WO2020031193A1

WO2020031193A1 - Stent-graft assembly

Info

Publication number: WO2020031193A1
Application number: PCT/IN2018/050639
Authority: WO
Inventors: Deveshkumar Mahendralal KOTHWALA; Rajnikant Gandalal Vyas; Pramod Kumar Minocha
Original assignee: Meril Life Sciences Pvt Ltd
Priority date: 2018-08-08
Filing date: 2018-10-09
Publication date: 2020-02-13

Abstract

A stent-graft assembly is disclosed. The stent-graft assembly is used for coronary applications. The stent-graft assembly includes a stent made of a biodegradable/biocompatible material and has strut thickness of 35-65 µm. The stent graft assembly also includes a graft which is provided with the stent. The graft includes at least one inner slab, at least one middle slab and at least one outer slab. The graft has a thickness of 25-40 µm. The crimp profile of stent-graft assembly is compatible up to 5 French catheters.

Description

STENT-GRAFT ASSEMBLY

FIELD OF INVENTION

[001] The present invention relates to a medical device, more specifically the present invention relates to a stent-graft assembly.

BACKGROUND

[002] Stent-graft assemblies are widely used for treatment of various conditions such as aortic lesions, perforations, arterial aneurysms, emboli, etc. due to coronary intervention procedures and/or perforations in an arterial system.

[003] Generally, conventional stent graft assemblies include a metallic or polymer stent with plurality of struts and a graft. The graft of stent graft assembly is provided over the stent and functions to increase the expansion performance of the stent and prevents any damage to the stent.

[004] However, the conventional stent-graft assemblies include stents with high strut thickness which increase the risk of restenosis and also reduce rate of endothelial cell growth. Moreover, the grafts of the conventional stent-graft assemblies have high thickness. The high strut thickness of stents and high thickness of grafts in conventional stent-graft leads to higher crimp profile. The high crimp profile of conventional stent-graft assemblies allows limited access inside the body vasculature and hence, may not be suitable in highly calcified lesion.

SUMMARY

[005] The present invention relates to a stent-graft assembly. The stent-graft assembly is used for coronary applications. The stent-graft assembly includes a stent made of a

biodegradable/biocompatible material and has strut thickness of 35-65 pm. The stent graft assembly also includes a graft which is provided with the stent. The graft includes at least one inner slab, at least one middle slab and at least one outer slab. The graft has a thickness of 25- 40 pm. The crimp profile of stent-graft assembly is compatible up to 5 French catheter.

BRIEF DESCRIPTION OF THE DRAWINGS

[006] The summary above, as well as the following detailed description of illustrative embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the present disclosure, exemplary constructions of the disclosure are shown in the drawings. However, the disclosure is not limited to specific methods and instrumentalities disclosed herein. Moreover, those in the art will understand that the drawings are not to scale.

[007] FIG.l represents a stent-graft in open mode in accordance with an embodiment of the present invention.

[008] FIG.2 (a) represents a cross-sectional view of a stent-graft covered with one or more polymeric slabs for coronary application in accordance with an embodiment of the present invention.

[009] FIG.2 (b) represents a cross-sectional view of a stent-graft sandwiched between one or more polymeric slabs for coronary application in accordance with an embodiment of the present invention.

[0010] FIG.3 (a) represents a cross-sectional view of a stent-graft covered with one or more polymeric slabs for peripheral application in accordance with an embodiment of the present invention.

[0011] FIG.3 (b) represents a cross-sectional view of a stent-graft sandwiched between one or more polymeric slabs for peripheral application in accordance with an embodiment of the present invention.

[0012] FIG.4 illustrates the electro-spinning coating technique in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0013] Prior to describing the invention in detail, definitions of certain words or phrases used throughout this patent document will be defined: the terms "include" and "comprise", as well as derivatives thereof, mean inclusion without limitation; the term "or" is inclusive, meaning and/or; the phrases "coupled with" and "associated therewith", as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have a property of, or the like; Definitions of certain words and phrases are provided throughout this patent document, and those of ordinary skill in the art will understand that such definitions apply in many, if not most, instances to prior as well as future uses of such defined words and phrases. [0014] Particular embodiments of the present disclosure are described herein below with reference to the accompanying drawings, however, it is to be understood that the disclosed embodiments are merely examples of the disclosure, which may be embodied in various forms. Well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present disclosure in virtually any appropriately detailed structure.

[0015] The present invention discloses a stent graft assembly with an ultralow crimp profile. The ultralow crimp profile of the stent graft assembly may range from 0.9-1.0 mm for coronary applications while 1.8-2.0 mm for peripheral applications. Such crimp profile allows the stent graft assembly to be compatible with up to a 5F delivery catheter for coronary applications. The stent graft assembly to be compatible with up to a 6F delivery catheter for peripheral applications. The stent graft assembly provides excellent trackability and rapid deployment in calcified or tortuous vessels due to the ultra-low crimping profile. The stent graft assembly of the present invention is used for treating free arterial perforation, restoring and improving the luminal patency, treating aneurysms by diverting blood flow, acute ruptures and fistulas, etc. The stent graft assembly can also be used to treat emergency condition in coronary and peripheral vasculature such as Below the Knee (BtK) vasculature, superficial femoral artery (SFA), iliac, abdominal aorta, biliary, esophageal, tracheal, digestive tract, carotid, renal and intracranial arteries including tapered vessel anatomy.

[0016] The stent graft assembly of the present invention includes a

biodegradable/biocompatible stent and a graft having at least three polymeric slabs. The stent of the stent-graft assembly is made of a biocompatible metal. The stent includes a low strut thickness, say, 35-65 pm for coronary applications and 150-170 pm for peripheral applications.

[0017] The polymeric slabs of the stent graft assembly may either be coated over the stent or the stent may optionally be sandwiched between the polymeric slabs. In an embodiment, the stent graft assembly includes five polymeric slabs for peripheral applications. In another embodiment, the stent graft assembly includes three polymeric slabs for coronary applications.

[0018] Further, for coronary applications, the three polymeric slabs may include an inner slab, a middle slab and an outer slab. In an embodiment, the inner slab is pervious while the outer slab is impervious. The three polymeric slabs may be made of a biodegradable and/or non- degradable. In an embodiment, the thickness of inner slab, middle slab and outer slab is 5, 10 and 15 miti respectively. In an embodiment, the average pore size of inner slab is less than 0.5 pm to allow growth of endothelial cell layer over the stent assembly. In another embodiment, the average pore size of outer slab is less than 1.5 pm which prevents tissue growth and avoids restenosis.

[0019] For peripheral applications, the number of inner and outer slabs may vary however; the thickness and average pore size of each of the inner and outer slabs remains same as that for coronary applications. In an embodiment, the graft includes two inner slabs, two outer slabs and a middle slab for peripheral applications.

[0020] The total thickness of the graft for coronary application ranges between 25-40 pm while for peripheral application the total thickness of the graft ranges between 50-70 pm.

[0021] Thus, the stent graft assembly of the present invention with ultralow strut thickness and thin polymeric slabs allows better wall adhesion and faster endothelial cell growth and thus providing remodelling/repair of arteries in a body vasculature.

[0022] Now referring to the drawings, Fig.l illustrates a schematic view of the stent graft assembly 100. The stent graft assembly 100 has high radial strength and flexibility. In an embodiment, the stent graft assembly 100 has controlled degradation rate inside the body. The degradation rate of the stent graft assembly 100 is dependent upon the properties of the biodegradable material used for it fabrication.

[0023] In an embodiment, the stent graft assembly 100 achieves an ultralow crimping profile and is compatible with up to a 5F catheter for coronary application while up to a 6F catheter for peripheral application. The value of the crimping profile ranges from about 0.9-1.0 mm for the treatment of a coronary vasculature. The crimping profile of the stent graft assembly 100 ranges from 1.5-1.7 mm for peripheral applications.

[0024] The ultralow crimping profile of stent graft assembly 100 is achieved due to ultralow strut thickness of a stent and low thickness of a graft (elaborated below). The stent-graft with ultralow crimp profile is suitable for implantation in highly calcified lesion and torturous vessel anatomy.

[0025] As represented, the stent graft assembly 100 includes, without limitation, a stent 1 and a graft 3. [0026] In an embodiment, the stent 1 is a tubular structure which includes an inner surface (not shown) and an outer surface 5. The stent 1 may be a balloon expandable stent or a self- expandable stent. In an embodiment, the stent 1 is self-expandable for peripheral application.

In another embodiment, the stent 1 is balloon expandable for coronary application.

[0027] The stent 1 may be a biodegradable stent or a biocompatible stent. In case of biodegradable stent, the stent 1 may be made of, without limitation, poly-L-Lactide (PLLA), poly-L-lactide-co-caprolactone (PLCL), polycaprolactone (PCL), poly-dl-lactic acid, (PDLLA), polyglycerol sebacate (PGS), poly(glycolic acid) (PGA), poly L-lactide co-glycolic acid (PLGA) or a combination thereof.

[0028] Alternately, in case of biocompatible stents, the stent 1 may be made of without limitation, metal tubes or metal wires. The metal tubes maybe made from, without limitation, cobalt chromium, stainless steel, nickel-titanium alloy, silver, gold, magnesium, iron or combination thereof. In an embodiment, the metal tubes are laser cut and transformed into expandable designs with specified cell dimensions to form stent 1. In an embodiment, the laser cut stent has a hybrid design with a plurality of open and closed cells. Said design confers radial strength and high flexibility to the stent 1 and hence, the stent 1 does not collapse on radial expansion.

[0029] The metal wire (s) may include, without limitation, nitinol wires or any other category of super elastic metal alloy wire. The metal wires may be transformed into stent 1 by way of, without limitation, braiding, weaving, knitting and/or other textile fabrication technology or combination thereof.

[0030] In an embodiment, the stent 1 is obtained by laser cutting a cobalt-chromium tube or braiding cobalt-chromium wires for coronary applications. In an embodiment, the strut thickness of stent 1 is 50 pm for coronary applications. In another embodiment, for peripheral application, the stent 1 is obtained by laser cutting a nitinol tube or braiding nitinol wires. The stent 1 used for peripheral application has a strut thickness of 150-170 pm.

[0031] As depicted in exemplary FIG., the graft 3 is mounted on the outer surface 5 of the stent 1. The graft 3 includes at least three polymeric slabs (described below). In an embodiment, the total thickness of the graft 3 is in the range of 25-40 pm. The graft 3 functions to increase the expansion performance of the stent 1, prevents the formation of micro cracks and notches at strut edges of the stent 1. [0032] Fig. 2 (a) illustrates a cross-sectional view of the stent graft assembly 100 covered with three polymeric slabs for coronary application. In an exemplary embodiment, the three polymeric slabs for coronary application include an inner slab 10, a middle slab 20 and an outer slab 30.

[0033] The inner slab 10 includes an inner surface and an outer surface. The inner surface of the inner slab 10 is in direct contact with the outer surface 5 of the stent 1. The inner slab 10 is pervious in nature and may be made of a biodegradable/non-biodegradable material. The materials may be selected from, without limitation, polydifluoromethylene (PDFE),

polytetrafluorethylene (PTFE), polyvinylidene fluoride (PVDF), perfluoropolyoxetane, polyvinylfluoride (PVF), ethylene tetrafluoroethylene (ETFE), ethylene chlorotrifluoroethylene (ECTFE), polychlorotrifluoroethylene (PCTFE), fluorinated ethylene propylene (FEP), or other perfluoroalkoxy (PFA), polyurethanes (PU), silicones, epoxides, polyamides, polyimides and/or elastomers, etc.

[0034] In an embodiment, the inner slab 10 is made of, without limitation, pervious

polytetrafluoroethylene (PTFE). For example, the concentration of PTFE is in the range of 55- 60% (v/v). PTFE is a high viscosity, thermal resistant, non-stick and electrically resistant polymer. The minimum viscosity range of PTFE is between 400-2500 poise.

[0035] In an embodiment, the thickness of the inner slab 10 is less than 5 pm. The pore size of the inner slab 10 may be less than 0.5 pm thereby providing support for growth of an endothelial cell layer.

[0036] The middle slab 20 includes an inner surface and an outer surface. The middle slab 20 is an adhesive layer disposed between the outer surface of the inner slab 10 and an inner surface of the outer slab 30. The middle layer 20 contains adhesives that bind the inner slab 10 and the outer slab 30 together. The adhesives used in the middle slab 20 may include, without limitation, FEP or other flourinated material or mixture of polycaprolactone (PCL) and its copolymer (PLC) with cross-linker hexamethylene diisocyanate (HDI).

[0037] In an embodiment, the adhesive used for the formation of the middle slab 20 is mixture of polycaprolactone (PCL) and its copolymer (PLC) with cross-linker hexamethylene diisocyanate (HDI). The concentration of the mixture may be in the range of 0.3-0.8%.

[0038] The thickness of the middle slab 20 is approximately 10 pm. [0039] The outer slab 30 may be made of, without limitation, a non-biodegradable material and/or a biodegradable material. The non-biodegradable material and/or a biodegradable material used for preparing the outer slab 30 may be amorphous or semi-crystalline in nature which aids in vessel repair and enhances the endothelial cell growth.

[0040] The non-degradable materials may include without limitation, fluoropolymer i.e. poly (1,1, 2, 2,) tetrafluoroethylene (PTFE), etc. In an embodiment, the outer slab 30 is made of fluoropolymer i.e. poly (1,1, 2, 2,) tetrafluoroethylene (PTFE), polydifluoromethylene (PDFE), polytetrafluorethylene (PTFE), polyvinylidene fluoride (PVDF), perfluoropolyoxetane, polyvinylfluoride (PVF), ethylene tetrafluoroethylene (ETFE), ethylene chlorotrifluoroethylene (ECTFE), polychlorotrifluoroethylene (PCTFE), fluorinated ethylene propylene (FEP), or other perfluoroalkoxy (PFA), polyurethanes (PU).

[0041] The biodegradable materials may include, without limitation, PLGA (Poly-L-lactide co- glycolide), PDLLA (Poly-DL-lactic acid), PCL (Poly Caprolactone), PLLA (Poly-L-lactic acid) and combination thereof. In an embodiment, the outer slab 30 is made of, without limitation a mixture of poly L-lactide, 50:50 poly DL-lactide co-glycolide. The viscosity of poly L-lactide polymer is ranging from 0.90-1. lOdL/g. The viscosity of poly DL-lactide co-glycolide lactide is ranging between 0.55-0.75dL/g. The concentration of the biodegradable material used may be in the range of 0.4-1%.

[0042] In an embodiment, the outer slab 30 is formed from a mixture of biodegradable material say, biodegradable polymer and an anti-proliferative drug. The anti-proliferative drug may be, without limitation, Sirolimus, Everolimus, Paclitaxel, etc. The quantity of drug in the outer slab 30 may be 1.25 pg/mm² approximately. For example, the outer slab 30 consists of a mixture of poly L-lactide, 50:50 Poly DL-lactide co-glycolide (IV range 0.90-1.10dL/g and 0.55- 0.75dL/g respectively) and a drug in ratio of around 35:65 (polymer: drug).

[0043] In an embodiment, the outer slab 30 is non-pervious in nature and degrades over time. In an embodiment, the thickness of the outer slab 30 is approximately lOpm and pore size less than 1.5pm. The reduced pore size of the outer slab 30 prevents tissue growth and avoids restenosis.

[0044] The inner slab 10, the middle slab 20 and the outer slab 30 are fabricated on the outer surface 5 of the stent 1 by means of, without limitation spray method, spinning method or electro-spinning method, etc. The inner slab 10, the middle slab 20 and the outer slab 30 are layered one on top of the other by means of electro-spinning (explained in FIG. 4).

[0045] Fig. 2 (b) illustrates a cross-sectional view of the stent-graft 100 sandwiched between one or more polymeric slabs for coronary applications. The inner slab 10, the middle slab 20 and the outer slab 30 may be structurally (composition, pore size and thickness) and

functionally similar to the inner slab 10, the middle slab 20 and the outer slab 30 as explained in Fig. 2 (a). However, the placement of the inner slab 10, middle slab 20 and outer slab 30 is different. As represented, the outer surface of the inner slab 10 is placed over the inner surface of the stent 1. The middle slab 20 is placed between the outer surface 5 of the stent 1 and an inner surface of the outer slab 30. The middle slab 20 acts as an adhesive for the inner slab 10 and outer slab 30. The outer slab 30 is placed over the outer surface of the middle slab 20.

[0046] Fig.3 (a) illustrates a cross-sectional view of the stent graft assembly 100 covered with one or more polymeric slabs for peripheral application. As represented, the outer surface 5 of the stent 1 is covered with five polymeric slabs for peripheral application: two inner slabs 10, a middle slab 20 and two outer slabs 30. The five polymeric slabs used in the peripheral application provide high radial strength to the stent graft assembly 100 which can withstand axial bending and torsional forces exerted by peripheral blood vessels. It must be noted that each of the multiple inner slabs 10 (or middle slabs 20 or outer slabs 30) is consecutively placed adjacent to the following inner slab 10 (or middle slab 20 or outer slab 30).

[0047] The inner slabs 10, middle slabs 20 and outer slabs 30 for the peripheral application may be structurally and functionally similar to the inner slab 10, middle slab 20 and outer slab 30 for coronary application as explained in Figs. 2 (a).

[0048] Fig.3 (b) illustrates a cross-sectional view of the stent graft assembly 100 sandwiched between one or more polymeric slabs for the peripheral application. As represented, the one or more polymeric slabs are placed in a way that the stent 1 is sandwiched between the one or more polymeric slabs. In an exemplary embodiment, the stent 1 may include without limitation five polymeric slabs for peripheral application: two inner slabs 10, the middle slab 20 and two outer slabs 30. It must be noted that each of the multiple inner slabs 10 (or middle slabs 20 or outer slabs 30) is consecutively placed adjacent to the following inner slab 10 (or middle slab 20 or outer slab 30). [0049] As shown in FIG. 3(b), the two inner slabs 10 are placed over the inner surface of the stent 1. The middle slab 20 is placed between the outer surface 5 of the stent 1 and the inner surface of the outer slab 30. The middle slab 20 acts as an adhesive for inner slabs 10 and outer slabs 30. The two outer slabs 30 are placed on the outer surface of the middle slab 20.

[0050] The inner slabs 10, middle slabs 20 and outer slabs 30 for the peripheral application may be structurally and functionally similar to the inner slab 10, middle slab 20 and outer slab 30 for coronary application as explained in Figs. 2 (a).

[0051] Fig.4 illustrates an electro-spinning machine 400 used for electro-spinning of the one or more polymeric slabs over the stent 1. The following description discloses electro-spinning PTFE for coating of one or more polymeric slabs over the surface of the stent 1 for coronary applications. However, it must be noted that the other materials which can be used for preparing may also be used by the same method. In an embodiment, the above procedure practised for casting polymeric slabs for coronary and peripheral applications is same.

[0052] In an embodiment, prior to electro-spinning the one or more polymeric slabs, the stent 1 is electro-polished. The electro-spinning process comprises of casting PTFE on the stent 1 by utilizing electrostatic field to form inner slab 10. As shown in FIG. 4, the electro-spinning machine 400 includes a hopper 401, a helical delivery pipe 403, a charged orifice 405 and a mandrel 407.

[0053] The hopper 401 is used to collect aqueous dispersion of PTFE. The aqueous dispersion of PTFE is obtained by mixing PTFE with a sizing agent and a solvent. In case of coronary applications, the PTFE used for preparing the aqueous dispersion of PTFE has an average viscosity between 400 and 2500 poise, preferably between 1000-1800 poise, more preferably between 1200-1600 poise. The molecular weight of PTFE is between 100000 and 500000 g/mol, preferably 200000-350000 g/mol and more preferably 275000-325000 g/mol with average particle size between 0.1 and 0.5pm.

[0054] The sizing agent acts as a lubricant. In an embodiment, polyethylene glycol (PEG) with average molecular weight 285000 - 320000 g/mol and viscosity 05 - 15 poise at 25°C is used as the sizing agent.

[0055] In an embodiment, the aqueous dispersion of PTFE is viscous and off -white in colour. The ratio of PTFE: PEG is approximately 9.8:0.2 which is dissolved in water. The aqueous dispersion of PTFE is further loaded into the hopper 401 of the electro-spinning machine 400. The helical delivery pipe 403 conveys the aqueous dispersion of PTFE from the hopper 401 to the charged orifice 405.

[0056] The charged orifice 405 electrostatically casts the aqueous dispersion of PTFE (e-PTFE) onto the stent 1 (mounted on the mandrel 407) to form the inner slab 10.

[0057] After the formation of the polymeric slabs (the inner slab 10, the middle slab 20 and the outer slab 30), the curing process of the stent graft assembly 100 takes place. The stent graft assembly 100 is cured at a high temperature to evaporate sizing agent and other solvents used during electrospinning process. This curing process involves contraction of slab without cracking at temperature range between 250°C- 550°C, preferably between 350°C -450°C temperature and more preferably 385°C-405°C for the specific period of time. In an

embodiment the curing process is performed at a temperature of 400°C for a time period of 5 minutes.

[0058] Subsequently, the stent graft assembly 100 is dried and passed for the further crimping process onto a delivery catheter. The crimping process utilized may be any conventional crimping process known in the art. The crimp profile of the stent graft assembly 100 is an ultralow crimp profile ranging from 0.9-1.0 mm. Such crimp profile allows the stent graft assembly 100 to be compatible with up to a 5F delivery catheter.

[0059] The present invention is explained with following examples.

Example 1: The stent 1 was fabricated from the nitinol super elastic alloy with one over two braiding pattern to provide greater flexibility and deliverability into the peripheral vasculature which is not limited to carotid and/or renal artery. The nitinol wires had a thickness of about 170pm. The nitinol wires were then annealed and subjected to the braiding process with 12 carrier braiding unit. The braided structure was constructed in such a way that, it neither creates open ends nor loses its radial strength by closing proximal and distal end.

[0060] The multiple polymeric slabs (the two inner slabs 10, the middle slab 20 and the two outer slabs 30) were formed by using the electro-statically charged PTFE dispersion. The average viscosity of PTFE is selected between 400 and 2500 poise and molecular weight between 100000 and 500000 g/mol with average particle size 0.5pm. The aqueous PTFE dispersion was prepared by using PEG and water. The PEG and water were used as sizing agent and solvent respectively. Initially, the PEG was mixed into the water. The average molecular weight of PEG is 285000 - 320000 g/mol and the viscosity 5 - 15 poise at 25°C. Further, the PEG solution was added to the 1000ml aqueous dispersion of PTFE and allowed to from gel at room temperature for 7 days followed by homogenization at a speed of BOrpm.

[0061] Initially, the two inner slabs 10 with thickness about lOpm were formed with the rotating speed of 75rpm. The two inner slabs were then cured at a temperature of 385°C for about 10 minutes. Then, the middle slab 20 with thickness less than lOpm was formed followed by the outer slabs 30 of thickness lOpm were formed with the mandrel 407 rotating at a speed of 45rpm and were cured at 385°C for 10 minutes.

[0062] The stent graft assembly 100 was then dried under vacuum environment at a room temperature for a period of 12 hours. Further, the stent graft assembly 100 is loaded into the catheter to deliver the stent graft assembly 100 at a specific treatment site.

[0063] Example 2: The stent 1 was fabricated from the CoCr balloon expansible tube into 50pm strut thickness. The multiple polymeric slabs (the inner slab 10, the middle slab 20 and the outer slab 30) were formed over the thin strut stent 1 to provide desired radial strength and high flexibility in torturous anatomical coronary vasculature. The multiple polymeric slabs (the inner slab 10, the middle slab 20 and the outer slab 30) were formed by using the electro statically charged PTFE dispersion and formulation is same as described in example 1.

[0064] The formed stent graft assembly 100 was crimped over Rx PTCA balloon dilatation catheter with a multi-stage crimping process. Through this process, the crimp profile was achieved to 0.9-1.0mm that provides more access to coronary vessels, compatible with 5F catheter and also gives excellent trackability into calcified arteries. The crimped stent graft assembly 100 was further protected with a protective PTFE heat shrink tubing layer at last stage of crimping process. The crimped stent graft assembly 100 was packed into tyvek pouch and subjected to ethylene oxide gas sterilization process.

[0065] Table 2 depicts the crimping parameters for the stent 1 as per SC500/SC600.

Table 2

[0066] Table 2a depicts the crimping parameters for the stent 1 as per SC775.

Table 2a

[0067] Table 2b depicts the diameter of the stent 1 at various stage

Table 2b

[0068] The stent graft assembly 100 with variable strut width provides excellent expansion and an open-closed intelligent hybrid cell design that gives greater flexibility. [0069] Example 3: The stent 1 was fabricated from the CoCr balloon expansible tube into 50pm strut thickness. The outer slab 30 and the inner slab 10 were formed over thin strut stent to provide desired radial strength and high flexibility in torturous anatomical coronary vasculature in which degradable slab resorbs in a body over a specific period of time.

[0070] The inner polymeric slab 10 was formed by using the electro-statically charged PTFE dispersion and formulation is same as described in example 2. The middle slab 20 acts as an adhesive layer containing mixtures of PCL and PLC with cross-linker. The outer slab 30 was formed by using regular spray coating technique. The outer non-pervious slab 30 consists of poly-L-lactide caprolactone and a drug in an approximate ratio of 35:65. The outer slab 30 degrades around 1-2 years and reduces chances of late restenosis.

[0071] The stent graft assembly 100 was then crimped over a Rx PTCA balloon dilatation catheter with a multi-stage crimping process. The crimp profile is achieved to 0.9-1. lmm which provides good access to coronary vessels, compatible up to 5F catheter and also gives excellent traceability into calcified arteries. The crimped stent graft assembly 100 was further protected with protective PTFE heat shrink tubing layer at last stage of crimping process and further packed into tyvek pouch and subjected to ethylene oxide gas sterilization process.

[0072] Table 3 depicts the crimping parameters for the stent 1 as per SC500/SC600.

Table 3 [0073] Table 3a depicts the crimping parameters for the stent 1 as per SC775.

Table 3a [0074] The scope of the invention is only limited by the appended patent claims. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the teachings of the present invention is/are used.

Claims

WE CLAIM:

1. A stent-graft assembly for coronary applications, the stent-graft assembly comprising:

• a stent made of a biodegradable/biocompatible material having strut thickness of 35-65 pm; and

• a graft provided with the stent, the graft including at least one inner slab , at least one middle slab and at least one outer slab, the graft having a thickness of 25-40 pm; wherein crimp profile of stent-graft assembly is compatible up to 5 French catheter.

2. The stent-graft assembly as claimed in claim 1, wherein the biodegradable material includes one or more of poly-L-Lactide (PLLA), poly-L-lactide-co-caprolactone (PLCL), polycaprolactone (PCL), poly-dl-lactic acid, (PDLLA), polyglycerol sebacate (PGS), poly(glycolic acid) (PGA), poly L-lactide co-glycolic acid (PLGA) or a combination thereof.

3. The stent-graft assembly as claimed in claim 1, wherein the biocompatible material includes one or more of cobalt chromium, nitinol, stainless steel, silver, gold, magnesium, iron, a nickel-titanium alloy, a super elastic metal alloy or combinations thereof.

4. The stent-graft assembly as claimed in claim 1, wherein the stent is made by one of a laser cutting technique or a braiding technique.

5. The stent-graft assembly as claimed in claim 1, wherein the stent-graft assembly

comprises:

• the at least one inner slab provided on an outer surface of the stent having a thickness of less than 5 pm;

• the at least one middle slab provided on an outer surface of the inner slab

having a thickness of approximately 10 pm ; and

• the at least one outer slab provided on an outer surface of the middle slab

having a thickness of approximately 10 pm.

6. The stent-graft assembly as claimed in claim 1, wherein the stent-graft assembly

comprises: • the at least one inner slab provided on an inner surface of the stent having a thickness of less than 5 pm;

• the at least one middle slab provided on an outer surface of the stent having a thickness of approximately 10 pm; and

• the at least one outer slab provided on an outer surface of the middle slab

having a thickness of approximately 10 pm.

7. The stent-graft assembly as claimed in claim 1, wherein pore size of the inner slab is less than 0.5 pm.

8. The stent-graft assembly as claimed in claim 1, wherein pore size of the outer slab is less than 1.5 pm.

9. The stent-graft assembly as claimed in claim 1, wherein the inner slab is made from one of polydifluoromethylene (PDFE), polytetrafluorethylene (PTFE), polyvinylidene fluoride (PVDF), perfluoropolyoxetane, polyvinylfluoride (PVF), ethylene

tetrafluoroethylene (ETFE), ethylene chlorotrifluoroethylene (ECTFE),

polychlorotrifluoroethylene (PCTFE), fluorinated ethylene propylene (FEP), or perfluoroalkoxy (PFA).

10. The stent-graft assembly as claimed in claim 1, wherein the inner slab is made from polytetrafluorethylene (PTFE) having a concentration of 55-60% (v/v).

11. The stent-graft assembly as claimed in claim 1, wherein the inner slab is made from a group consisting of polyurethanes (PU), silicones, epoxides, polyamides, polyimides and/or elastomers.

12. The stent-graft assembly as claimed in claim 1, wherein the middle slab is made from one of fluorinated ethylene propylene (FEP) or a mixture of polycaprolactone (PCL) and its copolymer (PLC) with cross-linker hexamethylene diisocyanate (HDI).

13. The stent-graft assembly as claimed in claim 12, wherein the concentration of the

mixture of polycaprolactone (PCL) and its copolymer poly-L-lactide-co-caprolactone (PLC) with cross-linker hexamethylene diisocyanate (HDI) is 0.3-0.8% (v/v).

14. The stent-graft assembly as claimed in claim 12, wherein the ratio of polycaprolactone (PCL), poly-L-lactide-co-caprolactone (PLC) and hexamethylene diisocyanate (HDI) in the mixture of polycaprolactone (PCL) and its copolymer poly-L-lactide-co-caprolactone

(PLC) with cross-linker hexamethylene diisocyanate (HDI) is 1.95:8:0.05.

15. The stent-graft assembly as claimed in claim 1, wherein the outer slab is made from a biodegradable material selected from a group consisting of one of a fluoropolymer or a polyurethane (PU) or combination thereof.

16. The stent-graft assembly as claimed in claim 14, wherein the concentration of the biodegradable material includes 0.4 - 1% (v/v).

17. The stent-graft assembly as claimed in claim 1, wherein the outer slab is made from a biodegradable material and a drug in the ratio of 35:65.