is held tightly there.

[0093] In a particular embodiment and in order to ensure a fluid seal between the inlet compartment 5 and the outlet compartment 6 of the filtration unit 1, each of the housing elements 2, 3 comprises an internal projection 30, 31 arranged to compress the filtration medium 4 along its periphery.

[0094] The inner projections 30, 31 are arranged to compress the filtration medium 4 along its periphery so as to create an inner fluid-tight zone.

[0095] Advantageously, each of the housing elements 2, 3 further comprises an external projection 32, 33 arranged to compress the filtration medium 4 along its periphery.

[0096] The outer projections 32, 33 are arranged to compress the filtration medium 4 so as to create an outer fluid-tight zone.

[0097] In the description and in relation to the filtration unit, the adjective "external" is to be understood in opposition to the adjective "internal". A so-called "internal" means means a means located in an area of ​​the filtration unit closer to the center of the filtration unit than a so-called "external" means.

[0098] Thus, if the fluid is not stopped or slowed sufficiently by the first pair of inner projections 30,31, the pair of outer projections 32,33 provides a second narrowed passage, sufficient to prevent the fluid from bypassing the filtration medium 4.

[0099] This may be the case if, for example, a defect or irregularity in the filtration medium 4 is located at the interior projections 30, 31, preventing the filtration medium 4 from being compressed sufficiently to create a fluid seal.

[0100] For example, on the figure 6 , the inner projections 30, 31 and outer projections 32, 33 are formed of continuous ribs. These ribs have a section of essentially triangular shape, with a rounded top.

[0101] In relation to the housing elements 2, 3, these comprise in particular a first and a second clamping part 34, 35, respectively arranged to hold said filtration medium clamped in the housing along its periphery.

[0102] The clamping parts 34, 35 of the housing elements compress the filtration medium 4 so as to reduce its thickness, without however being able to ensure a fluid seal.

[0103] In particular, the clamping parts 34, 35 are arranged on the bottom 9, 10 of the cavities of the housing elements 2, 3.

[0104] More particularly and as represented on the figures 7a et 7b , the first and second housing elements 2, 3 respectively comprise a first and a second cavity each provided with an outwardly directed peripheral platform forming the first and second clamping parts 34, 35 respectively, arranged to hold the filtration medium 4 clamped in the housing along its periphery.

[0105] In this configuration, the filtration medium 4 is held tight between the first and second platforms, which makes it possible to compress the filtration medium along its periphery. The inner 30, 31 and outer 32, 33 projections are then located on these platforms, in particular at their inner end.

[0106] According to a particular embodiment, the first housing element 2 and the second housing element 3 each comprise on their inner surface, in particular on the inner surface of the bottom 9, 10, a flow deflector formed from a plurality of reliefs 36, 37.

[0107] In relation to the figure 6 , each of the housing elements 2, 3 is provided on the inner surface of the bottom 9, 10 with a plurality of linear reliefs 36, 37 directed obliquely towards the inlet and outlet duct. On the side of the inlet compartment 5, the deflectors help to distribute the flow of fluid to be filtered over the entire surface of the filtration medium. On the side of the outlet compartment 6, the deflectors help to direct the filtered fluid towards the outlet duct of the filtration unit.

[0108] According to a second aspect and in relation to the figure 9 , the invention relates to a bag system 38 for filtering a fluid, comprising: a filtration unit 1 according to the first aspect of the invention, and a filtrate collection bag 39, said filtrate collection bag 39 being connected, via a first tube 40, to the outlet conduit 8 of the filtration unit 1.

[0109] To introduce the fluid to be filtered, the bag system 38 further comprises a bag 41 intended to contain the fluid to be filtered, said bag 41 for the fluid to be filtered being connected via a second tube 42 to the inlet conduit 7 of the filtration unit 1.

[0110] This pocket 41 for the fluid to be filtered is either connected during manufacture to the filtration unit 1 via the second tube 42, or connected by the user using a perforator-type connector provided at the free end of the second tube (not shown).

[0111] There figure 9more particularly represents an example of a bag system 38 used to separate a whole blood donation into plasma and red blood cell concentrate and to deleukocyteize the red blood cell concentrate.

[0112] The bag system 38 comprises a needle 43 for collecting blood from a donor, a primary bag 44 for collecting whole blood, a satellite bag 45 for receiving plasma in fluid communication with the primary bag, a satellite bag 41 for receiving the red blood cell concentrate in fluid communication with the primary bag, a filtration unit 1 as previously described for filtering leukocytes from the red blood cell concentrate in fluid communication with the satellite bag to receive the red blood cell concentrate, and a filtrate collection bag 39 in fluid communication with the filtration unit 1. The bags and the filtration unit 1 are connected to each other by means of flexible and sterilizable tubing 40, 42, 46, 47, 48.

[0113] The primary bag 44 contains a CPD type anticoagulant and the filtrate collection bag 39 contains an additive solution for the preservation of SAGM type red blood cells (Saline Adenine Glucose Mannitol).

[0114] In use, the bag system 38 containing the whole blood mixed with the anticoagulant solution in the primary bag 44 is placed in a centrifuge cup to be centrifuged so as to separate the blood into three layers: a supernatant comprising the plasma, an intermediate layer called a buffy coat comprising a mixture of platelets, plasma and red blood cells and a pellet comprising the red blood cell concentrate.

[0115] By pressing the primary bag 44, the plasma is sent to the satellite bag 45 intended to receive the plasma and the red blood cell concentrate is sent to the satellite bag 41 intended to receive the red blood cells. The buffy-coat remains in the primary bag 44.

[0116] The additive solution is then sent from the filtrate collection bag 39 to the satellite bag 41 intended to receive the red blood cells. The red blood cell concentrate, mixed with the additive solution, is finally filtered by gravity through the filtration unit 1 and the filtrate is received in the bag intended to collect the filtrate 39.

Claims

1. A filtration unit (1) for filtering a fluid comprising a housing formed by a first housing element (2) and a second housing element (3) between which a filtration medium (4) is disposed so as to define an inlet compartment (5) for the fluid to be filtered and an outlet compartment (6) for the filtered fluid, said housing having an inlet duct (7) opening into the inlet compartment (5) and an outlet duct (8) opening into the outlet compartment (6), each of said housing elements comprising a bottom (9, 10) extending in a median plane (P5, P6) and surrounded by a periphery, said housing elements (2, 3) being sealingly connected to each other at their periphery, said filtration unit being characterized in that the housing has a peripheral edge (27) with a curved outer profile extending between the median planes (P5, P6) of the bottoms.

2. Filtration unit according to claim 1, characterized in that the curved outer profile of the peripheral edge (27) has a radius of curvature which is greater than half the distance between the two median planes (P5, P6).

3. Filtration unit according to one of claims 1 or 2, characterized in that the peripheries of the housing elements (2, 3) have a complementary geometry which is arranged to form the peripheral edge (27) having a curved outer profile.

4. Filtration unit according to one of claims 1 or 2, characterized in that it further comprises an element (28) which is attached to the assembly of the peripheries of the housing elements (2, 3), the peripheral edge (27) having a curved outer profile being formed on said attached element (28).

5. Filtration unit according to claim 4, characterized in that the element (28) is added by overmolding on the assembly of the peripheries of the housing elements (2, 3).

6. Filtration unit according to one of claims 4 or 5, characterized in that the attached element (28) has a U-shaped profile, each leg of which extends substantially in a respective median plane (P5, P6) to be arranged in the extension of a bottom (9, 10).

7. Filtration unit according to any one of claims 4 to 6, characterized in that the peripheries of the housing elements (2, 3) have a complementary geometry which is arranged to form a peripheral recess (29) at their interface, the attached element (28) being disposed in said recess (29).

8. Filtration unit according to any one of claims 4 to 7, characterized in that the attached element (28) is made from a thermoplastic material, in particular a thermoplastic elastomer material.

9. Filtration unit according to any one of claims 4 to 8, characterized in that the attached element (28) has a hardness of between 50 and 100 shore A.

10. Filtration unit according to any one of claims 1 to 9, characterized in that the bottom (9, 10) of at least one of the housing elements (2, 3) comprises a main portion (11, 12) and at least one domed portion (13, 14) which is delimited by a perimeter while having an inner wall (15, 16) extending from said perimeter towards an apex (17, 18) and an outer wall (19, 20) extending from said apex (17,18) towards said perimeter, at least one of the inlet and outlet ducts (7, 8) opening through the outer wall (19, 20), the inner and outer walls extending respectively in a median plane (P1, P2, P3, P4, P5) forming between them an angle strictly greater than 90°, the apex (17, 18) having a curved outer profile which extends between said median planes at the junction between the inner (15, 16) and outer (19, 20) walls.

11. Filtration unit according to any one of claims 1 to 10, characterized in that the inlet duct (7) and the outlet duct (8) are arranged parallel to the filtration medium (4).

12. Filtration unit according to any one of claims 1 to 11, characterized in that at least one of the inlet and outlet ducts (7, 8) has an opening at its inner end (23, 24) with a cross-section smaller than the cross-section of the opening of said duct at its outer end (21, 22).

13. A filtration unit according to any one of claims 1 to 12, characterized in that each of the housing elements (2, 3) comprises an inner projection (30, 31) arranged to compress the filtration medium (4) along its periphery, or an inner projection (30, 31) and an outer projection (32, 33) arranged to compress the filtration medium (4) along its periphery.

14. Filtration unit according to any one of claims 1 to 13, characterized in that the first housing element (2) and the second housing element (3) each comprise on their inner surface a flow deflector formed by a plurality of reliefs (36, 37).

15. Filtration unit according to any one of claims 1 to 14, characterized in that the filtration medium (4) comprises an assembly of non-woven layers, particularly suitable for removing leukocytes from blood or a blood component.

16. A bag system (38) for filtering a fluid, characterized in that it comprises: - a filtration unit according to any of claims 1 to 15, and - a filtrate collection bag (39), said collection bag (39) being connected, via a first tube (40), to the outlet duct (8) of the filtration unit (1).