Fast drying silver paint

Six wire samples were cut from the same lot and mounted onto wire specimen holders using silver paint (Fast Drying Silver Paint, Ted Pella Inc., CA). The cut end of the wires and the silver-painted ends of the specimens were masked off using two coats of lacquer (MICCROStop, Tolber Chemical Division, AK). The rest of the wire specimen holder was wrapped with parafilm to assure that no part of the specimen holder came in contact with the PBS. ASTM F2129, “Standard Test Method for Conducting Cyclic Potentiodynamic Polarization Measurements to Determine the Corrosion Susceptibility of Small Implant Devices,” was performed on these specimens in PBS. ASTM F2129 in brief, involves deaerating PBS with pure nitrogen at 150 cc/min for 30 min after which the test sample is submerged into PBS. The OCP is measured and recorded for 1 h. The OCP measured at the end of the hour was established as the rest potential (E_r). The voltage is then scanned potentiodynamically in the positive direction up to 1000 mV versus SCE at the rate of 1 mV/s. The breakdown potential was determined to be the potential at which the current densities rose by at least two decades. The potential is then scanned in the negative direction back to the rest potential at the same scan rate.

Electrodes had 8 nickel-chromium recording microwires (12.5 μm in diameter, Part number: CFW2024598, California Fine Wire Co., Grover Beach, CA, USA), one reference wire of the same diameter as the recording wires, and one platinum-iridium stimulating channel, 127 μm in diameter, Part number: 778000, A-M Systems Inc, Sequim, WA, USA). The recording and stimulating wires were bundled within a 27-gauge stainless steel cannula, which also served as a current return for stimulation. The recording wires were connected via silver paint (Fast Drying Silver Paint, Ted Pella, Inc, Redding, CA, USA) and the stimulating wire was connected via soldering onto a mill-max connector (Digi-key Electronics, Thief River Falls, MN, USA), enabling recording and stimulation at the same location. A ground wire was fixed onto the connector and the whole electrode was protected with epoxy. Electrodes were sterilized with Ethylene Oxide (EtO) (AN74i, Anprolene gas sterilizer, Andersen Sterilizers Inc, Haw River, NC, USA) before surgery. Typical 1 kHz impedances were 200–300 kΩ for the recording wire and 10–50 kΩ for the stimulating wire.