Biomedical subjects

A Iglic

Publications and source records attributed to A Iglic.

At least 37 records · Page 2Linked to original sources

PubMed2000

Peak contact stress in human hip during gait.

The contact stress in a human hip is not uniform and it changes with different body positions. The changing location of the peak contact stress during gait may indicate the predilection sites for further development of osteoarthritis in the hip. On the basis of laboratory measurements and by using mathematical models of forces and stresses in human hip we determined the points of the peak contact stress in successive phases of gait. Results show that the peak stress points are mostly located in the posterior-medial portion of the weight bearing area, which corresponds well to the clinical observations. It is also shown that in the pathological conditions of hip dysplasia the peak contact stress trajectory is located more laterally and anteriorly.

Gait↗

PubMed2000

Evaluation of biomechanical status of dysplastic human hips.

The evaluation of the biomechanical status of human hip joint was performed. Required parameters were assessed from standard antero-posterior rentgenographs and the value of contact stress on the weight bearing area is calculated. We analysed 45 dysplastic human hips and compared measured values to 81 healthy hips. The peak contact stress on the weight bearing area is considerably and statistically significantly higher in dysplastic hips compared to healthy hips. The Wiberg centre-edge angle is statistically significantly smaller in group of dysplastic hips compared to healthy hips.

Arthrography↗

PubMed2000

Gemini (dimeric) surfactant perturbation of the human erythrocyte.

We studied the ability of di-cationic gemini surfactantsdi (amphiphiles), i.e. 1,4-butanediammonium-N,N-dialkyl-N,N,N',N'-tetramethyl bromides (Di-Cm-di-QAS (s = 4), where m = 8, 11, 13, 16 and s = the number of alkyl groups in the spacer) to induce shape alteration, vesiculation, haemolysis and phosphatidylserine exposure in human erythrocytes, and to protect erythrocytes against hypotonic haemolysis. At high sublytic concentrations the Di-Cm-di-QAS (s = 4) amphiphiles rapidly induced echinocytic (spiculated) shapes and a release of exovesicles, mainly in the form of tubes, from the cell surface. Following 60 min incubation erythrocytes were sphero-echinocytic and a few cells with invaginations/endovesicles were observed. No phosphatidylserine exposure was detected. The haemolytic potency increased with an increase of the alkyl chain length. At sublytic concentrations the Di-Cm-di-QAS (s = 4) amphiphiles protected erythrocytes against hypotonic haemolysis. It is suggested that the Di-Cm-di-QAS (s = 4) amphiphiles perturb the membrane in a similar way as single-chain cationic amphiphiles, but that they do not easily translocate to the inner membrane leaflet.

Cell Size↗

PubMed1999

Liposomes composed of a double-chain cationic amphiphile (vectamidine) induce their own encapsulation into human erythrocytes.

Vectamidine is a liposome-forming double-chain cationic amphiphile. The present work was aimed to microscopically study the interactions of Vectamidine liposomes with the human erythrocyte plasma membrane. Vectamidine rapidly induced stomatocytic shapes. Attachment of Vectamidine liposomes to the erythrocyte induced a strong local invagination of the membrane. This frequently resulted in a complete encapsulation of the liposome. Liposomes composed of phosphatidylcholine (neutral) or phosphatidylserine/phosphatidylcholine (anionic) did not perturb the erythrocyte shape. Our results indicate that besides an attraction of Vectamidine liposomes to the plasma membrane, there is a preference of Vectamidine for the inner bilayer leaflet. We suggest that cationic amphiphiles may transfer from membrane-attached liposomes to the plasma membrane and then translocate to the inner bilayer leaflet where they induce a strong local inward bending of the plasma membrane resulting in an encapsulation of the liposome.

Amidines↗

PubMed1999

Amphiphile-induced spherical microexovesicle corresponds to an extreme local area difference between two monolayers of the membrane bilayer.

It is shown that an increase of the area difference between the outer and the inner membrane lipid layers of the skeleton-free membrane segment as a result of exogenously added amphiphilic molecules results in budding of the segment. The process reaches its final point when the segment attains the shape of the local maximal area difference, corresponding to formation of a spherical microexovesicle.

Alkanesulfonates↗

PubMed1999

Torocyte membrane endovesicles induced by octaethyleneglycol dodecylether in human erythrocytes.

Endovesicles induced in human erythrocytes by octaethyleneglycol dodecylether (C12E8) were studied by confocal laser scanning microscopy, using fluorescein isothiocyanate dextran as a nonspecific fluid marker. The endovesicles appeared to consist mainly of a ring-formed toroidal part joined with a central flat membrane segment. The torocyte contour length was several microm. There was usually one torocyte endovesicle per cell. The endovesicles seemed to be located near the cell surface. In sections of C12E8-treated erythrocytes transmission electron microscopy revealed the frequent occurrence of flat membrane structures with a bulby periphery, which apparently are cross sections of torocyte endovesicles. The possible physical mechanisms leading to the observed torocyte endovesicle shape are discussed. The torocyte endovesicles seem to be formed in a process in which an initially stomatocytic invagination loses volume while maintaining a large surface area. Because intercalation of C12E8 in the erythrocyte membrane induces inward membrane bending (stomatocytosis) we assume that C12E8 is preferentially located in the inner lipid layer of the erythrocyte membrane, i.e., in the outer lipid layer of the endovesicle membrane. It is suggested that local disturbances of the lipid molecules in the vicinity of the C12E8 molecules in the outer lipid layer of the endovesicle membrane form membrane inclusions with the effective shape of an inverted truncated cone. If the interaction between the inclusion and the membrane is weak, the membrane of such an endovesicle can be characterized by its negative spontaneous curvature, which may lead to a torocyte endovesicle shape with a small relative volume. Effects of a possible strong interaction between the C12E8-induced membrane inclusions and the membrane on the stability of the torocyte endovesicles are also indicated.

Biophysical Phenomena↗

PubMed1999

Mathematical modelling of stress in the hip during gait.

A mathematical model is developed for calculating the contact stress distribution in the hip for a known resultant hip force and characteristic geometrical parameters. Using a relatively simple single nonlinear algebraic equation, the model can be readily applied in clinical practice to estimate the stress distribution in the most frequent body positions of everyday activities. This is demonstrated by analyzing the data on the resultant hip force obtained from laboratory observations where a stance period of gait is considered.

Acetabulum↗

PubMed1999

Cylindrical shapes of closed lipid bilayer structures correspond to an extreme area difference between the two monolayers of the bilayer.

The shapes of extreme area difference between the outer and the inner layer (deltaA) of the closed lipid bilayer structures at fixed membrane area (A) and fixed volume (V) are determined by stating and analytically solving a variational problem for axisymmetric shapes. It is shown that the spheres with at most two different radii and the cylinder are the solutions of this variational problem. The cylinder ended by a hemisphere on each end is the shape combined from these solutions and is therefore, itself the shape of the extreme deltaA at fixed V and A. The related cylindrical shapes of stearoyl-oleoyl-phosphocholine vesicles are shown.

Biomechanical Phenomena↗

PubMed1998

Membrane skeleton and red blood cell vesiculation at low pH.

Shapes of red blood cells at low pH were studied theoretically. It is assumed that the equilibrium shape of the red blood cell corresponds to the minimum of its membrane elastic energy which consists of the bending energy and relative stretching energy of the bilayer, the stretching energy of the skeleton and the interaction energy between the skeleton and the bilayer. It is shown that the aggregation of the skeleton at low pH can cause the red blood cell shape transformation from the stomatocytic shape to the cell shape composed of a spherical parent cell having the bilayer completely underlaid with the skeleton and spherical daughter vesicles without the skeleton.

Cell Size↗

PubMed1998

Stability of spiculated red blood cells induced by intercalation of amphiphiles in cell membrane.

The stability of spiculated red blood cells, induced by intercalation of amphiphilic molecules into the cell membrane, is studied. It is assumed that the stable red blood cell shape corresponds to the minimum of its membrane elastic energy, which consists of the local and non-local bilayer bending energies and of the skeleton shear elastic energy. The cell, volume and the membrane area are kept constant. It is calculated that the number of spicules of the stable echinocytic shape is larger when the amphiphile concentration is higher, which is in agreement with experimental observations. Also, it is established that, in explaining the stability of the echinocytic shape of the red blood cell, it is necessary to include the membrane skeleton shear elasticity.

Detergents↗

PubMed1998

Amphiphile induced echinocyte-spheroechinocyte transformation of red blood cell shape.

A possible physical explanation of the echinocyte -spheroechinocyte red blood cell (RBC) shape transformation induced by the intercalation of amphiphilic molecules into the outer layer of the RBC plasma membrane bilayer is given. The stable RBC shape is determined by the minimization of the membrane elastic energy, consisting of the bilayer bending energy, the bilayer relative stretching energy and the skeleton shear elastic energy. It is shown that for a given relative cell volume the calculated number of echinocyte spicula increases while their size decreases as the number of the intercalated amphiphilic molecules in the outer layer of the cell membrane bilayer is increased, which is in agreement with experimental observations. Further, it is show that the equilibrium difference between the outer and the inner membrane leaflet areas of the stable RBC shapes increases if the amount of the intercalated amphiphiles is increased, thereby verifying theoretically the original bilayer couple hypothesis of Sheetz and Singer (1974) and Evans (1974).

Biophysical Phenomena↗

PubMed1998

A possible physical mechanism of red blood cell vesiculation obtained by incubation at high pH.

The membrane of human red blood cells is essentially composed of two parts, the lipid bilayer and the membrane skeleton that interacts with the lipid bilayer. The normal resting shape of the red blood cells at physiological pH 7.4 is the discocyte. However, at alkaline pH approximately equal to 11 the shape of red blood cells is composed of a spherical parent cell and large spherical daughter vesicles. The daughter vesicles may be free or connected to the parent cell by a narrow neck. In this paper we show that the shapes of red blood cells at pH approximately equal to 11 correspond to some of the calculated shapes of a closed lipid bilayer having an extreme area difference between the outer and the inner monolayer. Therefore, it is suggested that the observed shapes of the red blood cells at pH approximately equal to 11 are a consequence of the abolishment of the skeleton bilayer interactions at this pH.

Biomechanical Phenomena↗

PubMed1997

Increased incidence of arthrosis in women could be related to femoral and pelvic shape.

In this study various femoral and pelvic geometrical parameters important for hip joint contact stress were determined. The parameters were measured from standard anteroposterior radiographs of healthy adult subjects and analysed by using descriptive statistical procedures. Women proved to have a significantly smaller femoral head radius and larger distance between the inner acetabular rims than men, both features which lead to an increase of contact stress in the hip joint articular surface. Since too high, long-lasting contact stress is unfavourable regarding the development of arthrosis, we propose that these differences in the femoral and pelvic geometry could be one of the reasons for the increased incidence of arthrosis in women.

Adult↗

PubMed1997

A possible mechanism determining the stability of spiculated red blood cells.

In this work the stability of spiculated red blood cells, called echinocytes, is studied. It is assumed that the stable echinocyte shape corresponds to the minimum of its membrane elastic energy. It is shown that if the membrane skeleton shear elasticity is not taken into account the calculated stable echinocyte shapes always have only one spicule. However, by considering the skeleton shear elastic energy also, the calculated stable echinocyte shapes have many spicula in agreement with experimental observations.

Biomechanical Phenomena↗

PubMed1996

Determination of the femoral and pelvic geometrical parameters that are important for the hip joint contact stress: differences between female and male.

The difference between male and female femoral and pelvic geometry was studied by considering some geometrical parameters such as interhip distance, inclination of the crista iliaca, diameter of the femoral head and centre-edge angle of Wiberg. The values of these parameters were determined for 79 healthy female and 21 healthy male subjects. Standard anterior-posterior radiographs were used and processed by the computer-aided system. The results show some important sex differences in femoral and pelvic geometrical parameters which determine the hip joint contact stress.

Female↗

PubMed1996

Stress distribution on the hip joint articular surface during gait.

The magnitude and the direction of the resultant hip joint force are different in different body positions during gait. Therefore the stress distribution in the hip joint articular surface also changes. The aim of this work is to study how the stress distribution changes if the magnitude and the direction of the hip joint force is changed during gait. For this purpose a three-dimensional mathematical model is developed. We calculated the values of the peak stress and the location of the pole on the articular surface (where the stress is maximal) in the successive phases of the walking cycle. The values of the peak stress range from 0.8 MPa in the one limb stance phase to 2.6 MPa in the heel strike phase.

Cartilage, Articular↗

PubMed1995

Biomechanical study of various greater trochanter positions.

A mathematical model was used in order to evaluate the mechanical situation after lateral, medial, distal and proximal displacements of the greater trochanter. It was calculated that lateral displacement may considerably reduce the hip joint contact force, while medial displacement greatly increases it. The influence of proximalization and distalization is much less pronounced. It was further shown that, regarding the postoperative relative hip abductor muscle strength, lateral and distal displacements of the greater trochanter are favourable, while proximal and medial displacements are not.

Adult↗

PubMed1995

Depletion of membrane skeleton in red blood cell vesicles.

A possible physical interpretation of the partial detachment of the membrane skeleton in the budding region of the cell membrane and consequent depletion of the membrane skeleton in red blood cell vesicles is given. The red blood cell membrane is considered to consist of the bilayer part and the membrane skeleton. The skeleton is, under normal conditions, bound to the bilayer over its whole area. It is shown that, when in such conditions it is in the expanded state, some cell shape changes can induce its partial detachment. The partial detachment of the skeleton from the bilayer is energetically favorable if the consequent decrease of the skeleton expansion energy is larger than the corresponding increase of the bilayer-skeleton binding energy. The effect of shape on the skeleton detachment is analyzed theoretically for a series of the pear class shapes, having decreasing neck diameter and ending with a parent-daughter pair of spheres. The partial detachment of the skeleton is promoted by narrowing of the cell neck, by increasing the lateral tension in the skeleton and its area expansivity modulus, and by diminishing the attraction forces between the skeleton and the bilayer. If the radius of the daughter vesicle is sufficiently small relative to the radius of the parent cell, the daughter vesicle can exist either completely underlaid with the skeleton or completely depleted of the skeleton.

Erythrocyte Membrane↗