The Synthesis Of Nanosized Hydroxyapatite Powders

41  Download (0)

Full text

(1)

THE SYNTHESIS OF NANOSIZED HYDROXYAPATITE POWDERS

by

TAN SU ANNE

Thesis submitted in fulfillment of the

requirements

for the

degree

of Masters of Science

April

2007

(2)

ACKNOWLEDGEMENTS

I would like to express my

gratitude

to Assoc. Professor Dr. Luay Bakir Hussain for

proposing

me this Master's position and also for his continuous

supervision

and support as my main advisor, and Assoc. Professor Dr.

Hj.

Ahmad Fauzi Bin Mohd.

Noor for his advice and support as my co-advisor. I wish also to thank Professor Dr.

Radzali Bin Othman for

financing

my research

through

his IRPA

grant.

The technical staff of the School of Material and Mineral Resources

Engineering

and their help,

especially

Madam Fong Lee Lee for all the technical know-how she had taught me, are very much

appreciated.

A

special

thanks also to Assoc. Professor Dr.

Azizan Aziz, Dr. Ahmad Sadri Bin Ismail, Professor Panchanan Pramanik of the Indian Institute of Technology

(liT) Kharagpur,

Dr. Sunara Purdawaria of Institut

Teknologi Bandung

(ITS), Mr. Ian Staton from the

University

of Sheffield and also Ms. Teoh Wah Tzu for encouraging me in my research,

helping

me with

practical

work and for

valuable discussions and advises.

Not

forgotten

are my

deeply

supportive parents and

family,

my

boyfriend,

Yew

Kuan Min, and friends for their prayer and support

throughout

my research. Most

important of all, I give thanks to God, who made

everything possible

and provided me

with wisdom and grace to complete my

journey.

(3)

TABLE OF CONTENTS

Page ACKNOWLEDGEMENTS

TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF PLATES LIST OF SYMBOLS LIST OF ABBREVIATION LIST OF APPENDICES

LIST OF PUBLICATIONS & SEMINARS ABSTRAK

ABSTRACT

ii iii vii viii

x

xi xii xiii xii xiv xvi

CHAPTER ONE: THE SYNTHESIS OF NANOSIZED HYDROXYAPATITE POWDERS

1.0 Introduction 1

1.1 Application of

hydroxyapatite

in various fields 1 1.2 Advantages of nanosized

hydroxyapatite

overconventional 2

hydroxyapatite

1.3 Economic and social impact of local

production

of

hydroxyapatite

4

1.4 Main

objective

of research 5

1.5 Approach 5

1..6 Scope of the thesis 7

CHAPTER TWO : BACKGROUND AND LITERATURE SURVEY

2.1

Composition

of bone 8

2.1.1

Organic

phase of bone tissue 8

(a) Collagen

9

(b) Non-collagenous

protein 9

2.1..2 Mineral phase of bone 9

(4)

2.2 Bone cells 2.2.1 2.2.1 2.2.1

Osteoblasts

Osteocytes

Osteoclasts

11 11 11 12 1.3 13 14 14 15 16 17 17 20 23 24 24 25 25 26 26 27 27 2.3 Biological implants

2.3.1

Body's

reaction to implants (a) Toxic response

(b) Nearly

inert

(c)

Bioactive

(d)

Dissolution 2.4

Hydroxyapatite

2.4.1

Hydroxyapatite

as an

implant

material

2.4.2 Dense

hydroxyapatite

2.5 Different methods of

producing hydroxyapatite

and their merits 2.5.1 Solid-state reaction

2.5.2

Mechanosynthesis

2.5.3 Wet methods

(a) Hydrothermal techniques (b) Hydrolysis method

(c) Wet

precipitation

Calcium

hydroxide

and orthophosphoric acid

ii Calcium nitrate and diammonium hydrogen

phosphate

2.6 The chemistry of

hydroxyapatite

28

2.6.1 The formation of

hydroxyapatite

from phosphate and calcium 29

salts

2.6.2 Ca/P ratio of hydroxyapatite 30

2.6.3 Kinetics of hydroxyapatite precipitation

2.6.4 Thermal behavior of

hydroxyapatite

2.6.5 PH and zeta

potential

of

hydroxyapatite

in an aqueus

32 33 34

(5)

(a)

(b)

XRF results XRD results

98 100 4.3.3 Effect of calcination temperature 106

CHAPTER FIVE: SUMMARY AND CONCLUSION 5.1 Conclusions

5.2 Recommendation for future work

107 109

BIBLIOGRAPHY 110

APPENDICES

(6)

2.1

3.1

4.1

4.2 4.3

4.4

4.5

LIST OF TABLES

Calcium phosphate salts thatarebiologically and chemically relevant to

hydroxyapatite and itsproduction.

Summaryof variable parameters ofsynthesis thatare investigated in this

research

Acomparison ofaging temperature versusaverage particle size obtained from the particle sizer.

Average particlesize measurement by the particlesizer.

Surface area and equivalent sphere diameter measurement from the BET method

Results fromXRF- the CaJP ratio forsamples co-precipitated at temperatures40,60 and 80°C

Resultsfrom XRF- the CaJP ratio forsamples co-precipitated at pH 9, 10 and 11.

Page

28

46

66

67 68

88

94

(7)

LIST OF FIGURES

Page

1'.1 Hierarchical levels of structural organization in a human long bone 10 2.1 Relationship between the timerequired forforming pure-phase 33

hydroxyapatite and the reaction temperature

2.2 Schematic representation ofzeta potential. 37

2.3 Plot of zeta potential versus pH showing the isoelectricpoint of 38 hydroxyapatite and the pH valueswhere thedispersion would be expected to

be stable.

3.1 Schematic representation of the setup oftheequipment used in thesynthesis 43

of hydroxyapatite powders

3.2 An x-ray is produced when an atom is hit bya photon orx-ray 56 4.1 Graphofequivalent sphere diameter, oraverage particle diameterversus 69

reaction temperature forhydroxyapatite samples reacted at pHiO and pH11.

4.2 Graph of equivalentspherediameter, oraverage particlediameter versus 70

various reaction pH.

4.3 Graph of particle sizeversus aging duration forsamples aged at room 74 temperature for24, 4B and 72 hours.

4..4 Particle size distribution forsample aged for 24 hours at room temperature 76 4.5 Particle size distribution forsampleaged for 4B hours at room temperature 77

4.6 Particle size distribution forsample aged for 72 hours at room temperature. 77

4.7 Graphof Equivalent Sphere Diameterofhydroxyapatite particles versus 85 calcination temperatureforsamples reacted at 40,60 and Booe.

4.8 Graphof Equivalent Sphere Diameterofhydroxyapatite particles versus 86

calcination temperaturefor samples reacted underpH 9, 10and 11.

4.9 Graphofcrystallitesize versus calcination temperaturefor hydroxyapatite 91 synthesized attemperatures40, 60 and aooe.

4.10 Graph of crystallitesize versus calcinationtemperatureforhydroxyapatite 92 synthesized at pH 9, 10 and 11.

4.11 Graph of ealP ratioversus calcination temperatureforhydroxyapatite 94 calcined attemperatures 40,60 and aooe.

4.12 XRD spectra of hydroxyapatitesynthesized at40°C and calcined atvarious 95 temperatures: (a) uncalcined (b)700°C (c)aoooe (d) gOOoe (e)1ooooe

(f)1100oe

4.13 XRD spectra ofhydroxyapatite synthesized atsooe and calcined atvarious 96 temperatures: (a) uncalcined (b) 7000e (c) BOOoe (d) 900De (e)1ooo-c

(f)1100oe

4.14 XRD spectraof hydroxyapatite synthesized at aooe andcalcined at various 97 temperatures: (a) uncalcined (b) 700°C (c) eco-c (d)soo-c (e)10000e

(f)11000e

(8)

4.15 GraphofCalP ratioversuscalcination temperature forhydroxyapatiteco- 99

precipitatedat pH9. 10 and 11.

4.16 XRD spectraof hydroxyapatitesynthesized atpH09 and calcined atvarious 103 temperatures: (a) uncalcined (b) 700°C (c) 800°C (d) 900°C (e)1000°C

(f)1i00°C

4.17 XRD spectra ofhydroxyapatite synthesized at pHiO and calcined atvarious 104 temperatures: (a) uncalcined (b) 700°C (c) 800°C (d) 900°C (e)i000°C

(f)1100°C

4.18 XRDspectra ofhydroxyapatite synthesized at pH11 and calcined atvarious 105 temperatures: (a) uncalcined (b) 700°C(c) 800°C(d) 900°C (e)1000°C

(f)ii00°C

(9)

LIST OF PLATES

Page

3.1 A photograph of the co-precipitation equipment set up within a fume 42

cupboard.

3.2 Maturation of

precipitation

at temperature 90°C for 30 minutes

using

a 48 hotplate stirrer.

3.3

Aged precipitates

within the

centrifuge

machine. 49

4.1 FeSEM photograph ofa

hydroxyapatite

Sample A, aged for 24 hours 78 at room temperature, viewed at 50,000x magnification.

4.2 FeSEM

photograph

of a

hydroxyapatite Sample

A, viewed at 10000x 79

magnification.

4.3 FeSEM photograph ofa hydroxyapatite

Sample

B,

aged

for 48 hours 80 at room temperature, viewed at 100000x

magnification.

4.4 FeSEM

photograph

of a hydroxyapatite Sample B, viewed at 10000x 81

magnification.

4.5 FeSEM photograph of a

hydroxyapatite Sample

C,

aged

for 72 hours 82

at room temperature, viewed at 100000x

magnification.

4.6 FeSEM

photograph

ofa

hydroxyapatite sample

11RT72RT, viewed at 84

50000x magnification.

4.7 Enlarged FeSEM photograph ofSample C 84

4.8 SEM

micrograph

of

hydroxyapatite

reacted at 40°C,

aged

at room 88 temperature for 24 hours and calcined at 1000 oe, viewed at 3k x

magnification.

4.9 SEM micrograph of

hydroxyapatite

reacted at40°C, aged at room 89 temperature for 24 hours and calcined at 1000 °C, viewed at 3.5 k x

magnification.

(10)

Tl

A V p d

m

Ssp

%wtc.

%wt,.

LIST OF SYMBOLS

Reaction temperature Aging temperature

Calcination temperature Surface area ofa particle Particle volume

Particle density

Diameter ofa

particle

Particle mass

Specific surface area per unit mass

Weight

percentage of Calcium atoms in

hydroxyapatite

Weight percentage of Phosphate atoms in

hydroxyapatite

Page

41 47 50 66 66·

66 66 66 73 73 73

(11)

DCPD DCPA OCP ACP TCP

HAp

TTCP

TCPM DAP XRF XRD SEM BET DLS ESD FeSEM

LIST OF ABBREVIATION

Dicalcium phosphate dehydrate, Ca(HP04hH20

Dicalcium Phosphate Anhydrous, Ca(HP04)

Octacalcium Phosphate, CaaH2(P04)s,5H20 Amorphouscalcium phosphate, Ca3(P04h.xH20

Tricalcium Phosphate, Ca3(P04)2 Hydroxyapatite, Ca1O(PO",)s(OHh

Tetracalcium Phosphate, Ca",P20a

Tetracalcium Phosphate monoxide, Ca4P207

Calcium Deficient Hydroxyapatite X-Ray Fluorescence

X-Ray Diffraction

Scanning Electron Microscope Brunauer, Emmett, Teller Dynamic Light Scattering EquivalentSphere Diameter

Field Emission Scanning Electron Microscopes

(12)

LIST OF APPENDICES

Appendix

1

Composition

ofchemicals used in the wet

precipitation

method

Appendix

2 Molecular

weights

ofelements and molecules used in the calculation of the Ca/P ratio from XRF results.

Appendix

3 The distribution of

particle

size:

Graphs

plotted by the

particle

sizer

Appendix

4 Results from the BET method

Appendix S

Crystallite

size from the XRD

LIST OF PUBLICATIONS & SEMINARS

1 S A Tan, M N Ahmad Fauzi., B H

Luay,

O Radzali. (2004)

Synthesis

of Nano­

sized

Hydroxyapatite.

Medical Journal of

Malaysia

59,

Supplement

B, pp162-

163.

(13)

SINTESIS SERBUK HIDROKSIAPATIT BERSAIZ NANO

ABSTRAK

Partikel

hidroksiapatit

disintesis melalui kaedah

mendapan

kimia dan dicirikan.

Ujikaji

ini

mengkaji bagaimana parameter

utama

seperti pH tindakbalas,

serta

suhu

tindakbalas,

penuaan dan

pengkalsinan mempengaruhi

saiz

partikel

dan

ketulenan fasa

hidroksiapatit

yang dihasilkan. Matlamat utama adalah untuk menentukan keadaan

paling optimum

untuk

menghasilkan hidroksiapatit

yang bersaiz nanometer dan berfasa

tulen,

serta

mengalami aglomerasi

yang

minimum

untulkdigunakan sebagai

bahan

pengganti tetulang.

Suatu larutan 0.2 M

Ca(N03)2.4H20 (Kalsium

Nitrat

Tetrahidrat)

dan larutan

0.12 M

(NH4)2HP04 (Diamonium Hidrogen Fosfat) dimendapkan

secara

serentak dalam kehadiran

dispersan K4P207

dibawah

pelbagai pH,

dan

pengkacauan

berterusan. Ini diikuti oleh proses penuaan

pada

suhu dan

tempoh

yang

berbeza,

dan

kemudiannya dikeringkan. Akhirnya, pengkalsinan

dilakukan

pada

suhu yang

meningkat,

bermula dari 700

hingga

1000°C.

Pencirian

dijalankan dengan pembelauan

sinar-X

(XRD)

serta

pendarflour-X (XRF)

untuk

penentuan fasa,

manakala

pengukuran

saiz

partikel

dilakukan

melalui

SEM,

kaedah

BET,

serta

pengukur

saiz

partikel.

Keputusan menunjukkan

bahawa kedua-dua

komposisi

dan

morfalagi hidroksiapatit dipengaruhi

oleh suhu

tindakbalas,

suhu penuaan,

pH

tindakbalas

serta suhu

pengkalsinan.

Suhu penuaan dan tindakbalas yang

tinggi

membolehkan

pembentukan hidraksiapatit

yang

cepat, tetapi juga

(14)

menghasilkan partikel

yang lebih

besar,

manakala suhu penuaan dan tindakbalas yang rendah memerlukan

tempoh

tindakbalas yang lebih lama

tetapi menghasilkan partikel

yang lebih kecil.

Didapati

bahawa

pH

tindakbalas

mempunyai pengaruh

yang

paling

kuat

terhadap komposisi hidroksiapatit

yang

terhasil, dengan pH tertinggi

yang

diuji, pH11,

memberikan

hidroksiapatit

yang

paling

tulen.

Penggunaan ejen pengurai

membantu dalam

pembentukan populasi

saiz

partikel

berbentuk dwimod yang

kebanyakannya

terdiri

daripada partikel primer

dan

peratusan

yang kecil

partikel

sekunder yang berdiameter 1-

2�m.

Kehabluran

hidroksiapatit

bertambah

dengan

suhu

pengkaisinan

yang

meningkat daripada

700

hingga

11

OO°C,

dan

begitu juga dengan

saiz

partikel,

dan suatu

peningkatan

yang amat ketara

bagi

saiz

partikel diperhati

untuk suhu

pengkalsinan

lebih

daripada

1000°C.

Saiz kristalit

berkurang

semasa

pengkalsinan pada

suhu 700°C

kepada

kira-kira 2

hingga 3nm, tetapi

bertambah semula

dengan

suhu

pengkalsinan

yang semakin

meningkat

dan

jatuh

sedikit

pada

suhu 900 dan 1000°C. Suhu tindakbalas yang lebih

tinggi (aO°C)

akan

menghasilkan

kristalit yang

besar,

berbanding dengan

suhu yang lebih

rendah,

manakala

pH

yang lebih

tinggi

(dalam

kes

ini, 11)

akan

menghasilkan

kristalit yang kecil.

(15)

THE SYNTHESIS OF NANOSIZED HYDROXYAPATITE POWDERS

ABSTRACT

Nanometer sized

hydroxyapatite particles

are

synthesized

via wet chemical

precipitation

and characterized. This research studies how

key parameters

such

as the

pH

of

synthesis,

and also the

reaction, aging

and calcination

temperatures

affect the size and

phase purity

of the

hydroxyapatite produced.

The main aim is to determine the

optimum

condition for

producing phase-pure,

nano-sized

hydroxyapatite

with minimum

agglomeration,

to be used as bone

replacement

material.

A 0.2 M solution of

Ca(N03)2.4H20 (Calcium

Nitrate

Tetrahydrate)

and a 0.12

M solution of

(NH4)2HP04 (Diammonium Hydrogen Phosphate)

are co­

precipitated

in the presence of a

dispersant. �P207 (Tetrapotassium Pyrophosphate Tetrabasic),

under various

temperatures, pH

and continuous

stirring.

This is followed

by aging

at various

temperatures

and

durations,

and

after that

drying,

and

finally

calcination at various

temperatures ranging

from

700 to 1000°C. Characterization was carried out

using X-ray powder

diffraction and

X-ray fluoroscopy

for

phase

identification while

particle sizing

was done via

Scanning

Electron

Microscopy (SEM),

the BET

method,

and also a

particle

sizer.

Results showed that both the

composition

and the

morphology

of the

hydroxyapatite

are affected

by

the reaction

temperature,

the

aging temperature,

the

pH

of the reaction and also the calcination

temperature. High aging

and

(16)

reaction

temperatures

allowed for

rapid

formation of

hydroxyapatite,

but also led

to

larger particles,

while lower

aging

and reaction

temperatures required

a

longer

reaction time but smaller

particles

are obtained.

Meanwhile,

the

pH

of the

reaction has the most intense effect upon the

composition

of the

hydroxyapatite,

with the

highest pH,

11,

yielding

the most

phase-pure hydroxyapatite powder.

The usage of a

dispersant

assisted in the

production

of a bimodal

population

of

particle

size

consisting mainly

of nanosized

primary particles

about 20 to 150nm in

diameter,

and a minor

percentage

of

larger secondary particles

about

1-2JJm

in diameter.

The

crystallinity

of the

hydroxyapatite

increased when the calcination

temperatures

increased from 700 to 11

ao°c,

as did the

particle

sizes, and a

sharp

increase of

particle

sizes from over 200nm to above 1 JJm was observed at calcination

temperatures

above 1000°C. The

crystallite

sizes

dropped

upon calcination at 700° to about 2 to 3 nmI but increased with

increasing

calcination

temperature

before

dipping slightly again

at 900 to 1000°C.

Higher

reaction

temperatures (80°C) produced larger crystallites,

while a

high pH (in

this case

11),

led tothe formation ofthe smallest

crystallites.

(17)

CHAPTER 1

THE SYNTESIS OF NANOSIZED HYDROXYAPATITE POWDERS

1.0 Introduction

The

importance

of calcium

hydroxyapatite

as a biomaterial has

long

been realized and studied worldwide in the field of

orthopedics

and

orthodontics due to its excellent

biocompatibility

and

bioactivity.

With the

chemical formula

Ca10 (P04)6(OH)2, hydroxyapatite

is

chemically

similar to

the mineral

component

of bones and hard tissues in

mammals,

and is a

very attractive material to be used as a bone

replacement

material.

Hydroxyapatite

is also one of few materials that are classed as

bioactive. When used as a

biological implant,

a bioactive material

encourages a

direct,

interfacial bond between the material and the tissue

surrounding it, lending stability

to the

implant

and

improving

clinical

success.

Thus,

it is the best candidate for hard tissue

replacement

in

terms of

compatibility (Muster, 1992,

Hench and

Wilson, 1993).

1.1

Application

of

hydroxyapatite

in various fields

Synthetic apatites

are

generally

used in bone

repair

I

augmentation

and

substitution,

as well as

coatings

on dental and

orthopedic implants.

Among

the innumerable

applications

of

hydroxyapatite

are the

reconstruction and

replacement

of

damaged

bone or tooth zones in

plastic

and dental surgery. Some

examples

are the

augmentation

of alveolar

(18)

ridge

for better denture fit in

orthopedic

surgery,

filling

in

bony

defects in

dental and

orthopedic

surgery, such as the

filling

of

periodontal

defects

with ceramic

powder

of

hydroxyapatite

and as extenders for

autogenous

bone or demineralized bone matrix

(Muster, 1992).

Metals coated with

hydroxyapatite

have been introduced as artificial

bones. The

coating helps

the

surrounding

tissue to bond

firmly

with the

implant

while

retaining

the

strength

of the metal

(Oonishi, 1991).

Other

medical

applications

include the usage of

nanocrystalline hydroxyapatite

as a carrier material for local

delivery

of antibiotics and time-controlled

drug

release in bone infections

(Rauschmann

et

al., 2005,

Komlev et

al., 2002).

Hydroxyapatite

also finds

applications

in other fields of industrial or

technological

interest as

packing

media for column

chromatography, catalysts,

gas sensors, host material for lasers and may also find

possible

uses in water

purification,

fertilizer

production

and also as a dielectric

coating.

HA

specimens

sintered to

transparency

may used as matched filters

(Hoepfner

and

Case, 2003).

(19)

makes it easier to prepare materials with a uniform and dense structure, therefore

greatly increasing

the

strength

of the sintered

body.

As

coatings,

the

greater

structural

integrity

of

closely packed nanoparticles gives

the

coatings improved

adhesive and cohesive

properties

for many

applications.

Most

importantly, biological implants

made from nanosized

hydroxyapatite

have been proven to exhibit enhanced osteoblast function

(better

cell

adhesion,

accelerated

growth

and tissue

deposition)

within the

body (Webster

et

al., 1999,

Balasundaram et

aL, 2006,

Webster et

al., 2000).

Meanwhile,

nanosized

hydroxyapatite

has found its own

application

niche as carriers of antibiotics to reduce bacterial infections in the bone­

implant

interface, as well as vectors for selective

delivery

of

drugs

to

tarqeted

cells in the treatment of cancer for better effectiveness

compared

to

conventionally

administered

drugs.

In non-medical

applications,

nanosized

particles

contribute to

higher sensitivity

as sensors and a much

higher reactivity

as

catalysts.

Nanoparticles

have also been known to exhibit

properties

far different from those of the same material but with

larger particles

or

grain

sizes. This

opens the door to unlimited

potential

for new

applications yet

to be

discovered.

Despite

the

high potential,

very few

applications

have been

developed

so far

using nanoparticles.

The

key

limitation is the lack of

large

quantities

of nanosized

particles

with

closely

controlled

properties

at a cost

(20)

that will allow scientists and

engineers

to

comfortably explore

new

practical applications

of these

particles

as well the science of

processing

these new materials. Therefore research should be focused on

developing

the science and

engineering

that would allow the

development

of

inexpensive technologies

for manufacture of

nanoparticles

that can be

densified into

nanocompacts.

1.3 Economic and Social

impact

of local

production

of

h

yd

roxyapatite

Having glanced

at the vast

potential

for this

material,

we now take a

look at the

impact

and aim of this research, which is

primarily

to

produce

nanosized

hydroxyapatite powders

which are intended for

processing

into

dense sintered material for

orthopedic implants.

In a

published

market survey

by

Medtech

Insight,

the market for

orthopedic

biomaterials sales in the USA was found to exceed US$980 million in 2001. The number was

predicted

to increase to US$1.16 billion

in 2002, and $3.32 billion

by

2006

(AZoM.com, 2002). Meanwhile, Malaysia

is

reported

to have

imported orthopedic (medical)

and

orthodontic

(dental) implants amounting

to

approximately US$6

million in

(21)

further

fuelling

research

activity

among the

engineering

and medical

communities in our nation.

Consequently,

more

people suffering

from bone

loss due to

injuries

or diseases would have access to

high quality orthopedic implants

at a low cost,

improving

the

quality

of lives for these

people.

1.4 Main

objective

of research

The main

objective

of this research is to

study

the effect of several parameters of

synthesis,

such as the reaction

temperature, aging

temperature and

duration,

as well as the calcination

temperature,

upon the

phase-purity

and

particle

size ofthe

hydroxyapatite produced.

The results will be used to select the most suitable

parameters

towards

producing

a

phase-pure, nanoparticulate hydroxyapatite.

1.5

Approach

The method used in this

experiment

is wet

precipitation

due to the

low

production

cost

involved, easily

available

equipment

and also

comparatively easily adjustable parameters.

The

key

to

obtaining

nano

powders

with this method is the

manipulation

of the reaction kinetics so as to encourage

particle

nucleation over

particle growth.

(22)

The raw materials used are calcium nitrate

tetrahydrate [Ca(N03)2.4H20]

and diammonium

hydrogen phosphate [(NH4)2HP04].

The calcium solution and

phosphate

solution are

co-precipitated

under

constant and

vigorous stirring (level

4 on

magnetic stirrer)

at various

temperatures

and various

pH,

and then allowed to mature under various

temperatures

and durations.

Finally,

it is

washed, dried,

and

ground loosely

before calcination under

temperatures ranging

from 700 to 11OO°C.

The

powders

obtained

using

this method are characterized

using

ray diffraction for

phase identification,

determination of

phase purity

and

also crystallite size;

x-ray

fluoroscopy

for chemical

analysis

to determine

the elemental content of the

powder

and the ratio of calcium to

phosphate

of the

powder; scanning

electron

microscope

for

particle

size and

morphology; particle

sizer to measure the distribution of

particle sizes,

and

finally

the BET to measure surface area and the

equivalent sphere

diameter.

A

comparison

is then made to compare the effect of the various

changes

in

temperature

upon the characteristics of the

powder

obtained in

order to determine the best

parameters

to be used to

synthesize

the

hydroxyapatite powder.

(23)

1.6

Scope

of the thesis

Chapter

two contains

background

information on the

composition

of

bone and the role

played by hydroxyapatite

in its structure. Also discussed

here, is the

potential

of

hydroxyapatite

as an

implant material,

its

characteristics,

various methods of

synthesis

of

hydroxyapatite

and also

previous

works other researchers have done on this same material.

Chapter

three describes the

co-precipitation

process,

including

the

equipment

and material

preparation.

The

synthesis parameters

to be

investigated

and the characterization of the

synthetic hydroxyapatite

are

also described here. In

Chapter

Four, the results obtained from the tests

are

presented

and correlated with the variable

parameters

that were tested.

Finally,

in

Chapter Five,

a conclusion is drawn about the

synthesis

and

properties

and an outline is drawn on the

optimum parameters

to be chosen for future

synthesis

of

hydroxyapatite powders

with the

targeted

properties.

(24)

CHAPTER2

BACKGROUND AND LITERATURE SURVEY

2.1

Composition

of bone

The skeletal

system

is

comprised

of "bone

organs"

- individual

bones, each

having

a distinctive size and

shape. Meanwhile,

each bone

organ is made up of bone

tissue,

which is our main interest here, and also

cartilage tissue,

otherconnective tissue and nerves.

Bone tissue is a

composite

made of 60 to 70% mineral substances and 30 to 40%

organic

tissues. This ratio holds true

although

the

properties

of a bone vary from

point

to

point,

and the ratio of the

substances in the skeleton differ from one bone organ to another. The

major

role of bone is to serve as a

support

for the

body's

muscles,

protection

forsome

parts

ofthe

body,

and also a reserve of calcium for the

body (Krajewski

and

Ravaglioli, 1991).

2.1.1

Organic phase

of bone tissue

The

organic phase

of bone tissue consists of

mainly collagen

and

non-collagenous protein,

as well as small amounts of

polysaccharides

and

(25)

(a) Collagen

Over 90% of the

composition

of

organic

bone tissue is made up of

collagen. Collagen,

which can be considered as the matrix of

bone,

is in

the form of small micro-fibers. The

deposition

of

collagen

as osteoid is the first

step

in the process of bone formation.

(b) Non-Collagenous protein.

There are two

major non-collagenous proteins

found in bone,

namely

osteocalcin and osteonectin.

They

are believed to be

synthesized by specific bone-forming

cells called osteoblasts. Osteocalcin has a

strong affinity

for

hydroxyapatite

and may constitute up to 2% of vertebrae bone

protein. Osteonectin,

on the other

hand,

has a

strong affinity

for both

hydroxyapatite

and

collagen.

Other

non-collagenous

bone

proteins present

in small amounts include

osteopontin,

some

proteoglycans,

bone

morphogenetic protein

and bone-derived

growth

factors.

2.1.2 Mineral Phase of Bone

The mineral

phase

of bone tissue contains calcium

phosphate,

of

which the

major

form is

hydroxyapatite,

and the less

abundant,

calcium

carbonate. Small amounts of

magnesium, fluoride, carbonate, citrate, potassium

and other ions are also found in the mineral

phase

of bone.

Hydroxyapatite

is a

crystalline

substance which

comprises calcium,

phosphate

and

hydroxyl

ions. It

provides

stiffness to the bone

by

way of

(26)

the

incorporation

of

hydroxyapatite crystals,

in the form of needles and

plates,

into the osteoid matrix

template.

Figure

1.1 shows the structure and location of the

apatite

mineral

crystals

within the human

long

bone. These

crystals

are

deposited parallel

to the

collagen

fibers so that the

larger

dimensions of the

crystals

are

along

the

long

axis of the fiber and reinforce the

collagen

similar to the way

glass

fibers reinforce

plastic

matrices in

fiberglass composites (Suchanek

and

Yoshimura,

1998, Woods and Ellis,

1994).

Nutrient artery- In

tramedulla;.;;,;ry::--...,;:

cavity

Articular

cartilage

rm �--

/ t���

Osteon

._

_

if

Collagen nbcrs

".

/�� \

1.:_, Concentric

:;_"\"")'"')..,.e�)

....

�-:

lamella '

Haversian (3-7 Ilm) Apatite

canal mineralcrystals

(20-40 nm long) Micro- toUltra-

Ultra- tomolecular Line of

Macro-

Figure

1.1: Hierarchical levels of structural

organization

in a human

long

bone

(Park, 2000).

(27)

2.2 Bone cells

There are three distinct cell

populations directly

involved with bone tissue and are derived from the bone marrow

cavity.

These bone cells are

osteoblasts,

osteocytes

and osteoclasts - each has its own role to

play

in

the process of

formation,

maintenance and removal of bone mineral.

2.2.1 Osteoblasts

Osteoblasts are

specialized bone-forming cells, belonging

to the

more

general category

of

fibroblasts,

which are cells

typical

of connective

tissue of any organ

(Krajewski

and

Ravaglioli, 1991). During

their

developmental

and maturation

stages, they actively synthesize

many

proteins

and secrete the matrix framework of

bone,

and thus create the conditions for mineralization. The matrix is

initially

laid down as

unmineralized

type

I

collagen,

the osteoid. Osteoblasts are rich in alkaline

phosphatase

and

osteocalcin,

both of which may have a role in the mineralization of the osteoid matrix.

2.2.2

Osteocytes

Osteocytes

are found within the bone itself.

They

are, in

fact,

mature bone cells derived from osteoblasts. As the

collagen

framework

becomes

mineralized,

some osteoblasts become

trapped

in the

newly­

formed osteoid matrix. These

remaining cells,

now known as

osteocytes,

reside in the bone matrix as

long

as the bone is functional. Juvenile

(28)

osteocytes

or those

trapped

in the osteoid for

only

a short

time,

are able to

participate

in bone

deposition

and

probably

some calcium

deposition.

Older

osteocytes

do not have this

ability,

and function

mainly

to

provide

the bone tissue around them with a

supply

of nutrients from the marrow

cavity through communicating

channels known as canaliculi. When

osteocytes

are cut off from blood

supply, they

die

(Woods

and

Ellis, 1994, Krajewski

and

Ravaglioli, 1991).

2.2.3 Osteoclasts

Lastly,

mineralized bone tissue is

degraded by specialized giant

cells known as osteoclasts. These multinucleated cells

playa

role in the

resorption

of bone mineral

by dissolving

the mineralized bone-matrix

extracellularly

and

releasing

the calcium ions into circulation. It is

thought

that

TGF�

and bone

morphogenic protein

are also released this

time,

promoting

bone formation

(Woods

and

Ellis, 1994, Krajewski

and

Ravaglioli, 1991).

(29)

2.3

Biologicallmplants

Implants

are

basically

devices made from inanimate materials that

are

placed

in the

body; they

may be made from one or more biomaterial which is

intentionally placed

within the

body,

and

designed

to remain there for a substantial

period

of time.

Meanwhile,

a biomaterial is an

object

able

to

replace

an

original living part

of the

body.

Although implants

may be utilized for medical reasons such as the

replacement

of diseased or

degenerated

tissues to

improve

the

quality

of

life,

they

are also

employed

for aesthetic purposes such as breast

augmentation

and other forms of

plastic

surgery.

Important

in

surgical implants,

however, is the host's response to the biomaterial

given by surrounding

tissue

(Krajewski

and

Ravaglioli, 1991).

2.3.1

Body's

reaction to

implants

When a

foreign

material is

implanted

into the

body,

the host tissue

responds

in a number of ways at the

tissue-implant

interface. The

response

given

is influenced

by

many

factors, induding

tissue conditions such as age,

health,

blood

condition,

as well as

implant properties

such as

composition, present phases,

surface

morphology

and the mechanical fit of the

implant.

These responses can be

categorized

into four

general

groups of

implant-tissue

response, that is:

toxic,

almost

inert,

bioactive and dissolution.

(30)

(a)

Toxic response

Some

implant

materials may cause a toxic response that kills cells

In the

surrounding

tissues or release chemicals that can

migrate

within

tissue fluids and cause

damage

to the

patient.

For obvious reasons,

implants

that elicit such a response from the

body's

tissues are avoided

(Hench

and

Wilson, 1993).

(b) Nearly

inert

The most common response of tissues to an

implant

is formation of

a non-adherent fibrous

capsule

around the

implant

as a

protective rnechanism

to isolate the

implant

from the host.

The thickness of the fibrous

layer depends

on the various tissue and

implant

conditions mentioned earlier.

Biologically inactive, nearly

inert

ceramics like alumina or zirconia will elicit a thin fibrous

capsule

at their interface. while metals and most

polymers

may cause a total

encapsulation

of the

implant

within the fibrous

layer.

The motion and fit between the

implant

and host is also very

important.

Even a

slight

movement at the interface between

implant

and

(31)

implant loosening

very

quickly

and

consequent

clinical failure of the said

implant

in the form of

implant

or host fracture.

Thus, for an

implant

made of inert

materials,

a

tight

mechanical fit with the host tissue is of utmost

importance

in order to

prevent

interfacial

movement and

subsequent

clinical failure

(Hench

and

Wilson, 1993).

(c)

Bioactive

A bioactive material is able to form a direct bond across the interface between

implant

and tissue. This bond is similar to the

type

of

interface that is formed when natural tissues

repair themselves,

and the

same bond now

prevents

interface motion between the

implant

and the

host tissue.

In order for an

implant

to

perform optimally,

its

properties,

such as a

controlled rate of chemical

reactivity, morphology

and

phase composition

need to be

carefully engineered according

to its function and rate of

bonding

to the host tissue. Even a small

change

in

composition

can

change

the

properties

of a bioceramic from

nearly

inert to resorbable to bioactive. Unlike resorbable

materials,

chemical reactions

only

occur atthe

surface while the rest of the

implant

remains

largely

unaffected

(Hench

and

Wilson, 1993).

(32)

(d)

Dissolution

Resorbable materials

gradually degrade

as

they

dissolve or resorb

and are

replaced by

the

surrounding

host tissues. Instead of

replacing

the

tissues,

the material encourages the

regeneration

of tissues to take their

place.

This

requires

a much

higher

rate of

change

at the material's

interface

compared

to a bioactive material.

There are,

however,

a few issues or criteria that need to be taken into consideration in order to

successfully implement

resorbable

implants.

Firstly,

the constituents of the material must be

metabolically acceptable, meaning

that the material needs to be of a

composition

that can be broken

down

chemically by body

fluids or

digested easily by macrophages.

The

degradation products

must be non-toxic chemical

compounds

that can be

easily disposed

of without

damaging

the

surrounding

cells or

harming

the

host's health.

Besides

that.

the

resorption

rate of the material must also match the

repair

rate of the

body

tissues even as the material

provides

a sufficient

mechanical

strength

to

support

the host tissue while the

regeneration

of

tissues takes

place (Hench

and

Wilson, 1993).

Figure

Updating...

References

Related subjects :