BACKGROUND OF THE INVENTION

The present invention relates generally to fluid filters which separate gas from liquid in a fluid stream and vent the gas and to a method of making same. More particularly, the present invention relates to such filters utilizing hollow fibers for separating an venting gas and for filtering liquids.

Fluid filters which utilize porous membrane or other filter media for filtering liquids, which als separate gas from liquid and vent the gas have been use in a variety of situations. One important use for suc filters is in filtering parenteral solution or othe fluid, as the fluid is administered to a living subject, usually human. In the administration of such fluids, i addition to filtering out particulate matter an potentially harmful micro-organisms, it is preferre that any gas suspended or entrained in the fluid also b removed so as to eliminate any hazard of embolism fro air or gas reaching the patient.

Filters which utilize both hydrophobic an hydrophilic membranes are well known. Present filter utilizing one or more hollow fibers are also known However, these filters typically have a number o drawbacks. A common shortcoming with these filters i that the filter must be maintained in an uprigh position in order to operate effectively in venting gas In other filters, the surface of the filtering membran is small, thereby having limited filtering capacity The cost factor also plays a considerable role, sinc such filters can or must, in medical applications, b used only once. Many current filters are relativel expensive to manufacture, which adds significantly t the total product cost.

U.S. Patent No. 4,568,366, for example,, dis¬ closes a medical fluid filter which utilizes hydrophilic fibers, and unlike the present invention, a hydrophobic membrane positioned at the top of the filter. This filter is position sensitive and must be maintained in an upright position in order for separated gas to be vented from the housing. Build-up of gas may result in partial blockage of the hydrophilic fibers and lead to reduced flow rates to the patient. European Patent Application No. 0086028 discloses a filter for water purification which uses both hydrophobic and hydrophilic fibers. However, unlike the present invention, the two different fibers are not contained in the same housing. The hydrophobic fibers are encased within a housing mounted on top of the liquid filtering housing, thereby making the effec¬ tiveness of the filter dependent upon its maintenance in an upright position. As such, this filter also requires two separate housings, thereby increasing manufacturing costs.

U.S. Patent No. 4,636,307 discloses a water purification filter which utilizes both hydrophilic and hydrophobic fibers. Unlike the present invention, the device disclosed in this patent does not separate and vent gas, but intentionally reentrains the gas into the liquid after it is filtered. Specifically, after the water has passed through the hydrophilic fibers and been filtered of impurities, the filtered water and the gas, which passed through the hydrophobic filters, exit the filter housing through the same outlet. This is not atypical. Water purification filters are seldom concerned with re-entrainment of the gas in the liquid after filtering. Indeed, a certain level of dissolved air enhances the taste of the water. Accordingly, it is a general object of the present invention to provide a gas separating and venting filter which does not suffer from the drawbacks described above.

Another object is to provide a gas separatin and venting filter which is substantially less expensiv to manufacture than existing filters.

These and other objects of the presen invention are set forth in the following detaile description of the illustrated embodiments of th present invention.

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SUMMARY OF THE INVENTION The present invention is directed to a liquid filter which also separates and vents gas from the liquid. In accordance with the present invention, a filter for separating and venting gas from liquid is defined by a housing having an interior chamber with a fluid inlet into the interior chamber and a gas outlet from the interior chamber. Located within the housing are two sets of microporous hollow fibers. One set of hollow fibers is of a hydrophilic nature and the interiors of the fibers are in communication with the liquid outlet. The other set of hollow fibers is of a hydrophobic nature and the interiors of the fibers are in communication with the gas venting outlet. Gas entrained in the fluid introduced into the housing is separated from the liquid by the hydrophilic fibers, which are impermeable to gas when wetted. The gas is vented from the housing by passing through the hydrophobic fibers, which are relatively impermeable to liquid, thus preventing the collection of gas on the surfaces of the hydrophilic fibers which would reduce the fibers' filtering ability. The gas passes from the hydrophobic fibers out of the housing through the gas venting outlet.

The hollow fibers herein may be two u-shaped bundles, one bundle hydrophilic and one hydrophobic, with the bundle of hydrophobic fibers adjacent to and in substantially side-by-side relation to the bundle of hydrophilic fibers. Use of u-shaped fibers has the advantage of minimizing manufacturing time and cost. One or both bundles of the fibers herein may extend sub¬ stantially the full length of the interior chamber, thus providing greater filtering and venting surface.

The bundle of hydrophilic fibers of the present invention may be substantially aligned between the fluid inlet and the liquid outlet of the filter housing, with the open ends of the fibers secured by potting compound in an aperture of a potting collar, and

in communication with the liquid outlet. The open ends of the hydrophobic fibers herein may be secured int another aperture of the potting collar so as to be i communication with the gas venting outlet. The hydrophilic fibers of the presen invention are preferably naturally hydrophilic and non chemical secreting, and there are preferably about twic as many hydrophilic fibers as hydrophobic fibers t provide a large filtering surface area for adequat liquid flow rates.

In an alternative embodiment, the housing ma be of a generally elongated and tubular shape, definin a fluid inlet at the upper end. The gas venting outle may be a lateral aperture located proximal to the lowe end of the housing. The open ends of the hydrophobi fibers may be secured within the gas venting outlet wit the ends opening to the exterior of the housing an spaced from the ends of the hydrophilic fibers. Th hydrophilic fibers may be positioned in a substantiall side by side relationship with the hydrophobic fiber with the open ends of the hydrophilic fibers in com munication with the open lower end of the housing.

A cap having a liquid outlet may be secured t the open lower end of the housing so as to seal th lower end of the housing and overlie and protect without blocking, the gas venting aperture.

The filter of an alternative embodiment may b manufactured from a one-piece housing having a branc arm extending from the side of the housing proximal t the open lower end of the housing. The hydrophobi fibers are inserted into the interior of the housin through the branch arm and extend substantially th entire length of the interior housing. The hydrophili fibers are inserted into the housing through the ope lower end of the housing and extend substantially th entire length of the interior housing. The housing i then clamped circumferentially adjacent the juncture o the branch arm and the lower end until both bundles o

fibers are tightly enclosed within the housing. Potting compound is then injected into the housing through the open end or branch arm, preferably the branch arm, thereby sealing the fibers together at the point above the clamp. After the potting compound has cured, the clamp is removed and the branch arm is cut from the housing at the base of the branch arm, thereby exposing the open ends of the hydrophobic fibers to the ambient atmosphere. A cap, having a liquid outlet port is sealingly placed over the open lower end of the housing so that the open ends of the hydrophilic fibers are in communication with the liquid outlet tube of the cap. The cap also overlies the gas venting aperture but is spaced therefrom to define an annular gas venting passageway between the interior sidewall of the cap and the exterior surface of the housing.

Additional features and advantages of the present invention will be apparent from the detailed description of the illustrated embodiments depicted in the drawings.

DESCRIPTION OF DRAWINGS Figure 1 is an exploded perspective view o the preferred filter of the present invention.

Figure 2 is a bottom plan view of the ca employed in filter of Figure 1. Figure 3 is a side view of the cap employed i the filter of Figure 1.

Figure 4 is a top plan view of the cap o Figure 4.

Figure 5 is a side elevational view of th filter of Figure 1.

Figure 6 is a side elevational view of th filter of Figure 1 showing the fibers potted in th collar.

Figure 7 is an exploded perspective view partially broken away, of an alternative filter housin and cap of the present invention.

Figure 8 is a series of perspective views partially broken away, depicting the manufacture of th alternative embodiment of the present invention depicte in Figure 9.

Figure 9 is a vertical cross-sectional view o an alternative embodiment of the present invention.

Figure 10 is a vertical cross-sectional vie of a second alternative embodiment of this invention. Figure 11 is a cross-sectional view of th second alternative embodiment taken along line 11-11 o Figure 10.

Figure 12 is a cross-sectional view of t second alternative embodiment of this invention tak along line 12-12 of Figure 10.

DETAILED DESCRIPTION OF THE DRAWINGS ^• Turning now to a detailed description of the present invention as shown in its preferred and alternative embodiments in the attached drawings. Referring to Figure 1, the present invention is generally embodied in a filter unit, generally at 8, which may be an integral part of an overall medical fluid administration set for administering parenteral solutions and the like to patients or, alternatively, as an add-on to a separate administration set. In the preferred filter unit, the present invention is embodied in a housing made of three molded plastic pieces. These are an upper housing 10 defining a elongated interior chamber 12, a potting collar 14 and a lowe ^** r end cap 16. The upper housing 10 is generally elongated and oval in cross-sectional shape. The housing 10 has a closed upper end 18 and an open lower end 20.

The upper housing 10 may be constructed from any material which is compatible with the fluid being filtered, but the material is preferably clear, so that the liquid within the filter may be observed. For filtering parenteral solutions, the housing 10 is preferably made of clear, rigid, ABS, PVC, or methyl- acrylic type plastic, such as that available under the trademark PLEXIGLAS from the Rohm and Haas Company of Philadelphia, Pennsylvania, USA. This material is relatively inexpensive and easy to mold.

The potting collar 14 is also of one-piece, molded construction having a generally oval cross- sectional shape. It may be constructed from the same material as the upper housing and may be either clear or opaque. Disposed within the potting collar are two cylindrical ports or apertures 22 and 24 in substan¬ tially side-by-side relation. The collar is sealingly joined, as by solvent or sonic bonding, to the lower open end of the upper housing 10 so that the collar's apertures are in direct communication with the interior

chamber 12 of the housing.

The cap 16 is of one-piece, molded con struction and may also be constructed of the sam material as the upper housing 10 and the potting colla 14. The cap 16 has a base 26 which has a generally ova shape, a gas outlet port 28 and a generally cylindrica liquid outlet tube 30 in substantially side-by-sid relationship to the gas outlet. The cap is εealingl joined to and covers the base of the potting collar 1 so that the gas outlet port 28 and the liquid outle tube 30 are substantially aligned with the two aperture 22 and 24, respectively, of the potting collar 14. A such, the gas outlet port 28 and the liquid outlet tub 30 are in communication, through the apertures of th potting collar 14 and the interior of the hollow fibers with the interior chamber 12 of the housing 10.

For permitting flow of fluid into th housing, an inlet port tube 32 is provided at the uppe end 18 of the housing 10. In the preferred embodiment the fluid inlet tube 32 is located to one side of th upper end 18 of the housing and is generally aligne with the liquid outlet tube 30.

Disposed within the interior chamber of th upper housing are two bundles or sets of open-ende hollow fibers, 34 and 36. One set of the fibers 34 i constructed of material of a hydrophilic (wate attracting) nature and the other set of fibers 36 i constructed of material of a hydrophobic nature (wate repelling) . The sets of fibers are positioned generall side-by-side within the interior chamber 12. In th preferred embodiment, the fibers are arranged in a U configuration and having their open ends positioned a the lower end 20 of the interior chamber 12. As a alternative structure, the fibers may be straight havin closed ends opposite the open ends of the fibers However, this embodiment involves the additional step o sealing closed one end of each fiber. In the preferre embodiment, there are approximately twice as man

hydrophilic fibers as hydrophobic fibers.

In the preferred embodiment the hydrophilic fibers 34 are non-chemical secreting and constructed of a naturally hydrophilic material such as mixed esters of cellulose, or nylon, which is compatible with the housing material and aqueous parenteral solutions. The hydrophilic fibers have an average pore size ranging from about 0.1 to 0.45 microns, and preferably about 0.22 microns to remove bacteria from the liquid being filtered. Such fibers are wetted by water and resistant to thl transmission of gas therethrough, so long as the gas pressure is below the bubble point of the material of thέ fibers. The bubble point generally describes the differential pressure across the membrane at which gas will be forced through the wetted fiber membrane, and, for the preferred material described above, is about 40- 60 PSIA.

A surfactant may be applied to the surfaces of the hydrophilic fibers 34 to facilitate the flow of aqueous liquid therethrough. For example, a mixture of monoesters of sorbitance with capric, lauric, myristic, palmitic, and/or oleic acids may be used.

The hydrophilic fibers 34 of the preferred embodiment extend the entire length of the interior chamber of the housing 10 for greater filtering capacity, and are substantially aligned between the fluid inlet tube 32 and the liquid outlet tube 30. When fluid is introduced into the housing through the fluid inlet tube 32, the liquid permeates the hydrophilic fibers and is discharged through the liquid outlet tube 30.

The ends of the hydrophilic fibers are open and substantially disposed and fastened within the aperture of the potting collar that is in communicatio with the liquid outlet tube. The fastening substance i in the form of a potting resin, such as adhesive o urethane resin, which sealingly joins the open ends o the hydrophilic fibers together and secures them withi

- li ¬ the potting collar aperture with the open ends openin to the liquid outlet tube 30.

The second set of fibers 36 is made o material of a hydrophobic nature. in the preferre embodiment, the set of hydrophobic fibers 36 is i side-by-side, substantially parallel relationship to th set of hydrophilic fibers 34 and extends substantiall the entire length of the interior chamber of th housing. Thus, gas entrained within the chamber wil come into contact with at least one hydrophobic fibe and pass through the fiber and out of the chambe through the gas outlet port, thus rendering the filte substantially position insensitive. The ends of th hydrophobic fibers are open and positioned at the lowe end of the interior housing and are secured by th potting resin in the second aperture of the pottin collar. As such, the ends are open to and i communication with the gas outlet port. When fluid i introduced into the housing through the fluid inle tube, gas entrained in the fluid is separated therefro by the hydrophilic fibers, permeates the hydrophobi fibers and is discharged from the open ends of t fibers and out the gas outlet port.

An alternative embodiment as shown in Figur 7-9 is a filter according to the present inventio including an upper housing 38 defining an interi chamber 40, and a liquid outlet cap 42. As in t preferred embodiment, the housing and the cap of th alternative embodiment is preferably molded from material which is compatible with the fluid to filtered. The upper housing 38 is of a general tubular shape having a tapered open upper end defining a fluid inlet port 46, and an open lower e 48. As shown in Figure 7, the housing 38 constructed of one-piece molded plastic having t general shape as described above, and having an ope ended branch arm 50 extending from the side of the low

end 48 of the housing 38 at an angle acute to the side of the housing. The interior of the branch arm 50 opens to the interior chamber 40 of the housing 38.

Referring to Figure 9, disposed within the housing are two bundles of substantially adjacent hollow fibers 52 and 54. One bundle 52 of hollow fibers is of a hydrophilic nature, the other bundle 54 is of a hydrophobic nature. The fibers may extend substantially the entire length of the interior housing and may be either u-shaped with open ends or straight with one open end and one closed or sealed end.

Figure 8 shows the various stages of manufacture of this embodiment of the present invention. As shown in Figure 8a, the hydrophobic fibers 54 are positioned within the interior chamber 40 of the housing. The closed ends 56 of the hydrophobic fibers are located in the region of the tapered upper end 44 of the housing 38. The lower portion of the hydrophobic fibers 54 extend into the branch arm 50 of the housing with the closed ends of fibers sticking out of the housing.

As shown in Figure 8b, the hydrophilic fibers are positioned in a substantially side-by-side relationship to the hydrophobic fibers also with their closed ends located in the tapered upper end of the housing. The open ends of the hydrophilic fibers are located at the open lower end of the housing, and away from the open ends of the hydrophobic fibers.

As shown in Figure 8c, the two sets of fibers are encased in potting compound from a point above the juncture of the branch arm and the open lower end of the housing. Preferably this occurs while pressure is being applied circumferentially at the juncture so that the fibers are circumferentially engaged by the interior surface of the housing. Potting compound is injected into the housing through the open end or the branch arm thereby sealing the fibers together above the clamp. After the fibers have been potted at this juncture, the

branch arm 50 of the housing, as shown in Figure 8d, i then cut off from the housing creating a latera aperture defining a gas vent 58 exposing the open end of the hydrophobic fibers to the outside of the filter When fluid is introduced into the interior chamber o the housing, gas entrained within the fluid passe through the hydrophobic fibers and out of the open end of the fibers through the lateral aperture.

The liquid outlet cap 42 is, in thi embodiment, generally cylindrical and includes a liqui outlet port 60. As shown in Figure 8e, after the branc arm 50 has been cut away from the housing, the cap 42 i secured over the open lower end of the housing. The ca extends to the uppermost portion of the gas ventin outlet so as to overlie and protect the outlet. Th inside diameter of the cap is sufficiently larger tha the housing to define an annular venting gap or pas sageway between the outside of the housing and th inside surface of the cap. As illustrated in Figure 8f, the open ends o the hydrophilic filters are in communication with th liquid outlet port of the cap. Liquid is introduce into the housing, in this illustration, through a tube and passes through the hydrophilic fibers and out of th housing through the liquid outlet port into anothe tube or the like. Gas entrained in the liquid passe through the hydrophobic fibers and out the annular ga into the atmosphere.

Another alternative embodiment is shown i Figures 10-12. As best seen in Figure 10, the filter o this embodiment includes a housing 62 defining an inte ior chamber 64, and a cap 66. As in the preferr embodiment, the housing and cap of this alternati embodiment may be molded from plastic or other materi which is compatible with the fluid to be filtered. T housing 62 is generally cylindrical and has an upper e 68 which includes a substantial tapered fluid inlet po 70. The housing 62 also includes a lower end porti

72 .

Two sets of hollow fibers, 74 and 76, are positioned within the interior chamber 64 of the housing 62 and run substantially the entire length of the interior chamber 64. As in the previous embodiments, the fibers may be either U-shaped or straight; and one set of fibers is hydrophilic 74 and the other set is hydrophobic 76. As best seen in Fig. 11, the hydrophobic fibers 76 are positioned generally in three bundles along the side of the interior chamber 64, and preferably positioned within axially-extending recesses 78 defined in the interior wall of the chamber 64. The hydrophilic fibers 74 are positioned in a side- by-side relationship to the hydrophobic fibers. The ends of the two sets of fibers 74 and 76 are disposed within the open lower end 72 of the housing and are encased in potting compound 80, with the ends of the fibers left open, as described above in connection with the preferred embodiment. The cap 66 is sealingly joined to the open lower end 72 of the housing 62. The cap 66 tapers 82 substantially towards a centrally located cylindrical liquid outlet port 84. One or more gas venting ports 86 may be located to one side of the fluid outlet port 84, in this embodiment. As best seen in Figs. 10 and 12, the cap 66 includes, in this embodiment, a cylindrical inner wall 88, which is circumscribed by the cap's outer wall 66. The inner wall 88 is of sufficient height to seal against the housing 62 and/or against the potting compound 80. In this manner, the inner wall 88 defines a liquid communication passage 90 between the hydrophilic fibers 74 and the liquid outlet port 84. In addition, the inner wall 88 of the cap 66 defines an annulatr gas venting chamber 92 which provides fluid communication between the hydrophobic fibers and the gas venting port 86.

Although the present invention has been described with reference to specific preferred and

alternative embodiments, the scope of the presen invention is not limited to those particula embodiments but defined by the appended claims.