Design and Characterization of Flexible and Implantable Electrodes

Abstract

Implantable bioelectrodes have the potential to advance neural sensing and muscle stimulation, especially in cases of peripheral nerve injuries. In such cases, the application of electrical stimulation to the muscles prevents muscular atrophy and helps to bridge the gap between the injured nerve and the corresponding muscle. Conventional materials for these implantable electrodes are usually metals, but they suffer from several limitations ranging from mechanical mismatch to immunological responses. Another problem is damage to tissues due to mechanical forces exerted on soft tissues by the stiff mechanical electrodes. Therefore, there is a need for the development of flexible, durable implantable electrodes with low interfacial impedance characteristics. This thesis discusses the fabrication and characterization of novel, low-cost, flexible bioelectrodes based on silicone polymer (polysiloxane) and other electrode materials, including titanium dioxide and stainless steel powder as well as their combinations. For this purpose, this work synthesized and characterized three types of implantable electrodes based on their electrochemical and mechanical properties; where titanium dioxide, stainless steel, and a mixture of the two were used as the main conducting components for fabrication. The titanium dioxide-based samples exhibited a bulk impedance of 353±13.5 Ω with an impedance of 198±183 kΩ at frequency of 1 kHz; in addition, they had a modulus of elasticity of 4.52±1.15 MPa. The stainless steel-based electrodes had a bulk impedance of 1.69±1.16 kΩ and an impedance of 1.21±1.13 MΩ at frequency of 1 kHz, and they had a modulus of elasticity of 0.722±0.393 MPa. The third type, which was a mixture of both titanium dioxide and stainless steel-based samples, had a bulk impedance of 1.71±0.849 kΩ and an impedance of 191 ± 160 kΩ at frequency of 1 kHz; along with a modulus of elasticity of 0.453±0.32 MPa. The results for the silicone with metal powders showed promising electrochemical and mechanical characteristics with flexible and ductile properties, with the titanium dioxide-based material performing the best. Compared with the values reported in the literature, the results show superior performance. Thus, supporting the composite material’s potential for being used in implantable electrode applications.