A unique structure for chronically implantable cortical electrodes using polyimide polymer was devised, which provides both flexibility between brain tissues and skull and stiffness for easy insertion. The fabricated implants are trishanks with 5 recording sites (20 x 20pm) and 2 vias per electrode of 40 x 40pm. Each recording site was connected to the external circuitry via a 15-channel connector, which is especially designed to facilitate processing of neural signals to the external circuitry. Measured impedance values are in -2Mohm at 1KHz. For a 5pm thick silicon backbone electrode, the stiffness was improved IO times larger than that of the electrode without silicon backbone layer. Stiff electrodes with 5pm and l0p.m thick backbone silicon penetrated pia of rat without buckling.

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Benzocyclobutene (BCB) based intracortical neural implants for basic neuroscience research in animal models was fabricated, in which microfluidic channel was embedded to deliver chemical reagents. BCB presents several attractive features for chronic applications: flexibility, biocompatibility, desirable chemical and electrical properties, and can be easily manufactured using existing batch microfabrication technology; The fabricated implants have single shank with three recording sites (20 x 20 microm) and two reservoirs (inlet and outlet). The channel had large volume (40 microm width and 10 microm height), and hydrophobic surface to provide a high degree of chemical inertness. All the recording sites were positioned near the end of the shank in order to increase the probability of recording neural signals from a target volume of tissue. In vitro biocompatibility tests of fabricated implants revealed no adverse toxic effects on cultured cells. The implant with a 5 microm silicon backbone layer penetrated rat's pia without buckling, a major drawback of polymer alone. The averaged impedance value at 1 kHz was approximately 1.2 MOmega. Water flowing through the channel was observed. Depending on the amount of the driving pressure from the syringes, the delivery speed of the water was totally controlled.

Abstract

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