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The medical industry has greatly benefited from the aid of various additive manufacturing (AM) technologies, especially for applications that include the fabrication of bespoke implants and guides, devices and surgical instruments. Manufacturing functional prototypes that can behave as close as possible to the final product is a key factor in developing successful anatomically compliant medical products. The current research is intended to evaluate the optimum AM technology to fabricate medical prototypes with thin wall structures, destined for anatomical functional tests and surgical practitioner feedback. The main criteria of evaluation were: speed of fabrication from *.STL file to final prototype, mechanical characteristics and manufacturing costs. Keywords: bespoke medical prototype, optimum additive technology, functional simulations, anatomical thin structures

In this paper, the elasto-plastic and viscoelastic properties of two grades of polyethylene are investigated by cylindrical macro-indentation. Indentation tests, including relaxation tests, are performed with a cylindrical indenter having a flat-tip diameter of 1 mm. The bulk properties, such as the indentation modulus and the yield stress, are extracted from the indentation stress-displacement curves. The indentation relaxation data of polyethylene are analyzed using the steady-state creep model and the generalized Maxwell model. Based on experimental data and the Prony series model, equilibrium stress, relaxation ratio and relaxation time are determined, while the creep exponent and the characteristic relaxation time are estimated using the steady-state creep model. Keywords:cylindrical macro-indentation, relaxation tests, steady-state creep model

Recently, there is market need to develop technologies focused on manufacturing custom and unique parts. Additive Manufacturing technologies create geometrical parts layer by layer and satisfy this necessity. In this article we try to establish a set of rules to be followed in FDM - Fused Deposition Modeling 3D printing process using ABS (Acrilonitril-Butadien-Styren) type plastic materials. The objects have been printed on a 3D “Ultimaker –2” printer. ABS (Acrilonitril-Butadien-Styren) filament was used to print the objects. The article also refers to printing constraints generated by the machine work load limitations and the extruded material. Keywords: Acrilonitril-Butadien-Styren, Fused Deposition Modeling, 3D printing

The paper presents the results obtained by the authors in the research of the mechanical behaviour variation of the polymeric reinforced with protein fibers composite (CFP) depending on the reinforcing material concentration in the elastomeric matrix. The determination of the mechanical behavior variation depending on the reinforcing material concentration is important not only to establish a convenient concentration to obtain some mechanical properties required in any field of application, but for obtaining an optimal method of choice of some values in its concentration, so that the composite material to satisfy a certain property (value) or even a number of mechanical properties. Keywords: CFP, variation, mechanical properties, reinforcing concentration

The electrochemical characteristics of polytetrafluoroethylene (PTFE) coating produced on NiTi orthodontic wires were investigated. Electrochemical impedance spectroscopy (EIS) and linear potentiodynamic polarization (LPP) techniques in the conventional three-electrode configuration was employed to test the PTFE-coated NiTi wire during their exposure to artificial saliva. For comparative purpose the same electrochemical measurements were performed on uncoated NiTi wire. In addition, scanning electron microscopy (SEM) was employed to observe the surface morphology of both uncoated and PTFE-coated NiTi wires after LPP in artificial saliva. It was found that the PTFE-coated NiTi wire had a lower corrosion rate (corrosion and passive current density), about one order of magnitude lower than the uncoated NiTi substrates. The NiTi substrate was actually passive in these experimental conditions. The EIS interpretation was performed in two-layer model of the coated sample. The corrosion mechanism for the PTFE-coated NiTi wires arises from electrolyte penetration in the pore of the PTFE deposits. Keywords: PTFE-coated NiTi wire, artificial saliva, EIS, LPP, SEM

The third part of the study is oriented toward emphasizing the effect of aggressive media on mechanical behaviour of orthodontic systems. As the incisive teeth are suffering the largest loads during feeding this study is focused on accidental failure of incisive-bracket systems after their use in a manner not recommended by doctors. As in the previous two articles the bovine rib is used to simulate the teeth but in this case the orthodontic systems are tested in aggressive conditions meaning the systems are employing to bite from apples considering that the apples are containing enough acids to chemically affect the bond between incisive and bracket – one hand and, on the other hand, they are enough hard peeled in order to mechanically load the orthodontic system. Another aspect concerns with the fact that apples are most eaten fruits in Romania, especially in schools, and being about kids a failure of orthodontic system caused by inattention is more probable. Forty teeth were prepared for this study and twenty of them were new while the other twenty were used before for other studies and the brackets were newly mounted. The number of bites was set after an analysis regarding the human feeding behaviour namely by considering that a normal person or a normal kid might eat three apples a day. The shear strength of orthodontic system was determined in accidental conditions if the system did not fail during the biting part of tests. Keywords: orthodontics, adhesive, bracket, shear strength

Natural polymers, or polymers derived from living creatures, are of great interest in the biomaterials field. Collagen is the most widely found protein in mammals (25% of our total protein mass!) and is the major provider of strength to tissue. The paper presents a study regarding obtaining and characterization of biocomposite based on vinyl-acrylic copolymers as latexes and collagen polypeptides, in the following variants: blends, intermolecular complexes and interpenetrated polymeric structures. The present work discusses the results obtained on the rheological behaviour of the fluid mixtures. Regression analysis of the experimental rheological data illustrates that the latex of vinyl-acrylic copolymer is characterized by a second-order polynomial model, while the composites including collagen hydrolysates are preferentially fitted with third-order polynomial model. It has been proved the influence of the molecular weight and the concentration of collagen hydrolysate aqueous solutions on the viscosity and flowing index of polymer mixture in fluid state. Keywords: biocomposite, collagen, blends, acrylic biopolymer

The paper presents the technological steps to obtain new electrodes, made by Cu-Zn alloy, coated with one flux layer, which may be used to welding-brazing of thin plates from ferritic steels, with applications in automotive industry. The experiments realised for elements casting, was made on induction furnace, and the production technology of experimental batch for flux coated electrodes, begins with the elaboration of the alloy and his casting. The obtained electrodes have low production costs and good welding properties. Keywords: electrodes, welding-brazing; flux; galvanized steel

The dimensional changes of the materials used for bite registrations are critical for the accuracy of the records meant for programming the dental articulators. The purpose of this study was to determine the long-term dimensional changes of three bite registration materials. We selected two polyvinyl siloxanes and a bis acrylate-based material. The study was carried out in a semi-adjustable articulator. The data were collected by a photo camera in standardized conditions and then analyzed using an appropriate program and statistical analysis. We did not find significant long-term dimensional changes of the used materials. In the limits of this study we concluded that the polyvinyl siloxane, as well as the bis acrylate based bite registration materials are accurate enough to provide reliable records to program the semi-adjustable articulators. Keywords: polyvinyl siloxane, bis acrylate, bite registration, dimensional changes

In this work the properties of PDLC film based on block copolymer film are presented. The FTIR; phase transition temperature properties are studied in order to see the absorption of block copolymer with the LC. Optical microscopic work showed the increase in droplet size with the increase in block copolymer contents. It is found absorption of block copolymer does not increase linearly with the increase in its contents. Moreover a decrease in refractive index is observed with the increase in block copolymer contents. The decrease in refractive index of block copolymer with temperature is interesting for thermo-optical and electro-optical devices simultaneously. Keywords: Polymer Dispersed Liquid Crystal (PDLC); Phase separation; Liquid Crystal (LC): FTIR spectroscopy