Electrical characterisation of conductive hydrogels for biomedical applications

Conductive hydrogels offer an exciting opportunity to combine the hydrophilicity, biocompatibility, and tuneable viscoelastic properties of hydrogels with the conductive properties of electroactive species and conducting polymers. Reported applications of conductive hydrogels include but are not limited to electroactive wound dressings, wearable electronics, stimuli-responsive drug delivery systems, and tissue-engineered implants. With the rise of electroactive materials in biomaterials research, the electrical and electrochemical measurement techniques used to characterise their conductive properties have also emerged. The vast range of novel materials and the wide scope for application-specific requirements may leave researchers unable to discern the appropriate techniques, measurement conditions, and analysis to apply within their research. This review concisely summarises the techniques utilised to characterise the electrical properties of conductive hydrogels, including four-point probe conductivity measurements, cyclic voltammetry, and electrochemical impedance spectroscopy. Furthermore, the limitations and practical considerations of each technique are detailed. Recommendations for optimal sample preparation and experimental parameters are made, referencing current literature where conductive hydrogels have been successfully characterised. The fundamental principles of conductivity, electrical percolation, and indirect electrical stimulation are also discussed, to provide researchers with a comprehensive resource to develop and translate conductive hydrogels within biomedical research. STATEMENT OF SIGNIFICANCE: Electrically conductive hydrogels have gained increasing attention in wearable electronics, drug-delivery systems, and tissue engineering research. In existing literature there is a lack of standardisation in the electrical and electrochemical characterisation of these materials, as well as a variation in reported experimental conditions and data interpretation. This review is significant in providing a concise and practical resource to guide researchers in conducting accurate and impactful characterisation of the electrical properties of conductive hydrogels. It will contribute to research as a unique guide for best practise, promoting the advancement and translation of conductive hydrogels and their ever-expanding applications.