ICMCTF 2025 Session MD1-2-MoA: Development and Characterization of Bioactive Surfaces/Coatings II

Magnesium (Mg) possesses unique properties that make it a promising candidate for various biomedical applications. That includes biodegradability and an elastic modulus that is closer to that of the human bone compared to titanium and stainless-steel implants, significantly reducing the risk of stress shielding. However, the use of magnesium in biomedical implants has been limited by its high chemical reactivity and limited strength. Therefore, a significant amount of research has been focused on enhancing the strength and corrosion characteristics of Mg-based biomedical implants by developing nanocomposites through novel fabrication methods. This study focuses on investigating the surface properties of novel Mg-based nanocomposites containing boron nitride and silicon carbide nanoparticles. The examination includes testing the morphology, corrosion characteristics, microhardness, wettability, and in-vitro cytotoxicity of the prepared surfaces. In this work, a novel acoustic powder mixing technique, combined with powder metallurgy, is utilized to prepare the Mg-based nanocomposite samples. The findings of this work provide a good understanding of the effect of the process parameters on the corrosion characteristics of these novel materials, which could pave the way for the manufacturing of Mg-based implants with superior properties, contributing to advanced applications in the biomedical field.

Carbide Derived Carbon (CDC) is a unique structure of carbon that is produced by extraction of the metal component from a ceramic carbide. When the conversion is carried out at a temperature below 1200 degrees Celsius, the result is a disordered graphitic structure with largely sp2 bonding. This is because there is not sufficient thermal energy under these conditions for the carbon to relax fully from the ceramic structure to the equilibrium graphitic state.

Carbide Derived Carbon (CDC) has a slick, hydrophobic surface and a low coefficient of friction when paired with most other materials. Because it is grown into a ceramic surface, rather than deposited onto the surface by a CVD or PVD process, CDC coatings can be applied with minimal dimensional changes and are resistant to spallation in comparison to other tribological coatings. CDC coatings have been applied to SiC and WC ceramics by exposure to chlorine gas at temperatures in the range of 800 to 1000 degrees Celsius. In this temperature range, the metal species form volatile chlorides, while the carbon is left behind as a solid.

Tribocorrosion, in which synergistic degradation by corrosion and wear is a particular concern for orthopedic implants such as artificial joints. The Ti-6Al-4V alloy is popular for this application, and carbide ceramics are not favored for this application because of their inherent brittleness. Titanium is a strong carbide former, so titanium carbide surface layers can be formed on titanium alloys by a carburization treatment in a packed bed of carbon. Subsequently, a layer of carbide derived carbon (CDC) can be formed on the surface of the titanium carbide layer by chlorination or by an anodic electrolysis treatment in molten chloride salt. The formation of CDC can be verified by Raman spectroscopy and the improvement of tribocorrosion resistance can be verified by tribocorrosion testing at the free corrosion potential. The results demonstrate a dramatic decrease in corrosion when a CDC layer is present during mechanical sliding.

The global pandemic caused by the SARS-CoV-2 virus has prompted a re-evaluation of surface hygiene practices, leading to an increased focus on the use of antimicrobial coatings.Sol-gel methodologies, known for their durability and cost-effectiveness, have emerged as a leading technology. MIRIA European project aims to advance sol-gel technologies, utilising nanoparticles such as silver or copper to enhance safety in a variety of public environments (e.g. hospitals, public transportation) and contribute to infectious disease management strategies.

In this work, antimicrobial thin films were deposited via dip coating on glass substrates starting from silicon-based hybrid organic-inorganic sol-gel formulations.The formulations differed in terms of the organosilicon additives and the presence of nanoparticles.A nanomechanical integrated protocol was applied to assess mechanical proprieties, adhesion and wear durability, by using three primary testing methodologies: nanoindentation, scratch, and wear testing. Nanoindentation was conducted using a KLA G200 Nanoindenter in CSM mode to extract the elastic modulus and hardness of the films, with appropriate models employed to correct for substrate influences. Subsequently, abrasive wear tests were conducted in accordance with the UNI-EN1071-6 standard, while scratch resistance was evaluated using the same nanoindenter, configured for nano-scratch testing with a rounded cone tip and lateral force measurement. Moreover, the antibacterial efficacy against Staphylococcus aureus and the antiviral efficacy against the MOI0.5 virus were evaluated.

Two data-based interpretation models were employed to extract intrinsic hardness and modulus of the films from nanoindentation data. An increase in stiffness was observed in the nanoparticle-filled formulations. This is associated with improved adhesion (scratch critical loads), as an increase in modulus results in the maximum contact shear stress occurring at higher depths, thereby causing later chipping during scratch. The wear performance of the coatings was evaluated through abrasive wear tests, which demonstrated that all coatings enhanced wear resistance compared to the uncoated glass substrate. The coatings containing copper oxide nanoparticles demonstrated the highest resistance and were the most effective in terms of antimicrobial performance, achieving a 3log (99.9%) reduction in microbial count after a 24-hour contact period.

Finally, a critical evaluation on the potential industrial scale-up of the proposed coating solutions is presented.