U.S. patent application number 11/356510 was filed with the patent office on 2007-01-04 for method for using tropoelastin and for producing tropoelastin biomaterials.
Invention is credited to Andrew D. Barofsky, Kenton W. Gregory.
Application Number | 20070005148 11/356510 |
Document ID | / |
Family ID | 35810553 |
Filed Date | 2007-01-04 |
United States Patent
Application |
20070005148 |
Kind Code |
A1 |
Barofsky; Andrew D. ; et
al. |
January 4, 2007 |
Method for using tropoelastin and for producing tropoelastin
biomaterials
Abstract
It is a general object of the invention to provide a method of
effecting repair or replacement or supporting a section of a body
tissue using tropoelastin, preferably crosslinked tropoelastin and
specifically to provide a tropoelastin biomaterial suitable for use
as a stent, for example, a vascular stent, or as conduit
replacement, as an artery, vein or a ureter replacement. The
tropoelastin biomaterial itself can also be used as a stent or
conduit covering or coating or lining.
Inventors: |
Barofsky; Andrew D.;
(Portland, OR) ; Gregory; Kenton W.; (Portland,
OR) |
Correspondence
Address: |
MARGER JOHNSON & MCCOLLOM, P.C.
210 SW MORRISON STREET, SUITE 400
PORTLAND
OR
97204
US
|
Family ID: |
35810553 |
Appl. No.: |
11/356510 |
Filed: |
February 17, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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08797770 |
Feb 7, 1997 |
7001328 |
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11356510 |
Feb 17, 2006 |
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08658855 |
May 31, 1996 |
5990379 |
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08797770 |
Feb 7, 1997 |
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08341881 |
Nov 15, 1994 |
5989244 |
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08797770 |
Feb 7, 1997 |
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Current U.S.
Class: |
623/23.72 ;
435/396; 600/36; 623/920 |
Current CPC
Class: |
A61L 27/227 20130101;
A61L 27/3804 20130101; A61L 27/3839 20130101 |
Class at
Publication: |
623/023.72 ;
435/396; 600/036; 623/920 |
International
Class: |
A61F 2/02 20060101
A61F002/02; C12N 5/08 20060101 C12N005/08 |
Goverment Interests
GOVERNMENT LICENSE RIGHTS
[0002] This invention was made with Government support under Grant
No. DAMD 17-96-1-6006 awarded by U.S. Army Medical Research
Acquisition Activity. The U.S. Government has certain rights in the
invention.
Claims
1. A method for producing a tissue substrate fusible biomaterial
consisting essentially of tropoelastin which is fusible to a tissue
substrate comprising: providing a polymerizable monomer consisting
essentially of tropoelastin; polymerizing said polymerizable
monomer to form a polymer consisting essentially of tropoelastin:
forming a layer of said biomaterial from said tropoelastin polymer
having a first and second outer major surface; and applying an
energy absorbing material, which is energy absorptive within a
predetermined range of light wavelengths, to a selected one of said
first and second outer surfaces of the biomaterial in an amount
which will cause fusing together of one of said first and second
outer surfaces of the biomaterial and one of said first and second
outer surfaces of said tissue substrate, said energy absorbing
material penetrating into the interstices of said biomaterial; and
irradiating the energy absorbing material with light energy in said
predetermined wavelength range with an intensity sufficient to fuse
together one of said first and second outer surfaces of the
biomaterial and the tissue substrate.
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11. The method of claim 1, wherein the tissue substrate is a live
tissue substrate.
12. The method of claim 1, wherein the average thickness of the
energy absorbing material which penetrates into the interstices of
the biomaterial is from about 0.5 to 300 microns.
13. (cancel)
14. The method of claim 1, wherein the tissue substrate is selected
from a group consisting of bladders, intestines, tubes, esophagus,
ureters, arteries, veins, stomachs, lungs, hearts, colons, and
skin.
15. The method of claim 1, wherein said polymerizable monomer
consists essentially of non-mammalian tropoelastin.
16. The method of claim 15, wherein said non-mammalian tropoelastin
consists essentially of recombinant tropoelastin.
17. The method of claim 15, wherein said recombinant tropoelastin
is produced by a protein expression system.
18. The method of claim 1, which further includes the step of
forming a cellular lining of human cells on one of the major
surfaces of said biomaterial layer.
19. The method of claim 18, wherein said cells which are employed
to form said cellular lining are at least one of endothelial cells,
epithelial cells and urothelial cells.
20. The method of claim 1, which further includes the step of
forming an inner lining consisting essentially of tropoelastin for
mechanical human structures to ensure their continued internal use
in a human body.
21. The method of claim 20, which further includes the step of
forming said inner lining in heart valves, heart implants, dialysis
equipment, or oxygenator tubing for heart-lung by-pass systems.
22. The method of claim 1, which includes the step of introducing a
drug into said biomaterial.
23. A method for producing a prosthetic device comprising:
providing a polymerizable monomer consisting essentially of
tropoelastin; polymerizing said polymerizable monomer to form a
polymer consisting essentially of tropoelastin: forming a layer of
said biomaterial from said tropoelastin polymer having a first and
second outer major surface; providing a support member comprising a
stent, a conduit or a scaffold; and applying said layer of said
biomaterial to said support member to form said prosthetic
device.
24. The method of claim 23, which includes the step of applying the
layer of said biomaterial so that it surrounds said support
member.
25. The method of claim 23, which includes the step of forming said
biomaterial by polymerization.
26. The method of claim 23, which includes the step of molding said
biomaterial of a suitable size and shape.
27. The method of claim 23, which includes the step of forming said
biomaterial into a sheet or tube, and then covering said support
member with said sheet or tube.
28. The method of claim 23, which includes the step of applying
said biomaterial layer to said support by grafting.
29. The method of claim 23, which includes the step of applying
said biomaterial layer to said support by mechanical bonding.
30. The method of claim 23, which includes the step of applying
said biomaterial layer to said support by laser bonding.
31. The method of claim 23, which includes the step of
incorporating a drug into said biomaterial layer thereby decreasing
the need for systemic intravenous or oral medications.
32. The method of claim 23, wherein said support member comprises
titanium, tantalum, stainless steel or nitinol.
33. The method of claim 23, wherein said polymerizable monomer
consists essentially of non-mammalian tropoelastin.
34. The method of claim 33, wherein said non-mammalian tropoelastin
consists essentially of recombinant tropoelastin.
35. The method of claim 34, wherein said recombinant tropoelastin
is produced by a protein expression system.
36. A method for producing a biomaterial, which comprises:
providing a polymerizable monomer consisting essentially of
non-mammalian tropoelastin; polymerizing said polymerizable monomer
to form a polymer consisting essentially of non-mammalian
tropoelastin; and forming a biomaterial consisting essentially of
non-mammalian tropoelastin from said polymer.
37. The method of claim 36, wherein said non-mammalian tropoelastin
consists essentially of recombinant tropoelastin.
38. The method of claim 37, wherein said recombinant tropoelastin
is produced by a protein expression system.
39. A method for producing a biomaterial, which comprises:
providing a crosslinkable monomer consisting essentially of
tropoelastin; crosslinking said crosslinkable monomer to form a
crosslinked polymer consisting essentially of crosslinked
tropoelastin; and forming a biomaterial from said crosslinked
polymer consisting essentially of crosslinked tropoelastin.
40. The method of claim 39, wherein said crosslinked tropoelastin
consists essentially of tropoelastin having non-naturally occurring
cross-links.
41. The method of claim 39, wherein said crosslinked tropoelastin
consists essentially of chemically crosslinked tropoelastin having
non-naturally occurring chemical cross-links.
42. The method of claim 41, wherein said chemically crosslinked
tropoelastin having non-naturally occurring chemical cross-links is
crosslinked using glutaraldelhyde as the crosslinking agent.
43. The method of claim 39, wherein said crosslinked polymer
consists essentially of crosslinked recombinant tropoelastin.
44. The method of claim 39, wherein said crosslinked tropoelastin
consists essentially of enzymatically crosslinked tropoelastin
having non-naturally occurring enzymatic cross-links.
45. The method of claim 39, wherein said crosslinked tropoelastin
consists essentially of radiatively crosslinked tropoelastin having
non-naturally occurring irradiated cross-links.
46. The method of claim 45, wherein said crosslinked tropoelastin
consists essentially of radiatively crosslinked tropoelastin having
non-naturally occurring .gamma.-irradiated crosslinks.
47. The method of claim 46, wherein said -y-irradiated cross-links
are produced by free radicals which result in crosslink
formation.
48. The method of claim 39, which further includes organizing the
crosslinkable tropoelastin monomer prior to the cross-linking
step.
49. The method of claim 48, wherein organizing the crosslinkable
tropoelastin monomer prior to the cross-linking step comprises
coacervation.
50. The method of claim 39, wherein the crosslinkable tropoelastin
monomer is combined with collagen and then crosslinked to form a
crosslinked tropoelastin-collagen composite.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent Ser. No.
08/797,770 filed Feb. 7, 1997 (pending) which is a
continuation-in-part of U.S. Pat. No. 5,989,244 issued Nov. 23,
1999 and a continuation-in-part of U.S. Pat. No. 5,990,379 issued
Nov. 23, 1999.
BACKGROUND OF THE INVENTION
[0003] This invention relates to a method for using tropoelastin,
and more particularly to a method for producing tropoelastin
biomaterials.
[0004] Elastic fibers are responsible for the elastic properties of
several tissues such as skin and lung, as well as arteries, and are
composed of two morphologically distinct components, elastin and
microfibrils. Microfibrils make up the quantitatively smaller
component of the fibers and play an important role in elastic fiber
structure and assembly.
[0005] The most abundant component of elastic fibers is elastin.
The entropy of relaxation of elastin is responsible for the
rubber-like elasticity of elastic fibers. In vertebrates elastin is
formed through the secretion and crosslinking of tropoelastin, the
72-kDa biosynthetic precursor to elastin. This is discussed, for
example, in an article entitled "Oxidation, Cross-linking, and
Insolubilization of Recombinant Crosslinked Tropoelastin by
Purified Lysyl Oxidase" by Bedell-Hogan, et al. in the Journal of
Biological Chemistry, Vol. 268, No. 14, on pages 10345-10350
(1993).
[0006] In vascular replacement and repair, the best current option
is to implant autologous veins and arteries where the obvious limit
is the supply of vessels which can be sacrificed from the tissues
they were intended to service. Autologous vein replacements for
damaged arteries also tend to be only a temporary measure since
they can deteriorate in a few years in high pressure arterial
circulation.
[0007] When autologous graft material is not available, the surgeon
must choose between sacrificing the vessel, and potentially the
tissue it sub-served, or replacing the vessel with synthetic
materials such as Dacron or Gore-tex. Intravascular compatibility
indicate that several "biocompatible polymers", including Dacron,
invoke hyperplastic response, with inflammation particularly at the
interface between native tissue and the synthetic implant.
Incomplete healing is also due, in part, to a compliance mismatch
between currently used synthetic biomaterials and native
tissues.
[0008] 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 internal
elastic lamina (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.
[0009] Prosthetic devices, such as vascular stents, 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, metal stents or scaffolds being
deployed presently in non-surgical catheter based systems to
scaffold damaged arteries are inherently thrombogenic and their
deployment can result in catastrophic thrombotic closure. Metal
stents have also been well demonstrated to induce a significant
intimal hyperplastic response within weeks which can result in
restenosis or closure of the lumen. Optimal arterial reconstruction
would restore the arterial architecture such that normal vascular
physiology and biology would be re-established thus minimizing
acute and long-term maladaptive mechanisms of vascular homeostasis.
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 fibrinogen
polymer polymerized with thrombin, has also been used (primarily in
Europe) as a tissue sealant and hemostatic agent.
[0010] Damage to the arterial wall through disease or injury can
involve the endothelium, internal elastic lamina, medial smooth
muscle and adventitia. In most cases, the endogenous host response
can repair and replace the endothelium, the smooth muscle and the
adventitial layers over a period of weeks to months depending upon
the severity of the damage. However, elastin does not undergo
extensive post-developmental remodelling and the capacity for
elastin synthesis declines with age. (See "Regulation of Elastin
Synthesis in Organ and Cell Culture" by Jeffrey M. Davidson and
Gregory C. Sephel in Methods in Enzymology 144 (1987) 214-232.)
Therefore, once damaged, elastic fibers are not substantially
reformed. Neosynthesis of elastin in arterial walls subject to
hypertension or neointimal hyperplasia represents the most
significant example of post developmental elastin synthesis. This
synthesis results in elastic structures mostly composed of elastin
fibrils whose organization is unlike normal elastin architecture
and probably contributes little to the restoration of normal
vascular physiology.
[0011] In animal models of intimal hyperplasia or atherosclerosis
it is well accepted that disruption of the internal elastic lamina
is a prerequisite to reliable production of intimal hyperplasia or
atherogenesis in large animals or primates. (See Schwartz R. S., et
al., in an article entitled "Restenosis After Balloon Angioplasty:
Practical Proliferation Model In Porcine Coronary Arteries" in
Circulation 1990: 82: 2190-2200.) This observation is supported by
several lines of evidence that suggest a role for elastin in the
biological regulation of several cell types. Pathological studies
indicate that elastin provides a secure attachment for endothelial
cells and can act as a barrier to macromolecules such as mitogens
and growth factors preventing these molecules from entering the
media of blood vessels. Lipids, foamy macrophages, and other
inflammatory cells do not appear to enter the intima as readily
when a substantial and continuous elastin membrane is present
immediately to the endothelium according to Sims, F. H., et al., in
an article entitled "The Importance of a Substantial Elastic Lamina
Subjacent to the Endothelium in Limiting the Progression of
Atherosclerotic Changes" in Histopathology (1993) at 23:307-317. In
addition, it has been shown by Ooyama, Toshiro and Sakamoto that
chemotactic effects of soluble elastin peptides and platelet
derived growth factor are inhibited by substratum bound elastin
peptides. (See "Elastase in the Prevention of Arterial Aging and
the Treatment of Atherosclerosis.) (See "The Molecular Biology and
Pathology of Elastic Tissues" edited by Chadwick, Derek J. and
Jamie A. Goode, John Wiley and Sons Ltd., Chichester, England
(1995).) In vitro experiments show that alpha elastin suppresses
the phenotypic transition (contractile to synthetic) of rabbit
arterial SMC by interacting with a 130 kDa cell surface elastin
binding protein for cell binding sequence VGVAPG. Rabbit smooth
muscle cells adhering to elastic fibers appears to favor the
contractile over the synthetic state which is identified with
restonotic responses to injury. (See "Changes in Elastin Binding
Proteins During Phenotypic Transition of Rabbit Arterial Smooth
Muscle Cells in Primary Culture" by Yamamoto, et al. in
Experimental Cell Research 218 (1995) pp. 339-345.) Similar work by
Ooyama and colleagues has demonstrated that the phenotypic change
of smooth muscle cells from the contractile to the modified type is
significantly retarded when the cells are grown on elastin coated
dishes.
[0012] 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.
[0013] 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.
[0014] The present invention combines the advantages of
tropoelastin-based products with the advantages of laser welding
techniques, and provides a unique method of tissue repair and
replacement. The invention makes possible tissue prostheses
(particularly, vascular prostheses) that are essentially free of
problems associated with prostheses known in the art.
[0015] Arterial replacement or reconstruction using tropoelastin
based biomaterials not only may provide normal strength and
elasticity but also may encourage normal endothelial re-growth,
inhibit smooth muscle cell migration and thus restore normal
vascular homeostasis to a degree not currently possible with
synthetic grafts.
[0016] U.S. Pat. No. 4,589,882 is directed to a method for
producing synthetic elastomeric polypeptide biomaterial which
replicates a portion of the crosslinked tropoelastin polypeptide
sequence. This synthetic elastomeric polypeptide biomaterial can be
employed in repairing a natural elastic system of an animal
body.
[0017] U.S. Pat. Nos. 4,721,096 and 4,963,489, which are
incorporated herein by reference, disclose a three-dimensional cell
culture system in which a living stromal tissue is prepared in
vitro by a framework composed of a biocompatible, non-living
material formed into a three dimensional structure having
interstitial spaces. Collagen has been considered for a
biodegradable biomaterials for use as a framework for a
three-dimensional, multi-layer cell culture system (see U.S. Pat.
No. 4,721,096 and No. 4,963,489).
[0018] An improved three-dimensional cell culture systems in which
metabolic cycling optimizes the formation of extracellular matrix
by cells grown on a three dimensional matrix is disclosed in U.S.
Pat. No. 5,478,739 which is herein included as a reference. U.S.
Pat. No. 5,478,739 reports production of collagens I, III, and IV,
fibronectin, decorin, and non-sulfated glycosaminoglycans by cells
in a three dimensional culture.
SUMMARY OF THE INVENTION
[0019] It is a general object of the invention to provide a method
of effecting repair or replacement or supporting a section of a
body tissue using tropoelastin, preferably crosslinked
tropoelastin.
[0020] It is a specific object of the invention to provide a
tropoelastin biomaterial suitable for use as a stent, for example,
a vascular stent, or as conduit replacement, for example, as an
artery, vein or a ureter replacement. The tropoelastin biomaterial
itself can also be used as a stent or conduit covering or coating
or lining.
[0021] It is a further object of the invention to provide a
tropoelastin graft material suitable for use in repairing a lumen
wall.
[0022] It is another object of the invention to provide a
tropoelastin material suitable for use in tissue replacement or
repair in, for example, 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.
[0023] It is also an object of the invention to provide a method of
securing a tropoelastin biomaterial to an existing tissue with or
without the use of sutures or staples.
[0024] The subject invention relates to method for using a
tropoelastin polymer and for producing a tropoelastin biomaterial.
Such methods comprise providing a tropoelastin monomer and then
polymerizing same as hereinafter described. This will form a
tropoelastin polymer which can be formed into a biocompatible
tropoelastin biomaterial from said tropoelastin polymer for use in
biomedical applications. For example, as shown in FIG. 1, the
tropoelastin mononer can be formed into a filamentous structure by
coacervation using moderating heating to effect same. Then, the
filamentous tropoelastin is crosslinked using a crosslinking agent,
such as lysyl oxidase, to form a crosslinked filamentous
tropoelastin material. Finally, the tropoelastin polymer is formed
into a layer of biocompatible tropoelastin biomaterial. It is this
biocompatible tropoelastin biomaterial which can be used in the
hereinafter described biomedical applications.
[0025] The subject invention provides a biocompatible, tropoelastin
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 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:
[0026] U.S. Pat. No. 5,478,739, U.S. Pat. No. 5,460,939, U.S. Pat.
No. 5,443,550, U.S. Pat. No. 5,266,480,
[0027] U.S. Pat. No. 5,518,915, U.S. Pat. No. 5,516,681, U.S. Pat.
No. 4,963,489, U.S. Pat. No. 5,032,508, U.S. Pat. No.
4,721,096,
[0028] U.S. Pat. No. 5,516,680, U.S. Pat. No. 5,512,475, U.S. Pat.
No. 5,510,254, and U.S. Pat. No. 5,160,490.
[0029] The tropoelastin structure 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 tropoelastin layer. Preferably, the cells which are employed to
form such a lining are one endothelial cells and/or epithelial
cells and/or urothelial cells.
[0030] The tropoelastin structure can also be formed into a
biocompatible lining for mechanical structures to ensure their
continued internal use in a human body. Examples of this are
biocompatible linings for heart valves, heart implants, dialysis
equipment, or oxygenator tubing for heart-lung by-pass systems.
[0031] The subject invention is directed to a method for producing
a tropoelastin biomaterial, typically a crosslinked tropoelastin
material, which is fused onto a tissue substrate, and the
tropoelastin biomaterial itself. It is also directed to a method
for using that tropoelastin biomaterial, a method for producing a
tropoelastin biomaterial fused onto a tissue substrate, and a
prosthetic device and a method of producing a prosthetic device
including tropoelastin,
[0032] The present invention also relates to a method of repairing,
replacing or supporting a section of a body tissue using
tropoelastin. The method comprises positioning tropoelastin 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.
[0033] A tissue-fusible tropoelastin biomaterial can be produced
using the method of the present invention which comprises a layer
of tropoelastin 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.
[0034] The energy absorbing material is energy absorptive within a
predetermined range of light wavelengths 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
tropoelastin biomaterial and the tissue substrate. Preferably, the
first and second outer surfaces of the tropoelastin biomaterial are
major surfaces.
[0035] Typically, an energy absorbing material is indirectly
irradiated by directing the light energy first through the
tropoelastin biomaterial or tissue substrate and then to the energy
absorbing 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.
[0036] In a preferred method 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 tropoelastin 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 tropoelastin 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 tropoelastin biomaterial. 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 tropoelastin biomaterial.
[0037] Some of the key properties which effect the method of the
present invention regarding fusing the tropoelastin 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 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 tropoelastin
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 method of this invention
is from about 0.5 to 300 microns.
[0038] The subject invention is also directed to a prosthetic
device comprising a support member comprising a stent, a conduit or
a scaffold having a layer of tropoelastin material located on the
support member. In the preferred case, the layer of the
tropoelastin biomaterial completely surrounds the support
member.
[0039] The support member of the prosthetic device is preferably
formed of a metal or a synthetic material. The metal preferably
comprises titanium, tantalum, stainless steel or nitinol. The
synthetic material typically comprises a polymeric material. This
polymeric material is generally selected from a group consisting of
polyethylene terepthalate (Dacron), Gore-tex, teflon, polyolefin
copolymer, polyurethane and polyvinyl alcohol. The support member
can be formed from a hybrid polymer comprising a synthetic
polymeric material and a natural polymeric material including
fibrin and/or elastin. The support member can also be formed from a
biological material, preferably from collagen.
[0040] The prosthetic device can comprise a layer of tropoelastin
biomaterial. Preferably this layer comprises a covering, a coating,
or a lining for the support member. The tropoelastin biomaterial
can be formed by polymerization, or formed to a suitable size and
shape by molding. The polymerized tropoelastin biomaterial can also
be further cross-linked using gamma radiation and/or a
cross-linking agent. In one form of the invention, the tropoelastin
biomaterial is formed into a sheet, and the sheet is employed as
the covering for the support. The sheet can also be attached to the
support by grafting, by mechanical bonding, or by laser
bonding.
[0041] The prosthetic device of this invention is implantable
within an artery, a vein, an esophagus, an intestine, a colon, a
ureter, a liver, a urethra, or a fallopian tube.
[0042] A drug can be incorporated into the layer of tropoelastin
material thereby decreasing the need for systemic intravenous or
oral medications. Also, photodynamic therapy drugs ("PTD") which
are activated with light can be employed herein.
[0043] In use, a method for producing the prosthetic device of the
present invention comprises first providing a layer of tropoelastin
biomaterial and a support member comprising a stent, a conduit or a
scaffold. Then, the layer of tropoelastin biomaterial is applied to
the support member to form the prosthetic device. For example, a
layer of tropoelastin material can be located on the support member
and can be fused together. This can be accomplished by applying an
energy absorbing material, which is energy absorptive within a
predetermined range of light wavelengths, to the tropoelastin
biomaterial in an amount which will cause fusing together thereof.
Thus, the energy absorbing material is irradiated with light energy
in the predetermined wavelength range with an intensity sufficient
to fuse together the tropoelastin biomaterial on said support
member thereby fusing together the tropoelastin biomaterial on the
tissue substrate.
[0044] Further objects and advantages of the invention will be
clear from the description that follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] FIG. 1 is a schematic representation of a reaction of
tropoelastin monomers for producing crosslinked tropoelastin.
[0046] FIG. 2 is a schematic representation of a reaction of
tropoelastin monomers in the presence of fibroblasts for producing
crosslinked fibroblast-tropoelastin matrix.
[0047] FIG. 3 is a schematic representation of a reaction of
tropoelastin monomers in the presence of a preformed collagen
lattice for producing tropoelastin fibrils supported on the
collagen latice structure.
DETAILED DESCRIPTION
Monomer Synthesis
[0048] Tropoelastin monomer is the soluble biosynthetic precursor
to elastin. It is formed naturally in vetebrates. Tropoelastin can
be isolated from the aortas of copper deficient swine by known
methods such as described by E. B. Smith, Atherosclerosis 37 (1980)
tropoelastin is a 72-kDa polypeptide which is rich in glycine,
proline, and hydrophobic amino acids. The exact amino acid
composition of tropoelastin differs from species to species. Any
polypeptide moiety that has art-recognized homology to tropoelastin
can be considered a tropoelastin monomer for the invention.
[0049] The tropoelastin can be isolated from mammalian tissue or
produced using recombinant expression systems. Furthermore,
tropoelastin splice variants from any species can also be used for
the invention.
[0050] The following are exemplary descriptions of methods of
producing tropoelastin monomers used in the invention:
[0051] 1. Tropoelastin can be extracted from mammals which have
been placed on copper deficient or lathyritic diets. The deficiency
of copper in the mammalian diet inhibits lysyl oxidase resulting in
the accumulation of tropoelastin in elastin rich tissues. Copper
deficient animals are grown rapidly on a diet composed largely of
milk products and must be kept isolated from contaminating sources
of copper. The protocol for raising copper deficient swine is
detailed by L. B. Sandberg and T. B. Wolt. Production of Soluble
Elastin from Copper Deficient Swine. Methods in Enzymology 82
(1982) 657-665. 150 mg of tropoelastin can be extracted from a
15-kg copper-deficient swine.
[0052] 2. In a method similar to copper deficiency method in No. 1
above, feeding animals chemicals that effectively inhibit the
action of lysyl oxidase (lathyrogens) also restricts the conversion
of tropoelastin to amorphous elastin. This method produces similar
yields of tropoelastin to copper-deficient swine. However, the
special cages, water and diet required to raise copper-deficient
animals are not required herein. To induce lathyrisim, animal diets
are supplemented with 0.1% by weight a-aminoacetonitrile-HCl and
0.05% a-aminocaproic acid as described by Celeste B. Rich and
Judith Ann Foster, Isolation of Soluble Elastin-Lathyrism. Methods
in Enzymology 82 (1982) 665-673.
[0053] 3. Tropoelastin can also be produced by mammalian cell
culture systems. Short term cultivation of bovine vascular
endothelial cells, nuchal ligament fibroblasts from cows and sheep,
human skin fibro-blasts, and vascular smooth muscle cells from pigs
and rabbits results in the accumulation of tropoelastin in the
culture medium.
[0054] 4. Recombinant tropoelastin produced by a protein expression
system is the preferred monomer for the invention. Recombinant
protein technology is the transfer of recombinant genes into host
organisms that grow and convert nutrients and metabolites into
recombinant protein products. Using this technology, cDNA encoding
tropoelastin can be cloned and expressed in protein expression
systems to produce biologically active recombinant tropoelastin.
Functionally distinct hydrophobic domains and lysine rich
crosslinking domains are encoded in separate exons. This existence
of multiple splice variants of tropoelastin in several species can
be attributed to Cassette-like alternative splicing of elastin
pre-mRNA. Expression of different recombinant splice variants of
tropoelastin can produce proteins with distinct qualities. In
addition, site directed in vitro mutagenesis can be used to alter
the polypeptide sequence of the naturally occurring gene, thus
creating alternate polypeptides with improved biological activity
and physical properties. Expression of the full length elastin cDNA
clone, cHEL2 and subsequent purification of recombinant human
tropoelastin (rTE) has been achieved by Joel Rosenbloom, William R.
Abrams, and Robert Mecham. Extracellular Matrix 4: The Elastic
Fiber. The Faseb Journal 7 (1993) 1208-1218. rTE produced by the
methods of Rosenbloom et al. can be used for the invention,
however, the methods are not considered to be part of the present
invention. In addition, the invention is not limited to rTE
produced from the expression of cHEL2. rTE produced from the
expression of any tropoelastin genomic or cDNA can be used for the
invention.
[0055] To help overcome the moderate yields of rTE recovered by
Rosenbloom and colleagues, Martin, Vrhovski and Weiss successfully
synthesized and expressed a gene encoding human tropoelastin in E.
Coli. In constructing the gene they tailored the rare codon bias of
the synthetic sequence to match the known preferences of E. Coli.
rTEtropoelastin produced by expression of synthetic genes can be
used for the invention.
[0056] rTE is used in the invention can be produced in
non-bacterial expression vector systems. Yeast expression vector
systems are well suited for expressing eukaryotic proteins and
tropoelastin is a potentially excellent candidate for expression in
yeast.
[0057] For large scale heterologous gene expression, the
baculovirus expression vector system (BEVS) is particularly
advantageous. BEVS has several advantages over other expression
systems for mammalian gene expression. It is safer, easier to scale
up, more accurate, produces higher expression levels, and is ideal
for suspension cultures permitting the use of large-scale
bioreactors. Generation of a recombinant baculovirus particle
carrying a clone of elastin cDNA coding for an isoform of
tropoelastin is achieved through homologous recombination or site
specific transposition and is followed by recombinant baculovirus
infection of insect cells (Sf9 or High Five) and subsequent
recombinant gene expression as follows:
[0058] Elastin cDNA encoding tropoelastin is identified and
isolated from a cDNA library. The gene is cloned into a pFastBac or
pFastBac HT donor plasmid using standard restriction endonucleases
and DNA ligase. Correct insertion of gene is verified by
restriction endonuclease digestion and PCR analysis. The DNA is
then transformed into DH10Bac cells which harbor a bacmid a
mini-attTn7 target site and a helper plasmid. Once cloned into the
DH10Bac cells, the elastin gene undergoes site-specific
transposition into the Bacmid. Transposition results in the
disruption of a LacZalpha gene and colonies containing recombinant
bacmids are white. High molecular weight mini-prep DNA is prepared
from selected E. Coli clones containing the recombinant bacmid and
is used to transfect SF9 or High Five insect cells using CellFECTIN
reagent. The insect cells produce actual baculovirus particles
harboring the tropoelastin encoding gene. The virus particles are
harvested and are subsequently used to infect insect cells which
produce high yields of the recombinant protein product,
tropoelastin.
[0059] Tropoelastin accumulated in elastin rich tissues by the
inhibition of lysyl oxidase through copper deficiency or lathyrism
can be isolated by exploiting tropoelastin's high solubility in
short-chain alcohols. Modified methods of this alcohol extraction
procedure can be used to purify rTE from expression hosts such as
bacteria, yeast, insect, and mammalian cells in culture. Methods
have been described in detail which involve precipitation of
tropoelastin with n-propanol and n-butanol. Tropoelastin expressed
in insect cells using the pFastBac HT baculovirus expression system
(Life Technologies, Gaithersburg, Md.) can be purified in a single
affinity chromatography step with Ni-NTA resin. The invention is
not limited to any particular method of tropoelastin isolation or
purification.
Polymer Synthesis
[0060] In tissue, tropoelastin is naturally crosslinked by several
tetra and bifunctional cross-links to form elastin. These
crosslinks arise through the oxidative deamination and condensation
of lysyl side chains. Both bifunctional lysinonorleucine and
allysine aldol and tetrafunctional desmosine crosslinks are formed.
Tetrafunctional desmosine crosslinks are a distinguishing feature
of elastin. Tropoelastin can be converted to a tropoelastin
biomaterial by oxidative deamination of lysyl residues and the
subsequent crosslinking of the monomeric moiety catalyzed by the
copper dependent enzyme lysyl oxidase (protein-lysine
6-oxidase).
[0061] A primary purpose of the invention is to produce
cross-linked elastic matrices that are identical to or closely
mimic those found naturally in elastic tissue. It is, therefore,
advantageous to crosslink tropo-elastin monomers with the same
bifunctional and tetrafunctional cross-links found in elastin.
However, the invention is not limited to these naturally occurring
cross-links and any type of cross-link formed between tropoelastin
monomers, whether produced chemically, enzymatically or
radiatively, can be used for the invention.
[0062] Crosslinking tropoelastin with lysyl oxidase will produce
matrices that closely resemble or imitate naturally occurring ones.
Lysyl oxidase protein-lysine 6-oxidase) catalyzes the oxidation of
lysine residues to a peptidyl .alpha.-aminoadipic
-.alpha.-semialdehyde. This aldehyde residue spontaneously
condenses with neighboring aldehydes or .alpha.-amino groups
forming interchain or intrachain crosslinkages (Kagan, 1991). Lysyl
oxidase from any source can be used so long as the tropoelastin it
is intended to oxidize is a suitable ligand. Lysyl oxidase is
typically extracted from bovine aorta and lung, human placentas,
and rat lung with 4 to 6 M urea extraction buffers. Recombinantly
produced lysyl oxidase can also be used to cross-link tropoelastin.
Recombinant tropoelastin (rTE26A) has been cross-linked with lysyl
oxidase in 0.1 M sodium borate, 0.15 M NaCl, pH 8.0 when incubated
for 24 hr at 37.degree. C. (Bedell-Hogan, 1993). Another preferred
method of crosslinking tropoelastin is with .gamma.-irradiation.
.gamma.-irradiation causes formation of free radicals which can
result in crosslink formation. 20 mrad of .gamma.-irradiation has
been shown to crosslink an elastin like polypeptide,
poly(GLy-Val-Gly-Val-Pro), into an elastomeric matrix and has
increased the elasticity and strength of a elastin-fibrin
biomaterial. The addition of chemical agents that form crosslinks
when activated with irradiation can also be used. Sulfur
derivatives combined with .gamma.-irradiation been shown to further
increase the strength of an elastin-fibrin biomaterial. Chemical
crosslinking reagents such as glutaraldelhyde may also be used to
cross-link tropoelastin matrices.
[0063] A preferred method of organizing tropoelastin monomers into
fibrous structures prior to cross-linking is by taking advantage of
the property of coacervation exhibited by tropoelastin.
Tropoelastin is soluble in water at temperatures below 37.degree.
C., however, upon raising the temperature to 37.degree. C.
tropoelastin aggregates into a filamentous structure called a
coacervate. Formation of tropoelastin coacervates may be a natural
step prior to cross-link formation during elastogenesis in tissue.
Coacervated tropelastin can be crosslinked by lysyl oxidase under
the appropriate conditions to produce filamentous elastin fibrils.
Alignment may be facilitated by exposure of the tropoelastin
coacervates to a magnetic field prior to crosslinking.
[0064] Collagen is the major structural polymer of connective
tissues. Artificial collagen fibers have been produced from soluble
collagen I extracts. Fibers such as these can be formed into
scaffoldings onto which tropoelastin can be cross-linked into
amorphous insoluble elastin producing a elastin/collagen composite
(see FIG. 3). The collagen fibers lend form and tensile strength to
the tropoelastin material and the crosslinked tropoelastin fibrils
lend elasticity thus creating a composite material that very nearly
approximates naturally occurring connective tissue.
[0065] Proteoglycans are major constituents of the extracellular
matrix. The addition of Hyaluronic acid, dermatan sulfate, keratane
sulfates, or Chondroitin sulfates as co-materials may further the
strength and cohesion of the material. In addition, cell function
is in part controlled by the extracellular matrix. Fibronectin,
vitronectin, laminin nad collagen, as well as various
glycosaminoglycans all mediate cell adhesion. Fibronectin has
several roles in the connective tissue matrix. It has an organizing
role in developing tissues and it plays a major role in cell
adhesion to the extracellular matrix. Incorporation of fibronectin
as a co-material may improve the cell adhesion properties of the
tropoelastin based biomaterial. Microfibrils are distributed
throughout the body, and are prevalent in elastic tissues and
fibers. The presence of microfibrils during polymerization of
tropoelastin monomers may help to organize monomers yielding a
material with improved structural organization. Also, microfibrils
are known to sequester calcium ions and are thought to play a role
in protecting tropoelastin from chronic calcification.
Product Synthesis
[0066] The utility of tropoelastin based biomaterials may be
further improved by combining them with synthetic or natural
polymer co-materials, forming composites, and by adding bioactive
impregnates.
[0067] Antibiotics and/or anticoagulants or other agents can be
added to the tropoelastin matrix providing localized drug therapy
and preventing infection. In surgical repair of abdominal traumatic
injuries, infection represents a major problem particularly when
vascular prosthetic implants are used. An tropoelastin graft with
antibiotic incorporation may be ideal because it avoids sacrifice
of an autologous artery or vein which decreases surgical time and
precludes the necessity to use synthetic prosthetic materials which
may be more prone to infection than tropoelastin grafts. Bioactive
impregnates may also include anti-coagulants (Hirudin), coagulants,
anti-proliferative drugs (Methatrexate), growth factors,
anti-virals, and anti-neoplastics.
[0068] Small diameter vascular grafts fail at an unacceptable rate
due to their inherent throm-bogenicity. This problem may be
decreased by the deposition of a living autologous endothelial cell
lining. Autologous endothelial cell transplantation can accelerate
the formation of an immunologically compatible, complete
endothelial lining using microvascular endothelial cells derived
from the adipose tissue of a recipient animal (Jarrell, et al.). In
the porcine model the peritoneal fat had been determined to be
optimal for this purpose due to the predominance of microvascular
and endothelial cells. Following extraction of peritoneal fat,
homogenization, collagenase digestion, and centrifugal separation,
cells are expeditiously transplanted onto the luminal surface of
crosslinked tropoelastin vascular grafts using an intra-operative
isolation technique combined with the rapid pressure sodding
techniques described by Jarrell and Williams.
[0069] The present invention constitutes a three dimensional matrix
made of elastin or tropoelastin for use as a framework for a
three-dimensional, multi-layer cell culture system. Populating
endogenous biologic materials such as a tropoelastin matrix with
stromal cells is preferable to populating matrices made of
synthetic biocompatible, non-living materials. Synthetic
biodegradable biomaterials must undergo enzyme catalyzed
degradation or spontaneous hydrolysis in order to avoid permanent
chronic foreign body reactions. On the contrary, elastin is a
naturally occurring protein in the extracellular matrix of many
tissues and, therefore, does not illicit a foreign body reaction.
Unlike collagen, elastin undergoes very little post-developmental
remodelling or breakdown and is a relatively permanent connective
tissue structure during the life of an organism. Tropoelastin
biomaterials can provide a relatively permanent, natural support
matrix for three dimensional cell cultures that when implanted acts
as a template for reconstruction of the organs and tissues. In
addition the longevity and integrity of implanted tropoelastin is
regulated in response to the biological needs of the tissue rather
than environmentally induced hydrolysis or enzymatic degradation of
a foreign substance.
[0070] Elastin 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 is
thought to only occur during development and ceases during
childhood (the only exceptions being hypertension and restenosis).
Elastogenesis is a complex method and formation of mature elastic
structures not likely to be achieved in relatively simple in vitro
cell culture systems. However, it has 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 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 elastin or elastin based biomaterials. This
insures the presence of biologically important elastic structures
in the living tissue grafts.
[0071] A method for both organizing tropoelastin fibrils and
providing a support for fibroblast growth is by coacervating
tropoelastin monomers in solution with fibroblasts. Tropoelastin
monomers mixed with stromal cells (fibroblasts) in a physiologic
buffer aggregate into fibers (coacervation) upon raising the
temperature of the solution to 37.degree. C. In doing so the
fibroblasts become trapped in a loose matrix of elastic fibers. The
tropoelastin fibers can be crosslinked either by including lysyl
oxidase in the buffer or a temperature sensitive recombinant form
of lysyl oxidase that, for example, is inactive at 20.degree. C.
and active at 37.degree. C. or by culturing the
tropoelastin-fibroblast matrix in such a manner that the
fibroblasts secrete natural lysyl oxidase into the coacervate
matrix. The contraction of the fibroblasts bound to the coacervated
tropoelastin monomers could preferentially align the tropoelastin
fibrils prior to crosslinking.
Sterilization
[0072] The tropoelastin biomaterial of the invention is normally
secured to existing tissue. Various techniques for effecting that
attachment can be used, including art-recognized techniques,
including suturing, staples and gluing. However, in some cases 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 tropoelastin 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 about 808 nm and a preferred dye is indocyanine green
(ICG), maximum absorbance 795-805 nm (see WO 91/04073). 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
tropoelastin 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 (e.g. 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 troptropoelastin
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.
[0073] 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 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.
[0074] In accordance with the present invention, the laser energy
can be directed to the target site (e.g. the dye) directly from the
laser by exposure of the tissue (e.g. during a surgical procedure).
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 800 nm can be used. Such
wavelengths are not well absorbed by many tissues, particularly
blood and 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 FIG. 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 (e.g. ICG) layer is ideally previously or
concurrently determined so that the optimal amount of light for
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.
[0075] 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. 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 (e.g.
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 device that assesses the adequacy of
the bonding or thermal effect.
[0076] 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 FIG. 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 or lung, 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 bio-materials to which the invention
relates can be used in a variety of other clinical and surgical
settings to effect tissue repair 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 arterial or venous location
using standard techniques. The balloon can then be inflated,
compressing the stent (tropoelastin biomaterial) against the vessel
wall and then laser light delivered through the balloon to seal the
stent in place (the dye can be present on the outside of the
biomaterial). The balloon can then be deflated and removed leaving
the stent in place. A protective sleeve (of plastic or the like)
can be used to protect the stent during its passage to the vessel
and then withdrawn once the stent is in the desired location.
[0077] The biomaterial of the invention can also be used as a
biocompatible covering for a metal or synthetic scaffold or stent.
In such cases, simple mechanical deployment can be used without the
necessity for laser bonding. Laser bonding can be employed,
however, depending upon specific demands, e.g., 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.
[0078] 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
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.
[0079] The tropoelastin-based 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 tropoelastin biomaterial can be deployed with a dye on
the tissue side and then fused with the appropriate wavelength and
laser energy.
[0080] 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, repair from acid
reflux for erosive esophagitis or, more preferably, for
refurbishing damaged esophageal segments during or following
surgery or chemotherapy for esophageal carcinoma.
[0081] 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 (see 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 tropoelastin material. Examples of other
prostheses that can be made from synthetics (or metals coated with
the tropoelastin based biomaterial or from the
biomaterial/synthetic hybrids include cardiac valve rings and
esophageal stents.
[0082] The tropoelastin-based prostheses of the invention can be
prepared so as to include a drug; that can be delivered, via the
prostheses, to particular body sites. For example, 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 or endothelial regrowth.
Vasodilators can also be included.
[0083] Prostheses formed from the tropoelastin bio-material can
also be coated with viable cells, cells from the recipient of the
prosthetic device. Endothelial cells, preferably autologous (e.g.
harvested during liposuction), can be seeded onto the elastin
bioprosthesis prior to implantation (e.g. for vascular stent
indications). Alternatively, the tropoelastin 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.
[0084] 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.
[0085] Having described and illustrated the principles of the
invention in a preferred embodiment thereof, it should be apparent
that the invention can be modified in arrangement and detail
without departing from such principles. I claim all modifications
and variation coming within the spirit and scope of the following
claims.
* * * * *