Journal of Mechanics in Medicine and Biology

The neoclassical growth model is being analyzed subject to spatially homogeneous perturbations by using the weak nonlinear method of solution and comparing its results to the numerical solution. The latter expands the analytical tools beyond the investigation of Turing instability. The results identify a Hopf bifurcation at a critical value of a controlling parameter, and their comparison to direct numerical solutions show an excellent match in the neighborhood of this critical value and for amplitudes of oscillations that are not too large.

Native heart valve leaflets are subjected to continuous pulsatile and homodynamic forces and can be as thin as 300 μm. For a proper function of the valve the materials selected for the leaflets need to be biocompatible, robust, flexible, and have comparable mechanical properties to the natural ones.

In this paper, biocompatibility and cell retention ability for gelatin–chitosan polyurethane (PU), polyglycolide (PGA)/PLA and collagen-coated bovine pericardium were examined and their mechanical properties were tested. Endothelial cells, isolated from ovine carotid arteries were seeded onto these materials and exposed to a range of shear-stresses for a period of 1–3 h.

The findings indicated that throughout the exposure time and the shear-stress range tested, a mean cell retention rate of 80% was obtained in the gelatin–chitosan PU group. However, for PGA/PLA and pericardium groups it was found that as the exposure time of shear-stress increased, a significant cell reduction was observed. Noticeably for all the range of physiological flow conditions tested, the electrospun gelatin–chitosan PU demonstrated good biocompatibility and cell retention properties and could be potentially used as a biomaterial for tissue engineering of heart valves.

Generally in the anterior cruciate ligament (ACL) injury assessment specific laxity tests (i.e., Lachman, drawer tests) are clinically performed to evaluate the presence of ligamentous lesion. At present these tests are qualitatively evaluated by the surgeon and some quantitative measurements can be performed only for Lachman/drawer tests by means of dedicated devices. This study aimed to characterize the accuracy of a novel integrated optical-based method that can be used both in intra-operative and in office assessment of ACL injuries; in particular this technology was addressed to measure the loads/torques applied during clinical laxity tests, extending the current possible quantitative evaluations. The system, based on a commercial optical localizer and common springs, was spatially characterized in order to verify displacement/rotation and corresponding applied load/torque measurements. Evaluated limits of agreement between measured and applied loads were from –0.541 to 1.781 N, with a bias of 0.621 N (P = 0.05) in a dedicated clinical-like setup. This approach reported an excellent accuracy in load measurements, showing its possible integration in computer-aided surgery (CAS).

Venous valves and sinuses are frequently observed in vein grafts in the coronary artery bypass grafts (CABG). However, from the biomedical engineering viewpoint, vein grafts are always assumed as smooth tubes in the existing simulations, and no effort has been made to investigate the effects of jaggedness of the graft inner wall due to the valve cusps remnants and valve sinus (in case of valve-stripped saphenous vein (SV) grafts) on the blood flow patterns and hemodynamic parameters (HPs). In this paper, the effects of the inner surface irregularities of a vein graft on the blood flow is investigated in the graft as well as in the distal anastomotic region, with a more realistic geometry of valve-stripped SV, by means of numerical simulation of pulsatile, Newtonian blood flow. The simulation results demonstrate that the valve remnants and sinuses cause disturbances in the flow field within the graft (due to vortices formation within the valve sinuses) and undesirable distribution of HPs, which can result in early atherosclerotic lesion development in the graft.

Surface electromyography (EMG) has been used to estimate deep trunk muscle activity. However, it remains unknown whether surface EMG provides an accurate estimation of this activity. The purposes of this study were to compare surface and intramuscular EMG activity measurements and investigate the efficacy of surface EMG measurement for the transversus abdominis (TrA) and the multifidus (MF) muscles. Eight healthy men participated in the study. TrA and MF activities were simultaneously measured by both intramuscular and surface EMG during isometric trunk exercises. Spearman correlation coefficients for the relationship between the two activity measurements for the right TrA, left TrA, right MF, and left MF were 0.55, 0.36, 0.67, and 0.79, respectively. For the TrA, Bland–Altman plots revealed that mean differences between measurements obtained by intramuscular EMG and surface EMG were not close to zero, with a systematic bias toward higher surface EMG values. In conclusion, surface and intramuscular EMG activity measurements were strongly correlated for MF muscles, but poorly correlated for TrA muscles.

Lubrication plays an important role in reducing prosthetic wear. Time-dependent elastohydrodynamic lubrication simulation for total knee replacements was carried out under physiological loading and motions of a gait cycle. In numerical implement, a simplified ellipsoid-on-plane configuration was introduced to represent the artificial knee joint. Load and motions came from ISO standard, and both anterior–posterior displacement and flexion–extension rotation were considered to realize sliding and rolling motions of the knee. The governing Reynolds and elasticity equations were solved simultaneously using the multigrid technique. The elastic deformation was calculated based on the constrained column model. The results show that: (i) under the combination of entraining and squeeze-film actions throughout the walking cycle, the predicted central film thickness decreases during stance phase and keeps a relatively larger value in swing phase; (ii) high joint conformity helps to reduce hydrodynamic pressure and increase lubrication film thickness; (iii) the thickness of ultra-high molecular weight polyethylene layer and its properties also have influence on the lubrication performance in artificial knee replacement. Based on the aforementioned EHL analysis, potential surface damage of knee implants can be further evaluated.

A three-dimensional (3D) geometric model for predicting muscle forces in the shoulder complex is proposed. The model was applied throughout the range of arm elevation in the scapular plan. In vitro testing has been performed on 13 cadaveric shoulders. The objectives were to determine homogeneous values of physiological parameters of shoulder muscles and to locate sites of muscular attachment to any bone of the shoulder complex. Muscular fiber lengths, lengths of contractile element (CE), and muscle volumes were measured, corresponding physiological cross-sectional area (PCSA) were calculated, and force/length muscle relations were found. An in vivo biplanar radiography was performed on five volunteers. The photogrammetric reconstruction of bone axes and landmarks were coupled with a geometric modeling of bones and muscle sites of attachment. Muscular paths were drawn and changes in lengths during movement have been estimated. Directions of muscle forces are the same as that of muscular path at the point of attachment to bone. Magnitudes of muscular forces were found from muscle lengths coupled with force/length relations. Passive forces were directly determined contrary to active muscle forces. A resulting active muscle force is calculated from balancing weight and passive forces at each articular center. Active muscle forces were calculated by distributing the resulting force among active muscles based on the muscular PCSA values.

This pilot study analyzed the loading on the medial forefoot (MF) region during walking in high-heel shoes. Eight healthy female volunteers have participated in this study with the heel height varied from 0 cm (flat), 4.5 cm (low), and 8.5 cm (high). The results showed that the load on MF increased with the heel height and the magnitude of the load could be effectively reduced by using foam inserts. Comparative studies of foams with different hardness and thicknesses showed that thicker soft foams had a significant advantage over thiner hard foams (P < 0.05) in reducing the peak pressures. An optimum condition with a thick soft insert could reduce MF pressure by 26%, impact force by 27%, and force time integral by 20% when compared to the condition without insert.

A computed tomography (CT) scanner is often used for visualization during the radiofrequency (RF) ablation (RFA) procedure. Temperatures at the ablation zone, power output, efficiency, and annotation are recorded once per second in the RF generator. Radiologists often review the RF and CT data post-operation for diagnostic and research purposes. However, they often rely on the CT data solely as it is difficult to relate the RF information to its CT counterpart. This paper describes the development of a graphical user interface application to co-register the CT images and the information from the RF generator temporally. Information from the RF generator, CT images during the RFA, and the pre-RFA CT images are displayed together. Users pinpoint a specific timestamp based on the RFA operation, and the corresponding CT images are retrieved and displayed.

To investigate the hemodynamic and hemorheological features related to circulatory diseases, in vitro experiments are carried out using a micro-particle image velocimetry (μ-PIV) technique. Numerical simulations using a commercial computational fluid dynamics (CFD) code are also performed to compare with the experimental results. Five different non-Newtonian blood models and a Newtonian water model are employed to investigate the blood flow characteristics through a stenotic right coronary artery (RCA). The in vitro model is made of two-dimensional (2D) polydimethylsiloxane (PDMS) channel based on the clinical angiogram of the RCA with stenotic lesion. The hemodynamic and hemorheologic behaviors in the control volume near the stenotic lesion are evaluated by velocity profiles. The predicted and measured velocity profiles at the center of the channel have a reasonable agreement.