Deformation in viscoelastic sandwich composites subject to moisture diffusion

This study analyzes the effect of moisture diffusion on the deformation of viscoelastic sandwich composites, which are composed of orthotropic fiber-reinforced laminated skins and viscoelastic polymeric foam core. It is assumed that the elastic and time-dependent (transient) moduli at any particular location in the foam core depend on the moisture concentration at that location. Sequentially coupled analyses of moisture diffusion and deformation are performed to predict overall performance of the studied viscoelastic sandwich systems. Time and moisture dependent constitutive model is used for the polymer foam core, while skins are assumed linear elastic. The overall time-dependent responses of the sandwich composites subject to moisture diffusion are analyzed using finite element (FE) method. Experimental data available in the literature and analytical solutions are used to support convergence studies in the FE analyses. Contributions of moisture dependent elastic and the time-dependent moduli to the overall stress, strain and displacement field are studied. FE analyses of the delamination between skins and core in sandwich composite under combined moisture diffusion and mechanical loading are also performed.     

Carrageenan-based superabsorbent biopolymers mitigate autogenous shrinkage in ordinary portland cement

We report the synthesis and characterization of biobased superabsorbent copolymers from κ-carrageenan and poly(acrylic acid) that mitigate autogenous shrinkage in ordinary portland cement paste. Synthesized via free radical graft polymerization, the biobased superabsorbent polymers (SAPs) were characterized with regard to their thermochemical properties and swelling behavior in both aqueous and ionic solutions. The biobased SAPs were incorporated into cement paste to investigate their ability to mitigate autogenous shrinkage cracking in high-performance concrete. Results demonstrate that the biobased SAPs absorb up to 438 and 94 [g/g] (by mass) in aqueous and ionic solutions, respectively, after 24 h. Furthermore, the biobased SAPs were successful in mitigating shrinkage in low water-to-cement ratio pastes. While the control paste exhibited negative strain and ultimate shrinkage cracking, the samples containing biobased SAP experienced net-positive expansion during cement hydration.     

A study on Dual-Scale data charts

We present the results of a user study that compares different ways of representing Dual-Scale data charts. Dual-Scale charts incorporate two different data resolutions into one chart in order to emphasize data in regions of interest or to enable the comparison of data from distant regions. While some design guidelines exist for these types of charts, there is currently little empirical evidence on which to base their design. We fill this gap by discussing the design space of Dual-Scale cartesian-coordinate charts and by experimentally comparing the performance of different chart types with respect to elementary graphical perception tasks such as comparing lengths and distances. Our study suggests that cut-out charts which include collocated full context and focus are the best alternative, and that superimposed charts in which focus and context overlap on top of each other should be avoided.     

The Functional Role of Loops and Flanking Sequences of G-Quadruplex Aptamer to the Hemagglutinin of Influenza a Virus

Nucleic acid aptamers are generally accepted as promising elements for the specific and high-affinity binding of various biomolecules. It has been shown for a number of aptamers that the complexes with several related proteins may possess a similar affinity. An outstanding example is the G-quadruplex DNA aptamer RHA0385, which binds to the hemagglutinins of various influenza A virus strains. These hemagglutinins have homologous tertiary structures but moderate-to-low amino acid sequence identities. Here, the experiment was inverted, targeting the same protein using a set of related, parallel G-quadruplexes. The 5′- and 3′-flanking sequences of RHA0385 were truncated to yield parallel G-quadruplex with three propeller loops that were 7, 1, and 1 nucleotides in length. Next, a set of minimal, parallel G-quadruplexes with three single-nucleotide loops was tested. These G-quadruplexes were characterized both structurally and functionally. All parallel G-quadruplexes had affinities for both recombinant hemagglutinin and influenza virions. In summary, the parallel G-quadruplex represents a minimal core structure with functional activity that binds influenza A hemagglutinin. The flanking sequences and loops represent additional features that can be used to modulate the affinity. Thus, the RHA0385–hemagglutinin complex serves as an excellent example of the hypothesis of a core structure that is decorated with additional recognizing elements capable of improving the binding properties of the aptamer.     

Silver Nanoparticles from Oregano Leaves’ Extracts as Antimicrobial Components for Non-Infected Hydrogel Contact Lenses

The oregano leaves’ extract (ORLE) was used for the formation of silver nanoparticles (AgNPs(ORLE)). ORLE and AgNPs(ORLE) (2 mg/mL) were dispersed in polymer hydrogels to give the pHEMA@ORLE_2 and pHEMA@AgNPs(ORLE)_2 using hydroxyethyl–methacrylate (HEMA). The materials were characterized by X-ray fluorescence (XRF) spectroscopy, X-ray powder diffraction analysis (XRPD), thermogravimetric differential thermal analysis (TG-DTA), derivative thermogravimetry/differential scanning calorimetry (DTG/DSC), ultraviolet (UV-Vis), and attenuated total reflection mode (ATR-FTIR) spectroscopies in solid state and UV–Vis in solution. The crystallite size value, analyzed with XRPD, was determined at 20 nm. The antimicrobial activity of the materials was investigated against Gram-negative bacterial strains Pseudomonas aeruginosa (P. aeruginosa) and Escherichia coli (E. coli). The Gram-positive ones of the genus of Staphylococcus epidermidis (S. epidermidis) and Staphylococcus aureus (S. aureus) are known to be involved in microbial keratitis by the means of inhibitory zone (IZ), minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC). The IZs, which developed upon incubation of P. aeruginosa, E. coli, S. epidermidis, and S. aureus with paper discs soaked in 2 mg/mL of AgNPs(ORLE), were 11.7 ± 0.7, 13.5 ± 1.9, 12.7 ± 1.7, and 14.3 ± 1.7 mm. When the same dose of ORLE was administrated, the IZs were 10.2 ± 0.7, 9.2 ± 0.5, 9.0 ± 0.0, and 9.0 ± 0.0 mm. The percent of bacterial viability when they were incubated over the polymeric hydrogel discs of pHEMA@AgNPs(ORLE)_2 was interestingly low (66.5, 88.3, 77.7, and 59.6%, respectively, against of P. aeruginosa, E. coli, S. epidermidis, and S. aureus) and those of pHEMA@ORLE_2 were 89.3, 88.1, 92.8, and 84.6%, respectively. Consequently, pHEMA@AgNPs(ORLE)_2 could be an efficient candidate toward the development of non-infectious contact lenses.     

ACE2 Is an Adjacent Element of Atherosclerosis and COVID-19 Pathogenesis

COVID-19 is a highly contagious new infection caused by the single-stranded RNA Sars-CoV-2 virus. For the first time, this infection was recorded in December 2019 in the Chinese province of Wuhan. The virus presumably crossed the interspecies barrier and passed to humans from a bat. Initially, the disease was considered exclusively in the context of damage to the respiratory system, but it quickly became clear that the disease also entails serious consequences from various systems, including the cardiovascular system. Among these consequences are myocarditis, myocardial damage, subsequent heart failure, myocardial infarction, and Takotsubo syndrome. On the other hand, clinical data indicate that the presence of chronic diseases in a patient aggravates the course and outcome of coronavirus infection. In this context, the relationship between COVID-19 and atherosclerosis, a condition preceding cardiovascular disease and other disorders of the heart and blood vessels, is particularly interesting. The renin-angiotensin system is essential for the pathogenesis of both coronavirus disease and atherosclerosis. In particular, it has been shown that ACE2, an angiotensin-converting enzyme 2, plays a key role in Sars-CoV-2 infection due to its receptor activity. It is noteworthy that this enzyme is important for the normal functioning of the cardiovascular system. Disruptions in its production and functioning can lead to various disorders, including atherosclerosis.     

Designing Red-Shifted Molecular Emitters Based on the Annulated Locked GFP Chromophore Derivatives

Bioimaging techniques require development of a wide variety of fluorescent probes that absorb and emit red light. One way to shift absorption and emission of a chromophore to longer wavelengths is to modify its chemical structure by adding polycyclic aromatic hydrocarbon (PAH) fragments, thus increasing the conjugation length of a molecule while maintaining its rigidity. Here, we consider four novel classes of conformationally locked Green Fluorescent Protein (GFP) chromophore derivatives obtained by extending their aromatic systems in different directions. Using high-level ab initio quantum chemistry calculations, we show that the alteration of their electronic structure upon annulation may unexpectedly result in a drastic change of their fluorescent properties. A flip of optically bright and dark electronic states is most prominent in the symmetric fluorene-based derivative. The presence of a completely dark lowest-lying excited state is supported by the experimentally measured extremely low fluorescence quantum yield of the newly synthesized compound. Importantly, one of the asymmetric modes of annulation provides a very promising strategy for developing red-shifted molecular emitters with an absorption wavelength of ∼600 nm, having no significant impact on the character of the bright S-S₁ transition.     

Engineering the Catalytic Properties of Two-Domain Laccase from Streptomyces griseoflavus Ac-993

Laccases catalyze the oxidation of substrates with the concomitant reduction of oxygen to water. Recently, we found that polar residues located in tunnels leading to Cu2 and Cu3 ions control oxygen entrance (His 165) and proton transport (Arg 240) of two-domain laccase (2D) from Streptomyces griseoflavus (SgfSL). In this work, we have focused on optimizing the substrate-binding pocket (SBP) of SgfSL while simultaneously adjusting the oxygen reduction process. SgfSL variants with three single (Met199Ala, Met199Gly, and Tyr230Ala) and three double amino acid residues substitutions (Met199Gly/His165Ala, His165Ala/Arg240His, Met199Gly/Arg240His) were constructed, purified, and investigated. Combination of substitutions in the SBP and in the tunnel leading to Cu2 ion (Met199Gly/Arg240His) increased SgfSL catalytic activity towards ABTS by 5-fold, and towards 2.6-DMP by 16-fold. The high activity of the Met199Gly/Arg240His variant can be explained by the combined effect of the SBP geometry optimization (Met199Gly) and increased proton flux via the tunnel leading to Cu2 ion (Arg240His). Moreover, the variant with Met199Gly and His165Ala mutations did not significantly increase SgfSL’s activity, but led to a drastic shift in the optimal pH of 2.6-DMP oxidation. These results indicate that His 165 not only regulates oxygen access, but it also participates in proton transport in 2D laccases.     

Determination of organic compounds in bottled waters

The presence of organic compounds in bottled waters available in the Greek market and their fate when the representative samples exposed at different conditions were the main purposes of this study. The determination of the organic compounds was performed by gas chromatography–mass spectrometry techniques. Disinfection by-products compounds, such as trihalomethanes (THMs) and haloacetic acids (HAAs), were detected at low concentrations in bottled waters. As far as it concerns other organic substances, Greek bottled drinking waters did not contain volatile organic compounds (VOCs), and carbonyl compounds as well as other carcinogen and hormone disrupter phthalates were not identified, except for the plasticiser phthalate, diethylhexyl phthalate (DEHP). Moreover, samples contained other organic chemicals, whose identity has not yet been confirmed. The behavior of organic compounds was influenced by parameters such as conditions of storage, type of water. Finally, a comparison has been performed between the analysis of bottled and local tap waters.     

Antiseptic Materials on the Base of Polymer Interpenetrating Networks Microgels and Benzalkonium Chloride

Polymer microgels, including those based on interpenetrating networks (IPNs), are currently vastly studied, and their practical applications are a matter of thriving research. In this work, we show the perspective for the use of polyelectrolyte IPN microgels either as scavengers or carriers of antiseptic substances. Here, we report that poly-N-isopropylacrylamide/polyacrylic acid IPN microgels can efficiently absorb the common bactericidal and virucidal compound benzalkonium chloride. The particles can form a stable aqueous colloidal suspension or be used as building blocks for soft free-standing films. Both materials showed antiseptic efficacy on the examples of Bacillus subtilis and S. aureus, which was approximately equal to the commercial antibiotic. Such polymer biocides can be used as liquid disinfectants, stable surface coatings, or parts of biomedical devices and can enhance the versatility of the possible practical applications of polymer microgels.