Abstract:
Method and device for manufacturing of expandable cylindrical metal meshes for use in expandable stents and in particular for customized manufacturing. The method includes determining the type and size of the stent to be implanted, electrochemically forming the stent with desired pattern of meshes and implanting the stent into patient. The method comprises using a cathode with desired pattern of meshes and a tubular blank, from which the stent is formed. Between the cathode and the blank is delivered an electrolyte and the cathode and the blank are simultaneously rotated during electrochemical forming process.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to the manufacture of expandable cylindrical metal meshes for use in expandable stents and in particular to the customized manufacture of expandable metal stents.  
         BACKGROUND OF THE INVENTION  
         [0002]    A cardiologist performing a stent implant procedure requires several stents of various geometrical shapes and lengths in order to be able to quickly choose an optimal stent during the surgery. Depending on the location and degree of damage being repaired, the cardiologist may need as many as eight different pattern stents with lengths ranging from about 6 mm to about 40 mm. During surgery, the cardiologist may have as little as five minutes to select the proper stent. Therefore, hospitals and clinics performing these procedures generally have a substantial number of stents on hand, perhaps as many as 40 or more, for use with a single patient. Given the relatively high cost of stents and their consumption, hospital and clinic expenditures on such operations may be substantial. As a result, many hospitals and clinics without adequate financial resources do not perform surgical procedures involving stent implantation.  
           [0003]    There exists, therefore, a need for a system that reduces the number of costly stents required during surgical procedures by allowing a surgeon or clinic staff to select and fabricate a custom stent during a surgical procedure and within a short period of time.  
           [0004]    Methods that have previously been used to manufacture stents are described in U.S. Pat. Nos. 4,856,516, 4,907,336, 5,116,365, 5,135,536, and 5,707,386. Stents produced by the methods disclosed therein contain bent wires that are knotted, which introduces stresses into the metal and decreases the quality of the stents. Moreover, these stents are not generally suitable for curved portions of blood vessels. More importantly, these methods only produce stents with a configuration that is tailored to a specific surgical instrument, limiting their usefulness. Other methods that have been used to manufacture stents are described in U.S. Pat. Nos. 5,725,548 and 5,907,893. Stents produced by the methods disclosed therein are joined along a line longitudinal to the length of the stent and then welded. However, at the high temperatures required to weld these joints, the crystalline structure of the metal can be affected and thereby reduce the reliability and strength of the stent and its compatibility in a biochemical environment.  
           [0005]    Still other methods of manufacturing stents are described in U.S. Pat. Nos. 4,383,896, 4,496,434, 5,030,329, 5,328,587 and 5,772,864. Stents produced by the methods disclosed therein are free from wire knots and welded joints. They are produced using an electrochemical process, which generally produces higher quality stents. However, the methods disclosed, most notably in U.S. Pat. No. 5,772,864, are complex and time consuming. For example, grooves outlining the stent must be etched on very small mandrels with instruments requiring precise control. Then, the cleaned mandrel must be dipped in an electrochemical bath containing a selected metal for up to approximately 12 hours. The stent material must then be carefully removed and further processed and polished. Because the entire process is costly and time consuming, it is not appropriate for use in a hospital or clinical setting during a shunting procedure.  
           [0006]    Still other methods of manufacturing stents are described in U.S. Pat. Nos. 4,733,665, 4,776,337, 5,421,955 and 5,514,154. Stents produced by the methods disclosed therein are made using laser technology to directly carve the geometrical contours of stents on tubular blanks. Manufacturing of stents by these methods is associated with formation of sharp edges and burrs on the outside and inside surface of the stent. This can affect the structure of the stent, thereby reducing its reliability. This also requires additional processing to remove these undesirable features. Moreover, the cost and complexity of this technology can limit its use in hospital and clinical settings.  
           [0007]    A solution to some of these problems is disclosed in U.S. Pat. No. 5,421,955, where laser technology is used to form a pattern on a mask material that is subsequently etched in an electrochemical process. However, this process requires complex instruments for precise laser control, an etching bath and solution, and extended processing time that may prohibit its use in a hospital or clinical setting.  
           [0008]    A proposed solution to the above mentioned problems is disclosed in U.S. Pat. No. 5,902,475 in which much of the stent processing may be carried out prior to its use in a surgical procedure, with the final processing done in the hospital or clinical setting. For example, a tubular blank is coated with a photoresistive polymer over a photo film that contains a stent pattern. It is mounted on a rotatable tube and exposed to ultraviolet rays, thereby creating a negative image of the stent. The film is developed such that the illuminated lines solidify. The film is then placed in an electrochemical bath and the non-illuminated surfaces dissolve. The steps of blank mounting and removing can require up to a total of approximately six minutes to accomplish. The step of transferring and immersing the blank in the electrochemical tank can require up to approximately ten minutes. The step of electrochemically removing the non-illuminated areas can require up to approximately six minutes, with the final step of polishing/processing taking up to approximately 3 minutes. In total, the process described in U.S. Pat. No. 5,902,475 takes about thirty minutes, limiting its usefulness during surgical procedures. Moreover, this process requires, for certain applications, use of cathode made from platinum, gold or their alloys to withstand the strong acidic electrolyte solutions, phosphoric or sulfuric acid. Additional processing steps to prepare the stent for subsequent use may also be required. It is apparent that the additional expense and hazards associated with this method prohibit its use in hospital or clinical settings.  
           [0009]    Stents produced by the methods described in U.S. Pat. Nos. 5,421,955, 5,772,864 and 5,902,475 rely on technology that prevents production of high quality stents. For example, the inner surface structure of the holes in the base stent tubes may be nonhomogeneous after the electrochemical treatment, e.g., includes sharp edges, protrusions, etc. Under certain conditions, the stent blank could become contaminated with impurities such as oxides or include other defects. Under these conditions, current supplied to the blank during processing would not be uniform. Further, an additional step is required to process the inner surface of the stent holes. Therefore, it would be desirable to apply the electric current to the external surface of the stent blank during processing rather than the inner surface.  
           [0010]    Additionally, the known manufacturing methods may require the use of a diamond dust polishing tool to treat not only the external surface of the final stent but also the internal surface area. This additional step adds to the cost and complexity of the manufactured stent.  
           [0011]    Accordingly, prior to the present invention, there have been no described methods of manufacturing stents: that allow surgical or clinical staff to fabricate custom stents as an integral part of the surgical procedure; that require relatively few complicated instruments or dangerous chemicals, that is relatively inexpensive; and that produces stents free from thermal stresses, sharp edges or surface irregularities.  
         SUMMARY OF THE INVENTION  
         [0012]    In accordance with the present invention, a method and device for manufacturing and implanting an expandable stent into a body lumen is carried out by electrochemically forming the expandable stent just prior to implantation. The electrochemical forming includes providing a cathode which includes a pattern for producing the stent; providing a tubular blank adjacent to the cathode; delivering an electrolyte between the cathode and the tubular blank; relative displacing the tubular blank and the cathode; and, electrochemically producing the stent with the stent pattern for subsequent implantation.  
           [0013]    Other features of the invention include using a tubular blank that has a diameter and thickness equal to the stent to be manufactured; cutting the ends of the tubular blank after the stent outline is formed; using a mandrel for receiving the tubular blank, in which the mandrel has a linear slit along its longitudinal length parallel to the tubular blank for the introduction of electrolyte and wherein the linear slit is narrower than the diameter of the tubular blank; removing an insulating coating on the cathode before electrochemically forming the stent; customizing the expandable stent according to the needs of a patient being treated; and implanting the stent into a body lumen.  
           [0014]    Still other features include electrochemically forming at a current density of about range 50 A/cm 2 , or more; delivering the electrolyte at a velocity of from 8 m/s to 10 m/s; and displacing the blank by centerless rotation.  
           [0015]    Also disclosed in a method of custom-forming an expandable stent in an operating or emergency room during a procedure to implant the stent into a body lumen of a patient, including providing a plurality of cathodes, at least some of which includes a different stent pattern, mounting the cathodes on a rotator; providing a plurality of tubular blanks, at least some of which includes a different material, diameter and thickness; selecting working cathode with a desired stent pattern; selecting a stent blank from the plurality of tubular blanks; mounting the stent blank in an operative relationship to the working cathode; rotating the rotator while delivering an electrolyte between the desired stent pattern and the stent blank to electrochemically form the stent having the desired stent pattern; and recovering and preparing the recovered stent for implantation into the patient&#39;s body lumen.  
           [0016]    Other features of the invention include using a mandrel for receiving the stent blank, in which the mandrel has a linear slit along its longitudinal length parallel to the stent blank for the introduction of electrolyte and wherein the linear slit is narrower than the diameter of the stent blank; removing an insulating coating on the plurality of cathodes before electrochemically forming the stent; electrochemical forming at a current density of about range 50 A/cm 2 , or more; cutting the ends of the electrochemically-formed stent outline; delivering the electrolyte at a velocity of from 8 m/s to 10 m/s; and rotating the tubular blank by centerless rotation.  
           [0017]    Also disclosed is an apparatus for custom-forming an expandable stent in an operating or emergency room during a procedure to implant the stent into a body lumen of a patient for implantation into a body lumen, which includes a rotator, for carrying one or more cathodes; a mandrel positioned parallel to the rotational axis of the rotator, for holding a tubular blank in operative relationship to the working cathode which is currently employed for custom forming; a conduit for delivering electrolyte to the working cathode and the tubular blank; means for simultaneously rotating the rotator and the tubular blank; and means for supplying electrical voltage to the working cathode and to the tubular blank to produce a stent.  
           [0018]    Other features of the apparatus aspects of the invention may include a grinding means for removing an insulating coating from the cathodes; means for separating the working cathode with the desired stent pattern and the tubular blank by a distance of not more than 0.05 mm; a mandrel with a linear slit directed parallel to the length of the tubular blank for the delivery of the electrolyte between the working cathode and the tubular blank and wherein the linear slit is narrower than the diameter of the tubular blank; one or more cathodes being made from a metal selected from the group consisting of gold, platinum, stainless steel, brass, copper, or alloys thereof; and a tubular blank that has a diameter and thickness equal to the stent.  
           [0019]    Another feature of the invention include a housing for containing therein the mandrel, the rotator, the tubular blank, the one or more cathodes, and the conduit and wherein the housing is positionable in an area substantially near a patient being treated for a stent implant.  
           [0020]    Still other features of the invention include a lateral support comprising two pairs of tubular rests, the pairs of tubular rests each containing longitudinal slits, for supporting the tubular blank in the mandrel in an operative relationship to the working cathode, and a means for self-aligning the mandrel in operative relationship to the working cathode.  
           [0021]    These and other objects, advantages and features of the invention will become better understood from a detailed description of the preferred embodiment of the invention, which is described in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    [0022]FIG. 1 is a schematic of a geometric pattern for a stent manufactured in accordance with the present invention;  
         [0023]    [0023]FIG. 2 is a detailed schematic of one cell of a cathode used for making the stent in accordance with the present invention;  
         [0024]    [0024]FIG. 3 is a schematic depicting the area of a metal blank that is removed to form the outline of a cathode used for making the stent in accordance with the present invention;  
         [0025]    [0025]FIG. 4 is a schematic showing a rotator carrying multiple cathodes for manufacturing of stents of the same or different patterns in accordance with the present invention;  
         [0026]    [0026]FIG. 5 is a schematic depicting the top view of a single cathode manufactured in accordance with the present invention;  
         [0027]    [0027]FIG. 6 is a partial cross-sectional view of the cathode depicted in FIG. 5.  
         [0028]    [0028]FIG. 7 is a cross-sectional view of the mandrel portion of the manufacturing apparatus of the present invention;  
         [0029]    [0029]FIG. 8 is a detailed schematic of the cross-section view of FIG. 7;  
         [0030]    [0030]FIG. 9 is a side and end view of the manufacturing equipment of the present invention;  
         [0031]    [0031]FIG. 10 is a broader cross-sectional view of the mandrel of FIG. 7;  
         [0032]    [0032]FIG. 11 is a plan-view (top) of the mandrel depicted in FIG. 7, FIG. 8 and FIG. 10;  
         [0033]    [0033]FIG. 12 is a cross-sectional view of the mandrel depicted in FIG. 10;  
         [0034]    [0034]FIG. 13 is another cross-sectional view of a mandrel according to the present invention;  
         [0035]    [0035]FIG. 14 is a cross-sectional view of the interface between the cathode of FIG. 4 and a mandrel according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0036]    [0036]FIG. 1 shows flat development of a cylindrical stent with an example of the pattern of an individual stent  100  manufactured in accordance with the present invention. The development of the stent  100  has a maximum length dimension, Lmax, and a maximum width dimension, which may be about 6.28 mm or wider. Shorter stent lengths may be produced by cutting along lines  3   a - 3   b ,  4   a - 4   b , or along any other line perpendicular to the length dimension of the stent.  
         [0037]    The stent  100  is prepared first by forming an outline of the stent  100  on a rounded or flat surface of a cathode metal plate  150  (FIG. 5). The material of the cathode may be gold, platinum, or alloys of the same, or stainless steel, brass or other copper alloys. The outline is created using one or more etching, drilling, photochemical, electroerosion or other process steps known in the prior art.  
         [0038]    [0038]FIG. 2 shows the result of this outlining step and the formation of individual stent cells defined by, stent bridges  7   a ,  7   b  and depressions  8  on the cathode metal plate. The bridges and depressions are made by removing material of cathode  150  at a depth of up to about 0.2 mm. This results in the formation of the outline band  9 , corresponding to the outline pattern of the stent  100 . This outline band after removal of the cathode material becomes a raised portion of the cathode metal plate  150 . The remaining lowered portions of the plate are filled with an insulating material, e.g. self-hardening resin.  
         [0039]    [0039]FIG. 3 shows an alternative process of forming the stent outline, for example, by drilling small holes  10  or by milling depressions  10 ′ of various sizes. If the size of the stent pattern is very small it is possible to form raising regions  8 ′, which are mirror representation of the stent outline.  
         [0040]    As shown on FIG. 4, once the cathode metal plate  150  is complete, it is mounted on the periphery of a rotator  200 . Other cathode plates  150 ′,  150 ″ . . .  150   n , selected by a system operator, may also be placed on the rotator  200 . Each cathode plate  150  . . .  150   n  may have the same or different stent pattern geometries. The cathode metal plate  150  is mounted tangentially to the rotator  200  such that the outline band pattern of the cathode metal plate  150  faces outward away from the center axis of the rotator  200 . An insulating coating S (FIG. 6) is applied to the surface of the cathode metal plate  150  before mounting it on the rotator  200 . The entire periphery of the rotator may then be ground, for example, on a circular grinding machine, as required, to remove excess insulating coating S and to ensure a uniform surface of each cathode. The insulating coatings, which can be used are known and need not be described herein.  
         [0041]    [0041]FIG. 5 shows the top view of the cathode metal plate  150 . Shorter length stents are formed by dividing the cathode metal plate  150  along the lines  3   a - 3   b ,  4   a - 4   b , etc. (FIG. 1) using one of more of the prior art methods mentioned above. Each shorter section of stent is electrically insulated from the others. They are individually secured to an insulating base  18  by use of conductive fasteners  19 , such as metal screws, which conduct current to that portion of the cathode metal plate  150 . The entire cathode metal plate  150  is secured to the insulating base  18  by pins K and L which extend through contact base end areas A and B and provide the electrical contact for the cathode metal plate  150 .  
         [0042]    Also as shown in FIG. 5, only a portion of the cathode metal plate  150 , with dimensions D×Lmax, contains the stent outline  9 . The rest of the plate  150 , with dimensions E×Lmax, is blank, except for the metal lead bands  14 ,  15 ,  16  and  17  (the number depending on the number of shorter stent lengths desired). These leads are formed in the same manner as the rest of the stent, using one or more of the prior art methods used to form stent outline  9 . The lead bands initiate from slots  20  cut in the cathode plate  150  along lines  3   a - 3   b ,  4   a - 4   b , etc. The slots are filled with electrically insulating material, e.g., self-hardening resin.  
         [0043]    It will be explained further in more details that final cutting of the stent blank can be performed electrochemically by supplying current through slots  20  to the selected lead bands of the cathode plate. This is possible since each shorter length section of the cathode plate may have its own autonomous current supply.  
         [0044]    [0044]FIG. 6 shows a partial cross-section of one-half of the cathode metal plate  150  cut at centerline O-O (FIG. 5). A thin pipe, called a stent blank  250 , from which the stent  100  is formed, is placed on the surface of the cathode metal plate  150 . The stent blank  250  is contained within a hollow mandrel, which is described in more detail below. The blank  250  is positioned within the mandrel in such a manner that it contacts the cathode at insulated base end areas A and B (FIG. 5). The rest of the blank is separated from the cathode stent outline  9  by space  11 , which is approximately 0.05 mm. The distance separating the cathode metal plate  150  and the stent blank  250  depends on the specific electrolyte that will be used during stent processing and the current strength, but should be about 0.05 mm. To ensure proper spacing, insulating base end areas A and B are electrically monitored by supplying to them a weak current; the position of the stent blank  250  is adjusted according to the electrical signal received. FIG. 6 also shows how the slots  20  extend above the insulating base  18 .  
         [0045]    [0045]FIG. 7 shows the tubular stent blank  250  contained within a hollow mandrel  318  (FIG. 9). It should be understood that the rotator  200  (FIG. 4) is located to the left of the mandrel  318  adjacent the outwardly facing portion of the mandrel. It should also be appreciated that the rotator  200  carries cathode plates  150 ,  150 ′,  150 ″, etc., and one of the cathode plates is brought in the working position opposite the stent blank  250 . The mandrel  318  contains a longitudinal slit  20 ′ having width W. By virtue of this provision the electrochemical treatment is localized to the area exposed by the slit. The width W is determined by stent blank diameter, minimal inter-electrode clearance, possible non-linearity of the stent blank  250  and other factors.  
         [0046]    The mandrel  318  includes an electrically non-conducting casing  23  which can be TEFLON® or any other conventional non-conductive material. A metal bushing  22  is positioned within casing  23 . Casing  23  extends a distance h, which is about 0.1 to about 0.2 mm, beyond metal bushing  22 . While this distance is not shown in the other drawings for simplicity purposes, it should be mentioned that a separation distance is provided to prevent contact between the metallic bushing  22  and the electrolyte and thus the condition where the metallic bushing  22  is worked out during the electrolytic process.  
         [0047]    The stent blank  250  is inserted into a hole  319  formed in the metal bushing  22 . Two metal rests  24  and  25  are tightly positioned into the hole  319  to support opposite sides of the blank. The rests are made with longitudinal cuts Q (FIG. 8) to provide elasticity and may be tubular (circular cross-sections), flat elastic springs, or other suitable devices for supporting the stent blank. Rests  24  and  25  press the stent blank  250  against the longitudinal slit  20 ′ to ensure that the blank is in contact with areas A and B of the cathode plate. At the same time, rests  24  and  25  supply electric power to the stent blank  250  from the positive pole of a power source  26 ′ (FIG. 7) through one or more of screw  26  into the bushing  22 . In this manner, electrical current is supplied to both sides of the tubular stent blank  250  simultaneously.  
         [0048]    As soon as the stent blank  250  is properly mounted, forcible rotation of the blank and of the rotator begins. Both the rotator  200  (FIG. 4) and the stent blank  250  are simultaneously rotated by use of a drive and guide roller, as discussed below. By virtue of simultaneous rotation the blank revolves with respect to the cathode plate without slippage on areas A and B.  
         [0049]    [0049]FIG. 8 shows the stent blank  250  contained within the hollow mandrel  318  in contact with cathode plate end areas A and B. During processing, the rotator  200 , with its attached cathode plate  150  and tubular blank  250 , are rotated simultaneously in the direction shown by arrows, such that the stent blank  250  makes two consecutive revolutions. An electrolyte is supplied under pressure between the stent blank and cathode plate for electrochemical processing, as explained hereinafter in greater detail. During the first revolution the stent pattern (FIG. 1) is electrochemically formed. During the second revolution, current is supplied to those lead bands of the cathode plate, which define the required length of the stent and thus its lateral ends are electrochemically cut from the stent blank. Because processing is restricted to the narrow opening slit  20 ′, a high current of about 50 A/cm 2  or greater can be used, the dynamic effect of electrolyte upon the stent blank  250  is minimized, and ionization scattering is reduced, thus minimizing distortion of the stent blank  250 . Further, the distance between the cathode outline bands,  27 , 28 , and the stent blank  250  is equal, that is, distance a-b is approximately the same as the distance c-d, as shown. This distance may be electrically monitored for precise control during fabrication of the stent  100 . Monitoring this separation distance reduces the possibility of short circuits between the cathode metal plate  150  and stent blank  250 .  
         [0050]    Also as shown in FIG. 8, the slit  20 ′ in the mandrel  318  restricts the emergence of the tubular stent blank  250  out of the mandrel  318  even where the stent blank  250  is substantially non-rectilinear. Similarly, in the course of the stent blank  250  processing, the slit prevents short circuits, which can reduce the cathode strength and rigidity. This would, therefore, prevent a decrease in the rigidity of the stent  100 .  
         [0051]    As previously mentioned, both the rotator  200  and the stent blank  250  rotate by use of a dedicated drive (not shown) and a guide roller  30 . As shown in FIG. 8, displacement of stent blank  250  with respect to mandrel  318  is restricted by the cathode metal plate  150  at a line m-n between contact areas A and B, and at points of contact F 1  and F 2  between the stent blank and rests  24  and  25 , respectively. Centerless rotation of the stent blank  250  is ensured by guide roller  30  driven by the drive, which rotates rotator  200 . The centerless rotation of the stent blank  250  eliminates the need for additionally cleaning and processing the internal surface of the stent after electrochemical treatment.  
         [0052]    Excess current load on stent bridges  7   a , 7   b  (FIG. 2), which may increase the temperature of the material at this location to an undesirable level, should be minimized. On the other hand, when stent processing begins, the maximum possible technological current can be supplied to the stent blank  250 . A computer  322  (FIG. 9) is used to maintain the current density at a rated value based on the selected stent configuration and length parameters. During processing, as soon as the section of the stent blank  250  is reduced to the point where it is necessary to reduce the current, and, consequently, to decrease the metal removal rate, the computer  322  reduces the rate of angular motion of the blank  250  (that is, the rate of approach of points a-b). As a result, the radial feed decreases, thus reducing the current load on the stent bridges.  
         [0053]    [0053]FIG. 9 shows the stent manufacturing apparatus  300 . During processing, pump  304  delivers electrolyte from tank  302  to mandrel  318  and into the spacing between the cathode metal plate  150  and the stent blank  250  at a velocity of about 8 to about 10 m/s. Although weak electrolytes, such as, NaCl, NaNO 3 , FeCl 3  solutions are preferred, other known electrolytes may be used. As a result, it is not necessary to use a cathode made from gold or platinum; rather, less expensive materials such as stainless steel, brass or other copper alloys may be used. Although not shown in FIG. 9, electrolyte conditioning means well known in the art may also be included.  
         [0054]    Also shown in FIG. 9, the apparatus includes a insulation flange  308  on which rotator  200  is mounted with removable insertions  310  carrying cathode metal plates  150 ,  150 ′ . . .  150   n  with outline patterns of various configurations. Also included are a rotation drive  312 , electrolyte tank  302 , pump  304 , electrolyte filtration unit  316 , mandrel  318 , casing  320 , with an opening  321  for reloading the mandrel  318 , computer (conventional)  322  and interface board  324 . Rotation drive  312  is capable of simultaneous rotating both the guide roller  30  and rotator  200 . Mandrel  318  is mounted in the roller casing  320  through the opening  3210  when it is turned to a position parallel to the O-O centerline.  
         [0055]    An operator must enter only two parameters into the digital computer  322  to produce a custom stent: the number of the cathode metal plate  150  (FIG. 5) on the rotator  200  (which identifies its position relative to the other cathodes and its particular outline pattern) and the required stent length. As mentioned above, the computer  322  monitors electrical current load to the stent blank  250  and electrolyte temperature. As material is removed from the stent blank  250  during operation, the computer  322  reduces the angular velocity of rotation of the stent blank  250  and decreases the current load on the stent blank  250  as the stent is being formed.  
         [0056]    [0056]FIG. 10 shows the mandrel  318  of the present invention in more detail. Prior to processing, the stent blank  250  is inserted into the hole  319  of metal bushing  22 , which is part of the mandrel  318 . Rigid spring  406  is provided for pressing mandrel  318  towards the cathode during operation. By virtue of this provision it is ensured that the blank always contacts cathode areas A and B. At the same time the spring is in electrical contact with a screw  314 , which touches rests  24 , 25  and thus positive voltage can be supplied from the source  26 ′ to the blank via screw  314  and rests  24 , 25 . It is seen also in FIG. 10 that forward portion of the mandrel casing which faces the cathode is configured with a cavity P. Into this cavity electrolyte is pumped under pressure from the tank  302  for carrying out the electrochemical process. FIG. 11 shows a partial plan-view (top) of the mandrel  318 . The stent blank  250  is mounted on rests  24  and  25  (FIG. 10), which were described above as two short metal tubes with longitudinal slits Q (FIG. 8). Rests  24 ,  25  are secured to the metal bushing  22  (FIG. 10). Ends  321 ,  323  of lateral surfaces C and D of the mandrel case are pressed against cathode metal plate contact areas A and B ensuring a constant inter-electrode clearance along the entire length of the stent blank  250  (FIGS. 5 and 8).  
         [0057]    [0057]FIG. 12 shows a cross-section of the mandrel  318  at surface A-A (FIG. 10), showing the relative positions of the metal bushing  22 , non-conductive casing  23 , rests  24  and  25 , stent blank  250  and cavity P.  
         [0058]    [0058]FIG. 13 shows a view of the mandrel  318  along with rotator  200 . Prior to processing the stent blank  250 , fingers of a robotic gripping device through openings d 1  and d 2  retain the mandrel  318 , already loaded by the tubular stent blank  250 . The robotic gripping device introduces the mandrel through opening  3210  into insulation flange  308  of the stent manufacturing apparatus  300 . Screw  402  is secured over a fixed electro-insulated strip  404 . Power is supplied through screw  402  and rigid spring  406 , strip  404 , screw  314  (FIG. 10) and lamella  31  to bushing  22  and through rests  24  and  25  (FIG. 10) to the stent blank  250 . The casing of mandrel  318  is configured so that its cathode adjacent end has a radius, R, equal to the radius of the rotator  200 . FIG. 13 also illustrates cavity P where electrolyte is introduced to enable establishing of electrochemical process between the cathode metal plate  150  (FIG. 4) and stent blank  250  (FIG. 10).  
         [0059]    [0059]FIG. 14 shows the mandrel  318  seated inside the hold-down roller casing  320 . In this configuration, the mandrel is fixed by a flat semi-spherical spring  407  secured on stationary plate  408 . This allows the mandrel  318  to self-align with respect to axis Z. Consequently, mandrel ends  321 ,  323  are forced against the cathode metal plate  150 , regardless of the geometric irregularities of the stent blank  250  (e.g., non-linearity of the generating line, etc.). The ends  410 ,  412  of casing  320  are encircled by elastic friction binding bands  414  to provide for reliable rotation on two sides of the stent blank  250  when driven by roller  30 . Additionally, longitudinal slit  20 ′ provided in mandrel  318  restricts the hydrodynamic effect associated with electrolyte pressure on the stent blank  250 . In this way, the electrochemical process is concentrated only in the area of slit  20 ′.  
         [0060]    It is to be understood that the invention is not limited to the exact details of construction, operation, exact materials or embodiments shown and described, as obvious modifications and equivalents will be apparent to one skilled in the art. Accordingly, the invention is therefore to be limited only by the scope as set forth in the claims.