Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METI30D OF PRODUCING HIOMATERIALS
TECFH1TICAL FIELD
The present invention relates to the biomaterials
in tissue repair and replacement. The invention
further relates to methods of securing the biomaterials
to existing tissue.
BACKGROUND OF THE INVENTION
Collagen, fibrin, elastin and various other
elastin-based biomaterials are known biomaterials.
Collagen is an insoluble fibrous protein that occurs in
vertebrates as the chief constituent of connective
tissue fibrils and in bones. Fibrin is a white
insoluble fibrous protein formed from fibrinogen by the
action of thrombin especially in the clotting of blood.
Elastin is an extracellular matrix protein that is
ubiquitous in mammals. Other biomaterials include
silicone) poly(etherurethane urea),poly(etherurethane),
poly(esterurethane), poly(ethylene), poly(prolene),
poly(tetrafluoroethylene), polyvinylidene fluoride,
polycarbonate, polyethylene terephthlate), poly(methyl
methacrylate), polystyrene, poly(vinylchloride),
poly(2-hydroxyethylmethacrylate),poly (vinyl-
pyrrolidone), poly(acrylonitrile), polygycolide)
poly(gycolide-L-lactide), polyester-ether),
poly(glycolide-E-caprolactone) copolymer, poly-
(glycolide-trimethylene carbonate), random block
copolymer, polyglycolic acid, collagen-based tissues
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and matrices, tissue engineered materials,
bioartificial tissues(living tissue grafts), and
bioinert ceramics.
Elastin is an extracellular matrix protein that is
ubiquitous in mammals. Elastin is found, for example,
in skin, blood vessels, and tissues of the lung where
it imparts strength) elasticity and flexibility. In
addition, elastin, which is prevalent in the internal
elastic lamina (IEL) and external elastic lamina (EEL)
of the normal artery, may inhibit the migration of
smooth muscle cells into the intima. Elastin in the
form of solubilized peptides has been shown to inhibit
the migration of smooth muscle cells in response to
platelet-derived factors (Ooyama et al, Arter-
iosclerosis 7:593 (1987). Elastin repeat hexapeptides
attract bovine aortic endothelial cells (Long et al, J.
Cell. Physiol. 140:512 (1989) and elastin nonapeptides
have been shown to attract fibroblasts (USP 4,976,734).
The present invention takes advantage of these physical
and biochemical properties of elastin.
Thirty to forty percent of~atherosclerotic
stenoses that are opened with balloon angioplasty
restenose as a result of ingrowth of medial cells.
Smooth muscle ingrowth into the intima appears to be
more prevalent in sections of the artery where the IEL
of the artery is ripped, torn, or missing, as in severe
dilatation injury from balloon angioplasty, vessel
anastomoses, or other vessel trauma that results in
tearing or removal of the elastic lamina. While repair
of the arterial wall occurs following injury, the
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elastin structures IEL and EEL do not reorganize.
Since these components play major structural and
regulatory roles, their destruction is accompanied by
muscle cell migration. There are also diseases that
are associated with weakness in the vessel wall that
result in aneurysms that can ultimately rupture, as
well as other events that are, at least in part,
related to abnormalities of elastin.
Prosthetic devices, such as vascular scents, have
been used with some success to overcome the problems of
restenosis or re-narrowing of the vessel wall resulting
from ingrowth of muscle cells following injury.
However) their use is often associated with thrombosis.
In addition, prosthetic devices can exacerbate
underlying atherosclerosis. Nonetheless, prostheses
are of ten used.
Until relatively recently, the primary methods
available for securing a prosthetic material to tissue
(or tissue to tissue) involved the use of sutures or
staples. Fibrin glue, a fibrin polymer polymerized
with thrombin, has also been used .(primarily in Europe)
as a tissue sealant and hemostatic agent.-
Laser energy has been shown to be effective in
tissue welding arterial incisions, which is thought to
occur through thermal melting of fibrin, collagen and
other proteins. The use of photosensitizing dyes
enhances the selective delivery of the laser energy to
the target site and permits the use of lower power
laser systems, both of which factors reduce the extent
of undesirable thermal trauma.
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OBJECTS AND SUD~dARY OF 'f~ INVE111TION
It is a general object of the invention to provide
a method of effecting tissue repair or replacement
using a biomaterial or supporting a section of a body
tissue.
It is a specific object of the invention to
provide an biomaterial 'suitable for use as a stent,
for example, a vascular stent, or as conduit
IO replacement, for example, as an artery) vein or a
ureter replacement. The biomaterial can also be used
as a stent or conduit covering or coating or lining.
It is a further object of the invention to provide
a biomaterial graft suitable for use in repairing a
lumen wall.
It is another object of the invention to provide a
biomaterial material suitable for use in tissue
replacement or repair, for example, in interior bladder
replacement or repair, intestine, tube replacement or
repair such as fallopian tubes, esophagus such as for
esophageal varicies, ureter, artery such as for
aneurysm) vein, stomach, lung, heart such as congenital
cardiac repair. or colon repair or replacement, or skin
repair or replacement, or as a cosmetic implantation or
breast implant.
It is also an object of the invention to provide a
method of securing a biomaterial to an existing tissue
Without the use of sutures or staples.
The subject invention is directed to a method for
producing biomaterials which can be used in biomedical
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applications, or the biomaterial can be fused onto a
tissue substrate, or the biomaterial can itself be
used. The invention can be also directed to a method
for using fusible biomaterial, to a method for
5 producing a biomaterial fused onto a tissue substrate,
to a prosthetic device, and to a method of producing a
prosthetic device including such biomaterials.
The present invention'relates to a method of
repairing, replacing or supporting a section of a body
tissue, preferably a live tissue substrate. The method
comprises positioning a biomaterial at the site of the
section and bonding the biomaterial to the site or to
the tissue surrounding the site. The bonding is
effected by contacting the biomaterial and the site, or
tissue surrounding the site, at the point at which said
bonding is to be effected, with an energy absorbing
agent. The agent is then exposed to an amount of
energy absorbable by the agent sufficient to bond the
biomaterial to the site or to the tissue surrounding
the site.
More specifically, a tissue-fusible biomaterial
can be produced using the process of the present
invention which comprises a layer of a biomaterial and
a tissue substrate each having first and second outer
surfaces, and an energy absorbing material applied to
at least one of the outer surfaces. Preferably, the
energy absorbing material penetrates into the
biomaterial.
The energy absorbing material is energy absorptive
within a predetermined range of light wavelengths
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depending on material thickness. The energy absorbing
material is chosen so that when it is irradiated with
light energy in the predetermined wavelength range, the
intensity of that light will be sufficient to fuse
together one of the first and second outer surfaces of
the biomaterial and the tissue substrate. Preferably,
the first and second outer surfaces of the biomaterial
are major surfaces. Typically, the energy absorbing
material is indirectly irradiated by directing the
ZO light energy first through the biomaterial or tissue
substrate and then to the energy absorbing material.
In a preferred process of this invention, the
energy absorbing material comprises a biocompatible
chromophore, more preferably an energy absorbing dye.
In one form of the present invention, the energy
absorbing material is substantially dissipated when the
biomaterial and the tissue substrate are fused
together. In another form of this invention, the
energy absorbing material comprises a material for
staining the first or second surface of the
biomaterial. The energy absorbing, material can also be
applied to one of the outer surfaces of the biomaterial
by doping a separate biomaterial layer with an energy
absorbing material and then fusing the doped separate
biomaterial layer to the biomaterial. In any case, the
energy absorbing layer is preferably substantially
uniformly applied to a portion of at least one of the
outer surfaces, and more preferably in a manner wherein
the energy absorbing material substantially covers
substantially the entire outer surface of the bio-
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material. Although the energy absorbing material can
be applied directly to the tissue substrate, it is not
the preferred method because of the difficulty in
controlling penetration into the intertices.of the
tissue substrate.
Some of the key properties which effect the
process of the present invention regarding fusing the
biomaterial and tissue substrate include the magnitude
of the wave length, energy level, absorption, and light
intensity during irradiation with light energy of the
energy absorbing material) and the concentration of the
energy absorbing material. These properties are
arranged so that the temperature during irradiation
with light energy for period of time which will cause
fusing together of one of the first and second outer
surfaces of the biomaterial and the tissue substrate is
from about 40 to 140 degrees C., and more preferably
from about 50 to 100 degrees C., but if well localized
to the biomaterial tissue interface can be as high as
600 degrees C. Furthermore, the average thickness of
the energy absorbing material in,the preferred process
of this invention is from about 0.5 to 300 microns.
The subject invention provides a biocompatible
biomaterial formed into a three-dimensional structure.
This structure can be used, for example, in a stromal
support matrix populated with actively growing stromal
cells. The stromal support matrix, which are
preferably fibroblasts, can then be used to provide
support, growth factors, and regulatory factors needed
to sustain long-term active proliferation of cells in
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culture. A living stromal tissue can be prepared
comprising stromal cells and connective tissue proteins
naturally secreted by the stromal cells which are
attached to and substantially enveloping a~framework
composed of a biocompatible, non-living material formed
into three dimensional structure having interstitial
spaces bridged by the stromal cells. The stromal cell
systems contemplated herein are described in the
following U.S. patents of Advanced Tissue Sciences,
Inc. (formerly Marrow-Tech Incorporated), which are
incorporated herein by reference: US 5,478,739, US
5,460,939, US 5,443,550, US 5,266,480, US 5,518,915, US
5,516,681, US 4,963,489, US 5,032,508, US 4,721,096,
US 5,516,680, US 5,512,475, US 5,510,254, and US
5,160,490.
The biomaterial structures can also have a
cellular lining of human cells. The cells can be
derived autologously, or otherwise) and formed into a
lining on one of the major surfaces of the elastin and
elastin-based biomaterials layer. Preferably, the
cells which are employed to form,such a lining are
endothelial cells and/or epithelial cells and/or
urothelial cells.
The present invention also relates to a method of
repairing, replacing or supporting a section of a body
tissue using biomaterials. ' The method comprises
positioning biomaterials at the site of the section and
bonding the biomaterial to the site or to the tissue
surrounding the site. The bonding is effected by
contacting the biomaterial and the site, or tissue
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surrounding the site, at the point at which said
bonding is to be effected, with an energy absorbing
agent. The agent is then exposed to an amount of
energy absorbable by the agent sufficient to bond the
biomaterial to the site or to the tissue surrounding
the site.
The absorbing material can comprise bio-
compatible materials, preferably energy absorbing dye.
In one form of the present invention, the energy
absorbing material is substantially dissipated when the
biomaterial and the tissue substrate are fused
together. In another form of this invention, the
energy absorbing material comprises a material for
staining the first or second surface of the elastin or
elastin-based biomaterial. The energy absorbing
material can also be applied to one of the outer
surfaces of the biomaterial by doping a separate
elastin layer with an energy absorbing material and
then fusing the doped separate elastin layer to the
biomaterials. In any case) the energy absorbing layer
is preferably substantially uniformly applied to at
least one of the outer surfaces, typically in a manner
wherein the energy absorbing material substantially
covers the entire outer surface of. the biomaterial.
Some of the key properties which effect the method
of the present invention regarding fusing the
biomaterial and tissue substrate include the magnitude
of the wavelength, energy level, absorption, and light
intensity during irradiation with light energy of the
energy absorbing material) and the concentration of the
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energy absorbing material. These properties are
arranged. so that the temperature during irradiation
with light energy for period of time which will cause
fusing together of one of the first and second outer
5 surfaces of the biomaterial and the tissue substrate is
from about 40 to 140 degrees C., and more preferably
from about 50 to 100 degrees C., but if well localized
to the biomaterial tissue interface can be as high as
600 degrees C. Furthermore, the average thickness of
10 the energy absorbing material in the preferred method
of this invention is from about 0.5 to 300 microns.
Further objects and advantages of the invention
will be clear from the description that follows.
Further objects and advantages of the invention
will be clear from the description that follows.
BRIEF DESCRIPTION OF THE DRATnTINGS
FIGURE 1. Application of laser energy to
biomaterial and exposed native tissue.
FIGURE 2 Placement of biomaterial into artery.
FIGURE 3. Use of biomaterial as intestinal patch.
FIGURE 4. Scanning electron micrograph of
biomaterial (prepared according to Rabaud et al using
elastin, fibrinogen and thrombin) fused to porcine
aorta using continuous wave diode laser.
FIGURE 5. Light microscopic picture of
biomaterial fused to porcine aorta using a pulsed diode
laser, where E = elastin biomaterial; A = aorta.
FIGURE 6. Light microscopic photomicrograph of
biomaterial derived from arterial digest welded to
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porcine carotid artery, where E = elastin biomaterial;
A = aorta.
DETAILED DESCRIPTION OF T8E INVENTION
The present invention relates to biomaterials and
to methods fusing of such biomaterials to tissue using
laser energy. Biomaterials suitable for use in the
present invention can be.prepared, for example, from
elastin (from bovine nuchal ligament), fibrinogen and
thrombin as described by Rabaud et al (USP 5,223,420),
as well as from collagen, fibrin, and various other
known biomaterials. (See-also Aprahamian et al, J.
- Biomed. Mat. Res. 21:965 (1987); Rabaud et al, Thromb.
Res. 43:205 (1986); Martin, Biomaterials 9:519 (1988).
Such biomaterials can have associated thrombogenic
property that can be advantageous in certain types of
tissue repair. Biomaterials suitable for use in the
invention can also be prepared from elastin and type
III collagen, also as described by Rabaud and
co-workers (Lefebvre et al, Biomaterials 13(1):28-33
(1992). Such preparations are not thrombogenic and
thus can be used for vascular stems, etc.- A further
type of biomaterial suitable for use in the present
invention is prepared as described by Urry et al (see,
for example, USP 4,132,746 and 4,500,700) (See also
USP's 4,187,852, 4,589,882) 4,693,718, 4,783,523,
4,870,055, 5,064,430, 5,336,256). Elastin matrices
resulting from digestion of elastin-containing tissues
(eg arteries) can also be used. Digestion results in
the removal of cells, proteins and fats but maintenance
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of the intact elastin matrix. The biomaterial used
will depend on the particular application.
Biomaterial of the invention prepared from soluble
elastin (see Rabaud et al above) can be molded so as to
render it a suitable size and shape for any specific
purpose. Molded biomaterial can be prepared as
follows. Elastin (eg soluble elastin MW 12-32,000
daltons) is washed and swollen in buffer. Fibrinogen or
cryoglobulins (prepared, for example, according to Pool
et al, New Engl. J. Med. 273 (1965 are added to the
swollen elastin, followed by thiourea, with or without
a protease inhibitor (such as aprotinin), and collagen.
Thrombin is added with stirring and the resulting
mixture is immediately poured into an appropriate mold.
The mold is then incubated (for example, at 37~C)
while polymerization of the fibrin/elastin material is
allowed to proceed, advantageously, for from between 15
minutes to 1 hour, 30 minutes being preferred. The
reaction can be carried out at temperatures less than
37~C., but the reaction proceeds more rapidly at 77~C.
Heating the reaction to over 40~C, however, can result
in denaturation of the thrombin. Cooling-of the
mixture while stirring allows more time for mixing to
occur. For polymerization to occur, it is important to
have calcium and magnesium in the buffer and to use
undenatured thrombin.
Following polymerization in the mold, the
resulting biomaterial can be further cross-linked using
gamma radiation or an agent such as glutaraldehyde (a
solution of glutaraldehyde, formic acid and picric acid
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being preferred). When radiation is used, the samples
are, advantageously, subjected to gamma-irradiation
from a Cobalt-60 source. The amount of irradiation can
range, for example, from 10 to 100MRAD, with 25MRAD
being preferred. It has been shown that the amount of
gamma-irradiation can affect the strength of the
material (Aprahamian, J. Biomed. Mat. Res. 21:965
(1987).
Sheets of biomaterial can be prepared that are of
a controlled thicknesses by using appropriate molds.
Sheets of the biomaterial can be made in thicknesses
ranging, for example, from 200 microns to 5 mm. Sheets
are generally made as thin as possible to allow for
penetration of laser energy while maintaining
sufficient strength. By way of example, a sheet
suitable for use as an intestinal patch can range in
thickness from 200 microns to 5 mm, with about 2 mm
being preferred. A patch requiring greater strength,
such a patch for use in the bladder, is typically
thicker. Arterial stents or patches can be thinner (eg
100 ~.an - 1000 ,can) .
Biomaterial prepared from soluble elastic or
insoluble elastin fragments can also be molded into
tubular segments for example, by injecting the material
into tubular molds. Crosslinkage of the elastin
solution present between the inner and outer tubes can
be effected prior to withdrawal of biomaterial from the
mold or after the tubes are removed. Tubular segments
of different inner and outer diameters, as well as of
different lengths, can be prepared using this approach
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by varying the diameters of the inner and outer tubes.
A mold of this type can be made in virtually any size
with the inner and outer tubes varying in diameter. A
small tube can be used for a coronary arterial stent.
A large tube of 1-5 inches in diameter can be made and
used as an angularly welded patch for anastomosis of
the small intestine or colon. Various molding
techniques and molding materials can be used; the
foregoing is merely an example.
As indicated above, biomaterial suitable for use
in the present invention can be prepared from digests
of tissue containing an elastin matrix. Tissues
suitable for use as a starting material include
arteries (e.g. coronary or femoral arteries, for
example, from swine), umbilical cords) intestines,
ureters, etc. Preferably, the matrix material is
(derived from the species of animal in which the
implantation is being performed so that bio-
compatibility is increased. Any method of removing
(digesting away) cellular material, proteins and fats
from the native matrix while leaving the extracellular
elastin matrix intact can be used. These methods can
involve a combination of acidic, basic, detergent,
enzymatic, thermal or erosive means, as well as the use
of organic solvents. This may include incubation in
solutions of sodium hydroxide, formic acid) trypsin,
guanidine, ethanol, diethylether, acetone, t-butanol,
and sonication. Typically) the digestion proceeds
more quickly at higher temperatures. The optimal
temperature and time (of incubation depend on the
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starting material and digestive agent used, and can be
readily determined.
One skilled in the art will appreciate that while
tubular segments result from digestion of tubular
5 starting materials, those segment can be opened and
shaped to yield sheets suitable for use as tissue
grafts. Alternatively, such segments can be opened and
then reconstructed as tubular segments having a
diameter different than the starting tissue.
10 Preferably, however, when tubular products are sought)
the starting material is selected so as to yield a
tubular segment after digestion having the appropriate
diameter so that subsequent manipulations (other than
adjustment of length) can be avoided.
15 The biomaterial of the invention, whether prepared
from elastin powder or from tissues digests, is
normally secured to existing tissue. Various
techniques for effecting that attachment can be used,
including art-recognized techniques. However, it is
preferred that the biomaterial be secured using a
tissue welding energy source and an agent that absorbs
energy emitted by that source. Advantageously, the
energy source is an electromagnetic energy source,
such as a laser) and the absorbing agent is a dye
having an absorption peak at a wavelength corresponding
to that of the laser. The elastin biomaterial and the
tissue to be welded have much less absorption of light
at this wavelength and the effect therefore is confined
to a zone around the dye layer. A preferred energy
source is a laser diode having a dominant wavelength at
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about 808 nm and a preferred dye is indocyanine green
(ICG), maximum absorbance 795-805 nm (see WO 91/,4073).
Other laser/dye combinations can also be used. It is
preferred that the dye be applied to that portion of
the biomaterial that is to be contacted with and
secured to the existing tissue. The dye can also be
applied to the surface of the structure to which the
elastin biomaterial is to be welded or secured. The
dye can be applied directly to the biomaterial or the
surface of the biomaterial can first be treated or
coated (eg primed) with a composition that controls
absorption of the dye into the biomaterial so that the
' .dye is kept as a discrete layer or coating.
Alternatively, the dye can be bound to the elastin
biomaterial so that it is secured to the surface and
prevented from leeching into the material. The dye can
be applied in the form of a solution or the dye can be
dissolved in or suspended in a medium which then can be
applied as a thin sheet or film, preferably, of uniform .
thickness and dye concentration.
Tissue welding techniques employing a soldering
agent can be used. Such techniques are known (WO
91/04073). Any.proteinaceous material that thermally
denatures upon heating can be used as the soldering
agent (for example, any serum protein such as albumin,
fibronectin, Von Willebrand factor, vitronectin, or any
mixture of proteins or peptides). Solders comprising
thrombin polymerized fibrinogen are preferred, except
where such materials would cause undesirable thrombosis
or coagulation such as within vascular lumens. Solders
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are selected for their ability to impart greater
adhesive strength between the biomaterial and the
tissue. The solder should be non-toxic and generally
biocompatible.
In accordance with the present invention, the
laser energy can be directed to the target site (eg,
the dye) directly from the laser by exposure of the
tissue (eg, during a surgical procedures . In some
cases, i.e. endovascular catheter-based treatments
where open surgical exposure does not occur, the laser
energy is directed to the bonding site via optical
fibers. When ICG is used as the dye) targeting media
wavelengths of around 800nm can be used. Such
wavelengths are not well absorbed by many tissues,
particularly vascular tissues, therefore, there will be
a negligible effect on these tissues and thermal
effects will be confined to the dye layer. The
biomaterial of the invention similarly has little
optical absorbance in this waveband, as compared to the
energy absorbing dye. Thus, the laser energy can pass
through either the biomaterial or the native tissue and
be absorbed by the dye layer as shown in-Figure 1. Once
the surgeon has exposed the surface or vessel where the
biomaterial reinforcement or replacement is to be
effected, the dye-containing surface of the biomaterial
is placed in contact with the native tissue at the site
and laser energy delivered by directing the laser beam
to the desired location. The absorbance of the dye (eg
ICG) layer is ideally previously or concurrently
determined so that the optimal amount of light for
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optimal bonding can be delivered. Pressure can be used
to ensure adequate approximation of the tissue and
biomaterial. With a diode laser source, the diode
laser itself, or a condenser or optical fiber based
optical delivery system, can be placed against the
material to ensure uniform light delivery.
In cases where a new elastin lining or new-
internal elastic lamina ~is required, for example,
following an open surgical endarterectomy) once the
artery has been surgically cleared of the atheroma or
other lesion, the biomaterial is then put in place, dye
side down (see Figure 2). The biomaterial can be
deployed as a flat patch or as a tubular segment. A
tubular segment can be hollow or filled with a material
that supports the lumen during placement and that is
melted with low grade heat or dissolved or removed with
a variety of means. When necessary, a small number of
surgical sutures (eg stay sutures) can be used to
appose the edges of the vessel together or to sew the
vessel. Once, the biomaterial is in place, the laser
energy is directed through the vessel wall or through
the biomaterial to the absorbing dye, the appropriate
laser energy having been previously determined based
upon the measured absorbance in the biomaterial.
Alternatively, the dye can be applied at the time of
the surgery to the biomaterial or the vessel wall or
both and then laser energy delivered. In this
embodiment, absorbance can be determined at the time of
the surgery to the biomaterial or the vessel wall or
both and then laser energy delivered or with a feedback
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device that assesses the adequacy of the bonding or
thermal effect. (Figure 4 is a SEM of elastin-based
biomaterial fused to porcine aorta.)
In addition to the above, the biomaterial of the
invention can be used as a patch material for use in
intestinal or colon repairs which frequently do not
heal well with current techniques, particularly when
the patient has nutritional or other problems or when
the patient is in shock, such as in the case of
multiple gunshot wounds or other abdominal injuries
(see Figure 3). The use of such a patch can, for
example, seal off intestinal contents and thereby
reduce the likelihood of peritonitis. In addition, a
patch can be used on a solid organ, such as the liver,
when lacerations have occurred. Similarly, the
biomaterial of the invention can be used to repair or
replace portions of the urinary system i.e., from the
calyces of the kidney on down to the urethra. The
patch can also be used to seal a defect in a cardiac
chamber, such as an atrial septal defect, as well as
bronchial or rectal fistulas. The biomaterial can
also be used as a cerebrovascular patch for an
aneurysm. The biomaterial can be sealed in place with
targeted laser fusion. For applications where direct
exposure is not possible or not desirable, a variety of
catheter or endoscopic systems can be employed to
direct the laser energy to the target site.
The elastin-based biomaterials to which the
invention relates can be used in a variety of other
clinical and surgical settings to effect tissue repair
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graft. For delivery of biomaterial in the form of an
intravascular stent, the biomaterial can be
pre-mounted upon a deflated balloon catheter. The
balloon catheter can be maneuvered into the desired
5 arterial or venous location using standard techniques.
The balloon can then be inflated, compressing the stent
(biomaterial) against the vessel wall and then laser
light delivered through the balloon to seal the stmt
in place (the dye can be present on the outside of the
10 biomaterial). The balloon can then be deflated and
removed leaving the stent in place. A protective
sleeve (eg of plastic) can be used to protect the
stent during its passage to the vessel and then
withdrawn once the stent is in the desired location.
15 The biomaterial of the invention can also be used
as a biocompatible covering for a metal or synthetic
scaffold or stmt. In such cases, simple mechanical
deployment can be used without the necessity for laser
bonding. Laser bonding can be employed, however,
20 depending upon specific demands, eg, where inadequate
mechanical bonding occurs, such as in stent deployment
for abdominal aortic aneurysms. An alternative
catheter-based vascular stent deployment strategy
employs a temporary mechanical stent with or without a
balloon delivery device.
A further catheter-based vascular stent deployment
strategy employs a heat deformable metal (such as
nitinol or other similar type metal) scaffold or stent
or coating that is incorporated into the catheter
tubing beneath the stent biomaterial. The stent is
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maneuvered into the desired location whereupon the
deformable metal of the stent is activated such that it
apposes the stent against the vessel wall. Laser light
is then delivered via an optical fiber based system,
also incorporated into the catheter assembly.
The biomaterial can also be used to replace
portions of diseased or damaged vascular or nonvascular
tissue such as esophagus, pericardium, lung plura, etc.
The biomaterial can also be used as a skin layer
replacement, for example, in burn or wound treatments.
As such, the biomaterial serves as a permanent dressing
that acts as a scaffolding for epithelial cell
regrowth. The biomaterial can include antibiotics,
coagulants or other drugs desirable for various
treatments that provide high local concentrations with
minimal systemic drug levels. The elastin biomaterial
can be deployed with a dye on the tissue side and then
fused with the appropriate wavelength and laser energy.
In addition to repair of tubular body structures,
the biomaterial of the present invention can also be
used in organ reconstruction. For example, the
biomaterial can be molded or otherwise shaped as a
pouch suitable for use in bladder reconstruction. The
biomaterial of the invention can also be molded or
otherwise shaped so as to be suitable for esophageal
replacement. Again) metal or synthetic mesh could also
be associated with the implant if extra wall support is
needed so as to control passage of food from the
pharynx to the stomach. This could be used for
stenosis of the esophagus, as a covering for bleeding
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esophogel varicies to prevent bleeding or to treat
bleeding, for repair from acid reflux for erosive
esophagitis or) more preferably, for refurbishing
damaged esophageal segments during or following surgery
or chemotherapy for esophageal carcinoma.
For certain applications, it may be desirable to
use the biomaterial of the invention in combination
with a supporting material having strong mechanical
properties. For those applications, the biomaterial
can be coated on the supporting material (see foregoing
stent description), for example, using the molding
techniques described herein. Suitable supporting
materials include polymers, such as woven polyethylene
terepthalate (Dacron), teflon, polyolefin copolymer,
polyurethane polyvinyl alcohol or other polymer. In
addition, a polymer that is a hybrid between a natural
polymer, such as fibrin and elastin, and a non-natural
polymer such as a polyurethane, polyacrylic acid or
polyvinyl alcohol can be used (sets Giusti et al,
Trends in Polymer Science 1:261 (1993). Such a hybrid
material has the advantageous mechanical properties of
the polymer and the desired biocompatibility of the
elastin based material. Examples of other prostheses
that can be made from synthetics (or metals coated with
the elastin biomaterial or from the biomaterial/
synthetic hybrids include cardiac valve rings and
esophageal stents.
The prostheses of the invention can be prepared so
as to include drug; that can be delivered, via the
prostheses, to particular body sites. For example,
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vascular stents can be produced so as to include drugs
that prevent coagulation, such as heparin) or
antiplatelet drugs such as hirudin, drugs to prevent
smooth muscle ingrowth or drugs to stimulate
endothelial damaged esophageal segments during or
following surgery or chemotherapy for esophageal
carcinoma.
For certain applications, it may be desirable to
use the biomaterial of the invention in combination
with a supporting material having strong mechanical
properties. For those applications, the biomaterial
can be coated on the supporting material (see foregoing
stent description), for example, using the molding
techniques described herein. Suitable supporting
materials include polymers, such as woven polyethylene
terepthalate (Dacron), teflon, polyolefin copolymer)
polyurethane polyvinyl alcohol or other polymer. In
addition, a polymer that is a hybrid between a natural
polymer, such as fibrin and elastin, and a non-natural
polymer such as a polyurethane, polyacrylic acid or
polyvinyl alcohol can be used (sets Giusti et al,
Trends in Polymer Science 1:261 (1993). Such a hybrid
material has the advantageous mechanical properties of
the polymer and the desired biocompatibility of the
elastin based material. Examples of other prostheses
that can be made from synthetics or metals coated with
the elastin biomaterial or from the biomaterial/
synthetic hybrids include cardiac valve rings and
esophageal~stents.
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The elastin-based prostheses of the invention can
be prepared so as to include drug; that can be
delivered, via the prostheses, to particular body
sites. For example, vascular stems can be.produced so
as to include drugs that prevent coagulation, such as
heparin, drugs to prevent smooth muscle ingrowth or
drugs to stimulate endothelial regrowth. Vasodilators
can also be included. Prostheses formed from the
elastin based biomaterial can also be coated with
viable cells, preferable, cells from the recipient of
the prosthetic device. Endothelial cells, preferably
autologous (eg harvested during liposuction), can be
seeded onto the elastin bioprosthesis prior to
implantation (eg for vascular stent indications).
Alternatively, the elastin biomaterial can be used as a
skin replacement or repair media where cultured skin
cells can be placed on the biomaterial prior to
implantation. Skin cells can thus be used to coat
elastin biomaterial.
Biomaterial structures constituting a framework
for a three-dimensional, multi-layer cell culture
system will provide intact elastic structures not
constructed by stromal cells populating synthetic
matrices. In vivo elastin production, for example, is
thought to only occur during development and ceases
during childhood (the only exceptions being
hypertension and restenosis). Elastogenesis is a
complex process and formation of mature elastic
structures not likely to be achieved in relatively
simple in vitro cell culture systems. However, it has
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not been reported that such three dimensional cell
culture systems can organize elastin into coherent
fibrous matrices analogous to those found in elastic
tissues. A method by which to produce a living tissue
5 graft with elastic structure and function most similar
to tissue which is high in elastin content is by'
culturing cells in three dimensional frameworks made of
biomaterials. This insures the presence of
biologically important elastic structures in the living
10 tissue grafts.
A method for both organizing biomaterials fibrils
and providing a support for fibroblast growth is by
coacervating elastin monomers in solution with
fibroblasts. Elastin monomers mixed with stromal cells
15 (fibroblasts) in a physiologic buffer aggregate into
fibers (coacervation) upon raising the temperature of
the solution. In doing so the fibroblasts become
trapped in a loose matrix of elastin fibers. The
contraction of the fibroblasts bound to the coacervated
20 elastin monomers could preferentially align the elastin
fibrils prior to crosslinking.
Certain aspects of the invention are described in
greater detail in the non-limiting Examples that
follow.
Example 1 Pre~~ara~ion of sheets of Elastin-Based
Bioma - 'a1 from o1_oble Peg-it-it des
Materials used for biomaterial production:
Phosphate buffer: The phosphate buffer used
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contained 1 mM sodium phosphate, 150 mM sodium
chloride, 2 mM calcium chloride) 1 mM magnesium
(chloride, pH 7.4. Soluble elastin peptides:
Bovine ligamentum nuchae elastin powder was obtained
from Sigma, St. Louis, Missouri. The following
procedure was used to obtain the soluble elastin
peptides: 2.7 g elastin powder was suspended in 35 ml
of a 1M KOL solution in $0~ ethanol. The suspension
was stirred at 50~C for 2.5 hr. Next, 10 ml deionized
water was added and the solution neutralized with
concentrated 12M HC1 to pH 7.4. The solution was
cooled at 4~C for 12 hrs. The clear solution was
decanted from the salt crystals, and the supernatant
centrifuged for 15 mins at 2000 rpm. The solution was
then dialyzed against three changes of tap water at two
hour intervals and one 15 hr interval using a 10,000 MW
cutoff dialysis tubing. The dialysis was continued
with six changes of deionized water at two hour
intervals and one for 15 hrs. The resulting dialyZate
was lyophilized and stored at -20~C. The yield was
40~.
Cryoglobulin preparation: A modification of the
method of Pool and Shannon was used to Produce the
cryoglobulins (New Engl. J. Med. 273 (1965).
Cryoglobulins are principally fibrinogen (40 mg/ml) and
fibronectin (10 mg/ml) (concentrations of fibrinogen
and fibronectin will vary). Briefly, blood was
collected from swine in a standard 500 ml blood
collection bag containing adenine, citrate and dextrose
anticoagulant. The blood was transferred to twelve 50
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ml plastic centrifuge tubes and centrifuged for 15 mins
at 1500 rpm. The plasma was decanted from the
erythrocyte layer and frozen at -70~C for 12 hrs. The
plasma was then thawed at 4~C. The cryoglobulins were
collected by centrifugation of the plasma at 4~C for 15
mins at 1500 rpm. The supernatant was decanted and the
cryoglobulins collected by removing the precipitate
with a pasteur pipette. Each tube was also rinsed with
3 ml of a sodium citrate solution containing 0.9~ NaCl,
and 0.66 sodium citrate. The cryoglobulins were
pooled, frozen at -70~C, lyophilized and stored at
-20~C until use.
Thiourea: Reagent grade thiourea. was obtained
from Sigma, St. Louis, Missouri. A O.S mg/ml solution
was used.
Type I collagen: Acid soluble type I collagen was
obtained from Sigma. It was preferred from rat tail
tendon by a modification of the method of Bornstein.
Two mg of collagen was heated in 0.6 ml phosphate
buffer to 60~C for 10 minutes until the collagen
dissolved. It was then cooled to 37~C and used.
Thrombin: Thrombin from bovine plasma was
obtained from Sigma in lyophilized from. When
reconstituted with 1 ml water, the solution contained
106 NIH units per ml.
Aprotinin: Aprotinin from bovin lung was obtained
from Sigma. It contained 15-30 trypsin inhibitory
units (TIU) per ml.
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Preparation:
Six molds were made by gluing a 620 ~,cm quartz
f fiber to one side of a glass plate --40 mm .x 25 mm and
attaching a second glass plate to the first using a
rubber band. Each mold so constructed held about 0.5
ml.
The biomaterial was. prepared by successively
adding and mixing the following: 200 mg soluble
kappa-elastin or kappa-elastin powder in 2m1 phosphate
buffer (PB) (1 mM P041 150 mM NaCl) 2 mM Ca21 1 mM
Mg21 PH 7.4) at 37aC
160 mg cryoglobin in 1 ml P:B (37~C)
2 mg collagen in 0.6 ml PB (60~C 37~C)
200 ,ctll thiourea (0.5 mg/ml)
2 00 ~,cl aprotinin ( 5 Units )
A 0.6 ml aliquot of the above solution was loaded
into a test tube and 50 ,ul thrombin solution was added
(-6 units). The resulting solution was immediately
loaded into the mold. Certain of the resulting sheets
were crosslinked with glutaraldehyde for 2 mins.
Results: The sheets prepared as described above
were slightly yellowish and opaque. The
glutaraldehyde-fixed sheets were less stretchy and tore
more easily than non-fixed sheets. Glutaraldehyde
fixed sheets were subjected to election microscopy.
These sheets had a smooth cohesive surface appearance
at 100X and 1000X.
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Example 2 Tissue Weldina of Sheets of Ela~t-~r-Based
Biomaterial
Pre-welding procedure: A 1 mg/ml ICG.solution was
applied to fresh swine aorta that had been carefully
trimmed of adventitia, washed in a sterile 0.9~ NaCl
solution, and cut into lcrn2 squares. The lmg/ml ICG
solution was applied to:.the lumenal side of the aorta
for --3 min and wiped off. (ICG was obtained from
Sigma and contained 90~ dye and 10~ sodium iodide.
Absorption coefficient measured at 780 nm with a 7.25 X
10-6 M solution was found to be 275, 000 M-lcm-1. The
adsorption maximum shifts to 805nm when ICG is bound to
serum proteins (Landsman et al, J. Appl. Physiol. 40
(1976). A small amount of cryoglobulins, containing
approximately 40mg/ml fibrinogen and l0mg/ml
fibronectin doped with ICG, was also applied and the
biomaterial placed on it. The two materials were
placed between two glass slides. This was submerged in
a 0.9~ saline solution.
Welding Procedure: Sheets of biomaterial made
as described in Example 1 were equilibrated in
phosphate buffer, pH 7.4, and welded to ICG stained
porcine aorta using an aluminum gallium arsenide diode
array laser. The maximum output was at 808 +/- l.5nm.
The laser was coupled to a l,can quartz fiber with
polyethylene cladding material. The laser energy was
collimated with a focusing lens and coupled to the
quartz fiber. The spot size at the distal end of the
fiber could be varied from lmm to 4mm by adjusting the
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distance between the focusing lens and the proximal end
of the fiber. The laser operated continuously, CW, and
the output measured at the distal end of the fiber was
1.5w.
5 The quartz fiber was positioned directly above
the glass slide, biomaterial, aorta. Before welding,
the spot size of the laser was measured. Welding
appeared to occur under,saline at irradiances of
0.85W but not 1.32W. Twenty seconds was sufficient
10 time to weld and 40 seconds caused a brown co:Lor
change and charring of the biomaterial.
Example 3 Preparation of EldStin-Race~r~ $'nmatcrial
from Artery Diaest
15 Fresh 4 cm lengths of porcine carotid artery were
dissected clean and washed in two changes of 0.9~
saline overnight. Vessels were then placed in 0.5M
NaOH and sonicated for 120 minutes (a modified method
of Crissman, R. 1987) See Crissman, Rogert S.
20 "Comparison of Two Digestive Techniques for Preparation
of Vascular Elastic Networks for.SEM Observation",
Journal of Electron Microscopy Techniques 6:335-348
(1987). Digested vessels were then washed in distilled
water and autoclaved at 225~F for 30 minutes. Digested
25 vessels appear translucent, pearly white in color and
collapsed when removed from water indicating the
absence of collagen and other structurally supportive
proteins.
Welding of the artery digests to porcine aorta was
30 accomplished through the following methods. Fresh
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porcine aorta was coated with 5 mJ/ml ICG for 5
minutes.. Excess ICG solution was blotted off. One x
one cm sections of NaOH-sonicated digested carotid
artery elastin segments were placed upon the freshly
stained aortas. An array of pulsed aluminum gallium
arsenide diode lasers (Star Medical Technologies) was
used to weld the segments. Five millisecond pulses at
790-810 light was emitted at 2 joules and applied to
the tissue with a condenser that created a uniform beam
4x4 mm which was placed on the elastin digest covered
by a glass coverslip. Good welds were achieved with up
to 10 pulses. A light microscopic photograph of the
elastin digest welded to the porcine aorta is shown in
Figure 6.
Example 4 Preparation o F~ ,n Ba d B~omateri ~
Fusion to Porcine Aorta
Materials: Bovine nuchal elastin powder (Sigma
St. Louis MO) Was sifted with a 40 ,can screen and
swollen. with phosphate buffer. Elastin fragments were
then reacted with 67 mg of fibrinogen (Sigma): in
phosphate buffer, 2m acid soluble Type 1 collagen
( Sigma) , 2 . 8 mg thiourea, 2 mM Caa;, 1mM Mgz+ and 75
units of thrombin and injected into molds and heated to
77°C. One mm thick sheets and tubes of this
biomaterial were removed and stored in 33~ ethanol for
later use.
Indocyanine green dye was dissolved in de-ionized
water to provide a 1~ solution and applied to the
lumenal surface of fresh porcine aorta. The dye was in
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place for 5 minutes then the residual dye was blotted
off. The elastin biomaterial was placed on the ICG
stained aorta and covered with a glass coverslip.
Laser energy was applied with a condenser which
collected the output of an array of gallium arsenide
diode lasers emitting light at 800nm in 5 msec pulses.
Six mm2 Spots were irradiated with 2.89 Joules for 1-10
pulses which provided adequate welds. Samples were
then bisected and fixed in formalin for microscopic
study. Figure 5 is a light microscopic photograph of
such a weld stained with an elastin stain. Excellent
welding of the elastin biomaterial to porcine aorta is
noted with no detectable thermal or other injury to the
biomaterial or aorta.
Example 5 Prenaratio_n_ o_f Elastin-Based Bioma-Pria1 &
Fusion to Porcine Aorta
Materials: Bovine ligamentum nuchae elastin,
Fibrinogen from porcine plasma, and acid soluble type I
collagen from rate tale tendon were obtained from Sigma
Chemical Corp. (St. Louis, MS.). Elastin was
solubilized in 1M KOL/80~ ethanol at 50~~C for 2.5 hrs.
(Hornebreck). Cryoprecipitates were obtained from
porcine plasma according to the method of Pool and
Shannon (Pool and Shannon). Fresh porcine aorta was
obtained from Carlton Packaging Co. (Carlton, Ore) and
stored at -20oC until thawed for use.
Elastin-fibrin biomaterials was prepared similarly
to methods developed by Rabaud (Rabaud). Patches made
of solubilized elastin and cryoprecipates were prepared
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by successive addition with thorough mixing of 200mg.
soluble_elastin dissolved in 2 ml buffer, 160 mg.
lyophilized cryoprecipitate dissolved in 1 ml buffer, 2
mg type I collagen dissolved in 0.6 ml buffer, and 0.2
ml thiourea solution (0.5 mg/ml Hz0).. 6 units of
thrombin were added to 0.5 ml. aliquots of the mixture,
thoroughly mixed in a 1 ml syringe, and injected into
4cma glass molds. The molds were incubated at 37oC for
30 min. and subjected to 25 mrad of ofg-radiation
(cobalt source. The biomaterial was stored at 4~C in
33~ etOH. Prior to use the biomaterial was washed
several times with saline.
Patches were also made with insoluble elastin and
fibrinogen. Lyophilized elastin from Sigma was passed
through a U.S. no 4000 mesh sieve (Tyler) prior to use.
Only the 40 ~.cm or smaller particles were used. 28-Omg
of the filtered elastin was swollen and washed
overnight in an excess of phosphate. buffer. the mixture
was centrifuged (1000 rpm, 10 min) and the excess
buffer discarded. The swollen elastin was suspended in
2 ml of phosphate buffer. Successively added to this
suspension are 67 mg. lyophilized fibrinogen dissolved
in 1 ml buffer, 2 mg type I collagen dissolved in 0.6
ml buffer, and 0.2 ml thiourea solution (0.5 ma/ml
H,0). Finally, 33 units of thrombin were added and the
mixture was thoroughly vortexed and quickly poured into
3 cm x 7 cm molds. The molds were incubated at 37~C
for 30 min.the biomaterial was stored in 4~C in 33~
EtOH. Prior to use the biomaterial was washed several
times with saline solution.
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The soluble elastin-cryoprecipitated patch was
fused to porcine aorta using an Aluminum Gallium
Arsenide diode array laser emitting 608 nm continuous
wave optical radiation. Fresh porcine aorta was washed
in 0.9$ NaCl and trimmed into 2 cm~ portions.
Indocyanine green (Sigma) in aqueous concentrated of 1
or 5 mg/ml was applied to aorta via a pasteur pipette,
left undisturbed for 5 min. and then blotted away. The
tissue was then equilibrated in a 0.9~ saline solution
for 15 minutes to remove any unbound dye. The
biomaterial was then applied to the lumenal surface of
the aorta. the laser beam was directed at the
biomaterial surface via a 1 fan fused silica fiber
(Polymicro Technologies Phoenix, Az.) through a glass
coverslip as shown in figure 1. the spot size of the
laser beam varied between 1-4 mm. The laser output
measured from the fiber tip was 1.5 Watts and exposed
durations varied from 5 to 4 seconds.
The insoluble elastin-fibrinogen patch was fused
to porcine aorta using an Aluminum Gallium Arsenide
diode array laser emitting 790=810 nm pulsed optical
radiation (Star Medical Technologies). Thawed porcine
aorta was prepared and stained with 5mg/ml aqueous ICG
solution as previously described for fresh aorta.
After applying the biomaterial to the stained luminal
surface of the aorta, laser radiation was directed at
the biomaterial via a copper coated condenser placed
against a glass coverslip. The laser output was set at
ZJ and 5 msec pulse durations.
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Example 6 pre~aratiOn Of Rlactin-RaSPri Rinmatc~r;a~~
end Fusinct of Same
Bovine ligamentum nuchae elastin, fibrinogen from
porcine plasma, and acid soluble type I collagen from
5 rat tale tendon were obtained from Sigma Chemical Corp.
(St. Louis, Mo).
1 mg. indo cyanine green is dissolved in 1 ml of
24~ human serum albumin.. 67 mg of fibrinogen was
dissolved in 1 ml phosphate buffer (@37~C). Just prior
10 to mixing 16.6 units of thrombin are added to the
indocyanine green solution. The mixtures were cooled
to 4~C. The two mixtures are rapidly mixed and
injected, or poured, into a 3 X 7 cm mold and incubated
for 30 min. at 37~C.
15 Lyophilized elastin from Sigma was passed through
a U.S. No. 400 mesh sieve (Tyler) prior to use. Only
the 40 E,tm or smaller particles were used. 210 mg of the
filtered elastin was swollen and washed overnight in an
excess of phosphate buffer. The mixture was
20 centrifuged (1000 rpm, 10 min.) and the excess buffer
discarded. The swollen elastin,was suspended in 1.5 ml
of phosphate buffer. Successively added to this
suspension were 67 mg lyophilized fibrinogen dissolved
in 0.75 ml buffer, 2 mg type I collagen dissolved in
25 0.45 ml buffer, and 0.15 ml thiourea solution (0.5mg/ml
Ha0). Finally, 26 units of thrombin were added and the
mixture was thoroughly vortexed and quickly poured onto
the fibrin matrix doped with indocyanine green in the 3
cm x 7 cm molds. The molds were again incubated at 37~C
30 for 30 minutes. When removed from the mold, the two
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36
layers are inseparable and the preparation yields a
single patch.
Example 7. Welding of Blast-in fibrin 1~~inmatcr;al rr,
~QOrc?ne intestine
Fresh porcine intestine was obtained from Carlton
Packing Co. (Carlton, OR). The intestine was rinsed
with tap water and stored at -20~C in Ziploc freezer
bags. Prior to use the intestine is thawed in ambient
air and kept on saline soaked gauze to prevent drying
out.
The elastin fibrin biomaterial prepared as
described in Example 4 was fused to porcine intestine
using a Aluminum Gallium Arsenide diode array laser
(Star Medical Technologies) as follows: Indocyanine
green in aqueous concentrations of 5 mg/ml was applied
to the serosa of thawed porcine intestine with a
pasteur pipette, left undisturbed for 5 minutes and
then blotted away with a Kimwipe EXL wipe.
Elastin-fibrin biomaterial was cut into 1 X 1 cm
patches an excess moisture was blotted away with a
Kimwipe EXL wipe. The biomaterial was then positioned
on top of the ICG stained serosa of the intestine and a
glass microscope coverlip is positioned on top of the
biomaterial. A scale was placed underneath the
intestine. Laser radiation was directed at the
biomaterial via a 4 X 4 mm copper coated condenser
placed against the glass coverslip. Laser output was
set at 1.99-2.19 joules and 5 msec pulses. During
laser exposure, manual force was applied to the glass
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coverslip with the condenser. The amount of pressure
applied was monitored on the scale placed underneath
the intestine. 5 pulses and 500 to 1600 grams of force
resulted in successful adhesion of the elastin-fibrin
biomaterial to the intestine. Figure XXX (Figure 14 of
army grant proposal) is a light microscope slide of
elastin fibrin biomaterial welded to porcine intestine
(1.99 joules per pulse, 10 pulses, 5008 force).
Example 8: Preparation and we~~~na of coronary
vessel diaests_
Fresh left anterior descending, right main, and
circumflex coronary arteries were excised from a
porcine heart. Excess fat and thrombus were removed
from the excised vessels. The vessels were cut in half
and the distal halves were washed in saline and
sonicated in 0.5M NaOH for 45 min at 65~C. The distal
halves were then removed from the alkali, immersed in
500 ml distilled water for 30 min, and finally
immersed in boiling distilled water for another 30 min.
The NaOH-sonicated vessels are hereafter-referred to as
heterografts. The proximal half of the vessels were
saved and stored on saline soaked gauze until use.
Right main coronary heterografts were welded to right
main and left anterior descending arteries with an
Aluminum Gallium Arsenide pulsed dioded laser emitting
790-810 nm optical radiation (Star Medical
Technologies). 5 mg of indocyanine green (ICG) was
dissolved in 1 ml of distilled water. This solution
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was then diluted with 4 ml of 25~ human serum albumin
(HSA) with careful mixing avoiding the formation of
excessive air bubbles. The heterografts were coaxed
onto a percutaneous transluminal coronary angioplasty
balloon measuring 3.0 mm in diameter when inflated.
The heterograft covered balloon was inflated to 4 psi
and immersed in the ICG-HSA for 5 minutes to stain the
heterograf t. After removing the heterograft and
balloon from the staining solution, the balloon is
deflated and inserted into the untreated proximal half
of a right main or LAD coronary artery. Following
insertion, the balloon is inflated to 8 psi. The
inflated balloon/heterograft is placed on a benchtop
and a coverslip is placed over the region to be welded.
A 4 X 4 mm copper coated condenser is placed against
the coverslip. The laser output was set for 2.3 joules
of energy and 5 msec pulse durations. After 5 pulses,
the balloon is rotated approximately 30 degrees and
another region is illuminated with 5 pulses. This
procedure is repeated until the entire circumference of
the balloon has been illuminated.. The balloon is then
deflated, leaving behind the heterograft, now fused to
the luminal surface of the artery.
All documents cited above are hereby incorporated
in their entirety by reference. One skilled in the art
will appreciate from a reading of this disclosure that
various changes in form and detail can be made without
departing from the true scope of the invention.
