Effect of Cavity Cleanser With Long-Term Antibacterial and Anti-Proteolytic Activities on Resin–Dentin Bond Stability

ObjectiveSecondary caries caused by oral microbiome dysbiosis and hybrid layer degradation are two important contributors to the poor resin–dentin bond durability. Cavity cleansers with long-term antimicrobial and anti-proteolytic activities are in demand for eliminating bacteria-induced secondary caries and preventing hybrid layers from degradation. The objectives of the present study were to examine the long-term antimicrobial effect and anti-proteolytic potential of poly(amidoamine) dendrimers with amino terminal groups (PAMAM-NH2) cavity cleanser.MethodsAdsorption tests by attenuated total reflectance–infrared (ATR-IR) spectroscopy and confocal laser scanning microscopy (CLSM) were first performed to evaluate whether the PAMAM-NH2 cavity cleanser had binding capacity to dentin surface to fulfill its relatively long-term antimicrobial and anti-proteolytic effects. For antibacterial testing, Streptococcus mutans, Actinomyces naeslundii, and Enterococcus faecalis were grown on dentin surfaces, prior to the application of cavity cleanser. Colony-forming unit (CFU) counts and live/dead bacterial staining were performed to assess antibacterial effects. Gelatinolytic activity within the hybrid layers was directly detected by in situ zymography. Adhesive permeability of bonded interface and microtensile bond strength were employed to assess whether the PAMAM-NH2 cavity cleanser adversely affected resin–dentin bonding. Finally, the cytotoxicity of PAMAM-NH2 was evaluated by the Cell Counting Kit-8 (CCK-8) assay.ResultsAdsorption tests demonstrated that the binding capacity of PAMAM-NH2 on dentin surface was much stronger than that of 2% chlorhexidine (CHX) because its binding was strong enough to resist phosphate-buffered saline (PBS) washing. Antibacterial testing indicated that PAMAM-NH2 significantly inhibited bacteria grown on the dentin discs as compared with the control group (p < 0.05), which was comparable with the antibacterial activity of 2% CHX (p > 0.05). Hybrid layers conditioned with PAMAM-NH2 showed significant decrease in gelatin activity as compared with the control group. Furthermore, PAMAM-NH2 pretreatment did not adversely affect resin–dentin bonding because it did not decrease adhesive permeability and microtensile strength. CCK-8 assay showed that PAMAM-NH2 had low cytotoxicity on human dental pulp cells (HDPCs) and L929.ConclusionsPAMAM-NH2 cavity cleanser developed in this study could provide simultaneous long-term antimicrobial and anti-proteolytic activities for eliminating secondary caries that result from a dysbiosis in the oral microbiome and for preventing hybrid layers from degradation due to its good binding capacity to dentin collagen matrix, which are crucial for the maintenance of resin–dentin bond durability.

Breathability performance of antiviral cloth masks treated with silver nanoparticles for protection against COVID-19

The global widespread of coronavirus disease 2019 (COVID-19) has caused shortage of medical face masks and led to developing of various types of cloth masks with different levels of protection and comfort to meet the market demands. Breathing comfort is a significant aspect that should be considered during the design of cloth masks along with the filtration efficiency; otherwise, the wearer will feel suffocated. In this work, different types of cotton and polyester knitted fabrics blended with spandex yarns were produced and treated with silver nanoparticles to be used as antiviral cloth masks. Scanning electron microscope, transmission electron microscope, and EDX were used to characterize the silver nanoparticles (AgNPs). Antiviral activity was assessed against SARS-CoV-2 coronavirus as well. The influence of using different fabric materials, number of layers, and hybrid layers on their air permeability and breathability were investigated to evaluate the comfortability of the cloth masks. Physiological impacts of wearing the cloth masks were evaluated by measuring oxygen saturation of hemoglobin and heart rate of the wearers while doing various activities. The results indicated that AgNPs have low cytotoxicity and considerable efficiency in inhibition of SARS-CoV-2. Adding spandex yarns with different count and ratios reduced the porosity and air permeability of the fabrics. Moreover, the combination of three hybrid layers’ mask made of polyester fabric in the outer layer with 100% cotton fabric in the inner layer showed high comfortability associated with high air permeability and breathability. Also, wearing these masks while doing activities showed no significant effect on blood oxygen saturation and heart rate of the wearers.

War and peace in a hybrid dimension

The monograph is devoted to the analysis of the current topic of hybrid war, in which the thin red lines separating it from peaceful life can both turn into an impenetrable iron curtain, and become a bright and attractive advertisement for another country and culture, forcing you to immerse yourself in another world, and not perceive it as a rival. Neither international law, nor the tools for identifying all the figures of international relations involved in resolving issues of war and peace, nor culture can correct the mutual distortions of hybrid war and hybrid peace. And yet, it is possible to find such facts that help to remove hybrid layers and reach the true interests, goals and means of those geopolitical actors who benefit from such a complex hybrid game of war and peace. It is intended for specialists in the field of international relations, history, culture. It will also arouse the interest of a wide range of readers.

Comparison of the Dielectric Properties of Ecoflex® with L,D-Poly(Lactic Acid) or Polycaprolactone in the Presence of SWCN or 5CB

The main goal of this paper was to study the dielectric properties of hybrid binary and ternary composites based on biodegradable polymer Ecoflex®, single walled carbon nanotubes (SWCN), and liquid crystalline 4′-pentyl-4-biphenylcarbonitrile (5CB) compound. The obtained results were compared with other created analogically to Ecoflex®, hybrid layers based on biodegradable polymers such as L,D-polylactide (L,D-PLA) and polycaprolactone (PCL). Frequency domain dielectric spectroscopy (FDDS) results were analyzed taking into consideration the amount of SWCN, frequency, and temperature. For pure Ecoflex®, two relaxation processes (α and β) were identified. It was shown that the SWCN admixture (in the weight ratio 10:0.01) did not change the properties of the Ecoflex® layer, while in the case of PCL and L,D-PLA, the layers became conductive. The dielectric constant increased with an increase in the content of SWCN in the Ecoflex® matrix and the conductive behavior was not visible, even for the greatest concentration (10:0.06 weight ratio). In the case of the Ecoflex® polymer matrix, the conduction relaxation process at a frequency ca. several kilohertz appeared and became stronger with an increase in the SWCN admixture in the matrix. Addition of oleic acid to the polymer matrix had a smaller effect on the increase in the dielectric response than the addition of liquid crystal 5CB. Fourier transform infrared (FTIR) results revealed that the molecular structure and chemical character of the Ecoflex® and PCL matrixes remained unchanged upon the addition of SWCN or 5CB in a weight ratio of 10:0.01 and 10:1, respectively, while molecular interactions appeared between L,D-PLA and 5CB. Moreover, adding oleic acid to pure Ecoflex® as well as the binary and ternary hybrid layers with SWCN and/or 5CB in a weight ratio of Ecoflex®:oleic acid equal to 10:0.3 did not have an influence on the chemical bonding of these materials.

Mechanical Properties of Nitrided Layer after Laser Modification

The aim of this work was to study the microstructure and friction coefficient of hybrid surface layers, produced by a controlled gas nitriding and laser modification. Nitriding is well-known technique of thermo-chemical treatment, applied in order to produce the surface layers of improved hardness and wear resistance. The phase composition and growth kinetics of the diffusion layer can be controlled using a gas nitriding with changeable nitriding potential. 42CrMo4 steel was treated by composite technology of gas nitriding and laser hardening. The nitriding processes were carried out at temperature of 580 °C for 8h. Next, the nitrided layer was laser-modified using laser TRUMPF TruDiode 3006 with maximal power of 3 kW using the two laser beam powers (P): 0.53 kW and 0.62 kW. Then, the microstructure and properties of the laser-modified nitrided layers were investigated using optical microscopy, Vickers hardness tester and friction wear testing machine. The nitrided layers were subjected to wear tests using a ball-on-disc method at room temperature. The results showed that the microstructure of the produced hybrid layers consisted of the re-melted and heat-affected zones in which martensite mainly occurred. Additional laser treatment effectively increased the hardness, especially in heat-affected zone, as well as the depth of the hardened layer. The layer after modification laser hest tretment were good friction coefficien. The curve of the friction coefficient after the nitrided layer was characterized by large fluctuations. Compared with nitriding technology , the hybrid treatment technology can effectively increase the hardness and wear resistance of the 42CrMo4 steel surface. The effect of LHT on the tribological properties was ambiguous. Although the relatively low value of the average friction coefficient (0.46) was calculated for nitrided layer, the course of friction coefficient was characterized by large fluctuations and the extended grinding-in time. Simultaneously, the course of friction coefficient was very smooth after nitriding and LHT. However, the average friction coefficient were higher, obtaining 0.60 and 0.57 for the hybrid layers, produced using P=530 W and P=620 W, respectively. Keywords: Nitriding; Laser Heat Treatment; Microstructure; Wear Resistance; Microhardness

Hard Protective Layers on Forging Dies—Development and Applications

The article presents a summary of many years of activities in the area of increasing the durability of forging dies. The results of comprehensive research work on the analysis of the destructive mechanisms of forging dies and the possibility of increasing their durability with the use of modern surface engineering methods are presented. Great possibilities in terms of shaping operational properties of forging dies by producing hybrid layers of the “Nitrided Layer + PVD Coating” (NL + PVD coating) type were confirmed. An analysis of changes in forging dies durability under various operating conditions was performed, i.e., forging—die—forging press—pressures. It has been shown that the variety of parameters of the forging process, including forgings’ geometry and weight, materials, precision, pressures applied, and, what is very important, quality of machines, makes it very difficult to compare the effectiveness of various PVD coating solutions in the process of increasing the durability of forging dies. Hybrid layers of the “NL + PVD coating” type create great possibilities in shaping the operational properties of tools and machine elements. However, in each application a precise diagnosis of the wear mechanism and the design of an individual PVD coating material solution is required.

Study on Porosity in Zinc Oxide Ultrathin Films from Three-Step MLD Zn-Hybrid Polymers

Deriving mesoporous ZnO from calcinated, molecular layer deposited (MLD) metal-organic hybrid thin films offers various advantages, e.g., tunable crystallinity and porosity, as well as great film conformality and thickness control. However, such methods have barely been investigated. In this contribution, zinc-organic hybrid layers were for the first time formed via a three-step MLD sequence, using diethylzinc, ethanolamine, and maleic anhydride. These zinc-organic hybrid films were then calcinated with the aim of enhancing the porosity of the obtained ZnO films. The saturation curves for the three-step MLD process were measured, showing a growth rate of 4.4 ± 0.2 Å/cycle. After initial degradation, the zinc-organic layers were found to be stable in ambient air. The transformation behavior of the zinc-organic layers, i.e., the evolution of the film thickness and refractive index as well as the pore formation upon heating to 400, 500, and 600 °C were investigated with the help of spectroscopic ellipsometry and ellipsometric porosimetry. The calculated pore size distribution showed open porosity values of 25%, for the sample calcinated at 400 °C. The corresponding expectation value for the pore radius obtained from this distribution was 2.8 nm.