Surface modification to develop hierarchical micro/nano topography on titanium based medical implants

Abstract

Self-organized nanostructured TiO2 layers were developed on micro rough planar, cylindrical, and threaded surfaces of Ti6Al4V alloy by electrochemical anodization (EA) performed in phosphate-fluoride solution (1M H3PO4 with different HF additions) by using different process parameters (electrolyte concentration, anodization potential U, potential ramp Ur, and sample rotational speed n). Optical microscopy and scanning electron microscopy (SEM) was used to evaluate the morphology of the oxide layers. Nanostructured oxide layers with nanotubes/nanopores internal diameter in 25-110 nm range were developed on surfaces with an initial micro rough topography (Ra = 0.5-2 µm, resulting by CNC turning or by sand blasting and acid etching - SLA). On planar surfaces, the optimal EA process parameters in our custom-built anodization cell are: 0.5 wt.% HF addition in electrolyte, U = 20 V, and Ur = 0.1 V/s - for turned surfaces, and 0.4 wt.% HF addition in electrolyte, U = 24 V, and Ur = 0.08 V/s - for SLA surfaces. For cylindrical surfaces the nanotubes were superimposed on micro rough surface by using 0.4 wt.% HF addition in electrolyte, U = 24 V, and Ur = 0.08 V/s. On threaded surfaces continuous nanoporous oxide layer covering all geometrical features-frontal apex, spiral channels, major diameter, minor diameter, thread flanks - was developed by using 0.4 wt.% HF addition in electrolyte, U = 24 V, Ur = 0.08 V/s, and n = 8 rev/min.