Agilent 5500 spm

The morphology and three-dimensional structure of specimen surface were inspected by atomic force microscopy (AFM, Agilent 5500 SPM; Agilent Technologies, Santa Clara, CA, USA). The qualitative analysis of GO loaded on Ti surface was recorded with Raman spectroscopy (HR800, HORIBA Ltd, Kyoto, Japan). Using X-ray photoelectron spectroscopy (XPS, AXIS ULTRA, Kratos Analytical Inc., Chestnut Ridge, NY, USA) the chemical composition and elemental distribution of Ti substrate modified with GO and Ag was analyzed. Nanoindentation (G200, Agilent Technologies) and nanoscratch (APEX, CETR, Campbell, Silicon Valley, CA, USA) were employed to test elastic modulus and friction of GO film coating respectively. The release of Ag ion coated on Ti-GO surface was monitored using inductively coupled plasma mass spectrometer (ICP-MS, X series II/SN 1007 C, MA, USA). Notably, specimens immersed in PBS must be incubated in the dark at 37°C. The PBS was replaced by fresh PBS and collected every 24 hours, which was stored in the dark at 4°C. In addition, before testing the samples, standard solutions of Ag ions have to be prepared and measured (0 ppb, 200 ppb, 400 ppb, 600 ppb, 800 ppb and 1,000 ppb). The aim was to calibrate the release of Ag ions in the study. Hydrophilic property of Ti-GO-Ag surface was characterized by contact angle tester (EasyDrop Standard, Krüss GmbH, Hamburg, Germany).