1. CHAPTER 4 Biomaterials Metals
Dr. Syafiqah Saidin
CHAPTER 4 Biomaterials Metals
SMBE3313
2017/2018 Semester 1

2. OUTLINE Introduction to Biomaterials Metal Stainless Steel
Dr. Syafiqah Saidin
OUTLINE
Introduction to Biomaterials Metal
Stainless Steel
Cobalt-based Alloys
Titanium-based Alloys
Biodegradable Metals
Other Implantable Metals
Mechanical Properties
Metal Processing

3. Element that donating electrons to form positive ions
Dr. Syafiqah Saidin
Introduction to Biomaterials Metal
Metals
Element that donating electrons to form positive ions
Alloy
Combination of two or more different metals for the improvement of materials properties
General properties
High thermal and electrical conductivity.
Metallic bonding cause metal atoms easy to slip and deform.
High strength metal is constructed of finer grain sizes instead of coarse grain.
Pure metal is typically soft, ductile and difficult to fabricate.
Add more dislocation to improve strength

4. General Requirement for Metallic Implant
Dr. Syafiqah Saidin
Introduction to Biomaterials Metal
Corrosion resistance
Bio-compatible
General Requirement for Metallic Implant
Appropriate mechanical properties for specific application
High fatigue strength
Platinum and palladium alloys: Application involves radiopacity
Cobalt based alloy, oxidized zirconium, aluminium oxide ceramic: Application involves wear such as articulation

5. Introduction to Biomaterials Metal
Dr. Syafiqah Saidin
Introduction to Biomaterials Metal
Major groups of implantable metals and their applications
P. J. Andersen et al., “Metals for use in medicine”, Comprehensive Biomaterials: Metallic, Ceramic and Polymeric Biomaterials, P. Ducheyne, Elsevier Ltd, 2011.

6. Nickel-titanium (Nitinol)
Dr. Syafiqah Saidin
Metallic Implant Materials
Metallic Implants
Titanium-based alloy
Cobalt-based alloy
Stainless steel
Nickel-titanium (Nitinol)
Other metals
(Zirconium, tantalum)

7. Stainless Steel Common ingredients for SS are:
Dr. Syafiqah Saidin
Stainless Steel
Common ingredients for SS are:
Chromium (Cr) – Improves corrosion resistance due to formation of chromium oxide (Cr2O3) layer as a passivation layer
Nickel (Ni)
Manganese (Mn)
Molybdenum (Mo) – Improves pitting corrosion
Nitrogen (N) – Stabiliser, improve strength and corrosion resistance
Low carbon content – Reduces chromium carbide formation, thus preventing intergranullar corrosion
Stabilise FCC structure
Chromium carbide will reduce proportion of CR making SS more likely to experience intergranullar corrosion (during cooling time) )

8. Stainless Steel Implantable metal Non-magnetic
Dr. Syafiqah Saidin
Stainless Steel
Implantable metal
Austenitic
Non-magnetic
Not harden by temperature
Ferritic
Magnetic
Duplex
Austenitic + ferritic
Martensitic
Harden by temperature
FCC crystal structure
Very easy to weld
BCC crystal structure
Easy to weld for low C grade
BCC & FCC crystal structure
Easy to weld
Non-magnetic important for MRI
Distorted tetragonal
Hard to impossible to weld

9. Stainless Steel Composition of different types of SS
Dr. Syafiqah Saidin
Stainless Steel
Composition of different types of SS

10. Development chronology of SS
Dr. Syafiqah Saidin
Stainless Steel
Development chronology of SS
Mid 1920s : SS (Fe 18%; Cr 8%; Ni) has been used as screws implant
: Improved version composed of Mo and been used as
fracture fixation device and hip implant
: Then, the application of SS316L takes place
: Rex has been introduced with superior mechanical
properties and corrosion resistance (addition of Cr, Mn
and N) TM
P. J. Andersen et al., “Metals for use in medicine”, Comprehensive Biomaterials: Metallic, Ceramic and Polymeric Biomaterials, P. Ducheyne, Elsevier Ltd, 2011.

11. Stainless Steel Composition of implantable SS Dr. Syafiqah Saidin
P. J. Andersen et al., “Metals for use in medicine”, Comprehensive Biomaterials: Metallic, Ceramic and Polymeric Biomaterials, P. Ducheyne, Elsevier Ltd, 2011.

12. Stainless Steel SS430 SS304 SS316L
Dr. Syafiqah Saidin
Stainless Steel
SS430
SS316L
SS304
Microstructure of different types of SS
O. A. Hilders et al., “Microstructure, Strength, and Fracture Topography Relations in AISI 316L Stainless Steel, as Seen through a Fractal Approach and the Hall-Petch Law”, Microstructural Science, vol. 12, pp , 1985
P. J. Kenny et al., “Bacterial-Induced corrosion of AISI Type 304 Stainless steel tanks”, International Journal of Metals, pp. 1-10, 2015
P. J. Kenny et al., “Electrochemical corrosion of ferritic 409 and 439 stainless steels 409 and 439 in NaCl and H2SO4 solutions”, International Journal of Electrochemical Sciences, vol. 11, pp , 2016

13. Dr. Syafiqah Saidin
Stainless Steel
Austenitic SS (eg: 302 and 304) with low amount of alloying ingredient has tendency to transform into martensitic SS
Catheter made of austenitic SS that already transformed into martensitic SS could break off in a patient, lead to serious injury
FDA warning on un-retrived device fragments :

14. Stainless Steel Common properties of different types of SS
Dr. Syafiqah Saidin
Stainless Steel
Common properties of different types of SS

15. Cobalt-based Alloys General description:
Dr. Syafiqah Saidin
Cobalt-based Alloys
General description:
Most composition is similar to SS (Cr, Ni, Mo, N)
Passivation layer of Cr2O3 protects against corrosion
Most implantable device made from Co-based alloys is in FCC structure
Deformation of Co-based alloys can lead to formation of less ductile HCP structure
Low Ni of Co-based alloys is used to fabricate hip and knee implants
Widely used in joint replacement implants, pacemaker leads, heart valve cage, etc

16. Cobalt-based Alloys Composition of implantable Co-based alloys
Dr. Syafiqah Saidin
Cobalt-based Alloys
Composition of implantable Co-based alloys
P. J. Andersen et al., “Metals for use in medicine”, Comprehensive Biomaterials: Metallic, Ceramic and Polymeric Biomaterials, P. Ducheyne, Elsevier Ltd, 2011.

17. Titanium-based Alloys
Dr. Syafiqah Saidin
Titanium-based Alloys
Categories of Ti-based alloys:
Alpha (α) alloys : HCP crystal structure
CP Ti
Alpha + Beta (α + ß) alloys : HCP and BCC structures
Ti6Al4V, TI6AL7Nb
Beta (ß) alloys : BCC structure
Ti12Mo6Zr2Fe
High corrosion properties
α stabiliser : To stabilise α phase (Eg: Al, O)
ß stabilizer : To stabilise ß phase (Eg: Mo, V, Nb)
Depends on cooling procedure to form different categories of alloys
If alpha beta is cooled using method of beta alloys, it will transform to martensitic property
*Ti6Al4V – Composed of fine dispersed equiaxed α + ß phases for excellent high cycle fatigue performance

18. Titanium-based Alloys
Dr. Syafiqah Saidin
Titanium-based Alloys
Composition of implantable Ti-based alloys
P. J. Andersen et al., “Metals for use in medicine”, Comprehensive Biomaterials: Metallic, Ceramic and Polymeric Biomaterials, P. Ducheyne, Elsevier Ltd, 2011.

19. Titanium-based Alloys
Dr. Syafiqah Saidin
Titanium-based Alloys
CP Ti
Ti6Al4V
Ti-6Al-2Mo-2Cr
Microstructure of different types of Ti-based alloys
Y. J. Chen et al., “Microstructure evolution of commercial pure titanium during equal channel angular pressing”, Materials Science and Engineering: A, vol. 527, pp , 2010
M. Yan and P. Yu, “An overview of densification, microstructure and mechanical property of additively manufactured Ti-6Al-4V — Comparison among selective laser melting, electron beam melting, laser metal deposition and selective laser sintering, and with conventional powder”, in Sintering Techniques of Materials, A. Lakshmanan, Science, Technology and Medicine, 2015

20. Titanium-based Alloys
Dr. Syafiqah Saidin
Titanium-based Alloys
Ti-6Al-2Mo-2Cr
Operation at high temperature such as welding and sintering will lead to transformation of ß phase with finer lamellae structure
This structure has low high-cycle fatigue strength
Not suitable for high loading joint implants
ß phase : Lamellae structure
However, it has low Young’s modulus, has an ability to work in hard and cold work shape
BCC structure is easy to slip and deform
M. Yan and P. Yu, “An overview of densification, microstructure and mechanical property of additively manufactured Ti-6Al-4V — Comparison among selective laser melting, electron beam melting, laser metal deposition and selective laser sintering, and with conventional powder”, in Sintering Techniques of Materials, A. Lakshmanan, Science, Technology and Medicine, 2015

21. Titanium-based Alloys
Dr. Syafiqah Saidin
Titanium-based Alloys
Common properties of different types of Ti-based alloys

22. Dr. Syafiqah Saidin
Materials
Young’s modulus
Femoral cortical bone
17-20 GPa
*For bone implants, low Young’s modulus materials is preferred to prevent surrounding bone experiencing extreme stress which can lead to loss of bone density
“Gunawarman et al., “Fatigue characteristics of low cost ß titanium alloys for medical and healthcare applications”, Materials Transactions, vol. 46, pp , 2005

23. Biodegradable Metals Iron (Fe), Magnesium (Mg) and Zinc (Zn):
Dr. Syafiqah Saidin
Biodegradable Metals
Iron (Fe), Magnesium (Mg) and Zinc (Zn):
Degrades in physiological environment
For temporary replacement to allow tissues healing while degrading when the tissues healed
To avoid second surgery
Principle is based on oxidation of metal ions which cause degradation
Application: Stent, plates, screws, etc
Controversy: The accumulation of degradation products and the release of toxic gas
Mg stent
Hydrogen release from Mg
Accumulation of Fe in brain and kidney
Mg screws
B. J. C. Luthringer et al., “Magnesium-based implants: a mini-review”, Magnesium Research, vol. 27, 2014

24. Other Implantable Metals
Dr. Syafiqah Saidin
Other Implantable Metals
Gold (Au), Platinum (Pt) and Palladium (Pd):
Application of gold suture wire in 1500 and 1600s
Those elements are expensive, thus only used in small component device
Low mechanical properties
Gold crown prosthesis
Gold suture wire
Gold/platinum eyelid implant

25. Other Implantable Metals
Dr. Syafiqah Saidin
Other Implantable Metals
Tantalum (Ta) and Zirconium alloy (Zr) :
Used in orthopedic implant application
Porous Ta is preferable for implant that requires bone ingrowth
Oxidised Zr alloy is used in articulating applications
Wear resistance
Total knee replacement, femoral head
Ta hip implant
Ta spine implant
Zr femoral head

26. Mechanical Properties
Dr. Syafiqah Saidin
Mechanical Properties
Mechanical properties of a metal is determined by:
Chemical composition
Fabrication process or processing technique
Single load Tensile test
Multiple loads Fatigue test
Mechanical Testing

27. Mechanical Properties
Dr. Syafiqah Saidin
Mechanical Properties
Static Properties:
Types of loading
Tensile, shear, compression and torsion loading
Results
Yield strength, ultimate tensile strength, elongation, Young’s modulus
Add more oxygen, less ductile
Sintering will harden the metal
Ageing can harden the metal
Tensile test
Shear stress
Compression test
Torsion test
*There are specific standards such as ASTM, BS to perform the mechanical testing

28. Mechanical Properties
Dr. Syafiqah Saidin
Mechanical Properties
Mechanical properties of several common metallic implant
Forces at hip: 3x during walking; 8x during running
P. J. Andersen et al., “Metals for use in medicine”, Comprehensive Biomaterials: Metallic, Ceramic and Polymeric Biomaterials, P. Ducheyne, Elsevier Ltd, 2011.

29. Mechanical Properties
Dr. Syafiqah Saidin
Mechanical Properties
Fatigue / endurance limit:
Reduction of mechanical properties due to cyclic loading that lead to materials failure
Involves three stages:
Crack initiation
Crack growth
Final failure
Fatigue failure of implant depends on :
Implant design
Fatigue strength
Materials composition
Surface properties of implant
Failure: Maximum stress level > endurance limit

30. Mechanical Properties
Dr. Syafiqah Saidin
Mechanical Properties
Fatigue test
Flat plate cantilever bending test
Rotating bending test
Fretting: Force between to joints implants
Rotating axial test

31. Mechanical Properties
Dr. Syafiqah Saidin
Mechanical Properties
Fatigue test :
Fatigue test is commonly perform at million cycles loading
Cardiovascular stent: 4 x 10 million cycles
Heart rate per year: 30 million cycle/year 7 8
Material
Material condition
10 Cycle endurance limit (Mpa)
Co-Cr-Mo
Investment cast
200 (min) – 450
Forged or warm worked
656 – 930
Ti-6Al-4V
Wrought
500 – 800
Ti-6Al-7Nb
540 – 750 7
Fatigue strength properties of several implantable metals at 10 million cycles loading 7
P. J. Andersen et al., “Metals for use in medicine”, Comprehensive Biomaterials: Metallic, Ceramic and Polymeric Biomaterials, P. Ducheyne, Elsevier Ltd, 2011.

32. Mechanical Properties
Dr. Syafiqah Saidin
Mechanical Properties
Fatigue failure : Metallic implant
Failure of metal plate at femur 7
S. M. Perren et al., “Biomechanical and biological aspects of defect treatment in fractures using helical plates”, ACTA CHIRURGIAE ORTHOPAEDICAE ET TRAUMATOLOGIAE ČECHOSL., vol. 81, pp , 2014.

33. Mechanical Properties
Dr. Syafiqah Saidin
Mechanical Properties
Fatigue failure : Metallic implant
Failure of dental implant
Failure of hip implant

34. Metal Processing - Casting
Dr. Syafiqah Saidin
Metal Processing - Casting
Formation of new deformable grain (recrystallisation) at recrystallisation temperature
Investment casting
Deformation
Annealing
Sintering / hardening at high temperature
Wrought alloy
Fabrication of small size implant form large ingots at high temperature (press forging, rotary forging, rolling, etc)
The deformation and annealing processes can be alternating repeated to achieve desired mechanical properties
Inclusion will affect mechanical properties depends on its position and size of implant
After casting, Required high temperature: Low forces needed and metal is ductile
The melting process need to be controlled to reduce the entrapment of oxide/inclusion particles and alloy segregation
Pouring of molten metal into metal mold to form cast alloy

35. Metal Processing - Casting
Dr. Syafiqah Saidin
Metal Processing - Casting
Forging
Casting
Rolling
Annealing

36. Metal Processing - Powder Metallurgy
Dr. Syafiqah Saidin
Metal Processing - Powder Metallurgy
Process of powder metallurgy
Powders are mixed, compacted into a shape

37. Metal Processing – Isostatic Pressing
Dr. Syafiqah Saidin
Metal Processing – Isostatic Pressing
Cold isostatic pressing
Hot isostatic pressing
Powders are mixed, pressurized compacted into a shape either at room temperature or elevated temperature

38. Metal Processing – Injection Molding
Dr. Syafiqah Saidin
Metal Processing – Injection Molding
Powders are mixed, injected into a mold. The mold is removed to collect the molded metal

39. Metal Processing – Powder Rolling
Dr. Syafiqah Saidin
Metal Processing – Powder Rolling
Powders are mixed, compressed in a rolling mill to become a metal sheet