جستجوی مقالات مرتبط با کلیدواژه « Mechanical properties » در نشریات گروه « پزشکی »

Conventional methods for the skin aging are based mainly on physiological or biochemical observations. The aim of this study is to provide a non-invasive method based on the extraction of biomechanical parameters of the skin resulting from the processing of sequential high-frequency ultrasound images in order to investigate the process of skin lesions.

Consecutive ultrasound images of the epidermal and dermal layers were recorded and saved with a 40 MHz imaging system. In order to evaluate the process of skin damage, 25 C57BL6 mice were exposed to UVB radiation. The mechanical parameters of the skin derived from the processing of sequential ultrasound images were also estimated weekly with the motion estimation algorithm (gradient and block matching) during the injury generation process and results were reported as a mean and standard deviation. Validation of the method was performed by invasive tensiometric test. Correlation between the two methods was performed by Pearson correlation analysis. Statistical  repeated measures analysis of  variance was used to compare the statistical trend of changes over 5 weeks.

Significant correlation was obtained between elasticity extracted from non-invasive ultrasonic image processing method and invasive tensiometric method with a correlation coefficient of more than 0.79. By processing the sequential ultrasound images, the axial elastic and the shear modulus of the skin layers were significantly increased, which indicate the increased skin firmness during  the ultraviolet radiation (p <0.05). Also, the ratio of changes in the elastic modulus on the thirty-fifth day was 11 times more than zero-day. The shear modulus on the 35th day of ultraviolet radiation was 2.2 times more than zero-day. The results of repeated measures analysis of  variance showed that during irradiation with ultraviolet waves, the axial elastic modulus and the shear modulus of the skin layers obtained by processing sequential ultrasound images also increased significantly, indicating an increase in skin firmness (p <0.05).

Based on the findings of the present study a non-invasive method according to the extraction of local biomechanical parameters of skin based on the processing of sequential high-frequency ultrasound images for detecting the skin damage caused by ultraviolet radiation is proposed.

 This studied aimed to measure the yield strength and stress relaxation properties of three commercially available thermoplastic aligner materials.

 The three different thermoplastics aligner materials Duran (Scheu, Iserlohn, Germany), Erkodur (Pfalzgrafenweiler, Erkodent, Germany) and Track (Forestadent, Germany) were selected. A three-point bending test was carried out via the universal testing machine to measure their yield strength and stress relaxation properties. An independent t-test was performed for intergroup comparison. P-value < 0.05 was set as the level of significance.

 All the selected three polymers liberate a notable amount of stress during 24 hours. The highest stress release was observed in Duran i.e. 18.96 N/cm2 as compared to Erkodur, which was 13.96 N/cm2 and Track, which was 13.18 N/cm2. The yield strength of Duran was the highest (75.85 Mpa) compared to Track and Erkodur with the yield strength of 52.75 Mpa and 55.86 Mpa, respectively.

 Tooth movement is influenced by the composition of aligner material and its thickness. Duran had the highest stress release and yield strength. Stress released by different aligners exceeds around half of the initial stress value, which directly affects the orthodontic force application and subsequent tooth movement.

Glass ceramic materials have multiple applications in various prosthetic fields. Despite the many advantages of these materials, they still have limitations such as fragility and surface machining and ease of repairing. Crack propagation has been a typical concern in fullceramic crowns, for which many successful numerical simulations have been carried out using the extended finite element method (XFEM). However, XFEM cannot correctly predict a primary crack growth direction under dynamic loading on the implant crown.

In this work, the dental implant crown and abutment were modeled in CATIA V5R19 software using a CT-scan technique based on the human first molar. The crown was approximated with 39514 spherical particles to reach a reasonable convergence in the results. In the present work, glass ceramic was considered the crown material on a titanium abutment. The simulation was performed for an impactor with an initial velocity of 25 m/s in the implant-abutment axis direction. We took advantage of smooth particle hydrodynamics (SPH) such that the burden of defining a primary crack growth direction was suppressed.

The simulation results demonstrated that the micro-crack onset due to the impact wave in the ceramic crown first began from the crown incisal edge and then extended to the margin due to increased stress concentration near the contact region. At 23.36 µs, the crack growth was observed in two different directions based on the crown geometry, and at the end of the simulation, some micro-cracks were also initiated from the crown margin. Moreover, the results showed that the SPH algorithm could be considered an alternative robust tool to predict crack propagation in brittle materials, particularly for the implant crown under dynamic loading.

The main achievement of the present study was that the SPH algorithm is a helpful tool to predict the crack growth pattern in brittle materials, especially for ceramic crowns under dynamic loading. The predicted crack direction showed that the initial crack was divided into two branches after its impact, leading to the crown fracture. The micro-crack initiated from the crown incisal edge and then extended to the crown margin due to the stress concentration near the contact area.

The active films composed of polyvinyl alcohol/Alyssum homolocarpum seeds gum (PVA-AHSG) in corporatinglysozyme (LY) are developed and characterized. The LY affects the thickness, solubility, and water vapor permeability, mechanical, microstructural, and optical properties of PVA-AHSG films and also the antimicrobial activities of obtained films are evaluated. The LY content increased the thickness of composite films. The LY addition led to an increase in water solubility, moisture contents, and contact angle, and decreased density. The control films without LY had the lower opacity and acted as a weak barrier against the water vapor. The LY reduced elongation at break and slightly increased tensile strength and elastic modulus. The electron micrographs showed that the control films had a smoother structure, and the addition of LY formed films with a rough surface. Fourier Transform-Infrared Spectra indicated some interactions between PVA and AHSG chains and LY. Functional activities were found against Gram-positive Listeria monocytogenes and Staphylococcus aureus.

Drying affects quality parameters of the grains. The objective of this study was to investigate effects of drying methods, moisture contents at harvesting time and corn hybrids on mechanical properties (deformation, rupture force, firmness, necessary energy and power and toughness at rupture points) and electrical conductivity of corn kernels.

The study assessed four corn hybrids (Ns640, Jeta600, Konsur580 and SC704) harvested at various moisture contents (20, 30 and 40%) and dried using two drying methods (sun dried and artificially dried using oven at 85–90 oC).

Results revealed that corn variety significantly affected mechanical properties since Ns640 included the maximum and Konsur580 the minimum properties, compared to that other hybrids did. Furthermore, variety affected electrical conductivity. Konsur580 variety exhibited a higher electrical conductivity in both drying methods. Moisture contents at harvesting time significantly affected all mechanical properties, except deformation and firmness, in the two drying methods. Higher values of mechanical properties were achieved at 20% moisture. Moreover, effects of the moisture contents on electrical conductivity were significant and kernels with 40% moisture at harvesting time included higher electrical conductivities.

Drying methods of corn significantly affected quality parameters and electrical conductivity. Corn kernels dried in sun included higher levels of properties such as rupture force, necessary energy and power, toughness and lower levels of electrical conductivity.and kernels with 40% moisture at the time of harvest had higher electrical conductivity. The drying method of corn significantly influenced the mechanical properties and electrical conductivity. Corn kernels dried in sun had higher levels of properties including rupture force, the energy required, the power required, toughness and lower level of electrical, conductivity.

For a new biomaterial which is going to be applied in bone tissue regeneration, bioactivity (bone bonding ability) and desirable mechanical properties are very essential parameters to take into consideration. In the present study, the gehlenite's mechanical properties and bioactivity are assessed and compared with hydroxyapatite (HA) for bone tissue regeneration.

Gehlenite and HA nanoparticles are synthesized through sol–gel method and coprecipitation technique, respectively, and their physical and chemical properties are characterized through X‑ray diffraction, Fourier transform infrared spectroscopy, and transmission electron microscopy.

The results prove that the gehlenite and HA phases without any undesirable phase are obtained, and the particles of both compounds are in the nanometer range with spherical morphology. The compressive strength of both compounds are assessed, and the values for gehlenite and HA disks are 144 ± 5 and 150 ± 4.8 MPa, respectively. Next, their bioactivity potential is assessed into simulated body fluid (SBF) up to 21 days, and the results show that after 14 days, gehlenite disk’s surface is completely covered with newly formed Ca‑P particles. However, some sporadic precipitations after 21 days soaking into SBF are formed onto the HA disk’s surface.

This comparative study shows that nanostructured gehlenite disk with desirable mechanical properties and faster bioactivity kinetic than HA can be considered as a promising bioceramic for bone tissue regeneration.