In esthetic restorative dentistry, resin composites are generally encountered. Because of their excellent biocompatibility, lack of taste, odour, tissue discomfort, and toxicity, insolubility in body fluids, ease of use, good clinical/ aesthetic properties, stable colours, optical characteristics, efficient pigmentation, low cost, and repairability, they are becoming more common. Currently used composite resins have some flaws, particularly inconsistent mechanical properties. For a long time, particles of various sizes have been used as fillers to enhance these properties. In prosthodontics, poly(methyl methacrylate) (PMMA) is commonly used as a dental base material. It does, nevertheless, have several weaknesses, including low strength and weak thermal properties. The effects of different sizes of alumina (Al2O3) particles on the poly(methyl ethacrylate) (PMMA) denture base were determined in this experiment. PMMA powder was blended with Al2O3 added to methyl methacrylate (MMA).For PMMA polymeric materials strengthened with Al2O3 (40 nm, 140 nm and 0.3-0.8 μm) in various concentrations, the mechanical properties were studied.Also, the synergetic influence of the three nanoparticle sizes in the resin matrix was studied.Furthermore, thermogravimetric (TGA) analysis and water absorption and solubility characteristics of the composites prepared were also examined. Among the most significant properties to be obtained for good denture materials is high mechanic properties, water absorption and solubility, since they have different attributes in the aqueous condition of the oral cavity. Results showed clear properties optimization, especially for the size-hybrid alumina composites.
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Abstract: The presented experimental research aims to compare the degradation degree of five different types of surgical sutures used in clinical practice and to discuss the influence of local pH on the degradation of a suture material. The surgical sutures were tested in terms of stability and hydrolytic biodegradation in Phosphate Buffer Saline (PBS) solution varying the pH and the immersion time of the samples in the liquid medium. The surface properties, structural characteristics and the effects of hydrolytic biodegradation on the mechanical properties were studied using Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Degradation degree and Tensile Strength tests, respectively.
The article presents the optimization of a production process with the help of FDM technology of a fertigation pump prototype that does not require other energy source than that given by the flow and pressure of water for irrigation. In the research presented in this article specimens of PETG material are tested in terms of mechanical properties by using a tensile test equipment. The results of these tests are used to dimension and simulate with finite element the component elements of the pump.
Previous studies have shown that marine drug propylene glycol alginate sodium sulfate (PSS) plays important roles in human diseases. This study mainly explored the effects of PSS on hyperglycemia and hyperlipidemia in diabetic db/db mouse models. The db/db mice were randomly divided into 5 groups (n=12), which were model control group (distilled water), positive control group (metformin), PSS low, medium, and high dose groups (PSS25, PSS50, PSS100) and normal control group (C57/BL, distilled water). The mice in each group had free diet and water for 90 days. During the experiment, food intake was recorded every day and body weight was recorded weekly. In addition, fasting blood glucose and glycosylated hemoglobin levels were measured regularly. Finally, the contents of triglyceride (TG), low-density lipoprotein (LDL-c), high-density lipoprotein (HDL-c) and total cholesterol (TC) in the serum of mice were determined. PSS can significantly reduce fasting blood glucose and glycosylated hemoglobin levels in db/db mice, and improve insulin sensitivity. Moreover, PSS can reduce the fat accumulation of db/db mice and significantly improve the blood lipid level of db/db mice. PSS can significantly improve the symptoms of glucose and lipid metabolism disorders in db/db mice.
An original functionalization strategy is proposed here to design chitosan (CS)-based cryogels with ethylenediaminetetraacetic acid (EDTA) moieties. Cryogels with aligned micro-sized tubular structures were further engineered through an unidirectional freezing approach. Attachment of EDTA groups onto CS chains was proved by 1H-RMN and FT-IR spectroscopy. The formation of EDTA-functionalized 3D porous CS-based cryogels was demonstrated by several methods of characterization (FTIR spectroscopy, optical microscopy, SEM, porosity measurements, swelling behavior, copper (II) retention capacity). The sorption tests pointed out the high potential of EDTA-functionalized CS-based cryogels for heavy metal ions retention.
The purpose of this research is to study and develop the formulation of a rheological law for composite materials with elasto-plastic behaviour in cold compression. Starting from the generally known relationships in literature, the hypoelastic model proposed for the composite materials behaviour (as powder materials) has been developped/explained, ensuring the understanding of the research. The hypolastic theory has been used for modeling the continuous transition from elastic to plastic state for a powder material. The material behaviour is described through an isotropic tensor relationship between the deformation speed tensor, Cauchy’s stress tensor and its derivative in relation to time (the Jaumann’s derivative). Only the linear part has been used from the general form of the law which depends on scalar functions. The calculations lead to relationships depending on five parameters which are identified according to experimental data. A numerical simulation of the stress-strain evolution during the simple compression of a diepressed powder sample is made; the numerical simulation has been validated by the experimental results.
The paper presents the study on the static mechanical properties of PLA (Polylactic Acid) produced with entry-level additive technologies using three printing directions. During the experimental work were tested a total of 15 “dog bone” ASTM D638-14 standard specimens made from additively manufactured polymer (PLA) through FDM (Fused Deposition Modelling) technique, where the material and rectilinear pattern infill geometry and infill percentage of 100% were constant and the printing orientation was varied. Usually technical data sheets that are delivered by filament materials producers include the most satisfactory data which are valid for only one specific printing direction. The printing direction is deliberately selected, in such way that the best material characteristics are achieved. In addition to this matter, as the additive manufacturing market grew significantly in the past couple of years, the filament production market showed a consequential growth. The aftermath of this expansion had a direct impact towards the quality and costs of the filaments used for 3D printing, in order to satisfy both the low-end and high-end users. Therefore, in this frame, the present research provides entry-level additively manufactured PLA performances showing significant changes depending on the different printing directions and determine the build orientation influence on the mechanical properties, in the aim of providing aid for both mechanical designer and product manufacturer at the stage of the printed product mechanical properties.
This article aims to identify the behavior of light and heavy micro-plastics on the southern shore of the Caspian Sea during different seasons of the year. For this purpose, data from 15 sampling stations were gathered in four seasons, and subjected to various analyses after the samples were prepared. To separate light and heavy micro-plastics, the samples were washed with water. Analysis of TGA-DSC and FTIR imaging was used to quantitatively and qualitatively identify microplastic samples and optical microscope images were used to quantify the number of particles. According to the results, the amount of light microplastics in the spring and winter is less than in the summer and autumn. In the spring, the highest levels of pollutants are PVC, PES, PET and PU. In the summer and autumn, the values of PE, PP, PA, PAT, PU and PVC are at a relatively equal range. In the winter, most pollutants are PVC, PES, and PU. In conclusion, PE, PP, PPA, and PET should be removed from the environment before they can be modified by physical and chemical processes.
A biomaterial must be biologically compatible, mechanical, functional, corrosion resistant and easily adapt to clinical and laboratory technologies. Dental biomaterials are materials used to replace a part of a living system or to work closely with living tissue. Many scientific articles present different polymeric biocomposites with possible application in dentistry and this is a proof of the opportunity of a research in a field in full ascent and with great availability in the promotion of materials destined to “work under biological constraint” and which must also meet the functional requirements of a dental implant. The objectives of this research were to obtain and to comparatively evaluate different polymeric microparticles that can be used in dentistry. The samples based on poly(lactic-co-glycolic acid) and respectively polyurethane microparticles were characterized by pH and Zetasizer measurements, and in vitro cytotoxicity assays. The results indicate the obtaining of particles with a neutral pH, medium homogeneity, and with different tendencies to form agglomerations. Their low cytotoxicity, tested on the primary human gingival fibroblasts by MTT and LDH techniques, indicates that these microparticles are safe to be tested in further clinical evaluations.
Polypropylene (PP) has a wide range of applications in the automobile bumpers due to its many excellent properties. Mechanical properties of PP for automobile bumpers are investigated through an artificial accelerated aging test. The aging rules after different years of normal use and the artificial accelerated aging test are analyzed. The correlation between natural and artificially accelerated aging is also explored. It provides a reference for the study of the aging properties of polymers for automotive applications. Results show that the UV aging test can effectively simulate changes in tensile and bending strengths after natural aging and can be used to evaluate the weathering resistance of PP materials used in automotive bumpers. The tensile and bending strengths of these materials remain good during aging, and elongation is sensitive to aging. The short-term artificial accelerated aging test does not exert a significant influence on the impact strength of materials, and artificial accelerated aging does not completely reproduce the aging process of the material.