Tailoring Cell-Material Interactions via Poly(acrylic acid) Brushes to Enhance Nonviral Substrate-Mediated Gene Delivery

Nonviral gene delivery modifies gene expression by transferring exogenous genetic material into cells and tissues, typically through a bolus of complexes formed by electrostatic interactions between cationic lipid or polymer vectors with negatively charged nucleic acids (e.g. DNA). Although nonviral gene delivery is safer, more cost-effective, and more flexible compared to viral systems, nonviral transfection suffers from low efficiency due to extracellular and intracellular barriers. Much research has focused on tuning physiochemical properties of the complexing vectors to improve transfection, yet the cell-material interface may prove a better platform to immobilize DNA complexes for substrate-mediated delivery (SMD) and modulate the cellular response to improve transfection to overcome transfection barriers, especially in ex vivo or site-specific applications (e.g. biomedical implants). Natural and synthetic substrate modifications have both been investigated to improve transfection via SMD, but synthetic polymer films are often considered more reproducible and tunable compared to natural substrate modifications. While synthetic polymers films have been shown improve the efficacy of SMD (e.g. self-assembled monolayers or polyelectrolytes multilayers), these films have issues with degradation and impeded release of the DNA cargo and, moreover, are not typically studied in the context of clinically relevant metals (i.e. titanium (Ti)). In this dissertation, polymer films formed with pH-responsive poly(acrylic acid) (PAA) brushes were investigated to resolve these issues by grafting to a Ti substrate, immobilizing DNA complexes through electrostatic interactions with the PAA brushes, and modulating cellular response via conjugated adhesion moieties (i.e. RGD) and adsorbed free PEI. We showed our PAA-RGD platform increased transfection in cells cultured on PEI-DNA complexes immobilized to PAA-RGD compared to PAA alone. Investigations into further tuning the PEI vector and the RGD ligand showed that reduced cytotoxicity and increased proliferation, focal adhesion formation, and endocytic pathway activation may have improved our transfection success, suggesting that PAA-RGD brushes have the potential to immobilization of therapeutic DNA complexes for applications such as Ti biomedical devices, implantable sensors, and diagnostics tools. Advisor: Angela K. Pannie