Abstract:
A plasma filter is provided for separating aggregates and targeted blood cell species from plasma comprising a filter housing with an inlet and an outlet and an internal flow path between the inlet and outlet. A filter media is disposed in the flowpath between the inlet and the outlet for filtering plasma that passes therethrough. The filter media comprises a filter configured to substantially remove targeted blood cell types from the plasma and a prefilter upstream of the filter, the prefilter having at least one reinforcement layer.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of the filing date of U.S. Provisional Application Ser. No. 61/451,716 filed Mar. 11, 2011, the entire contents of which is incorporated by reference herein. 
    
    
     FIELD OF THE DISCLOSURE 
     This disclosure relates generally to the processing of whole blood and, more particularly, to a filter assembly for use in such processing. 
     BACKGROUND 
     Most whole blood collected today is separated into its clinically useful components for storage, further processing and/or administration. This includes plasma, which is required by regulation to contain no more than specified maximum levels of residual red blood cells, leukocytes and platelets. As a result, the systems for collecting and/or processing plasma commonly include filtration devices to remove cellular blood species. 
     SUMMARY OF THE DISCLOSURE 
     The present subject matter has a number of aspects which may be used in various combinations, and the disclosure of one or more specific embodiments is for purposes of disclosure and description and not limitation. This summary only highlights a few of the aspects of this subject matter and additional aspects are disclosed in the drawings and more detailed description that follows. 
     In connection with one aspect of the present disclosure, a plasma filter is provided for separating aggregates and targeted blood cell species from plasma comprising a filter housing with an inlet and an outlet and an internal flow path between the inlet and outlet. A filter media is disposed in the flowpath between the inlet and the outlet for filtering plasma that passes therethrough. The filter media comprises a filter configured to substantially remove targeted blood cell types from the plasma and a prefilter upstream of the filter, the prefilter having at least one reinforcement layer. 
     In another aspect of the disclosure, a plasma filter is provided comprising a first housing layer, a prefilter for removing aggregates from the plasma; first and second filter membranes having pore sizes to remove targeted cellular blood species from plasma by exclusion; a mesh layer; and a second housing layer, wherein the prefilter is laminated to at least one reinforcement layer. Preferably, the reinforcement layer for the prefilter comprises a non-woven polyester fabric. The prefilter maybe laminated either to a single reinforcement layer or between two reinforcement layers. 
     In a further aspect of the disclosure, the reinforced prefilter may be sealed only to the first housing layer at a seal which is interior of the seal of the first and second housing layers with the first and second filter membranes. Additionally, the mesh layer may be sealed only to the second housing layer at a seal which is interior of the seal of the first and second housing layers with the first and second filter membranes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of one embodiment of a plasma filter according to the present disclosure. 
         FIG. 2  is an exploded perspective view of the plasma filter of  FIG. 1 . 
         FIG. 3  is an exploded perspective view of a first embodiment of a prefilter membrane according to the present disclosure. 
         FIG. 4  is a plan view of the inlet side of an alternate embodiment of the plasma filter of  FIGS. 1 and 2 . 
         FIG. 5  is a plan view of the outlet side of a plasma filter according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     A more detailed description of a plasma filter in accordance with the present disclosure is set forth below. It should be understood that the description below of specific devices is intended to be exemplary, and not exhaustive of all possible variations. Thus, the scope of the disclosure is not intended to be limiting, and should be understood to encompass variations or embodiments that would occur to persons of ordinary skill. 
     Examples of manual blood processing and storage systems are described generally in U.S. Pat. No. 6,669,905, which is incorporated herein by reference. The systems described therein include a membrane filter for removing the residual red blood cells, platelets, and leukocytes from plasma. 
     With reference to  FIGS. 1 and 2 , a filter  20  for use in a blood processing and storage system such as disclosed in the above-identified &#39;905 patent is shown. Such a filter  20  is typically used for plasma filtration. For ease of understanding, only the plasma filter  20  is shown, although it should be understood that it forms part of a system that also typically may include one or more blood collection, processing and storage containers, donor tubing connected to a phlebotomy needle, a sampling device, transfer tubing interconnecting the various containers, auxiliary containers for various additives (such as red blood cell additive solution), and a leukocyte filter, as well as various combinations of one or more of the above, none of which is shown. 
     Typically, after whole blood has been collected from a donor into a blood processing container, the processing container, together with the integrally attached downstream containers and tubing, is placed into a conventional centrifuge. There, the whole blood is centrifugally separated into red blood cells and blood cell-depleted plasma. The cell-depleted plasma or “cell-poor” plasma is then expressed from the blood processing container into a plasma collection container, from which it may be passed through the filter  20  into a plasma storage container. 
     The filter  20  comprises a filter media, generally designated  60 , that may be made up of three layers  36 ,  38  and  40  which are designed to remove by exclusion the red blood cells, platelets, and leukocytes typically found in plasma. The filter media  60  is enclosed within a housing  30  comprising first and second portions or sheets  32  and  34  of a preferably flexible, medical grade plastic material, such as polyvinyl chloride plasticized with di-2-ethylhexyl-phthalate (PVC-DEHP). A peripheral seal S of the various layers is formed using conventional sealing techniques, such as radio frequency heat sealing technology, to join the sheets  32  and  34  about the filter media. 
     Three layers  36 ,  38  and  40  make up the illustrated filter media  60  and are arranged serially in the flow path within the housing, one downstream of the other in the order of blood flow through the filter. 
     The first layer  36  comprises a prefilter that serves to remove fibrin clots and other large sized aggregates from the plasma, but may also retain cellular blood species by affinity, mostly the red cells. In practice, the prefilter layer  36  may comprise a borosilicate microfiber glass material with an acrylic binder resin, and will be described in greater detail below. 
     Second and third filter media layers  38  and  40  possess pore sizes which are approximately 10-fold smaller than the size of leukocytes, and which decrease in the direction of flow. Due to their pore size, the second and third filter media layers  38  and  40  remove red blood cells, platelets and leukocytes by exclusion. In practice, the second and third layers  38  and  40  may be of any suitable material and may comprise, solely or in combination with other materials, hydrophilic polyvinylidene fluoride (PVDF) membranes. The PVDF material of the second filter media layer  38  has an average pore size of about 1.0 microns, while the PVDF material of the third filter media layer  40  has a smaller average pore size of about 0.65 micron. The filter may also, if appropriate, employ only one of the second or third filter layers, or more than two such filter layers. 
     The downstream-most, in the direction of flow, last layer  42  comprises a mesh material preferably made from a polyester or polypropylene material. The mesh material of the last layer  42  provides mechanical support for the filter and prevents the PVDF material of the third filter layer from sticking, during use, to the portion or PVC sheet  34  around the outlet port  46  of the filter. 
     The plasma filter  20  includes inlet and outlet ports  44  and  46 , and the filter media  60  is located in the flow path within the housing between the inlet and outlet. In use, the inlet port  44  conveys plasma into the housing and into contact with the prefilter layer  36 . Plasma flows through the prefilter layer  36  and then through the second and third PVDF layers  38  and  40  where the removal of red blood cells and platelets, and leukocytes, occurs by exclusion. The outlet port  46  conveys plasma essentially free of blood cells through the mesh material. 
     In use, it has been found that the prefilter layer  36  is sometimes damaged such as by mishandling during, e.g., blood collection and centrifugation. For example, the prefilter may be damaged by handling impact or pressure from other portions of the fluid filter set or system during centrifugation. This can compromise the effectiveness of the filter  20 , resulting in long filtration times due to clogging of the PVDF filter membranes. 
     In keeping with the present disclosure, a plasma filter having a more robust prefilter membrane  36  is provided. With reference to  FIG. 3 , the prefilter layer  36  comprises a glass fiber membrane  36 A that is carried by or adhered to (for example, laminated to) a reinforcing material  36 B. The reinforcing material  36 B is preferably a relatively high strength porous material, such as a textured, non-woven polyester fabric. The glass fiber membrane  36 A is preferably laminated between two sheets of such reinforcing material  36 B. One such laminated membrane  36  is available from Lydall Filtration/Separation Inc., of Manchester, Conn., as LyPore Grade 9390-A/A micro glass filtration material. In an alternative embodiment, the glass fiber membrane  36 A may be carried by or adhered to (e.g., laminated to) only a single sheet of the reinforcing material  36 B, preferably on the upstream side of the glass fiber membrane  36 A. 
     The laminated prefilter  36  described in the preceding paragraph may be sized to have the same dimensions as the first and second filter layers  38 ,  40 , as shown in  FIG. 1 . This results in the peripheries of the layers  36 ,  38 ,  40  all being sandwiched together between the sheets  32 ,  34  and all being heat sealed together by the application of, e.g., radiofrequency energy. If the reinforced prefilter is laminated to only a single layer of reinforcing material  36 B, the filter is assembled with the reinforcing material  36 B positioned on the upstream side of the glass fiber membrane  36 A. 
     In an alternative configuration, the laminated prefilter  36  and the first and second filter layers  38 ,  40  may be all sized at the same dimensions and all sealed only to one of the housing portions, such as the sheet  32  of the housing  30  at S 1  inboard of the conjoined edges S 2  of the sheets  32 ,  34  as shown in  FIG. 4 . It is believed that such a separate seal S 1  for the prefilter layer  36  and the filter layers  38 ,  40  to the housing layer  32  helps to ensure a better tightness of seal S 2  and to enhance the integrity of the prefilter. The glass fiber membrane  36 A reinforced on the upstream side helps to minimize the forces to which the glass fiber membrane  36 A is subjected during centrifugation and other handling of the processing and storage system, thus reducing the likelihood of damage during handling of the blood processing and storage system. Similarly, the fourth layer  42  may be smaller in size than the layers  38 ,  40  and be sealed independently of the other filter layers on a portion of the PVC sheet  34  surrounding the outlet port sealing area by a peripheral seal S 3 , as best seen in  FIG. 5 . 
     Thus, the plasma filter may be preferably manufactured by first pre-cutting the three filter materials (pre-filter  36 , first filter layer  38 , and second filter layer  40 ) all to the same size and shape. Then the three filter materials may be pre-sealed at S 1  to the inlet housing sheet  32 . After the mesh support layer is sealed at S 3  to the outlet housing sheet  34 , the housing sheets  32  and  34  are sealed together at S 2 . 
     Thus, an improved plasma filter has been disclosed, both alone and in combination with other fluid flow elements, such as tubing, clamps and other filters, that may be employed in a pre-assembled system for blood plasma collection and processing. The description provided above is intended for illustrative purposes only, and is not intended to limit the scope of the invention to any particular embodiment described herein. Instead, the scope is to be as set forth in the appended claims.