Method and apparatus for direct laser cutting of metal stents

• US 5,780,807 A
• Filed: 01/15/1997
• Issued: 07/14/1998
• Est. Priority Date: 11/28/1994
• Status: Expired due to Term

• Current Assignee: Advanced Cardiovascular Systems Incorporated
• Original Assignee: Advanced Cardiovascular Systems Incorporated
• Inventors: Saunders, Richard J.
• Primary Examiner(s): Gorski, Joseph M.
• Application Number:
  US08/783,698
• Time in Patent Office: 545 Days
• Field of Search: 219/121.69, 219/121.71, 29/2.1, 29/2.12, 29/557, 83/54, 83/178
• US Class Current: 219/121.71
• CPC Class Codes: A61F 2/91 made from perforated sheet material or tubes, e.g. perforated by laser cuts or etched holes
• CPC Class Codes: A61F 2/915 with bands having a meander structure, adjacent bands being connected to each other
• CPC Class Codes: A61F 2002/91508 the meander having a difference in amplitude along the band
• CPC Class Codes: A61F 2002/91533 characterised by the phase between adjacent bands
• CPC Class Codes: A61F 2230/0013 Horseshoe-shaped, e.g. crescent-shaped, C-shaped, U-shaped
• CPC Class Codes: B23K 2103/05 Stainless steel
• CPC Class Codes: B23K 2103/50 Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26
• CPC Class Codes: B23K 26/073 Shaping the laser spot
• CPC Class Codes: B23K 26/0823 Devices involving rotation of the workpiece
• CPC Class Codes: B23K 26/142 for the removal of by-products
• CPC Class Codes: B23K 26/1435 involving specially adapted flow control means
• CPC Class Codes: B23K 26/1436 for pressure control
• CPC Class Codes: B23K 26/1438 for directional control
• CPC Class Codes: B23K 26/1462 Nozzles; Features related to nozzles
• CPC Class Codes: B23K 26/1476 Features inside the nozzle for feeding the fluid stream through the nozzle
• CPC Class Codes: B23K 26/18 using absorbing layers on the workpiece, e.g. for marking or protecting purposes
• CPC Class Codes: B23K 26/40 taking account of the properties of the material involved
• CPC Class Codes: G05B 19/182 characterised by the machine tool function, e.g. thread cutting, cam making, tool direction control G05B19/21 - G05B19/40 take precedence
• CPC Class Codes: G05B 2219/45041 Laser cutting
• CPC Class Codes: G05B 2219/45171 Surgery drill
• CPC Class Codes: Y10T 29/49995 : Shaping one-piece blank by removing material
• CPC Class Codes: Y10T 29/49996 : Successive distinct removal operations

Abstract

An improved expandable stent for implantation in a body lumen, such as an artery, and an improved method for making it from a single length of tubing. The stent consists of a plurality of radially expandable cut cylindrical elements generally aligned on a common axis and interconnected by one or more interconnective elements, the elements having a rectangular cross-section from cut-to-cut. The individual radially expandable cylindrical elements are disposed in an undulating pattern. The stent is manufactured by direct laser cutting from a single metal tube using a finely focused laser beam passing through a coaxial gas jet structure to impinge on the working surface of the tube as the linear and rotary velocity of the tube is precisely controlled.

Claims

1. A method of producing a stent, comprising the steps of:

providing a generally tubular member having a working outer tube surface, an inner tube surface defining an inside diameter of said generally tubular member, and a tubular wall between said working outer tube surface and said inner tube surface;

providing a protective mandrel within said generally tubular member, said mandrel having an outer surface defining an outer diameter that is smaller than said inside diameter of said tubular member;

supporting said generally tubular member, with said protective mandrel therewithin, in operative association with a laser beam;

moving said generally tubular member linearly and rotationally relative to, said laser beam, thereby causing said protective mandrel to roll on a portion of said inner tube surface such that a space is formed between said inner tube surface and said outer surface of said mandrel; and

impinging said laser beam upon said working outer tube surface while said generally tubular member is moving linearly and rotationally relative to said laser beam, thereby causing said laser beam to cut a desired stent pattern through said tubular wall, then pass through said space and then contact said protective mandrel such that said laser beam is prevented from contacting said portion of said inner tube surface upon which said protective mandrel is rolling.

2. A method as set forth in claim 1, wherein said tubular member is stainless steel.

3. A method as set forth in claim 1, wherein said protective mandrel is stainless steel.

4. The method of claim 1, and further comprising the step circularly polarizing said laser beam prior to impinging said laser beam upon said working outer tube surface.

5. The method of claim 4, wherein said step of circularly polarizing said laser beam includes the step passing said laser beam through a quarter wave plate.

6. The method of claim 1, and further comprising the step of spatially filtering said laser beam prior to impinging said laser beam upon said working outer tube surface.

7. A method as set forth in claim 1, wherein said laser beam includes a focused laser beam spot and a depth of field, and further comprising the step of controlling the size of said focused laser beam spot and said depth of field by varying a laser beam diameter.

8. The method of claim 7, and further comprising the steps of passing said laser bema through a focusing lens prior to impinging said laser beam upon said working outer tube surface, and controlling the size of said focused laser beam spot and said depth of field by varying a focal length of said focusing lens.

9. The method of claim 1, and further comprising the step of passing said laser beam through a coaxial gas jet prior to impinging said laser beam upon said working outer tube surface, thereby cooling the region where said laser beam impinges against said generally tubular member.

10. A method as set forth in claim 9, wherein said gas jet is an oxygen gas jet.

11. The method of claim 1, and further comprising the step of ultrasonically cleaning said generally tubular member after said desired stent pattern has been cut through said tubular wall.

12. The method of claim 11, and further comprising the step of electropolishing said generally tubular member after said desired stent pattern has been cut through said tubular wall.

13. The method of claim 11, wherein said ultrasonically cleaning step includes ultrasonically removing slag from said generally tubular member while said generally tubular member soaks in an alcohol and water solution, and then further ultrasonically removing slag from said generally tubular member while said generally tubular member soaks in an said solution.

14. The method of claim 13, and further comprising the step of electrochemically polishing said generally tubular member in an acidic aqueous solution after said ultrasonically cleaning step.

15. A method as set forth in claim 1, wherein cutting said desired stent pattern includes a plurality of struts each having a substantially rectangular cross-section.

16. A method as set forth in claim 1, wherein the step of providing said mandrel includes sizing said diameter of said mandrel to be about one-half said inside diameter of said tubular member.

17. A method of making an expandable stent, comprising the steps of:

providing a generally tubular member having a working outer tube surface, an inner tube surface defining an inside diameter of said generally tubular member, and a tubular wall between said working outer tube surface and said inner tube surface;

providing a protective mandrel within said generally tubular member, said mandrel having an outer surface defining an outer diameter that is smaller than said inside diameter of said tubular member;

supporting said generally tubular member, with said protective mandrel therewithin, in operative association with a laser beam;

moving said generally tubular member linearly and rotationally relative to said laser beam, thereby causing said protective mandrel to cover a portion of said inner tube surface with a space formed between another portion of said inner tube surface and said outer surface of said protective mandrel;

impinging said laser beam upon said working outer tube surface while said generally tubular member is moving linearly and rotationally relative to said laser beam, thereby causing said laser beam to cut a desired stent pattern through said tubular wall, then pass through said space and then contact said protective mandrel such that said laser beam is prevented from contacting said portion of said inner tube surface upon which said protective mandrel is covering then;

ultrasonically removing slag from said generally tubular member; and

electrochemically polishing said generally tubular member.

18. A method of producing a stent, comprising the steps of:

providing a generally tubular member having a working outer tube surface, an inner tube surface defining an inside diameter of the generally tubular member, and a tubular wall between said working outer tube surface and said inner tube surface;

providing a protective mandrel within said generally tubular member, said mandrel having an outer surface defining an outer diameter that is smaller than said inside diameter of said tubular member;

supporting said generally tubular member, with said protective mandrel therewithin, in operative association with a laser beam;

moving said generally tubular member linearly and rotationally relative Lo said laser beam, thereby causing said protective mandrel to roll on a portion of said inner tube surface such that an air gap is formed between said inner tube surface and said outer surface of said mandrel; and

impinging said laser beam upon said working outer tube surface while said generally tubular member is moving linearly and rotationally relative to said laser beam, thereby causing said laser beam to cut a desired stent pattern through said tubular wall, then pass through said air gap and then contact said protective mandrel such that said laser beam is prevented from contacting said portion of said inner tube surface upon which said protective mandrel is rolling.

19. A method a set forth in claim 18, wherein the step of providing a mandrel includes sizing said diameter of said mandrel to about one-half said inside diameter of said tubular member.

20. A method of making a stent, comprising the steps of:

providing a generally tubular member having a working outer tube surface, an inner tube surface defining an inside diameter of the generally tubular member, and a tubular wall between said working outer tube surface and said inner tube surface;

providing a protective mandrel within said generally tubular member, said mandrel having an outer surface defining an outer diameter that is smaller than said inside diameter of said tubular member;

supporting said generally tubular member on a fixture, with said protective mandrel positioned within the generally tubular member, and positioning said fixture at a laser beam output stage of a laser having an optical system;

delivering a laser beam through said optical system, and Q-switching said laser beam, thereby transforming said laser beam into laser pulses;

moving said generally tubular member linearly and rotationally relative to said laser pulses, thereby causing said protective mandrel to roll on a portion of the inner tube surface such that a space is formed between said inner tube surface and said outer surface of said mandrel; and

impinging said laser pulses upon said working outer tube surface while said generally tubular member is moving linearly and rotationally relative to said laser pulses, thereby causing said laser pulses to cut a desired stent pattern through said tubular wall, then pass through said space and then contact said protective mandrel such that said laser pulses are prevented from contacting said portion of said inner tube surface upon which said protective mandrel is rolling;

wherein said Q-switching step minimizes heat biuldup in said generally tubular member during said impinging step.

21. The method of claim 20, wherein the step of Q-switching said laser beam includes the step of frequency doubling said laser beam, thereby approximately quadrupling the power density of said laser beam.

22. The method of claim 20, wherein said mandrel is formed from stainless steel.

23. The method of claim 20, and further comprising the step of passing said laser pulses through a coaxial gas jet prior to impinging said laser pulses upon said working outer tube surface, thereby cooling the region where said laser pulses impinge against said generally tubular member.

24. The method of claim 23, wherein said gas is pressurized oxygen.

25. The method of claim 20, wherein said generally tubular member has a first end and a second end, said step of moving said generally tubular member includes supporting and driving said first and second ends with a synchronized precision drive mechanism.

26. The method of claim 20, wherein said delivering step includes passing said laser beam through a beam expander, thereby increasing the diameter of said laser beam such that thermal damage to said laser during operation thereof is minimized.

27. The method of claim 20, wherein said step of delivering includes passing said laser beam through a curricular polarizer, thereby eliminating polarization effects during cutting by said laser pulses.

28. The method of claim 27, wherein said circular polarizer is a quarter wave plate.