The development of graphene/biocomposites for biomedical applications

The development of biomaterials with appropriate properties is a requirement in biomedical research, particularly in tissue engineering. The aim of this thesis was to develop biocompatible, processable biocomposites for biomedical applications using graphene and graphene oxide (GO) as filler. Graphene, a unique two-dimensional carbon structure with excellent electrical, thermal and mechanical properties has been shown to be an appropriate filler for the development of composites for biomedical applications. Chemically converted graphene (CCG) dispersions were synthesized through reduction of GO, also a suitable filler for developing biocomposites. Polycaprolactone (PCl), a synthetic biodegradable and biocompatible aliphatic polyester with high processability and low cost, was chosen for development of biocomposites in Chapter 3. Two synthetic approaches were taken to develop graphene/PCl composites, a mixing method where graphene is mixed with the polymer (mixPCl-CCG), and a covalent attachment method by which graphene nanosheets are linked to the polymer chains (cPCl-CCG). In both methods, the addition of graphene resulted in significant improvement in the conductivity and the mechanical properties of PCl. Covalent links between PCl and CCG resulted in a homogenous dispersion of CCG sheets in the polymer matrix and higher flexibility of the cPCl-CCG composites. The synthesis of graphene/PCl composites was also achieved by a microwaveassisted method in which GO was reduced to graphene during the polymerization process. Graphene/PCl samples were subjected to enzymatic degradation to study the effect of graphene addition on the degradation of PCl. The composites were successfully processed into fibres and 3D structures using an additive fabrication approach that demonstrates the excellent processability of the graphene/PCl composites. The biocompatibility of the composites was also confirmed through cell culture experiments. Chitosan, a natural polymer, was used for the development of graphene biocomposites in Chapter 4. .Lactic acid was utilised as a crosslinking agent to form the composites. Similar to PCl-CCG composites, graphene/chitosan composites were prepared through mixing and covalent attachment methods. Graphene/chitosan composites, prepared by the mixing approach, showed great improvement in their conductivity and mechanical properties. Furthermore, the swelling rate of the composites could be controlled on addition of CCG. The composites were also extruded into multilayer 3D scaffolds using an extrusion printing technique. The composites and printed scaffolds exhibited excellent biocompatibility with fibroblast cells. The covalent attachment of the chitosan polymer chains and graphene sheets did not considerably improve the properties of the polymer compared to noncovalent ones, leaving the process open for further optimization in the future. The development of a UV-crosslinkable biocomposite was undertaken in Chapter 5. UV-crosslinkable chitosan (ChiMA) was developed through methacrylation of the polymer backbone. ChiMA composites were fabricated using both GO and CCG aqueous dispersions. The addition of either GO or CCG resulted in improvement in the mechanical properties of the polymer. The incorporation of CCG into the ChiMA matrix also greatly improved the electrical conductivity of the composites. The composites showed good biocompatibility with L929 murine fibroblasts, highlighting their suitability for biomedical applications. The excellent processability of the ChiMA biocomposites was demonstrated by the fabrication of multilayer 3D scaffolds via extrusion printing.