Sputtered polymeric hydrogenated amorphous carbon thin films for temporary medical implants

Presently, temporary metallic implants, like bone nails, based on stainless steel and titanium are widely employed. Since, these implants have to be removed after fracture healing, there are reflections about bio-degradable implants based on magnesium. To ensure that the magnesium based implant is stable during the healing process, a biocompatible diffusion barrier to the surrounding tissue is required. For this task, hydrogenated amorphous diamond-like carbon (DLC) may be a potential candidate. Within this work, hydrogen containing DLC coatings were produced by reactive unbalanced magnetron sputtering in an argon/acetylene (Ar/C2H2) atmosphere with an increasing C2H2/Ar – flow ratio. These coatings were studied concerning their structure and mechanical properties. The following investigations were done: coating thickness measurements, Elastic Recoil Detection Analysis, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy for structure information as well as nanoindentation and residual stress measurements to determine mechanical properties. The coatings show an amorphous and dense structure with a smooth surface as well as a decreasing nanohardness (from ~25 to 8 GPa) and Young’s modulus (from ~187 to 55 GPa) with an increasing C2H2/Ar – flow ratio, which indicates an increasing graphitic film structure.