Leak prevention in blood oxygenators

A tight seal is achieved in a blood oxygenator between the potting of the heat exchanger fibers and the rim of the heat exchanger container by extending the potting material over the rim and down, so that when the potting material shrinks during cure, the potting will become prestressed in the sealing direction against an outwardly facing wall of the container. The invention also provides a ring coextensive with the rim and spaced therefrom. The potting extends into the ring. This forms an air gap between the rim and the ring through which potting can extend. As a result, there is no possible leakage path between the blood and the heat exchange medium. Any leak that does occur discharges to atmosphere outside the container.

FIELD OF THE INVENTION 
This invention relates to blood oxygenators, and more particularly to an 
oxygenator heat exchanger construction which prevents water or blood from 
leaking around the potting of the heat exchanger. 
BACKGROUND OF THE INVENTION 
Blood oxygenators typically consist of two major components: a heat 
exchanger section in which blood is conveyed through hollow fibers or 
tubes washed by heat exchange water, and an oxygenator section in which 
cooled blood washes around microporous hollow fibers filled with oxygen 
and other gases which are to be introduced into the blood. 
The fiber bundles which constitute the heat exchanger may be formed from a 
rolled-up mat of parallel fibers which is placed into a heat exchanger 
container, then potted at both ends in the container and cut so as to 
present a large number of individual fiber paths from an inflow manifold 
to an outflow manifold. This conventional technique typically involves 
potting the heat exchanger fibers with polyurethane in a polycarbonate 
container. 
In addition to providing support for the cut fiber ends, the potting of the 
heat exchanger provides a barrier which prevents water from entering the 
blood paths of the oxygenator. Unfortunately, the characteristics of the 
polyurethane potting and the polycarbonate container impose a tensile 
stress on the potting material which makes it want to pull away from the 
container walls as the polyurethane potting material shrinks during 
curing. Leaks at the potting-container interface are unacceptable. 
The oxygenator fibers are conventionally wound on a hollow oxygenator core 
which, in the assembly of the oxygenator, is fitted over the heat 
exchanger container. The annular space between the oxygenator core and the 
heat exchanger container serves as a water leak path to atmosphere in the 
event of a failure of the core-to-core bond, as an additional safeguard. 
In the assembly of the oxygenator, the top of the oxygenator core is 
suspended from the rim of the heat exchanger container by an inwardly 
extending flange which engages the rim of the heat exchanger container. In 
order to prevent water leakage between the oxygenator section and the 
atmosphere, it is important that the core-to-container interface be a 
polycarbonate-to-polycarbonate interface so that ultraviolet-curable 
adhesives can be used to produce a strong, tight seal. 
A need consequently exists for an arrangement in which the heat exchanger 
potting is effectively locked to the container so that it provides a tight 
seal and cannot pull away from the container wall during or after curing, 
while still preserving a polycarbonate-to-polycarbonate bond between the 
heat exchanger container and the oxygenator core, and providing a leak 
path to atmosphere. 
SUMMARY OF THE INVENTION 
The present invention fills the above need by overpotting, i.e. causing the 
potting to flow around the lip or rim of the heat exchanger container and 
lying against the outside as well as the inside of the container. In that 
manner, not only is the stress on the inner potting-container interface 
relieved, but any shrinkage which causes the potting to pull away from the 
inner container surface merely pulls the outer part of the potting even 
tighter against the outer container surface. A tight seal is thus achieved 
regardless of any shrinkage stresses in the potting. 
In another aspect of the invention, a gap which allows the potting material 
to flow around the lip of the container is created by suspending the 
oxygenator core from a separate ring positioned above the heat exchanger 
container and spaced therefrom. This allows not only the above-described 
overpotting, but it also allows a polycarbonate-to-polycarbonate interface 
between the heat exchanger container and the oxygenator core. That type of 
interface is superior to the urethane-to-polycarbonate interface which the 
overpotting would otherwise require, because it allows the use of 
ultraviolet-curable adhesives which provide a superior sealing bond. 
Another advantage of the spaced separate ring is that the air gap between 
the ring and the container lip prevents a water-to-blood leak even if a 
leak were to develop at the potting-container interface. This is true 
because any leakage path would go around the lip and be vented downward to 
atmosphere on the outside of the container, but would be blocked from 
reaching the blood path by the potting material filling the gap.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a blood oxygenator 10 using the invention. The major 
components of the oxygenator 10 are the heat exchanger 12 contained in the 
container 14, and the oxygenation section 16 consisting of hollow fibers 
18 wound on the oxygenator core 20. The upper and lower ends of the hollow 
heat exchanger fibers 22 are potted at 24 and 26, respectively, and are 
cut level with the surface of the container 14 to expose a multitude of 
openings permitting blood to flow through the heat exchanger fibers 22 
from blood manifold 28 to blood manifold 30. 
The heat exchanger fibers 22 are washed by water which flows through the 
annular space 32 molded into the the heat exchanger container 14 and 
enters the heat exchanger 12 at 34. Used water flows from the heat 
exchanger 12 at 36. 
FIG. 2 shows in detail how the heat exchanger 12 and the oxygenator core 20 
would normally be assembled in the prior art. The hooked flange 38 of the 
oxygenator core 20 engages a channel 40 in the rim of the heat exchanger 
container 14. In that channel, the flange 38 is bonded to the container 14 
preferably by an ultraviolet-curable adhesive which firmly bonds the 
polycarbonate core 20 to the polycarbonate container 14. This produces a 
strong, tight seal between the heat exchanger 12 and the blood manifold 
30. 
A problem with the construction of FIG. 2 is that the urethane potting 26 
of the heat exchanger fibers 22 shrinks during cure, and although it 
adheres to the polycarbonate container 14, the shrinking tends to pull the 
potting 26 in a direction away from the inner wall of container 14. The 
interface between the potting 26 and the container 14 is thus prestressed 
in the direction of failure. 
In accordance with the invention, as shown in FIG. 3, the potting 26 is 
extended upward and outward over the rim 42 of the heat exchanger 
container 14. When the urethane potting now shrinks during cure, the area 
44 of the potting-container interface is still prestressed in the 
direction of separation, but the area 46 on the outside of container 14 is 
prestressed toward a tighter seal. Consequently, even if a fissure occurs 
in the area 44, water in the heat exchanger fiber area 22 remains tightly 
contained by the area 46 of the potting-container interface. 
It will be noted in FIG. 3 that the overpotting prevents the use of the 
polycarbonate-to-polycarbonate bond of FIG. 2 between the oxygenator core 
20 and the container 14 when the oxygenator core is slipped over the 
container 14. This problem is solved, in accordance with another aspect of 
the invention, by the structure of FIG. 4 in which a separate core 
suspension ring 50 is disposed above the rim 42. The ring 50 is attached 
to, and held spaced from, the rim 42 by a few small feet 52. In this 
manner, the potting 26 is firmly held against the area 46 of the outer 
surface of container 14, yet the water manifold 32 and the blood manifold 
30 are sealed off from each other by a tight 
polycarbonate-to-polycarbonate adhesive seal as was the case in FIG. 2. 
The ring 50 also has another, even more significant, function. In the 
construction of FIG. 2, an adhesion defect at the potting-container 
interface 60 creates a leakage path between the blood in manifold 30 and 
the heat exchange water in the container 14. The air gap 62 (FIG. 4) 
between the ring 50 and the lip of container 14, which is filled with the 
potting 26, causes any leakage that does develop between the potting 26 
and the container 14 to be diverted over the lip of container 14, down 
along the outer surface 46 of container 14, and out to atmosphere in the 
annular space 32. Likewise, any blood seepage that may occur in a 
defective seal at the inner surface 65 of the ring 50 would have to flow 
along interfaces 66 and 68 and would also be discharged to atmosphere in 
space 32. The solid layer of potting extending all the way out to 
interface 68 provides a barrier which prevents any leakage between the 
blood manifold 30 and the interior of the heat exchanger container 14. 
FIGS. 6a-6f show, by way of example, other ways of obtaining a potting 
configuration in which shrinkage of the potting causes an area 54 of the 
potting-container interface to be prestressed in the tightening rather 
than lossening direction. In some of the embodiments of FIGS. 6a-f, the 
overpotting according to the invention involves filling a channel such as 
the channel 54 of FIG. 6d. There may be a danger in such structures that 
the bottom of the channel may trap air and prevent the potting material 
from filling the channel. This problem can be prevented by either 
providing exhaust slots such as 56, or by omitting the channel structure 
as in FIGS. 6b and 6c. 
It is understood that the exemplary water leak prevention in blood 
oxygenators described herein and shown in the drawings represents only a 
presently preferred embodiment of the invention. Indeed, various 
modifications and additions may be made to such embodiment without 
departing from the spirit and scope of the invention. Thus, other 
modifications and additions may be obvious to those skilled in the art and 
may be implemented to adapt the present invention for use in a variety of 
different applications.