Journal of Mechanics in Medicine and Biology

The temperature of body fluids is expected to affect tissues mechanical properties, including respiratory system tissues. This is because of the changes in airway smooth muscle tone and contractile properties, influencing airway frictional resistance to airflow, and because of the temperature effects on the stress–strain relationships of elastin and collagen, which determinates the elastic behavior of the lungs as reflected by their pressure–volume relationship. Alveolar surfactant biological and physical properties have also been shown to be affected by temperature changes, suggesting influences on the respiratory system hysteretic properties.

Experimental works describing the effects of body temperature variations on respiratory mechanics are reviewed, including recent findings dealing with investigations on respiratory mechanics carried out by the end-inflation occlusion method in the rat. This method allows to determine, together with the elastance of the respiratory system, its resistive properties too. In particular, both the ohmic airway resistance due to frictional forces in the airway and the additional visco-elastic resistance exerted because of tissues stress-relaxation may be quantified.

The effects of body temperature variations were assessed, and experimentally induced temperature increments and/or decrements allowed to conclude that respiratory system tissues stiffness, both the ohmic and the stress-relaxation linked resistances, and the hysteretic behavior of the respiratory system, decrease with temperature increments. The mechanisms responsible for these effects are analyzed.

Local hemodynamic environment is a determinant factor in drug delivery from a drug eluting stent (DES) to the target arterial tissue. By using a simplified model of a DES, we demonstrated that if a DES had a drug release mode of uniform rate the drug released from the stent will distribute non-uniformly along the stent due to the flowing blood, with a significantly higher drug concentration at the distal part of the stent than that at the proximal one. This may explain why a DES could retard neointimal formation and vascular remodeling in downstream coronary segments. To solve this problem, we thereafter optimized the drug release mode of the DES as an exponential function. The simulation results showed that the optimized drug release mode could lead to a fairly uniform drug concentration distribution along the stent. Therefore, the present study suggested that to achieve a more effective result, optimization of drug eluting strategy (drug release mode) for the DES would be essential.

Nowadays, because of great biomedical applications of state-of-the art prototyping (bio-printing), many studies have been conducted in this field with focus on three-dimensional prototyping. There are several mechanisms for bio-printing of live cells such as piezoelectric and thermal and pneumatic inkjeting systems. Cell viability should be preserved during the bio-printing process. Lots of researches have been carried out to investigate and compare cell viability through different prototyping mechanisms. In order to quantify percentage of the cells that are killed during the proto-typing process, applied stresses on the cell and consequently its deformation should be calculated. A maximum strain energy density that the cell can tolerate is reported in the range of 25 Kj ⋅ m^-3 to 100 Kj ⋅ m^-3. This can be considered as a criteria to find the percentage of the damaged cells during the bio-printing processes. In this study, the bio-printing of the cell has been modeled and the cell viability have been investigated. Firstly, it is shown that in modeling of the bio-printing process, the effects of dynamic flow on calculating the applied stress on the cell is not negligible and must be considered. In the next step, the percentage of damaged endothelial cell aggregate under 80 kPa applied pressure (64 MPa/m) and 200 micron nozzle diameter is reported. Based on findings of this study, the percentage of endothelial cells viability under mentioned condition is reported 76%. The proposed method of this study can be utilized to examine the cell viability and performance of each prototyping systems.

The auditory peripheral system, which takes care of collection and enlargement in hearing processing, is an important part of the overall auditory system. This system is the key of sound source identification and location, and an important basis for a variety of audio equipment design and sound quality evaluation. In order to better recognize the acoustic characteristics of the auditory peripheral system, and effectively guide the audio equipment design as well as the sound quality evaluation, this study presents a numerical model based on the finite element/infinite element method (FEM/IFEM) to compute the near-field head-related transfer function (HRTF) on a reversed head model. A spherical sound source is positioned at different locations in the horizontal, median and lateral planes. The HRTFs and sound field distributions are computed for a frequency range up to 6 kHz. The present model is qualitatively validated against experimental data from MIT database. The results confirm the potentiality of the proposed approach which can efficiently detect the diffraction region, diffraction angle and tails in the sound field.

Cell adhesion to the extracellular matrix is accomplished by the clustering of receptor–ligand bonds into focal contacts on the cell-substrate interface. The contractile forces applied onto these focal contacts lead to elastic deformation of the surrounding, which results into a cellular mechanosensory capability that plays a key role in cell adhesion, spreading, and migration, among many others. The mechanosensitivity can be manipulated by the substrate anisotropy, by which focal contacts may align into certain directions so to minimize the total mechanical potential energy. Using the elastic anisotropic contact analysis, this work systematically analyzes the dependence of the alignment on the elastic anisotropy, and more importantly, the direction of the inclined contractile forces. The contact displacement fields are a complex function of the elastic constants, so simple analysis based on tensile or shear softest direction cannot properly predict the alignment orientation. It is also proved that if these focal contacts are of elongated shape, the major axis will be parallel to the alignment direction.

In biological and artificial adhesive systems, the lowest-scale unit is oftentimes the adhesive contact between a mushroom-shaped fiber and the surrounding material. Contact mechanics analysis in literature suggests that such a shape leads to more uniform interface stress, and thus a more superior adhesive performance, than the cylindrical fiber. In this work, we prove that this concept only works in the limit of linear elastic fracture mechanics (LEFM). When the interface behavior has a large crack bridging zone, de-adhesion occurs more easily in the center of mushroom-shaped indenter and the pull-off force becomes lower than that of cylindrical fiber. Combining the analysis of stress intensity factor and crack bridging characteristics, and tuning the substrate by a layered structure, we have established design rules that can significantly widen the parametric space in which the mushroom-shaped indenter enhances the bio-adhesive performance.

Human neuroblastoma (SH-SY5Y) cells, with its ability to differentiate into neurons, have been widely used as the in vitro cell culture model for neuroscience research, especially in studying the pathogenesis of Parkinson's disease (PD) and developing therapeutic strategies. Cellular elasticity could potentially serve as a biomarker to quantitatively distinguish undifferentiated and differentiated SH-SY5Y cells. The goal of this work is to characterize the retinoic acid (RA) induced alternations of elastic properties of SH-SY5Y cells using atomic force microscopy (AFM). The elasticity was measured at multiple points of a single cell. Results have shown that the differentiation of SH-SY5Y cell led to a larger elastic modulus, which is three times more than that of undifferentiated cells. A higher indentation rate applied during AFM measurements led to a larger elastic modulus of the cell. This work provides new insights into the differentiation process identified by the elasticity marker, which could be extended to investigate the function, health and ageing of cells.

Plastic deformation and wear of the ultra-high molecular weight polyethylene (UHMWPE) insert have been pointed out as major issues relating to the long-term stability of an orthopaedic implant. The deposition of protective hard, tough and well-adhered zirconia (ZrO₂) thin films directly on the surface of the UHMWPE component via the Pulsed Plasma Deposition (PPD) technique has been already demonstrated to be a feasible way to approach this problem. In the current study, the tribo-mechanical properties of ZrO₂-coated UHMWPE with respect to pristine UHMWPE were investigated in detail. Specifically, strength to local plastic deformation, indentation work portioning and creep behavior were evaluated through nanoindentation and micro-scratch tests. Further, preliminary wear data (i.e., rate and volume) were obtained by tribology tests mating coated and pristine UHMWPE with an alumina ball under dry conditions. The results of the mechanical tests evidenced a strong reduction of plastic deformation under both normal and tangential local loads and a drop of the 80% of the creep phenomenon for coated UHMWPE compared to pristine UHMWPE. Despite tribological tests showed similar wear data for coated and pristine UHMWPE, a different wear mechanism was detected between the two groups. The reported results supported the possibility to pursue this novel approach of depositing ZrO₂ thin film to protect the UHWMPE insert and enhance the long-term stability of the orthopaedic implants.

Bioconvection flow of non-Newtonian nanofluids along a horizontal flat plate in a porous medium saturated with gyrotactic microorganisms is investigated by combined group similarity numerical technique. A linear group of transformations is used to develop similarity transformations and the corresponding similarity equations of the governing coupled, nonlinear ordinary differential boundary layer transport equations. The resulting nonlinear boundary value problem with appropriate boundary conditions is solved numerically by an MAPLE software algorithm. The effects of the controlling parameters on the flow, heat, nanoparticle concentration and the density of motile microorganisms characteristic as well as on the local Nusselt, Sherwood and the motile microorganism numbers have been examined. It is found that the bioconvection parameters have strong effects on the flow, heat and mass transfer and motile microorganism numbers. The present study finds application in microbial fuel cells.

The Adomian decomposition method (ADM) is applied to analyze Newtonian bio-magneto-tribological squeeze film flow with magnetic induction effects incorporated. Robust solutions are developed for the transformed radial and tangential momentum and radial and tangential induced magnetic field conservation equations. The effects of squeeze Reynolds number (N₁ = Re_m/Bt where Bt = Batchelor number), dimensionless axial magnetic force strength parameter (N₂), dimensionless tangential magnetic force strength parameter (N₃), magnetic Reynolds number (Re_m) are depicted graphically. ADM is observed to demonstrate excellent convergence, stability and versatility in simulating both magnetic squeeze film problems. Numerical verification is achieved with Nakamura's tridiagonal finite difference method (NTM). The simulations are relevant to "smart" biological bearings and prosthetics (e.g., "smart knees") exploiting magnetic fluids.

Biofabrication technologies involve the incorporation of living cells into various bioproducts by employing different cell manipulation techniques. Among them, bioprinting, delivering cell suspension through a fine needle under pressurized air, has been widely used because of its capability of precise process control. In the cell-printing process of bioprinting, cells are exposed to fluid stresses due to the velocity gradient in the fine needle. If the stresses exceed a certain level, the cell membrane may be overstretched, leading to membrane failure and thus causing mechanical cell damage. Modeling the mechanical cell damage in the bioprinting process is a challenging task due to the complex fluid flow and cell deformation involved. This paper introduces a novel method based on computational fluid dynamics (CFD) to represent the mechanical cell damage in the bioprinting process using a conical needle. Specifically, the cell deformation and movement during the cell-fluid interaction processes were represented by the immersed boundary method (IBM). A strain energy density (SED)-based cell damage criterion was developed and used to determine cell damage. Experiments were performed by using 3T3 fibroblasts and the results agree well with the proposed model.

Composition-structure-property relations of bone provide fundamental understanding of bone quality. The objective of this paper was to investigate age dependent changes in the composition, structure and mechanical properties of porcine femoral cortical bone at mid-diaphysis region from six age groups (1, 3.5, 6, 12, 30, 48 months). This study was motivated by the fact that limited data is available in the literature on young porcine cortical bone. Nanoindentation technique with Berkovich fluid cell tip was employed to measure the elastic modulus and hardness. Individual lamellae were indented in the longitudinal direction of bone in different microstructural components (osteonal, interstitial and plexiform bone). A grid of indentations was also made on one bone sample to obtain spatial variations in the elastic modulus and hardness. Ash and water content tests were performed to measure water, organic and mineral contents of bone as a function of age. Finally, high resolution micro-computed tomography was used to measure porosity and visualize three-dimensional void structures. We found that the elastic modulus and hardness of bone increased with age but at different rates in each microstructural component. The mineral content increased correspondingly with age while the porosity decreased. The obtained structure, composition, and mechanical properties data give new insights on the age related changes in young cortical bone and can serve as inputs for and validation of multiscale models of bone.

The walls of the blood vessels involved with cerebral aneurysms present different mechanical properties, when compared with those of normal artery. Consequently the models which may describe then predict an aneurysm rupture need as input their mechanical properties. This paper describes the experimental determination of the mechanical properties of the tissues of the blood vessels affected with a cerebral aneurysm. In particular, we determine and discuss the critical elongation and the rupture strength. The affected tissues were obtained from surgical clipping and extraction; six specimens were tested. The mechanical tests were performed in a tensile device. The experimental data was fitted numerically with a Mooney–Rivlin hyper elastic model. The model was compared with previous published data.

The aim of our work is the segmentation of healthy and pathological brains to obtain brain structures and extract strokes. We used real magnetic resonance (MR) images weighted on diffusion. The brain was isolated, and the images were filtered by an anisotropic filter, and then segmented by support vector machines (SVMs). We first applied the method on synthetic images to test the performance of the algorithm and adjust the parameters. Then, we compared our results with those obtained by a cooperative approach proposed in a previous paper.

The mechanical properties of cells are important in regulation of many aspects of cell functions. The cell may respond differently to a 2D plate and a 3D scaffold. In this study, the finite element analysis (FEA) was adopted to investigate mechanical deformation of chondrocyte on a 2D glass plate and chondrocyte seeded in a 3D scaffold. The elastic properties of the cell differ in these two different compression tests. This is because that the cell sensed different environment (2D plate and 3D construct) which can alter its structure and mechanical properties. It reveals how the apparent Poisson's ratio of a cell changes with the applied strain depends on its mechanical environment (e.g., the elastic moduli and Poisson's ratios of the scaffold and extracellular matrix) which regulates cell mechanics. In addition, the elastic modulus of the nucleus also plays a significant role in the determination of the Poisson's ratio of the cell for the cells seeded scaffold. It also reveals the intrinsic Poisson's ratio of the cell cannot be obtained by extrapolating the measured apparent Poisson's ratio to zero strain, particularly when scaffold's Poisson's ratio is quite different from the cell.

The principle of this study is experimental measurement and description of behavior of transpedicular fixation during cyclic loading due to convergence of screw insertion. Investigations were made of three configurations of assemblies of posterior stabliization with converging screws at 0°, 20° and 40°. The experiment was inspired ASTM Standard F1717 and modified to minimize the effect of other parameters. The MTS 858.2 Mini Bionix testing system was used during the experiment, in conjunction with the Interface 1010ACK load cell. Data processing and analysis were carried out by Matlab R 20102b, MathWorks. The probed assemblies were cyclically loaded until structural failure occurred, always at the screwbone (or PUR block) interface, i.e., the "windshield wiper" effect. The measurement results show that while the rigidity of the assembly increases with increased convergence of transpedicular screws, they also indicate an increased initial rate of assembly damage accumulation, together with assembly failure during a reduced number of cyclic loading cycles. The mechanical behavioral study of transpedicular fixation is limited by the conditions of simplification of interpretation of complex movements and spinal pathophysiology in the attempt to minimize the effect of other parameters and exaggerated measurements.

Deviation of a needle from its intended path can be minimized by using a robotic device to steer the needle towards its target. Such a device requires information about the interactions between the needle and soft tissue, and this information can be obtained using finite element (FE) analysis. In this study, we present an FE analysis that integrates the Johnson–Cook damage model for a linear elastic material with an element deletion-based method. The FE analysis is used to model a bevel-tipped needle interacting with gel. The constants for the damage model are obtained using a compression test. We compare simulation results with experimental data that include tip–gel interaction forces and torques, and three-dimensional (3D) in situ images of the gel rupture obtained using a laser scanning confocal microscope. We quantitatively show that the percentage errors between simulation and experimental results for force along the insertion axis and torque about the bevel edge are 3% and 5%, respectively. Furthermore, it is also shown qualitatively that tip compression is observed at the same locations in both experimental and simulation results. This study demonstrates the potential of using an FE analysis with a damage model and an element deletion-based method to accurately simulate 3D gel rupture, and tip–gel interaction forces and torques.

This study set out to investigate if a relationship exists between weight change and changes in 3D acceleration signals associated with walking. In addition to giving biomechanical information, this relationship could be applied in conjunction with new weight management solutions to address the excess weight problem currently plaguing the world. The study was conducted with 15 subjects. For a period of two months, they were weighed every morning and carried a 3D accelerometer during the working day. Daily accelerometric signals were recorded and signals recognized as walking were analyzed. To obtain information in a more controlled situation and higher weight change, a separate follow-up study was carried out involving one test subject performing controlled walking exercises. Our results show that a relationship does exist between weight change and 3D acceleration signals. The obtained correlation coefficient between weight change and the acceleration-related parameter was 0.21 for the combined result of all test subjects (n = 147, p = 0.01). Higher correlations were recorded for individual subjects (r = 0.97, p < 0.001). Also the follow-up with controlled walking exercises showed a high correlation (r = 0.89, p < 0.001). On the other hand, statistically significant results were not obtained for all subjects, and identical signal parameters did not always produce similar results.

A method for automatic classification of Arrhythmias from Electrocardiogram based on features generated from a new Continuous Wavelet Transform (CWT) is presented in this paper. The classification performance was studied using the most commonly available database, the MIT-BIH arrhythmia database. The new wavelet for classification was evolved using Genetic Algorithm (GA). The optimum wavelet for classification was obtained after several runs of the GA algorithm. The class labeling was followed according to the Association for the Advancement of Medical Instrumentation (AAMI). The wavelet scales corresponding to the different frequency levels giving maximum classification performance was identified. Probabilistic Neural Network (PNN) classifier was used for classification. The proposed classification system offered an overall sensitivity of 97% for Normal beats (N), 75% for Supraventricular beats (S_v) and 93% for Ventricular beats (V) which is better than existing results reported in literature. This technique could exclusively identify some of the isolated abnormalities compared to other results reported.

We consider the problem of electrocardiogram (ECG) denoising using source separation. In this study, a hybrid technique using empirical mode decomposition (EMD) and source separation, is proposed. This technique consists of two steps, the first step consists in applying the EMD to two different mixtures. These mixtures are obtained by corrupting in additive manner, the same ECG signal by a white Gaussian noise with two different values of the signal-to-noise ratio (SNR). The second step consists in computing the entropy of each obtained intrinsic mode function (IMF) and finds the two IMFs having the minimal entropy. These two IMFs are used to estimate the separation matrix of the ECG signal from noise by using the source separation. The proposed technique is evaluated by comparing it to the denoising technique based on source separation in time domain using runica and the technique based on Bionic wavelet transform (BWT) and also using source separation. The obtained results from SNR and the mean square error (MSE) computations, show that the proposed technique outperforms the other two techniques used in this evaluation.

This paper deals with growth control of cancer cells population using type-1 and interval type-2 fuzzy logic. A type-1 fuzzy controller is designed in order to reduce the population of cancer cells, adjust the drug dosage in a manner that allows normal cells re-grow in treatment period and maintain the maximum drug delivery rate and plasma concentration of drug in an appropriate range. Two different approaches are studied. One deals with reducing the number of cancer cells without any concern about the rate of decreasing, and the other takes the rate of malignant cells damage into consideration. Due to the fact that uncertainty is an inherent part of real systems and affects controller efficacy, employing new methods of design such as interval type-2 fuzzy logic systems for handling uncertainties may be efficacious. Influence of noise on the system is investigated and the effect of altering free parameters of design is studied. Using an interval type-2 controller can diminish the effects of incomplete and uncertain information about the system, environmental noises, instrumentation errors, etc. Simulation results confirm the effectiveness of the proposed methods on tumor growth control.

Natural selection, survival of the fittest. Through millions of years' evolution, shark has become one of the fastest swimming animals in the ocean, and it is very well-known for sharkskin effect, especially for "sharkskin swimsuit". Due to its great superior properties in drag reduction, anti-wear, self-cleaning and so on, the investigations on the essential mechanisms and fabricating methods have attracted so much attention from all over the world, and the achievements have been widely put into application in industry, agriculture, transportation, airspace and so on, and so lots of profits have been obtained so far. In this paper, the method of fabricating artificial composite drag reduction surface based on biological sharkskin morphology and mucus nano-long chain is investigated and studied, the chemical, mechanical and hydrodynamic properties are explored from different aspects in depth, in which, the experimental results in water tunnel showed that the drag-reducing efficiency could surpass 20% with the smooth skin as reference, and the drag reduction mechanism is systematically explained and discussed from different aspects, which has important significance to understand the recent research status and expand the applications of sharkskin in the fluid engineering.

Diabetes affects retinal structure of a diabetic patient by generating various lesions. Early detection of these lesions can avoid the loss of vision. Automation of detection process can be made easily feasible to masses by the use of fundus imaging. Detection of exudates is significant in diabetic retinopathy (DR) as they are earlier signs and can cause blindness. Finding the exact location as well as correct number of exudates play vital role in the overall treatment of a patient. This paper presents an algorithm for automatic detection of exudates for DR. The algorithm combines the advantages of supervised and unsupervised techniques. It uses fuzzy-C means (FCM) segmentation on coarse level and mahalanobis metric for finer classification of segmented pixels. Mahalanobis criterion gives significance to most relevant features and thus proves a better classifier. The results are validated using DIARETDB0 and DIARETDB1 databases and the ground truth provided with it. This evaluation provided 95.77% detection accuracy.

Computational fluid dynamics (CFD) is an excellent computational tool to assess the hemodynamics and detailed blood-flow structure for cardiovascular applications. Modeling turbulence for cardiovascular applications can be achieved (to some extent) using available numerical models such as Reynolds average Navier–Stokes (RANS), the large eddy simulation (LES) and the direct numerical solution (DNS). In order to develop an efficient model which is as accurate as DNS and as quick as RANS, our laboratory's focus is on LES. In this study, we develop an efficient numerical model which is based on LES and structured but non-orthogonal finite volumes. Using the proposed model, the detailed flow structure and turbulent features of the blood stream in a complicated geometry is captured. The aim of this study is to model blood-flow through an eccentric stenosis accurately and quickly. The results are similar to those obtained using DNS but in a fraction of the CPU time. The computational tools implemented in this study are based on a FORTRAN based in-house code coupled with parallel computing using SHARCNET. The developed model is a significant computational tool which can be used to assess the hemodynamic properties for cardiovascular applications, e.g., prosthetic heart valves and atherosclerosis.

Impaired balance is one of the most disabling multiple sclerosis (MS) symptoms. It is known that, in the presence of predictable perturbations, the central nervous system (CNS) utilizes both anticipatory (APAs) and compensatory (CPAs) postural adjustments to maintain balance. The main purpose of this study was to investigate the relationship between APAs and CPAs during self-induced postural perturbation in patients with MS. Participants performed a load release task while standing on a force platform. Electrical activity of six leg and trunk muscles, as well as displacements of the center of pressure (COP), was recorded. The results revealed significant APAs deficits in MS patients reflected in short APAs duration and reduced magnitude. The reduced APAs were not accompanied by significant compensatory muscle activity. It can be concluded that there is an impairment of feed-forward postural control in MS, and feedback-based mechanisms (CPAs) are unable to compensate for these APA deficits. These results should be considered in the rehabilitation programs for balance training of MS patients.

In magnetic fluid hyperthermia (MFH), nanoparticles are injected into a diseased tissue and then subjected to an alternating high frequency magnetic field. The produced heat may have a key asset to destroy the cancerous cells. The blood flow in a tissue is considered as the most complicated part of the MFH which should be taken into account in the analysis of the MFH. This study was aimed to perform an experimental study to investigate the heat transfer of agar gel which contains fluid flow. Fe₃O₄ as a nanoparticle was injected into the center of a cylindrical gel. It was also embedded with other cylindrical gels and subjected to an alternating magnetic field of 7.3 (kA/m) and a frequency of 50 (kHz) for 3600 (s). The temperature of the gel was measured at three points. The temperature distribution was measured via the experimental data. Moreover, specific absorption rate (SAR) was quantified with time differential temperature function at t = 0 by means of experimental data. Finite element method (FEM) was employed to establish a model to validate the SAR function. Results revealed the effects of fluid flow and accuracy of the SAR function for heat production in gel. The proposed function have implications in hyperthermia studies as a heat generation source. Finally, the condition of experimental setup was simulated to find the blood perfusion.

Atherosclerosis is a world-spread and well-known disease. This disease strongly relates to the endothelial cells (ECs) function. Normally, the endothelial cells align in the flow direction in the atheroprotected sites; however, in the case of atheroprone sites these cells orient randomly. The mechanical stimuli such as wall shear stress and strains could determine the morphology and function of the endothelial cells. In the present study, we numerically simulated the left main coronary artery (LCA) and its branches to left anterior descending (LAD) and left circumflex coronary (LCX) artery using fluid–structure interaction (FSI) modeling. The results were presented as longitudinal and circumferential strains of ECs as well as wall shear stress. Wide ranges of heart rate, cardiac motion, systolic and diastolic pressures were considered and their effects on mechanical stimuli were described in detail. The results showed that these factors could greatly influence the risk of atherosclerosis and the location of atherosclerotic lesions.