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Nanostructured Diamond Coating of Nitinol Stents

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Kink Resistant. Good Biocompatibility. Radiopaque. Super-Elasticity of Nitinol ... Kink Resistant. Good Biocompatibility. Radiopaque. Very good material for ... – PowerPoint PPT presentation

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Title: Nanostructured Diamond Coating of Nitinol Stents


1
Nanostructured Diamond Coating of Nitinol Stents
  • Stephen Evans, Dr. Aaron Catledge,
  • Dr. Yogesh Vohra,
  • Jerry Sewell

2
What are Stents?
  • Biomedical implants used to support collapsed or
    narrowed arteries
  • Allow the blood to flow normally
  • Function to prevent heart attacks and strokes

3
What is Nitinol?
  • Nickel-Titanium Naval Ordnance Laboratory
  • Intermetallic compound of Nickel and Titanium
  • Created by the Navy in the early 60s
  • 55 percent Nickel by weight
  • Known for its very peculiar properties

4
Properties of Nitinol
  • Super-Elastic Property
  • Shape-Memory Effect
  • Provides a Constant Force
  • Kink Resistant
  • Good Biocompatibility
  • Radiopaque

5
Super-Elasticity of Nitinol
  • Allows Nitinol to be deformed and reassume its
    original shape
  • Stress results in a reversible phase change of
    Nitinol from austenite to martensite
  • Austenite Phase
  • Rigid\Hard
  • Cubic lattice structure
  • Martensite
  • Manipulative\Soft
  • Rhombohedral lattice structure
  • Upon the relief of stress Nitinol returns to its
    austenite phase and its original shape

6
Super-Elasticity of Nitinol
Schematic presentation of lattice structure
changes caused by outer stress in Nitinol.
7
Properties of Nitinol
  • Super-Elastic Property
  • Shape-Memory Effect
  • Provides a Constant Force
  • Kink Resistant
  • Good Biocompatibility
  • Radiopaque
  • Very good material for making stents

8
Applications of Nitinol
9
Nitinol Stents and Dissolution of Nickel
  • Can dissolve Nickel into the body
  • Nickel is an essential element in the body
  • Can be harmful if deposited in large quantities
  • May cause allergenic or toxic reactions
  • Can this be avoided?

10
Nitinol with CVD Diamond The Perfect Material
for Stents
  • Chemical Vapor Deposition (CVD) of Diamond
  • Process used to deposit thin diamond films onto
    non-diamond substrates
  • Can avoid the release of nickel from Nitinol
    stents
  • Diamond is biocompatible and extremely hard
  • Can prevent stress corrosion cracking of stents

11
Research Goal
  • To identify the conditions needed to grow a
    continuous and adherent crystalline carbon
    coating on a Nitinol substrate using CVD

12
The Deposition Process
  • Mechanical Polishing
  • Annealing step
  • Seeding
  • Ultrasonic Agitation
  • Dry Seeding
  • CVD

13
Annealing
  • Gas Flow Rates
  • Hydrogen 100 ccm
  • Nitrogen 50 ccm
  • Average Temperature- 600C to 900C
  • Time- 30 minutes
  • Forms an oxide layer on the Nitinol surface
    allowing for faster growth of the diamond film

14
The Deposition Process
  • Mechanical Polishing
  • Annealing step
  • Seeding
  • Ultrasonic Agitation
  • Dry Seeding
  • CVD

15
Chemical Vapor Deposition
  • Flow Rates
  • Hydrogen 500 ccm
  • Nitrogen 8.8 ccm
  • Methane 88 ccm
  • Average Temperature- 600C to 900C
  • Number of Fringes- 2-5
  • Film thickness measured by the number of fringes

16
Optical Interference
  • Is detected as fringes in the time vs.
    temperature plot during CVD
  • Caused by destructive and constructive
    interference to the pyrometers detection of
    light waves emitted from the substrate

17
Research Considerations
  • Substrate temperature during the annealing step
  • Ratio of the intensity of the Austenite Phase to
    the intensity of the Oxide Layer on the substrate
  • Substrate temperature during CVD

18
Substrate Annealing Temperature and Austenite to
Oxide Ratio (AO)
  • May have a very large effect on the condition of
    a diamond film grown on Nitinol
  • There is Negative correlation between the
    substrate annealing temperature and AO
  • The lower the substrate temperature during
    annealing the higher the AO on the surface

19
Substrate Annealing Temperature and Austenite to
Oxide Ratio (AO)
High Temperature Annealing
20
Substrate Annealing Temperature and Austenite to
Oxide Ratio (AO)
Low Temperature Annealing
21
Substrate Annealing Temperature and Austenite to
Oxide Ratio (AO)
Correlation between Substrate Mean Annealing
Temperature and Austenite to Oxide Ratio After CVD
22
Substrate Austenite to Oxide Ratio and Diamond
Film Condition
  • There is a correlation between the AO and the
    film condition
  • The most adherent and continuous diamond films
    are grown on substrates that have high AO

23
Substrate Austenite to Oxide Ratio and Diamond
Film Condition
A low AO yields a poorly adhered and
discontinuous film
24
Substrate Austenite to Oxide Ratio and Diamond
Film Condition
A high AO yields an adherent and largely
continuous film
400x
25
Substrate Deposition Temperature and Diamond Film
Condition
  • The substrate temperature during CVD has a
    correlation to the condition of the resulting
    film
  • Diamond films grown with a mean substrate
    temperature below 800ºC are poor in condition
  • Diamond films grown with a mean substrate
    temperature above 900ºC are also poor in quality
  • Diamond films grown between 800ºC and 900ºC are
    the best adhered and closest to continuity

26
Substrate Deposition Temperature and Diamond Film
Condition
Shows a film after growth below 800ºC
27
Substrate Deposition Temperature and Diamond Film
Condition
Shows a film after growth above 900ºC
28
Substrate Deposition Temperature and Diamond Film
Condition
Shows a film after growth between 800ºC and 900ºC
843
29
Conclusions
  • The best diamond films are grown when
  • The substrate annealing temperature is low and
    the resulting AO is high
  • The substrate CVD temperature is between 800ºC to
    900ºC

30
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