Nano-Pt ennobling of stainless steel for biomedical applications

A simple, one-step synthesis technique for simultaneous removal of the passivating oxide layer of Type 304 stainless steel (SS) and subsequent electrodeposition of platinum nanoparticles is presented. This method was compared to electrodes that were first acid pickled in HCl and subsequently platinized. Electrochemical impedance spectroscopy (EIS) in PBS and equivalent circuit modeling using an (R(Q(R(QR))) circuit indicated that the one-step synthesis of platinized SS electrodes has lower charge transfer resistance (4.56 × 10³ Ω cm²) when compared to a two-step platinization procedure (2.05 × 10⁴ Ω cm²) and non-modified SS (1.36 × 10⁶ Ω cm²), indicating removal of the passive layer and addition of conductive nanoparticles. Cyclic voltammograms measured in an equimolar ferricyanide/ferrocyanide redox probe at multiple scan rates indicated that the one-step method resulted in the highest electroactive equivalent surface area of all controls tested (one-step: 65.4%, two-step: 43.1%). Temporal studies of current densities measured in HCl over 48 h yielded higher exchange current densities for one-step platinized SS (4.90 × 10⁻⁶ A cm⁻²) than SS (6.50 × 10⁻⁷ A cm⁻²). Scanning electron and atomic force micrographs of electrodes were used to characterize surfaces before and after platinization. One-step platinized Type 304 SS mesh electrodes were used to study pH-responsive poly(HEMA-co-AEMA) hydrogels as a function of pH by EIS. The one-step platinized electrodes produced similar valued but more stable pH-dependent (pH 6.0–9.0) membrane resistance with regression coefficient of R² = 0.97 compared to that of pristine SS that was R² = 0.57.