Manufacturing Stents A review of an AILU meeting held in Nov 09

1. Manufacturing StentsA review of an AILU meeting held in Nov ‘09 Dr Martin Sharp Photonics in Engineering Group General Engineering Research Institute Liverpool John Moores University This will give a brief review of nine generic laser processes.This will give a brief review of nine generic laser processes.

2. Introduction The laser cutting of stents is regarded as a modern example of a successful laser application It has promoted the development of high speed motion systems for fine tubular components And it has overlapped with the development and introduction of fibre lasers and high power ultrashort pulsed lasers.

3. Introduction (2) But the laser cutting of stents is just one part of the manufacturing process. As chair of the Medical Special Interest Group of AILU, I wanted to hold a meeting looking at the whole manufacturing process. A lot of the additional processes have relevance to fine laser cutting in general

4. Introduction (3) Equally important was to understand why stents are needed, what are their limitations and the future development requirements This presentation is a review of the various presentations given at the AILU meeting Thanks to all the authors for allowing me to use extracts of their presentations

5. Stents (1) Atheroscleris Thickening of the artery walls caused by the build up of fatty materials such as cholesterol

6. Stents (2)

7. Stents (3)

8. Stents (4) Stents are considered when Drug Therapies are not achieving satisfactory control of the condition Previously the only other option was cardiac artery bypass grafting, a major operation involving opening the chest Stents provide a less invasive method of potentially stabilising the problem and allowing the vessels to restore acceptable function

9. Stents (5) The basic procedure is balloon angioplasty. A balloon is inserted in the groin and moved through the body until the balloon is positioned in the narrowed artery. It is inflated to widen the artery. Often the artery narrows again after the operation A stent is inserted to support the opened vessel

10. Stents (6) Initially bare metal stents were used Found there was restenosis: Smooth muscle cells proliferation caused by the stent. This once again narrowed the artery Drug Eluting Stents Stents carried drugs to prevent proliferation. However drugs delayed healing and risk of late stage thrombi was identified. Stents are not perfect!

11. Stents (7) The ideal stent:

12. Stents (8) Stent materials

13. Stents (9) Ideal Stent Suitable radial strength (primary function) Must favour enodthelial coverage Decrease restenosis Drugs must reduce smooth muscle cell proliferation Polymers (used to carry drugs) must not create allergic reaction Polymer to biodegrade High fatigue life – Heart rate 72/min, 40 million cycles p.a., required life 10-15 years (200 stent fractures reported in 2009) Whole stent biodegradable (iron and magnesium alloy base)

14. Stent cutting systems (1) Swiss Tec Ag are a leading supplier of stent cutting machines Sponsor of the AILU meeting Produce complete system for laser cutting Able to select best laser for the system based on speed, quality and cost.

15. Stent cutting systems (2) Main Challenges: Stents are small – typically made from 2-3mm OD and c50µm wall thickness Small kerf widths are required because of intricacy of cut path required to create expanding struts Cut edge and dross are important – dross will need to be removed Heat affected zone from laser cutting must not affect performance and life No “back wall” damage

16. Stent cutting systems (3) Many things are considered in implementation of laser cutting

17. Stent cutting systems (4) Typical system:

18. Stent cutting systems (5) Laser comparison:

19. Stent cutting systems (6) Picosecond laser offers great potential:

20. Stent cutting (1) Laser cutting is just one process in the manufacturing chain for stents. Note some stents are manufactured by welding wire “crowns”

21. Stent cutting (2) Requirements vary from customer to customer, but the following are generally all required Not of all of these can be met by laser cutting alone

22. Stent cutting (3) Cutting parameters have to be carefully balanced: Too small a kerf width gives: A slow cutting speed Lot of assist gas wastage

23. Fibre laser processes(1) The fibre laser is the fastest growing laser type at the beginning of the 21st century and predicted to displace many other types of lasers in laser processing: It is robust, solid state Its efficient with wall plug efficeincies greater than any other laser type It has excellent beam quality and focussability It offers stent cutting and welding many advantages

24. Fibre laser processes (2) Fibre laser cutting : high speed cutting of thin stainless steel

25. Fibre laser processes (3) Fibre laser cutting: not only speed but control of heat input

26. Fibre laser processes (4) Welded Stents – an alternative to tube cutting:

27. Finishing of laser cut stents (1) Laser cut stents are not the final product They must be cleaned of all dross and other debris from the cutting process Sharp edges must be removed Roughness of cut face reduced Must be passivated for corrosion resistance Must be easily cleaned and sterilised

28. Finishing of laser cut stents (2) The laser cut surface needs to be smoothed and any deleterious HAZ removed. Anodic Polisihing is one method

29. Finishing of laser cut stents (3) For stents, at least 9 processes are required With volume production automated plant is necessary

30. Parylene Coating (1)

31. Parylene Coating (2)

32. Parylene Coating (3) Polymer coating is used to carry the drug Other medical devices can benefit as well

33. Testing(1) New stents have to be tested for medical device approval, typically to FDA and EU standards A stent is: Class III medical device Active Implant Delivery device included Stent testing must cover: Functional Testing Biological Safety Testing Packaging Validation Clinical Testing

34. Testing(2) The whole system needs testing

35. Testing(3) Stent Testing

36. Testing(4) Stent Testing Many, many standards to be tested against Fatigue testing for implants is essential as are a large range of dimensional and build quality tests. Many hours of testing required, 2+ years needed to bring product to market

37. Summary Successful and informative meeting with 50+ attendees Illustrates the importance of both photonics and materials And the laser can’t do it all on its own!

38. Thank You Martin Sharp General Engineering Research Institute Liverpool John Moores University Tel. 0151 231 2031 m.sharp@ljmu.ac.uk