Advanced Materials and Structures IV

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Authors: Bebe Adrian Olei, Oana Gîngu, Nicoleta Lupu, Gabriela Sima
Abstract: The objective of this research is the development of a detailed structural analysis of biocomposites with ceramic matrix of hydroxyapatite (Hap) reinforced by titanium (Ti), elaborated by powder metallurgy technology. Nanometric Hap powders (<200nm) 75% wt and micrometric Ti powders (<150μm) are homogenized in a high energy ball mill Pulverisette 6. Spark plasma sintering (SPS) is the sintering route able to lead to nanostructured sintered samples when nanopowders are used as raw material. The SPS parameters are: the sintering temperature, T=(1000-1100)°C and the maintaining time, t=(10-20) minutes in vacuum. The influence of the sintering parameters on the composites structures is monitored using the optical microscopy (OM), electronic microscopy (SEM) and the X-Ray diffraction (XRD).
Authors: Doina Raducanu, Vasile Danut Cojocaru, Ion Cinca, Ioan Dan
Abstract: The design of novel Ti-based alloys for biomedical load-bearing implant application, such as hip or knee prostheses, aims at providing structural materials which are characterized by good corrosion stability in the human body, high fatigue resistance, high strength-to-weight ratio, good ductility, low elastic modulus, excellent wear resistance, low cytotoxicity and a negligible tendency to provoke allergic reactions. Low elastic modulus is required to be close to that of a human bone, in order to transfer the adequate mechanical stress to the surrounding bone. The Young’s modulus of biomaterials is desired to be equal to that of cortical bone because if the Young’s modulus of biomaterials is much greater than that of cortical bone, bone resorption occurs. Investigated samples were subjected to mechanical tests, having provided these mechanical properties: ultimate tensile strength (σUTS), yield strength (σYS), elongation to fracture (εf) and elastic modulus (E).
Authors: Mihaela Amarandei, Lucian Bogdan, Anghel Cernescu, Liviu Marşavina, Jenel Marian Pătraşcu, Dinu Vermeşan
Abstract: Nitinol (NiTi) is a biocompatible nickel titanium alloy widely used in medical applications and devices. In anterior cruciate ligament (ACL) reconstruction surgery of the knee, fine wires of NiTi are used because of its high elasticity and good memory shape behavior. In surgical procedures these wires are exposed to mechanical stress and high deformations. This paper presents the results of the tests performed on fine NiTi wires of 1.1 mm and 0.73 mm in diameter, exposed to tensile load, which frequently appears in orthopedic surgery. The tests were done at a temperature of 37o C, in order to observe the influence of tensile stress on the mechanical properties of NiTi. The obtained material properties are in good correlation with data from manufacturers. These results are useful in durability evaluation of fine NiTi wires utilized in surgical procedures.
Authors: Monica Cretan Stamate, Carmen Gafitanu, Ciprian Stamate, Eliza Gafitanu
Abstract: Since, anti-inflamatory drugs have a high demand due to increased incidence of pain associated with different pathology; the objectives of this paper are the synthesis, the physicochemical characterization and analysis of the tribological properties for the ketoprofen-cyclodextrin complexes. The analysis of solubility for these complexes was carried out using MathCAD software. Tribological factors were evaluated by the wear resistance of cylindrical tablets containing ketoprofen-cyclodextrin complex, methocel and magnesium stearate. The tablets with ketoprofen-cyclodextrin complexes provide good solubility and wear resistance and these are ideal for preparation of extended release systems like implantable tablets or for orally administration tablets.
Authors: Angelica Enkelhardt, Cristian Sorin Nes, Nicolae Faur
Abstract: This paper presents a comparative bibliographic study of different materials with elevated biomechanical biocompatibility regarding the stent-blood vessel interaction. Only the materials used in coronary stents’ manufacturing are considered: stainless-steel (316L), Cobalt-Chromium alloys (CoCrMo, CoNiCrMo), Nickel-Titanium alloys (Nitinol), Tantalum. The main characteristics that result from the stress-strain curve of each material are presented, as well as the biocompatibility and durability. The stainless-steel has good mechanical properties, excellent biocompatibility and low price. Cobalt-Chromium alloys have excellent mechanical properties, excellent biocompatibility, acceptable shape memory properties, but high density and low flexibility. The Nitinol represents the best choice, with excellent mechanical properties, excellent biocompatibility, good corrosion resistance, high flexibility (super-elastic behavior), low density, but high price. Tantalum alloys present the best biocompatibility and high flexibility, but the mechanical properties are relative modest.
Authors: Corina Mărcăuţeanu, Florin Topală, Meda Lavinia Negrutiu, Eniko Tunde Stoica, Cosmin Sinescu
Abstract: Abfractions are wedge-shaped cervical lesions which appear due to flexure of enamel and/or dentin at some location distant from the actual point of loading. The tensions may reach the fatigue limit and lead to rupture of the amelar and dentinal materials. We used the finite element method (FEM) to investigate the effect of high occlusal forces on the dental and restorative materials placed in the cervical buccal region. We developed two 3D models of maxillary premolars in order to compare the stress profiles in the buccal cervical regions under functional (20 N) and parafunctional (800 N) occlusal loads. The discretization of the tooth morphology resulted in 18889 elements and 31425 nodes. The models was subjected to occlusal analysis. The equivalent tensions (Pa) found in the buccal cervical region of the premolars at the application of parafunctional occlusal loads (800 N) are high enough to induce the breakdown of dentinal and compomer materials (over 2.41E+08 Pa). Cervical stresses induced by masticatory forces (20 N) have much lower values, which are not harmful for the dental materials. In conclusion, occlusal overload can cause damage to both the dentinal and compomer restorative materials placed in the cervical buccal region of teeth.
Authors: Alexandru Ogodescu, Cosmin Sinescu, Meda Lavinia Negrutiu, Riham Naghib, Florin Topală, Dorin Dodenciu, Emilia Ogodescu
Abstract: In the Romanian population, during the fixed orthodontic treatment, sometimes appear white spot lesions (WSLs). These are areas of demineralized enamel witch untreated lead to the formation of cavited carious lesions. Until now the therapy of choice for such lesions was fluoridation that proved itself inadequate in terms of aesthetics. The innovative solution of the German Firma DMG (Icon®) proposes the filling and reinforcing of the pore system of a WSL with a light-curable resin (Icon-Infiltrant). The purpose of this study was to assess whether the optical coherence tomography (OCT) can evaluate, in vitro, by en face scans the penetration of this advanced new material into natural enamel caries. We applied the classic therapeutic procedures proposed by the German company. After infiltration of the WSL we observed a deep resin penetration. Clinically there was a significant improvement in the aesthetics of the affected tooth surfaces and their evolution was stopped demonstrating that this technique is effective in the therapy of WSLs at patients with fixed orthodontic therapy. Also OCT proved to be a reliable technique for acquiring images of resin infiltrated WSLs recommending this technology for further fundamental studies in the field.
Authors: Alexandru Ghiban, Brandusa Ghiban, Cristina Maria Borţun, Nicolae Ghiban, Iulian Antoniac
Abstract: A new composition of a dental cobalt alloy was proposed from the system CoCrMoTi, which was compared with a commercial dental alloy, type Wironit. Some heat treatments were applied either for stabilizing the structure, or to simulate welding conditions (such as sensibilization treatments in the range of temperature about 550°C÷-650°C). Corrosion tests were made in two body simulated fluids, respectively infusion NaCl solution and Ringer solution. The results showed that titanium alloying may improve corrosion resistance of the alloy, and also the best state considering corrosion resistance is normalizing at 1100°C with one hour maintaining in air cooling at both alloys, with or without titanium. The worse corrosion resistance is obtained in sensibilized state.
Authors: Andreea Mihaela Magheru, Brandusa Ghiban, Nicolae Ghiban, Iulian Antoniac
Abstract: The present paper take in consideration two titanium alloys, with different molybdenum contents in order to show the corrosion behavior in Ringer body simulated fluid. The samples were corrosion tested in three states, respectively non-treated state, annealed at 850°C/1 h and annealed at 1050°C/1 h.
Authors: Maria Dumitraşcu, Mădălina Georgiana Albu, Marian Vîrgolici, Cătălin Vancea, Viorica Meltzer
Abstract: In the past years an increased interest to create new polymeric blends with application in the medical area for development of new types of biomaterials has appeared. Electron beam irradiation is well known as a method of producing important changes in polymer structure, being an alternative to chemical synthesis of biomaterials based on polymeric materials. The aim of the present study was to investigate the behaviour of some polyvinylpyrrolidone-dextran (PVP/DEX) blends under electron beam irradiation. Aqueous solutions of PVP with molecular weights of 360 000 Da (PVP 360), 40 000 Da (PVP 40), and DEX with molecular weight of 500 000 Da (DEX), were mixed as to obtain 50:50 blends of PVP40/DEX and PVP360/DEX. The obtained blends were irradiated with electron beam at different radiation doses and after irradiation treatment were processed by freeze-drying. PVP/DEX blends were characterized by infrared spectroscopy (FT-IR) and thermal analysis. The analyses were conducted in order to establish the relation between radiation dose and changes of structural and thermal properties.

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