Ming Li, Ph.D.
Professor of Materials Science and Engineering
Central South University
E-mail:[email protected]
Office: Room 308, Chemistry Building, Main Campus
BIOMATERIALS
Lecture 3: Metals as Biomaterials
Sept. 16, 2019
2
Last Lecture
• Nature of matter and materials
• Bulk properties of materials
• Surface properties of materials
• Surface analysis techniques
• Role of water
3
Contents
• Properties and challenges
• Commonly used metals
Stainless steel
Titanium
Cobalt alloys
• Smart metal biomaterials
Shape memory metals
Magnetostrictive materials
4
Most elements are metals. 88 elements to the left of
the stair-step line are metals or metal like elements
Metallic biomaterials
1. Properties and challenges
5
Metallic biomaterials: applications
• Bone and joint replacement
• Dental implants
• Maxillo and Cranio/facial reconstruction
• Cardiovascular devices
Titanium is regularly used for pacemaker cases and
defibrillators, as the carrier structure for replacement
heart valves, and for intra-vascular stents.
• External prostheses
• Surgical instruments
1. Properties and challenges
6
Pacemaker
7
Medical tubingStents
Catheters
1. Properties and challenges
8
Logic of Materials Science
1. Properties and challenges
9
Physical properties of Metallic Biomaterials
• Luster (shininess)
• Good conductors of heat and electricity
• High density (heavy for their size)
• High melting point
• Ductile (most metals can be drawn out
into thin wires)
• Malleable (most metals can be
hammered into thin sheets)
1. Properties and challenges
10
Tensile properties of metals
1. Properties and challenges
11
Chemical properties of metallic biomaterials
• Easily lose electrons
• Surface reactive
• Loss of mass (some corrode easily)
• Corrosion is a gradual wearing away
• Change in mechanical properties
1. Properties and challenges
12
Contents
• Properties and challenges
• Commonly used metals
Stainless steel
Titanium
Cobalt alloys
• Smart materials
Shape memory metals
Magnetostrictive materials
13
Commonly used metals
2. Commonly used metals
14
Stainless steel
• Stainless steels were the first metals
to be used in orthopaedics in 1926.
Steel used in the hip implants
until the end of 1970s
Sir John Charnley (1911-1982)
In 1960, Late Sir John Charnley has
done pioneer work in all aspect of
total hip arthroplasty (THA),
including the concept of low
frictional torque arthroplasty,
surgical alteration of hip
biomechanics, lubrication,
materials, design and clear air
operating room environment.
2. Commonly used metals
15
Stainless steel
• Types 316 and 316L are most widely used for implant
fabrication
• The only difference in composition between 316L and 316
stainless steel is the content of carbon.
• A wide range of properties exists depending on the heat
treatment or cold working (for greater strength and hardness).
• Even the 316L stainless steels may corrode inside the body
under certain circumstances in a highly stressed and oxygen
depleted region, such as contact under screws or fracture
plates.
• Thus, stainless steels are suitable to use only in temporary
implant devices, such as fractures plates, screws and hip
nails.
2. Commonly used metals
16
2. Commonly used metals
17
• Good corrosion and fatigue resistance in
short-term applications
• Low cost
• Easy to be machined
Stainless steel: pros & cons
• Tend to be corroded in long-term applications
• High modulus (stress shielding effect)
• Ni and Cr allergy
Pros:
Cons:
2. Commonly used metals
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Typical applications: Temporary implants
such as fixation screws and plates
2. Commonly used metals
19
Titanium and Nitinol (NiTi)
1. 2.2 million pounds of Ti implanted every year
2. hip joints, bone screws, knee joints, bone plates, dental
implants, surgical devices, and pacemaker cases
3. due to its total resistance to attack by body fluids, high
strength and low modulus.
4. commercially pure titanium (ASTM F67)
5. Ti-6Al-4V (ASTM F136)
6. most load bearing permanent implants
7. due to their low density, good corrosion
8. poor properties in articulation
2. Commonly used metals
20
Pros:
1. More flexible than stainless steel and closer to the
stiffness of bone
2. Good behavior under fretting corrosion and fatigue
although not specially good with respect to wear
3. Light
4. Greatest corrosion resistance;
5. Excellent biocompatibility
Cons:
1. Relatively low Young’s modulus
2. Lower shear strength
3. Low wear resistance
Titanium and its alloys
4. Expensive
5. High modulus (stress
shielding effect)
2. Commonly used metals
21
Crystal structure
2. Commonly used metals
22
α phase:
• corrosion resistance, biocompatibility
• weldability
• poor forgeability, low strength
α-β phase:
• can be strengthened by heat treatment
β phase:
• high hardenability
• good ductility and toughness
• high density
• low creep strength
• low tensile ductility in the aged state
• low wear resistance
2. Commonly used metals
Titanium
23
Ti-O binary phase diagram
What can you tell about the microstructure of titanium?
2. Commonly used metals
24
Titanium and alloys:
mechanical properties
2. Commonly used metals
25
Ti applications: vascular implants
1. Heart valve (Starr-Edwards
1961)
2. Packaging of pacemaker
3. Artificial hearts
4. Stents (nitinol)
2. Commonly used metals
26
Ti applications
2. Commonly used metals
27
Contents
• Properties and challenges
• Commonly used metals
Stainless steel
Titanium
Cobalt alloys
• Smart materials
Shape memory metals
Magnetostrictive materials
28
Smart materials
1. Shape Memory (Nitinol)
2. Magnetostriction (Terfenol-D)
3. Piezoelectric
3. Smart materials
29
Shape memory metals
3. Smart materials
Schematic of the shape memory effect created when the surrounding temperature
changes; NiTi alloy modifies its shape to a preprogrammed structure due to the
austenite-to-martensite phase transformations.
30
Shape memory metals
https://www.youtube.com/watch?v=-K57cbOhA5g
3. Smart materials
31
Nitinol stents
3. Smart materials
32
Magnetostrictive materials
No magnetic field
S N
Magnetic field applied
3. Smart materials
33
Magnetostrictive materials
3. Smart materials
34
Bone lengthening now...
Magnetostrictive materials
3. Smart materials
35
Bone lengthening in the future
*Synoste is a start-up from Aalto, FINLAND
Magnetostrictive materials
36
• Biodegradable metals
✓Mg, MgAl, FeMn
• Self-cleaning surfaces
✓Ag, ZnO, CuO, TiO2
• Nanoparticles
✓drug delivery
Future metallic biomaterials
37
Reading Materials:
Book: Biomaterials Science: An Introduction to Materials
in Medicine (3rd Edition, 2013)
• Metals: Basic Principles
38
Lecture 4: Ceramics, Glasses, and Glass-
Ceramics
On Wednesday, Sept. 18 , 2019
Next Lecture