Metallic Nanotexturing via RF Plasma Processing for Advanced Biomedical Devices : Antibiofouling Neural Electrodes and Hybrid Drug-Eluting Bare-Metal Stents

Metallic nanopillar/nanowire radial surface structures may by formed on alloy wire via a controlled capacitively coupled radio frequency plasma processing technique. Fully metal nanotexturing of sufficient depth and flexibility allows for enhanced performance biomedical implants, but prior to this work exploration on the technique had been limited to simple wire geometries, few materials, and exhibited a self-limiting structure depth of ̃1-2 µm precluding applications dependent on increased surface area. The objective of this research was to improve and extend the RF plasma metal nanotexturing technique with the intention to develop advanced surface morphologies for biomedical implant applications, particularly antibiofouling neural electrodes and hybrid drug-eluting bare-metal stents. Systematic review of the texturing technique included investigation into alternative plasma materials and variation of process power, chamber pressure, and exposure duration to obtain an optimal combination for maximizing surface structure depth. Experimentation led to successful texturing of diverse materials including multi- phase, single-phase, and pure metals. Procedures were developed to nanotexture additional geometries including foils, plates, and electrochemically sharpened tips. A multi-step process repetition in the parameter-controlled RF environment increased nanopillar height to at least 10 µm, a 400% expansion over previous results. Textured MP35N wire, Pt-Ir wire, and 316L stainless steel foil electrodes were produced by repetitive RF plasma processing; each exhibited decreased surface impedance opening the possibility for improved neural recording or stimulation. Low-impedance electrodes selectively coated with hydrophobic polytetrafluoroethylene resulted in conductive antibiofouling surfaces resistant to cell adhesion. Subsequent human aortic endothelial cell culture revealed a nearly 90% decrease in cell coverage compared to an untreated electrode. Sets of hybrid bare-metal drug- eluting stents were created from repetitively textured MP35N wires loaded with sirolimus or paclitaxel anti- restenosis agents by mechanically deforming the textured drug-loaded surface to physically confine the agents. Over the course of a 40 day in vitro release trial, the initial drug release burst upon injection was statistically suppressed and elution from the hybrid stent surface continued until at least the 20th day of the trial. Further developments potentially extend release over periods similar to commercial stents approved for clinical us