Bioceramic-based composites reinforced with carbonaceous nanomaterials
Date of Issue2017-01-26
School of Mechanical and Aerospace Engineering
Carbon nanotubes (CNTs) and graphene have been widely used to toughen bioceramics such as 45S5 Bioglass® (45S5) and hydroxyapatite (HA). However, it remains a challenge to homogeneously disperse them in the matrix and achieve adequate interfacial strength. In this thesis, two approaches have been successfully used to address these issues. They are: (1) using graphene oxide (GO) as a precursor to graphene, and (2) coating CNTs with a SiO2 shell. Spark plasma sintering (SPS) was used to sinter the bioceramic-based samples as it can provide high heating and densification rates and preserve the structural integrity of carbon-based reinforcements. Novel 45S5 composites reinforced with reduced graphene oxide (rGO) were prepared using the strategy of in situ GO reduction by SPS to realize homogeneous dispersion of the reinforcing phase. Prior to the fabrication of rGO/45S5 composites, the thermal reduction of as-synthesized GO by SPS was systematically investigated. SPS was proven to be highly effectual in minimizing the residual oxygen content and creating hierarchically roughened rGO sheets. The incorporation of rGO in 45S5 resulted in significant enhancement in its fracture toughness and in vitro cytocompatibility. Using HA as the representative material system, silica-coated CNTs (S-CNTs) were utilized to reinforce bioceramics for the first time. It was found that the S-CNTs could lead to higher sinterability of the composite powder than the raw CNTs, and were easier to be dispersed and more tightly bonded to the HA matrix. The incorporated S-CNTs could refine the HA grains and absorb fracture energy through their pull-out and by bridging the cracks, which led to improved fracture toughness. MG63 cells cultured on the S-CNT/HA pellets proliferated faster and possessed significantly higher alkaline phosphatase activities than those grown on HA compacts reinforced with raw CNTs. Therefore, the work reported in this thesis demonstrated the effectiveness for fabricating tough and biocompatible bioceramic-based composites with carbonaceous nanostructured reinforcements with the two aforementioned strategies.