Abstract:
Tangential flow filtration device is provided wherein liners are provided between the filtration element and the top and bottom holders or manifolds. The liners incorporate the flow channels and inlet and outlet ports that were previously present in the manifolds. The liners are made of an inexpensive material and therefore are disposable after a single use, making it more cost effective to dispose of them than to clean the conventional manifolds. In addition, the liners can be pre-sterilized.

Description:
[0001]    This application is a continuation of U.S. patent application Ser. No. 11/404,287 filed Apr. 14, 2006, the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Tangential Flow Filtration (TFF) is a separation process that uses membranes to separate components in a liquid solution or suspension on the basis of size or molecule weight differences. Applications include concentration, clarification, and desalting of proteins and other biomolecules such as nucleotides, antigens, and monoclonal antibodies; buffer exchange; process development; membrane selection studies; pre-chromatographic clarification to remove colloidal particles; depyrogenation of small molecules such as dextrose and antibiotics; harvesting, washing or clarification of cell cultures, lysates, colloidal suspensions and viral cultures; and sample preparation. 
         [0003]    In TFF, the solution or suspension to be filtered is passed across the surface of the membrane in a cross-flow mode. The driving force for filtration is the transmembrane pressure, usually created with a peristaltic pump. The velocity at which the filtrate is passed across the membrane surface also controls the filtration rate and helps prevent clogging of the membrane. Because TFF recirculates retentate across the membrane surface, membrane fouling is minimized, a high filtration rate is maintained, and product recovery is enhanced. 
         [0004]    Conventional TFF devices are formed of a plurality of elements, including a pump, a feed solution reservoir, a filtration module and conduits for connecting these elements. In use, the feed solution is directed from the feed solution reservoir to the filtration module while the retentate from the filtration module is recirculated from the filtration module to the feed solution reservoir until the desired volume of retentate is obtained. The membrane is sandwiched between top and bottom manifolds or holders, which serve to provide accurate mechanical constraint against the internal hydraulic pressure of the device, and also serve to distribute the filtration stream across the multiple flow paths within the device. These manifolds or holders are typically made of stainless steel and must be cleaned and validated prior to each use, particularly in biopharmaceutical and other sanitary applications. This is an expensive and time-consuming process. 
         [0005]    It would be desirable to provide a filtration device that eliminates the need for the aforementioned cleaning and validation steps when replacing the filtration medium. 
       SUMMARY OF THE INVENTION 
       [0006]    In accordance with the present teachings, a tangential flow filtration device is provided wherein liners are provided between the filtration element and the top and bottom holders or manifolds. The liners incorporate the flow channels and inlet and outlet ports that were previously present in the manifolds. The liners are made of an inexpensive material and therefore are disposable after a single use, making it more cost effective to dispose of them than to clean the conventional manifolds. In addition, the liners can be pre-sterilized. In order to provide sufficient strength and rigidity under operating conditions, the liners have a grid pattern of ribs that abut the holder plates to help prevent the liners from torquing under clamping force. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is an exploded view of the filtration device in accordance with the present invention; 
           [0008]      FIG. 2  is a top perspective view of a liner in accordance with the present invention; and 
           [0009]      FIG. 3  is bottom perspective view of a liner in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0010]    Turning first to  FIG. 1 , there is shown an exploded view of a filtration device  10  in accordance with the instant teachings. The device  10  includes a top holder plate  12  and a spaced bottom holder plate  13 . The holder plates  12 ,  13  are preferably made of stainless steel and are sufficiently rigid and durable to provide accurate and effective mechanical constraint of the assembly against internal hydraulic operating pressures, such as 50-60 psi. Apertures  28  are provided in the holder plates  12 ,  13  and in each layer of the assembly to accommodate tie rods or threaded pins or bolts  14  or other clamping device to secure the assembly together. Spacers  15  are provided, and can be spring-loaded. No filtration stream passageways are present in the holder plates  12 ,  13 . 
         [0011]    Positioned beneath holder plate  12  in the assembled state is disposable liner  16 . The liner  16  is preferably made of inexpensive material, suitable for the application, that is acceptable for pharmaceutical assays (and preferably is government approved). Suitable materials of construction include plastics, such as polystyrene, preferably polyolefins, such as polypropylene, polyethylene, copolymers and mixtures thereof. Polysulfone is particularly preferred in view of its strength and rigidity. The liner  16  is preferably molded with passageways and openings. Alternatively, and less preferred, it may be formed by milling, drilling and other such methods. 
         [0012]    As best seen in  FIG. 2 , the liner  16  includes a first port  17 A, five sub-ports  17 C a second port  17 B and four sub-ports  17 D. Port  17 A is for introduction of feed or removal of retentate depending on its orientation within the assembly, with port  17 B for removal of permeate, while preventing admixture of the filtrate with the retentate or feed, as is conventional. Port  17 A is connected to the five sub-ports  17 C in a manifold arrangement. Port  17 B is connected to the four sub-ports  17 D in a similar manner. The ports  17 A and  17 B may be located on opposite sides of the liner in order to provide adequate spacing and avoid interferences with other components. However, in the application shown, where spacing is sufficient or no interference occurs, they may be located on the same side. Each port  17 A,  17 B is in fluid communication with flow paths or passageways that communicate with respective apertures to accommodate flow of feed, retentate or permeate as is conventional, thereby defining multiple flow paths for the filtration stream within the device. 
         [0013]    The passageways are preferably tapered, narrowing as they proceed away from their respective port, to normalize pressure at each of the sub-ports  17 C and  17 D. 
         [0014]    Turning back to  FIG. 1 , there is shown positioned below liner  16  a filtration element  20 . The filtration element  20  can be a single membrane, and is preferably a plurality of stacked membranes, such as stacked ultrafiltration or microfiltration membranes, most preferably provided in the form of a cassette. Although a single cassette of membranes is shown, those skilled in the art will appreciate that multiple cassettes can be used. Suitable cassettes are sold under the name PELLICON® and are commercially available from Millipore Corporation. 
         [0015]    Positioned below the filter element  20  is a second liner  22 . Preferably the second liner  22  is identical in construction to the first liner  16 , but is when the device is in the assembled state, the liner  22  is inverted relative to the position of the first liner  16 , as shown. This allows Port  17 A to communicate with the feed ports of the device in its normal orientation, while communicating with the retentate ports while in the inverted position. Port  17 B of the liner communicates with the permeate ports in both orientations. 
         [0016]    Preferably one side of the liners  16 ,  20  includes a plurality of inter-engaging ribs, as best seen in  FIG. 3 . The ribs provide added rigidity to the liners, and can be formed in the molding process. The ribs are positioned on the side of the liner that contacts the holder plate. The ribs extend from one side of the liner to the other, except where interrupted by a port. In the rib configuration shown, a grid is formed by a plurality of longitudinal and latitudinal ribs, with nine latitudinal ribs  25 A- 25 I and nine longitudinal ribs  25 A- 26 I. The latitudinal ribs are preferably parallel with one another, and the longitudinal ribs are preferably parallel with one another and perpendicular to the latitudinal ribs. The latitudinal ribs  25 B- 25 H are preferably equally spaced, whereas the respective spaces between latitudinal rib  25 A and  25 B and  25 A and the sidewall  225  of the liner are smaller, as are the spaces between ribs  25 H and  25 I and rib  25 I and the opposite sidewall  226  of the liner. Clustering the ribs more closely together at the sidewalls provides additional strength to the liner. Longitudinal ribs  25 A- 26 I are all equally spaced, with the spacing preferably the same or substantially the same as that of latitudinal ribs  25 B- 25 H, so that the grid defined between ribs  25 B- 25 H and ribs  26 A- 26 I includes a plurality of squares, the grid formed between ribs  25 H, sidewall  226 , and ribs  26 A- 26 I includes a plurality of rectangles, and the grid formed between ribs  25 B and sidewall  225  and ribs  26 A- 26 I includes a plurality of rectangles. A U-shaped rib  27 A is formed around the permeate port  17 B, as is U-shaped rib  27 B around retentate port  17 A. 
         [0017]    The intricate rib configuration shown provides strength and rigidity to the liner. When assembled, there is significant clamping force applied to the filter element and the liner, with sealing taking place between the smooth side of the liner and the filter element  20 . Without the rib configuration, the liner would not remain flat, and therefore would not seal properly to the filter element  20 . The ribs make it possible to effectively assemble the liners in the filtration device of the invention, in sealing engagement upon the application of pressure, without the necessity of having corresponding grooves in the holder plates to mate with the ribs. Accordingly, the respective surfaces of the holder plates that abut the grids of the liners are preferably flat, and need not be specially designed to fit the liners.