Ceramics Biomaterials

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3. Ceramic biomaterials: contents 3.0 Ceramics (1) Definition (2) Characteristics 3.1 Outline of ceramic biomaterials (1) Applications (2) Classification 3.2 Ceramic biomaterials (1) Oxides (2) Glasses (3) Calcium phosphates 1

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Ceramic Biomaterials

Transcript of Ceramics Biomaterials

Page 1: Ceramics Biomaterials

3. Ceramic biomaterials: contents 3.0 Ceramics

(1) Definition

(2) Characteristics

3.1 Outline of ceramic biomaterials

(1) Applications

(2) Classification

3.2 Ceramic biomaterials

(1) Oxides

(2) Glasses

(3) Calcium phosphates 1

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3.0 Ceramics

(1) Definition

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Definition

“Ceramics” from keramos (the Greek word)

the art and science of making and using solid

articles formed by the action of heat on earthy raw

materials

the art and science of making and using solid articles

which have as their essential component, and are

composed in large part of, inorganic materials

(Introduction to ceramics, 2nd edition, 1976)

Inorganic and nonmetallic solid materials

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Ceramics

metal-nonmetal compounds: TiC, Al2O3, ZrN, ・・・ semi metal-nonmetal compounds: SiC, SiO2, BN, ・・・ crystalline, non-crystalline oxide, carbide, nitride, boride, ・ ・・ pottery, glass, refractory, cements, structural clay products , ・ ・・ + new ceramics (fine ceramics)

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Fine ceramics

According to ISO 20507: Fine ceramics (advanced ceramics,

advanced technical ceramics) - Fine Ceramics are " highly

engineered, high performance, predominantly non-metallic,

inorganic, ceramic material having specific functional

attributes".

the 1980s: fine ceramics boom

(magnetic, ferroelectronic, structural,,,)

1986: High-temperature superconductor

(La-Ba-Cu-O system)

Improvement in processing and purity of ceramic source powders

development of bioceramics 5

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3.0 Ceramics

(2) Characteristics

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Characteristics of ceramics Chemical bonding: ionic and covalent bonding

high melting point

high hardness

high chemical stability

high elastic modulus

high creep property

low density

low thermal expansion coefficient

brittle(脆性)

poor workability(難加工性)

sensitive to flaw(欠陥に敏感)

Anisotropy in bonding direction

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Mechanical properties of ceramics

(A. Nozue, Bull. Ceramic Soc. Jpn., 38 (2003), 21.)

Materials Tensile strength (MPa)

Bending strength (MPa)

Compressive strength (MPa)

Elastic modulus (GPa)

Fatigue limit (MPa)

Fracture toughness (MPa/m1/2)

Cortical bone

Cancellous bone

Ti-6Al-4V alloy

Co-Cr-Mo alloy

Titanium

Alumina

Zirconia

Hydroxyapatite

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Stress-strain curves

Figure 1-1 Schematic illustration of stress-strain curves of biomaterials.

(中野貴由:医療用金属材料概論, (2010), 191)

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Comparison with other biomaterials

Materials Examples Advantages Disadvantages

Metals

Titanium and its alloys

Co-Cr alloys

Stainless steels

Au, Ag, Pt

Excellent balance of strength

and ductility

Shape memory effect

Electrical conductivity

Thermal conductivity

May corrode

High density

Ceramics

Alumina(Al2O3)

Zirconia(ZrO2+oxide)

Hydroxyapatite

(Ca10(PO4)6(OH)2)

Calcium phosphate

Very biocompatible

High strength

High wear resistance

Inert

Brittle

Not resilient

Difficult to make

Polymer

Silicone

Polymethylmethacrylate

(PMMA)

Polyethylene

Easy to fabricate

Low density

Resilient

Not strong

Deforms with time

May degrade

Ceramics Wear resistance

Chemical stability

Biocompatibility with bone

Table 1-3 Classification of biomaterials by structure and chemical bond.

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3.1 Outline of ceramic biomaterials

(1) Applications

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Applications

Orthopedic (整形外科)

Dental (歯科)

Coating (コーティング材)

+

Scaffold (足場材料)

(Biomaterials Science, An Introduction to Materials in

Medicine 2nd Ed. Elsevier, (2004), p.162.) 12

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Ceramic biomaterials

耐摩耗性 人工股関節骨頭 人工歯(上部構造) 生体活性 骨と化学的に結合する 人工骨(骨充填材) 生体吸収性 骨と置換する 人工骨(骨置換材) 再生医療用足場材料

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Orthopedic field: materials used in Japan

Figure 2-1 Mass of biomaterials in orthopedic field in Japan. (T. Narushima, J. Jpn. Inst. Light Metals, 55 (2005), 561-565.) 14

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stem

ball

cup

backing

Figure 3-1 Artificial hip joint. a: backing, b: cup, c: ball, d: stem

Figure 3-2 Biomaterials used in artificial hip joint. (Biomedical Engineering Handbook, Vol.1 (2000), 44-16.)

Orthopedic field: artificial hip joint Orthopedic load-bearing applications

: alumina (Al2O3), zirconia

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Coating: artificial hip joint and dental implant

Rapid and strong fixation at

bone/titanium interface

Coating for chemical bonding with bone

(Ca10(PO4)6(OH)2, hydroxyapatite, HAp)

(bioglass)

artificial hip joint dental implant

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Coating: processing

Currently, plasma spraying is the primary

method used commercially to fabricate a

calcium phosphate coating on dental implants.

However, plasma-sprayed calcium phosphate

coating exhibits a poor adherence to titanium

substrates and nonuniformity.

New coating

processes

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Figure 3-3 Reconstruction of right calf bone

using b-TCP(Ca3P2O8) porous body. (H. Irie, Bull. Ceramic Soc. Jpn., 38 (2003), 57.)

Temporary bone space filler

After 18 months

b-TCP

(Tricalcium phosphate,

Ca3P2O8)

Bioresorbable or

biodegradable material

The porous b-TCP body was

substituted with bone.

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Parameters in scaffold materials

Stability

Resorption rate

Bioactive molecules / ligands

Soluble factors

Strength

・・・・

Signaling

molecule Scaffold

Cell

Three factors required for tissue engineering

Porous calcium phosphate

tissue

engineering

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Figure 3-4 Hydroxyapatite porous body. (M. Nakasu et al., Bull. Ceramic Soc. Jpn., 40 (2005), 828.)

Scaffold in tissue engineering

The structure of a substrate

made of synthetic materials

is needed for the growth of a

new tissue using living cells.

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3.1 Outline of ceramic biomaterials

(2) Classification

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Classification (1) From composition and crystalline structure

of ceramic biomaterials

Oxides alumina, zirconia,・・・

Glasses bioglass, crystallization glass,・・・

Calcium phosphates hydroxyapatite, tricalcium phosphate,・・・

In this lecture, we use the above classification.

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Classification (2) When materials are implanted into bone, there are four types of

response at the interface between implant and bone.

Capsule:

bioinert

Implantation

Dead: toxic

Dissolved:

bioresorbable

Bonding:

bioactive

Material

bone

Figure 3-5 Response at the interface between implant and bone. 23

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Classification (2) When materials are implanted into bone, there are four types of

response at the interface between implant and bone.

material: toxic

The surround tissue dies.

not practical materials

material: non-toxic and biologically inactive

A fibrous tissue of variable thickness forms.

Bioinert materials

material: non-toxic and biologically active

An interfacial bond forms.

Bioactive materials

material: non-toxic and dissolved

The surrounding bone replaces it.

Bioresorbable or Biodegradable materials

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Classification (2) When materials are implanted into bone, there are four types of

response at the interface between implant and bone.

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3.2 Ceramic biomaterials

(1) Oxides

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Oxide: Alumina

Alumina: Al2O3

Excellent wear resistance

Chemically stable

ball for artificial hip joint

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Artificial hip joint

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Alumina: properties

(Biomaterials Science, An Introduction to Materials in

Medicine 2nd Ed. Elsevier, (2004), p.157.)

Single crystalline

alumina

99.9

3.95

392

1270

2100

0.01

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Oxide: zirconia

Zirconia: ZrO2

Pure zirconia (ZrO2): not an engineering material

because

There are two allotropic transformations.

monoclinic ⇆ tetragonal ⇆ cubic

At around 1400 K, t-m transformation causes

4.6% volume change.

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Pure zirconia: properties

(Biomaterials: An Introduction,

Springer, (2007), p.145.)

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(T. Miyazaki, J. Jpn. Soc. Biomater., 25 (2007), 374.)

Zirconia: transformation

●: Zr

○: O expansion

monoclinic tetragonal cubic shrinkage

Temperature

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Zirconia: stabilizing

Fully stabilized

zirconia

Partially stabilized

zirconia

When oxide such as CaO,

MgO or Y2O3 was added

to pure zirconia, cubic and

tetragonal phases are

stabilized.

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Zirconia: properties

(Biomaterials: An Introduction, Springer, (2007), p.147.)

CSZ: calcia stabilized zirconia

Y-Mg-PSZ: yttria and magnesia partially stabilized zirconia

Y-TZP: yttria-stabilized tetragonal zirconia polycrystal

The fracture toughness of PSZ is larger than that of alumina

(5-6 MPa・m1/2),because

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One of toughening mechanisms

(Biomaterials: An Introduction, Springer, (2007), p.147.)

Crack before

transformation

Crack arrestment due to

t-m transformation

(t→m: expansion!) 35

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Practically, partially stabilized zirconia (PSZ) with 3mol%Y2O3

(tetragonal phase) is only commercially available.

Zirconia: current status

Wear property

Fracture toughness Zirconia > Alumina

However,

Reaction between zirconia and water ?

Zr-O-Zr + H2O Zr-OH + HO-Zr

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3.2 Ceramic biomaterials

(2) Glasses

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Bioactive glass ceramics

Some glass ceramics: bioactivity

A lot of bioactive glass ceramics have

been developed so far. They are

classified into two groups, that is,

bioglass (バイオガラス) and

crystallization glass (結晶化ガラス).

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(Manual of orthopaedic materials, (1992), 49.)

Glass: structure

glass crystal

○ long-range order × long-range order

○ short-range order

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(Handbook of ceramics, 2nd edition, application, (2002), 491)

Crystallization glass Composite of glass phase and crystalline phase

glass particles

at room temp.

Fusion of

glass particles

at 850 ℃ for 0 h.

start of crystallization

at 950 ℃ for 0 h.

end of crystallization

at 1100 ℃ for 1 h.

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Table 3-3

A-W GC: apatite- and wollastonite-containing glass-ceramics

MB GC: machinable bioactive glass-ceramic (Biomaterials Science, An Introduction to Materials in Medicine 2nd Ed. Elsevier, (2004), p.159.)

Composition of bioactive glasses and crystallization glass

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Bioglass

In 1971 Hench: SiO2-Na2O-CaO-P2O5

glass can bond with bone.

45S5: 45SiO2-24.5CaO-24.5Na2O-6P2O5 (mass%)

It had a great impact because such a

inorganic material has bioactivity.

(bioactivity of synthesized hydroxyapatite:

1977)

He named this material “bioglass”.

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(Biomaterials: An Introduction, Springer, (2007), p.156.)

All compositions in region A have a

constant 6 mass% P2O5.

45S5

Compositional dependence of bioactivity

Region A: bonding in 30 days

with bone (Bioactive)

Region B: non bonding

- too low reactivity

(Bioinert)

Region C: non bonding

- too high reactivity

(Bioresorbable)

Region D: not technically

practical

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Properties of bioglass

Advantage : high bioactivity

Application : artificial bone in middle ear

Disadvantage: poor mechanical strength

Bioactive crystallization glass

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Bioactive crystallization glass

Composite of glass phase and crystalline phase

to increase mechanical strength

Ceravital In 1972, Brömer: SiO2-Na2O-CaO-P2O5 glass

with less Na2O contents

Crystalline phase: apatite (Ca10(PO4)6O)

Ex.

46SiO2-37.5CaO-5Na2O-11.5P2O5 (mass%)

(cf. 45S5: 45SiO2-24.5CaO-24.5Na2O-6P2O5)

Bending strength: 100 MPa >> Bioglass

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Bioactive crystallization glass: A-W GC

To increase mechanical strength for hard tissue replacement

A-W GC(apatite and wollastonite glass ceramics) In 1982, Kokubo (Kyoto University, Japan)

SiO2-CaO-MgO-P2O5(–CaF2) glass

Crystalline phase: apatite (Ca10(PO4)6(O・F2))

wollastonite (CaSiO3)

Composition(mass%)

34.2SiO2-44.9CaO-16.3P2O5-4.6MgO-0.5CaF2

Bending strength: 220 MPa >> Ceravital

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Strength of glass ceramics

(バイオマテリル, (2008), 101.)

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Figure 3-6 TEM image of microstructure of A-W GC. (Manual of orthopaedic materials, (1992), 51.)

A-W GC: microstructure

White: glass phase

Grey and Black:

two crystalline phases

Small crystallites

dispersed in glass

matrix

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A-W GC: bioactivity

Figure 3-7 TEM image of the interface between A-W GC

and bone after implantation for 8 weeks in tibia in rat. (Manual of orthopaedic materials, (1992), 51.)

Apatite phase formed at the

interfacial bonding

Bonding via apatite

(アパタイトを介した結合)

A: bone

B: apatite (hydroxyapatite)

C: A-W GC

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A-W GC: apatite formation on surface

Figure 3-8 Apatite formation on A-W GC in body fluid.

(Manual of orthopaedic materials, (1992), 86.)

Dissolution of Ca2+ ion or HSiO3- ion might be important:

Ca2+ ion : increase in supersaturation of apatite in body fluid

HSiO3- ion : surface charge to positive

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3.2 Ceramic biomaterials

(3) Calcium phosphates

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(a) Calcium phosphate as biomaterials

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(Structure and Chemistry of the Apatite and Other Calcium Orthophosphates, (1994), 49.)

Figure 3-9

Phase diagram of CaO-P2O5 system

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Calcium phosphates as biomaterials

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(Structure and Chemistry of the Apatite and Other Calcium Orthophosphates, (1994), 8.)

Table 3-1

Thermodynamic data of calcium phosphates

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Important calcium phosphates as biomaterials

Hydroxyapatite: Ca10(PO4)6(OH)2

bioactive

can directly bond to bone

b type tricalcium phosphate: b-Ca3P2O8

bioresorbable

Octacalcium phosphate: Ca8H2 (PO4)6 ・5H2O

Amorphous calcium phosphate (ACP)

may be precursor of hydroxyapatite in body

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(b) Hydroxyapatite

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Hydroxyapatite, HAp

The most important ceramic biomaterials

Why?

HAp can bond with bone at the atomic scale.

Why?

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(Introduction of the human body 6th Ed.,

(2004), 118, 482.)

Cross section of bone and tooth

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Microstructure of bone

(T. Kokubo et al., Bull. Ceramic Soc. Jpn., 38 (2003), 2.)

bone

osteon

concentric lamellae

(3-7 mm) collagen fiber

biological apatite

(length: 20-49 nm)

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inorganic component

Bone and tooth (hard tissue): organic component

water

Table 3-2 Component in tooth and bone (mass%).

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(Hydroxyapatite and related materials, CRC, (1994), 6.)

Components of hard tissues

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Components of hard tissues

(Structure and Chemistry of the Apatite and Other Calcium Orthophosphates, (1994), 260.)

inorganic component

Bone and tooth (hard tissue): organic component

water

Component Enamel Dentine Bone Ca 37.6 40.3 36.6 P 18.3 18.6 17.1

CO2 3.0 4.8 4.8 Na 0.7 0.1 1.0 K 0.05 0.07 0.07 Mg 0.2 1.1 0.6

Sr 0.03 0.04 0.05 Cl 0.4 0.27 0.1 F 0.01 0.07 0.1

Ca/P(molar) 1.59 1.67 1.65

Table 3-3 Inorganic component in tooth and bone (mass%).

Inorganic

component

Calcium

phosphate

Biological

apatite

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Biological apatite

Structure: Hydroxyapatite (Ca10(PO4)6(OH)2) type

Chemical composition: (Ca, Na, Mg, K, X)10(PO4, CO3, HPO4)6(OH, Cl, F)2

X = trace elements such as Sr

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Sr: introduce to bone (99%)

In nuclear power generation: 235U → 90Sr(→90Y→ 90Zr)

half-life of 90Sr: 28.8 years half-life of 90Y: 64 hours

yield of 90Sr: 5.75 %

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Hydroxyapatite, HAp

The bone mainly consists of collagen fiber and

biological apatite. The composition and structure

of biological apatite are very close to those of

hydroxyapatite.

Bioactivity

(Bonding to bone)

In the 1970s, direct bonding with bone was discovered.

Hydroxyapatite

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HAp

Interface between HAp and new bone

New bone (Handbook of ceramics, 2nd edition, application, (2002), 1512.) 65

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Bonding to bone

P.-I. Brånemark

1952年:チタンと骨が結合することを発見

L. Hench

1969年:骨と結合するガラス発見

人工物であるハイドロキシアパタイトは骨と化学的に結合 (1974年)

(ハイドロキシアパタイト:生体アパタイトと同じ結晶構造・近い組成)

実はハイドロキシアパタイトを介した結合 66

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Bioactivity of HAp: osteoconductivity

骨伝導性: 骨形成細胞存在下において、

その場で新生骨を形成させる特性

Osteoconductivity: bone forming ability

under the conditions with osteogenic cells

骨誘導性: 本来骨形成細胞の存在しない部位において新生骨を形成する特性

Osteoinductivity: bone forming ability under

the conditions without osteogenic cells 67

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(c) Anisotropy of hydroxyapatite

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(Structure and Chemistry of the Apatite and Other Calcium Orthophosphates, (1994), 73.)

Crystallographic structure of HAp

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Crystallographic structure of HAp

hexagonal structure

OH ion aligned (001) direction

two sites for Ca ion

Columnar site Ca(1)

Screw axis site Ca(2)

Ca(2)6Ca(1)4(PO4)6(OH)2

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Anisotropy of HAp

a face

c face

Atomic arrangements on a and

c faces are completely different.

Anisotropy in crystallographic face of HAp

Mechanical properties

Adsorption of molecules

Dissolution in acid solution 71

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Anisotropy in mechanical property of HAp

(Hoepfner and Case, Mat. Lett., 58 (2004), 489.)

Lack of the data on mechanical and chemical anisotropy of HAp

because of

the difficulty in fabrication of big HAp single crystals

Thermal expansion data

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Anisotropy in bone

bone

Stress

direction

c axis of biological apatite

crystallites is oriented to the

stress induced direction.

c axis

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Anisotropy in enamel of tooth

Enamel consists of apatite

crystals.

(1) The c face of the apatite

crystals is oriented to the

outside.

(2) The crystallinity of the

apatite crystals is much

higher than that of bone.

c axis

c axis c axis

c axis

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Crystallinity of enamel of tooth

Enamel

(block)

Enamel

(powder)

Dentine

Bone

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Apatite

(002)

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(d) Solubility of calcium phosphate

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Fig. 3-10 Solubility of calcium phosphates in aqueous system.

Solubility of calcium phosphate

HAp: most stable calcium phosphate in body fluid

main inorganic component of bone

hydroxyapatite, Ca10(PO4)6(OH)2

High

Low

Tetracalcium phosphate, Ca4P2O9

a-tricalcium phosphate, a-Ca3P2O8

b-tricalcium phosphate, b-Ca3P2O8

Octacalcium phosphate, Ca8H2(PO4)6・5H2O Solubility

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Solubility products

Solubility product (溶解度積): Ks

The solubility product of HAp(Ca10(PO4)6(OH)2) in aqueous

solution can be expressed by

ai: activity of i (=gi×[ i ])

gi: activity coefficient of i

[ i ]: concentration of i in mole/L

Ks = a10 ・a6 ・a2 Ca2+ PO4

3- OH-

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Value of solubility products of HAp in aqueous solution

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●gi: evaluated using Debye-Hückel model

g : 0.36 Ca2+

g : 0.06

g : 0.72 PO4

3-

OH-

Ks = 5.5 × 10-118 at 410 K

●Body fluid: supersaturated to HAp

K. Hata et al., J. Am. Ceram. Soc., 78 (1995) 1049.

s = = S – 1 > 0 IP - Ks Ks

IP: ionic activity product of body fluid

s: relative supersaturation

S: supersaturation ratio

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Effect of temperature on solubility of apatite in aqueous system

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Fig. 3-11 Solubility of Ca10(PO4)6(OH)2 in the system Ca(OH)2-H3PO3-H2O.

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Figure 3-12 Solubility of calcium phosphates in Ca(OH)2-H3PO4-H2O system at 310 K.

(村上ら: バイオマテリアル, 28 (2010) 274-280.)

Effect of pH on solubility of calcium phosphate

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HAp: low solubility,

not bioresorbable material

-TCP: the most common

bioresorbable material

Bioresorbable material

The moderate solubility

is required for the

bioresorbable materials.

hydroxyapatite, Ca10(PO4)6(OH)2

Solubility

High

Low

Tetracalcium phosphate, Ca4P2O9

a-tricalcium phosphate, a-Ca3P2O8

b-tricalcium phosphate, b-Ca3P2O8

Octacalcium phosphate, Ca8H2(PO4)6・5H2O

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(e) Applications

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HAp dense HAp porous β-TCP porous

(M. Kawashita, J. Jpn. Soc. Biomater., 25 (2007), 393.)

Applications of calcium phosphates

Dense and porous

calcium phosphate

Bone space filler

scaffold Table 3-4 Properties of calcium phosphates for bone space filler

porous dense porous porous dense Morphology

Porosity

pore size

bend.stren.

comp.stren.

Composition

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