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Description  |
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FIELD OF THE INVENTION
This invention relates to an improved infusion device of the type which can
be implanted for drug delivery within a patient's body, and supplied with
infusate without the need for surgical removal.
BACKGROUND OF THE INVENTION
Relatively recently, infusion ports or portals have been developed which
can be implanted in the body and remain there for a prolonged period of
time by being serviced percutaneously without having to be removed from
the body. Infusate is injected into the port by means of a conventional
hypodermic syringe.
Known infusion devices of this general type have an infusate chamber formed
within a housing of cup-like configuration with a top end closed by a
needle-penetrable, resealable septum. The septum is typically a flat block
of rubber contained, for example, axially within a cylindrical channel
formed near the open end of the housing. With this arrangement, the
exposed surface of the septum is generally recessed within the housing.
The chamber is situated immediately below the septum for receiving the
infusate. The infusate is delivered to a desired site within the patient
by means of a catheter connected to a hollow stem leading from the
chamber.
Typically, such infusion devices are made by first joining the stem to an
open-ended, cylindrical wall of the housing. This is often accomplished by
electron beam welding the stem along the inside of the cylindrical wall.
In this operation, the welding head typically directs the electron beam
through the open bottom end of the housing wall against the inner end of
the stem to form a continuous weld bead. Then, the weld area is cleaned
and polished to remove all traces of weld debris. When this is done, the
septum is inserted into the housing from below, and positioned so as to
close the top end. A top wall of the housing channel extends partially
over the top of the septum and a ledge in the channel engages under the
septum to prevent the septum from being dislodged vertically.
Subsequently, the bottom end of the housing is closed by a base plate
which is welded into place all around the housing. The base's external
weld seam area is then cleaned.
This method of construction, and particularly the welding and finishing
operations, tends to be exacting, tedious and expensive. Needless to
state, the welds must be fluid impervious to prevent leakage of infusate
from the housing. Furthermore, the quality of the finish of the weld seam
about the base plate must be assuredly high to avoid sites conducive to
bacterial growth after implantation. A complication in welding and
finishing the base plate's weld seam is the presence of the septum.
Extreme care must be taken not to damage or contaminate the septum during
these procedures, making automated manufacture of such devices quite
difficult, if not impossible.
While such prior art infusion ports are generally suitable for their
intended purpose, although not entirely satisfactory, certain inherent
limitations and inadequacies have been identified.
It is apparent from the foregoing description that if the infusion device
is to have a long service life after it is implanted in the body, the
penetrable septum must be capable of retaining its sealing properties even
after a large number of injections. In other words, the hypodermic needle
used to inject the infusate into the device must not "core" the septum so
as to create possible avenues of leakage therethrough.
Also, when injecting infusate into the portal it is important that the
hypodermic needle completely penetrate the portal's septum with only one
puncture of the patient's epidermis to avoid undue discomfort to the
patient and to assure that the infusate being injected flows into the
device's chamber as it is supposed to, rather than being deposited locally
in the patient's body and causing possible harm to the patient. Bearing in
mind that such implantable devices actually move to some extent in the
patient's body and may be situated at different depths below the skin
depending upon the weight of the patient, proper targeting of the
hypodermic needle on the infusion device's penetrable septum is not a
simple matter. This is all the more the case considering that it is
desirable to make implantable devices of this type as small and compact as
possible so as to occupy a minimum amount of space in the body. Not only
that, but the arrangement by which the septum is retained typically
restricts the exposed surface of the septum to a mere fraction of its
total area, making it an even smaller target.
Another disadvantage arises out of the configuration of the top end of the
housing in which the septum is seated. By virtue of the fact that the
septum is recessed in the housing, a generally flat surface is presented
to the skin of the patient. This creates the opportunity for seroma or
pocket formation at the top of the device. Such a dead space may collect
body fluid thereby promoting bacterial growth and infection or collect
fibrin that can interfere with access to the chamber. Such an irregular,
unyielding surface at that end of the portal also raises the potential for
abrasion and tissue breakdown if palpation is used to locate the infusion
port in order to service it.
SUMMARY OF THE INVENTION
Accordingly, the present invention aims to provide an implantable,
percutaneously accessible infusion device of improved construction.
Another object of the invention is to provide an implantable infusion
device made by an improved method of high precision manufacture which is
less exacting, tedious, and expensive than for known devices, while at the
same time produces a device of high quality.
Still another object of the invention is to provide an infusion port or
portal having improved septum and housing configurations, with almost no
dead space at which body fluid or fibrin can collect and promote infection
or interfere with access to the port.
A further object of the invention is to provide an infusion port having an
atraumatic profile which, on subcutaneous implantation, presents a rounded
and smoothly contoured, cushioned surface to the overlying tissue to
create a congruent interface therewith.
It is a more general object of the present invention to provide an improved
implantable infusion device which overcomes to some extent the
above-mentioned limitations and disadvantages of the prior art.
Other objects of the invention will, in part, be obvious and will, in part,
appear hereinafter.
The invention accordingly comprises the features of construction,
combination of elements and arrangement of parts which will be exemplified
in the following detailed description, and the scope of the invention will
be indicated in the appended claims.
Briefly, an implantable, infusion port or portal in accordance with the
invention has a housing forming an infusate chamber and an entry port into
the chamber, a self-sealing, penetrable septum of resilient material
disposed on a ledge or shoulder portion of the housing for closing the
entry port, and a fluid outlet passage from the chamber for delivering
infusate therefrom to a selected infusion site in the body.
In accordance with a first aspect of the invention, the septum is generally
dome-shaped, with a convex top extending from the housing, and an
insignificant top margin or lip of the housing being present around the
edge of the septum. This improved geometry for the septum is intended to
provide superior service during repeated use of the device. The
dome-shaped septum combines increased depth and improved shape to more
securely engage a hypodermic needle, even during lengthy ambulatory
infusion. The larger exposed surface area and increased number of possible
puncture paths through the septum extends its useful life by preserving
the self-sealing properties of the septum over a greater number of
infusions. Furthermore, the infusion device presents a rounded, cushioned
surface to overlying tissue, to create a congruent interface without dead
space between skin and device.
In accordance with a second aspect of the invention, the septum is retained
by an improved arrangement. In an exemplary practice of the invention, the
septum is provided with a frusto-conical side surface widening away from
the convex top. An interior surface of the housing adjacent to the entry
port is contoured so as to narrow towards the free end of the housing,
mating with the frusto-conical wall of the septum and, thereby, holding
the septum in place. In a preferred practice, the interior surface is
formed with a plurality of axially-spaced notches or step-like overhangs
extending, for example, circumferentially about the entry port. The septum
resiliently grips the notches, which therefore exert axially- and
radially-acting holding forces on the septum. Further, the top-most notch
is located at or near the free end of the housing so as to extend radially
a short distance over the convex top of the septum for additional vertical
containment of the septum.
The forces generated by this septum-retaining arrangement not only hold the
septum, but also improve needle engagement and retention. While the
conventional septum described above employs axial "squeeze" across a thin
horizontal plane to hold the needle, this improved septum retaining
arrangement exerts radially acting, compressive forces substantially
throughout the septum's thickness for improved needle-holding force
distribution. Also, it improves the self-sealing characteristics of the
septum.
The invention embraces not only the improved infusion device described
briefly hereinabove and in greater detail below, but also an improved
method of making such devices.
The method entails the steps of providing a housing preferably of one-piece
integral construction, welding a hollow stem to the exterior of a wall
section of the housing for forming an outlet passageway, cleaning and
otherwise finishing the continuous weld seams produced by the foregoing
welding step, and, only after the welding and finishing steps, seating the
septum in the entry port by installing the septum from the top end of the
housing. Since the septum is inserted after the welding and finishing
steps are completed, there is no danger that such steps may damage the
septum.
Where the septum retaining arrangement includes the notched and contoured
interior housing surface, the septum is installed by shoehorning the
septum into place in the housing, which entails resiliently compressing
the septum laterally with an installation tool while driving the septum
downward into its seat at the housing interior surface. When seated, the
septum resiliently engages and interfits with the housing interior surface
due to the elastic restoring forces generated within the septum material
itself. In this way, the septum is preloaded with radial force components
so that it is very securely retained in its seat, able to more securely
engage a syringe needle that penetrates it, and better able to reseal
itself after needle puncture.
The stem welding step in one practice of the invention entails providing
the stem with an axially-extending circular ridge of reduced cross-section
at one end thereof. This end is then seated within a socket formed with a
housing wall. Resistance welding is employed to generate sufficient heat
so as to melt the ridge and flow the melted material about the stem end,
thus creating a secure butt weld with the wall of the socket.
The foregoing manufacturing techniques provide improved structural strength
and integrity and reduce the potential for leakage. Overall, they provide
an improved method of high precision manufacture of a quality infusion
device easily adaptable to automation. Furthermore, by employing
single-piece construction for the housing, dead spaces and cracks are
eliminated which otherwise could trap blood, drugs or bacteria. This
construction of the port also enables it to be more easily flushed clean.
BRIEF DESCRIPTION OF THE DRAWING
For a fuller understanding of the features, advantages, and objects of the
invention, reference should be made to the following detailed description
and the accompanying drawing, in which:
FIG. 1 is a perspective view of an infusion port in accordance with the
invention;
FIG. 2 is an enlarged side view, partially cut away, of the infusion port
of FIG. 1 showing aspects of its internal construction;
FIGS. 3A and 3B are partial side views, partially cut away, of the infusion
port of FIG. 1 along with a septum-installation tool being used at
different times during assembly; and
FIGS. 4A and 4B, respectively, are enlarged detail views in section of the
housing-to-stem joint before and after welding.
DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT
Referring now to FIGS. 1 and 2, there is shown an implantable, infusate
portal 10 made in accordance with an illustrative practice of the
invention. In use, such devices are typically subcutaneously implanted for
delivery of an infusate, although in some instances they are used for
removal of a body fluid, e.g., blood. For example, such devices can
provide for controlled drug delivery to a selected infusion site in a
human or animal body for any of a variety of therapeutic purposes.
The illustrated infusion portal 10 has a cup-like housing 20 forming an
infusate chamber 30 and an entry port 40 (see FIG. 3A) into the chamber
30, a self-sealing, penetrable septum 50 of resilient material for closing
the entry port 40, and a fluid outlet passage in the form of a tubular
stem 60 from the chamber 30 for selectively delivering infusate therefrom.
The infusion portal 10 is accessed by means of a conventional hypodermic
syringe (not shown)--i.e., the syringe needle penetrates the septum 50 and
injects a fresh charge of infusate into the chamber 30. On removal of the
needle, the septum 50 seals itself. This process is repeatable as needed
over the implanted life of the device.
The housing 20 is preferably of unitary construction, hermetically sealing
its infusate contents. Desirably also, the housing is made of a rigid
material, for example, titanium, while the septum 50 is made of an elastic
material such as silicone rubber. These materials are selected for their
inertness, endurance, lightness, and biocompatibility and body is capable
of being fusion welded.
More specifically, the illustrated housing 20 is formed by a generally
tubular side wall section 62 disposed about the chamber 30 and entry port
40 and having lower and upper ends, designated 64 and 66 respectively. The
lower end 64 is provided with a radially-extending flange portion 67 for
mounting the device. The housing 20 also has a bottom or base 68 for
closing the lower end of the wall section 62. The septum-filled entry port
40 is located proximate to the upper end 66. This end constitutes the free
edge or top margin of the wall section 62. The entry port 40 extends
axially therefrom approximately half of the distance to the base 68. As
depicted, the chamber 30 makes up the balance of the space within the
housing 20. Further details of the housing 20 shall be given below, but
first it is necessary to describe the novel geometry of the septum 50.
As can be seen in FIGS. 2 and 3A, the illustrated septum 50 is generally
shaped as a dome, having a rounded convex top section 80 and a generally
frusto-conical (at least in its undeformed state) bottom section 82. After
installation, as depicted in FIG. 2, the septum 50 is seated in the entry
port 40 with its convex top section 80 extending from the housing 20
beyond the top edge margin 66 thereof. An exterior portion 84 of the
illustrated housing wall section 62 is laterally rounded so as to complete
the generally hemispherical geometry of the device, and provide the
infusion port 10 with a smoothly contoured, aesthetically-pleasing
appearance.
The septum's geometry provides a large usable surface area on the septum in
the order of 0.2 square inches (or approximately 0.5 inches across) making
it an easy target for the hypodermic needle used to access the device
after implantation. In other words, nearly the entire top surface of the
infusion device consists of septum, the housing edge margin 66 around the
septum being as small as practical, e.g., 0.06 inches (0.15 cm).
Furthermore, the convex top section 80 of the septum 50 eliminates the
dead volume that exists at the surface of block-like septums of implanted
prior art devices of this type. As mentioned above, body fluids can
collect there and promote bacterial growth. For this reason, the housing
20 has been provided with a smooth curvilinear exterior to the maximum
extent possible. On implantation of the improved infusate port 10, the
dome-shaped septum 50 presents a cushioned, congruent interface to the
overlying tissue, echoing the natural body contours.
Overall, the geometry of the infusate port 10 has been designed to better
fulfill the port's medical purposes as an implanted infusate delivery
device. Similarly, the arrangement by which the septum 50 is retained
within the housing 20 has been designed to improve the performance of the
infusion port 10.
As illustrated, the interior surface of the wall section 62 that defines
the entry port 40 is specifically contoured so as to retentively engage
and grip the frusto-conical section 82 of the septum 50. This is achieved
in the depicted embodiment by giving that interior surface a matching
generally frusto-conical configuration with superimposed axially-spaced,
substantially-rigid notches or steps 90 that extend all around the entry
port 40, and a relatively wide annular ledge or shoulder 92 at the bottom
of port 40. The notches 90 form a series of axially-spaced-apart
circumferential overhangs that extend above ledge 92. The outer diameters
of the overhangs 90 are all larger than the inner diameter of ledge 92
even as they become progressively smaller towards the top of port 40. In
other words, the illustrated frusto-conical interior surface narrows
nearer the top edge margin 66 of the housing 22. The septum 50, which is
inserted into port 40 in a manner to be presently described, seats on
ledge 92. In this position, the septum 50 compressively engages the wall
of port 40 so that the overhangs 90 deform the side of septum section 82
to create a series of notches or steps 80A there which interlock with
those overhangs to prevent upward displacement of the septum from its seat
on ledge 92.
To assure a very positive retention of the septum 50 in port 40, the
upper-most notches 90A are designed so as to extend over a portion of the
convex top section 80 of the septum 50. This portion is insubstantial in
radial extent though sufficient to vertically contain the septum 50. Those
interfitting notches 80A and 90A prevent blowouts due to internal
pressure. Thus, while known prior art infusion devices can handle internal
pressures of 125 psi, the improved retention arrangement just described
can safely accommodate pressures of 200 psi or more.
Assembly of the septum 50 into the housing 20 shall now be described with
reference to FIGS. 3A and 3B. The use of a domed, frusto-conical septum
shape in combination with the retaining arrangement described above
enables the septum 50 to be inserted into the entry port 40 from the top
of the housing 20. To do this, the septum 50 is cocked and inserted into
the entry port 40 so that its lower edge rests on ledge 92 as shown in
FIG. 3A. Then an installation tool 106 similar to a shoe horn is inserted
into the top of port 40 at the opposite side of the septum. A downward
force applied to the side of the septum along with a lateral jacking force
applied via tool 106 wedge the septum into the port so that its bottom
edge margin seats on ledge 92 as shown in FIG. 3B. Due to the elastic
restoring forces generated within the material of the septum 50, the
septum section 82 deforms about and conforms to the notches 90. In effect,
the notches 90 dig into the septum 50, gripping it and holding it in
place. With the septum 50 properly seated and retained, its top section 80
extends in dome-like fashion above the housing 20.
With the septum 50 inserted from the top of the housing 20, it is not
necessary nor desirable to use the conventional approach to manufacturing
the housing 20. As such, a further aspect of the invention relates to the
improved fabrication of a hermetically sealed housing structure for the
infusion port 10. With reference to FIGS. 1 through 3B, the improved
fabrication process starts for purposes hereof with the stem 60 being
fusion welded onto the exterior wall of section 62 with a continuous weld
seam. The weld seam then is cleaned and otherwise finished. Not until the
welding and finishing steps are completed is the septum 50 inserted, as
described above.
A novel method of securing the stem 60 to the housing 20 shall now be
described with reference to FIGS. 4A and 4B. The stem 60 is furnished (as
by machining) with a circular ridge 110 of reduced cross-section at one
end of 112 thereof. The stem 60 and housing 20 are then assembled as
depicted by seating the stem end 112 in a socket 114 formed in the wall
section 62. As can be appreciated from the drawing, the desire here is to
align an axial passage or bore 116 in the stem 60 with a through-hole 118
in the housing 20. As such, the through-hole can be formed as a stepped or
countersunk bore with the socket 114 being the wider, larger diameter
portion thereof. Resistance welding is then employed to generate
sufficient heat to melt the ridge 110, and flow the melted material about
the stem end 112, creating a secure butt weld with the wall of the socket.
This is achieved by, applying an axially directed force, as indicated by
arrow "F" in FIG. 4A, while establishing a DC voltage potential between
the electrically-conductive wall section 62 and stem 60. This is
represented schematically by the battery 120 and leads 122, 124 for
electrically connecting the battery 120 to the stem 60 and wall section
62, respectively, so as to complete the circuit. In practice, the applied
force can be approximately twenty to thirty pounds, while approximately
75 watt seconds of welding energy achieved by capacitive discharge is
applied. The resulting welded, hermetically-sealed joint is shown in FIG.
4B.
It is noteworthy that the foregoing method of securing the stem 60 permits
it to be welded from the outside of the housing 20. In the prior art
described above, the welding was done from within the housing,
necessitating an awkward angle of attach for the welding tool. Another
reason to avoid inside welds is that it discolors the area around the weld
seam and creates debris within the housing which has to be cleaned out,
typically a difficult, time consuming process. Also, conventional welding
techniques typically require that the device be placed in an inert gas
atmosphere. The present invention's improved approach can be efficiently
performed in the open, using otherwise conventional welding apparatus and
procedures that are readily automated. In fact, the entire manufacturing
process described herein can be automated for economic fabrication of the
infusion port 10.
With the housing 20, stem 60 and septum 50 formed, it is only necessary to
attach a flexible catheter to complete the device. Here, too, an improved
arrangement is proposed, as shown in FIG. 2. As illustrated there, an end
of the catheter 130, which should be made of a biocompatible material,
e.g., silicone rubber, is slid onto the stem 60 and retained there by
using a crimp ring 132 to press the catheter radially into a narrowed stem
portion 133. If desired, a sleeve 134 can also be used to hold the
catheter in place. The sleeve 134 preferably is made of a plastic material
which can be shrink fitted over the catheter. In one example, a silicone
rubber sleeve is used which expands when immersed in Freon prior to being
installed and when dry shrinks radially around the catheter. Also, silicon
adhesive can be applied to the inside surface of the sleeve 134 and at its
end surface abutting the housing 20 to assure a fluid tight seal between
the sleeve 134 and both the catheter 130 and the housing 20.
The foregoing description has been limited to a specific embodiment of this
invention. It will be apparent, however, that variations and modifications
may be made without departing from the spirit of the invention. For
example, the convex top of the septum can be formed from a series of short
planar segments rather than being a single smooth frustospherical segment.
Furthermore, other forms of ridges or projections can be substituted for
the retaining notches.
It is accordingly intended that all matter contained in the above
description or shown in the accompanying drawing be interpreted as
illustrative rather than restrictive, with the scope of the invention
being indicated by the appended claims. All changes which come within the
meaning and range of equivalency of the claims are therefore intended to
be embraced therein.
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