- FIELD OF THE INVENTION
This application is a continuation-in-part of U.S. patent application Ser. No. 10/977,545, filed Oct. 28, 2004, which is herein incorporated by reference in its entirety.
- BACKGROUND OF THE INVENTION
Methods and devices for preventing vascular device migration using autologous growth factor composition-coated vascular devices are disclosed. Specifically, methods for producing autologous growth factor compositions and coating vascular devices with the compositions before device implantation are provided.
A variety of implantable vascular devices, including stent grafts and stents, have been developed to treat abnormalities of the vascular system. Stent grafts are used to treat aneurysms of the vascular system and have also emerged as a new treatment for a related condition, acute blunt aortic injury, where trauma causes damage to an artery. Stents are used to treat areas of vessel narrowing or atherosclerosis.
Aneurysms arise when a thinning, weakening section of vessel wall balloons out to more than 150% of its normal diameter. These thinned and weakened sections of vessel walls can burst, causing an estimated 32,000 deaths in the United States each year. Additionally, aneurysm deaths are suspected of being underreported because sudden unexplained deaths, about 450,000 in the United States alone, are often simply misdiagnosed as heart attacks or strokes while many of them may be due to aneurysms.
U.S. surgeons treat approximately 50,000 abdominal aortic aneurysms each year, typically by replacing the abnormal section of vessel with a plastic or fabric graft in an open surgical procedure. A less-invasive procedure that has more recently been used is the placement of a stent graft at the aneurysm site. Stent grafts are tubular devices that span the aneurysm to provide support without replacing a section of the vessel. The stent graft, when placed within the artery at the aneurysm site, acts as a barrier between blood flow and the weakened wall of the artery, thereby decreasing pressure on the damaged portion of the artery. This less invasive approach to treating aneurysms decreases the morbidity seen with conventional aneurysm repair. Additionally, patients whose multiple medical comorbidities make them excessively high risk for conventional aneurysm repair are candidates for stent grafting.
Stents are rigid, or semi-rigid, tubular scaffoldings that are used to treat vessel narrowing or atherosclerosis, the leading cause of death in the United States. Specifically, atherosclerosis and other forms of coronary artery narrowing are treated with percutaneous transluminal angioplasty (“angioplasty”). The objective of angioplasty is to enlarge the lumen of an affected vessel by radial hydraulic expansion. The procedure is accomplished by inflating a balloon within the narrowed lumen of the affected artery. After (or during) such an angioplasty procedure, stents are deployed at the treatment site within the vessel to reduce the risks of reclosure. Stents are generally positioned across the treatment site, and then expanded to keep the passageway clear. The stent provides a scaffold which overcomes the natural tendency of the vessel walls of some patients to renarrow, thus maintaining the openness of the vessel and resulting blood flow.
While stent grafts and stents (hereinafter collectively referred to as “vascular devices”) represent improvements over previously-used vessel treatment techniques, there are still risks associated with them. The most common of these risks is migration of the vascular device due to hemodynamic forces within the vessel. Stent graft migrations lead to endoleaks, a leaking of blood into the aneurysm sac between the outer surface of the graft and the inner lumen of the blood vessel. Stent migration can leave a treated area of a vessel more susceptible to reclosure. Such migrations of vascular devices are especially possible in curved portions of vessels where asymmetrical hemodynamic forces in the area can place uneven forces on the vascular device. Additionally, the asymmetrical hemodynamic forces can cause remodeling of an aneurysm sac which leads to increased risk of aneurysm rupture and increased endoleaks.
Based on the foregoing, one goal of treating aneurysms and vessel narrowings is to provide vascular devices that do not migrate. To achieve this goal, vascular devices with stainless steel anchoring barbs that engage the vessel wall have been developed. Additionally, endostaples that fix vascular devices more readily to the vessel wall have been developed. While these physical anchoring devices have proven to be effective in some patients, improvements continue to be sought to assure the position of stent grafts once placed.
Additionally, the combination of the metal scaffolding of most stent grafts and graft migration in a small percentage of cases has led to the contraindication of magnetic resonance imaging (MRI) in some patients having stent grafts. The magnetic fields used in this imaging process, when moving across the body, may cause insufficiently fixated metal-containing stents to migrate.
One way to improve vascular device fixation is to administer to the treatment site, either before, during or relatively soon after implantation, a cell growth-promoting factor. This administration can be beneficial because, normally, the endothelial cells that make up the portion of the vessel to be treated are quiescent at the time of vascular device implantation and do not multiply. As a result, the vascular device rests against a quiescent endothelial cell layer. If cell growth-promoting compositions are administered immediately before, during or relatively soon after vascular device deployment, the normally quiescent endothelial cells lining the vessel wall, and in intimate contact with the vascular device, will be stimulated to proliferate. The same will occur with smooth muscle cells and fibroblasts found within the vessel wall. As these cells proliferate they can grow into, on and/or around the vascular device such that the vascular device becomes physically attached to the vessel lumen rather than merely resting against it. This endothelialization helps promote vascular device fixation.
Endothelialization has been observed to naturally occur in some human stent grafts within weeks of implantation. This natural endothelialization is not complete or consistent, however, and therefore does not in some cases prevent the stent graft migration and endoleak. Methods to increase endothelialization are sought to improve clinical outcome after stent grafting.
- SUMMARY OF THE INVENTION
Based on the above discussed issues, additional methods for fixating stent grafts to vessel walls are needed to further prevent occurrences of endoleaks and stent graft migration.
The risk of stent graft migration can be reduced by delivering to the treatment site, as a coating on the stent graft, endothelialization factors such as autologous growth factor compositions. This administration can be beneficial because, normally, the endothelial cells that make up the portion of the vessel to be treated are quiescent at the time of stent graft implantation and do not multiply. As a result, the stent graft rests against a quiescent endothelial cell layer. If autologous growth factor compositions are administered to the treatment site with the stent graft deployment, the normally quiescent endothelial cells lining the vessel wall, and in intimate contact with the stent graft, will be stimulated to proliferate. The same will occur with smooth muscle cells and fibroblasts found within the vessel wall. As these cells proliferate they can grow into and around the stent graft lining such that the stent graft becomes physically attached to the vessel lumen rather than merely resting against it. This endothelialization helps to prevent stent graft migration. These methods can promote healing, reduce endoleaks and minimize device migration by promoting endothelial tissue in-growth.
Based on the foregoing, embodiments according to the present invention provide stent grafts having autologous growth factor compositions coated thereon for the treatment of aneurysms, and associated methods for using and/or manufacturing the stent grafts. Additionally, stent grafts are disclosed which provide structural support for weakened arterial walls while the accompanying compositions promote tissue in-growth to reduce the chance of graft migration and endoleaks.
Therefore, embodiments according to the present invention provide methods for providing a stent graft and a cell growth-promoting composition comprising obtaining autologous platelet rich plasma (PRP) from a patient in need of a stent graft, activating the PRP to form autologous growth factor composition, coating the stent graft with the autologous growth factor composition and implanting the autologous growth factor composition-coated stent graft into a vessel at a treatment site in a patient wherein the autologous growth factor composition-coated stent graft induces endothelialization of the stent graft.
In one embodiment of the method for providing a stent graft and a cell growth-promoting composition, the coating step comprises injecting autologous growth factor composition through at least one injection port in a delivery catheter such that said autologous growth factor composition wets the stent graft disposed within the delivery catheter.
In another embodiment of the method for providing a stent graft and a cell growth-promoting composition, the method further comprises providing a drug in combination with the autologous growth factor composition wherein the drug is selected from the group consisting of small molecules, peptides, proteins, hormones, DNA or RNA fragments, cells, genetically engineered cells, genes, cell growth promoting compositions, matrix metalloproteinase inhibitors, antibiotics, cyclooxygenase-2 inhibitors, angiotensin-converting enzyme inhibitors, glucocorticoids, beta blockers, nitric acid synthase inhibitors, antioxidants and cellular adhesion molecules.
In yet another embodiment of the method for providing a stent graft and a cell growth-promoting composition, the activating step comprises mixing said PRP with an activating agent such as, but not limited to, a platelet agonist. In one embodiment the platelet agonist is adenosine diphosphate (ADP), preferably at a concentration of 5 to 20 μM, or thrombin receptor activating peptide (TRAP), preferably at a concentration of 5 to 10 μM.
In an embodiment of the method for providing a stent graft and a cell growth-promoting composition, the autologous growth factor composition is centrifuged to remove cells and cellular particulates prior to the coating step.
In another embodiment of the method for providing a stent graft and a cell growth-promoting composition, the said treatment site is an aneurysm site
In another embodiment of the method for providing a stent graft and a cell growth-promoting composition, the stent graft is pre-coated with a base coating material selected from the group consisting of heparin, hyaluronate, alginate, collagen, fibrin, dextran, β-cyclodextrin, polyvinyl alcohol and hydrogel prior to coating with said autologous growth factor composition.
Another embodiment according to the present invention provides a delivery catheter for delivering a stent graft to a vessel in a patient in need thereof, having disposed therein a stent graft, comprising at least one injection port through which coating composition(s) are injected to coat the stent graft. In another embodiment, the coating composition(s) is autologous growth factor composition or a pre-coating material.
In another embodiment of the delivery catheter, the delivery catheter comprises a plurality of injection ports wherein the plurality of injection ports are disposed along the length of the delivery catheter such that the entire stent graft is accessible by the plurality of injection ports.
One embodiment of the present invention provides an endothelialization promoting stent graft for implantation into a patient in need thereof comprising a stent graft having an autologous growth factor composition deposited thereon.
In an embodiment of the endothelialization promoting stent graft, the stent graft further comprises a base coat between the stent graft and the autologous growth factor composition coating wherein the base coat comprises a material selected from the group consisting of heparin, hyaluronate, alginate, collagen, fibrin, dextran, β-cyclodextrin, polyvinyl alcohol and hydrogen.
- BRIEF DESCRIPTION OF THE FIGURES
In another embodiment of the endothelialization promoting stent graft, the autologous growth factor composition is isolated from the patient at the time of stent graft implantation. In yet another embodiment, the stent graft is coated with the autologous growth factor composition at the time of stent graft implantation.
FIG. 1 depicts a fully deployed stent graft with an exterior metal scaffolding as used in one embodiment according to the present invention.
FIGS. 2 a-b depict a stent graft delivery catheter containing injection ports for coating the stent graft with autologous growth factor composition(s) immediately prior to deployment in accordance with the teachings of the present invention. FIG. 2 b is a cross-section of the stent graft delivery catheter depicted in FIG. 2 a.
FIG. 3 depicts the effects of autologous platelet gel on human microvascular endothelial cell proliferation.
FIG. 4 depicts the effects of autologous platelet gel on arterial smooth muscle cell proliferation.
- DEFINITION OF TERMS
FIG. 5 depicts the effects of autologous platelet gel on endothelial cell migration.
Prior to setting forth embodiments according to the present invention, it may be helpful to an understanding thereof to set forth definitions of certain terms that will be used hereinafter. Unless otherwise explained, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The singular terms “a,” “an,” and “the” include plural referents unless context clearly indicates otherwise. Similarly, the word “or” is intended to include “and” unless the context clearly indicates otherwise. The term “comprises” means “includes.”
Activating Agent(s): As used herein, “activating agent(s)” shall include platelet agonist(s) that are capable of inducing platelet activation which lead to platelet degranulation and release of growth factors stored within alpha granules. Exemplary, non-limiting examples of activating agents include adenosine diphosphate (ADP) and thrombin receptor agonist peptide (TRAP).
Animal: As used herein, “animal” shall include, without limitation, mammals, fish, reptiles and birds. Mammals include, but are not limited to, primates, including humans, dogs, cats, goats, sheep, rabbits, pigs, horses and cows.
Autologous Growth Factor Composition: As used herein, “autologous growth factor composition” includes to growth factors released from platelets after activation of the platelets with an activating agent. Autologous growth factor composition can refer to a composition that either contains, or have been centrifuged to remove, platelet cellular material after activation.
Biocompatible: As used herein “biocompatible” refers to any material that does not cause injury or death to the animal or induce an adverse reaction in an animal when placed in intimate contact with the animal's tissues. Adverse reactions include, without limitation, inflammation, infection, fibrotic tissue formation, cell death, embolizations and/or thrombosis.
Bioactive Material: As used herein, “bioactive material(s)” shall include any compound or composition that creates a physiological and/or biological effect in an animal. Non-limiting examples of bioactive materials include small molecules, peptides, proteins, hormones, DNA or RNA fragments, genes, cells, genetically-modified cells, cell growth promoting compositions, matrix metalloproteinase inhibitors, autologous platelet gel, platelet rich plasma, either inactivated or activated, other natural and synthetic gels, such as, without limitation, alginates, collagens, and hyaluronic acid, polyethylene oxide, polyethylene glycol, and polyesters, as well as combinations of these bioactive materials.
Cell Growth Promoting Compositions: As used herein, “cell growth promoting factors” or “cell growth promoting compositions” shall include any bioactive material having a growth promoting effect on vascular cells. Non-limiting examples of cell growth promoting compositions include vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF), platelet-derived epidermal growth factor (PDEGF), fibroblast growth factors (FGFs), transforming growth factor-beta (TGF-β), platelet-derived angiogenesis growth factor (PDAF) and autologous platelet gel (APG) including platelet rich plasma (PRP), platelet poor plasma (PPP) and thrombin.
Drug(s): As used herein, “drug” shall include any bioactive compound or composition having a therapeutic effect in an animal. Exemplary, non limiting examples include small molecules, peptides, proteins, hormones, DNA or RNA fragments, genes, cells, genetically-modified cells, cell growth promoting compositions, matrix metalloproteinase inhibitors, antibiotics, cyclooxygenase-2 inhibitors, angiotensin-converting enzyme inhibitors, glucocorticoids, beta blockers, nitric acid synthase inhibitors, antioxidants, cellular adhesion molecules, and autologous platelet composition.
Endoleak: As used herein, “endoleak” refers to the presence of blood flow past the seal between an end of the stent graft and the vessel wall, and into the aneurysmal sac, when all such flow should be contained within its lumen.
Implantable Medical Device: As used herein, “implantable medical device” includes, without limitation, stents and stent grafts used in the repair of vascular injuries.
Migration: As used herein, “migration” refers to displacement of a stent or stent graft sufficient to be associated with a complication, for example, endoleak.
- DETAILED DESCRIPTION
Treatment Site and Administration Site: As used herein, the phrases “treatment site” and “administration site” includes a portion of a vessel having a stent or a stent graft positioned in its vicinity. A treatment site can be, without limitation, an aneurysm site, the site of an acute traumatic aortic injury, the site of vessel narrowing or other vascular-associated pathology.
Embodiments according to the present invention provide devices and related methods useful for preventing post-implantation migration of implantable vascular devices using autologous growth factor composition to promote implantable vascular device attachment to blood vessel luminal walls. A delivery device, which allows the application of autologous growth factor compositions to the stent graft while the stent graft is disposed within the delivery device, prior to the deployment of the stent graft is provided.
For convenience, the devices and related methods according to the present invention discussed hereinafter will be exemplified using stent grafts intended to treat aneurysms. As discussed briefly above, an aneurysm is a swelling, or expansion of a blood vessel lumen at a defined point and is generally associated with a vessel wall defect. Aneurysms are often a multi-factorial asymptomatic vessel disease that if left unchecked may result in spontaneous rupture, often with fatal consequences. Previous methods to treat aneurysms involved highly invasive surgical procedures where the affected vessel region was removed and replaced with a synthetic graft that was sutured in place. However, this procedure was extremely risky and was generally only employed in otherwise healthy vigorous patients who were expected to survive the associated surgical trauma. Elderly and more feeble patients were not candidates for many aneurysmal surgeries and remained untreated and thus at continued risk for sudden death.
In order to overcome the risks associated with invasive aneurysmal surgeries, stent grafts were developed that can be deployed with a cut down procedure or percutaneously using minimally invasive procedures. Essentially, a catheter having a stent graft compressed and fitted into the catheter's distal tip is advanced through an artery to the aneurysmal site. The stent graft is then deployed within the vessel lumen juxtaposed to the weakened vessel wall forming an inner liner that insulates the aneurysm from the body's hemodynamic forces thereby reducing, or eliminating the possibility of rupture. The size and shape of the stent graft is matched to the treatment site's lumen diameter and aneurysm length. Moreover, branched grafts are commonly used to treat abdominal aortic aneurysms that are located near the iliac branch.
Stent grafts generally comprise a metal scaffolding having a biocompatible covering such a Dacron® (E.I. du Pont de Nemours & Company, Wilmington, Del.) or a fabric-like material woven from a variety of biocompatible polymer fibers. Other embodiments include extruded sheaths and coverings. The scaffolding is generally on the luminal wall-contacting surface of the stent graft and directly contacts the vessel lumen. The sheath material is stitched, glued or molded onto the scaffold. In other embodiments, the scaffolding may be on the graft's blood flow contacting surface or interior. When a self-expanding stent graft is deployed from the delivery catheter, the scaffolding expands to fill the lumen and exerts circumferential force against the lumen wall. This circumferential force is generally sufficient to keep the stent-g raft from migrating and thus preventing endoleak. However, stent migration and endoleak may occur in vessels that have irregular shapes or are shaped such that they exacerbate hemodynamic forces within the lumen. Stent migration refers to a stent graft moving from the original deployment site, usually in the direction of the blood flow. Endoleak (as used herein) refers specifically to the seepage of blood around the stent ends to pressurize the aneurysmal sac or between the stent graft and the lumen wall. Stent graft migration may result in the aneurysmal sac being exposed to blood pressure again and increasing the risk of rupture. Endoleaks occur in in a small percentage of aneurysms treated with stent grafts. Therefore, it would be desirable to have devices, compositions and methods that minimize post implantation stent graft migration and endoleak.
Co-pending U.S. patent application Ser. No. 10/977,545, filed Oct. 28, 2004 discloses injecting autologous platelet gel (APG) into the aneurysmal sac and/or between an implanted stent graft and the vessel wall to induce endothelialization of the stent graft to prevent endoleak and stent graft migration. Autologous platelet gel is produced by activating autologous platelet-rich plasma with thrombin to form a gel containing an increased concentration of growth factors over unactivated platelet rich plasma (PRP). However, the APG is extremely viscous and cannot be injected after formation. Therefore, the components of APG, PRP and thrombin, must be co-injected at the treatment site such that APG is formed in situ. The present inventors sought to provide an autologous growth factor-containing composition which is less viscous than APG and can be used to coat a stent graft prior to implantation. The autologous growth factor composition of the present invention, wherein PRP is activated to produce growth factors in the absence of thrombin, is a liquid composition which can be used to coat a stent graft prior to deployment and implantation. This approach is especially beneficial because it avoids the potential embolization concerns associated with thrombin use.
Activation of PRP, either by thrombin or the activating agents adenosine diphosphate or thrombin receptor activating peptide, produces a cocktail of growth factors, the composition of which is not dependent on the type of activation. Therefore activation of PRP by thrombin or another activating agent, produces an equivalent composition of growth factors.
In one embodiment, autologous growth factor compositions are administered to a treatment site within a vessel lumen as a coating on a stent graft. The vessel wall's blood-contacting lumen surface comprises a layer of endothelial cells. In the normal mature vessel the endothelial cells are quiescent and do not multiply. Thus, a stent graft carefully placed against the vessel wall's blood-contacting luminal surface rests against a quiescent endothelial cell layer. However, if cell growth-promoting compositions are administered with the stent graft, the normally quiescent endothelial cells lining the vessel wall, and in intimate contact with the stent graft luminal wall contacting surface, will be stimulated to proliferate. The same will occur with smooth muscle cells and fibroblasts found within the vessel wall. As these cells proliferate they will grow into and around the stent graft lining such that the stent graft becomes physically attached to the vessel lumen rather than merely resting against it. In one example, the stent graft has a metallic scaffolding on the graft's luminal wall contacting surface and the cell growth-promoting factor is an autologous growth factor composition.
The autologous growth factor composition comprises activated platelets, unactivated platelets, and platelet releasate(s) and it is obtained by activating platelets in autologous PRP to release their contents (i.e., platelet releasates). Platelets are cytoplasmic portions of marrow megakaryocytes which have no nucleus for replication and an expected lifetime of five to nine days. Upon activation by a variety of activating agents, platelets release pre-formed stores of growth factors from alpha granules. A wide variety of growth factors are released by activated platelets including, but not limited to, platelet-derived growth factor (PDGF), platelet-derived epidermal growth factor (PDEGF), fibroblast growth factor (FGF), transforming growth factor-beta (TGF-β), insulin-like growth factor (IGF) and platelet-derived angiogenesis growth factor (PDAF). These growth factors have been implicated in wound healing by increasing the rate of collagen secretion, vascular in-growth and fibroblast proliferation. Platelet rich plasma also contains a concentrated population of white blood cells (WBC) which, following activation, secrete a variety of factors, including but not limited to, growth factors, cytokines, chemokines, prostaglandins, and matrix metalloproteinases. Non-limiting examples of growth factors released from WBCs include IGF, basic FGF, TGF and others. Non-limiting examples of cytokines released from WBCs include, granulocyte colony stimulating factor (G-CSF), granulocyte macrophage colony stimulating factor (GM-CSF) and others. Many of these WBC-derived factors are also capable of promoting proliferation and enhancing migration of a variety of cell types.
Platelet-rich plasma is generated from variable speed centrifugation of autologous blood using devices such as, but not limited to, the Magellan™ Autologous Platelet Separator System (Medtronic, Inc., Minneapolis, Minn.). The Magellan™ Separator is a small, portable platelet separator suitable for use in a variety of clinical settings, including an operating room. Additionally, the Magellan™ system is particularly suited for producing PRP from a small amount of autologous blood in a closed system that minimizes contamination.
In one embodiment, the autologous growth factor composition is formed from PRP mixed with one or more activating agents for about 5, about 10, or about 15 minutes. In one specific example, the autologous growth factor composition is formed from PRP mixed with an activating agent for about 10 minutes. In some embodiments, the autologous growth factor composition is further centrifuged to remove some or all of the platelets in the mixture after activation and prior to coating the stent graft.
Activating agents are platelet agonists such as adenosine diphosphate (ADP) or thrombin receptor activating peptide (TRAP). In some embodiments, the autologous growth factor composition is formed from PRP mixed with about 5 to about 20 μM, about 7 to about 18 μM, about 9 to about 17 μM, or about 11 to about 15 μM of ADP. In one example, the autologous growth factor composition is formed from PRP mixed with about 10 μM of ADP. In some other embodiments, the autologous growth factor composition is formed from PRP mixed with about 5 to about 10 μM, about 6 to about 9 μM, or about 7 to about 8 μM of TRAP. In one specific example, the autologous growth factor composition is formed from PRP mixed with about 7 μM of TRAP.
Implantable medical devices, specifically stent grafts, are advantageously sealed to the vessel lumen using the autologous growth factor composition. Once associated with the stent graft, the autologous growth factor composition, with its rich composition of growth and healing factors, can promote the integration of the stent graft into the vessel wall. Enhanced healing and tissue in-growth from the surrounding vessel may lessen the chances of stent graft migration and endoleak. Additionally, drugs that induce positive effects at the aneurysm site can also be delivered with autologous growth factor composition and the methods described.
Because of the physical properties of the autologous growth factor composition, it is particularly useful in promoting endothelialization of vascular stent grafts. The autologous growth factor composition not only can coat the exterior surface of the stent graft but also fills the pores of the stent graft, inducing migrating cells into the stent graft fabric. As a result, engraftment of endothelial cells will occur preferentially at those sites where autologous growth factor composition is present. Previously, vascular prostheses were seeded with non-autologous materials, enhancing the possibility of graft rejection. Autologous growth factor composition will not cause antigenicity or rejection effects.
Endothelialization may be stimulated by induced angiogenesis resulting in formation of new capillaries in the interstitial space and surface endothelialization. This has led to modification of medical devices with vascular endothelial growth factor (VEGF) and fibroblast growth factors 1 and 2 (FGF-1, FGF-2). The discussion of these factors is for exemplary purposes only, as those of skill in the art will recognize that numerous other growth factors have the potential to induce cell-specific endothelialization. VEGF is endothelial cell-specific however it is a relatively weak endothelial cell mitogen. FGF-1 and FGF-2 are more potent mitogens but are less cell specific. The development of genetically-engineered growth factors is anticipated to yield more potent endothelial cell-specific growth factors. Additionally it may be possible to identify small molecule drugs that can induce endothelialization.
Additional embodiments provide coatings for stent grafts that incorporate endothelialization factors in addition to the autologous growth factor composition. Stent grafts can be coated with endothelialization factors, including growth factors and drugs. The field of medical device coatings is well established and methods for coating stent grafts with bioactive compositions, with or without added polymers, are well known to those of skill in the art.
The autologous growth factor composition is generated and applied to the stent graft in the operating room immediately prior to deployment and implantation of the stent graft. In one embodiment, activation agents are added to the PRP and the resultant growth factor-rich plasma, the autologous growth factor composition, is applied directly to a stent graft loaded within a delivery device, such as a delivery catheter.
The stent graft is optionally pre-coated with a material to enhance growth factor attachment to the stent graft including, but not limited to, heparin, hyaluronate, alginate, collagen, fibrin, dextran, β-cyclodextrin, polyvinyl alcohol hydrogel.
In one embodiment, the stent graft is provided “pre-loaded” into a delivery catheter and the autologous growth factor composition is applied to the stent graft while the stent graft is disposed within the delivery catheter. In normal stent deployment protocols, a vascular stent graft 100 is fully deployed through the left iliac artery 114 to an aneurysm site 104 (FIG. 1). Stent graft 100 has a distal end 102 and an iliac leg 108 to anchor the stent graft in the iliac artery 116. Stent graft 100 is deployed first in a first delivery catheter and the iliac leg 108 is deployed in a second delivery catheter. The stent graft 100 and iliac leg 108 are joined with a 2 cm overlap of the two segments 106.
A stent graft is pre-loaded into a delivery catheter such as that depicted in FIG. 2 a. Stent graft 100 is radially compressed to fill the stent graft chamber 218 in the distal end 202 of delivery catheter 200. The stent graft 100 is covered with a retractable sheath 220. Catheter 200 has two injection ports 208 and 210 for delivering the autologous growth factor composition to the compressed stent graft. In this embodiment, the autologous growth factor composition is injected through either or both of injection ports 208 and 210 to wet stent graft 100. Stent graft 100 is then deployed to the treatment site as depicted in FIG. 1. FIG. 2 b depicts a cross-sectional view of stent graft 100 loaded into the delivery catheter 200 and the delivery catheter's retractable sheath 220 illustrating an injection port 208, 210 for delivering autologous growth factor composition to stent graft 100.
In an additional embodiment, the stent graft is pre-coated with a material to enhance attachment of growth factors from autologous growth factor composition, either prior to or after the stent graft is loaded into the delivery catheter. The stent graft can be pre-coated using standard coating methods including, but not limited to, dipping and spraying. Alternatively, the pre-coat can be applied through injection ports 208 and/or 210 prior to the application of the autologous growth factor composition.
- EXAMPLE 1
Properties of Platelet Rich Plasma
The following examples are meant to illustrate one or more embodiments according to the invention and are not meant to limit the scope of the invention to that which is described below.
Aliquots of human peripheral blood (30-60 mL) are passed through the Magellan™ Autologous Platelet Separator System (the Magellan™ system, Medtronic, Inc., Minneapolis, Minn.) and the concentrated, platelet-rich plasma fraction (PRP) assayed for platelets (PLT), white blood cells (WBC) and hematocrit (Hct) (Table 1). The Magellan™ system concentrated platelets and white blood cells six-fold and three-fold respectively.
|TABLE 1 |
|Blood cell yields after passing through the Magellan ™ system. |
|Mean ± SD || || || |
|n = 19 ||Initial Blood ||PRP ||Yield |
|PLT (×1000/μL) ||220.03 ± 48.58 ||1344.89 ± 302.00 ||6.14 ± 0.73 |
|WBC ||5.43 ± 1.43 ||17.04 ± 7.01 ||3.12 ± 0.90 |
|Hct (%) ||38.47 ± 2.95 ||6.81 ± 1.59 |
Cell Yield = cell count in PRP/cell count in initial blood = [times baseline]
- EXAMPLE 2
Autologous Platelet Gel Generation
Additionally, PRP was assayed for levels of the endogenous growth factors platelet-derived growth factor (PDGF), transforming growth factor-beta (TGF-β), basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), and endothelial growth factor (EGF). As a result of increased platelet and white blood cell counts in PRP, increased concentrations of growth factors were found.
|TABLE 2 |
|Growth Factor Content of Blood and PRP |
| ||Mean ± SD; n = 9 ||Initial Blood ||PRP |
| || |
| ||PDGF-AB (ng/mL) ||10.2 ± 1.4 ||88.4 ± 28.8 |
| ||PDGF-AA (ng/mL) ||2.7 ± 0.5 ||22.2 ± 4.2 |
| ||PDGF-BB (ng/mL) ||5.8 ± 1.4 ||57.8 ± 36.6 |
| ||TGF-β1 (ng/mL) ||41.8 ± 9.5 ||231.6 ± 49.1 |
| ||bFGF (pg/mL) ||10.7 ± 2.9 ||48.4 ± 25.0 |
| ||VEGF (pg/mL) ||83.1 ± 65.5 ||597.4 ± 431.4 |
| ||EGF (pg/mL) ||12.9 ± 6.2 ||163.3 ± 49.4 |
| || |
- EXAMPLE 3
Effects of Platelet Releasates on Cell Proliferation
Autologous Platelet Gel (APG) is generated from the PRP fraction produced in the Magellan™ system by adding thrombin and calcium to activate the fibrinogen present in the PRP as well as causing the platelets to release additional stores of growth factors. For each approximately 7-8 mL of PRP, approximately 5000 units of thrombin in 5 mL 10% calcium chloride are required for activation. The APG is formed immediately upon mixing of the activator solution with the PRP. The concentration of thrombin can be varied from approximately 1-1,000 U/mL, depending on the speed required for setting to occur. The lower concentrations of thrombin will provide slower gelling times.
A series of in vitro experiments were conducted evaluating the effect of released factors from platelets on the proliferation of the human microvascular endothelial cells and human coronary artery smooth muscle cells. Primary cell cultures of both cell types were established according to protocols well known to those skilled in the art of cell culture. Autologous platelet gel was used as the source of platelet releasates. For each cell type, five culture conditions were evaluated; basal medium (BM)+APG; BM+platelet-free plasma (PFP); growth medium (GM); BM alone; and BM+thrombin. Growth medium is the standard culture medium for the cell type and contains optimal growth factors and supplements.
- EXAMPLE 4
Effect of APG on Endothelial Cell Migration
Autologous platelet gel had a significant growth effect on human microvascular endothelial cells after four days of culture (FIG. 3) and on human coronary artery smooth muscle cells after five days of culture (FIG. 4).
Human microvascular endothelial cell migration was performed in a Boyden chemotaxis chamber which allows cells to migrate through 8 μm pore size polycarbonate membranes in response to a chemotactic gradient. Human microvascular endothelial cells (5×105) were trypsinized, washed and resuspended in serum-free medium (DMEM) and 400 μL of this suspension was added to the upper chamber of the chemotaxis assembly. The lower chamber was filled with 250 μL serum-free DMEM containing either 10% APG-derived serum, 10% PFP-derived serum or DMEM alone. After a pre-determined amount of time, the filters were removed and the cells remaining on the upper surface of the membrane (cells that had not migrated through the filter) were removed with a cotton swab. The membranes were then sequentially fixed, stained and rinsed to enable the visualization and quantification of cells that had migrated through the pores to the other side of the membrane. The number of migrated cells was significantly higher in the 10% APG serum culture than the basal medium or 10% platelet-free serum cultures (FIG. 5).
Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained. Each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of embodiments according to the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
Recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context.
Groupings of alternative elements or embodiments are not to be construed as limitations. Each group member may be referred to and claimed individually or in any combination with other members of the group or other elements found herein. It is anticipated that one or more members of a group may be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.
Embodiments according to the invention are described herein, variations on those embodiments will become apparent to those of ordinary skill in the art upon reading the foregoing description.
Furthermore, numerous references have been made to patents and printed publications throughout this specification. Each of the above cited references and printed publications are herein individually incorporated by reference in their entirety.
It is to be understood that the embodiments according to the invention disclosed herein are illustrative and that other modifications may be employed. Thus, by way of example, but not of limitation, alternative configurations may be utilized in accordance with the teachings herein.