IRANIAN JOURNAL OF BIOMEDICAL ENGINEERING
Year:2005 | Volume:1 | Issue:2|Papers Count:16

Current research in foot biomechanics includes studies on prevention of recurrence of neuropathic foot ulcers. This prescribes accommodative insoles, which reduce plantar pressure levels particularly under the hallux. There is little quantitative information available regarding the effects of insole materials. The insole models available in the literature are mostly two- dimensional (2-D). Hence, there is a need to develop a three-dimensional (3-D) model with actual geometry which includes sufficient details. In this study a 3-D model of the insole was constructed. A linear and non-linear static analysis using finite element method (FEM) was done. To construct the 3-D finite element model, 14736 nodes and 16170 elements were used. This research has shown that Silicone Gel is very effective in terms of reduction of stress concentrations. The techniques used in this research provide a promising approach to understand the behavior of insole material as well as a guideline in the design of therapeutic footwear and orthoses for insensate feet.

This paper presents a CAD system for detection and diagnosis of microcalcification clusters in mammograms. The proposed algorithm is composed of three main stages. In the first stage, the image pixels are examined for corresponding to individual microcalcification objects. For this purpose, the wavelet transform of the image is computed. Then two wavelet coefficients as well as two statistical features are used with a neural network for a primary classification of the image pixels. In the second stage, some noisy pixels extracted by the first step are eliminated. Then 18 features defined for each microcalcification are used with a nonlinear classifier for accurate detection of microcalcifications. For training of this classifier we used 16 regions from a database containing 379 microcalcifications. Finally, in the third stage five features defined for each microcalcification cluster with a neural network are used to recognize malignant microcalcification clusters. For training of this network, 22 clusters including 8 malignant and 14 benign cases were used. The performance of the algorithm was evaluated using a separate image set composed of 22 clusters including 10 malignant and 12 benign cases. Using these tests images and the threshold value of 0.45, the sensitivity of the algorithm was 100% and its specificity was 91.6%.

Nowadays in the industrial world, because of increase of heart transplantation demand, long-term ventricular assist devices (VAD) are more needed. Implantable sac-type is one of the newest of them producing pulsatile flow. In this research, three different models of sac-type VAD are numerically simulated. Simple motion is supposed for moving wall in model 1. In model 2, the motion of moving wall is assumed wavy form to study the effect of moving wall form on blood flow. In model 3, the pressure boundary condition is added to model 2. In this model, the effect of actual blood pressure on flow pattern is considered. Results of each model demonstrate the viscose term of blood flow stresses applied to the membrane is negligible, and only pressure term is effective. However, the motional pattern of membrane and also applied pressure on boundary are approximately ineffective on blood flow pattern.

Crystallization behavior and in vitro bioactivity of the bioactive glasses in the system MgO-CaO-P2O5-SiO2 were studied. Crystallization of bulk glasses led to the formation of large cracks in crystallized product that was attributed to the precipitation of fibrous b-wollastonite crystals growing perpendicular to the outer surface of the glasses. Crack-free dense crystallized products were formed by crystallization of the same glasses in a powder compact. By substituting SiO2 for P2O5, there was no change in the kind of formed crystalline phases but the apatite contents decreased and wollastonite contents increased. The whitlockite phase was formed when glass powder compacts were heated above wollastonite crystallization temperature. The in vitro bioactivity of the glasses and glass-ceramics was evaluated by examining apatite layer formation on their surfaces in the simulated body fluid (SBF) with SEM/EDXA. All samples showed an apatite layer on their surfaces after immersion in SBF.

The main objective of this study is to present a mathematical model for frictional forces in orthodontic tooth movements. In order to produce lighter and more efficient sliding movement, good estimation of frictional forces must be determined. For the purpose of analysis, a typical bracket with a circular cross section arch wire is considered with a view to examine the effect of ligation technique (shape), geometry and properties of ligature, and arch wire on the friction forces between ligature and arch wire. Both uniform and non-uniform distributions of contact forces are considered. The result presented herein indicated that, for circular orthodontic arch wires, friction force between ligature and wire is proportional to tensile force in elastomeric ligature. This force is depended on the shape of ligation, material properties and geometries of wire, bracket and ligature.

Several linear and nonlinear finite element models of intact and fixed lumbar spine were analyzed. The intact model was developed based on CT images, and following verification, was employed to simulate the spinal fixation procedure using two different commercial pedicle screw systems. The results including the force-deformation behavior and the stress distribution within the structures were studied in detail. The effects of pedicle morphology, insertion errors and material properties of bone graft on the stress distribution pattern within the vertebrae and implant components were also studied. The results suggest superiority of titanium implants over steel implants, necessity of bone graft insertion, and a higher failure risk for screws due to osteoporosis. It has been recommended that surgeons use thicker screws when dealing with pedicels with larger anterior posterior length and avoid insertion errors to minimize the risk of screw fracture.

Polyurethane micro spheres have been synthesized by solvent evaporation technique with castor oil, Polycaprolacton (PCL), Hexamethylen diisocyanate (HMDI) and Ethyl diamine (ED) as carriers for controlled drug delivery systems. Release behavior of micro spheres has been investigated using Bromocresol purple die. Fourier transmission infrared (FTIR), Scanning Electron Microscope (SEM), Optical microscope, dissolution instrument and UV spectrophotometer were used to investigate the polymerization process, surface morphology, particle size, rate of release and calibration curve respectively. Results showed that urethane bonds were formed at 3300-3400cm-1 and 1650-1700 cm-1. SEM micrographs showed surface irregularities as a result of solvent evaporation. Particle sizes were higher for castor oil/HMDI rather than PCL/HMDI microbe ads and in both cases, particle size and Bromocresol purple die release increased with rising NCO/OH ratio.

Tooth straightening with superelastic wire requires exertion of continued bending as well as tensional forces exerted by the wires to the teeth. The applied force can influence on properties of the wire. Knowing the amount and mechanism of this change results in both improvement of the clinical operation as well as the recovery of the used alloy. Investigating the possibility of exertion of a stable force during the curing period is substantial to orthodontists. Studying the possibility of recovery and re-circulation of the used material is of interest to engineers. The latest results obtained on the effect of bending on transformation temperatures, crystal structure and mechanical properties of four different orthodontic commercial wires are discussed in this paper. It is seen that the width of the hysteresis loop is reduced, percentage of the marten site phase is increased and the possibility of stress induced Rphase formation is increased due to the application of the deflection strains on the samples. The structural phase change occurring during mechanical and/or heating operations indicates that the alloy property can change from superelastic towards shape memory effect via heat treatment after cold working. Microstructural and transformation temperature studies show that R-phase formation is concomitant with the presence of marten site in the wires. These results indicate that the superelastic effects are correlated to the formation and elimination of small forcible hysteresis loop of the R phase.