Volume 60, Issue 4

Abstract: This study focuses on the covalent functionalization of the carboxylated graphene oxide layers with human serum albumin for developing new nanoplatforms capable of efficient drug loading and release for antitumor therapy. Thus, new GO-HSA conjugates have been developed and their interactions with methotrexate (MTX) molecules were evidenced through FT-IR, UV-Vis and Raman spectroscopy. The cumulative in vitro release profiles of MTX drug from GO-HSA-MTX nanoplatforms were analyzed through UV-Vis spectroscopy showing a more controlled release behavior of MTX drug under acidic conditions that simulate the tumor microenvironment demonstrating the potential use of GO-HSA-MTX as antitumoral nanocarriers.

Abstract: The piezocomposites from poly-(vinylidene fluoride) (PVDF) with BaTiO3 (BT) are largely presented in literature, but the composites from polydimethylsiloxane (PDMS) with BT consist a very new scientific preoccupation. The novelty of the paper lies in a new simpler route of preparation of the two composites with PDMS and respectively PVDF matrix, with tailored deposition on specific substrates for microelectronic use (e.g. indium-tin-oxide ITO/glass, Si/Pt, polyethylene terephthalate PET), along with an extensive comparation of their dielectric features, a consistent comparison of the influence of polymer matrix upon the piezoelectric features, and a demonstration of direct use for microelectronic applications of the composites of BT with PDMS. An interesting effect is observed around 100 kHz domain, determined by the activity and architecture of BT particles mainly for the BT-PDMS composites, which induce an additional ionic-dipolar conjugated polarization, as a displacement due to the balance between the resonance and anti-resonance frequency. Such phenomena explain the potential use of such composites as resonators/filters, and BT-PDMS composites should be further investigated for tailored applications in radiofrequency electronic field. We can appreciate that superior piezoelectric features are offered by the composites of BT with PDMS, comparing to the composites with PVDF, which means that the composites of BT with PDMS were worth to study, leading to more versatile variants of electronic characteristics and with superior values.

Abstract: In the realm of petrochemical and other industries, metal materials face threats such as impact and high-temperature electrochemical corrosion. Consequently, there has been significant attention towards organic coatings that effectively attenuate impact forces while simultaneously providing a barrier against corrosive agents. The thermosetting phenolic resin 2130, known for the facile curing process, exceptional thermal stability, water resistance, corrosion resistance, and superior mechanical properties post-curing, finds extensive applications in the field of coatings. To address the challenge of depositing a complete and uniform resin coating on complex workpieces, coatings with varying thicknesses on the surface of 304 stainless steel were deposited via rotary evaporation combined with long-term low-temperature drying. The relationship between coating thickness and mechanical properties, as well as corrosion resistance, was investigated and analyzed through a comprehensive approach involving mechanical testing, electrochemical analysis, and long-term service weight loss assessment. The results demonstrated that the coatings deposited on the metal surface exhibited excellent integrity and compactness. Moreover, an increase in coating thickness led to a significant reduction in material corrosion rate. The coatings exhibited excellent substrate adhesion and flexibility, thereby providing effective protection against impact on the metal substrate. The relationship between the thickness of the coating and the surface roughness was evident, while the flexibility of the coating first increased and then decreased with the increase of coating thickness. When the coating thickness was 7 μm, the maximum surface roughness of the coating measured 0.44 μm. Under these conditions, the impact toughness of the coating reached the peak, exhibiting a ductile fracture mode and showcasing superior comprehensive mechanical properties. The findings of this study will offer theoretical support for the investigation and formulation of resin coatings in subsequent industrial production.

Abstract: Aromatic amines are the significant compounds used as intermediates in the organic synthesis, for obtaining such as azo dyes, antioxidants, fuel additives, corrosion inhibitors, pesticides, antiseptic agents, poultry medicine, and pharmaceutical synthesis. However, the presence of aromatic amines in water, even at very low concentrations, is extremely harmful to aquatic life and human health. Pollution of natural waters by aromatic amines is a serious environmental concern. The aim of this work was to obtain new adsorbents for use in the removal of aromatic amines from aqueous solutions. Styrene-15%divinylbenzene copolymers grafted with aminophosphonate groups (code: AP-S15%DVB) and amino acid-phosphonate groups (code: AM-S15%DVB) were used for the removal of pollutants such as: aniline, 2-methyl-aniline and 4-methyl-aniline. The adsorption capacity and the adsorption kinetic using the pseudo-first order and pseudo-second order equations were examined. From a kinetic point of view, it was established that the adsorption of the studied amino derivatives on the used adsorbents took place according to the pseudo-second order model. It was found that the adsorption rate constant increased with the increase of temperature, so the speed of the adsorption process increased. The obtained results confirm that the polymer adsorbents studied can be successfully used for the removal of aromatic amino derivatives from aqueous solutions for the purpose of wastewater treatment.

Abstract: This article presents a finite element study based on tests of characterizations to find the properties of the materials studied, the injection-blowing technique, chosen in this case, is characterized by the bi-axial of the material, and one benefits from the orientation of the macromolecules in the directions of use of the material. The objective of this work is to link all the mechanical and thermal parameters during the treatment of molten polymer materials subjected to high-stress rates that can lead to significant temperature increases due to viscous heating in the order of 200°C. Predicting the temperature range is essential for good temperature control and is a major factor in determining the quality of the final product. This forces us to choose an adequate law of behavior, capable of translating the mechanical evolution under the thermal effect while explaining the rheological response of the viscoelastic metal. So this process is usually accompanied by geometric defects resulting from the original residual stresses cooling speed and the process itself. In the packaging of food products, as in this case, the bottles require to have a stable filling and a certain storage capacity.

Abstract: Metal-composite joints, or hybrid joints are prevalent in aerospace structures due to their high strength and low weight. Such structures are usually found in areas where because of the load configuration, the use of composite materials is possible. Thereby, the analysis of such areas needs to consider both components, the metallic and the composite part. In this paper a hybrid joint is analyzed, consisting of a metallic stiffener, a multilayered honeycomb composite material, and joining fasteners, which constitute the joint between the isotropic and orthotropic materials. The present article has two main purposes: the first is to illustrate a pre-design procedure aimed to evaluate the load-carrying capability of a hybrid joint structure, thereby giving an estimate if the structure can withstand the given loading conditions; the second purpose is to present two types of finite element modeling techniques, one that captures the real geometric structure of the composite material and another which uses a simplified equivalent model, based on the desired level of evaluation of the composite material part. A comparison between the two models is made, highlighting the advantages and disadvantages of the two forms of evaluations. For the metallic parts – stiffener and fasteners, both static and fatigue analyses were performed, as fatigue failure represents the common service failure mode for this type of structural components.

Abstract: Combining polimers with polyphenols such as gallic acid opens up new directions in healthcare system. By encapsulating secondary metabollites within PLGA nanoparticles, we tried to enhance their stability, solubility, and obtain a targeted delivery system. In this study, we synthesized a PLGA-gallic acid sustained release system, using the solvent evaporation method. This approach improved the therapeutic efficacy of gallic acid. The numerical distribution showed that most PLGA-GA nanoparticles have a size of 10 nm. Through the method of solvent evaporation, an incorporation efficiency of 49% was obtained.

Abstract: In this study, hybrid composite material composed of Poly Lactic Acid (PLA) and Cassia Auriculata (CA) were fabricated and the mechanical properties were evaluated to assess the impact of bio filler loading in the bio polymer (PLA) matrix. In order to fabricate the composite specimens, the CA bio filler was added to the PLA matrix in proportions of 10%, 20%, 30%, 40% and 50% by volume. In line with ASTM specifications, experiments were conducted to establish how the hybrid bio matrix, which was composed of both PLA and CA influenced the composite`s mechanical characteristics. The test results indicated that adding 30 percent CA to PLA enhanced the material`s mechanical, dynamic mechanical analysis, thermogravimetric properties. The composite composition with better properties was considered for further fabrication of a colposcopy fixture, the component was fabricated using additive manufacturing methodology.

Abstract: Simvastatin, a lipid-lowering drug from the statins group, is used in various dyslipidemias. It appears like a very useful medication to decrease the level of total cholesterol, of the low-density-lipids and triglycerides from blood, but it is well-known that the administration of statins have serious side effects, like muscle pain and weakness that can lead to kidney damage, rash on the skin and inflammation of the joints and of the blood vessels, shortness of breath, inflammation of the liver, dark urine, anemia, memory and sleep disorders, and problems in performing the sexual act. The main aims of this research were to obtain and to characterize a polymer carrier used for the transmembrane transfer of simvastatin. Hepatic arterial variations are common knowledge and it has been studied that these types of arteries have a narrower endoluminal diameter, therefore the patients may be prone to develop atherosclerosis more rapid that the ones with standard hepatic arterial patterns. The samples based on polyurethane structures with and respectively without the active agent were synthesized and characterized by measurements of pH, encapsulation efficacy, cumulative drug release in a simulated body fluid, scanning electron microscopy, Zetasizer measurements, thermal stability, cytotoxicity assay, and non-invasive skin irritation assessment. The results indicate the obtaining of heterogenous polyurethane structures with mean sizes between 80-440 nm and neutral pH, that have a good stability against the agglomeration tendency and a prolonged release rate. The results on structures cytotoxicity and their non-irritative potential are important clues that can be used in further clinical investigations.

Abstract: This paper presents an analysis of 3D amplitude and functional parameters for worn surfaces of composites with polyamide 6 as matrix and different glass bead concentrations (0%, 2.5%, 5%, 10%, 20%, 30% and 50%wt). The worn surfaces after dry sliding of a steel pin on a disk, for 10 km, at constant velocity (0.5 m/s, 1 m/s and 1.5 m/s) and under an average pressure of 1 MPa. There were done two tests under the same conditions. On each worn track, there were investigated three surfaces of 500 μm x 500 μm with a contact profilometer. The number of points on the scan line was 200 points and the step between lines was 5μm. The following amplitude parameters were measured and calculated for assessed surfaces: the arithmetic mean deviation, Sa, the root mean square deviation, Sq, the maximum height of surface prominence, Sp, the maximum surface depth, Sv, the maximum height, St, the skewness factor, Ssk and the kurtosis, Sku. The discussed functional parameters are the reduced peak height, Spk, the height of the core of the surface, Sk and the depth of the valley zone, Svk. The comparison of their values makes posible to evaluate if the worn surface could function in a new running or the replacement of the component is recommended. Considering that machine components have intermittent operation, these worn surfaces becoming initial surfaces for the following cycle of contact operation. Based on the average values of amplitude and functional parameters, it was found that a relatively good surface quality is preserved for concentrations of 10...30%wt glass beads, for v=0.5...1 m/s (Sa and Sq having similar trend); for lower concentrations and for 50% glass beads, the parameter values increase but without identifying a distinct relationship with the working regime, especially for 2.5 and 5% glass beads.

Abstract: Virtual reality technologies are important auxiliary tools in the process of learning and acquiring the manual skills necessary for clinical maneuvers in dental prosthodontics. This study shows the particularities in the use of the virtual simulation system designed for dental prosthodontics, compared to the classically preparations performed on resin models. The interactively simulation systems reproduce real clinical situations in which students practice specific dental prosthetics maneuvers. Resin models do not reproduce the accuracy of the dental structures at the time of the preparation. The advantages of using virtual technology are efficient clinical training, allowing for repeatability, self-assessment of procedures and the acquisition of manual skills. In this way, the advantages conferred by virtual simulators are superior to those resulting from the use of resin models in the acquirement of manual skills.

Abstract: Among the properties of materials for direct coronal restorations, water absorption is particularly important, influencing the mechanical properties, color and adhesion of the restorations made.The aim of this study was to compare the water absorption of six dental restorative materials, two composite, two compomers and two glass ionomers. Water absorption was determined on disk samples. 30 discs were prepared, 5 of each studied material, with a diameter of 15 mm and a thickness of 1 mm. The water absorption test was carried out based on the ISO 4049 specification. The composites and compomers showed a water absorption within the standard limits (40 µg/mm3). Glass ionomers show high water absorption, therefore to be used as coronal restorative materials they need to be coated with a protective varnish.

Abstract: Recent progress in Material Extrusion-based Additive Manufacturing (MEX) has introduced active foaming agents in filaments composition, thus allowing for the tuning, by various process parameters, the hardness and the mechanical behavior of 3D-printed parts. In case of thermoplastic polyurethane (TPU) filaments, these advances significantly broaden the range of applications, particularly in the domains of comfort and orthotics (wrist-hand orthoses, insoles), offering the dual benefits of design flexibility inherent in MEX and the comfort of lightweight and customizable structures. However, the field is still in its early stages, with only a limited number of research efforts dedicated to characterizing these novel materials. In this context, this study is focused on determining the influence of printing temperature (190°C, 220°C, 240°C), infill density (25%, 35%, 45%) and infill pattern (honeycomb, gyroid) over the hardness of cylindrical specimens made of Colorfabb varioShore TPU. A comprehensive methodology of calibration is also presented as mandatory for obtaining good quality and accurate products by establishing correlations between flow rate and printing temperatures. The findings showed that the printing temperature is the most relevant factor impacting the hardness of varioShore TPU prints. At a printing temperature of 190°C, which corresponds to less foamed prints, the honeycomb infill yielded higher hardness compared to the gyroid infill, but the difference was not significant. Also, at 220°C and 240°C, the mean values of hardness remain relatively consistent, regardless of infill density and pattern.

Abstract: This article examines the impact of surface treatment of glass fibers on the strength of a composite material with an unsaturated polyester polymer matrix reinforced with glass fibers. The strength tests conducted include tensile, bending, and impact strength tests, as well as weight loss measurements. The research was conducted in two stages: in the first stage, the time was kept constant while the fibers were treated with varying concentrations of an alkaline NaOH solution; in the second stage, the concentration was fixed and the variable parameter was the treatment time. The results of the study indicate that surface treatment of glass fibers significantly improves their adhesion to the matrix materials, resulting in improved strength test results for the composite samples. The impact resistance, bending resistance, and tensile strength values all increased compared to the reference samples. However, certain changes in the individual parameters of fiber processing led to a slight decrease in tensile strength when it fell below the reference values. Additionally, it was observed that as the concentration of the solution and treatment time increased, the weight of the fibers decreased.

Abstract: Last years research in polymers registered an increase of interest regarding polymer mixtures aiming to obtain materials with properties of the mixed polymers. In this respect many studies are pointing the mixtures between a thermoset polymer and a thermoplastic polymer. It is known the fact that thermoplastic polymers are much more malleable than the thermoset ones and the goal is to obtain a mixture with the general properties of the thermoset polymer and with a machining ability proper to the thermoset polymer. The vitrimers are this type of polymers and, some of them, can be obtained by mixing polymers form the two categories. This study is about using solutions of two thermoset polymers to modify the basic properties of three epoxy resins. The results show that the presence of PMMA, respectively, PLA inside the epoxy resin matrix determines changes of the mechanical properties of the formed materials. Without analysing the adhesive properties of new materials is hard to decide about their value from the composites applications point of view.