Biomechanical characteristics of silver enriched diamond-like carbon coatings for medical applications

Silver enriched diamond-like carbon (Ag/DLC) coatings are gaining a reputation for medical applications as Ag doping improves the intrinsic biocompatibility and antimicrobial features of DLC, and higher Ag amounts improve its hemocompatibility and growth inhabitation of tumours etc. However, higher Ag amounts in DLC coatings can also lead to increased cytotoxic effects. This work presents the co-sputter deposition of Ag-enriched DLC coatings with 17, 40, and 65 at% Ag in a DLC matrix. The structural and mechanical properties of the coatings are studied with field emission scanning electron microscopy, electron dispersive X-ray, X-ray diffraction, contact surface profiler, and nanoindentation. The biocompatibility of 72 h and 168 h leached extracts of Ag/DLC coatings are assessed through Ag ion release rates in Dulbecco’s modified eagle medium using inductively coupled plasma optical emission spectroscopy and their corresponding biocompatibility profiles are mapped against the L929 mouse fibroblast cell line. EDX mapping shows a throughout distribution of Ag in DLC matrix instead of localization distributions and clustering. The XRD diffraction peaks reflect the amorphous-like behaviour of 17 at% Ag/DLC and prominent Ag crystallinity for 40 and 65 at% Ag/DLC coatings. The leached Ag ions concentration of 8 ppm demonstrated by the 65 at% Ag/DLC coating completely diminishes its biocompatibility. The results suggest that 17 at% Ag enriched DLC coatings are a safe candidate for biomedical application and retain biocompatibility when treated with extracts prepared over prolonged ion leaching periods of 168 h, when compared to 40 and 65 at% Ag/DLC coatings. Similarly, the 17 at% Ag/DLC coatings show less compromise on mechanical properties, which decline by over 50% for 40 and 65 at% Ag/DLC coatings. This work has extended the typical range of Ag for depositing safe and biocompatible DLC coatings for medical applications.