FORM 2

THE PATENTS ACT  1970
(39 OF 1970)

COMPLETE SPECIFICATION
(Section 10  Rule 13)

TITLE
ELECTRO-POLISHING TOOL FOR IMPLANT DEVICES

Name : M/s. Relisys Medical Devices Limited

Nationality : Indian Company

Address : Survey No.312  Pocharam Road 
Mangalpally Village  Ibrahimpatnam Mandal 
Ranga Reddy District  Andhra Pradesh  INDIA

The following specification particularly describes the invention and the manner in which it is to be performed:-

FIELD OF THE INVENTION

The present disclosure relates to provide a smooth surface of metallic prostheses that are configured for implantation and deployment in a body cavity. Specifically  the application is directed to electro-polishing to medical stents and a small tubular small prosthesis  in particu-lar intravascular stents  the disclosure is not limited to such medical products.

BACKGROUND OF THE INVENTION

The fact that stents are widely accepted and used in the cure of coronary occlusions in to-day""s angioplasty is well known. Stents are reticular metal prostheses positioned in the portion of the vessel subject to stenosis  which remain at the site of the lesion after the release system and balloon system have been retracted. Thus the stent compresses the plaque and provides a mechanical support for the vessel wall to maintain the vessel diameter re-established by expansion of the balloon and to prevent collapse of the vessel. However  the long-term efficacy of the use of intracoronary stents still presents the major problem of post-angioplasty coronary instent restenosis  which is the phenomenon of reocclusion of the coro-nary vessel.

The stent may be  for example  a sandwich of metals having outer layers of a biocompatible material  such as stainless steel  with an inner layer providing the radiopacity to the stent for tracking by imaging devices during placement. A stent made of such material may be  for example  a thin layer of titanium between layers of stainless steel. In forming such stents from metal  a roughened outer surface of the stent may result from the manufacturing process. It may be desirable for the surface of the stent to be smooth so that it may be more readily in-serted and traversed with reduced friction through the blood vessels or other body lumens toward the site of implantation. A rough outer surface may not only increase frictional ob-struction  but may also damage the lining of the vessel wall during insertion. Furthermore  smooth surfaces may reduce thrombus formation and/or corrosion.

Electro-polishing is an electrochemical process by which some of the surface metal may be electrolytically dissolved. In general  the metal stent serves as an anode and is connected to a power supply while immersed in an electrolytic solution having a metal cathode connected to the negative terminal of the power supply. Current therefore flows from the stent  as the anode  causing it to become polarized. The rate at which the metal ions on the stent are dis-solved may be controlled by the applied current and/or voltage. The positioning of the cathode relative to the stent may provide an even distribution of current to the stent. According to the theory of electro-polishing  the current density is typically highest at high points protruding from a surface and is typically lowest at the surface low points. Thus  the higher current density at the raised points may cause the metal to dissolve faster at these points  which may level the surface. Electro-polishing therefore may smooth the surface  even to the point where it is shiny and reflective.

One application in which electro-polishing is particularly useful is for finishing endovascular stents and other medical implants. Medical implants require exceptionally smooth surfaces since any rough edges may cause tissue irritation during or after being implanted into a per-son""s body. Some of the medical problems that may be encountered when rough edges are not properly removed from a medical implant include inflammation  bleeding and/or scarring of the surrounding tissues. In the case of endovascular stents  such conditions can be partic-ularly harmful and dangerous. For example  one risk that may result from the use of stents with rough edges is restenosis. Restenosis refers to the re-narrowing of a vessel which sometimes occurs after balloon angioplasty procedures. Although restenosis may occur for a number of reasons  tissue irritation and disturbance caused by rough edges on a stent may be one cause of restenosis.

Various apparatuses for electro-polishing stents have been tried. One such apparatus involves wrapping a platinum wire (i.e.  the anode) around the outer surface of the stent. The stent is then lowered into an electrolytic both in a horizontal orientation (i.e.  with the two ends of the stent being positioned at approximately the same height above the bottom of the bath). The cathode is formed as a single horizontal loop that surrounds the stent (i.e.  the loop defines a plane that is approximately parallel to the bottom of the bath).

The process of electro polishing is achieved by applying a voltage  or potential difference  be-tween a device to be polished (such as a stent) acting as an anode  and a cathode while both the anode and the cathode are submerged in a conductive electrolyte bath. This arrangement permits current to flow from the stent as anode  through the electrolyte  to the cathode. When the parameters are adjusted properly  this process removes metal ions from the surface of the stent in such a manner as to smooth the surface to a mirror finish.
Thus there is a need in the art for a system and method to overcome the above described shortcomings in the art  by which the disadvantageous effects of preferential electro polishing may be reduced. The present invention addresses these and other needs.

The present disclosure provides a tool used for electro polishing a metallic device made from a metal alloy more particularly a medical implant such as stents simultaneously to consistently produce smooth surfaces.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a tool for electro-polishing the medical implants such as stents  the electro-polishing apparatus may include a cathode formed of a tubular rod and an anode formed by the stent with tool to be electro polished; an electrolytic solution; both the tubular rod and the medical stent are positioned within an elec-trolytic solution and current is passed through the anode to effect the electro polishing process  wherein the said tool is made of titanium alloy and titanium wires of which the tita-nium alloy rod is grinded at the edge and a hook bend made at the said grinded edge. Further  two titanium alloy rods are fixed with the titanium wires. In addition  the apparatus provides a more uniform polishing of the stent.

The present invention is directed to an apparatus for electro-polishing a medical stent utilizing a novel cathode design. More specifically  the new and improved cathode is used to substan-tially or completely surround a metallic device  which is the anode  and provide a more uniformly electro-polished surface. By substantially surrounding the medical stent being elec-tro-polished  substantially all exposed surfaces of the stent are electro-polished. Further  the cathode does not need to completely surround the stent  neither radially or longitudinally.

The invention is directed to an improved product or device  such as a stent  formed from a metal alloy which possesses an ultra-smooth shiny exterior surface. This invention is also directed to an apparatus for electro-polishing such a stent using an acidic electrolytic solution to produce an exceptionally smooth surface. This invention also contemplates use of a com-position of the electrolytic solution that serves to produce the ultra-smooth surface.

In keeping with the invention  an apparatus is provided  along with a process  for electro-polishing a device made from a metal alloy. More particularly  the electro-polishing apparatus includes a cathode and an anode submerged in an electrolytic solution for the purpose of removing metal from the surface of the metal alloy. The cathode design is intended to sub-stantially surround the anode  which is the device made from the metal alloy  to remove metal from all exposed surfaces.

In one embodiment  a wire coiled in a spiral or helix configuration is submerged in a container of an electrolytic solution. The device  for example  an intravascular stent is the anode and is positioned within the coil and a current is applied from the anode  polarizing it  and thus encouraging metal ions of the stent to diffuse through the solution to the cathode. As the metal ions from the stent continue to diffuse  the surface irregularities diminish such that  after a predetermined time period  the surface of the stent becomes ultra-smooth and shiny. Importantly  all of the exposed surface areas of the stent  including the outer and inner sur-faces of the stent are polished smoother than a stent polished using conventional methods of electro-polishing. It is important for the outer tubular surface and the inner tubular surface of the stent to be smooth  since the outer surface contacts the vessel or arterial wall  and the inner surface is in contact with the blood flowing through the vessel or artery.

Other features and advantages of the invention will become apparent from the following de-tailed description  taken in conjunction with the accompanying drawings  which illustrate  by way of example  the features of the invention.

Additional details and advantages are further described below.

These and other objects and features of the present disclosure will become more fully ap-parent from the following description and appended claims  or may be learned by the practice of the disclosure as set forth hereinafter.

DEFINITIONS

As used herein throughout  the term "comprising" means that other steps and ingredients that do not affect the final result can be added. This term encompasses the terms "consisting of" and "consisting essentially of".

The term "method" or "process" refers to manners  means  techniques and procedures for accomplishing a given task including  but not limited to  those manners  means  techniques and procedures either known to  or readily developed from known manners  means  tech-niques and procedures by practitioners of the chemical  pharmacological  biological  bio-chemical and medical arts.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the figures  the present invention specification discloses various embodi-ments of systems and methods for electro polishing metal prostheses having features of the present invention

FIG. 1 is a sectional view of a system known in the prior art for electro-polishing stents.

FIG. 2 is a schematic diagram of the electro-polishing apparatus of the present invention

DETAILED DESCRIPTION

The invention is herein described  by way of example only  with reference to the accompany-ing drawings. With specific reference now to the drawings in detail  it is stressed that the par-ticulars shown are by way of example and for purposes of illustrative discussion of the pre-ferred embodiments of the present invention only  and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard  no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention  the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

Turning now to the problem that is noted above with reference to FIG. 1  which figure dis-closes a known method of electro-polishing in an electrolyte solution: FIG. 1 shows how a cathode 100 in the form of a cylindrical tube may be used to surround a stent 111 having an-odic charge during an electrolytic polishing process. Typically  the cathode of this kind is made of a wire mesh  in particular platinum-iridium alloy. The stent is supported by a holder element 102 which is anodically charged  and positioned to hold the stent 111 in an electrolyte solution 104 in a container 106. The holder element 102 may comprise a blade portion 103 for supporting the stent  and a connector portion 105 for connection to a current source. A current source 110 is provided to charge the anode and cathode. As noted above  the stent 111 may require to be manually removed from the electrolyte and rotated end over end be-tween polishing sessions before being repositioned on the blade 103 in order to give it a more evenly polished surface from one end to the other. This requirement for manually reorienting the stent 111 presents a problem in that it is time consuming  it exposes the user to corrosive electrolyte  and it may result in stent damage by accidental manual action.

In an embodiment of the invention  and with reference with FIG. 2  electro-polishing apparatus 200 is described wherein  the electro-polishing apparatus is made of titanium alloy rods 202 and titanium wires 201  the titanium alloy rod 202 is grinded at the edge and a hook bend (202 a) is made at the grinding area which holds the medical implant/ stent 203 in a electrolytic solution 204 The said rods are fixed with titanium wires as depicted in FIG.2.

Further  the titanium rods with the wires acts a tool for holding the stent or medical implants which in turn is connected to titanium gripper (not shown) which connects to the anode post of the machine. (not shown)  the said titanium rods forms the base and the titanium wires which is varied with the varying dimensions of the medical implants to get the better conductivity and ultra-smooth surface and further the number of turns and dimension of the wire used is varied with the varying dimensions of the medical implants to get the ultra-smooth surface.

A special feature of electro-polishing is the creation of current differentials across the micro-scopic surface of the anode. The current density is greatest at high points on the surface and lowest at the low points. The rate of the electrochemical reaction is directly proportional to the current density so that increased current density at the raised points causes the anodic metal to dissolve faster at these points thus levelling the surface material. The smoothed surface of many metals can  with sufficient electro-polishing techniques including use of the proper electrolytic solution  be made sufficiently smooth to an extent as to become shiny and reflective. The finish may also be dependent on the level of current applied  the duration of applied current  and the temperature of the electrolytic solution.

In preparation for the electro-polishing of the stent 203  the electrolytic solution 204 is pre-pared. While under a vented hood  and at standard conditions  10 ml of 37% concentrated hydrochloric acid (HCl) is poured into a 50 ml beaker or container. 30 ml of 98% concentrated sulphuric acid (H.sub.2 SO.sub.4) is then poured gradually into the HCl at a rate of about 1.5 ml per second to prevent a violent reaction. Both acids  whether individually or as a mixture  are extremely corrosive. Contact with skin or tissue  whether through liquid spill or in the form of exposure to fumes  can be severely injurious. Appropriate safety gear should be employed when handling and disposing of such acids.

The electro-polishing procedure employing the solution of the present invention removes ma-terial from the stent surface to provide an ultra-smooth and shiny surface. Electro-polishing also provides a protective corrosion-resistant oxide layer on the stent surface.

As is the nature of many parameters of various processes  parameters of the electro-polishing process may be altered by degree to provide similar results. It is the intention to include such modification  within the scope of the invention  and as is known in the art  of time  temperature  humidity  pressure  voltage  current  cathode material  cathode dimension  degree of descaling  rinsing  polishing/solution chemicals  size and material composition of the medical device or stent  as well as other variable parameters not heretofore mentioned.

The embodiments heretofore discussed are in no way intended to limit the scope of the in-vention. Various changes and improvements may also be made to the invention without de-parting from the scope thereof.

It is appreciated that certain features of the invention  which are  for clarity  described in the context of separate embodiments  may also be provided in combination in a single embodi-ment. Conversely  various features of the invention  which are  for brevity  described in the context of a single embodiment  may also be provided separately or in any suitable sub combination.

This invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law.

CLAIMS
I/ We claim:

1. An apparatus for use in electro-polishing a stent  comprising: a cathode formed of a tubular rod and an anode formed by the stent being positioned with tool to be electro polished; a container for retaining an electrolytic solution; both the tubular rod and the tool are positioned within an electrolytic solution and current is passed through the anode to effect the electro polishing process  wherein the said tool is made of plurality of titanium rods and titanium wires positioned for removably retaining the stent .
2. The apparatus of claim 1  further comprising providing a positive electric current to the cathode and providing a negative electric current to the anode.
3. The apparatus of claim 1  wherein the distal end of the plurality of titanium rods is configured with a hook for removably retaining the medical stent.
4. The apparatus of claim 1  wherein the stent is made from a metal alloy taken from the group of metal alloys including stainless steel  cobalt-chromium  cobalt-chromium-tungsten  nickel-titanium  titanium  tantalum  and tungsten.

Dated this 06th day of January  2012.

ABSTRACT

5. The present invention relates to a apparatus for use in electro-polishing a stent  comprising: a cathode formed of a tubular rod and an anode formed by the stent being posi-tioned with tool to be electro polished; a container for retaining an electrolytic solution; both the tubular rod and the tool are positioned within an electrolytic solution and current is passed through the anode to effect the electro polishing process  wherein the said tool is made of plurality of titanium rods and titanium wires positioned for removably retaining the stent .