Bacterial adhesion reduction on a biocompatible Si+ ion implanted austenitic stainless steel

On the antimicrobial properties and endurance of eugenol and 2-phenylphenol functionalized sol-gel coatings

Preventing microbiological surface contamination in public spaces is nowadays of high priority. The proliferation of a microbial infection may arise through air, water, or direct contact with infected surfaces. Chemical sanitization is one of the most effective approaches to avoid the proliferation of microorganisms. However, extended contact with chemicals for cleaning purposes such as chlorine, hydrogen peroxide or ethanol may lead to long-term diseases as well as drowsiness or respiratory issues, not to mention environmental issues associated to their use. As a potentially safer alternative, in the present work, the efficacy and endurance of the antimicrobial activity of different sol-gel coatings were studied, where one or two biocides were added to the coating matrix resulting on active groups exposed on the surface. Specifically, the coating formulations were synthesized by the sol-gel method. Using the alkoxide route with acid catalysis a hybrid silica-titania-methacrylate matrix was obtained where aromatic liquid eugenol was added with a double function: as a complexing agent for the chelation of the reaction precursor titanium isopropoxide, and as a biocide. In addition, 2-Phenylphenol, ECHA approved biocide, has also been incorporated to the coating matrix. The antibacterial effect of these coatings was confirmed on Gram-positive (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli). Additionally, the coatings were non cyto-toxic and displayed virucidal activity. The coating chemical composition was characterized by 29Si NMR, and ATR-FTIR. Furthermore, the thickness and the mechanical properties were characterized by profilometry and nanoindentation, respectively. Finally, the durability of the coatings was studied with tribology tests. Overall, our data support the efficacy of the tested sol-gel coatings and suggest that added features may be required to improve endurance of the antimicrobial effects on operational conditions.

Kinetic of Adhesion of S. epidermidis with Different EPS Production on Ti6Al4V Surfaces

Controlling initial bacterial adhesion is essential to prevent biofilm formation and implant-related infection. The search for surface coatings that prevent initial adhesion is a powerful strategy to obtain implants that are more resistant to infection. Tracking the progression of adhesion on surfaces from the beginning of the interaction between bacteria and the surface provides a deeper understanding of the initial adhesion behavior. To this purpose, we have studied the progression over time of bacterial adhesion from a laminar flow of a bacterial suspension, using a modified Robbins device (MRD). Comparing with other laminar flow devices, such as the parallel plate flow chamber, MRD allows the use of diverse substrata under the same controlled flow conditions simultaneously. Two different surfaces of Ti6Al4V and two strains of Staphylococcus epidermidis with different exopolymer production were tested. In addition, the modified Robbins device was examined for its convenience and suitability for the purpose of this study. Results were analyzed according to a pseudofirst order kinetic. The values of the parameters obtained from this model make it possible to discriminate the adhesive behavior of surfaces and bacteria. One of the fitting parameters depends on the bacterial strain and the other only on the surface properties of the substrate.

A review on nickel-free nitrogen containing austenitic stainless steels for biomedical applications

The field of biomaterials has become a vital area, as these materials can enhance the quality and longevity of human life. Metallic materials are often used as biomaterials to replace structural components of the human body. Stainless steels, cobalt-chromium alloys, commercially pure titanium and its alloys are typical metallic biomaterials that are being used for implant devices. Stainless steels have been widely used as biomaterials because of their very low cost as compared to other metallic materials, good mechanical and corrosion resistant properties and adequate biocompatibility. However, the adverse effects of nickel ions being released into the human body have promoted the development of "nickel-free nitrogen containing austenitic stainless steels" for medical applications. Nitrogen not only replaces nickel for austenitic structure stability but also much improves steel properties. Here we review the harmful effects associated with nickel and emphatically the advantages of nitrogen in stainless steel, as well as the development of nickel-free nitrogen containing stainless steels for medical applications. By combining the benefits of stable austenitic structure, high strength, better corrosion and wear resistance and superior biocompatibility in comparison to the currently used austenitic stainless steel (e.g. 316L), the newly developed nickel-free high nitrogen austenitic stainless steel is a reliable substitute for the conventionally used medical stainless steels.

Mechanical forces regulate stem cell response to surface topography

The interactions between bone tissue and orthopedic implants are strongly affected by mechanical forces at the bone-implant interface, but the interplay between surface topographies, mechanical stimuli, and cell behavior is complex and not well understood yet. This study reports on the influence of mechanical stretch on human mesenchymal stem cells (hMSCs) attached to metallic substrates with different roughness. Controlled forces were applied to plasma membrane of hMSCs cultured on smooth and rough stainless steel surfaces using magnetic collagen-coated particles and an electromagnet system. Degree of phosphorylation of focal adhesion kinase (p-FAK) on the active form (Tyr-397), prostaglandin E2 (PGE2) and vascular endothelial growth factor (VEGF) levels increased on rough samples under static conditions. Cell viability and fibronectin production decreased on rough substrates, while hMSCs maturated to the osteoblastic lineage to a similar extent on both surfaces. PGE2 production and osteoprotegerin/receptor activator of nuclear factor kappa-B ligand ratio increased after force application on both surfaces, although to a greater extent on smooth substrates. p-FAK on Tyr-397 was induced fairly rapidly by mechanical stimulation on rough surfaces while cells cultured on smooth samples failed to activate this kinase in response to tensile forces. Mechanical forces enhanced VEGF secretion and reduced cell viability, fibronetin levels and osteoblastic maturation on smooth surfaces but not on rough samples. The magnetite beads model used in this study is well suited to characterize the response of hMSCs cultured on metallic surfaces to tensile forces and collected data suggest a mechanism whereby mechanotransduction driven by FAK is essential for stem cell growth and functioning on metallic substrates.