FIELD OF THE .INVENTION

The invention generally relates to filter devices. More particularly, the invention relates to filter devices utilizing hydrophobic filter material. The invention also generally relates to the wetting of porous hydrophobic material.

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BACKGROUND AND OBJECTS OF THE INVENTION

At the present time, over 12,000,000 units of whole blood are collected from volunteer donors in the United States each year. With the advent of blood component therapy, approximately 60% to 80% of the whole blood collected today is not itself stored and used for transfusion. Instead, the whole blood is separated into its clinically proven cellular and noncellular components, which are themselves stored and used to treat a multiplicity of specific conditions and diseased states.

The clinically proven cellular components of whole blood include red cells, which can be used to treat chronic anemia; and platelets, Which can be used to treat thro bocytopenia. The clinically proven noncellular components of whole blood include plasma and plasma-based fractions, such as albumin, protein fraction, gamma globulin, and various other specific coagulation protein concentrates.

The present concensus is that patient care is improved by providing only the therapeutic components of whole blood which are required to treat the specific disease. .The demand for therapeutic components of whole blood is thus ever increasing. Likewise, the demand for safe and effective systems and methods for collecting, separating and storing the cellular and noncellular components of whole blood grows accordingly.

Whole blood can be separated into its cellular and noncellular components by filtration. Often, blood filtration devices utilize hydrophobic microporous material. Because the material is hydrophobic, the membrane needs first to be "wetted" to accommodate fluid flow through the membrane. A porous membrane has been "wetted" when the pore volume of the membrane has been completely filled with a liquid. A conventional method of wetting hydrophobic materials includes the application of surfactants, alcohol, or other fluids which spontaneously wet the hydrophobic material. For example, attention is directed to the σopending U.S. Patent Application of Boggs et al, entitled "WΞTTABLE HYDROPHOBIC HOLLOW FIBERS", Serial No. 387,988, filed June 14, 1982.

Another conventional wetting method involves the use of chemical means to alter the surface characteristics of the material. By their very nature, conventional wetting techniques involve the introduction of nonphysiological substances into the pore volume of the filter material. They also require the subsequent step of washing or flushing the nonphysiological substances from the pore volume of the filter material prior to use. Regardless of the thoroughness of the washing step, however, there is the possibility that traces of the nonphysiological substances used to wet the filter material will remain associated with the material.

In addition, conventional substances which spontaneously wet hydrophobic materials may craze, or stress crack, plastic housings in which the hydrophobic materials are carried. Cracks and actual leaks in the housing can develop.

It is one of the principal objects of this invention to provide a filter device having a hydrophobic porous material which has been wetted using only physiological substances, without the use of any surfactants, wetting agents, or other nonphysiological material which would spontaneously wet the hydrophobic material.

SUMMARY OF THE INVENTION

To achieve this and other objects, the invention provides a device having a porous material which has been wetted without the use of a substance which, would spontaneously wet the material. In accordance with the invention, it has been discovered that, surprisingly, by applying pressure, a liquid which does not spontaneously wet the porous material can nevertheless be forced into the pore volume of the material. Thus, in accordance with the invention, the porous material is wetted with, a liquid which would not spontaneously wet the material.

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In one embodiment, the porous material is first subjected to reduced pressure or a vacuum prior to exposure to ^" the pressurized liquid. It is believed that this additional step facilitates the overall effectiveness of the wetting process conducted in accordance with the invention.

By virtue of the invention, a physiological liquid, such as water or an aqueous saline solution, can be used alone to wet a hydrophobic microporous membrane. Exposure of the membrane to surfactants or other nonphysiological liquids can thereby be completely avoided. The resulting filter device is preprimed with the physiological liquid and ready for immediate use, without any subsequent washing step and without the possibility of residual traces of surfactant or other nonphysiological substances.

Other features and advantages of the invention will be pointed out in, or will be apparent from, the Specification and claims, as will obvious modifications of the embodiments shown in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a perspective view of a prewetted and preprimed filter device which embodies the features of the invention;

Figure 2 is a partially cut away perspective view of the prewetted and preprimed filter device shown in Figure 1;

Figure 3 is a partially perspective view of a filter device and an apparatus which may be used to wet and preprime the filter device in accordance with the invention; and

Figure 4 is a perspective view of a filter device and an alternate apparatus which may be used to wet and preprime the filter device in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

A prewetted and preprimed filter 10 which embodies the features of the invention is shown in Figs. 1 and 2. The filter 10 can be variously constructed and used for different purposes. Because the invention is well suited for use with medical purpose filters, in the illustrated embodiment, the filter 10 is one suitable for separating the cellular and noncellular components of whole blood.

The filter 10 includes a housing 12, which can be molded from a plastic material. The housing 12 includes end caps 14 and 16 which have suitable blood outlet and inlet ports, respectively 18 and 20. The housing 12 also includes a plasma port 22

and an optional fill port 24, the purpose of- which will be explained later. A porous hydrophobic filter material 17, illustrated in Figure 2, is contained within the housing 12. As shown in Figure 2 , the hydrophobic filter material 17 consists of a plurality of hollow microporous fibers 27 having a desired pore size. It should be appreciated that the filter material 17 can be alternately configured, such as in a flat sheet. The pore size and porosity of the hydrophobic material will depend on the particular filter application and is not a limitation on the general aspects of the invention. Thus, the pore size will generally be chosen on the basis of the components to be removed or the type of treatment that is desired. The desired pore size to separate cellular blood components from noncellular blood components is well known in the art. Suitable types of such microporous hydrophobic materials include those manufactured from polypropylene, for example. Other suitable types of such hydrophobic microporous membrane materials include those constructed of polyethylene.

The filter 10 can be constructed by any suitable method. For example, the bundle of the hydrophobic filter fibers 27 can be placed in housing 12 in a direction substantially parallel to the longitudinal axis of housing 12 and secured at both

ends within housing 12 by use of a suitable potting compound. This concept is well known in the art and is not a limitation on the invention as any suitable construction can be used. A liquid 26 fills the interior of housing 12 and the pore volume of the hydrophobic hollow fibers 27. The liquid 26 is retained in the housing 12 by end caps 19, 21, 23, and 25 which seal the respective ports 18, 20, 22, and 24. In accordance with the invention, the liquid

26 which fills the housing 12 does not include any substances which would spontaneously wet the hydrophobic filter material 17, such as a surfactant or surfactants. Nevertheless, in accordance with the invention, the liquid 26 alone has been used to wet hydrophobic filter material 17.

More particularly, in Figure 3, an apparatus is shown which may be used to prewet and preprime the filter devices 54 and 56 in accordance with the invention.

The apparatus includes a chamber 30 and peripheral equipment 32 for providing air and other fluids under pressure. Chamber 30 is designed to withstand positive and negative pressures. The peripheral equipment 32 includes lines for the delivery of fluid under pressure to chamber 30. As illustrated in Figure 3, the peripheral equipment 32 includes a solution line 34 and a liquid

storage tank 36 having a valve 38. The liquid 26 in the tank 36 does not include any surfactant or the like which would spontaneously wet the porous material of the filter devices 54 and 56. In the embodiment illustrated in Fig. 3, the peripheral equipment 32 also includes a pressure and vacuum line 40 which communicates with the interior of the chamber 30. The line 40 includes suitable valves 42, 44, and 45; a vacuum source 47; a pressure regulator 46; and a source of compressed gas 48. A vent line 50 with a valve 52 is also provided for venting the chamber 30.

All of the valves 38, 42, 44, 45, and 52 are initially closed. The filter devices 54 and 56, similar to the filter 10, but not yet filled with the liquid 26, are placed in the chamber 30. One or more of the inlet and/or exit ports 18, 20, 22, and 24 of each of filters 54 and 56 are opened. It should be appreciated that, in accordance with the invention, only one of the inlet or outlet ports 18, 20, 22, and 24 associated with each filter 54 and 56 need be open.

With the valves 42 and 44 open, the chamber 30 is first evacuated by means of pressure and vacuum line 40. The interior of each filter 54 and 56, including the pore volume of each associated hollow fiber, are thereby evacuated through the open port or ports.

After evacuation of the chamber 30, the valves 42 and 44 are again closed. The valve 38 is opened, and the chamber 30 is filled with the liquid

26 from the storage tank 36 via the solution- line 34. The interior of each filter 54 and 56 is also thereby filled through the open port or ports.

After the chamber 30 and filters 54 and 56 have been filled with the solution 26, the valve 38 is closed. In accordance with the invention, the valve 45 is opened, and the interior of chamber 30 is pressurized by compressed gas from the compressed gas source 48. The pressure regulator 46 is utilized to provide the desired pressure.

Surprisingly, even though the liquid 26 will not itself spontaneously wet the porous material 17 of the filter devices 54 and 56, it is nevertheless forced under the applied pressure into the- pore volume of the material 17. The end result is that the material 17 is wetted with the liquid 26 which would not spontaneously wet the material 17.

The amount of pressure applied to achieve these surprising results will vary, depending on the particular type of hydrophobic filter material utilized.

The amount of pressure for a particular material can be determined empirically. While it is believed that there is a finite time required for the solution to wet the material, it is believed that pressure is the primary consideration. Generally, the actual time required to wet the material will be less than one minute, although it is to be understood that this is not a limitation of the invention.

Alternatively, the pressure requirements to wet the microporous hollow fiber material can be estimated by the equation:

4 γ cos 0 Pressure = g

where γ = liquid surface tension (dynes/cm) ■Θ = contact angle (degrees) d = hollow fiber pore size (cm). The liquid 26 used to achieve the surprising results of the invention can comprise virtually any liquid which does not spontaneously wet the porous filter material. For example, when the porous material is hydrophobic, the liquid 26 can comprise only water. The liquid 26 can also be a solution containing water, such as an aqueous saline solution. In the context of the illustrated embodiment, the use of the aqueous saline solution is preferred.

After the liquid 26 has been forced under pressure into the pore volume of the material 17, the valve 45 is closed, the valve 52 is opened, and the chamber 30 is vented via the vent line 50. The filters 54 and 56 can then be removed from chamber 30. The ports which were opened during the wetting process are closed, using the heretofore discussed caps, to retain the liquid 26 in the filter housing. The filter 10 as shown in Figs. 1 and 2 is thereby provided in which the previously unwetted hydrophobic fibers are now in a fully wetted

condition. The liquid 26 remains in the housing 12 until time of use. The filter 10 is thus not only prewetted, but is also preprimed.

The prewetted and preprimed filter 10 can be sterilized by autoclaving, radiation sterilization, or the like.

It is belived that the above-discussed step of first evacuating the chamber 30 prior to subjecting the filter material to the pressurized liquid 26 serves to facilitate wetting process. By first subjecting the filter material to a vacuum, or simply to a reduced pressure, air which is normally present within the pore volume of the material is removed. The liquid 26, which is thereafter forced into the pore volume under pressure, will then remain in the pore volume after the pressure is removed. Otherwise, it is believed that air compressed within the pore volume by the entry of the pressurized liquid 26 could expand after the pressure is removed and force the liquid 26 from the pore volume.

However, the initial evacuation step could be eliminated and other methods used to remove the air from the pore volume.

For example, by introducing the liquid 26 at a sufficient pressure, the air present in the pore volume can be driven, or dissolved, into solution.

This alternative technique could be enhanced by first purging the pore volume with carbon dioxide or another gas which will readily dissolve in the

liquid 26. Any comparable technique which serves to increase the overall diffusion of gas into solution can also be utilized, such as the application of heat. In yet.another- alternate embodiment which 5 does not employ the evacuation step, the introduction of the pressurized liquid could be followed by a sudden decrease in pressure on one side of the porous material. This will rapidly draw the fluid through the pore volume toward the side of lesser pressure to

10 effectively "flush" the air from the pore volume.

The foregoing descriptions with respect to Figure 3 represent several methods for fabricating the prewetted and preprimed filter 10 in accordance with the invention. However, other techniques could

15 also be used.

For example, the filter housing 12 could itself serve as the ^~ equiva-lent of pressure chamber 30. In this embodiment, the housing 12 would be made of a material sufficient to withstand the pressures

20 applied. In this arrangement, the chamber 30 could be eliminated, and the lines 34 and 40 would be attached directly to the desired inlet and/or outlet ports or ports of the filter, as generally shown in Fig. 4.

25. Yet another alternate arrangement is more specifically shown in Figure 4. In this embodiment, an air pressure chamber 58 is provided having a gas pressure line 62 which communicates with a source of compressed air. A filter 60, which is of similar

30 design to filter 10 but not yet filled with the

liquid 26, is placed within the chamber 58. .A fluid line 64 communicates directly with at least one of the ports 66, 70, or 72. The fluid line 64 does not communicate with the chamber 58. In the illustrated embodiment, the line 64 communicates directly with the plasma port 66 and blood exit port 72.

The liquid 26 is thus directed under pressure through the line 64 directly into the interior of filter 60. The interior of chamber 58 is at the same time pressurized to an external air pressure generally equal to the internal fluid pressure. This arrangement prevents the filter housing 12 from exploding as the pressurized liquid is driven into the pore volume of the filter material. In yet another arrangement, all of the inlet and outlet ports 18, 20, and 22 of the filter 10 (see Fig. 1) could have their final closure caps 19, 21, and 23 preattached. In this arrangement, the pressurized liquid 26 could be introduced into the filter device via the separate fill port 24, as shown in Figs. 1 and 2. The fill port 24 could communicate with either the blood side or plasma side of the filter material, or both sides. After the filter material has been wetted, the fill port 24 could then be closed by its own cap 25.

In still yet another embodiment, one of the inlet or outlet blood ports 18 or 20 could be closed, and a stream of pressurized liquid 26 directed through the other open port 18 or 20. The pressurized stream of the liquid 26 will be forced

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through the pore volume of the filter material and exit the filter housing 12 via the plasma port 22, which is left open. The pressurized stream of the liquid 26 alone wets the filter material. In yet another alternate arrangement, the liquid 26 could include a surfactant present in an amount substantially less than that required to spontaneously wet the filter material. The presence of small amounts of the surfactant will reduce the overall amount of pressure required to force the liquid 26 into the pore volume of the filter material. Regardless of which particular embodiment of the invention used, the porous material of the filter is wetted without the use of any surfactant or other nonphysiological material that spontaneously wets the hydrophobic material.

EXAMPLE I A filter device similar to that shown in Figure 1 was wetted and preprimed in accordance with the invention. The microporous filter media which was utilized in the filter was a hydrophobic polypropylene hollow fiber material having the following physical specifications: inside diameter

320 μ , wall thickness 150 μ ; effective length 214

2 mmmm;; ee:ffective surface .17 m ; and maximum pore size

.55μ.

Apparatus similar to that shown in Fig. 3 was utilized. The filter was placed in the chamber 30. With all of the filter ports open, the chamber

30 was evacuated to about 0.3 inches of mercury absolute. The chamber 30 was then filled only with saline and thereafter pressurized to about 150 psi for less than one minute. The filter was removed from the chamber and tested by connecting the blood inlet of the filter to a low pressure water line. The blood outlet was closed, and water exited freely from the plasma exit port.

Further testing with whole blood demonstrated that the filtration characteristics of the filter material wetted in accordance with the invention were the same as those of a filter material wetted with a conventional surfactant.

EXAMPLE II Another filter device similar to that shown in Fig. 1 was wetted and preprimed in accordance with the invention. The microporous filter material used was the same polypropylene same hollow fiber material described in Example I. In this procedure, no external chamber was used. The blood outlet side of the device was closed. The plasma outlet side was opened. A pressurized stream of water was directed for approximately one minute through the blood inlet side at about 95 psi. The pressurized stream of water exited the device via the open plasma outlet side at a flow rate of about 22 liters per minute, indicating that the hydrophobic filter material had been wetted.

While the invention has been described with respect to numerous specific embodiments, it is to be understood that the invention is capable of numerous other rearrangements, changes and modifications and it is intended to cover all such rearrangements, modifications and changes as fall within the scope of the appended claims.