Polyaniline-based flexible implantable electrodes for neural sensing/stimulation applications

Abstract

Implantable bioelectrodes have the potential to advance neural sensing and muscle stimulation, mainly in patients with peripheral nerve injuries. The current emerging prostheses rely on the use of conductive and capacitive materials to assist the nerve recovery process, which is often slow. Therefore, implantable electrodes are used to stimulate and restore muscle function after injury. The function of implantable electrodes is to work as an interface between the damaged nerve and the muscle which is controlled by that nerve. There are conventional implantable electrodes that are fabricated from precious metals, such as platinum and gold. Aside from the cost, they have many disadvantages such as high impedance, toughness, and they make damage to the soft tissue. This thesis discusses the fabrication and characterization of novel, low-cost, flexible bioelectrodes based on silicone, and polyaniline (PANI), and polymethyl methacrylate (PMMA) in addition to their combinations. Implantable electrodes were fabricated from variant combinations of these polymers and their electrochemical and mechanical properties were evaluated. PANI was used as the main conducting components for fabrication. The characterization methods included conductivity, capacitive behaviour, cost, long term impedance, and their mechanical properties. The results of the fabricated PANI-silicone based samples displayed a bulk impedance of 600 Ω with an impedance of 1.6 kΩ at the frequency of 1 kHz and a modulus of elasticity of 75.312 MPa. The charge storage capacity of the fabricated sample was equal to 138.14 C/ Cm² which is the highest compared to the literature materials. The samples did not have any peaks so they were considered as stable samples. The mechanical test results of the fabricated batches were compared to those found in the literature such as PEDOT: PSS (poly 3,4-ethylenedioxythiophene): polystyrene sulfonate) and skin tissue. The young modulus of the fabricated samples (sample 1 and sample 9) were 0.1468 MPa and 75.312 MPa respectively, while the young modulus from the literature were 1.8 ± 0.2 GPa and 83.33 ± 4.9 MPa respectively. The results for the silicone with PANI showed promising electrochemical and mechanical characteristics with flexible and ductile properties.