SciCombinator

Discover the most talked about and latest scientific content & concepts.

Journal: Journal of biomechanics

28

Three-dimensional analysis of the entire sequence in ski jumping is recommended when studying the kinematics or evaluating performance. Camera-based systems which allow three-dimensional kinematics measurement are complex to set-up and require extensive post-processing, usually limiting ski jumping analyses to small numbers of jumps. In this study, a simple method using a wearable inertial sensors-based system is described to measure the orientation of the lower-body segments (sacrum, thighs, shanks) and skis during the entire jump sequence. This new method combines the fusion of inertial signals and biomechanical constraints of ski jumping. Its performance was evaluated in terms of validity and sensitivity to different performances based on 22 athletes monitored during daily training. The validity of the method was assessed by comparing the inclination of the ski and the slope at landing point and reported an error of -0.2±4.8°. The validity was also assessed by comparison of characteristic angles obtained with the proposed system and reference values in the literature; the differences were smaller than 6° for 75% of the angles and smaller than 15° for 90% of the angles. The sensitivity to different performances was evaluated by comparing the angles between two groups of athletes with different jump lengths and by assessing the association between angles and jump lengths. The differences of technique observed between athletes and the associations with jumps length agreed with the literature. In conclusion, these results suggest that this system is a promising tool for a generalization of three-dimensional kinematics analysis in ski jumping.

Concepts: Measurement, Mathematical analysis, Skiing, Finland, Animal locomotion, Jump, Ski jumping, Ski jumping at the Winter Olympics

28

In the aerials event of freestyle skiing, athletes perform three somersaults with up to five twists. This study investigated the twisting limits of such movements using a computer simulation model of aerial movement. The abilities of various asymmetrical arm and hip techniques to produce twist during flight were investigated using 10 simulations to maximise twist and allow reorientation prior to landing. It was found that 4-6 twists could be produced during three somersaults. The main limiting factor was the increased whole body frontal moment of inertia due to the equipment which restricted the amount of tilt resulting from an asymmetrical arm movement. It was concluded that reductions in equipment mass might make such movements easier to achieve but would be unlikely to allow advances beyond the limits found.

Concepts: Computer graphics, Computer simulation, Skiing, Mathematical model, Moment of inertia, Inertia, Twist, Freestyle skiing

28

The long-term success of the endovascular procedure for the treatment of Abdominal Aortic Aneurysms (AAAs ) depends on the secure fixation of the proximal end and the geometry of the stent-graft (SG) device. Variations in SG types can affect proximal fixation and SG hemodynamics. Such hemodynamic variations can have a catastrophic effect on the vascular system and may result from a SG/arterial wall compliance mismatch and the sudden decrease in cross-sectional area at the bifurcation, which may result in decreased distal perfusion, increased pressure wave reflection and increased stress at the interface between the stented and non-stented portion of the vessel. To examine this compliance mismatch, a commercial SG device was tested experimentally under a physiological pressure condition in a silicone AAA model based on computed tomography scans. There was a considerable reduction in compliance of 54% and an increase in the pulse wave velocity of 21%, with a significant amount of the forward pressure wave being reflected. To examine the SG geometrical effects, a commercial bifurcated geometry was compared computationally and experimentally with a geometrical taper in the form of a blended section, which provided a smooth transition from the proximal end to both iliac legs. The sudden contraction of commercial SG at the bifurcation region causes flow separation within the iliac legs, which is known to cause SG occlusion and increased proximal pressure. The blended section along the bifurcation region promotes a greater uniformity of the fluid flow field within the distal legs, especially, during the deceleration phase with reduced boundary layer reversal. In order to reduce the foregoing losses, abrupt changes of cross-section should be avoided. Geometrical tapers could lead to improved clinical outcomes for AAA SGs.

Concepts: Causality, Fundamental physics concepts, Fluid dynamics, Geometry, Aortic aneurysm, Fluid mechanics, Hemodynamics, Abdominal aortic aneurysm

28

About 1-2% of the babies are born with bicuspid aortic valves instead of the normal aortic valve with three leaflets. A significant portion of the patients with the congenital bicuspid valve morphology suffer from aortic valve stenosis and/or ascending aortic dilatation and dissection thus requiring surgical intervention when they are young adults. Patients with bicuspid aortic valves (BAVs) have also been found to develop valvular stenosis earlier than those with the normal aortic valve. This paper overviews current knowledge of BAVs, where several studies have suggested that the mechanical stresses induced on the valve leaflets and the abnormal flow development in the ascending aorta may be an important factor in the diseases of the valve and the aortic root. The long-term goals of the studies being performed in our laboratory are aimed towards potential stratification of bicuspid valve patients who may be at risk for developing these pathologies based on analyzing the hemodynamic environment of these valves using fluid-structure interaction (FSI) modeling. Patient-specific geometry of the normal tri-cuspid and bicuspid valves are reconstructed from real-time 3D ultrasound images and the dynamic analyses performed in order to determine the potential effects of mechanical stresses on the valve leaflet and aortic root pathology. This paper describes the details of the computational tools and discusses challenges with patient-specific modeling.

Concepts: Aortic dissection, Aorta, Ascending aorta, Left ventricle, Aortic valve, Aortic valve stenosis, Aortic insufficiency, Bicuspid aortic valve

28

There is evidence that vibrations of soft tissue compartments are not appropriately described by a single sinusoidal oscillation for certain types of locomotion such as running or sprinting. This paper discusses a new method to quantify damping of superimposed oscillations using a wavelet-based time-frequency approach. This wavelet-based method was applied to experimental data in order to analyze the decay of the overall power of vibration signals over time. Eight healthy subjects performed sprinting trials on a 30m runway on a hard surface and a soft surface. Soft tissue vibrations were quantified from the tissue overlaying the muscle belly of the medial gastrocnemius muscle. The new methodology determines damping coefficients with an average error of 2.2% based on a wavelet scaling factor of 0.7. This was sufficient to detect differences in soft tissue compartment damping between the hard and soft surface. On average, the hard surface elicited a 7.02s(-1) lower damping coefficient than the soft surface (p<0.05). A power spectral analysis of the muscular vibrations occurring during sprinting confirmed that vibrations during dynamic movements cannot be represented by a single sinusoidal function. Compared to the traditional sinusoidal approach, this newly developed method can quantify vibration damping for systems with multiple vibration modes that interfere with one another. This new time-frequency analysis may be more appropriate when an acceleration trace does not follow a sinusoidal function, as is the case with multiple forms of human locomotion.

Concepts: Muscle, Tissues, Wave, Vibration, Harmonic oscillator, Simple harmonic motion, Damping, Mechanical vibrations

28

During orthodontic tooth movement (OTM), alveolar bone is resorbed by osteoclasts in compression sites (CS) and is deposited by osteoblasts in tension sites (TS). The aim of this study was to develop a standardized OTM protocol in mice and to investigate the expression of bone resorption and deposition markers in CS and TS. An orthodontic appliance was placed in C57BL6/J mice. To define the ideal orthodontic force, the molars of the mice were subjected to forces of 0.1N, 0.25N, 0.35N and 0.5N. The expression of mediators that are involved in bone remodeling at CS and TS was analyzed using a Real-Time PCR. The data revealed that a force of 0.35N promoted optimal OTM and osteoclast recruitment without root resorption. The levels of TNF-α, RANKL, MMP13 and OPG were all altered in CS and TS. Whereas TNF-α and Cathepsin K exhibited elevated levels in CS, RUNX2 and OCN levels were higher in TS. Our results suggest that 0.35N is the ideal force for OTM in mice and has no side effects. Moreover, the expression of bone remodeling markers differed between the compression and the tension areas, potentially explaining the distinct cellular migration and differentiation patterns in each of these sites.

Concepts: Osteoporosis, Bone, Polymerase chain reaction, Developmental biology, Bone resorption, Osteoclast, Force, Cathepsin K

28

Tendinopathy is a widespread and disabling condition characterized by collagen fiber disruption and accumulation of a glycosaminoglycan-rich chondroid matrix. Recent clinical reports have illustrated the potential of mechanical loading (exercise) therapies to successfully treat chronic tendinopathies. We have developed a new murine tendinopathy model which requires a single injection of TGF-β1 into the Achilles tendon midsubstance followed by normal cage activity for 2 weeks. At this time, tendon maximum stress showed a dramatic (66%) reduction relative to that of normal controls and this persisted at four weeks. Loss of material properties was accompanied by abundant chondroid cells within the tendon (closely resembling the changes observed in human samples obtained intra-operatively) and increased expression of Acan, Col1a1, Col2a1, Col3a1, Fn1 and Mmp3. Mice subjected to two weeks of daily treadmill exercise following TGF-β1 injection showed a similar reduction in tendon material properties as the caged group. However, in mice subjected to 4 weeks of treadmill exercise, tendon maximum stress values were similar to those of naive controls. Tendons from the mice exercised for 4 weeks showed essentially no chondroid cells and the expression of Acan, Col1a1, Col2a1, Col3a1, and Mmp3 was significantly reduced relative to the 4-week cage group. This technically simple murine tendinopathy model is highly amenable to detailed mechanistic and translational studies of the biomechanical and cell biological pathways, that could be targeted to enhance healing of tendinopathy.

Concepts: Gene, Collagen, Extracellular matrix, Muscle, Tendon, Achilles tendon, Tendinopathy, Tendons

28

Tissue level characteristics of bone can be measured by nanoindentation and microspectroscopy, but are challenging to translate to whole bone mechanical behavior in this hierarchically structured material. The current study calculated weighted section moduli from microCT attenuation values based on tissue level relationships (Z(lin,a) and Z(lin,b)) between mineralization and material properties to predict whole bone mechanical behavior. Z(lin,a) was determined using the equation of the best fit linear regression between indentation modulus from nanoindentation and mineral:matrix ratio from Raman spectroscopy. To better represent the modulus of unmineralized tissue, a second linear regression with the intercept fixed at 0 was used to calculate Z(lin,b). The predictive capability of the weighted section moduli calculated using a tissue level relationship was compared with average tissue level properties and weighted section moduli calculated using an apparent level relationship (Z(exp)) between Young’s Modulus and mineralization. A range of bone mineralization was created using vitamin D deficiency in growing rats. After 10 weeks, left femurs were scanned using microCT and tested to failure in 3 point bending. Contralateral limbs were used for co-localized tissue level mechanical properties by nanoindentation and compositional measurements by Raman microspectroscopy. Vitamin D deficiency reduced whole bone stiffness and strength by ∼35% and ∼30%, respectively, but only reduced tissue mineral density by ∼10% compared with Controls. Average tissue level properties did not correlate with whole bone mechanical behavior while Z(lin,a), Z(lin,b), and Z(exp) predicted 54%, 66%, and 80% of the failure moment respectively. This study demonstrated that in a model for varying mineralization, the composite beam model in this paper is an improved method to extrapolate tissue level data to macro-scale mechanical behavior.

Concepts: Regression analysis, Bone, Vitamin D, Prediction, Futurology, Prediction interval, Young's modulus, Forecasting

27

Surgical replacement of the pulmonary valve (PV) is a common treatment option for congenital pulmonary valve defects. Engineered tissue approaches to develop novel PV replacements are intrinsically complex, and will require methodical approaches for their development. Single leaflet replacement utilizing an ovine model is an attractive approach in that candidate materials can be evaluated under valve level stresses in blood contact without the confounding effects of a particular valve design. In the present study an approach for optimal leaflet shape design based on finite element (FE) simulation of a mechanically anisotropic, elastomeric scaffold for PV replacement is presented. The scaffold was modeled as an orthotropic hyperelastic material using a generalized Fung-type constitutive model. The optimal shape of the fully loaded PV replacement leaflet was systematically determined by minimizing the difference between the deformed shape obtained from FE simulation and an ex-vivo microCT scan of a native ovine PV leaflet. Effects of material anisotropy, dimensional changes of PV root, and fiber orientation on the resulting leaflet deformation were investigated. In-situ validation demonstrated that the approach could guide the design of the leaflet shape for PV replacement surgery.

Concepts: Blood, Engineering, Continuum mechanics, Materials science, Young's modulus, Valves, Structural analysis, Constitutive equation

27

To date, there is only a fragmentary understanding of the fundamental mechanisms of airway mucociliary transport. Application of the latest measurement techniques can aid in deciphering the complex interplay between ciliary beat and airway surface liquid (ASL) transport. In the present study, direct, quasi-simultaneous measurements of the cilia-induced fluid and bead transport were performed to gain a better insight into both transport mechanisms. In this study cilia-induced periciliary liquid (PCL) transport is measured by means of micro Particle Image Velocimetry (μPIV) with neutrally buoyant tracers. Particle Tracking Velocimetry (PTV) with heavier polystyrene-ferrite beads is performed to simulate particle transport. Contrary to recent literature, in which the presence of mucus was deemed necessary to maintain periciliary liquid (PCL) transport, effective particle and fluid transport was measured in our experiments in the absence of mucus. In response to muscarine or ATP stimulation, maximum fluid transport rates of 250μm/s at 15μm distance to the tracheal epithelia were measured while bead transport rates over the epithelia surfaces reached 200μm/s. We estimated that the mean bead transport is dominated by viscous drag compared to inertial fluid forces. Furthermore, mean bead transport velocities appear to be two orders of magnitude larger compared to bead sedimentation velocities. Therefore, beads are expected to closely follow the mean PCL flow in non-ciliated epithelium regions. Based on our results, we have shown that PCL transport can be directly driven by the cilia beat and that the PCL motion may be capable of driving bead transport by fluid drag.

Concepts: Fluid dynamics, Measurement, Viscosity, Arithmetic mean, Respiratory epithelium, Particle image velocimetry, Particle tracking velocimetry, Velocimetry