Nanopatterned silk-coated AZ31 magnesium alloy with enhanced antibacterial and corrosion properties.

Because of unique properties such as the lightweight, natural biodegradability, and biocompatibility, magnesium alloys are promising in biomedical implants. However, inadequate corrosion resistance in the physiological environment remains a technical hurdle and application of coatings is a viable means to overcome the deficiency. Also, the antibacterial properties are very important in order to mitigate post-implantation complications arising from bacterial infection. In this study, a biocompatible silk film is deposited on AZ31 Mg alloy to enhance the corrosion resistance and by means of oxygen plasma etching, nature-inspired nanopatterns are fabricated on the surface of the silk film to improve the inherent antibacterial properties. The biocompatibility and antibacterial properties are determined with MC3T3-E1 osteoblast cells and E. coli and S. aureus, respectively. The antimicrobial properties of the silk coated AZ31 are better than those of the bare alloy probably due to the combined effects of the nanopatterns and alkalinity associated with leaching of Mg ions. The ß-sheets formed on the silk film is found to result in 104 times reduction in the corrosion current density and 50% reduction in Mg leaching after 1 day. Although degradation of the ß-sheets is observed to begin after 1 day, the amount of Mg ions leached to the medium from silk-coated AZ31 is still 17% lower than that from the bare one. The biomimicking nanopatterns on the natural silk film improve the corrosion resistance, biocompatibility, and antibacterial properties simultaneously and have large clinical potential.

Antibacterial and Cytocompatible Nanoengineered Silk-Based Materials for Orthopedic Implants and Tissue Engineering.

Many postsurgical complications stem from bacteria colony formation on the surface of implants, but the usage of antibiotic agents may cause antimicrobial resistance. Therefore, there is a strong demand for biocompatible materials with an intrinsic antibacterial resistance not requiring extraneous chemical agents. In this study, homogeneous nanocones were fabricated by oxygen plasma etching on the surface of natural, biocompatible Bombyx mori silk films. The new hydroxyl bonds formed on the surface of the nanopatterned film by plasma etching increased the surface energy by around 176%. This hydrophilic nanostructure reduced the bacterial attachment by more than 90% for both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria and at the same time improved the proliferation of osteoblast cells by 30%. The nanoengineered substrate and pristine silk were cultured for 6 h with three different bacteria concentrations of 107, 105, and 103 CFU mL-1 and the cell proliferation on the nanopatterned samples was significantly higher due to limited bacteria attachment and prevention of biofilm formation. The concept and materials described here reveal a promising alternative to produce biomaterials with an inherent biocompatibility and bacterial resistance simultaneously to mitigate postsurgical infections and minimize the use of antibiotics.

Antibacterial effects of titanium embedded with silver nanoparticles based on electron-transfer-induced reactive oxygen species.

Although titanium embedded with silver nanoparticles (Ag-NPs@Ti) are suitable for biomedical implants because of the good cytocompatibility and antibacterial characteristics, the exact antibacterial mechanism is not well understood. In the present work, the antibacterial mechanisms of Ag-NPs@Ti prepared by plasma immersion ion implantation (PIII) are explored in details. The antibacterial effects of the Ag-NPs depend on the conductivity of the substrate revealing the importance of electron transfer in the antibacterial process. In addition, electron transfer between the Ag-NPs and titanium substrate produces bursts of reactive oxygen species (ROS) in both the bacteria cells and culture medium. ROS leads to bacteria death by inducing intracellular oxidation, membrane potential variation, and cellular contents release and the antibacterial ability of Ag-NPs@Ti is inhibited appreciably after adding ROS scavengers. Even though ROS signals are detected from osteoblasts cultured on Ag-NPs@Ti, the cell compatibility is not impaired. This electron-transfer-based antibacterial process which produces ROS provides insights into the design of biomaterials with both antibacterial properties and cytocompatibility.