Journal of Mechanics in Medicine and Biology

The fabrication of vascularized parenchymal organs to alleviate donor shortage in organ transplantation is the holy grail of tissue engineering. However, conventional tissue-engineering strategies have encountered huge challenges in recapitulating complex structural organization of native organs (e.g., orderly arrangement of multiple cell types and vascular network), which plays an important role in engineering functional vascularized parenchymal constructs in vitro. Recent developments of various advanced tissue-engineering strategies have exhibited great promise in replicating organ-specific architectures into artificial constructs. Here, we review the recent advances in top-down and bottom-up strategies for the fabrication of vascularized parenchymal constructs. We highlight the fabrication of microfluidic scaffolds potential for nutrient transport or vascularization as well as the controlled multicellular arrangement. The advantages as well as the limitations associated with these strategies will be discussed. It is envisioned that the combination of microfluidic concept in top-down strategies and multicellular arrangement concept in bottom-up strategies could potentially generate new insights for the fabrication of vascularized parenchymal organs.

In vitro mechanical testing of spinal specimens is extremely important to better understand the biomechanics of the healthy and diseased spine, fracture, and to test/optimize surgical treatment. While spinal testing has extensively been carried out in the past four decades, testing methods are quite diverse. This paper aims to provide a critical overview of the in vitro methods for mechanical testing the human spine at different scales. Specimens of different type are used, according to the aim of the study: spine segments (two or more adjacent vertebrae) are used both to investigate the spine kinematics, and the mechanical properties of the spine components (vertebrae, ligaments, discs); single vertebrae (whole vertebra, isolated vertebral body, or vertebral body without endplates) are used to investigate the structural properties of the vertebra itself; core specimens are extracted to test the mechanical properties of the trabecular bone at the tissue-level; mechanical properties of spine soft tissue (discs, ligaments, spinal cord) are measured on isolated elements, or on tissue specimens. Identification of consistent reference frames is still a debated issue. Testing conditions feature different pre-conditioning and loading rates, depending on the simulated action. Tissue specimen preservation is a very critical issue, affecting test results. Animal models are often used as a surrogate. However, because of different structure and anatomy, extreme caution is required when extrapolating to the human spine. In vitro loading conditions should be based on reliable in vivo data. Because of the high complexity of the spine, such information (either through instrumented implants or through numerical modeling) is currently unsatisfactory. Because of the increasing ability of computational models in predicting biomechanical properties of musculoskeletal structures, a synergy is possible (and desirable) between in vitro experiments and numerical modeling. Future perspectives in spine testing include integration of mechanical and structural properties at different dimensional scales (from the whole-body-level down to the tissue-level) so that organ-level models (which are used to predict the most relevant phenomena such as fracture) include information from all dimensional scales.

Huntington's disease (HD) is one of the neural diseases with movement disorders like chorea, ballism, and athetosis. These symptoms play an important role on gait asymmetry, thus gait recordings are considered important resources for studying this disease. Diagnosing HD in its early stages is important and critical. We aimed to discover differences between HD and normal behavior. As the gait is semi-periodic, analyzing frequency could reveal disorders. We made an attempt to extract some proper features using power spectra density. Studies revealed that HD adds high frequencies to the spectrum on all gait phases. Statistical analysis of the gait features showed significant differences between normal and HD groups. At the end, we tried to separate the patients and healthy individuals using a new intelligent mathematical system. An artificial neural network classifier was used for this reason,and our best separation accuracy was 96.6%. This study could be the basis of designing a practical decision support system. This system can diagnose patients at the first stages of the disease, and it also can recommend suspected persons to the specialist.

In this study, the mathematical observations for the peristaltic flow of a Williamson fluid model (e.g., chyme) in a cross-section of a rectangular duct having compliant walls were considered. The flow was assumed incompressible and unsteady. The constitutive equations were reduced under the assumptions of low Reynolds number and long wavelength approximations. The resulting dimensionless governing equations were solved using the homotopy perturbation method (HPM) and eigenfunction expansion method. The results obtained were explained graphically. The velocity distribution was plotted for physical parameters both in two and three dimensions. The streamline graphs are presented in the end, which explain the trapping bolus phenomenon. All theoretical and graphical results are then discussed simultaneously.

The purpose of this study was to investigate the influence of stent grafts on the wall pressure of aneurysms and find out what kind of stent graft is suitable for curing aneurysm. A set of experiment apparatus that simulated the human heart and artery was set up, including an elastic abdominal aortic aneurysm (AAA) model which was made of rubber. The influence of healing induced by stent grafts with different diameters and either permeable or impermeable on the AAA were investigated by comparing experiments using the AAA model with clinical stent grafts in a pulsatile flow system that simulated human blood circulation. The experiment results show that the pressure on the AAA wall reduced after the insertion of a stent graft. The permeable stent graft is not propitious to the pressure reduction. Furthermore, the reduction of pressure is related to stent graft diameter, that is, stent grafts whose diameter is 10–15% larger than the arterial diameter leads to the optimal reduction of the wall pressure. The results are unprecedented and expected to have significant clinical applications.

Walking is daily physical activity and a common way of exercise during pregnancy, but morphological changes can modify the gait pattern. Biomechanical models can help in evaluating joint mechanical loads and kinetics and kinematics during gait, and provide patterns. This study aimed to describe the gait pattern during the second trimester of pregnancy and give an orientation for biomechanical modeling for pregnant women. The ankle and hip joints seem to be more overloaded, mainly in the sagittal and frontal planes, respectively. Results show that pregnant women have a similar walking pattern to the normal gait. This model construction was revealed to be appropriate for describing gait during the second trimester of pregnancy.

Although the direction of loads applied to the proximal human femur is unpredictable during sideways fall, most in vitro and numerical simulations refer to a single loading condition (15° internal rotation; 10° adduction), which has been anecdotally suggested in the 1950s. The aim of the present study was to improve in vitro simulations of sideways falls on the proximal femur.

An in vitro setup was developed that allowed exploring a range of loading directions +/-90° internal–external rotation; 0°–50° adduction). To enable accurate control of the loading conditions (direction and magnitude of all load components applied to the femur), the setup included a number of low-friction linear and rotary bearings. The setup was instrumented with an axial and a torsional load cell, three displacement transducers and a rotation transducer to monitor the most significant components of load/displacement during testing. The strain distribution was measured on the bone surface (16 triaxial strain gauges, 2,000 Hz). Fracture was recorded with a high-speed camera.

The setup was successfully tested on a cadaveric femur non-destructively (12 loading configurations) and destructively (15° internal rotation; 10° adduction). All measurements were highly repeatable (the displacements of the femoral head varied by < 2% between repetitions; the tilt in the frontal plane by < 0.05°; and strain varied on average 0.34% between repetitions). The displacement of the femoral head varied by over 50% when the same force was applied in different directions. Principal strains at the same location varied by over 70%, depending on the direction of the applied force. The high-speed video enabled the identification of the point of fracture initiation.

This study has shown that a new paradigm for testing the proximal femur (including improved testing conditions and a variety of loading configurations) can provide more accurate and more extensive information about the state of strain.

Gait symmetry has been considered as one of the primary indicators in gait analysis. A symmetrical gait offers several benefits. Among them is a stable and adaptive gait. With wide adoption of wireless inertial sensors i.e., the gyroscope in clinical and rehabilitation settings, this work aimed to investigate the application of symmetry index (SI), symmetry ratio (SR) and normalised symmetry index (SInorm) in defining gait symmetry using measurement collected from wireless gyroscope network. Thigh and shank angular rates during mid-swing, heel-strike and toe-off are used to determine SI, SR and SInorm. In this study, participants were not only instructed to walk naturally on the ground and on a treadmill, but were also requested to walk with restricted knee movement on the ground and on a treadmill to emulate asymmetrical gait. This study demonstrated that the gyroscope can be used to determine gait symmetry. It also shows that SI and SR are not the right indicators to examine gait symmetry using gyroscope data. SI can exceed more than 1,000% at several instances. SR exhibits similar behavior too i.e., it can be as high as 1,000. SInorm performs better in both overground walking and treadmill walking and there are significant difference between symmetrical and asymmetrical gait (p < 0.01).

Low energy efficiency of Fontan-type connections in exercise conditions may lead to limited post-operative exercise capacity of patients. The objective of this study was to compare the energy efficiency of different types of Fontan modifications in exercise conditions. In this study, the flow rate of the inferior vena cava (IVC) was increased artificially to simulate exercise conditions. The control volume power loss and energy efficiency were investigated in three types of Fontan modifications using the method of computational fluid dynamics (CFD). In the intracardiac tunnel Fontan, the power loss was 7.9 times of that calculated in resting state when the flow rate of IVC increased to three times of that measured at the right pulmonary artery flow ratio of 50%. The energy efficiency of it decreased prominently from 91.9% to 79.9%. On the contrary, in the extracardiac Fontan with direct cavopulmonary anastomosis (direct Fontan), the magnitude of power loss was only 2.9 times of that in resting state and the energy efficiency changed only from 91.8% to 89.1%. The results of extracardiac conduit Fontan fell in between. It showed that direct Fontan had higher energy efficiency than intracardiac tunnel or extracardiac conduit Fontan in exercise conditions.

Young females with mild hallux valgus (HV) have been identified as having an increased risk of first ray deformation. Little is known, however, about the biomechanical changes that might contribute to this increased risk. The purpose of this study was to compare kinetics changes during walking for mild HV subjects with high-heel-height shoes. Twelve female subjects (six with mild HV and six controls) participated in this study with heel height varying from 0 cm (barefoot) to 4.5 cm. Compared to healthy controls, patients had significantly higher peak pressure on the big toe area during barefoot walking. When the heel height increased, loading was transferred to medial side of the forefoot, and the big toe area suffered more impact compared to barefoot in mild HV. This study also demonstrated that the center of pressure (COP) inclines to medial side alteration after high-heeled shoes wearing. These findings indicate that mild HV people should be discouraged from wearing high-heeled shoes.

In this paper, the finite element method (FEM) with web-spline computer modeling were applied to study corneal surface temperature increase during microwave irradiation. The heat conduction model of the microwave-irradiated eye, which assumed to be 3D, was constructed. The mechanism of heat transfer from the eye and the selection of the thermal parameters of the media of the eye are also discussed. The implementation of these parameters in the web-spline solution of heat conduction was then developed. Furthermore, temperature rise calculations were compared with the values found in the literature pertaining to microwave-induced cataract formation.

Palpation is an essential skill of manual therapy. Clinical techniques of physical therapy usually assume that the movement direction of palpating spinous process (SP) is the direction of the vertebral body center (VBC). This study investigated the distance [SP–projected VBC (PVBC)] between the surface palpation of the five SPs and the radiographically projected vertebral center locations (PVBC) on the skin of the lumbar spine in 37 patients with low back pain (LBP). The measurement of SP–PVBC was intended to describe if palpation on SPs could explain the positions of the VBC. The SP–PVBC distance was the greatest at L1 (35.9 mm) and the smallest at L4 (15.1 mm). The predictive analysis investigated the relationships between SP–PVBC and the geometric measurements of the lumbar anatomical structures. The geometric characteristics of the lumbar spine affected the SP–PVBC distance in different levels, with the R² values from 0.66–0.89, except 0.38 in the L4 level. Increases in the SP inclination as well as vertebral inclinations, and increases in the SP height (SPH) were factors that were found to be significantly related to the SP–PVBC distance (p < 0.05). The results indicate that the orientation of the VBC and the SP may not be the same, and tilting and rotation of the vertebrae may occur when applying manual techniques through SPs. Physical therapists need to be aware that the tilting or rolling effect of vertebrae may not be avoidable once the treatment is done via palpation on SPs.

A computational fluid dynamics (CFD) simulation of laminar convection of Al₂O₃–water bio-nanofluids in a circular tube under constant wall temperature conditions was conducted, employing a single-phase model and three different two-phase models (volume of fluid (VOF), mixture and Eulerian). The steady-state, three-dimensional flow conservation equations were discretised using the finite volume method (FVM). Several parameters such as temperature, flow field, skin friction and heat transfer coefficient were computed. The computations showed that CFD predictions with the three different two-phase models are essentially the same. The CFD simulations also demonstrated that single-phase and two-phase models yield the same results for fluid flow but different results for thermal fields. The two-phase models, however, achieved better correlation with experimental measurements. The simulations further showed that heat transfer coefficient distinctly increases with increasing nanofluid particle concentration. The physical properties of the base fluid were considered to be temperature-dependent, while those of the solid particles were constant. Grid independence tests were also included. The simulations have applications in novel biomedical flow processing systems.