Ming Li, Ph.D.

Professor of Materials Science and Engineering

Central South University

E-mail:liming0823@csu.edu.cn

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

18

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