Low-Energy Electron Beam Modification of Metallic Biomaterial Surfaces: Oxygen and Silicon-Rich Amorphous Carbon as a Wear-Resistant Coating

Abstract

Metallic biomaterials, such as cobalt chrome molybdenum (CoCrMo), Ti-6Al-4V, and 316L stainless steel are commonly used in orthopedic implant devices. Damage modes such as corrosion and wear are associated with the use of these alloys. One solution to limit wear and corrosion damage is to apply a surface coating to the medical device. In this study, using the low-energy electron beam (LEEB) of scanning electron microscopy (SEM), we induced a highly scratch-resistant oxygen and silicon-rich amorphous carbon film to grow on each of the above metallic biomaterials. LEEB interaction with adventitious surface carbon, silicone, and oxygen deposited on the above three alloys resulted in the layered-deposition formation (LEEB-LD) of a surface coating. Coating chemistry, morphology, and nano-scratch wear properties on each of the three alloys were characterized using atomic force microscopy (AFM) scratch testing and SEM/Energy dispersive spectroscopy (EDS) analysis. We hypothesized that LEEB-LD coatings could be deposited on these three metallic biomaterials with improved tribological properties than the underlying metal substrate. First, we generated coatings on all three biomaterials and documented the coating morphology (thickness and heterogeneity) and chemistry as a function of alloy, exposure time, and scan rate with coating thicknesses generated between 5 and 50 nm after 60 min of treatment, with each factor affecting the thickness. EDS maps showed high amounts of carbon, oxygen, and silicon in the modified surface which depended on the alloy (e.g., CoCrMo and SS had similar compositions while Ti had higher oxygen in the coatings). Coated and uncoated surfaces were then subjected to diamond scratch testing in an AFM at increasing force until the coating delaminated from the surface. Scratch-depth versus load and nominal Hertzian stress were plotted for both the uncoated and coated surfaces. We found that scratch depths were 40%, 75%, and 38% smaller on CoCrMo, Ti, and SS coatings, respectively, at the peak contact stresses tested (⍺ < 0.05), indicating higher hardness and wear resistance for the coatings. These results support the hypothesis that controlled thickness LEEB-LD oxygen and silicon-rich amorphous carbon coatings can be systematically generated using low-power electron beams and that these coatings have increased tribological (scratch-resistance) properties compared to the substrate metal.