Electrospun Biodegradable Nanofibers Coated Homogenously by Cu Magnetron Sputtering Exhibit Fast Ion Release. Computational and Experimental Study

Copper-coated nanofibrous materials are desirable for catalysis, electrochemistry, sensing, and biomedical use. The preparation of copper or copper-coated nanofibers can be pretty challenging, requiring many chemical steps that we eliminated in our robust approach, where for the first time, Cu was deposited by magnetron sputtering onto temperature-sensitive polymer nanofibers. For the first time, the large-scale modeling of PCL films irradiation by molecular dynamics simulation was performed and allowed to predict the ions penetration depth and tune the deposition conditions. The Cu-coated polycaprolactone (PCL) nanofibers were thoroughly characterized and tested as antibacterial agents for various Gram-positive and Gram-negative bacteria. Fast release of Cu2+ ions (concentration up to 3.4 µg/mL) led to significant suppression of E. coli and S. aureus colonies but was insufficient against S. typhimurium and Ps. aeruginosa. The effect of Cu layer oxidation upon contact with liquid media was investigated by X-ray photoelectron spectroscopy revealing that, after two hours, 55% of Cu atoms are in form of CuO or Cu(OH)2. The Cu-coated nanofibers will be great candidates for wound dressings thanks to an interesting synergistic effect: on the one hand, the rapid release of copper ions kills bacteria, while on the other hand, it stimulates the regeneration with the activation of immune cells. Indeed, copper ions are necessary for the bacteriostatic action of cells of the immune system. The reactive CO2/C2H4 plasma polymers deposited onto PCL-Cu nanofibers can be applied to grafting of viable proteins, peptides, or drugs, and it further explores the versatility of developed nanofibers for biomedical applications use.

Mechanical properties of plasma polymer films: a review

Plasma polymers are micro-, or more commonly, nano-sized coatings that can be deposited on a variety of substrates through different approaches. The versatility of these polymers is incremented by the possibility to use other precursors than conventional polymerization reactions and by potential changes in the polymerization mechanisms according to the intrinsic physical and chemical properties of the plasma. That flexibility offers a fruitful ground to a great range of scientific and engineering fields, but it also brings many challenges for universalization of empirical observations. In this review, the use of different precursors, substrates and changes in plasma external parameters were evaluated as common, but not necessarily ideal nor exhaustive, variables for the analysis of mechanical properties of plasma polymer films. The commonly reported trends are complemented with the exceptions, and a variety of hypothesis drawn by the empirical observations are shown. The techniques and methods used for determining the mechanical properties of plasma polymers, the effect of post-treatments on them and some applications are evaluated. Finally, a general conclusion highlighting the challenges of the field is provided. Article highlights The mechanical properties of plasma polymers are evaluated as a function of selected parameters. The techniques of characterization of mechanical properties of plasma polymers are summarized. A discussion of future and current demands for the analysis of mechanical properties of plasma polymers is done.

Effect of Sulfur on Nitrogen-Containing Plasma Polymers in Promoting Osteogenic Differentiation of Wharton’s Jelly Mesenchymal Stem Cells

The role of sulfur and its synergistic effects with nitrogen moieties in mediating stem cell proliferation and differentiation has become of interest to the tissue engineering community due to chemical similarities with the glycosaminoglycans found in human tissues and cells. Glycosaminoglycans are biomolecules known to influence stem cell differentiation, but the roles of sulfur with different oxidation states on nitrogen-containing polymers have not been fully understood nor investigated. In this study, we used the plasma polymerization of 1,7-octadiene (ppOD), n-heptylamine (ppHA), ppHA grafted with vinyl-sulfonate via Michael-type addition (ppHA-SO3), thiophene (ppT), and ppT with air plasma treatment (ppT-air) to produce controlled amounts of nitrogen and sulfur moieties having different oxidation states, as confirmed by x-ray photoelectron spectroscopy. Assays of the proliferation and osteogenic activities of Wharton’s jelly mesenchymal stem cells (WJ-MSCs) showed the highest activities for ppHA, followed by ppHA-SO3, due to high percentages of amines/amides and the absence of SO3 moieties in ppHA. Other plasma polymers showed less proliferation and osteogenic differentiation than the positive control (glass substrate); however, WJ-MSCs grown on ppT-air with its high percentages of SO4 displayed cytoskeletons intensified with actin stress fiber, unlike the thiol-dominated ppT. Finally, the presence of methyl groups in ppOD severely limited WJ-MSCs proliferation and differentiation. Overall, these results confirm the beneficial effects of amine/amide groups on WJ-MSCs proliferation and osteogenic differentiation, but the combination of these groups with sulfur of various oxidation states failed to further enhance such cellular activities.