WO2021100057A1

WO2021100057A1 - Tapered coronary stent system and method to manufacture thereof

Info

Publication number: WO2021100057A1
Application number: PCT/IN2020/050946
Authority: WO
Inventors: Pramod Kumar Minocha; Deveshkumar Mahendralal KOTHWALA; Hitendra Arjanbhai GHIYAD
Original assignee: Meril Life Sciences Pvt Ltd
Priority date: 2019-11-22
Filing date: 2020-11-10
Publication date: 2021-05-27

Abstract

A stent system (100) is disclosed. The system (100) includes a balloon catheter (10) having a balloon (10b). The balloon (10b) has a tapered intermediate portion (D3) disposed between a second proximal end (a2) and a first distal end (b1) of the balloon (10b). The system (100) further includes a stent (20) with a proximal end (20c), a distal end (20d) and a pre-defined length extending between the proximal end (20c) and the distal end (20d). The stent (20) has a crimped state and a deployed state and is mounted over tapered intermediate portion (D3) of the balloon (10b) in the crimped state with a guide-catheter compatibility of 5F. In the deployed state, the stent (20) attains a tapered profile corresponding to the tapered intermediate portion (D3) of the balloon (10b). The tapered profile of stent (20) includes a taper from the proximal end (20c) to the distal end (20d).

Description

TAPERED CORONARY STENT SYSTEM AND METHOD TO MANUFACTURE THEREOF

FIELD OF INVENTION

[001] The present invention relates to a medical device. More specifically, the present invention relates to a stent system for treating long lesions in tapered coronary arteries. BACKGROUND

[002] Coronary artery disease (CAD) is the most often found cardiovascular disease all around the globe. CAD tends to develop when cholesterol builds up on the artery walls of a patient, thereby creating plaques. These plaques render the arteries narrow, thus, reducing blood flow to the heart. [003] A lot of treatment strategies for curing the said disease have been suggested/devised, however, treating complex lesions in coronary arteries still remains challenging due to high-risk and vessel-stent diameter mismatch. It becomes a particular concern in cases where arterial diameter changes to a significant degree over the length of a coronary lesion. Such diameter changes are commonly encountered due to anatomy of the coronary artery or due to a need to deploy a stent from parent vessel into its narrower branch.

[004] As a promising treatment strategy, percutaneous coronary intervention (PCI) with stent implantation is the most widely used approach for CAD. Moreover, current generation drug eluting coronary stents have remarkable features to improve the clinical outcomes of PCI. However, treatment of long diffused lesions is still a challenge for interventional cardiologists, especially in coronary arteries where the vessel diameter discrepancies may warrant using more than one stent for a long lesion.

[005] Currently available balloon-expandable stents exhibit limitations such as stent malapposition (alignment of stent), conformability, no self-adjustment to tapered lesions, stent over-expansion at distal end, stent under-expansion at proximal end, edge dissection, and/or immediate vascular injury while treating long lesions in coronary arteries.

[006] Further, when coronary lesions involve segments having a length greater than 48 mm, the only treatment possibility is utilization of overlapping multiple stents. A technical paper titled "Multiple Stent Implantation in Single Coronary Arteries: Acute Results and Six-Month Angiographic Follow-Up " published in journal, Catheterization and Cardiovascular Diagnosis (42:158-165 (1997)) discloses multiple stenting for the treatment of a single coronary artery. As disclosed in the paper, a plurality of stents are implanted in an overlapping manner.

[007] However, it should be noted that stent overlapping is associated with higher neointimal proliferation (formation of a thickened layer of arterial intima) which leads to more restenosis. Also, stent overlapping increases the risk of inflammation and delayed healing which further aggravates the condition of the patient. It is also important to note that the use of overlapping multiple stent in long lesion segments is associated with concerns of increased costs.

[008] Therefore, there arises a requirement of a stent system which overcomes the aforementioned challenges associated with the conventional treatment systems for CAD. SUMMARY

[009] The present invention relates to a drug eluting coronary stent system (or 'stent system') and a method of manufacturing the same. The stent system addresses the challenges posed by the conventional systems by utilizing a single and long drug eluting stent which is capable of being implanted as a tapered stent in long and diffused lesions in the tapered arteries. The use of such a stent in the present invention provides better procedural and post-implantation safety over overlapping stents, minimizes over-exposure to drug/metal and/or also saves the time of intervention as well as the cost involved for the intervention.

[0010] Further, the stent of the present invention includes a hybrid design having a combination of closed cells and open cells. The closed cells are disposed at both ends of the stent while the open cells are disposed between the closed cells in the middle of the stent. Such disposition allows morphology mediated expansion of the stent at an implantation site which enables adequate conformability and lesser edge dissections.

[0011] The stent of the present invention is mounted over a percutaneous transluminal coronary angioplasty balloon catheter having a tapered balloon. The use of a tapered balloon allows even expansion of the stent thereby causing the stent to be implanted as a tapered stent. Thus, the stent system of present invention adapts to the tapering arterial anatomy with excellent vessel conformability and homogenous radial force throughout the length of the tapered stent. [0012] The foregoing features and other features as well as the advantages of the invention will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF DRAWINGS [0013] 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.

[0014] Fig. 1 depicts a stent system 100 in accordance with an embodiment of the present invention.

[0015] Fig. la represents a tapered balloon 10b in accordance with an embodiment of the present invention. [0016] Fig. lb illustrates the metallic stent 20 in accordance with an embodiment of the present invention.

[0017] FIG. lc depicts the bioresorbable stent 20 in accordance with an embodiment of the present invention.

[0018] Fig. Id shows the hybrid design of the stent 20 in accordance with an embodiment of the present invention.

[0019] Fig. le depicts a magnified view of the S link 204 and the Y connector 206 of the stent 20 in accordance with an embodiment of the present invention.

[0020] FIG. If depicts the tapered stent 20 implanted at an implantation site in accordance with an embodiment of the present invention. [0021] FIG. 2 depicts the steps involved in manufacturing the balloon 10b in accordance with an embodiment of the present invention.

[0022] FIG. 2a depicts a mold 10b' for fabrication of the balloon 10b in accordance with an embodiment of the present invention. [0023] FIG. 3 depicts the steps involved in manufacturing the metallic stent 20 in accordance with an embodiment of the present invention.

[0024] FIG. 4 depicts the steps involved in manufacturing the bioresorbable stent 20 in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0025] 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.

[0026] Reference throughout this specification to "one embodiment," "an embodiment," or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases "in one embodiment," "in an embodiment," and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment, but mean "one or more but not all embodiments" unless expressly specified otherwise. The terms "including," "comprising," "having," and variations thereof mean "including but not limited to" unless expressly specified otherwise. An enumerated listing of items does not imply that any or all of the items are mutually exclusive and/or mutually inclusive, unless expressly specified otherwise. The terms "a," "an," and "the" also refer to "one or more" unless expressly specified otherwise.

[0027] Although the operations of exemplary embodiments of the disclosed method may be described in a particular, sequential order for convenient presentation, it should be understood that the disclosed embodiments can encompass an order of operations other than the particular, sequential order disclosed. For example, operations described sequentially may in some cases be rearranged or performed concurrently. Further, descriptions and disclosures provided in association with one particular embodiment are not limited to that embodiment, and may be applied to any embodiment disclosed herein. Moreover, for the sake of simplicity, the attached figures may not show the various ways in which the disclosed system, method, and apparatus can be used in combination with other systems, methods, and apparatuses.

[0028] Furthermore, the described features, advantages, and characteristics of the embodiments may be combined in any suitable manner. One skilled in the relevant art will recognize that the embodiments may be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments. These features and advantages of the embodiments will become more fully apparent from the following description and appended claims, or may be learned by the practice of embodiments as set forth hereinafter.

[0029] It should be noted that 'stent' and 'coronary stent' in the following description are interchangeably used to confer the same meaning. Likewise, 'delivery catheter', 'balloon catheter' and 'catheter' have been interchangeably used to confer the same meaning. Also, 'biodegradable' and 'bioresorbable' have been interchangeably used to confer the same meaning. It should be further noted that the term 'diameter' in the following description corresponds to outer diameter until and unless specified otherwise.

[0030] In accordance with the present disclosure, a coronary stent mounted over an expandable member of a delivery catheter (collectively referred to as a 'stent system') is disclosed. The coronary stent of the present invention is deployed with the help of the balloon catheter at an implantation site. The implantation site in the present invention corresponds to for example, a long and diffused lesion in a tapered artery of a patient. In an embodiment, the present invention may also be used for other implantation sites such as tapered peripheral arteries, below the knee arteries etc.

[0031] The stent of the present invention includes a pre-defined length which eliminates the use of multiple overlapping stents as used in the conventional systems. Further, the stent includes a hybrid design having a combination of open and closed cells connected by a plurality of S-shaped links and/or Y-shaped connectors. The disposition of the open and closed cells in the present invention allows morphology mediated expansion of the stent at the implantation site.

[0032] The balloon catheter may have a tapered expandable member, say balloon, to suit the tapering coronary anatomy. Hence, the use of the tapered balloon allows even expansion of the stent in a way that the stent is implanted as a tapered stent at the implantation site. The tapered stent hence, mimics the natural anatomy of the coronary artery, thus overcoming the challenges associated with the conventional systems due to tapered anatomy of the coronary arteries.

[0033] Now referring to figures, FIG. 1 shows the stent system 100 of the present invention. The stent system 100 is employed to be used for treating of multiple blockages of a tapered coronary artery as well as the long length lesions therein.

[0034] The crimp profile of the stent system 100 may range from 0.85 mm to 1.10 mm. In an embodiment, the crimp profile of the stent system 100 ranges from 0.90 mm to 1.05 mm (depending on the stent diameter which may range from 2.25 mm to 3.50 mm). The stent system 100 includes a guide-catheter compatibility as low as 5F which is similar to shorter conventional cylindrical stents. Thus, the stent system 100 provides superior conformability in the tapered anatomy of the coronary artery as compared to multiple overlapping stents. The stent system 100 allows an interventional cardiologist to safely expand the stenosed segment to the diameter of the artery. [0035] As depicted in FIG. 1, the stent system 100 includes a balloon catheter 10 and a stent 20 mounted over the same. The balloon catheter 10 in turn includes a shaft 10a and a balloon 10b. Further, the balloon catheter 10 may include a plurality of radio opaque markers (not shown). The radio opaque markers may be mounted on an inner lumen of the balloon catheter 10 for better visibility during radio graphic examination. [0036] The shaft 10a of the balloon catheter 10 may be structurally and functionally equivalent to any conventionally known/used shaft of a balloon catheter.

[0037] The balloon 10b of the present invention may be made of one or more medical grade polymers which include, without limitation, polyamide (nylon 6, nylon 12, etc.), plasticizer-free poly (ether-b-amide)s, polyurethane, etc. In an embodiment, the balloon 10b is made of polyamide i.e. nylon 12. The use of nylon 12 for preparation of the balloon 10b offers excellent abrasion resistance and provides a smooth surface to the balloon 10b.

[0038] In an embodiment, the balloon 10b may be manufactured using a polyamide tubing as described in FIG. 2 below. The rated burst pressure of the balloon (10b) is around 14 Bar and the actual burst pressure is > 19 Bar.

[0039] As shown in FIG. la, the balloon 10b includes two tapered end portions i.e. a proximal end portion 'Dl' and a distal end portion 'D2'. The proximal end portion 'Dl' includes a first proximal end 'al' and a second proximal end 'a2'. Likewise, the distal proximal portion 'D2' includes a first distal end 'bl' and a second distal end 'b2'.

[0040] The distance between the first proximal end 'al' and the second distal end 'b2' corresponds to the length 'L' of the balloon 10b. The length 'L' of the balloon 10b from the first proximal end 'al' to the second distal end 'b2' may range between 20 mm to 61 mm. In an embodiment, the length 'L' of the balloon 10b is example 31mm.

[0041] The inner diameter of the second proximal end 'a2' ranges between 7.00 mm to 11.00 mm and the inner diameter of the first distal end 'bl' ranges between 0.58 mm to 0.71 mm. The double wall thickness at the second proximal end 'a2' ranges between 0.020 to 0.050 mm. The double wall thickness at the first distal end 'bl' ranges between 0.025 to 0.045 mm.

[0042] In an embodiment, the outer diameters of the balloon 10b at the first proximal end 'al' and the second distal end 'b2' are same. However, the outer diameters of the balloon 10b at the second proximal end 'a2' and the first distal end 'bl' are different. In an embodiment, the outer diameter of the second proximal end 'a2' is greater than the outer diameter of the first distal end 'bl'. The outer diameter of the second proximal end 'a2' may range between 2.75 mm and 3.50 mm. The diameter of the first distal end 'bl' may lie between 2.25 mm to 2.75 mm. In an embodiment, the aforesaid diameters include a deviation of ± 0.15 mm at a nominal pressure of 7.09 bar.

[0043] Owing to the difference in the outer diameters of the second proximal end 'a2' and the first distal end 'bl', the balloon 10b defines a tapered intermediate portion 'D3' which is disposed between the second proximal end 'a2' and the first distal end 'bl'.

[0044] The intermediate portion 'D3' defines a surface for mounting the stent 20. The stent 20 is mounted over the intermediate portion 'D3' of the balloon 10b in a crimped condition. The balloon 10b is inflated for expanding the crimped stent 20 at the time of its implantation. As the intermediate portion 'D3' is tapered, the balloon 10b allows the expansion of the stent 20 in a tapered manner. The balloon 10b may be inflated by any conventional means known in the art such by passing buffer saline, etc.

[0045] The purpose of using such a tapered balloon 10b in the present invention is to expand the stent 20 in a tapered manner so that the stent 20 can mimic the physiology of the implantation site, say, tapered lesion in the coronary artery.

[0046] The stent 20 of the present invention may be made of any metallic material, without limitation, stainless steel (316LVM), cobalt chromium alloy (L605), etc. In an embodiment, the stent 20 is fabricated from a cobalt-chromium alloy which is widely used for manufacturing implants in the medical industry due to its shape memory and bio-compatibility property. Further, the use of cobalt-chromium alloy offers various advantages over other materials which include, without limitation, kink resistance, crush resistance, flexibility and high amount of recoverable deformation. The process of manufacturing a metallic stent 20 is provided in FIG. 3.

[0047] Alternately, the stent 20 may be fabricated from conventional bioresorbable polymers or biodegradable metals known in the art. The bioresorbable polymers may be selected from, without limitation, poly-L-lactide, poly-DL-lactide, poly-L-lactide-co-glycolide, poly-L-lactide-co- caprolactone or combination thereof. The biodegradable metals used for the present invention may be magnesium, iron or alloys thereof.

[0048] The stent 20 of the present invention includes features such as flexibility, vessel wall coverage, and deployment accuracy to ensure lesion coverage, etc.

[0049] As shown in FIGs. lb and lc, the stent 20 of the present invention includes an inner surface 20a (FIG. lc) and an outer surface 20b (FIGs. lb and lc). The inner surface 20a and the outer surface 20b of the stent 20 may be provided with a coating of a drug (as described below).

[0050] The inner surface 20a and the outer surface 20b both define an inner diameter as well as an outer diameter of the stent 20 respectively. The difference between the inner diameter and the outer diameter defines a strut thickness of the stent 20.

[0051] In an embodiment, the strut thickness of the stent 20 made from a metal and the stent 20 made of a bioresorbable material are different. The strut thickness of the metallic stent 20 ranges between 35 micron and 75 micron while the bioresorbable stent 20 may have a strut thickness of 80 micron to 130 micron.

[0052] The stent 20 further includes a proximal end 20c and a distal end 20d. The distance between the proximal end 20c and distal end 20d defines a length of the stent 20. In an embodiment, the length of the stent 20 may range from 30 mm to 60 mm. In an embodiment, the length of the stent 20 is 50 mm.

[0053] The length of the stent 20 impacts the radial strength of the stent 20. In an embodiment, for smaller length stents like 30 mm and 40mm, the radial strength ranges from 10 N to 65 N. Likewise, the radial strengths for longer length stents like 50 mm and 60 mm may range from 40 N to 90 N.

[0054] The proximal end 20c and the distal end 20d may have same or different diameter prior to implantation. In an embodiment, the metallic stent 20 as represented in FIG. lb, includes a uniform diameter from the proximal end 20c to distal end 20d. The diameter of the proximal end 20c and the diameter of the distal end 20d may range between 2.25 mm and 3.50 mm. In an embodiment, the proximal diameter 20c of the stent 20 is 2.75 mm and distal diameter 20d of the stent 20 is 2.25 mm.

[0055] On the contrary, as shown in FIG. lc, in the bioresorbable stent 20, the diameter of the proximal end 20c is greater than the diameter of the distal end 20d. Hence, the bioresorbable stent 20 includes a tapered design prior to implantation. In an embodiment, the bioresorbable stent 20 includes decremental diameters ranging from 0.5 mm to 1.0 mm from proximal end 20c to distal end 20d.

[0056] Post implantation, the metallic stent 20 as well as the bioresorbable stent 20 a tapered profile with the diameter of the proximal end 20c is greater than the diameter of the distal end 20d. Hence, the stent 20 tapers from the proximal end 20c to the distal end 20d and the taper of the stent 20 is selected from a range of 0.50mm to 1.00 mm.

[0057] As shown in FIG. Id, the stent 20 of the present invention includes a plurality of circumferential rows of struts 202 which are interconnected with at least one non-linear S link 204 and at least one Y connector 206. Though the description elaborates the use of non-linear S links 204 and Y connectors 206 in particular, other types of links and connectors may also be utilized for interconnection of rows of the present invention. The use of such links and connectors provide high flexibility to the stent 20 with adequate side branch access and uniform radial strength throughout the length of the stent 20.

[0058] Each circumferential row of struts 202 includes peaks and valleys and forms a crown. The numbers of crowns in the stent 20 may ranges from 4 to 12 depending upon the length of the stent 20.

[0059] In case two adjacently placed circumferential row of struts 202 are directly connected with each other without the use of any link 204 and/or connector 206 in a way such that the peaks of a first row of struts 202 contacting the valleys of the other row of struts 202, closed cells 208a are formed. Hence, it is evident from FIG. Id that the proximal end 20c and distal end 20d of the stent 20 include closed cells 208a.

[0060] Likewise, in case two adjacently placed circumferential row of struts 202 are connected with each other via one or more chains of links 204 and/or connectors 206, open cells 208b are formed. As evident from FIG. Id, the open cells 208b in the present invention are disposed at an intermediate region of the stent 20 between the closed cells 208a.

[0061] In an embodiment, S links 204 are used to form a linkage between two adjacently placed circumferential rows of struts 202 as clearly depicted in FIG. le. Two Y connectors 206a, 206b connect the ends of an S link 204 with a first circumferential row of struts 202a and as second circumferential row of struts 202b at a predefined position as evident from FIG. le. The predefined position may be any location between a peak and a valley. Therefore, the order of links 204 and connector 206 in the chain connecting the two adjacently placed circumferential rows of struts 202 in accordance with the depicted embodiment (FIG. le) is as follows:

1^st row of struts (202a) — l^st Y connector (206a) —

link (204) — ►2^nd Y connector (206b)

2^nd row of struts (¾)¾>)

[0062] The aforesaid combination of closed cells 208a and open cells 208b constitutes to be the hybrid design of the stent 20. The said hybrid design of stent 20 allows morphology mediated expansion of the stent 20 at the implantation site. The disposition of the closed cells 208a at proximal end 20c and distal end 20d of the stent 20 provide strength to the stent 20 when implanted in the tapering arteries. Likewise, the placement of the open cells 208b in the intermediate region of the stent 20 provides flexibility to the stent 20 when implanted in longer diffused lesions in the coronary arteries. Further, owing to the hybrid design of the stent 20, the expansion of the stent 20 does not include dog-boning which is a common effect in conventional stent designs. Also, such a hybrid design ensures minimal edge injury during the deployment and implantation of the stent 20.

[0063] The stent 20 may be coated with an anti-proliferative drug or a formulation of anti- proliferative drug as well as a polymer (or multiple polymers) as elaborated below.

[0064] The bench testing of stent 20 of the present invention post coating demonstrates a uniform radial strength across the entire length of the stent 20. Further, the stent 20 has a recoil less than 4% and foreshortening within ±1%. Moreover, the stent 20 was found to be free from cracks, scratches and change in stent geometry when expanded at rated burst pressure. [0065] The stent 20 as described above is crimped over the balloon 10b of the balloon catheter

10 and deployed within the patient's body. Once, the stent system 100 approaches the implantation site, the balloon 10b is inflated and the stent 20 is expanded to achieve a tapered profile. FIG. If illustrates the stent 20 implanted within the implantation site i.e. tapered coronary artery. Angiographic data suggests that the coronary arteries have approximately 0.50 mm to 0.99 mm taper. Hence, as taper of the implanted stent 20 (from proximal end 20c to distal end 20d) ranges from 0.50 mm to 1.00 mm, the stent 20 fully compliments the tapering coronary anatomy post implantation.

[0066] FIG. 2 shows the steps for fabrication of the balloon 10b using a polyamide tubing. At step 201, the polyamide tubing is subjected to a parison forming process using a double end stretcher machine to yield a parison tube. Various parameters such as temperature and pressure may be maintained for axially stretching the tubing from both ends during the aforesaid process. The temperature for the given process may range between 140° C and 170° C while the pressure may lie between 45 psi and 75 psi.

[0067] Post parison forming, at step 203, the parison tube is subjected to a process of stretch blow molding using a pre-defined mold 10b'. The mold 10b' may be made up of any metal known in the art that can withstand high temperatures and pressures during the stretch blow molding process. The mold 10b' in the present invention is made up of beryllium copper as shown in FIG. 2a. The mold 10b' includes a seamless inner surface with tapering edges so that a tapered balloon may be obtained after stretch blow molding process. [0068] In an embodiment, the stretch blow molding is executed in two phases. In the first phase, the parison tube is subjected to a temperature ranging between 50° C to 70° C and the medical grade nitrogen gas pressure is maintained between 20 bar to 40 bar. In the second phase, the temperature of the first phase is maintained while the nitrogen gas pressure is reduced and set between 15 bar to 25 bar.

[0069] Subsequently, at step 205, the molded tube is subjected to a heat setting process in order to enhance the shape memory of the balloon 10b. The temperature range at the time of heat setting process may be between 125° and 145° C. The mold 10b' is then subjected to immediate cooling by subjecting it to a temperature ranging between 15° and 25° C to obtain a tapered balloon.

[0070] The tapered balloon may then be subjected to an annealing process at step 207. In an embodiment, the annealing process is performed in a hot air oven at a temperature ranging between 55°C and 65°C for 1 hour to 2 hours. Following annealing, the annealed balloon may be cooled to room temperature to form the balloon 10b.

[0071] FIG. 3 illustrates the steps involved in manufacturing of the stent 20 made up of metal. In an embodiment, a cobalt chromium tube is used for manufacturing the stent 20. The diameter and wall thickness of the tube may be varied depending upon the desired characteristics of the stent 20 such as radial strength, flexibility, holding capacity, etc.

[0072] At step 301, the cobalt chromium tube of desired diameter is laser cut in a pre-defined configuration to obtain a laser cut tube. Alternately, other processes may also be followed to fabricate the stent 20. In an embodiment, the pre-defined configuration includes the hybrid structure i.e. a combination of open and closed cells as depicted in FIG. Id (as described above). The said hybrid structure of the stent 20 allows for the morphology mediated expansion of the stent 20.

[0073] Laser cutting of the cobalt chromium tube is conducted at pre-defined parameters, such as laser power setting, frequency, oxygen gas pressure, etc. The average laser power setting may range from 4 watts to 6 watts. The frequency may range from 4500 Hz to 7500 Hz. The oxygen gas pressure during the process may range from 7 bar to 11 bar.

[0074] Post laser cutting, the laser cut tube is subjected to descaling process to form a descaled stent 20 at step 303. The laser cut tube may be dipped in a descaling solution for removing the burrs and/or particles from the surface of the laser cut tube. The descaling solution used for the above purpose may be one of, purified water, nitric acid, hydrofluoric acid, sodium tetrafluoro borate, etc.

[0075] At step 305, the descaled stent may be annealed to remove hardness, increase ductility and to eliminate internal stress in the stent 20 to form an annealed stent. The annealed stent may be further subjected to electro-polishing process for removal of oxide layer formed over the descaled stent at step 307. Further, electro-polishing highly improves the finish of metallic stent 20. It is used to polish, passivate, and deburr metal parts from the surface of stent. The process of electro-polishing stent utilizes ethylene glycol solution. [0076] The stent 20 formed from the above process has a uniform diameter in the range of 1 mm to 2 mm. In an embodiment, the diameter of the stent 20 is 1.8 mm.

[0077] Optionally/additionally, the stent 20 obtained at step 307, may be drug coated at step 309. The stent 20 may be coated with an anti-proliferative drug or a formulation of anti proliferative drug as well as a polymer or multiple polymers. Such a coating may be executed by any method known in the art, such as spray coating, spin coating, electro-spin coating, rolling, painting, sputtering, vapor deposition, etc. The said coating may be performed on the inner surface 20a, outer surface 20b or both surfaces of the stent 20.

[0078] In an embodiment, a formulation of the anti-proliferative drug includes sirolimus and a mixture of poly DL-lactide co-glycolide and poly L-lactide. The formulation may include a drug polymer ratio of 35:65. Such a formulation may be prepared in any solvent known in the art such as without limitation, methylene chloride, chloroform, acetone, methanol and mixtures thereof. In an embodiment, the formulation is coated on the outer surface 20b of the stent 20 with a drug dose of approximately 1.0 pg/mm² to 1.5 pg/mm² of the stent surface area.

[0079] The thickness of the coated layer may be less than 7 pm. In an embodiment, the thickness of the coating is between 2 pm and 3 pm. The drug coating on the stent 20 helps in preventing initial thrombosis after the implantation of stent 20.

[0080] FIG. 4 depicts the process of fabrication of the stent 20 made up of biodegradable polymers/metals. At step 401, a bioresorbable stent is prepared using a known process as mentioned in Indian patent application number 201723000297. [0081] At step 403, the bioresorbable stent is subjected to deformation. Deformation in the present invention corresponds to gradual decrement in diameter from one end to other end of the bioresorbable stent. In an embodiment, deformation includes mounting the bioresorbable stent over a tapering mandrel and subsequently annealing the same. [0082] The mandrel used for the aforesaid process may be made up of any material known in the art that can withstand high temperatures under vacuum. The material may be without limitation, stainless steel, teflon or teflon coated stainless steel. The mandrel may include a tapering design thereby replicating the tapering anatomy of coronary arteries.

[0083] Annealing may be performed at a temperature ranging approximately between 90°C and 120°C for a time period ranging from 30 min to 20 hours. In an embodiment, vacuum of up to 650 to 700 mm Hg (absolute pressure of 60 - 110 mm Hg) is applied to remove monomers.

[0084] The bioresorbable stent is then cooled to ambient temperature in few seconds (20 sec to 10 minutes preferably between 30 sec to 2 minutes). The bioresorbable stent at this stage achieves the shape of the tapered mandrel with the decremental diameters ranging from 0.5 mm to 1.0 mm to form the stent 20 having adequate radial strength throughout its length.

[0085] At step 405, the stent 20 may be provided with a drug coating as elaborated in paragraph 72 and 73 of the present invention.

[0086] The aforesaid invention is now described with the help of the following examples:

[0087] Example 1: Two non-tapered overlapping stents having a length of 28mm each and diameter of 3.0mm each were implanted in very long coronary lesions and were studied for feasibility and safety. The pooled analysis from the said conventional non-tapered and overlapping stents in prospective multicenter trials demonstrated a target lesion failure rate of 8.9%.

[0088] Example 3: The stent 20 of the present invention with a hybrid design having combination of closed cell and open cells was implanted in very long coronary lesions and was studied for its feasibility and safety. The study involved implantation of the stent 20 having a length of 60 mm and a tapered stent diameter of 3.50 - 3.00mm (proximal to distal end) for treatment of diffused lesions having a length of < 56mm). A total of 255 patients were followed up to a duration of 12 months. At the end of 12 months, the cumulative incidence of target vessel failure was observed in 2 patients (i.e., 0.78%). Hence, the results at one year follow up demonstrated favorable clinical outcomes with a target lesion failure rate of 0.78%.

[0089] The above experimental data suggests that there is a considerable reduction in target lesion failure rate when the stent 20 of the present invention is implanted in very long and diffused coronary lesions.

[0090] 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 system (100) comprising: a balloon catheter (10) having a balloon (10b), the balloon (10b) including a tapered intermediate portion (D3), the intermediate portion (D3) disposed between a second proximal end (a2) and a first distal end (bl) of the balloon (10b); and a stent (20) including a proximal end, a distal end and a pre-defined length extending between the proximal end and the distal end, the stent (20) having a crimped state and a deployed state, the stent (20) being mounted over the tapered intermediate portion (D3) of the balloon (10b) in the crimped state with a guide-catheter compatibility of 5F; wherein in the deployed state, the stent (20) attains a tapered profile corresponding to the tapered intermediate portion (D3) of the balloon (10b); and wherein the tapered profile of the stent includes a taper from the proximal end (20c) to the distal end (20d).

2. The stent system (100) of claim 1 wherein the second proximal end (a2) includes a diameter ranging between 2.75 mm and 3.50 mm.

3. The stent system (100) of claim 1 wherein the first distal end (bl) includes a diameter ranging between 2.25 mm to 2.75 mm.

4. The stent system (100) of claim 1 wherein the balloon (10b) includes a length ranging between 20 mm-61 mm.

5. The stent system (100) of claim 1 wherein the pre-defined length of the stent may range between 30mm-60mm.

6. The stent system (100) of claim 1 wherein the stent (20) is coated with one of an anti proliferative drug, or a formulation of the anti-proliferative drug and at least one polymer.

7. The stent system (100) of claim 1 wherein the stent (20) comprising: a plurality of circumferential rows of struts (202) extending from the proximal end (20c) to the distal end (20d) of the stent (20); and at least one non-linear S link (204) and at least one Y connector 206, wherein the plurality of circumferential rows of struts (202) disposed at the proximal end (20c) and the distal end (20d) are directly connected with each other without the non linear S link(s) (204) and the Y connector(s) 206 to form a plurality of closed cells (208a), wherein two adjacent rows of the plurality of circumferential rows of struts (202) disposed at an intermediate portion of the stent (20) are connected with each other via multiple chains of connecters to form a plurality of open cells (208b), each chain of connectors includes a first Y connector (206a) followed by the non-linear S link (204) and a second Y connector (206b).

8. The stent system (100) of claim 1 wherein the stent system (100) includes a crimp profile ranging between 0.85 mm to 1.10 mm.

9. The stent system (100) of claim 1 wherein the stent system (100) includes a taper of the stent (20) is selected from a range of 0.50mm to 1mm.

10. The stent system (100) of claim 1 wherein the stent (20) includes a metallic stent having a strut thickness ranging between 35 micron and 75 micron.

11. The stent system (100) of claim 1 wherein the stent (20) includes a bioresorbable stent having a strut thickness ranging between 80 micron and 130 micron.