The behaviour of CoCrMo orthopaedic alloy has been studied in two simulated physiological solutions – NaCl and Hanks’ solutions – each containing the sodium salt of hyaluronic acid. Hyaluronic acid is a component of synovial joint fluid, so the behaviour of orthopaedic alloys in its presence needs to be assessed. Electrochemical methods, X-ray photoelectron spectroscopy and scanning electron microscopy have been used to analyse the composition, thickness and morphology of any layers formed on the alloy. The addition of hyaluronic acid shifts the corrosion potential and increases the value of polarization resistance. The presence of hyaluronic acid in simulated Hanks’ physiological solution stimulates the formation of a calcium phosphate layer, opening up the possibility for tailoring the surface properties of CoCrMo alloy. The viability of human osteoblast-like was determined using the Alamar Blue Assay, while the osteogenic activity was evaluated by alkaline phosphatase activity. The presence of hyaluronic acid affects the alkaline phosphatase activity.
Anodic oxidation in acetic acid was investigated as a means of improving the corrosion resistance, in simulated physiologic solution, of titanium and two titanium-based alloys, Ti-6Al-7Nb and Nitinol. The composition and thickness of the surface layers formed by anodization was analyzed by X-ray photoelectron spectroscopy. The electrochemical characteristics were investigated by linear polarization, cyclic polarization and electrochemical impedance spectroscopy at the open circuit potential. Anodization of all three metals resulted in the formation of TiO2 as the main oxide. These layers improved the corrosion behavior in simulated physiological solution, as evidenced by significant increase in polarization resistance and decrease in corrosion current density. Electrochemical impedance results were interpreted based on the two-layer structure of the passive film. Anodization has thus been shown to provide a simple and effective means of improving the corrosion behavior of titanium-based alloys in simulated physiological solution.
Metallic materials used for manufacture of dental implants have to exhibit high corrosion resistance in order to prevent metal release from a dental implant. Oral cavity is aggressive towards metals as it represents a multivariate environment with wide range of conditions including broad range of temperatures, pH, presence of bacteria and effect of abrasion. An increasing use of various Ti-based materials for dental implants and orthodontic brackets poses the question of their corrosion resistance in the presence of fluoride ions which are present in toothpaste and mouth rinse. Corrosion behaviour of Ti metal, Ti-6Al-7Nb and Ti-6Al-4V alloys and constituent metals investigated in artificial saliva is significantly affected by the presence of fluoride ions (added as NaF), as proven by electrochemical methods. Immersion test was performed for 32 days. During that time the metal dissolution was measured by inductively coupled plasma mass spectrometry. At the end of the test the composition, thickness and morphology of the surface layers formed were investigated by X-ray photoelectron spectroscopy and scanning electron microscopy.