The goal of this thesis work was to make a compliant microcable electrode that could fit into spatially constrained spaces, including deployment into the cortical layers of the cortex. Previous studies have indicated that reducing the bending stiffness of an implanted cortical electrode also reduces the injury and inflammatory response at the implant site. The electrode was designed in a microcable geometry that can be used either individually or in an array, as a shank-style electrode or as a string-like electrode that can be threaded around features such as the peripheral nerve.

The fabrication process, using spin cast molding (SCμM), is simple and adaptable to different patterns. We have successfully demonstrated the fabrication of both sinusoidal and straight microcables. SCμM patterning was also used on the substrate that framed the microcables, as an open, net-like sheet, as well as the patterning of the recording sites on the microcable electrodes. The creation of these different features, and their implementation in microelectrode fabrication demonstrates the versatility of a simple process technique. The microcables were fabricated using polydimethyl siloxane (PDMS) and the conductive element for the electrodes was thin-film gold.

The microcable electrode recording sites were electrically characterized using frequency-based impedance modeling and the impedance parameters were compared and shown to agree with the estimated values and trends from a circuit-based model. The microcables were also threaded around a peripheral nerve and used to record elicited action potentials to demonstrate functionality as compliant electrodes.

The thin metal film and the low tensile modulus of the PDMS substrate created an electrode with a composite tensile modulus lower than other compliant electrodes described in the literature. The gold film increased the composite modulus approximately three-fold compared to the unaltered PDMS. The durability of the electrodes and tolerance for stretch was also tested. The microcables were found to be conductive up to 6% strain and to regain conductivity after release from multiple applications of 200% strain. As the number of 200% strain applications increased (1,000-5,000), the electrodes lost conductivity at lower strains (1-2%). The tolerance for high-strain shows that the electrodes can be deployed for use and stretched or pulled into place as needed without damaging the conductivity.

The microcable electrodes were also tested for a suitable insertion mechanism for use as shank-style cortical electrodes. The microcables were coated on one side with fibrin, which when dry, stiffens the microcables for insertion into the cortex. A 28-day implant study comparing fibrin coated PDMS microcable electrodes showed a positive, but relatively low inflammatory response, as measured by glial fibrillary astrocytic protein (GFAP;​ indicating activated astrocytes) immediately at the tissue edge of the implant site. The response of the control, silicon shank-style electrodes, was varied, but also trended toward low levels of GFAP expression. The GFAP staining was possibly due to the clearance of the fibrin from the implant site or low-grade gliosis. Implant studies extending beyond 28 days are necessary to determine whether and to what degree the inflammation persists at the PDMS microcable implant site.