U.S. patent application number 10/656218 was filed with the patent office on 2004-03-11 for endoprosthesis that can be percutaneously implanted in the patient's body.
Invention is credited to Strecker, Ernst Peter.
Application Number | 20040049259 10/656218 |
Document ID | / |
Family ID | 6462733 |
Filed Date | 2004-03-11 |
United States Patent
Application |
20040049259 |
Kind Code |
A1 |
Strecker, Ernst Peter |
March 11, 2004 |
Endoprosthesis that can be percutaneously implanted in the
patient's body
Abstract
An endoprosthesis in the form of an elongated hollow structure
that can be implanted percutaneously with a catheter in a blood
vessel or other cavity of the body and once correctly positioned
will expand from an initial state with a narrow lumen into a state
with a lumen that is as wide as its placement will allow. It has a
lining of a wrapping material that deforms plastically without
fissuring as it expands from the state with the narrow lumen to the
state with the wide lumen. Another embodiment is a stent with a
wrinkled lining that smoothes out as the stent expands. The lining
is impregnated with at least one medication that will gradually and
preferably at a uniform rate be released to the patient once the
prosthesis is in place.
Inventors: |
Strecker, Ernst Peter;
(Karlsruhe, DE) |
Correspondence
Address: |
KENYON & KENYON
1500 K STREET, N.W., SUITE 700
WASHINGTON
DC
20005
US
|
Family ID: |
6462733 |
Appl. No.: |
10/656218 |
Filed: |
September 8, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10656218 |
Sep 8, 2003 |
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09776850 |
Feb 6, 2001 |
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6645241 |
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09776850 |
Feb 6, 2001 |
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08707820 |
Sep 4, 1996 |
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6193746 |
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08707820 |
Sep 4, 1996 |
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08393950 |
Feb 22, 1995 |
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08393950 |
Feb 22, 1995 |
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08087520 |
Jul 2, 1993 |
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Current U.S.
Class: |
623/1.13 ;
623/1.42 |
Current CPC
Class: |
A61F 2/90 20130101; A61F
2210/0004 20130101; A61F 2210/0076 20130101; A61F 2250/0067
20130101 |
Class at
Publication: |
623/001.13 ;
623/001.42 |
International
Class: |
A61F 002/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 8, 1992 |
DE |
P 42 22 380.6 |
Claims
1. Endoprosthesis in the form of an elongated hollow structure that
can be implanted percutaneously with a catheter -in a blood vessel
or other cavity of the body and once correctly positioned will
expand from an initial state with a narrow lumen into a state with
a lumen that is as wide as its placement will allow, characterized
by a lining (12 & 13, 21, 22, 25, & 26, or 42 & 43) of
a wrapping material that deforms plastically without fissuring as
it expands from the state with the narrow lumen to the state with
the wide lumen and that is impregnated with at least one medication
that will gradually and preferably at a uniform rate be released to
the patient once the prosthesis (10, 20, 30, or 40) is in
place.
2. Endoprosthesis in the form of an elongated hollow structure or
stent that can be implanted percutaneously with a catheter in a
blood vessel or other cavity of the body and once correctly
positioned will expand from an initial state with a narrow lumen
into a state with a lumen that is as wide as its placement will
allow, characterized by a wrinkled lining (12 & 13, 21, 22, 25,
& 26, or 42 & 43) around the as yet unexpanded stent that
smoothes out as the stent expands from the state with the narrow
lumen to the state with the wide lumen and that is impregnated with
at least one medication that will gradually and preferably at a
uniform rate be released to the patient once the prosthesis (10,
20, 30,or 40) is in place.
3. Endoprosthesis as in claim 1 or 2, characterized in that the
lining (12 & 13, 22 & 23, or 42 & 43) is against either
the outer surface or the inner surface of the prosthesis (10, 20,
or 40) of both.
4. Endoprosthesis as in claim 1 or 2, characterized in that the
lining (12 & 13, 22 & 23, or 42 & 43) rests against all
supporting areas of the prosthesis (10, 20, or 40).
5. Endoprosthesis as in claim 1 or 3, characterized in that the
lining (12 & 13 or 22 & 23) impregnated with at least one
medication is applied by introducing the hollow structure or stent
that supports the prosthesis (10 or 20) into a mold along with
liquid wrapping material that subsequently solidifies elastic.
6. Endoprosthesis as in claim 5, characterized in that the lining
(12 & 13 or 22 & 23) is applied to the hollow structure or
stent that supports the prosthesis (10 or 20) once it has expanded
to approximately half its final size.
7. Endoprosthesis as in one of claims 1 through 4, characterized in
that the lining (12 & 13, 22 & 23, or 42 & 43) is a
flexible tubular membrane wrapped around the prosthesis (10 or 20)
and secured.
8. Endoprosthesis as in claim 7, characterized in that the flexible
tubular membrane adheres to the inner surface and/or the outer
surface of the prosthesis (10, 20, or 40) and folds back around its
ends.
9. Endoprosthesis as in one of claims 1 through 8, characterized in
that medications in the lining (12 & 13, 22 & 23, or 42
& 43) are dissolved in the wrapping material or included in the
form of beads.
10. Endoprosthesis as in claim 7 or 8, characterized by openings in
the inner and/or outer component of the lining (12 & 13, 22
& 23, or 42 & 43) that expand as the prosthesis expands to
the state with the wider lumen to the extent that medications are
released once the lining has expanded to the utmost.
11. Endoprosthesis as in claim 10, characterized in that there are
more or less openings in the wall of the lining (12 & 13, 22
& 23, or 42 & 43) next to the lumen than there are in the
wall next to the inner surface of the vessel.
12. Endoprosthesis as in one of claims 1 through 11, characterized
in that the wrapping material that the lining (12 & 13, 22
& 23, or 42 & 43) is made of is biodegradable.
13. Endoprosthesis as in one of claims 1 through 12, characterized
in that the lining (12 & 13, 22 & 23, or 42 & 43) is
made of polymers or compounds thereof and especially of
poly-D,L-lactide or poly-D,L-lactide co-trimethylene carbonate or
of albumin cross-linked with glutalaldehyde, which is removed once
the albumin is cross-linked.
14. Endoprosthesis as in one of claims 1 through 11, characterized
in that the lining (12 & 13, 22 & 23, or 42 & 43) is of
polyacrylic or compounds thereof.
15. Endoprosthesis as in one of claims 1 through 14, characterized
in that once the prosthesis is in place the lining (12 & 13, 22
& 23, or 42 & 43) is permeable enough for any metabolites
that occur to enter the blood circulation through the wall of the
vessel and for oxygen or nutrients for example to diffuse out of
the blood through the lining to the wall of the vessel.
16. Endoprosthesis as in claim 15, characterized in that the wall
(11, 21, or 41) with the lining (12 & 13, 22 & 23, or 42
& 43) of wrapping material is either perforated at many points
or is a knitted, crocheted, or otherwise produced mesh.
17. Endoprosthesis as in one of claims 1 through 16, characterized
by pores in the lining (12 & 13, 22 & 23, or 42 & 43)
for the substances to diffuse through.
18. Endoprosthesis as in claim 17, characterized in that the
diameter of the pores in the lining (12 & 13, 22 & 23, or
42 & 43) is no longer than 0.5 .mu.m.
19. Endoprosthesis as in one of claims 1 through 18, characterized
in that the lining (12 & 13, 22 & 23, 25, & 26, or 42
& 43) is of several layers, each impregnated with different
medications.
20. Endoprosthesis as in claim 19, characterized in that the layers
of the lining (12 & 13, 22 & 23, 25, & 26, or 42 &
43) are made of materials that biodegrade at different rates.
21. Endoprosthesis as in claim 20, characterized in that the inner
layer of the lining (12 & 13, 22 & 23, 25, & 26, or 42
& 43) biodegrades more rapidly than the outer layer.
22. Endoprosthesis as in one of claims 19 through 21, characterized
in that the inner layer of the lining (12 & 13, 22 & 23, or
42 & 43) is impregnated with antithrombotics and the outer with
antiproliferatives and/or other medicational substances.
23. Endoprosthesis as in claim 22, characterized in that the outer
layer of the lining, the layer impregnated with antiproliferatives
and/or other medicational substances, consists of a short cuff (25
& 26) at each end.
24. Endoprosthesis as in claim 23, characterized in that the cuffs
(25 & 26) at each end are provided with pores.
25. Endoprosthesis as in one of claims 19 through 24, characterized
in that the outer layer of the lining (12 & 13, 22 & 23, 25
& 26, or 42 & 43) is impregnated with cytostatics to keep
tumorous stenoses open or to act as an antiproliferative against
hyperplasia of the intima and the inner layer with Theologically
beneficial substances.
26. Endoprosthesis as in one of claims 1 through 25, characterized
by a lateral aperture (31 & 31') that expands extensively in
accordance with the expanding lumen.
27. Endoprosthesis as in one of claims 7 through 11, characterized
by at least one flexible medicating tube (47) extending outward
along a lining (42 & 43) in the form of a membranous tube.
28. Endoprosthesis as in claim 27, characterized in that the
medicating tube (47) is attached to and can be detached from the
lining (42 & 43).
29. Endoprosthesis as in claim 27: or 28, characterized in that
medicating tubes (47) are uniformly distributed around the lining
(42 & 43).
30. Endoprosthesis as in claim 29, characterized in that a group of
openings in the lining is associated with each medicating tube
(47).
31. Endoprosthesis as in one of claims 7 through 9, characterized
in that the lining (42 & 43) in the form of a membranous tube
has an outward-extending medicating tube (47) that accommodates
radioactive liquids.
32. Endoprosthesis as in one of claims 1 through 31, characterized
in that the lumen of a hollow structure that supports the
prosthesis (19, 20, or 40) and has netting or meshes narrows to
such an extent when axial tension is applied to the prosthesis that
it can be intercepted in a catheter and removed with the catheter
from the vessel.
Description
[0001] The present invention concerns an endoprosthesis. It is in
the form of an elongated hollow structure. The structure can be
implanted percutaneously with a catheter in a blood vessel or other
cavity of the body. Once correctly positioned it will expand from
an initial state with a narrow lumen into a state with a lumen that
is as wide as its placement will allow.
[0002] Percutaneously implanted endoprostheses with variable lumens
are known. They are employed to open or expand narrow blood-vessel
lumens. The lumens can be expanded by mechanically stretching them
with a known balloon catheter. They can also be compressed prior to
implantation and stretch out on their own subject to the resilience
introduced by the compression.
[0003] One endoprosthesis is disclosed in European A 0 292 587. It
is mounted on a balloon catheter and can be dilated and removed
from the catheter and left in a blood vessel. It is a stent
manufactured by knitting, crocheting, or some other process for
producing netting from metal or plastic filament of satisfactory
tissue compatibility. The individual meshes consist of loosely
interconnected loops. The loops undergo plastic deformation as the
balloon expands, and the expanded prosthesis will remain
expanded.
[0004] Self-expanding stents are described for example in European
A 0 183 372 and U.S. Pat. No. 4,732,152. Such a prosthesis is prior
to implantation compressed to a reduced cross-section against the
force of its own resilience. It is then implanted in the body of a
patient. Once the prosthesis has been correctly positioned, the
compression is discontinued and the prosthesis springs back to its
original shape inside the vessel, where it remains secured.
[0005] The endoprosthesis described in European A 0 183 372 is
compressed to a reduced cross-section for purposes of implantation
and then, while compressed, advanced with what is called a pusher
through a catheter that has already been inserted in a vessel until
the prosthesis arrives at the correct position in the vessel.
Thrusting the prosthesis through the catheter requires considerable
force because of the powerful friction encountered.
[0006] The system described in U.S. Pat. No. 4,732,152 includes a
woven and resilient endoprosthesis kept compressed by a double
wrapper closed at the distal end. The wrapping is removed from the
compressed prosthesis as a stocking is removed from a leg. The
ensuing friction can be avoided by injecting liquid between the
wrapper's two sheets. This approach, elegant at first glance
because of the way it reduces friction, is nevertheless very
difficult.
[0007] The object of the present invention is accordingly to
completely improve the initially described generic endoprosthesis,
which can be implanted with a catheter and has a variable lumen.
The improved prosthesis will provide communication with or between
cavities in the body and maintain that communication permanently.
It will also be therapeutically useful.
[0008] This object is attained in accordance with the invention in
the endoprosthesis recited in the preamble to claim 1 by a lining
of a wrapping material that deforms plastically without fissuring
as it expands from the state with the narrow lumen to the state
with the wide lumen and that is impregnated with at least one
medication that will gradually and preferably at a uniform rate be
released to the patient once the prosthesis is in place.
[0009] A vascular prosthesis comprising a porous flexible tube of
plastic with an elastomeric coating bonded to its outer surface and
with both components medicated is admittedly known from German OS 2
941 281. This prosthesis, however, can expand to only a limited
extent, and the expanding coating has a considerable range of
elasticity. A considerable force of restoration is accordingly
exerted on the stent in the expanded state and can undesirably
reduce the expansion situation.
[0010] The present invention on the other hand exploits a wrapping
material that plastically deforms as it expands and accordingly
exerts no restoration force on the stent, ensuring persistent
expansion.
[0011] Furthermore, the medicated wrapping material ensures
precisely sited treatment of vascular conditions. The prosthesis
can also be employed as a splint for tumorous stenoses and tumorous
obstructions in the bile tract for example if it is impregnated
with cytostatics or antiproliferatives.
[0012] Another embodiment of the prosthesis is a stent that can be
implanted percutaneously with a catheter in a blood vessel or other
cavity of the body. Once correctly positioned, the stent will
expand from an initial state with a narrow lumen into a state with
a lumen that is as wide as its placement will allow. This
embodiment has a wrinkled lining around the as yet unexpanded
stent. The lining smoothes out as the stent expands from the state
with the narrow lumen to the state with the wide lumen. The lining
is also impregnated with at least one medication. The medication
will gradually and preferably at a uniform rate be released to the
patient once the prosthesis is in place.
[0013] This prosthesis can also be adapted individually to the
cross-section of the blood vessel it is implanted in even through
the wrapping material itself does not stretch. Adaptation to the
particular cross-section is, rather, achieved by the unfolding of
the folded wrapping and its smoothing out against the wall of the
vessel as the stent expands.
[0014] The lining in one practical advanced version of the
invention is against either the outer surface or the inner surface
of the prosthesis or both. It turns out to be practical in another
advanced version of the invention for the lining to rest against
all supporting areas of the prosthesis instead of just having a
layer that rests against the inner and outer surfaces. This
approach provides additional stabilization for the prosthesis in
place.
[0015] This feature can easily be achieved when in accordance with
still another advanced version the lining impregnated with at least
one medication is applied by introducing the hollow structure or
stent that supports the prosthesis into a mold along with liquid
wrapping material that subsequently solidifies elastic. The
advantage is that the walls of the embedded prosthesis will be
absolutely smooth.
[0016] An implant is admittedly known from German OS 3 503 126 with
a medicated collagen coating on the surface of a tubular support or
stent. This coating, however, expands to only a limited extent, and
the medication is released non-linearly. The lining in another
advantageous advanced version of the present invention is applied
to the hollow structure or stent that supports the prosthesis once
it has expanded to approximately half its final size. This ensures
that the prosthesis will be uniformly coated even at maximal
expansion.
[0017] To ensure the maximal possible absorption of medication
while retaining the desirable mechanical properties of the
prosthesis, the lining can be a flexible tubular membrane or sleeve
wrapped around the prosthesis and secured. It will be practical in
this event to ensure that the flexible tubular membrane adheres to
the inner surface and/or the outer surface of the prosthesis and
folds back around its ends.
[0018] Another sensible advanced version is characterized in that
medications in the lining are dissolved in the wrapping material or
included in the form of beads. This embodiment can also have
openings in the inner and/or outer component of the lining to
release the medication through. The openings expand as the
prosthesis expands to the state with the wider lumen to the extent
that medications are released once the lining has expanded to the
utmost.
[0019] It can be practical for there to be more or less openings in
the wall of the lining next to the lumen than there are in the wall
next to the inner surface of the vessel. The ratio can be exploited
to prescribe the dosage of medication to the lumen or wall of the
blood vessel.
[0020] The wrapping material can also to advantage be biodegradable
as long as its breakdown products provoke no undesirable side
effects. When the material is biodegradable, the medication will be
released not by diffusing out of the vehicle but by escaping as the
vehicle that the medication is dissolved in or that accommodates
the beads that encapsulate the medication at its surface decomposes
and by accordingly coming into contact with body fluids.
Administration is accordingly dependent on the rate of
biodegradability of the vehicle, which can be adjusted.
[0021] The lining can to advantage be made of polymers or compounds
thereof. It can in particular be made of poly-D,L-lactide or
poly-D,L-lactide co-trimethylene carbonate. It can also be made of
albumin cross-linked with glutalaldehyde. In this event the
aldehyde, which is thrombogenic, is removed once the albumin is
cross-linked. The lining can also be made of polyacrylic or
compounds thereof.
[0022] Stents coated with polymer and impregnated with medication
are admittedly already .known, for example from R. C Oppenheim et
al, Proc. Int. Symp. Contr. Rel. Bioact. Mat. 15 (1988), pages 52
to 55. These coatings, however, which are applied by spraying a
dispersion of acrylic onto the stent, are not biodegradable, and
there are no means of expanding the cross-section of the
prosthesis.
[0023] It has also be demonstrated practical to ensure that once
the prosthesis is in place the lining impregnated with at least one
medication will be permeable enough for any metabolites that occur
to enter the blood circulation through the wall of the vessel and
for oxygen or nutrients for example to diffuse out of the blood
through the lining to the wall of the vessel.
[0024] The wall with the lining of wrapping material in another
important embodiment is either perforated at many points or is a
knitted, crocheted, or otherwise produced mesh.
[0025] Another advanced version is characterized by pores in the
lining for the substances to diffuse through. It is practical for
the diameter of the pores to be no longer than 0.5 .mu.m to prevent
smooth-muscle cells from escaping through them from the wall to the
lumen of an artery. It is important in this event for all areas of
the endoprosthesis, especially intersections in the mesh, to be
covered by the lining. When the prosthesis is made of filament by
knitting or otherwise producing a mesh, it is important to ensure
that only the filament that constitutes the endoprosthesis, which
is usually a metal vehicle, is completely wrapped. It is simple in
this event to make the mesh as open as possible.
[0026] It can be of advantage for the lining to be of several
layers, each impregnated with different medications. The layers of
the lining can be made of materials that biodegrade at different
rates. The inner layer in particular can biodegrade more rapidly
than the outer layer.
[0027] It has also been demonstrated practical for the inner layer
of the lining to be impregnated with antithrombotics and the outer
with antiproliferatives and/or other medicational substances. If
the inner layer biodegrades more rapidly than the outer layer, the
risk of thrombosis that is present during the first days after
implantation will be effectively counteracted. The
antiproliferative action on the other hand must be maintained
longer, at least seven weeks. This can be ensured by the slower
rate of biodegradation on the part of the outer layer.
[0028] The outer layer of the lining, the layer impregnated with
antiproliferatives and/or other medicational substances, consists
in another important embodiment of a short cuff at each end of the
prosthesis. This measure takes advantage of the information
obtained from animal testing that constrictions will form rather
rapidly after implantation at the ends of a prosthesis with a
waterproof or non-porous inner and outer lining component. This
effect is of course due to thromboses and proliferation at the
intima. The cuffs themselves can be provided with pores. Small
pores ensure constant fluid exchange accompanied by diffusion. The
pores at the ends of the prosthesis counteract proliferation.
[0029] The outer layer of the lining in another advanced version of
the invention can be impregnated with cytostatics to keep tumorous
stenoses open. The inner layer can be impregnated with
Theologically beneficial substances in order for example to promote
the flow of bile through a stent in the bile tract. This feature is
particularly significant because for example bile-tract stenoses
are frequently associated with secondary infections of the tracts
that lead to lumps adhering to the stent and obstructing the
lumen.
[0030] A final advanced version of the endoprosthesis in accordance
with the invention is characterized by a lateral aperture that
expands extensively in accordance with the expanding lumen. This
measure-will keep branching blood vessels open. If the prosthesis
is woven from metal, the aperture can be produced by cutting
through one of the filaments in a mesh prior to expansion. As the
stent expands, accordingly, the aperture will become wide enough to
allow blood to flow through the branch. An endoprosthesis with a
lateral aperture can also be employed in a branching bile tract. It
must of course be ensured during implantation that the prosthesis
is positioned properly with respect to the branch.
[0031] One practical embodiment is characterized by at least one
flexible medicating tube extending outward along a lining in the
form of a tubular membrane. The tube is intended to provide
constant medication inside the lining. The measure ensures
long-term supply of medication to the wall of the vessel. Blood
flow, however, will in contrast to what are called spraying
balloons, be maintained, and the medication can be supplied at low
pressure without the mechanical damage to the wall of the vessel
that occurs at the state of the art.
[0032] The medicating tube in one practical advanced version can be
attached to and detached from the lining. It can accordingly be
extracted from the membrane upon termination of medication. Several
medicating tubes can also be uniformly distributed around the
lining. A group of openings in the lining can be associated with
each medicating tube. This measure will allow the medication to be
introduced more or less isotropically along the circumference and
hence applied to the surrounding wall of the blood vessel at a
radially uniform pressure. A lining in the form of a tubular
membrane can have an outward-extending medicating tube that
accommodates radioactive liquids. The wall of the vessel can
accordingly be exposed to temporary radiation without risk to the
other tissues.
[0033] The lumen of a hollow structure that supports the prosthesis
and has netting or meshes, finally, can narrow to such an extent
when axial tension is applied to the prosthesis that it can be
intercepted in a catheter and removed with the catheter from the
vessel. The prosthesis can accordingly be extracted from the vessel
and from the patient's body.
[0034] Embodiments of an endoprosthesis in accordance with the
invention will now be specified with reference to the schematic
drawing, wherein
[0035] FIG. 1 illustrates an endoprosthesis in the form of an
elongated hollow structure with a lining of medicated biodegradable
wrapping material,
[0036] FIG. 2 is a larger-scale longitudinal section through the
endoprosthesis along the line II-II in FIG. 1,
[0037] FIG. 3 is a section illustrating the structure of an
endoprosthesis knitted out of metal filament and with meshes
constituted of loosely interconnected loops,
[0038] FIG. 4 is a view similar to that in FIG. 2 of an
endoprosthesis with a multiple-layer lining and with its ends
coated with medication,
[0039] FIG. 5 is an illustration at a scale smaller than those of
FIGS. 1 through 4 of a vascular prosthesis with a lateral opening
implanted in an artery with a branch,
[0040] FIG. 6 is a view similar to that in FIG. 5 of a vascular
prosthesis with a lateral opening that allows blood to flow through
a major artery, whereas the stent itself extends along a
branch,
[0041] FIG. 7 is a longitudinal section through an endoprosthesis
implanted in a vessel with a coating in the form of a tubular
membrane with outer walls provided with openings to administer
meditation through, and
[0042] FIG. 8 is a section illustrating the openings and pores in
the lining illustrated in FIG. 7.
[0043] The endoprosthesis 10 illustrated in FIG. 1 is a tube with a
variable lumen. Its wall 11 is completely enclosed in an inner
lining component 12 and an outer lining component 13. The lining is
applied by immersing the prosthesis in a liquid that subsequently
solidifies. Medications are dissolved in the wrapping material. The
material biodegrades without leaving deleterious decomposition
products, while the medications gradually release.
[0044] FIG. 3 illustrates a section of the wall of the tube. The
wall is knit from metal filament 15 into an open mesh of loosely
engaged loops 16. There are particular advantages to this
structure. It is flexible and elastic enough to follow the
curvature of the vessel while being implanted. Once implanted it
will be resilient enough to resist deformation from outside
forces.
[0045] The thread itself in an endoprosthesis of the type
illustrated in FIG. 3 can also be wrapped in a coat of medicated
and biodegradable wrapping material. The wall of such a prosthesis
is accordingly characterized by the presence of an open mesh. The
prosthesis can of course alternatively be enclosed in a
flexible-tubular coat.
[0046] The wall 21 of the endoprosthesis 20 illustrated in FIG. 4
has inner and outer layers 22 and 23 as well as multiple layer
cuffs 25 & 26 of a biodegradable wrapping material at each end.
Layers 22 and 23 of lining, which extend along the whole
prosthesis, are impregnated with antithrombotics. Cuffs 25 and 26,
which extend only slightly along it on the other hand, are
impregnated with antiproliferatives to prevent any overgrowth of
the ends due to thromboses or thromboarteritis as the prosthesis
remains in place long-term.
[0047] It can also be practical to impregnate only the ends of the
type of prosthesis illustrated in FIG. 4 in order to ensure release
of only a low dose and avoid systemic action. The endoprosthesis in
accordance with the invention can for example concern a sterile
metal stent. The stent is 4 cm long with an inside diameter of 4.0
mm. It is soaked in aseptic conditions in a solution of 4.00 g of
poly-D,L-lactide (which has an inherent viscosity of 0.3), 0.35 g
of triacetin, and 270 g of acetone. It is then allowed to dry (for
5 days at room temperature and for 16 days at a low pressure of 20
torrs) and at 40.degree. C. at low pressure (4 days). The polymer
coating (24 mg/cm) will now have a phase-transition temperature of
25.+-.2.degree. C. The polymeric solution can, however, also have
0.40 g of heparin suspended in it. The polymer coating will in this
event comprise 2.0 mg/cm of heparin. The polymer coatings finally
can be stored at 37.degree. C. in an isotonic phosphate buffer with
a pH of 37.degree. C. In a test of this approach the polymer began
to lose mass in 18 days and yielded a subsequent half time of 12
days. The molar mass-reduction half time was 10 days.
[0048] The endoprosthesis 30 illustrated in place in FIG. 5 has a
lateral aperture 31. This aperture expands considerably as the
prosthesis' lumen expands from its initially narrow state to the
width characteristic of the in-place prosthesis. The expanded
aperture allows unimpeded supply to a branch 33 of the artery 32
accommodating the endoprosthesis.
[0049] FIG. 6 on the other hand illustrates an endoprosthesis 30'
with a lateral aperture 31' that allows the blood to flow
essentially unimpeded through main artery 32, whereas the stent
itself extends into a subsidiary branch 33'. The subsidiary branch
could just as well be a bypass, in which event the lateral aperture
would be coaxial with the main branch.
[0050] The endoprosthesis 40 in the embodiment illustrated in FIG.
7 comprises a stent 41 enclosed in a lining 42 and 43 in the form
of a double walled sleeve. The outer lining component 43 of the
in-place and expanded stent rests against the inner surface 46 of
the blood vessel. Inner lining component 42 rests against the
stent. Between the two walls is enough room to accommodate
medications, which can penetrate to inner surface 46 through
openings 18 that extend through outer lining component 13. Inner
lining component 12 can also have (unillustrated) openings, even
more or less than outer lining component 13. A flexible tube 47 can
extend through the space between lining components 42 and 43 more
or less coaxial with the axial extent of endoprosthesis 40 and
along the inner surface of the blood vessel, allowing a continuous
supply of medication.
[0051] Flexible medicating tube 47 can also be attached to and
detachable from the lining so that it can be removed once enough
medication has been supplied. An appropriate plug can be provided
on the lining to plug up the opening of the tube. FIG. 8
illustrates a section of the membrane-like lining with pores 49
that extend through both components in addition to openings 48 that
extend only through outer lining component 43. The pores constitute
radial channels of communication that allow the diffusion of
metabolites between the wall and the lumen of the vessel.
[0052] A medication can be supplied long-term to the inner surface
46 of the vessel by the endoprosthesis 40 illustrated in FIGS. 7
and 8 without essentially interfering with the flow of blood. The
infusions can be introduced into the flexible lining subject to
slight pressure, whence they will accordingly exit also subject to
only slight pressure through the openings in lining components 42
and 43. The risk of mechanical damage to the wall 46 of the vessel
is accordingly negligible.
[0053] The infusions can also be administered at an appropriate and
defined concentration, extensively avoiding damage to the vessel or
cells.
[0054] Substances other than medications can also be introduced
into the flexible lining in order to supply nutrients to the wall
of the vessel. Glucose and/or such chemical buffers as bicarbonate,
to obtain a pH beneficial to the treatment, can in particular be
administered. Among the medications that can be administered are
anti-arteriosclerotics and genetic mechanisms to regulate the
vascular metabolism. Antithrombotics can be administered,
preferably through the holes in the inner wall of the flexible
lining, to inhibit thromboses on the inner surface.
[0055] The lining in all the embodiments specified hereintofore by
way of example can plastically deform to advantage to prevent
fissuring as it expands. This feature is characteristic not only of
the embodiments in the form of flexible tubes but also of stents
with a non-tubular (bulk) lining.
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