Flexible biological fluid filters and methods for manufacturing such filters
Patent Information
- Application Number
- EP2023821906
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2023-11-30
- Publication Date
- 2026-09-09
Smart Images
Figure EP2023083771_05062025_PF_FP_ABST
Abstract
Description
[0001] FLEXIBLE BIOLOGICAL FLUID FILTERS AND METHODS FOR MANUFACTURING SUCH FILTERS
[0002] DESCRIPTION
[0003] TECHNICAL FIELD
[0004] The present disclosure generally relates to filters used in the collection and processing of blood and blood components or other biological fluids. More particularly, the present disclosure relates to flexible "soft housing" filters and methods for manufacturing such filters.
[0005] BACKGROUND
[0006] Using various manual and automated systems and methods, whole blood is collected and separated into its clinical components (typically red blood cells, platelets, and plasma). The collected components are typically individually stored and used to treat a variety of specific conditions and diseased states.
[0007] Before transfusing the collected blood components to a recipient in need of the components, or before subjecting blood components to treatment (such as, but not limited to, pathogen inactivation), it is often desirable to minimize the presence of impurities or other materials that may cause undesired side effects in the recipient. For example, because of possible reactions, it is generally considered desirable to reduce the number of leukocytes in blood components before storage, or at least before transfusion (i.e. , "leukoreduction").
[0008] Filters are widely used to accomplish leukoreduction in blood products today (e.g., warm and cold filtration of leukocytes from whole blood, red cells, and / or platelet products). Filters typically include a filter media disposed between mating walls of a filter housing. Inlet and outlet ports associated with the housing provide flow paths to and from the interior of the filter. The walls of the housing may be made of a rigid, typically plastic, material or may instead be formed of a soft or flexible material, with soft housing filters providing the advantage of being able to withstand handling and centrifuging without breakage of the filter. Examples of soft housing filters are disclosed in U.S. Patent No. 6,367,634; U.S. Patent No. 6,422,397; U.S. Patent No. 6,745,902; U.S. Patent No. 7,353,956; U.S. Patent No. 7,332,096; U.S. Patent No. 7,278,541 ; U.S. Patent No. 7,445,124; U.S. Patent No. 9,796,166; and U.S. Patent Application Publication No. 2003 / 0209479, all of which are hereby incorporated by reference herein.
[0009] Figs. 1-4 illustrate a “soft housing” leukocyte reduction filter 10 according to a conventional configuration and components thereof. The illustrated filter 10 includes a pair of outer sheets 12 and 14, which have a generally oval shape and are formed of a flexible material, such as a plasticized polyvinyl chloride (“PVC”) material.
[0010] A fluid inlet port 16 is secured to one of the housing sheets 12 toward an upper end of the filter 10 by a weld or adhesive or the like, while a fluid outlet port 18 is secured to the other housing sheet 14 and to an intermediate layer or frame 20 by a weld or adhesive or the like. The inlet port 16 and the outlet port 18 are formed of rigid or semi-rigid materials and configured to be attached to tubes of a fluid flow circuit.
[0011] The housing sheets 12 and 14 are secured to each other and, optionally, to the intermediate layer or frame 20 along the perimeters of the sheets 12 and 14 by a weld to define an outer seal 22. The intermediate layer or frame 20 may be formed of the same material as the housing sheets 12 and 14 (e.g., a plasticized PVC material) to facilitate attachment of the intermediate layer or frame 20 to the sheets 12 and 14. A fluid being filtered will not flow through plasticized PVC, so the intermediate layer or frame 20 defines one or more openings or apertures through which fluid may flow. According to one conventional design, the intermediate layer or frame 20 is generally oval-shaped, defining one large central opening or aperture, with an outer perimeter that is similarly shaped to the perimeter of sheets 12 and 14.
[0012] Filter media 24 overlays the opening(s) or aperture(s) of the intermediate layer or frame 20, such that fluid entering into the interior of the filter 10 via the fluid inlet port 16 will flow through an inlet side or chamber (defined in part by sheet 12), through the filter media 24, and into an outlet side or chamber (defined in part by sheet 14) before exiting the filter 10 via the outlet port 18. The filter media 24 may be variously configured, including being formed of a single layer or a plurality of layers, which may be either substantially identical or differently configured. This may include a plurality of fibrous layers, a plurality of non-fibrous layers, or a combination of fibrous layers and non-fibrous layers. In one typical embodiment, the filter media 24 is formed of a melt-blown, nonwoven, fibrous material, such as a polybutylene terephthalate (“PBT”) material, which has been found to be effective in removing leukocytes from a biological fluid.
[0013] In one conventional configuration, which is shown in Fig. 4, the intermediate layer or frame 20 is provided with an embossed, three-dimensional structure, which may include the intermediate layer or frame 20 being embossed with a substantially diamond-shaped pattern having regularly arranged protrusions or “ridges” 26 and rhomboidal depressions or “valleys” 28 of a certain height. Providing the intermediate layer or frame 20 with an embossed structure helps to prevent the intermediate layer or frame 20 from sticking to adjacent components of the filter 10 during sterilization of the filter 10. In particular, the textured side 30 of the intermediate layer or frame 20 (i.e. , the side of the intermediate layer or frame 20 having the peaks of the protrusions or “ridges” 26 and oriented facing upwardly in Fig. 4, as opposed to the “flat” side 32 of the intermediate layer or frame 20, which has the larger, flat depressions or “valleys” 28 and is oriented facing downwardly in Fig. 4) is placed into contact with the filter media 24 to ensure that a certain amount of air is present, which prevents the intermediate layer or frame 20 from sticking to the filter media 24.
[0014] In addition to the filter media 24, a pre-filter 34 may be provided, being positioned upstream of the filter media 24 (i.e., between sheet 12 and the filter media 24). The pre-filter 34 is configured to allow the passage of biological fluid therethrough. Typically, the pre-filter 34 has different filtration properties (e.g., porosity) than the associated filter media 24, which may include the pre-filter 34 having larger pores than the associated filter media 24. For a leukoreduction filter, the pre-filter 34 may be configured to remove microaggregates from a biological fluid prior to the fluid encountering the filter media 24. In a conventional embodiment, the pre-filter 34 is formed of a polyethylene terephthalate (“PET”) material. The pre-filter 34 may be provided as a single-sheet or single-piece component or as a multi-sheet or multi-piece, stacked component.
[0015] The filter 10 may also include a post-filter 36 (Fig. 2) positioned between the filter media 24 and the intermediate layer or frame 20. If provided, the postfilter 36 helps to improve the flow of fluid through the filter 10 by acting as a spacer or manifold that prevents the filter media 24 from pressing against housing sheet 14 during use, which can slow the flow of fluid through the filter 10. The post-filter 36 may be formed of different materials, including being formed of the same material (e.g., PBT) as the filter media 24 or the same material (e.g., plasticized PVC) as the housing sheets 12 and 14 and the intermediate layer or frame 20, provided that the post-filter 36 is suitably configured to provide the intended spacer or manifold function without having a porosity or configuration that impedes the flow of fluid through the filter 10.
[0016] The filter 10 includes an inner seal 38, which joins housing sheet 12, as well as the pre-filter 34 and post-filter 36 (if provided), the filter media 24, and the intermediate layer or frame 20. Notably, housing sheet 14 is not included in the inner seal 38, but remains separate from the inner seal 38, as shown in Fig. 2. The inner seal 38 is formed by application of pressure and heat (e.g., radiofrequency heating) to housing sheet 12 and the various layers of material positioned between housing sheet 12 and the intermediate layer or frame 20 (which are collectively referred to herein as the “interior components” of the filter 10) by a pair of electrodes. It is important for the inner seal 38 to form a complete seal at or adjacent to the perimeters of the interior components of the filter 10 to prevent the biological fluid from “shortcutting” the interior components (i.e. , passing from the inlet port 16 to the outlet port 18 without passing through all of the interior components of the filter 10).
[0017] When the inner seal 38 of the filter 10 is strong, the filter 10 can be expected to perform very well. However, it may be difficult for a strong inner seal 38 to be formed for a variety of reasons. For one, there is a large amount of material that is being compressed and sealed together to form the inner seal 38. Additionally, the different materials being welded together at the inner seal 38 (which may include PVC, PET, and PBT) have different melting temperatures. Yet another factor affecting the strength of the inner seal 38 is the possible misalignment of the two electrodes used to form the inner seal 38. This can be understood with reference to Fig. 3, which shows a section of the inner seal 38. It will be seen that there is a difference “D” between the position of the lower end of the inner seal 38 at the left side of the inner seal 38 and at the right side of the inner seal 38. This difference D arises due to a misalignment between the two electrodes used to form the inner seal 38. A strong seal will not be formed at the upper and lower ends of the inner seal 38, where the electrodes are out of alignment with each other because there is incomplete application of pressure and electrical current or heat when the inner seal 38 is being formed.
[0018] Due to the importance of a strong inner seal 38, there exists an ongoing need to improve the structure of a filter 10 of the type shown in Figs. 1-4 and the manner in which the inner seal 38 is formed.
[0019] SUMMARY
[0020] There are several aspects of the present subject matter which may be embodied separately or together in the devices and systems described and claimed below. These aspects may be employed alone or in combination with other aspects of the subject matter described herein, and the description of these aspects together is not intended to preclude the use of these aspects separately or the claiming of such aspects separately or in different combinations as set forth in the claims appended hereto.
[0021] In one aspect, a leukocyte removal filter includes a flexible housing having first and second sheets, a filter media at least partially positioned between the first and second sheets of the housing, and an intermediate layer at least partially positioned between the filter media and the second sheet of the housing. The intermediate layer is embossed, with a textured side including a plurality of protrusions and a flat side including a plurality of flat depressions, with the flat side of the intermediate layer being placed into contact with the filter media.
[0022] In another aspect, a method for manufacturing a leukocyte removal filter includes providing a first flexible housing sheet and a second flexible housing sheet, positioning an intermediate layer adjacent to the second flexible housing sheet, and positioning a filter media between the first flexible housing sheet and the intermediate layer. With the materials so positioned, an inner seal is formed so as to join the first housing sheet, the intermediate layer, and the filter media. Forming the inner seal includes determining a roughness of the intermediate layer and applying a pressure and an electrical current to the first housing sheet, the intermediate layer, and the filter media using a pair of electrodes. The magnitude of the electrical current is based at least in part on the roughness of the intermediate layer.
[0023] BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Fig. 1 is a front elevational view of a leukocyte reduction filter according to conventional design;
[0025] Fig. 2 is a side cross-sectional view of an upper portion of the filter of Fig. 1 ;
[0026] Fig. 3 is a photograph of a portion of an inner seal of the filter of Fig. 1 ;
[0027] Fig. 4 is a perspective view of a portion of an intermediate layer or frame of the filter of Fig. 1 ;
[0028] Fig. 5 is a front elevational view of a leukocyte reduction filter according to an aspect of the present disclosure;
[0029] Fig. 6 is a side cross-sectional view of the filter of Fig. 5;
[0030] Fig. 7 is a cross-sectional view of a pair of electrodes used to form an inner seal of the filter of Fig. 5; and
[0031] Fig. 8 is a photograph of a portion of the inner seal of the filter of Fig. 5.
[0032] DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0033] The embodiments disclosed herein are for the purpose of providing a description of the present subject matter, and it is understood that the subject matter may be embodied in various other forms and combinations not shown in detail. Therefore, specific embodiments and features disclosed herein are not to be interpreted as limiting the subject matter as defined in the accompanying claims.
[0034] Figs. 5 and 6 show an exemplary embodiment of a filter 40 according to an aspect of the present disclosure. As noted above, when the inner seal 38 of a conventional filter 10 is strong, the filter 10 can be expected to perform well. Accordingly, the filter 40 of Figs. 5 and 6 is similarly configured to the conventional filter 10 shown in Figs. 1-4 and described above (with the same reference numbers being used to refer to corresponding components of the two filters 10 and 40), except for certain differences in its structure and method of manufacture that allow for the formation of a stronger inner seal 38a. It should be understood that the components of the filter 40 identified by the same reference numbers as used above in the description of the components of the conventional filter 10 are provided in accordance with the above description, except as noted herein to the contrary.
[0035] One notable difference between the structure of the conventional filter 10 and the structure of the filter 40 of Figs. 5 and 6 is the reversal of the orientation of the intermediate layer or frame 20 (which modification is represented in Fig. 6 and in the description by the use of reference number 20a to identify the reverseorientation intermediate layer or frame). As described above, in the conventional filter 10, the intermediate layer or frame 20 is oriented so as to place the textured side 30 of the intermediate layer or frame 20 into contact with the filter media 24. In the filter 40 of Figs. 5 and 6, the textured side 30 of the intermediate layer or frame 20a is instead placed away from the filter media 24, with the flat side 32 of the intermediate layer or frame 20a being placed adjacent to and in contact with the filter media 24. While the orientation of the intermediate layer or frame 20a is reversed compared to the orientation of the intermediate layer or frame 20 in the conventional filter 10, the position of the intermediate layer or frame 20a within the filter 40 (namely, between housing sheet 14 and the filter media 24) is unchanged.
[0036] As described above, and as can be seen in Fig. 4, the flat side 32 of the intermediate layer or frame 20, 20a (which includes the larger, flat depressions or “valleys” 28) will provide more surface area to contact the filter media 24 than the textured side 30 (which provides only the peaks of the protrusions or “ridges” 26 to contact the filter media 24). As also described above, the intermediate layer or frame 20, 20a is formed of a dielectric material (plasticized PVC), which is not well-suited to conducting electrical current, such that increasing the amount of contact between the intermediate layer or frame 20a and the filter media 24 will help to more uniformly transmit more electrical current and, thus, heat to the filter media 24.
[0037] While it may be presumed that the orientation of the intermediate layer or frame 20a is not relevant to the strength of the inner seal 38a (on account of the intermediate layer or frame 20a being compressed by a pair of electrodes when forming the inner seal 38a), it has instead been found that reversing the orientation of the intermediate layer or frame 20a does allow for a stronger inner seal 38a to be formed. This may be partly on account of mechanical stoppers typically being used in combination with the electrodes when forming an inner seal, with the mechanical stoppers preventing the welding pressure from being entirely discharged on the materials that form the inner seal 38, 38a. This is in contrast to the approach typically employed in the formation of the outer seal 22, with mechanical stoppers being omitted and welding pressure being applied directly to the housing sheets 12 and 14.
[0038] When a weld or seal is formed by thermal heating generated by the passage of electrical current (as is the case with the inner seal 38a), it is important for the electrical current to be as uniformly transferred throughout the material being sealed as possible; otherwise, portions of the material that receive less electrical current will be heated less than other portions of the material, resulting in a weak points of the seal. By placing the flat side 32 of the intermediate layer or frame 20a against the filter media 24 instead of the textured side 30, a greater surface area of the intermediate layer or frame 20a is in contact with the filter media 24 (on a microscopic level) and available to transmit electrical current to the filter media 24. This allows for the filter media 24 within the inner seal 38a to be more uniformly heated, resulting in the filter 40 of Figs. 5 and 6 having an inner seal 38a that is stronger than the inner seal 38 of the conventional filter 10.
[0039] As for the electrical current that is applied to the various components of the filter 40 by a pair of electrodes to form the inner seal 38a, one aspect of the present disclosure is an improvement in which the magnitude of the applied electrical current is informed by the roughness of the intermediate layer or frame 20a. In particular, an intermediate layer or frame 20a having a greater roughness will provide less surface area to contact the filter media 24 (on a microscopic level) than an intermediate layer or frame 20a having a lower roughness. With less surface area in contact with the filter media 24, an intermediate layer or frame 20a having a greater roughness will be able to transfer a relatively low level of electrical current to the filter media 24 when forming the inner seal 38a. Accordingly, it has been found that a stronger inner seal 38a may be achieved by determining the roughness of the intermediate layer or frame 20a and then adjusting the magnitude of the electrical current that is applied to form the inner seal 38a based on the roughness of the intermediate layer or frame 20a.
[0040] More particularly, when creating an inner seal 38a via radio-frequency heating, the electrical current supplied to the electrodes is ramped up to a maximum or setpoint value, which may be a default or predetermined value. The operation of the electrodes (and, optionally, of other equipment that is used in manufacturing the filter 40) may be controlled by a controller (e.g., a computer) that receives instructions from an operator and directs the operation of the electrodes according to those instructions (which may include instructing the electrodes to move toward each other so as to apply pressure to filter materials, instructing the electrodes to apply a certain amount of electrical current, and instructing the electrodes to move away from each other so as to release the filter 40). According to an aspect of the present disclosure, the maximum or setpoint value is informed by the surface roughness of the intermediate layer or frame 20a according to the following equation: l% = gamma * Rz% [Equation 1], in which l% is the magnitude of the adjustment that is made to increase the maximum or setpoint value,
[0041] Rz% is the percentage of the specification range of the intermediate layer or frame 20a that is available to be welded to an adjacent component of the filter 40, and gamma is a factor or multiplier that is based on the measured roughness of the intermediate layer or frame 20a (and which may be experimentally determined), with gamma being 0.2 for Rz < 50 microns, 0.3 for Rz between 50 and 85 microns, and 0.4 for Rz > 85 microns in one exemplary embodiment. It should be understood that other values for gamma may be experimentally determined for different materials and employed when determining the adjusted electrical current to be applied when forming an inner seal using an intermediate layer or frame comprised of such a material.
[0042] In one embodiment, the controller is provided with the input required to calculate the adjusted electrical current to be employed, which may include the controller receiving data directly from a device that is used to measure the roughness of the intermediate layer or frame 20a or from an operator. The controller may then calculate the adjusted electrical current that is to be applied by the electrodes and then control the electrodes to apply the appropriate electrical current. In another embodiment, the adjusted electrical current may be separately calculated and then provided to the controller (which then controls the electrodes to apply the appropriate electrical current), which may include instructing the controller as to the percentage by which to adjust the default value or providing the controller with the adjusted value that is to be used.
[0043] The actual linear roughness Rz of the intermediate layer or frame 20a may be determined according to any suitable approach but, in one exemplary embodiment, it is determined using a microscope of the type marketed by Keyence Corporation Of America of Itasca, Illinois. While linear roughness is used in Equation 1 , it should be understood that other metrics for roughness (e.g., surface roughness) may be employed without departing from the scope of the present disclosure. Additionally, while it may be advantageous to employ a contactless approach to measurement of the roughness of the intermediate layer or frame 20a, it is also within the scope of the present disclosure for roughness to be measured via methods in which the intermediate layer or frame 20a is contacted by a stylus or other measurement device.
[0044] An intermediate layer or frame 20a configured as a diamond-embossed PVC sheet of material may have a nominal or specified roughness Rz of 69 + / - 15 microns (i.e. , a linear roughness Rz in a range of approximately 54 to 84 microns), which corresponds to a gamma of 3%. For a moderately rough specimen having a measured roughness Rz of 69 microns, the Rz% will be 50%, which is determined by calculating the percentage of the available specification range: (69 microns - 54 microns) I (84 microns - 54 microns) = 50%. Inserting those values for gamma and Rz% into Equation 1 results in an l% of 1 .5% (0.3 * 50%), such that the maximum or setpoint value of the electrical current applied when forming the inner seal 38a would be increased to an adjusted value that is 1.5% greater than the maximum or setpoint value that would otherwise be employed.
[0045] It will be seen that a specimen of a diamond-embossed PVC sheet of material having a greater roughness will require a larger adjustment or increase in the maximum or setpoint value of the applied electrical current, with a specimen having a measured roughness Rz of 84 microns calling for a maximum or setpoint value that is increased by 3% (on account of Rz% being calculated to be 100%, with the same gamma of 0.3 being employed). In contrast, a very smooth specimen having a measured roughness Rz of 54 microns would require no adjustment to the maximum or setpoint value (on account of Rz% being calculated to be 0%). It should be understood that the values presented herein are merely exemplary and intended to illustrate this aspect of the present disclosure. It should also be understood that this approach to adjustment of the applied welding current may be employed without reversing the orientation of the intermediate layer or frame 20, 20a, although it may be advantageous to employ both aspects of the present disclosure in order to further improve the strength of the resulting inner seal 38a.
[0046] As for the electrodes themselves, Fig. 7 shows a pair of electrodes 42 and 44 having an improved configuration, according to an aspect of the present disclosure. In the illustrated embodiment, each electrode 42, 44 is provided with an inner perimeter 46 and an outer perimeter 48, with each of the inner perimeter 46 and the outer perimeter 48 having an optimized radius that is at least 0.5 mm. The inner perimeters 46 of the electrodes 42 and 44 are used to define an inner end of the inner seal 38a (such that the inner end of the resulting inner seal 38a will have a radius of at least 0.5 mm on each side), while the outer perimeters 46 of the electrodes 42 and 44 are used to define an outer end of the inner seal 38a (such that the outer end of the resulting inner seal 38a will have a radius of at least 0.5 mm on each side). The electrodes used to form the inner seal 38 of a conventional filter 10 may have inner and outer perimeters defining comers or having relatively small radii, which may allow for discontinuities in the otherwise uniform application of electrical current to the region of the filter 10 at which the inner seal 38 is formed, while also possibly damaging the materials being compressed by the electrodes. As explained above, applying a more uniform electrical current during formation of an inner seal will help to avoid the creation of weak points within the inner seal, so providing the inner and outer perimeters 46 and 48 of the electrodes 42 and 44 with optimized radii will result in a stronger inner seal 38a being created by allowing for electrical current (and, thus, heat) to be more uniformly applied when forming the inner seal 38a.
[0047] In addition to optimizing the radii of the inner and outer perimeters 46 and 48 of the electrodes 42 and 44, according to another aspect of the present disclosure, the alignment of the electrodes 42 and 44 is improved, compared to the typical alignment of the electrodes used to form the inner seal 38 of the conventional filter 10. This may include the electrodes 42 and 44 being aligned with a centering having a delta of less than 1 mm or, more preferably, a delta of less than 0.5 mm. Such an approach, especially in combination with electrodes 42 and 44 also having inner and outer perimeters 46 and 48 with optimized radii, results in an inner seal 38a as shown in Fig. 8. Compared to the inner seal 38 of the conventional filter 10 shown in Fig. 3, it will be seen that there is little to no difference between the position of the lower or inner end of the inner seal 38a at the left side of the inner seal 38a and at the right side of the inner seal 38a, such that the entire height or length of the inner seal 38a is formed between two aligned electrodes 42 and 44. In contrast, the upper / outer and lower / inner ends of the conventional inner seal 38 may each be formed with a portion of one electrode out of alignment with the other electrode, in which case the ends of the inner seal 38 will be relatively weak and not contribute to the “effective” length of the inner seal 38 (due to being relatively weak). As such, it will be seen that, by improving the alignment of the electrodes 42 and 44 (even without also optimizing the radii of the inner and outer perimeters 46 and 48), the inner seal 38a may be provided with a greater effective length than the inner seal 38 of the conventional filter 10 using electrodes having the same width, resulting in an inner seal 38a having a greater strength.
[0048] The improved strength of the inner seal 38a compared to the inner seal 38 of the conventional filter 10 (and the corresponding risk of the inner seal failing) may be quantified in any of a number of ways. This may include measuring the strength of the inner seal by employing a delamination test according to an aspect of the present disclosure. Such a test not only detects whether a filter leaks (i.e. , testing the filter vs. the external environment), but also determines the force necessary to tear off the critical welding at the inner seal 38a (i.e., testing the filter vs. the risk for bypass). Such a test has been found to be advantageous because an imperfection or weakness in an inner seal may be undetectable at manufacturing, with a microchannel possibly arising after sterilization (inflation) or after centrifugation (bending, due to inappropriate positioning of the filter within a centrifuge).
[0049] The delamination test is carried out by gradually increasing the pressure within a filter, which may include increasing the pressure within a filter in steps of 100 mbar from 300 mbar to 700 mbar. This may be done using a commercially available pressure decay leak tester, including one of the type marketed by ForTest Italia S.R.L. of Modena, Italy, which inflates the filter to the selected pressure and detects whether a leak or a delamination occurs by means of a measurement of flow or, alternatively, a pressure decay. The delamination test is passed if the filter withstands a pressure between 300 mbar and 700 mbar. If the filter does not delaminate at an internal pressure of 700 mbar, the test is not only passed, but the filter is designated as having a “strong” inner seal. In one embodiment, when the filter does not delaminate at an internal pressure of 700 mbar, the pressure may be increased beyond 700 mbar until it does delaminate in order to quantify the strength of the inner seal.
[0050] Assessing a single filter is a poor indicator of improvement in the strength of an inner seal 38a formed according to the present disclosure compared to the strength of the inner seal 38 of a conventional filter 10, so testing was carried out on several filters of both types in order to determine the percentage of such filters having a “strong” inner seal. To ensure that such results would be reliable and indicative of improvements arising from the principles described in the present disclosure, care was taken to eliminate variation in other factors of the configurations of the two types of filters and their manufacturing processes, with the same materials being used, the same operator carrying out the manufacturing processes for both types of filters, etc. The results of such testing indicated that filters configured and manufactured according to the principles described in the present disclosure resulted in a 10% increase in the number of filters having a “strong” inner seal (with such filters not delaminating at an internal pressure of 700 mbar) compared to the filters formed according to the conventional design and manufacturing process. It should be understood that this is only one possible approach to quantifying the improvement that may be realized by employing the principles described herein, with other approaches also verifying that the principles described herein (whether practiced separately or in combination) are effective in creating a filter having a stronger inner seal than one of conventional design.
[0051] Variations to the configuration of the filter 40 may be made without departing from the scope of the present disclosure and without weakening the strength of the inner seal 38a. For example, in the illustrated embodiment, the post-filter 36 of the conventional filter 10 is replaced with a loop of tubing or material 50 that is incorporated into the filter 40, downstream of the filter media 24 and serves as a spacer or manifold to prevent the filter media 24 from pressing against housing sheet 14. It will be seen that, unlike the post-filter 36, the loop 50 is not incorporated into the inner seal 38a, so replacing the post-filter 36 with the loop 50 may further strengthen the inner seal 38a. Similarly, the pre-filter 34 may be omitted from the filter 40, which may also tend to increase the strength of the inner seal 38a by reducing the amount of materials and the variety of different materials incorporated into the inner seal 38a.
[0052] Aspects
[0053] Aspect 1 . A leukocyte removal filter comprising: a flexible housing having first and second sheets; a filter media at least partially positioned between the first and second sheets of the housing; and an intermediate layer at least partially positioned between the filter media and the second sheet of the housing, wherein the intermediate layer is embossed, with a textured side including a plurality of protrusions and a flat side including a plurality of flat depressions, and the intermediate layer is oriented to place the flat side into contact with the filter media.
[0054] Aspect 2. The leukocyte removal filter of Aspect 1 , further comprising a seal which joins the first sheet of the housing, the intermediate layer, and the filter media, wherein the seal includes an inner end having opposing sides and an outer end having opposing side, and each side of the inner and outer ends of the seal has a radius that is greater than or equal to 0.5 mm.
[0055] Aspect 3. The leukocyte removal filter of Aspect 2, further comprising an outer seal positioned radially outwardly of and spaced away from the seal, wherein the outer seal joins the first and second sheets of the housing.
[0056] Aspect 4. The leukocyte removal filter of Aspect 3, wherein a portion of the intermediate layer is incorporated into the outer seal.
[0057] Aspect 5. The leukocyte removal filter of any one of Aspects 2-4, further comprising a post-filter at least partially positioned between the filter media and the second sheet of the housing, wherein a portion of the post-filter is incorporated into the seal.
[0058] Aspect 6. The leukocyte removal filter of any one of Aspects 2-4, further comprising a loop of material at least partially positioned between the filter media and the second sheet of the housing, wherein the loop is not incorporated into the seal.
[0059] Aspect 7. The leukocyte removal filter of any one of Aspects 2-6, wherein the seal is generally oval-shaped.
[0060] Aspect 8. A method for manufacturing a leukocyte removal filter, comprising: providing a first flexible housing sheet and a second flexible housing sheet; positioning an intermediate layer adjacent to the second flexible housing sheet; positioning a filter media between the first flexible housing sheet and the intermediate layer; and forming an inner seal which joins the first housing sheet, the intermediate layer, and the filter media, wherein forming the inner seal includes determining a roughness of the intermediate layer, and applying a pressure and an electrical current to the first housing sheet, the intermediate layer, and the filter media using a pair of electrodes, with a magnitude of the electrical current being based at least in part on the roughness of the intermediate layer.
[0061] Aspect 9. The method of Aspect 8, wherein the magnitude of the electrical current is greater for an intermediate layer having a relatively large roughness than for an intermediate layer having a relatively small roughness.
[0062] Aspect 10. The method of any one of Aspects 8-9, wherein the intermediate layer has a specification range, the magnitude of the electrical current is increased by a calculated percentage from a default value to an adjusted value, the calculated percentage is equal to the product of the percentage of the specification range that is available to contact an adjacent component of the inner seal, and a multiplier that is based on the determined roughness of the intermediate layer.
[0063] Aspect 11 . The method of any one of Aspects 8-10, wherein each electrode includes an inner perimeter configured to define a portion of an inner end of the inner seal, each electrode includes an outer perimeter configured to define a portion of an outer end of the inner seal, and each inner perimeter and each outer perimeter has a radius that is greater than or equal to 0.5 mm. Aspect 12. The method of any one of Aspects 8-11 , wherein the pair of electrodes are misaligned by less than 1 mm.
[0064] Aspect 13. The method of any one of Aspects 8-12, wherein the pair of electrodes are misaligned by less than 0.5 mm.
[0065] Aspect 14. The method of any one of Aspects 8-13, wherein the intermediate layer is embossed, with a textured side including a plurality of protrusions and a flat side including a plurality of flat depressions, and the intermediate layer is oriented to place the flat side into contact with the filter media.
[0066] Aspect 15. The method of any one of Aspects 8-14, wherein the inner seal is generally oval-shaped.
[0067] It will be understood that the embodiments and examples described above are illustrative of some of the applications of the principles of the present subject matter. Numerous modifications may be made by those skilled in the art without departing from the spirit and scope of the claimed subject matter, including those combinations of features that are individually disclosed or claimed herein. For these reasons, the scope hereof is not limited to the above description but is as set forth in the following claims, and it is understood that claims may be directed to the features hereof, including as combinations of features that are individually disclosed or claimed herein.
Claims
CLAIMS1 . A leukocyte removal filter comprising: a flexible housing having first and second sheets; a filter media at least partially positioned between the first and second sheets of the housing; and an intermediate layer at least partially positioned between the filter media and the second sheet of the housing, wherein the intermediate layer is embossed, with a textured side including a plurality of protrusions and a flat side including a plurality of flat depressions, and the intermediate layer is oriented to place the flat side into contact with the filter media.
2. The leukocyte removal filter of claim 1 , further comprising a seal which joins the first sheet of the housing, the intermediate layer, and the filter media, wherein the seal includes an inner end having opposing sides and an outer end having opposing side, and each side of the inner and outer ends of the seal has a radius that is greater than or equal to 0.5 mm.
3. The leukocyte removal filter of claim 2, further comprising an outer seal positioned radially outwardly of and spaced away from the seal, wherein the outer seal joins the first and second sheets of the housing.
4. The leukocyte removal filter of claim 3, wherein a portion of the intermediate layer is incorporated into the outer seal.
5. The leukocyte removal filter of any one of claims 2-4, further comprising a post-filter at least partially positioned between the filter media and the second sheet of the housing, wherein a portion of the post-filter is incorporated into the seal.
6. The leukocyte removal filter of any one of claims 2-4, further comprising aloop of material at least partially positioned between the filter media and the second sheet of the housing, wherein the loop is not incorporated into the seal.
7. The leukocyte removal filter of any one of claims 2-6, wherein the seal is generally oval-shaped.
8. A method for manufacturing a leukocyte removal filter, comprising: providing a first flexible housing sheet and a second flexible housing sheet; positioning an intermediate layer adjacent to the second flexible housing sheet; positioning a filter media between the first flexible housing sheet and the intermediate layer; and forming an inner seal which joins the first housing sheet, the intermediate layer, and the filter media, wherein forming the inner seal includes determining a roughness of the intermediate layer, and applying a pressure and an electrical current to the first housing sheet, the intermediate layer, and the filter media using a pair of electrodes, with a magnitude of the electrical current being based at least in part on the roughness of the intermediate layer.
9. The method of claim 8, wherein the magnitude of the electrical current is greater for an intermediate layer having a relatively large roughness than for an intermediate layer having a relatively small roughness.
10. The method of any one of claims 8-9, wherein the intermediate layer has a specification range, the magnitude of the electrical current is increased by a calculated percentage from a default value to an adjusted value, the calculated percentage is equal to the product of the percentage of the specification range that is available to contact an adjacent component of the inner seal, and a multiplier that is based on the determined roughness of the intermediate layer.11 . The method of any one of claims 8-10, wherein each electrode includes an inner perimeter configured to define a portion of an inner end of the inner seal, each electrode includes an outer perimeter configured to define a portion of an outer end of the inner seal, and each inner perimeter and each outer perimeter has a radius that is greater than or equal to 0.5 mm.
12. The method of any one of claims 8-11 , wherein the pair of electrodes are misaligned by less than 1 mm.
13. The method of any one of claims 8-12, wherein the pair of electrodes are misaligned by less than 0.5 mm.
14. The method of any one of claims 8-13, wherein the intermediate layer is embossed, with a textured side including a plurality of protrusions and a flat side including a plurality of flat depressions, and the intermediate layer is oriented to place the flat side into contact with the filter media.
15. The method of any one of claims 8-14, wherein the inner seal is generally oval-shaped.