SYSTEMS AND METHODS FOR MAKING ENCAPSULATED HOURGLASS SHAPED STENTS

[0001] This application is a continuation patent application of U.S. patent application Ser. No. 15/608,948, filed May 30, 2017, which claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 62/343,658, filed May 31, 2016, the entire contents of each of which are incorporated herein by reference in their entirety.

[0002] This application relates to systems and methods for the manufacture of hourglass or “diabolo” shaped encapsulated stents for treating congestive heart failure and other disorders treated with encapsulated hourglass shaped stents.

[0003] Heart failure is the physiological state in which cardiac output is insufficient to meet the needs of the body and the lungs. Congestive Heart Failure (CHF) occurs when cardiac output is relatively low due to reduced contractility or heart muscle thickening or stiffness. There are many possible underlying causes of CHF, including myocardial infarction, coronary artery disease, valvular disease, and myocarditis.

[0004] CHF is associated with neurohormonal activation and alterations in autonomic control. Although these compensatory neurohormonal mechanisms provide valuable support for the heart under normal physiological circumstances, they also have a fundamental role in the development and subsequent progression of CHF. For example, one of the body's main compensatory mechanisms for reduced blood flow in CHF is to increase the amount of salt and water retained by the kidneys. Retaining salt and water, instead of excreting it into the urine, increases the volume of blood in the bloodstream and helps to maintain blood pressure. However, the larger volume of blood also stretches the heart muscle, enlarging the heart chambers, particularly the ventricles. At a certain amount of stretching, the hearts contractions become weakened, and the heart failure worsens. Another compensatory mechanism is vasoconstriction of the arterial system. This mechanism, like salt and water retention, raises the blood pressure to help maintain adequate perfusion.

[0005] In low ejection fraction (EF) heart failure, high pressures in the heart result from the body's attempt to maintain the high pressures needed for adequate peripheral perfusion. However, the heart weakens as a result of the high pressures, aggravating the disorder. Pressure in the left atrium may exceed 25 mmHg, at which stage, fluids from the blood flowing through the pulmonary circulatory system flow out of the interstitial spaces and into the alveoli, causing pulmonary edema and lung congestion.

[0006] CHF is generally classified as either Heart Failure with reduced Ejection Fraction (HFrEF) or Heart Failure with preserved Ejection Fraction (HFpEF). In HFrEF, the pumping action of the heart is reduced or weakened. A common clinical measurement is the ejection fraction, which is a function of the blood ejected out of the left ventricle (stroke volume), divided by the maximum volume remaining in the left ventricle at the end of diastole or relaxation phase (End Diastolic Volume). A normal ejection fraction is greater than 50%. HFrEF has a decreased ejection fraction of less than 40%. A patient with HFrEF may usually have a larger left ventricle because of a phenomenon called cardiac remodeling that occurs secondarily to the higher ventricular pressures.

[0007] In HFpEF, the heart generally contracts normally, with a normal ejection fraction, but is stiffer, or less compliant, than a healthy heart would be when relaxing and filling with blood. This stiffness may impede blood from filling the heart, and produce backup into the lungs, which may result in pulmonary venous hypertension and lung edema. HFpEF is more common in patients older than 75 years, especially in women with high blood pressure.

[0008] Both variants of CHF have been treated using pharmacological approaches, which typically involve the use of vasodilators for reducing the workload of the heart by reducing systemic vascular resistance, as well as diuretics, which inhibit fluid accumulation and edema formation, and reduce cardiac filling pressure. However, pharmacological approaches are not always successful, as some people may be resistant or experience significant side effects

[0009] In more severe cases of CHF, assist devices such as mechanical pumps have been used to reduce the load on the heart by performing all or part of the pumping function normally done by the heart. Chronic left ventricular assist devices (LVAD), and cardiac transplantation, often are used as measures of last resort. However, such assist devices are typically intended to improve the pumping capacity of the heart, to increase cardiac output to levels compatible with normal life, and to sustain the patient until a donor heart for transplantation becomes available. Such mechanical devices enable propulsion of significant volumes of blood (liters/min), but are limited by a need for a power supply, relatively large pumps, and the risk of hemolysis, thrombus formation, and infection. In addition to assist devices, surgical approaches such as dynamic cardiomyoplasty or the Batista partial left ventriculectomy may also be used in severe cases. However these approaches are highly invasive and have the general risks associated with highly invasive surgical procedures.

[0010] U.S. Pat. No. 6,468,303 to Amplatz et al. describes a collapsible medical device and associated method for shunting selected organs and vessels. Amplatz describes that the device may be suitable to shunt a septal defect of a patient's heart, for example, by creating a shunt in the atrial septum of a neonate with hypoplastic left heart syndrome (HLHS). Amplatz describes that increasing mixing of pulmonary and systemic venous blood improves oxygen saturation. Amplatz describes that depending on the hemodynamics, the shunting passage can later be closed by an occluding device. However, Amplatz is silent on the treatment of CHF or the reduction of left atrial pressure, and is also silent on means for regulating the rate of blood flow through the device.

[0011] U.S. Pat. No. 8,070,708 to Rottenberg describes a method and device for controlling in-vivo pressure in the body, and in particular, the heart. The device described in Rottenberg involves a shunt to be positioned between two or more lumens in the body to permit fluid to flow between the two lumens. The Rottenberg patent further describes that an adjustable regulation mechanism may be configured to cover an opening of the shunt to regulate flow between the two lumens. The shunt is configured such that the flow permitted is related to a pressure difference between the two lumens. The adjustable regulation mechanism may be remotely activated. The Rottenberg patent describes that the device described may be used to treat CHF by controlling pressure difference between the left atrium and the right atrium. While Rottenberg describes a mechanism for treating CHF by controlling the flow between the left atrium and the right atrium, it does not describe the encapsulation of an hourglass shaped stent.

[0012] U.S. Patent Publication No. 2005/0165344 to Dobak, III describes an apparatus for treating heart failure that includes a conduit positioned in a hole in the atrial septum of the heart, to allow flow from the left atrium into the right atrium. Dobak describes that the shunting of blood will reduce left atrial pressures, thereby preventing pulmonary edema and progressive left ventricular dysfunction, and reducing LVEDP. Dobak describes that the conduit may include a self-expandable tube with retention struts, such as metallic arms that exert a slight force on the atrial septum on both sides and pinch or clamp the valve to the septum, and a one-way valve member, such as a tilting disk, bileaflet design, or a flap valve formed of fixed animal pericardial tissue. However, Dobak states that a valved design may not be optimal due to a risk of blood stasis and thrombus formation on the valve, and that valves can also damage blood components due to turbulent flow effects. Dobak does not provide any specific guidance on how to avoid such problems.

[0013] U.S. Pat. No. 9,034,034 to Nitzan, incorporated herein by reference, describes a device for regulating blood pressure between a patient's left atrium and right atrium which comprises an hourglass-shaped stent having a neck region and first and second flared end regions, the neck region disposed between the first and second end regions and configured to engage the fossa ovalis of the patient's atrial septum. Nitzan describes that the hourglass shaped stent is also encapsulated with a biocompatible material. While Nitzan describes a method for the manufacture of an hourglass shaped stent for the treatment of CHF, Nitzan is silent on the method of encapsulating the stent.

[0014] U.S. Pat. No. 6,214,039 to Banas, incorporated herein by reference, describes a method for covering a radially endoluminal stent. In the method described by Banas, the encapsulated stent is assembled by joining a dilation mandrel and a stent mandrel, placing the graft on the dilation mandrel where it is radially expanded, and passing the expanded graft over the stent that is positioned on the stent mandrel. While Banas describes a method for encapsulating a cylindrical stent, the method in Banas does not describe encapsulation of an hourglass shaped stent intended for treatment of CHF. The method for assembling the covered stent and mandrel assembly described in Banas would be inappropriate for assembly of an hourglass stent described in Nitzan.

[0015] U.S. Pat. No. 6,797,217 to McCrea, incorporated herein by reference, describes a method for encapsulating stent grafts. McCrea describes methods for encapsulating an endoluminal stent fabricated from a shape memory alloy. The Method described by McCrea involves an endoluminal stent encapsulated in an ePTFE covering which circumferentially covers both the luminal and abluminal walls along at least a portion of the longitudinal extent of the endoluminal stent. McCrea further describes applying pressure to the stent-graft assembly and heating the assembly to complete the encapsulation. While McCrea describes an encapsulated endoluminal stent, it does not describe the encapsulation of an hourglass shaped stent for the treatment of CHF.

[0016] In view of the above-noted drawbacks of previously known systems, it would be desirable to provide systems and methods of manufacture of encapsulated hourglass shaped stents for treating congestive heart failure and other disorders treated with hourglass shaped stent-graft assemblies.

[0017] The present invention overcomes the drawbacks of previously-known systems and methods by providing systems and methods for making encapsulated hourglass shaped stents for treating CHF and other conditions benefited by encapsulated hourglass shaped stents such as pulmonary hypertension. The hourglass or “diabolo” shaped stents are configured to be encapsulated using a mandrel assembly.

[0018] In accordance with one aspect, a method for making an encapsulated stent-graft may involve, providing a mandrel having a first conical region with a first apex and a second conical region with a second apex, placing an expandable stent having an hourglass shape in an expanded form on the mandrel so that a first flared end region of the expandable stent conforms to the first conical region and a second flared end region of the expandable stent conforms to the second conical region, associating a biocompatible material with the expandable stent to form a stent-graft assembly, and compressing the stent-graft assembly against the mandrel to form the encapsulated stent-graft. The first conical region and the second conical region may be aligned so that the first and second apexes contact one another.

[0019] The biocompatible material may have first and second ends and associating the biocompatible material with the expandable stent involves placing the biocompatible material within a lumen of the expandable stent. The method may further include placing a second biocompatible material over the expandable stent. Compressing the stent-graft assembly may involve winding a layer of tape over the biocompatible material to compress the stent-graft assembly against the mandrel. The expandable stent may include through-wall openings, and the method may further involve heating the stent-graft assembly to cause the biocompatible material and the second biocompatible material to bond to one another through the through-wall openings. Heating the stent-graft assembly may cause the biocompatible material and the second biocompatible material to become sintered together to form a monolithic layer of biocompatible material. The method may further involve applying a layer of Fluorinated Ethylene Propylene (FEP) to biocompatible material or second biocompatible material. The biocompatible material may be pre-formed. The method may further involve manipulating the encapsulated stent-graft to a compressed shape and loading the encapsulated stent-graft into a delivery sheath. A first end diameter of the expandable stent may be different in size from a second end diameter. The mandrel may have a neck region disposed between a first conical region and a second conical region and the mandrel may be configured to be removably uncoupled at the neck region into a first half having at least the first conical region and a second half having at least the second conical region.

[0020] In accordance with another aspect, a method for making an encapsulated stent-graft may involve providing a mandrel assembly having an asymmetric shape, providing an expandable stent in an expanded form, coupling a biocompatible material to the expandable stent to form a stent-graft assembly, and compressing the stent-graft assembly on the mandrel assembly to form the encapsulated stent-graft. The expandable stent may be configured to conform to the asymmetric shape formed by the mandrel assembly.

[0021] The expandable stent and the biocompatible material may be coupled on the mandrel assembly or before placement on the mandrel assembly. The method may further involve coupling a second biocompatible material to an opposing surface of the expandable stent to form the stent-graft assembly. The second biocompatible material may be formed of a same or different material as the biocompatible material. The mandrel assembly may include a first mandrel and a second mandrel, and the method may further involve, positioning the first mandrel within the first end of the expandable stent such that a portion of the second biocompatible material is positioned between the first mandrel and the expandable stent, and positioning the second mandrel within the second end of the expandable stent such that a portion of the second biocompatible material is positioned between the second mandrel and the expandable stent. The biocompatible material may be a pre-formed biocompatible graft layer having the expandable stent. The pre-formed biocompatible graft layer may engage the expandable stent on the mandrel assembly.

[0022] In accordance with yet another aspect, a method for making an encapsulated stent-graft may involve providing an asymmetrical stent, placing a first biocompatible material over the asymmetrical stent, providing a second biocompatible material for placement within the asymmetrical stent, inserting a balloon catheter having an inflatable balloon within the asymmetrical stent in a deflated state such that the second biocompatible material is between the asymmetrical stent and the inflatable balloon, and inflating the inflatable balloon to an inflated state conforming to the shape of the asymmetrical stent, thereby causing the second biocompatible material to engage with the asymmetrical stent to form the encapsulated stent-graft.

[0023] The method may further involve controlling the pressure within the balloon to achieve a desired adhesion between the first biocompatible material and the second biocompatible material. The method may further involve controlling the pressure within the balloon to achieve a desired inter-nodal-distance of the graft material. The second biocompatible material may be placed within the asymmetrical stent prior to inserting the balloon catheter within the asymmetrical stent. The second biocompatible material may be disposed on the inflatable balloon, and inflating the inflatable balloon may cause the second biocompatible material disposed on the inflatable balloon to contact and inner surface of the asymmetrical stent thereby engaging the second biocompatible material with the asymmetrical stent.

[0024] In accordance with yet another aspect, a method for making an encapsulated stent-graft may involve providing a funnel having a large end and a small end, placing an asymmetric stent with a first end, a second end, an exterior surface and an interior surface within the large end of the funnel, placing a biocompatible tube over the small end of the funnel, the biocompatible tube having a stent receiving portion and a remaining portion, advancing the asymmetric stent through the funnel and out the small end of the funnel, thereby depositing the asymmetric stent into the biocompatible tube such that the stent is positioned within the stent receiving portion of the biocompatible tube, thereby engaging an exterior surface of the asymmetric stent with the biocompatible tube, pulling the remaining portion of the biocompatible tube through the first end of the asymmetric stent and out the second end, introducing a first mandrel having a shape similar to the first side of the asymmetric stent into the first side of asymmetric stent thereby engaging the interior surface of the first side of the asymmetric stent with a portion of the remaining portion of the biocompatible tube, and introducing a second mandrel having a shape similar to the second side of the asymmetric stent into the second side of the asymmetric stent thereby engaging the interior surface of the second side of the asymmetric stent with a portion of the remaining portion of the biocompatible tube.

[0025] In accordance with yet another aspect, an hourglass shaped mandrel assembly for making an encapsulated stent-graft may involve a first portion having at least a first conical region having a flared end with a first diameter and an apex end with a second diameter, a second portion having at least a second conical region having a flared end with third diameter and an apex end with a fourth diameter, and a tapered region coupled to the flared end of the first portion and extending away from the flared end of the first portion. The tapered region may have a flared end with a fifth diameter and a tapered end with a sixth diameter such that the fifth diameter is equal to the first diameter and the sixth diameter is smaller than the fifth diameter. The first conical region of the first portion and the second conical region of the second portion may be aligned so that apexes of the first portion and second portion are contacting one another. The hourglass shaped mandrel assembly may further include a neck region positioned between the apex end of the first portion and the apex end of the second portion such that the neck region is affixed to at least the first portion or the second portion. The first portion and the second portion may be removably coupled at the apex end of the first portion and the apex end of the second portion. The hourglass shaped mandrel may be configured to expand radially.

[0041] Embodiments of the present invention are directed to systems and methods for the manufacture of hourglass or “diabolo” shaped stents encapsulated with biocompatible material for treating subjects suffering from congestive heart failure (CHF) or alternatively pulmonary hypertension. The hourglass or “diabolo” shaped stents are configured to be encapsulated using an hourglass shaped mandrel assembly having a dilation portion and two conical regions that may be removably coupled. The hourglass shaped stents may be specifically configured to be lodged securely in the atrial septum, preferably the fossa ovalis, to allow blood flow from the left atrium to the right when blood pressure in the left atrium exceeds that on the right atrium. The resulting encapsulated stents are particularly useful for the purpose of inter-atrial shunting as they provide long-term patency and prevent tissue ingrowth within the lumen of the encapsulated stent. However, it is understood that the systems and methods described herein may also be applicable to other conditions benefited from an encapsulated hourglass shaped stent such as pulmonary hypertension wherein the encapsulated hourglass shaped stent is used as a right-to-left shunt.

[0042] Referring now to FIG. 1, stent 110 is illustrated. Stent 110 is hourglass or “diabolo” shaped and may be radially self-expandable. Alternatively, stent 110 may be expandable but not self-expandable. For example, stent 110 may be balloon expandable. Stent 110 has three general regions: first flared end region 102, second end flared region 106, and neck region 104 disposed between the first and second flared end regions. First flared end region 102 has first end region diameter D1, second flared end region 106 has second end region diameter D2, and neck region 104 has neck diameter D3. As shown in FIG. 1, neck region 104 of stent 110 is significantly narrower than flared end regions 102 and 106. Also shown in FIG. 1, stent 110 may be asymmetric. For example, stent 110 may be asymmetric to take advantage of the natural features of the atrial septum of the heart as well as the left and right atrium cavities. Alternatively, hourglass shaped stent 110 may be symmetric with the first end region diameter D1 being equal to the second end region diameter D2. First flared end region 102 and second flared end region 106 also may have either straight or curved profiles or both. For example, strut 111 has a straight profile and strut 108 has a curved profile. Additionally, first flared end region 102 and second flared end region 106 may assume any angular position consistent with the hour-glass configuration.

[0043] Stent 110 is preferably comprised of a self-expanding material having superelastic properties. For example, a shape-memory metal such as nickel titanium (NiTi), also known as NITINOL may be used. Other suitable materials known in the art of deformable stents for percutaneous implantation may alternatively be used such as other shape memory alloys, self-expanding materials, superelastic materials, polymers, and the like. The tube may be laser-cut to define a plurality of struts and connecting members. For example, as illustrated in FIG. 1, the tube may be laser-cut to define a plurality of sinusoidal rings connected by longitudinally extending struts. Struts 108 and 111 and sinusoidal rings 112-116 illustrated in FIG. 1 may be laser cut to form an integral piece of unitary construction. Alternatively, struts 111 and sinusoidal rings 112-116 may be separately defined to form different pieces of shape-memory metal and subsequently coupled together to form stent 110. The stent may also be electropolished to reduce thrombogenicity.

[0044] Stent 110 may be expanded on a mandrel to define first end region 102, second end region 106, and neck region 104. The expanded stent then may be heated to set the shape of stent 110. The stent may be expanded on a mandrel in accordance with the teachings of U.S. Pat. No. 9,034,034 to Nitzan, incorporated herein. In one example, stent 110 is formed from a tube of NITINOL, shaped using a shape mandrel, and placed into an oven for 11 minutes at 530° C. to set the shape. The mandrel disclosed in FIGS. 3-4 may be configured as a shaping mandrel to set the shape of stent 110 or, alternatively, a different mandrel may be used as the shaping mandrel.

[0045] Referring now to FIG. 2, stent 110 is at least partially covered with biocompatible material, as shown in FIG. 2, to create stent-graft assembly 120. Biocompatible material may be expanded polytetrafluoroethylene (ePTFE), silicone, polycarbonate urethane, DACRON (polyethylene terephthalate), Ultra High Molecular Weight Polyethylene (UHMWPE), or polyurethane, or of a natural material such as pericardial tissue, e.g., from an equine, bovine, or porcine source or human tissue such as human placenta or other human tissues. The biocompatible material is preferably smooth so as to inhibit thrombus formation, and optionally may be impregnated with carbon so as to promote tissue ingrowth. Alternatively, to promote tissue ingrowth and endothelization, the biocompatible material may form a mesh-like structure. The biocompatible material may be pre-shaped using a dedicated pre-shaping mandrel and heat treatment to simplify the mounting of the biocompatible material on an encapsulation mandrel, as discussed in detail below. Pre-shaping the biocompatible material has been shown to simplify the handling and mounting of the biocompatible material on the mandrel, thereby reducing stretching and the risk for tears in the biocompatible material and may be especially beneficial for encapsulating asymmetrical stents. Portions of stent 110 such as first flared end region 102 may not be covered with the biocompatible material.

[0046] Generally, the stent is positioned between a first and second layer of graft material by covering an inner surface of stent 121 with first graft layer 170, and covering the outer surface of stent 123 with second graft layer 190. First graft layer 170 and second graft layer 190 each may have a first end and a second end and may have lengths that are about equal. Alternatively, first graft layer 170 and second graft layer 190 may have different lengths. Stent 110 may have a length that is shorter than the length of first graft layer 170 and second graft layer 190. In other embodiments, stent 110 may have a length that is longer than the length of first graft layer 170 and/or second graft layer 190. As discussed in detail below, the graft layers may be securely bonded together to form a monolithic layer of biocompatible material. For example, first and second graft tubes may be sintered together to form a strong, smooth, substantially continuous coating that covers the inner and outer surfaces of the stent. Portions of the coating then may be removed as desired from selected portions of the stent using laser-cutting or mechanical cutting, for example.

[0047] In a preferred embodiment, stent 110 is encapsulated with ePTFE. It will be understood by those skilled in the art that ePTFE materials have a characteristic microstructure consisting of nodes and fibrils, with the fibrils orientation being substantially parallel to the axis of longitudinal expansion. Expanded polytetrafluoroethylene materials are made by ram extruding a compressed billet of particulate polytetrafluoroethylene and extrusion lubricant through an extrusion die to form sheet or tubular extrudates. The extrudate is then longitudinally expanded to form the node-fibril microstructure and heated to a temperature at or above the crystalline melt point of polytetrafluoroethylene, i.e., 327° C., for a period of time sufficient to sinter the ePTFE material. Heating may take place in a vacuum chamber to prevent oxidation of the stent. Alternatively, heating may take place in a nitrogen rich environment. A furnace may be used to heat the stent-graft assembly. Alternatively, or in addition to, the mandrel upon which the stent-graft assembly rests may be a heat source used to heat the stent-graft assembly.

[0048] FIGS. 3-11 generally illustrate one method of making stent-graft assembly 120, as depicted in FIGS. 1-2. FIG. 3 is a partially exploded view of assembly apparatus 130. Assembly apparatus 130 may comprise tapered dilation mandrel 131, stent retaining mandrel 134 and stent enclosing mandrel 138. Tapered dilation mandrel 131 comprises first end 132 having a taper diameter and second end 133 wherein the diameter of second end 133 is greater than the taper diameter. Where other techniques are used to dilate stent 110 and biocompatible graft material, tapered dilation mandrel 131 may not be necessary and thus assembly apparatus 130 may comprise stent retaining mandrel 134 and stent enclosing mandrel 138.

[0049] Stent retaining mandrel 134 may be permanently affixed to second end 133 of tapered dilation mandrel 131 or alternatively may be removably coupled to tapered dilation mandrel. For example, stent retaining mandrel 134 may be screwed into tapered dilation mandrel 131 using a screw extending from stent retaining mandrel 134 and a threaded insert embedded into tapered dilation mandrel 131. However, it will be understood by those in the art that couplings are interchangeable and may be any of a wide variety of suitable couplings.

[0050] Stent retaining mandrel 134 may comprise a conical region defined by large diameter end 135 and an apex end 136. Large diameter end 135 may be equal in diameter with second end 133 of tapered dilation mandrel 131, and larger in diameter than apex end 136. It is understood that stent retaining mandrel 134 may alternatively be other shapes including non-conical shapes. Stent retaining mandrel 134 may optionally incorporate neck region 137. Neck region 137 may extend from apex end 136, as shown in FIG. 3, and may have the same diameter as apex end 136. Alternatively, neck region 137 may extend from stent enclosing mandrel 138.

[0051] Stent enclosing mandrel 138 is removably coupled to stent retaining mandrel 134. For example, stent enclosing mandrel 138 may be screwed into stent retaining mandrel 134 using screw 139 extending from stent enclosing mandrel 138 and threaded insert 140 embedded into stent retaining mandrel 134. Alternatively, screw 139 may extend from stent retaining mandrel 134 and threaded insert may be embedded into stent enclosing mandrel 138. While the figures depict threaded coupling, it will be understood by those in the art that the couplings are interchangeable and may be any of a wide variety of suitable couplings. In another example, stent retaining mandrel 134 may be a female mandrel having a receiving portion and stent enclosing mandrel 138 may be a male mandrel having a protruding portion. However, it is understood that stent retaining mandrel 134 may be a male mandrel having a protruding portion and stent enclosing mandrel 138 may be a female mandrel having a receiving portion.

[0052] Stent enclosing mandrel 138 may comprise a conical region defined by large diameter end 142 and an apex end 141, wherein large diameter end 142 is larger in diameter than apex end 141. It is understood that stent enclosing mandrel 138 alternatively take other shapes including non-conical shapes. Stent enclosing mandrel 138 may be permanently affixed to handle segment 144 at large diameter end 142. Alternatively, stent enclosing mandrel 138 may be removably coupled to handle segment 144. Where stent enclosing mandrel 138 is removably coupled to handle segment 144, handle segment 144 may be removed and replaced with a taper mandrel segment similar to taper dilation mandrel 131, as shown in FIG. 8C.

[0053] Referring to FIG. 4, when coupled together, stent retaining mandrel 134 and stent enclosing mandrel 138 form hourglass shaped mandrel assembly 143. Hourglass shaped mandrel assembly 143 is configured such that the conical region of stent retaining mandrel 134 is oriented toward the conical region of stent enclosing mandrel 138, wherein apex end 136 of stent retaining mandrel 138 having extending neck region 137 is in contact with apex end 141 of stent enclosing mandrel 138. Neck region 137 is configured to conform to the diameter of apex end 136 of stent retaining mandrel 138 and apex end 141 of stent enclosing mandrel 138, whether or not apex end 141 and apex end 136 are equal in diameter. Neck region 137 may vary in diameter or may be eliminated entirely.

[0054] The size and shape of hourglass shaped mandrel assembly 143 and specifically the size of the conical regions of stent retaining mandrel 134 and stent enclosing mandrel 138 preferably correspond to the size and shape of flared end region 102, neck region 104 and second flared end region 106 of stent 110. Hourglass shaped mandrel assembly 143 may be asymmetrical such that diameter D4 of large diameter end 135 is different than diameter D5 of large diameter end 142. Alternatively, diameter D4 and diameter D5 may be the same. Similarly, angle θ1 and angle θ2 may be different, resulting in an asymmetrical mandrel, or may be the same. Angle θ1 and angle θ2 also may vary along the length of hourglass shaped mandrel assembly 143 to better conform to stent 110. While neck diameter D6 may vary at different points along neck region 137, diameter at neck region 137 is at all times smaller than diameter D4 and D5.

[0055] FIGS. 5-7, represents sequential views of first graft tube 122 being loaded onto the tapered dilation mandrel 131 and being concentrically engaged about hourglass shaped assembly 143 in an exemplary sequence. Engagement of first graft tube 122 over tapered dilation mandrel 131 may be facilitated by forming tabs on first end 153 of first graft tube 122 by cutting longitudinal slits (not shown) along diametrically opposing sides of the graft tube. The tabs can then be used to retain first graft tube 122 while axial force 150 is applied to assembly apparatus 130. Alternatively, the tabs may be used to manually pull first graft tube 122 over tapered dilation mandrel 131 and hourglass shaped mandrel assembly 143. To prevent formation of seams or wrinkles, it is important to avoid applying torsional forces to graft tubes by twisting the graft during engagement of the graft member onto the assembly apparatus. Cutting crevice 151 and 152 may be incorporated into stent retaining mandrel 134 and stent enclosing mandrel 138 to provide a guiding indentation for a cutting element to cut first graft tube 122 and second graft tube 124.

[0056] Referring now to FIG. 5, first graft tube 122 may be engaged with tapered dilatation mandrel 131 by applying an axial force 150 to assembly apparatus 130 which causes the tapered dilatation mandrel to pass into and through lumen 154 of first graft tube 122. As first graft tube 122 passes over second end 133 of tapered dilatation mandrel 131, the inner diameter of first graft first 122 is expanded radially to that of the outer diameter of second end 133 of tapered dilation mandrel 131. As first graft tube 122 is moved axially over large diameter end 135 of stent retaining mandrel 134 the inner diameter of first graft tube 122 is greater than the outside diameter of hourglass shaped mandrel assembly 143. Axial force 150 is applied until first end 153 of first graft tube 122 is near large diameter end 142 of stent enclosing mandrel 138. As first graft tube moves axially over second end 133 of tapered dilatation mandrel 131 and is positioned over hourglass shaped mandrel assembly 143, first graft tube 122 undergoes radial recoil so that the inner diameter of first graft tube 122 reduces until it's met with resistance from hourglass shaped mandrel 143. As illustrated in FIG. 6, first graft tube 122 has radially recoiled onto hourglass shaped mandrel assembly 143 as well as into cutting crevices 151 and 152.

[0057] FIGS. 6 and 7 illustrate the steps for separating first graft tube 122 and depositing graft layer 170 upon hourglass shaped mandrel 143. Cutting blades 160 and 161 may be used to make circumferential cuts in first graft tube 122 near the large diameter ends of stent retaining mandrel 134 and stent enclosing mandrel 138. For example, cutting blades may make circumferential cuts at the position of cutting crevices 151 and 152. Cutting crevices 151 and 152 are positioned at a length longer than the length of stent 110 to account for recoil of graft material after being cut. Alternatively, where the stent is only partially encapsulated, cutting crevices 151 and 152 may be positioned at a length shorter than the length of stent 110. After cutting first graft tube 122 with cutting blades 160 and 161, first graft layer 170 is deposited onto stent 110. Alternatively, only cutting crevice 151 and cutting blade 160 may be used to create a circumferential cut near the large diameter end of stent retaining mandrel 134. In this manner first end 153 of first graft tube 122 having tabs at the end, may serve as one end of first graft layer 170. First graft layer 170 has a length longer than stent 110. As such, a section of first graft layer 170 extends beyond opposing ends of stent 110. After removing excess grafting material, first graft layer 170 remains on the assembly apparatus and covers hourglass shaped mandrel assembly 143. Tape may be applied to first graft layer 170 to secure graft layer 170 to stent retaining mandrel 134. Upon depositing first graft layer 170 on hourglass shaped mandrel assembly 143, an optional step involves applying a layer of Fluorinated Ethylene Propylene (FEP), or any other adhesive material, to first graft layer 170 for improving adhesion during encapsulation process.

[0058] Referring now to FIGS. 8A-8C, after depositing first graft layer 170 on hourglass shaped mandrel assembly 143, stent 110 may be loaded onto hourglass shaped mandrel assembly 143. One method for loading stent 110 onto hourglass shaped mandrel assembly 143 is to uncouple stent retaining mandrel 134 and stent enclosing mandrel 138. When stent retaining mandrel 134 is uncoupled from stent enclosing mandrel 138, the portion of first graft layer 170 in contact with stent retaining mandrel 134 and neck region 137 will remain supported by the stent retaining mandrel 134 but the portion that was in contact with stent enclosing mandrel 138 will become unsupported beyond neck region 137. As shown in FIG. 8A, by uncoupling stent retaining mandrel 134 and stent enclosing mandrel 138, stent 110 may be loaded onto stent retaining mandrel 134 over first graft layer. During this step, the unsupported region of first graft layer 170 may be manipulated in shape and guided through an interior opening of neck region 104 and through an interior of second flared end region 106. Where first end 153 of first graft tube 122 is used as the end of first graft layer 170, the tabs on first end 153 of first graft tube 122 described above, may be used to help guide first graft layer 170 through stent 110.

[0059] Stent 110 is engaged about the stent retaining mandrel 134 by concentrically positioning the stent 110 over first graft layer 170 and stent retaining mandrel 134. When loaded onto stent retaining mandrel 134, first flared end region 102, and neck region 104 of stent 110 engage with stent retaining mandrel 134 while second flared end region 106 does not. Stent retaining mandrel 134 and first graft layer 170 are configured to have a combined diameter which is less than the inner diameters of first flared end region 102 and neck region 104 of stent 110, allowing stent to slide onto stent retaining mandrel 134.

[0060] Referring now to FIG. 8B, upon loading stent 110 on stent retaining mandrel 134 and first graft layer 170, stent enclosing mandrel 138 is coupled to stent retaining mandrel 134, completing the hourglass shaped mandrel assembly. First graft layer 170 may be manually manipulated to avoid being damaged and prevent the occurrence of any wrinkles during recoupling of stent enclosing mandrel 138. For example, first graft layer 170 may be held by the tabs described above while the stent enclosing mandrel is recoupled to the stent retaining mandrel. If first graft layer was taped to stent retaining mandrel 134, the tape may be removed after recoupling. When stent enclosing mandrel 138 is coupled to stent retaining mandrel 134, stent enclosing mandrel 138 engages both first graft layer 170 and second flared end region 106 of stent 110, locking stent 110 into position between large diameter end 135 and large diameter end 142. Stent enclosing mandrel 138 and first graft layer 170 are configured to have a combined outside diameter which is less than the inner diameter of second flared end region 106 of stent 110, allowing stent 110 to slide into position on stent enclosing mandrel 138. Upon placing stent 110 on first great layer 170, an optional step involves applying a layer of FEP, or any other adhesive material, to first graft layer 170 and stent 110 for improving adhesion during encapsulation process.

[0061] While FIGS. 5-7 illustrate one sequence for generating first graft layer 170, it is appreciated that first graft layer 170 may be deposited onto assembly apparatus 130 in different ways. For example, first graft layer 170 may not be separated from first graft tube 122 until after stent 110 has been loaded onto assembly apparatus 130. In this approach, after first end 153 of first graft tube 122 is positioned near large diameter end 142 of stent enclosing mandrel 138 and first graft tube 122 undergoes radial recoil so that the inner diameter of first graft tube 122 reduces until it is met with resistance from hourglass shaped mandrel 143, as shown in FIG. 6, stent retaining mandrel 138 may be uncoupled from stent enclosing mandrel 134. Like in the sequence described above, the portion of the first graft tube extending beyond neck region 137 will become unsupported after stent enclosing mandrel 138 has been uncoupled. The unsupported region of first graft tube 122 may then be manipulated in shape and guided through an interior opening of neck region 104 and through an interior of second flared end region 106 as described above. After the stent enclosing mandrel has been recoupled as shown in FIGS. 8A-8B and discussed above, cuts may be made using cutting blades 160 and 161 to separate first graft tube 122 from first graft layer 170.

[0062] In yet another example, first graft layer 170 may be deposited onto hourglass shaped mandrel 143 using an electrospinning process. Electrospinning is a process in which polymers are electrospun into ultrafine fibers which are deposited upon a target surface. The electrospinning process involves applying an electric force to draw fibers out of polymer solutions or polymer melts. Using electrospinning, ultrafine fibers, such as ePTFE fibers may be deposited onto hourglass shaped mandrel 143 to form first graft layer 170. Assembly apparatus may be continuously rotated about its longitudinal axis to evenly apply the ePTFE fibers. In one example, stent retaining mandrel 134 and stent enclosing mandrel 138 may be coupled together during the eletrospinning process. In another example, stent retaining mandrel 134 and stent enclosing mandrel 138 may be uncoupled and the conical region of stent retaining mandrel 134 including neck region 137 may be subjected to the electrospinning process separate from the conical region of stent enclosing mandrel 138. Subsequently, when stent enclosing mandrel 138 and stent retaining mandrel 134 are coupled together, the ePTFE fibers on stent retaining mandrel 134 may be sintered together to form a continuous first graft layer 170. Second graft layer 190 may similarly be deposited using electrospinning.

[0063] Referring now to FIG. 8C, assembly apparatus 130 may be configured such that first graft tube 122 and second graft tube 124 may be loaded onto assembly apparatus 130 from the side closest to stent enclosing mandrel 138. As discussed above, stent enclosing mandrel 138 may be removably coupled to handle segment 144. In the alternative configuration shown in FIG. 8C, stent enclosing mandrel 138 may be uncoupled from handle segment 144 and tapered dilation mandrel 131′ may be coupled to stent enclosing mandrel 138 instead. It will be understood by those in the art that the couplings are interchangeable and may be any of a wide variety of suitable couplings. Tapered dilation mandrel 131′ has first end 132′ and second end 133′ wherein the diameter of second end 133′ is greater than the diameter of first end 132′ and the diameter of second end 133′ is equal to the diameter of large diameter end 142 of stent enclosing mandrel 138. In the configuration shown in FIG. 8C, large diameter end 135 may also perform as handle segment 144′ for pushing.

[0064] Using the configuration shown in FIG. 8C, an axial force 165 may be applied to assembly apparatus 130 to cause tapered dilatation mandrel 131′ having first end 132′ to pass into and through the lumen of the first graft tube 122. Similarly, axial force 165 may be applied to assembly apparatus 130 to guide assembly apparatus 130, and specifically first end 132′, into stent 110 which is configured to expand as tapered dilatation mandrel 131′ is pushed into stent 110. Axial force 165 may be applied by using handle segment 144′ to push assembly apparatus 130. By engaging first end 132′ with expandable stent 110 exhibiting spring tension, stent 110 may be dilated as it moves along tapered dilatation mandrel 131′. In this manner, first end region diameter D1, second end region diameter D2, and neck diameter D3 of stent 110, as shown in FIG. 1, may be expanded to a diameter equal to or larger than large diameter end 142 of stent enclosing mandrel 138, thus permitting stent 110 to traverse large diameter end 142. As stent 110 exhibiting spring tension is passed over hourglass shaped mandrel assembly 143, it encounters no resistance to radial recoil and thus radially recoils into position over first graft layer 170 and between large diameter end 135 and large diameter end 142. Alternatively, stent 110 may be expanded to a slightly larger diameter than second diameter end 142 by applying a radially expansive force on stent 110 using an external expansion tool. In this example, after expanding stent 110 to the appropriate diameter, stent 110 may be concentrically placed over stent enclosing mandrel 138 and allowed to radially recoil into position over hourglass shaped mandrel 143 having first graft layer 170 deposited on top.

[0065] In yet another alternative arrangement, stent enclosing mandrel 138 may alternatively be comprised of a cylindrical region instead of a conical region. The cylindrical region may have the same diameter as neck region 137 such that the cylindrical region of stent enclosing mandrel 138 may appear as an extension of neck region 137 when stent enclosing mandrel 138 is coupled to stent retaining mandrel 134. In this alternative embodiment, stent enclosing mandrel 138 also may be coupled to tapered dilation mandrel 131′ which may have second end 133′ that is equal in diameter to neck region 137 and smaller in diameter than first end 131′. Stent enclosing mandrel 138 having the cylindrical region instead of a conical region, may be used to encapsulate a stent having a conical region and a neck region that forms a conduit. Any of the methods and techniques described herein to encapsulate the hourglass shaped stent may be used to encapsulate the stent having the cylindrical region instead of the conical region. Upon completion of encapsulation, the encapsulated stent may be gently removed from assembly apparatus 130 by sliding the encapsulated stent over the tapered dilation mandrel 132′. Alternatively, stent enclosing mandrel 138 may be uncoupled from stent retaining mandrel 134.

[0066] FIGS. 9-11 represent sequential views of the second graft tube 124 being loaded onto the tapered dilation mandrel 131 and being concentrically engaged about the stent member 110. Engagement of second graft tube 124 over tapered dilation mandrel may be facilitated by forming tabs on first end 171 of second graft tube 124 similar to the method described above, involving cutting longitudinal slits (not shown) along diametrically opposed sides of the graft member. The tabs can then be used to retain the second graft tube 124 while axial force 170 is applied to assembly apparatus 130. Alternatively, the tabs may be used to manually pull second graft tube 124 over tapered dilation mandrel 131 and hourglass shaped mandrel assembly 143.

[0067] Referring now to FIG. 9, second graft tube 124 may be engaged with tapered dilatation mandrel 131 in much the same way as first graft tube 122—by applying axial force 180 to assembly apparatus 130 which causes the tapered dilatation mandrel to pass into and through lumen 173 of second graft tube 124. As second graft tube 124 passes over second end 133 of tapered dilatation mandrel 131, the inner diameter of second graft tube 124 is radially expanded to that of the outer diameter of second end 133 of tapered dilation mandrel 131. The assembly apparatus 130 is passed into and through lumen 173 of second graft tube 124 until first end 171 of second graft tube 124 is close to large diameter end 142 of stent enclosing mandrel 138. As second graft tube moves axially over stent 110 and to a position over large diameter end 142 of stent enclosing mandrel 138, second graft tube 124 undergoes radial recoil so that the inner diameter of second graft tube 124 reduces until it is met with resistance. As illustrated in FIG. 10, second graft tube 124 is radially recoiled onto stent 110. Second graft tube 124 also may be radially recoiled into cutting crevices 151 and 152.

[0068] Alternatively, second graft tube 124 may be positioned onto stent 110 via an assembly apparatus 130 that is configured to expand and/or contract radially. Assembly apparatus may be comprised of material having expansion properties or contraction properties which may be responsive to exterior conditions. For example, hourglass shaped mandrel assembly 143 may be compressible by applying a force normal to the surface of hourglass shaped mandrel 143. Instead, assembly apparatus 130 may be comprised of material having a high coefficient of thermal expansion permitting the hourglass shaped assembly to contract when placed in a low temperature environment and expand when placed in a high temperature. Alternatively, assembly apparatus may have a rigid core and multiple surfaces that move independently from one another, the surfaces being connected to the core by a number of springs that are configured to permit movement of the surfaces relative to the core when a normal force is applied to the surfaces. For example, a surface may compress towards the core when a normal force is applied and the same surface may expand radially out from the rigid core when the normal force is released. In addition, or alternatively, the core of the assembly apparatus 130 may have a screw assembly embedded within the core and configured to translate a rotational force applied to the screw assembly into a radial force which is applied to the surfaces to push the surfaces radially outward, or pull the surfaces radially inward.

[0069] Expandable stent 110 having spring tension may be positioned on compressible hourglass shaped mandrel assembly 143 and stent and assembly together may be compressed when a compressive radial force is applied. At a certain compressive force, first end region diameter D1 and second end region diameter D2 of stent 110 may be compressed to neck diameter D3. In this compressed state, second graft tube 124 may be easily moved axially over compressed stent 110 and first graft layer 170. Subsequent to positioning second graft tube 124 over compressed stent 110 and first graft layer 170, compressive force applied to stent 110 and compressible hourglass shaped mandrel assembly 143 may be released. At the same time, hourglass shaped mandrel assembly 143 may expanded. In this way second graft tube 124 may be engaged with stent 110.

[0070] FIGS. 10 and 11 illustrate the steps for separating second graft tube 124 from stent-graft assembly 120. After depositing second graft tube 124 on stent 110, cutting blades 160 and 161 may again be used to make circumferential cuts in second graft tube 124 at a position near the large diameter ends of stent retaining mandrel 134 and stent encompassing mandrel 138. For example, cutting blades 160 and 161 may make circumferential cuts at the position of cutting crevices 151 and 152. As explained above, cutting crevices 151 and 152 may be positioned at a length longer than the length of stent 110 to account for recoil of graft material upon being cut. After cutting second graft tube 124 with cutting blades 160 and 161, second graft layer 190 is deposited onto stent 110 which is positioned over graft layer 170. Second graft layer 190 has a length longer than stent 110. As such, a section of second graft tube 124 extends beyond opposing ends of stent 110 and is similar in length to first graft layer 170. Waste portion of second graft tube 124 remaining on assembly apparatus 138 may be discarded. Where stent 110 is only partially encapsulated, first graft layer 170 and/or second graft layer 190 may have a length shorter than stent 110 and thus may not extend beyond opposing ends of stent 110. For example, only first flared end region 102 or second flared end region 106 may be encapsulated. Where stent 110 takes a different asymmetric shape, such as an hourglass shape on one side and a straight tube shape on the other side, only one portion of asymmetric stent 110 may be encapsulated.

[0071] To securely bond first graft layer 170 to second graft layer 190, pressure and heat may be applied the stent-graft assembly to achieve sintering. Sintering results in strong, smooth, substantially continuous coating that covers the inner and outer surfaces of the stent. Sintering may be achieved by first wrapping the ends of first graft layer 170 and second graft layer 190 with strips of tape such as TFE or ePTFE tape to secure the stent-graft assembly to the mandrel. To apply pressure, stent-graft assembly 120 attached to assembly apparatus 130 may be placed in a helical winding wrapping machine which tension wraps the stent-graft assembly 120 with at least one overlapping layer of tape. For example, stent-graft assembly 120 may be wrapped with a single overlapping layer of ½ inch ePTFE tape with an overlap of the winding of about 70%. The force exerted by the TFE or ePTFE wrapping tape compresses the stent-graft assembly against the hourglass shaped mandrel assembly 143, thereby causing the graft layers to come into intimate contact through interstices of stent 110. In stent 110 shown in FIG. 1., interstices exist in the between the struts and sinusoidal rings. Varying tape thickness may reduce or improve ePTFE conformance. For example, thicker tape may result in more compression uniformity than thinner tape material.

[0072] Stent-graft assembly 120 attached to assembly apparatus 130 may then be heated by placing the stent-graft assembly and assembly apparatus into a radiant heat furnace. For example, stent-graft assembly 120 may be placed into a radiant heat furnace which had been preheated. In one example, sintering may be achieved at 327° C. The humidity within the radiant heat furnace may preferably be kept low. The stent-graft assembly may remain in the radiant heat furnace for a time sufficient for first graft layer 170 to sinter to second graft layer 190. In one example, stent-graft assembly 120 may remain in the furnace for about 7-10 minutes. The heated assembly may then be allowed to cool for a period of time sufficient to permit manual handling of the assembly. After cooling, the helical wrap may be unwound from stent-graft assembly 120 and discarded. The encapsulated stent may then be concentrically rotated about the axis of the mandrel to release any adhesion between the first graft layer 170 and hourglass shaped mandrel assembly 143. The encapsulated stent, still on the mandrel, may then be placed into a laser trimming fixture to trim excess graft materials away from stent-graft assembly 120. In addition, the encapsulated stent may be trimmed at various locations along the stent such as in the middle of the stent, thereby creating a partially encapsulated stent.

[0073] Alternatively, first graft layer 170 may be sintered to second graft layer 190 by inducing pressure. For example, assembly apparatus 130 or at least hourglass shaped mandrel assembly 143 may have small perforations which may be in fluid communication with a vacuum pump situated in an inner lumen of assembly apparatus 130 or otherwise in fluid communication with an inner lumen of assembly apparatus 130. Additionally or alternatively, the assembly apparatus 130 may be placed in a pressurized environment that is pressurized using a compressor pump, for example. In another example, a balloon such as a Kevlar balloon may also or alternatively be applied to the exterior of the stent-graft assembly to apply pressure to the stent-graft assembly. Via the pressure applied, the first graft layer 170 may collapse on the second graft layer 190 forming even adhesion. A combination of both pressure and heat may also be used to sinter the first graft layer 170 to the second graft layer 190. Trimming may then take place in the same manner as described above.

[0074] After trimming excess graft materials, stent-graft assembly 120 may be removed by decoupling stent retaining mandrel 134 from stent enclosing mandrel 138. Upon decoupling stent retaining mandrel 134 and stent enclosing mandrel 138, stent-graft assembly 120 remains supported by stent retaining mandrel 134. Stent-graft assembly 120 may then be removed from stent retaining mandrel 134 by axially displacing stent-graft assembly 120 relative to stent retaining mandrel 134.

[0075] Upon removal of stent-graft assembly 120 from assembly apparatus 130, stent-graft assembly 120 may be manipulated to a reduced first end region diameter D1, second end region diameter D2 and neck region diameter D3. The assembly stent-graft assembly may achieve these smaller diametric dimensions by methods such as crimping, calendering, folding, compressing or the like. Stent-graft assembly 120 may be constrained at this dimension by disposing stent-graft assembly 120 in a similarly sized cylindrical sheath. Once positioned in the sheath, stent-graft assembly 120 may be delivered to an implantation site using a catheter based system including a delivery catheter. The catheter based system may further comprise an engagement component for temporarily affixing stent-graft assembly 120 to the delivery catheter. The engagement component may be configured to disengage the stent-graft assembly 120 from the delivery catheter when stent-graft assembly 120 has reached the delivery site. At the delivery site, the sheath may be removed to release the constraining force and permit the intraluminal stent to elastically expand in the appropriate position.

[0076] While the approach set forth above describes depositing a layer of biocompatible material on an interior surface of stent 110 and an exterior surface of stent 110, it is understood that the stent 110 may be coated with only one layer of biocompatible material. For example, stent 110 may be engaged with only first graft layer 170 along an interior surface, following only the appropriate steps set forth above. Alternatively, stent 110 may be engaged with only second graft layer 190 along an exterior surface, following only the appropriate steps set forth above.

[0077] As explained above, stent 110 may be comprised of a plurality of sinusoidal rings connected by longitudinally extending struts. However, it is understood that stent 110 may be constructed from a plurality of interconnected nodes and struts having varying distances and forming various shapes and patterns. In one embodiment the inter-nodal-distance (IND) of stent 110 may be manipulated by controlling the tension of the biocompatible material layers during encapsulation. For example, the stent may be encapsulated in a manner providing different pulling forces on stent 110. This may enable different functionality of various areas of the encapsulated stent which are known to be influenced by IND. In one example, by controlling tension of the biocompatible material layers during encapsulation, different functionality of various areas with respect to tissue ingrowth characteristics may be achieved. Further, it is understood that encapsulation may be performed such that stent 110 is constrained in a restricted or contracted state by the encapsulation material. For example, the neck diameter may be decreased from 6mm to 5mm. This may permit controlled in-vivo expansion to a fully expanded state using, for example, balloon inflation, whereby the constraint is removed. This procedure may be beneficial in a case where a clinical condition dictates an initial restricted state for delivery but requires a larger unconstrained state for implantation or treatment.

[0078] Referring now to FIGS. 12A-D, an alternative method of making stent-graft assembly 120, as depicted in FIGS. 1-2, is illustrated. FIGS. 12A-D represent sequential views of first graft tube 122 and second graft tube 124 being loaded onto and concentrically engaged about stent graft assembly 120. As shown in FIG. 12A the process may start by engaging first graft tube 122 over stent 110. Stent 110 may be crimped to a diameter smaller than first graft tube 122 and guided into graft tube 122. Alternatively, or in addition to, first graft tube 122 may be stretched to a diameter slightly larger than stent 110 using an expanding mandrel or other stretching technique and guided over stent 110.

[0079] Upon positioning first graft tube 122 over stent 110, second graft tube 124 may be positioned within and along the entire length of stent 110, shown in FIG. 12B. Second graft tube 124 may be pulled through stent 110 while stent 110 remains engaged with first graft tube 122. Subsequently, as shown in FIG. 12C, female mandrel 195 may be introduced near second flared end region 106 of stent 110. Female mandrel 195 may have a similar shape as second flared end region 106 only with slightly smaller dimensions. Female mandrel 195 may have receiving portion 196 designed to receive male mandrel 197. Having a conical shape, female mandrel 195 may be gently advanced within second graft tube 124 until female mandrel 195 takes up nearly the entire space within second flared region 106. In this manner, second graft tube 124 may be engaged with stent 110 along an interior surface of second flared region 106 and in some embodiments neck region 104.

[0080] Referring now to FIG. 12D, male mandrel 197 may be introduced near first flared end region 102. Male mandrel 197 may be similar in shape to first flared end region 102 only with slightly smaller dimensions. Male mandrel 195 may have protruding section 198 sized and shaped to be received by female mandrel 195. Having a conical shape, male mandrel 197 may be gently advanced within second graft tube 124 toward female mandrel 195 until female assembly 195 takes up nearly the entire space within first flared region 102 and protruding section is fully received by receiving portion 196. In this manner, second graft tube 124 may be engaged with stent 110 along an interior surface of second flared region 106 and in some embodiments neck region 104.

[0081] Upon engaging female mandrel 195 and male mandrel 197, stent 110 may be entirely covered on an exterior surface by first graft tube 122 and entirely covered on an interior surface by second graft tube 124. First graft tube 122 and second graft tube 124 may be appropriately cut away according to the same procedures illustrated in FIGS. 6 and 10 resulting in first graft layer 170 and second graft layer 190. Further, stent graft assembly 120 may be produced using the same procedures detailed above including the procedures for securely bonding first graft layer 170 to second graft layer 190 involving pressure and heat applied to the stent-graft assembly to achieve sintering. It is understood that the mandrel placed in the first flared region 102 may alternatively be a female mandrel and the mandrel placed in second flared region 106 may alternatively be a male mandrel. It is also understood that the process depicted in FIGS. 12A-D may start first with the mandrel entering the first flared region 102 of stent 110.

[0082] Referring now to FIGS. 13A-13E, another alternative method of making stent-graft assembly 120, as depicted in FIGS. 1-2, is illustrated. As shown in FIG. 13A, first graft layer 170 may be pre-formed into an hourglass shaped pre-shaped first graft layer 199 using a dedicated mandrel and heat treatment. The pre-formed shape may have dimensions similar to that of stent 110. Upon forming pre-shaped first graft layer 199, female mandrel 200 may be introduced into one side of pre-shaped first graft layer 199, such that female mandrel 200 takes up nearly the entire space within one hourglass side of pre-shaped first graft layer 199 as shown in FIG. 13B. Female mandrel 200 may have receiving portion 201 designed to receive male mandrel 203.

[0083] Upon placing female mandrel 200 within pre-formed first graft layer 199, stent 110 may be placed over pre-shaped first graft layer 199, as show in in FIG. 13C. Stent 110 may be positioned over first graft layer 199 or first graft layer 199 may be positioned within stent 110. Stent 110, having a shape similar to that of pre-formed first graft layer 199 should fit into place on pre-formed first graft layer 199.

[0084] Once stent 110 is deposited on pre-shaped first graft layer 199, second pre-shaped graft layer 202, formed into an hourglass shape having dimensions similar to stent 110 may be deposited on stent 110 as is illustrated in FIG. 13D. Pre-shaped second graft layer 202 may be formed in a similar manner as pre-shaped first graft layer 199, using a dedicated mandrel and heat treatment. Pre-shaped second graft layer 202 may be expanded and positioned over stent 110. Pre-shaped second graft layer 202, may recoil into its pre-shaped form upon releasing any radial expansion force on pre-shaped second graft layer 202. Alternatively, or in addition to, stent 110 may be crimped to facilitate mounting of second graft layer 202.

[0085] Referring now to FIG. 13E, male mandrel 203 may be introduced near the end of pre-formed first graft layer 199 not occupied by female mandrel 200. Male mandrel 203 may be similar in shape to this end of pre-formed first graft layer 199 only with smaller dimensions. Male mandrel 203 may be have protruding section 204 sized and shaped to be received by receiving portion 201 of female mandrel 200. Having a conical shape, male mandrel 203 may be gently advanced within pre-formed first graft layer 199 toward female mandrel 200 until protruding section 204 is fully received by receiving portion 201.

[0086] Upon engaging female mandrel 200 and male mandrel 203, stent 110 may be at least partially covered on an exterior surface by pre-shaped second graft layer 202 and at least partially covered on an interior surface by pre-shaped first graft layer 199. Stent graft assembly 120 may be produced using the same procedures detailed above including the procedures for securely bonding first graft layer 170, in this case pre-shaped first graft layer 199, to second graft layer 190, in this case pre-shaped second graft layer 202. These procedures may involve pressure and heat applied to the stent-graft assembly to achieve sintering. This process simplifies the mounting of the graft tubes and reduces risk of tears and non-uniformities. It is understood that the mandrel inserted first into pre-formed first graft layer 199 may alternatively be a male mandrel and the mandrel inserted second may alternatively be a female mandrel.

[0087] Referring now to FIGS. 14A-14D, another alternative method of making stent-graft assembly 120, as depicted in FIGS. 1-2, is illustrated. As shown in FIG. 14A, the process may start by engaging first graft tube 122 over stent 110. Stent 110 may be crimped using dedicated crimping tools, such as ones detailed in U.S. Patent Publication No. 2014/0350565 to a diameter smaller than first graft tube 122 and guided into graft tube 122. Alternatively, or in addition to, first graft tube 122 may be stretched to a diameter slightly larger than stent 110 using an expanding mandrel or other stretching mechanism and guided over stent 110. The approach illustrated in FIG. 14A may achieve a firm engagement between crimped stent 110 and the first graft layer 170, enabling improved encapsulation.

[0088] Upon positioning first graft tube 122 over stent 110, second graft tube 124 may be positioned within and along the entire length of stent 110, shown in FIG. 14B. Second graft tube 124 may be pulled through stent 110 while stent 110 remains engaged with first graft tube 122. Alternatively, stent 110, with first graft tube 122 engaged with stent 110 may be expanded, using well-known expansion techniques, and positioned over second graft tube 124. Subsequently, as shown in FIG. 14C, balloon catheter 205 having inflatable balloon 206 may be inserted into second graft tube 124 such that the balloon catheter 205 is surrounded by stent 110 and first graft layer 122. Alternatively, second graft tube 124 may be positioned over inflatable balloon 206 and inflatable balloon 206 may be positioned within stent 110 via balloon catheter 205.

[0089] Referring now to FIG. 14D, upon positioning balloon catheter 205 into second graft tube 124, inflatable balloon 206 of balloon catheter 205 may be inflated to engage second graft tube 124 with an interior surface of stent 110. Using inflatable balloon 206 to engage second graft layer 124 with stent 110 permits uniform contact between and engagement between second graft tube 124 and stent 110 as well as second graft tube 124 and first graft layer 122 between the interstices of stent 110, thus optimizing the adhesion during encapsulation. The degree of inflation may be manipulated to achieve a desired pressure within the balloon and a desired adhesion between first graft tube 122 and the second graft tube 124. Additionally, the degree of inflation may be manipulated to achieve a desired inter-nodal-distance of the graft material. Different pressures may also be achieved by varying the wall thickness of the balloon. Furthermore, interlocking balloons may be used to reduce bond lines.

[0090] First graft tube 122 and second graft tube 124 may be appropriately cut away according to the same procedures illustrated in FIGS. 6 and 10 resulting first graft layer 170 and second graft layer 190. Further, stent graft assembly 120 may be produced using the same procedures detailed above including the procedures for securely bonding first graft layer 170 to second graft layer 190 involving pressure and heat applied to the stent-graft assembly to achieve sintering.

[0091] Referring now to FIGS. 15A-15F, another alternative method of making stent-graft assembly 120, as depicted in FIGS. 1-2, is illustrated. As shown in FIG. 15A, the process may start by placing stent 110 within funnel 207 and advancing stent 207 within funnel 207 towards a reduced section of funnel 207, using, for example, a dedicated pusher tool like the one described in U.S. Patent Publication No. 2014/0350565, to reduce the diameter of stent 110. Stent 110 may be constructed in a manner that, upon reduction caused by funnel 207, the shape of stent 110 morphs such that the flared ends are tapered and eventually turned inward toward a longitudinal axis of stent 110, resulting in stent 110 having a substantially reduced cross-sectional diameter.

[0092] As is shown in FIG. 15B, funnel 207 may have introducer tube 208 extending from the narrow side of the funnel 207 which may receive stent 110 after stent 110 has been fully restricted by funnel 207. Introducer tube 208 may have a diameter smaller than that of first graft tube 122. Introducer tube may thus be inserted into first graft tube 122, as is illustrated in FIG. 15C, and stent 110 having the reduced diameter, may be advanced out of introducer tube 208 and into first graft tube 122.

[0093] Referring now to FIG. 15D, stent 110 is illustrated after having been advanced from introducer tube 208 and into first graft tube 124. As is shown in FIG. 15D, upon the removal of inward radial force from introducer tube 208, stent 110 may expand radially to a diameter larger than the diameter of first graft tube 122, thereby engaging first graft tube 122 along the outer surface of stent 110. An end of first graft tube 122 may have been positioned a distance beyond introducer tube 208 such that upon depositing stent 110 into first graft tube 122, remaining portion 209 of first graft tube 122 extends beyond stent 110 a distance of more than one length of stent 110.

[0094] Referring now to FIG. 15E, remaining portion of first graft tube 122 may be used as a second graft layer along the internal surface of stent 110 by pushing remaining portion 209 through the interior of stent 110 and out an opposing side of stent 110, in the direction indicated by the arrows in FIG. 15D. In this manner, first graft layer 122 may extend along an exterior surface of stent 110, curve around an end of stent 110 and travel along the interior of stent 110.

[0095] To engage remaining portion 209 with the interior surface of stent 110, female mandrel 200 having receiving portion 201 and male mandrel 203 having protruding section 204 may be inserted into the stent-graft combination. Female mandrel 200 may be introduced first to one end of the stent-graft combination having a size slightly larger than the dimensions of female mandrel 200. Subsequently, male mandrel 203 may be introduced into the opposing end of the stent-graft combination and advanced until protruding section 204 is received by receiving section 201. As female mandrel 200 and male mandrel 201 are inserted, stent 110 may be guided into its original hour-glass shape. This method may induce improved adhesion between first graft tube 122, remaining portion 209 and stent 110.

[0096] Upon engaging female mandrel 200 and male mandrel 203, first graft tube 122 and remaining portion 209 may be appropriately cut away according to the same procedures illustrated in FIGS. 6 and 10 resulting first graft layer 170 and second graft layer 190, with the exception that only one side of stent graft assembly needs to be cut or otherwise removed first graft tube 122 and remaining portion 209. Stent graft assembly 120 may be produced using the same procedures detailed above including the procedures for securely bonding first graft layer 170 to second graft layer 190 involving pressure and heat applied to the stent-graft assembly to achieve sintering. It is also understood that the process depicted in FIG. 15F may start with the male mandrel entering the stent graft combination first.

[0097] While various illustrative embodiments of the invention are described above, it will be apparent to one skilled in the art that various changes and modifications may be made therein without departing from the invention. For example, assembly mandrel 130 may include additional or fewer components of various sizes and composition. Furthermore, while stent encapsulation is described herein, it is understood that the same procedures may be used to encapsulate any other bio-compatible material. The appended claims are intended to cover all such changes and modifications that fall within the true spirit and scope of the invention.