WO1993011807A1

WO1993011807A1 - Biphasic foam blood mass transfer device

Info

Publication number: WO1993011807A1
Application number: PCT/US1992/010795
Authority: WO
Inventors: Leonard A. Trudell; Anthony D. Whittemore
Original assignee: Brigham And Women's Hospital
Priority date: 1991-12-13
Filing date: 1992-12-14
Publication date: 1993-06-24

Abstract

The present invention relates to apparatus for transferring constituents into and out of a fluid such as blood. The apparatus may be in the form of a blood oxygenator (10) configured with a foam cylinder (16) potted within a housing (18). The blood can enter through either access port (12) and flow through the oxygenator (10) while the oxygen can enter/exit through either access port (14), as the design is symmetrical.

Description

Title Of The Invention

-lasic Foam Blood Mass "er Device

Field of the Inve .

The presc r-t invention relates to apparatus for transferring constituents into and out of blood. More particularly, the invention uses a biphasic foam as a blood oxygenator or dialyzer.

Background of the Invention

The field of this r -ition is blood mass transfer devices, particularly oxygenators, wherein some desirable constituent (e.g., oxygen) is transferred into the blood and/or some undesirable consti: it (e.g., carbon dioxide) is transferred out of the blood. Three basic types of oxygenators have developed over time: film oxygenators (e.g., U.S. Patent No. 3,070,092); bubble oxygenators (e.g., U.S. PatentNos. 3,915,650 and 4,428,934); and membrane oxygenators (e.g., U.S. Patent No. 4,698,207).

Film oxygenators are characterized by exposing a continuous thin .film of blood to an oxygen atmosphere. The surface upon which the blood is 5 filmed must be chemically inert and not damage the blood. Additionally, the surface must sustain a very thin film in order to maximize the diffusion of

oxygen into the blood. In bubble oxygenators, oxygen is introduced into the blood as bubbles which oxygenate the blood and drive off carbon dioxide. In these oxygenators, the bubbling or foaming mixture must be passed through 10_. a "defoamer" to eliminate gas bubbles from the oxygenated blood before it is returned to the patient. In a typical membrane oxygenator, blood is carried in or around hollow membrane fibers. Oxygen passes through the membrane from an oxygen-rich gas stream to the bloodstream, and carbon dioxide passes through the membrane from the blood to the gas stream. The number and size 5 of the hollow membrane fibers are selected to transfer sufficient oxygen to

satisfy the metabolic requirements of the patient. Before the blood is returned

to the patient from the membrane oxygenator, it is usually passed through a filter to remove any particulate emboli or gas bubbles. The filter is usually

in the arterial line outside of the oxygenator itself. 0 Various types and configurations of foam have been used for specific

purposes in bubble and film oxygenators. Blood oxygenators which use foam material to "defoa " the blood-oxygen mixture, i.e., remove bubbles from the blood, are well known as illustrated by the blood oxygenator in U.S. Patent No. 4,158,693 to Reed et al. Foam material is also used in the Reed et al. bubble oxygenator to provide an enlarged surface area for oxygen-blood

contact, and to disperse the blood so it will rise uniformly through the

oxygenating chamber. The film oxygenator in U.S. Patent No. 3,070,092 to Wild et al. uses a porous sponge material as the surface on which the blood is filmed. None of these types of oxygenators contemplates using a foam material as both the blood pathway and the membrane across which oxygenation occurs.

Certain parameters must be considered when designing an oxygenator, whether of the film, bubble, or membrane type. Parameters which must be considered include the overall size and geometry of the oxygenator, blood volume that can be oxygenated, damage to the blood, the rate of gas exchange, and the volume of blood physically held by the oxygenator (known as "priming volume").

The physical size of an oxygenator is determined in large part by the effective exchange surface area, that is, the exchange surface area the blood

is exposed to for oxygenation. The total volume of blood that can be oxygenated must be sufficient to satisfy the metabolic requirements of a patient. As discussed in U.S. Patent No. 4,698,207 to Bringham et al., this can require using 41,000 to 71,000 hollow fibers in a hollow fiber membrane

oxygenator. In order to minimize the size of a blood oxygenator, a large

exchange surface area must be contained in a small volume. As a result, the exchange surface area may have to assume intricate geometries which is made difficult by the structures of conventional membrane oxygenators. Intricate geometries are also difficult to achieve with conventional film and bubble oxygenators, as illustrated by the grid of plates in the film oxygenator in U.S. Patent No. 3,070,092 to Wild et al. and the aluminum oxygenator tubes in

5 U.S. Patent No. 4,280,981 to Harnsberger.

Blood is a very delicate body tissue and is damaged when handled and exposed to foreign surfaces and gas atmospheres. Requiring the blood to flow through or around fibers or through tubes composed of substances such as aluminum or styrenes physically damage the blood by denaturation of proteins

10. and mechanical damage to cells and formed elements.

In film and bubble oxygenators, the oxygen diffuses directly into the blood from the oxygen-rich atmosphere; carbon dioxide diffuses out of the blood to that atmosphere. In the membrane oxygenator, the oxygen and carbon dioxide diffusion take place across a permeable membrane. The design 5 of the oxygenator, e.g., choice of membrane material, should maximize the rate of gas exchange, that is, the rate of absorption of the oxygen by the blood

without exposing the blood directly to a gas atmosphere.

It is apparent that a blood oxygenator which maximizes the rate of gas exchange may require a large exchange surface area and oxygenator volume, 0 and may also damage the blood. The design parameters conflict such that optimizing one parameter may degrade another. Therefore, the problem remains to optimize all the parameters to design a blood oxygenator that has

a large exchange surface area per unit volume, can take on different geometries, minimizes damage to the blood, and maximizes the rate of gas exchange.

The same conflicting parameters exist for other mass transfer devices,

such as dialyzers. Dialyzers perform the function of removing metabolic waste products without removal of essential constituents such as proteins. The problem to be solved here, analogous to that of blood oxygenators, is to

design a dialyzer which has a large exchange surface area per unit volume, can take on different geometries, minimizes damage to the blood, and

maximizes the rate of removal of the waste products from the blood. Accordingly, prior to the development of the present invention, no single blood mass transfer device provided a large exchange surface area in a small volume capable of different geometries, and which minimized damage to the blood while providing a high rate of mass transfer. It is therefore an object of the present invention to provide a mass transfer device which has a large exchange surface area in a small volume, and which minimizes damage to the blood while achieving a high rate of mass transfer. It is a further object of this invention to provide a blood oxygenator which has a large exchange surface area in a small volume, and which minimizes damage to the blood

while achieving a high rate of gas exchange. It is a further object of this invention to provide a blood dialyzer which has a large exchange surface area

in a small volume, and which minimizes damage to the blood while achieving a high rate of molecular transport. It is a feature of this invention to use a pliable foam material in the mass transfer device as both the blood pathway and the membrane across which the transfer occurs. It is an additional feature of this invention that the blood mass transfer devices can take on varied and intricate geometries to satisfy the requirements of the particular application.

Summary of the Invention

The present invention is a device for facilitating the exchange of

constituents into and out of a fluid such as blood. The device includes a body of a pliable open-cell foam material. The open-cell structure forms channels through which the blood flows. These channels are formed of inter-connecting cells within the foam body lined by a skin (or membrane) which forms as a consequence of the manner in which the material itself polymerizes. The paths of these channels through the foam body are random and very varied or

"tortuous." When blood is the fluid flowing through the channels, a polyurethane foam is preferable due to its excellent blood handling properties.

The rest of the cells in the foam body are open and not sealed by the foam membrane; these cells constitute the matrix of the material. In one aspect of the invention, these cells form a gas pathway to allow oxygen to migrate throughout the foam material and across the membrane into the blood

while allowing carbon dioxide to migrate across the membrane out of the

blood. Porous fibers can be used in the gas pathway portion of the foam body to more efficiently distribute oxygen throughout the foam body. The porous fibers are contained within the foam matrix and do not come in contact with blood. Alternatively, a gas distribution foam can be used in the gas pathway portion of the foam body to more efficiently distribute oxygen throughout the foam body.

When configured as a blood oxygenator, a hydrophilic ("wettable")

foam can be used so that water from the plasma portion of blood wets the membrane. Oxygen and carbon dioxide are both carried in aqueous solution, dissolved in the water portion of plasma, and are therefore easily transferred across the membrane.

In another aspect, the unsealed cells form a dialysate pathway for _ transport of molecules out of the blood. The blood flows through the skinned

channels and the molecules migrate across the skin membrane from the blood into the dialysate.

In a third aspect of the invention, the fluid flowing through the skinned channels can be a fluid other than blood. The unsealed portion of the foam

body can then contain a gas, or another fluid, so that the gas or fluid constituents will migrate across the membrane into or out of the fluid in the skinned channels.

Brief Description of the Drawings

Various objects, features, and advantages of the present invention will be more fully appreciated as the same becomes better understood from the following detailed description of the present invention when considered in connection with the accompanying drawings, in which:

FIGURE 1 shows a blood oxygenator comprising the foam material configured as a cylinder; FIGURE 2 shows a cross section of a foam cylinder taken along line

2-2 in FIGURE 1;

FIGURE 3 shows an enlarged cross section of a foam cylinder taken along line 3-3 in FIGURE 1;

FIGURE 4 shows a highly enlarged cross section of a porous fiber which distributes oxygen throughout the foam cylinder;

FIGURE 5 shows a cross section of a blood channel illustrating the diffusion across the skin membrane; and

FIGURE 6 shows a cross section of a foam cylinder taken along line 2-2 in FIGURE 1, illustrating the use of an alternate embodiment for the distribution of oxygen throughout the foam cylinder.

Detailed Description of the Drawings

With continuing reference to the drawing figures in which similar reference numerals are used throughout the description to describe similar features of the invention, FIGURE 1 shows a blood oxygenator 10 configured with a foam cylinder 16 potted within a housing 18. The blood can enter

through either access port 12 and flow through the oxygenator while the oxygen can enter/exit through either access port 14, as the design is

symmetrical.

The blood oxygenator 10 in FIGURE 1 receives oxygen-poor (venous)

blood from the patient into access port 12 through devices and tubing which are well known in the blood oxygenator art. Similarly, once the blood has

been oxygenated, the oxygen-rich blood is returned to the patient via well known devices. The oxygen source which is connected to the blood oxygenator 10 at access port 14 is also one commonly used in blood

oxygenation. FIGURE 2 shows a cross section of the foam cylinder 16 from

FIGURE 1. The foam cylinder comprises two series of voids which constitute two distinct phases or portions of the foam. The first portion comprises the large voids which form the blood channels or blood pathway 30. The large

voids are interconnected and "skinned" with the foam material to form a skinned layer or membrane 20 on the voids, thus forming channels. These channels take on random, tortuous paths and define blood channels or blood pathway 30. Due to the random, tortuous paths of the blood channels 30, the blood pathway confines a large surface area in a small volume.

The second portion of the foam cylinder 16 comprises the smaller voids of cells in the foam body which are not "skinned"; these cells constitute the

matrix of the material. Some cells in this portion may be interconnected, but

all the cells in this portion are unsealed and form the gas pathway 40 for the delivery of oxygen to and removal of carbon dioxide from the blood. To minimize gas diffusion distances, hollow porous fibers 50 carry the gases throughout the foam cylinder to cut down the diffusion distance between the source of the gas and the blood pathway 30. The porous fibers 50 are shown in FIGURE 2 and FIGURE 3 as perpendicular to the blood pathway 30. However, the porous fibers are not restricted to such a configuration and could be parallel or at any angle to the blood pathway.

FIGURE 3 shows a vertical cross section of the foam cylinder 16

which illustrates the random and tortuous nature of the blood pathway 30. The porous fibers 50 serve to distribute the gas within the foam cylinder to minimize the diffusion distance. The porous fibers are contained within the foam matrix and do not come in contact with blood. Without the porous fibers, oxygen would have to diffuse from the source on one side of the foam

cylinder, shown at 14 in FIGURE 1, all the way through to the other side. The porous fibers act as a ventilation system to deliver the oxygen and remove the carbon dioxide throughout the foam cylinder more efficiently.

As shown in FIGURE 4, the fibers 50 are porous, thus allowing molecules to pass into and out of the gas channel 52 through the pores 54. In

the preferred embodiment, the fiber is hydrophobic ("non-wettable") so no fluids pass into the fiber channel, with pore size sufficient to allow molecules

of oxygen and carbon dioxide to easily exit and enter the porous fibers. For example, porous fibers made of polyacrylonitrile can be used, such as the DIAFLO™ ultra-filter XM50 sold by Amicon, which has a pore size of 50,000 amu (atomic mass units). FIGURE 6 shows an alternate embodiment for distribution of the gas within the foam cylinder. As shown in FIGURE 6, a second open cell foam is used to create a gas distribution pathway 80 within the oxygenator. ^■ The

second open-cell foam can be made in the same manner and from the same type of material as the first foam. However, the second foam is preferably of

a different formulation so that it forms smaller cells. As shown in FIGURE 6, the first foam contains skinned membrane cells 42. The second open cell foam forms smaller skinned membrane cells 82 which are contained within

cells 42. The skinned membrane cells 82 form a blood channel or pathway 30. Because cells 82 of the second foam are smaller than the cells 42 of the first foam, there will be a physical interstitial space or interface created between the cells 82 of the second foam and the cells 42 of the first foam.

This interstitial space forms a gas distribution pathway which has an extremely high surface area in a small volume for distributing oxygen or other gasses throughout the foam cylinder.

The density and porosity of the second foam are selected so that it forms cells smaller than those in the first foam. To form this embodiment, a

first foam is produced, in the manner described below, which contains the

larger cells 42. The second foam is then foamed through the first foam. The first foam can be coated to prevent the second foam from sticking to it during

the foaming of the second foam. As a result of the foaming process, the cells 82 of the second foam are contained within the cells 42 of the first foam. The

interstitial space between the cells 82 and the cells 42 forms a gas distribution pathway for distribution of the oxygen throughout the cylinder. In this embodiment, distribution of the oxygen is not limited by the surface area of the fibers 50 used in the embodiment illustrated in FIGURE 2.

FIGURE 5 illustrates the process by which oxygenation takes place within the foam cylinder. A blood channel 30, defined by the skinned membrane 20, is shown in FIGURE 5. As the skinned membrane is hydrophilic, the aqueous components of the blood wet the skinned membrane

to form a matrix wetted with water 22. As oxygen is soluble in water, the

oxygen from the surrounding gas pathway or gas phase of the foam cylinder dissolves in the water of the wetted membrane 22 as shown by the arrow 60. Similarly, carbon dioxide is also soluble in water, and the carbon dioxide in the blood channel 30 also dissolves in the water of the wetted membrane 22

as shown by the arrow 70. In this manner, water becomes the functional membrane and serves as the gas transport medium. Once dissolved in the water, oxygen will then migrate into the blood and carbon dioxide will migrate into the surrounding gas phase as a result of the diffusion gradient since both gases will be moving from an area of high concentration to an area of low concentration. More particularly, carbon dioxide is in high concentration in the blood and oxygen is in high concentration in the gas phase of the foam

cylinder. Therefore, a diffusion gradient is established such that oxygen will

migrate from the gas phase into the blood in the blood channel, and carbon dioxide will migrate from the blood in the blood channel to the gas phase of the foam cylinder. The wetted membrane 22 allows this transfer to take place across the membrane due to the solubility of the two gases in water.

In the preferred embodiment, the foam cylinder, or other foam body,

is comprised of a hydrophilic, polyurethane open cell foam such as HYPOL™ 5100. HYPOL™ foams are commercially available from W.R. Grace & Co. HYPOL™ foams have excellent blood handling properties. They are biocompatible in that there is little chemical reaction with the blood or tissues, or extraction into the blood of foreign material such as plasticizers. HYPOL™ 5100, configured as a foam cylinder as shown in FIGURE 1, can be used with

pressures comparable to human blood pressure, and above human blood pressure, as may be found in heart-lung machine circuits.

HYPOL™ polymers are a family of foamable hydrophilic polyurethane prepolymers derived from toluene diisocyanate or methylene

diphenylisocyanate (MDI). HYPOL™ 5100 is one of the HYPOL™ Plus MDI- based prepolymers. In the production of polyurethane foams, excess

isocyanate groups in the polymer react with water to produce carbon dioxide which "blows" the foam at the same time that crosslinking is occurring. This results in a crosslinked product containing bubbles of trapped carbon dioxide. The "skin" forms as a consequence of phase interface phenomena because the

gases that "blow", or form, the foam structure are generated by chemical reaction between thepre-polymer and solvent (water) within the material itself.

, The porous fibers used to carry the gases in the blood oxygenator embodiment are placed in with the reactants prior to adding the water or carboxylic acids so that the reaction occurs around the porous fibers. In this way, the foam forms around the fibers, so that the fibers are included in the matrix of the foam. Additionally, surfactants such as silicone or Pluronic L-62 and P-75 (BASF Wyandotte Corporation) are added so that the bubbles formed

during the "blowing" process result in a three dimensional array of sealed, connected voids. The sealed, connected voids form random channels, each of which takes a tortuous path. As a result, the foam body comprises a multiplicity of channels containing a large surface area in a small volume. The second foam used in the embodiment shown in FIGURE 6 is formed in like manner. Although the Figures show a foam cylinder, the foam can be

produced in varied and intricate geometries and still comprise a multiplicity of channels containing a large surface area in a small volume.

When configured as a blood oxygenator, the blood travels in the skinned channels and the second portion of the foam body contains the gas

pathway, with diffusion of oxygen and carbon dioxide occurring across the

skin membrane. In one embodiment, fibers are used to distribute the oxygen throughout the oxygenator. In another embodiment, a gas distribution pathway created through use of a second open cell foam is used to distribute the oxygen throughout the oxygenator. The foam body can also be configured to perform dialysis by making a minor modification to the polymer molecular weight of

the HYPOL™ foam. The foam with the modified molecular weight retains its blood handling properties and the blood still flows through the skinned channels. However, the second portion of the foam body, the matrix, becomes a dialysate pathway rather than a gas pathway.

Dialysate is a solution of electrolytes and other naturally occurring

solutes at concentrations normally found in the blood at physiologic concentration. The molecules of metabolic waste products (e.g., excess

sodium or excess potassium, urea, creatinine, etc.) will migrate across the skinned membrane from the blood to the dialysate phase because of the concentration gradient established. That is, the concentration in the blood of

sodium, potassium, and metabolic waste products is higher than the concentration in the dialysate phase of the foam body. Waste products from the blood (e.g., creatinine, urea, etc.) will migrate across the membrane from the blood in the blood channel into the dialysate phase of the foam body

because of the concentration gradient. That is, the concentration of waste products in the blood is higher than the concentration of the waste products in the dialysate phase of the foam body. The molecular weight and resulting porosity of the foam are selected to allow transport across the membrane of

low and middle molecular weight molecules, but not protein molecules, which are large, complex molecules, and which must be retained within the blood.

The invention which is intended to be protected herein should not be construed as limited to the particular forms disclosed, as these are to be regarded as illustrative rather than restrictive. For example, the foam body could be used as any blood mass transfer device, and is not limited to use as an oxygenator or dialyzer, and the geometries of the foam body are not limited to a cylinder. Additionally, the foam body could be used as a mass transfer device between a fluid other than blood, and another fluid or a gas.

Variations and changes may be made by those skilled in the art without departing from the spirit of the invention. Accordingly, the foregoing detailed description should be considered exemplary in nature and not limited to the scope and spirit of the invention as set forth in the following claims.

Claims

What is Claimed is:

1. A blood oxygenator comprising: a body of hydrophilic, open-cell foam; a first portion of said body comprising cells, said cells forming a gas pathway; a second portion of said body comprising interconnected cells forming a channel, said channel forming a blood pathway;

a permeable membrane comprised of said foam separating said first portion from said second portion, wherein water from the blood in said blood pathway wets said membrane such that oxygen from said gas pathway dissolves in said water and carbon dioxide from blood in said blood pathway dissolves in said water, whereby oxygen is transferred across said membrane into the blood and carbon dioxide is transferred across said membrane out of the blood.

2. A blood oxygenator according to claim 1 , wherein said first portion is comprised of unsealed cells.

3. A blood oxygenator according to claim 2, wherein said first portion further

comprises a plurality of porous fibers for distributing oxygen within said body.

4. A blood oxygenator according to claim 1, wherein said second portion further comprises a plurality of said channels randomly disposed in said body,

wherein each said channel follows a tortuous path.

5. A blood oxygenator according to claim 4, wherein said first portion further comprises a plurality of porous fibers for distributing oxygen within said body.

6. A blood mass transfer device comprising:

a body of open cell foam; cells formed within said body defining a pathway through said body; interconnected cells formed within said body defining a channel within said body; and skin formed on said channel comprised of said foam wherein said skin is a permeable membrane separating said channel from said cells whereby said

skinned channel forms a blood pathway.

7. A blood mass transfer device according to claim 6, wherein said cells

are unsealed.

8. A blood mass transfer device according to claim 6, wherein said body

of open cell foam comprises hydrophilic foam.

9. A blood mass transfer device according to claim 6, wherein each said channel follows a tortuous path.

10. A blood mass transfer device according to claim 6, further comprising a plurality of said channels randomly disposed in said body.

11. A blood mass transfer device according to claim 6, further comprising

a plurality of said channels randomly disposed in said body, wherein each said channel follows a tortuous path.

12. A blood mass transfer device according to claim 6, wherein said body of open cell foam comprises polyurethane.

13. A blood mass transfer device according to claim 6, wherein said cells form a gas pathway whereby oxygen is transferred across said permeable membrane into the blood and carbon dioxide is transferred across said

permeable membrane out of the blood.

14. A blood mass transfer device according to claim 13, wherein said body of open cell foam comprises hydrophilic foam.

15. A blood mass transfer device according claim 13, further comprising

means for distributing oxygen within said body. - 20

16. A blood mass transfer device according to claim 15, wherein said means for distributing oxygen within said body comprises a plurality of porous fibers.

17. A blood mass transfer device according to claim 6, wherein said cells form a dialysate pathway whereby waste products move out of the blood in

said blood pathway.

18. A foam structure comprising: a first phase formed of cells disposed within said foam structure;

a second phase formed of interconnected cells disposed within said foam structure defining a channel; skin formed on said channel comprised of said foam wherein said skin is a permeable membrane separating said first phase from said second phase whereby said skinned channel forms a pathway.

19. A foam structure according to claim 18 wherein said foam structure comprises polyurethane.

20. A foam structure according to claim 18 further comprising a plurality of

porous fibers. 21. A blood oxygenator comprising: a body of hydrophilic, open-cell foam; a first portion of said body comprising a first foam having unsealed

cells and interconnected cells; a second portion of said body comprising a second foam having interconnected cells smaller than said first portion interconnected cells so that a gas distribution pathway is formed in the interstitial space between said first portion interconnected cells and said second portion interconnected cells, said second portion interconnected cel ^' arming a channel, said channel forming a blood pathway;

a permeable membran ^;sed of said second foam separating said blood pathway from said gas - pathway so that water from the blood in said blood pathway wets s. brane such that oxygen from said gas

distribution pathway dissolves vater and carbon dioxide from blood in said blood pathway dissolves water, whereby oxygen is transferred across said membrane into t . j and carbon dioxide is transferred across

said membrane out of the blooα.

22. A blood oxygenator according _i;r- 21 , wherein said second portion further comprises a plurality of said channels randomly disposed in said body, wherein each said channel follows a tortuous path. - 22 -

23. A blood mass transfer device comprising: a body of open-cell foam; unsealed cells within said body; first interconnected cells formed within said body; second interconnected cells smaller than said first interconnected cells so that a pathway is formed in the interstitial space between said first interconnected cells and said second interconnected cells, said second interconnected cells defining a channel within said body; and skin formed on said channel comprised of said foam wherein said skin is a permeable membrane separating said channel from said pathway whereby said skinned channel forms a blood pathway.

24. A blood mass transfer device according to claim 23, wherein said body of open cell foam comprises hydrophilic foam.

25. A blood mass transfer device according to claim 24, further comprising a plurality of said channels randomly disposed within said body, wherein each said channel follows a tortuous path. [received by the International Bureau on 15 April 1993 (15.04.93⁾ ; original claims 1-25 replaced " y amended claims 1-25 (6 pages⁾ ]

1. A blood oxygenator comprising:

a body of hydrophilic, open-cell biphasic foam; blood connection means connected to said body for transporting blood into and out of said body; a first phase of said body comprising cells, said cells forming a gas pathway; and a second phase of said body formed by a gas permeable membrane comprised of said foam which creates interconnected cells to define a channel within said body, said channel

forming a blood pathway, wherein said gas permeable membrane separates said channel from said first phase so that water from blood in said blood pathway wets said membrane such that oxygen within said gas pathway dissolves in the water and carbon dioxide from the blood in said blood pathway dissolves in the water, whereby oxygen is transferred across said

membrane into the blood and carbon dioxide is transferred across said membrane out of the blood.

2. A blood oxygenator according to claim 1, wherein said first phase of said body is comprised of cells not sealed by said membrane.

3. A blood oxygenator according to claim 2, wherein said first phase of said body further comprises a plurality of porous fibers disposed within said body for distributing oxygen within said body.

4. A blood oxygenator according to claim 1, wherein said second phase of said body further comprises a plurality of said channels randomly disposed within said body, wherein

each said channel follows a tortuous path. 5. A blood oxygenator according to claim 4, wherein said first phase of said body further comprises a plurality of porous fibers disposed within said body for distributing oxygen within said body.

6. A blood mass transfer device comprising: a body of biphasic, open cell foam; blood connection means connected to said body for transporting blood into and out of said body; a first phase of said body formed of cells within said body defining a first pathway through said body for gas; and a second phase of said body formed by a permeable membrane comprised of said foam which creates interconnected cells to define a channel within said body, said permeable membrane separating said channel from said first phase so that said channel forms a second pathway for blood.

7. A blood mass transfer device according to claim 6, wherein said cells of said first phase are not sealed by said membrane.

8. A blood mass transfer device according to claim 6, wherein said body of biphasic, open cell foam comprises hydrophilic foam.

9. A blood mass transfer device according to claim 6, wherein said channel follows a tortuous path. 10. A blood mass transfer device according to claim 6, further comprising a plurality of said channels randomly disposed within said body.

11. A blood mass transfer device according to claim 6, further comprising a plurality of

said channels randomly disposed within said body, wherein each said channel follows a tortuous path.

12. A blood mass transfer device according to claim 6, wherein said body of biphasic,

open cell foam comprises polyurethane.

13. A blood mass transfer device according to claim 6, wherein said permeable membrane is gas permeable so that oxygen is transferred across said permeable membrane into the blood and carbon dioxide is transferred across said permeable membrane out of the blood.

14. A blood mass transfer device according to claim 13, wherein said body of biphasic, open cell foam comprises hydrophilic foam.

15. A blood mass transfer device according to claim 13, further comprising means disposed within said body for distributing oxygen.

16. A blood mass transfer device according to claim 15, wherein said means for

distributing oxygen comprises a plurality of porous fibers. 17. A blood mass transfer device according to claim 6, wherein said permeable membrane is permeable to metabolic waste products so that waste products move out of the blood in said blood pathway.

18. A biphasic foam structure comprising: a first open-celled phase formed of cells disposed within said foam structure; and a second phase formed by a permeable membrane which creates interconnected cells

to define a channel within said foam structure.

19. A foam structure according to claim 18, wherein said foam structure comprises polyurethane.

20. A foam structure according to claim 18, further comprising a plurality of porous fibers disposed within said first phase.

21. A blood oxygenator comprising:

a body of hydrophilic, open-cell biphasic foam; blood connection means connected to said body for transporting blood into and out of said body;

a first phase of said body comprising a first foam, said first phase including a first gas permeable membrane comprised of said first foam which creates first phase interconnected cells and cells not sealed by said first gas permeable membrane; a second phase of said body comprising a second foam, said second phase including

a second gas permeable membrane comprised of said second foam which creates second phase interconnected cells which are smaller than said first phase interconnected cells so that a gas distribution pathway is formed in the interstitial space between said first phase interconnected cells and said second phase interconnected cells, said second phase interconnected cells defining a channel within said body, said channel forming a blood

pathway, wherein said second gas permeable membrane separates said blood pathway from said gas distribution pathway so that water from blood in said blood pathway wets said second gas permeable membrane such that oxygen within said gas pathway dissolves in the water, whereby oxygen is transferred across said second gas permeable membrane into the blood and carbon dioxide is transferred across said second gas permeable membrane out of the blood.

22. A ood oxygenator according to clam 21, wherein said second phase of said body further comprises a plurality of said channels randomly disposed within said body, wherein each said channel follows a tortuous path.

23. A blood mass transfer device comprising: a body of biphasic, open-cell foam;

blood connection means connected to said body for transporting blood into and out of said body;

a first phase of said body including a first gas permeable membrane which creates first phase interconnected cells;

a second phase of said body including a second gas permeable membrane which creates second phase interconnected cells which are smaller than said first phase

interconnected cells so that a gas distribution pathway is formed in the interstitial space between said first phase interconnected cells and said second phase interconnected cells, said second phase interconnected cells defining a channel within said body, said second gas permeable membrane separating said channel from said gas distribution pathway so that said channel forms a blood pathway.

24. A blood mass transfer device according to claim 23, wherein said body of biphasic, open-cell foam comprises hydrophilic foam.

25. A blood mass transfer device according to claim 24, further comprising a plurality of said channels randomly disposed within said body, wherein each said channel follows a tortuous path.