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Carbon Dots-Based Polymer Composites for Conductive Electrodes
Ali, Amaal Abdulraqeb
Ali, Amaal Abdulraqeb
Date
2023-04
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Thesis
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Description
A Master of Science thesis in Biomedical Engineering by Amaal Abdulraqeb Ali entitled, “Carbon Dots-Based Polymer Composites for Conductive Electrodes”, submitted in April 2023. Thesis advisor is Dr. Mohammad H. Al-Sayah and thesis co-advisors are Dr. Amani Al-Othman and Dr. Hasan Al-Nashash. Soft copy is available (Thesis, Completion Certificate, Approval Signatures, and AUS Archives Consent Form).
Abstract
Flexible electrodes have become a topic of interest for implantable applications such as stimulation of muscles atrophying due to nerve damage. Implantable electrodes used for signal recording and/or signal stimulation are composed of metals and metal alloys to benefit from metal’s high conductivity, corrosion resistance, and stability. However, due to their inherent rigidity, metal electrodes are limited by their mechanical mismatch with the soft biological tissues. Therefore, flexible alternatives are needed to replace metal electrodes. Several conductive and flexible polymers have been explored to replace metal composites. However, polymer-based composites still possess limitations including high rigidity or toxicity issues. This study presents flexible electrodes based on the highly elastic polymer polydimethylsiloxane (PDMS) and the conductive dopant boronic acid-modified carbon dots (BA-CDs). The potential of the composites as flexible electrodes was evaluated based on their: 1) electrochemical properties (conductivity, bulk resistance, impedance at 1 kHz, charge storage capacity (CSC), and electrochemical stability), 2) elasticity (Young’s modulus), 3) biocompatibility, 4) stability in body-like environment and 5) ability to record electrophysiological signals. The developed electrodes composed of 10% BA-CDs and 74% PDMS with 16% glycerol (dispersant) showed a promising conductivity of 9.62±3 .45×10⁻³ S/cm, bulk resistance 0.058±0.0135 kΩ, impedance at 1 kHz of 0.964± 0.361 MΩ, and a CSC of 21.4±5.9 𝜇C/cm². Mechanically, the electrodes had a flexibility of 0.0505 ± 0.0218 MPa that is compatible with biological tissues. Post-incubation in phosphate buffer saline (body-like environment), the electrodes performance improved electrochemically but deteriorated mechanically (0.1562 ± 0.0274 MPa) although to a degree still compatible with biological tissues. As surface electrodes, the electrodes recorded heart activity (electrocardiography) and muscle activity (electromyography) with a signal quality comparable to that of the commercial Ag/AgCl electrodes. In terms of biocompatibility, the electrodes showed some toxicity toward cells in vitro. However, future dose-response experiments using the conventional fibroblast L929 cells need to yet be conducted to obtain a more accurate understanding of the toxicity of the material.