Journal of Mechanics in Medicine and Biology

In this paper, the mechanical performance of braided nitinol stents was systematically studied to provide guidelines for optimum stent designs. The influences of braiding patterns, braiding angles, wire diameters, and strand numbers on the mechanical behavior of the stent in terms of crimping strain, radial strength, longitudinal flexibility, and stability were characterized utilizing finite element method. Our results have shown that the two key design factors of braided stents are the braiding angle and wire diameter. A smaller braiding angle can increase radial stiffness and have better longitudinal flexibility and can maintain the stent stability. The wire diameter has less influence on the radial stiffness than the braiding angle, but the longitudinal flexibility is most sensitive to the wire diameter. The strand number is directly proportional to the radial stiffness and inversely proportional to the longitudinal flexibility. Compared to the classical crossing pattern, we have also proposed two patterns. These patterns have a minimal impact on the crimping and radial stiffness of stents, but the stent made from them are more flexible. Among three crossing patterns, it is interesting to see that the classical pattern is the most stable crossing pattern for stand numbers larger than 36, but it became the most unstable pattern at the strand number of 24. This work has shed light on the optimum design of braided stents.

The powered prosthesis for people with transtibial amputation offers the opportunity to more appropriately restore gait functionality with benefits, such as powered plantar flexion. In particular, various software control architectures provide unique capabilities for regulating the powered prosthesis during gait. One highly novel approach applies the winding filament hypothesis, which enables an advanced modeling of muscle characteristics, such as through introducing the attributes of titin into the muscle model. The objective of the research is to contrast the conventional control architecture of the BiOM-powered prosthesis compared with the winding filament hypothesis control architecture through machine learning classification. Four machine learning algorithms are applied through the Waikato Environment for Knowledge Analysis (WEKA): J48 decision tree, $K$-nearest neighbors, logistic regression, and the support vector machine. The feature set is derived from the force signal acquired from a force plate, which is a conventional gait analysis system. The feature set applied five attributes representing temporal and kinetic aspects of the stance phase of gait. The $K$-nearest neighbors algorithm achieves the best machine learning classification accuracy of 95%. The preliminary research establishes the foundation for more sophisticated endeavors respective of the powered prosthesis, such as determining the appropriateness of modifying the software control architecture to best accommodate the progressive lifestyle evolutions and adaptations of the person with amputation.

Background: Oral appliances for treating patients with sleep related disorders such as snoring and disturbed sleep could alter the morphology of the pharyngeal airway and thus its flow dynamics as well as airway patency. Splint therapy, i.e., positioning the mandibular condyles in centric relation (CR) with maxillary anterior guided orthotics (MAGO), with regard to pharyngeal airway patency, is causing increased attention. The goal of this work is to quantitatively examine the fluid dynamic changes within the pharyngeal airway when the mandible is positioned in CR and its association with airway patency. Materials and Methods: Patient-specific computational fluid dynamics models were reconstructed from pre- and post- treatment high-resolution cone-beam computed tomography images for two patients who had undergone MAGO therapy. The minimal cross-sectional area and total volume of the pharyngeal airway were measured in the pre- and post-treatment for a total of four models. These two subjects were chosen out of 18 patients based on the airway volume changes in pre- and post-treatment. Subject 1 had a dramatic increase in the airway volume, whereas subject 2 kept a similar airway volume following the therapy. Both subjects anecdotally reported improvement in snoring, breathing and overall sleep quality. Results: We examined three parameters, i.e., the classically defined resistance of airway in terms of pressure drop, the minimal cross-sectional area, and the pharyngeal airway volume. We also proposed a new fluid dynamic parameter: the percentage area of higher vorticity, to be correlated with the clinical efficacy of the appliance for airway patency. All four parameters could be used as index factors for subject 1 to explain the measurable clinical outcomes and the subjective report regarding quality of breathing, snoring cessation, and improvement in sleep of the patient. But only the minimal cross-sectional area and percentage area of higher vorticity could explain the clinical observations and subjective outcome in subject 2 who reported similar effects after the treatment. Conclusion: Splint therapy expanded the minimal cross-sectional area in both subjects, but did not necessarily influence the pharyngeal airway volume. The airway shape changed in terms of the percentage area of higher vorticity and the minimal cross-sectional area. Further studies are needed to assess the clinical efficacy of MAGO in reducing or eliminating the sleep-related breathing difficulties and snoring.

Entropy generation ($S_{\mathrm{\text{gen}}}$) is associated with the irreversibility of any thermodynamic system. It provides an indication of lost energy of a system. The main objective of this study is to show a method for calculating entropy generation in the human respiratory tract. In this work, human respiratory tract geometries from two different approaches are considered, first one is based on Hess–Murray theory and the second one is based on Weibel’s experimented result. The entropy generation has been calculated considering duct wall friction along with effect of bifurcation and diffusion. In this study, two different physiological conditions have been contemplated, i.e., at rest and at heavy physiological activities. It has shown that $S_{\mathrm{\text{gen}}}$ of human respiratory is lowest at 23rd level of bifurcation. The outcome of the study reveals that the entropy generation rates per day based on Hess–Murray theory at rest and under heavy physiological activities are $8.42\times 10^{-5}$kJ/K and 0.013kJ/K, whereas the same based on Weibel’s experimented result at rest and under heavy physiological activities are $0.221\times 10^{-3}$kJ/K and 0.05kJ/K, respectively.

In this study, in order to improve the accuracy of human hand motion pattern recognition, a novel pattern recognition method for optimizing the support vector machine (SVM) by using a cloud adaptive quantum chaos ions motion optimization (AQCIMO-SVM) algorithm is proposed. The maximum values of wavelet coefficients were extracted as feature samples from the de-noised surface electromyography (sEMG) signals, which were collected from the forearm muscles of several subjects, and then the extracted feature was inputted into an SVM to classify action recognition. In addition, the AQCIMO algorithm was applied to optimize the penalty parameters and the kernel parameters of the SVM, which are used to avoid the uncertainty and complexity of parameter selection and improve the recognition precision of the model, thus improving the model recognition accuracy. The simulation results demonstrated that the two types of movement, which included basic gestures (rest, hand grasp, hand extension, wrist down, and wrist up) and object grabbing gestures (pre-grab, grab, transport and place, release hand, and return to the original position) were successfully identified by the SVM method combined with the AQCIMO algorithm. Compared to mainstream and classic classifiers, namely, GA-SVM, PSO-SVM, and AFSA-SVM, the accuracy of the proposed method was higher by 4.2% to 8.2% than that of the aforementioned classifiers. Therefore, the AQCIMO-SVM algorithm can efficiently solve the problem of the classification of the action pattern of the sEMG signals, which has a very important practical value.

Auditory training (AT) may strengthen auditory skills that help human not only in on-task auditory perception performance but in continuous speech-shaped noise (SSN) environment. AT based on musical material has provided some evidence for an “auditory advantage” in understanding speech-in-noise (SIN), but with a long period training and complex procedure. Experimental research is essential to develop a simplified method named auditory target tracking training (ATT) which refined from musical material is necessary to determine the benefits of training. We developed two kinds of refined AT method: basic auditory target tracking (BAT) training and enhanced auditory target tracking (EAT) training to adult participants ($n=30$) separately for 20 units, assessing performance to perceive speech in noise environment after training. The EAT group presented better speech perception performance than the other groups and no significant differences between BAT group and control group. The training effect of EAT is the most significant when uni-gender SSN and $\mathrm{\text{SNR}}=-4$ dB. Outcomes suggest that efficacy of trained EAT can improve speech perception performance and selective attention during SSN environment. These findings provide an important link between musical-based training and auditory selective attention in real-world, and extended to special vocational training.

Impedance-based sensors represent a promising tool for cell monitoring to improve current invasive biological assays. A novel research field is represented by measurements performed in dynamic conditions, monitoring cells (e.g., myocytes) for which the mechanical stimulus plays an important role for promoting maturation. In this picture, we applied printed and stretchable electronics principles, developing a system able to evaluate cells adhesion during substrate cyclic strain. Cytocompatible and stretchable sensors were ink-jet printed using carbon-based ink on crosslinked poly($\epsilon$-caprolactone) electrospun mats. Moreover, a customized stretching device was produced, with a complete user interface to control testing condition, validated in order to correlate impedance changes with myoblasts — i.e., myocytes precursors — adhesion. Overall system sensitivity was evaluated using three different cell concentrations and DAPI imaging assay was performed to confirm myoblast adhesion. Preliminary results showed the possibility to correlate an average increase of impedance magnitude of 1k$\mathrm{\Omega }$ every 15,000 cells/cm² seeded, suggesting the possibility to discriminate between different cell concentrations, with a sensitivity of 80m$\mathrm{\Omega }$/(cells/cm²). In conclusion, the present system might be generalized in the development of future applications, including the differentiation process of cardiac myocytes with the aid of mechanical stimuli.

Flat foot is the most common foot disorder that influences the alignment of the lower limb structure. It is controversial whether the use of foot insole influences kinetic and kinematic of the leg or not. Therefore, this study investigated the influence of foot insole on the gait performance in subjects with flat foot disorder.

A group of flat foot subject was recruited into this study (the number of subjects was 15). The motion of the leg joints was determined using the Qualysis motion analysis system. Moreover, the force applied on the lower limb was recorded by a Kistler force plate. The range of motion of the lower limb joints, the moments applied on the lower limb joints and force transmitted through the leg were the parameters used in this study. The difference between these parameters during walking with and without insole was evaluated using the paired $t$-test. Significant value was set at $p\le 0.05$.

There was no significant difference between the range of motion of ankle joint while walking with and without insole. However, the medial directed force applied on the leg decreased significantly $(p<0.05)$. The use of foot insole did not influence the moments transmitted through the hip and knee joints. The walking speed of the subjects improved while walking with foot insole.

Use of foot insole influenced the magnitude of the force applied on the leg and the adductor moment of ankle joint due to its influence on foot alignment. As the walking speed of the improved subjects follows the use of insole, it can be concluded that it may have a positive effects on the performance of flat foot subjects.

Total hip Arthroplasty is one of the most common surgeries in elderly people around the world. In spite of many successful cases, a few failures are still reported, a significant number of which relates to the effects of stress shielding. Many scientists have been working on solving this problem by enhancing the material and/or the geometry of the hip prostheses’ stems. For example, hollow-stemmed hip prostheses have been designed and tested. In this study, 30 hollow-stemmed samples were designed which were different in terms of geometry and dimension of their holes as well as the materials defined for them. Then, they were tested through finite element modeling along with validating and verifying the results using experimental and convergence tests. The results including displacements, maximum stress values and consequent safety factors were compared based on the reactions of the samples against various static loads including the loads predefined by ISO 7206-4 as well as the loads which had been previously obtained. $D$2 designs show the least stiffness compared to other designs. Designs with 132.66mm² hole area are the most promising layouts for reducing weight and providing the most amount of medullary space for revascularization of the femur. In spite of designs which predictably help revascularization more than $D$2 designs, these designs which are of the multi-hole patterns seemed to represent the best outcomes in terms of preventing stress shielding and consequently the best pattern for creating holes in the stem according to the precedence of stress shielding over other problems. The results prove the possibility of representing a promising structure which helps to reduce the weight, stress shielding and the lack of revascularization of the femur.

Purpose: Diseases of the coronary arteries represent critical cardiovascular bleakness and mortality around the world. The main focus of this study is to simulate hemodialysis patients undergoing Coronary Artery Bypass Graft (CABG) surgery by the left internal mammary artery. The survey is to investigate whether subclavian-coronary steal syndrome will occur in patients with stenosis in their left subclavian.

Methods: A three-dimensional model of Brachial—Radial—Ulnar tree arterial system and dialysis graft are constructed and then simulated by the implementation of fluid–structure interaction (FSI) and non-FSI models. After consent was obtained, data attributed to dialysis patients who had undergone coronary bypass surgery at the Tehran Heart Center (THD) was collected.

Results: Stenosis in the subclavian artery causes the left internal mammary artery (LIMA) graft to lack flow that, in CABG cases, is supplying the heart muscle. With the increase of stenosis from zero to 54%, the flow results show a negative flow indicating reversed flow in the artery. Meanwhile, the comparison between flow quantity of a normal Left Anterior Descending (LAD) and LIMA in case of 38% stenosis in subclavian shows that the amount of flow reaching the heart is less than standard. The threshold stenosis in the subclavian artery for which subclavian-coronary steal phenomena occurs is simulated to be around 54%. Furthermore, investigation of the effect of flow quantity in cases of hemodialysis versus nonhemodialysis shows that the flow is lessened in case of hemodialysis.

Conclusions: In hemodialysis patients with more than 38% stenosis in left subclavian, it is well advised that LIMA bypass graft is not the preferred graft choice, and at 54% of subclavian stenosis, the steal phenomenon occurs.

Solute transport is one of the important aspects involved in maintaining the physiological activity of tissues. The mechanical environment drives nutrition in and waste out in articular cartilage due to its avascularity, which plays a key role in the biological activity of articular cartilage. The human knee joint motion is a complex interaction between different bones including relative rolling and/or sliding movements. Rolling-compression process is a typical physiological load in knee joint motion. To investigate solute transport behavior in articular cartilage under rolling-compression load, fluorescence tracers with molecular weights of 40kDa and 0.43kDa were used respectively to mark the transport in fresh articular cartilage of mature pigs. Solute fluorescence intensity changing with time and depth of cartilage layer was measured under rolling-compression load and static state, respectively, and the distribution of corresponding relative concentration was calculated by the fluorescence microscope imaging method. The experiment results show that the solute relative concentration in articular cartilage under rolling-compression load increases significantly, even up to 62.4%, comparing with that under static state, and the changes of concentration vary in different layers and that small molecular weight solute is easier to transport than relatively large molecular weight solute in articular cartilage. Therefore, rolling-compression load can promote the solute transport in cartilage, and the mechanical loading may have application in functional cartilage tissue engineering.

Advanced laboratory technology has made blood testing more automated, robust and tests are being implemented comprehensively. Leukocytes type differentiation is a critical hematological images analysis step of blood film as it delivers valuable information in diagnosis of several diseases. At present, the morphological examination of leukocytes is done manually and this process is very tedious, inefficient and slow. Although many white blood cells detection or classification techniques are presented by different researchers, there is still a need of fully automated and an efficient detection system of blood cells with its particular types for an early diagnosis of leukemia. This paper presents a technique for the classification of protuberant types of leukocytes and early diagnosis of leukemia. The work is divided into the following main stages: (a) image augmentation, (b) wavelet composition and decomposition for attaining high and low frequency bands of the cell image, (c) convolutional neural network (CNN) training model for the classification of leukocytes categories and (d) prediction of leukemia. The main intention behind this study is to develop an automated, robust and efficient classification and detection system of leukocytes for microscopic blood images.

The properties of meshes: Surgimesh^®, Technomesh${}^{\circledR }$ and Surgipro^TM aged for up to four years were assessed using tensile tests. We discovered that the elasticity of Technomesh${}^{\circledR }$ increased in both directions, Surgimesh${}^{\circledR }$ became more elastic in the longitudinal direction while the elastic properties of Surgipro^TM remained unchanged. The mesh samples did not significantly change their strength and deformability with age. Samples from umbilical and inguinal area of the abdominal wall were isolated from 14 donors. The investigation included 90 specimens divided into three age subgroups — A (up to 60 years), B (61–80 years) and C (over 80 years). The long-term mechanical compatibility of human fascia and meshes was compared. The elastic properties of the meshes are closer to the elastic properties of the fascia in the direction parallel to fibers if the donors’ age is up to 60 years.

The low-intensity ultrasound effects on MCF7 (human breast adenocarcinoma) and MCF10A (healthy breast cells) have been investigated at different sonication protocol to probe the effectiveness and the selectivity of the ultrasound (US) treatment and to understand the implications between cell mortality, biomechanical interactions and cell elastic modulus. Experiments performed at fixed and variable frequency demonstrated the effectiveness of some protocols in killing carcinogenic cells and the healthy cells insensitivity. Variation of elastic properties of MCF7 cells exposed to US under varying sonication conditions was examined. Sonication was carried out at fixed frequency (as it is usually done in therapy protocols), between 400kHz and 620kHz, following two protocols: (i) at fixed power output; (ii) at fixed voltage of the US generator. Evolution of cell stiffness during the US treatment was monitored via atomic force spectroscopy (AFS). It was found that cell mortality has a similar trend of variation with respect to sonication frequency regardless of the way specimens are exposed to US. Mechanical properties do not show a uniform trend with respect to frequency, but variations of Young’s modulus are more marked near the very low (400–480) kHz or very high frequencies (580–620) kHz. The observed variations may be related to mechanical interactions occurring in the cell culture, suggesting a primacy of the environment on other factors.

Facing the gradually increased prevalence of heart failure (HF) and the shortage of donated hearts, the blood pump is widely used to prolong the life of end-stage HF patients: however, the pump generates continuous flow under constant rotational speed, declining the arterial pulsatility and causing related complications. Previous studies show that synchronous copulsation might be the best control strategy for restoring pulsatility, but synchronous strategies are needed to monitor the phase of the heartbeat, which will make the controller complex and impair its robustness. Here, we compare constant speed, synchronous copulsation in a model of a cardiovascular system with a blood pump, which shows that copulsation offers more arterial pulsatility, less pump power-consumption, and thus better battery endurance, and constant speed offers a greater ventricular unloading effect. Meanwhile, we design a strategy based on transforming left ventricular pressure, which is easier to implement and has similar effect to synchronous copulsation.

The aim of this paper is to compare the biomechanical characteristics of a newly designed assembly locking compression plate (NALCP) and traditional locking compression plate (LCP) for internal fixation of femoral-shaft comminuted fractures. A femoral-shaft wedge fracture model (AO classification 32-C2.1) was created in six pairs of femoral specimens ($n=12$) randomly divided into two equal groups. Biomechanical properties were tested with axial and torsional loading tests. The relative maximum displacement of fracture blocks and strain was recorded. A strain diagram was made; the fatigue test results of NALCP specimens under axial load were recorded. Under axial load, the relative maximum displacement of fracture blocks in the $X$, $Y$, and $Z$ axes was smaller in NALCP specimens than in LCP specimens ($P<0.05$ and 0.01, respectively). Under torsional load, the relative maximum displacement of fracture blocks in the $X$ and $Z$ axes in NALCP specimens was less than that in LCP specimens ($P<0.01$) but no statistically significant difference in the $Y$ axes ($P>0.05$) was found. In both cases, the main NALCP strain was higher than the LCP strain ($P<0.01$) but no statistically significant difference in mean strain ($P>0.05$) was found. Our NALCP provides strong mechanical stability for comminuted femoral fractures and can effectively avoid stress concentration, reduce stress shielding, and facilitate bone healing.

During the percutaneous puncture for robot-assisted brachytherapy, a medical needle is usually inserted into fiber-structured soft tissue which has transverse isotropic elasticity, such as muscle and skin, to deliver radioactive seeds that kill cancer cells. To place the radioactive seeds more accurately, it is necessary to assess the effect of the transverse isotropic elasticity on the needle deflection. A mechanics-based model for simulating the needle deflection in transverse isotropic tissue is developed in this paper. The anisotropic needle–tissue interaction forces are estimated and used as inputs to drive the model for simulating needle deflections for different insertion orientation angles. Automatic insertion experiments were performed on a single-layered porcine muscle at five different insertion orientation angles. The results show that the maximum difference in the tip deflection for the different insertion orientation angles is 2.99mm when the insertion depth is 50mm. The maximum simulated error of the needle axis deflection is 0.62mm for all insertion orientation angles. The developed model can successfully simulate the needle deflections inside transverse isotropic tissue for different insertion orientation angles. This work is useful for predicting and compensating for the deflection error for automatic needle insertion.

The bacterial biofilm is a microbial community in which bacteria are embedded in the extracellular matrix and can also be used as a solid composite. It was found that internal stresses are generated during pellicle growth, which exists between the air and the liquid. But we do not know if there is the internal stress in the biofilm, which exists between the air and the solid, and how does the internal stress evolve and distribute in the growing biofilm. So, in this paper, we make the growing substrate into the micropillar array to grow biofilms, each micropillar has the deformation due to the growing heterogeneity of the biofilm around the micropillar, and we can get the internal stress by measuring each micropillar’s deformation. First, we find that the direction of the internal stress is approximately along the biofilm expansion at the early time, colonies are formed in the biofilm at the later time, which cause the internal stress locally along the expansion of the colony. Second, the internal stress is proportional to the biofilm thickness. Finally, we find that the matrix producing cells contribute more the internal stress, and the internal stress evolving is closely related to the secretion of the extracellular matrix. Form our work, we obtain the distribution of the internal stress direction, we also can use the biofilm thickness, which is easy to measure, express the internal stress approximately, by doing so, we can further study other phenomena of biofilms, such as self-healing and mechanical resistance.