Development of Egnineered Biointerfaces for the Incorporation and Release of Bioactive Molecules

Abstract

This thesis aims to contribute to and deepen the arsenal of synthetic extracellular matrix (ECM) mimetic substrates for in vitro cell research. Particularly, this thesis focuses on creating substrates capable of investigating mechanotransduction and biochemical signalling in tandem. Two bioengineered systems were explored for this: polystyrene-block-polyethylene oxide (PS-b-PEO) and poly(N-isopropylacrylamide)/polypyrrole (pNIPAM/PPy) platforms. The PS-b-PEO block copolymer system aims to achieve a local cell-mediated release of biomolecules near integrin binding sites. This system incorporated lysozyme and FITC-TAT as model biomolecules, and qualitative and quantitative release studies confirmed the biomolecule release. The final stage before the system could fully realise its potential in cell studies was controlling the rapid release. Layer-by-layer (LbL) films were chosen and constructed atop the block copolymer films so cells could degrade this layer and locally release cargo. Altering polyelectrolyte and PS-b-PEO surface parameters improved LbL buildup. It was ultimately shown through protein release studies that LbL films could not be formed on PS-b-PEO without losing or deactivating the cargo. The pNIPAM/PPy conducting polymer hydrogel system was selected due to its ability to control the substrate's mechanical properties and capacity for controlled cargo release. This system has been previously mechanically and electrochemically characterised, and the primary focus of this thesis was to electrically incorporate and release biomolecules from this hydrogel-based system. Fluorescein was incorporated into the conducting polymer phase as a model drug, and a comprehensive quantitative release study was conducted. This investigated release via oxidation and reduction, fluorescein reloading, release around the pNIPAM phase transition temperature, release with PPy thickness, and release stability over time. Finally, the corticosteroid drug dexamethasone was electrically incorporated and released from PPy films with a biphasic pulsed potential. Release of dexamethasone from pNIPAM/PPy was also demonstrated, but repeatability was an issue. The results presented provide advancements in two different synthetic systems regarding their abilities to mimic the biochemical and biophysical properties of the ECM. Creating such systems to study mechanotransduction and biochemical signalling in vitro enhances our understanding of cell behaviour in vivo. Through deepening our understanding of these processes, cell therapies and regenerative medicine become safer and more accessible globally.