IE42305B1 - Improved blood filter medium - Google Patents

Description

This invention relates to an improved blood filter medium.

The filtration of blood is a delicate and critical operation. Blood filtration requires that the debris, such as clots and various types of agglomerates, be removed without removing desirable red cells or other desirable portions of the blood and without degradation of the blood. · Whole blood comprises plasma, red cells, white cells and platelets. The red cells have diameters of from about 8 to 10 microns and the white blood cells have diameters of from about 12 to 20 microns. Whole blood, after storage for a relatively short period of time, and blood which is passing through an extra15 corporeal circuit, such as is used in open heart surgery, or through a dialysis operation will tend to degrade and build debris in the blood. This debris must be filtered from the blood before the blood is returned or given to a patient. The debris may comprise blood clots or various types of aggregates of the platelet type or the leucocyte type and may include agglomeration of protein precipitates and other undesirable debris.

In filtering this blood, the ultimate is to remove all of the undesirable debris while not removing any of the desirable red blood cells or white blood cells or the platelets. Hence, a medium used in the filtration of blood must meet certain requirements. It must have no - 3 harmful effects on the blood or degrade the blood. The medium should be stable during filtration, that is its pore size distribution range should not be altered.

Very often some media will start to plug and after limited use will remove some of the desirable red and white blood cells from the blood. The medium should have as much open area as possible to make the most efficient use of the medium area and make the filter small and easy to handle.

We have developed an improved blood filter medium. Our improved medium has a nominal pore size rating of 20 microns. Our improved medium is stable during use and retains this pore size rating even after considerable quantities of blood have been filtered. Our improved filter medium has minimal deleterious effects on the blood being filtered. Unexpectedly, our new blood filter medium has a very narrow pore size distribution range and while it removes all of the undesirable debris from the blood it does not remove the desirable red blood cells and while blood cells in the blood.

In accordance with the present invention we provide a filter medium for a blood filter unit, said medium comprising an uncalendered unbonded woven fabric having a nominal pore size rating of 20 microns, the pore sizes being in the range from 17 to 23 microns, and woven with monofilament yarns in a two up and two down twill weave. Preferably our improved blood filter medium is woven with monofilament yarns having a diameter of 32 microns.

The invention will be further described in conjunction with the accompanying drawings wherein: FIGURE 1 is a plan view of the improved filter 2305 - 4 medium of the present invention; and FIGURE 2 is a cross-sectional view of a blood filter unit incorporating the medium of the present invention. Referring to the drawings, in Figure 1, there is shown the improved blood filter medium 10 of the present invention. The medium is woven with nylon monofilament yarns 11 and these yarns are used in both the warp and the weft directions. The medium is woven in a regular, even-sided, two up and two down twill weave. Though nylon monofilament yarns are preferred, the medium may alternatively be woven with polyester monofilament yarns or other monofilament yarns which will not degrade or have a deleterious effect on the blood. It is important that monofilament yarns be used as it is believed that such yarns, being smoother and with less rough areas such as are present in multifilament or spun yarns, have a longer life and have less deleterious effects on the blood. The size of the monofilaments should be as small as possible. The smaller the diameter of each yarn, the more open area in the filter while still maintaining a desired pore size. Sizes of from about 30 microns in diameter to 36 microns in diameter have been found suitable in accordance with the present invention.

The medium is not calendered nor are the yarns bonded or held together at their cross-over points.

This is important as it appears that calendering or bonding tends to disrupt the pore size rating and distribution range and, surprisingly, does not have any improved effect on the stability of the two up and two down twill weave. By stability, it is meant that its initially rated pore size is maintained throughout its expected life. The improved blood filter medium has a nominal 42303 - 5 pore size rating of 20 microns. If its rating is less than 20 microns, it will remove desirable portions such as white and red blood cells from the blood being filtered. If its pore size rating is greater than 20 microns, it will not remove all of the undesirable debris. The medium has pore sizes in the range from 17 microns to 23 microns. This is a narrow range; however, it is important to the present invention. A wider range will either remove too many important portions of the blood or not remove sufficient debris or, in some instances, may have both harmful effects. Furthermore, the wider ranges do not maintain that range during extended uses and hence are unsatisfactory.

The two up and two down twill weave using substantially the same size yarns in the warp and weft direction produces a fabric having very uniform openings which is essential to the present invention. The fact that our fabric medium is not calendered or heat set allows us to ensure the maintenance of this opening in a blood filter unit.

It has been theorized that the above-described twill weave combined with the lack of calendering produces some depth to the fabric medium or depth to the openings or pores in the fabric. This slight depth to the pore helps in preventing slightly larger particles than the size of the opening from changing shape and squeezing through an opening or pore.

In Figure 2, there is shown one embodiment of a blood filter unit 15 that utilizes the blood filter medium of the present invention. The unit comprises a housing 16 and a filter cartridge 17 disposed within the housing. At the top of the housing is an inlet 2 3 0 5 opening 18 for the incoming blood and an air vent 19 to allow air to escape from the filter unit. The filter cartridge is cylindrical in shape. The peripheral walls of the cylinder are formed by the filter medium 20 of the present invention. The medium may be flat or fluted in its cylindrical form. The inside surface of the medium is supported by an open mesh-like cylinder 21. The upper end of the medium is sealed by a cap 22. The lower end of the medium is sealed into the bottom portion of the housing. In the centre of the bottom portion of the housing and positioned adjacent the centre of the filter cartridge is the blood outlet opening 23. in operation, the blood flows in the path as shown by the arrows in the drawing. The blood enters through the inlet 18 and flows from outside the filter cartridge into the centre of the cartridge and out of the outlet 23.

Though a cylindrical blood filter unit has been shown, the unit may be of any desired shape and the medium may take any configuration desired.

Claims (4)

1. A filter medium for a blood filter unit, said medium comprising an uncalendered, unbonded woven fabric having a nominal pore size rating of 20 microns, the pore 5 sizes being in the range from 17 to 23 microns, and woven with monofilament yarns in a two up and two down twill weave.

2. A filter medium according to Claim I, wnerein tne monofilament yarns are nylon yarns. 10

3. A filter medium according to Claim 1 or 2, wherein the monofilament yarns have a diameter of from 30 microns to 36 microns.

4. A blood filter medium substantially as described with reference to the accompanying drawings.