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Development of Porous 3D Melt-Derived Bioactive Glass Scaffold

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Development of novel 3D porous melt-derived bioactive glass scaffolds Zoe Yunxie Wu September 2010 A thesis submitted to the Department of Materials, Imperial College London in partial fulfilment of the requirement for the degree of Doctor in Philosophy Declaration I hereby certify that the work presented in this thesis is the result of my own investigations carried out at Imperial College London during the period from October 2006 to October 2009, except where otherwise stated. Zoe Yunxie Wu September 2010 ~ 2 ~ Abstract The aim of this thesis is to develop a method to produce melt-derived bioactive glass scaffolds, without the glass crystallizing into a glass-ceramic, while establishing an interconnected pore network suitable for bone tissue regeneration. In order to achieve this, the scaffold must have the ability to closely mimic the porous structure of cancellous bone and its mechanical properties. Two bioactive glasses were used in this project, both are modified from the Bioglass® composition: ICIE 16 (49.46% SiO2, 36.27% CaO, 6.6% Na2O, 6.6% K2O and 1.07% P2O5, all in mol%) and ICIE 16M (49.46% SiO2, 27.27% CaO, 6.6% Na2O, 6.6% K2O, 3% ZnO, 3% MgO, 3% SrO and 1.07% P2O5, all in mol%). Gel-cast foaming produced improved pore networks over alternative methods for producing porous scaffolds. There are many variables in the process. An initial protocol was established and each of the variables assessed systematically. The relationships between each component, the gelling time and the foam body volume were evaluated to develop an optimized protocol for the process. The size of the glass powder was critical in determining the sintering efficiency. A suitable drying and sintering program was also determined to prevent crystallization of the glass and formation of crystal species from by-products of the process. The scaffolds were characterized in terms of the interconnect size, the rate of hydroxycarbonate apatite (HCA) formation in simulated body fluid (SBF) solutions, the ion release rate and the compressive strength. The results showed that ICIE 16M sintered better and was stronger than ICIE 16, however in the bioactivity aspect of view, the rate of HCA formation in SBF was faster for ICIE 16 than ICIE 16M. ~ 3 ~ To my parents Jianming Zhong and Jianwei Wu Acknowledgement First and foremost I would like to express my deepest and most sincere gratitude to my supervisors, Dr. Jones and Prof. Hill for this wonderful opportunity to work closely with their brilliant minds. Four years ago I would not have dreamed in my wildest dreams to be at this stage of my life. I would like to thank my parents for their endless support, both financially and psychologically, without them I would never have made it this far. I am most grateful for the help I received from Mr. Richard Sweeney on the XRD analysis, Dr. Mahmoud Ardakani on the SEM analysis, Dr. Gowsihan Poologasundarampillai and Sheng Yue on µCT imaging and analysis, Bobo Yu on ICP analysis, and Hannah Choi and Donovan Nightingale with their assistance in data analysis as part of their final year projects. I would also like to thank everyone in Dr. Jones’s and Prof. Hill’s group, in particular Dr. Gowsihan Poologasundarampillai and Dr. Sally Watts who have helped me since I was a final year project student, for their kind assistance, friendship and countless laughter and interesting moments we have shared together. My most heartful thanks goes to my friends, especially to Wei, Xinwen, Sayma, Fanyin, Akiko, Noriko, Hiroko, Sheng and Jin, Jingqi and Liliang for their never-ending warm support, advice and encouragement. At last I would like to thank Dr. Jones and Professor Hill again for their immense amount of patience, kind considerations and valuable advices. ~ 5 ~ Contents Declaration .............................................................................................................................. 2 Abstract ................................................................................................................................... 3 Acknowledgement .................................................................................................................. 5 List of Figures ......................................................................................................................... 9 List of Abbreviations ............................................................................................................ 13 1. Introduction ................................................................................................................... 14 2. Literature review ........................................................................................................... 18 2.1 Human Bone .......................................................................................................... 18 2.2 Bone tissue engineering ........................................................................................ 20 2.3 Biomaterials for bone tissue engineering ............................................................ 21 2.4 Bioactive glasses ................................................................................................... 23 2.4.1 Sol-gel derived BGs .......................................................................................... 32 2.4.2 Melt-derived BGs .............................................................................................. 34 2.4.3 Summary ............................................................................................................ 35 2.5 Bone Scaffolds and potential scaffold materials ................................................. 36 2.5.1 Summary ............................................................................................................ 40 2.6 Production techniques of porous bioceramic foams ........................................... 40 2.6.1 Freeze casting .................................................................................................... 41 2.6.2 Polymeric sponge impregnated with ceramic slurry ....................................... 42 2.6.3 Slip casting foaming process ............................................................................ 45 2.6.4 Gel-casting foaming technique ......................................................................... 47 2.6.5 Sol-gel foaming ................................................................................................. 52 2.6.6 Rapid prototyping (RP) ..................................................................................... 54 2.6.7 Summary ............................................................................................................ 56 3 Glass production and characterization ......................................................................... 57 3.1 Introduction ........................................................................................................... 57 6 3.2 Materials and methods .......................................................................................... 58 3.2.1 Glass composition ............................................................................................. 58 3.2.2 Glass production ................................................................................................ 60 Differential Scanning Calorimetry (DSC) ............................................................... 63 Particle size analysis.................................................................................................. 63 3.3 Results and discussion .......................................................................................... 64 3.3.1 Influence of composition .................................................................................. 64 3.3.2 Influence of particle size ................................................................................... 65 3.3.3 Influence of heating rates .................................................................................. 67 3.3.4 Determining the activation energies (Ea) ........................................................ 69 3.4 Summary ................................................................................................................ 72 4 Identifying and optimizing of the standard protocol of the gel-cast foaming process.. ........................................ ……………………………………………………………73 4.1 Introduction ........................................................................................................... 73 4.2 Experimental.......................................................................................................... 75 4.3 Results and discussion .......................................................................................... 78 4.3.1 Effect of Water ................................................................................................... 78 4.3.2 Effect of Catalyst ............................................................................................... 79 4.3.3 Effect of Initiator ............................................................................................... 80 4.4 Summary ................................................................................................................ 86 5 Optimizing the drying and sintering program ............................................................. 87 5.1 Introduction ........................................................................................................... 87 5.2 Experimental.........................................................................................................
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