Journal of Mechanics in Medicine and Biology

Nanoindentation is an (almost) non-invasive method for obtaining material properties of different types of materials from the interpretation of experimental data related to indenter load (P) and penetration depth (h). In most cases, the material properties that are obtained by nanoindentation are elastic modulus (E), shear modulus (G) and hardness (H). The main advantages of this method are that no extensive preparation of the test specimen is required and that the mechanical properties can be probed at small scales. Moreover, nanoindentation test procedure is automated and the test equipment is easy to use. In this paper, we review different analytical methods that could be used for obtaining the mechanical properties of biomaterials based on the force-displacement curves generated by nanoindentation machines. Some practical issues including different types of machines and tips, calibration of nano-indentation machines, sources of error and specimen preparation are also briefly discussed. The main interest of this paper is the elastic behavior of biological tissues and biomaterials. Nevertheless, there is one section on elasto-plasticity, because purely elastic deformation of linearly elastic materials is difficult to achieve. The analytical solutions found in the literature for different material models are presented including the relationships found for linear elastic, elasto-plastic, hyperelastic, viscoelastic and poroelastic materials. These material models are relevant material models for studies of biological tissues and biomaterials.

Fluid dynamics, especially forces and velocity distribution, influence the development of plaques. Flow parameters: pulsatility, the non-Newtonian flow behavior of blood and wall elasticity are considered. Flow visualization techniques (dyes and birefringent solution with a photo-elasticity apparatus) and LDA measurements demonstrate the importance of the flow. Accurate in vivo velocity measurements are necessary to calculate shear stresses. Different bifurcation angles and flow rate ratios were tested in true to life artery models. The most important fluid dynamic factors at bifurcations are the flow rate ratio and the geometry which create flow separation regions which are responsible for platelet aggregation and intima damage. It is necessary to measure all three velocity components to calculate the velocity vector. The highest shear stresses in a healthy carotid artery are 16 Pa and are found just at the apex. In artery models with 90% stenosis, shear stresses up to 250 Pa were found. Distally, vortices were created where particles remained over several pulse cycles. Measurements show that stents must be selected carefully and placed precisely. Filters must be closed during the systolic phase before removal, so that no trapped particles can escape.

Although rarely discussed, material modeling of the myxomatous leaflet is considered as the cornerstone of mitral valve finite element analysis. The present study presents an incompressible, hyperelastic constitutive model to characterize myxoid mitral leaflet tissue mechanics. The model incorporates the transversely isotropic response and the layered structure of the tissue. First, an analytical constitutive model for the tissue is developed based on continuum mechanics and layered composites theory. Second, the material constants of the constitutive equation are determined by fitting the model to the experimental data. The analytical material model is then implemented using solid finite element methods by simulating a biaxial tensile test. A numerical simulation of the out-of-plane pressure loading is also conducted. Both the analytical outcomes and the simulated results agree well with experimental data and show good mutual agreement. The calculated strain distribution of the out-of-plane pressure loading simulation indicates myxoid leaflets exhibit enhanced extensibility and decreased stiffness compared to normal valves; the radial direction is more extensible than the circumferential direction. The presented material approximation is able to capture the myxomatous mitral leaflet mechanics. The results of the numerical simulation conform to those of the experimental tests.

This study addressed side asymmetry between human lower limb long bones.

A multiscale approach was taken to investigate differences between contralateral femurs, tibias and fibulas, at body-level (total-body CT-scans, anatomical dissection), organ-level (volume and moments of areas; structural stiffness and strain distribution in bending and torsions) and tissue-level (mineral density, elastic modulus, hardness).

Because of the large amount of measurements taken, the study was limited to two donors. However, high statistical power within the same donor was achieved thanks to a large number of highly-repeatable measurements. Muscle cross-sections suggested that both donors were right-legged. The right bones had higher structural stiffness (up to +115%, statistically significant, except for the tibia). The right bones also experienced generally lower strain than the contralateral ones (up to -25%, statistically significant). The right bones had larger volume (up to +16%) and moments of area (up to +116%, statistically significant in most cases) than the left ones. Difference in tissue density between contralateral bones (< 7%) was not statistically significant in most cases. Also the differences found in elastic modulus of the femur cortical tissue (2–5%) were not statistically significant. Similarly, tissue hardness in the right bones was only marginally higher than in the contralateral ones (+1% to +4%, not statistically significant). Therefore, it seems that structural differences between contralateral bones associated with laterality are mainly explained by differences in bone quantity (volume) and organization (area moments). Bone tissue quality (density, hardness) seems to give a marginal contribution to structural side asymmetry.

The primary renal arteries transport up to one fourth of cardiac output to the kidneys for blood plasma ultrafiltration, with a functional dependence on the vessel geometry, composition and mechanical properties. Despite the critical physiological function of the renal artery, the few biomechanical studies that have focused on this vessel are either uniaxial or only partially describe its bi-axial mechanical behavior. In this study, we quantify the passive mechanical response of the primary porcine renal artery through bi-axial mechanical testing that probes the pressure-deformed diameter and pressure-axial force relationships at various longitudinal extensions, including the in-vivo axial stretch ratio. Mechanical data are used to parameterize and validate a structure-motivated constitutive model of the arterial wall. Together, experimental data and theoretical predictions of the stress distribution within the arterial wall provide a comprehensive description of the passive mechanical response of the porcine renal artery.

This work investigates the effect of eardrum perforations and myringosclerosis in the mechanical behavior of the tympano-ossicular chain. A 3D model for the tympano-ossicular chain was created and different numerical simulations were made, using the finite element method. For the eardrum perforations, three different calibers of perforated eardrums were simulated. For the micro perforation (0.6 mm of diameter) no differences were observed between the perforated and normal eardrum. For the numerical simulation of the eardrum with the largest perforation caliber, small displacements were obtained in the stapes footplate, when compared with the model representative of normal ossicular-chain, at low frequencies, which is related with major hearing loss in this frequency range. For the numerical simulations of myringosclerosis, the larger differences in the displacement field between the normal and modified model were obtained in the umbo. When observing the results in the stapes footplate, there were no significant differences between the two models, which is in accordance to the clinical data. When simulating an eardrum perforation along with myringosclerosis, there is a decrease in the displacements, both from the umbo and the central part of the stapes footplate, often associated with a pronounced hearing loss. It could be concluded that the reduced displacement of the stapes footplate may be related to a greater hearing loss.

Electroencephalography (EEG) is a measure which represents the functional activity of the brain. We show that a detailed analysis of EEG measurements provides highly discriminant features which indicate the mental state of patients with clinical depression. Our feature extraction method revolves around a novel processing structure that combines wavelet packet decomposition (WPD) and non-linear algorithms. WPD was used to select appropriate EEG frequency bands. The resulting signals were processed with the non-linear measures of approximate entropy (ApEn), sample entropy (SampEn), renyi entropy (REN) and bispectral phase entropy (Ph). The features were selected using t-test and only discriminative features were fed to various classifiers, namely probabilistic neural network (PNN), support vector machine (SVM), decision tree (DT), k-nearest neighbor algorithm (k-NN), naive bayes classification (NBC), Gaussian mixture model (GMM) and Fuzzy Sugeno Classifier (FSC). Our classification results show that, with a classification accuracy of 99.5%, the PNN classifier performed better than the rest of classifiers in discriminating between normal and depression EEG signals. Hence, the proposed decision support system can be used to diagnose, and monitor the treatment of patients suffering from depression.

Whole body vibration affects neuromuscular systems through the stimulation of receptors in muscles and tendons. This study investigated the acute effects of different training intensities of WBV on knee joint proprioception. A total of 18 untrained males participated in this study. Joint position sense was tested as an index of joint proprioception ability. Frequencies of 20, 35, and 50 Hz with two mm of displacement vibration training were tested. Each frequency was tested in different numbers of sets (four, six, eight, and ten sets). As it turned out, the results indicated a significant improvement in active JPS at 35 Hz for all testing sets, and only at 20 Hz with ten sets. As for passive JPS, significant improvements were obtained only at 35 Hz with ten sets of training. WBV training affected knee joint proprioception in active JPS with shorter vibration exposure at lower frequencies and amplitude. Coaches, athletes and physical therapists should consider using WBV training for its potential benefits in warm-ups and rehabilitation.

This study presented optimal estimation of total plantar force with a suitable sensor layout and a reliable equation for monitoring gait in daily life activities. The plantar pressure of 10 subjects during level walking was measured by Pedar^® insoles at 100 Hz for establishing models and selecting the optimal one. Four types of virtual sensors with different sizes were designed. Stepwise linear regressions were performed to reconstruct total plantar force based on each particular type of virtual sensor. 14 models were established, which met the requirements of the explained variance of the regression model and the multicollinearity of the predictors. Estimated total plantar force from each model was compared with the real data from the Pedar^® insoles. According to the correlation coefficient (R) and the root mean square error divided by the peak force (RMSE/PF), the optimal model had three sensors located under the heel and metatarsal. Another four subjects were used for validating the optimal model by performing level walking, running, vertical jump-landing, stair ascending and descending. For these five common activities, the correlation was high (R > 0.970) and the error was low (RMSE/PF < 10%). Therefore, this model can accurately estimate total plantar force in daily life activities.

Various designs of cervical total disc replacement (CTDR) have been introduced and employed in an attempt to avoid disadvantages of the fusion surgery. The purposes of this study were to evaluate the effects of the range of motion (ROM), the instantaneous center of rotation (ICR) and the facet joint force (FJF) with different constrained types of CTDR devices. A three-dimensional finite element (FE) model of intact cervical spine (C3-7) was made from CT scans of a normal person and validated. Postoperative FE models simulating CTDR implantation at the C5-6 disc space were made for CTDR-I (constrained design) and CTDR-II (nonconstrained design), respectively. Hybrid protocol (intact: 1 Nm) with a compressive follower load of 73.6 N was applied at the superior endplate of the C3 vertebral body. The inferior endplate of C7 vertebral body was constrained in all directions. At the index level, CTDR-I showed a higher increase in segmental motion and FJF than CTDR-II in extension, lateral bending and axial rotation. The CTDR-II with an elastomer-type core reproduced a near physiological ICR of the intact model in extension and axial rotation. Abnormal kinetic and kinematic changes related to the CTDR may induce surgical level problems and cause long-term failure of spinal surgery.

Laminar magnetohydrodynamic Marangoni-forced convection boundary layer flow of a water-based biopolymer nanofluid containing nanoparticles from a non-isothermal plate is studied. Magnetic induction effects are incorporated. A variety of nanoparticles are studied, specifically, silver, copper, aluminium oxide and titanium oxide. The Tiwari–Das model is utilized for simulating nanofluid effects. The normalized ordinary differential boundary layer equations (mass, magnetic field continuity, momentum, induced magnetic field and energy conservation) are solved subject to appropriate boundary conditions using Maple shooting quadrature. The influence of Prandtl number (Pr), magnetohydrodynamic body force parameter (β), reciprocal of magnetic Prandtl number (α) and nanofluid solid volume fraction (φ) on velocity, temperature and magnetic stream function distributions is investigated in the presence of strong Marangoni effects (ξ i.e., Marangoni parameter is set as unity). Magnetic stream function is accentuated with body force parameter. The flow is considerably decelerated as is magnetic stream function gradient, with increasing nanofluid solid volume fraction, whereas temperatures are significantly enhanced. Interesting features in the flow regime are explored. The study finds applications in the fabrication of complex biomedical nanofluids, biopolymers, etc.

The work presented in this paper deals with the description of an analytic modeling of the neuromusculoskeletal system responsible for the finger movement. This simulation task is complex due to the interacting processes (physiological and biomechanical) represented by muscles, joints and bones. In this study, we focused on the presentation of a complete model for the finger motion decomposed in quasi-static positions. In fact, this model can be considered as a preliminary step before dynamic modeling. The proposed model is composed of several compartments: biomechanical finger model, mechanical muscle model and muscle/neural activation model. The main objective of this study is to estimate, by inverse procedure, the muscle forces, muscle activations and neural activations that are responsible for generating a given finger movement decomposed in successive quasi-static positions. The anatomical model contains six muscles which control the decomposed movement of the three joints of the system. To estimate the model unknowns, an optimization technique is proposed for improving robustness to initial conditions and physiological reliability. After, an experimental protocol for recording surface electromyogram (sEMG) data, from three extrinsic muscles, according to specific finger positions is applied on five subjects to evaluate the model reliability.

From analysis of the obtained results, both in simulation and experiment, the presented model seems to be able to mimic, in a realistic way, the finger movement decomposed in quasi-static positions. Finally, results, model limitations and further developments are discussed.

The estimation of the hip joint contact stresses and contact pressure distribution during stumbling activities is a critical task for selecting the best material pair in the hip prosthesis design. This paper utilizes a three-dimensional finite element model of acetabular component to analyze the dynamic stumbling activity using ANSYS^®. The present study investigates the maximum von Mises stress, contact pressure and deformation developed for different combinations of materials under the stumbling load condition. The different combination of bearing couplings considered for the analysis are metal in contact with plastic, metal on metal, metal on ceramic, ceramic on plastic, ceramic on metal and ceramic on ceramic combinations. The results concluded that the Alumina femoral head paired with ultra-high molecular weight polyethylene (UHMWPE) cup reduces the maximum von Mises stress and maximum contact pressure developed between the interface regions when compared with other combinations. The obtained results are compared with the result of Hai-bo-Jiang et al., for available combinations, and higher correlation of 92% was found between the two results.

Hemodialysis vascular access failure is related to increased morbidity and mortality in hemodialysis patients, representing a challenging clinical problem which results in a high percentage of hospital entrance and an important economic burden on government's disbursement. In this paper, the feasibility of using the needle adapter to reduce the biomechanical risk factors within arteriovenous grafts is considered. The three-dimensional (3D) tapered 6 to 8 mm loop graft in the presence of venous and arterial needles with and without adapter was numerically simulated. Navier–Stokes equations for incompressible Newtonian fluid are the governing equation of this problem. k – ω two equations turbulence modeling were applied to capture flow features of low Reynolds turbulent flow regions in this simulation. The physiological velocity waveform was used as an arterial inlet boundary condition. The venose outlet boundary condition was a time dependent physiological pressure waveform. The results for the dialysis without the adapter demonstrated that the graft wall experiences increased hemodynamic stresses as a result of the hitting needle jet flow. The dialysis with the adapter demonstrated that the venous anastomosis experiences lower biomechanical risk factors in comparison to the dialysis without the adapter and it reduced the vascular access failure. Using adapter caused less damage to endothelial cells during hemodialysis.

A mathematical and numerical study is presented for simulating temperature distribution in a two-dimensional tissue medium using Pennes bioheat transfer equation, when the tissue is subjected to ultrasonic waves. Following nondimensionalization of the governing partial differential equation, a novel variational iteration method (VIM) solution is developed. This excellent technique introduced by He [Variational iteration method — a kind of non-linear analytical technique: Some examples, Int J Non-Linear Mech.34:699–708, 1999] employs Lagrange multipliers which can be identified optimally via variational theory. The space and time distributions of temperature are studied and solutions visualized via Mathematica. The influence of thermal conductivity and relaxation time are also examined. Excellent stability and convergence characteristics of VIM are demonstrated. Validation is achieved with a Chebyschev spectral collocation method (CSCM). The present work demonstrates the excellent potential of this powerful semi-numerical method in nonlinear biological heat transfer and furthermore provides an alternative strategy to conventional finite element and finite difference computational simulations. The model finds applications in minimally-invasive spinal laser treatments, glaucoma therapy in ophthalmology and thermoradiotherapy for malignant tumors.

The progression of intimal hyperplasia is considered to be the main cause of bypass failure and is directly related to the individual blood rheology, local arterial geometry and placement of the junctions, graft diameter and graft surface characteristics as well as the degree of compliance. In this paper we use commercial computational fluid dynamics (CFD) ANSYS to examine under the correct physiological flow conditions the hemodynamic forces of composite bypass with internal mammary artery in Y-grafting and consequence grafting which is known to achieve high patency rate and highly recommended by clinicians. Particular emphasis is given here on the parameters that could initiate the development of intimal hyperplasia within these bypass configurations. The hemodynamic flow patterns between the consequence grafting and the composite Y-grafting are observed here to be different. Moreover, on both end-to-side and side-to-side configurations, the circulating flows are detected in the vicinity of the junction area, while the Dean flow vortexes are only observed on the end-to-side configuration. Likewise, the hemodynamic flow on the end-to-side configuration on the LCX of both 45° and 90° Y-grafting is found to be smoother than that of the junction on the LCA, regardless of the changing of anastomosis angles. The high WSS gradients are observed at the vicinity of the toe and on the bed of the junction, while the low WSS are presented at the distal of the stenosis and at the stagnation point. The clinical relevance of the results are presented and discussed with particular focus on the factors and the flow patterns that trigger the development of intimal hyperplasia.

Hydraulic performance is an especially important factor for maglev axial blood pumps that have been used in patients with heart disease. Most maglev axial blood pumps basically consist of a straightener, an impeller and a diffuser. The diffuser plays a key role in the performance of the maglev axial blood pump to provide an adequate pressure head and increase the hydraulic efficiency. Maglev axial blood pumps with various structural diffusers exhibit different hydraulic performance. In this study, computational fluid dynamics (CFD) analysis was performed to quantify hydrodynamic in a maglev axial blood pump with a flow rate of 6 L/min against a pressure head of 100 mmHg to optimize the diffuser structure. First, we design the prototype of diffuser structure based on traditional design method, establish blood flow channel models using commercial software ANSYS FLUENT. Specifically, compare the performance of pump with the diffusers of different parameters, such as the leading edge blade angle, blade-thickness and blade-number. The results show that the diffuser structures with the thickening blade by arc airfoil law, blade-number of 6, leading edge blade angle of 24°, and trailing edge blade angle of 90° exhibited the best hydraulic performance which could be utilized in the optimization design of maglev axial blood pumps.