ABSTRACT
New ecological trends and changes in consumer behavior are known to favor biofilm formation in household appliances, increasing the need for new antimicrobial materials and surfaces. Their development requires laboratory-cultivated biofilms, or biofilm model systems (BMS), which allow for accelerated growth and offer better understanding of the underlying formation mechanisms. Here, we identified bacterial strains in wildtype biofilms from a variety of materials from domestic appliances using matrix-assisted laser desorption/ionization-time of flight mass spectroscopy (MALDI-TOF-MS). Staphylococci and pseudomonads were identified by MALDI-TOF-MS as the main genera in the habitats and were analyzed for biofilm formation using various in vitro methods. Standard quantitative biofilm assays were combined with scanning electron microscopy (SEM) to characterize biofilm formation. While Pseudomonas putida, a published lead germ, was not identified in any of the collected samples, Pseudomonas aeruginosa was found to be the most dominant biofilm producer. Water-born Pseudomonads were dominantly found in compartments with water contact only, such as in detergent compartment and detergent enemata. Furthermore, materials in contact with the washing load are predominantly colonized with bacteria from the human.
ABSTRACT
Polyurethane vacuum casting with silicone molds is a widely used industrial process for the production of prototypes and small batches. Since the silicone casting molds absorb the isocyanate component of the curing PUR casting resin at the cavity surface, the service life of the molds is typically restricted to very few casting cycles. The successive deterioration of the material properties results from the polymerization of the absorbed isocyanate with moisture to polyurea derivatives within the silicone matrix. In this study, we show for the first time the influence of isocyanate absorption on the mechanical properties of silicone elastomers as well as quantitative differences between commercial materials. The changes in mechanical properties were quantified in terms of Shore A hardness, Young's modulus, tensile strength, elongation at break, and complex shear modulus. It was found that the influence of the isocyanate type on the relative property changes of the silicone was significantly greater than that of the silicone used. The results show that, regardless of its hardness, the silicone absorbs considerably less methylene diphenyl diisocyanate (MDI) than hydrogenated MDI, although the latter causes less deterioration of the mechanical properties and achieves a longer mold service life.
ABSTRACT
Highly magnified micrographs are part of the majority of publications in materials science and related fields. They are often the basis for discussions and far-reaching conclusions on the nature of the specimen. In many cases, reviewers demand and researchers deliver only the bare minimum of micrographs to substantiate the research hypothesis at hand. In this work, we use heterogeneous poly(acrylonitrile) nanofiber nonwovens with embedded nanoparticles to demonstrate how an insufficient or biased micrograph selection may lead to erroneous conclusions. Different micrographs taken by transmission electron microscopy and helium ion microscopy with sometimes contradictory implications were analyzed and used as a basis for micromagnetic simulations. With this, we try to raise awareness for the possible consequences of cherry-picking for the reliability of scientific literature.
ABSTRACT
Thermally stabilized and subsequently carbonized nanofibers are a promising material for many technical applications in fields such as tissue engineering or energy storage. They can be obtained from a variety of different polymer precursors via electrospinning. While some methods have been tested for post-carbonization doping of nanofibers with the desired ingredients, very little is known about carbonization of blend nanofibers from two or more polymeric precursors. In this paper, we report on the preparation, thermal treatment and resulting properties of poly(acrylonitrile) (PAN)/poly(vinylidene fluoride) (PVDF) blend nanofibers produced by wire-based electrospinning of binary polymer solutions. Using a wide variety of spectroscopic, microscopic and thermal characterization methods, the chemical and morphological transition during oxidative stabilization (280 °C) and incipient carbonization (500 °C) was thoroughly investigated. Both PAN and PVDF precursor polymers were detected and analyzed qualitatively and quantitatively during all stages of thermal treatment. Compared to pure PAN nanofibers, the blend nanofibers showed increased fiber diameters, strong reduction of undesired morphological changes during oxidative stabilization and increased conductivity after carbonization.
ABSTRACT
Electrospinning is a new technology whose scope is gradually being developed. For this reason, the number of known polymerâ»solvent combinations for electrospinning is still very low despite the enormous variety of substances that are potentially available. In particular, electrospinning from low-toxic solvents, such as the use of dimethyl sulfoxide (DMSO) in medical technology, is rare in the relevant scientific literature. Therefore, we present in this work a series of new polymers that are applicable for electrospinning from DMSO. From a wide range of synthetic polymers tested, poly(vinyl alcohol) (PVOH), poly(2ethyl2oxazolene) (PEOZ), and poly(vinylpyrrolidone) (PVP) as water-soluble polymers and poly(styrene-co-acrylonitrile) (SAN), poly(vinyl alcohol-co-ethylene) (EVOH), and acrylonitrile butadiene styrene (ABS) as water-insoluble polymers were found to be suitable for the production of nanofibers. Furthermore, the influence of acetone as a volatile solvent additive in DMSO on the fiber morphology of these polymers was investigated. Analyses of the fiber morphology by helium ion microscopy (HIM) showed significantly different fiber diameters for different polymers and a reduction in beads and branches with increasing acetone content.
