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theses

Given the general increase in human lifespan, there is a growing need for bioactive bone implant material to repair bone defects caused by trauma, infection and tumor. To repair these bone defects, bone implant material should possess biomechanical and biochemical compatibility with natural bone and osteoinductivity to expedite the healing process. The implant material 45S5 bioglass, having great biocompatibility and osteoinductivity properties, gives best biological response. However, it has poor mechanical properties. Therefore, a material is needed that possesses all the required properties. In this study, our overall research goal is to produce CaSiO3-based ceramic composites that are mechanically and biologically compatible with human cortical bone and have osteoinductivity comparable to 45S5 bioglass that will promote bone growth and healing. To meet this need, we propose Low Temperature Solidification (LTS, carbonation) method to increase density of High Temperature Sintering (HTS) processed CaSiO3 that could enhance mechanical properties of CaSiO3 scaffolds, and control the concentration of Ca and Si ions released from HTS CaSiO3 to promote biocompatibility and osteoinductivity. For this purpose, we investigated the effect of combining HTS and LTS processes on the microstructure, mechanical properties, the dissolution behavior, in-vitro biocompatibility, and osteoinductivity of CaSiO3 scaffolds. Processing CaSiO3 compacts by HTS and LTS methods produced CaSiO3-CaCO3-SiO2 composites. XRD patterns indicated development of CaCO3 phases after carbonation process. Proportional to degree of carbonation, an increase in relative density up to 16 % accompanied by a decrease in porosity, pore size was achieved. Observation of the reaction products filling the pores of CaSiO3 indicated the compacts effectively densified. The maximum compression strength of 279 MPa and bending strength of 65.5 MPa and fracture toughness of 1.87 MPa.m1/2 were achieved with the samples sintered and then hydrothermally reacted. The enhanced relative density and strength and toughness reached by carbonation of green bodies and sintered CaSiO3 scaffolds improved mechanical compatibility with natural bone, increasing their potential as bone replacement material. The dissolution behavior of processed CaSiO3 scaffolds were evaluated by Simulated Body Fluid (SBF) immersion. Soluble factor concentrations were found to decrease with increasing degree of carbonation. The drawbacks of rapid dissolution of sintered CaSiO3 were addressed by carbonation process lowering release of soluble ions. In-vitro cell proliferation and osteogenic differentiation tests were performed to evaluate biocompatibility and osteoinductive potential of processed CaSiO3 scaffolds, respectively. In-vitro cell experiments showed CaSiO3 composites produced by carbonation of sintered CaSiO3 possessed significantly greater proliferation and osteogenic differentiation (p < 0.05) compared to only sintered CaSiO3 and osteoinductive 45S5 bioglass. Our results suggested that CaSiO3-CaCO3-SiO2 composites produced by processing CaSiO3 ceramics via HTS and LTS methods meet the requirements for repair of bone defects and might be a potential candidate as osteoinductive bone implant material

ETD_8659

Ph.D.

Includes bibliographical references

by Berra Beyoglu Siglam

doi:10.7282/T3MK6H3C

ETD doctoral

The author owns the copyright to this work.