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The aim of this study is to investigate the interaction between pure collagen and mineral phases like hydroxyapatite. For that purpose, collagen fibers were mineralized starting from hydroxyapatite aqueous precursors. The mineral phase identification was made by XRD, the collagen-hydroxyapatite interaction was studied by IR spectroscopy, the microstructure of the composite materials was investigated by SEM and the amount of mineral phases’ deposition was evaluated by ATD-TG. Ultrasonication was used in order to evaluate the strength of the collagen-hydroxyapatite bond. The obtained results showed that it was obtained a collagen – hydroxyapatite composite material, characterized by a strong interaction between the collagen fibers and the hydroxyapatite crystals, which can be successfully used as a bone substitute. Keywords: collagen fibres mineralization, hydroxyapatite, electrostatic interactions

The dynamics of the plasma discharge through spontaneous symmetry breaking as double layer Langmuir, anodic patterns etc., is treated by means of the fractal description. Considering that the charge carrier movements take place on fractal curves, the electric charge transport is studied in an extended model of scale relativity. Using the motion equation for the complex speed field for the irrotational movement the generalized Schrödinger equation is obtained, and in the absence of dissipation a generalized Korteweg de Vries type equation is obtained. The process is also analyzed at the microscopic scale, when the electrical conductance increase is controlled by means of the soliton coherence. When the external field exceeds a critical value, the solitons which stocks the energy break down and simultaneously release the energy to the environment. The same mechanism can explain the charge transport in composite materials (e. d. nanostructures). Moreover, some correspondences between the theoretical model and the behaviour of the patterns generated by laser ablation are analyzed. Keywords: fractal space-time, charge transport mechanism, nanostructures, composite materials

This work presents a theoretical model of calculation of cylindrical assemblies joined with adhesive, based on an energy method. After the determination of the cinematically acceptable field of stresses, according to the applied load, a variational calculus on the expression of elastic potential energy leads to the complete expression of the stress field in the whole assembly. A first parametric analysis (geometrical and physical parameters) is carried out on an assembly of tubes and makes it possible to deduce the optimal length and the thickness of the adhesive. The model is validated by comparison with a finite elements model. For the assembly, the total force-displacement behavior is well defined. Thus the analytical model makes it possible to determine the rigidity of the assembly and to obtain a simple formulation very rapidly which gives the total behavior of the assembly. Keywords: adhesive joints; glass fibers; modeling; finite element analysis, stress transfer

This paper contains the results of an experimental study regarding the thermal stability of the urethane and alophanate groups from model compounds obtained in chemical reactions between phenylisocyanate and mono- or bifunctional stabilizers. The results can be used to estimate the thermal stability of the polyurethanes which were thermal and photo-oxidative (additive and reactive) stabilized. Keywords: urethane, alophanate, phenylisocyanate, antioxidant compound, photo-stabilizer compound

The aim of this study was to optimize microwave post-polymerization treatment parameters, power and irradiation time, in order to achieve the maximum applicable flexural and impact strength of autopolimerizing poly(methyl-methacrylate) denture reline resins. Specimens were produced from two types of commercial materials. Control group was left untreated, while the other twelve were post-irradiated in a microwave oven with different power and time settings: 500, 550, 600 and 650 W; and 3, 4 and 5 minutes. The amount of residual monomer was determined using DSC and FTIR. Furthermore, visual control has been conducted, in order to check if there any surface changes have appeared. Microwave post-irradiation resulted in increase of all tested mechanical properties, for all specimens. The highest mechanical properties were obtained with maximum irradiation power, which was confirmed by the results of ANOVA statistical analysis. It has been found that residual monomer content strongly influences the benefits in all tested mechanical properties, increasing biocompatibility. The fracture mode of all specimens in untreated and treated conditions was found to be mostly brittle. However, the highest power (650 W) and the longest irradiation time (5 min) resulted in unacceptable surface color and roughness modifications. Keywords: biopolymers, microwave post – polymerization, mechancal properties, residual monomer

Orthopedic research in hip endoprosthesis is advancing rapidly. The new techniques that are being used in the domain of Rapid Prototyping (RP) have given the possibility to build scaffold structures from metallic and plastic materials. This paper presents the designing process and a FEM simulation of a tailored hip endoprosthesis with a scaffold structure which is placed all over the stem and also brings into discussion the fixation place, which is influenced by the in-growth process of the bone tissue. The hip endoprosthesis simulation use as material Ti6Al4V because it is biocompatible and can be used to manufacture the endoprosthesis using RP technology like Electron Beam Melting (EBM). Keywords: scaffold structures, orthopedic implants, electron beam melting, modeling

The paper presents the use of FEM (Finite Element Method) for calculus performing at the injection moulding of a high accuracy part made of plastic material type Polyacetal, referring at: pumping of the mould cavity, thermal resistance and mechanical strength. There are presented: diagrams of variation for the pumping full degree function of time at four temperatures of the mould, thermal representation of the part for the temperature of the mould at 80oC, the results obtained after the part’s testing at drop-test, the results of static stress for the part made of injected plastic material. Keywords: injection moulding, pumping, thermal resistance, mechanical strength

Water soluble cadmium selenide (CdSe) nanoparticles were chemically obtained by polymer assisted synthesis at 70 Celsius degree from aqueous solution, using Cd(CH3COO)2·2H2O or Cd(NO3)2·4H2O as cadmium source and H2SeO3 as selenium source. The clustering of CdSe nanoparticles synthesized in poly(amidehydroxyurethane) matrix was clearly revealed by X-ray diffraction and Atomic Force Microscopy films studies. The obtained CdSe nanocrystallites have hexagonal symmetry with an average dimension of 25 nm. The Fourier Transform Infrared spectra show the interaction between the nanoparticles and urethane carbonyl and C – O – C etheric groups of polymer. The dimension of CdSe – polymer entities in water solution was explored by Laser Diffraction method and confirmed the capping of CdSe nanoparticles by the polymer. Keywords: CdSe, nanoparticles, polymer assisted synthesis, structural characterization

The flow rate coefficient was calculated both theoretically, based on calculus relationships, and experimentally, based on data obtained on two extruders with screw diameters of 45 mm and 90 mm, respectively. The concordance of the theoretical results with those obtained experimentally in two situations were verified, namely: free discharge, no backpressure, and discharge with backpressure. Keywords: flow rate coefficient; feeding zone; single screw extruder; flow rate

Due to their lightweight, exceptionally high strength and modulus, high stiffness, good fatigue life, and excellent corrosion resistance, polymer matrix composites are increasingly being used in the aircraft and spacecraft industry. Nowadays, a significant amount of advanced polymer composites is used for military and commercial aircraft and satellite components. Due of their low density, higher physical and mechanical properties and low manufacturing cost, these materials have replaced metals, such as aluminum alloys, in many applications. This paper deals with the class of polymer composites, new material recipes and testing results. This approach refers to the possible use of ferrite additive to improve mechanical and magnetic properties of polymer composites. Keywords: lightweight, polymer, composite, ferrite