SYNTHESIZE AND CHARACTERIZATION OF BIOACTIVE GLASS POWDER BASED ON
SiO
2-CaO-Na
2O-P
2O
5SYSTEM
NURUL FARHANA BINTI IBRAHIM
UNIVERSITI SAINS MALAYSIA
2019
SYNTHESIZE AND CHARACTERIZATION OF BIOACTIVE GLASS POWDER BASED ON SiO2-CaO-Na2O-P2O5 SYSTEM
by
NURUL FARHANA BINTI IBRAHIM
Thesis submitted in fulfilment of the requirements for the degree of
Doctor of Philosophy
March 2019
ii
ACKNOWLEDGEMENTS
Alhamdulillah. Praise to Allah The Almighty. The research and thesis would never have been completed without His guidance. Thanks to my husband as willing to engage with the struggle since the day I decided to pursue my studies.
Thank you for your practical and emotional support. I would like to express my sincere gratitude to my mentor and supervisor, Assoc. Prof. Dr. Hasmaliza Mohamad for her excellent cooperation, guide, continuous support, tolerance, motivation and all opportunities given during my research and writing of thesis. It was a great pleasure working with her for the past few years since undergraduate.
Special thanks to my co-supervisor, Assoc. Prof. Dr. Siti Noor Fazliah Mohd Noor for the support and the access given to the laboratory and research facilities in Advanced Medical & Dental Institute, USM. Sincere thanks also go to my co-supervisor Nurazreena Ahmad for the moral support. I also wish to express my sincere thanks to Dean of SMMRE, all lectures, administrative and technical staffs in School of Materials and Mineral Resources Engineering, USM for the helps and assistances during the research. Great thanks to the lab mates, particularly Nurul Shazwani Mohd Zain for the discussion, help and fun during the research.
Lastly, I would like to thank my parents, my sister and brother for the inspiration and moral support for the research completion.
May Allah bless all of you. Amen.
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TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS ii
TABLE OF CONTENTS iii
LIST OF TABLES viii
LIST OF FIGURES x
LIST OF ABBREVIATIONS xv
LIST OF SYMBOLS xvi
ABSTRAK xvii
ABSTRACT xviii
CHAPTER ONE : INTRODUCTION
1.1 Biomaterials 1
1.1.1 Bioactive glass 2
1.1.2 45S5 Bioglass 4
1.2 Problem statement 6
1.3 Research objective 8
1.4 Scope of research 9
CHAPTER TWO : LITERATURE REVIEW
2.1 Ceramic as biomaterials 11
2.2 Biomaterial 12
2.2.1 Bioglass 14
2.3 Bioactive material 16
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2.4 Glass as a biomaterial 18
2.4.1 Glass formation 20
2.5 Bioactive glass 23
2.5.1 Synthesize of bioactive glass 26
2.5.1(a) Melt derived 27
2.5.1(b) Sol gel 31
2.5.2 Bioactive Glass Composition 33
2.5.2(a) Silicon dioxide (SiO2) 37
2.5.2(b) Sodium oxide (Na2O) 39
2.5.2(c) Calcium Oxide (CaO) 41
2.5.2(d) Phosphorus Pentoxide (P2O5) 43 2.5.3 Network connectivity (Nc) of bioactive glass 44
2.5.4 Bioactive glass surface reactions 46
2.5.5 Growth of apatite layer on the surface of bioactive glass 47 2.5.6 Bioactivity assessment of bioactive glass 49
2.6 Bioactive glass application 52
2.7 Summary 55
CHAPTER THREE : MATERIALS AND METHODOLOGY
3.1 Introduction 56
3.2 Raw materials 56
3.3 Methodology 57
3.3.1 Synthesize of bioactive glass powder 57
3.3.1(a) Batching 58
3.3.1(b) Melting 62
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3.3.1(c) Quenching 63
3.3.1(d) Drying 64
3.3.1(e) Milling 64
3.3.1(f) Sieving 64
3.4 Characterizations 66
3.4.1 X-ray fluorescence (XRF) 66
3.4.2 Particles size analysis (PSA) 67
3.4.3 Different Scanning Calorimetric (DSC) 67
3.4.4 X-ray diffraction analysis (XRD) 68
3.4.5 Fourier transform infrared analysis (FTIR) 69 3.4.6 Scanning electron microscopy (SEM) &
Energy-Dispersive X-ray (EDX)
69
3.4.7 In vitro test 70
3.4.8 Elemental analysis of ionic BG using ICP-OES 71
3.4.9 pH measurement analysis 71
3.4.10 Cell culture 72
3.4.11 Variability Gauge Chart 72
3.4.12 Oneway analysis 74
CHAPTER : FOUR RESULTS AND DISCUSSION
4.1 Introduction 76
4.2 Characterization of raw materials 76
4.2.1 Silicon dioxide (SiO2) 76
4.2.2 Calcium carbonate (CaCO3) 77
4.2.3 Sodium carbonate (Na2CO3) 78
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4.2.4 Phosphorus pentoxide (P2O5) 79
4.3 Synthesize of BG powder with different composition 80
4.3.1 Physical appearance 80
4.3.2 Thermal analysis 82
4.3.3 XRF analysis 86
4.3.4 Particle size analysis 88
4.3.5 XRD analysis 90
4.3.6 FTIR analysis 93
4.3.7 SEM and EDX analysis 95
4.4 Synthesize of BG powder at different melting temperature and soaking time
97
4.4.1 Physical appearance 98
4.4.2 XRF analysis 99
4.4.3 Particle size analysis 103
4.4.4 XRD analysis 109
4.4.5 FTIR analysis 112
4.5 Bioactivity evaluation via in vitro test using Tris buffer solution 115
4.5.1 XRD analysis 116
4.5.2 FTIR analysis 123
4.5.3 pH analysis 132
4.5.4 SEM and EDX analysis 137
4.5.5 Ion release analysis 149
4.6 Bioactivity evaluation via in vitro test using simulated body fluid (SBF)
153
4.6.1 XRD analysis 153
4.6.2 FTIR analysis 155
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4.6.3 pH analysis 159
4.6.4 SEM and EDX analysis 161
4.6.5 Ion release analysis 165
4.7 Reaction of bioactive glass powder in cell culture 167
CHAPTER : FIVE CONCLUSIONS
5.1 Conclusion 170
5.2 Recommendation for Further Work 171
REFERENCES 173
APPENDICES
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LIST OF TABLES
Page Table 2.1 Various composition of BG available in the laboratory 34 Table 2.2 Example of melt derived bioactive glass and its network
connectivity
46
Table 2.3 The different stages in bone development on BG surface 49 Table 3.1 Raw materials and their properties that have been used in
synthesized of bioactive glass powder
57
Table 3.2 The bioactive glass composition used in this research 58 Table 3.3 Oxides composition for synthesized 45S5 bioactive glass
powder
59
Table 3.4 Oxides composition for synthesized 50S8P bioactive glass powder
59
Table 3.5 Oxides composition for synthesized 54S4P bioactive glass powder
60
Table 3.6 Oxides composition for synthesized 46S0P bioactive glass powder
60
Table 3.7 Minimum and maximum in weight percentage (wt. %) of each oxides use to synthesize bioactive glass
62
Table 3.8 Melting temperature (°C) and soaking time for each bioactive glass composition
63
Table 4.1 Elemental analysis (wt. %) of SiO2 by XRF 77 Table 4.2 Elemental analysis (wt. %) of CaCO3 by XRF 78 Table 4.3 Elemental analysis (wt. %) Na2CO3 of by XRF 79 Table 4.4 Mass reduction (wt. %) over temperature (°C) 85 Table 4.5 Average particle size (μm) for different composition of
milled BG powder
89
Table 4.6 Average particle size for milled 45S5 synthesized at different temperature and soaking time
104
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Table 4.7 Average particle size for milled 50S8P synthesized at different temperature and soaking time
105
Table 4.8 Average particle size for milled 54S4P synthesized at different temperature and soaking time
106
Table 4.9 Average particle size for milled 46S0P synthesized at different temperature and soaking time
107
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LIST OF FIGURES
Page Figure 1.1 General experimental procedure to synthesize BG powder 10 Figure 2.1 Illustration on two dimensional structures of SiO2 19 Figure 2.2 Diagram on the effects of temperature towards glass
formation with function of temperature and enthalpy
21
Figure 2.3 Surface reactions induced by different types of glasses 26 Figure 2.4 Liquidus surfaces and equilibrium phase in system
SiO2-CaO-Na2O
29
Figure 2.5 The process of synthesize BG powder through melt derived route
30
Figure 2.6 The process flow to synthesize BG powder through sol gel route
32
Figure 2.7 Compositional dependence (in wt. %) for bone bonding and soft tissue bonding for bioactive glass and glass ceramic
35
Figure 2.8 Two dimensional structure of silicon tetrahedral 39 Figure 2.9 Two dimensional structure of silicate glass with sodium
oxide as network modifier
41
Figure 2.10 Two dimensional structure of silicate glass with sodium and calcium oxide as network modifier
42
Figure 2.11 Schematic diagram on the interface reaction between glass and solution on calcium phosphate (Ca-P) formation
47
Figure 2.12 Surface morphologies of 45S5 BG via SEM 50 Figure 2.13 XRD pattern of glass after immersion in Tris solution for
several days
51
Figure 2.14 FTIR spectra of 45S5 BG after immersion in SBF after one day
51
Figure 2.15 SEM images for BG particles produced by NovaBone 54 Figure 3.1 Correlation between moving factor and the output factor 61
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Figure 3.2 Moving factor design based on minimum and maximum percentage of each oxide (wt. %) using software JMP PRO 12
62
Figure 3.3 Melting profile for synthesized BG powder 63
Figure 3.4 Process flow on synthesized BG powder 65
Figure 3.5 The procedure during in vitro evaluation 71 Figure 3.6 Examples of variability chart (comparison graph) 73
Figure 3.7 Variability chart window 74
Figure 3.8 Example of oneway analysis 74
Figure 3.9 Oneway analysis chart window 75
Figure 4.1 XRD pattern of SiO2 powder 77
Figure 4.2 XRD pattern of CaCO3 powder 78
Figure 4.3 XRD pattern of Na2CO3 powder 79
Figure 4.4 XRD pattern of P2O5 powder 80
Figure 4.5 Image of BG frit obtained after quenched 81 Figure 4.6 DSC result for different composition of BG powder 83 Figure 4.7 TGA result for different composition of BG powder 86 Figure 4.8 Comparison between XRF and calculated weight on oxides
for all BG composition
87
Figure 4.9 Particle size distribution for milled BG powder 88 Figure 4.10 XRD pattern for all BG composition after melting 91 Figure 4.11 Scatter plot matrix for XRD with different BG composition 92 Figure 4.12 FTIR spectrum for all BG composition after melting 94 Figure 4.13 SEM (5kX mag) and EDX result for BG powder after
milling
96
Figure 4.14 Image of BG frit 98
Figure 4.15 Comparison between XRF and calculated weight on 45S5 BG powder
100
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Figure 4.16 Comparison between XRF and calculated weight on 50S8P BG powder
101
Figure 4.17 Comparison between XRF and calculated weight on 54S4P BG powder
101
Figure 4.18 Comparison between XRF and calculated weight on 46S0P BG powder
102
Figure 4.19 Particle size distribution for milled 45S5 BG powder 104 Figure 4.20 Particle size distribution for milled 50S8P BG powder 105 Figure 4.21 Particle size distribution for milled 54S4P BG powder 106 Figure 4.22 Particle size distribution for milled 46S0P BG powder 107
Figure 4.23 XRD pattern for 45S5 BG powder 110
Figure 4.24 XRD pattern for 50S8P BG powder 110
Figure 4.25 XRD pattern for 54S4P BG powder 111
Figure 4.26 XRD pattern for 46S0P BG powder 111
Figure 4.27 FTIR spectrum for 45S5P BG powder 113
Figure 4.28 FTIR spectrum for 50S8P BG powder 113
Figure 4.29 FTIR spectrum for 54S4P BG powder 114
Figure 4.30 FTIR spectrum for 46S0P BG powder 114
Figure 4.31 XRD pattern for 45S5 BG powder after immersion in Tris solution
116
Figure 4.32 XRD pattern for 50S8P BG powder after immersion in Tris solution
117
Figure 4.33 XRD pattern for 54S4P BG powder after immersion in Tris solution
118
Figure 4.34 XRD pattern for 46S0P BG powder after immersion in Tris solution
119
Figure 4.35 FTIR spectrum for 45S5 BG powder after immersion in Tris solution
125
Figure 4.36 FTIR spectrum for 50S8P BG powder after immersion in Tris
126
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Figure 4.37 FTIR spectrum for 54S4P BG powder after immersion in Tris solution
127
Figure 4.38 FTIR spectrum for 46S0P BG powder after immersion in Tris solution
128
Figure 4.39 pH trend of Tris solution 132
Figure 4.40 SEM (10kX mag) and EDX result of BG powder after immersion for 7 days
137
Figure 4.41 SEM (10kX mag) and EDX result of BG powder after immersion for 14 days
140
Figure 4.42 SEM (10kX mag) and EDX result of BG powder after immersion for 21 days
143
Figure 4.43 SEM (10kX mag) and EDX result of BG powder synthesized at lower temperature after immersion for 7 days
145
Figure 4.44 SEM (10kX mag) and EDX result of BG powder synthesized at lower melting temperature after immersion for 14 days
146
Figure 4.45 SEM (10kX mag) images and EDX result of BG powder synthesized at lower melting temperature after immersion for 21 days
147
Figure 4.46 Ion dissolution trend from BG in Tris solution 150 Figure 4.47 XRD pattern of BG powder after immersion in SBF
solution
154
Figure 4.48 FTIR spectrum of BG powder after immersion in SBF solution
156
Figure 4.49 pH trend of SBF solution 159
Figure 4.50 SEM (10kX mag) and EDX results of BG powder after immersion for 7 days
161
Figure 4.51 SEM (10kX mag) and EDX result of BG powder after immersion for 14 days
163
Figure 4.52 SEM (10kX mag) and EDX result of BG powder after incubation for 21 days
164
Figure 4.53 Ion dissolution trend from BG in SBF solution 166
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Figure 4.54 Optical images (10X mag) of DPSC cell incubated with 45S5 BG powder
168
Figure 4.55 Optical images (10X mag) of DPSC cell incubated with 50S8P BG powder
168
Figure 4.56 Optical images (10X mag) of DPSC cell incubated with 54S4P BG powder
169
Figure 4.57 Optical images (10X mag) of DPSC cell incubated with 46S0P BG powder
169
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LIST OF ABBREVIATIONS
BG Bioactive glass
CTE Coefficient of thermal expansion DMEM Dulbecco’s Modified Eagle Medium DPSC Dental pulp stem cell
DSC Differential scanning calorimetry EDX Energy dispersive x-ray
FTIR Fourier transform infrared spectroscopy FESEM Field emission scanning electron microscopy
HA Hydroxylapatite
HCA Hydroxylcarbonate apatite
ICP-OES Inductively coupled plasma optical emission spectroscopy PDF Powder diffraction file
PSA Particle size analysis RMM Relative molecular mass
rpm Revolutions per minute
SBF Simulated body fluid
TE Tissue engineering
TTT Time temperature transformation XRD X-ray diffraction
XRF X-ray fluorescence
45S5 45SiO2-24.5CaO-24.5Na2O-6P2O5 (wt. %) 50S8P 50SiO2-22CaO-20Na2O-8P2O5 (wt. %) 54S4P 54SiO2-22CaO-20Na2O-4P2O5 (wt. %) 46S0P 46SiO2-24CaO-30Na2O-0P2O5 (wt. %)
xvi
LIST OF SYMBOLS
mol. % Mole percentage
Nc Network connectivity
Tc Crystallization temperature
Tm Melting temperature
Tg Glass transition temperature
t Time
% Percentage
wt. % Weight percentage
° Degree
a.u Arbitrary unit
θ Incidence angle of X-ray beam
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SINTESIS DAN PENCIRIAN SERBUK KACA BIOAKTIF BERASASKAN SISTEM SiO2-CaO-Na2O-P2O5
ABSTRAK
Serbuk kaca bioaktif (BG) telah digunakan sebagai pengisi dalam kecacatan tulang kerana keupayaan untuk berhubung dengan tisu tulang melalui pembentukan ikatan dengan lapisan apatit. Walau bagaimanapun, suhu lebur yang lebih tinggi (1450 °C-1570 °C) atau masa lebur yang lebih lama (3 jam) diperlukan untuk menghasilkan serbuk BG melalui kaedah lebur kaca konvensional. Dalam penyelidikan ini, komposisi baru (50S8P, Nc = 2.69), (54S4P, Nc = 2.60) dan (46S0P, Nc
= 1.62) serbuk kaca bioaktif telah dibangunkan daripada sistem SiO2-CaO-Na2O- P2O5 untuk mendapatkan sifat-sifat pemprosesan dan biologi yang baik.
Penghasilan BG termasuk pengelompokan, pencampuran, peleburan pada suhu yang berbeza, lindap kejut air, pengisaran dan pengayakkan. BG dengan komposisi 45S5 digunakan sebagai kawalan. Pembelaun sinar-X (XRD) memperlihatkan struktur kaca amorfus sepenuhnya diperolehi untuk semua komposisi BG dengan puncak lebar antara 30-35°. Kaca berasaskan rangkaian silika juga disahkan melalui transformasi Fourier spektroskopi inframerah (FTIR) dengan kumpulan berfungsi Si- O-Si (tetrahedral) dikenalpasti dalam spektrum. Analisis haba membuktikan bahawa semua komposisi BG boleh dileburkan pada suhu lebih rendah iaitu 45S5 pada 1377
°C, 50S8P dan 54S4P pada 1348 °C dengan 46S0P pada 1347 °C. Oleh itu, kesan suhu dan masa lebur yang berlainan (1.5, 1 dan 0.5 jam) juga dikaji. Berdasarkan XRD, struktur amorfus masih kekal walaupun serbuk BG dihasilkan pada suhu lebur yang lebih rendah pada 0.5 jam untuk semua komposisi BG. Bioaktiviti BG dinilai dengan pengeraman serbuk BG dengan larutan penimbal Tris (pH 8) selama 7, 14 dan 21 hari. Ujian in vitro mengesahkan pembentukan hidrosilapatit (HA) pada permukaan BG dengan kemunculan puncak berhablur dalam XRD dan ciri-ciri kumpulan berfungsi karbonat (C-O) dan fosfat (P-O) yang kelihatan dalam FTIR dengan keamatan puncak yang lebih tinggi telah diperhatikan pada 45S5 dan 50S8P BG berbanding dengan 54S4P dan 46S0P BG. Tindak balas biologi yang lebih baik diperhatikan pada BG yang dibuat pada suhu 1400 °C setelah pengeraman dan seterusnya diuji dengan in vitro simulasi cecair badan (SBF), pH 7.3 dan media sel.
Namun, ciri-ciri pengamatan HA yang kurang telah diperhatikan pada XRD dan FTIR pada permukaan BG setelah direndam dalam SBF berbanding dengan larutan penimbal Tris. Kebolehserasian yang baik diperhatikan apabila sel stem pulpa gigi (DPSC) didedahkan kepada semua komposisi BG. Kesimpulannya, komposisi baru serbuk BG telah berjaya dibangunkan pada suhu dan masa lebur yang rendah dengan sifat biologi yang baik walaupun mempunyai sambungan rangkaian yang tinggi.
xviii
SYNTHESIZE AND CHARACTERIZATION OF BIOACTIVE GLASS POWDER BASED ON SiO2-CaO-Na2O-P2O5 SYSTEM
ABSTRACT
Bioactive glass (BG) powder have been used as a filler in bone defects due to the ability to connect with bone tissue through bonding formation with apatite layer.
However, higher melting temperature (1450 °C-1570 °C) or longer soaking time (3 hours) is required to produce BG powder via conventional glass melting route. In this research work, new composition (50S8P, Nc =2.69), (54S4P, Nc =2.60) and (46S0P, Nc =1.62) of bioactive glass powder was developed from SiO2-CaO-Na2O-P2O5 system to obtain good processing and biological properties. The BG preparations included batching, mixing, melting at different temperature, water quench, milling and sieving. BG with 45S5 composition was used as a control. X-ray diffraction (XRD) revealed that fully amorphous glass structure was obtained for all BG composition with broad peaks between 30-35°. Silica network based glass was also confirmed through Fourier transform infrared spectroscopy (FTIR) with Si-O-Si (tetrahedral) functional group was observed in the spectrum. Thermal analysis proved that all BG composition can be melted at lower temperature where 45S5 at 1377 °C, 50S8P and 54S4P at 1348 °C with 46S0P at 1347 °C. Hence, the effect of different melting temperature and time (1.5, 1 and 0.5 hour) were also studied.
Amorphous structure was still retained based on XRD although BG powder was synthesized with lower melting temperature at shorter melting time, 0.5 hour for all BG composition. The BG bioactivity was evaluated by incubating the BG powder with Tris buffer solution (pH 8) for 7, 14 and 21 days. In vitro test confirmed on the hydroxylapatite (HA) formation on the BG surface with emerging of crystalline peaks in XRD. Characteristic of carbonate (C-O) and phosphate (P-O) functional group noticed in FTIR with more intense peaks was observed on 45S5 and 50S8P BG compared to 54S4P and 46S0P BG. Better biological responds was observed on BG synthesized at 1400 °C upon incubation and was further evaluated by in vitro test in simulated body fluid (SBF), pH 7.3 and cell culture. However, less intense HA characteristic was observed in XRD and FTIR on the BG surface upon immersion in SBF compared to Tris buffer solution. Good compatibility was observed when dental pulp stem cell (DPSC) was exposed to all BG composition. In conclusion, new composition of BG powder was successfully developed at lower melting temperature and soaking time with good biological properties although possess high network connectivity.
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CHAPTER ONE
INTRODUCTION
1.1 Biomaterials
A material that is able to interact with biological system by providing treatment, tissue or organ replacement and function of body is known as biomaterial.
Initially, the first generation of biomaterial was focused on the mechanical performances of implant material and the material selection was limited to those that exhibit inert characteristics (Crovace et al., 2016). Inert material such as steels, carbon materials, silicones, and poly (methyl methacrylate) were examples of biomaterials. These materials exhibit biocompatibility characteristic yet suffer on non-degradation properties which limit their usage in clinical applications (Wang, 2016). These provided the basis for the invention of second and third generation of biomaterials (Crovace et al., 2016).
Development of biomaterials for clinical applications require some additional excellent important characteristic such as the ability of the biomaterial to be harmonized with micro-environment of defective tissue, ability to support the mechanical stability of defective tissue during tissue repair and possess the adaptable biodegradability characteristic which matches the new tissue formation (Wang, 2016). The second generation of biomaterials demonstrate such characteristic as the ability to induce reaction in the physiological environment. Meanwhile, the growth of third generation of biomaterials received great attention due to the capability of the biomaterials to stimulate specific cellular responses at the molecular stage and able to activate genes responsible for living tissue regeneration. Bioactive glass and glass ceramic are examples of third generation of biomaterials (Crovace et al., 2016).
2
Biomaterials is widely used in clinical applications such as in repairing bone defects. Several reasons that induced bone defects are infection, trauma, tumor and congenital deformity. The autogenous bone transplantation is optimum alternative for the treatment. However this procedure has drawbacks such as limited source, might induce damage at the site of transplantation. The other option is to introduce biomaterials that have potential restorative effects in bone defects. Biomaterial such as bioactive glass (BG) is widely used to repair bone defect due to the ability to bond and integrate with bone in living body through rapid formation of apatite layer on the material surface upon exposure to biological environment (Mosbahi et al., 2016).
Biomaterials also being implemented in dental treatment applications. The use of bioactive glass in dental treatment enables the induction of remineralization and assist against local irritation. In addition, the possibility to use BG in periodontal disease treatment is also recognized. It was reported that the combination of BG and clodronate enhanced ion exchange resulting in apatite formation in dental application to treat periodontitis during maintenance phase (Rosenqvist et al., 2014). Tooth sensitivity can also be treated using biomaterial such bioactive glass where the BG is added in tooth paste for the treatment (Fernando et al., 2017). The use of biomaterial in wound healing treatment (Lv et al., 2017) and bone fracture (Arcos et al., 2014) due to osteoporosis also has been widely explored and studied.
1.1.1 Bioactive glass
A glass is a material which is obtained by heating a solid mixture material until it reaches a viscous state and quickly cooled to prevent the formation of crystalline structure. Upon quenching, the atom remains in the disordered state characteristic of liquids (Salinas, 2014). The glass structure exhibit random array of atoms and are linked by directional bonding and glass network which contains no
3
regular pattern to the spacing among neighbour, and thus are often called
‘amorphous’ or without form (Kelly and Benetti, 2011; Wright, 2014). The open structure of amorphous glass facilitates the inclusion of network modifiers inducing the discontinuity of the glass network. The disordered structure leads to the high reactivity of glass in aqueous environments. The high surface reactivity of glass is the prime advantages of their application in bone repair and replacement (El- Kheshen et al., 2008).
The use of bioactive glass (BG) has received a great attention for bone and dental treatment since its first invention by Hench in the 1970s. The primary characteristic of BG which includes the ability to integrate with living tissue has induced rapid development of BG in biomedical applications (Rahaman et al., 2011).
Formerly, implant material exhibit only bioinert character and tends to evoke undesirable fibrous encapsulation around the material upon implantation. However, BG demonstrates a positive response upon implantation by developing a stable bond and interface with living tissue without formation of contact between fibrous tissue and the living tissue. The bond between BG and tissue is formed through apatite layer formation (Miguez-Pacheco et al., 2015).
The important characteristics of BG such as high bioactivity which has the ability to develop hydroxyapatite layer on the glass surface, osteoconduction and osteostimulation make them suitable to be used for bone and tooth repair regeneration (Miguez-Pacheco et al., 2015). The bioactivity depends on the ability to develop a bone-like mineral on the glass surface when in contact with physiological fluids (Orgaz et al., 2016). BG also shows excellent osteogenic characteristic due to ion released during glass dissolution which has the ability to stimulate expression of numerous genes that promote osteoblastic cell proliferation
4
and differentiation (Xynos et al., 2001; Hench, 2009). The classic application of BG includes bone filling materials, bioactive coating on orthopedic implant, dental applications and small bone implant (Jones, 2015).
1.1.2 45S5 Bioglass
The first bioactive glass was synthesized based on SiO2-CaO-Na2O-P2O5
system. The classical bioactive glass is generally referred as 45S5 Bioglass® and originally developed by Hench. The glass is characterized in nominal composition of 45% silicon dioxide (SiO2), 24.5% calcium oxide (CaO), 24.5% sodium oxide (Na2O) and 6% phosphorus pentoxide (P2O5) (in weight percent) (Desogus et al., 2015). The unique glass composition was reported as 45S5 to indicate the weight percentage of silica (SiO2) used as the network former and a 5-fold ratio of Ca/P (Hench, 2013). The lower content of network former silicon dioxide (SiO2) and higher content of glass network modifier, sodium oxide (Na2O) and calcium oxide (CaO) is the key feature that contributes in the bioactivity of 45S5 glass (Rahaman et al., 2011). P2O5 was added in the glass composition in order to stimulate the Ca/P component of hydroxyapatite (HA), the inorganic mineral of bone (Hench, 2013).
The oxide composition of 45S5 allows it to bond with both hard and soft tissues (Faure et al., 2015). In vitro experiment using 45S5 glass, heterogeneous nucleation of the HA layers on the glass surface was observed indicating the process of mimicking bone mineralization during bone repair. This finding indicated the possibility to develop HA layer on the implant glass which later will provide interfacial bonding with living bone. During, in vivo experiment in mid shaft femur of rats, evidence of development of polycrystalline HA layer on the implant 45S5 glass was observed to form bonding between collagen fiber (Hench, 2016). 45S5 bioactive glass has been widely used since mid 1980s in clinical treatments in
5
powder form as regenerative bone filler with product names such as Perioglas® and Novabone® (Novabone Corporation, Alachua Florida) (Jones et al., 2007). It has been use clinically in medical and dental application since then (Hench et al., 2014).
45S5 bioactive glass powder was first synthesized via conventional melt derived route. Melt derived route is a simple method and able to produce BG in massive production (Ma et al., 2010). Bioactive glass produced via melt derived is fully amorphous without existence of other crystalline phase. The amorphous phase is obtained due to the sudden cooling effect after quenched (Aguilar-Reyes et al., 2017). The bioactive glass produced via melt derived also exists in more disordered three-dimensional glass structure. The fully amorphous glass structure induced higher ability in formation of apatite layer compared to crystalline phase due to lower solubility that might be due to strong bonding between atoms in crystal lattice (Dziadek et al., 2016). This route requires mixing stoichiometric amounts of oxides which is high purity silica (SiO2), calcium carbonate (CaCO3), sodium carbonate (Na2CO3) and phosphorus pentoxide (P2O5). The mixture will then be melted at high temperature 1450 °C (Hench et al., 1971). Available literature also indicate range of melting temperature to synthesize 45S5 bioactive glass from above oxides, melted at 1400 °C for four hours (Lefebvre et al., 2008; Yang et al., 2013) and 1380 °C for two hours (Zarifah et al., 2015). The molten glass was then subsequently quenched in graphite (Yang et al., 2013) or stainless steel (Aguilar-Reyes et al., 2017) mold to obtain glass block or in water to obtain glass frit (Zarifah et al., 2015). In order to obtain glass powder, the glass frit or even glass block was crush and ground via mortar or milling process (Yang et al., 2013; Araújo et al., 2015). Synthesize of BG powder through melt derived is an alternative method to obtain glass without destructing the amorphous network structure. The mixture of reactants will be
6
subjected to high melting temperature and undergo sudden cooling process to prevent crystallization (Groh et al., 2014).
1.2 Problem statement
Bioactive glass is widely required for medical application as bone replacement materials owing to its capability in allowing the growth of the reactive layer (apatite) which stimulates chemical bond between BG implant and the host tissue (Bellucci et al., 2011). The golden composition of 45S5 is still use widely in commercial and still received much attention as a subject of research (Jones, 2015;
Polymeris et al., 2017).
It has been proven that alteration of BG composition (Mezahi et al., 2013), method of synthesize (Li et al., 2017) and heat treatment (Leenakul et al., 2016) can improve the BG properties in order to be used for various medical application.
Modification of BG composition will affect the reactivity and the biological characteristic of the BG. BG consisting more than 60% of SiO2 (in weight percent)in the composition have low rate of degradation due to the high level of oxygen bridges in the glass structure (Plewinski et al., 2013). The glass reactivity can be predicted through glass network connectivity (Nc) where glass with high Nc showed a decrease in bioactivity compared to glass with low Nc (Hill and Brauer, 2011). 45S5 has a Nc of 2.12. BG that have Nc greater than 2.6 show resistance to dissolution which limits their bioactivity. For instance, 13-93 BG takes 7 days to develop hydroxycarbonate (HCA) layer upon immersion in simulated body fluid (SBF) due to high Nc at 2.6. However, melting temperature that is use for 13-93 BG preparation in melt derive route is lower at 1350 °C compared to 45S5. Different from 45S5 BG, other oxides such as potassium oxide (K2O) and magnesium oxide (MgO) is added in 13-93 composition (Fu et al., 2010, Jones, 2015).
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Alteration of oxide content in glass composition such as Na2O will also affect the processing parameter and glass transition temperature of the BG (Kouyate et al., 2013).
Typically, mixture of raw oxides is subjected to high melting temperature in preparing BG particle through melt derived route. Temperature as high as 1450 °C and 1570 °C have been used to synthesize BG particle (different composition from 45S5) (Kapoor et al., 2016; Bellucci et al., 2017). However, it is also reported that BG particle derived from 45S5 composition is able to be melted at temperature of 1300 °C with longer period of soaking time of 3 hours. Additional steps are also introduced to produce glass particles where the molten glass is air quenched in the steel plate at room temperature prior to being crushed into powder form. The use of high temperature during glass synthesize will have impact on the cost of manufacturing (Leenakul et al., 2016).
Another route to synthesize BG powder is through sol gel method. The flexibility on the wide range of composition in BG synthetization can be obtained through sol gel method (Rezabeigi et al., 2014). The precursors is mixed and stored over period of time to obtain gel. The gel is then dried for several days before calcinations (Santos et al., 2016). However, this route is time consuming as longer time is required to obtain powder compared to BG synthesized via melt derived route. Heat treatment during calcinations might also induce the crystallization of the BG (Bellucci et al., 2014).
Various elements such as metallic ions (copper, magnesium, potassium and silver) are introduced in SiO2-CaO-Na2O-P2O5 system for enhancement of processing and biological properties. The introduction of the dopants in the glass system has shown to preserve or even improve the biological properties of BG such
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as the rate of apatite formation (Cannillo and Sola, 2009). However, it was reported that introduction of magnesium oxide (MgO) and calcium fluoride (CaF2)in the glass system reduce the chemical degradation of glass which restrain the crystallization of apatite on the glass surface (Tulyaganov et al., 2013). In addition, uncontrolled dissolution rate of metal ions due to certain amount of dopant can induce possible toxicity effects on cells which can cause inflammatory reactions (Rabiee et al., 2015).
Thus, in this work several compositions were developed in order to improve the processing parameter such as melting temperature (Tm) which consists of different Nc respectively at 2.69, 2.6 and 1.62. BG with high Nc was chosen also in order to develop glass with well connected structure but able to preserve the biological properties. New composition of BG was developed in order to improve the processing window such as melting temperature of BG where temperature below than 1450 °C was used during glass melting in this work. In addition, the effect on variation of soaking time during glass melting towards glass properties were also studied where shorter time was advocated at 30 minutes. The BG powder was obtained directly from glass frit following quenching in water in order to preserve the amorphous structure of glass. Water quench is preferable in this work in order to prevent crystallization. This technique is much simpler and less time consuming. To eliminate possibilities such as toxicity effects, BG compositions derived for this work only consist of oxides from this system, SiO2-CaO-Na2O-P2O5.
1.3 Research objective
The general aim of this work is to produce bioactive glass powder with specific objectives as follows:
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i. To develop new composition of bioactive glass (BG) powder from SiO2-CaO-Na2O-P2O5 through melt derived route.
ii. To evaluate the effects of melting parameters on the development of new BG.
iii. To evaluate the ability of BG to develop hydroxyapatite (HA) layer through in vitro test.
1.4 Scope of research
This research embraced several aspects in bioactive glass (BG) powder synthetization. The first part involved derivation of new composition of BG powder and it was synthesized through melt derived route. The BG powder was synthesized from the mixture of silica (SiO2), calcium carbonate (CaCO3), sodium carbonate (Na2CO3) and phosphorus pentoxide (P2O5). Parameters considered during synthesize of BG powder were melting temperature (depends on glass composition with 1400 °C as a control for each composition) and soaking time (0.5, 1 and 1.5 hours). The properties of each BG composition was characterized using thermal analysis, particle size analysis, X-ray fluorescence analysis (XRF), Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD) and scanning electron microscope (SEM). The apatite formation on each BG surface was validated by immersion in Tris buffered solution (pH=8) for several period of incubation time (7, 14 and 21 days). BG with good biological responses were evaluated for further characterization with Inductively coupled plasma optical emission (ICP-OES) test, immersion in SBF (pH=7.3) and cell culture compatibility. Two different biological solution (TRIS and SBF) were selected in order to study the response of synthesized BG towards different pH in human body. General experimental structure for this work is summarized in Figure 1.
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Figure 1.1: General experimental procedure to synthesize BG powder Raw oxides powder preparation
Mixing
Melting
Quenching
Drying
Dry milling
In Vitro Characterization
Characterization
Study on various composition of oxides
in BG synthetization
Effect of melting temperature
Effect of soaking time during melting
Effect of different BG composition on HA
development in in vitro test
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CHAPTER TWO
LITERATURE REVIEW
2.1 Ceramic as biomaterial
Materials are grouped into categories of metal, ceramic, polymers and semiconductor. Ceramic are compound of metallic and non-metallic elements consisting of oxides, nitrides and carbides. Common advanced ceramic materials include aluminium oxide (alumina, Al2O3), silicon dioxide (silica, SiO2), and silicon nitride (Si3N4). Meanwhile traditional ceramic is composed of clay minerals, cement and glass. Ceramic can be divided into crystalline and non-crystalline group (Carter and Norton, 2007). Crystalline ceramic exhibit regular atomic arrangement when it is slowly cooled from liquid state to solid state. Meanwhile ceramic such as silica, SiO2
demonstrate amorphous solid silica glass also known as non crystalline when cooled rapidly from liquid state without regular atom arrangement. Initially, main ingredient in glass consists of element from Na2O-CaO-SiO2 system (Gilmore, 2014).
Significant characteristic of ceramic include excellent stiffness, strength and hardness. Meanwhile drawbacks such as brittleness and fracture have been improved with engineered ceramic which show resistance to fracture (Callister Jr and Rethwisch, 2012). In addition, the ability of ceramic to sustain their properties and able to withstand with high temperature and harsh environment makes them being utilized in diesel engine parts (İŞCAN, 2016), tiles and bricks (Mahmoudi et al., 2017), transparent armor such as security window (Benitez et al., 2017), electrical component such as sensor and capacitor (Khan et al., 2016) and even in medical application (Dittmer et al., 2017).
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Development of ceramic for medical application began in 1970s when glass is utilized to form bond with the host tissue. The use of ceramic in medical field began to receive attention due to the fact that human body tends to reject metallic and synthetic polymeric materials by forming interfacial layer of scar tissue. This happens as living tissue such as cell, bone, soft tissue and hard tissue does not consist of material such as polymer and metal (Hench, 2006; Jones, 2015). The following section will discuss on bioactive glass in term of materials requirement, material selection, composition, methods of processing, physical properties as well as its applications as biomaterial.
2.2 Biomaterial
Biomaterial usage in orthopaedic, neurosurgery and dental field shows a drastic positive trending since past decades. The role of biomaterial includes the use as a passive structural-support replacement for bone graft (He et al., 2015), as scaffolds for drug delivery cell (Soundrapandian et al., 2014) and carrier for growth factor in human body (Quinlan et al., 2015). Biomaterial can be synthesized by utilizing component from ceramic (Drosos et al., 2012), metal (Ren and Yang, 2013), polymer (Bliley and Marra, 2014) and composite (Frajkorová et al., 2015) for medical implantation with variation in degree of bioactivity.
Biomaterial research area can be divided into a few main fields such as material science and engineering processing, biology and physiology cell and clinical sciences (Zavaglia and Prado da Silva, 2016). Material science and engineering processing field covers the knowledge of structure, processing and properties of material towards response to biological environment. Numerous continuous improvements has been performed for the materials to be used such as improvement in wear resistant, mechanical properties and reliability to be used in living body for
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indefinite period without side effects such as toxicity and inflammatory (Citron and Nerem, 2004).
Briefly, biomaterial can be defined as a material that has the ability to form interface with biological system by delivery or replacing tissue, organ or function of the living body. Biomaterial has the adaptability to create micro environment with native micro environment of tissue in situ (Wang, 2016). Similarities between biomaterial and surrounding tissue in term of mechanical properties are important for tissue reconstruction. Matching mechanical properties is required to support the stability of defected tissue during tissue repairing stage. Flexibility to degrade upon new tissue formation also needs to be considered during material selection (Nair and Laurencin, 2007).
Biomaterial can be used solely in living body or use as a scaffold for delivery of cells or growth factors. Implant material should not cause toxic responses and inflammatory effects upon implantation in living body and need to be degraded with controlled rate without inducing toxicity (Segers and Lee, 2011). The use of metallic material and elements in human body such as copper (Cu) can create toxic effects if the material usage is beyond the limited dose (Letelier et al., 2010; Jin et al., 2016). The material should also have a minimum and limited foreign body reaction and inflammatory responses (Cui et al., 2016). The use of polymeric material such as polyethylene glycol (PEG) has been proven to generate foreign body reaction with giant cells (Dobner et al., 2009; Segers and Lee, 2011).
Adequate shelf life or lifespan of an implant material is also an important feature that needs to be established. This is to assure that the degradation time of implant material corresponds to the regeneration process of new tissue. In addition, the degradation composition should be toxic free and able to be cleared from the
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body through metabolism (Nair and Laurencin, 2007). Inert material such as carbon, steels, silicones and polymer such as poly (methylmethacrylate) demonstrate good biocompatibility responses yet posses limitation due to non-degradation properties (Wang, 2016).
Unlike them, the use of glass as bone fillers and substitutes for instance show a good biological response without interrupting the remodelling bone capacity.
Based on clinical observation, BG slowly undergone dissolution, surface reaction and osteoclastic activity within one to four years depends on the cavity and defect size (Lindfors et al., 2010; Ylänen, 2011).
2.2.1 Bioglass
The glass has the ability to form interfacial bonding with bone without being rejected by the body. Material which demonstrates bonding with living tissue is known as bioactive material where the biological response was observed as the bioactive glass interface reacted to form bond with rat femur during in vivo study (Hench, 1988; Hench, 2006; Bi et al., 2014). The most successful invention of glass in medical application is known as Bioglass®, 45S5 where the recipe and formulation was first designed by Hench (Hench, 1998; Deliormanlı, 2015). The Bioglass® mainly contains silicon, calcium, sodium and phosphorus ions in the composition.
This ultimate component promotes the formation of a dual layer of silica and amorphous calcium phosphate on the surface layer which later promotes bonding with surrounding tissues (Xynos et al., 2000; Gentleman and Polak, 2006).
Bioactive glass offers good chemical durability and reactivity in body solution which makes them robust to be used in clinical applications. The chemical durability and reactivity can be controlled by altering and varying the glass composition prior to synthetization (Ylänen, 2011; Vaid and Murugavel, 2013).
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Hence, glass composition is one of the prime factors that manage the biological response of glass surrounding tissue. However, by manipulating the composition, it is unable to enhance the mechanical properties of the glass to be used alone clinically especially during surgery due to limitation in impact and loading (Keenan et al., 2016). Thus, bioactive glass in the form of particles and granules is often used compared to monolithic shape as it can be pressed into defect easily without fracture failure due to brittleness nature or even use as reinforcement with other materials for mechanical and biological improvement (Jones, 2015; Bellucci et al., 2011b).
Many studies and researches have been conducted for several decades on bioactive glass and researches on the development of this kind of biomaterial are continuously growing. Studies on the potential of raw materials, characteristics, properties as well as application are examples of researches done for bioactive glass.
Nevertheless, until now research on the 45S5 bioactive glass is still in constructive trending (Jones, 2015). Original glass composition containing 45SiO2-24.5CaO-24.5 Na2O-6P2O5 in weight percentages (wt. %) was the first material that was successfully proven to develop chemical bond with bone (Jones, 2015). 45SS can be easily prepared through melt derived since the composition is close to a ternary eutectic and small concentration of SiO2 in45S5 composition which is low than 55 (wt. %) makes the glass has the ability to develop hydroxycarbonate (HCA) layer more rapidly (Rehman et al., 1994, Hench, 2006).
Bioglass® have been used in repairing bone defects in the jaw, orthopedic and serve as active repair agent in tooth paste. Fast development of hydroxyapatite on the glass surface as well as the ability to form bond with living tissue and to induce formation of new tissue have receive much attentions after the finding (Rehman et al., 1994; Miguez-Pacheco et al., 2015). In addition, Bioglass®
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demonstrate positive responses on repairing bone defects due to significant biological performance and sufficient surface area for nutrient diffusion for newly formed bone (Fan et al., 2016; Hench and Thompson, 2010).
Interestingly, until today there are ongoing researches focuses on the new formulation from original Bioglass® composition for improvement in mechanical and biological responses. The glass has poor mechanical properties due to limitation for thermal treatment require for the densification. It tends to crystallize when sintered at 550-650 °C (Desogus et al., 2015). The glass crystallization needs to be controlled for good bioactivity level (Crovace et al., 2016). The composition of Bioglass® being improvised either by reformulation of original composition or by adding and doping other element such as silver, magnesium, strontium, zinc and aluminum in order to improve the Bioglass® properties. However, some of the dopants alter the material properties of bioactive glass such as bioactivity and rate of HA formation (Rabiee et al., 2015). In addition, the risk of toxicity effects due to uncontrolled of metal ions should not be neglected. Corrosion of this kind of glass can generate complication such as inflammatory reactions (Mouriño et al., 2012).
2.3 Bioactive material
Materials that have the capability to promote specific biological responses resulting in bone bonding between tissue and implant material is defined as bioactive material. Bioactive material can be classified into two categories, group A and group B. Both groups indicate different rate and mechanism of interaction between implant material and defective tissues. Group A is classified as osteoproductive material meanwhile group B is classified as osteoconductive material. The bioactivity of group A is observed when the implant material evokes intracellular and extracellular responses at the implant interface. Intracellular and extracellular are terms that
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describe the location either within or outside the cell (Leonard, 2017). Bioactive material from this group is able to form bond with bone and soft tissues. Meanwhile material from the group B only shows extracellular responses at the implant interface. Bioactive glass such as 4SS5 also known as Bioglass® falls under category A and B due to the ability to promote new bone growth with or without in contact with host bone (Jones et al., 2007). Synthetic hydroxyapatite (HA) is example of bioactive material which falls under category B (Asthana and Bhargava, 2014).
Bioactive material includes bioactive glass, bioactive glass ceramic, bioactive calcium phosphate, HA, bioactive coatings and composites (El-Bassyouni et al., 2016). Bioactive material behaves as intermediate character between bioinert material and biodegradable material. High surface reactivity of bioactive material induces strong bond formation of implant material with defective tissue upon implantation in the living body (Magri et al., 2017). The bond interaction between interfaces is induced through a hydroxycarbonate apatite (HCA) layer which is biologically active. HCA layer chemically and physically mimic the mineral phase of bone and responsible for the union between implant material and defective tissues (Caruta, 2006).
The mechanism of bond formation, the strength of the bonding and the thickness of the bond formation varies depending on types of the bioactive materials.
The rate of development of bonding interface depends on the level of bioactivity (Cao and Hench, 1996). Excellent bioactivity level of BG makes them a suitable candidate for defective bone regeneration and tooth restoration (Miguez-Pacheco et al., 2015). The fundamental of bone bonding formation is due to the reaction of BG with biological surrounding solution. A series of interfacial reaction leads to the formation of HCA layer upon implantation and established the interfacial bonding
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(Mancuso et al., 2017). The key advantages of using BG as implant material is due to the capability in controlling bone bonding formation ability and degradation kinetics (van Gestel et al., 2017). It can be achieved through modification of BG composition where BG with lower silica content resulted in faster apatite layer formation on surface due to higher solubility (Dziadek et al., 2016). Tailoring on the geometrical dimension such as by controlling the BG size would also impact on the biological properties such as on the dissolution rate. The cell proliferation is increased with decreasing size of BG particle (Ajita et al., 2015)
2.4 Glass as a Biomaterial
Glass wording originated from Latin which refers to a transparent or translucent body. Since the index of glass reflection is comparable to the air, the glass reflects very little when light waves pass through. Non-reflected photon will interact with the atoms in glass molecules giving a transparent appearance (Banjuraizah et al., 2011). Glass substances are also called vitreous. Glass can be produced either from organic (carbon) or inorganic (non-carbon) base (Harper, 2001). According to the hypothesis suggested by Rosenhain and Zachariasen, glass is a structure that is built in a random array of atoms connected by directional bonding.
However, details on the random network term were first introduced by Warren in 1933 (Wright et al., 2004).
Random network in glass structure can be defined as a non-crystalline solid that lacks the systematic and regular atom arrangement over relative atomic distance.
Such behaviour, lead to glass being also called as amorphous, supercooled liquid (atomic structure resembles liquid). An overview of amorphous structure can be explained by understanding the illustration on comparison between crystalline and non-crystalline of the ceramic compound, silicon dioxide (SiO2). Figure 2.1 present
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schematic diagram on two dimensional structure of both state of SiO2. Atom in disordered and irregular arrangement is observed for non-crystalline SiO2 structure.
The transformation into crystalline or amorphous structure depends on the conversion of random atomic structure in the liquid into ordered state during solidification (Callister Jr and Rethwisch, 2012).
Figure 2.1: Illustration on two dimensional structures of SiO2; (a) crystalline SiO2
and (b) non-crystalline SiO2 (Callister Jr and Rethwisch, 2012)
Other common characteristic of glass is glass transformation behaviour which is time dependant (Marinoni et al., 2017).
Glass is a common group of ceramic that has been typically used in wide range of applications such as insulating materials, structural flat glass, packaging, electrical devices or even as bioactive materials (Cormier et al., 2011). Glass is also known as non-crystalline silicate normally contain of oxides such as lime (CaO), potassium oxide (K2O), sodium oxide (Na2O) and alumina (Al2O3) which will influence the end product properties of glass such as the mechanical properties (Erdem et al., 2017), physical properties such as viscosity, electrical conductivity and thermal expansion (Cormier et al., 2011) as well as biological properties (Bellucci et al., 2017). The most well-known type of glass is soda-lime glass. Typically, soda-
(a) (b)
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lime glass contains 75% of silicon dioxide (SiO2), sodium oxide (Na2O), lime (CaO) and other minor additives. Sodium oxide (Na2O) is added in the glass structure in order to reduce the melting points of glass while oxide such as CaO is added as glass stabilizer in the structure (Harper, 2001). Traditionally, glass is formed by cooling (liquid state) from melt to solid state. The melt will be poured into stainless steel compartment and then annealed for several hours to obtain bulk glass samples (Mitang et al., 2010). However, other techniques have been adopted over the years in glass synthesize for wide range of applications such as through physical vapour deposition for high mechanical strength glass application (Bokas et al., 2017), neutron irradiation of material for high level waste immobilization application in nuclear reactor (Tang et al., 2014) and sol-gel technique for optical semiconductor application (El Hamzaoui et al., 2017). However, prominent techniques in glass synthesize for biomaterial application is either through melt-derive route or sol gel method (Mezahi et al., 2013).
2.4.1 Glass formation
Illustration of glass transformation stage is projected through enthalpy or volume versus temperature diagram as shown in Figure 2.2 respectively, which also known as time-temperature-transformation diagram (TTT). As substance is subjected to a temperature above its melting temperature (Tm), the glass liquid volume is increased. As the liquid is cooled from high temperature, two phenomena may occur at the point of solidification, Tm:
1. Atomic structure of the melt liquid is gradually changed resulting in long range order and the atomic arrangement become periodic as crystalline state nature. If the temperature is continuously lowered below the melting
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temperature, decreasing trend on the enthalpy is also observed due to lower heating process.
2. Discontinuous atomic structure arrangement with no abrupt change in enthalpy due to supercooled liquid formation without crystallization structure (Carter and Norton, 2007).
Figure 2.2: Diagram on the effects of temperature towards glass formation with function of temperature and enthalpy (Lopes and Shelby, 2005)
Glass is characterized as a material of fusion that undergoes cooling to a rigid condition without crystallization. The most common approach to obtain glass is by rapidly cool a liquid from above its melting point temperature (Tm) to a temperature which the rate of network rearrangement in the liquid is out of equilibrium (Jiang and Zhang, 2014). Transformation of solid-like (high degree
Temperature
Tm
Tf Fast Tf Slow
Crystal Fast cooled glass
Slow cooled glass
Crystal
Liquid
Supercooled liquid Glass transformation
range
Tf slow Tf fast Tm
Temperature
Enthalpy
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connectivity) to liquid-like (lower degree connectivity) can be achieved through temperature increment which resulting in bond breaking. As the temperature increase between glass transition temperature (Tg) and melting temperature (Tm) supercooled melt occurs. At this stage, the atom distribution is in disordered condition. At lower temperature below Tg, the glass network is categorized as an ideal disordered structure. Conversion of melt liquid into a glass can be achieved at higher melt cooling rates in order to prevent kinetic of crystallization. Amorphous glass with disorder unit cells in the system is obtained if rate of cooling is high enough to prevent crystallization (Ojovan, 2013).
Thermodynamic properties such as enthalpy, volume, or specific heat across the glass transition is depend at the cooling or heating rate of the liquid.
Microstructure changes in the glass transition range are kinetic phenomena which depend on the cooling or heating rate and temperature (Jiang and Zhang, 2014).
Cooling or quench rate is a key factor on glass formation. The rate of crystallization and quench is competitive in preserving amorphous glass structure. In order to prevent nucleation and crystal growth, optimum rate of quench should be implemented. Several factors need to be considered in order to achieve optimum rate of quench such as:
1. The temperature when the quench is applied. The viscosity of melt is lower at higher temperature. Hence, it facilitates in glass formation due to large spreading of melt to cold surface due to high rate of heat removal.
2. The size and amount of the melt to be quenched. An increase in melt volume will decrease the rate of quench since longer time interval is consumed to extract heat. This period ultimately offer a time for crystallization occurrence.
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3. Method of quench. A common method of quench is to quench using media such as water, oil and air. The rate of heat removal is affected by the degree of agitation of each medium. Among them, water is the most efficient medium to be used as a quenching media (Pye, 2012).
2.5 Bioactive glass
The development of bioactive glass during that time was driven by the requirement to find a material that is able to replace metallic and synthetic polymer as they tend to be rejected by the human body upon implantation by formation of scar tissue, non adherent layer of fibrous tissue at the implant interface (Hench, 2006). The glass is known as bioactive glass due to the ability to induce a specific biological response at the interface of the implant BG which encourages the formation of bond between host tissue and the implant (Hench et al., 2014).
Bioactive glass is considered as a second generation of biomaterial based on its ability to form interfacial bonding between implant and host tissue. The ability to regenerate and repair defective tissue by the gene activation properties of bioactive glass is a foundation to be nominated as third generation of biomaterial (Xynos et al., 2001). The first composition of bioactive glass that has been in clinical use since 1985 is 45S5, also known as Bioglass®. The main composition of 45S5 is a silicate based composition with oxides such as calcium oxide (CaO) and sodium oxide (Na2O) acting as network modifier and phosphorus pentoxide (P2O5) (Bretcanu et al., 2009).
Originally, BG composed of 45SiO2-24.5CaO -24.5Na2O -6P2O5 (wt. %) was selected in order to provide a large amount of CaO with minimal amount of P2O5 in SiO2-Na2O matrix. The composition indeed made them easy to melt. During the first trial as an implant, Bioglass® was melted, casted and designed into small rectangular
