Effect of copper (Cu2+) inclusion on the bioactivity and antibacterial behavior of calcium silicate coatings on titanium metal

Abstract

The present study is an investigation of the effect of copper (Cu²⁺) inclusion on the bioactivity, antibacterial behavior, corrosion resistivity and leaching characteristics of calcium silicate coatings on titanium metal. The synthesis of stoichiometric CaSiO₃ and five different concentrations of Cu²⁺ substitutions in CaSiO₃ was carried out. The incorporation of Cu²⁺ in the crystal lattice of CaSiO₃ was investigated by means of the Rietveld refinement technique. The results from the structural investigation have shown that stoichiometric CaSiO₃ crystallizes in the monoclinic system (space group = P₁₂₁/a₁ and unit cell parameters a = 15.4241 (5) Å, b = 7.3276 (7) Å and c = 7.0620 (8) Å with α = 90°, β = 95.404° and γ = 90°) and are in good agreement with the literature data for crystalline CaSiO₃. The substitution limit of Cu²⁺ in the crystal lattice of CaSiO₃ was determined as 4.399 wt% of Cu²⁺ and the increased level of Cu²⁺ substitution resulted in the formation of an additional phase in the form of tenorite (CuO). The fabrication of stoichiometric CaSiO₃ and Cu²⁺ substitutions in CaSiO₃ coatings on Ti metal was achieved through an electrophoretic deposition technique and no change in the phase behavior of the coatings was noted until the heat treatment temperature reached 800 °C. Immersion tests of CaSiO₃ coatings in simulated body fluid solution resulted in the formation of an apatite layer within 3 days of immersion. Antibacterial tests showed that pure CaSiO₃ powders did not exhibited any antibacterial activity whereas the presence of Cu²⁺ in CaSiO₃ resulted in good activity against E. coli and S. aureus. Potentiodynamic polarization tests performed on the Cu²⁺ doped CaSiO₃ coatings resulted in its better corrosion resistivity when compared to the pure metal and dissolution tests performed on coatings resulted in the leaching of Cu²⁺ at low levels.