Deposition and characterization of coatings of Hydroxyapatite, Chitosan, and Hydroxyapatite-Chitosan on 316L for biomedical devices

In the last decades, the scientific community has turned on great interest towards the development of increasingly performing biomedical systems. In the orthopedic field, biomedical devices are made up by metallic materials (mainly steel and titanium alloys), which have low/medium resistance to corrosion and a low osteointegration capacity when implanted inside the human body. This can lead to infection or inflammation that can damage the tissues surrounding the implant. The use of biocompatible coatings allows cancelling or mitigating these phenomena. The coating interposing between aggressive environment and biomedical device inhibits corrosion so limiting the metal ions release into the body. Furthermore, the coating must be bio-compatible in order to guarantee the osteointegration of the device. In this work, calcium hydroxylapatite (HA) and chitosan (CS) have been investigated as possible coatings of 316L stainless steel devices. HA has been selected owing to its osteoinductive and osteoconductive features having a composition similar to bones. CS is highly biocompatible and also widely used for controlled drug delivery. HA, CS, and HA/CS composite coatings were fabricated by an innovative method based on galvanic deposition. It is a spontaneous electrochemical-based process where material with different standard electrochemical potential are immersed in an electrolyte and short circuited. The driving force is the electromotive force, between the coupled materials, where the less noble material oxidizes and supplies electrons for the noblest process that leads to the deposition of the material of interest. The process therefore advances without external power supply, without use of specific equipment, and with deposition of both pure and composite coatings. The chemical-physics characterization of the coatings was conducted by SEM, EDS, XRD and RAMAN; the corrosion behaviour was investigated by TAFEL’s curves and impedance measurements; while the biological features were ascertained through in-vitro cytotoxicity assays.