U.S. patent number 5,443,495 [Application Number 08/122,158] was granted by the patent office on 1995-08-22 for polymerization angioplasty balloon implant device.
This patent grant is currently assigned to Scimed Lifesystems Inc.. Invention is credited to Fertac Bilge, Andrew W. Buirge, Paul J. Buscemi.
United States Patent |
5,443,495 |
Buscemi , et al. |
August 22, 1995 |
Polymerization angioplasty balloon implant device
Abstract
A balloon/stent device for enlarging in situ to fit against a
vessel wall and hardening in place.
Inventors: |
Buscemi; Paul J. (Long Lake,
MN), Buirge; Andrew W. (Minneapolis, MN), Bilge;
Fertac (Arden Hills, MN) |
Assignee: |
Scimed Lifesystems Inc. (Maple
Grove, MN)
|
Family
ID: |
22401049 |
Appl.
No.: |
08/122,158 |
Filed: |
September 17, 1993 |
Current U.S.
Class: |
623/1.21;
604/103.05; 604/913; 606/191; 623/1.38 |
Current CPC
Class: |
A61F
2/82 (20130101); A61F 2/958 (20130101); A61M
25/104 (20130101); A61F 2210/0004 (20130101); A61F
2250/0067 (20130101); A61M 2025/1086 (20130101) |
Current International
Class: |
A61F
2/06 (20060101); A61M 29/02 (20060101); A61F
2/00 (20060101); A61F 2/02 (20060101); A61F
002/06 (); A61M 029/00 () |
Field of
Search: |
;604/96,103 ;623/1
;606/191-195 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
0442657 |
|
Aug 1991 |
|
EP |
|
PCT/US90/02406 |
|
Apr 1990 |
|
WO |
|
9116864 |
|
Apr 1991 |
|
WO |
|
Other References
Polymers for Engineering Applications, p. 12. .
8. Technora Aramid Fiber, p. 271..
|
Primary Examiner: Isabella; David
Assistant Examiner: Fossum; Laura
Attorney, Agent or Firm: Vidas, Arrett & Steinkraus
Claims
What is claimed is as follows:
1. A balloon for catheters, the balloon comprising a body portion
and two end portions, the balloon being inflatable from a first
condition to a second enlarged condition, and wherein:
a) said body portion of the balloon is made of a material which
will undergo a transformation from a flexible, elastic condition to
a rigid, inelastic condition upon an application of energy thereto;
and
b) said two end portions detach from said body portion by a
degradation of a scission material, said degradation initiated by
the application of energy thereto.
2. The device of claim 1 wherein the body portion comprises a
prepolymer containing polymerizable groups.
3. The device of claim 2 wherein the polymerizable groups are
selected from the group consisting of acrylates and
methacrylates.
4. The device of claim 2 wherein the body portion further comprises
activating agents.
5. A balloon for use on a catheter having a shaft, the balloon
comprising a body portion and two end portions, the balloon being
inflatable from a first condition to a second enlarged condition,
and wherein:
a) said body portion of the balloon is made of a material which
will undergo a transformation from a flexible, elastic condition to
a rigid, inelastic condition upon an application of energy thereto;
and
b) said end portions detach from said body portion and adhere to
the shaft of the catheter upon application of energy thereto.
6. A balloon for catheters, the balloon comprising a body portion
and two end portions, the balloon being inflatable from a first
condition to a second enlarged condition, wherein:
a) said body portion of the balloon is made of a material which
will undergo a transformation from a flexible, elastic condition to
a rigid, inelastic condition and said end portions comprise a
material which will degrade, both transformations occurring upon an
application of energy to the balloon; and
b) said body portion contains a mixture of poly-D-L-lactic acid,
polyethylene glycol dimethacrylate, isobornyl acrylate, neopentyl
glycol diacrylate and 2-hydroxy-methyl-1-phenylpropan-1-one.
7. A balloon for catheters, the balloon comprising a body portion
and two end portions, the balloon being inflatable from a first
condition to a second enlarged condition, wherein:
a) said body portion of the balloon is made of a material which
will undergo a transformation from a flexible, elastic condition to
a rigid, inelastic condition and said end portions comprise a
material which will degrade, both transformations occurring upon an
application of energy to the balloon; and
b) said body portion contains a mixture of poly-L-lactic acid,
polyethylene glycol dimethacrylate, isobornyl acrylate, neopentyl
glycol diacrylate, and 2-hydroxy-2-methyl-1-phenylpropan-1-one.
8. A balloon for catheters, the balloon comprising a body portion
and two end portions, the balloon being inflatable from a first
condition to a second enlarged condition, wherein:
a) said body portion of the balloon is made of a material which
will undergo a transformation from a flexible, elastic condition to
a rigid, inelastic condition and said end portions comprise a
material which will degrade, both transformations occurring upon an
application of energy to the balloon; and
b) the body portion comprises:
i) a prepolymer containing polymerizable groups; and
ii) activating agents selected from the group consisting of
peroxides and azides.
9. A balloon for catheters, the balloon comprising a body portion
and two end portions, the balloon being inflatable from a first
condition to a second enlarged condition, wherein:
a) said body portion of the balloon is made of a material which
will undergo a transformation from a flexible, elastic condition to
a rigid, inelastic condition and said end portions comprise a
material which will degrade, both transformations occurring upon an
application of energy to the balloon; and
b) the body portion comprises:
i) a prepolymer containing polymerizable groups; and
ii) activating agents encapsulated in micelles.
10. A balloon for catheters, the balloon comprising a body portion
and two end portions, the balloon being inflatable from a first
condition to a second enlarged condition, wherein:
a) said body portion of the balloon is made of a material which
will undergo a transformation from a flexible, elastic condition to
a rigid, inelastic condition and said end portions comprise a
material which will degrade, both transformations occurring upon an
application of energy to the balloon; and
b) the end portions contain a mixture of a linear polyester
prepared from
2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone,
dimethyl succinate and zinc stearate, and 4-methoxyphenol.
11. A balloon for catheters, the balloon comprising a body portion
and two end portions, the balloon being inflatable from a first
condition to a second enlarged condition, wherein:
a) said body portion of the balloon is made of a material which
will undergo a transformation from a flexible, elastic condition to
a rigid, inelastic condition and said end portions comprise a
material which will degrade, both transformations occurring upon an
application of energy to the balloon; and
b) the end portions contain a mixture of a linear polyester
prepared from
2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone,
dimethyl fumarate, dimethylsebacate and zinc stearate, and
4-hydroxyphenyloctyl ether.
12. A balloon for catheters, the balloon comprising a body portion
and two end portions, the balloon being inflatable from a first
condition to a second enlarged condition, wherein:
a) said body portion of the balloon is made of a material which
will undergo a transformation from a flexible, elastic condition to
a rigid, inelastic condition and said end portions comprise a
material which will degrade, both transformations occurring upon an
application of energy to the balloon; and
b) the body portion is biodegradable.
Description
FIELD OF THE INVENTION
This invention relates generally to a polymerizable balloon for use
in balloon angioplasty and other procedures involving balloon
catheters. More particularly, this invention relates to a balloon
of polymerizable material, the cylindrical body portion of which,
or a sleeve thereon, is caused to harden after inflation of the
balloon in a body vessel duct or the like to form a liner or stent
therein.
BACKGROUND OF THE INVENTION
Development of the balloon angioplasty technique began about
fifteen years ago. The purpose of this technique is to open
arteries in which the flow of blood has been impeded by build-up of
arteriosclerotic plaques on the interior walls of the arteries.
This technique consists of inserting a small diameter catheter into
a blocked artery, the catheter having a small flexible balloon
attached to its distal end. The catheter is moved through the
artery until the balloon is placed in the area of the artery in
which blood flow is impeded by plaque build-up. The balloon is then
inflated in order to shear and disrupt the wall components of the
vessel to obtain an enlarged lumen. With respect to arterial
arthrosclerotic lesions, the relatively incompressible plaque
remains unaltered, while the more elastic medial and adventitial
layers of the vessel stretch around the plaque, thus opening the
artery to permit improved blood flow. The balloon is then deflated
and removed leaving plaque flattened against the artery walls.
After a period of several months, however, approximately one-third
of the treated arteries sometimes undergo restenosis or a reclosing
of the artery at the treated area, requiring repetition of balloon
angioplasty. The restenosis problem has received considerable
attention and several proposals have been made to deal with it.
The most promising approach to restenosis prevention has been the
placement of a stent in a blood vessel which has undergone balloon
angioplasty at the position in the vessel where the balloon was
inflated. The stent is generally implanted inside a body vessel in
a procedure immediately following the balloon angioplasty
procedure. A stent (also referred to as a graft prosthesis,
arterial endoprosthesis, intraluminal graft or intravascular
mechanical support) is typically placed or implanted within the
vascular system to reinforce collapsing, partially occluded,
weakened or abnormally dilated localized sections of blood vessels
or the like. Because stents generally have too large a diameter to
fit through a pre-angioplasty, unexpanded, diseased portion of a
vessel, conventional metal stenting procedures implant a stent or
other intraluminal vascular graft subsequent to the initial balloon
angioplasty procedure in which the vessel has been expanded. The
simultaneous placement of a stent during the primary dilatation
phase of a balloon angioplasty or other procedure would alleviate
the restenosis problems and the need for a two-step procedure
wherein the angioplasty procedure is performed first, followed by
the stent placement procedure.
Another disadvantage of balloon angioplasty is the tendency of the
balloon to adhere to the vessel wall during the dilatation phase of
the angioplasty procedure. If a balloon adheres to a vessel wall,
the procedure could produce dissection, or a splitting and tearing
of the vessel wall layers, wherein the intima or internal surface
of the vessel suffers fissuring. This dissection forms a "flap" of
underlying tissue which may reduce the blood flow through the
lumen, or block the lumen altogether. Typically, the distending
intraluminal pressure within the vessel can hold the disrupted
layer or flap in place. If the intimal flap created by the balloon
dilation procedure is not maintained in place against the expanded
intima, the intimal flap can fold down into the lumen and close off
the lumen or become detached. When the intimal flap closes off the
body passageway, immediate surgery is necessary to correct this
problem. Thus, the adhesion of the balloon to the vessel wall can
cause undesirable defects or irregularities in the wall surface,
resulting in thrombosis, and restenotic episodes.
It would be advantageous to be able to provide a liner or a stent
to cover and reinforce the interior portion of the vessel with a
material that would provide a non-thrombogenic protective and
supporting surface. Ideally, this protective liner would be
provided during the primary dilatation phase of the angioplasty
procedure rather than after the initial expansion of the vessel
wall as in conventional angioplasty procedures. Thus, it would be
extremely advantageous if the balloon itself, or a sleeve encasing
the balloon, could be converted into a device capable of overcoming
the two previously mentioned disadvantages: resentosis and
adhesion.
SUMMARY OF THE INVENTION
In one aspect, the present invention is an angioplasty balloon
having a cylindrical body portion adapted to harden in an enlarged
state within a body vessel after the primary dilatation phase of a
balloon angioplasty procedure. In another aspect, the present
invention is a balloon sleeve adapted to cylindrically encase a
conventional angioplasty balloon, thereby protecting the balloon
and giving it a low profile for insertion into and through the
diseased portion of a vessel, the sleeve being adapted to enlarge
upon inflation of an angioplasty balloon and to harden in an
enlarged state such that the balloon sleeve covers and provides
mechanical support to the luminal surface of the vessel after
removal of the angioplasty balloon. In short, both aspects of the
invention provide a stent which can be placed simultaneously with
the primary dilatation phase of the angioplasty procedure. The
device may also be used to create or sustain openings or vessels in
the renal, urinary, hepatic organs or other vessels, ducts and the
like.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a portrayal of a balloon in the folded or wrapped
conformation. The balloon deflated and stretched slightly to form
essentially longitudinal creases in the balloon. The darkened
regions (B) of the balloon represent regions of the balloon
material which are chemically altered to degrade under the
influence of heat or light. Regions A, B, C of the balloon may be
of differing chemical compositions to allow either stiffening or
degradation of the material.
FIG. 2 shows the balloon of FIG. 1 in inflated form to
approximately one to 12 arms atmospheres. All portions of the
balloon inflate uniformly despite the differing chemical
compositions.
FIG. 3 shows the balloon of FIGS. 1 and 2 after the application of
heat or light energy that has activated regions B and C. Region B
has disintegrated; region C has become more rigid. The catheter
shaft and the attached cones are withdrawn through the placed
stent.
FIG. 4 shows a chemically alterable stent loaded onto a folded
balloon for delivery. The stent may contain slits or holes or slots
which expand when the balloon expands the stent.
FIG. 5 shows the expanded stent of FIG. 4 on inflated balloon. The
slots have increased in open area. The cross sectional area of the
stent has decreased with the increase in diameter. The stent is
activated by light or heat to cause an increase in stiffness.
FIG. 6 shows a stent as in FIG. 4a except that in place of slots or
slits, the stent is comprised of a microporous material, which
again increases in cross sectional area as the balloon expands the
stent.
FIG. 7 shows the balloon of FIG. 6 expanded.
FIG. 8 shows a balloon with a resistance heating element.
FIG. 9 shows a balloon with a radiation diffusing optical
fiber.
FIG. 10 is an enlarged portion of FIG. 9.
DETAILED DESCRIPTION OF THE DRAWINGS AND THE PREFERRED EMBODIMENTS
OF THE INVENTION
One approach according to this invention for the percutaneous
repair of cardiovascular anomalies is that the balloon itself may
become a stent if it is released from the catheter by separation of
the central body from the end cones. An extension of this approach
is to make a balloon that hardens in the middle and degrades at the
ends upon delivery.
Such a device would be delivered to the desired portion of
vasculature in the usual manner for a percutaneous dilatation. The
actual device would closely resemble a percutaneous transliminal
coronary angioplasty ("PCTA") balloon catheter. After the device
was positioned, it would be inflated so that the body of the
balloon would come in contact with the vessel wall. At this point,
energy would be supplied to the balloon through the catheter, in
the form of heat or light, causing the center (cylindrical) portion
of the balloon body to harden while the ends would dissolve or
degrade away. The ends may also be made to detach from the
cylindrical body of the balloon by the degradation of an adhesive
or the like holding the cone ends to the balloon body initiated by
the delivery of energy. Thirdly, the ends of the balloon may be
made to detach by shrinking away from the hardening balloon section
and adhering to the shaft of the catheter upon delivery of the
energy. The implanted portion of the balloon provides support for
the vasculature and/or may be a drug delivering matrix. The
implanted section of the balloon may be biodegradable, thus
eventually being resorbed into the body.
Another approach comprises a sleeve which encases an ordinary PTCA
balloon. The sleeve would be the equivalent of the balloon body
described above. After hardening the sleeve, the balloon would be
deflated and removed, leaving the sleeve in place.
FIG. 1 illustrates an angioplasty balloon of the first preferred
embodiment of the present invention. The balloon, shown generally
by 10 is incorporated into a conventional angioplasty balloon
catheter 12 by being wrapped about the catheter as shown for
insertion into the lumen of a vessel. The balloon as seen in FIG. 2
in an inflated condition comprises a cylindrical body portion 14
and two end or cone portions 16. In use, the balloon is positioned
in the area of a vascular lesion and is thereafter inflated. After
inflation, energy is supplied to the balloon, causing the
cylindrical body portion 14 of the balloon to harden while
simultaneously causing the cone portions 16 of the balloon to
dissolve or degrade or otherwise separate from body 14 as seen in
FIG. 3. The cylindrical body portion 14 of the balloon, in its
enlarged state, lies against the luminal surface of the vessel
wall, providing mechanical support thereto. The body portion of the
balloon provides the vessel wall with a protective,
non-thrombogenic surface during the primary dilatation phase of the
angioplasty procedure, while also acting as a stent. The catheter
along with end portions or cones 16 is withdrawn through the
emplaced stent.
The material comprising the body portion 14 of the balloon 10 is
made to undergo a transformation such that it becomes rigid and
inelastic upon the application of appropriate energy thereto. Upon
transformation, the material comprising the body portion of the
balloon remains within place in the vessel due to its tight fit. It
may also adhere to the luminal surface of the vessel wall. A
prepolymer is a material containing polymerizable groups such as
acrylate or methacrylate. Acrylated or methacrylated materials such
as polyethylene glycol (PEG) dimethacrylate, isobornyl acrylate,
and neopentyl glycol diacrylate are all prepolymers. These
materials, when in the presence of
2-hydroxy-2-methyl-1-phenylpropan-1-one and irradiated with
ultraviolet light, will form a crosslinked, insoluble polymer
matrix. For example, the hardenable balloon material may be a
mixture of poly-D-L-lactic acid, (polymer), polyethylene glycol
dimethacrylate (prepolymer) and isobornyl acrylate, neopentyl
glycol diacrylate and/or 2-hydroxy-methyl-1-phenylpropan-1-one
(initiators). Other initiator materials which are able to produce
free radial bearing fragments upon irradiation may also be used.
Such radical compositions are UV hardenable. A second balloon
material can be formulated from all the above components, with the
substitution of poly-DL-lactic acid or polycaprolactone for
poly-L-lactic acid as the polymer. The crosslinking component need
not be physically separate from the predominant polymer. It could
be attached to the backbone or a sidechain, or the end of the
polymer. Non degradable polymers as well as polyanhydrides.
Polyphosphazines and other aliphatic could be interdeposed to form
copolymers with the lactides and glycolides. Copolymers may be
formed with carbohydrates and other biocompatible molecules.
Radiation from a UV laser catheter introduced through a lumen of a
balloon catheter via an optical fiber may be used to supply the
requisite energy to polymerize the material.
Other pre-polymer examples:
______________________________________ ethylene glycol
dimethacrylate cyclohexyl methacrylate diethylene glycol diacrylate
diethylene glycol dimethacrylate neopentyl gylcol diacrylate
polyethylene glycol (600) dimethacrylate tripropylene glycol
diacrylate lauryl methacrylate stearyl methacrylate ethoxylated
bisphenol A dimethacrylate ethoxylated bisphenol A diacrylate
di-trimethylol propane tetraacrylate (LTX) isodecyl acrylate dipert
acrythritol pentaacrylate isobornyl methacrylate ethoxylated
trimethylol propane triacrylate (LTX) highly ethoxylated bispenol A
dimethacrylate propoxylated trimethylol propane triacrylate dodecyl
methacrylate ethoxylated pentaerythritol tetraacrylate caprolactone
acrylate highly ethoxylated TMPTA (trimethylolpropane triacrylate)
highly propoxylated TMPTA highly ethoxylated TMPTA bobrnyl acrylate
propoxylated neopentyl glycol diacrylate glyceryl propoxy
triacrylate highly propoxylated gylceryl triacrylate acrylated or
methacrylated metabolic fragments dervied from reduction of Krebs
diacids and subsequent esterification
______________________________________
The material comprising the body portion 14 may contain activating
agents which are incorporated directly into the polymer material.
Examples of such activating agents include peroxides, azides, and
other UV activated or heat activated agents as known in the art.
The activating agents are incorporated into the polymer material
and allow the polymer material to rapidly cross-link upon exposure
to an activating energy source, such as fiber optic light. The
energy will initiate the polymerization and/or cross-linking
reaction to occur. The polymerization and or cross-linking causes
the sleeve material to form a hardened or rigid material capable of
supporting the interior surface of the lumen for an indefinite
period of time. The transformation from flexible to rigid and self
supporting causes the central balloon portion to stay in place.
The polymerization and/or cross-linking of the material of body
portion 14 causes an increase in the modulus elasticity of the
material from values typical of soft polymers, i.e., 0.1 GPa
(Gigapascal) to that of stiffer molecules with moduli elasticity
near 4.0 GPa for example. When the activating agents are located on
the outside surface of the balloon, the polymerization and/or
cross-linking reaction takes place on the surface of the vessel
itself. This allows for bonding of the surface agents to both the
polymer and the vessel wall.
Lower concentrations of polymerization and/or cross-linking agents
on the lumen or interior side of the balloon cause that portion to
degrade density enhances blood compatibility of the outer layer of
the balloon since rapidly degrading materials will prevent a
protein, platelet or leukocyte accumulation.
In addition, the polymerization and/or cross-linking agents that
cause the modulus of elasticity to increase within the bulk of the
polymer may not necessarily be the same one or ones that are
preferred on the outside surface of the balloon where actual
contact with the vessel is made. Cross-linking agents may be part
of the polymer chains or may be incorporated into the bulk of the
polymer by exposing preferably the exterior surface to a solution
of the agent or agents so that the exterior side develops a higher
concentration of agents than the lumen side.
In another preferred embodiment of the present invention highly
active cross-linking agents are encapsulated within micelles. When
the body 14 of the balloon 10 is stressed, i.e., expanded by
inflation of the balloon, the micelles collapse releasing the
activating agents. Upon expansion, the stress in the inflating body
portion will be the greatest in the outer layers. If the body
portion of the balloon comprises multiple layers, it is thus
preferable to concentrate the micelles in the outer layers of body
portion. The micellar encapsulated material may also be released by
other suitable forms of stress energy, such as ultrasonic
disruption. Thus, after the body portion of the balloon is
inflated, an ultrasonic probe or transducer is inserted through a
lumen in the catheter into or near the balloon cavity and
activated, causing the release of activating agents. An example of
such a system would be the incorporation of methylene diisocyanates
(MDI) contained within phospholipid micelles composed of sodium
dodecysulfate. The MDI micelles would be incorporated as an oil or
oil in water emulsion into the stent material, which in this case
may contain reactive amine groups, when it was cast from solution
so that the micelles would not be physically stressed. Upon
expansion of the balloon, the walls of the stent become thinner in
proportion to the expansion of the stent. The shear stress placed
on the micelles would cause them to burst or otherwise crack. The
MDI would immediately react with the amines to crosslink the
polymer comprising the stent.
Alternatively the micelles could be comprised of
phosphatidylethanolamine or any other short chain polymer that
would form micelles or microparticles. If the micelles contained
peroxides or other free radical producing agents and if the polymer
contained reactive double bonds as acrylates, then upon stressing
the micelles, the free radicals would cause crosslinking of the
polymer to occur. Alternately, the transducer may be the balloon
itself which is then activated to release the micellar encapsulated
activating agents. To accomplish this, the balloon may be comprised
of a piezoelectric material as PVDF (e.g. polyvinylidinefluoride)
that is electrically connected to a power source at the proximal
end of the catheter. Upon the application of an alternating
voltage, the polymer will vibrate in response to the polarity of
the voltage and in accordance to how the material was polled
(dipoles set).
The balloon of the first preferred embodiment of the present
invention as shown in FIGS. 1-3 is incorporated into a catheter
device which closely resembles a conventional percutaneous
translumial coronary angioplasty ("PCTA") balloon catheter. The
balloon is delivered to the desired portion of the vasculature in
the usual manner for a percutaneous dilation. After the balloon is
properly positioned in the area of the vascular lesion, it is
inflated so that the balloon contacts and pushes back the material,
generally plaque, which lines the vessel wall. Once the balloon is
sufficiently inflated, energy is supplied to the balloon. The
energy, preferably in the form of heat or light, causes the center
body portion of the balloon to harden. The cones or ends 16
separate as described below and catheter 12 is then removed from
the body as shown in FIG. 3, leaving the hardened body portion 14
of the balloon inside the vessel to provide mechanical support and
to cover the vessel in order to prevent the formation of thrombus.
The result is an in situ formed stent.
Energy may be delivered to the stent during its formation in the
following manner. If the energy is thermal the inner shaft of the
balloon may be coated with a semiconductive material or wrapped
with a wire resistance heating element 30 as shown in FIG. 8 such
that, upon application of a current through leads 32 and 34,
resistive heating occurs. The energy is conductively transferred to
the surface of the balloon by the liquid filling the balloon (not
shown).
If the material in the stent or sleeve is activatible by light
energy, then the center shaft of the catheter will contain an optic
fiber 40 as shown in FIGS. 9 and 10 for diffusing radiation
outwardly through the balloon. The fiber may be made such that it
will diffuse light transmitted down the optic fiber to the interior
surface of the balloon. This light energy would be absorbed by the
reactive species in the stent and induce the crosslinking of the
polymer comprising the stent or the formation of an
interpenetrating network. Alternatively, vibrational energy,
delivered by a piezo element (not shown) placed in the center of
the balloon, could be delivered to the fluid filling the balloon
causing it to heat, or the balloon itself could be caused to
vibrationally heat if it were piezoelectric in nature.
In the first preferred embodiment of the balloon of the present
invention shown in FIGS. 1-3, the cone or end portions 16 of the
balloon spontaneously dissolve or degrade and separate from body 14
upon the application of energy thereto while the body portion 14
hardens.
The hardenable balloon body material is preferably a mixture of
poly-L-lactic acid (molecular weight>1.4M), polyethylene
glycol(Mw=600) dimethacrylate, isobornyl acrylate, neopentyl glycol
diacrylate, and 2-hydroxy-2-methyl-1-phenylpropan-1-one. A second
preferred balloon body material may be formulated from all the
above components, with the substitution of poly-DL-lactic acid or
poly caprolactone for the poly-L-lactic acid.
The end or cone portions 16 of the balloon may comprise a polymer
which has labile components adapted to cause a chain scission
reaction or may incorporate a polymer which are cleaved by a
secondary, energy activated compound and which break down into
components which are soluble and disperse. The polymers which may
be used for the end portions of the balloon can be natural,
synthetic or a modified natural polymer such as a conjugated
protein. An example of a material for the scission regions 18 is a
linear polyester prepared from
2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone,
dimethyl succinate and zinc stearate. Along with the linear
polyester is mixed 4-methoxyphenol. A second polymer would be a
linear polyester prepared from
2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propone,
dimethyl fumarate, dimethylsebacate, and zinc stearate mixed with
4-hydroxyphenyloctyl ether.
In another embodiment, the cones of a balloon may detach from the
cylindrical body of the balloon by the degradation of material at
the scission regions 18 (See FIG. 2) attaching the cones 16 to the
body 14. The degradation is initiated by the application of energy
from the catheter. In yet another embodiment, the cones 16 of the
balloon 10 detach by shrinking away from the hardening body section
14 of the balloon and adhere to the shaft 12 of the catheter upon
delivery of energy as seen in FIG. 2. Such an arrangement is made
possible if the cones are made of polyethylene, or polyolefin
copolymer that has been formed into a cone. In such an embodiment,
the cone material changes its physical properties sufficient to
become soft and easily pulled away from the hardened balloon
portion upon the application of energy thereto.
In order to provide a conventional angioplasty balloon with a low
profile and to protect it from tearing, many manufacturers often
wrap or coil a conventional angioplasty balloon inside a protective
tube or sleeve, which is removed from the balloon prior to the
procedure. It would be extremely advantageous if the protective
sleeve did not have to be removed but could serve an additional
purpose, such as a stent. This is provided by the second embodiment
of this invention as seen in FIGS. 4-5.
In that embodiment of the present invention, a conventional
angioplasty balloon 20, see FIG. 4, is folded and encased in a
balloon sleeve 22 comprising a material having the same properties
as the body portion 14 of the balloon 10 described above in
connection with FIGS. 1-3. The sleeve 22 cylindrically encases a
conventional angioplasty balloon 20, giving the balloon 20 a low
profile for insertion into a diseased area and protects the balloon
from ripping or tearing.
In use, the balloon 20 encased in the sleeve 22 is positioned
adjacent the diseased portion of the vessel and is enlarged from a
first insertion diameter to a second enlarged diameter as shown in
FIG. 5 upon expansion of the balloon. Thereafter, the sleeve 22 is
caused to harden or become rigid in its enlarged state. The sleeve
material stretches during the primary expansion phase, conforming
first to the shape of the balloon and then, as the balloon impinges
on the vessel wall, to the shape of the combination of the balloon
and wall.
The sleeve 22 is generally cylindrical in shape as seen in FIGS. 2
and 3 and is comprised of a polymer material which is capable of
stretching to and maintaining a second, enlarged diameter
configuration. The sleeve is formed by immersion of a mandrel in a
solution or by spraying a mandrel. The transformation of the sleeve
material to a rigid or hardened state can be induced by any of the
methods previously described. Thus, the application of energy may
be used to initiate polymerization and cross-linking reactions,
which causes the sleeve material to harden. Alternately, the
transformation may also be caused by the release of chemical
components encapsulated in the wall of the sleeve induced by
stretching or the application of energy.
FIGS. 6 and 7 show a stent as in FIG. 4 except that in place of
slots or slits, the stent is comprised of a microporous material in
which the slots or slits increase in cross sectional area as the
balloon expands the stent.
In order to perform both functions, i.e., encasing the balloon and
as an arterial lining, the sleeve material must be able to maintain
sufficient strength to keep the folds of the balloon in place. It
must also be capable of being expanded by the balloon without the
addition of any form of energy prior to expansion, since this may
lock the unexpanded sleeve in place. The sleeve will be relatively
thin walled and sufficiently flexible to negotiate bends and curves
encountered in the coronary and other arteries. The sleeve will
generally range before expansion from about 1 mm to 3 mm ID with
wall thickness typically ranging from about 0.1 to 0.5 min. The
wall thickness will decrease depending on the expansion of the
sleeve. Also, the thickness will decrease in proportion to the
differences determined by Area-pi(r1 2-r2 2) where r1 and r2 are
the inner and outer radius, generally speaking.
The sleeve may be comprised of a single polymeric material or
multiple layers of different polymeric materials. A sleeve
comprising multiple layers may, for example, include an interior
layer of a non-adhesive swellable hydrogel such as collagen or
polyvinylpyrrolidone which is suitable for release from the balloon
surface, one or more middle layers such as polylactic acid (PLA),
specifically poly-L-lactic acid (PLLA), and cross-linking which are
suitable for uniform expansion under stress (plastic and formation)
and cross-linking and an exterior layer such as collagen or other
polyesters, which are suitable for adhesion to the vessel wall by
cross-linking or the like. In addition, the sleeve may comprise a
polymer or polymers which contain therapeutic or pharmacological
agents incorporated thereon.
Both the polymerizable balloon and sleeve embodiments of the
present invention may comprise materials such as PLA which will
biodegrade after a predetermined amount of time and/or may comprise
materials capable of releasing drugs or other pharmaceuticals into
the surrounding tissue.
It should be appreciated that the device and methods of the present
invention are capable of being incorporated in the form of a
variety of embodiments, only a few of which have been illustrated
and described above. The invention may be embodied in other forms
without departing from its spirit or essential characteristics. The
described embodiments are to be considered in all respects only as
illustrative and not restrictive and the scope of the invention is,
therefore, indicated by all the appended claims rather than by the
foregoing description. All changes which come within the meaning
and range of equivalency of the claims are to be embraced with
their scope.
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