Patent Publication Number: US-2022226550-A1

Title: Filter Assembly and Container for Collecting a Body Fluid Containing the Same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of and priority to European Application No. 19181285.8, filed Jun. 19, 2019, the disclosure of which is hereby incorporated by reference in its entirety. 
     The present invention relates to a filter assembly, to an appropriate use of such a filter assembly, and to a container for collecting a body fluid comprising such filter assembly. 
     DESCRIPTION 
     Filtering assemblies known from prior art are used to filter different types of fluids, e.g. body fluids, for removing aggregates, particles or specific cells from said fluids. A particular appropriate application of filter assemblies is the filtration of blood. Whole blood or blood components may be separated and further processed for a variety of uses, particularly for use as transfusion products. 
     Filtering assemblies are also used in auto transfusion processes during surgeries procedures; i.e. blood of a patient is recovered during surgery and re-infused into the patient. This is also known as intraoperative blood salvage (IOBS), or autologous blood transfusion or cell salvage. It has been used for many years and gained greater attention over time as risks associated with allogenic (separate-donor) blood transfusion have seen greater publicity and become more fully appreciated. Several medical devices have been developed to assist in salvaging the patient&#39;s own blood in the perioperative setting. The procedure is frequently used in cardiothoracic and vascular surgery, during which blood usage has traditionally been high. 
     Whole blood recovered during surgery, but being exposed to surgery, air etc. has different characteristics than blood collected in a blood bank from a donor for allogeneic transfusion purpose. For example, blood salvage requires a removal of blood clots, non-cellular substances, such as drugs or fluids used during surgery, bone fragments and surgery debris. 
     Autologous blood recycling or intraoperative blood salvage is often accompanied by foam formation. Blood foam formation (sometimes referred to as “skimming”) is related to collection or transportation of blood in presence of air in large tubes (e.g. collected with Yankauer cannulae) and thus related to turbulence in the suction process. 
     One approach to avoid foam formation in shed blood is the use of antifoam agents in reservoirs where shed blood is collected for autotransfusion or extracorporeal circulation. In the past polydimethylsiloxane (PDMS)—hydrophobed silica was widely used as antifoam. However, PDMS may be partially leached into the blood, where it emulsifies. In IOBS, it is presumed that most of it will be found in the waste after the washing procedure, but it cannot be excluded that part of it is found in the Red Cell Concentrate that is autotransfused to the patient. Even though PDMS-hydrophobed silica is non-toxic it was associated as a possible source for emboli due to capillaries blockage and postoperative deaths and is no longer used as antifoam. Thus, nowadays only PDMS without silica is used. The defoaming principle remains the same for PDMS, while the physical way of action, a silica particle that “breaks” the bubble is no longer applied for medical devices, but is still used in non-medical defoaming. 
     However, there is still a need for alternative antifoaming concepts. 
     It is an object of the present invention to provide a filter system that allow a reduction or even prevention of foam formation in filtered body fluids, such as shed blood, and at the same time reduce the risk of leaching chemicals into the filtered body fluid. 
     This object is achieved by a filter assembly having the features explained in the following. 
     Accordingly, a filter assembly for filtering a body fluid comprising a filter system and a filter holder is provided, wherein the filter system and the filter holder are in contact with each other or are connected to each other. 
     The filter system consists of at least two layers, 
     wherein the first layer is a defoaming layer made of a monofilament woven open mesh fabric and with an embossed three dimensional structure configured, in particular for entrapping foam built up in the body fluid, 
     wherein the second layer is a mesh filter layer, and 
     wherein the mesh filter layer is arranged downstream of the defoaming layer. 
     The terms “downstream” and “upstream” refer to a flow direction of a fluid to be filtered by the filter assembly. Thus, the fluid to be filtered contacts at first the defoaming layer followed by the mesh filter layer. 
     Such a filter assembly can well be used for filtering blood and other body fluids. If such a filter assembly is used, foam formation in the blood and in other body fluids is effectively prevented. The present filter assembly allows to remove foam mechanically. Thereby, no anti-foaming agents are necessary so that the risk of leaching chemicals into the filtrated body fluid is fully avoided. The present filter assembly is in particular useful for an autotransfusion reservoir or container. 
     It was surprisingly found that the use of a defoaming layer with an embossed 3D structure removes or reduces foam. The underlying mechanism may be an entrapment of the foam within the defoaming layer. The spatial 3D structure allows for an entrapment of gas bubbles formed in the body fluid; i.e. gas bubbles are entrapped within the spatial structure. Another mechanism could be that the bubbles of the foam are blown up when the pass through the downstream mesh filter. 
     The embossed 3D structure may be in form of a diamond pattern with regularly arranged protrusions and depressions of a certain height. One can describe the spatial pattern also as a zig-zag-structure or pyramid like structure. 
     As mentioned previously, the defoaming layer is a structured open mesh fabric. 
     In an embodiment the defoaming layer comprises a mesh opening between 100-500 μm, in particular between 150-400 μm, in particular between 200-350 μm, and more particular between 250-300 μm, for example 250 μm. 
     The mesh count (typically the number of threads per cm) of the open mesh fabric forming the defoaming layer may be between 10-50 n/cm, in particular between 10-30 n/cm, more particular between 10-20 n/cm, such as 12-16 n/cm. 
     The fabric of the defoaming layer is made of monofilament fibers with a diameter between 100-350 μm, in particular 150-300 μm, more particular 200-300 μm, such as 200, 250, 300 μm. The monofilament fibers can be made of any thermoplastic material, but preferably of polypropylene (PP), polyethylene (PE), polyether ether ketone (PEEK) and others. Polypropylene is the most preferred one. 
     The defoaming layer can have a weight of 50-250 g/m2, in particular 100-200 g/cm2, more particular 150-200 g/cm2, such as 98-103 g/cm2, 180-190 g/cm2, 156 g/cm2. 
     The thickness of the defoaming layer may be 150-650 μm, in particular 200-500 μm, in particular 250-400 μm, in particular 300-350 μm. 
     The defoaming layer may also be of a sponge-like structure, for example made of polyurethane or polyester foam. 
     In an embodiment, the first mesh layer is made of a plurality of interconnecting threads forming a grid or a net. Thus, vertically arranged threads and horizontally arranged threads are connected to each other at connecting points so as to form a grid. 
     In an embodiment, the threads or filaments of the mesh filter layer have a circular cross-section. However, other cross sections, such as an elliptic, a rectangular, a quadratic or a triangular cross-section would also be possible. Likewise, mixtures of threads or filaments having different cross sections are also possible. 
     In an embodiment, the mesh size of the mesh filter layer is in a range between 20 and 160 μm, in particular between 30 and 140 μm, in particular between 40 and 130 μm, in particular between 50 and 120 μm, in particular between 60 and 110 μm, in particular between 70 and 100 μm, in particular between 80 and 90 μm. Ranges of 100 to 130 μm, 105 to 125 μm, 70 to 90 μm, 75 to 85 μm, 30 to 45 μm and 35 to 40 μm are particularly appropriate. 
     In an embodiment, the mesh filter layer can comprise or can be entirely made of a polymer such as a polyester, polyethylene, polypropylene, polybutylene, polymethylpentene, polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, poly(butylene terephthalate-co-polyalkylene glycol terephthalate), nylon 6,6, nylon 6,9, nylon 6/12, nylon 11, nylon 12, cellulose acetate, cellulose acetate propionate, or a combination thereof. Thereby, a non-hydrophobic or hydrophilic material is particularly appropriate to produce the mesh filter layer. It is also possible to increase the hydrophilicity of the material which is used to produce the mesh filter layer or to increase the hydrophilicity of the already produced filter. Thereby, a physical treatment is more appropriate than the deposition of chemicals because such chemicals might potentially be leached from the mesh filter during use of the container. 
     An appropriate surface area of the mesh filter layer is in a range of 300 to 1000 cm 2 , in particular 400 to 900 cm 2 , in particular 500 to 800 cm 2 , in particular 600 to 700 cm 2 . 
     In a further, preferred embodiment the filter assembly comprises a prefilter layer (depth filter) arranged downstream of the defoaming layer and upstream of the mesh filter layer; i.e. sandwiched between defoaming layer and mesh filter layer. 
     The prefilter layer comprises or essentially consists of a non-woven fabric of fibers. Thereby, the fibers are arranged such that gaps are formed between the randomly deposited fibers. The gaps can be defined as openings with an average pore size. Consequently, a pore size of the non-woven fabric results. 
     The pore size of the prefilter material is smaller than the upstream defoaming layer but larger than the downstream mesh filter material. 
     In an embodiment, the prefilter layer comprises or essentially consists of a spunbond nonwoven fabric. The individual fibers of this fabric may have any desired cross-section, such as a circular, elliptic rectangular, quadratic or triangular cross-section. Mixtures of fibers having different cross sections are also possible. 
     The fibers of the prefilter layer can also generally have any shape. However, it turned out that particularly good filtering can be achieved if the fibers, or at least a part of the fibers, comprise at least one groove extending in the longitudinal direction of the respective fiber. To give an example, the fibers may comprise three grooves each extending in a longitudinal direction of the fiber. Then, aggregates, fat and/or platelets can be particularly well filter from blood or another body fluid flowing through the filter assembly. 
     In an embodiment, at least a part of the fibers has a lobate cross-section. Such a lobate cross-section can be achieved, in an embodiment, by forming a groove in the fibers in the longitudinal direction. A trilobal cross-section is a particularly well-suited example of a lobate structure. Such trilobal fibers are generally known, e.g., from WO 2013/110694 A1, the entire content of which is hereby incorporated by reference. 
     The fibers making up the non-woven fabric of the prefilter layer can be, in an embodiment, spunbond fibers or melt-blown fibers. While spunbond fibers typically have a fiber diameter that is at least 20 μm or larger, melt-blown fibers may have lower diameters of less than 20 μm. 
     The prefilter layer comprises or essentially consists of continuous filament spunbond nonwoven fabric. Said fabrics are obtained in continuous filament nonwoven processes (meltblowing and spunbonding) that start extruding chips or pellets of raw material. The length of the filament is theoretically infinite. 
     The fibers of the prefilter material may be monocomponent, bicomponent or multicomponent fibers, including “island in the sea” fibers. The fibers may consist of one polymer or a blend of polymers. Suitable materials for the fibers are, for example, a polyester, polyethylene, polypropylene, polybutylene, polymethylpentene, polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, poly(butylene terephthalate-co-polyalkylene glycol terephthalate), nylon 6,6, nylon 6,9, nylon 6/12, nylon 11, nylon 12, cellulose acetate, cellulose acetate propionate, or a combination thereof. Thereby, a non-hydrophobic or hydrophilic material is particularly appropriate to produce the fibers. It is also possible to increase the hydrophilicity of the material which is used to produce the fibers or to increase the hydrophilicity of the already produced fibers. Thereby, a physical treatment is more appropriate than the deposition of chemicals because such chemicals might potentially be leached from the fibers or the fabric produced therefrom during use of the filter assembly. 
     In an embodiment, the pore size of the prefilter layer is in a range of between 20 and 150 μm, in particular between 30 and 140 μm, in particular between 40 and 130 μm, in particular between 50 and 120 μm, in particular between 60 and 110 μm, in particular between 70 and 100 μm, in particular between 80 and 90 μm. Ranges of 100 to 130 μm, 105 to 125 μm, 70 to 90 μm, 75 to 85 μm, 30 to 45 μm and 35 to 40 μm are particularly appropriate. 
     As mentioned above the filter system may comprise two layers or three layers. 
     In case of the two-layer system the first layer is a defoaming layer and the second layer is a mesh filter layer. Such a two layer system may be used for large pore size filtration. The mesh size of the mesh filter may be 120 μm, with 50% of open permeability and 34% of closed permeability, 
     In case of a three-layer system the first layer is a defoaming layer, the second (sandwiched) layer is prefilter layer (depth filter material) and the third layer is a mesh filter layer. Such a three-layer system may be used for low pore size filtration. The mesh size of the mesh filter layer may be 40 μm, with 40% of open permeability and 12% of very closed permeability, 
     In a specifically preferred embodiment the filter system comprises a defoaming layer with a mesh size between 200 and 300 μm, preferably 250 μm, a prefilter layer with a pore size between 50 and 100 μm, preferably 70 μm and a mesh filter layer with a mesh size between 30 and 50 μm, preferably 40 μm. 
     The filter assembly further comprises a filter holder. This filter holder contacts the filter system of defoaming layer, optional prefilter layer and mesh filter layer. In doing so, it also stabilizes the filter system. Thus, the filter holder serves for keeping the different layers of the filter system in place; it acts as structural support. The filter assembly is a stand-alone filter assembly (self-sustained filter assembly) or it can be one part (overmolded) with filter layers. 
     The filter holder is made from plastic and is overmolded over at least a part of the filter system. It is preferred, if the overmolding is over all filter material layers of the filter system and not only the outer one. This can be achieved by dipping the filter material in molten plastic. When the plastic cools down, and becomes rigid, a holder structure (a sort of cage) is created that englobes the filter material layers. It tightly connects the layer of the filter system together and serves particularly easy for a good stabilization of the layer of the filter system. 
     It was surprisingly found that such a filter assembly can well be used for filtering blood and other body fluids. If such a filter assembly is used, foam formation in the blood and in other body fluids is effectively prevented. Thereby, no anti-foaming agents are necessary so that the risk of leaching chemicals into the filtrated body fluid is fully avoided. 
     In an embodiment, the filter assembly does not comprise any anti-foaming agents. By avoiding the use of such anti-foaming agents the risk of leaching anti-foam chemicals into a fluid that is flowing through the filter assembly is fully prevented. This enhances the quality of the fluid filtered by the filter assembly. 
     The present invention relates in an aspect to the use of the filter assembly having the features explained above for filtering a body fluid in vitro. Thereby, the body fluid can be blood, urine, bile, tissue fluid, sperm, lymph, saliva or cerebrospinal fluid. Blood is a particularly appropriate body fluid to be filtered. 
     In a further aspect, the present invention relates to a method of filtering a body fluid by letting the body fluid flow through a filter assembly according to the preceding explanations. The flow of the body fluid can be accomplished by gravity or by applying external forces such as low pressure to the body fluid or a container into which the filter body fluid is to be drawn. This method can be done in vitro or while a patient donating the body fluid to be filtered is connected to a filter appliance in which the body fluid is filtered. 
     In an embodiment, the method is a medical method for drawing intraoperative cell salvage (ICS) from a patient in need thereof. ICS is typically used for patients undergoing surgery or invasive procedures and is intended to provide those patients with an autotransfusion of blood or blood components. More details on such a method are given in subsequent sections. 
     In yet a further aspect the present invention relates to a container for collecting a body fluid comprising a filter assembly as described in detail above as a filter module. 
     Such a container comprises a container housing with a body fluid inlet that allows a body fluid to enter an inlet section of the container housing. The container housing furthermore comprises a body fluid collection section and a vacuum connector for connecting a vacuum source to the container housing. In doing so, a negative pressure can be applied to the inlet section and to the body fluid collection section. Thereby, the vacuum source is typically connected via a vacuum line to the vacuum connector of the container housing. 
     Furthermore, the container housing comprises the filter module that separates the inlet section from the body fluid collection section. To be more specific, the filter module is arranged between the inlet section and the body fluid collection section so that a body fluid needs to pass the filter in order to flow from the inlet section to the body fluid collection section. Expressed in other words, the filter module has a raw side and a clean side. The raw side faces the inlet section and the clean side faces the body fluid collection section. 
     In particular, the filter assembly as filter module is arranged between the inlet section and the body fluid collection section, such that the defoaming layer faces the inlet section and the mesh filter layer faces the body fluid collection section. 
     In an embodiment, the container housing comprises a hydrophobic filter (i.e. separate from the filter assembly) that is arranged between the body fluid collection section and the vacuum connector. Thereby, the term “between” relates to a flow direction of air drawn by a vacuum source from the container (or the body fluid collection section of the container housing) during the intended operation of the container. I.e., any fluid that is drawn from the interior of the container housing (in particular air and smoke) needs to pass the hydrophobic filter prior to entering a vacuum line connected to the vacuum connector. Thus, the hydrophobic filter serves as protective element for a vacuum line being connected to the vacuum connector of the container housing, when vacuum is generated by a vacuum pump. 
     The novel filter module and the hydrophobic filter synergistically act together so that this combination results in the effects explained in the following. By constructing the filter module with a filter holder and a filter assembly comprising a defoaming layer, an optional prefilter layer and a mesh filter layer, much more flexibility is given for the design of the filter holder than in case of using prefabricated filter sockets like in prior art. Furthermore, it is possible to manufacture the filter holder together with the filter assembly in a single manufacturing step, and the connection of the co-molded filter assembly component to the container is easily automatable. This significantly reduces manufacturing costs and increases the performance of the container due to more reliable and reproducible manufacturing steps. 
     The additional hydrophobic filter arranged in flow direction before the vacuum connector serves both as overfill protection and as smoke filter. Thus, it combines the properties of these elements, which are used in form of individual components according to prior art, in a single element. This single element is thereby included in the container housing. Thus, it is not necessary to connect it with a separate vacuum line. There is no need to clean and/or sterilize the hydrophobic filter. Rather, it can be designed as disposable that is discarded together with the whole container. This additionally facilitates the use of the container. 
     Using a filter assembly comprising a defoaming layer, an optional prefilter layer and a mesh filter layer instead of a regular filter (made only of fibers or foam or a membrane) is connected to the effect that extremely reproducible filtering conditions can be met. While regular filters have an average pore size with many pores being bigger or smaller than the average pore size, a mesh filter has a clearly defined mesh size that essentially does not vary. Besides, the use of the defoaming layer reduces or even prevents foam formation. 
     In an embodiment, a top cover or an inlet section of the container housing and the filter holder are manufactured as one piece, i.e., they are integrally formed. This facilitates the manufacturing steps significantly since no manual attachment of a filter to the container housing is necessary anymore. To give an example, the filter holder and (at least parts of) the container housing can be co-molded in one single injection molding step. Then, an outlet of the inlet section of the container housing turns integrally into an inlet of an interior of the filter holder. Any body fluid that enters the inlet section will then flow or will be drawn from the inlet section of the container housing towards an interior space of the filter holder. It has then to pass the filter assembly in order to reach the body fluid collection section. 
     As mentioned previously, the filter holder and the filter assembly are free of antifoam agents. While certain antifoam agents are necessary in case of regular filters to avoid an undesired foaming of blood, the design of the blood path through the filter element tend to induce foam formation in blood only to a very low extent. If no antifoam agents are used, no such agents can be leached into body fluids so that no corresponding contamination of the body fluid needs to be feared. 
     In an embodiment, the filter holder comprises bars or struts that stabilize the filter material which is located in an interior of the filter holder. Such bars can be easily produced by injection molding, e.g., directly on the filter material. They prevent the filter material to collapse and to stick wet. Furthermore, they can be used during injection molding to carry molten plastics to create a punt at the bottom of the filter element. 
     In an embodiment, an inlet area of the filter module is funnel-shaped. Such a funnel shape reduces the risk of foam formation in the body fluid. Thus, the funnel shape of the inlet area can also be considered as part of the concept “defoaming by design” that is, in an embodiment, applied to the filter module. Thereby, typically the filter holder has this specific funnel-shaped inlet area, whereas the filter assembly does not need to have any specific design (as long as it fits into the filter holder). 
     In an embodiment, the bottom of the filter module is not entirely flat, but rather comprises an indention towards an interior space of the filter module. Thereby, this indention extends, in an embodiment, over essentially the full area of the bottom of the filter module (in particular of the filter holder). Then, the bottom of the filter module has a concave shape when looked from the outside of the filter module and a convex shape when looked from the inside of the filter module. Such a design of the bottom of the filter module plays also a role in the “defoaming by design” approach taken in an embodiment. The indention of the bottom of the filter module can also be described as a shape like a champagne&#39;s bottle punt. This shape avoids spurts of body fluid passing through the filter module and reduces the falling height of the body fluid passing through the filter module. The lower the falling height, the lower the risk of foam formation in the body fluid. 
     In an embodiment, the hydrophobic filter is integrated into the top cover of the container housing. Then, it is arranged in an upper location of the container so that the risk of getting into contact with the body fluid is significantly reduced. Furthermore, such integration in the top cover of the container still allows a compact design of the whole container. 
     The hydrophobic filter comprises, in an embodiment, a filter housing and a filter material placed in the filter housing. While it would be generally possible to design the hydrophobic filter as exchangeable element, it is intended, in an embodiment, that the hydrophobic filter is a disposable element that is discarded together with the whole body fluid collecting container. The lifetime of the hydrophobic filter is generally longer than the lifetime of the body fluid collecting container so that it is generally not necessary to replace the hydrophobic filter during the intended operation of the body fluid collecting container. 
     The hydrophobic filter may also be a mesh filter, wherein a mesh size of 2 to 20 μm, in particular 3 to 19 μm, in particular 4 to 18 μm, in particular 5 to 17 μm, in particular 6 to 16 μm, in particular 7 to 15 μm, in particular 8 to 14 μm, in particular 9 to 13 μm, in particular 10 to 12 μm is appropriate. 
     The hydrophobic filter is intended to filter air drawn by a vacuum source from the container for collecting a body fluid, or, to be more precisely, from the body fluid collecting section of this container. The hydrophobic filter protects the vacuum source from smoke (in particular surgical smoke), particles (such as bone or tissue fragments), and blood and also reduces the load of contaminations of the hydrophobic antibacterial filter that is associated to the pump and thus located downstream from the hydrophobic filter. 
     In an embodiment, the hydrophobic filter comprises a filter material comprising or consisting of a hydrophobic polymer such as polytetrafluoroethylene (PTFE), in particular expanded PTFE (ePTFE). 
     In an embodiment, the hydrophobic filter comprises a filter material comprising or consisting of a non-hydrophobic polymer such as polyester (such as PET) treated with a hydrophobic polymer, in particular a hydrophobic PET mesh. Since the contact with blood of this element is occasional and very limited in time (spurts) and due to the position (top cover), the risk that the hydrophobic treatment is leached into the blood is minimal. However, the hydrophobic treatment has to be biocompatible. 
     In an embodiment, the hydrophobic filter comprises a pleated filter material. By pleating the filter material, the effective filter surface can be increased while not increasing the overall space needed for the hydrophobic filter. 
     In an embodiment, the pleated filter material has a filter surface area being at least 3 times, in particular at least 4 times, in particular at least 5 times, in particular at least 6 times in particular at least 7 times, in particular at least 8 times as high as the surface area of the filter element that houses the hydrophobic filter. The filter surface area might be 3 to 8 times, in particular 4 to 7 times, in particular 5 to 6 as high as the surface area of the filter element that houses the hydrophobic filter. E.g., if the filter element has a surface area of 5 to 20 cm 2 , the total filter surface might be in a range of 15 to 160 cm 2 . Thus, by such an arrangement it is possible to incorporate a quite big filter surface area in a filter element that has only very low space requirements. This facilitates incorporating the hydrophobic filter into the top cover of the container housing while not increasing the dimensions of the top cover as compared to the top covers known from prior art. 
     In an embodiment, the container is specifically adapted to receive blood as body fluid. I.e., the body fluid referred to in the present description is, in this embodiment, blood. 
     The less foam formation in the collected body fluid, the better quality or higher yield of the collective body fluid is achieved. In case of blood as body fluid, lower foam formation results in lower hemolysis and lower platelets activation which in turn result in a higher blood recovery and better quality from the individual shed-blood processing steps. Mechanical stress of red blood cells is one ground of hemolysis. Foam formation may be an indicator of biological stress. 
     In an aspect, the invention relates to a body fluid collecting arrangement comprising a vacuum source and a container according to the preceding explanations. Thereby, the vacuum source is directly connected to a vacuum connector of the container via a vacuum line. No component parts other than the vacuum line is present between the vacuum source and the container. 
     Body fluid collecting arrangements known from prior art have the following general setup: body fluid collecting container—vacuum line—overfill protection—smoke connector—smoke filter—vacuum line—vacuum pump. Thus, six connection points need to be established in total. If the vacuum source is directly connected to the connector like in the currently discussed aspect of the present invention, only two connection points need to be established: body fluid collecting container—vacuum line—vacuum source. Thus, the integration of the hydrophobic filter into the container housing of the body fluid collecting container renders a separate overflow protection, a separate smoke connector and a separate smoke filter superfluous. Three separate parts each having two connecting points can be fully skipped when relying on this aspect of the present invention. This significantly reduces the workload for medical staff preparing a body fluid collecting arrangement ready to be used. 
     In case of massive overflow of the body fluid collecting section of the container housing, it might happen that the collected body fluid passes through the hydrophobic filter. Then, the body fluid might enter the vacuum line that is connected to the vacuum connector of the container housing. In an embodiment, the vacuum line comprises a hydrophobic antibacterial filter to protect the pump. Then, such overflow of small amounts of body fluids will not have any consequences. Rather, some hydrophobic vacuum lines are able to keep working also in the presence of accumulation of contaminations or liquids. A guiding principle is to reduce complexity of assembly of the vacuum line to enhance usability. 
     In an embodiment, the vacuum line comprises an integrally formed antibacterial filter. Thus, this antibacterial filter does not represent an additional component part, but rather is an integral part of the vacuum line. 
     In an embodiment, the antibacterial filter is a hydrophobic filter. Then, it can also be used to effectively prevent any liquid that has entered the vacuum line, e.g., due to overfill events of the body fluid collection section of the container housing, from entering into the pump being arranged downstream of the antibacterial filter. It is possible to equip such an antibacterial filter with an additional chamber to accommodate any contaminations of the filter. Then, such chamber can also serve for receiving excessive body fluid drawn through the vacuum line due to an overfill event. 
     In an embodiment, the antibacterial filter has a pore size or mesh size that is sufficiently small to also filter viruses out of the fluid (in particular air) drawn through the vacuum line. In such a case, the antibacterial filter has also anti-viral properties. Then, it can be denoted as anti-viral filter. 
     In an aspect, the present invention relates to a method for manufacturing a container according to the preceding explanations. Thereby, a top cover of a container housing of the container and a filter holder of the container are co-molded. I.e., they are manufactured as one piece or, expressed in other words, they are integrally formed or integrally molded. Such a manufacturing process is significantly easier than the manufacturing processes known from prior art. It combines the previous method steps of producing a container housing and subsequently attaching a filter into the container housing into one single manufacturing step, namely a co-molding step. It can be accomplished, e.g., by injection molding. 
     While it is also possible to co-mold the filter assembly together with the filter holder, other approaches are taken in an embodiment of the manufacturing method. To be more precisely, in this embodiment, the filter assembly is applied (e.g., by molding) into the filter holder after the filter holder has been produced. Thereby, the filter holder itself may be co-molded with the top cover of the container housing. In doing so, it is not necessary to produce different molds for different mesh sizes to be applied for a filter module of the container housing. Rather, in this embodiment, only a single mold is necessary to produce a large number of container housing top covers with an integrally formed filter holder, wherein afterwards different filter assemblies filters can be applied into the filter holder, thus resulting in container housing top covers providing different filter properties (in particular different mesh sizes of the filter assembly). 
     In an aspect, the present invention relates to medical method for drawing intraoperative cell salvage (ICS) from a patient in need thereof. ICS is typically used for patients undergoing surgery or invasive procedures and is intended to provide those patients with an autotransfusion of blood or blood components. This method comprises the steps explained in the following. First, a blood suction line is connected to a blood inlet of a container for collecting blood. Furthermore, vacuum line is connected to a vacuum connector of this container and to a vacuum source, such as a vacuum pump. In doing so, a low pressure can be applied to an interior of the container, when the vacuum source is activated. The container is a container according to the preceding explanations. Thus, it comprises a container housing with the blood inlet that allows blood to enter an inlet section of the container housing. The container housing furthermore comprises a blood collection section. Thereby, the vacuum source is typically connected via a vacuum line to the vacuum connector of the container housing. 
     Furthermore, the container housing comprises a filter module that separates the inlet section from the blood collection section. To be more specific, the filter module is arranged between the inlet section and the blood collection section so that the blood drawn from the patient needs to pass the filter in order to flow from the inlet section to the blood collection section. Expressed in other words, the filter module has a raw side and a clean side. The raw side faces the inlet section and the clean side faces the blood collection section. 
     If all elements are assembled, the vacuum source is activated. Then, blood is drawn from a patient (e.g., during a surgical intervention) through the blood suction line into the receiving section of the blood-collecting canister. It then passes the filter and reaches the blood-collecting section. Afterwards, it can be drawn from the blood-collecting container in order to be further processed and/or auto-transfused to the patient. 
     In an aspect, the present invention relates to a method for manufacturing a filter assembly according to the preceding explanations. As already mentioned, such a filter assembly comprises a filter holder, defoaming layer, an optional prefiltering layer and a mesh filter layer. 
     The filter holder is arranged downstream the mesh filter layer. The mesh filter layer, in turn, is arranged downstream of the defoaming layer and optional prefiltering layer. 
     The method is characterized in that the that the filter holder (which is made from plastic) is overmolded over a part of the filter system of defoaming layer, opt. prefiltering layer and mesh filter layer so that it contacts and stabilizes filter layers of the filter system. Thus, only a single manufacturing step is necessary in order to place the filter holder around the layers of filter material since it is manufactured in situ. This significantly facilitates the manufacturing of the filtering assembly as compared to filtering devices known from prior art. The filter holder can also form the ground area of the filter assembly. Thus, it may form the base of the filter assembly and at the same time embeds the filter material layers near the base to fix them. 
     In an embodiment, the different layers of the filter system initially form a flat ribbon. This flat ribbon is then brought into the desired shape of the filter assembly. This desired shape can be, e.g., the shape of a cylinder jacket, wherein the cylinder has a circular ground area, an elliptic ground area, a rectangular ground area or a quadratic ground area. The free ends of the shaped ribbon are then connected to each other. The connection of the free ends of the shaped ribbon can be accomplished, in an embodiment, by a welding process. Alternatively, the connection can be formed as a non-welded joint. The given shape is fixed by partially overmolding the layers of the filter system with the filter holder. This manufacturing method of a filter assembly according to an aspect of the present invention is significantly easier than manufacturing techniques applied according to prior art. To be more precise, in prior art regularly a tubular filter arrangement made of two welded ribbons needs to be cut. The according manufacturing steps are significantly more difficult and increase the risk of particle contamination since welding and cutting two tubular ribbons may generate particulates that can be leached into a fluid that passes the filter. 
     All embodiments of the described filter assembly can be combined in any desired way and can be transferred to the described use, the described container for collecting a body fluid and the described methods, and vice versa in each case. 
    
    
     
       Further details of aspects of the present invention will be explained in the following with respect to exemplary embodiments and accompanying Figures. In the Figures: 
         FIG. 1  is a perspective view of an embodiment of a blood-collecting canister; 
         FIG. 2  is a side view onto the broad side of the canister of  FIG. 1 ; 
         FIG. 3  is a detailed view of an upper part of the canister of  FIG. 1  seen from the narrow side of the canister; 
         FIG. 4A  is a schematic view of a first embodiment of the filter system according to the invention; and 
         FIG. 4B  is a schematic view of a second embodiment of the filter system according to the invention. 
     
    
    
       FIG. 1  is perspective view of a blood-collecting canister  1  that serves as container for collecting a body fluid. The blood-collecting canister  1  comprises a canister housing  2  having a top cover  3 . Three different blood inlets  4  are arranged in the top cover  3 . Typically, only one of these blood inlets  4  is used for connecting a blood suction line with the blood-collecting canister  1  in order to draw blood from a patient into the interior of the canister housing  2 . The right-most (with reference to  FIG. 1 ) blood inlet  4  is designed as a ⅜ inch connection. The middle blood inlet  4  is designed as luer inlet, wherein the most left blood inlet  4  is designed as suction line connector sized for accommodating typical blood suction lines. 
     Each of the blood inlets  4  is fluidly connected with a blood receiving section  5  that is arranged on an inner side of the top cover  3 . This blood receiving section  5  is in fluid communication with an interior of a filter module  6  (serving as filter assembly) that comprises a skeletal structure  7  that serves as filter holder. 
     Inside the skeletal structure  7 , the material layers of the filter system  8  are arranged. The filter material or filter system  8  comprises a defoaming layer and a mesh filter layer made of a medical grade mesh. If blood enters through the blood inlet  4  into the receiving section  5  of the blood-collecting canister  1 , it flows or it is drawn into the interior of the filter module  6 . Afterwards, it passes the filter material  8  and reaches a blood collection section  9  of the canister housing  2 . 
     The blood-collecting canister  1  comprises in the top section  3  of the canister housing  2  a vacuum connector  10  that is intended to be connected to a vacuum line and, via the vacuum line, with a vacuum pump that serves as vacuum source. Air or any other gases being present in the blood-collecting section  9  that are drawn through the vacuum connector  10  into a connected vacuum line need to pass a hydrophobic filter  11  that is arranged between the blood-collecting section  9  and the vacuum connector  10 . 
     The blood-collecting canister  1  further comprises a safety valve  12  that limits the amount of negative pressure that can be achieved within the interior of the canister housing  2 . Thus, the safety valve  12  serves for reducing the risk of the blood-collecting canister  1  to implode due to an undesired low negative pressure in the interior of the canister housing  2 . 
     When seen from the outside, a bottom  13  of the filter module  6  has a concave shape, i.e., it comprises an indention towards the interior of the filter module  6 . 
     Blood that has entered the canister housing  2  through the blood inlet  4  and has passed the filter material  8  collects in the blood-collecting section  9 . It can then be drawn through a blood outlet  14  out of the blood-collecting canister  1  in order to be further processed and/or auto-transfused to the patient. 
       FIG. 2  shows the blood-collecting canister  1  from  FIG. 1  in a side view onto the broad side of the blood-collecting canister  1 . Thereby, the same numeral references for the same elements are used. Reference is made to the explanations given with respect to  FIG. 1 . In  FIG. 2 , a connection between the filter module  6  and the blood receiving section  5  of the canister housing  2  can be seen. It is apparent from  FIG. 2  that blood can enter from the blood receiving section  5  only the interior of the filter module  6  and then needs to pass the filter material  8  in order to reach the blood-collecting section  9  of the canister housing  2 . Thus, the filter module  6  separates the blood receiving section  5  from the blood-collecting section  9 . 
       FIG. 3  shows a partially cut view from the narrow side onto the blood-collecting canister  1  of  FIG. 1 . Thereby, once again the same numeral references are used for the same elements. Reference is made once again to the explanations given above. 
     In the depiction of  FIG. 3 , a funnel-shaped inlet  15  is arranged in an inlet area of the filter element can be seen. Blood entering the filter module  6  from the blood receiving section  5  needs to pass needs to pass this funnel-shaped inlet  15 . The funnel-shaped inlet  15  serves—together with the filter material  8  and the concavely shaped bottom  13  of the filter module  6  for a reduced foam formation in the blood that passes through the filter module  6 . Such a reduced formation of foam leads to blood having better quality than foamed blood and to a higher collection yield due to a lower hemolysis rate. 
     It can be furthermore seen in the depiction of  FIG. 3  that the hydrophobic filter  11  comprises a pleated filter material. Due to this folding of the filter material, the effective filter surface area is significantly increased. To give an example, the filter material of the hydrophobic filter  11  has an overall filter surface area of approximately 60 cm 2 . Thereby, the hydrophobic filter itself takes only approximately 10 cm 2  space in the top cover  3  of the canister housing  2 . Thus, by folding the filter material, the effective filter surface area is made six times as big as the surface area needed by the hydrophobic filter element  11 . 
       FIG. 4A  shows a first embodiment of the filter system  8  according to the invention. It shows that the filter system  8  is made a defoaming layer  8   a  and a mesh layer  8   b.    
     The defoaming layer  8   a  is made of an open mesh fabric with a three-dimensional (3D), embossed structure for foam entrapment. In the case of the embodiment shown in  FIG. 4A  (and also in  FIG. 4B ) the spatial structure of the defoaming layer is a diamond pattern with regularly arranged protrusions and depressions of a certain height. This structure or weave pattern is also known as Gauffree Diamond. The depressions form cells for capturing the formed foam of the biological fluid. 
     Defoaming layer  8   a  may have a thickness greater than the thickness of the downstream pre-filter layer  8   c  or mesh layer  8   b.  In an embodiment, defoaming layer  8   a  may have a thickness greater than the thickness of 2 to 3 filaments. The three-dimensional structure and thickness of the defoaming layer means that the pores in the fabric are not all within the same plane. 
     The fiber material of the defoaming layer is polypropylene (PP) with fiber diameters between 200-300 μm, such as 200, 250, 300 μm. The mesh count is between 12-16 n/cm. The mesh size or opening is between 250-300 μm. 
     The mesh filter layer  8   b  is made of interconnecting threads forming a grid or a net. The mesh size of mesh filter material  8   b  is between 40 μm and 120 μm and thus smaller than the mesh size of the defoaming layer. In case of the embodiment shown in  FIG. 4A  wherein the filters system consists only of the defoaming layer and the mesh filter layer the mesh size of the mesh filter material may be 120 μm. Such a filter system is applicable for large pore size filtration. 
     The filter system as shown in  FIG. 8B  consists of three layers: defoaming layer  8   a,  mesh filter layer  8   b  and a prefilter layer  8   c  arranged (or sandwiched) between defoaming layer  8   a  and mesh filet layer  8   b.    
     The prefilter layer  8   c  consists of non-woven fibers with a trilobal cross-section, whereas the mesh filter layer  8   b  consists of a regularly formed medical grade mesh. 
     In case of the embodiment shown in  FIG. 4B  wherein the filters system consists three layers (defoaming layer  8   a,  prefilter layer  8   c  and mesh filter layer  8   b ) the mesh size of the mesh filter material may be 40 μm. Such a filter system is applicable for low pore size filtration. 
     As depicted in both  FIGS. 4A and 4B  the blood flow enters the filter system  8  through the defoaming layer  8   a.  The foam bubbles contained in the blood are entrapped within the 3D structure of the defoaming layer  8   a  and are thus prevented to enter the downstream prefilter layer  8   c  and the mesh filter layer  8   b . The blood flow leaving the filter system on the mesh filter side is foam free. 
     The pressure depends on the pore size of the material used and from its basis weight. The pressure is determined by Capillary flow porometry. This method allows for determining the pore size of the filter material (MFP, Mean Flow Pore).