AbstractThe related two-dimensional nanomaterials graphene and MXene have unique and distinctive properties which suggest a potential use in the remediation of contaminants that accumulate in body tissues during infection and chronic disease. However, the comparative biological impact of these nanomaterials and the mechanisms by which they interact with the cellular environment have not been fully characterised. The properties of pristine graphene and graphene nanocomposites were investigated in comparison to titanium carbide (Ti3C2) MXene variants to compare their biological interactions, antibacterial activity and adsorptive performance, and maintenance of functional activity following incorporation into electrospun scaffold composites.
Graphene nanoplatelets (GNP), graphene oxide (GO), graphene oxide silver (GO-Ag), multilayer Ti3C2 MXene (ML-MXene) and delaminated Ti3C2 MXene (DL-MXene) were synthesised and their physicochemical properties characterised using electron microscopy, dynamic light scattering, spectroscopy, porosimetry and conductivity measurements. In vitro cell culture and blood based assays were conducted to investigate variations in material propensity to induce necrosis, apoptosis, oxidative stress, haemolysis, blood cell activation and coagulation. Antibacterial activity was assessed using representative Gram-negative and Gram-positive bacteria Escherichia coli and Staphylococcus aureus. Capacity to impact dysregulated inflammatory pathways following bacterial endotoxin exposure was investigated by analysis of inflammatory cytokine and endotoxin adsorption followed by a study to measure cytokine clearance from endotoxin stimulated human monocytic THP-1 cells. Loading efficiency for bioactive molecules was evaluated through ML-MXene intercalation with tetracycline followed by the development of methods to incorporate materials into electrospun polymer scaffolds to assess maintenance of antibacterial and adsorptive properties.
The predominantly hydrophobic graphitic domains of the graphene variants contrasted with the transition metal based hydrophilic MXenes. Whilst GNP had the largest available surface area for adsorption, delamination of ML-MXene doubled its surface area and negative surface charge. No significant impact on cell viability, induction of oxidative stress, apoptosis, necrosis or blood platelet activation was observed for GNP, GO, ML-MXene and DL-MXene. GO-Ag significantly reduced cell viability, induced apoptosis and significantly reduced bacterial viability at a lower concentration than the conventional silver nanoparticles in contrast to GNP, GO, ML-MXene and DL-MXene. This study showed for the first time that ML-MXene intercalation of an antibiotic (tetracycline) significantly preserved bacteriostatic activity. No direct removal of bacterial endotoxin by GNP, GO, ML-MXene and DL-MXene was observed and these materials adsorbed cytokines to varying extents. However, all significantly repressed cytokine production by endotoxin stimulated THP-1 monocytes indicating potential interference with endotoxin binding to cell receptors alongside cytokine adsorption. This was the first study to show effective pro-inflammatory cytokine adsorption by graphenes and MXenes, and repression of cellular cytokine production by MXenes. Nanomaterial cytokine adsorptive activity was not retained upon incorporation into electrospun cellulose acetate and polycaprolactone (PCL) scaffolds. However, GO-Ag antibacterial activity was preserved upon surface attachment to plasma treated PCL scaffolds, indicating potential use in antibacterial applications.
This thesis deepens understanding of the impact of the physicochemical properties of graphenes and Ti3C2 MXenes on their biological interactions and adsorptive performance. It also extends current knowledge on the biomedical utility of these materials to include blood contacting applications for removal of tissue contaminants. Further investigation is required to further characterise cellular interactions and optimise nanomaterial incorporation into composite systems for significant retention of biotoxin adsorption.
|Date of Award||Feb 2020|
|Supervisor||Susan Sandeman (Supervisor), Patrick Dyer (Supervisor) & Ganesh Ingavle (Supervisor)|