Optimization of Cu and Zn co-doped PEO titania coatings produced in a novel borate-based electrolyte for biomedical applications

•A sodium borate electrolyte was used to increase Cu and Zn in PEO coatings.•Optimized PEO conditions of J = 50 mA/cm2, up to 300 V, 7 min were defined.•A tuned surface with 900 nm average pore size and 8% porosity was produced.•The coating shows an externally porous, internally compact bilayer structure.