U.S. patent application number 13/349803 was filed with the patent office on 2012-05-10 for self-sealing vascular graft.
This patent application is currently assigned to Artegraft, Inc.. Invention is credited to Steven Weinberg.
Application Number | 20120111489 13/349803 |
Document ID | / |
Family ID | 38049214 |
Filed Date | 2012-05-10 |
United States Patent
Application |
20120111489 |
Kind Code |
A1 |
Weinberg; Steven |
May 10, 2012 |
SELF-SEALING VASCULAR GRAFT
Abstract
The present invention relates to a segmental self-sealing graft
for implantation in a patient including a base tubing element, a
tubular access element overlying the base tubing, and a strand-like
compression element wound over the access element so as to provide
radially inward compression, and a method of making same.
Inventors: |
Weinberg; Steven; (League
City, TX) |
Assignee: |
Artegraft, Inc.
North Brunswick
NJ
|
Family ID: |
38049214 |
Appl. No.: |
13/349803 |
Filed: |
January 13, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11517683 |
Sep 8, 2006 |
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13349803 |
|
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60736385 |
Nov 14, 2005 |
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Current U.S.
Class: |
156/242 |
Current CPC
Class: |
A61M 2039/0072 20130101;
A61M 39/0208 20130101 |
Class at
Publication: |
156/242 |
International
Class: |
B32B 27/00 20060101
B32B027/00 |
Claims
1. A method of making a self-sealing vascular graft comprising:
providing a base tubing element of biocompatible material, adhering
at least one tubular access element of biocompatible material to
the exterior surface of said base tubing element over substantially
the entire length of said access element by compression molding or
liquid injection molding technique so that said base tubing element
and said access element do not delaminate when punctured, wherein
said access element is a homogeneous continuous structure over
substantially the entire length of said access element, providing a
compression element of a biocompatible material over the exterior
surface of said at least one tubular access element, said
compression element providing radially inward compression about
said access element sufficient to increase the self-sealing ability
of said access element without causing said base tubing element to
collapse, wherein said compression element is a homogeneous
continuous structure over substantially the entire length of said
access element.
2. The method of claim 1, wherein said biocompatible material for
said base tubing element is polyurethane or polyester.
3. The method of claim 1, wherein said biocompatible material for
said base tubing element is expanded polytetrafluoroethylene.
4. The method of claim 1, wherein said access element is comprised
of two access elements, wherein one of said two access element is
adapted for removal of untreated blood and the other access element
is adapted for the return of filtered blood.
5. The method of claim 1, wherein said biocompatible material for
said access element is selected from the group consisting of a gum
silicone elastomer, liquid silicone elastomer, polyether based
polyurethane, polycarbonate based polyurethane, polyurethane and
urethane.
6. The method of claim 1, wherein said biocompatible material for
said access element is a platinum-cured gum silicone elastomer.
7. The method of claim 1, wherein said access element has a wall
thickness of about 0.3 mm to about 1.5 mm.
8. The method of claim 1, wherein said access element has a wall
thickness of about 0.5 mm to about 1.0 mm.
9. The method of claim 1, wherein said biocompatible material for
said compression element is selected from the group consisting of a
platinum cured silicone gum elastomer, liquid silicone elastomer,
polyether based polyurethane, polycarbonate based polyurethane,
polyurethane, and urethane.
10. The method of claim 1, wherein said compression element has a
durometer hardness of about 20 to about 35 Shore A.
11. The method of claim 1, wherein the wall thickness of said
compression element is from about 0.25 mm to about 0.55 mm.
12. The method of claim 1, wherein the exterior surface of said
compression element is microporous or textured.
13. The method of claim 1, wherein said biocompatible material for
said base tubing element is expanded polytetrafluorethylene; said
biocompatible material for said access element is a platinum-cured
gum silicone elastomer; and said biocompatible material for said
compression element is a platinum cured silicone gum elastomer.
14. The method of claim 13, wherein said access element has a wall
thickness of about 0.33 mm to about 1.5 mm; and said compression
element has a wall thickness of about 0.25 mm to about 0.55 mm,
wherein the exterior surface of said compression element is
microporous or textured.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 11/517,683, filed Sep. 8, 2006, which claims the benefit of the
filing date of U.S. Provisional Patent Application No. 60/736,385
filed Nov. 14, 2005, the disclosures of which are hereby
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] Grafts, for example hemodialysis grafts, are often used for
patients who need to receive frequent injections, blood filtration,
or vascular access procedures. For example, patients who receive
kidney dialysis typically received several treatments per week. In
order for the patient to receive treatment, the patient's skin must
be punctured with a hemodialysis needle. Such needles are typically
about 15-17 gauge, and they leave a puncture which takes some time
to heal. With the frequency of dialysis treatments, puncture wounds
accumulate, and there is a danger of undermining the patient's
veins.
[0003] It has become common to implant a graft in the patient's arm
to receive the punctures. Typically, the graft is a tubular member
which is implanted in the patient's forearm, although other
locations may be used. The graft is connected between two spaced
points in the circulatory system. In the past, veins from animals
were used as the graft material, but today it is common to use an
artificial material, such as polymer tubing. However, the punctures
in such tubing tend to leak under the pressure of the circulatory
system. In all cases, the graft can not be used immediately and
must be allowed to heal-in or mature, before it can be punctured.
Efforts have been made to use tubes made of a self-sealing polymer
or to provide a multilayered structure to resolve these problems;
but such grafts have not been proven to be a reliable solution to
long term patency.
[0004] It would therefore be desirable to provide a graft made of
an artificial material which can reliably prevent blood leakage
from repeated punctures when in use. Preferably, it should be
relatively simple in construction, made of medically accepted and
biologically compatible materials, and its implantation and use
should be no more complicated than the existing grafts.
SUMMARY OF THE INVENTION
[0005] In accordance with an embodiment of the present invention,
an artificial graft includes a base tubing element, a tubular
access element overlying the base tubing, and a compression element
formed over the access element so as to provide radially inward
compression thereto. The compression element may be a strand-like
compression element wound over the access element. The base tubing
element is preferably made of a polymer, such as expanded
polytetrafluoroethylene (ePTFE), a material which is commonly
approved for surgical and medical purposes. The tubular access
element is preferably made of a material which exhibits
self-sealing properties, such as by way of one example, a gum
silicone elastomer, which is preferably bonded to the base tubing
surface. The compression element may be a polytetrafluoroethylene
(PTFE) tape or yarn, which may be helically wound about the
exterior of the access element in order to provide radial
compression of the access element and improve its leakage
resistance. The compression element may also be a biocompatible
silicone layer molded directly over the access element so as to
provide sufficient radial compression of the access element to
improve its leakage resistance.
[0006] It is a feature of one aspect of the present invention that
a compression member formed about the access element improves the
leakage resistance of the access element after it has been
punctured by applying radially inward pressure. The compression
member may be a strand-like compression member wound about the
access element or a biocompatible silicone layer formed over the
access element.
[0007] It is a feature of one aspect of the present invention that
an artificial graft is constituted of a tubular base element, an
overlying sleeve-like access element made of a material exhibiting
self-sealing properties upon being punctured and mounted in contact
with the base element, and a compression member formed about the
access element so as to provide sufficient radial compression
thereto to improve the leakage resistance of the graft after being
punctured. The compression element may be a strand-like compression
element wound over the access element or a biocompatible silicone
layer formed over the access element.
[0008] It is a feature of an aspect of the present invention that
an artificial graft is constituted of a tubular base element made
of ePTFE, an overlying sleeve-like access element made of a gum
silicone material or other suitable elastomer exhibiting
self-sealing properties upon being punctured and molded on the base
element, and a compression band or tape member having a width which
avoids being severed when pierced by a hemodialysis needle, such as
a spiral or helical band wound about the access element so as to
provide sufficient radial compression thereto to improve the
leakage resistance of the graft after being punctured. The
transition of the silicone segment from the ePTFE tubing provides
for smooth surgical tunneling of the graft. It is also contemplated
that a biocompatible silicone layer could be molded over the access
element and compression member so as to enclose them and to provide
sealing properties. This outer layer may be micro-porous or contain
a textured outer surface to enhance tissue healing and graft
stabilization.
[0009] It is a feature of an aspect of the present invention that
an artificial graft is constituted of a tubular base element made
of ePTFE, an overlying sleeve-like access element made of a gum
silicone material or other suitable elastomer exhibiting
self-sealing properties upon being punctured and molded on the base
element, and a biocompatible silicone layer formed over the access
element so as to provide sufficient radial compression of the
access element to improve its leakage resistance after being
punctured.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The foregoing brief description and further objects,
features, and advantages of the present invention will be
understood more completely from the following detailed description
of presently preferred, but nonetheless illustrative, embodiments
in accordance with the present invention, with reference being had
to the accompanying drawings in which:
[0011] FIG. 1 is a longitudinal cross sectional view of one
embodiment of an artificial graft in accordance with the present
invention, showing the internal construction thereof; and
[0012] FIG. 2A is a side elevational view of the artificial graft
of FIG. 1 showing a helically wound compression element;
[0013] FIG. 2B is a side elevational view of another embodiment an
artificial graft in accordance with the present invention showing a
compression element that is wound in the pattern of a double
helix;
[0014] FIG. 3 is a longitudinal cross sectional view of still
another embodiment of an artificial graft in accordance with the
present invention showing the internal construction thereof,
wherein a biocompatible silicone layer is formed over the access
element and compression member; and
[0015] FIG. 4 is a longitudinal cross sectional view of another
embodiment of an artificial graft in accordance with the present
invention showing the internal construction thereof, wherein a
biocompatible silicone layer is formed directly over the access
element.
DETAILED DESCRIPTION
[0016] Turning now to FIG. 1, graft 10 broadly comprises a base
tubing element 12, a tubular access element 14 overlying the base
tubing element, and a compression element 16 wound over the access
element so as to provide radially inward compression thereto.
[0017] Base tubing element 12 preferably has a circular
cross-section but it may have any cross-sectional shape commonly
used for surgical and implantation applications. Base tubing
element is preferably made of implant grade ePTFE tubing having an
inside diameter of, by way of preferred example only, about 6.0 mm
and a wall thickness of about 0.5 mm. Preferably the graft 10 is
provided in a fixed length, usually longer then required and cut by
a surgeon, for example to the length of base tubing element 12,
which is convenient for implantation, for example about 13.5 cm.
However, tubing element of other length, diameter and wall
thickness will work equally well, as will be appreciated by those
skilled in the art. Tubing made of ePTFE is preferred for element
12 because this material has enjoyed wide application in medicine
and surgery, particularly for implant applications. However, those
skilled in the art will appreciate that tubing made of other
biocompatible materials approved for implant applications may work
equally well, such as tubing made of polyurethane or polyester and
the like.
[0018] The graft 10 will have one or more access elements 14.
Typically, most grafts would have two access elements--one for
removal of untreated blood and one for the return of filtered
blood, but those skilled in the art will appreciate that there may
be some instances in which it would be convenient to provide
additional access elements. In this regard, the access elements may
be positioned adjacent one another about the tubing element 12.
Notwithstanding the foregoing, the invention contemplates a single
access element 14 for removal and return of blood.
[0019] Preferably, access element 14 is made of implant grade,
platinum-cured gum silicone elastomeric material. It is preferred
that this elastomeric material has a 20-35 Shore durometer hardness
(NuSil MED-4020/4035 or equivalent). However, other self-sealing
materials will also work well, such as urethane or other
biocompatible elastomers. In any event, the material should be
biocompatible, capable of withstanding multiple punctures with
minimal leakage, and sufficiently soft to permit a medical
practitioner to pierce it without using undue force. Other
materials that could be used include gum and liquid silicone
rubber, polyether or polycarbonate based polyurethanes. It is also
contemplated that access element 14 have a wall thickness of
approximately about 0.3 mm to about 1.5 mm, and preferably about
0.5 to about 1.0 mm.
[0020] In the preferred embodiment, access element 14 is
compression molded or liquid injection molded onto the outside of
base tubing element 12. This is preferably done by placing tubing
element 12 on a mandrel that has the same outside diameter as the
inside diameter of the tubing element. A mold is then placed around
the tubing element 12 and liquid or gum silicone is introduced into
the mold at a pressure which is preferably in the range of about
200 to about 300 psi. Alternatively, the access element 14 may be
formed as a gum silicone sheet material and partially cured. It can
then be applied over tubing element 12, a two part mold applied
around it and compressed in a 7-8 ton press at a temperature of
about 200.degree. F. In order to improve the adhesion of the access
element 14, the outside surface of that portion of tubing element
12 underlying the access element or the interior surface of access
element may be subjected to surface activation such as by applying
a chemical treatment or physical treatment (e.g. abrasion) to
ensure that the bond between elements 12 and 14 is secure and
lasting, so that the two elements will not separate in use. An
access element 14 with the above composition will exhibit
self-sealing properties. That is, when access element 14 is
punctured with a fine point, such as a hemodialysis needle, it will
tend to close up the puncture when the needle is removed.
[0021] It has been found that, upon being pierced by a needle, a
non-coated tubing element 12 develops a tiny inwardly hanging tab
at the site of the puncture. As the graft 10 may be punctured
several times per week, leakage will occur through the opening left
by this hanging tab. The molding pressure for access element 14 was
selected to be relatively high so as to assure that the silicone
material forming access element 14 works into the surface pores of
tubing element 12. As a result, it is contemplated that after a
piercing needle is withdrawn, the resilience of access element 14
causes the hanging tab to be drawn up into the puncture in tube
element 12 to block it. By minimizing or eliminating the hanging
tab, blood flow through the graft lumen will not be impeded.
[0022] Compression element 16 is preferably a strand-like elongated
member which can be wound about access element 14 to provide
radially inward compression to improve the leak resistance of that
element after it is punctured. Preferably, compression element 16
is made of a yarn in tape form, most preferably a tape or band
material generally available in the form of PTFE tape. However,
other forms of the compression element 16 other than tape, such as
round, oval, square and the like are within the scope of the
invention. It is preferred that the width of compression element 16
be such that, with the intended gauges of needles to be used,
element 16 may be pierced without being severed. Preferably,
compression element 16 is wound with a tension approximately in the
range of about 10 to about 300 grams, most preferably about 40
grams. However, any tension will be effective which causes a
increase in the self-sealing ability of access element 14 but does
not cause the tubing element 12 to collapse.
[0023] As may be seen in FIGS. 1 and 2A, compression element 16 is
secured at ocation 18 near one end of access element 14 and is
thereafter wound about access element 14, preferably in a helical
or spiral pattern which advances about 1.5 mm per rotation. When
the other end of access element 14 is reached, the compression
element 16 is once again secured to it at location 18'. Preferably,
the securement of compression element 16 at locations 18 and 18' is
achieved by some suitable means, such as forming slits 18a, 18a' in
access element 14 at locations 18, 18', respectively, and inserting
an end of compression element 16, after which the end of
compression element 16 is bonded in place, preferably by means of
an RTV (Room Temperature Vulcanizing) adhesive. Those skilled in
the art will appreciate that other biocompatible bonding materials
may be used, such as cyanoacrylate. The ends of compression element
16 could alternately be secured by other methods, such as being
tied off to the access element 14 and knotted.
[0024] In an alternate embodiment 10', which is illustrated in FIG.
2B, compression element 16 is secured at the first end 18 of access
element 14, as above, is wound in a helical pattern towards the
second end 18' of access element 14, and is then wound in a helical
pattern back towards the first end of access element 14 so as to
cross the previous windings. When the first end 18 of access
element 14 is reached, the end of compression element 16 is once
again secured to it, as above. In this double helix pattern, the
compression element 16 preferably advances about 2 mm per
rotation.
[0025] FIG. 3 illustrates a third embodiment of an artificial graft
20 in accordance with the present invention. This embodiment is
similar to embodiments 10 and 10' in FIGS. 1, 2A and 2B except that
an outer covering 22 is provided over compression element 16 in the
structures. In FIG. 3, those elements which are identical to
elements in FIG. 1 have been indicated with the same reference
numbers.
[0026] Preferably, the covering 22 is made of platinum-cured
silicone gum or a liquid silicone with a durometer hardness of
20-35 Shore A (NuSil MED-4035 or equivalent). This material is
compression molded on the structure after compression element 16
has been secured, in a manner similar to access element 14. In the
preferred embodiment, covering 22 has a wall thickness of about
0.25 to about 0.5 mm. It is also preferred that cover 22 have an
exterior surface #45 "texturing" (Charmilles Technologies, VDI
3400), or a micro-porosity (50 to 200 microns) providing an
environment to allow for biological connective material attachment
and to assist in the long term stability of the graft 20 within the
patient's subcutaneous tissue. Except for its durometer, this
material can be made of the same material as access element 14.
However, those skilled in the art will appreciate that cover 22
need not be made of the same material as access element 14.
Alternate materials that could be used include biocompatible
elastomers such as polyurethane.
[0027] FIG. 4 illustrates a fourth embodiment of an artificial
graft 30 in accordance with the present invention. Graft 40 broadly
comprises a base tubing element 12, a tubular access element 14
overlying the base tubing, and an outer covering 32 formed over
access element 14 so as to provide radial compression to the access
element. In the embodiment illustrated, the covering 32 may extend
past the extent of the access element 14 and about a portion of the
tubing element.
[0028] Base tubing element 12 preferably has a circular
cross-section but it may have any cross-sectional shape commonly
used for surgical and implantation applications. Tubing element 12
is preferably made of implant grade ePTFE tubing having an inside
diameter about 6.0 mm and a wall thickness of about 0.5 mm.
Preferably the graft 30 is provided in a fixed length, usually
longer then required and cut by surgeon, for example to the length
of base tubing element 12, which is convenient for implantation,
for example about 30 cm. However tubing element 12 of other length,
diameter and wall thickness will work equally well, as will be
appreciated by those skilled in the art. Tubing made of ePTFE was
selected for tubing element 12 because this material has enjoyed
wide application in medicine and surgery, particularly for implant
applications. However, those skilled in the art will appreciate
that tubing made of other biocompatible materials approved for
implant applications may work equally well, such as tubing made of
polyurethane or polyester and the like.
[0029] There may be one access element 14. However, most grafts
would have two access elements--one for removal of untreated blood
and one for the return of filtered blood, but those skilled in the
art will appreciate that there may be some instances in which it
would be convenient to provide additional access elements. In this
regard, the access elements 14 may be portioned adjacent one
another about the tubing element 12. Notwithstanding the foregoing,
the invention contemplates a single access element 14 for removal
and return of blood.
[0030] Preferably, access element 14 is made of implant grade,
platinum-cured gum silicone elastomeric material. It is preferred
that this elastomeric tubing has a 20-35 Shore A durometer hardness
(NuSil MED-4020/4035 or equivalent). However, other self-sealing
materials will also work well, such as urethane or other
biocompatible elastomers. In any event, the material should be
biocompatible, capable of withstanding multiple punctures with
minimal leakage, and sufficiently soft to permit a medical
practitioner to pierce it without using undue force. Other
materials that could be used include gum and liquid silicone
rubber, polyether or polycarbonate based polyurethanes. It is also
preferred that access element 14 have a wall thickness of about 0.3
mm to about 1.5 mm, and preferably about 0.5 to about 1.0 mm.
[0031] In this embodiment, access element 14 is compression molded
or liquid injection molded onto the outside of base tubing element
such a previously described. This is preferably done by placing
tubing element 12 on a mandrel that has the same outside diameter
as the inside diameter of the tubing. A mold is then placed around
the tubing element 12 and liquid or gum silicone is introduced into
the mold at a pressure which is preferably in the range of about
200 to about 300 psi. Alternately, the access element 12 may be
formed as a gum silicone sheet material and partially cured. It can
then be applied over tubing element 12, a two part mold is applied
around it, and it is compressed in a 7-8 ton press at a temperature
of about 200.degree. F. In order to increase the adhesion of the
access element 14, the outside surface of that portion of tubing
element 12 underlying the access element 14 may be subjected to
surface activation such as applying a chemical treatment or
physical treatment (e.g. abrasion) to ensure that the bond between
elements 12 and 14 is secure and lasting, so that the two elements
will not separate in use. An access element 14 with the above
composition will exhibit self-sealing properties. That is, when
access element 14 is punctured with a fine point, such as a
hemodialysis needle, it will tend to close up the puncture when the
needle is removed.
[0032] In this embodiment, covering 32 also acts as a compression
element, applying sufficient inward radial compression to provide
an increase in the self-sealing ability of access element 14,
without causing the tubing element 12 to collapse.
[0033] Preferably, the covering 32 is made of platinum-cured
silicone gum or a liquid silicone with a durometer hardness of
20-35 Shore A (NuSil MED-4035 or equivalent). This material is
compression molded or liquid injection molded about the access
element 14, and optionally about a portion of the tubing element
12, in a manner similar to access element 14 as described with
respect to FIG. 1. In this embodiment, covering 32 has a wall
thickness of approximately 0.25 to 0.5 mm. It is also preferred
that cover 32 have an exterior surface #45 "texturing" (Charmilles
Technologies, VDI 3400), or a micro-porosity (50 to 200 microns)
providing an environment to allow for biological connective
material attachment and to assist in the long term stability of the
graft 30 within the patient's subcutaneous tissue. Except for its
durometer, this material is made of the same as the material
comprising access element 14. Those skilled in the art will
appreciate that cover 32 need not be made of the same material as
access element 14. Alternate materials that could be used include
biocompatible elastomers such as polyurethane.
[0034] Although preferred embodiments of the invention have been
disclosed for illustrative purposes, those skilled in the art will
appreciate that many additions, modifications, and substitutions
are possible without departing from the scope and spirit of the
invention.
* * * * *