IE45128B1 - Blood filter - Google Patents

Description

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

It has been recently determined that there are many situations when 5 stored, donated blood, as wall as other types of blood and bleed components, should be filtered to remove nicroemboli 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 microsmboli 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 commercially available for use with stored, whole blood, or for reprocessing fresh blood in heat-lung machines, as well as blood which has passed through cardiotcmy machines.

In a blood filtering device, it is, of course, desirable that the device 15 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 rate of Blood through the filter, and a high capacity. Accordingly, the device does not have to be replaced e,xcessively often when a patient is receiving a - 2 Z ο1 2 3 large amount of blood.

Furthermore, afiltering 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 described in this application exhibits excellent highflow 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.

According to one aspect, the present invention provides a filtering device for blood including a housing defining an inlet for fluids to be filtered, an outlet for filtered fluid, and a fibre-containing filter pad positioned within said housing, said filter pad being treated with a binder material to provide increased stiffness to the filter pad, the side of said filter pad facing said inlet carrying more binder material than the side of said filter pad facing said outlet, said filter pad being compressed in the housing to define a density gradient across its width with the outlet-facing side of said filter pad being compressed more than said inlet-facing side.

The invention also resides in a method of manufacturing a filtering device for blood comprising a fibre-containing filter pad accommodated in a housing, having an inlet and an outlet, the method including applying binder material to both sides of said filter pad to cause the fibres to adhere together, and thereafter compressing said filter pad in the filter housing, the method including applying more binder material to one side of said filter pad than to the other side, tc provide increased stiffness to said one side of the filter pad compared with the other side thereof, and inserting said filter pad into said housing with said one side facing the inlet, whereby upon compression in the housing, said filter defines a compression gradient across its width caused by the differential amount of binder material on said one side compared with the other, - 3 with said other side of the filter pad being compressed more than said one side.

A natural filtering gradient is, therefore, presided for selectively removing the largest particles first and smaller particles afterwards, as the fluid passes through the pad.

Reference is now made to the accompanying drawings, wherein: 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 an eleyational 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 as 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, 15. 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, also respectively define mating flanges 22, 24, which may fit together by sonic sealing or the like at area 26. Each shell 14, 15 defines a series of radial vanes 27, 28, for the purpose of defining flow channels to distribute fluid between the filter material and inlet IS, as well as outlet 20.

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 - 4 process is indicated by Figure 3, showing how tubular heat-seal dies 34, 35 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 mass, surrounded by fused flange 32.

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. Gripper rings 38 moulded on flanges 22, 24 in shells 14, 16 press against the flange 32 of stack 30 to provide a mechanical seal between stack 30 and shells 14, 16. Ti:is prevents the formation of by-pass channels leading around stack 30. Optionally a heat seal may be provided in the same area, along with the mechanical seal.

In the specific embodiment shown, stack 30 comprises five different types of filter pads. lg 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 oe 14 to 16 and preferably 15 denier (0.00392 centimeter in diameter), although the diameter may vary substantially depending upon the desired results for the filter. Pad 40 may typically be of the order of 1 to Ij inches thick (specifically about IJ inches in thickness) prior to being sealed together into stack 30, which results in compression and reduction of the thickness.

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 & Haas Rhoplex 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 with a 25 percent solids emulsion, while the bottom surface 44 of pad 40 may be sprayed with a 5 percent solids emulsion, so that - 5 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 of 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 0.00264 cm. Of course, other size ranges and materials for filter p-'d 4-5 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 J to 1 inch, or specifically, I inch. The material may be treated with the same binder agent and in a manner similar to filter pad 40, with 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 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, 43b, 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. - 6 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 the pad volume. Typically, the materials of layers 48a and 48b are not treated with a binder. The specific filter pads 48a,, 48jj 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 to 6 denier (i.e. strand diameters of 0.00171 cm. to 0.00264 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 v/eight of fibres having a denier of 1.5. The pad may have an uncompressed thickness of about 0.05 tc 0.06 inch, and is supported on a polyester woven mesh scrim material. The density may he 10 to 14 ounces per square yard, and the fibres occupy about 30 percent of the pad volume. No binder is typically used.

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

The overall compressed thickness of filter stack 30, as installed in casing 12, may be about 1 to 1 inch in this embodiment, specifically 5 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 - 7 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 heat-sintered 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 cf the pad during use. Generally, the hgat-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 400°F., 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 melt, 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 tirna of about 1.5 seconds, a pressure of 30 p.s.i., and a hold time of 1 second.

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. - 8 Also, the hern 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 small, exhibits a high flow capacity and excellent levels of particle removal, while being susceptible to automated and inexpensive manufacture.

Performance of ths invention described above involves use of the inventions described and claimed in Patent Specifications Nos. 4512/ and 45129.

Claims (5)

1. A filtering device for blood including a housing defining an inlet for fluids to be filtered, ar. outlet for filtered fluid, and a fibre-containing filter pad positioned within said housing, said filter pad being treated with a binder material to provide increased stiffness to the filter pad, the side of said filter pad facing said inlet, carrying more binder material than the side of said filter pad facing said outlet, said filter pad being compressed in the housing to define a density gradient across its width with the outlet-facing side of said filter pad being compressed more than said inlet-facing side.

2. A filtering device according to Claim 1 in which approximately five times as much binder is present on the inlet-facing side of said filter pad compared with the amount of binder present on the outlet-facing side of said filter pad.

3. A filtering device for blood comprising first and second housing members, and a filter pad having first and second opposite surfaces, each of said housing members including a fluid inlet and a fluid outlet, with said first surface facing the inlet and said second surface facing the outlets and filter pad compression means, the surfaces of said filter pad being impregnated with binder, said first surface of the filter pad being impregnated with a higher concentration of binder than the second surface thereof so as to render said first surface relatively more rigid than said second surfaces said filter pad compression means cooperatively functioning to compress said filter pad therebetween in such a manner as to compress said second surface to a greater extent than said first surface, and to provide density gradient from said second surface to said first surface.

4. A method of manufacturing a filtering device for blood comprising a fibre-containing filter pad accommodated in a housing, having an inlet and an outlet, the method including applying binder material to both sides of said filter pad to cause the fibres to adhere together, and thereafter compressing said filter pad in the filter housing the method including: applying more binder material to one side of said filter pad than to the other side, to provide increased stiffness to said one side of the filter pad compared with the other side thereof, and inserting said filter pad into said housing with said one side facing the inlet, whereby, upon compression in the housing, said filter pad defines a compression gradient across its width caused by the differential amount of binder material on said one side compared with the other, with said other side of the filter pad being compressed more than said one side.

5. A Method according to Claim 4 in which said fibre-containing filter pad is the first pad of a stack of filter pads, said fibre-containing filter pad defining an up-stream outer surface of said filter stack.