Journal of Mechanics in Medicine and Biology

Purpose: The aim of this study is to explore how pedicle screws (PSs) and cortical bone trajectory (CBT) screws differ in fixation strength when implanted in L1–L5 with osteoporosis, providing support for choosing implants and trajectories in spine internal fixation surgeries. Methods: We filtered 30 lumbar segments out from CT images of eight osteoporotic participants and simulated PS or CBT screw implantation in each segment, generating 60 vertebra-screw assembly FE models. To evaluate the fixation effect, we performed a pull-out force test simulation in each model and analyzed the maximal pull-out force, pull-out stiffness, and equivalent stress of vertebrae and screws. Results: The maximal pull-out force of PS and CBT screws in L1–L5 was in the range of 905–1552 (N) and 587–1012 (N), while the pull-out stiffness was in the range of 1990–2617 (N/mm) and 1007–1681 (N/mm). The fixation strength of PS in L4 and L5 was higher ($p<0.05$), while in L1–L3 PS and CBT screws are similar ($p>0.05$). The maximal stress of vertebrae and screws when PS was pulled at 0.25mm was larger than that of CBT screws. Conclusions: For patients with moderate osteoporosis, it is recommended to insert PS into L4 and L5 to attain better fixation strength, but vertebrae are more prone to fracture. Consequently, under severe osteoporosis, the implantation of CBT screws should be considered first. Bone cement injection may be necessary to consolidate the screw-vertebrae interface with osteoporosis.

In order to analyze the mechanical properties of a new type of retrievable vena cava filter, the Denali and Aeginsy retrievable filters are selected, and the in vivo and in vitro mechanical properties of the three types of retrievable vena cava filters are compared. The nonlinear deformation process of the filter which is pressed into the transport sheath, flicked and released into the vascular vessel is simulated by using the finite element method, and the mechanical behaviors of the filter and the blood vessel wall are analyzed. During the crimping process, the elastic strain peak value of the filter wall increases with increasing amount of grip. The maximum elastic strain peak value of the three filters is less than 8%, and the safety factor is greater than 2, which meets the strength requirement. Equivalent stress and strain on the vascular wall decreases along the direction of blood flow after the filter is opened. The peak value of equivalent stress and strain on the vascular wall corresponding to Aegisy filter is the largest, and the impact on the vascular wall is the largest. The total displacement of the three filters under the action of thrombus and blood fluids is not more than 80$\mu$m. The impact of the new filter on the vascular wall is smaller than that of Aegisy filter, and the total displacement after implantation is smaller than that of Denali filter. The results are valuable for the evaluation and clinical application of the new vena cava filter.

In this paper, we evaluate the initial biomechanical properties of an anterior cruciate ligament (ACL) reconstruction technique that inverts the anatomical location of the commonly used hardware and relies the tibial fixation on the subcortical bone to increase tibial site strength. Four 7-specimen groups were tested in a porcine model: for the control ACL reconstruction technique, the femur with a cross-pin fixation supported in the trabecular bone and the tibia with a biodegradable interference screw (BIS); for the new proposed technique, the femur with a BIS and the tibia with a cross-pin fixation leaned on the tibial subcortical bone. The specimens were subjected to cyclic and load-to-failure tests to compute their biomechanical performance. At the tibia, the cross-pin fixation revealed higher resistance than the BIS ($p=0.000$ for ultimate load and $p$ = 0.006 for yield load), additionally cyclic and total displacement at representative loads showed extremely high values with BIS fixation (in two specimens greater than 9mm for 250 N and greater than 10mm for 450N). At the femur, no differences between fixations were observed. The inverted ACL reconstruction improves resistance at the tibial site with respect to the control technique, with similar resistance at the femoral site and no differences in total displacement at representative loads. It offers a useful and robust solution when greater tibial resistance is required.

The effect of sand therapy on the hemodynamics of the popliteal artery (POA) was investigated to elucidate its mechanism in atherosclerosis physiotherapy. The hemodynamic parameters of the POA before and after sand therapy were obtained from 58 subjects and statistically analyzed. A three-dimensional finite element model of POA bifurcation was established. Blood was regarded as a triple-phase flow composed of plasma, red blood cells (RBCs), and white blood cells (WBCs). Using computational fluid dynamics (CFD), blood flow velocity, wall shear stress (WSS), and blood cell volume distribution before and after sand therapy were calculated. Sand therapy could reduce the vortex and reflux in blood vessels. The maximum increase in blood axial velocity was 34.38%. The maximum WSS increased by 22.82 Pa and the blood cells gradually moved away from the vessel wall and toward the axis of the blood vessel. The reduction in vortex and reflux, and the increase in blood axial velocity after sand therapy are beneficial in reducing the accumulation of cholesterol and other substances, thereby alleviating the formation of atherosclerotic plaques and lipid streaks. The rise in WSS slows the tendency of arterial vascular thickening in regions of low WSS. The movement of blood cells to the axis of blood vessels can reduce the possibility of thrombosis caused by blood cells squeezing on the blood vessel walls. These findings suggest that sand therapy may slow atherosclerosis progression.

This work aims at the investigation of 2D, steady, laminar, viscous, incompressible boundary layer and heat transfer flow of a biomagnetic fluid over a convectively heated moving horizontal plate in the presence of a magnetic dipole. It is assumed that the fluid viscosity is the inverse linear function of temperature and the temperature at the wall varies as power law function. The governing equations involve a system of coupled PDEs (momentum and energy equations) which are converted into a system of nonlinear ODEs by utilizing similarity transformations. The transformed ODEs along with the boundary conditions are then solved numerically by adopting a finite difference algorithm. The physical effects of the governing parameters (i.e., ferrohydrodynamic interaction parameter, buoyancy force parameter, viscosity-temperature parameter, wall parameter) on the flow fields along with the skin friction and heat transfer rate are presented. Verification of this work has been done by comparing former published results and acceptable agreement is found. It has been analyzed theoretically by using suitable transformations, that the ferrohydrodynamic interaction parameter, has a great enhancement effect on biomagnetic fluid rather than that on a regular fluid. It has been discovered that the inclusion of certain intensity of magnetic field along with the consideration of the variable viscosity and temperature, has significant effects on the flow and heat transfer mechanism. These outcomes could be of interest in medical as well as bioengineering implementations, like magnetic drug delivering in blood cells, separating RBCs (Red Blood Cells), controlling the flow of blood during surgeries and treating cancer by producing magnetic hyperthermia.

Chronic kidney disease is a gradual loss of kidney function. Determining the important attributes that describe this disease plays a key role in screening and examining the disease by field specialists. The main aim of this study is to comprehensively compare the attribute selection algorithms for predicting this disease. With this aim, several models were built and compared using well-known performance metrics such as accuracy, sensitivity, and specificity in the experiments. Two different attribute selection methods; the stability selection and the minimum redundancy maximum relevance were compared comprehensively on the unbalanced and balanced datasets. In this framework, the stability selection method gave the important attributes. The support vector machines with radial bases function kernel successfully performed the classification using these attributes for this problem.

Human activity recognition (HAR) has a wide application in daily life. With wearable sensors, people’s activity can be monitored, recorded and analysed. However, most existing methods did not make full use of human activity data and their features. In this paper, a new method based on feature selection and clustering algorithm is proposed. We established two-layer classification models, respectively, in the ankle, the chest, the wrist and the mixed accelerometer data. K-means clustering algorithm was first used to obtain a broad classification of the activities and then we conducted two rounds of classification, among which feature selection was performed in each layer. A significance analysis was also carried out in the final experiment and we compared the performance of the final model from the mixed accelerometer data with other algorithms, the results showed that the recognition performance of our model was significantly better, and the average $F$1 score was as high as 0.969 in publicly available PAMAP2 dataset. Compared with other methods, our model achieved the highest recognition rate. The method proposed in this paper can greatly improve the recognition rate of human activity and effectively evaluate daily activity.

In this paper, we construct the exact solution of blood flow of Oldroyd-B fluids to represent the non-Newtonian characteristics of biofluids and to study the unsteady flow of blood and heat transfer through arterial segment with external magnetic field applied normal to the flow direction in the presence of thermal radiation and body acceleration. In the study, we investigate the influence of Caputo time-fractional parameter, heat transfer, external body acceleration, and magnetic field on the blood velocity and temperature distribution in a straight circular cylindrical vessel. The constitutive partial differential equation and temperature equation governing blood flow in the arterial wall are solved using Laplace and finite Hankel transforms. In addition, Gaver Stehfest’s algorithm is used for the inverse Laplace transform. The results obtained are interpreted graphically and discussed from the physiological point of view. The graphs show that the rate of heat transfer and blood velocity become less with the increase in the external magnetic field strength which is very good in regulating blood flow as well as temperature distribution during treatment. Based on the graphical representations, blood velocity and temperature distribution both decrease in ascending order of the fractional parameter as memory effect. Further, owing to the dissipation of energy caused by blood viscoelasticity and magnetic field effect, during pulsatile flow of blood, the heat transfer rate at the wall of the artery is enhanced. The significance of this study can be found in the application fields such as biomedical engineering, medicine and pathology.

Most human teeth have an exposed surface layer of calcified enamel, which is harder than the inner layer of dentin. The interface between the enamel and dentin is called the dentin–enamel junction (DEJ), which ensures that teeth do not collapse and fall off. The purpose of this study was to use finite element analysis software through the $J$-integral method and the extended finite element method (XFEM) to simulate three models of DEJ structures: (i) wavy DEJ with no thickness, (ii) rectangle DEJ with a thickness of 0.3mm, and (iii) wavy DEJ with a thickness of 0.3mm. This paper demonstrates that the layered structure of human teeth plays a positive role in enhancing the fracture strength and preventing the crack from spreading to the depths of teeth. At the same time, we also justify of the scalloped structure and concave orientation of the DEJ interface. The residual stresses in DEJ and its adjacent dentin region are also an important factor of tooth resistance to crack propagation. In addition, the configuration of the DEJ interface and residual stresses in DEJ and dentin areas are further justified by means of XFEM method. The findings in this study provide potential inspiration for the biomimetic design toward strengthening the dentin and dentin-like materials.

Cerebrospinal fluid (CSF) is a symmetric flow transport that surrounds brain and central nervous system (CNS). Hydrocephalus is an asymmetric and unusual cerebrospinal fluid flow in the lateral ventricular portions. This dumping impact enhances the elasticity over the ventricle wall. Henceforth, compression change influences the force of brain tissues. Mathematical models of transport in the hydrocephalus, which constitutes an excess of fluid in the cavities deep within the brain, enable a better perspective of how this condition contributes to disturbances of the CSF flow in the hollow places of the brain. Recent approaches to brain phase spaces reinforce the foremost role of symmetries and energy requirements in the assessment of nervous activity. Thermophysical and mass transfer effects are therefore addressed in this paper to quantify the transport phenomena in pulsatile hydrocephalus CSF transport with oscillating pressure variations that characterize general neurological activity and transitions from one functional state to another. A new mathematical model is developed which includes porous media drag for brain tissue and solutal diffusion (concentration) effects. A classical Laplace transform method is deployed to solve the dimensionless model derived with appropriate boundary conditions. The analysis reveals that with increasing permeability of the subarachnoid space, the CSF velocity is increased, and a significant fluid flux enhancement arises through the brain parenchyma as the pressure of the fluid escalates drastically due to hydrocephalus disorder. Stronger thermal buoyancy (Grashof number) also results in deceleration in the flow. CSF temperature is reduced with progression in time. Particle (e.g. ion) concentration is suppressed with increasing Schmidt number. As heat conduction parameter increases, there is a substantial depletion in CSF velocity with respect to time. Increasing Womersley parameter displaces the CSF velocity peaks and troughs. The present effects are beneficial in determining the thermo-fluidic transport mechanism of the pathological disorder hydrocephalus. Also, the present results are compared with those clinical studies for some cases. We have confirmed that our validity provides a decent justification with the neurological studies.