MONOFILAMENT SPACING OF HOLLOW FIBER MEMBRANES AND BLOOD OXYGENATION DEVICES INCORPORATING SAME

Abstract: Disclosed are improved hollow fiber semipermeable membranes having monofilamentous spacer members spirally disposed or formed on the outer surface thereof, and extracorporeal blood treatment devices incorporating such improved hollow fiber membranes. Also disclosed are methods for manufacturing the hollow fiber membranes and a continuous method for manufacturing a blood processing apparatus which incorporates the hollow fiber membranes.

Description: MONOFILAMENT SPACING OF HOLLOW FIBER MEMBRANES AND BLOOD OXYGENATION DEVICES INCORPORATING SAME Present Invention The present invention pertains generally to medical equipment and, more particularly, to improved hollow fiber semi-permeable membranes having monofilamentous spacer member(s) spirally disposed on the outer surface thereof, and extracorporeal gas exchange devices incorporating such hollow fiber semi-permeable membranes. Background of the Invention Extracorporeal blood oxygenation systems are typically utilized to a) oxygenate and b) remove carbon dioxide from the blood of patients whose cardiopulmonary function has been interrupted. The most common clinical situations wherein extracorporeal blood oxygenation systems are utilized is during cardiothoracic surgical procedures wherein cardiopulmonary bypass is employed. The typical extracorporeal blood oxygenation system in use today comprises a rigid housing having a multiplicity of tubular semi-permeable membranes known as "hollow fiber membranes" disposed therewithin. Pure oxygen or an oxygen- containing gas mixture is channeled through the lumens of the hollow fiber membranes, while the patient's blood is passed over the outer surfaces of the hollow fiber membranes. Contact of the patient's blood with the outer surfaces of the membranes permits oxygen to diffuse through the membranes and into the blood, with concomitant back- diffusion of carbon dioxide from the blood and into the gas. The partial pressures of oxygen (P0 2 ) and carbon dioxide (PC0 2 ) are influenced by numerous factors including; a) the available surface area for gas exchange (i.e., the area wherein blood actually contacts the outer surfaces of the hollow fiber membranes; b) the relative concentrations of oxygen and carbon dioxide in the gas mixture; c) the pressure of the gas mixture within the lumens of the hollow fiber membranes; d) the flow rate of blood over the outer surfaces of the hollow fiber membranes; e) the film thickness of blood passing over the outer surfaces of the hollow fiber membranes; and f) the pressure and flow rate of blood passing over the outer surfaces of the hollow fiber membranes. Although a number of the above-listed variables may be controlled by adjusting the pressures, flow rates and/or relative concentrations of blood and/or gases flowing through the device, the variable of "blood film thickness" is largely a function of the design of the device and is primarily dictated by the size of the spaces which exist between the individual hollow fibers within the device. Inconsistencies or variations in spacing between the individual membranes may result in large variations in oxygenator efficiency due to varying blood film thicknesses (i.e., too thick or too thin) and/or the presence of "dead spots" (i.e., constricted areas where blood does not flow) within the fiber network. In view of the desirability of maintaining consistent inter-fiber spacing of the individual hollow fiber membranes, some of the blood oxygenator devices of the prior art have incorporated various spacer means for maintaining the desired spacing between the individual hollow fiber membranes. Examples of the types of spacer means which have been utilized for spacing of hollow fiber membranes or other similar apparatus are found in the following: U.S. Patent No. 4,066,553 (Bardonnet) ; U.S. Patent No. 4,368,124 (Brumfield) ; U.S. Patent No. 4,341,631 (Hargitay) ; U.S. Patent No. 4,622,206 (Torgeson) ; U.S. Patent No. 4,840,227 (Schmidt); U.S. Patent No. 4,869,059 (Austin); U.S. Patent No. 4,874,514 (Casey, Jr.); U.S. Patent No. 4,911,846 (Akasu, et al.); U. S. Patent No. 4,950,391 (Weickhardt) ; U.S. Patent No. 5,063,009 (Mizutani) ; U.S. Patent No. 5,141,031 (Baurmeister) ; U.S. Patent No. 5,198,110 (Hanai) ; U.S. Patent No. 4,140,637 (Walter); U.S. Patent No. 4,031,012 (Gics) ; U.S. Patent No. 4,900,314 (Quackenbush) ; U.S. Patent No. 4,293,418 (Fuji, et al.); and U.S. Patent No. 4,428,403 (Lee, et al.) (related to heat exchangers) . In particular, U.S. Patent No. 4,293,418 (Fuji, et al.) purports to describe the use of spacer yarns wrapped about the outer surfaces of individual hollow fibers to maintain a prescribed spacing between the individual hollow fibers. The individual spacer yarns described in U.S. Patent No. 4,293,418 (Fuji, et al.) are characterized as textured yarn which is spirally wound so that substantially equal and consistent spaces are formed between the hollow fibers (Col. 2, Line 67-Col. 3, Line l). Although the textured "spacer yarns" described in U. S. Patent No. 4,293,418 (Fuji, et al.) are purported to maintain specific spacing between individual hollow fibers in various types of fluid separation apparatus, the use of such textured yarns as to space individual hollow fiber membrane in a blood oxygenator device may be less than desirable due to the fact that the textured yarn may act as a filtering medium such that blood will filter through the texture of the yarn, rather than simply passing around the individual yarns. Such filtering effect of the textured yarn may result in retention of blood cells within the textured yarn and on attendant potential for thrombogenic clot formation. Additionally, the multifilament yarns made of many fine fibers present a greater than necessary inactive surface area which is contacted by the blood, such unnecessary surface contact presenting an increased chance of inducing an undesirable bioreactive clotting response or other bioincompatability reaction due to contact of the blood with the constituents of the yarn surfaces with which the blood comes in contact. Furthermore, because of its compliant nature, yarn may tend to flatten out or compress against the hollow fiber membranes, thereby resulting in a change of the desired spacer width resulting from the yarn with a resultant variation or change in the blood flow space (i.e., blood film thickness) between adjacent gas exchange surfaces of the individual hollow fiber membranes. Another problem associated with multifiliament textured "yarns" is that such yarns tend to flatten and spread out upon compression thereof, thereby covering more of the surface of the adjacent hollow fiber membrane than is necessary to effect the desired spacing function. In view of these factors, multifilament textured "spacer yarns" are less than optimal when employed for purposes of maintaining specific lateral spacing between adjacent hollow fiber membranes. Another prior art method of spacing hollow fiber membranes, as described in Japanese Kokai Patent Application No. HEI3[1991]-278821 (Fuji), utilized two spacer yarns wound in spiral fashion on the outer surface of the hollow fiber membrane, such that the "spacer yarns" repeatedly cross one another in opposite directions. Such oppositely wound crossing spacer yarns may be monofilament. The oppositely wound crossing "spacer yarns" described in Japanese Kokai Patent Application No. HEI3 (1991)-278821 can not serve to guide a flow of blood or other liquid in a substantially laminar flow path over the outer surfaces of the hollow fiber membranes due to the fact that the opposite crossing configuration of the "spacer yarns" would result in blocking or disruption of such laminar liquid flow. Such blocking or disruption of blood flow may result in turbulence of the blood, with resultant hemolysis or thrombogenic clot formation. Furthermore, oppositely wound crossing "spacer yarns" of HE13(1991)-278821 can not perform a consistent spacing function because they overlap one another at cross-points, such overlapping of the "spacer yarns" resulting in a doubling of the spacer yarn width at the repetitive cross-point. Thus, if abutted against an adjacent housing surface or an adjacent hollow fiber membrane surface, the cross-points of the spacer yarns of HE13(1991)-278821 would result in approximately two times the desired spacing because of the overlapping or crossing of the individual "spacer yarn" elements. Yet, another prior art method of spacing hollow fiber membranes requires the weaving or knitting of a separate weft fiber among individual hollow fibers, as described in U.S. Patent No. 5,141,031 (Baurmeister) . The process of weaving or knitting the weft fibers among the individual hollow fibers may result in damage to the hollow fiber membranes, because such process exerts force upon the surfaces of the fibers. To minimize fiber damage during the weaving or knitting process, it is necessary to use relatively strong fibers at increased expense. Additionally, in at least some membrane oxygenator devices, the weft fibers are positioned perpendicular to the direction of blood flow, thereby resulting in .undesirable turbulence or disruption of the flow of blood over the outer surfaces of the hollow fiber membranes. There remains a need in the art for development of new spacer apparatus which may be wound about or otherwise formed on the outer surfaces of individual hollow fiber membranes to maintain consistent prescribed spacing between the individual membranes, while at the same time, promoting the surface of the membranes. Summary of the Invention In accordance with the present invention, there are provided elongate tubular hollow iber membranes having one or more monofilament spacer member(s) disposed or formed on the outer surfaces thereof. Preferably, the monofilament spacer member(s) is/are disposed or formed in a spiral configuration. Although two or more spiral monofilament spacer members may be ' disposed or formed on a single tubular hollow fiber membrane in accordance with the present invention, it is preferable that such spiral monofilament spacer members not overlap or cross one another at any point so as not to block or disrupt laminar blood flow over the outer surfaces of the hollow fiber membranes. In a first embodiment of the invention, a separate monofilament member (e.g., a monofilamentous thread or line) is spirally wound or wrapped about the outer surface of a tubular hollow fiber membrane. In accordance with a second embodiment of the invention, the spiral monofilament spacer member may be formed as a raised spiral rib of solid or monofilamentous construction on the outer surface of the hollow fiber membrane. Such raised monofilamentous rib may be formed by creating a notch or recess in an extrusion dye utilized to extrude the tubular hollow fiber membrane. Rotational force may then be applied to the extrusion dye, and/or to the extruded hollow fiber emerging therefrom, so as to cause the extruded rib to assume the desired spiral configuration to the raised rib on the outer surface of the tubular membrane. Further in accordance with the invention, hollow fiber membranes having the spiral monofilament spacer member of the above-described first or second embodiment may be operatively disposed (e.g., packed) in close-spaced parallel, side-by-side relation to one another such that the spiral monofilamentous member of each membrane is in abutment with the outer surface of an adjacent membrane. By such arrangement, the spiral monofilament spacer members disposed or formed on the outer surfaces of adjacent side- by-side positioned membranes will serve to define and maintain consistent prescribed spacing distances between the outer surfaces of such adjacent membranes. Similarly, the spiral monofilament spacer members disposed or formed on the outer surfaces of membranes which are positioned next to a solid bulkhead or wall of a housing will serve to maintain specific prescribed spacing between the outer surfaces of such membranes and the adjacent bulkhead or wall. Still further in accordance with the invention, there is provided an extracorporeal membrane oxygenation device which incorporates the spirally wound or spirally ribbed hollow fiber membranes of the above-described first and/or second embodiment therein such that the membranes- are disposed in close-spaced generally parallel side-by-side relation to one another with the monofilamentous member or rib of each such membrane being in abutment with the outer surface of an adjacent membrane so as to define and maintain prescribed and consistent spacing therebetween. Still further in accordance with the invention, a group or packet of individual hollow fiber membranes positioned in close-spaced parallel side-by-side relation to one another may be positioned within a membrane oxygenator or other extracorporeal blood processing device and a flow of blood is channeled or passes over the outer surfaces of the hollow fiber membranes such that the spiral monofilament spacer members disposed on the outer surfaces of the hollow fiber membranes will guide the path of the blood flow over the outer surfaces of the membranes. In embodiments wherein the flow of blood is directed parallel to the longitudinal axis of the hollow fiber membranes, the spiral monofilament spacer members will serve to cause the blood to flow in a spiral flow path. In embodiments where the flow of blood is other than parallel to the longitudinal axis of the hollow fiber membranes, the spiral monofilament spacer members will cause the blood to undergo periodic deflection or offsetting each time the blood flow comes into contact with or impinges against one of the spiral monofilament spacer members. Further objects and advantages of the invention will become apparent to those skilled in the art upon reading and understanding of the following detailed description and the accompanying drawings. Brief Description of the Drawings Figure 1 is a perspective view of an individual hollow fiber membrane having a monofilament spacer of the present invention spirally disposed on the outer surface thereof. Figure 2 is an enlarged perspective view of two side- by-side hollow fiber membranes having monofilament spacers of the present invention disposed thereon. Figure 2a is a partial elevational view of a portion of Figure 2. Figure 3a is a perspective view of a heat exchanger/membrane oxygenator device having the monofilament-spaced hollow fiber membrane of the present invention incorporated therein. Figure 3b is a top plan view of the membrane oxygenator device shown in Figure 3. Figure 3c is an exploded view of the blood heat exchanger/membrane oxygenator device of Figure 3a. Figure 3d is a cross-sectional view through line 3d-3d of Figure 3a. Figure 4 is a cut-away elevational view of the heat exchanger/membrane oxygenator device of Figure 3. Figure 4a is a cross-sectional view of a portion of the heat exchanger/membrane oxygenator device of Figure 4. Figure 4b is an enlarged cross-sectional view of region 4b of Figure 4a. Figure 5a is a perspective view of an extrusion die which may be utilized to manufacture the hollow fiber membranes of the second embodiment of the present invention having a spiral monofilamentous rib formed on the outer surface thereof. Figure 5b is a perspective view of a hollow fiber membrane of the second embodiment of the present invention emerging from the extrusion die of Figure 5a. Figure 6 is a schematic diagram of a continuous manufacturing method whereby a continuous hollow fiber membrane is a) passed through a pirn apparatus which wraps a monofilament spirally about the outer surface of the hollow fiber membrane and b) subsequently wound onto a core component of a blood processing apparatus, such as a membrane oxygenator device. Figure 6a is an enlarged perspective view of segment 6a of Figure 6. Detailed Description Preferred Embodiments The following detailed description, and the accompanying drawings, are provided for purposes of describing and illustrating presently preferred.embodiments of the invention only and are not intended to limit the scope of the claimed invention in any way. i. Hollow Fiber Membranes Having Monofilamentous Spacers Disposed Thereon With reference to Figures 1-6, each preferred hollow fiber membrane 10 of the present invention comprises a tubular semi-permeable membrane having an outer surface 14 and a hollow lumen 16 which extends longitudinally through the membrane 10. One or more monofilamentous spacer members are disposed upon or formed upon the outer surface 14 of the membrane 10. Each membrane 10 has a semipermeable tubular wall of substantially consistent thickness T. Each monofilamentous spacer member 12 on the membrane 10 has a cross-sectional dimension (e.g., diameter) spacer width SW. Abutment of each spacer 12 against an adjacent surface (e.g., the outer surface 14 of an adjacent hollow fiber membrane) will serve to hold the outer surface 14 of the membrane 10 upon which the spacer 12 is disposed a distance of one spacer width SW from the outer surface 14 of an adjacent membrane and/or any adjacent surface of the device against which the spacer 12 is abutted. When intended for use in blood membrane oxygenator applications, the hollow fiber membranes 10 of the present invention will preferably be formed of semi-permeable materials suitable for blood-gas exchange including cellulose esters such as cellulose diacitate and cellulose triacetate, cellulose derivatives such as cellulose ether, polyamide, polyester, methacrylic or acrylic polymers such as polymethyl methacrylate, polyurethane, organic silicone polymer, polyacrylonitrile and copolymer thereof, polysulfones, and polyolefins such as polyethylene and polypropylene. The hollow fiber membranes 10 are extruded to a preferred wall thickness T in the range of 40-60 microns and have a preferred inner luminal diameter ID in the range of 270-290 microns and a preferred outer diameter OD in the range of 350-410 microns. When disposed or formed on the outer surface of such preferred hollow fiber membrane 10, the spiral spacer member 12 of the present invention preferably has an effective spacer width SW (e.g., the diameter if the spacer is of round cross- sectional configuration) of 38-63 microns. Thus, when the spiral spacer member 12 of one hollow fiber membrane 10 abuts against the outer surface 14 of an adjacent hollow fiber membrane 10, such adjacent hollow fiber membranes 10 will be held apart from one another by a distance equal to the effective spacer width SW of the spacer member(s) 12. The longitudinal distance within which the spacer member 12 makes one full spiral revolution about the outer surface 14 of the membrane 10 is referred to herein as the "pitch interval" P. In blood membrane oxygenator applications wherein the wall thicknesses T of the hollow fiber membranes 10 are in the preferred range of 40-60 microns, it will typically be preferable for the spiral monofilament spacer member(s) 12 to have pitch intervals P in the range of 2.6-3.7 millimeters. By maintaining such pitch intervals P within the range of 2.6-3.7 millimeters, the points at which each spacer member 12 makes contact with the outer surface 14 of an adjacent hollow fiber membrane 10 will be sufficiently close together to result in a consistently sized gap or space between the adjacent outer surfaces 14 equal to the spacer width SW or diameter of the spacer member(s) 12. It will be appreciated that the prescribed pitch interval P may be varied depending on the relative pliability, flexibility or wall thickness T of the hollow fiber membrane 10. In embodiments wherein the hollow fiber membranes 10 are relatively flexible or pliable, it may be desirable to utilize a short pitch interval P so as to minimize the distance between the points at which each spacer member 12 contacts the outer surface 14 of an adjacent hollow fiber membrane 10. On the other hand, in embodiments wherein the hollow fiber membranes 10 are relatively rigid or less pliable, longer pitch intervals P may be employed so as to maximize the distance between the points at which each spacer member 12 contacts the outer surface 14 of an adjacent hollow fiber membrane 10. One significant advantage of the hollow fiber membranes 10 of the present invention is that such membranes 10 may be wrapped, laid, wound, or otherwise deployed into any shape of channel or receiving structure, and will conform to the shape of the particular channel or receiving structure while maintaining constant surface-to- surface spacing between the outer surfaces of individual hollow fiber membranes 10. Additionally, the hollow fiber membranes 10 of the present invention will also maintain constant desired spacing between the outer surfaces of the hollow fiber membranes 10 and any adjacent structural members, bulkheads or walls of the particular housing, groove or channel into which the hollow fiber membranes 10 have been placed. This ability of the hollow fiber membranes 10 of the present invention to be individually deployed within any size or shape of channel, and to conform thereto, constitutes a significant advantage over the prior art woven ribbons and other woven designs wherein multiple individual fibers were specifically preformed or woven into a specifically shaped group or network. ii. Incorporation Of The Hollow Fiber Membranes Of The Present Invention Into A Preferred Blood Membrane Oxygenator Device The monofilament-spaced hollow fiber membranes 10 of the present invention may be incorporated into many different types and sizes of blood oxygenators. One particular blood oxygenator device wherein the hollow fiber membranes 10 of the present invention may be incorporated is that described in United States Patent No. 5,120,501 and sold commercially as the Univox™ Membrane Oxygenation System, Baxter Healthcare Corporation, Bentley Laboratories Division, Irvine, California 92714. The membrane oxygenator device of United States Patent No. 5,120,501 is shown in Figures 3, 4, and 5 of this patent application for purposes of describing how the hollow fiber membranes 10 of the present invention may be incorporated into that particular membrane oxygenator device. Additionally, the entire disclosure of United States Patent No. 5,120,501 is expressly incorporated herein by reference. With reference to Figures 3-3d, and 4-4b the heat exchanger/membrane oxygenator device 40 shown is connectable to an extracorporeal blood circuit for purposes of a) controlling the blood temperature and b) maintaining the P0 2 and PC0 2 of the blood within prescribed ranges. In general, the heat exchanger/membrane oxygenator device 40 comprises an outer housing or shell 42 within which there is mounted a heat exchange body or bellows 44 and a heat exchange jacket 46. The bellows 44 comprises a generally cylindrical body or core having a series of annular ribs or pleats 48 formed circumferentially about the outer surface thereof. The series of annular ribs 48 define a corresponding series of annular, generally parallel, blood receiving grooves or channels 50 between adjacent ribs 48. The heat exchange jacket 46 comprises a generally cylindrical wall 54 having a plurality of annular flanges or ribs 56 extending about the outer surface thereof so as to form a continues fluid flow path through which heat exchange fluid may be passed about the outer surface of the cylindrical wall 54 and into contact with the surrounding inner surface of bellows 44. As such, the circulation of heat exchange fluid through the flow path 58 between the cylindrical wall 54 and the surrounding bellows 44 will operate to either heat or cool the bellows 44 thereby concomitantly heating or cooling the blood passing through the blood passage channels 50 on the outer surface of bellows 44. In the particular embodiment of the heat exchanger/membrane oxygenator device 40 shown, a single elongate hollow fiber membrane 10 is repeatedly wound about the outer surface of the bellows 44 such that multiple convolutions of the hollow fiber membrane 10 become disposed within each channel 50 on the outer surface of bellows 44, with each such convolution being in generally parallel side-by-side position to an adjacent convolution. A vertical cut is subsequently made through the long hollow fiber membrane such that each convolution becomes an individual hollow fiber membrane 10 wound about the outer surface of bellows 44 such that a separate individual group or packet 84 of hollow fiber membranes 10 arranged in substantially parallel side-by-side relation to one another, resides within each channel 50. Each individual group 84 of hollow fiber membranes 10 preferably consists of approximately 240-260 individual hollow fiber membranes 10 laid or wound into each channel 50. The monofilament spacer member 12 (e.g., separate monofilament member or raised rib) of each membrane 10 is in abutment with the outer surface of an adjacent membrane 10, thereby maintaining consistent prescribed spacing between the individual membranes 10. Also, for those hollow fiber membranes 10 which lie adjacent the annular ribs or pleats 48 of bellows 44, the monofilament spacer member 12 disposed or formed thereon will abut against the adjacent rob or pleat 48, thereby maintaining consistent prescribed spacing between the outer surfaces of those hollow fiber membranes 10 and the adjacent surfaces of the bellows 44. Prior to winding or laying of the individual membranes 10 into each groove 50, a space occupying member such as a spiral plastic spring may be placed in the bottom region of each channel 50 to prevent the hollow fiber membranes 10 from packing all the way down into the bottom portion of the channel 50. Thus, the presence of the space occupying members (e.g., plastic spring) in the bottom portion of each channel 50 will form a blood passage gap 86 in the innermost region of each channel 50. As such, blood may be initially shunted or channeled into the blood flow gap 86 at the base of each channel 50 and subsequently permitted to percolate or pass outwardly over the outer surfaces of the individual hollow fiber membranes 10 grouped in each such channel 50. Thus, the direction of the initial outward blood flow is generally perpendicular to the longitudinal axes of the hollow fiber membranes 10 disposed in each channel 50. As the blood percolates or passes outwardly over the outer surfaces of the individual hollow fiber membranes 10, the blood will come into contact with the monofilament spacer members 12 disposed or formed on the outer surfaces of the individual hollow fiber membranes 10. Each such contact or impingement against a spiral spacer member causes the flowing blood to undergo lateral deflection or shifting in the direction of the longitudinal axis of the hollow fiber 10. Thus, a single spiral monofilamentous spacer member 12 disposed on the outer surface of each hollow fiber membrane 10 will serve the additional function of creating a desired spiral or laterally shifted flow path of the blood as it passes over the outer surfaces 14 of the hollow fiber membranes 10. This aspect of the present invention is specifically illustrated by the arrows on Figure 2a. This flow directing or flow channeling function of the single monofilamentous spacer members 12 could not be achieved by multiple spacer members wrapped in opposite criss-crossing directions as described in Japanese Kokai Patent Application No. HEI-3(1991)-278821 (Fujii) as the existence of an oppositely wound spacer member would result in impairment of such spirally directed blood flow and/or undue turbulence of the blood due to cross stream impingement with the second oppositely directed spacer member. The initial shunting or channeling of the blood into each gap 86 allows the blood to initially come in contact with the adjacent outer surface 48 of the bellows 44 so as to immediately effect warming or cooling of the blood in accordance with the temperature of the heat exchange medium being circulated on the inner surface of the bellows 44. Thus, the blood being circulated through the device 40 will be at a controlled temperature before it begins to percolate or flow outwardly from the gap 86, over the gas exchanging outer surfaces of the individual hollow fiber membranes 10. The opposite ends of the hollow fiber membranes 10 of each packet 84 are anchored within a solid potting material which forms a solid block 78 on the back of a blood inlet manifold 60. The back surface 79 of the potting material 78 is flush cut such that the open ends of the hollow fiber lumens 16 form openings at surface 79 to permit gas to flow into and out of such lumens 16 of membranes 10. Passage of the desired gas or gas mixture through the lumens 16 of the individual hollow fiber membranes 10 is facilitated by a gas passage manifold 70 positioned on one side of the shell 42 of the device 40, immediately outboard of the blood inlet manifold 60. Gas passage manifold 70 comprises a rigid shell or casing having a generally hollow interior with a solid bulkhead 72 extending vertically through the mid-region thereof. The bulkhead 72 divides the inner chamber of the gas passage manifold 70 into a gas inlet chamber 74 and a gas outlet chamber 76. The first (inlet) ends of the hollow fiber membranes 10 are disposed in a vertical column along the left side of the potting material block 78 so as to be in alignment and fluidic contact with gas inlet chamber 74 of gas manifold 70. Similarly, the second ends of the hollow fiber membranes 10 are disposed in a vertical column on the right side of the potting material block 78 so as to be positioned in alignment and fluidic contact with gas outlet chamber 76 of the gas manifold 70. By such construction, a gas or gas mixture (i.e., pure oxygen, oxygen/air mixture, oxygen/nitrogen mixture) infused into the gas inlet chamber 74 of manifold 70 through a gas inlet connector 80 will subsequently pass into the first open ends of the lumens 16 of hollow fiber membranes 10 and will subsequently flow through the lumens 16 of the hollow fiber membranes 10. After passing through the lumens of the hollow fiber membranes 10, the gas or gas mixture will pass outwardly through the second ends of the lumens 16 of the hollow fiber membranes 10 and into the gas outlet chamber 76 of gas passage manifold 70. Thereafter, the gas or gas mixture may be exhausted through a gas outlet connector 82. To facilitate circulation of blood through the blood receiving channels or grooves 50, a blood inlet manifold 60 is formed or mounted on one side of the shell 42 and a blood outlet manifold 62 is formed or mounted on the opposite side of shell 42. A blood inlet connector 64 is positioned on blood inlet manifold 60 to facilitate passage of blood into the inlet manifold 60, while a blood outlet connector 66 is positioned on blood outlet manifold 62 to facilitate passage of blood out of blood outlet manifold 62. A blood inlet flow path within blood inlet manifold 60 is configured to divide the flow of incoming .blood into separate streams passing out of slots 67 formed in the inner face of the blood inlet manifold 60. Slots 67 of blood inlet manifold 60 are positioned in correspondence and fluidic connection with the substantially hollow blood circulation gaps 86 formed on the innermost region of each groove or channel 50 such that blood passing out of slots 67 will initially flow into the circulation gaps 86, and will subsequently pass outwardly through the channels 50, flowing over the outer surface of the hollow fiber membranes 10 disposed within each channel 50, thereby passing a film of blood over the outer surfaces 14 of the membranes 10. Such contact of the blood with the outer surfaces 14 of the hollow fiber membranes 10 allows the blood to receive oxygen, and to give off carbon dioxide, through the semipermeable walls of the membranes 10. The resultant PC02 and P02 of the blood may be controlled by adjusting the gaseous content (i.e., Fi0 2 and FiC0 2 ) and pressure of the gas mixture being passed through the lumens 16 of the individual hollow fiber membranes 10. iii. Operation Of A Preferred Membrane Oxygenator Device Incorporating The Hollow Fiber Membranes Of The Present Invention Again, with reference to Figures 3a-3d and 4-4b, the blood inlet connector 64 of the device 40 is connected to a vein of the patient such that venous blood from the patient will enter the blood inlet manifold 60 through inlet connector 64. Similarly, the blood outlet flow connector 66 is connected to the arterial vasculature of the patient via tubing such that oxygenated blood flowing out of blood outflow connector 66 will be returned to the arterial circulation of the patient. Appropriate pumping means, such as peristaltic blood pumps or other blood pumping apparatus are utilized to facilitate the above- described flow of blood to and from the patient. Source(s) of the prescribed oxygen-containing gas mixture (e.g., either pure oxygen or blends of oxygen with other suitable gases such as nitrogen) is connected to gas inlet connector 80 by way of tubing. By such arrangement, the prescribed oxygen-containing gas mixture enters gas inlet chamber 74 and passes through the lumen 16 of the individual hollow fiber membranes 10 disposed within the blood receiving grooves 50 of the device 40. After passing through the lumens 16 of the individual hollow fiber membranes 10, the used gas subsequently passes into gas outlet chamber 76 and is exhausted through gas outlet connector 82. Apparatus for monitoring the concentration of oxygen or other gases may be connected to the flow path adjacent either the gas inlet connector 80 or the gas outlet connector 82 so as to provide for ongoing monitoring of the relative concentrations of oxygen or other gases passing into or out of the device 40. Also, pressure sensing means may be positioned at one or more points along the gas- mixture pathway to permit monitoring of the pressure of the gas-mixture within the device 40. A device for providing a recirculating flow of temperature-controlled heat exchange liquid (e.g., saline or water) is connected to a heat exchanger inlet connector 88 and a heat exchanger outlet connector 90 so as to provide a recirculating flow of temperature-controlled heat exchange medium through heat exchanger jacket flow path 58 and into contact with the inner surface of the surrounding bellows 44. The temperature of the blood exiting the device 40 through blood outlet connector 66 may be monitored and the temperature of the heat exchange medium circulated through flow path 58 may be thermostatically or otherwise adjusted so as to maintain or control the temperature of the blood exiting the blood outflow connector 66 within a prescribed temperature range. It will be appreciated that the efficiency and consistency with which the partial pressures of 0 2 and C0 2 within the blood may be controlled is dependent upon the maintenance of consistent prescribed spacer widths SW between the outer surfaces 14 of the individual hollow fiber membranes 10 such that the film thickness and surface area contacted by the blood flowing through the device 40 may be optimized and maintained in a consistent fashion. The disposition of the spiral monofilamentous spacer members 12 about the outer surfaces 14 of the individual hollow fiber membranes 10 within each membrane packet 84 serves to hold the individual hollow fiber membranes 10 within each packet 84 a desired prescribed spacer width SW from one another, thereby making certain that the film thickness and amount of blood circulating into contact with the outer surfaces 14 of the hollow fiber membranes 10 is consistent and predictable, with minimal unit-to-unit variation. Additionally, as described in detail herein, the spiral or helical disposition or formation of the spacer members 12 on the outer surfaces 14 of the hollow fiber membranes 10 serves to direct the blood flow in a non- turbulent laminar flow path about the outer surfaces 14 of the individual hollow fiber membranes 10 without unnecessary damming, disruption or turbulence of the blood as may result in thrombogenic consequences. Additionally, because the individual spacer members 12 are formed of non-wetting monofilamentous material, such spacer members 12 do not wet with blood and do not result in hang-up or holding of blood within the device 40, as may occur with multifilament, woven or yarn-type wettable spacer members. iv. Methods of Manufacturing the Monofilament Spaced Hollow Fiber Membranes of the Present Invention The monofilament spaced hollow fiber membranes 10 of the present invention may be manufactured by any suitable means, including the two (2) alternative manufacturing methods described herebelow. In embodiments wherein the monofilamentous spacer member 12 consists of a separate monofilament member which is not formed continuous with the hollow fiber wall, such separate monofilament member 12 may be spirally wrapped around the outer surface 14 of an elongate tubular hollow fiber membrane 10. Such spiral wrapping of a separate monofilamentous spacer member 12 about the outer surface 14 of a tubular hollow fiber membrane 10 may be accomplished manually or by automated machinery. One example of an automated fiber-wrapping machine which may be utilized to spirally wrap monofilamentous fibers around an elongate hollow fiber membrane is a power driven hollow cored pirn having a quantity of the monofilamentous fiber wrapped therearound. The hollow fiber membrane is fed longitudinally through the center of the spinning pirn and the monofilamentous fiber is spun off of the pirn and onto the outer surface of the advancing hollow fiber membranes, such that the monofilamentous fiber become spirally wrapped about the outer surface of the hollow fiber membrane. In embodiments of the invention wherein the monofilamentous spacer member 12 comprises a spiral rib formed on the outer surface 14 of a tubular hollow fiber membrane 10, such rib may be extruded as part of the body of the hollow fiber membrane 10 as shown in Figures 5a and 5b. An extrusion die 100 usable to form a monofilamentous ribbed hollow fiber membrane lOd comprises a round inner core member 102 disposed within the hollow inner bore of a cylindrical outer member 104. A recess 106 or recesses is/are formed in the luminal surface of the cylindrical outer core 104 such that the workpiece extruded by the die 100 will be in the form of a generally round hollow tube lOd having a single raised rib 12d formed on the outer surface thereof. A rotational force may be applied to the outer die member 104 and/or the emerging workpiece so as to cause the rib 12d to become spiralled about the outer surface of the tubular hollow fiber membrane lOd. The rate at which the outer die member 104 and/or workpiece are rotated, relative to the rate at which the extruded workpiece emerges from the die 100, will determine the tightness or pitch interval of the spiral rib 12d. Figure 6 shows a schematic diagram of a continuous manufacturing process whereby a separate, hollow monofilamentous spacer member may be initially wrapped about the outer surface of an advancing hollow fiber membrane and whereby the spirally wrapped hollow fiber membrane may be subsequently wrapped or mounted onto the outer surface of a core member, such as the core of a membrane oxygenator device, in a continuous fashion. As shown in Figure 6, an elongate hollow fiber membrane 100 is initially wound about a spool 102. The hollow fiber membrane 100 is continually baled or pulled off of spool 102 and fed through the central passageway 104 of a powered pirn 106. A length of monofilamentous spacer material 108 (i.e., monofilament line or thread) is initially wrapped about the outer surface of the pirn 106. As the pirn 106 spins, the monofilamentous spacer member 108 is unwound from the outer surface of the pirn 106 and correspondingly wrapped about the outer surface of the advancing hollow fiber membrane 100. The spiral pitch interval P at which the monofilamentous spacer member 108 is wrapped about the outer surface of the advancing hollow fiber membrane 100 may be controlled and/or adjusted by controlling or varying the feed rate of the hollow fiber membrane 100. After the powered pirn 106 has operated to spirally wrap the monofilamentous spacer fiber 108 about the outer surface of the advancing hollow fiber membrane 100, the spirally wrapped hollow fiber membrane is subsequently advanced over rollers 110, 112 and wrapped about the outer surface of a core member 114, such as the inner core of a blood membrane oxygenator device, an example of which is the central bellows 44 of the heat exchanger/membrane oxygenator device 40 shown in Figures 3a-3d and 4-4c of this patent application. Thus, the spiral wrapping of the monofilamentous spacer member 108 about the outer surface of the hollow fiber membrane 100 and the subsequent deployment or wrapping of the spirally wrapped hollow fiber membrane 10 about the outer surface of the device core member 114 is accomplished in a continuous process, without the need for intervening handling or manipulation of the hollow fiber membrane 100. Although the invention has been described herein with reference to certain presently preferred embodiments, it will be appreciated that various additions, modifications or alterations may be made to the herein described embodiments without departing from the intended spirit and scope of the invention. For example, instead of a single monofilamentous spacer member or rib 12 being wound or formed about the outer surface 14 of a hollow fiber membrane 10, plural or multiple spacer members or ribs 12 may be utilized on each such hollow fiber membrane 10, provided that the individual spacer members or ribs 12 do not overlap one another as to cause doubling or widening of the effective spacer width at the point of overlap or crossing thereof. Accordingly, two or three parallel spacer members or ribs 12 may be disposed on the outer surface 14 of a single hollow fiber membrane 10 without causing impairment of the desired flow characteristics described herein and/or the desired consistent spacing between the individual hollow fiber membranes 10 and their adjacent surfaces.

Claims: WHAT IS CLAIMED IS: 1. A hollow fiber membrane oxygenator device for extracorporeal blood oxygenation, said device comprising: a. a substantially fluid-tight housing defining an inner chamber therewithin; b. a multiplicity of elongate, tubular hollow fiber membranes disposed in generally parallel side- by-side relation to one another within the inner chamber of said housing, each said hollow fiber membrane having a longitudinal axis, a first end, a second end, a hollow lumen extending longitudinally therethrough, an inner luminal surface and an outer surface; c. a blood inlet port formed in said housing to permit a flow of blood to enter said inner chamber; d. a blood outlet port formed in said housing to permit blood to exit said inner chamber; e. a gas inlet port formed in said housing and fluidly connected to the first ends of said hollow fiber membranes to permit a flow of gas to enter the lumens of said hollow fiber membranes through the first ends thereof; f. a gas outlet port formed in said housing and fluidly connected to the second ends of said hollow fiber membranes to permit gas to exit the lumens of said hollow fiber membranes through the second ends thereof; an , g. a spiral monofilament spacer member on the outer surface of each hollow fiber membrane; h. said hollow fiber membranes being packed within said chamber such that the monofilament spacer member of each hollow fiber membrane is in abutment with the outer surface of an adjacent hollow fiber membrane, thereby maintaining a spaced distance between the outer surfaces of said membranes. 2. The device of Claim 1 wherein said monofilament spacer members comprise monofilament members formed separately from said hollow fiber membranes and spirally wound about the surfaces of said hollow fiber membranes. 3. The device of Claim 1 wherein said monofilament spacer members comprise raised ribs formed on the outer surfaces of said hollow fiber membranes, in spiral configuration. 4. The device of Claim 1 wherein said monofilament spacer members have effective spacer widths of 0.002-0.004 inches, thereby maintaining spacing of 0.002-0.004 inches between the outer surfaces of adjacent hollow fiber membranes. 5. The device of Claim 1 wherein a series of hollow fiber receiving grooves are formed within said housing and wherein a number of hollow fiber membranes are disposed in parallel side-by-side relation to one another within each said groove. 6. The device of Claim 5 wherein each of said grooves has a basal region devoid of said hollow fiber membranes and wherein a blood inlet passageway is provided to initially channel incoming blood into said basal regions of said grooves such that said blood will subsequently flow outwardly from said basal regions of said grooves in a direction generally perpendicular to the longitudinal axes of the hollow fiber membranes disposed within said grooves, and will thereby pass over the outer surfaces of said hollow fiber membranes. 7. The device of Claim 6 wherein blood flowing in said generally perpendicular direction relative to the longitudinal axis of said hollow fiber membranes will abut against the spiral monofilament spacer members disposed on said membranes and will be thereby deflected to an altered flow path. 8. The device of Claim 1 wherein a single spiral monofilament spacer member is on the outer surface of each hollow fiber membrane. 9. The device of Claim 1 wherein a plurality of monofilament spacer members are on the outer surface of each hollow fiber membrane, said plurality of spacer members being in substantially parallel non-crossing spiral configurations. 10. The device of Claim 1 wherein said monofilament spacer members have widths of 38-63 microns. 11. The device of Claim 1 wherein said monofilament spacer members have spiral pitch intervals of 2.6-3.7 millimeters. 12. The device of Claim 1 wherein said tubular hollow fiber membranes have wall thicknesses of 40-60 microns. 13. The device of Claim 1 wherein the hollow lumens of said tubular hollow fiber membranes have diameters of 270-290 microns. 14. The device of .Claim l wherein said hollow fiber membranes have outer diameters of 350-410 microns. 15. A tubular semi-permeable hollow fiber fluid exchange membrane having a monofilament spacer member disposed or formed in spiral configuration thereon, said membrane comprising: a tubular membrane body formed of semi-permeable membrane material, said membrane body having a longitudinal axis, an outer surface and a hollow lumen extending longitudinally therethrough; a monofilament spacer member in a spiral configuration on the outer surface of said membrane body; said monofilament spacer member being substantially non-compressable and having a pre¬ determined width. 16. The membrane of Claim 15 wherein said monofilament spacer member comprises a separate monofilament spirally wound about the outer surface of said hollow fiber membrane body. 17. The membrane of Claim 15 wherein said spiral monofilament spacer member comprises a raised spiral rib formed on the outer surface of said hollow fiber membrane body. 18. The membrane of Claim 17 wherein said raised rib is formed by a process comprising the steps of: a) providing an extrusion dye configured to extrude the tubular hollow fiber membrane body with at least one raised rib on the outer surface thereof; b) extruding a formable plastic material through said extrusion dye such that an extruded work piece will emerge from said extrusion dye, said extruded work piece comprising said tubular hollow fiber membrane body with at least one raised rib formed on the outer surface thereof; and c) applying a rotational force to said work piece emerging from said extrusion dye to as to cause said raised rib to assume said spiral configuration on the outer surface of said membrane body. 19. The membrane of Claim 17 wherein said raised rib is formed by a process comprising the steps of: a) providing an extrusion dye configured to extrude a tubular membrane body having at least one raised rib on the outer surface thereof; b) extruding a formable plastic material through said extrusion dye such that an extruded work piece will emerge from said extrusion dye, said extruded work piece comprising said tubular membrane body having said at least one raised rib formed on the outer surface thereof; and c) rotating at least a portion of said extrusion dye while extruding said formable plastic material therethrough so as to cause said raised rib to assume said spiral configuration on the outer surface of said hollow fiber membrane body. 20. The membrane of Claim 17 wherein a single monofilament spacer member is on the outer surface of said membrane body. 21. The membrane of Claim 15 wherein a plurality of monofilament spacer members are on the outer surface of said membrane body, said spacer members being in substantially parallel non-crossing spiral configurations. 22. The membrane of Claim 15 wherein said monofilament spacer member has a width of 38-63 microns. 23. The membrane of Claim 15 wherein said spiral monofilament spacer member has a spiral pitch interval of 2.6-3.7 millimeters. 24. The membrane of Claim 15 wherein said tubular membrane body has a wall thickness of 40-60 microns. 25. The membrane of Claim 15 wherein the hollow limen extending longitudinally through said membrane body has a diameter of 270-290 microns. 26. The membrane of Claim 15 wherein said membrane body has an outer diameter of 350-410 microns. ■ 27. A fluid exchange system comprising a group of unattached separate tubular hollow fiber membranes positioned in close-spaced parallel side-by-side relation to one another, wherein each membrane within said group comprises: a tubular membrane body formed of semi-permeable membrane material, said membrane body having a longitudinal axis, an outer surface and a hollow lumen extending longitudinally therethrough; a monofilament spacer member in a spiral configuration on the outer surface of said membrane body; Each said monofilament spacer member being substantially non-compressable and having a pre¬ determined width; and wherein; the monofilament spacer member on each membrane body abuts against the outer surface of an adjacent membrane body, thereby causing the outer surfaces of said membrane bodies to be spaced apart from one another by a distance equal to the width of said monofilament spacer member. 28. The fluid exchange system of Claim 27 further comprising: a first fluid flow path for passing a first exchange fluid through the lumens of said membrane bodies; and a second fluid flow path for passing a second exchange fluid between the spaced-apart outer surfaces of the semi-permeable membrane bodies and in contact with the outer surfaces thereof. 29. The system of Claim 28 wherein said second fluid flow path is configured to provide an initial flow of said second exchange fluid in a direction generally perpendicular to the longitudinal axes of said tubular hollow fiber membranes such that said second exchange fluid will pass into contact with said spiral monofilament spacer members and be thereby diverted toward the direction of the longitudinal axes of said hollow fiber membranes. 30. The system of Claim 27 wherein said monofilament spacer members comprise separate monofilaments spirally wound about the outer surfaces of said hollow fiber membrane bodies. 31. The system of Claim 27 wherein said spiral monofilament spacer members comprise raised spiral ribs formed on the outer surfaces of said hollow fiber membrane bodies. 32. The system of Claim 31 wherein said raised rib is formed by a process comprising the steps of: a) providing an extrusion dye configured to extrude the tubular hollow fiber membrane body with at least one raised rib on the outer surface thereof; b) extruding a formable plastic material through said extrusion dye such that an extruded work piece will emerge from said extrusion dye, said extruded work piece comprising said tubular hollow fiber membrane body with at least one raised rib formed on the outer surface thereof; and c) applying a rotational force to said work piece emerging from said extrusion dye to as to cause said raised rib to assume said spiral configuration on the outer surface of said membrane body. 33. The system of Claim 31 wherein said raised rib is formed by a process comprising the steps of: a) providing an extrusion dye configured to extrude a tubular membrane body having at least one raised rib on the outer surface thereof; . b) extruding a formable plastic material through said extrusion dye such that an extruded work piece will emerge from said extrusion dye, said extruded work piece comprising said tubular membrane body having said at least one raised rib formed on the outer surface thereof; and c) rotating at least a portion of said extrusion dye while extruding said formable plastic material therethrough so as to cause said raised rib to assume said spiral configuration on the outer surface of said hollow fiber membrane body. 34. The system of Claim 27 wherein a single monofilament spacer member is on the outer surface of said membrane body. 35. The system of Claim 27 wherein a plurality of monofilament spacer members are on the outer surface of each membrane body, said spacer members being in substantially parallel non-crossing spiral configurations. 36. The system of Claim 27 wherein said monofilament spacer members have widths of 38-63 microns. 37. The system of Claim 27 wherein said spiral monofilament spacer members have spiral pitch intervals of 2.6-3.7 millimeters. 38. The system of Claim 27 wherein said tubular membrane bodies have wall thicknesses of 40-60 microns. 39. The system of Claim 27 wherein the hollow lumens extending longitudinally through said membrane bodies have diameters of 270-290 microns. 40. The system of Claim 27 wherein said membrane bodies have outer diameters of 350-410 microns. 41. A method of guiding blood-flow over a group of semipermeable hollow fiber membranes having longitudinal axes and outer surfaces disposed within an extracorporeal blood treatment apparatus, said method comprising the steps of: a. providing a spiral monofilament spacer member on the outer surface of each hollow fiber membrane within said group; b. causing said hollow fiber membranes to be disposed in close-spaced side-by-side relation to one another such that the longitudinal axes of the hollow fiber membranes are generally parallel to one another and further such that the spiral monofilament spacer member on the outer surface of each hollow fiber membrane abuts against the outer surface of an adjacent hollow fiber membrane, thereby maintaining a first spaced distance between the outer surfaces of adjacent hollow fiber membranes within said group; c. causing blood to flow between the outer surfaces of the individual hollow fiber members within said group such that said bloodflow will impinge against, and be guided by, said spiral monofilament spacer members. 42. The method of Claim 41 wherein step a. further comprises: causing said monofilament spacer members to have spiral pitch intervals of 2.6-3.7 millimeters. 43. The method of Claim 41 wherein step a. further comprises: causing said monofilament spacer members to have widths of 350-410 microns such that said first distance between outer surfaces of adjacent hollow fiber membranes is maintained between 350-410 microns. 44. The method of Claim 41 wherein step c. further comprises: causing blood flow initially in a direction nonparallel to the longitudinal axes of the individual hollow fiber membranes such that each impingement of said blood flow against said monofilament spacer members will cause said blood flow to be diverted toward the direction of the longitudinal axes of the longitudinal axis of the hollow fiber membranes. 45. A continuous method of spirally wrapping a monofilament spacer member on the outer surface of an elongate hollow fiber membrane and subsequently winding said hollow fiber membrane about the inner core of a blood processing apparatus, said method comprising the steps of: a) providing an elongate tubular hollow fiber membrane having an outer surface; b) providing an elongate monofilament member; c) advancing said hollow fiber membrane longitudinally along a first path; d) winding said monofilament member about the outer surface of said hollow fiber membrane as said hollow fiber membrane advances along said path such that said monofilament member becomes spirally wound about the outer surface of said hollow fiber membrane; e) winding said hollow fiber membrane, with said monofilament spacer member spirally wound thereon, about an inner core member of a blood processing apparatus. 46. The method of Claim 45 wherein said monofilament member is initially disposed on a pirn having a hollow passageway formed therethrough and wherein said hollow fiber membrane is additionally advanced through the hollow passageway of said pirn and said pirn is utilized to spirally wrap said monofilament member about the outer surface of said hollow fiber membrane as said hollow fiber membrane is advanced along said first path. 47. The method of Claim 45 wherein said core member of said blood processing apparatus has a series of grooves formed about the outer surface thereof and wherein said hollow fiber membrane, having said monofilament spacer spirally disposed about the outer surface thereof, is wound about the outer surface of said core member such that a predetermined number of revolutions of said hollow fiber membrane are wrapped into each of said grooves. 48. The method of Claim 45 wherein winding step (d) is performed by a pirn. 49. The method of Claim 45 further comprising the step of: f) controlling the rate of advancement of said hollow fiber membrane relative to the rate of winding of said monofilament member to cause said monofilament spacer member to have a predetermined spiral pitch interval. 50. The method of Claim 49 wherein said rate of advancement is controlled relative to said rate of said winding such that said monofilament spacer member will have a spiral pitch interval of 2.6-3.7 millimeters.

Inventors: CARTER R SYKES, REINHART FREDERICK J, CARTER, R., SYKES, REINHART, FREDERICK, J.
Applicants: BAXTER INT, BAXTER INTERNATIONAL INC.
Application year: 1995
Main classification: B01D69
IPC codes: A61M1, B01D63, B01D69