Thick Conducting Polymer Coatings for Safe Electric Field Delivery to the Spinal Cord

Spinal cord injury (SCI) is a devastating condition that disrupts neural pathways in the central nervous system, resulting in sensorimotor dysfunction, loss of independence, and a significant reduction in quality of life. The societal and economic impact is substantial; in the United Kingdom alone, the lifetime cost of SCI exceeds £1.43 billion, with more than 60% of these costs projected to fall on public health systems. Despite this burden, current clinical interventions are limited to the management of complications and rehabilitation to maximise independence, as effective regenerative therapies remain unavailable. Electric field-guided stimulation has emerged as a promising approach to promote axonal regeneration after SCI, yet clinical translation has been constrained by the electrochemical and mechanical limitations of conventional metal electrodes. This thesis addresses these challenges by establishing a quantitative and operational framework for the application of thick-film poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) electrodes in sustained direct current and ultra-low frequency stimulation of the injured spinal cord. Finite element modelling in anatomically realistic spinal cord geometries demonstrates that electrode area, spacing, and placement are the principal determinants of uniform and safe electric field delivery, superseding applied current as the primary operational parameter. Guided by these criteria, thick-film PEDOT:PSS electrodes were fabricated and systematically characterised, exhibiting high charge storage capacity, low interfacial impedance, and electrochemical stability under continuous stimulation. In vitro studies confirm neuronal viability under stimulation. Ex vivo studies demonstrate device stability and anatomical conformance. In vivo implantation in rodent models demonstrates mechanical stability with no evidence of gross adverse effects over a 10-day survival period. Limitations of the present work include the absence of molecular or functional assays of axonal regeneration and the restriction of in vivo assessment to short-term implantation, precluding conclusions about chronic integration or long-term efficacy. Nevertheless, these findings define essential design criteria, safety considerations, and translational milestones for the development of soft, polymer-based neural interfaces in regenerative neuromodulation. Collectively, this work provides a defensible and quantitative pathway for advancing thick-film film PEDOT:PSS electrodes from benchtop validation toward clinical translation, informing the rational engineering of next-generation bioelectronic therapies for spinal cord injury.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2025

Author dc:creator

• Ansong Snr, Yaw

Advisors dc:contributor.advisor

• Proctor, Christopher
• Malliaras, George

• Conducting polymers
• direct current stimulation
• Electric currents
• Electrochemical impedance spectroscopy
• Electrochemistry
• Energy storage
• neural regeneration
• PEDOT:PSS
• Spinal Cord Injury
• Spinal cord regeneration
• Thick films
• Thin films
• Ultra low frequency
• Ultra low frequency stimulation

Licence

• https://www.repository.cam.ac.uk/bitstreams/a3b668c6-54a7-4b75-b133-9cd0f1106c2c/download
• http://purl.org/NET/rdflicense/allrightsreserved

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.126815

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/397779