Improvement of corrosion performance of 316L stainless steel via PVTMS/henna thin film

Metallic materials are the most used materials as orthopedic or dental implants due to their excellent mechanical properties. However they are not able to create a natural bonding with the mineralized bone and occasionally suffer localized corrosion. This work describes the electrochemical behavior of a hybrid sol–gel thin film with the addition of green inhibitor. These films enhance the ability of the implant to make a union with the existing bone and improve its resistance to aggressive environment. An ethanol solution of the polymerized vinyltrimethoxysilane (PVTMS) was mixed with an aqueous solution of henna extract (Lawsonia inermis) and refluxed to give homogeneous sols. Nanostructure hybrid PVTMS/henna thin films were deposited on the stainless steel 316L by spin-coating. The morphology, composition and adhesion of hybrid sol–gel coatings have been examined by SEM, EDX and pull-off test, respectively. Addition of high additive concentrations (0.1%) did not disorganize the sol–gel network. Direct pull-off test recorded a mean coating-substrate bonding strength larger than 20.6 MPa for the hybrid sol–gel coating. The effect of henna extract, with various added concentrations from 0.012% to 0.1%, on the anticorrosion properties of sol–gel films have been characterized by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests in simulated body fluid (SBF) solution and has been compared to the bare metal. Henna extract additions (0.05%) have significantly increased the corrosion protection of the sol–gel thin film to higher than 90%. The in vitro bioactivity of prepared films indicates that hydroxyapatite nuclei can form and grow on the surface of the doped sol–gel thin films. The present study shows that due to their excellent anticorrosion properties, bioactivity and bonding strength to substrate, doped sol–gel thin films are practical hybrid films in biomedical applications.