Year

2019

Degree Name

Doctor of Philosophy

Department

Australian Institute for Innovative Materials

Abstract

In 2004, mono-layer carbon material, i.e. graphene, was discovered and prepared by Geim and Novoselov using a scotch tape method. Sourcing from one of the most bountiful natural materials (carbon) and emerging as a single layer atom-thick film arranged in a honeycomb lattice, graphene presents exceptional surface area, high carrier mobility, excellent electrical, optoelectronic and mechanical properties. Graphene and its derivatives, in 2D form, have already found applications in many research fields, namely: energy storage, environmental protection, flexible electronics and tissue engineering. Especially in tissue engineering, 2D graphenebased materials have already found applications in the reconstruction of bone, cartilage, neural, cardiac, skin and several other tissues/organs. The extraordinary performance of 2D graphene-based materials in tissue engineering originates from their capability in resembling in vivo extracellular matrix (ECM), which is essential to direct cell performance towards amending damaged body parts. From a clinical standpoint, it is essential that these materials are produced using non-toxic and nonhazardous methods and have predictable properties and reliable performance under variable physiological conditions, especially when used with a cellular component. In addition, transition from a 2D structure to 3D systems empowers graphene for many new applications, as the 3D graphene-based structures (3DGBSs) not only possess intrinsic graphene properties, but also higher surface to volume ratio, more conducive to decoration, abundant embedded binding sites and other remarkable interfacial properties. Especially, 3DGBSs with large surface area, micropores/ channels, biocompatibility, appropriate mechanical property and good electrical conductivity, are emerging as platforms for tissue engineering and other bionic areas, including in vivo human tissue regeneration. In addition, previous studies have shown that cell activity can be enhanced by 3D graphene scaffolds through improved cell adhesion, interaction, migration, proliferation and differentiation.

A variety of 2D/3D graphene-based structures have been systematically developed and investigated towards stem cell support in the work described herein. RGO coating on 3D porous polydimethylsiloxane (PDMS) can improve its biocompatibility and the obtained 3D RGO/PDMS scaffold showed potential application towards improved osseointegration. In addition, transformation from a 2D graphene-based structure to 3D graphene-based scaffold was also investigated. Initially, 2D graphene-cellulose (G-C) paper was prepared using commercially available cellulose tissue paper as a substrate that was coated by immersiondeposition with graphene oxide (GO), followed by reduction to reduced graphene oxide (RGO). G-C papers were configured to 3D constructs by lamination with alginate and further modified by folding and rolling for 3D “origami-inspired” scaffolds. Fabrication procedures of these 3DGBSs have limited controllability over scaffold inner structure and property. Therefore, a 3D printing technique was utilized whereby 3D alginate (Alg) based scaffolds with tunable pore size and inner structure were printed and coated with graphene oxide (GO), followed by reduction to obtain electrically conductive 3D RGO/Alg scaffold. Each 3DGBS variant was applied for adipose-derived stem cell (ADSC) support and osteogenic differentiation. The 3D scaffolds may be useful for in vitro modelling of human bone development and regeneration, including ossification and mineralisation, with cell culture emulating cell behaviour and function within natural tissue. Furthermore, G-C paper and 3D RGO/Alg have also been incorporated into 2D and 3D electrical stimulation (ES) devices to investigate the influence of ES on stem cell proliferation and differentiation. ES effects on osteoinduction may shed light on the use of ES for treating bone injury and disease.

In conclusion, the graphene-based 2D and 3D structures described in this thesis may be useful platforms for human tissue engineering and modelling, as well as devices for regenerative medicine.

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.