Equalized tangential flow filtration

Abstract

The technology provides systems and methods to isolate a biologic product from a process fluid by performing tangential flow filtration or a tangential flow depth filtration. The technology performs the filtration by drawing or pumping the fluid downward through the filter and controlling the flow rate such that a consistent pressure is maintained along the length of the filter.

Description

Docket No. 1580.00234WGEQUALIZED TANGENTIAL FLOW FILTRATIONFIELD OF THE INVENTION

[0001] The invention relates to bioprocessing systems and methods for the filtration of biologic products produced by cultured cells.BACKGROUND

[0002] In the biotechnology and pharmaceutical industries, a number of different process operations are generally used in the purification of cell-produced biologic products from bioreactor systems. One common process operation is a filtration operation. Conventional filtration processes may concentrate and wash cells and cell debris out of the system using tangential flow filtration (TFF) processes. Improved TFF processes and techniques are needed to prevent filter plugging or fouling of the filters. These techniques are needed to improve filter life, improve yields, and reduce downtime.BRIEF SUMMARY

[0003] The present technology provides a method to filter a product from a process fluid. The method includes configuring a vertical filter to perform tangential flow filtration (TFF) or a tangential flow depth filtration (TFDF) to remove biologic products or other particles from a fluid, drawing the fluid from a bottom port of the filter with a recirculation pump, directing the fluid to a process feed vessel with the recirculation pump, delivering the fluid from the process feed vessel to a top port of the filter, performing a TFF or TFDF process on the fluid to separate a permeate from the fluid. The method may also include measuring a transmembrane pressure (TMP) at a top of the filter and at a bottom of the filter. The method may also include pressurizing a shell of the filter to force liquid out of the shell back through the filter into a flow stream of the fluid.

[0004] In one aspect, the method may also include comparing the pressure at the top of the filter to the pressure at the bottom of the filter, determining a pressure drop along the length of the filter by subtracting the pressure at the bottom of the filter from the pressure at the top of the filter. The method may also include decreasing a flow rate of the recirculation pump when the determined pressure drop is greater than zero. The method may also include increasing a flow rate of the recirculation pump when the determined pressure drop is less than zero. The methodDocket No. 1580.00234WO may also include maintaining a flow rate of the recirculation pump when the determined pressure drop is approximately equal to zero.

[0005] In one aspect, the flow rate is controlled by controlling a speed of the recirculation pump. In one aspect, the speed of the recirculation pump is controlled by a processor based control system. In one aspect, each TMP is calculated using one or more one or more measured pressure sensors.

[0006] In one aspect, a method includes comparing a TMP at the top of the filter to a TMP at the bottom of the filter, determining a pressure drop along the length of the filter by subtracting the TMP at the bottom of the filter from the TMP at the top of the filter, increasing a flow rate of the recirculation pump when the determined pressure drop is greater than zero, and decreasing a flow rate of the recirculation pump when the determined pressure drop is less than zero.

[0007] In one aspect, a filter is provided to isolate a biologic product from a process fluid. The filter includes a vertical filter housing, a filter medium to perform TFF or a TFDF to remove biologic products from a fluid, a recirculation pump that provides a motive force to cause the fluid to flow downward through the filter medium, and a process feed vessel that receives filtered retentate and provides product feed to the filter.

[0008] In one aspect, a method is provided to filter a product from a process fluid using a series of serpentine filters. The method includes configuring a first vertical filter to perform tangential flow filtration (TFF) or a tangential flow depth filtration (TFDF) to remove biologic products from a fluid, providing the fluid to a top of the first filter with a recirculation pump, performing an equalized TFF or equalized TFDF process on the fluid in the first filter to separate a permeate from the fluid, directing the fluid from a bottom port of the first filter to a top of a second filter, performing an equalized TFF or equalized TFDF process on the fluid in the second filter to separate the permeate from the fluid, and directing the fluid from a bottom port of the second filter to a process feed vessel.

[0009] In one aspect a series of filters to isolate a product from a process fluid includes a first vertical filter housing and a second vertical filter housing, a filter medium in each of the two or more vertical filter housings to perform tangential flow filtration (TFF) or a tangential flow depth filtration (TFDF) to remove products from a fluid, a recirculation pump that provides a motive force to cause the fluid to flow downward through the filter medium in the first filter housing, out of the first filter housing, to a top of the second filter housing, and downward through theDocket No. 1580.00234WG filter medium in the second filter housing, and a process feed vessel that receives filtered retentate from the second filter housing and provides product feed to the first filter housing.

[0010] Other technical features may be readily apparent to one skilled in the art from the following figures, descriptions, and claims.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0011] Non-limiting embodiments of the present disclosure are described by way of example with reference to the accompanying drawings, which are schematic and not intended to be drawn to scale. The accompanying drawings are provided for purposes of illustration only, and the dimensions, positions, order, and relative sizes reflected in the figures in the drawings may vary. In the figures, identical or nearly identical or equivalent elements are typically represented by the same reference characters, and similar elements are typically designated with similar reference numbers, with redundant description omitted. For purposes of clarity and simplicity, not every element is labeled in every figure, nor is every element of each embodiment shown where illustration is not necessary to allow those of ordinary skill in the art to understand the disclosure.

[0012] FIG. 1 illustrates a system that may be utilized to perform equalized TFF in accordance with an aspect of the invention.

[0013] FIG. 2 illustrates a system that may be utilized to perform equalized TFF in accordance with an aspect of the invention.

[0014] FIG. 3 is a block flow diagram depicting a control scheme to perform equalized TFF in accordance with an aspect of the invention.

[0015] FIG. 4 illustrates a system that may be utilized to perform testing of equalized TFF in accordance with an aspect of the invention.

[0016] FIG. 5A illustrates data from a conventional TFF process in accordance with an aspect of the invention.

[0017] FIG. 5B illustrates data from an equalized TFF process in accordance with one embodiment.

[0018] FIG. 6A illustrates data collected in testing of an equalized TFF process with a motive force at the top of a filter in accordance with an aspect of the invention.

[0019] FIG. 6B illustrates data collected in testing of an equalized TFF process with a motive force at the top of a filter and with a pressurized filtrate shell in accordance with one embodiment.Docket No. 1580.00234WG

[0020] FIG. 7 is a graph of the transmembrane pressure of an equalized TFDF process and a conventional TFDF process in accordance with one embodiment.

[0021] FIG. 8 illustrates a system with multiple filters that may be utilized to perform equalized TFF in accordance with an aspect of the invention.

[0022] FIG. 9 illustrates data from a serpentine TFF co-flow process and from a serpentine equalized TFF co-flow process in accordance with an aspect of the invention.DETAILED DESCRIPTION

[0023] Recovery of cell-produced biologic products, which may include antibodies and other recombinant proteins, virus particles, viral vectors, including adeno associated virus (AAV) particles or lentivirus (LV) particles or AAV vectors, or LV vectors, as well as other nucleic acid vectors including e.g., eukaryotic or bacterial plasmid vectors, and other nucleic acid based products, including antisense oligonucleotides, mRNA, siRNA, shRNA, cDNA, etc., involves the physical separation of the biologic product from producer or host cells and / or cell debris in the cell culture fluid or lysate, abbreviated herein as “CF.” Product recovery operations are typically initiated when producer cells have reached a certain predetermined cell density, characterized as a viable cell density (VCD) or total cell density (TCD). Generally, the CF at this stage contains a high density of cells and cell debris. In operations where the cells are lysed to release the biologic product, the CF will contain high concentrations of host cell protein (HCP) and DNA (hcDNA) as well as other cell debris and / or virus particles and will typically also have a viscosity greater than 1 centipoise (cP), for example in a range of 2-30 cP, or 2-20 cP, or 2-10 cP. In either case, at the initial stage of product recovery from the CF, the CF will be characterized by high cell density or high turbidity, or both, and may also have a viscosity greater than 1 cP. Due to its high cell density and / or high turbidity, the CF is typically subjected to several clarification and concentration operations, including centrifugation, filtration, and diafiltration, to obtain a fluid of sufficient purity and concentration to be further purified by column chromatography, including affinity chromatography.

[0024] In the filtration process, the product is typically passed through or captured by a filtration module to remove biologic products. Other particles, contaminants, or solids may be similarly filtered out of a fluid flow.

[0025] The filtration module comprises a filter medium, which may include a tangential flow filtration (TFF) medium, a tangential flow depth filtration (TFDF) medium. The filtration of theDocket No. 1580.00234WG product may include a series of diafiltration and / or concentration steps. In examples herein, any suitable tangential filtration module may be referred to as TFF process or module, even if other types of filtration modules, such as TFDF, may be used.

[0026] In conventional TFF systems, the product feed flow is supplied to the filter module from the bottom entrance port of the filter housing. The product feed flows upwards through the a center of the filter and out of the top of the filter. Material that escapes through the filter medium of the filter becomes a permeate stream. In aspects of the technology described herein, the product feed flow is pulled from the bottom of the filter by a suction side of a pump. The product feed enters at the top of the filter and flows downward towards the pump. In another example, the pump provides a motive force to deliver the product feed to the top of the filter, and the product feed flows downward through the filter.

[0027] The filtration methods described herein provide a biologic product of high purity. For example, as described in detail infra, where the biologic product is recombinant virus particles, the recovered virus particles have low levels of contaminating host cell protein and nucleic acids. Alternatively, where the biologic product is recombinant protein, such as an antibody or monoclonal antibody, the recovered antibody has low levels of contaminates, including viruses.

[0028] FIG. 1 illustrates a system that may be utilized to perform equalized TFF in accordance with an aspect of the invention.

[0029] The TFF (or TFDF) process includes a feed vessel 120, which may be a primary process vessel, such as a bioreacter. FIG. 1 illustrates a recirculation pump 122 that pumps material to the feed vessel 120. The recirculation pump 122 draws retentate from the bottom of the filter 104 and pumps the retentate to the feed vessel 120. The valve 106 may serve to isolate the filter 104 from the recirculation pump 122.

[0030] The recirculation pump 122 pumps the retentate from the filter 104 into the feed vessel 120. The product in the feed vessel 120 is fed to the top of the filter 104. In one example, the feed vessel 120 maintains a product height that is above the height of the top of the filter 104. This difference in height allows the product to flow into the top of the filter 104 via gravity. In another example, a separate pump provides the force to deliver the product to the top of the filter 104. In another example, the feed vessel 120 is a pressurized vessel and the force of recirculation pump 122 or an elevated air pressure causes the product in the feed vessel 120 to be delivered to the top of the filter 104. Any suitable component or natural force may deliver the product to the top of the filter 104.Docket No. 1580.00234WO

[0031] The product is received by a port or other entrance to the interior of the filter 104. The product flows downward in a hollow center section, or lumen, of the filter housed by the filter housing. Via the TFF or TFDF process, particles and fluids that are small enough to pass through the openings or channels in the filter medium exit through the filter 104 and become the permeate. The remaining product, particles, and / or fluids become the retentate. The retentate is pumped by the recirculation pump 122 out of the bottom of the filter 104 to complete the recirculation loop.

[0032] The permeate may exit the housing of the filter 104 via a port or other opening in the filter housing. In the example, the port is located at the bottom of the filter housing. This location may allow a minimal amount of liquid to reside in the filter housing outside of the filter medium. Liquid permeate outside of the filter medium provides backpressure to the filter 104 and changes the transmembrane pressure across the filter 104. The permeate may pass through an isolation valve 108. The permeate may be pumped to a product vessel 116 by a permeate pump 124. Alternatively, the permeate may be delivered to a product vessel 116 via any other motive force, such as gravity.

[0033] The system may also comprise one or more of a flowmeter, a pressure sensor, and a controller. In an optional step, an analysis device, such as a Repligen FlowVPX system or a Repligen KONDUiT, may be mounted in the permeate line such as after the permeate pump 124. Any type of device may be used to measure characteristics of the permeate flow, such as the conductivity or concentration of product in the fluid.

[0034] A benefit of the process of FIG. 1 is that the pressure drop along the length of the filter is minimized or eliminated creating an equalized TFF. The equalized TFF process balances the effects of gravity and friction with the motive force of the recirculation pump 122. A model of the pressure profile through the filter 104 using the extended Bernoulli's Equation is illustrated below: . , IJ- ~r ”-2 i f riction

[0035] In this equation, P is the pressure, with P being the pressure at the top of the filter 104 and P-i is the pressure at the bottom of the filter 104. The velocity of the flow is represented by v and the gravitational acceleration is represented by g. Hpumprepresents the head added by the pump, and H friction represents the head loss due to friction.

[0036] The extended Bernoulli Equation may be applied to a conventional TFF process in which the product flow is pumped upwards through the filter 104 by the recirculation pump 122. In aDocket No. 1580.00234WO conventional TFF process, the pressure is separated into a few components. Pressure can be generated by the pump moving the fluid pressure changes with the height of fluid due r to gravity ( / r), pressure changes with the velocity of the fluid (—2) which decreases along the 2.? length of a membrane due to filtrate flux, and the pressure loss due to the fluid interaction with the wall of the membrane

[0037] In conventional TFF processes, pressure is maximized at the feed side of the filter 104 due to its position relative to the discharge of the recirculation pump 122, the height of the fluid entering the lumen relative to the full length of the filter 104 in the vertical position, and the velocity of the fluid entering the filter 104. At the outlet (top) of the filter 104, pressure is reduced due to the height of fluid being higher than the inlet, pressure drop due to resistance to flow through a tube, and a change in velocity from filtrate flux through the membrane. Consequently, a pressure gradient is formed along the length of the filter 104 that increases with length.

[0038] The transmembrane pressure (TMP) is the average pressure difference between the inside, or lumen, of the fiber that makes up the filter 104 and the outside of the fiber. The TMP indicates the direction and magnitude of liquid force on the membrane. TMP is calculated by subtracting the filtrate side pressure (permeate pressure) from the average pressure occurring at the inlet (feed) and outlet (retentate) of the filter 104. A positive TMP indicates that a force is being applied on the membrane from the lumen of the filter 104 to the filtrate, or permeate, side of the filter 104. A negative TMP indicates that force is being applied from the permeate side to the lumen of the filter 104.

[0039] Although this calculation provides a good measure of the pressure difference between the inside and outside of the fiber, experimentation and modeling indicates that the true TMP is not uniform along the length of the filter 104. A more accurate term would describe a measure of “localized TMP.” In conventional TFF applications where significant backpressure is not applied, TMP typically transitions from positive to negative along the length of a filter 104 due to the pressure gradient described herein. In practice, a high / positive TMP may exist at the inlet of the filter 104 and a low / negative TMP may exist at the outlet of a filter 104. This change in TMP indicates an uneven flux and filter performance along the length of the filter 104. In many cases a phenomenon occurs where fluid will permeate through the membrane at the bottom ofDocket No. 1580.00234WG the filter 104 and return to the product flow in the lumen of the filter 104 at the top. This change in flow direction is known as starling flow.

[0040] Starling flow will often lead to poor filter performance due to particles and fluids that were in the permeate stream freely passing back and forth through the membrane of the filter 104 back into the retentate. Conventional methods to reduce starling flow or high localized TMP include reducing filter length, membrane permeability, crossflow rate, and / or increasing the lumen diameter.

[0041] The process described in FIG. 1 reduces the pressure gradient along the length of the filter 104. Because the TMP is balanced along the length of the filter 104, starling flow is eliminated, the performance of the filter 104 is consistent along the length of the filter 104, and plugging and fouling of the filter 104 is reduced. An alternative process to reduce the pressure gradient along the length of the filter 104 is illustrated in FIG. 2.

[0042] FIG. 2 illustrates a system that may be utilized to perform equalized TFF in accordance with an aspect of the invention.

[0043] The process of FIG. 2 provides a motive force from above the inlet to the filter 104 to cause the product feed stream to flow downwards through the filter 104 in a similar manner as the flow of material described in FIG. 1. However, the process of FIG. 2 uses the recirculation pump 122 to provide a motive force to move the product to the top of the filter 104 instead of drawing the product feed from the bottom of the filter 104.

[0044] As illustrated, the recirculation pump 122 draws the product feed from the feed vessel 120 and pumps the product feed to the top of the filter 104. The product feed flows downward through the filter 104, and permeate that passes through the filter is pumped by a permeate pump 124 to the product vessel 116.

[0045] The retentate from the filter 104 flows out of the bottom of the filter housing, through a valve 106, and to the feed vessel 120. In an example, the motive force of the recirculation pump 122 is sufficient to overcome the forces of gravity and / or friction to force the retentate into the feed vessel 120.

[0046] In the example of FIG. 2, the flow of the product feed is similar to the flow provided by the example of FIG. 1. A similar pressure gradient is achieved. In these two examples, a flow control algorithm or control process is used to balance the pressure in the filter 104.Docket No. 1580.00234WG

[0047] FIG. 3 is a block flow diagram depicting a control scheme 300 to perform equalized TFF in accordance with an aspect of the invention.

[0048] In block 302, a start recirculation pump is performed. A product feed is introduced to a recirculation loop that includes a filter 104 and a feed vessel 120. The position and flow path of the recirculation pump 122 may be configured as described in either FIG. 1 or FIG. 2.

[0049] The product feed may be a biologic product. The term “biologic product” refers to a product produced by cells. Exemplary biologic products include recombinant proteins, antibodies, nucleic acid vectors, including viral vectors such as AAV vectors or lentiviral (LV) vectors, virus particles, including AAV and LV particles and virus-like particles (VLPs). Producer cells may be bacterial cells, yeast cells, insect cells, or mammalian cells. The biologic product may be secreted from the cells or otherwise released from the cells into the cell culture fluid (CF), for example by cell lysis. Where the cells are lysed to release the biologic product, the CF may also be referred to as the “lysate”.

[0050] As discussed above, the CF at this stage will be characterized by high cell density or high turbidity, or both, and may also have a viscosity greater than 1 centipoise (cP). For example, in some aspects, the CF may have for a cP of from 1.5-30 cP, or 1.5-20 cP, or 1.5-10 cP, or a cP of about 1.5, about 2, about 3, about 4, abut 5, about 6, about 7, about 8, about 9, about 10, about 12, about 14, about 16, about 18, or about 20. In the following discussion, the CF is referred to as “the process fluid.”

[0051] In aspects where the process fluid is characterized by a high cell density, cell density may be measured as viable cell density or “VCD”, including VCD pre-lysis where the cells are lysed to release the cell product to be recovered, or total cell density “TCD” which includes both viable and non-viable cells. For example, the process fluid may have a VCD or TCD of from lxl0A5 (10E5) to 10E9 cells per milliliter (ml). In some aspects, the process fluid may have a VCD or TCD of from about 10E5 to 10E6 cells / ml or about 10E6 to 10E7 cells / ml, or about 10E8 to f OE9 cells / ml, for mammalian and insect cells. In other aspects, for example where the cells are bacterial cells, cell density may be measured in units of optical density (OD). For example, where the cells are E. coli cells, the process fluid may have an OD of from 1-350 at 600 or 620 nm, or from 30-300 or from 30-250.

[0052] In aspects where the process fluid is characterized by a high turbidity, turbidity may be measured in nephelometric turbidity units (NTUs). In some aspects, the process fluid may have a turbidity of from about 100-30,000 NTU. In some aspects, the process fluid may have aDocket No. 1580.00234WO turbidity of from about 100-10,000 NTU, or from about 100-5,000 NTU, or from about 100- 2,500 NTU, or from about 100-1,000 NTU, or from about 100-500 NTU. In some aspects, the process fluid may have a turbidity of from about 200-1 ,000 NTU or about 300-1 ,000 NTU, or about 400-1,000 NTU. In some aspects, the process fluid may have a turbidity of about 300, about 400, about 500, about 600, about 700, about 800, or about 900 NTU.

[0053] In aspects where the process fluid is characterized by a viscosity greater than 1 cP, the process fluid may have a viscosity of from about 5-100 cP, or from 5-50 cP, or from 5-25 cP. In some aspects, the process fluid may have a viscosity of about 2, about 5, about 10, or about 15 cP.

[0054] In some aspects, the process fluid is characterized by one or more of a high cell density, which may be a high viable cell density (VCD), a high total cell density (TCD) or high optical density (OD), a high turbidity, and / or a viscosity greater than 1 , where high cell density, high turbidity, and viscosity are defined by the ranges discussed above.

[0055] The product feed in the recirculation vessel is recirculated through a system that includes a TFF or TFDF filter.

[0056] In aspects where the cells are lysed in order to release biologic product, the cells may be lysed prior to initiating the capture operation using any suitable method.

[0057] A TFF module that may be used in a conventional TFF process or the equalized TFF process described herein includes one or a plurality of hollow fiber elements which form a filter medium encased in a filter housing. As used herein, the term “hollow fiber” may refer to both “fibers” which are generally characterized in the industry as having lumens of less than 2 mm in diameter, and “tubes” which term may be used where the lumen has a diameter larger than 2 mm, for example in the range of 2-12 mm. Accordingly, the term “hollow fiber” is used herein to refer to fiber or tube-shaped filter elements which collectively encompass lumens ranging from 1-12 mm in diameter, which is also referred to as the internal diameter or “ID” of the filter element. In some aspects, the hollow fiber elements constructed of non-woven fibers having a pore size in the range of 50-200 microns.

[0058] In aspects, the filter medium may be in the form of a flat sheet spiral wound into a tubular form, which may also be referred to as “tubular / spiral wound.” In aspects, the filtration medium is constructed from a nonwoven polypropylene / polyethylene polymer having a pore size of from 50-200 microns. Suitable membranes include nonwoven wetlaid membranes.Docket No. 1580.00234WO

[0059] The filter housing of the TFF module includes a process fluid inlet to bring process fluid into the housing at an upstream or proximal end of the module and a retentate outlet to bring retentate fluid out of the housing from the downstream or distal end of the module. The filter housing will also include at least one permeate outlet to bring permeate fluid out of the housing. The housing may include other ports, for example a vent port and a drain port. In some aspects, the filter medium is encapsulated in the filter housing to provide an integral device that may be a single-use or disposable unit. In some aspects, the single-use or disposable unit may be sterile. In some aspects, the single-use or disposable unit may be sterilized by ethylene oxide gas sterilization or by irradiation, for example X-ray irradiation, gamma irradiation or electron beam irradiation.

[0060] Each hollow fiber element of the filter medium is comprised of a plurality of non-woven polymer fibers characterized by a pore rating of from 10-50 microns, or from 20-50 microns, or about 30 microns, about 40 microns, or about 50 microns. In other filter mediums, a hollow fiber element of 60-80 microns may be used, or about 70 microns. In aspects, the polymer fibers are sintered. In other aspects, the polymer fibers are melt-blown.

[0061] In some aspects, the hollow fiber filter medium is a “depth filter” medium and each hollow fiber element of the plurality is defined by a thick porous wall defining a lumen having an internal diameter (ID). In some aspects, the internal diameter (ID) is from about 1-12 millimeters (mm), or from about 3-6 mm, or from about 4-5 mm. In some aspects, the porous wall has a thickness of from about 2-10 mm, or from about 4-10 mm, or from about 4-6 mm, or from about 2-6 mm. In some aspects, the wall has a porosity in the range of from about 50-70% (0.50-0.70). In some aspects, the hollow fiber element(s) have a pore rating of from 10-50 microns. In some aspects, the hollow fiber element(s) have a length of from 5-150 centimeters (cm). In some aspects, the hollow fiber element(s) have a length of 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, or 150 cm. In some aspects, the hollow fiber element(s) have a length of about 20 cm or about 110 cm.

[0062] Porosity (P) is calculated as a weight percentage based on the density (d) of the hollow fiber element(s) measured in grams per cubic centimeter (g / cc). Where the hollow fiber element(s) consist of more than one type of polymer, a “dA” term takes into account the aggregate or blended density of the material (dA) such that porosity of the aggregate material is calculated as:

[0063] P = l-(d / dA).Docket No. 1580.00234WO

[0064] For example, where the hollow fiber element(s) are made of bi-component materials, dA is calculated as a sum of each polymer's density multiplied by its weight percentage in the material. Thus, for a material comprised of two polymers, Pl and P2, present in amounts of 70 / 30 weight percent, respectively, each having a density dl and d2, respectively, the aggregate density is calculated as

[0065] dA = (0.70 x dl) + (0.3 x d2)

[0066] In some aspects, the hollow fiber elements are defined by a porous wall of from about 0.075-10 mm thick, or from about 0.075-0.5 mm for a tangential flow filtration (TFF) medium and about 2-10 mm thick for a tangential flow depth filtration medium (TFDF), where the porous wall defines a lumen of from about 0.5-12 mm in diameter, where the porosity of the wall is in the range of from about 50-80% (0.50-0.80) or from about 50-70%. In some aspects, the hollow fiber element(s) have a pore rating of from 10-50 microns, or from 20-50 microns, or from 30- 50 microns. In some aspects, the hollow fiber element(s) have a pore rating of about 30 microns, about 40 microns, or about 50 microns.

[0067] In some aspects, the hollow fiber tangential flow filtration (TFF) elements are defined by a thin porous wall of from about 0.075-0.3 millimeters (mm) thick. In embodiments, the porous wall defines a lumen having an ID of from about 0.5 to 6 mm in diameter or from about 0.5-2 mm in diameter, where the porosity of the wall is in the range of from about 50-80% (0.50- 0.80) or from about 50-70%. In some aspects, the hollow fiber element(s) have a pore rating of from 10-50 microns, or from 20-50 microns, or from 30-50 microns. In some aspects, the hollow fiber element(s) have a pore rating of about 30 microns, about 40 microns, or about 50 microns.

[0068] In some aspects, the hollow fiber depth filtration (TFDF) elements are defined by a porous wall of from about 2-10 mm thick or about 2-6 or 4-10 mm thick, defining a lumen having an ID if from about 1-12 mm in diameter or from about 3-6 mm or about 4-5 mm in diameter, where the porosity of the wall is in the range of from about 50-80% (0.50-0.80) or from about 50-70%. In some aspects, the hollow fiber element(s) have a pore rating of from 10-50 microns, or from 20-50 microns, or from 30-50 microns. In some aspects, the hollow fiber element(s) have a pore rating of about 30 microns, about 40 microns, or about 50 microns.

[0069] The hollow fiber depth filter medium may be defined by its cross-sectional area and number of hollow fiber elements that comprise the medium, as well as by parameters of the hollow fiber element(s) that form the medium, such as the ID, wall thickness, porosity, and length of the hollow fiber element(s). In some aspects, the hollow fiber depth filter medium may beDocket No. 1580.00234WO defined by its permeability in terms of its normalized water permeability (NWP) measured as LMH / psi. In some aspects, the NWP of the hollow fiber depth filter medium is from about 7,000 to about 12,000 LMH / psi.

[0070] In some aspects, the hollow fiber elements of the TFF or TFDF filtration media are constructed of a material that includes one or more of polysulfone, polyethersulfone (PES) or modified polyethersulfone (mPES). In embodiments, the polysulfone, PES or mPES has an anisotropic structure.

[0071] The hollow fibers for use in the filter units may be formed from a variety of materials using a variety of processes. For example, hollow fibers may be formed by assembling numerous particles, filaments, or a combination of particles and filaments into a tubular shape. The pore size and distribution of hollow fibers formed from particles and / or filaments will depend on the size and distribution of the particles and / or filaments that are assembled to form the hollow fibers. The pore size and distribution of hollow fibers formed from filaments will also depend on the density of the filaments that are assembled to form the hollow fibers. For example, mean pore sizes ranging from 0.5 microns to 50 microns may be created by varying filament density.

[0072] Suitable particles and / or filaments include both inorganic and organic particles and / or filaments. In some embodiments, the particles and / or filaments may be mono-component particles and / or mono-component filaments. In some embodiments, the particles and / or filaments may be multi-component (e.g., bi-component, tri -component, etc.) particles and / or filaments. For example, bi-component particles and / or filaments having a core formed of a first component and a coating or sheath formed of a second component, may be employed, among many other possibilities.

[0073] In various embodiments, the particles and / or filaments may be made from polymers. For example, the particles and / or filaments may be polymeric mono-component particles and / or filaments formed from a single polymer, or they may be polymeric multi-component (i.e., bi- component, tri-component, etc.) particles and / or filaments formed from two, three, or more polymers. A variety of polymers may be used to form mono-component and multi-component particles and / or filaments including polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyamides such as nylon 6 or nylon 66, fluoropolymers such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), among others. Suitable polyethylene polymers include, withoutDocket No. 1580.00234WO limitation, high-density polyethylene (HDPE) and high- or ultra-high-molecular weight polyethylene (UHMWPE).

[0074] Particles may be formed into tubular shapes by using, for example, tubular molds. Once formed in a tubular shape, particles may be bonded together using any suitable process. For instance, particles may be bonded together by heating the particles to a point where the particles partially melt and become bonded together at various contact points (a process known as sintering), optionally, while also compressing the particles. As another example, the particles may be bonded together by using a suitable adhesive to bond the particles to one another at various contact points, optionally, while also compressing the particles.

[0075] Filament-based fabrication techniques that can be used to form tubular shapes include, for example, simultaneous extrusion (e.g., melt-extrusion, solvent-based extrusion, etc.) from multiple extrusion dies, or electrospinning or electrospraying onto a rod-shaped substrate (which is subsequently removed), among others.

[0076] Filaments may be bonded together using any suitable process. For instance, filaments may be bonded together by heating the filaments to a point where the filaments partially melt and become bonded together at various contact points, optionally, while also compressing the filaments. As another example, filaments may be bonded together by using a suitable adhesive to bond the filaments to one another at various contact points, optionally while also compressing the filaments.

[0077] In particular embodiments, numerous fine extruded filaments may be bonded together to at various points to form a hollow fiber, for example, by forming a tubular shape from the extruded filaments and heating the filaments to bond the filaments together, among other possibilities.

[0078] In some aspects, the hollow fiber elements of the depth filter medium are formed from sintered or melt-blown polymer fibers. The terms “fibers” and “filaments” in the context of “polymer fibers” or “polymer filaments” are used interchangeably herein. Polymers that may be used include polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyamides such as nylon 6 or nylon 66, fluoropolymers such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), among others. Suitable polyethylene polymers include, high-density polyethylene (HDPE) and high- or ultra-high-molecular weight polyethylene (UHMWPE). In some aspects, the polymer is selected from polypropylene, a polyester, and mixtures thereof.Docket No. 1580.00234WO

[0079] The term “sintered” in this context refers to the use of heat and optionally pressure in a bonding process. In this process, the polymer fibers are heated to a point where the filaments partially melt and become bonded together at various contact points, optionally, while also compressing the filaments. Thus, sintering bonds fibers where they touch, creating void spaces between the fibers. Numerous fine extruded filaments may be bonded together to at various points to form a hollow fiber, for example, by forming a tubular shape from the extruded filaments and heating the filaments to bond the filaments together.

[0080] The term “melt-blown” refers to the use of a gas stream at an exit of a filament extrusion die to attenuate or thin out the filaments while they are in their molten state. Melt-blown filaments are described, for example, in US 5607766 to Berger. Mono- or bi-component filaments may be attenuated as they exit an extrusion die using known melt-blowing techniques to produce a collection of filaments. The collection of filaments may then be bonded together in the form of a hollow fiber.

[0081] In some aspects, hollow fibers for use in the filter medium of the filter module described here may be formed by combining bicomponent filaments having a sheath of first material which is bondable at a lower temperature than the melting point of the core material. For example, hollow fibers may be formed by combining bicomponent extrusion technology with melt-blown attenuation to produce a web of entangled biocomponent filaments, and then shaping and heating the web, for example in an oven or using a heated fluid such as steam or heated air, to bond the filaments at their points of contact. An example of a sheath-core melt-blown die is schematically illustrated in US 5,607,766 in which a molten sheath-forming polymer and a molten core-forming polymer are fed into the die and extruded together. The molten bicomponent sheath-core filaments are extruded into a high velocity air stream, which attenuates the filaments, enabling the production of fine bicomponent filaments. US 3,095,343 to Berger shows an apparatus for gathering and heat-treating a multi-filament web to form a continuous tubular body, such as a hollow fiber, of filaments randomly oriented primarily in a longitudinal direction, in which the body of filaments are, as a whole, longitudinally aligned and are, in the aggregate, in a parallel orientation, but which have short portions running at random in non-parallel diverging and converging directions. In this way, a web of sheath-core bicomponent filaments may be pulled into a confined area, for example by using a tapered nozzle having a central passageway forming member, where it is gathered into tubular rod shape and heated or otherwise cured to bond the filaments.Docket No. 1580.00234WO

[0082] The hollow fiber depth filter medium does not have a defined pore size. However, pore size may be determined using methods known in the art, for example a “bubble point test.” The bubble point test is based on the fact that, for a given fluid and pore size, with constant wetting, the pressure required to force an air bubble through a pore is inversely proportional to the pore diameter. In practice, this means that the largest pore size of a filter can be established by wetting the filter material with a fluid and measuring the pressure at which a continuous stream of bubbles is first seen downstream of the wetted filter. The point at which a first stream of bubbles emerges from the filter material is a reflection of the largest pore(s) in the filter material, with the relationship between pressure and pore size being based on Poiseuille's law which can be simplified to P=K / d, where P is the gas pressure at the time of emergence of the stream of bubbles, K is an empirical constant dependent on the filter material, and d is pore diameter. In this regard, pore sizes determined experimentally may be measured using a device such as a POROLUX™ 1000 Porometer (Porometer NV, Belgium), or similar device.

[0083] Practically, given the large pore sizes of the filter media for use in the methods described here, a passage / retention test may be used to determine pore size, rather than a bubble point test. In accordance with the methods described here, the mean pore size of the hollow fiber element or elements forming the filter medium is selected based on the process conditions. In some aspects, the mean pore size of the material forming the porous wall of the hollow fiber element or elements is from 1.5 to 10 times smaller, or from about 2-5 times smaller, than the mean diameter of the resin. In some aspects, the wall of the hollow fiber element(s) is characterized by a porosity of from about 50-70% (0.50-0.70), or from about 55-70%. In some aspects, the hollow fiber element(s) have a pore rating of from 10-50 microns, or from about 20 microns, about 30 microns, about 40 microns, or about 50 microns.

[0084] In some aspects, the as-formed hollow fiber element may be further coated with a suitable coating material such as PVDF either on the inside or outside of the fiber, which coating process may also act to reduce the pore size of the hollow fiber.

[0085] In some aspects, the filter medium comprises hollow fiber elements in which porosity of the wall is in the range of from about 50-90% (0.50-0.90) or about 50%, about 60%, about 70%, about 80%, or about 90%. In some aspects, the hollow fiber element(s) have a pore rating of from 10-50 microns, or about 10 microns, about 20 microns, about 30 microns, about 40 microns, or about 50 microns.Docket No. 1580.00234WO

[0086] Returning to FIG. 3, at block 304, the control scheme 300 measures the pressure drop from the top to the bottom of the filter 104. For example, a pressure sensor at the top of the filter 104 measures the pressure at the inlet of the filter 104 and a pressure sensor at the bottom of the filter 104 measures the pressure at the exit of the filter 104.

[0087] In the examples, certain actions of the control scheme 300 illustrated in FIG. 3 are performed by a computing device, or other control system. The control system may operate on a desktop computer, a laptop computer, a manufacturing plant control system, or any other type of device. The control system may operate a computer software or hardware function to perform the steps of the process. In another example, the control scheme 300 is performed by a human operator. In examples herein, the functions are performed by an algorithm on a control system.

[0088] In decision block 306, the control scheme 300 determines whether the pressure drop is equal to zero. In examples, a range is configured to determine if a pressure drop is determined to be zero. For example, based on the precision of the pressure sensors, a calculated pressure drop that is between negative 0.5 PSI to positive 0.5 PSI is considered to be “zero.” In another example, the range is configured to be “zero” when the calculated pressure drop is between negative 0.1 PSI to positive 0.1 PSI. Any suitable range may be configured.

[0089] If the pressure drop is determined to be zero, then the control scheme 300 follows the YES branch to block 308. In block 308, the control scheme 300 maintains the flow rate. For example, the control scheme 300 maintains the operations of the recirculation pump 122 to continue the flow rate of the product feed through the filter 104.

[0090] If the pressure drop is determined not to be zero, then the control scheme 300 follows the NO branch to block 310. In decision block 310, the control scheme 300 determines if the pressure drop is above zero. For example, if the range used in block 306 was plus or minus 0.5 psi, and the measured pressure was 1.0 psi, then the pressure drop is determined to be greater than zero.

[0091] If the pressure drop is determined to be greater than zero, then the control scheme 300 follows the YES branch to block 320. If the pressure drop is determined not to be greater than zero, then the control scheme 300 follows the NO branch to block 314. If the pressure drop is not greater than zero in block 310 and was not equal to zero in block 306, then the pressure drop must necessarily be less than zero.Docket No. 1580.00234WO

[0092] Following the NO branch of block 310 to block 314, the control scheme 300 determines if the high flow boundary is met. The high flow boundary may be a configured flow rate limit for the flow of the product.

[0093] If the high flow boundary is determined to be met, then the control scheme 300 follows the YES branch to block 316. In block 316, the control scheme 300 maintains the flow rate. The flow rate may not be increased further because the recirculation pump 122 is already providing a maximum suitable flow rate. In this example, the control scheme 300 maintains the operations of the recirculation pump 122 to continue the flow rate of the product feed through the filter 104.

[0094] If the high flow boundary is determined not to be met, then the control scheme 300 follows the NO branch to block 318. In block 318, the control scheme 300 increases the flow rate of the product. For example, the recirculation pump 122 is configured to increase the flow rate of the product feed to the filter 104. The flow rate may be increased in any amount so long as the high flow boundary is not exceeded. Increasing the flow rate of the product feed causes the negative pressure drop to increase towards zero. The flow rate may be increased incrementally to monitor the results the changed flow rate has on the pressure drop. In another example, a tuned process control loop may make predictions about the amount that the flow rate should be increased to drive the pressure drop towards zero. Any suitable control loop process may be used to control the speed of the recirculation pump 122 to increase the flow rate a suitable amount.

[0095] Following the YES branch of block 310 to block 320, the control scheme 300 determines if the low flow boundary is met. The low flow boundary may be a configured flow rate limit for the flow of the product.

[0096] If the low flow boundary is determined to be met, then the control scheme 300 follows the YES branch of block 320 to block 322. In block 322, the control scheme 300 maintains the flow rate. The flow rate may not be decreased further because the recirculation pump 122 is already providing a minimum suitable flow rate to operate the filter 104. In this example, the control scheme 300 maintains the operations of the recirculation pump 122 to continue the flow rate of the product feed through the filter 104.

[0097] If the low flow boundary is determined not to be met, then the control scheme 300 follows the NO branch of block 320 to block 324. In block 324, the control scheme 300 decreases the flow rate of the product feed. For example, the recirculation pump 122 is configured to decrease the flow rate of the product feed to the filter 104. The flow rate may be decreased inDocket No. 1580.00234WG any amount so long as the low flow boundary is not exceeded. Decreasing the flow rate of the product feed causes the pressure drop to decrease towards zero. The flow rate may be decreased incrementally to monitor the results the new flow rate has on the pressure drop. In another example, a tuned process control loop may make predictions about the amount that the flow rate should be decreased to drive the pressure drop towards zero. Any suitable control loop process may be used to control the speed of the recirculation pump 122 to decrease the flow rate.

[0098] In this control scheme 300, the recirculation pump 122 is operated to provide a product feed flow rate that maintains pressure drop approaching zero. The zero pressure drop means that the TMP is equalized along the length of the filter 104. The equalized TMP provides reduced starling flow and longer filter life before plugging or fouling.

[0099] FIG. 4 illustrates a system that may be utilized to perform testing of equalized TFF in accordance with an aspect of the invention.

[0100] In the process of FIG. 4, a filter 104, a recirculation pump 122, and a feed vessel 120 are illustrated as described in FIG. 1. A pressure sensor, PTOP, is illustrated at the top of the filter housing. PBOT is a pressure sensor illustrated at the bottom of the filter housing. Along the length of the filter, six pressure transmitters Pl - P6 are illustrated as measuring pressures along the length of the filter 104 and the filter housing. Additionally, a pressure sensor, TOP, is illustrated on the top of the feed vessel 120 to illustrate or record head pressure that is placed on the filter housing head, such as from gravity or other head pressure.

[0101] In other examples, the recirculation pump 122 may direct the product flow from the bottom of the filter 104 upwards to illustrate conventional TFF processes.

[0102] The results of tests operated using a system such as FIG. 4 are illustrated in FIG. 5A, 5B, 6A, and 6B.

[0103] FIG. 5A illustrates data from a conventional TFF process in accordance with an aspect of the invention.

[0104] In the examples, a 65cm TFDF with a 4.6 mm ID was potted into an N size (1.5 inch diameter) filter housing. Pressure sensors were arrayed along the filter 104 as illustrated in FIG. 4. Water was pumped in the forward direction through the filter 104 to replicate a conventional TFF process and in a reverse direction to simulate equalized TFF.

[0105] For forward flow as in FIG. 5A, the pump outlet leads directly to the filter bottom and out of the filter top before returning to the feed reservoir. The flow path is a closed loop and theDocket No. 1580.00234WO pressure in the headspace of the feed reservoir was manipulated to simulate different liquid level heights. All tests were conducted at 1.2 liters per minute crossflow rate, the pressure sensors were zeroed in air, the flux was set to 1000 LMH, and permeate was returned to the feed vessel.

[0106] The head space of the feed vessel was pressurized to different pressures to show the scalability of the design for different liquid levels above the filter 104. The resulting pressure along the length of the filter 104 was measured and the localized TMP was calculated using the equations:

[0107] Local TMPBottom = PBOT - Pl

[0108] Local TMP top = PTOP - P6

[0109] The shell liquid volume was measured and illustrated based on the amount of permeate liquid that is collected outside of the filter medium in the filter housing.

[0110] FIG. 5B illustrates data from an equalized TFF process in accordance with one embodiment. The process of FIG. 5B is configured to operate using equalized TFF as described in FIG. 1. The pressure sensors are arranged as in FIG. 4. The process was operated under flow conditions as described in FIG. 5A.

[0111] FIG. 5A illustrates that forward flow generates a high localized TMP that switches from positive at the bottom of the filter to negative at the top of the filter, as described. FIG. 5B maintains a positive localized TMP that is lower in magnitude at the top and bottom of the filter compared to the forward flow of FIG. 5 A. In FIG. 5B, the localized TMP at the top of the filter is constant at around 0.5 psi regardless of pressure in the head space, whereas the localized TMP at the bottom of the filter began to drift lower as the pressure in the head space increases. The decrease in localized TMP at the bottom of the filter can be attributed to liquid building up in the filtrate shell creating an uneven opposing force on the filtrate side.

[0112] FIG. 6A illustrates data collected in testing of an equalized TFF process with a motive force at the top of a filter 104 in accordance with an aspect of the invention. The process of FIG. 6A is configured for equalized TFF with components operating as described in FIG. 2. The pressure sensors are arranged as in FIG. 4. The process was operated under flow conditions as described in FIG. 5A.

[0113] The data indicates that in the forward flow orientation (with the pump delivering the process feed to the top of the filter 104) the process will have a similar localized TMP trends as with suction flow illustrated in FIG. 5B. One notable difference between the two methods is thatDocket No. 1580.00234WG for FIG.6A, the Bottom and Top pressures matched the head space pressure. This may provide more favorable conditions for processes with low pressure in the vessel.

[0114] FIG. 6B illustrates data collected in testing of an equalized TFF process with a motive force at the top of a filter 104 and with a pressurized filtrate shell in a similar process as described in FIG. 6A. One modification in this example was that the filter 104 was wetted, and the filtrate shell was pressurized to remove the liquid in the shell outside of the filter 104. When pressurized, at least a portion of the liquid in the shell exits the shell because the liquid is forced back through the filter 104 and into the product flow stream. All other experiment parameters were kept the same. The purpose of this experiment was to observe the difference in localized TMP without a liquid column of permeate in the filtrate shell creating backpressure on the bottom of the filter medium.

[0115] This example verified that by pressurizing the filtrate shell with air and removing almost all liquid permeate in the shell, the localized TMP was consistent regardless of the head space pressure. Preventing a liquid column in the shell prevents the hydrostatic pressure from the liquid to create an opposing force on the outside of the filter 104. Ultimately, this creates a more uniform TMP along the length of the fiber regardless of pressure from the vessel.

[0116] FIG. 7 is a graph of the transmembrane pressure of an equalized TFDF process 704 and a conventional TFDF process 702 in accordance with one embodiment. This experiment was designed to compare the fouling behavior a conventional TFDF process and an equalized TFDF process.

[0117] In this example, a conventional TFDF process 702 and an equalized TFDF process 704 were performed, and the results were charted. In the conventional TFDF process 702 a pump provided the product feed to the bottom of the filter as described herein for conventional processes. In the equalized TFDF process 704, the recirculation pump 122 provided the product feed to the top of the filter 104 as illustrated in FIG. 2.

[0118] The filter 104 effective length was oversized to 110cm to increase the effects of high localized TMP that exists at larger scales. In the example, 1200 mL of spent perfusion media was added to each feed vessel. The recirculation flow rate was set to 1.25 L / min (2200s’1) for each feed recirculation pump 122. This flow rate is in the correct range for N-l perfusion applications. At this flow rate the feed and retentate pressure for the equalized TFDF process were approximately matching.Docket No. 1580.00234WG

[0119] The permeate flux was set to 125 mL / min (500 LMH). The permeate was recycled back into the main feed vessel. Nonsterile CHO cell culture was added in 50mL increments at a cell density of 100e6 cells / mL.

[0120] Midway through the experiment additional cell culture was added to increase the foulants in the feed stream. An additional 50mL of 100e6 cell culture was added to both feed vessels at approximately 18 hours. The TMP of the conventional TFDF process 702 and an equalized TFDF process 704 following this addition are illustrated in FIG. 7. As illustrated the TMP of the conventional TFDF process 702 increased from 0.1 PSI to over 2 PSI in the subsequent 35 hours. The TMP of the equalized TFDF process 704 only increased from -0.1 PSI to 0.1 PSI.

[0121] This result illustrates that the conventional TFDF design with high localized TMP at the bottom of the filter 104 is likely fouling and losing effective surface area at the feed end of the filter 104. The equalized TFDF design distributes the foulants evenly along the length of the fiber, thereby using all the surface area at the same time. A low to medium amount of foulants does not challenge the filter in the same way as in the conventional TFDF design.

[0122] FIG. 8 illustrates a system with multiple filters that may be utilized to perform equalized TFF in accordance with an aspect of the invention.

[0123] In some examples, a filtration system may be configured with multiple filters to increase contact of the material from the feed vessel 120 with the filtration media. Some features of this system of FIG. 8 are similar to the features of FIG. 1 or FIG.2. For example, a similar feed vessel 120 may be used to provide material. A similar recirculation pump 122 may be used to provide a motive force to move the material into and / or out of a filter housing. A permeate pump 124, an isolation valve 108, and a product vessel 116 may be used to extract the permeate from the filtration housings and store the permeate. These features and other features may be changed to account for additional flow path, longer residence times, or other changes.

[0124] The filters 104 and 804 may be provided in series to filter the material. In the example, equalized TFF or TFDF filtration process may be performed by the filters 104 and 804. The filtrate exiting the first filter 104 may be directed to the second filter 804 for additional filtering before being returned to the feed vessel 120. In other examples, additional filters may be included in the series, for a total of series filters of two, three, four, five, or more filters.

[0125] In the example, the filters 104 and 804 perform the filtration using an equalized TFF in both filters 104 and 804. That is, the material is fed to the filter 104 at the top of the filter 104,Docket No. 1580.00234WG via the recirculation pump 122, via gravity, and / or via any other motive force. The TMP of the material in the filter is equalized along the length of the filter 104 as described herein. The retentate exiting the filter 104 is directed to a top of the second filter 804. The second filter 804 performs an equalized TFF process in a similar manner. The retentate exits the bottom of the second filter 804 and is directed back to the feed vessel 120.

[0126] The filters 104 and 804 perform the filtration in a serpentine, series process. The permeate from the filter 104 and the second filter 804 are extracted by one or more permeate pumps 124 and separately or jointly are directed to the product vessel 116 or another location. As illustrated, a single pump 124 extracts the permeate from both filters 104 and 804. In another example, multiple permeate pumps 124 are used. Permeate from each filter may be extracted by a different pump 124. For example, filter 104 has a permeate pump and filter 804 has a separate permeate pump. Using dedicated permeate pumps for each filter may allow the system to more precisely modulate the TMP for each filter.

[0127] This process results in greater protein and LDH passage in typical applications. Because multiple filters, such as filters 104 and 804, can be used inline, the system is scalable to account for different filtration volumes and rates.

[0128] FIG. 9 illustrates data from a serpentine TFF co-flow process and from a serpentine equalized TFF co-flow process in accordance with an aspect of the invention.

[0129] The serpentine ETFF process represented in the data is based on a system as described in FIG. 8. The serpentine TFF process represented in the data is based on a system using two filters in series similar to the process in FIG. 8 except the material is fed to each filter from the bottom. Accordingly, the serpentine TFF process is not an equalized TFF process as described herein. Each filter performs the TFF process in a conventional process in which the flow of the material is from the bottom of the filter housing to the top of the filter housing.

[0130] The process illustrated in the graph is a high cell density perfusion filtration process after 1300 L / m2 of volumetric throughput. The cell conditions during the testing were 70 million cells / mL at 72% viability. The graph illustrates the feasibility of utilizing a much longer effective length without generating a large pressure drop.

[0131] In the graph, the TMP of each system is represented. The TMP of the serpentine TFF is approximately 0.55 psi and the TMP of the serpentine ETFF process is approximately 0.3 psi. To obtain this data, the TMP was calculated as the average pressure inside the filtrate stream minus the average pressure outside the filtrate stream (the permeate). In the example of FIG. 8,Docket No. 1580.00234WO the TMP of the serpentine ETFF process would be calculated using the pressure transmitters illustrated as P7 through P14. The calculation would be as follows:Serpentine ETFF TMP = Average (P7, P8, P9, PIO) - Average (P 11 , Pl 2, P13, Pl 4)

[0132] The average TMP for the serpentine TFF process was calculated using a similar methodology.

[0133] As illustrated, the serpentine ETFF TMP is lower than the serpentine TFF process. This indicates that the longer effective length did not adversely affect the TMP.

[0134] In the graph, the pressure drop of each system is represented. The pressure drop of the serpentine TFF is approximately 2.4 psi and the pressure drop of the serpentine ETFF process is approximately 0.4 psi. To obtain this data, the pressure drop was calculated as the pressure of the feed to the first filter 104 to the retentate outlet of the second filter 804. In the example of FIG. 8, the pressure drop of the serpentine ETFF process would be calculated as follows:Serpentine ETFF pressure drop = P7 - P10

[0135] The average pressure drop for the serpentine TFF process was calculated using a similar methodology.

[0136] As illustrated the serpentine ETFF pressure drop was minimal and significantly lower than the serpentine TFF process. Accordingly, the addition of the second filter 804 did not introduce significant pressure drop in the system.

[0137] While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.

[0138] It will be appreciated that the present invention is set forth in various levels of detail in this application. In certain instances, details that are not necessary for one of ordinary skill in the art to understand the invention, or that render other details difficult to perceive may have been omitted. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting beyond the scope of the appended claims. Unless defined otherwise, technical terms used herein are to be understood as commonly understood by one of ordinary skill in the art to which the disclosure belongs.

[0139] Various features of a process system may be used independently of, or in combination, with each other. It will be appreciated that a system as disclosed herein may be embodied inDocket No. 1580.00234WO different forms and should not be construed as limited to the illustrated embodiments of the figures.

[0140] It should be understood that, as described herein, an “embodiment” (such as illustrated in the accompanying Figures) may refer to an illustrative representation of an environment or article or component in which a disclosed concept or feature may be provided or embodied, or to the representation of a manner in which just the concept or feature may be provided or embodied. However, such illustrated embodiments are to be understood as examples (unless otherwise stated), and other manners of embodying the described concepts or features, such as may be understood by one of ordinary skill in the art upon learning the concepts or features from the present disclosure, are within the scope of the disclosure. In addition, it will be appreciated that while the Figures may show one or more embodiments of concepts or features together in a single embodiment of an environment, article, or component incorporating such concepts or features, such concepts or features are to be understood (unless otherwise specified) as independent of and separate from one another and are shown together for the sake of convenience and without intent to limit to being present or used together. For instance, features illustrated or described as part of one embodiment can be used separately, or with one or more other features to yield a still further embodiment. Thus, it is intended that the present subject matter covers such modifications and variations as come within the scope of the appended claims and their equivalents.

[0141] In view of the above, it should be understood that the various embodiments illustrated in the figures have several separate and independent features, which each, at least alone, has unique benefits which are desirable for, yet not critical to, the presently disclosed vessel, system, and associated method. Therefore, the various separate features described herein need not all be present in order to achieve at least some of the desired characteristics and / or benefits described herein.

[0142] The foregoing discussion has broad application and has been presented for purposes of illustration and description and is not intended to limit the disclosure to the form or forms disclosed herein. It will be understood that various additions, modifications, and substitutions may be made to embodiments disclosed herein without departing from the concept, spirit, and scope of the present disclosure. In particular, it will be clear to those skilled in the art that principles of the present disclosure may be embodied in other forms, structures, arrangements, proportions, and with other elements, materials, and components, without departing from the concept, spirit, or scope, or characteristics thereof. For example, various features of theDocket No. 1580.00234WO disclosure are grouped together in one or more aspects, embodiments, or configurations for the purpose of streamlining the disclosure. However, it should be understood that various features of the certain aspects, embodiments, or configurations of the disclosure may be combined in alternate aspects, embodiments, or configurations. While the disclosure is presented in terms of embodiments, it should be appreciated that the various separate features of the present subject matter need not all be present in order to achieve at least some of the desired characteristics and / or benefits of the present subject matter or such individual features. One skilled in the art will appreciate that the disclosure may be used with many modifications or modifications of structure, arrangement, proportions, materials, components, and otherwise, used in the practice of the disclosure, which are particularly adapted to specific environments and operative requirements without departing from the principles or spirit or scope of the present disclosure. For example, elements shown as integrally formed may be constructed of multiple parts or elements shown as multiple parts may be integrally formed, the operation of elements may be reversed or otherwise varied, the size or dimensions of the elements may be varied. Similarly, while operations or actions or procedures are described in a particular order, this should not be understood as requiring such particular order, or that all operations or actions or procedures are to be performed, to achieve desirable results. Additionally, other implementations are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the claimed subject matter being indicated by the appended claims, and not limited to the foregoing description or particular embodiments or arrangements described or illustrated herein. In view of the foregoing, individual features of any embodiment may be used and can be claimed separately or in combination with features of that embodiment or any other embodiment, the scope of the subject matter being indicated by the appended claims, and not limited to the foregoing description.

[0143] In the foregoing description and the following claims, the following will be appreciated. The term “about” refers to a range of 1-10% around the stated value. The phrases “at least one”, “one or more”, and “and / or”, as used herein, are open-ended expressions that are both conjunctive and disjunctive in operation. The terms “a”, “an”, “the”, “first”, “second”, etc., do not preclude a plurality. For example, the term “a” or “an” entity, as used herein, refers to one or more of that entity. As such, the terms “a” (or “an”), “one or more” and “at least one” can be usedDocket No. 1580.00234WO interchangeably herein. All directional references (e.g., proximal, distal, upper, lower, upward, downward, left, right, lateral, longitudinal, front, back, top, bottom, above, below, vertical, horizontal, radial, axial, clockwise, counterclockwise, and / or the like) are only used for identification purposes to aid the reader’s understanding of the present disclosure, and / or serve to distinguish regions of the associated elements from one another, and do not limit the associated element, particularly as to the position, orientation, or use of this disclosure. Connection references (e.g., attached, coupled, connected, and joined) are to be construed broadly and may include intermediate members between a collection of elements and relative movement between elements unless otherwise indicated. As such, connection references do not necessarily infer that two elements are directly connected and in fixed relation to each other. Identification references (e.g., primary, secondary, first, second, third, fourth, etc.) are not intended to connote importance or priority but are used to distinguish one feature from another.

[0144] In the claims, the term “comprises / comprising” does not exclude the presence of other elements, components, features, regions, integers, steps, operations, etc. Additionally, although individual features may be included in different claims, these may possibly advantageously be combined, and the inclusion in different claims does not imply that a combination of features is not feasible and / or advantageous. In addition, singular references do not exclude a plurality. Reference signs in the claims are provided merely as a clarifying example and shall not be construed as limiting the scope of the claims in any way.

Claims

Docket No. 1580.00234WOCLAIMSWhat is claimed is:

1. A method to filter a product from a process fluid, comprising: configuring a vertical filter to perform tangential flow filtration (TFF) or a tangential flow depth filtration (TFDF) to remove biologic products from a fluid; drawing the fluid from a bottom port of the filter with a recirculation pump; directing the fluid to a process feed vessel with the recirculation pump; delivering the fluid from the process feed vessel to a top port of the filter; performing a TFF or TFDF process on the fluid to separate a permeate from the fluid.

2. The method of claim 1, further comprising measuring a pressure at a top of the filter and at a bottom of the filter.

3. The method of claim 2, further comprising: comparing the pressure at the top of the filter to the pressure at the bottom of the filter; determining a pressure drop along the length of the filter by subtracting the pressure at the bottom of the filter from the pressure at the top of the filter.

4. The method of claim 3, decreasing a flow rate of the recirculation pump when the determined pressure drop is greater than zero.

5. The method of claim 3, increasing a flow rate of the recirculation pump when the determined pressure drop is less than zero.

6. The method of claim 3, maintaining a flow rate of the recirculation pump when the determined pressure drop is approximately equal to zero.

7. The method of any one of claims 3 to 5, wherein the flow rate is controlled by controlling a speed of the recirculation pump.

8. The method of claim 7, wherein the speed of the recirculation pump is controlled by a processor based control system.

9. The method of claim 2, wherein each pressure is measured with one or more pressure sensors.Docket No. 1580.00234WO10. The method of claim 1, further comprising pressurizing a shell of the filter to force liquid out of the shell back through the filter into a flow stream of the fluid.

11. The method of claim 1, wherein gravity provides the motive force to deliver the fluid from the process feed vessel to the top port of the filter.

12. A method for isolating a product from a process fluid, comprising: configuring a vertical filter to perform tangential flow filtration (TFF) or a tangential flow depth filtration (TFDF) to remove products from a fluid; pumping the fluid to a top port of the filter with a recirculation pump from a process feed vessel; performing a TFF or TFDF process on the fluid to separate a permeate from the fluid; and returning the fluid to the process feed vessel when exiting the filter.

13. The method of claim 12, further comprising: comparing a pressure at the top of the filter to a pressure at the bottom of the filter; determining a pressure drop along the length of the filter by subtracting the pressure at the bottom of the filter from the pressure at the top of the filter; decreasing a flow rate of the recirculation pump when the determined pressure drop is greater than zero; and increasing a flow rate of the recirculation pump when the determined pressure drop is less than zero.

14. The method of claim 12, further comprising pressurizing a shell of the filter to force liquid out of the shell back through the filter into a flow stream of the fluid.

15. A filter to isolate a product from a process fluid, comprising: a vertical filter housing; a filter medium to perform tangential flow filtration (TFF) or a tangential flow depth filtration (TFDF) to remove products from a fluid; a recirculation pump that provides a motive force to cause the fluid to flow downward through the filter medium; and a process feed vessel that receives filtered retentate and provides product feed to the filter.Docket No. 1580.00234WO16. The filter of claim 15, wherein the recirculation pump is configured to pull the fluid from a bottom port of the vertical filter housing.

17. The filter of claim 15, wherein the recirculation pump is configured to pump the fluid to a top port of the vertical filter housing.

18. The filter of claim 15, further comprising a control system configured to control a flow rate of the pump.

19. The filter of claim 18, wherein the control system is configured to: compare a pressure at the top of the filter to a pressure at the bottom of the filter; determine a pressure drop along the length of the filter by subtracting the pressure at the bottom of the filter from the pressure at the top of the filter; decrease a flow rate of the recirculation pump when the determined pressure drop is greater than zero; and increase a flow rate of the recirculation pump when the determined pressure drop is less than zero.

20. The filter of claim 18, wherein the control system is further configured to maintain a flow rate of the recirculation pump when the determined pressure drop is approximately equal to zero.21 . A method to filter a product from a process fluid using a series of serpentine filters, comprising: configuring a first vertical filter to perform tangential flow filtration (TFF) or a tangential flow depth filtration (TFDF) to remove biologic products from a fluid; providing the fluid to a top of the first filter with a recirculation pump; performing an equalized TFF or equalized TFDF process on the fluid in the first filter to separate a permeate from the fluid; directing the fluid from a bottom port of the first filter to a top of a second filter; performing an equalized TFF or equalized TFDF process on the fluid in the second filter to separate the permeate from the fluid; and directing the fluid from a bottom port of the second filter to a process feed vessel.

22. The method of claim 21, wherein providing the fluid to a top of the first filter is performed with a recirculation pump.Docket No. 1580.00234WO23. The method of claim 21, wherein directing the fluid from the bottom port of the second filter to the process feed vessel is performed with a recirculation pump.

24. The method of claim 21, further comprising measuring a pressure at a top of the first filter and the second filter and at a bottom of the first filter and the second filter.

25. The method of claim 24, further comprising: comparing the pressure at the top of the first filter to the pressure at the bottom of the second filter; determining a pressure drop along the length of the series of filters by subtracting the pressure at the bottom of the first filter from the pressure at the top of the second filter.

26. A series of filters to isolate a product from a process fluid, comprising: a first vertical filter housing and a second vertical filter housing; a filter medium in each of the two or more vertical filter housings to perform tangential flow filtration (TFF) or a tangential flow depth filtration (TFDF) to remove products from a fluid; a recirculation pump that provides a motive force to cause the fluid to flow downward through the filter medium in the first filter housing, out of the first filter housing, to a top of the second filter housing, and downward through the filter medium in the second filter housing; and a process feed vessel that receives filtered retentate from the second filter housing and provides product feed to the first filter housing.

27. The series of filters of claim 26, wherein a single permeate pump extracts permeate from the first filter housing and the second filter housing.

28. The series of filters of claim 26, wherein a first permeate pump extracts permeate from the first filter housing and a second permeate pump extracts permeate from the second filter housing.

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