masoud tahani

Primary biliary cholangitis (PBC), formerly known as primary biliary cirrhosis, is a liver disease. This is a chronic autoimmune disease, which can worsen over time and recur periodically. If left untreated, biliary cirrhosis may lead to liver failure. Considering that PBC is a rare disease in all age groups, especially in children, the purpose of this report was to describe a girl with hepatitis A virus (HAV) who was then diagnosed with PBC. This child is the first case reported in Iran. The patient is a 7-year-old girl with a pale complexion and eyes with a yellowish cross who was referred to the doctor. Considering that this patient had hepatitis, a blood test was requested to check the level of cholesterol and liver enzymes. The absence of cholestatic liver enzymes was observed in tests. Then, an anti-mitochondrial (AMA) test was requested for the patient, the result of which was negative. Finally, with imaging and biopsy, the diagnosis of PBC was confirmed for the patient. After the definite diagnosis of the disease, the child was treated with ursodeoxycholic acid (UDCA). The child in question is suffering from two medical and immunological diseases, HAV and PBC. Since this child was first infected with HAV, it is possible that the cause of PBC was HAV.

There are ongoing concerns about the safety of endoscopic retrograde cholangiopancreatography (ERCP) in children, as recorded cases have shown complications.

The objective of this study is to investigate the indications, complications, and outcomes of ERCP in pediatric patients.

This cross-sectional study was conducted at Namazi and Abu Ali Sina Hospitals between September 2022 and December 2023. The study focused on pediatric patients aged 1 month to 18 years undergoing ERCP. The demographics, indications for ERCP, pre-procedural imaging findings, and complications within 72 hours and up to 6 months after ERCP were extracted from medical records.

During the study period, a total of 100 ERCP procedures were performed on 56 pediatric patients. The mean age of the patients was 10.22 ± 4.80 years, with females accounting for 53.6% of the group. The main indications for performing ERCP were the presence of a stricture after orthotopic liver transplantation (22%) and the presence of a common bile duct stone (19%). The incidence of complications was notable for acute pancreatitis (3%) and bleeding (2%), while the failure rate for ERCP operations was determined to be 4%.

The infrequent occurrence of failures and complications highlights the substantial benefit of ERCP in treating biliary and pancreatic illnesses in children.

COVID-19 is an epidemic viral infection that has especially caused great concern for those with chronic diseases. Few studies have been conducted in Asian countries on the prevalence and severity of COVID-19 complications among celiac patients. This study aimed to determine the frequency, severity, and prevalence of COVID-19 complications among celiac patients in Sistan region.

In this descriptive cross-sectional study, a total of 200 patients including 40 celiac patients and 160 matched controls were studied from September to October 2021. All celiac patients in our registry were contacted and a detailed questionnaire was administered to collect required data. In addition, polymerase chain reaction (PCR) was performed on patients to detect COVID-19. Recorded variables were compared between celiac patients and controls using t-test and Chi-square test. Statistical analysis was carried out using Stata 14 software.

Out of 200 patients, 25% of celiac patients and 18.13% of controls were infected with COVID-19. Additionally, 60% of COVID-19 infected celiac patients had severe gastrointestinal symptoms and none were hospitalized, while 31% of COVID-19 infected controls had gastrointestinal symptoms and 3.45% were hospitalized. The frequency of Marsh score above 2 was significantly lower among COVID-19 infected celiac patients compared with uninfected celiac patients.

The presence of celiac disease posed no additional risk for COVID-19 infection in terms of prevalence and frequency. However, in comparison to the general population, celiac patients experienced more severe gastrointestinal complications when infected with COVID-19.

With Currently, Endoscopic retrograde cholangiopancreatography (ERCP) has evolved as a therapeutic intervention for treating disorders related to the biliary system and plays an important role in treating benign and malignant strictures of the biliary system.
The placement of biliary stents is a frequent and useful procedure to decompress the biliary system, and endoscopic biliary stenting seems relatively simple. However, in some cases, it can lead to several complications. Distal or proximal migration of endoscopically placed biliary stents is one of the known complications of ERCP and can affect up to 6-10% of patients.
Several factors, including those related to the patient, endoscopy, or stent, are involved in stent migration. When migration occurs, it is necessary to remove or replace endoprosthesis to prevent recurrent biliary complications and more severe consequences such as cholangitis and sepsis.
This review explores the frequency, etiology, risk factors, complications, and management strategies pertaining to biliary stent migration, consolidating diverse management approaches for informed decision-making.

Liver transplantation is a critical treatment option for end-stage liver disease, albeit associated with potential complications. Among the most common post-transplant complications are biliary issues, including leaks, strictures, and obstructions. Endoscopic retrograde cholangiopancreatography (ERCP) is frequently employed to manage these complications despite its inherent risks. While the complications of ERCP in the general population are well-documented, specific risks and protective factors for liver transplant recipients have not been extensively studied.

We conducted a systematic review and meta-analysis in accordance with PRISMA guidelines. In order to find relevant studies published between 1/1/2011 and 1/3/2023, two independent researchers conducted searches (MT, I SH). A literature search of English language publications was conducted using MEDLINE through PubMed, EMBASETM through Ovid, the Cochrane Library, and Trip. In addition to Magiran and SID, we searched KoreaMed and LILACS for literature published in other languages. Endoscopic retrograde cholangiopancreatography OR ERCP, OR liver Transplantation, OR Complication are terms used in the search strategy. The Newcastle-Ottawa Scale (NOS) was used to assess the quality of the studies, and data were independently extracted by two researchers.

A total of 274 studies were selected. After analyzing their correspondence with the required criteria, a final review of eleven studies was conducted. Our meta-analysis identified several risk and protective factors for complications following ERCP in liver transplant patients. Protective factors included male sex and intraoperative stenting, which were associated with reduced complications. Conversely, high serum bilirubin and creatinine levels and a history of hepatitis B were found to increase the likelihood of complications or failure after ERCP. Factors such as age, history of diabetes, serum Alanine Aminotransferase (ALT) level, steroid administration, Mammalian Target of Rapamycin (mTOR) inhibitor use, and sphincterotomy did not significantly impact ERCP outcomes and complications.

This systematic review and meta-analysis provide valuable insights into the risk and protective factors associated with complications following ERCP in liver transplant recipients. These findings can inform clinical decision-making and guide healthcare providers in optimizing the management of post-transplant biliary complications.

Celiac disease (CD) is an enteropathy associated with a genetic disorder and several constitutive genes. This study examines the genes and factors affecting CD.

This review was conducted on structured findings up to September 2023 regardless of language published according to the protocol of systematic review articles (PRISMA). To identify relevant studies, online searches were generally conducted in PubMed, Google Scholar, MEDLINE, and SCOPUS databases.

Many studies have been conducted on CD genes, and researchers have achieved good results. So far, 60 genomic loci related to CD have been discovered, which is the most important genetic loci of CD related to HLA(Human Leukocyte Antigen). Most of the gene loci identified in autoimmune diseases have pleiotropic effects and cause disruption of the immune system, which in turn causes CD.

According to the linkage studies conducted on genetic regions, the most important genetic positions identified in CD are HLADQ2 and HLA-DQ8. Due to the progress of genetic science and the uncertainty of the genomic position of this disease, they have not been able to use genetic science to prevent this disease. Considering the common genes that this disease has with other gastrointestinal diseases as well as thalassemia, there may be newer and more effective genetic approaches to treat this disease in the future.

Hepatitis A is a widespread viral infection with significant public health implications. Assessing glucose 6-phosphate dehydrogenase (G6PD) deficiency in hepatitis A patients is essential for various reasons, including prognosis, disease severity evaluation, encephalopathy risk identification, tailored management, and advancing scientific understanding. This study aimed to investigate the prevalence and clinical implications of G6PD impairment in individuals with fulminant hepatitis A.

A cross-sectional descriptive analysis was conducted, involving hospitalized patients with fulminant hepatitis A. Demographic data, prevalence rates, and clinical findings were recorded in a database. The diagnosis of hepatitis A infection was confirmed using an anti-HAV IgM antibody test, and G6PD enzyme activity was measured with a fluorescent spot assay.

Out of 81 patients with hepatitis A, 57 (70.4%) were males, and 24 (29.5%) were females, with an average age of 24.6 years. Dark yellow urine and anorexia were the most common clinical symptoms. Notably, 30 (37%) patients lacked G6PD. The group with G6PD deficiency showed significantly higher rates of encephalopathy and mortality (P<0.01), along with elevated bilirubin (P=0.00), abnormal coagulation parameters, and low hemoglobin levels (P=0.00).

In light of these findings, the present study proposes the implementation of routine G6PD level assessments and the evaluation of other relevant markers in regions where hepatitis A is endemic. Furthermore, the study underscores the need for vigilant monitoring of hemolysis and encephalopathy in affected patients to optimize clinical management and reduce morbidity and mortality associated with this condition.

 It has been shown that hyperlipidemia occurs in 71% of patients following liver transplantation. Multiple risk factors, including obesity, diabetes mellitus, and diet, as well as the immunosuppressive medications used, influence the lipid profiles that are seen in these individuals, contributing to the multifactorial etiology of lipid problems.

 The aim of the present study is to compare the lipid profile in liver transplant recipients from living-related (LR) and deceased donors (DDs).

 This is a retrospective cross-sectional study performed at Shiraz University of Medical Science between 2005 and 2018. Patients under 18 years old who received liver transplants were included in the study and divided into 2 groups who received from LR and DDs, and lipid profiles were compared between the 2 groups.

 A total of 397 patients were included in the study; in the first group, 234 received a liver from a DD, and in the second group, 161 from an LR donor. The mean body mass index (BMI) was 17.51 ± 5.49 in the first group and 16.25 ± 3.29 in the second group. The most common underlying diseases were biliary atresia (22%) and autoimmune hepatitis (15%). The mean triglyceride (TG) and high-density lipoprotein (HDL) levels were 133 and 46 mg/dL in the first group and 118 and 54 mg/dL in the second group, while the differences were statistically significant. As age increased, there was a significant difference in the mean values of fasting blood sugar (FBS) and HDL, with FBS increasing and HDL decreasing. There was no significant difference in the use of immunosuppressant drugs between the 2 groups.

 Patients who received a liver from an LR donor have a significantly lower TG, higher HDL, and a lower cardiovascular risk.

Inflammatory bowel diseases (IBDs) are complex and multifaceted disorders characterized by recurrent and persistent intestinal inflammation. The incidence of inflammatory bowel disease (IBD) is on the rise among both children and adults worldwide. In this review, we provide an update on genomic studies of IBD, with a particular focus on Very Early-Onset IBD (VEO-IBD), which often presents with a more severe phenotype than IBD at an older age.

The methods used in this systematic review were performed according to the guidelines of the PRISMA checklist. A search was conducted by two independent researchers in international databases (PubMed, Web of Science, Scopus, and Google Scholar) to find relevant studies published in English.

Patients with VEO-IBD have rare or novel genes associated with immunodeficiency that may play a role in the pathogenesis of the disease. To date, ten regions for 240 genes, which are usually monogenic, have been identified for this disease, mostly due to mutations. But the most important cause of VEO-IBD is mutation in interleukin 10. It has also been reported that VEO-IBD is associated with increased expression of S100A8 and S100A9 genes in rectal mucosa and serum.

Considering the multifactorial nature of IBD, all the changes that cause protein expression and function should be taken into account; so for early diagnosis and timely treatment of this disease, more extensive phenotypic sequencing is needed to discover new gene loci. And these children can be treated with hematopoietic stem cell transplantation, as the most efficient method.

This paper introduces piezoelectric excitation as a balancing mechanism for mode-localized mass micro-sensors. To this end, adopting the Hamilton principle together with the Ritz method, the non-linear reduced equations of motion governing electrostatically coupled micro-beams with piezoelectric layers are obtained. The free vibration equations associated with the present system are also extracted by linearizing the motion equations around the previously determined static configuration of the system. Solving the free vibration equations, the eigenvalue loci of the system are then plotted. Afterward, the influence of piezoelectric excitation on the veering phenomenon is studied. The results, whose accuracy is successfully validated by those available in the literature, reveal that piezoelectric excitation can drastically affect the veering phenomenon. For instance, it is observed that the application of the electrostatic voltage of 4V can be compensated by the piezoelectric excitation of -35.4695 mV so that the veering phenomenon will occur at the same coupling voltage. Given this important observation, the possibility of employing piezoelectric excitation in designing tunable resonant mass micro-sensors that operate based on the mode-localization phenomenon suggests itself.

The presence of autoantibodies is a prerequisite for the diagnosis of autoimmune hepatitis (AIH). However, most autoantibodies are not disease-specific, and serological overlap between AIH and other chronic liver diseases is common. Since the prognostic parameters of AIH are limited, this study aimed to investigate the relationship between histopathological findings on liver biopsy with different types of autoantibodies associated with AIH and how autoantibodies can predict the severity and extent of disease. The present study was performed on 30 patients with a definite diagnosis of AIH according to the International Autoimmune Hepatitis Group (IAIHG) criteria. Pediatric AIH patients underwent liver tissue examinations at the time of diagnosis at accession, which confirmed characteristic histological changes. AIH-related serologic major and minor autoantibodies were measured using indirect immunofluorescence assays and ELISA kit (EUROIMMUN, Germany), respectively, and were compared within all patients, and the results were recorded. Finally, the obtained data were analyzed using SPSS V25 software. Out of 30 patients, 17 (56.66%) were female, and the age range of patients was 17-11 years (8.46 ± 6.95). Anti-nuclear antibody (ANA) (73.3%), smooth muscle antibody (SMA)-anti-smooth muscle actin antibody (ASMA) (70%), perinuclear anti- neutrophilic cytoplasmic antibodies (p-ANCA) (63%), and liver kidney microsomal (LKM) (43.3%) were the most common autoantibodies found in children with AIH. There was a significant relation between the severity of histological findings and the presence of LKM antibodies (P < 0.05). The highest sensitivity for predicting severe AIH based on histopathological findings was ANA autoantibody positivity and the presence of at least two primary autoantibodies (LKM and SMA-ASMA). On the other hand, positive LKM antibodies had the highest specificity and positive predictive value (PPV) in AIH severity prediction. The results of the present study suggested that there might be a significant correlation between the presence of primary LKM autoantibodies and biopsy results, so it can possibly act as an accurate autoantibody for predicting the severity of AIH, while other AIH-related autoantibodies did not seem to have a significant correlation with biochemical and histological findings.

Although the invention of more specialized duodenoscopes helped to develop Endoscopic Retrograde Cholangiopancreatography (ERCP) as a Therapeutic Method in children, there is a general perception that ERCP is practically challenging and dangerous in children. This has limited its widespread use in children. The aim of this meta-analysis is to update the previous reviews and evaluate more recent outcomes and complications of therapeutic ERCP among children with HPB disease.

A systematic literature search based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) was performed in Web of Science, Embase, PubMed, and Cochrane library databases to find and evaluate all articles regarding therapeutic ERCP in children with HPB diseases published from January 2017 to July 2022. The analysis included studies that evaluated patients less than 18 years old undergoing ERCP with the objective of HPB diseases, and had reported the success rate and side effects. The main outcome measures were the success and complication rate of therapeutic ERCP. This meta-analysis was performed using STATA version 16 (StataCorp LP, College Station, Texas).

A total of 10 articles consisting of 1924 ERCP, performed on 958 children, were included. Out of all ERCPs, 96% (95%CI: 96-97, I2:95.8%) were conducted with therapeutic goals. The overall success rate among therapeutic ERCPs was 91% (95CI:90-92%, I2:97.1%) ranging from 65% to 95% among different studies. An overall of 9% (95%CI: 8-10, I2:97.8%) of all therapeutic ERCPs were associated with different adverse effects such as postoperative pancreatitis (6%) and Hemorrhage (1%).

Our analysis suggested ERCP as a safe therapeutic method for pediatric patients suffering HPB patients, having a success rate of 91% and a complication rate of 9%, none of which led to in-hospital mortality.

 Genetic modifications in the adiponectin receptor 2 (AdipoR2) gene can affect phenotypes associated with insulin resistance and diabetes. The purpose of this study was to evaluate the possible role of genetic modifications in the AdipoR2 gene, to determine the frequency of genotypes and polymorphism alleles of this gene at rs11061971 (+219 A>T), and to investigate its correlation with type 2 diabetes (T2D) and its related metabolic profile.

 In this case-control study, the single-nucleotide polymorphism (SNP) of AdipoR2 in 116 T2D patients and 102 controls was evaluated using RFLP PCR and FOK 1 enzyme. Fasting blood sugar, cholesterol, triglyceride, insulin, HDL-C, LDL-C and HbA1c were also measured and their correlation with the studied genetic modifications was assessed. The collected data were analyzed using Chi-square test and Hardy-Weinberg equation.

 There was a significant association in AT and TT genotypes in rs11061971 (+219 A>T) with T2D. However, no significant difference was observed in the frequency of alleles between the case and control groups. In addition, in LDL-C and total cholesterol in the control group, there was a significant difference between AA and TT genotypes as well as with AA and AT genotypes. However, no correlation was found between the other studied serum parameters and the genotype of individuals in the rs1106197171 polymorphism.

 It can be concluded that rs11061971 (+219 A>T) polymorphism is associated with T2D incidence. The findings suggest that AT and TT genotypes in this gene compared to AA genotype increase the risk of diabetes.

 Since the distribution of HBV genotypes in patients with hepatitis B indicates the predominant genotypes in specific geographical area, this study aimed to investigate the prevalence of S gene mutations in high-risk children with maternal HBV in southeastern Iran.

 This cross-sectional prospective study was performed from March 2019 to March 2020. We studied 26 patients infected with hepatitis B virus through vertical route. Serological markers of HBV were tested for HBs Ag, anti-HBs, HBe Ag, anti-HBe, and anti-HBc through ELISA. HBV-positive DNA-HBV samples were examined by nested PCR. The correlation between categorical variables was estimated using Spearmen correlation coefficient.  All statistical analyses were performed using SPSS version 22 software.

 Our study showed that no S gene mutation occurred in studied children. However, 4 (15.4%) of the children were HBe Ag positive, while the frequency of positive HBe antibody positive in the serum of children was 18 (69.2%).

 In general, since different types of Pre-S / S variants are predominantly identified in patients with chronic HBV that can affect the progression of liver disease, it is therefore necessary to evaluate the types of Pre-S / S variants regularly in HBV. Carriers should be identified to help discover people at higher risk for liver disease. Our study, as a single center study in southeastern Iran, indicated no mutation in this gene in hepatitis B patients.

In this paper an efficient and accurate solution method is developed for transient analysis and free vibration of functionally graded truncated conical shell, subjected to symmetric internal or external moving pressure. The material properties of the shell are graded continuously in the radial direction according to a Mori-Tanaka and volume fraction power-law distribution. A hybrid solution method composed of the layerwise theory, differential quadrature method, and Fourier series expansion is employed to investigate the aforementioned problem. A Fourier series expansion is used for the displacement components and dynamic pressure in the axial direction. Then the layerwise theory across the thickness direction in conjunction with the Hamilton’s principle is employed to obtain equations of motion and boundary conditions. Eventually, the differential quadrature method is implemented to discretize the governing equations in the time domain. This research shows some interesting results that can be helpful for design of functionally graded shells subjected to moving pressure. The developed results are successfully compared with the available results in the literature. The convergence study demonstrate the fast convergence rate with relatively low computational cost. The results reveal that a free vibration with significant amplitude is generated due to excitation from transition of the moving pressure. Also increasing the area of moving pressure in the case of constant load magnitude leads to reducing in the magnitudes of displacements and stresses components.

In this paper, the nonlinear vibration of a Euler–Bernoulli nanobeam resting on a non-linear viscoelastic foundation is investigated. It is assumed that the nanobeam is subjected to a harmonic excitation that can be representative of an electrostatic field. The non-linear viscoelastic foundation is considered for both hardening and softening cases. By neglecting of the in-plane inertia, Eringen's nonlocal elasticity theory is used to model and derive the equation of motion of the nanobeam. Using the Galerkin method and the first mode shape, the obtained partial differential equation is reduced to the ordinary differential equation. Calculating the system's equilibrium points lead to heteroclinic bifurcation and the heteroclinic orbits are obtained. Then, using the Melnikov integral method, the chaotic motion of the system is studied analytically, and the safe region of the system is determined respect to the parametric space of the problem. When the viscoelastic foundation has a hardening characteristic, the chaotic behavior in the system does not occur. It has been observed that the use of nonlocal elasticity theory is necessary to investigate the chaotic behavior of nanobeam, and using the classical theory of elasticity may place the system in the chaotic region.

The aim of the proposed study is to investigate the size dependent behavior of the micro-bridge gyroscopes under the combined effects of instantaneous DC voltage and harmonic base excitation. To do so, modified couple stress theory is utilized to model the size-dependent behavior of the micro-gyroscope. To avoid resonance, viscous damping is used. Hamilton’s principle is then employed to derive the governing equations of motion. Afterwards, to convert the partial differential equations of motion to ordinary differential equations of motion, a Galerkin based single mode approximation is made. Then fourth-order Range-Kutta method is used to solve the governing equations of motion. To check the accuracy of the present model, the results are then validated through comparison with the available results in the literature and the comparison shows good agreements. In addition to the previous comparison, the present results are the validated through comparison with the results of COMSOL simulation. Furthermore, the effects of different parameters on the dynamic pull-in instability and amplitude of the vibrations are investigated. The observation shows that for the case of the harmonic base excitation, the system will be excited on two frequencies.

The purpose of this paper is to deal with fracture behavior of carbon nanotubes with presenting a revised structural molecular mechanics model in the finite element method. Structural molecular mechanics modified model, uses a three-dimensional beam element with general section to make nanotube structural model in which bending stiffness and inversion are defined independently. In analysis which are done, a bridged carbon nanotube with constant strain rate is examined under tensile stress until the failure of nanotube. Carbon-carbon bonds behavior has been assumed nonlinearly and will be ruptured when the strain reaches 19%. It is predicted that fracture behavior in carbon nanotubes depends on the environment temperature due to mechanical behavior of carbon nanotube's bonds. Based on the present research, we found that by increasing the temperature, Poisson's ratio increases and Young's modulus decreases. Further, it can be said while the temperature increases, both the fracture ultimate strain and stress decrease. Finally, a nonlinear relationship is presented in which the constants depend on chirality of the carbon nanotubes.

Based on elastic continuum mechanics, the nonlinear free and force vibrational analysis of an embedded single walled carbon nanotube (SWCNT) with waviness along its axis is analyzed. The single-walled carbon nanotube embeds in a Pasternak elastic foundation. Two analytical approaches utilize to obtain the frequency-amplitude relationship of the free vibrational model, and another analytical approach propose to obtain the forced vibrations of the curved single walled carbon nanotube on the Pasternak elastic foundation. Subsequently, a parametric study is performed to study the importance of different parameters, such as the amplitude of oscillation and the curvature radius, on the nonlinear behavior of the system. Finally, numerical simulation is carried out to obtain the results and investigate the accuracy of the analytical solution methods. Comparison of the results obtained by proposed methods show excellent agreement with those obtained by numerical solution.

Friction stir welded butt joints were performed on sheets made of AA2024-T351 aluminum alloy at tool rotational speeds of 400, 630, 800 rpm and traverse speeds of 8, 16, 25 mm/min. The fatigue crack propagation rate was investigated according to standard ASTM-E647 in CT specimens. FE simulation of FSW process was implemented for different welding conditions and next the fatigue crack propagation was simulated using XFEM method. In this analysis, to assess the damage in the joints, maximum stress criterion is used. The maximum principal stress in element was the fracture criterion. Numerical results are in good agreement with the experiments so the simulation is reliable. The obtained results show that the tool rotational and traverse speed affect the fatigues crack growth rate. For all welded specimens crack propagation rate was slower than that of the base metal for low values of ∆K (∆K≤13 Mpa) but is much faster at high values of ∆K. Furthermore fatigue properties of specimens that welded with lower speeds are better than base metal and increase in rotational or traverse speeds of the tool will increase the crack propagation rate of the welded specimens.

This research aims to provide new information about the mechanical behavior of double-stranded DNA (dsDNA). For this purpose, a series of extended atomic resolution molecular dynamics (MD) simulations of DNA dodecamer is performed. The MD calculations are carried out using Generalized Born solvent-accessible surface area method and Langevin dynamics. The stress-strain curves of DNA obtained under various pulling rates and pulling angles are analyzed, and the role of pulling angle and velocity in determining biomechanical properties of short dsDNA is discussed. The results illustrate that how much the behavior of DNA under action of tensile forces could be complicated. By means of at base pair level analyses of the molecule conformation during the stretching processes, the structural stability of the DNA molecule subjected to the angled pulling with different pulling rates and different pathways to the dsDNA rupture are studied. The structural stability of dsDNA can be dependent on the pulling velocity and pulling angle. Whereas the DNA stability can decrease significantly with the reduction of pulling velocity, stretching the DNA under different angles has different unpredictable effects on its structural stability.

Rrectangular plates-based resonant micro-sensors utilize the resonance frequency of electrically pre-deformed clamped micro-plates for sensing. Free vibration analysis of such systems in order to find their resonance frequency is the objective of present paper. For this aim، the modified couple stress theory (MCST) together with the Kirchhoff plate model is considered and the size-dependent equation of motion which accounts for the effect of axial residual stresses as well as the non-linear and distributed electrostatic force is derived using the Hamilton''s principle. The lowest frequency of the system as the resonance frequency of these micro-plates is extracted using a single mode Galerkin based reduced order model (ROM). It is found that the fundamental frequency of the system is decreased with an increase of applied voltage and becomes zero when the input voltage reaches the pull-in voltage of the system. The findings of present paper are compared and validated by available results in the literature and an excellent agreement between them is observed. Also it is found that using the MCST in pull-in analysis of clamped rectangular micro-plates can remove the existing gap between the results of classical theory (CT) and available empirical observations. Furthermore، it is observed that accounting for the size-effect on free vibration analysis of electrostatically pre-deformed micro-plates is more essential than flat ones.

Orthopedic screws are widely used devices for fixation of bone fractures. Progressive loosening of bone fixation screws, induced by stress shielding and subsequent adaptive bone remodeling, results in bone loss around the screw. A set of two-dimensional finite element models including cortical and cancellous bone with a functionally graded Ti-Hap screw was developed. A dimensionless set of stress-transfer parameters (STP) and strain energy density-transfer parameter (SEDTP) were developed to quantify the screw–bone load sharing. Lower STP and SEDTP values indicate weak stress and strain energy density transfer to bone which is a sign of stress shielding. The results indicated that STP and SEDTP values for FGM screw are higher than those of a fully metal screw. Moreover, reducing elastic modulus of metal fraction and increasing the volume fraction of ceramic decrease the stress shielding. For a partially graded screw (with both homogenous and FGM parts), the longer FGM part is, the greater are STP and SEDTP values. Furthermore, the results showed that decreasing compositional distribution exponent which shows composition change of FGM content from metal fraction toward ceramic fraction, increases the parameters. Results from this study are in admissible agreement with available clinical and experimental study.