WO2024137334A2

WO2024137334A2 - Smoothing technique for perforated parts by means of magnetically circulating particles

Info

Publication number: WO2024137334A2
Application number: PCT/US2023/084023
Authority: WO
Inventors: Hitomi Greenslet; Julian LONG; Hiroyuki Matsumura; Chen Kai Hsu
Original assignee: University of Florida; University of Florida Research Foundation Inc
Current assignee: University of Florida; University of Florida Research Foundation Inc
Priority date: 2022-12-23
Filing date: 2023-12-14
Publication date: 2024-06-27
Anticipated expiration: 2025-06-23
Also published as: WO2024137334A3

Abstract

Various examples are provided related to polishing of stents or other perforated parts. In one example, a method includes supporting a perforated workpiece on a rod by wires extending along and about the rod; positioning a pole tip adjacent to the workpiece where a magnetic field extends from the pole tip to the rod through the workpiece; providing a mixture including magnetic particles, abrasive and lubricant between the pole tip and workpiece and supported by the magnetic field; and rotating the workpiece by rotating the rod, where surfaces of the workpiece are polished by circulation of the mixture. In another example, a polishing system includes a workpiece holder including a rod configured to axially support a perforated workpiece; a pole tip for positioning adjacent to the workpiece that can provide a magnetic field that extends through the workpiece to the rod; and a workpiece drive that can rotate the rod.

Description

SMOOTHING TECHNIQUE FOR PERFORATED PARTS BY MEANS OF MAGNETICALLY CIRCULATING PARTICLES

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to, and the benefit of, co-pending U.S. provisional application entitled “Smoothing Technique for Perforated Parts by Means of Magnetically Circulating Particles” having serial no. 63/434,984, filed December 23, 2022, which is hereby incorporated by reference in its entirety.

BACKGROUND

[0002] Coronary artery disease is caused by plaque forming on the inner walls of troubled blood vessels, thus reducing the flow of blood, oxygen, and nutrients through the body. In order for the blood vessels to expand and allow normal flow again, metallic stents are placed within the troubled blood vessels. The metallic stents are designed to be surgically placed within the blood vessel and then are expanded to hold the inner walls of the blood vessel at a fixed diameter, allowing the blood vessel to heal around the stent thus healing the blood vessel. The effectiveness of the stents depends upon the surface finishing of the stent.

[0003] Manufacturing of a mesh stent starts with metallic alloy ingots produced from raw materials. The metallic alloy ingots are initially prepared through induction melting and solution heat treatment. After being prepared the metallic alloy ingots are cut into cylindrical billets. Through a process of repeated cutting and hot extrusion of the cylindrical billets, thinwalled tubes are formed. The thin-walled tubes go through an annealing process followed by cold drawing. Use of a fixed wire mandrel in the cold drawing process increases the accuracy and consistency of the stents' diameter and thickness. Lastly, the tubes are laser cut to form mesh stents. During the manufacturing process of a stent, unevenness forms on all of the surfaces of the stent. The unevenness is in the form of burrs, pits, and semicircular grooves. SUMMARY

[0001] Aspects of the present disclosure are related to polishing of stents or other perforated parts. In one aspect, among others, a method comprises supporting a perforated workpiece on a rod that extends axially through the perforated workpiece, the perforated workpiece supported by a plurality of wires extending axially along the rod, the plurality of wires distributed about the rod thereby spacing the perforated workpiece away from the rod; positioning a pole tip adjacent to and extending over at least a portion of the workpiece where a magnetic field extends from the pole tip to the rod through the perforated workpiece; providing a mixture comprising magnetic particles, abrasive and lubricant between the pole tip and the workpiece, the magnetic field supporting the mixture; and rotating the perforated workpiece by rotating the rod, where external, internal, and sidewall surfaces of the perforated workpiece are polished by circulation of the mixture during rotation of the perforated workpiece. In one or more aspects, the pole tip can be axially oscillated during rotation of the perforated workpiece. Oscillation of the mixture across the perforated workpiece can be produced by movement of the pole tip. The perforated workpiece can be a flexible tubular workpiece or a straight tubular workpiece. The perforated workpiece can be a stent. In various aspects, a mixture cap can extend from a side of the pole tip over the perforated workpiece. The mixture cap can be a nonmagnetic cap or can be a magnetic cap.

[0002] In another aspect, a polishing system comprises a workpiece holder comprising a rod configured to axially support a perforated workpiece, the perforated workpiece separated from the rod by a plurality of wires distributed about the rod and extending axially along the rod, the plurality of wires thereby spacing the perforated workpiece away from the rod; a pole tip configured to be positioned adjacent to and extending over at least a portion of the workpiece, the pole tip configured to provide a magnetic field that extends from the pole tip to the rod through the perforated workpiece, where the magnetic field supports a mixture comprising magnetic particles, abrasive and lubricant positioned between the pole tip and the workpiece; and a workpiece drive configured to rotate the rod, where rotation the perforated workpiece by the rod polishes external, internal, and sidewall surfaces of the perforated workpiece by circulation of the mixture. In one or more aspects, the pole tip can be configured to axially oscillate during rotation of the perforated workpiece. Oscillation of the mixture across the perforated workpiece can be produced by axial movement of the pole tip. In various aspects, the pole tip can comprise a mixture cap that extends from a side of the pole tip over the perforated workpiece. The mixture cap can be a nonmagnetic cap or can be a magnetic cap.

[0003] In another aspect, a method comprises supporting a perforated workpiece on a rod that extends axially through the perforated workpiece, the rod comprising a ferromagnetic core covered by nonferromagnetic material, the ferromagnetic core having a diameter greater than end openings of the perforated workpiece, the perforated workpiece supported by a plurality of wires extending axially along the rod, the plurality of wires distributed about the rod thereby spacing the perforated workpiece away from the rod; positioning an outer surface of a turning wheel against an external surface of the perforated workpiece, where the outer surface comprises a mixture of ferromagnetic particles, abrasive particles, and lubricant and the external surface of the perforated workpiece is held against the outer surface, and the spacing provided by the plurality of wires allowing circulation of the mixture of ferromagnetic particles, abrasive particles, and lubricant about the external surface, an internal surface, and an sidewalls through perforations of the perforated workpiece; and rotating the perforated workpiece by rotating the turning wheel, where the external and internal surfaces and sidewall surfaces of the perforated workpiece are polished by circulation of the mixture during rotation of the perforated workpiece. In one or more aspects, the perforated workpiece can be axially oscillated on the rod during rotation. The method can comprise rocking the rod about a center of the turning wheel thereby producing an axial reciprocation of the perforated workpiece. In various aspects, the turning wheel can have a cylindrical-shape or barrel-shape with a center diameter greater than an end diameter of the magnetic turning wheel. The perforated workpiece can be a flexible tubular workpiece or a straight tubular workpiece. The perforated workpiece can be a stent. [0004] Other systems, methods, features, and advantages of the present disclosure will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims. In addition, all optional and preferred features and modifications of the described embodiments are usable in all aspects of the disclosure taught herein. Furthermore, the individual features of the dependent claims, as well as all optional and preferred features and modifications of the described embodiments are combinable and interchangeable with one another.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

[0006] FIGS. 1 A and 1 B are graphical representations illustrating an example of a finishing (or polishing) system for processing a stent, in accordance with various embodiments of the present disclosure.

[0007] FIGS. 1C and 1 D are images of an example of an experimental setup of FIG.

1A, in accordance with various embodiments of the present disclosure.

[0008] FIGS. 2A-2C illustrate an example of mixture conditions during processing of the stent of FIG. 1A, in accordance with various embodiments of the present disclosure.

[0009] FIGS. 3A and 3B illustrates an example of processing a stent with a cap extending from an upper side of the pole tip, in accordance with various embodiments of the present disclosure.

[0010] FIGS. 4A-4C illustrate an example of mixture action during processing of the stent of FIG. 3A, in accordance with various embodiments of the present disclosure. [0011] FIG. 5A is a table illustrating an example of stent polishing conditions and FIGS. 5B-5D include images showing examples of stent processing results, in accordance with various embodiments of the present disclosure.

[0012] FIG. 6A is a table illustrating an example of stent polishing conditions of a two- stage process and FIGS. 6B and 60 include images showing examples of stent processing results, in accordance with various embodiments of the present disclosure.

[0013] FIGS. 7A and 7B are graphical representations illustrating an example of a finishing (or polishing) system comprising a barrel-shaped turning wheel for processing a stent, in accordance with various embodiments of the present disclosure.

[0014] FIGS. 7C and 7D are images of an example of an experimental setup of FIG.

7A, in accordance with various embodiments of the present disclosure.

[0015] FIGS. 8A and 8B illustrate an example of a finishing system configured to oscillate a workpiece holder with an eccentric wheel (or cam), in accordance with various embodiments of the present disclosure.

[0016] FIGS. 9A and 9B illustrate an example of mixture action during processing of the stent of FIG. 7A with and without wires, in accordance with various embodiments of the present disclosure.

[0017] FIG. 10A is a table illustrating examples of stent polishing conditions and FIGS. 10B- 101 illustrate examples of stent processing results, in accordance with various embodiments of the present disclosure.

DETAILED DESCRIPTION

[0018] Disclosed herein are various embodiments of methods related to polishing of stents or other perforated parts. Polishing can be carried out on internal and/or external surfaces of the flexible tubes. Reference will now be made in detail to the description of the embodiments as illustrated in the drawings, wherein like reference numbers indicate like parts throughout the several views. [0019] Nitinol (nickel-titanium) alloys also exhibit a combination of properties which make these alloys well suited for stents. Nitinol offers corrosion resistance and biocompatibility is similar to other implant materials. Other shape-memory alloys may also be utilized.

[0020] This disclosure presents a finishing principle for perforated parts such as, e.g., stents or other flexible tubes and describes an experimental setup designed to realize the principle. Finishing experiments demonstrate the feasibility and finishing characteristics of the process.

[0021] Minimizing the creation of uneven stress in a stent during finishing can avoid impairing the stent’s performance. Unlike workpieces finished with other mechanical machining processes, stents should not be rigidly clamped or chucked for finishing. Referring to FIG. 1A, shown is a schematic representation illustrating an example of the processing principle. A perforated workpiece 103 (e.g., a stent) can be mounted on a workpiece assembly 106 comprising a rod 109 (or other appropriate workpiece support) and a plurality of nonferromagnetic wires 112 (e.g., nonmagnetic metals (e.g., nichrome), polymers, or other nonferromagnetic material) extending axially along the rod 109. The workpiece 103 is supported by the wires 112 (e.g., two, three, or more) distributed about the rod 109 to provide spacing of the perforated workpiece 103 away from the rod 109. The wires 112 can be held in place on the rod 109 by blocks 130 formed of, e.g., tape, epoxy, adhesive, or other appropriate materials. For example, one side of the wires 112 can be secured in position on the rod 109 by a block 130, and the workpiece 103 positioned on the rod 109 over the wires 112 before securing the other side of the wires 112 on the rod 109. FIG. 1B schematically illustrates an example of a perforated workpiece (e.g., a stent) 103 positioned over wires 112 extending along the rod 109. FIG. 1C is an image of a stent 103 on nichrome wires 112 which are secured to a steel rod 109 by frictionless tape.

[0022] As shown in FIG. 1 A, a magnet assembly 115 comprising a magnet 118 (e.g., a permanent magnet) and a steel pole tip 121 can be positioned adjacent to the workpiece assembly 106 leaving clearance between the pole (e.g., steel) tip 121 and workpiece 103, which can include a mixture 124 of magnetic particles (e.g., iron particles), abrasive, and lubricant located between the pole tip 121 and workpiece assembly 106. The mixture 124 is suspended in a magnetic field and forms a particle brush between the pole tip 121 and the rod 109 (or magnetic core of the support) of the workpiece assembly 106. As illustrate in FIG. 2A, the particle brush contacts the outside, sidewall, and inside surfaces the perforated workpiece 103 by extending through the openings of the perforated workpiece 103 into the clearance between the workpiece 103 and the rod 109.

[0023] The rod 109 (or other workpiece support) can be coupled to a rotary drive (e.g., a motor driven chuck) to rotate the workpiece assembly 106. FIG. 1 D is an image of showing an example of an experimental setup of FIG. 1A including the stent 103 on the nichrome wires 112 of FIG. 1C. When the workpiece assembly 106 is rotated, a portion of the particle brush is dragged by the rotating workpiece assembly 106 as shown in FIG. 2B but tends to remain in the magnetic field. The two nonferromagnetic (e.g., nichrome) wires 112 shown in FIG. 2B function to move the particles allowing for consistent relative motion between the iron particles and the workpiece interior. As illustrated in FIG. 2C, this creates a circular motion of the particle brush opposite to the direction of the rotation of the workpiece assembly 106, which facilitates relative motion between the particle brush and the workpiece surfaces. If the magnet assembly 115 is translated in a direction parallel to the workpiece axis (as shown in FIG. 1A), the particle brush follows the magnet assembly motion, resulting in polishing of a longer workpiece area. The blocks 130 at the ends of the wires 112 can limit the axial movement of the workpiece 103 during translation.

[0024] The mixture 124 of iron particles, abrasive, and lubricant can be further concentrated between the pole tip 121 and workpiece assembly 106 by including a mixture cap 127 such as, e.g., a nonmagnetic cap. FIG. 3A is a schematic representation illustrating an example of the processing of FIG. 1A with a nonmagnetic cap 127 extending from an upper side of the pole tip 121 over the workpiece 103 on the workpiece assembly 106. FIGS. 4A-4C illustrate a process sequence similar to that shown in FIGS. 2A-2C. FIG. 3B is an image of showing an example of an experimental setup of FIG. 3A including a perforated workpiece 103 on the wires 112. The mixture 124 of iron particles, abrasive, and lubricant forming the particle brush contacts the outside, sidewall, and inside surfaces the perforated workpiece 103 as shown in FIG. 4A. When the workpiece assembly 106 is rotated, a portion of the particle brush is dragged by the rotating workpiece assembly 106 as shown in FIG. 4B but tends to remain in the magnetic field. As illustrated in FIG. 40, this creates a circular motion of the particle brush opposite to the direction of the rotation of the workpiece assembly 106. The mixture cap 127 can constrain any buildup of the circular motion, and thus concentrate the mixture 124 of particles and abrasive against and around the workpiece 103.

[0025] The movement of the mixture of iron particles and abrasive 124 relative to the stent enables successful polishing of its surfaces. The nonferromagnetic wires 112 function to move the particles in the mixture 124 allowing for consistent relative motion between the iron particles and the stent interior and sidewall surface, resulting in more material removal. The use of a two-step polishing is effective for finishing both the internal and external surfaces. Larger abrasives can be used in the first stage for more effective removal of burrs and texture left by the laser cutting process. Smaller abrasives can be used in the second stage to further smooth the surfaces. The effect of lubricant on the magnetic particle motion can be significant. Parameters that may influence the polishing characteristics include, e.g., lubricant, polishing time, magnetic field, abrasive size, magnetic rod (workpiece holder) rotational speed, nonmagnetic wire size and configuration, etc. For example, a condition with excessive lubricant in a weak magnetic field allows the magnetic particles to leave the polishing area, while insufficient lubrication can increase friction and may fracture the stent 103.

[0026] Experimental testing was carried out to examine the polishing effects on a stent 103 using two sets of conditions. For a first experimental test, a stent 103 was polished using a constant set of conditions which are listed in the table of FIG. 5A. The stent 103 was processed using the same mixture 124 of magnetic particles, abrasive and lubricant over three 15-minute intervals to examine the surface change over time. FIG. 5B includes images showing the progression of the external surface (top row), internal surface (middle row), and sidewall (bottom row) at an initial state and after 15, 30 and 45 minutes of processing. As seen in the images, the surface condition improved over each time interval. FIGS. 50 and 5D illustrate the initial external surface roughness and final external surface roughness after 45 minutes of processing, respectively. A measurable improvement was found.

[0027] For a second experimental test, a stent 103 was polished using a two-step process under a set of conditions which are listed in the table of FIG. 6A. The stent 103 was processed using a first mixture 124 of magnetic particles, course abrasive and lubricant over a first 15-minute interval and a second mixture 124 of magnetic particles, fine abrasive and lubricant over a second 15-minute interval. FIG. 6B includes images showing the progression of the external surface at the five locations (1-5) indicated in the diagram, beginning with an initial state and after the first and second stages of processing. FIG. 6C includes images showing the progression of the internal surface at the four locations (1-4) indicated in the diagram, beginning with an initial state and after the first and second stages of processing. As seen in the images, the surface condition improved over each time interval and the final result is very similar to that shown in FIG. 5B with less processing time.

[0028] Referring to FIGS. 7A and 7B, shown is a schematic representation illustrating another processing methodology disclosed herein. As previously discussed, a perforated workpiece 203 (e.g., a stent) can be mounted on a workpiece assembly comprising a rod 209 (or other appropriate workpiece support) and a plurality of nonferromagnetic wires 212 (e.g., nonmagnetic metals (e.g., nichrome), polymers or other nonferromagnetic material) extending axially along the rod 209. The workpiece 203 is supported by the wires 212 (e.g., two, three, or more) distributed about the rod 209 to provide spacing of the perforated workpiece 203 away from the rod 209. The wires 212 can be held in place on the rod 209 by blocks 230 formed of, e.g., tape, epoxy, adhesive, or other appropriate materials. FIG. 7C is an image of a stent 203 on nonferromagnetic wires 212 which are secured to a rod 209 by blocks 230 made of frictionless tape. [0029] A permanent magnet 218 is installed inside a turning wheel 230 made of, e.g., austenitic stainless steel. The stent (or other workpiece) 203 is held a rod 209 inserted into the stent 103 and the turning wheel 230. The rod 209 consists of a ferromagnetic material core covered by nonferromagnetic material to avoid direct contact between the ferromagnetic core and the mixture of magnetic particles, abrasive, and lubricant 224 introduced to the turning wheel 230. The stent 203 rotates as it is passively driven by the turning wheel 230. The mixture 224 can include diamond and/or magnetic abrasives. Magnetic particles (e.g., iron powders can be used as a holder to transfer magnetic force to the mixture 224). The relative motion between the mixture 224 and stent 203 finishes the stent surface and edges.

[0030] FIG. 7D shows an image of an example of a polishing system including the finishing equipment developed to realize the disclosed processing principle. A workpiece 203 is positioned on nonmagnetic wires 212 extending axially along a rod 209 that is set on a workpiece holder and the turning wheel 230 is set down on the workpiece 203 with a certain clearance for particles to travel between the wheel and stent. Additional details of the polishing system can be found in U.S. Patent Application Pub. No. 2018/0311781 and 2019/0366501, both of which are hereby incorporated by reference in their entireties.

[0031] Referring to FIG. 8A, shown is an example of a workpiece holder assembly for oscillating the workpiece holder with the eccentric wheel. The workpiece holder includes grooves 303 on opposite sides of a recessed cavity 306 to hold the rod 203 in position. A hinge mounted on the base plate includes a shaft that passes through the lower section of the workpiece holder to allow it to tilt about the shaft. The “tilting” plate of the workpiece holder includes a cam arm 309 extending from a side of the workpiece holder in a direction that is substantially perpendicular to the axial length of the shaft. The free end of the cam arm 309 is in contact with the eccentric wheel (or cam) 312, which is driven by a motor 315 (e.g., a stepping motor). One or more compression springs 318 provide a lever force that presses the free end of the cam arm 309 against the contact point of the eccentric wheel 312 to ensure continuous contact to avoid bumping and bouncing. [0032] FIG. 8B illustrates the variation in the tilt of the workpiece holder about the shaft as the eccentric wheel 312 rotates. As shown, the perforated workpiece (stent) 203 moves on the nonferromagnetic wires 212 extending along the rod 209 in response to the tilt. Movement of the stent 203 along the length of the wires 212 on the rod 209 can be limited by the blocks 230 provided to secure the wires 212 to the rod 209.

[0033] FIGS. 9A and 9B illustrate the benefits of supporting the perforated workpiece 203 on the nonmagnetic wires 212 (e.g., two, three, or more) distributed about the rod 209 to provide spacing of the perforated workpiece 203 away from the rod 209. As shown in FIG. 9A, the workpiece 203 is pressed against the rod 209 by the turning wheel 230 which limits or prevents access of the abrasive to the interior surfaces of the workpiece 203. In contrast, supporting the perforated workpiece 203 on the wires 212 as shown in FIG. 9B maintains separation of the workpiece 203 from the rod 209.

[0034] When the workpiece 203 is rotated by the turning wheel 230, a portion of the particle brush is dragged by the rotating workpiece assembly 106 as shown in FIG. 9B. The two nonferromagnetic (e.g., nichrome) wires 212 can function to allow for consistent relative motion between the abrasive and the workpiece interior. To verify the effectiveness of the process, testing was carried out on stents 203 under two sets of conditions which are listed in the table of FIG. 10A.

[0035] FIG. 10C includes images showing the effect of processing on the external surface at three locations (1-3) indicated in the diagram of FIG. 10B. FIG. 10C shows an image of each location on a stent 203 before polishing and on two stents 203 after the polishing process. FIG. 10D includes images showing the effect of processing on the sidewall surface at two locations (4-5) indicated in the diagram of FIG. 10B. FIG. 10D shows an image of each location on the stent 203 before polishing and on the two stents 203 after the polishing process. FIG. 10E includes images showing the effect of processing on the interior surface at three locations (6-8) indicated in the diagram of FIG. 10B. FIG. 10E shows an image of each location on the stent 203 before polishing and on the two stents 203 after the polishing process. As seen in the images, the surface condition improved over the processing interval.

[0036] FIGS. 10F and 10G illustrate the initial external surface roughness and final external surface roughness after processing for the first sample (sample 13) and FIGS. 10H and 101 illustrate the initial external surface roughness and final external surface roughness after processing for the second sample (sample 12). As indicated by the bar charts of FIGS. 10G and 101, a measurable improvement was found.

[0037] The wires 212 in the workpiece-mounting method provide space for the abrasive to travel in and out of the stent 209 and facilitate circulation of the abrasive around the stent 209. The second processing method enabled finishing of stent 209 similar to a commercial product. Adjusting the ratio of the iron particles to diamond powder from 10:1 to 3:2 increased the viscosity of the mixture 224 (i.e. , iron particles, diamond powder, and oil-based lubricant). However, the oil-based lubricant allowed smooth circulation of the mixture 224 around the stent 203, preventing fracture and enabling effective surface polishing as indicated by the test results.

[0038] It should be emphasized that the above-described embodiments of the present disclosure are merely possible examples of implementations set forth for a clear understanding of the principles of the disclosure. Many variations and modifications may be made to the above-described embodiment(s) without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.

[0039] It should be noted that ratios, concentrations, amounts, and other numerical data may be expressed herein in a range format. It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. To illustrate, a concentration range of “about 0.1% to about 5%” should be interpreted to include not only the explicitly recited concentration of about 0.1 wt% to about 5 wt%, but also include individual concentrations (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.5%, 1.1%, 2.2%, 3.3%, and 4.4%) within the indicated range. The term “about” can include traditional rounding according to significant figures of numerical values. In addition, the phrase “about ‘x’ to ‘y’” includes “about ‘x’ to about ‘y’”.

Claims

CLAIMS Therefore, at least the following is claimed:

1. A method, comprising: supporting a perforated workpiece on a rod that extends axially through the perforated workpiece, the perforated workpiece supported by a plurality of wires extending axially along the rod, the plurality of wires distributed about the rod thereby spacing the perforated workpiece away from the rod; positioning a pole tip adjacent to and extending over at least a portion of the workpiece where a magnetic field extends from the pole tip to the rod through the perforated workpiece; providing a mixture comprising magnetic particles, abrasive and lubricant between the pole tip and the workpiece, the magnetic field supporting the mixture; and rotating the perforated workpiece by rotating the rod, where external, internal, and sidewall surfaces of the perforated workpiece are polished by circulation of the mixture during rotation of the perforated workpiece.

2. The method of claim 1, wherein the pole tip is axially oscillated during rotation of the perforated workpiece.

3. The method of claim 1, wherein oscillation of the mixture across the perforated workpiece is produced by movement of the pole tip.

4. The method of claim 1, wherein the perforated workpiece is a flexible tubular workpiece or a straight tubular workpiece.

5. The method of claim 1, wherein the perforated workpiece is a stent.

6. The method of claim 1 , wherein a mixture cap extends from a side of the pole tip over the perforated workpiece.

7. The method of claim 6, wherein the mixture cap is a nonmagnetic cap.

8. The method of claim 6, wherein the mixture cap is a magnetic cap.

9. A polishing system, comprising: a workpiece holder comprising a rod configured to axially support a perforated workpiece, the perforated workpiece separated from the rod by a plurality of wires distributed about the rod and extending axially along the rod, the plurality of wires thereby spacing the perforated workpiece away from the rod; a pole tip configured to be positioned adjacent to and extending over at least a portion of the workpiece, the pole tip configured to provide a magnetic field that extends from the pole tip to the rod through the perforated workpiece, where the magnetic field supports a mixture comprising magnetic particles, abrasive and lubricant positioned between the pole tip and the workpiece; and a workpiece drive configured to rotate the rod, where rotation the perforated workpiece by the rod polishes external, internal, and sidewall surfaces of the perforated workpiece by circulation of the mixture.

10. The polishing system of claim 9, wherein the pole tip is configured to axially oscillate during rotation of the perforated workpiece.

11. The polishing system of claim 10, wherein oscillation of the mixture across the perforated workpiece is produced by axial movement of the pole tip.

12. The polishing system of claim 9, wherein the pole tip comprises a mixture cap that extends from a side of the pole tip over the perforated workpiece.

13. The polishing system of claim 12, wherein the mixture cap is a nonmagnetic cap.

14. The polishing system of claim 12, wherein the mixture cap is a magnetic cap.

15. A method, comprising: supporting a perforated workpiece on a rod that extends axially through the perforated workpiece, the rod comprising a ferromagnetic core covered by nonferromagnetic material, the ferromagnetic core having a diameter greater than end openings of the perforated workpiece, the perforated workpiece supported by a plurality of wires extending axially along the rod, the plurality of wires distributed about the rod thereby spacing the perforated workpiece away from the rod; positioning an outer surface of a turning wheel against an external surface of the perforated workpiece, where the outer surface comprises a mixture of ferromagnetic particles, abrasive particles, and lubricant and the external surface of the perforated workpiece is held against the outer surface, and the spacing provided by the plurality of wires allowing circulation of the mixture of ferromagnetic particles, abrasive particles, and lubricant about the external surface, an internal surface, and an sidewalls through perforations of the perforated workpiece; and rotating the perforated workpiece by rotating the turning wheel, where the external and internal surfaces and sidewall surfaces of the perforated workpiece are polished by circulation of the mixture during rotation of the perforated workpiece.

16. The method of claim 15, wherein the perforated workpiece is axially oscillated on the rod during rotation.

17. The method of claim 15, comprising rocking the rod about a center of the turning wheel thereby producing an axial reciprocation of the perforated workpiece.

18. The method of claim 15, wherein the turning wheel has a cylindrical-shape or barrelshape with a center diameter greater than an end diameter of the magnetic turning wheel.

19. The method of claim 15, wherein the perforated workpiece is a flexible tubular workpiece or a straight tubular workpiece.

20. The method of claim 15, wherein the perforated workpiece is a stent.