Production of Ultrafine-Grained Titanium with Suitable Properties for Dental Implant Applications by RS-ECAP Process

Mehdi Abbasi,Farshid Ahmadi,Mahmoud Farzin 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.4

The only problem of pure titanium for dental implant applications is its low strength and failure under different loadings. Various studies have shown that the utilization of severe plastic deformation processes such as Equal Channel AngularPressing (ECAP), through reducing the grain size of titanium, can improve not only its mechanical properties but also itscorrosion resistance and biocompatibility. In this study, a reduced-scale ECAP process on pure titanium was performed toinvestigate the effects of scale reduction. An ECAP die was made with an internal diameter of d = 3 mm, and the tests wereperformed at 250 °C for several number of passes. It was found out that after 10 passes of reduced-scale ECAP, the grainsize of CP Ti had strongly been reduced from 25 to 122 nm. This sharp reduction in grain size resulted in an increase inmicro-hardness from 205.5 to 321.3 Hv. Moreover, Nano-hardness test results showed that after 10 passes, the hardness oftitanium increased from 2461 to 3812 MPa, and simultaneously elastic modulus decreased from 108.1 to 94.8 GPa. Suchreduction of elastic modulus of titanium for dental implant applications decreased stress-shielding and jaw bone damages. According to the results of this research, after RS-ECAP process the strength of titanium is greatly increased and its elasticmodulus is reduced, which are desirable features for dental implant applications. Since dental implants are small in size, thereduced ECAP process (d = 3–5 mm) can produce titanium implants with improved properties.

Exact solution for transverse bending analysis of embedded laminated Mindlin plate

Mohammad Mehdi Heydari,Reza Kolahchi,Morteza Heydari,Ali Abbasi 국제구조공학회 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.49 No.5

Laminated Rectangular plates embedded in elastic foundations are used in many mechanical structures. This study presents an analytical approach for transverse bending analysis of an embedded symmetric laminated rectangular plate using Mindlin plate theory. The surrounding elastic medium is simulated using Pasternak foundation. Adopting the Mindlin plate theory, the governing equations are derived based on strain-displacement relation, energy method and Hamilton’s principle. The exact analysis is performed for this case when all four ends are simply supported. The effects of the plate length, elastic medium and applied force on the plate transverse bending are shown. Results indicate that the maximum deflection of the laminated plate decreases when considering an elastic medium. In addition, the deflectionof the laminated plate increases with increasing the plate width and length.

Chitosan Scaffold Containing Periostin Enhances Sternum Bone Healing and Decreases Serum Level of TNF-α and IL-6 after Sternotomy in Rat

Salehiamin Mehdi,Toolee Heidar,Azami Mahmoud,Tafti Seyed Hossein Ahmadi,Mojaverrostami Sina,Halimi Shahnaz,Barakzai Shogoofa,Sobhani Aligholi,Abbasi Yasaman 한국조직공학과 재생의학회 2022 조직공학과 재생의학 Vol.19 No.4

BACKGROUND: In the aftermath of bone injuries, such as cranium and sternum, bone wax (BW) is used to control bleeding from the bone surfaces during surgery. Made up of artificial substances, however, it is associated with many complications such as inflammation, increased risk for infection, and bone repair delay. We, therefore, in this study set out to design and evaluate a novel BW without the above-mentioned side-effects reported for other therapies. METHODS: The pastes (new BW(s)) were prepared in the laboratory and examined by MTT, MIC, MBC, and degradability tests. Then, 60 adult male Wistar rats, divided into six equal groups including chitosan (CT), CT-octacalcium phosphate (OCP), CT-periostin (Post), CT-OCP-Post, Control (Ctrl), and BW, underwent sternotomy surgery. Once the surgeries were completed, the bone repair was assessed radiologically and thereafter clinically in vivo and in vitro using CT-scan, H&E, ELISA, and qRT-PCR. RESULTS: All pastes displayed antibacterial properties and the CT-Post group had the highest cell viability compared to the control group. In contrast to the BW, CT-Post group demonstrated weight changes in the degradability test. In the CT-Post group, more number of osteocyte cells, high trabeculae percentage, and the least fibrous connective tissue were observed compared to other groups. Additionally, in comparison to the CT and Ctrl groups, higher alkaline phosphatase activity, as well as decreased level of serumtumor necrosis factor-a, interleukin-6, andOCNin the CT-Post group was evident. Finally, Runx2, OPG, and RANKL genes’ expression was significantly higher in the CT-Post group than in other groups. CONCLUSION: Our results provide insights into the desirability of pastes in terms of cellular viability, degradability, antibacterial properties, and surgical site restoration compared to the BW group. Besides, Periostin could enhance the osteogenic properties of bone tissue defect site.

Is there an association between platelet and blood inflammatory indices and the risk of gestational diabetes mellitus?

( Mahta Abbasi Fashami ),( Sepideh Hajian ),( Maryam Afrakhteh ),( Mehdi Khabaz Khoob ) 대한산부인과학회 2020 Obstetrics & Gynecology Science Vol.63 No.2

Objective Gestational diabetes mellitus (GDM) is the most prevalent medical complication in pregnancy. Early diagnosis of GDM can influence maternal/neonatal outcomes. To assess the association between platelet and blood inflammatory indices and the risk of GDM occurrence using the complete blood count (CBC) test. We also aimed to determine the sensitivity of each parameter for an early screening of this disorder during pregnancy. Methods This case-control study included 2 groups of 110 pregnant women with and without GDM. The women in each group were compared after the routine screening for GDM and after the CBC test at 24-28 weeks’ gestation after being matched according to the inclusion criteria. Data were analyzed using SPSS version 16 and Medcalc version 14.8.1 software. Results There were statistically significant intergroup differences in white blood cell (WBC) count, platelet count, mean platelet volume (MPV), plateletcrit (PCT), MPV to platelet ratio, platelet to lymphocyte ratio, and Rh values. The values of lymphocyte count, neutrophil count, neutrophil to lymphocyte ratio, and blood group were not significantly different between groups. The logistic regression analysis showed the predictive values of WBC, platelet, MPV, and PCT in GDM. According to the receiver operating characteristic curve for all 3 variables, the level below the PCT chart was more than that of the others. Conclusion Increasing platelet and inflammatory indices on the CBC test in the second trimester of pregnancy seemed to be associated with the probability of GDM occurrence.

Response modification factor of suspended zipper braced frames

Gholamreza Abdollahzadeh,Mehdi Abbasi 국제구조공학회 2015 Steel and Composite Structures, An International J Vol.18 No.1

The suspended zipper bracing system is suggested to reduce the flaws of ordinary zipper braced and concentric inverted V braced frames. In the design procedure of suspended zipper bracing systems, columns and top story truss elements are strengthened. This bracing system show different performances and characteristics compared with inverted V braced and ordinary zipper frames. As a result, a different response modification factor for suspend zipper frames is needed. In this research paper, the response modification factor of suspended zipper frames was obtained using the incremental dynamic analysis. Suspended zipper braced frames with different stories and bay lengths were selected to be representations of the design space. To analyze the frames, a number of models were constructed and calibrated using experimental data. These archetype models were subjected to 44 earthquake records of the FEMA-P695 project data set. The incremental dynamic analysis and elastic dynamic analysis were carried out to determine the yield base shear value and elastic base shear value of archetype models using the OpenSEES software. The seismic response modification factor for each frame was calculated separately and the values of 9.5 and 13.6 were recommended for ultimate limit state and allowable stress design methods, respectively.

Assessment of Blood Clot Composition by Spectral Optical Coherence Tomography: An In Vitro Study

Ding Yonghong,Abbasi Mehdi,Eltanahy Ahmed M.,Jakaitis Daniel R.,Dai Daying,Kadirvel Ramanathan,Kallmes David F.,Brinjikji Waleed 대한신경중재치료의학회 2021 Neurointervention Vol.16 No.1

Purpose: Optical coherence tomography (OCT) has the potential for <i>in vivo</i> clot composition characterization in difficult mechanical embolectomy cases. We performed an <i>in vitro</i> study to determine the OCT characteristics of red blood cells (RBCs) and fibrin rich clots.Materials and Methods: Analogues of 5 compositions of clots (5% to 95% RBCs from Group A to E) were created from human blood. The blood mixture was injected into the bifurcation of a 3D printed bifurcated silicone tube. The OPTISTM Integrated System (St. Jude Medical Inc.) was used to identify the magnitude of OCT signals from different compositions of clots. Martius Scarlett Blue trichrome (MSB) staining was performed to confirm the composition of RBCs and fibrin in each clot.Results: Group A and B showed less signal attenuation (less than 30%) from its surface to the inside, which indicated high penetration (low-back scattering). Group C indicated intermediate signal attenuation (60%) from its surface to inside the clots, in which signals were found even at the periphery of the clot. Group D and E were superficially signal rich with more signal attenuation (more than 80%) from its surface to the inside indicating low penetration (high-back scattering). Signal-free shadowing was shown in 3 clots in Group E. MSB staining indicated color change (from red in fibrin-rich clots to yellow in RBC-rich clots).Conclusion: Different compositions of clots can be assessed using OCT. Fibrin-rich clots have homogeneous signals with high penetration, while RBC-rich clots can be recognized as superficially signal rich with low penetration.

Exact solution for transverse bending analysis of embedded laminated Mindlin plate

Heydari, Mohammad Mehdi,Kolahchi, Reza,Heydari, Morteza,Abbasi, Ali Techno-Press 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.49 No.5

Laminated Rectangular plates embedded in elastic foundations are used in many mechanical structures. This study presents an analytical approach for transverse bending analysis of an embedded symmetric laminated rectangular plate using Mindlin plate theory. The surrounding elastic medium is simulated using Pasternak foundation. Adopting the Mindlin plate theory, the governing equations are derived based on strain-displacement relation, energy method and Hamilton's principle. The exact analysis is performed for this case when all four ends are simply supported. The effects of the plate length, elastic medium and applied force on the plate transverse bending are shown. Results indicate that the maximum deflection of the laminated plate decreases when considering an elastic medium. In addition, the deflection of the laminated plate increases with increasing the plate width and length.

Fragility based performance evaluation of mid rise reinforced concrete frames in near field and far field earthquakes

Mokhtar Ansari,Amir Safiey,Mehdi Abbasi 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.76 No.6

Available records of recent earthquakes show that near-field earthquakes have different characteristics than far-field earthquakes. In general, most of these unique characteristics of near-fault records can be attributed to their forward directivity. This phenomenon causes the records of ground motion normal to the fault to entail pulses with long periods in the velocity time history. The energy of the earthquake is almost accumulated in these pulses causing large displacements and, accordingly, severe damages in the building. Damage to structures caused by past earthquakes raises the need to assess the chance of future earthquake damage. There are a variety of methods to evaluate building seismic vulnerabilities with different computational cost and accuracy. In the meantime, fragility curves, which defines the possibility of structural damage as a function of ground motion characteristics and design parameters, are more common. These curves express the percentage of probability that the structural response will exceed the allowable performance limit at different seismic intensities. This study aims to obtain the fragility curve for low- and mid-rise structures of reinforced concrete moment frames by incremental dynamic analysis (IDA). These frames were exposed to an ensemble of 18 ground motions (nine records near-faults and nine records far-faults). Finally, after the analysis, their fragility curves are obtained using the limit states provided by HAZUS-MH 2.1. The result shows the near-fault earthquakes can drastically influence the fragility curves of the 6-story building while it has a minimal impact on those of the 3-story building.

Constitutive Analysis and Processing Map for Hot Working of a Ni-Cu Alloy

Gholam Reza Ebrahimi,Amir Momeni,Seyed Mehdi Abbasi,Hossein Monajatizadeh 대한금속·재료학회 2013 METALS AND MATERIALS International Vol.19 No.1

The hot deformation behavior of a Ni-Cu alloy was studied using hot compression testing in the temperature range of 950 °C-1150 °C and at strain rates of 0.001 s.1-1 s.1. Flow curves at low strain rates, up to 0.01 s.1, were typical of DRX characterized by a single peak, while at higher strain rates, the typical form of a DRX flow curve was not observed. The power-law constitutive equation was used to correlate flow stress to strain rate and temperature, and the apparent activation energy of hot deformation was determined to be about 462.4 kJ/mol. The peak strain and stress were related to the Zener-Hollomon parameter and the modeling formula was proposed. The dependence of flow stress to the Z changed at ln Z=38.5,which was considered to be a critical condition for the change in the mechanism of dynamic recrystallization. The efficiency of power dissipation was determined to be between 10-35 percent at different deformation conditions. According to the dynamic material model, stable flow was predicted for the studied temperature and strain rate ranges. Highly serrated grain boundaries at low strain rates were considered to be a reason for the occurrence of continuous dynamic recrystallization. On the contrary, at high strain rates, equiaxed grain structure was attributed to the typical discontinuous dynamic recrystallization.