Development and Evaluation of Drug-Eluting Protein Based Hydrogel Coatings on Graphene Fibres for Neural Prostheses Applications

Implantable neural microelectrodes play a critical role in advancing neuro-prosthetic technologies aimed at restoring function in individuals with neurological disorders. Despite significant progress, the long-term performance of these devices remains hindered by mechanical mismatch with neural tissue, inadequate biocompatibility, and the foreign body response (FBR) that leads to chronic inflammation and signal degradation. Conventional rigid metallic electrodes, while electrically efficient, induce persistent tissue trauma and fail to integrate harmoniously with the delicate neural environment. In recent years, the development of soft, flexible, and multifunctional electrodes has emerged as a promising strategy to overcome these challenges. Graphene-based fibres, owing to their exceptional electrical conductivity, mechanical compliance, and high surface area, offer a unique platform for next-generation neural electrodes. However, their direct integration with neural tissue is limited by insufficient bioactivity, necessitating functional coatings to promote compatibility and reduce inflammatory responses.To address these limitations, this thesis investigates the fabrication, characterisation, and functional enhancement of graphene fibre-based neural microelectrodes through the application of silk fibroin (SF) hydrogel coatings, electro-compaction processing, and drug incorporation. Silk fibroin, a naturally derived protein polymer, combines biocompatibility, tuneable degradation, and mechanical flexibility with ease of chemical modification, making it an ideal candidate for bio-functional coatings. In this work, electro-compaction was employed to form thin, uniform SF coatings around graphene fibres, providing structural reinforcement while retaining the underlying electrical properties. Additionally, dexamethasone (Dex), a potent anti-inflammatory corticosteroid, was incorporated into the SF matrix to deliver localized, sustained release directly at the electrode–tissue interface, aiming to mitigate FBR and improve chronic electrode performance.The first experimental chapter presents the synthesis and characterisation of graphene fibres prepared from edge-functionalised graphene (EFG) and liquid crystalline graphene oxide (LCGO) dispersions. Controlled wet-spinning and post-treatment processes were optimised to yield fibres with high electrical conductivity, tensile strength, and flexibility suitable for microelectrode fabrication. Morphological analyses revealed dense, well-aligned graphitic domains, while structural characterisation confirmed the preservation of conductive networks after processing. Electrical measurements demonstrated conductivities in the range required for neural stimulation and recording, while mechanical testing highlighted a balance between strength and compliance. These properties established the graphene fibres as a robust and adaptable substrate for subsequent functionalisation.The second experimental chapter focuses on the development of silk fibroin coatings via electro-compaction directly onto graphene fibres. Processing parameters, including SF concentration and compaction time, were tuned to achieve uniform, conformal coatings with nanoscale thickness control. Scanning electron microscopy revealed coherent, crack-free coverage, while Raman spectroscopy confirmed the β-sheet-rich structural transformation induced by electro-compaction, contributing to coating stability in aqueous environments. Mechanical testing indicated that the SF coating improved fibre toughness without significantly compromising flexibility, while electrical impedance analysis showed that the thin hydrogel layer minimally affected conductivity. These results demonstrate the potential of electro-compacted SF as a multifunctional interface material, combining mechanical reinforcement with biological compatibility.The third experimental chapter investigates the incorporation of dexamethasone into SF coatings to create drug-eluting graphene fibres. Dex was first solubilised in ethanol and blended with SF solutions at varying concentrations before electro-compaction onto graphene substrates. Drug loading and release profiles were evaluated over 21 days, revealing sustained release kinetics influenced by SF and Dex concentrations. Theoretical and actual loading analyses indicated that drug-loading efficiency decreased with increasing initial Dex concentration, consistent with matrix saturation effects reported in literature. Higher SF concentrations enhanced retention efficiency due to increased protein–drug interactions, while balancing mechanical integrity and diffusional release. Importantly, electrochemical characterisation confirmed that drug incorporation did not significantly impair the electrical performance of the fibres, preserving their suitability for neural signal transmission. The combination of sustained anti-inflammatory delivery with mechanical and electrical functionality represents a significant advancement toward clinically viable, long-term neural implants.In summary, this thesis demonstrates a comprehensive materials engineering approach to design of multifunctional graphene fibre-based neural microelectrodes. Starting from the controlled fabrication of mechanically compliant, electrically conductive graphene fibres, the work introduces electro-compacted silk fibroin coatings to enhance biocompatibility, followed by the incorporation of dexamethasone to enable sustained local anti-inflammatory therapy. The resulting constructs exhibit a synergistic combination of properties i.e. mechanical compliance, structural stability, electrical conductivity, and bio-functionality, that address the key challenges of the electrode–neural interface. These findings not only advance the field of neural prosthetics but also establish a versatile platform for integrating bioactive coatings and controlled drug delivery into next-generation implantable devices. Future work may explore in vivo evaluation of these drug-eluting fibres, multi-drug release strategies, and integration into multi-channel neural interfaces to further enhance their therapeutic potential.