Note: Descriptions are shown in the official language in which they were submitted.
88
HEMOPERFUSION DEVICE FOR SPECIFIC r~ODIFICATION
OR REMOVAL OF COMPONENTS OF WHOLE BLOOD
BACKGROUND OF THE INVENTION
The processes of blood filtration and hemoperfusion
for purification of blood are well known. With few excep-
tions, the devices which are employed for these purposes arecapable of removing substances only in a nonspecific manner.
Removal of toxic or undesirable species from the blood is
accomplished on the basis of molecular size, as by dialysis
employing semipermeable membranes (see U.S. Patent No.
3,619,423); on the basis of ionic nature, as by perfusion
, over ion-exchange resins (see U.S. Patent No. 3,794,584;
4,031,010); or on the basis of affinity for adsorbents, as
i by perfusion over activated charcoal. These techniques
exhibit severe limitations arising from lack of specificity.
Within the fraction removed from the blood are hormones,
nutrients, drugs, electrolytes, and other species, whose
deletion from circulation may well result in adverse effects
upon the perfused patient. Since patients requiring such
treatment are suffering from drug overdose, renal or hepatic
i 20 failure, or other conditions severely diminishing their
- vitality, further metabolic imbalance may be poorly tolerated.
A further disadvantage of lack of specificity in hemoperfusion
devices is the limited capacity for the target species. The
target species must compete with other substances for the
available binding sites on the adsorbent. Such devices must
be inordinately large to ensure sufficient capacity for the
target species.
In addition to the nonspecificity problems exhibited
by these devices, further cornplications have arisen with
respect to structure and 1OW properties. Damage to formed
I elements and macromolecular components of the blood, by
i hemolysis, platelet aggregation, fibrin formation, and
leukocyte destruction, for example, are often observed when
blood is exposed to nonbiological surfaces or to turbulent
flow. Heparinizing patients is only partially effective in
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preventing such damage. Hemoperfusion devices incorporating
randomly dispersed particulate adsorbents have shown a
propensity to pack under flow conditions. The result is an
excessive pressure drop and diminished flow across the device.
Blood damage increases under such conditions.
Many attempts have been made to overcome these
problems and to design devices that exhibit specificity and
applicability and to a wider range of molecular species, in
particular high-molecular-weight species. Some synthetic
matrices which have been examined show specific affinity for
particular solutes. One such device employs fluorocarbon
plastics for the specific removal of endotoxin. (U.S. Patent
No. 3,959,128)
; Further specificity has been achieved by the use of
bioactive substances bound to inert organic or inorganic
materials in hemoperfusion systems. Examples of this type
are the following. The affinity of bilirubin and chenodeoxy-
cholic acid for serum albumin has been exploited by several
researchers. The antigen-antibody interaction has also been -
employed (Canadian Patent No. 957,922). Immobilized antigenshave been perfused with blood to remove antibodies to ~SA,
¦ to DNA, to HSA and ovalbumin, to blood factor VIII, and to
immunoglobulin fractions IgG and ImG. Immobilized antibodies
(IgG IgM) have been employed in hemoperfusion systems to
diminish circulating levels of drugs and endogenous species.
Antibodies to digoxin, to DNA, to BSA, to tumor-associated
antigens, and to donor-kidney antigens and multiple myeloma
protein, and low-density lipoproteins have been immobilized
in extracorporeal systems for a variety of therapeutic
purposes.
; Among the enzymes, cell extracts, and whole cells
that have been immobilized in extracorporeal systems (Canadian
Patent No. 957,922) are urease, uricase, aspariginase, pan-
creatic cells, liver cells, and liver microsomes, nuclease,
and catalase.
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88
The properties of materials and devices brought
into contact with circulating biological fluids have been
extensively studied. Weetall et al. have listed the follow-
ing criteria as a checklist in device design: "Some In Vivo
and In Vitro studies of Biologically Active Molecules on
Organic Matrixes for Potential Therapeutic Applications" in
Biomedical Applications of Immobilized Enzymes and Proteins,
T.M.S. Chang, Ed., Plenum Press, New York, N. Y. "1) laminar
flow, 2) velocity gradient should exceed 350/sec, 3) material
in contact with blood should be relatively nonthrombogenic,
4) smooth surfaces should be maintained, 5) minimum flow
channel diameter of about 100 um, 6) avoidance of crushing
- or grinding action of support material." Two further
` criteria are of considerable importance: 1) maximum loading
of active blood altering species per unit of priming volume,
and 2) minimal resistance to active contact of said species
with the blood component to be altered, i.e. contact should
require a minimum of diffusion-controlled transport and the
transport should be through minimally resistant matter.
To date all hemoperfusion systems employing highly
specific detoxifying species isolated within the device have
employed one of four arrangements: 1) isolation of the
- detoxifying species by partitioning it from the perfusing
blood, employing semipermeable membranes (e.g. U. S. Patent
25 No. 3,619,423) or hollow-fiber tubes; 2) encapsulation in
or attachment to particulate materials (e.g. U. S. Patent
No. 3,865,726); 3) attachment of the species to a nonporous
membrane or other planar surface (e.g. U. S. Patent No.
3,959,128); or 4) attachment to the internal surface of
polymeric tubes through which blood is passed (e.g. Canadian
Patent No. 957,922?.
None of these systems meets all of the criteria
listed above. Semipermeable membrane and hollow-fiber
` devices impose strong diffusion requirements for active
participation of isolated elements and are limited to
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activity with low-molecular-weight species in the blood.
Devices employing particulate components in which the active
species is microencapsulated or sequestered within the pores
of the support suffer from the same limitations of diffusion
resistance, and additionally exhibit flow resistance due to
packing, as well as blood damage arising from the grinding
action of particulate movement. Nonporous planar surfaces
and polymeric tubes have low surface area and thus insuffi-
cient capacity for active elements.
An alternative to these arrangements is the use of
fiber-filled cartridges. Fibers have long been employed in
blood contacting devices for removing aggregates of blood
components during transfusion (e.g. U.S. Patent No.3,462,361).
Polymeric fibers having pyrolytic carbon deposited on their
surface and deployed in a random mass have been employed as
nonspecific adsorbants in hemoperfusion (e.g. U.S. Patent
No. 3,972,81a). Antibodies and other proteins have been
incorporated into cellulose fibers by entrapment, for appli-
cation in radioimmunoassay and for industrial use (e.g. U.S.
Patent No. 4,031,201). Antigens have been attached to nylon
catheters and inserted into arteries for the removal of
antibodies from the circulation.
- In the art of hemoperfusion, devices designed for
highly specific alteration of blood composition and contain-
ing fibers have been employed with limited success. Hersh
and Weetall (supra) used a cartridge containing bio-active
I molecules bound to randomly dispersed, nonporous, polyester
! fibers. Both enzymes and antibodies have been immobilized
by their technique. These devices represent a significant
improvement over previous he~operusion systems with respect
to minimizing damage to formed elements of the blood. Some
problems with this design still remain however. Unanchored,
randomly dispersed fibers tend to pack under the desired
flow rates when sufficient fiber is available to furnish
the requisite amounts of the bound active species. Further-
more, channeling (uneven distribution of flow) which is
88
inevitable with this fiber arrangement results in diminished
efficiency for the device.
Antibodies attached in a rigidly fixed 2-dimensional
array have been described and employed for the removal of
whole cells from blood in vitro (e.g. U.S. Patent No.3,843,324).
This system, however, would not be applicable to hemoperfusion.
Polymeric fibers having carbon particles encapsu-
lated within the polymer and being deployed in a nonrandom
fashion within a hemoperfusion cartridge have been described
10 by Davis et al. (Trans. Amer. Soc. Artif. Int. Org. 20:353).
Although limited to application in nonspecific adsorption,
this device exhibited superior properties with respect to
capacity, cost, flow properties, and diminished damage to the
perfusing blood.
BRIEF SUMMARY OF THE INVENTION
According to the present invention the problems
discussed herein are avoided by a 3-dimensional arrangement
of fibers to maximize the exposed fiber surface and the flow-
channel diameter and to reduce the tortuosity of the flow
path.
The hemoperfusion device of the present invention
exhibits many features of the device described by Davis but
- has been extended and modified to allow its application to
highly specific alteration to biological fluid composition.
The fiber cartridge employs a fixed, nonrandom, three-
dimensional array of fibers whose chemical composition is
such that additional chemical species may be grafted onto
the surface or encapsulated within the matrix of the fibers.
The additional species are fixed in such manner that they may
efficiently effect highly specific alterations upon biological
fluids perfused through said cartridge. It is a further
purpose of this invention to disclose generalized formulations
and processes by which said cartridge may be manufactured.
Lastly it is the purpose of this invention to disclose appli-
cations of said cartridge to effect the removal, collection,
1~51~88
degradation, or modification of chemical species contained inbiological fluids perfused through said cartridge.
According to the invention there is provided a
hemoperfusion device comprising an elongated housing of impermeable
material, closed at its ends by means of impermeable end plates,
said housing on its interior having a plurality of axial ribs
extending substantially throughout the length thereof, an inlet
port in one of said end plates, an outlet port in the other of said
end plates, said ribs continuing radially in said other of said
end plates, an impermeable spindle axially disposed in said
housing and having axially disposed grooves in its periphery, a
conical port secured to one end of said spindle and in communication
with said inlet port and with said grooves, said spindle at its
other end terminating in a conical tip axially disposed with
respect to said outlet port with an annular space therebetween,
and a spool of fiber helically wound on said spindle to sub-
stantially fill the interior of said housing to said ribs, whereby
blood entering said inlet port flows along said spindle grooves,
passes through said fiber spool, flows along the inside of said
housing between said ribs, and thence between said conical tip and
said outlet port, said fiber having attached thereon specific
effector molecules having activity to remove biological fluid
components of endogenous or exogenous origin from blood being
perfused through said device.
BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWING
-
Figure 1 is a cutaway perspective view of an assembled
hemoperfusion cartridge.
Figure 2 is a perspective view of the spindle for the
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cartridge.
DETAILED DESCRIPTION
The present invention consists generally of a fixed 3-
dimensional array of fibers contained within a housing, which
provides for a continuous flow of fluid through the housing with
maximum contact between fluid and fibers. Further it is a property
of this device that specific bioactive effector molecules can be
bound to the fibers thus to allow the effector molecules to contact
target components of the fluid and thus alter the composition of
the fluid.
Fibers - Necessary Properties, and Suitable Categories.
The art of attaching biologically active molecules to
insoluble materials is well known. The specific insoluble
materials applicable to the present invention are defined by several
criteria: 1) the material must be able to be formed into fibers
strong enough for processing into a three-dimensional array; 2)
the fibers must be essentially insoluble under neutral aqueous
conditions; 3) the fibers should possess a smooth nonporous surface
to reduce blood damage and decrease nonspecific adsorption; 4)
the fibers must release no toxic substances or fragments into the
aqueous media percolating through them; 5) the degree of bio-
compatibility of the fiber composition should be commensurate with
the intended application. For long-term or chronic applications
in hemoperfusion, the fiber must cause no irreversible cumulative
deleterious alterations of the quantity or vital capacity of
circulating species. In short-term or emergency applications, the
fibers need only permit efficient passage of heparinized or otherwise
-6a-
1151~88
anticoagulated blood without the occurrence of thrombosis
or hemolysis beyond the limits of the patient's vital
capacity. 6) The fibers employed must exhibit properties
which will allow the nonreversible attachment or englobement
of the active species. The preferred fibers would be those
shown to be substantially compatible for implantation within
the body. Such fibers may be chosen from one of the follow-
ing categories: 1) substances of biological origin or pro-
ducts arising from them, i.e., cellulose, perfluoroethyl
cellulose, cellulose triacetate, cellulose acetate, nitro-
cellulose, dextran, chitin, collagen, fibrin, elastin,
keratin, crosslinked soluble proteins, polymerized soluble
organic species of biological origin (polylactic acid,
polylysine,nucleic acids), silk, rubber, starch, and hydroxy-
ethyl starch; 2) heterochain synthetic polymers, such aspolyamides, polyesters, polyethers, polyurethanes, poly-
carbonates, and silicones; 3) hydrocarbon polymers such
as polyethylene, polypropylene, polyisoprenes, polystyrenes,
polyacrylics such as polyacrylamide, polymethacrylate, vinyl
polymers such a polyvinylacetate, and halogenated hydrocarbon
; plastics such as polyvinylcholoride, polyfluorocarbons like
Teflon, fluorocarbon copolymers and polychlorotrifluoro-
~ ethylene; 4) inorganic fibers such as fiberglass.
The above examples of polymers vary widely in their
blood compatibility. Several techniques have been described,
however, which modify the blood compatibility of otherwise
unacceptable materials, among these are coating the materials
with more compatible substances (e.g. U.S. Patent No.
4,073,723) or with antithrombogenic substances such as
heparin.
Fiber Configuration and ~Iousing.
Fiber dimension and the specific 3-dimensional
array of fibers within the cartridge will determine the flow
properties, available polymer surface area, and priming
volume exhibited by the device. The last two conditions
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will be optimized when the fiber diameter is at the minimum
value yielding sufficient strength and when the fiber array
is chosen to yield a maximally compact bed. The flow pro-
perties will be affected in the opposite manner to that of
available surface area and priming volume. These conditions
must then be adjusted in order to optimize the overall
efficiency with minimal blood damage.
The deployment of the fixed fiber array between
the inlet and outlet of the cartridge jacket may be chosen
from innumerable configurations. Among the more convenient
configurations are the following. 1) Deployment of fibers
by winding about the outlet or inlet port. Such configura-
tions may possess cylindrical symmetry about a tubular port
having means for influx or efflux of fluid along the length
of the tube. In another possible configuration of wound
fibers, the fibers may be woundwith spherical symmetry
about a single central port. 2) In cartridges wherein the
fluid flows axially through the cartridge, the fibers may be
deployed parallel to the direction of flow, being attached
at each end of the cartridge. Another configuration
employing an axial flow cartridge may have the fibers
deployed transversely to the flow of blood by attachment
of the fibers to the lateral portions of the cartridge.
A combination of parallel and transverse configuration may
also be employed in which the fibers may be attached at
both the ends and the lateral portions of the cartridge
thus deployed in an interwoven fashion.
Fibers may be deployed as monofilaments or as
multifilament yarns, and the device may contain one continu-
ous fiber or numerous fibers. It is required only that theconfiguration of the cartridge housing and fiber deployment
be consistent with fluid dynamics, compatible with minimal
damage to the formed fluid components perfused through the
device. These restrictions are well known to those skilled
in the art.
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g
Effec-tor Molecules.
The highly specific effector molecules having
activity toward biological fluid components of endogenous or
exogenous origin, and being attached to the fibers within the
device, may be selected from one or more of the following
species. The molecules may be all or a fragment of an anti~
body, antigen, allergin, complement factor, clotting factor,
enzyme, substrate of an enzyme, cell surface receptor mole-
cule, vaccine, enæyme inhibitor, hormone, tissue homogenate,
purified protein, toxin, nucleic acid, polysaccharide, lipid,
intact cell, microcapsule, liposome, polymer, antibiotic,
chemotherapeutic agent, therapeutic drug, organic species
having high affinity for a specific biological fluid compo-
nent, or an inorganic species having high affinity for
specific biological fluid component.
Means of Attachment of Effector Mole~cule to Fiber.
.
The chosen effector molecule may be bound to the
device by means well known to those skilled in the art,
particularly for immobilized enzymes (e.g. U.S. Patent No.
20 4,031,201), affinity chromatography (e.g. U.S. Patent No.
3,652,761), solid phase immunoassay (e.g. U.S. Patent No.
4,059,685), bonded stationary phase chromatography hemoper-
- fusion (e.g. U.S. Patent No. 3,865,726), enzyme-linked
immune-sorbant assay, cell labeling and separating, and
25 hemodialysis (e.g. Canadian Patent No. 957,922).
Attachment of the effector molecule to the fibers
may be performed during polymer preparation, fiber spinning,
just prior to placement of said fibers into the cartridge,
or following the deployment of the fibers in the cartridge.
Cartridges may be stored dry after lyophilization
or filled with a buffer containing antimicrobial agents.
Sterilization of the device may be performed prior to the
incorporation of the active species onto the fibers with all
subsequent steps performed with sterile reagents, or sterili-
zation may be performed following the incorporation.
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The Cartridge.
The assembled cartridge is composed of a glass or
plastic jacket 1, capped at one end by a circular glass or
plastic disk 2, and at its other end by a similar disk 2a.
The disk 2 has at its center a cylindrical exit port 3. The
jacket and cap have raised elements in the form of ribs 4
allowing for the unhindered axial flow of fluid along the
surface of the jacket and cap, and allowing the exit thereof
via the port. Within the jacket is a spool of fiber 5,
- 10 helically wound about a glass or plastic spindle 6. The
spindle and fiber fill the entire volume of the jacket with
the exception of the space between ribs.
FIG. 2 shows the spindle 6 which is a glass or
plastic rod which is conical at its base 7 and is slotted
along its length as at 8. The rod is fitted at its top into
a,conical port 10, which is attached to the circular spindle
cap of like composition 2a. The diameter of the cap is
chosen so that it makes a tight fit with the jacket and forms
a sealed vessel when the spindle is inserted into the jacket.
The external surface of the spindle cap has affixed to it a
cylindrical entrance port 11 which is opposed to the conical
port 10 and has an internal diameter which allows access of
fluid passing through it to the slots 8 of the spindle 6.
~, Furthermore, the conical base of the spindle is of dimensions
such that placement of the spindle base into the exit port
results'in contact of the spindle only with the ribs 4 of
the jacket cap. This allows the fluids which accumulate
between the ribs to exit through the lumen between the
conical base 7 of the spindle 6 and the exit port 3. Thus,
when the spindle is wound with a iber, the flux of fluids
entering through the device is that denoted by the arrows
in FIG. 1.
The fiber wound about the spindle is a monofilament
having a diameter'in the range 0.05 to 2.0 mm. It is com-
posed of hydroxyethyl cellulose (HEC). Following the
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incorporation of the wound spindle into the housing, thedevice is sealed and filled with dioxane containing 20%
of hexamethylenediisocyanate. The fibers are allowed to
stand for 48 hours at room temperature and are then washed
with distilled water. This operation generates a fiber coil
exhibiting covalently bound primary amines on its surface.
The distilled water is then replaced by an aqueous solution
containing 0.25% of IgG and 1% of water-soluble carbodimide,
pH 5.5. The IgG may have been acylated to eliminate
endogenous primary amines. Following 24 hours of exposure to
this solution, the device is washed exhaustively with
distilled water and sterilized for use in in vivo perfusion
applications.
Modifications may be made in details of the
invention and therefore no limitation which is not specifi-
cally set forth in the claims is intended and no such
limitation should be implied.
