Journal of Advanced Materials in Engineering (Esteghlal)

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Tarnish and Corrosion behavior of three Commercial dental amalgams namely Am.1, Am.2, Am.3, have been investigated by utilizing in vitro tests. The corrosion and/or dissolution rate of the three dental amalgams were studied in 0.9 wt% NaCl Solution, artificial saliva and Ringer's solution. Potentiodynamic polarization technique was employed to study cathodic and anodic polarization behavior, from which the corrosion potentials and corrosion current densities were calculated. The corrosion potential and the corrosion current density of each amalgam was found to be affected by the nature of electrolyte used, as well as the Pre-immersion time. However, the order of corrosion potentials and corrosion current densities of the three dental amalgams examined, was found to be independent of the electrolyte used.

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Hydroxyapatite coatings have been used on metallic substrates in a variety of applications, including modifying the surface of human implants, bone osseointegration and biological fixation. In this paper, the effects of various kinds of metallic substrate on clinical and pathological results of in vivo tests are presented. Four kinds of endodontic implants i.e, stainless steel, cobalt base alloy, plasma sprayed hydroxyapatite coated stainless steel, plasma sprayed hydroxyapatite coated cobalt base alloy were prapared and implanted in mandibular canine of cats. After a healing period of 4 months, investigation by SEM and histopathological interpretation and evaluation showed significant differences in tissue response and osseointegration between coated and non-coated metallic implants. It was concluded that the results were affected by the kind of metallic substrate . Keywords: Hydroxyapatite coating, Dental endodontic implant, Osseointegration, Corrosion, Stainless steel, Cobalt base alloy

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In welded tubular joints, when the fatigue crack depth is less than 20% of chord wall thickness, the crack growing process is highly affected by weld geometry. Hence, T-butt solution and weld magnification factor (Mk) are applicable tools for evaluating the crack growth rate in this domain. In this research, the capability of Artificial Neural Network (ANN) for estimating the Mk of weld toe cracks in T-butt joints is investigated. Four Multi-Layer Perceptron (MLP) networks are designed and trained to predict the Mk in deepest point and ends of weld toe cracks under membrane and bending stresses. Training and testing data of networks are extracted from a reputable resource on finite element modeling. Comparison of the results obtained and those from the most recently published equations shows that using ANN seems to be very beneficial in this field

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The addition of ZrO2 particles to the HA coating has received considerable attention because ZrO2 particles increase the bonding strength between HA coating and substrate. In this study, nanostructured hydroxyapatite (HA)/yttria stabilized zirconia (YSZ) coatings were prepared by a sol–gel method. It was found that at 950ºC, the dominant phases were HA and tetragonal (t)-zirconia in 3YSZ, cubic (c)-zirconia in 8 YSZ and t-c-Zirconia in 5YSZ phases with the small amounts of β-tricalcium phosphate (β-TCP) and CaZrO3. The crystallite size of the coating was about ~20-30 nm for tetragonal and cubic zirconia grain size and 40-80 nm for hydroxyapatite grain size. Crack-free and homogeneous HA/YSZ composite coatings were obtained with no observable defects. In vitro evaluation in 0.9% NaCl showed that Ca2+ dissolution rate of composite coatings was lower than that of pure HA coatings. The decrease in electrochemical performance of these coated samples in comparison with the uncoated type 316L St.St could be associated with chloride ion and water penetration into the coating, transport of ions through the coating, and the subsequent electrochemical reactions at the coating–metal interface.

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In this study, forsterite nanopowder was prepared by mechanical alloying and post-heat treatment method. Bioactive properties of forsterite nanopowder were studied by immersing the powder in the SBF. Nanostructure forsterite bulk dense form was prepared by the two step sintering method. It was found that pure forsterite nanopowder with 25-60nm particle size was produced. The results of soaking of forsterite nanopowder in the SBF showed that forsterite nanopowder is bioactive. Also, forsterite dense bulk with the optimal hardness of 940 Hv and fracture toughness of 3.61 MPa.m1/2 was produced. These findings suggest that forsterite nanostructure ceramics possess good biocompatibility, bioactivity and mechanical properties and could be suitable for orthopedic and dental implant materials.

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In the last decade, Calcium Titanate has been introduced as a bioceramic with acceptable mechanical and biological properties for orthopaedic implant applications. In this study, CaTiO3 nano-structure coating was produced by sol-gel dip-coating route for biomedical applications. Calcium nitrate and titanium isopropoxide were used as a precursor. After coating process, the specimen was subjected to rapid thermal annealing (RTA) at 800°C. The phase structure, functional groups and surface morphology of coating were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Uniform crack-free nano-structured coatings were obtained with perovskite crystal structure.

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Fabrication of biomaterials with ability to form a bond with bone tissue for bone skeletal system repair is one of the biomaterial science aims. Bioactive glasses containing CaO-SiO2-P2O5 are among the most important groups used in biomedicine and dentistry such as bone defect repair and maxillo-facial reconstruction. The aim of this work was preparation and characterization of nano particle bioactive glass with optimum bioactivity. Bioactive glasses with three different compositions (45S, 49S and 58S) were prepared via sol- gel technique. X- ray diffraction (XRD) technique and X- ray fluorescent (XRF) method were utilized for the phase analysis and also to investigate the chemical composition of the obtained bioactive glass nanopowders. Transmision electron microscopy (TEM) and Scanning electron microscopy (SEM) were utilized to study the structure, morphology and particle size of synthesized bioactive glass nanopowders. In order to investigate the bioactivity, the prepared bioactive glasses were immersed in the simulated body fluid (SBF) solution at 37◦C for 30 days. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) were utilized to recognize and confirm the apatite layer on the prepared bioactive glass nanopowders. TEM images showed that the prepared bioactive glasses had the particle sizes less than 100 nanometers. SEM, FTIR and XRD confirmed the formation of bone-like apatite layer formed on the bioactive glass nanopowders surface, confirming the bioactivity of synthesized bioactive glass nanopowders. It was concluded that the amount of apatite on the 45S bioactive glasse was greater in comparison with 49S and 58S bioactive glasses. It is notable that by optimizing the chemical composition, bioactive glass nanopowder could be used in applications such as repair of bone defects and bone replacement.

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Due to its biocompatibility, bioactivity and high durability properties, hydroxyapatite (HA) has a wide range of applications in medical cases such as bone defect treatment and bone tissue regeneration. Biological apatite as the most important integrity of the mineral part of hard tissues consists of tiny hydroxyapatite crystals in nanoregime. It seems that using the artificial hydroxyapatite with similar structure and chemical composition to biological apatite could increase its durability inside the natural hard tissues. The aim of the present work was the synthesis of nano structured hydroxyapatite via different routes, comparison of their characterization and enhancement of the bioactivity and bioresorbability of prepared hydroxyapatite by controlling its crystal size and chemical composition. Nano structured hydroxyapatite was prepared by mechanical activation and sol-gel routes. X-ray diffraction technique (XRD), Fourier transform infra red spectroscopy (FTIR) and transmission electron microscopy (TEM) were used to characterize the prepared hydroxyapatite powders. The synthesized powder was soaked in simulated body fluid (SBF) for various periods of time in order to evaluate its bioresorbability and bioactivity after immersion in SBF. Atomic absorption spectroscopy (AAS) was used to determine the dissolution rate of calcium ions in SBF media. Results showed that the mechanical activation prepared HA powder had nano scale structure with mean size of 29 nm and the sol gel prepared HA powder had nano scale structure with mean size of 25 nm. Ionic dissolution rate of prepared nano structured powders was higher than the conventional HA (with micron size) and were similar to biological apatite. It could be concluded that bioactivity behavior of hydroxyapatite powder is affected by its crystalline size. By using the nano structure HA powder with less than 50 nm crystalline size, the optimum bioactivity and bioresorbability would be achieved.

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Despite excellent bioactivity of bioactive ceramics such as hydroxyapatite, their clinical applications have been limited due to their poor mechanical properties. Using composite coatings with improved mechanical properties could be a solution to this problem. Therefore, the strength of metal substrate and the bioactivity of the improved composite coating combined could yield suitable results. The aim of this work was fabrication and characterization of hydroxyapatite-forsterite-bioactive glass nanocomposite coating. The sol-gel technique was used to prepare hydroxyapatite-forsterite-bioactive glass nanocomposite in order to coat on 316L stainless steel (SS) by deep coating technique. The X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and energy dispersive X-ray analysis (EDX) techniques were used to investigate the microstructure and morphology of the prepared coating. The results obtained from XRD analysis showed that the suitable temperature for calcination is 600 °C. At this temperature, the homogenous and crack-free coating could attach to the 316L SS substrate. The crystallite size of composite coatings determined via AFM was lower than 100 nm. Overall, the results obtained from this work indicate that hydroxyapatite-forsterite-bioactive glass nanocomposite coating can be a good candidate for biomedical applications.

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Short life of current total hip replacement metallic implants is generally dependent on the aseptic loosening of the implant, which occurs due to mismatch of elastic modulus between bone and metallic implant materials. Decreasing in elasticmodulus of implant could be successful. Forsterite is biocompatible and bioactive ceramic which has suitable mechanical properties. In presented research the composite materials based on Co-Cr-Mo alloy with 10, 15 and 20wt% of forsteritenanopowder as reinforcement were fabricated and mechanical behavior of the composites were evaluated. Composites were fabricated by ball milling, cold pressing and sintering. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used for characterization and evaluation phase composition and microstructure of the composites. Density, microhardness, compressive strength and elastic modulus of fabricated composites were evaluated. Obtained results showed elastic modulus of composite materials based on Co-Cr-Mo alloy reinforced with 10, 15 and 20wt% of forsteritenanopowder decreased significantly. Results also showed that the compressive strength of Co-base alloy composites reinforced with 10, 15 and 20 wt% forsterite were lower than cast Co-Cr-Mo alloy. With increasing in the content of reinforcement, compressive strength of the composites were decreased. Microhardness of prepared composites were higher than cast Co-Cr-Mo alloy. With increasing in content of bioceramic reinforcement, microhardness of the composites were increased.

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The objective of this study was to synthesize glass ionomer–forsterite nanocomposite and study the effect of incorporating forsterite nanoparticles to the ceramic part of glass ionomer cement in order to improve mechanical properties and bioactivity. So, Forsterite nanoparticles were made by the sol-gel process using different weight percentages added to the ceramic part of commercial GIC (Fuji II GC). X-ray diffraction (XRD) was used in order to characterize and determine grain size of the produced forsterite nanopowder. In order to study the mechanical properties of the produced glass ionomer cement-forsterite nanocomposite, the compressive strength (CS), three-point flexural strength (FS) and diametral tensile strength (DTS) of specimens were measured. Statistical analysis was done by one Way ANOVA and differences were considered significant if P‹0.05. The morphology of fracture surface of specimens was studied using scanning electron microscopy (SEM) technique. Bioactivity of specimens was investigated by Fourier transitioned-infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). The results of XRD analysis confirmed the nanocrystalline and pure forsterite synthesis. According to the mechanical properties measurements, the optimum weight percentages of forsterite nanoparticles for enhancement of CS, FS, and DTS were obtained equal to 3, 1 and 1 wt.%, respectively. Statistical analysis showed that the differences between all the groups were significant (P<0.05). SEM images and results of the ICP-OES and FTIR tests confirmed the bioactivity of the nanocomposite. Glass ionomer-forsterite nanocomposite containing 1 to 3 wt.%-forsterite nanoparticles can be a suitable candidate for dentistry and orthopedic applications due to the improvement of mechanical properties and bioactivity.

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