U.S. patent number 3,862,031 [Application Number 05/309,024] was granted by the patent office on 1975-01-21 for multi-layer membrane type mass transfer device and process.
This patent grant is currently assigned to Baxter Laboratories, Inc.. Invention is credited to Ronald James Leonard.
United States Patent |
3,862,031 |
Leonard |
January 21, 1975 |
MULTI-LAYER MEMBRANE TYPE MASS TRANSFER DEVICE AND PROCESS
Abstract
A foldable cardboard backing is secured to one surface of a
flexible mass transfer membrane to enable rapid formation of a
folded multi-layered device by compressing the backing and membrane
connected thereto into folds and then fixing the folds by sealing
their ends.
Inventors: |
Leonard; Ronald James (Elk
Grove Village, IL) |
Assignee: |
Baxter Laboratories, Inc.
(Morton Grove, IL)
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Family
ID: |
26754567 |
Appl.
No.: |
05/309,024 |
Filed: |
November 24, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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73524 |
Sep 18, 1970 |
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Current U.S.
Class: |
210/321.77;
264/257; 422/48 |
Current CPC
Class: |
B01D
63/14 (20130101) |
Current International
Class: |
B01D
63/14 (20060101); B01d 031/00 () |
Field of
Search: |
;23/258.5 ;210/22,321
;29/163.5F ;264/258 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Spear, Jr.; Frank A.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation of U.S. application Ser. No.
73,524, filed Sept. 18, 1970, now abandoned.
Claims
That which is claimed is:
1. A method of securing a semipermeable membrane made of
difficultly adhering material to an impermeable backing, which
comprises:
applying a tape member which is adhesive on both sides
longitudinally along a face of said backing;
laying said membrane on said tape member with a longitudinal edge
of said membrane overlying said tape member;
applying a bead of sealant over said tape member and said membrane
longitudinal edge; and thereafter
folding said backing and membrane along transverse lines of folding
to encase and squeeze said bead of sealant between folds of
membrane.
2. A mass transfer device which comprises a flexible semipermeable
membrane folded to provide a plurality of membrane layers arranged
for flow of a fluid in a plurality of parallel first flow paths and
for flow of another fluid in a plurality of parallel second flow
paths positioned between and separated from said first flow paths
by said membrane, an integral backing folded and arranged on one
side of said membrane for support thereof, said membrane being
attached to the backing at lateral edges of said membrane by a tape
member which is attached at opposite sides thereof to the backing
and membrane respectively, the sides of said folded membrane layers
opposite to the tape member being sealed together in leak-proof
manner with a bead of elastomeric sealant which also overlaps the
lateral edges of the membrane to adhere to the tape member.
3. The mass transfer device of claim 2 in which said membrane
comprises cellulose.
4. The mass transfer device of claim 2 in which said membrane
comprises polytetrafluoroethylene.
5. The mass transfer device of claim 2 in which said bead of
sealant comprises a silicone rubber room temperature vulcanizing
elastomer.
Description
BACKGROUND OF THE INVENTION
This invention relates to mass transfer. Particularly, it relates
to a mass transfer device of the type having a plurality of layers
formed from a flexible folded semipermeable membrane to provide two
sets of interconnected pockets for plural paths of flow for a first
fluid along one surface of the membrane and plural paths of flow of
a second fluid along the other surface of the membrane.
Devices of the designated type have been successfully used as
extracorporeal oxygenators of blood in which both oxygen and
CO.sub.2 are transferred in opposite directions across a membranous
barrier separating the blood and the oxygen. Representative of the
state of the prior art are U.S. Patent Nos. 3,370,710; 3,396,849;
3,318,747; and 3,560,340.
According to the first patent, a pleated semipermeable membrane is
assembled with tie bolts for holding the membrane pleats in a
compressed condition. The unit thus formed is secured within a
housing fashioned for managing flow of blood and oxygen
therethrough. Within the unit, blood flows along random paths so
that there is no assurance of uniformity of gas exchange.
The second patent and the copending application are for oxygenators
with membrane supports disposed in the pockets formed along the
oxygen engaging surface. These supports provide orderly flow paths
for blood across membrane layers. For example, in said copending
application each support member is fashioned with cross strands
which produce flow channels arranged for maximum gas transfer. But
a folded membrane is a difficultly controlled structure; and its
management according to heretofore known technique while inserting
the membrane supports during assembly of a mass transfer device is,
at best, burdensome. Reflected costs of overcoming the difficulty
tend to place prior oxygenators beyond the economic capability of
many potential users and economically burden others.
SUMMARY OF THE INVENTION
In accordance with the present invention, the control of folded
membranes during assembly of mass transfer devices of the described
class is facilitated, and costs of such devices are correspondingly
minimized. To effect the invention, a flexible semipermeable
membrane for a mass transfer device, such as a diffusion cell of
the type characterized by a plurality of membrane layers having two
separated sets of oppositely directed interconnected openings
forming plural paths on opposed membrane surfaces for separated
flow of a first fluid and a second fluid, respectively, is secured
to one surface of a stiff backing in overlying relationship
therewith. To obtain this structure, a membrane and the backing are
folded into a plurality of pleats to form two sets of oppositely
opening pockets. The opposite ends of the pockets are then sealed;
and one set is connected to inlet and outlet means for a first
fluid and the other set of pockets is connected to inlet and outlet
means for a second fluid.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded perspective view of portions of a membrane,
spacer means, and a foldable stiff backing comprising a mass
transfer device embodying the present invention.
FIG. 2 is a perspective view of the components of FIG. 1 in
subassembly form.
FIG. 3 is an inverted perspective view of said subassembly in a
pleated stage of completion following the condition of FIG. 2.
FIG. 4 is a perspective view of a flow divider.
FIG. 5 is an elevational view illustrating the steps of assembling
a plurality of dividers and said subassembly.
FIG. 6 is a perspective view of a membranous unit in stage of
completion following the condition of FIG. 5.
FIG. 7 is a perspective view of said mass transfer device with
manifolds added.
FIG. 8 is an enlarged sectional view according to the line 8--8 on
FIG. 6, with parts broken away to conserve drawing area.
FIG. 9 is an enlarged sectional view according to line 9--9 on FIG.
6, with parts broken away to conserve drawing area.
FIG. 10 is an exploded perspective view of a mass transfer device
incorporating another embodiment of the stiff backing used in this
invention.
FIG. 11 illustrates the three layers of FIG. 10 assembled and taped
together.
FIG. 12 is a detailed plan view of a portion of the stiff backing
used in FIG. 10.
FIG. 13 is an inverted perspective view of the assembled structure
of FIG. 11 in its pleated configuration.
FIG. 14 is a detailed sectional view taken along line 14--14 in
FIG. 13.
FIG. 15 is a highly magnified detail at the top of FIG. 14.
FIG. 16 is a detailed plan view of a portion of another embodiment
of the stiff backing used in this invention.
FIG. 17 is a detailed plan view of a portion of still another
embodiment of the stiff backing used in this invention.
FIG. 18 is a detailed view of the assembly of FIG. 11 showing an
intermediate step in the preferred method of securing the membrane
to the stiff backing.
FIG. 19 is a partial sectional view of the structure of FIG. 18
after folding, taken through a plurality of folded membrane and
backing layers, showing construction details of the finished seal
between the membrane and the stiff backing.
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring now more particularly to FIGS. 1 through 9, FIG. 1 shows
a length of membrane 10 having, in terms of orientation with
respect to FIG. 1, a top or blood engaging surface 12 and an
opposed or gas engaging under surface 14. The membrane comprises
mass transfer means in a mass transfer device such as an oxygenator
16 (FIG. 7); and is flexible and semipermeable for transmission of
oxygen and carbon dioxide from opposed surfaces in opposite
directions.
Oxygenator 16 is adapted for connection with a human circulatory
system to enable extracorporeal oxygenation of blood. To that end,
as will be apparent from ensuing description, membrane 10 is
arranged to effectively separate two fluids so that blood will
contact only surface 12, whereas (except for membrane transmitted
gas) oxygen will contact only surface 14.
A length of a stiff backing 18, typically corresponding in
dimensions to the membrane 10, is weakened by a plurality of
transversely extending, equally spaced parallel score lines 20
along which the backing may be folded or pleated into a plurality
of uniformly dimensioned segments 62. The backing may be of
paperboard about the thickness of a conventional shirt stiffener. A
hydrophobic coating or sealer such as polyethylene and the like may
be applied to the surfaces of the backing. The backing is disposed
adjacent surface 14 longitudinally of membrane 12.
A length of flexible spacer 22 is disposed between surface 14 and
backing 18. Preferably it is the same length as the membrane, but
narrower. The spacer 22 can preferably be plastic, fluid-permeable
screening or netting made of crossed, woven or nonwoven strands for
providing flow channels in and along the membrane 10 when the
latter is forced into engagement with the spacer as pressurized
blood or other fluid is passed along one side of the membrane 10.
Suitable nonwoven netting comprising two sets of parallel strands
lying against each other, each set in a different plane and
defining an angle to the other set, is commercially available under
the trademark Polynet, from Nordeutschen Seekabelwerke Nordenham,
of West Germany. Suitable woven netting or screening made from
vinyl-coated glass fibers or monofilament nylon fibers is also
commercially available. Woven screening is generally preferred for
use in the blood oxygenator disclosed herein. Alternatively, spacer
22 can be a flexible sheet of plastic or the like having
protrusions or ridges on the membrane side to define fluid flow
channels, for example, similar to the type shown in U.S. Pat. No.
3,077,268, but with protrusions typically on only the one side
facing the membrane 10.
From the components of FIG. 1, a subassembly 24 (FIG. 2) is
produced by securing spacer 22 to the membrane proximate surface 26
of backing 18 in a manner such that a pair of parallel margins 28
and 30 are formed longitudinally of the backing. The securance may
be through the agency of any suitable adhesive, such as an RTV
(room temperature vulcanizable) silicone rubber. Membrane 10
overlies the backing and is arranged with its surface 14 disposed
against spacer 22. Its opposite side portions 32 and 34 overhang
said spacer and are sealed to opposite side margins 28 and 30 of
said backing, preferably with the above stated adhesive. Its
opposite ends are sealed to ends 40 and 42 of said backing.
Subassembly 24 thus fashioned then readily may be folded by manual
compression, that is to say, by application of manual pressure to
opposed ends 40 and 42 to produce a pair of sets 44 and 46 of
oppositely opening pockets, only some of which are numbered (FIGS.
3 and 5). Each pocket of set 44 is lined with a pair of adjacent
membrane sections or layers and each pocket of set 46 is lined with
a stiffener comprised of a pair of adjacent backing segments 62.
Generally, backing 18 is prefolded into convoluted form before
assembly into subassembly 24, and then stretched out again to
receive membrane 10. The subassembly 24 is then readily convoluted
without effort and without vigorous manipulation and abrasion which
is likely to damage membrane 10.
The subassembly 24 thus folded is readily manageable and may be
loosely hand or machine held while a flow divider 48 (FIGS. 4, 5,
8, and 9) may be inserted into each pocket 44 in the direction of
arrow 50 (FIG. 5). Each flow divider may be fabricated from the
same material as that of spacer 22. After all of the flow dividers
have been inserted, the subassembly 24 is completely manually
compressed and its opposite ends 52 and 54 are secured and sealed
as by potting with a suitable sealant such as RTV silicone rubber
while the subassembly continues to be hand or machine held.
Thereby, the opposite ends of pockets 44 and 46 are closed and a
membranous unit 64 (FIG. 6) is formed with its pockets opening
toward opposite sides of said unit and defining a plurality of
parallel flow paths for blood and oxygen in separated pockets as
shown in said copending application.
The length of dividers 48 is such that pockets 44 are filled from
their inner angles 56 (FIG. 9) to their openings. However, the
width of each divider is about the same as the width of spacer 22,
so that a pair of spaces 58 (FIG. 8) are formed in each pocket 44
between adjacent membrane sections or layers of such pocket. Spaces
58 register with portions 60 of the sections of membrane 10 which
are not supported by spacer 22 because of its narrower width,
aforedescribed. In consequence, normal blood pressure in pockets 44
will cause the membrane portions 60 to balloon out beyond spacer 22
at opposite ends 52 and 54 of unit 64.
An oxygen manifold 66 is rigidly secured to one side of the
diffusion or exchange unit 64 in a manner such that a medial
section of pockets 46 are sealed, leaving said pockets open at
opposite end portions 52 and 54. The manifold has oxygen inlet
means 68 and oxygen outlet means 70 arranged in communication with
open ends of pockets 46.
A manifold 72 adapted for blood is rigidly secured to the other
side of unit 64. It is fashioned to seal a medial part of pockets
44 so that said pockets are open only at opposite ends 52 and 54.
Manifold 72 has blood inlet means 74 and blood outlet means 76 in
communication with the open ends of pockets 44, the inlet and
outlet means of the manifolds preferably being arranged for flow of
blood and oxygen in opposite directions.
To enable oxygen to get through the backing which lines pockets 46,
port means comprised of a plurality of elongated slots 78 (FIGS. 1,
3, and 9), only some of which are numbered, are provided in backing
18 at the folded angles between segments 62. The opposite end
portions of said slots extend into margins 28 and 30 and are
registered with inlet and outlet means 68 and 70. As a result,
oxygen entering through the inlet 68 will pass through backing 18
and through the spacer 22 into contact with surface 14 of membrane
10.
While the mass transfer device specifically described above is an
oxygenator, it will be apparent to those knowledgeable in the art
that the inventive concept embodied therein is adaptable for other
uses and purposes within the scope and spirit of the invention. For
example, the mass transfer device of this invention can also be
used as an artificial kidney.
When employed as an oxygenator, the semipermeable membrane in the
mass transfer device is usually made of material impermeable to
liquid but of sufficient permeability to allow carbon dioxide to
pass from the blood and oxygen to pass to the blood. This material
preferably is an elastomeric plastic material, such as silicone
rubber, which is antithrombogenic or otherwise biologically inert.
It can also be fabricated of a plastic base, for example, a mesh of
glass or polyester fibers to which is applied a thin coating of
said silicone rubber elastomer. Other suitable materials for making
the oxygenator membrane are polyethylene, polytetrafluoroethylene,
a cast silicone rubber sheet, a cast sheet of a copolymer of
silicone rubber and polycarbonate, and the like plastic
materials.
When employed as an artificial kidney device, the semipermeable
membrane is usually made of a material that is impermeable to the
blood proteins but is permeable to nitrogenous bodily waste
products such as urea, uric acid, water, and creatinine, which will
then pass from the blood through the membrane and into the dialysis
solution of suitable ionic concentration. Such materials as
cellulosic products, e.g., cellophane or cuprophane, or synthetic
hydrophobic or hydrophilic films, or foils capable of passing such
waste products, can be readily employed.
The flow of the two fluids, which can be in either direction
relative to each other in the oxygenator, are generally
countercurrent to each other in the artificial kidney for most
effective operation of the mass transfer device described
herein.
The folded stiffener 18 which is employed for rigidifying the
folded or pleated layers of the semipermeable membrane preferably
is made of a paperboard of about 10 to 20 mils thickness, although
other thicknesses can be used, depending in part upon the material
of construction. The stiffener can also be made of materials such
as, for example, plastics, e.g., polypropylene or polyethylene,
vinyl plastics, or even a rubberized fabric material. Paperboard
stiffeners or backings 18 are preferably coated with a plastic such
as one of the above, or silicone rubber.
The spacer means 22 for defining flow channels in the folded or
pleated layers of the semipermeable membrane can be sandwiched
between the semipermeable membrane and the folded stiffener, it can
be secured to one or both sides of the folded backing or stiffener;
or it can comprise an embossed surface on one or both sides of the
backing or stiffener. Such a structure might be made by gluing
strands, screening, or netting to one surface of stiffener or
backing 18. Alternatively, backing or stiffener 18 can be
fabricated with a surface having strandlike or other irregularities
corresponding to flexible spacer 22 integrally defined by the
surface of backing 18. Such a union of backing 18 and spacer 22
into a single or laminated piece provides greater ease of assembly
of the device of this application and substantial cost savings.
Securance of the spacer means to the backing or stiffener 18 and/or
securance of the backing or stiffener to the membrane can be by
threading, taping, or by use of adhesives such as RTV silicone
rubber, epoxy cement, and the like adhesive materials which are
compatible with the respective surfaces. To impart suitable
flexibility to the spacer means 22 and 48, materials such as low
density polyethylene, vinyl, or glass fibers coated with vinyl can
be used in their construction.
FIGS. 10 through 15 show aspects of a mass transfer device similar
to that of FIGS. 1 through 9 in which the backing 80 (which
corresponds to backing 18 in the previous embodiment) defines
longitudinally extending cutaway portions 82, 83 which are located
adjacent longitudinal edges 84 of the panels 86 in backing 80. The
purpose of cutaway portions 82, 83 is to facilitate the
introduction of fluid to and from the convoluted space between the
membrane 10 and backing 80. Transverse score lines 85 are provided
for folding in a manner similar to that previously described.
FIGS. 10 and 11 are similar to FIGS. 1 and 2 in that they both show
membrane 10 and spacer 22 and the respective backings 18, 80
assembled in similar manner. Flow dividers 48 can be utilized in
the folded membrane device, if desired.
Referring to FIGS. 13 and 14, the assembled but incompletely folded
device is shown in inverted position with respect to FIG. 11, with
backing 80 at the top and membrane 10 and spacer 22 underneath. The
upwardly and downwardly facing pockets 88, 90 are defined by folded
backing 80 and the other parts. It can be seen that it is necessary
for a fluid introduced into any of the set of pockets 88 to pass
through backing 80 and then to pass along spacer 22 in the
convoluted space between backing 80 and membrane 10 in order for
mass transfer to take place with respect to fluid passing through
pockets 90.
Cutaway portions 82, 83 provide the route of access for fluid in
pockets 88 to pass through backing 80 into contact with membrane 10
in improved volume and with a high degree of spreading across the
surface of the membrane. In use, the mass transfer device of FIG.
13 is tightly folded as in FIG. 6, which puts a degree of
constriction into the flow path along membrane 10. This
constriction is selectively relieved by cutaway portions 82, 83 to
provide relatively large manifold-like areas in the membrane and
spacer region adjacent cutaway portions 82, 83 to facilitate the
rapid spreading of fluid entering into each pocket by way of entry
ports 92 at the top of the folded backing 80 and cutaway portions
82, and the uniform collection of flowing fluid into cutaway
portions 83 and its removal from exit ports 94.
For example, oxygen gas can be supplied to a tightly folded
structure having an assembly similar to that of FIG. 13 by a
manifold as shown in FIG. 7, from which manifold oxygen gas passes
into ports 92. Because of the relief of constriction provided by
cutaway portions 82, the oxygen or other fluid quickly migrates
downwardly through the area defined within cutaway portions 82.
From there the oxygen migrates transversely across and between
membrane 10 and backing 80 toward cutaway portions 83, while
undergoing mass transfer across membrane 10. The fluid then is
collected in the manifoldlike areas within cutaway portions 83,
from which it flows out of exit ports 94 and away from the device
by way of the manifold system of FIG. 7, if desired. This system
provides a wide, uniform flow path of fluid along membrane 10 for
efficient mass transfer.
Additionally, backing 80 defines central, transversely extending
cutaway portions 96, spaced from the longitudinal edges of backing
80 at alternate transverse fold-lines of the backing. These can be
used to eliminate an undesirable low resistance flow path which is
defined (when there is no cutaway portion 96) by a linear space 97
(FIG. 15) between the apex of the fold of backing 80 and spacer 22.
This linear space is created by the fact that spacer 22 is
frequently incapable of forming as sharp a fold as is backing 80,
thus causing the linear space to form. When such a space is formed,
it provides a flow path of low resistance, permitting fluid to pass
from entrance 92 to exit 94 without coming into intimate filming
contact with membrane 10, as it is forced to do if it passes on a
flow path which is deeper within pocket 88. Cutaway portions 96
permit the manufacturer to apply a small bead of adhesive sealant
98 into portions 96 to occlude the linear space 97 and thus to
improve the mass transfer characteristics of the device.
Referring to FIG. 16, another embodiment of a stiff backing 95 is
disclosed for use instead of backing 80. One set of alternating
panels 99 defines pairs of longitudinally extending cutaway
portions 100, each cutaway portion being positioned adjacent a
separate longitudinal edge 101 of the backing. The remaining set of
alternate panels 102 defines no longitudinally extending cutaway
portions.
The backing of FIG. 16 defines scored fold lines 85 and
transversely extending cutaway portions 96 similar to the backing
of FIG. 12 and for the same purposes.
FIG. 17 discloses another embodiment of a stiff backing 103 which
can be used in place of previously described backings in a mass
transfer device of this invention. The backing 103 has fold lines
104 and central, transversely extending, cutaway portions 106
similar to the stiff backings previously described. Additionally,
each panel 108 defines a pair of cutaway portions 110 which
communicate with a corresponding pair of cutaway portions in one
adjacent panel. However, each pair of cutaway portions 110 is
spaced from the fold line 104 connecting each panel in which said
portions 110 are found from its other adjacent panel, so that each
pair of cutaway portions in each panel 108 communicate only with
the cutaway portions 110 of one adjacent panel. This structure
provides a high degree of manifolding to permit fluid to pass
through the stiff backing and to percolate uniformly through the
spacer 22 against membrane 10 for mass transfer.
If desired, extra cutaway, portions or slits 112 can be prepared to
extend inwardly from the longitudinal edges of the backing at
alternate fold lines to relieve stress on the membrane when folded
with the backing. As transverse cutaway portions 106 can be used to
provide access to fill the linear space which may be formed between
the membrane and spacer and the backing, cutaway portions 112 are
provided to provide relief to the membrane at a point where
otherwise it would undergo a severe amount of tension as the
assembly is folded, to avoid breakage of the membrane. This tension
is increased by the fact that the membrane is typically taped into
place with the tape between backing and membrane, which increases
the radius of curvature of the membrane about the fold lines 104,
along which slits 112 are defined. The presence of slits 112
relieves this tension in the area where the presence of tape may
cause an unduly large tension on the membrane.
Referring to FIGS. 18 and 19, a desirable technique for taping a
membrane 10 to the backing 80 is disclosed. The adherence of the
membrane to the backing can be a difficult problem, particularly in
the case where cellulose membranes are used, since cellulose
generally adheres poorly to plastic materials. (Even when the
backing is made of cardboard, it may have a plastic coating.) The
technique shown is to lay tape or another adhesive bead 114 which
is adherent on both sides along each longitudinal edge 84 of the
backing 80. Following this, an edge of membrane 10 is placed on the
tape and gently pressed down. Thereafter, a curable, flexible
adhesive, such as silicone rubber room temperature vulcanizing
elastomer, is placed as a bead 116 along the upper sticky side of
tape 114 to cover the edge of membrane 10 lying on tape 114.
Following this, the backing 80, membrane support, and membrane 10
are folded together in the usual manner along transverse lines of
folding 104 to encase and squeeze the uncured bead of sealant 116
between folds of membrane 10. This provides a good lateral seal to
each pocket defined by membrane 10 after the folding. The edges of
membrane 10 are in turn bracketed by lengths of tape 114, which in
turn is bracketed by the edge of backing 80, to form a strong,
leakproof seal. The membrane, even though it may not have a high
degree of adhesion to sealant 116, is held in place by a pressure
seal after sealant 116 has cured in the folded position.
The above has been presented for purposes of disclosure only, and
is not to be construed as limiting the scope of this invention,
which is defined by the claims below.
The mass transfer device herein described will generally comprise a
disposable unit in an ordinary oxygenator housing, container or
bracket and can be similarly employed as a disposable unit in a
complete artificial kidney machine in which the manifolding or
distribution of fluids is carried out by conventional means.
* * * * *