Abstract:
A filter, in particular for the separation of leucocytes from further blood components, has an outer sheath, at least one intermediate layer which is a component of a frame or which forms a frame, an inlet chamber which is in communication with an inlet for the medium to be filtered, an outlet chamber which is in communication with an outlet for the filtrate, and a filter material which separates the inlet chamber from the outlet chamber. The filter is particularly low in dead space and can be centrifuged in a simple manner since the filter material is encompassed between the outer sheath and the intermediate layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This is a nationalization of PCT/EP03/013596 filed Dec. 2, 2003 and published in German. 
   BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   The present invention relates to a filter, in particular for the separation of leucocytes from further blood components, having an outer sheath, having at least one intermediate layer which is a component of a frame or forms a frame, having an inlet chamber which is in communication with an inlet for the medium to be filtered and an outlet chamber which is in communication with an outlet for the filtrate, and having a filter material which separates the inlet chamber from the outlet chamber. 
   Filters of this kind are, for example, used to liberate blood or blood components from leucocytes prior to storage or to transfusion to the recipient, since said leucocytes can cause unwanted side effects. There is therefore a necessity to separate leucocytes and, optionally, further interfering materials prior to the storage or transfusion of the blood or of its components (e.g. erythrocites, plasma). 
   2. Description of the Prior Art 
   Filters of this kind are known in numerous different embodiments. The filter disclosed in EP 0 526 678 B2 has an outer sheath made of flexible material which is connected to an intermediate layer of two soft foils which form a frame. The filter material which separates the outlet chamber of the filter from the inlet chamber is received in the frame. The filter material is welded into the frame formed by the foils and has the effect in this manner that the blood to be filtered or the blood components to be filtered only have to flow through the filter surface to enter into the outlet chamber. 
   An embodiment of a filter is known from WO 01/91880 A1, wherein the outer sheath consists of two foils which are directly welded to one another. No intermediate layer is provided. The filter has in inwardly disposed welding seam and an outwardly disposed welding seam, with the outwardly disposed welding seam directly connecting the foils forming the outer sheath to one another and the inwardly disposed welding seam connecting the filter material to the outer sheath. A non-welded region comprising a filter medium is located between the two welding seams and is resilient due to the lack of a welding seam and damage during centrifuging can be largely avoided by means of it. The filter known from WO 01/91880 A1 has the disadvantage that it has stubs on both oppositely disposed sides of the outer sheath for the inlet of the blood and for the outlet of the filtrate respectively, whereby a flat surface is prevented on both sides of the filter which would be desired for the purpose of centrifuging. 
   There is a disadvantage with the filter apparatus known from EP 0 526 678 B2 in that dead spaces in which no blood can be filtered arise in the region of the frame encompassing the filter material. This is unwanted because, on the one hand, the available filter volume is not fully used. On the other hand, there is a disadvantage in that valuable blood components can accumulate in the dead spaces which cannot be regained or can only be regained with difficulty after the end of the filtration. The accompanying loss of blood components not regained is unwanted. 
   SUMMARY OF THE INVENTION 
   It is therefore the object of the present invention to further develop a filter of the kind initially named such that it opens up the possibility of a simple centrifuging and such that the probability for the occurrence of dead spaces is reduced. 
   This object is solved by a filter as described herein. Accordingly, the filter material is encompassed between the outer sheath and the intermediate layer. The advantage is achieved by the connecting of the filter material to a side of the outer sheath that the occurrence of dead spaces can be prevented at least on this side and the available space of the filter is used correspondingly better. Furthermore, at least one contact side of the filter can be made without stubs, which is of advantage for the centrifuging. 
   The advantage further results over the aforesaid EP 0 526 678 B2 due to the design of the filter in accordance with the invention that the filter in accordance with the invention can consist of three layers, of which one forms the intermediate layer and two form the outer sheath, whereas the filter disclosed in the named printed document consists of at least four layers, namely of two intermediate foils to fix the filter material in place and of two layers forming the outer sheath. The filter in accordance with the present invention can generally also have more than three layers. 
   The intermediate layer is a component of the frame encompassing the filter material or forms the frame and has the advantage that, due to the number of welded layers, the welding seams can be made comparatively soft, whereby damage during the centrifuging can largely be avoided. The filter material extends in the recess formed by the frame. 
   If the intermediate layer is only a component of a frame, the further frame components, i.e. the further sections fixing the filter material in place or encompassing it, are formed, for example, by the outer sheath. In an aspect of the invention of this kind, the arrangement of the filter material between the intermediate layer and the outer sheath in accordance with the invention is accordingly only provided regionally. The arrangement of the filter material between the intermediate layer and the outer sheath in accordance with the invention thus does not have to be present in the whole filter periphery region, but can also only be provided for partial regions, for example for the region of the outlet. 
   The shape of the intermediate layer can be any desired one and can be selected freely depending on the existing demands. It is, for example, feasible to design the intermediate layer in the form of a straight or curved strip, in U shape, in the form of a semi-circle, etc., or also in a peripheral manner, whereby a closed frame is created. 
   To avoid damage during centrifuging, it is advantageous for the filter to have an outer sheath consisting of flexible material. 
   The outer sheath can consist of two parts, in particular foils, which are welded to one another, with the filter material being encompassed between one of these parts and the intermediate layer. In a preferred aspect of the invention, the outer sheath and/or the intermediate layer consist of PVC. 
   It is particularly advantageous for the filter material to be encompassed between the outer sheath on the inlet side and the intermediate layer. 
   The filter material can be welded to the outer sheath and to the intermediate layer. 
   In an advantageous aspect of the invention, the intermediate layer consists of flexible material. 
   A first inwardly disposed welding seam can be provided which connects the filter material to the intermediate layer and to the outer sheath, and a second outwardly disposed welding seam can be provided which connects the intermediate layer to the outer sheath. The inwardly disposed welding seam fixes the filter material in place in this manner between the intermediate layer and the outer sheath. The outwardly disposed welding seam connects the intermediate layer to the outer sheath. 
   In an embodiment of this kind, the marginal region of the filter material is preferably arranged in a region which extends between both welding seams around the filter material. It is particularly advantageous for the intermediate layer to have one or more apertures which connect the marginal region of the filter material encompassed in the frame to the inlet chamber and the outlet chamber. Such apertures bring along the advantage that no or comparatively little material remains in this region of the filter material, but flows from there either into the outlet chamber or back into the inlet chamber and can be filtered again. The loss of e.g. blood or blood components can be minimized in this manner. 
   The aperture(s) of the intermediate layer is/are preferably arranged in a region between the first and second welding seams. It can be achieved in this manner that the filtered medium, in particular blood, preferably flows, starting from this region, into the outlet chamber. With a corresponding design of the apertures, it is likewise possible to guide the filtered blood back into the inlet chamber and to filter it again. 
   In accordance with a further aspect of the present invention, a plurality of intermediate layers are provided. In this case, the filter has four or more layers of which e.g. two form the outer sheath and e.g. two are made as intermediate layers. More than four layers can also be used. The risk of damage during centrifuging is reduced if more layers are welded to one another. The softness and resilience of the welding seams and thus of the filter can be increased by the number of intermediate layers. 
   It is particularly advantageous for the outer sheath to consist of two foils welded to one another. They can be directly welded to one another or can receive one or more intermediate layers between them. 
   In a further aspect of the present invention, provision is made for the filter material to be elliptic in its plan view. This aspect permits an optimum filter utilization by a uniform distribution of blood on the filter material. Furthermore, the occurrence of dead zones can be largely avoided by an elliptic design. 
   The inlet for the medium to be filtered, for example for the concentrate of erythrocites, can consist of a stub welded to the outer sheath which consists of two limbs arranged at right angles to one another and of which the limb welded to the outer sheath substantially extends perpendicular from the outer sheath. 
   The outlet can consist of a cylindrical stub which is welded to the outer sheath and/or to the intermediate layer and whose longitudinal axis extends in a plane which extends parallel to the plane formed by the filter material and is offset with respect to it. The outlet stub is thus arranged “asymmetrically”. It can be welded between the outer sheath and the intermediate layer or also directly between two foils forming the outer sheath. 
   It is particularly advantageous for the filter material to be pressed or needled. A design of the filter material of this kind reduces the filter volume with an unchanged filter mass and thus increases the filter density. This has the advantage that the stability of the filter medium is in particular increased during the centrifuging. Furthermore, the regaining of blood from the filter is improved due to the lower volume with an unchanged filter performance. 
   Further details and advantages of the present invention will be explained in more detail with reference to an embodiment shown in the drawing. There are shown: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1 : a side view and a plan view of the leucocyte filter in accordance with the invention; 
       FIG. 2 : a sectional representation in accordance with section line A-A in  FIG. 1 ; 
       FIG. 3 : an enlarged representation of detail B and detail C in  FIG. 2 ; and 
       FIG. 4 : different representations of a further embodiment of a filter in accordance with the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     FIG. 1  shows the leucocyte filter  10  in accordance with the invention in a side view. It has an outer sheath consisting of the foils  12 ,  14 . The foils  12 ,  14  are made in flexible form and consist of PVC. The outer foil  14  is welded to the inlet stub  20  which has two limbs which are arranged at right angles to one another and of which the limb welded to the foil  14  extends perpendicular thereto, whereas the other limb extends substantially parallel to the outer foil  14 . 
   Furthermore, the outlet stub  30  is provided which is substantially cylindrical. It is welded to the outer foil  12  and to a foil  16  forming an intermediate layer (see  FIG. 3 , detail B). 
   The foils  12 ,  14  are welded at their periphery to the intermediate layer  16 , whereby an outwardly disposed welding seam  35  is formed. 
   As can be seen from  FIG. 1 , the longitudinal axis of the stub  30  is not located in the plane of the welding seam  35 , but in a plane which extends parallel to it and which is offset with respect to the plane of the welding seam  35 . 
   It can be seen from the plan view of the leucocyte filter in accordance with  FIG. 1 , right hand illustration, that it has an elliptic shape. The inlet stub  20  is not arranged at the center of the elliptic region, but—in accordance with FIG.  1 —above it. The elliptic design of the filter permits an ideal distribution of the medium to be filtered, whereby the filter is largely utilized. In addition, dead zones can be largely avoided. 
     FIG. 2  shows the sectional representation of the leucocyte filter in accordance with the sectional line A-A in  FIG. 1 . The arrangement of the filter material  40  can be seen from this which separates the inlet side  50 , into which the medium to be filtered flows after exiting the inlet stub  20 , from the outlet side  60 , into which the filtrate flows through the filter and exits through the stub  30 . The filter material  40  consists of polybutylene terephthalate fibers which can be coated. The filter material  40  can be made in multilayers. 
   The filter material  40  is a pressed or needled filter element which should be indicated in a schematic manner by the recesses  42 . A filter element of this kind has the advantage that its mechanical stability is increased, which is in particular necessary for the purpose of centrifuging. A further advantage consists of the fact that the regaining of the medium located in the filter material is facilitated. The filter performance is not negatively influenced by the reduced volume of the filter material. The amount of the filter material remains identical with respect to a non-pressed or non-needled embodiment. 
     FIG. 3  shows the details B and C in accordance with  FIG. 2 . Detail B relates to the region of the outlet stub  30  which is welded between the outer foil  12  and the intermediate foil  16  welded to the outer foil  14 . The outlet stub  30  extends parallel to the longitudinal axis of the elliptically made filter. As can in particular be seen from  FIG. 2 , the outlet stub  30  is arranged at the lowest point of the outlet chamber  60  so that it can be fully emptied. As can in particular be seen from  FIG. 2 , a substantially flat support of the filter can be formed in this manner which is formed in the present case by the outer foil  12 . 
   As can likewise be seen from  FIG. 2  and detail B in  FIG. 3 , the central axis of the cylindrical outlet stub  30  is not located in the plane which is formed by the filter material  40 , but is made offset thereto. 
   An enlarged view of the upper end region of the filter  10  can be seen from Figure C. The outer foil  14 , the filter material  40  and the intermediate foil  16  are shown here which are welded to one another by means of a first, inwardly disposed welding seam  37 . Furthermore, the second, outwardly disposed welding seam  35  can be seen which connects the foils  12  and  14  to the intermediate foil  16 . The marginal zone of the filter material  40  is located between these welding seams. As can be seen from detail C, the intermediate foil  16  has a recess  18  which connects the marginal region of the filter material  40  to the outlet chamber. It is thereby achieved that blood or blood components can also be regained from this marginal region of the filter material  40 . As can be seen from  FIG. 3 , the filter material  40  is welded between the foil  14  forming the outer sheath on the inlet side and the intermediate layer  16 . The advantage thereby results that the filter is made free of dead space on the inlet side since the filter material  40  is welded directly to the outer foil  14 , as can also be seen from  FIG. 2 . 
   The following example illustrates the influence of the apertures of the intermediate layer in accordance with the invention and the treatment of the filter material: 
   EXAMPLE 1 
   35 cm 2  filter area, 26 layers of coated PBT (average diameter 2 μm, surface density 50 g/m 2 ); design of the welding seams in accordance with  FIGS. 1-3 :
     WBC (white blood cells): fewer than 200,000/RCC (red cell concentrate) unit;   Filtration time: 10-13 minutes;   RCC yield: 93%.   

   EXAMPLE 2 
   The filter corresponds to the filter of Example 1, but in the non-needled or pressed state of the filter material;
     WBC: 200,000-400,000;   Filtration time: 15-17 minutes;   RCC yield: 89%.   

   EXAMPLE 3 
   The filter corresponds to the filter of Example 1, but without apertures of the intermediate layer;
     WBC: fewer than 200,000/RCC unit;   Filtration time: 10-13 minutes;   RCC yield: 91%.   

     FIG. 4  shows a further embodiment of the present invention in different views in which the joining of the marginal region of the filter material to the intermediate layer is shown in simplified form. 
   In the embodiment in accordance with  FIG. 4 , two filter media  40 ′ arranged in series are provided. They are welded in their marginal regions to a foil  16 ′ made as an intermediate layer. The foil  16 ′ is furthermore welded to the foils  12 ′ and  14 ′ which form the outer sheath of the filter. 
   The medium to be filtered flows through the inlet stub  90  which is also cylindrical like the outlet stub  100  and first flows through the filter material  40 ′ shown on the right from the bottom to the top. From there, the medium is guided through corresponding recesses on the upper side of the filter material  40 ′ arranged on the left hand side, flows through it and is finally removed through the outlet stub  100 . 
   The foils  12 ′,  14 ′ forming the outer sheaths and also the foil  16 ′ forming the intermediate layer are made of PVC. 
   The filter shown in  FIG. 4  is symmetrical and can be folded about a central axis, as is reproduced in  FIG. 4 , lower illustration. In this state, the filter can be centrifuged particularly advantageously. 
   The invention being thus described, it will be apparent that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be recognized by one skilled in the art are intended to be included within the scope of the following claims.