IE45129B1 - Blood filter - Google Patents

Description

This invention relates to a filtering device and tp a method of manufacturing a filtering device, for use in filtering blood or blood components.

It has been ►’ecently determined that there are many situations 5 where stored, donated blood, as wail as other types of blood and blood components, should be filtered to remove microemboli of aggregated blood elements and the like, prior to administration to a patient, in particular, . older stored blood which is nearing its expiration date has been found to be greatly improved by filtering, to prevent the microemboli from lodging in the lungs, brain, and elsewhere, thus avoiding various degrees and types of injury to the patient.

A considerable number of blood filtering devices are now comsrcially available for use with stored, whole blood, or for reprocessing fresh blood in heart-lung machines, as well as blood which has passed through cardiotomy machines In a blood filtering device it is, of course, desirable that the device remove as many particles as possible which are larger than red cells, which have an average size of 7 microns, while at the same time exhibiting a rapid flow - 2 rate of blood through the filter, and a high capacity. Accordingly, the device does not have to be replaced excessively often when a patient is receiving a large amount of blood.

Furthermore, a filtering device should be susceptible to automated commercial production techniques, so as not to be excessively expensive. It must also be reliably leak-free. Also it must be free of by-pass passages which permit blood to pass around the filter element without filtering action.

The filtering device descrioed in this application exhibits excellent high-flow characteristics. At the same time it provides surprisingly excellent levels of particle removal from blood. Furthermore, it is susceptible to reliable, automated sealing against blood by-passing and to sterile sealing of the contents from the exterior, on a low-cost basis.

In accordance with one aspect of this invention, there is provided a method of manufacturing a filtering device fo·'· blood which comprises assembling a stack of filter pads comprising fibres, and including a first pad defining an upstream cuter surface and a last pad defining a downstream outer surface, sealing the peripheral edges of said pads in the stack together to form an integral filter unit defining an integral peripheral flange, whereby the depth of the filter unit reduces from a maximum at the centre of the unit to a minimum at the flange, and thereafter inserting and sealing said filter unit into a filter housing having an inlet and an outlet by forming a seal between said integral filter unit and tbe filter housing along said integral peripheral flange, so as to separate tne inlet and the outlet, whereby the inlet faces the pad at one end of the unit and the outlet faces the pad at the opposite end of the unit.

The invention also resides in a filtering device for blood comprising a housing having an inlet and an outlet and a stack of filter pads comprising fibres accomodated in the housing, the stack including a first pad facing the inlet and defining an upstream outer surface and a last pad facing the outlet defining a downstream outer surface, the peripheral edges of the pads being sealed together in the stack to form an integral peripheral flange of an integral filter unit, the - 3 « ι J filter· unit having a depth which reduces from a maximum at the centre of the unit to a minimum at the flange, the filter unit being sealed in the housing along the integral peripheral flange, so as to separate the inlet and the outlet.

Preferably, the fibres are thermoplastic and the peripheral edges of the pads are heat-sealed together. A sonic sealer may be used. The result is a non-porous peripheral flange which may serve as a sealing gasket for insertion between two parts of the housing. Polyester fibres are especially useful, although other materials may be used.

Reference is now made to the accompanying drawings, v/herein: Figure 1 is a perspective view of one embodiment of a filtering device according to this invention, adapted specifically for the processing of donated, stored blood; Figure 2 is an enlarged, sectional view of the filtering device; Figure 3 is ar. elevational view of a stack of filter pads used in the device of Figures 1 and 2, being joined together at their peripheries to form an integral filter unit prior to assembly into the filter housing as shown in Figure 2; Figure 4 is a fragmentary sectional view of a portion of the structure of Figure 2, shown prior to a heat sealing step for sealing the housing, the completion of which is shown in Figure 2.

Referring to the drawings, a filtering device is shown defining a housing 12, made of a pair of mating shells 14, 16. The filtering device may be connected to a blood administration set or the like for use, for receiving blood from a blood bag. Shell 14 defines an inlet 18 for fluids to be filtered, while shell 16 defines an outlet 20 for filtered fluid. Shells 14, 16 also respectively define mating flanges 22, 24, which may fit together by sonic sealing or the like at area 26. Each shell 14, 16 defines a series of radial vanes 27, 28, for the purpose of defining flow channels to distribute fluid between the filter material and inlet 18, as well as outlet 20. - 4 <5120 integral filter unit 30 comprises a stack of filter pads of thermoplastic fibres, positioned within housing 12 and joined together by a peripheral flange 32, which may be prepared by heat sealing, forcing the periphery of all of the pads of stack 30 into an integral, fused mass forming flange 32. This process is indicated by Figure 3, showing how tubular heat-seal dies 34, 36 can pinch the pads together at the area of peripheral flange 32 and effect heat sealing, by means of sonic sealing, R.F. sealing, or any other desired technique, so that the stack of pads 30 form an integral filter unit comprising a fibrous mass surrounded by fused flange 32, and in which the depth of the filter unit reduced from a maximum at the centre of the unit to a minimum at the flange, as shown in Fig. 3.

Thereafter, stack 30 is inserted between shells 14, 16, and the shells are heat sealed together about flanges 22, 24 in the manner shown in Figure 2, so as to separate the inlet 18 and the outlet 20. Sripper rings 38 moulded on flanges 22, 24 in shells 14, 16 press anairst the flange 32 of stack 30 to provide a mechanical seal between stack 30 and shells 14, 16, This prevents the formation of by-pass channels leading around stack 30. Optionally a heat seal may be provided in the .‘«me area, along with the mechanical seal.

In the specific embodiment shown, stack 30 comprises five different types of filter pads.

Filter pad 40 comprises the first pad of the stack. Typically, it is made of nonwoven, polyester fibres of the largest fibre diameter in the filter. Specifically, the fibres may be 14 to 16 and preferably 15 denier (0.00392 centimeter to diameter), although the diameter may vary substantially depending upon the desired resuits for the filter. Pad 40 may typically be of the order of 1 to IJ inches thick (specifically about lj inches in thickness) prior to being sealed together into stack 30, which results in compression and reduction of the thickness. - 5 ί'«5 Prior to assembly, the layer of nonwoven material from which fibrous pad 40 is manufactured may preferably be coated on both sides with a binder material such as a water emulsion of a self-crosslinking acrylic material, specifically Rohm δ Haas Rohplex HA 12.

Approximately 2.5 ounces of binder material solids may be applied per square yard of fibrous material of pad 40. The upper, inlet-facing surface 42 of fibrous pad 40 is sprayed v/ith a 25 percent solids emulsion, while the bottom surface 44 of pad 40 may be sprayed with a 5 percent solids emulsion, so that about 5 times as much binder material is applied to surface 42 than to surface 44.

Thus, when the fibrous pad 40 is compressed by the sealing step of Figure 3 and further compressed by being placed in housing 12, most of the compression takes place in the lower portion Of pad 40, in the vicinity of bottom surface 44, while the fibrous material in the vicinity of surface 42 remains in less compressed condition. This provides a natural filtering gradient, selective for removing ct the largest particles first as fluid passes through pad 40. The inlet-facing surface of the first pad 40 defines a convex, curved surface with the inlet located adjacent a central area of the convex surface.

The total typical weight per square yard of the material of the first pad 40 after binder application is about 9 to 11 ounces, and the fibres occupy about 4 percent of the pad volume.

The second filter pad 46 may comprise nonwoven polyester fibres of about 6 denier, i.e. a fibre diameter of G.00264 cm. Of course, other size ranges and materials for filter pad 46 can also be used in accordance with this invention.

Typically, before sealing into stack 30 as shown in Figure 3, the uncompressed thickness of filter pad 46 is about | to 1 inch, or specifically, inch. The material may be treated v/ith the same binder agent and in a manner similar to filter pad 40, v/ith about one fourth of the weight of the resulting product constituting binder material. The overall weight per square yard of the material of pad 46, after application of the binder material, may be in the order - 6 < 5f 1 SO of 3.5 to 4.5 ounces, specifically about 4 ounces, and the pad volume occupied by its fibres may also be about 11 percent.

The next two layers of filter pads 48a, 48b may be of the same polyester fibre. Before compression into stack 30 each layer 48a, 48b may be about 0.03 to 0.07 inch thick, specifically 0.05 inch. This material tends to compress much less upon processing and placement into housing 12 than the previous layers. It also can have a fibre denier of 6, but it may be a denser material than pad 46, weighing from about 6.5 to 8.4 ounces (e.g. 8 ounces) per square yard, with the fibres occupying about 11 percent of tbe pad volume. Typically, the materials of layers 48a and 43b are not treated with a binder. The specific filter pads 48a, 48b used may contain a polyester spunbonded scrim material as a support.

Filter pad 50 may typically contain a mixture of fibres, 50 percent by weight of which are from 3 co 6 denier (i.e. strand diameters of 0.00171 cm. to 0.Q0264 cm.), and 50 percent by weight of 1.5 denier fibres (a diameter of 0.00122 cm.). The material is typically made of polyester fibres, having an uncompressed thickness of about 0.03 to 0.05 inch (specifically 0.04 inch). It may have a density of about. 6 ounces per square yard, and the fibres may occupy about 15 percent of the pad volume. The material is supported with a nonwoven rayon scrim material, and, in the specific embodiment, it is not treated with a binder material.

Finally, last pad 52 may be a polyester fibre mixture of 50 percent by weight of fibres having a denier of about 3 or 4, and 50 percent by weight of fibres having a denier of 1.5. The pad may hays an uncompressed thickness of about 0.05 to 0.06 inch, and is supported on a polyester woven mesh scrim material. The density may be 10 to 14 ounces per square yard, and the fibres occupy about 30 percent of the pad volume. Ho binder is typically used.

Of course, other filter pads, having different characteristics and properties may be used in this invention, the above description being purely for exemplary purposes.

The overall compressed thickness of filter stack 30, as installed in casing 12, may be about | to 1 inch in this embodiment, specifically 2 inch.

After the filter pads are sealed together into stack 30 by means of sonic sealing member 34, 36, and stack 30 is cut away from the rolls of bulk material, either simultaneously with the sealing process or later from the layers of bulk filter material, stack 30 is thoroughly washed. The washing solution may comprise one quarter percent by weight each of Duponol RA detergent material sold by the DuPont Chemical Company, and sodium carbonate, in distilled water. This is followed by rinsing stack 30 three times in distilled water, and drying stack 30 in a tumble dryer at a temperature below the softening temperature of the softening or degradation temperature of the plastic fibres in stack 30.

After drying of stack 30, the bottom surface 37 of the stack is heatsintered prior to placing the stack into casing 12. This tends to cause individual, free fibres and other particles to adhere to the pad, reducing the amount of particulate matter falling out of the pad during use. Generally, the heat-sintering step can be accomplished by exposing the bottom surface 37 of stack 30 to hot air at a temperature of at least about 380°F., and preferably about 40o°F.t for a few seconds, for example five seconds, Thereafter, stack 30 is placed into housing 12, with shells 14, 16 being brought together first as shown in Figure 4. Shells 14, 15 may be sonically sealed together, for example by the use of a series 400 sonic sealer from the Branson Sonic Power Company of Danbury, Connecticut. Sonic sealing horn 54 presses shell 14 against flange 32 and lower shell 16. Simultaneously, the sonic sealing energy causes annular plastics ridge 56 to malt, resulting in the fusion of flanges 22 and 24 together in zone 26, as shown in Figure 2.

For sealing of the shells 14, 16 of casing 12, the above described Branson sonic sealer can be used for a weld time of about 1.5 seconds, a pressure of 30 p.s.i., and a hold time of 1 second. - 8 <1512 9 For sealing of the various filter pads to form flange 32 and integral stack 30, the same machine may be used for a weld time of about 5 seconds, a pressure of about 50 p.s.i.. and a hold time of about 6 seconds.

The horn of the sonic sealing device may be adapted to cut stack 30 away from the rolls of layers of filter material, simultaneously with the sealing operation which forms flange 32.

Also, the horn of the sonic sealing device desirably contains a resilient plug to compress the fibres, particularly of filter pads 40 and 46, during the sealing operation. This can reduce the overall thickness of stack 30, resulting in a flatter filter having a lower blood volume.

The filter described above is generally capable of processing 5 or 10 units of blood (a unit being the amount in a standard storage container) without needing replacement, and has successfully removed about 64 percent of 12 micron particles; 94 to 95 percent of 16 micron particles; 98 to 99 percent or more of 20 to 32 micron particles; and all larger particles.

Casing 12 may be about 9 cm. in diameter. However, the filtering device described, although sr .H, exhibits a high flow capacity and excellent levels of particle removal, while being susceptible to automated and inexpensive manufacture.

Performance of the invention described above involves use of the invention described and claimed in Patent Specifications Nos. 45127 and

Claims (5)

1. A method of manufacturing a filtering device for blood which comprises assembling a stack of filter pads comprising fibres, and including a first pad defining an upstream outer surface and a last pad defining a downstream outer 5 surface, sealing the peripheral edges of said pads in the stack together to form an integral filter unit defining an integral peripheral flange whereby the depth of the filter unit reduces from a maximum at the centre of the unit to a minimum at the flange, and thereafter inserting and sealing said filter unit into a filter housing having an inlet and an outlet by forming a seal between said 10 integral filter unit and the filter housing along said integral peripheral flange, so as to separate the inlet and the outlet, whereby the inlet faces the pad at one end of the unit and the outlet faces the pad at the opposite end of the unit.

2. A method according to Claim 1, wherein the fibres are thermoplastic 15 and the peripheral edges' of rhe pads are heat-sealed together.

3. A method according to Claim 2, in which said downstream surface is heated prior to insertion of the stack of pads into the housing at a temperature sufficient to increase the adhesion of any loose thermoplastic particles and fibres adjacent said downstream surface to said stack of pads. 20

4. A method according tc Claim 1, 2 or 3, in which the filter pad defining said upstream outer surface is treated on both sides thereof with a binder material, the amount of binder material applied to the side of said first filter pad which defines the upstream outer surface being greater than the amount of binder material applied to the other side of said first filter pad, whereby the 25 side of said filter pad defining said upstream outer surface is less compressible than the other side of said filter pad, and thereafter compressing said stack as it is sealed in the housing to obtain a differential density gradient across said first filter pad. 5. A filtering device for blood comprising a housing having an inlet and an 30 outlet and a stack of filter pads comprising fibres accommodated in the housing, - 10 .. ι« λ on 6. A filtering device according to Claim 5, wherein the fibres are thermoplastic and the peripheral edges of the pads are heat-sealed together. 7. A filtering device according to Claim 5 or 5, in which the filter pad defining said upstream outer surface is treated on both sides thereof with a binder material, the amount of binder material applied to the side of said first filter pad which defines the upstream outer surface being greater than the amount of binder material applied to the other side of said first filter pad, whereby the side ef said filter pad defining said upstream outer surface is less compressible than the other side of said filter pad, and means compressing said stack in the housing to obtain a differential density gradient across said first filter pad. 8. A filtering device according to Claim 7, in which substantially five times as much binder material is placed cn the upstream outer surface of the first pad as on the opposite surface. 9. A filtering device according to any preceding claim, wherein the inlet is carried by a housing wall which has means compressing the stack of filter pads whereby the shape of the inlet-facing surface of the stack of filter pads is convex, with the inlet being positioned adjacent a central area of the convex surface. 10. A filtering device for blood or liquid blood components, the device including a housing having an inlet for liquid to be filtered, an outlet for filtered liquid and a stack of fibre-containing filter pads positioned within said housing, the pads of the stack being joined together at their peripheral edges - 11 by a solid seal to define at said peripheral edges a non-porous, gasket-like flange retaining said pads together as an integral filter unit, the depth of said filter unit reducing from a maximum at the centre of the unit to a minimum at the flange, said filter unit being joined to said housing at said periphery by a second seal between said housing and said flange, the inlet of said housing being carried by a housing wall which defines means for compressing said stack of filter pads whereby'the shape of the inlet-facing surface of said stack of filter pads defines a convex, curved surface with said inlet being positioned adjacent to a central area of said convex surface. 11. A filtering device according to any one of Claims 5 to 10, in which the inlet is adjacent a first pad of said stack and said outlet is adjacent a last pad of said stack, the average diameter of the fibres of said last pad being smaller than the average diameter of the fibres of said first pad. 12. A filtering device .according to Claim 11, in which the average diameter of the fibres of each pad in said stack is at least as great as the average fibre diameter of the immediately adjacent pad in the direction of said last pad, said average.fibre diameter generally decreasing from pad to pad in the direction of said last pad. 13. A filtering device according to Claim 11 or 12, in which the fraction of the pad volume occupied by said fibres in the last pad is greater than said fraction in the first pad. 14. A filtering device according to Claim 13, in which the fraction of the pad yolume occupied by said fibres generally increases from pad to pad in the direction of said last pad. 15. A filtering device according to any one of Claims 5 to 14, in which most of the fibres of said stack of filter pads are nonwoven. 15. A filtering device according to any one of Claims 5 to 15, in which said first pad exhibits a fibre denier of 14 to 16 and a weight of 9 to 11 ounces per square yard, and said last pad exhibits a fibre denier of substantially 1.5 to 4 and a weight of 10 to 14 onces per square yard; and intermediate pads, - 12 positioned between said first and last pads, having fibre deniers which fall between the fibre deniers of said first and last pads. V. A filtering device according to any one of Claims 5 to 16, in which said fibres of the pads consist substantially of polyester fibres.

5. 18. A filtering device according to any one of Claims 5 to 17, in which said stack includes five different pads.