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Glycerol-Enhanced Gum Karaya Hydrogel Films with a Sandwich-like Structure Enriched with Octenidine for Antibacterial Action against Multidrug-Resistant Bacteria
(2025-07-02) Černá, Eva; Neděla, Vilém; Tihlaříková, Eva; Brtníková, Jana; Fohlerová, Zdenka; Lipový, Břetislav; Vacek, Lukáš; Růžička, Filip; Matulová, Jana; Vojtová, Lucy
This study explores the innovative approach in the development of freeze-dried hydrogel films, leveraging the unique properties of gum Karaya (GK), poly(vinyl alcohol) (PVA), poly(ethylene glycol) (PEG), and glycerol with a coating of octenidine dihydrochloride (OCT). These innovative hydrogel films exhibit at a certain glycerol concentration a sandwich-like structure, achieved through a tailored freeze-drying process, which enhances transparency and mechanical stability. OCT provides superior antibacterial performance, effectively combating multidrug-resistant bacteria with a controlled and gradual release mechanism, surpassing conventional OCT solutions that require frequent reapplication for infected wound treatment without the creation of bacterial resistance. Advanced environmental scanning electron microscopy (A-ESEM) reveals the complex microstructure of the hydrogel, highlighting the dense surface layer and interconnected porous bulk. Variations in glycerol concentrations proved to significantly impact hydrogels' properties. Increasing the glycerol concentration decreases the pore size (around 4.5 mu m) while enhancing the polymer network density and flexibility. However, low concentration increases the pore size (7.8-15.6 mu m), impacting enhanced swelling behavior and hydrolytic stability. OCT's rapid antibacterial action, releasing over 30% within the first hour and maintaining prolonged activity for up to 2 weeks, emphasizes the material's potential for diverse applications. Hydrogels' remarkable transparency, porosity, structural stability, and antibacterial efficacy against both Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli strains suggest promising uses as transparent dressings, biomedical devices, and infection-resistant surfaces.
Issues Concerning Manufacture and Recycling of Lead
(MDPI, 2023-06-01) Bača, Petr; Vanýsek, Petr
This article gives an overview of historical and present uses of lead against the backdrop of gradual realization that lead is an environmental hazard. In this paper the lead in the lead-acid batteries is investigated from the view of its present use. This use continues because there does not exist economical and practical alternative to lead for this purpose. In fact the use is still steadily increasing. This may not be a concern as it has been demonstrated that in countries with strong economies, recycling of lead from the batteries can near 100%. Here, we take a look at reality, by comparing select countries on both sides of the economic spectrum. In poorer countries, recycling suffers more on the safe and clean side of the process. Historical uses of lead are also reviewed, as well as a new approach of using lead compounds in soluble lead flow batteries.
Analysis of the Degradation of Pearlitic Steel Mechanical Properties Depending on the Stability of the Structural Phases
(MDPI, 2023-01-05) Smak, Radim; Votava, Jiří; Lozrt, Jaroslav; Kumbár, Vojtěch; Binar, Tomáš; Polcar, Adam
The paper is focused on analysing the pearlitic steel phase transformations and their influence on the mechanical properties. The intention is to perform a detailed analysis of the heat treatment process using the exact heating temperature and chemical composition to achieve the optimal mechanical properties of the tool. The key area is monitoring and regulating the heat treatment. This technology is constantly undergoing an optimisation process and is an effort to introduce new trends in monitoring phase transformations and processes. The use of non-destructive methods is an adequate tool. The principle is to determine the exact structural phase at a given moment, which can be very difficult when a complex shaped part is heat treated. Which precludes the use of some other methods of phase transformation analysis. Specifically, the determination of the exact moment of finish of the austenitisation process is eminent. The monitoring of these processes will be ensured by both a non-contact pyrometer and also by the AE method with an adequate sensor and waveguide. The resulting structural phases formed after the heat treatment will be evaluated by electron microscopy, followed by the analysis of the mechanical properties of selected steels.
Carrageenan as an Ecological Alternative of Polyvinylidene Difluoride Binder for Li-S Batteries
(MDPI, 2021-09-26) Kazda, Tomáš; Capková, Dominika; Jaššo, Kamil; Straková Fedorková, Andrea; Shambel, Elena; Markevich, Alex; Sedlaříková, Marie
Lithium-sulfur batteries are one of the most promising battery systems nowadays. However, this system is still not suitable for practical application because of the number of shortcomings that limit its cycle life. One of the main problems related to this system is the volumetric change during cycling. This deficiency can be compensated by using the appropriate binder. In this article, we present the influence of a water-soluble binder carrageenan on the electrochemical properties of the Li-S battery. The electrode with a carrageenan binder provides good stability during cycling and at high C-rates. Electrochemical testing was also carried out with a small prototype pouch cell with a capacity of 16 mAh. This prototype pouch cell with the water-based carrageenan binder showed lower self-discharge and low capacity drop. Capacity decreased by 7% after 70 cycles.
Application of Prandtl’s Theory in the Design of an Experimental Chamber for Static Pressure Measurements
(MDPI, 2021-09-02) Šabacká, Pavla; Neděla, Vilém; Maxa, Jiří; Bayer, Robert
Pumping in vacuum chambers is part of the field of environmental electron microscopy. These chambers are separated from each other by a small-diameter aperture that creates a critical flow in the supersonic flow regime. The distribution of pressure and shock waves in the path of the primary electron beam passing through the differentially pumped chamber has a large influence on the quality of the resulting microscope image. As part of this research, an experimental chamber was constructed to map supersonic flow at low pressures. The shape of this chamber was designed using mathematical–physical analyses, which served not only as a basis for the design of its geometry, but especially for the correct choice of absolute and differential pressure sensors with respect to the cryogenic temperature generated in the supersonic flow. The mathematical and physical analyses presented here map the nature of the supersonic flow with large gradients of state variables at low pressures at the continuum mechanics boundary near the region of free molecule motion in which the Environmental Electron Microscope and its differentially pumped chamber operate, which has a significant impact on the resulting sharpness of the final image obtained by the microscope. The results of this work map the flow in and behind the Laval nozzle in the experimental chamber and are the initial basis that enabled the optimization of the design of the chamber based on Prandtl’s theory for the possibility of fitting it with pressure probes in such a way that they can map the flow in and behind the Laval nozzle.

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