CaP-Bioglass composite coating by galvanic deposition

Orthopedic devices are increasingly used in our life to improve the health of patients after bone fractures due to accidents, aging, or sports injuries. Metallic materials (i.e. stainless steel, titanium alloys chromium alloys) are widely employed to fabricate prostheses, screws, and osteosynthesis plates. Although metals could be good mechanical properties like human bone, corrosion phenomena could occur, causing in the worst cases the failure of orthopedic implants. In addition, metal ions released around periprosthetic tissues could arise allergenic and cancerogenic effects. Nowadays, the research was focused on coating science to deal with these issues. In particular, the development of composite coatings could be a viable way to provide not only corrosion resistance but also great biocompatibility with bone tissues. Calcium Phosphate-based biomaterials such as hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 ) are widely used in orthopedics since their chemical composition is close to the mineralized fraction of bones. There are characterized by low mechanical stability and brittleness. However, it can be applied to coating [1], thanks to its biocompatibility and osteoconductivity. Bioglass is a family of bioactive glasses composed of silicon dioxide, sodium oxide, calcium oxide, and phosphorous pentoxide. This biomaterial has aroused great technological interest as a coating material [2] and it exhibits different degrees of bioactivity, which strongly depends on its composition [3]. Calcium Phosphate-Bioglass composite coating on AISI 316L was investigated in this study. These coatings were realized by an alternative method of deposition compared to traditional ones based on galvanic coupling. This process doesn’t demand any external power supply and it is very easy to carry out. The key role of the entire process consists in the difference of the electrochemical redox potential between the substrate (cathode) and a sacrificial anode [4-6]. The ratio between cathodic and anodic exposed areas drives the rate of the process. Briefly, electrons generated by dissolution of anode flow towards to more noble metal thanks to an external short-circuit. As soon as electrons arrive at the cathode, the base electrogeneration reactions of nitrate ions and water molecules occur. The effect of these reactions is the increase of pH at the interface between substrate and solution that generate calcium phosphate. Suspended bioglass particles in solution by stirring were entrapped between calcium phosphate crystals during galvanic deposition. Physical-chemical characterizations of the coatings were carried out in order to investigate the morphology and chemical composition. In addition, corrosion tests (potentiodynamic polarization and electrochemical impedance spectroscopy) were executed in Simulated Body Fluid (SBF) to scrutinize the corrosion resistance. Furthermore, cytotoxicity was been investigated through cell viability assays with MC3T3-E1 osteoblastic cells.