Stability of phosphonic self assembled monolayers (SAMs) on cobalt chromium (Co–Cr) alloy under oxidative conditions

Abstract

Cobalt Chromium (Co-Cr) alloys has been widely used in the biomedical arena for cardiovascular, orthopedic and dental applications. Surface modification of the alloy allows us to tailor the interfacial properties to address critical challenges of Co-Cr alloy in medical applications. Self assembled monolayers (SAMs) of Octadecylphosphonic acid (ODPA) have been used to form thin films on the oxide layer of the Co-Cr alloy surface by solution deposition technique. The SAMs formed were investigated for their stability to oxidative conditions of ambient laboratory environment over periods of 1, 3, 7 and 14 days. The samples were then characterized for their stability using X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM) and Contact Angle Measurements. Detailed high energy XPS elemental scans confirmed the presence of the phosphonic monolayer after oxidative exposure which suggested that the SAMs were firmly attached to the oxide layer of Co-Cr alloy. AFM images gave topographical data of the surface and showed islands of SAMs on Co-Cr alloy surface, before and after SAM formation and also over the duration of the oxidative exposure. Contact angle measurements confirmed the hydrophobicity of the surface over 14 days. Thus the SAMs were found to be stable for the duration of the study. These SAMs could be subsequently tailored by modifying the terminal functional groups and could be used for various potential biomedical applications such as drug delivery, biocompatibility and tissue integration

Functionalization of biodegradable magnesium alloy implants with alkylphosphonate self-assembled films

“…The chemisorption of carboxylic acids on the native oxide surfaces of many metals including magnesium and its alloys yields stable SAMs in a simple immersion process [13,[16][17][18][19]. Phosphonic acid SAMs have also been reported on the native oxide surfaces on many metals and alloys such as aluminum [20][21][22][23], copper [24,25], nickel [26], iron [27], titanium [23,28,29], steel [30,31], nitinol [31,32], cobalt-chromium [33] and so on. The preparation of alkylphosphonic acid SAMs on magnesium alloys by vapor deposition and simple immersion methods has been reported recently by Ishizaki et al [34,35].…”

Organic corrosion inhibitors: where are we now? A review. Part IV. Passivation and the role of mono- and diphosphonates

“…Samples of the alloy modified in this way were tested for resistance to oxidizing conditions in a laboratory medium and in phosphate buffer solution (PBS) with a pH of 7.4 for 1 to 14 days, and then studied by XPS, AFM and measurements. The stability of the SAM and the hydrophobicity of the alloy surface throughout the study were confirmed [101,103].…”

“…Although it has not been possible to find reports on the formation of SAMs upon adsorption of APhs on Co itself, studies of this kind are widely known for Co-Cr alloys [100][101][102][103]. These alloys are widely used in cardiovascular stents, orthopedics and dentistry.…”

Effective and Environmentally Friendly Nickel Coating on the Magnesium Alloy

“…The O 1s emission peaks were deconvoluted using four Voight curves with BEs of 530.9 eV, 531.8 eV, 532.9 eV, and 533.9 eV, which can be attributed to the oxide ions (O 2− ), mainly MgO [34,38,39], phosphonate oxygen bonded to the metal (P-O-M) [30,[37][38][39][40][41], P-OH group [38][39][40]42], and P=O group [39,40]. A dominant peak attributed to phosphonate oxygen bonded to the metal (P-O-M) [30,[37][38][39][40][41] has been attributed to metallic hydroxide by Ishizaki et al, and a few other authors have attributed it to the P=O bond [30,37,39,41] as well as phosphonate oxygen-metal bond. The presence of P-OH groups can contribute to cross-link stabilization of the SAM by allowing hydrogen bond interactions between adhesive groups.…”