Journal of Mechanics in Medicine and Biology

The considerations are based on the understanding that somitic cells polarization in bistability window of embryonic (pre-somitic) mesoderm is a dynamical process. It occurs in the form of a polarization wavefront of somite cells spread in anterior–posterior direction of the embryonic mesoderm. It is assumed that a macroscopic cell polarization has a bistable behavior corresponding to the molecular mechanism of bistability window formation. Moreover this type of polarization is supposed to be transmittable to the other cells by contact interaction. At the end, a volume of polarized cells is taken, which is able to create mechanical tension in the volume of nonpolarized neighbor cells and to inhibit their polarization. On this basis we explore the leading aspect of somitogenesis robustness by considering a simple wavefront model of polarization and analyzing its propagation in terms of the standard methods of qualitative theory of differential equations. The obtained theoretical results are interpreted in the context of their possible experimental verification.

Numerical study is performed on the thermal fluid-flow transport phenomena in a disk-shape cavity. Consideration is given to the movement and growth of the crystal in solution layer. Here the lysozyme is employed as the crystal. The mechanism is numerically investigated by solving the two-dimensional governing equations through discretization by means of a finite-difference technique and simultaneously the crystal movement is predicted by the Basset–Boussinesq–Oseen (BBO) equation. It is found that (i) the crystal circulates in the cavity with fluid current and shows the circulation pattern of a donut shape, like the flow in a typical Benard cell, (ii) when the particle makes the second circulation with a larger loop, it falls on to the bottom near the vertical side-wall, and (iii) the size of the falling particle becomes larger as the Rayleigh number, i.e. the temperature difference between the heat sink and the vertical side-wall is increased.

The stress field developed in the human lumbar vertebral bone due to the presence of transpedicular fixation screws is studied in an attempt to quantify the force required to pull the screw out of the bone. The study is focused on the pure pull-out phenomenon, namely the case in which the external loads act parallel to the longitudinal axis of the screw. The parameters considered are the penetration ratio, i.e. the ratio of the screw length divided by the distance from the posterior pedicle entrance site to the anterior vertebral cortex, and the filling ratio, i.e. the ratio of the major diameter of the screw divided by the transverse diameter of the pedicle. The study is carried out numerically with the aid of the finite element method. The analysis takes into account both the variation of the mechanical properties of the bone in terms of the distance from its surface as well as the geometrical details of a typical transpedicular screw. The results of the analysis are compared with existing experimental data from the literature and the comparison is very satisfactory.

CAD reconstruction of anatomical regions from computerized tomography (CT) scans is a very common approach in orthopaedic biomechanics. The CAD model is discretized into finite volume sub-domains and finite element (FE) analyses are performed in order to predict the distribution of stresses generated by applied loads. However, quality and reliability of numerical results depend on the level of accuracy reached in the meshing process. This paper analyzes some critical parameters that may affect the overall efficiency of the CT–FEM transformation process: scan threshold range, object size, and complexity. An optimization procedure for minimizing geometric errors on size and shape of reconstructed objects is presented. Finally, accuracy of stress predictions is evaluated for FE models that include known amounts of geometric errors. Compression and bending loads are considered. Results show that geometric and stress errors rapidly decrease as the objects to be reconstructed become larger in size. Optimal threshold ranges can be identified clearly for both an epoxy-resin benchmark model and a real bone specimen cut from a human lumbar vertebra. This allows geometric errors to be reduced significantly.

Assessment of locomotion quality subsequent to neurological trauma, such as stroke or traumatic brain injury is imperative for the correct allocation of therapy dosage and strategy. In light of the limited amount of medical professionals in contrast with the rising number of people with neurological disorders; a new paradigm for addressing therapeutic strategies for neurological trauma is advocated. An important aspect for therapy of neuro-motor disorders is the characterization of gait. There are devices presently used for evaluating gait, such as EMG, optical sensors, electrogoniometers, metabolic energy expenditure devices, foot stride analyzers, and ground reaction force sensors. These devices have inherent issues, such as spatial constraints, line of sight requirements, and specialization requirements. A solution for improved autonomy of gait assessment is demonstrated by the use of fully wireless 3D MEMS accelerometers, which are light weight and minimally intrusive. To minimize specialization issues, the accelerometers may be positioned at a standard anatomical anchor. The role of traumatic brain injury with respect to gait dysfunction is addressed. Enclosed is the initial test and evaluation of a wireless 3D MEMS accelerometer for gait analysis. The gait analysis is conducted in outdoor conditions, while walking on a sidewalk.

Independent component analysis (ICA) is a technique capable of separating independent components (ICs) from complex electrocardiogram (ECG) signals. The basic intention behind using multidimensional independent component analysis (MICA) is to find stable higher dimensional source signal subspaces. This study highlights the ability of ICA for parametrization of ECG signals to reduce the amount of redundant ECG data if any in a data set.

The aim of this paper is to justify the underlying theory of the use of ICA and how it can be extended to for MICA separation of the ECG signals for combinational leads to attain most useful diagnostic information, which was not discussed in other some similar previous publications in this field.

It is also investigated that the value of kurtosis coefficients for the ICs, which represents the noise component, can be further reduced using parametrized multidimensional independent component analysis (PMICA) technique. The indeterminacies available in the ECG data are also analyzed using modified version of Jade algorithm for PMICA and parametrized standard independent component analysis (PSICA). For the ECG data set, Jade algorithm is applied first to find smaller subspaces for MICA analysis and can therefore be regarded as a basis algorithm for PMICA analysis. The simulation results are obtained in Matlab environment to indicate that, ICA can definitely improve signal–noise ratio (SNR) in minimizing the reconstruction errors.

The future scope of MICA expected by author is that, by reconsidering the notion of ICA, a more general perspective can be envisioned: i.e. modified multidimensional independent component analysis (MMICA). It would be based on a morphological geometric parametrization (MGP) which would further reduce the indeterminacies involved in matrix-based modeling (MBM).

The present theoretical investigation is based on the flow characteristics of blood in a catheterized bifurcated artery under stenotic conditions through the use of a mathematical model. The geometry of the bifurcated arterial segment having stenosis in the daughter arterial lumen frequently appearing in the diseased arteries causing malfunction of the cardiovascular system, is constructed mathematically with the introduction of suitable curvatures at the lateral junction and the flow divider. The changed flow pattern in the catheterized artery is studied by considering the pressure gradient as pulsatile in nature. The flowing blood contained in the arterial segment under consideration is treated to be Newtonian and the flow is considered to be two dimensional. The motion of the arterial wall and its effect on local fluid mechanics is not ruled out from the present study. The flow analysis applies the two-dimensional unsteady incompressible nonlinear Navier–Stokes equations for Newtonian fluids. The resulting nonlinear differential equations together with the boundary conditions following the radial coordinate transformation are solved numerically by adopting a finite difference scheme. An extensive quantitative analysis is performed at the end of the paper in order to estimate the effects of the catheter, the wall distensibility, the stenosis and the viscous dissipation of blood in the flow characteristics of the blood stream and the wall shear stress so as to validate the applicability of the present mathematical model. Some of the several important findings of the present investigation discussed at length include the changing pattern of the flow-field in the parent aorta, the occurrence of back flow at and beyond the apex with the formation of several flow separation zones, and the generation of higher wall shear stresses on the inner wall than on the outer wall surface owing to the arterial catheterization. The arterial catheterization does influence the viscous dissipation more remarkably in the parent duct till its apex than in the branch arteries.

The general author's mesomechanical concept is applied to constitutive modeling of rheological behavior of human blood. The thermomechanical properties of blood are very complicated and their mathematical modeling — although studied for many years — deserves still attention, as phenomenological descriptions do not seem to achieve the due generality and accuracy. Our mesomechanical approach is rooted within the mesoscale description of the substructure of erythrocyte aggregates and their changes in the course of different time-dependent loading paths. Good agreement of the outcomes of our model with experimental findings received under complicated conditions corroborates the usefulness of this approach.

Quality of bone tissue deteriorates with age and disease. Mechanical techniques that evaluate properties of cadaver bone help in understanding mechanisms behind aging and disease and by extension in the quality assurance of engineered bone tissue. Use of inverse engineering methods help in interpreting bone properties from experimental data. Correlation of these properties to noninvasive or minimally invasive measurements aids in assessment of the quality and fracture risk of live bone tissue.

A pilot study on different age groups has shown that the removal energy dissipated per volume during the scratch may be a representative of the toughness of bone. A 3D finite element model was proposed to perform numerical simulation of bone scratch tests in order to aid in formulation of a quantitative scratch approach and assessment of in-situ properties by inverse engineering methods. Finite element modeling procedures for simulation of bone scratch test were developed. Simulation of scratch test was carried out using contact analysis. The results of finite element simulation were compared with experimental data. The simulation gave a preliminary understanding of deformation produced in the bone scratch test.

The pulsatile flow characteristics of a power law fluid in a channel filled with a homogeneous porous medium are investigated by employing the Darcy–Brinkman–Forchheimer model. Finite element method in conjunction with β-family of time discretization schemes for parabolic equation have been used to numerically solve the model for analyzing the flow. Influence of various parameters, such as power law index (n), Darcy number (Da*), Forchheimer coefficient (Γ), pulsatile amplitude parameter (A), and Womerseley parameter (α), on the flow properties have been analyzed. Increasing Γ or decreasing Da* leads to decrease in velocities and shear stress for all values of n.