Volume 61, Issue 3

Abstract: Bone substitutes are found in natural or synthetic form. Different types of bone substitutes are used, including alloplasts or xenografts. These materials should be biocompatible, and have adequate mechanical properties. Bone substitute materials have become a clinical procedure in the treatment of periodontitis. In current practice, various bone substitutes are used, including alloplasts (β-tricalcium phosphate) and xenografts with good results. The aim of this study was to evaluate the efficacy of alloplasts (β-tricalcium phosphate) and xenografts in the preprosthodontic periodontal therapy of intrabony defects. The study was carried out on a group of patients with severe periodontitis treated by periodontal surgery, in which these materials were used as bone substitutes. Patients presented or not performed fixed prosthetic restorations. These biomaterials function as osteoconductive scaffolds. Both materials ensure the filling of bone defects in periodontal intrabony defects through their own capabilities. Alloplasts (β-tricalcium phosphate) and xenografts are effective in periodontal regeneration. The evaluation of periodontal parameters after the surgical interventions with bone substitutes indicates the favorable prognosis over time of the two types of materials used.

Abstract: The study aims to present the results obtained following the burned patients micrografting, from the perspective of analyzing the physical and chemical properties of polyamide as a support for skin micrografts. To carry out the project, the data was obtained from the use of 100 micrografting kits with polyamide support which were analyzed and the results were interpreted in order to obtain relevant information regarding the effect of polyamide in accelerating the healing process, the rate of postoperative complications, as well as the acceleration in integration of the skin grafts.The comparative analysis was performed with a control group consisting of 108 free split skin grafts covered with classic cotton tulle. The conclusions of the study show that the use of polyamide in the therapeutic protocol of micrografting accelerates the process of grafts integration, while reducing the rate of postoperative complications, as well as decreasing the lenght of hospitalization.

Abstract: The shell, as the main structure of 3D printed fused filament fabrication (FFF) models, plays a key role in the tensile strength of FFF models. In order to optimise the structural parameters of the shell and improve the tensile strength of FFF models, especially those printed with low-density infill. In this paper, polylactic acid (PLA) filament was selected as the printing material, and the influence of shell structural parameters (shell texture angle, shell layer height, and shell thickness) on the tensile strength of FFF models was investigated by one-way and orthogonal tests. The results of the one-way test show that the tensile strength of the FFF models increases as the shell texture angle decreases, the shell layer height decreases, and the shell thickness increases. Orthogonal test results show that the shell structure parameters affect the tensile strength of the FFF models in the following degree: shell thickness ] shell texture angle ] shell layer height. The optimised shell structure parameters are: shell texture angle of 0°, shell layer height of 0.1 mm, shell thickness of 2.0 mm, and the tensile strength of the FFF models is the largest with this optimised parameter, which is 19.68 MPa.

Abstract: As the amount of agricultural waste produced annually worldwide is very high, numerous studies have been conducted with the aim of using them in the structure of composite materials that have a minimal impact on the environment, reduced costs, and can be used in various fields of activity. In this research, four types of composite materials were cast, with a reinforcement of chopped corn cobs and with a matrix of acrylic resin, respectively, of three hybrid resins having various mass proportions, where Dammar natural resin prevailed. The chemical structure of the composites with hybrid matrix was determined using molecular spectroscopic microanalysis, and some mechanical properties of all the composites were investigated. It was found that the values of the obtained mechanical characteristics were limited.

Abstract: The paper presents the results of experimental research conducted in the laboratory with the aim of obtaining new composite materials used for automotive brake pads. The friction material consists of seven components; five of them were kept in a constant proportion (60%wt), and two (40%wt) were varied in fraction volume, namely phenolic resin and hemp fiber. For each recipe, the effect of phenolic resin on density, porosity, hardness, thermal stability, and friction-wear characteristics was analyzed. The study indicates that finding the optimal balance between phenolic resin and hemp fiber constitutes an efficient approach in improving friction performance. Additionally, the study demonstrates the viability of organic composite materials in braking applications, as they are capable of meeting the performance levels established by traditional materials.

Abstract: The monoclonal antibody bevacizumab, which neutralizes vascular endothelial growth factor, significantly affects the migration, survival, and proliferation of cells - all of which are critical for the growth and spread of tumors. The current study`s objective was to create polyurethane structures that are more soluble in water so they may be employed as this active agent`s transmembrane carrier. A polymer drug delivery system was created using an aliphatic isocyanate and a combination of ether and ester polyols, resulting in a suitable release profile and membrane penetrability. The solubility, pH, and refractivity index measurements, the size distribution and surface charge, the encapsulation efficacy and release profile, the proliferation of cells, and skin irritation tests on mice were used to describe the two samples. Our findings reveal that nearly neutral acido-basic polymer structures were achieved, ranging in size from 187 to 423 nm. Zeta potential values suggest a minor alteration in the propensity to form clusters in the sample with increased solubility, and UV-Vis analyses demonstrate an approximately 63±2% encapsulation efficacy. In terms of the samples` biosafety profile, the tests conducted on mouse skin and cell cultures did not result in significant adverse effects at the concentrations that were examined. The results of this preclinical investigation indicate that adding polar groups to polyurethane macromolecular chains improves aqueous solubility without changing the polymer carrier`s other properties.

Abstract: The paper presents a parallel between the calculation of deformations for uniaxially compressed rubber spheres, by direct measurement on the experimental stand. Generalities about rubber, definition, properties, main characteristics and examples of use, are presented. An own experimental study is then presented to study the deformability of rubber spherical bodies and to analyze the deviations of rubber behavior from the Hertzian model. An experimental rig was designed for this. Its operation and the working method used, as well as the force-deformation characteristics for different experimental situations are presented, the compression of two or three rubber spheres, with three different ways of supporting them. Considering that a model that accurately describes the behavior of rubber is the Money-Rivlin model, which is characterized by two constants, C10 and C01, these constants were determined by a simple method, using the hardness of the material as a basic element hyperelastic, measured on the Shore A scale. After determining the material constants, the deformation value was determined by numerical modeling with the help of Ansys software. For validation, the experimental curve for the deformation of a rubber sphere on a plane and the numerical curve for the similar situation with the experimentally determined mechanical characteristics, were plotted on the same graph. Finally, the conclusions resulting from the conducted research are presented: - highlighting two ways of evaluating the deformation of rubber spheres experimentally and numerically, determining the Monney-Rivlin specific constants to the material through a simple, efficient and valid method.; - an elegant way to calculate deformations is to model the contact by axisymmetric finite elements, because it uses a minimum number of finite elements and saves significant resources; - both the calculation method and the experimental methods used are validated by a good correspondence between the experimental curve and numerical results.

Abstract: The paper presents our studies regarding the superior valorization of recycled low-density polyethylene (rLDPE) by compounding with thermoplastic starch (TPS) and ethylene propylene terpolymer elastomer (EPDM). Low-density polyethylene post-consumer waste from foil packaging was used for the experiments. The waste was mechanically recycled and the rLDPE granules obtained were characterized both from a physical-mechanical and structural point of view. In order to obtain new sustainable materials, rLDPE granules were mixed with TPS, EPDM, compatibilizers and crosslinking agents. The mixtures were obtained in a PlastiCorder Brabender mixer at 140°C, 30-80 rpm, working time 7 minutes. The samples made show very good resistance to bending and abrasion, they have very good values of Charpy impact resistance and tear strenght, they show very good behavior to accelerated aging and to the action of some liquids, they have high hardness (51-53) °ShD and a Vicat softening point of 93-96°C. The new materials can be processed by methods specific to plastic materials (extrusion, injection, compression) in order to obtain finished products, and their field of applications can include: the footwear industry, the automotive industry, construction, packaging, agriculture, etc. The LCA analysis of the composites show a low environment impact. The values of the carbon footprint range between 0.58 Kg CO2 eq/kg and 0.75 Kg CO2 eq /kg due to the use of recycle low-density polyethylene and optimised efficient production process.

Abstract: From the desire to produce environmentally friendly composites, sandwich composites with a matrix made of a Dammar-based hybrid resin, a core of chopped corn cobs, and faces made of natural fabrics were cast and researched in terms of their mechanical properties. The low production cost and the mechanical characteristic values obtained for these sandwich composites have shown that they represent an alternative to MDF, or PAL (Medium Density Fiberboard, or Chipboard). As an application, two elements of a bathroom cabinet were made. The cabinet was exposed to a high-humidity environment, and it was found that the humidity level did not cause any changes in shape or appearance of the elements made from the sandwich composite.