TRANSFER MEMBRANE ASSEMBLY

Abstract: A conduit assembly (23) for an artificial lung is formed from two sheets (30) of thermoplastic transfer membrane material which are sealed together along sinuous lines (24) to provide a unitary assembly of tubular conduits (26) each having longitudinally spaced hollows (27) which promote eddies in, and mixing of, blood when passed through the conduits with a pulsatile flow.

Description: TRANSFER MEMBRANE ASSEMBLY The invention is concerned with apparatus for effecting transfer of heat or mass between two fluids, of which at least one is usually a liquid, through a - transfer- membrane. Such apparatus is used in blood 5. oxygenators, that is artificial lungs, and dialysers, such as artifical kidneys, in which case one fluid is blood, and the other is oxygen or dialysate. In practice the efficiency of the transfer across the membrane is limited by the extent to which the total volume of fluid 10. can be brought into close proximity with the membrane. It is not sufficient to reduce the thickness of the fluid layers, by reducing the thiclmess of- the conduits in which they flow, as this increases undesirably the pressure drop across the apparatus and leads to uneven 15* perfusion and regions of stagnation, which, in the case of blood, provides a danger of thrombosis. We believe that the proper solution lies in so shaping the fluid flow conduits that significant mixing of the fluid occurs within the conduits. It has pre- 20. viously been proposed in British Patent Specification No. 1,442,754 to provide an apparatus comprising a conduit for flow of one of the fluids at least partially defined by the membrane, a transverse dimension of the conduit varying in a regularly repeating manner along the leng of the conduit, to provide a multiplicity of hollows i the membrane, the apparatus also comprising means communicating with the conduit for passing fluid throu 5. the conduit in pulsatile flow, the arrangement being such that pulsation of fluid past the hollows give ris in the hollows to rotational fluid flow having compon¬ ents of motion parallel and perpendicular to the gener direction of flow in the conduit of the fluid * Such 10. apparatus is hereinafter referred to as of the kind described. The conduit may be defined between two pre- dominently planar surfaces, so that it has an elongate cross section transverse to the general direction of 15. flow through the conduit, at least one of the surfaces then being provided by a membrane in which the requisi hollows are provided by furrowing at least one of the surfaces defining the conduit. Alternatively, the conduit may be tubular, that is essentially axisymme r 20. with its wall provided by a membrane. Tubular conduit have the advantage of being self supporting' and do not require complex moulded support plates. However, they have not been cheap to produce in the numbers required in a typical apparatus. 25. In accordance with the present invention, a conduit assembly for use in an apparatus of the kind described comprises two sheets of plastics material, a least one of which is a transfer membrane material, whichare sealed together face to face along a number 30« of pairs of sinuous lines extending generally in the same direction alongside one another with the undul¬ ations of the lines of each pair of lines out of phase with one another thereby providing, upon inflation of the passageways between the sheets and between each pair of lines, a tubular conduit with longitudinally and substantially regularly spaced hollows with intervening constrictions. 5- In this manner there is readily provided a unitary construction consisting of a generally planar array of tubular conduits, with walls of transfer membrane material, and of the required internal con¬ figuration. 10. If the.undulations in the adjacent lines of each adjacent pair of lines are also out of phase with one another, a tubular conduit with the required internal configuration will also be provided between each adjacent pair of lines with the annular hollows 15. in one conduit in lateral alignment with the constrictions in each adjacent conduit. This layout provides maximum saving of space and material. The unitary structure comprising the array of conduits may also incorporate fluid inlet and 20. outlet manifolds by providing additional lines of * • sealing which define between the two sheets spaces communicating with respective ends of the conduits. Inlet and outlet passages to the respective man¬ ifold spaces may also be provided between the two 25. sheets by means of further seal lines. However, a preferred way of leading fluid into or out of at least one of the manifolds is by the provision of a distributor which is sealed to and between the two sheets in the manifold, the distributor having a 30. passage which opens, in. use,through at least one of the sheets and into the respective manifold. In order to- keep the interior of the assembly clean, prior to use, it may be manufactured with the distributor between imperforate sheets and a hole cut through at least one 35. of the sheets in alignment with the passage in the distributor immediately prior to use. In use, one or a stack of the unitary assemblies of tubular conduits will be provided with a housing and connected to appropriate pumping 5. arrangements so that one fluid can be pumped through the conduits in parallel with a pulsatile flow and t other fluid will be pumped through the housing aroun the assembly or assemblies in contact with the transfer membrane material. The second fluid will 10. preferably flow in countercurrent or crosscurrent to the first fluid through the housing. When a stack of the assemblies are used and the assembly manifold have the distributors referred to, the passages of t distributors of the corresponding assembly manifolds 15. may be sealed to one another to provide a continuous passage leading to or from all the assemblies. The plastics material from which each of the two sheets of the conduit assembly is made will be o a suitable hygienic grade when the assembly is for u 20. in a medical application. The plastics material wil usually be a thermoplastic material, i.e. one which softens upon being, heated and then resets upon cooling, such as polypropylene, polyethylene or polytetrafluoroethylene (PTFE). The seal lines may 25. then be produced by heat sealing, for example by direct application of a hot die or by an ultrasonic welding tool. Alternatively a solvent weld may be possible. In order to inflate, and preferably set, the 30. walls of the tubular conduits in their desired configuration, the conduits may be' inflated by being filled with a fluid, preferably a liquid, under, a pressure sufficient to stretch the sheet material just beyond its elastic limit.. • After this treatment the tubular conduits adopt a- cross section throughout which is substantially circular. It may be possible to carry out-the, inflation step more quickly using heated,air under pressure. 5. In order that the conduits are set in a shape in which the transition between the annular constrictions and hollows is smooth, the conduits are preferably longitudinally stretched, for example by being clamped in a frame, or indeed in the final housing in which they 10. are to be used, during the setting. Some appropriate sheet materials are produced with the facility for stretching more easily in one direction than in the perpendicular direction. It is desirable to use such material with the direction of easier stretching 15. extending- substantially parallel to the lengths of the tubular conduits. An example of an artificial lung incorporating a conduit assembly in accordance with the invention is illustrated in the accompanying drawings, in which_- 20. Figure 1 is a plan with a cover of the .artificial lung removed; Figure 2 is a section taken on the line II-II in Figure 1 through the articial lung with the cover in place; 25. Figure 3 is a section taken on line III-III in Figure 1 but to a scale larger than that of Figure 2;and, Figure 4 is a perspective view of the conduit assembly with parts broken away. The illustrated articial lung has a rectangular 30. housing formed by a cover 10 and base 11 which are of. similar shape and which are secured together at their corners by screws 12 which pass through holes 13 in the cover and screw into tapped holed 14 in the base. A sealing gasket 15 is interposed between the edges of 35. the cover 10 and base 11 to seal a chamber within the O PI /., WIIPPOO - housing. The inner surfaces of the cover and base are stepped at 16 so that the chamber within the housing consists of a central portion 17 of greater depth, and at each end, portions 18 of lesser depth. 5. The cover 10 is provided centrally at each end with a larger opening 19 to which external hoses 20 ar coupled, and, at diagonally opposite positions, smalle openings 21 to which external hoses 22 are fitted. The housing contains a conduit assembly 23 in t 10. shape of an elongate octagon. The assembly is formed two sheets 30 of microporous polytetrafluoroethylene membrane material * of a kind sold under the trade name Gore-tex which are heat sealed together along a number of generally parallel ' but sinuous lines 24 and along a 15. peripheral octagonal line 25- The lines 24 define between them, and between the two membrane sheets a side by side array of tubular conduits 26 which, when the conduits are expanded, are of circular section and repeatedly increasing and decreasing diameter, thereby 20. providing a series of longitudinally spaced hollows 27 separated by constrictions 28. It will be appreciated that the hollows and constrictions, of adjacent conduit 26 are out of phase with cne another so that they nest together and are joined along the sinuous lines 24 25. which remain substantially coplanar. The maximum diameter of each conduit 26, in each of its hollows, is substantially 5 mm. and the pitch between adjacent hollows is a similar dimension. At each end of the conduit assembly, the 30. peripheral seal line 25 defines, between the membrane - sheets, and in coπimunication with the adjacent ends of the conduits , inlet and outlet manifolds 29 of rhombic shape. Within each manifold is positioned a . rigid annular distributor 31 made from a plastics 35. material such as a polycarbonate, heat sealed to the O W inner faces of the two membrane sheets. The distri¬ butor has ' a series of radial ports 32 opening into the respective manifold from a central passage 33 through the distributor-. On one face the distributor 5. has a projecting annular flange 34, in alignment with the passage ■_ 33 and extending through a hole in the upper membrane sheet of the conduit assembly into the adjacent passage 19. The extension of these flanges 34 into the two openings 19 locates the conduit assembly 10. in the housing and the fixing is completed by the distributors 31 with the membrane sheets above and below, being clamped between the cover 10 and base 11, thereby determining the narrower depth of the chamber portions 18. 15. In use the hose 20 a; the left hand end of the housing as shown in Figures 1 and 2 will be connected to a blood supply which is pumped to the articial lung with a pulsatile flow, for example by means of a uni¬ directional roller pump in series with a reciprocatory 20. pump. Similarly the hose 20 at the right hand end as seen in Figures 1 and 2 will.be connected to the return blood circuit. Blood will thus flow in through the left hand hose 20, through the left hand distributor 31. and the inlet manifold 29, in parallel through the 25. conduits 26, into the outlet manifold 29 and through the outlet distributor 31 and the right hand outlet hose 20. The blood flows with a mean flow velocity through the conduits 26 but the superimposed reciprocatory component causes the blood alternately to accelerate and 30. decelerate and this sets up eddies B in the hollows 27, as shown in Figure . These promote intimate mixing of the blood and contact between the blood and the transfer membranes. At the same time oxygen is pumped in a steady 35. stream through the oxygen inlet hose 22 at the right hand end of the housing as seen in Figures 1 and 2, essentially diagonally through the housing in contact with the outside of the conduit assembly 23 . and out of the oxygen outlet hose 22 at the left hand end of 5. the housing.The " oxygen 0 thus flows partly in cross¬ current and partly in countercurrent to the blood and good transfer occurs through the membrane walls of the conduit assembly 23. In vitro tests of the lung have been carried ou 10. using sheep blood. The blood was pumped at a mean flo rate of 75 ml. per min. with a superimposed recipro¬ catory component using a reciprocatory pump with a stroke volume of 1.3 ml. and a pulse frequency of 200 per min. Oxygen transfer rates reached 200 ml./min. 2 15. The surface area of the articial lung was 106 cm . The same articial lung was tested in a live sheep, in veno-venous bypass using cannulae in the external jugular veins. At a mean blood flow rate of 75 ml/___in.the lung raised the oxygen-saturation of the 20. blood from 63% at the inlet to 83% at the outlet, achieving oxygen transfer rates of 226 ml/min.m . Clearly the depth of the housing could be increased to accommodate two or more of the conduit assemblies stacked together, in which case the annular 25. flanges 34 on the distributors of the lower assemblies would project up through holes in the lower membrane sheets of the assemblies above and project into and be sealed within the lower ends of the passages 33 of the assemblies above. Single supply and return lines of 30. blood would then be provided for all the assemblies in the stack. The illustrated conduit assembly is produced by cutting two sheets to the appropriate elongate octagon shape, and placing them face to face on a heat sealing 35. die formed by a number of upstanding metal strips corresponding in shape to the lines 24 and 25. The metal strips are embedded in rubber or asbestos sub¬ strate and connected into -an electrical heating circuit. The sheets are then covered by a soft pad to '. • . 5. press the sandwiched sheets down against the die and heating ..curr.ent is passed through the metal strips in turn. Each pair of sinuous lines require sealing for about 2 to 3 seconds utilizing a power of 170 watts.. After all the lines of heat sealing have been set, the 10. assembly is pressurised with water at about 16 C and a superatmospheric pressure of about 15 psi. This is sufficient to inflate the conduits 26 and indeed stretch the membrane sheet material just beyond its elastic limit so that, upon subsequent depressurisation, 15. the conduits maintain their * 'tubular shape with smooth transition between the hollows and constrictions. During the inflation step, the assembly is stretched parallel to the lengths of the conduits 26 either on a frame or possibly simply by locating the assembly in 20. the illustrated housing by means of the distributors 33 and the clamping pressure in the region of the distri¬ butors.

Claims: CLAIMS 1. A conduit assembly for use in an apparatus of the kind described, the assembly comprising two sheets (30) of plastics material, at least one of which is a transfer membrane material, which are sealed together face to face, characterised in that the sheets are sealed together along a number of pairs of sinuous lines (24) extending generally in the same direction alongside one another with the undulations of the lines'of each pair of lines out of phase-with one another thereby providing, * upon inflation of the passageways between the sheets and between each pair of lines, a tubular conduit (26) with longitudinally and substantially •# regularly spaced hollows (27) with intervening con¬ strictions (28). 2. An assembly according to claim 1, in which the undulations in the adjacent lines of e.ach adjacent pair of lines are also out of phase with one another to provide further similar tubular conduits (26) between each adjacent pair of lines. 3. An assembly according to claim 1, in which the two sheets are sealed together along additional lines (25) defining between the two sheets spaces communicatin with respective ends ~ -of the conduits to act as fluid inlet and outlet manifolds (29). 4. An assembly according to claim 3, in which in at least one.of the manifolds (29) there is provided a distributor (31) sealed to and between the two sheets, the distributor having a passage(32,33) which opens, in use, _ through at least one of the sheets and into the respective manifold for leading fluid into or out of the assembly. 5. An assembly according to any one of the preceding claims, in which the plastics material from which each of the * two- sheets (30) is * made is a thermoplastic material. 6. An assembly according to claim 5, in which the lines (24,25) are lines of heat sealing. 7« An apparatus of the kind described comprising at least one conduit assembly according to any one of claims 1 to 5, mounted within a housing (10,11); means (20) for passing a first fluid with a pulsatile flow through the tubular conduits of the or each assembly; and means (22) for passing a second fluid through the housing in contact with the transfer membrane of the or each conduit assembly. 8. A method of making a conduit assembly according- to claim 5, in which, after the two sheets (30) have been sealed together along the lines (24), the tubular conduits are inflated by being filled with a fluid ' under a pressure sufficient to stretch the sheet material just beyond its elastic limit. 9. A method according to claim 8, in which, whilst being subjected tothe inflation step, the assembly is stretched in the longitudinal direction of the tubular conduits. 10. A method according to claim 9, in which the sheets are made of a plastics material which is more easily stretched in one direction than in the perpendi- cular direction, the direction of easier stretching being substantially parallel to the longitudinal direction of the tubular conduits.

Inventors: BELLHOUSE B, BELLHOUSE F
Applicants: BELLHOUSE B, BELLHOUSE F
Application year: 1979
Main classification: B01D13
IPC codes: A61M1, B01D63, B29C49, B29C65, F28F3, F28F21