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 4: Ceramics, Glasses, and Glass-

Ceramics

Sept. 18, 2019

2

Book: Biomaterials Science: An Introduction to Materials

in Medicine (3rd Edition, 2013)

• Two points for each error found

in the book

• Only count for the first person

who finds the error

NOTE

3

Last Lecture

• Properties and challenges

• Commonly used metals

Stainless steel

Titanium

Cobalt alloys

• Smart metal biomaterials

Shape memory metals

Magnetostrictive materials

4

Contents

• Properties of ceramics

• Ceramics as biomaterials

Inert ceramics

Porous ceramics

Bioactive Ceramics, Active

Glasses and Glass Ceramics

Biodegradable ceramics

5

Contents

• Properties of ceramics

• Ceramics as biomaterials

Inert ceramics

Porous ceramics

Bioactive Ceramics, Active

Glasses and Glass Ceramics

Biodegradable ceramics

6

Ceramic biomaterials

❑ Ceramics are refractory polycrystalline compounds;

• Inorganic

• Hard and brittle

• High compressive strength

❑ Applications:

• Orthopaedic load-bearing coatings

• Dental implants

• Bone graft substitutes

• Bone cements

1. Properties of ceramics

7

1. Inert (Al2O3, ZrO2)

2. Nearly inert, porous (hydroxyapatite)

3. Bioactive (bioglass)

4. Resorbable/degradable (Ca3(PO4)2)

Types of ceramic biomaterials

Bioactive compound is a compound that has an effect on a

living organism, tissue or cell.

Bioresorbable compounds are designed to degrade safely

within the body.

1. Properties of ceramics

8

Definitions

If the material is...

• toxic surrounding tissue dies

• nontoxic and biologically inactive (nearly inert)

fibrous tissue of variable thickness forms

• nontoxic and biologically active (bioactive): an

interfacial bond form

• nontoxic and dissolves: surrounding tissue

replaces it

1. Properties of ceramics

9

Pros:

1. inert or bioactive

2. high wear resistance

3. high stiffness and compression strength

4. aesthetic (dental)

Cons:

1. brittle

2. low tensile strength

3. low fatigue strength

Ceramic biomaterials

1. Properties of ceramics

10

1. Properties of ceramics

Types of ceramic biomaterials

11

Bioactivity spectra for

various bioceramic implants

(A) Relative rate of bioreactivity

(B) Time-dependence of

formation of bone bonding at

an implant interface.

1. Properties of ceramics

12

Ceramic Biomaterials

1. Properties of ceramics

BIOLOX®* delta ceramic femoral head

13

Natural hard tissues are ceramic-polymer composites

• Bones, Teeth, Shells

Hydroxyapatite Ca5(PO4)3OH gives teeth and bones their

hardness!

Hard tissues

14

Bonding structure

The extent to which a ceramic lattice is ionic or covalent in

nature will depend on the electro-negativities of the atoms

involved

15

Contents

• Properties of ceramics

• Ceramics as biomaterials

Inert ceramics

Porous ceramics

Bioactive Ceramics, Active Glasses

and Glass Ceramics

Biodegradable ceramics

16

Inert Ceramics

Alumina (Al2O3) and Zirconia (ZrO2)

2. Ceramics as biomaterials

17

Used in total hip arthroplasty since 1970

• high-purity alumina (around 99.7%)

• MgO controls grain size during the

sintering process

Alumina used in orthopaedic applications

should have a grain size <7 μm

Alumina (Al2O3)

2. Ceramics as biomaterials: Inert Ceramics

18

Crystal structure of alumina (○: aluminum; ●: oxygen)

2. Ceramics as biomaterials: Inert Ceramics

Rhombohedral structure (a = 4.758 Å

and c = 12.991 Å)

19

Production of Alumina

Three stages:

1. Extraction: The aluminum-bearing minerals in bauxite are

selectively extracted from the insoluble components by

dissolving them in a solution of sodium hydroxide.

Al(OH)3 + Na+ + OH− → Al(OH)4− + Na+

2. Precipitation: Crystalline aluminum trihydroxide is precipitated.

This is the reverse of the extraction process, except the

chemistries are well-controlled.

Al(OH)4− + Na+ → Al(OH)3 + Na+ + OH−

3. Calcination: Aluminum trihydroxide is calcined to form

alumina. The water is driven off to form alumina. This process

dictates the properties of the final product.

2Al(OH)3 → Al2O3 + 3H2O

20

Total hip

replacement

implants

Total knee

replacement

implants Ceramic

Dental

ImplantsBIOLOX®* delta

ceramic femoral

head.

Alumina: Applications

2. Ceramics as biomaterials: Inert Ceramics

21

Zirconia (ZrO2)

Yttrium stabilizes the tetragonal phase

2. Ceramics as biomaterials: Inert Ceramics

22

Zirconia failures

Long term tension and moisture...

Monoclinic content from 1%→30% on the surface

→Surface roughness from 0.006 m up to 0.12 μm

2. Ceramics as biomaterials: Inert Ceramics

23

Zirconia

Still widely used in dental applications

2. Ceramics as biomaterials: Inert Ceramics

24

• Good mechanical tissue-implant fixation

• Poor mechanical properties

Porous Ceramics

When pore sizes exceed 100 µm, bone will grow within the

interconnecting pore channels near the surface and maintain

its vascularity and long-term viability.

2. Ceramics as biomaterials

25

2. Ceramics as Biomaterials

Bioactive Ceramics, Active

Glasses and Glass-Ceramics

• Bonding to bone was first demonstrated for a compositional range of

bioactive glasses that contained SiO2, Na2O, CaO, and P2O5 in specific

proportions

• Many bioactive silica glasses are based upon the formula called 45S5,

signifying 45 wt.% SiO2 (S = the network former) and 5:1 ratio of CaO

to P2O5.

• Glasses with lower ratios of CaO to P2O5 do not bond to bone.

Substitutions in the 45S5 formula of 5–15wt.% B2O3 for SiO2 or 12.5

wt.% CaF2 for CaO or heat treating the bioactive glass compositions to

form glass-ceramics have no measurable effect on the ability of the

material to form a bone bond. However, adding as little as 3 wt.% Al2O3

to the 45S5 formula prevents bonding to bone.

26

The compositional dependence of bone and soft tissue bonding

on the Na2O–CaO–P2O5–SiO2 glasses

Compositional dependence (in wt.%) of

bone bonding and soft tissue bonding of

bioactive glasses and glass-ceramics. All

compositions in region A have a constant

6 wt.% of P2O5. A-W glass ceramic has

higher P2O5 content. IB, Index of

bioactivity.

2. Ceramics as Biomaterials: Bioactive Ceramics,

Active Glasses and Glass-Ceramics

• All the glasses contain a constant 6 wt.% of

P2O5.

• Compositions in the middle of the diagram

(region A) form a bond with bone.

• Consequently, region A is termed the

bioactive bone bonding boundary.

• Silicate glasses within region B (e.g.,

window or bottle glass or microscope

slides) behave as nearly inert materials and

elicit a fibrous capsule at the implant–tissue

interface.

• Glasses within region C are resorbable and

disappear within 10 to 30 days of

implantation.

• Glasses within region D are not technically

practical, and therefore have not been

tested as implants

27

Glasses and Glass-ceramics

2. Ceramics as Biomaterials: Bioactive Ceramics,

Active Glasses and Glass-Ceramics

28

Types of silicate glass interfaces with

aqueous or physiological solutions

29

30

Calcium Phosphate Ceramics• Bone typically consists by weight of 25% water, 15% organic materials,

and 60% mineral phases. The mineral phase consists primarily of calcium

and phosphate ions, with traces of magnesium, carbonate, hydroxyl,

chloride, fluoride, and citrate ions.

• Calcium phosphates occur naturally in the body

• But they also occur within nature as mineral rocks, and certain

compounds can be synthesized in the laboratory.

Mineral name, chemical name, and composition of various phases

of calcium phosphates

2. Ceramics as Biomaterials: Bioactive Ceramics,

Active Glasses and Glass-Ceramics

31

Thermodynamic stability of calcium

phosphates in a water atmosphere

32

Hydroxyapatite(Ca10(PO4)6(OH)2), HAP

2. Ceramics as Biomaterials: Bioactive Ceramics,

Active Glasses and Glass-Ceramics

33

Optical properties

Raman spectrum of HAP samples

Hydroxyapatite

34

960 cm-1

mouse cortical bone (785-nm laser)

Hydroxyapatite

35

Raman FTIR

poorly crystalline HAP

bovine cortical bone

HAP ceramic

highly crystalline HAP

Hydroxyapatite

36

Hydroxyapatite

37

XRD patterns

Hydroxyapatite

38

Hydroxyapatite

39

Hydroxyapatite: Mechanical Properties

Hydroxyapatite

40

Biodegradable bioceramics

Degradation Mechanism:

Degradation = chemical breakdown of the bulk materials

1. Physiochemical dissolution

2. Physical disintegration into small particles at grain

boundaries

3. Biological factors, such as phagocytosis

2. Ceramics as Biomaterials

41

❑ All calcium phosphate ceramics biodegrade to varying degrees;

the rate of biodegradation increases as:

1. Decreasing Ca/P ratio

2. Surface area increases (powders > porous solid >dense solid);

3. Crystallinity decreases;

4. Crystal perfection decreases;

5. Crystal and grain size decrease;

6. There are ionic substitutions of CO32-, Mg2+, and Sr2+ in HA.

❑ Factors that tend to decrease the rate of biodegradation include:

(1) F− substitution in HA;

(2) Mg2+ substitution in β-TCP; and

(3) lower β-TCP/HA ratios in biphasic calcium phosphates.

2. Ceramics as Biomaterials: biodegradable bioceramics

42

Typical forms of calcium phosphates

2. Ceramics as Biomaterials: biodegradable bioceramics

43

Degradation of ceramic biomaterials

Osteoclasts (bone-resorbing cells) mediate true degradation of

the ceramic component of bone

Takeway is that osteoclasts "eat"crystal fragments, which are

then metabolized intracellularly

2. Ceramics as Biomaterials: biodegradable bioceramics

44

α-TCP:

• dissolution speed limits usage

β-TCP:

• Osteoinductive degradation similar to

bone resorption

Tricalcium phosphates (TCP)

2. Ceramics as Biomaterials: biodegradable bioceramics

45

• preservation of strength

• degradation speed = regeneration speed

• degradation products

Challenges for degradable ceramics

2. Ceramics as Biomaterials: biodegradable bioceramics

46

Reading Materials:

Book: Biomaterials Science: An Introduction to Materials

in Medicine (3rd Edition, 2013)

• Ceramics, Glasses, and Glass-Ceramics: Basic Principles

47

Lecture 5: Carbon Biomaterials

On Tuesday, September 23, 2019

Next Lecture