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Biomedical subjects

Ales Iglic

Publications and source records attributed to Ales Iglic.

30 records · Page 2Linked to original sources
PubMed2002

Charged cylindrical surfaces: effect of finite ion size.

A simple statistical mechanical approach is applied to calculate the profile of the density of the number of particles and the profile of the electrostatic potential of an electric double layer formed by a charged cylindrical surface in contact with electrolyte solution. The finite size of particles constituting the electrolyte solution is considered by including the excluded volume effect within the lattice statistics while the electrostatic interactions are considered by means of the mean electrostatic field. It is shown that the excluded volume effect decreases the density of the number of counterions and increases the electrostatic potential near the charged cylindrical surface. The effect is more pronounced for high area densities of charge of the charged surface and for larger counterions. Further, it is shown that the ratio between the density of the number of the counterions near the charged cylindrical surface and the density of the number of counterions far from the charged surface reaches a plateau at large linear charge densities for ions of finite size, while no plateau is reached for dimensionless ions. The effective thickness of the electric double layer in cylindrical geometry is introduced. It is shown that the effective thickness increases with increasing counterion size while its dependence on the area density of charge of the charged surface exhibits a minimum. The theoretical approach presented in this work can be used for description of the electrostatics of the thin cylindrical structures in biological systems such as DNA, protein macromolecules and charged micro and nano tubes.

Electrochemistry↗
PubMed2002

Computer determination of contact stress distribution and size of weight bearing area in the human hip joint.

The mathematical models and the corresponding computer program for determination of the hip joint contact force, the contact stress distribution, and the size of the weight bearing area from a standard anteroposterior radiograph are described. The described method can be applied in clinical practice to predict an optimal stress distribution after different operative interventions in the hip joint and to analyze the short and long term outcome of the treatment of various pathological conditions in the hip. A group of dysplastic hips and a group of normal hips were examined, with respect to the peak contact stress normalized by the body weight, and with respect to the functional angle of the weight bearing area. It is shown that both these parameters can be used in the assessment of hip dysplasia.

Bone Diseases, Developmental↗
PubMed2002

The influence of the biomechanical parameters of the hip on the outcome of treatment of hips subject to avascular necrosis of the femoral head.

We were interested in whether or not the biomechanical status of the hip influences the course of avascular necrosis of the femoral head. To investigate this, we used a computer aided system based on a three dimensional mathematical model for determining the stress distribution in the hip joint from standard anteroposterior rentgenographs (X-ray images) of both hips and pelvis. Based on the results of our study, we suggest that the biomechanical parameters of the hip play an important role in the outcome of treatment of hips affected by avascular necrosis of the femoral head.

Biomechanical Phenomena↗
PubMed2002

Sphericity of the femoral head on anterior-posterior radiographs of dysplastic hips.

We analyzed the sphericity of the femoral head of dysplastic hips. Using standard anterior-posterior radiographs of the hips, we assessed the femoral head's deviation from a spherical shape using a computer algorithm and via Severin grading. The method presented could serve as a useful tool to quantify differences in sphericity in cases where it is difficult to grade the hip radiologically.

Bone Diseases, Developmental↗
PubMed2002

How should dysplastic human hips be evaluated?

Dysplasia of the human hip is characterised by insufficient anterolateral covering of femoral head by the acetabulum. In our study, we evaluated dysplastic human hip joints using biomechanical parameters (the peak contact stress in the weight-bearing area of the hip - pmax) and X-ray image parameters (the centre-edge angle - thetaCE, the transverse acetabular inclination angle - thetaUS, the acetabular index of the weight-bearing zone - thetaAC, the ACM angle - thetaACM, and the hip value - HV). The purpose of this study is to make use of X-ray and biomechanical parameters to evaluate hips diagnosed with "hip dysplasia", and to establish whether or not there is a correlation between the two. Our results show a statistically significant correlation between pmax and thetaCE, thetaUS and thetaAC. The correlation between pmax and thetaACM and HV is not statistically significant.

Biomechanical Phenomena↗
PubMed2002

Hip biomechanics in orthopaedic clinical practice.

Radiographic and clinical studies, coupled with biomechanical assessment of the hip, are important tools for predicting the development of osteoarthitis of the hip. In order to better understand the treatment of hip dysplasia, it is necessary to determine the contact stress in the hip joint. In this study, a three-dimensional mathematical model was used to determine hip joint contact stress. Because of the discrepancy in the results of analyses of different radiographic indicators of hip dysplasia, the calculation of hip joint contact stress is proposed for a more accurate assessment of the severity of hip dysplasia.

Cartilage, Articular↗
PubMed2002

Biomechanical analysis of Chiari osteotomy.

The decrease in contact hip joint stress after Chiari osteotomy is studied using a mathematical model. In the model, additional coverage of the femoral head by the ala ossis ilei segment is taken into account. It is shown that this additional coverage significantly decreases stress, mostly by the indirect effect caused by the shift of the stress pole.

Computer Simulation↗
PubMed2002

Planar, cylindrical and spherical electrical double layers in biological systems. The effect of counterion size.

The effect of counterion size on the electrical properties of an electrolyte solution in contact with charged planar, cylindrical and spherical surfaces is considered. Electrostatic interaction is considered by means of the mean electrostatic field, while the finite size of particles constituting the electrolyte solution is considered via the excluded volume effect within the lattice statistics. Different sizes of counterion are described by different values of the lattice constant. It is shown that the excluded volume effect considerably decreases the calculated number density of counterions near the charged surface. This effect is more pronounced in cylindrical geometry than in spherical geometry, and less pronounced than in planar geometry.

Electrolytes↗
PubMedDate not supplied

The influence of anisotropic membrane inclusions on curvature elastic properties of lipid membranes.

A membrane inclusion can be defined as a complex of protein or peptide and the surrounding significantly distorted lipids. We suggest a theoretical model that allows for the estimation of the influence of membrane inclusions on the curvature elastic properties of lipid membranes. Our treatment includes anisotropic inclusions whose energetics depends on their in-plane orientation within the membrane. On the basis of continuum elasticity theory, we calculate the inclusion-membrane interaction energy that reflects the protein or peptide-induced short-ranged elastic deformation of a bent lipid layer. A numerical estimate of the corresponding interaction constants indicates the ability of inclusions to sense membrane bending and to accumulate at regions of favorable curvature, matching the effective shape of the inclusions. Strongly anisotropic inclusions interact favorably with lipid layers that adopt saddlelike curvature; such structures may be stabilized energetically. We explore this possibility for the case of vesicle budding where we consider a shape sequence of closed, axisymmetric vesicles that form a (saddle-curvature adopting) membrane neck. It appears that not only isotropic but also strongly anisotropic inclusions can significantly contribute to the budding energetics, a finding that we discuss in terms of recent experiments.

Algorithms↗
PubMedDate not supplied

Shape and size of giant unilamellar phospholipid vesicles containing cardiolipin.

The effect of cardiolipin content on the shape and size of giant palmitoyloleylphosphatidylcholine/cardiolipin vesicles was studied. Unilamellar vesicles were prepared in sugar solution by the method of electroformation, from mixtures containing up to 50% weight ratio of cardiolipin. At room temperature the vesicles containing cardiolipin exhibited abrupt changes in the curvature of the vesicle contour indicating regions of phase separation. The deviations from the spherical shape were larger if vesicles were made from mixtures with a higher content of cardiolipin. Numerous vesicles with soft fluctuating walls were observed. The estimated size of the vesicles containing cardiolipin was found to be smaller than the size of pure palmitoyloleylphosphatidylcholine vesicles.

Cardiolipins↗
PubMedDate not supplied

Curvature-dependent lateral distribution of raft markers in the human erythrocyte membrane.

The distribution of raft markers in curved membrane exvaginations and invaginations, induced in human erythrocytes by amphiphile-treatment or increased cytosolic calcium level, was studied by fluorescence microscopy. Cholera toxin subunit B and antibodies were used to detect raft components. Ganglioside GM1 was enriched in membrane exvaginations (spiculae) induced by cytosolic calcium and amphiphiles. Stomatin and the cytosolic proteins synexin and sorcin were enriched in spiculae when induced by cytosolic calcium, but not in spiculae induced by amphiphiles. No enrichment of flotillin-1 was detected in spiculae. Analyses of the relative protein content of released exovesicles were in line with the microscopic observations. In invaginations induced by amphiphiles, the enrichment of ganglioside GM1, but not of the integral membrane proteins flotillin-1 and stomatin, was observed. Based on the experimental results and theoretical considerations we suggest that membrane skeleton-detached, laterally mobile rafts may sort into curved or flat membrane regions dependent on their intrinsic molecular shape and/or direct interactions between the raft elements.

Biomarkers↗