BIOMATERIALS

ENT 219

Ceramic

Biomaterials

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1.0 INTRODUCTION

• Ceramics are inorganic materials composed of non-

directional ionic bonds between electron donating and

electron –accepting elements.

• Mechanical properties of ceramics:

– Hard

– Brittle

• Allow for little deformation before failure

– Can withstand high compression stress

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• BIOMEDICAL

APPLICATION

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• WHY CHOOSE CERAMIC AS BIOMATERIALS?

– Have an appropriate mechanical properties for particular medical application such as dental crowns.

– Biocompatible:

• Relative inertness to the body fluid.

• More resistant to degradation.

– Have a similar chemistry and mechanical properties with natural bone → more often used as a part of orthopaedic implant (coating material) or as dental materials (crowns, dentures).

– High wear resistance

1.0 INTRODUCTION

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2.1 MICROSTRUCTURE OF CERAMIC

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2.1 MICROSTRUCTURE OF CERAMIC

• MICROSTRUCTURAL FEATURES

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3.0 BIOMEDICAL APPLICATION

• DENTISTRY

– Dental filling, Dental crown, dentures

– Why widely used in dentistry

• Relatively inert to body fluid

• High compressive strength

• Aesthetically pleasing apparent

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3.0 BIOMEDICAL APPLICATION

• Artificial hip joint

• Femoral head/ball of hip implant

• Coating of hip stem

• Acetabular inner cup of hip implant

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Femoral component

• femoral stem (metal)

• neck (metal)

• head/ball (metal or

ceramic)

Acetabular component

• Inner cup (Polymer or ceramic)

• Outer cup (Metal)

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3.0 BIOMEDICAL

APPLICATION

• Bone Reconstruction

Materials

– Dense

– Porous

– Granular

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3.0 BIOMEDICAL APPLICATION:

Bone Reconstruction Materials

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3.0 BIOMEDICAL APPLICATION

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Bone Reconstruction Materials

4.0 DESIRED PROPERTIES OF BIOCERAMICS

In order to be classified as a bioceramic, the ceramic

material must exceed such properties:

1. Should be nontoxic

2. Should be noncarcinogenic

3. Should be nonallergic

4. Should be non inflammatory

5. Should be biocompatible

6. Should be biofunctional for its lifetime in host

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• Some typical room temperature properties of

bioceramics and corticol bone

5.0 TYPE OF BIOCERAMICS

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5.0 CLASSIFICATION OF BIOCERAMICS

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• Can be classified based on:

1. Behavior in the body environment

1. BIOINERT CERAMICS

2. BIOACTIVE CERAMICS

3. BIORESORBABLE BIOCERAMICS

2. Morphology

• Dense or Porous

3. Application fields

• Orthopedic, Bone substitute materials, Dental or Drug delivery

5.0 CLASSIFICATION OF BIOCERAMICS –

behaviour in body environment

5.1 BIOINERT CERAMICS

5.2 BIOACTIVE CERAMICS

5.3 BIORESORBABLE BIOCERAMICS

Notes

Absorbable : Capable of being absorbed or

taken in through the pores of a surface17

5.1 BIOINERT CERAMICS

• Bioceramics that are stable and do not show any harmful effect

or bioactivity in human body.

• Resist corrosion and wear

• Have all the six (6) desired properties of implantable

bioceramics.

• Have a reasonable fracture toughness.

• Typically used as structural-support implant such as bone

plates, bone screw and femoral heads.

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5.1.1 ALUMINA or Aliminum oxides (Al203)

• The main source of alumina or aluminium oxide is

bauxite and native corundum.

• Highly stable oxide – very chemically inert

• Low fracture toughness and tensile strength – high

compression strength

• Very low wear resistance

• Quite hard material, varies from 20 to 30 GPa.

5.1 BIOINERT CERAMICS

Notes

Bauxite and corundum is type of minerals19

5.1 BIOINERT CERAMICS

• Mechanical properties requirement:

– Compressive strength: 4 -5 Gpa

– Flexural strength : > 400MPa

– Elastic modulus: 380 GPa

– Density : 3.8 – 3.9 g/cm3

– Generally quite hard : 20 to 30 GPa

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5.1 BIOINERT CERAMICS

ALUMINA

High hardness + low friction + low wear+ inert to in vivo environment

Ideal material for use in:

• Orthopaedic joint replacement component, e.g. femoral head of hip

implant

• Orthopaedic load-bearing implant

• Implant coating

• Dental crown21

5.1 BIOINERT CERAMICS

5.1.2 ZIRCONIA (Zr202)

• Pure zirconia can be obtained from chemical conversion

of zircon, which is an abundant mineral deposit.

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5.1 BIOINERT CERAMICS

• Has a high melting temperature

and chemical stability.

• The bending strength and

fracture toughness are 2-3 and

2 times greater than alumina.

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5.1 BIOINERT CERAMICS

• The improved mechanical properties plus excellent

biocompatibility and wear properties make this material

the best choice the new generation of orthopaedic

implant.

• Has already widely use to replace alumina and metals.

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5.1 BIOINERT CERAMICS

5.1.3 CARBON

• Light, excellent in lubricating activity, strong against wear

and fatigue.

• Carbon can be made in many allotropic forms:

– Crystalline diamond

– Graphite

– Nanocrystalline glassy carbon

– Quasicrystalline pyrolitic carbon

• Only Pyrolitic carbon is widely utilized for implant

fabrication.

• Application: surface coating, artificial heart valve (anti wear,

anti-thormbosis.25

5.2 BIOACTIVE CERAMICS

• Bioceramics that bond directly with tissue without

having fibrillar connective tissue between the

bioceramics and bone

• Used as fixation of implants in the skeletal system

• Low mechanical strength and fracture toughness

• Examples of materials:

– Apatite

– Bioglass

– Dense nonporous glasses 26

Similarity of bioactive and bioinert

ceramics • Bioactive ceramics and bioinert ceramics exist in human

body for lifetime without being resorbed except of

carbonate apatite.

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Calcium Phosphate

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Adapted from Ishikawa, K., Matsuya, S., Miyamoto, Y. & Kawate, K. 2003. Bioceramics. In:

Milne, I., Ritchie, R. O. & Karihaloo, B. (eds.) Comprehensive Structural Integrity. Oxford:

Pergamon.

Calcium Phosphate

• Low values of mechanical strength and fracture toughness,

thus cannot be used in load bearing materials.

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5.2 BIOACTIVE CERAMICS

5.2.1 Hydroxyapatite

• Calcium phosphate can be crystallized into salts such as

Hydroxyapatite.

• Hydroxyapatite (HAP) has a similar properties with

mineral phase of bone and teeth.

• Important properties of HAP:

– Excellent biocompatibility

– Form a direct chemical bond with hard tissue

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5.2 BIOACTIVE CERAMICS

• Application:

1. Bone graft substitute in a granular or a solid block.

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5.2 BIOACTIVE CERAMICS

• Application (cont):

2. Temporary scaffold which is gradually replaced by tissue

3. Orthopaedic and dental implant coating

4. Dental implant materials

• Drawback:

– Complicated fabrication process and difficult to shape

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5.2 BIOACTIVE CERAMICS

5.2.2 Bioactive glass

• Glass-ceramics are crystalline materials obtained by the

controlled crystallization of an amorphous parent glass.

• Controlled crystallisation requires:

– specific compositions

– usually a two-stage heat-treatmen

– Controlled nucleation

• Controlled crystallization will growth of crystal of small

uniform size

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5.2 BIOACTIVE CERAMICS

• Type of glass ceramic

– Bioglass

– Ceravital

• Both are SiO2, CaO, Na2O and P2O5 systems

• Bioglass composition manipulated to induce direct bonding

with the bone

– Must simultaneously form a calcium phosphate and SiO2 – rich film

layer on surface of ceramic for this to happen

– With correct composition will bond with bone in approximately 30

days

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Bioglass structure

3D printed test structures for porosity

analysis.

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5.2 BIOACTIVE CERAMICS

• Glass ceramic properties

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5.2 BIOACTIVE CERAMICS

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5.2 BIOACTIVE CERAMICS

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5.2 BIOACTIVE CERAMICS

• Application of Glass Ceramic

– Orthopaedic and dental implant coating

– Dental implant

– Facial reconstruction components

– Bone graft substitute material

• Main limitation:

– Brittleness

– Cannot be used for making major load bearing implant such as joint

implant

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5.3 BIORESORBABLE CERAMICS

• Gradually and steadily chemically broken down and resorbed

in the body

• The resorbed material is replaced by endogenous tissue

• Chemicals produced as the ceramic is resorbed must be able to

be processed through the normal metabolic pathways of the

body without evoking any deleterious effect.

• Synthesize from chemical (synthetic ceramic) or natural sources

(natural ceramic)

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5.3 BIORESORBABLE CERAMICS

• Examples:

1. Tricalcium phosphate

2. Calcium Carbonate

3. Carbonate apatite

4. Calcium sulfate dihydrate or gypsum

• Plaster of paris, POP

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5.3 BIORESORBABLE CERAMICS

Tricalcium phosphate

• Three polymorphs – ß, α, α’ with different crystal structure

according to the order of temperature

• Composition similar to hydroxyapatite

• Degrades faster than calcium phosphate

• More soluble than synthetic HAP

• Allow good bone in growth and eventually is replaced by

endogenous tissue.

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5.3 BIORESORBABLE CERAMICSCalcium Carbonate

• Occurring in nature

– Calcite

• Stable phase

– Aragonite

• metastable

• Corals/Seashells transformed into HAP

• Biocompatible

• Facilitate bone growth

• Used to repair traumatized bone, replaced disease bone and correct various

bone defect.

• Bone scaffold

– Vaterite

• matastable 44

5.3 BIORESORBABLE CERAMICS

• Carbonate apatite

– Biological apatite –constituent of booth tooth and bone

– Contains 3-5% of carbonate ions in its lattice sites for

phosphate and hydroxyl ions.

– A -type : substitution of carbonate ion for OH site

– B-type : substitution of carbonate ion for PO4 site

• The main constituent of the biological apatite

– Solubility increases with carbon content

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5.3 BIORESORBABLE CERAMICS

• Application of bioresorbable ceramics

– Bone substitute materials

• Bone cement

• Bone granule

– Bone scaffold

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6.0 BIODEGRADATION OF CERAMIC

DEFINITION

• Biodegradation: chemical breakdown of a material

mediated by any component of the physiological

environment ( such as water, ions, cells, proteins, and

bacteria).

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BIODEGRADATION

Uncontrolled

degradation

Controlled

degradation

ceramic degrade

primarily via dissolution,

this because ceramic formulation

are highly soluble in

aqueous environment

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6.1 UNCONTROLLED DEGRADATION• DEPEND ON TWO FACTOR

– Mechanical environment

• Stress induced degradation can occur in ceramics under tension.

• If crack is formed in these materials, the tensile stress may lead

to further dissolution at the crack tip and material fracture.

– Ceramic porosity

• Pores are stress raiser thus may increase the formation of cracks

or the rate of their propagation.

• The presence of pores promotes degradation by creating more

surface area for reaction with environment

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Cracks

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6.1 UNCONTROLLED DEGRADATIONUncontrolled

degradation

Mechanical

environment

Ceramic porosity

-stress raiser

Stress induced

degradation

Wear

-main problem

Produces biologically

active particles

Lead to inflammation and

implant loosening52

6.1 UNCONTROLLED DEGRADATION

• Uncontrolled degradation will cause WEAR.

• WEAR → the generation of fine wear particles that can lead to

inflammation and implant loosening.

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6.1 UNCONTROLLED DEGRADATION

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6.2 CONTROLLED DEGRADATION

• Degradation is desirable.

• Controlled biomaterial degradation can be used as an

important part of tissue engineering and drug delivery

therapies.

• For these application, the temporary nature of the

material is ideal to promote localized tissue healing or

release of a bioactive agent without the need for second

surgery to remove implant.

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6.2 CONTROLLED DEGRADATION

• Biodegradable ceramics are usually type of calcium

phosphate, such as

– Hydroxyapatite, HA (Ca10(PO4)6(OH)2)

– Tricalcium phosphate, TCP (Ca3(PO4)2)

• Biodegradable ceramic generally degrade by dissolution

(influenced by the solubility of the ceramic formulation

in media and the pH of the media) coupled with physical

disintegration.

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6.2 CONTROLLED DEGRADATION

FACTOR THAT INFLUENCE DEGRADATION RATE

1. Chemical susceptibility of the material

• Hydrated forms such as hydrated calcium sulphate

degrade faster than their nonhydrated counterparts.

• Ionic substitution of CO32- ,Mg2+ or Sr2+ in

Hydroxyapatite decrease the overall degradation

time, while F- substitution makes this material less

susceptible to dissolution.

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6.2.1 FACTOR THAT INFLUENCE DEGRADATION RATE

2. Amount of crystallinity

• Ceramic degradation depend on water penetration.

• A more tightly packed crystalline material is less

susceptible to dissolution than a ceramic that is mainly

amorphous (unstructured).

• Polycrystalline ceramics degrade more quickly than single

crystal ceramic due to presence of grain boundaries.

• Ceramic contain many smaller crystals is more susceptible to

dissolution than one with fewer, larger crystal. 58

6.2.1 FACTOR THAT INFLUENCE DEGRADATION RATE

3. Amount of media (water) available

• High amount of water → increase degradation rate

• Low amount of water → slower degradation rate

4. Material surface area to volume ratio

• Highly porous ceramic will dissolve more quickly than

the same ceramic with fewer pores due to increase in

area for interaction with the environment.

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6.2.1 FACTOR THAT INFLUENCE DEGRADATION RATE

Highly porosity Low porosity

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6.2.1 FACTOR THAT INFLUENCE DEGRADATION RATE

5. Mechanical environment

• Ceramic degradation is encouraged in areas with high

mechanical stress, either due to

– Implant site location

– Presence of stress raiser in the device

– Production of wear particles will caused inflammatory

response → pH drop → accelerate degradation of

material

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Extra: Bone scaffold

Perfection regained: the perfect fit of the

Sandia ceramic scaffolding in the model jaw

also recreates the upper line of the original

jawbone. The scaffold layering, which cross

each other like a child's Lincoln Logs,

are approximately 500 microns apart to

expedite passage of new bone and blood

vessels.62

The milled implant from a wax-embedded

scaffold of hydroxyapatite.Once the device is milled, the wax is melted out, and

the implant is finished.

The porous structure of the scaffold allows bone to

grow into it,

providing the future basis for the growth of new bone

in a patient.

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The final implant scaffold fit

tested in the patients jaw.

The underside of the final implant scaffold,

showing the modeled canal for the nerve path.

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Attachment

• Allotropy is the property of some chemical elements to be

able to take two or more different forms, where the atoms

are arranged differently by chemical bonds.

• The forms are known as allotropes of that element.The

phenomenon of allotropy is sometimes also called

allotropism.

• For example, carbon has two common allotropes: diamond,

where the carbon atoms are bonded together in a tetrahedral

lattice arrangement,

• And graphite, where the carbon atoms are bonded together

in sheets of a hexagonal lattice.

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Thank you

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