WO2004004873A1

WO2004004873A1 - Hollow fiber membrane systems

Info

Publication number: WO2004004873A1
Application number: PCT/US2003/020742
Authority: WO
Inventors: Kazumi Aoyama; Hideki Kurashima; Takumi Goto
Original assignee: Pall Corporation
Priority date: 2002-07-10
Filing date: 2003-07-02
Publication date: 2004-01-15
Also published as: AU2003248780A1

Abstract

Methods and systems for processing a fluid to provide a retentate and permeate are provided, wherein a feed fluid is passed into the bores (26) of one or more hollow fiber membranes (20) to provide a retentate and a permeate while maintaining the feed fluid flow rate along the inner surfaces (28) of the membranes at an average velocity of about 0.7 m/s or less and maintaining a substantially constant permeate flux.

Description

HOLLOW FIBER MEMBRANE SYSTEMS

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS [0001] This patent application claims the benefit of U.S. Provisional Patent Application No. 60/394,650 filed July 10, 2002, which is incorporated herein by reference.

FIELD OF THE INVENTION [0002] This invention pertains to processing fluids, particularly, cell-containing fluids, by tangential flow filtration through hollow fiber membranes.

BACKGROUND OF THE INVENTION [0003] A variety of systems are used to process cell-containing fluids, e.g., to separate and/or concentrate cells and cell products present in the feed fluid. For example, a cell-containing suspension can be processed by tangential flow filtration (TFF, sometimes referred to as cross flow filtration) through hollow fibers such that a feed or process fluid containing the cells is directed through the bores of the hollow fiber membranes, a cell-containing retentate passes tangentially to the inner surface of each membrane, and a permeate or filtrate, depleted of cells (e.g., a cell broth containing cell products), passes from the inner surface of each membrane to the outer surface.

[0004] Such systems direct the feed fluid through the membranes with a high average velocity, e.g., about 2 m/sec or more, to provide adequate shear force, reduce fouling of the inner surface of the membrane, and provide adequate flux (e.g., about 30-40 liters/m²/hr (LMH)).

[0005] However, these systems suffer from a number of drawbacks. For example, the cells can be damaged during processing, reducing the yield of useful cells and/or producing a cell broth containing a high level of undesirable cellular contents and debris mixed with the desired cell products. Alternatively, or additionally, the filtration systems (e.g., including the housings, the associated tubing, and the pump(s)) have a large footprint, and retain a large volume of fluid after processing. This can be highly undesirable, as some cell-containing solutions, e.g., for biotechnical and/or pharmaceutical applications, are available in limited volumes.

[0006] The present invention provides for ameliorating at least some of the disadvantages of the prior art. These and other advantages of the present invention will be apparent from the description as set forth below. BRIEF SUMMARY OF THE INVENTION [0007] The invention provides a method of processing a feed fluid to provide a retentate and a permeate comprising directing the feed fluid into a hollow fiber filtration module comprising a housing, a feed fluid inlet, a retentate outlet, a permeate outlet, and one or more hollow fiber membranes, preferably, at least two hollow fiber membranes, each hollow fiber membrane having a bore, an inner surface and an outer surface, and passing the feed fluid into the bores of the membrane(s) while maintaining a retentate flow rate at an average velocity of about 0.7 m/s or less and applying a backpressure through the permeate out

[0008] In another embodiment of the invention, a method of processing a feed fluid to provide a retentate and a permeate is provided, the method comprising directing the feed fluid into a hollow fiber filtration module comprising a housing, a feed fluid inlet, a retentate outlet, a permeate outlet, and one or more hollow fiber membranes, wherein each hollow fiber membrane has a bore, an inner surface and an outer surface, and passing the feed fluid into the bores of the one or more membranes while applying a backpressure through the outer surfaces to the inner surfaces of the at least two membranes and maintaining a permeate flux at about 15 LMH or less.

[0009] In another embodiment of the invention, a method of processing a feed fluid to provide a retentate and a permeate is provided, the method comprising directing the feed fluid into a hollow fiber filtration module comprising a housing, a feed fluid inlet, a retentate outlet, a permeate outlet, and one or more, preferably, two or more, hollow fiber membranes, wherein each hollow fiber membrane has a bore, an inner surface, and an outer surface, and passing the feed fluid into the bores of one or more membranes to provide a retentate and a permeate while maintaining the feed fluid flow rate along the inner surfaces of the membranes at an average velocity of about 0.7 m/s or less and maintaining a permeate flux of about 15 LMH or less.

[0010] In yet another embodiment, a method of processing a feed fluid to provide a retentate and a permeate is provided, the method comprising directing the feed fluid into a hollow fiber filtration module comprising a housing, a feed fluid inlet, a retentate outlet, a permeate outlet, and one or more hollow fiber membranes, wherein each hollow membrane has a bore, an inner surface and an outer surface, and passing the feed fluid into the bores of one or more membranes while applying a backpressure through the outer surfaces to the inner surfaces of the membranes and maintaining a substantially constant permeate flux. [0011] In another embodiment, a method of processing a feed fluid to provide a retentate and a permeate is provided, the method comprising directing the feed fluid into a hollow fiber filtration module comprising a housing, a feed fluid inlet, a retentate outlet, a permeate outlet, and one or more hollow fiber membranes, wherein each hollow membrane has a bore, an inner surface and an outer surface, and passing the feed fluid into the bores of the membranes while maintaining a retentate flow rate at an average velocity of about 0.7 m/s or less, applying a backpressure through the permeate outlet, passing a first retentate through the retentate outlet and a first permeate through the permeate outlet, passing additional feed fluid into the hollow fiber filtration module, the additional feed fluid comi sing the first retentate, passing the additional feed fluid into the bores of the membranes while maintaining a retentate flow rate at an average velocity of about 0.7 m/s or less, applying a backpressure through the permeate outlet, and passing a second retentate through the retentate outlet and a second permeate through the permeate outlet. [0012] In yet another embodiment, a method of processing a feed fluid to provide a retentate and a permeate is provided, the method comprising directing a feed fluid into two or more hollow fiber filtration modules comprising a housing, a feed fluid inlet, a retentate outlet, a permeate outlet, and at least two hollow fiber membranes, wherein each hollow membrane has a bore, an inner surface and an outer surface, and passing the feed fluid into the bores of the membranes in each of the filtration modules while maintaining a retentate flow rate at an average velocity of about 0.7 m/s or less, applying a backpressure through the permeate outlet in each of the filtration modules, passing a first retentate through the retentate outlet in each filtration module and a first permeate through the permeate outlet in each filtration module, combining the first retentate from each of the filtration modules to provide a combined first retentate, passing additional feed fluid into the hollow fiber filtration module, the additional feed fluid comprising the combined first retentate, passing the additional feed fluid into the bores of the membranes in each filtration module while maintaining a retentate flow rate at an average velocity of about 0.7 m/s or less, applying a backpressure through the permeate outlet in each of the filtration modules, and passing a second retentate through the retentate outlet in each of the filtration modules and a second permeate through the permeate outlet in each of the filtration modules. [0013] Embodiments of the method further comprise passing retentate through the retentate outlet and passing permeate through the permeate outlet.

[0014] In accordance with other embodiments of the invention, a system for processing a cell-containing fluid is provided, hi one embodiment, the system is adapted to provide a permeate flux of about 15 LMH or less, more preferably, to maintain a permeate flux in the range of from about 4 to about 12 LMH. Alternatively, or additionally, embodiments of the system are adapted to provide for maintaining a retentate flow rate at an average velocity of about 0.7 m/s or less. In preferred embodiments of a system according to the invention, the system has a reduced retentate priming volume compared to a conventional system for processing the same volume of fluid.

BRIEF DESCRIPTION OF THE DRAWINGS [0015] Figure 1 is a cross-sectional view of an illustrative hollow fiber filtration module.

[001 _^ Figure 2 is a schematic of a fluid processing system according to an embodiment of the invention.

[0017] Figure 3 is a schematic of a fluid processing system according to another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION [0018] In accordance with an embodiment of the present invention, a method of processing a feed fluid to provide a retentate and a permeate comprises directing the feed fluid into a hollow fiber filtration module comprising a housing, a feed fluid inlet, a retentate outlet, a permeate outlet, and one or more hollow fiber membranes, preferably, at least two hollow fiber membranes, each hollow fiber membrane having a bore, an inner surface and an outer surface, passing feed fluid into the bore while maintaining a retentate flow rate at an average velocity of about 0.7 m/s or less, applying a backpressure through the permeate outlet and passing retentate through the retentate outlet and passing permeate through the permeate outlet. In some embodiments, the retentate comprises a first retentate and the permeate comprises a first permeate, and the method further comprises passing additional feed fluid into the hollow fiber filtration module, the additional feed fluid comprising the first retentate, passing the additional feed fluid into the bores of at least two membranes while maintaining the retentate flow rate at an average velocity of about 0.7 m/s or less, applying a backpressure through the permeate outlet and passing a second retentate through the retentate outlet and a second permeate through the permeate outlet. [0019] In another embodiment of a method of processing a feed fluid to provide a retentate and a permeate, the method comprises directing the feed fluid into a hollow fiber filtration module comprising a housing, a feed fluid inlet, a retentate outlet, a permeate outlet, and one or more hollow fiber membranes, each membrane having a bore, an inner surface and an outer surface, passing feed fluid into the bores of the membranes while applying a backpressure through the outer surfaces to the inner surfaces of the membranes and passing a retentate through the retentate outlet and a permeate through the permeate outlet. Preferably, the method includes maintaining a permeate flux at about 15 LMH or less, and even more preferably, the method includes maintaining a substantially constant permeate flux.

[0020] In another embodiment of a method of processing a feed fluid to provide a retentate and a permeate, the method comprises directing the feed fluid into a hollow fiber filtration module comprising a housing, a feed fluid inlet, a retentate outlet, a permeate outlet, and one or more hollow fiber membranes each having a bore, an inner surface and an oute surface, passing feed fluid into the bores of the hollow fiber membranes to provide a retentate and a permeate while maintaining a feed fluid flow rate along the inner surfaces of the membranes at an average velocity of about 0.7 m/s or less and maintaining a permeate flux of about 15 LMH or less.

[0021] In accordance with another embodiment of the invention, a system for processing a cell-containing fluid is provided comprising at least one hollow fiber filtration module comprising a housing, a feed fluid inlet, a retentate outlet, a permeate outlet, and at least two hollow fiber membranes, wherein each hollow membrane has a bore, an inner surface and an outer surface, and a permeate flow control device adapted to provide a backpressure through the outer surfaces to the inner surfaces of the at least two membranes, wherein the system is arranged to provide a permeate flux of about 15 LMH or less. [0022] A system for processing a cell-containing fluid according to another embodiment of the invention comprises at least two hollow fiber filtration modules, each comprising a housing, a feed fluid inlet, a retentate outlet, a permeate outlet, and one or more hollow fiber membranes, wherein each hollow membrane has a bore, an inner surface and an outer surface; and, a permeate flow control device adapted to provide a backpressure through the outer surfaces to the inner surfaces of the one or more hollow fiber membranes in the at least two hollow fiber filtration modules, wherein the system is arranged to provide a permeate flux of about 15 LMH or less.

[0023] In preferred embodiments, the system is suitable for processing about 1300 L of cell-containing fluid or less, and has a retentate priming volume of less than 13 L. In other embodiments, the system is adapted to maintain a permeate flux in the range of from about 4 to about 12 LMH. Alternatively, or additionally, embodiments of the system are adapted to provide for maintaining a retentate flow rate at an average velocity of about 0.7 m/s or less. [0024] In embodiments of the invention, the method of processing a feed fluid to provide a retentate and a permeate includes directing a feed fluid into at least one hollow fiber filtration module. Using the exemplary module illustrated in Figure 1 for reference, a typical hollow fiber filtration module 10 comprises a housing 12, a feed inlet 14, a retentate outlet 16, a permeate outlet 18, and a plurality of hollow fiber membranes 20 (i.e., two or more hollow fiber membranes; module with a single hollow fiber membrane not shown) disposed in the housing 12 between the inlet 14 and the outlets 16 and 18. The housing may include other fluid ports, for example, some standard hollow fiber membrane housings include additional inlet port(s) and/or outlet port(s), which may simply be blocked when such housing is utilized in the present invention (e.g., as shown in Figures 2 and 3). The housing 12 includes a first fluid flow path 22 extending between the feed inlet 14 and retentate outlet 16 and a second fluid flow path 24 extending between the feed inlet 14 and the permeate outlet 18. The hollow fiber membranes 20 are disposed in the housing 12 tangentially to the first fluid flow path 22 and across the second fluid flow path 24. The hollow fibers 20 each include a bore 26, an inner (or upstream) surface 28, and an outer (or downstream) surface 30. The feed fluid is directed into the hollow fiber filtration module 10 through the feed inlet 14 and through the bores 26 of the hollow fiber membranes 20. A retentate, typically containing cells, passes tangentially to the inner surface 28 of each membrane (i.e., along the first fluid flow path 22), and a permeate or filtrate (typically a cell-depleted fluid, e.g., containing a cell product) passes from the inner surface 28 of each membrane to the outer surface 30 (i.e., along the second fluid flow path 24). [0025] In accordance with the invention, one or more hollow fiber filtration modules are utilized in a fluid processing system, and, as will be described in more detail below, the flow rate of retentate tangentially to the inner surface 28 of each membrane is preferably maintained at an average velocity of less than about 0.7 m/s, even more preferably, while backpressure is applied through the outer surfaces 30 of the hollow fiber membranes to the inner surfaces 28.

[0026] For example, Figure 2 shows an illustrative fluid processing system 100 including one hollow fiber filtration module 10 as described above. The fluid processing system 100 illustrated in Figure 2 also shows a feed container or reservoir 110, and a permeate container or reservoir 112, wherein the hollow fiber filtration module 10 fluidly communicates with the feed container 110 via a feed fluid conduit 109 and feed inlet 14, and the permeate container 112 via a permeate conduit 111 and permeate outlet 18. The retentate outlet 16 also fluidly communicates with the feed container 110 via a retentate conduit 113, such that retentate may be recirculated to the hollow fiber filtration module 10 as feed fluid. Typically, the system 100 is suitable for processing about 1500L of cell-containing fluid or less, for example, about 1300 L or less, more typically, in the range of from about 600 to about 1100 L. In one more preferred embodiment, the system is suitable for processing in the range of about of from about 800 to about 1100 L of cell-containing fluid, and has a retentate priming volume (i.e., the volume of the pump, the tubing, and the retentate portion of the module(s)) of less than 13 L, even more preferably, about 12.5 L or less. In some embodiments, e.g., for use in some laboratories, the system is suitable for processing about 500 L of cell-containing fluid or less, and has a retentate priming volume of about 7 L or less, more preferably, about 5.5 L or less. [00 ] The illustrated fluid processing system 100 also includes a pump 120 for providing feed flow disposed between the feed container 110 and the hollow fiber filtration module 10, preferably between the feed container 110 and the feed valve 116. Typically, the pump 120 is capable of providing a feed fluid flow rate of about 100 L/min or less, and in some embodiments, about 80 L/min or less. Preferably, the system also includes at least one permeate flow control device adapted to provide a backpressure through the outer surfaces 30 to the inner surfaces 28 of the membranes, and in this illustrated embodiment, system 100 includes a permeate flow control device comprising a permeate valve 114 disposed downstream of the permeate outlet 18 to provide the backpressure. The system can include additional components, and in the embodiment illustrated in Figure 2, the system 100 includes additional flow control devices, i.e., comprising a feed valve 116 disposed at or near the feed inlet 14 and a retentate valve 118 disposed at or near the retentate outlet 16. In some embodiments, the fluid processing system 100 may also include a pressure storage reservoir such as an accumulator (not shown), e.g., disposed downstream of the permeate valve 114 for ease in providing backpressure to the hollow fiber membranes 20. The illustrated embodiment of the system also includes pressure gauges, e.g., for measuring the feed, retentate, and permeate pressures.

[0028] In operation of the system, the flow rate of retentate tangentially to the inner surface 28 of each membrane is preferably controlled. More preferably, the flow rate is maintained at an average velocity of less than about 0.7 m/s, preferably from about 0.1 m/s to about 0.5 m/s. In one embodiment, the flow rate tangentially to the inner surface 28 of each membrane is maintained at an average velocity of about 0.2 m/s. The flow rate of retentate tangentially to the inner surface 28 of each membrane may be maintained at the desired average velocity by a variety of arrangements. For example, in some embodiments, the flow rate of retentate may be controlled using a flow control device such as valve 118 (preferably a variable flow valve), disposed at or near the retentate outlet 16 or pump 120 to control the feed fluid flow rate into the feed inlet 14 and the membrane bore(s) 26. [0029] In preferred embodiments of the invention, backpressure is applied to the hollow fiber membranes 20. Backpressure is applied through the outer surfaces 30 of the hollow fiber membranes to the inner surfaces 28, preferably through the permeate outlet 18. Typically, the backpressure is applied by a permeate flow control device (e.g., by partially closing valve 114) disposed at or near the permeate outlet 18. Alternatively, for example, backpressure can be applied by a permeate flow control device such as a permeate pump (not shown) controlling the permeate flow, e.g., disposed downstream of the permeate outlet 18. ^"desired, a pressure storage reservoir such as an accumulator can also be used in applying backpressure.

[0030] Preferably, backpressure is used in manipulating the permeate flux. For example, in some embodiments, backpressure is utilized in maintaining the permeate flux at about 15 liters/m²/hr (LMH) or less, more preferably in the range from about 4 to about 12 LMH, and in some embodiments, in the range from about 7 to about 10 LMH. The particular permeate flux rate may be chosen based on a variety of factors, such as the properties of the feed fluid and the retentate average velocity through the bore 26. Preferably, the permeate flux is maintained at a substantially constant value, e.g., varying by about 25% or less, in some embodiments, varying by about 15% or less, or even about 10% or less, throughout the process.

[0031] In preferred embodiments of the invention, backpressure is also used to manipulate the transmembrane pressure (TMP), i.e., the pressure drop across the membrane surface. Since transmembrane pressure typically varies along the length of a membrane, reference is commonly made to the average transmembrane pressure. The average transmembrane pressure comprises the difference between the average pressure on the inner surface of the membrane (i.e., the average of the feed pressure and retentate pressure) and the pressure on the outer surface of the membrane (i.e., the permeate pressure). In embodiments of the invention, backpressure may be applied to maintain, for example, an average transmembrane pressure of preferably about 0.075 MPa or less, more preferably about 0.055 MPa or less, even more preferably about 0.015 MPa or less. Advantageously, low backpressures can be utilized in accordance with preferred embodiments of the invention, thus minimizing possible damage to the hollow fiber membranes being used. As a result, a wide variety of hollow fiber membranes, even some less robust membranes, can be used according to embodiments of the invention. [0032] Preferred embodiments of systems according to the invention include a plurality of hollow fiber filtration modules, and any number of modules can be utilized in accordance with the invention. The use of a plurality of modules, e.g., 2, 3, 4, or 5 modules, or more, can be especially desirable for processing a large volume of fluid in less time. Figure 3 illustrates an embodiment of a fluid processing system 200 including five hollow fiber modules 10a- lOe. The embodiment of the fluid processing system 200 illustrated in Figure 3 includes many of the components shown in the embodiment of the system 100 shown in Figure 2. For example, Figure 3 also shows a feed container or reservoir 110, and a permeate container or reservoir 112, and the hollow fiber filtration modules 10a- lOe which eacl aclude a feed inlet (14a-14e, respectively), retentate outlet (16a-16e, respectively), and permeate outlet (18a-18e, respectively). The system 200 also includes the feed fluid conduit 109 and the retentate conduit 113 communicating with the feed reservoir 110 and the permeate conduit 111 communicating with the permeate reservoir 112. Each of the hollow fiber filtration modules 10a- lOe communicates with the feed fluid conduit 109 via the feed inlet (14a-14e, respectively) and a module feed fluid conduit (109a-109e, respectively), and the permeate conduit 111 via the permeate outlet (18a-18e, respectively) and a module permeate conduit (11 la-11 le, respectively). Each of the hollow fiber filtration modules 10a- lOe communicates with the retentate conduit 113 via the retentate outlet (16a-16e, respectively) and a module retentate conduit (113 a- 113 e, respectively). The feed fluid conduit 109 and module feed fluid conduits 109a-109e, the permeate conduit 111 and the module permeate conduits 11 la-11 le, and the retentate conduit 113 and the module retentate conduits 113a- 113e may be connected using standard connectors and/or connections known in the art, such as T-joints, welds, and the like. The illustrated system 200 also includes a pump 120 preferably disposed between the feed container 110 and the feed valve 116 for providing a flow of feed fluid to the modules lOa-e. [0033] Preferably, the system 200 also includes at least one permeate flow control device such as a valve and/or pump adapted to provide a backpressure through the outer surfaces 30 to the inner surfaces 28 of the membranes 20 in the modules. In the illustrated embodiment, a single permeate flow control device comprising a permeate valve 114 disposed downstream of all of the permeate outlets 18 provides the backpressure for all of the modules 10a- lOe. However, if desired, the system can include a plurality of permeate flow control devices for providing the backpressure. Illustratively, a separate permeate flow control device can be utilized with each module, or, for example, a plurality of permeate flow control devices, wherein each flow control device provides backpressure to two or more modules, can be utilized. [0034] The embodiment of the system illustrated in Figure 3 can be generally operated as described with respect to the system illustrated in Figure 2, e.g., with respect to maintaining an average velocity of about 0.7 m/s, or less, providing a backpressure, maintaimng a permeate flux at about 15 LMH or less and/or maintaining an average TMP of about 0.075 MPa or less.

[0035] Embodiments of the invention are suitable for use with a variety of fluids. For example, fluids in the pharmaceutical and/or food and beverage industries may be processed according to the present invention. Embodiments of the invention include processing fluids containing at least one of cells, cell products, molecules and/or species of interest. [002 J Embodiments of the invention are particularly suitable for processing cell- containing fluids, such as fluids containing mammalian cells, bacterial cells, yeast cells and fungal cells. Fluids containing particularly fragile cells, for example, mammalian cells, especially Chinese Hamster Ovary (CHO) cells, can also be processed according to embodiments of the invention without causing an unacceptable level damage to the cells. For example, embodiments of the invention provide for processing CHO cell-containing fluids while maintaining the viability of about 60% or more of the cells, preferably, about 75% or more of the cells, and in some embodiments, 90% or more of the cells. [0037] Embodiments of the invention are also suitable for processing fluids containing cells and cell products. Processing cell-containing fluids according to the invention may include harvesting, separating and/or purifying the cells. Alternatively or additionally, processing cell-containing fluids can include harvesting, separating, concentrating, and/or purifying the cell products (e.g., cell products such as proteins and enzymes). For example, in some embodiments of the invention, a cell-containing feed fluid maybe processed to provide a cell-concentrated retentate and/or a cell product-concentrated permeate. [0038] However, the invention is not limited to processing cell-containing fluids, as, for example, a cell product-containing feed fluid can be processed to harvest, separate, concentrate and/or purify one or more desired cell products. Embodiments of the invention can provide, for example, for separating desired molecules (e.g., separating larger macromolecules from smaller macromolecules) or species in the feed fluid. [0039] In accordance with preferred embodiments of the invention, a portion of fluid (typically, retentate) is recirculated through the system. For example, retentate passing through the retentate outlet 16 (Figure 2) or the retentate outlets 16a-16e (Figure 3) is subsequently passed into the hollow fiber filtration module 10 (Figure 2) or the hollow fiber filtration modules 10a- lOe (Figure 3) as additional feed fluid. The additional feed fluid is processed to provide a retentate and permeate as described above. For example, using Figure 2 for reference, after a first retentate is obtained and passed as additional feed fluid into the bores 26 of the hollow fiber membranes 20, a second retentate passes through the retentate outlet 16 and a second permeate passes through the permeate outlet 18. Retentate passing through the retentate outlet 16 may be recirculated as additional feed fluid any suitable number of times. Illustratively, the second retentate can be passed as additional feed fluid into the bores of the membranes to provide a third retentate and a third permeate. In some embodiments, recirculation advantageously provides, for example, a final retentate that has a high concentration of the component of interest, e.g., the desired cells. [0040] Embodiments of the system, which is preferably a sterile system, can include a vari y of configurations. Additionally, a variety of fluid processing system components, e.g., one or more hollow fiber filtration modules, housings, hollow fiber membranes (such as polymer membranes, skinned (including single-skinned and double-skinned) and non-skinned membranes), tubing, flow control devices (such as valves and pumps), feed and permeate containers, and pressure storage reservoirs, are suitable for use in accordance with the invention and are commercially available. Illustratively, the particular module(s), membrane(s), number of membranes, pore size(s) or molecular weight cut off(s) utilized will depend on, for example, the cell-containing feed fluid being processed and/or the desired cell product, as is known in the art.

[0041] Suitable flow control devices include clamps, ball valves, diaphragm valves, needle valves, and pumps. Flow control devices can be variable flow, i.e., capable of providing varying flow rates, and binary on/off that open to permit flow and close to block flow. Suitable pumps include, but are not limited to, vane pumps, tubing pumps, rotary pumps, and diaphragm pumps, and may be chosen based upon, for example, the desired flow rate.

[0042] The system can include a plurality of types of flow control devices. The system can include a plurality of types of valves, for example a first variable flow valve (e.g., valve 114) arranged to provide backpressure through the outer surfaces of the hollow fiber membranes to the inner surfaces, a second variable flow valve (e.g., valve 118) arranged to provide retentate pressure, and a binary on/off valve (e.g., valve 116) arranged to permit feed flow into the module when open and to block flow when closed. [0043] The following examples further illustrate the invention but, of course, should not be construed as in any way limiting its scope. EXAMPLE 1 [0044] This example demonstrates the concentration of bakery yeast cells in accordance with an embodiment of the invention.

[0045] A fluid processing system is arranged as generally shown in Figure 2. The system includes a MICROZA® Lab Module (Asahi Chemical Industry Co., Ltd., Japan; Model XULP-143) with hollow fiber membranes having a pore size of 0.45 μm and a total membrane area of 0.2 m . The pump is a vane pump (Toshm Technical Co., Ltd., Japan, Model TOP-HIAS-3T) rated for a maximum flow rate of 3L/min. The tubing used to connect the components of the system has an inner diameter of 8 mm. The system has a prir αg volume of 250 ml.

[0046] The system is prepared for fluid processing by opening the feed and retentate valves fully and closing the permeate valve. A solution including a 10% concentration of bakery yeast cells is introduced into the hollow fiber filtration module through the feed fluid inlet at a pressure of 0.025 MPa and retentate flow is regulated to establish a flow rate of about 0.25 m/s (2 L/min). The retentate valve is closed slightly to establish a retentate pressure of about 0.01 MPa. The permeate valve is opened gradually to establish a backpressure of about 0.015 MPa, a permeate flux of about 7 LMH, and a transmembrane pressure (TMP) of about 0.0025 MPa. Retentate passing through the retentate outlet is recirculated and introduced into the feed fluid inlet, and permeate passing through the permeate outlet is passed to a permeate tank. No valve adjustments are made during the processing.

[0047] Processing is continued until the feed pressure rises to about 0.040MPa, indicating an increase in the viscosity of the solution due to the increased concentration of bakery yeast cells therein. The processing yields a 50% concentration of bakery yeast cells (nearly the concentration limit) in the retentate. Permeate flux remains substantially constant throughout the process without valve adjustments.

EXAMPLE 2 [0048] This example demonstrates fragile CHO cells can be concentrated in accordance with an embodiment of the invention.

[0049] A fluid processing system arranged as generally shown in Figure 2, including a Microza® Lab Module (Model XULP-143) with hollow fiber membranes having a pore size of 0.45 μm and a total membrane area of 0.2 m² and a vane pump (Toshin Technical Co., Ltd., Japan, Model TOP-HIAS-3T) rated for a maximum flow rate of 3 L/min. [0050] The system is prepared for processing by opening the feed and retentate valves fully and closing the permeate valve. A solution including CHO cells at a concentration of 1 x 10⁵ cells/mL is introduced into the system through the feed fluid inlet at a pressure of 0.021 - 0.022 MPa, and the retentate valve is closed slightly to establish a retentate pressure of 0.010 MPa. The permeate valve is opened gradually to establish a backpressure of about 0.010 MPa, a TMP of .0058 MPa, and a permeate flux of about 6 LMH. Retentate passing through the retentate outlet is recirculated and introduced into the feed fluid inlet, and permeate passing through the permeate outlet is passed to a permeate tank. No valve adjustments are made during the processing. '

[00, ] After approximately 2.5 hours, the initial four liters of solution are reduced to 1 liter, yielding a concentration of 4 x 10⁵ CHO cells per mL retentate. After concentration, the cells are tested for viability and greater than about 95% of the cells are found to be viable. Permeate flux remains substantially constant throughout the process without valve adjustments.

[0052] All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0053] The use of the terms "a" and "an" and "the" and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0054] Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Of course, variations of those preferred embodiments will become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims

WHAT IS CLAIMED IS:

1. A method of processing a feed fluid to provide a retentate and a permeate comprising: directing the feed fluid into a hollow fiber filfration module comprising a housing, a feed fluid inlet, a retentate outlet, a permeate outlet, and one or more hollow fiber membranes, wherein each hollow membrane has a bore, an inner surface and an outer surface; passing the feed fluid into the bores of the membranes while maintaining a retentate flo\ ate at an average velocity of about .7 m/sec or less; applying a backpressure through the permeate outlet; and, passing a retentate through the retentate outlet and a permeate through the permeate outlet.

2. The method of claim 1 , wherein processing the feed fluid comprises passing the feed fluid into the bores of at least two hollow fiber membranes while maintaining the retentate flow rate at an average velocity of about .7 m/sec or less.

3. The method of claim 1 or 2, including maintaining a substantially constant permeate flux.

4. The method of any one of claims 1 -3 , wherein the retentate flow rate is maintained at an average velocity of about .1 to about .5 m/sec.

5. A method of processing a feed fluid to provide a retentate and a permeate comprising: directing the feed fluid into a hollow fiber filtration module comprising a housing, a feed fluid inlet, a retentate outlet, a permeate outlet, and one or more hollow fiber membranes, wherein each hollow membrane has a bore, an inner surface and an outer surface; passing the feed fluid into the bores of the membranes while applying a backpressure through the outer surfaces to the inner surfaces of the membranes and maintaining a permeate flux of about 15 LMH or less; and passing a retentate through the retentate outlet and a permeate through the permeate outlet.

6. The method of claim 5, wherein processing the feed fluid comprises passing the feed fluid into the bores of two or more hollow fiber membranes while applying a backpressure through the outer surfaces to the inner surfaces of the membranes and maintaining a permeate flux of about 15 LMH or less.

7. The method of claim 5 or 6, including applying the backpressure through the permeate outlet.

8. The method of any of claims 5-7, including maintaining the permeate flux in the range of from about 4 to about 12 LMH.

9. A method of processing a feed fluid to provide a retentate and a permeate comprising: directing the feed fluid into a hollow fiber filtration module comprising a housing, a feed fluid inlet, a retentate outlet, a permeate outlet, and two or more hollow fiber membranes, wherein each hollow fiber membrane has a bore, an inner surface and an outer surface; passing the feed fluid into the bores of at least two membranes to provide a retentate and a permeate while maintaining the feed fluid flow rate along the inner surfaces of the at least two membranes at an average velocity of about 0.7 m/s or less and maintaining a permeate flux of about 15 LMH or less.

10. A method of processing a feed fluid to provide a retentate and a permeate _ι comprising: directing the feed fluid into a hollow fiber filtration module comprising a housing, a feed fluid inlet, a retentate outlet, a permeate outlet, and two or more hollow fiber membranes, wherein each hollow membrane has a bore, an inner surface and an outer surface; passing the feed fluid into the bores of at least two membranes while applying a backpressure through the outer surfaces to the inner surfaces of the at least two membranes and maintaining a substantially constant permeate flux; and passing a retentate through the retentate outlet and a permeate through the permeate outlet.

11. The method of any preceding claim, wherein the feed fluid comprises a cell-containing fluid.

12. The method of claim 11, wherein the cell-containing fluid comprises at least one of mammalian cells, bacterial cells, yeast cells, and fungal cells.

13. The method of claim 11 or 12, wherein the method includes providing a cell-concentrated retentate and a cell-depleted permeate.

14. The method of any of claims 11-13, wherein the feed fluid comprises a cell- and cell product-containing fluid, and the method includes providing a cell product-concentrated permeate.

15. The method of claim 11 or 12, wherein the cells in the cell-concentrated retentate have a viability of at least about 60%.

16. The method of any of claims 11-13, wherein the cell-concentrated retentate comprises mammalian cells, bacterial cells, yeast cells, or fungal cells.

17. The method of any of claims 12-16, wherein the cell-concentrated retentate comprises mammalian cells.

18. The method of claim 17, wherein the mammalian cells comprise Chinese Hamster Ovary (CHO) cells.

19. The method of any preceding claim, further comprising recirculating retentate through the hollow fiber filtration module, wherein the feed fluid comprises recirculated retentate.

20. A method of processing a feed fluid to provide retentate and permeate comprising: directing a feed fluid into a hollow fiber filfration module comprising a housing, a feed fluid inlet, a retentate outlet, a permeate outlet, and one or more hollow fiber membranes, wherein each hollow membrane has a bore, an inner surface and an outer surface; passing the feed fluid into the bores of the one or more membranes while maintaining a retentate flow rate at an average velocity of about .7 m/sec or less; applying a backpressure through the permeate outlet; passing a first retentate through the retentate outlet and a first permeate through the permeate outlet; passing additional feed fluid into the hollow fiber filtration module, the additional feed fluid comprising the first retentate; passing the additional feed fluid into the bores of the one or more membranes while maintaining a retentate flow rate at an average velocity of about .7 m/sec or less; applying a backpressure through the permeate outlet; and passing a second retentate through the retentate outlet and a second permeate through the permeate outlet.

21. The method of claim 20, wherein processing a feed fluid comprises passing the feed fluid into the bores of at least two membranes while maintaining a retentate flow rate at an average velocity of about .7 m/sec or less.

22. A method of processing a feed fluid to provide a retentate and a permeate comprising: directing a feed fluid into two or more hollow fiber filtration modules, each module comprising a housing, a feed fluid inlet, a retentate outlet, a permeate outlet, and at least two hollow fiber membranes, wherein each hollow fiber membrane has a bore, an inner surface and an outer surface; passing the feed fluid into the bores of at least two membranes in each of the filtration modules while maintaining a retentate flow rate at an average velocity of about .7 m/s or less; applying a backpressure through the permeate outlet in each of the filfration modules; passing a first retentate through the retentate outlet in each filfration module and a first permeate through the permeate outlet in each filfration module; combining the first retentate from each of the filtration modules to provide a combined first retentate; passing additional feed fluid into the plurality of hollow fiber filfration modules, the additional feed fluid comprising the combined first retentate; passing the additional feed fluid into the bores of at least two membranes in each of the filfration modules while maintaining a retentate flow rate at an average velocity of about .7 m/s or less; applying a backpressure through the permeate outlet in each of the filtration modules; and passing a second retentate through the retentate outlet in each of the filtration modules and a second permeate through the permeate outlet in each of the filtration modules.

23. A system for processing a cell-containing fluid comprising: at least one hollow fiber filtration module comprising a housing, a feed fluid inlet, a retentate outlet, a permeate outlet, and at least two hollow fiber membranes, wherein each hollow membrane has a bore, an inner surface and an outer surface; and, a permeate flow control device adapted to provide a backpressure through the outer surfaces to the inner surfaces of the at least two membranes; wherein the system is arranged to provide a permeate flux of about 15 LMH or less.

24. A system for processing a cell-containing fluid comprising: at least two hollow fiber filtration modules, each comprising a housing, a feed fluid inlet, a retentate outlet, a permeate outlet, and one or more hollow fiber membranes, wherein each hollow membrane has a bore, an inner surface and an outer surface; and, a permeate flow control device adapted to provide a backpressure through the outer surfaces to the inner surfaces of the one or more hollow fiber membranes in the at least two hollow fiber filtration modules; wherein the system is arranged to provide a permeate flux of about 15 LMH or less.

25. The system of claim 23 or 24, arranged to process about 1300 L of , cell-containing fluid or less, having a retentate priming volume less than 13 L.

26. The system of any of claims 23-25, having a retentate priming volume of about 12.5 L or less.

27. The system of any of claims 23-26, including a feed pump adapted to provide a feed flow rate of about 100 L/min or less.

28. The system of any of claims 23-27, adapted to maintain a permeate flux in the range of from about 4 to about 12 LMH.

29. The system of any of claims 23-28, adapted to provide for maintaining a retentate flow rate at an average velocity of about 0.7 m/s or less.

30. The system of any of claims 23, or 25-27, wherein the permeate flow control device adapted to provide a backpressure is disposed downstream of the permeate outlet.

31. The system of claim 24, wherein the permeate flow control device adapted to provide a backpressure is disposed downstream of the permeate outlets of the hollow fiber filtration modules.

32. The system of any of claims 23-31 , wherein the permeate flow control device adapted to provide a backpressure comprises a permeate pump.

33. The system of any of claims 23, and 25-30, wherein the hollow fiber filtration module comprises at least two hollow fiber filtration modules.

34. The system of any of claims 24-33, wherein the hollow fiber filtration module comprises at least two hollow fiber filtration modules.