Accepted Manuscripts

Brandon Zimmerman and Dr. Gerard A. Ateshian
J Biomech Eng   doi: 10.1115/1.4040497
This study formulates a finite element algorithm for frictional contact of solid materials, accommodating finite deformation and sliding. The algorithm is implemented in the open source software FEBio (febio.org), and the source code is made available to the general public. The algorithm uses a penalty method regularized with an augmented Lagrangian scheme to enforce contact constraints in a non-mortar segment-to-segment approach. Use of a novel kinematical approach to contact detection and enforcement of frictional constraints allows solution of complex problems previously requiring mortar methods or contact smoothing algorithms. Patch tests are satisfied to a high degree of accuracy with a single-pass penalty method, ensuring formulation errors do not affect the solution. The accuracy of the implementation is verified with Hertzian contact and illustrations demonstrating the ability to handle large deformations and sliding are presented and validated against prior literature. A biomechanically relevant example addressing finger friction during grasping demonstrates the utility of the proposed algorithm. This study's development of a robust algorithm for frictional contact, and its implementation into FEBio, provides a useful resource to the biomechanics community.
TOPICS: Deformation, Algorithms, Finite element analysis, Mortar, Biomechanics, Friction, Grasping, Computer software, Errors
Erika Nelson-Wong, Michal Glinka, Mamiko Noguchi, Helene Langevin, Gary J. Badger and Jack P. Callaghan
J Biomech Eng   doi: 10.1115/1.4040452
Recent work utilizing ultrasound imaging demonstrated that individuals with low back pain (LBP) have increased thickness and decreased mobility of the thoracolumbar fascia (TLF); an indication that the TLF may play a role in LBP. This study used a porcine injury model (microsurgically induced local injury) - shown to produce similar results to those observed in humans with LBP - to test the hypothesis that TLF mechanical properties may also be altered in patients with LBP. Perimuscular TLF tissue was harvested from the non-injured side of vertebral level L3-4 in pigs randomized into either control (n=5) or injured (n=5) groups. All samples were tested with a displacement-controlled biaxial testing system using the following protocol: cyclic loading/unloading and stress relaxation tests at 25%, 35%, and then 45% of their resting length. Tissue anisotropy was also explored by comparing responses to loading in longitudinal and transverse orientations. Tissues from injured pigs were found to have greater stretch-stretch ratio moduli (measure of tissue stiffness), less energy dissipation, and less stress decay compared to tissues from control pigs. Responses across these variables also depended on loading orientation. Clinical Significance: These findings suggest that a focal TLF injury can produce impairments in tissue mechanical properties away from the injured area itself. This could contribute to some of the functional abnormalities observed in human LBP.
TOPICS: Surgery, Tensile strength, Wounds, Biological tissues, Stress, Mechanical properties, Relaxation (Physics), Anisotropy, Energy dissipation, Testing, Displacement, Stiffness, Mechanical admittance, Ultrasonic imaging
Wenbin Mao, Qian Wang, Susheel Kodali and Wei Sun
J Biomech Eng   doi: 10.1115/1.4040457
Paravalvular leak (PVL) is a relatively frequent complication after transcatheter aortic valve replacement (TAVR) with increased mortality. Currently, there is no effective method to pre-operatively predict and prevent PVL. In this study, we developed a computational model to predict the severity of PVL after TAVR. Nonlinear finite element (FE) method was used to simulate a self-expandable CoreValve deployment into a patient-specific aortic root, specified with human material properties of aortic tissues. Subsequently, computational fluid dynamics simulations were performed using the post-TAVR geometries from the FE simulation, and a parametric investigation of the impact of the TAV skirt shape, TAV orientation, and deployment height on PVL was conducted. The predicted PVL was in good agreement with the echocardiography data. Due to the scallop shape of CoreValve skirt, the difference of PVL due to TAV orientation can be as large as 40%. Although the stent thickness is small compared to the aortic annulus size, we found that inappropriate modeling of it can lead to an underestimation of PVL up to 10 ml/beat. Moreover, the deployment height could significantly alter the extent and the distribution of regurgitant jets, which results in a change of leaking volume up to 70%. Further investigation in a large cohort of patients is warranted to verify the accuracy of our model. This study demonstrated that a rigorously developed patient-specific computational model can provide useful insights into underlying mechanisms causing PVL and potentially assist in pre-operative planning for TAVR to minimize PVL.
TOPICS: Valves, Leakage, Shapes, Simulation, Jets, Materials properties, Biological tissues, Computational fluid dynamics, Finite element analysis, Modeling, stents, Annulus, Echocardiography
Antonio Copploe, Morteza Vatani, Rouzbeh Amini, Jae-Won Choi and Hossein Tavana
J Biomech Eng   doi: 10.1115/1.4040456
Delivery of biological fluids, such as surfactant solutions, into lungs is a major strategy to treat respiratory disorders including respiratory distress syndrome that is caused by insufficient or dysfunctional natural lung surfactant. The instilled solution forms liquid plugs in lung airways. The plugs propagate downstream in airways by inspired air or ventilation, continuously split at airway bifurcations to smaller daughter plugs and simultaneously lose mass from their trailing menisci, and eventually rupture. A uniform distribution of the instilled biofluid in lung airways is expected to increase the treatments success. The uniformity of distribution of instilled liquid in the lungs greatly depends on the splitting of liquid plugs between daughter airways, especially in the first few generations from which airways of different lobes of lungs emerge. To mechanistically understand this process, we developed a bioengineering approach to computationally design three-dimensional bifurcating airway models using morphometric data of human lungs, fabricate physical models, and examine dynamics of liquid plug splitting. We found that orientation of bifurcating airways has a major effect on the splitting of liquid plugs between daughter airways. Changing the relative gravitational orientation of daughter tubes with respect to the horizontal plane caused a more asymmetric splitting of liquid plugs. Increasing the propagation speed of plugs partially counteracted this effect. Using airway models of smaller dimensions reduced the asymmetry of plug splitting. This work provides a step toward developing delivery strategies for uniform distribution of therapeutic fluids in the lungs.
TOPICS: Bifurcation, Lung, Surfactants, Fluids, Bioengineering, Dimensions, Ventilation, Design, Dynamics (Mechanics), Rupture
Francesca Berti, Luigi La Barbera, Agnese Piovesan, Dario Allegretti, Claudia Ottardi, Tomaso Villa and Giancarlo Pennati
J Biomech Eng   doi: 10.1115/1.4040451
Posterior spinal fixation based on long spinal rods is the clinical gold standard for the treatment of severe deformities. Rods need to be contoured prior to implantation to fit the natural curvature of the spine. The contouring processes is known to introduce residual stresses and strains which affect the static and fatigue mechanical response of the implant, as determined through time- and cost-consuming experimental tests. Finite Element (FE) models promise to provide an immediate understanding on residual stresses and strains within a contoured spinal rods and a further insight on their complex distribution. The present study aims at investigating two rod contouring strategies, French bender (FB) contouring (clinical gold standard) and uniform contouring, through validated FE models. A careful characterization of the elasto-plastic material response of commercial implants is led. Compared to uniform contouring, FB induces highly localized plasticizations in compression under the contouring pin with extensive lateral sections undergoing tensile residual stresses. The sensitivity analysis highlighted that the assumed post-yielding properties significantly affect the numerical predictions, therefore an accurate material characterization is recommended.
TOPICS: Residual stresses, Plasticity, Rods, Titanium, Sensitivity analysis, Fatigue, Finite element analysis, Compression, Finite element model
Yong Teng, Hugo Giambini, Asghar Rezaei, Xifeng Liu, A. Lee Miller II, Brian E. Waletzki and Lichun Lu
J Biomech Eng   doi: 10.1115/1.4040458
A wide range of materials have been used for the development of intervertebral cages. Poly(propylene fumarate) (PPF) has been shown to be an excellent biomaterial with characteristics similar to trabecular bone. Hydroxyapatite (HA) has been shown to enhance biocompatibility and mechanical properties of PPF. The purpose of this study was to characterize the effect of PPF augmented with HA (PPF:HA), and evaluate the feasibility of this material for the development of cervical cages. PPF was synthesized and combined with HA at PPF:HA wt:wt ratios of 100:0, 80:20, 70:30, and 60:40. Molds were fabricated for testing PPF:HA bulk materials in compression, bending, tension and hardness according to ASTM standards, and also for cage preparation. The cages were fabricated with and without holes, and with porosity created by salt leaching. The samples as well as the cages were mechanically tested using a materials testing frame. All elastic moduli as well as the hardness increased significantly by adding HA to PPF (p<0.0001). 20 wt% HA increased the moduli significantly compared to pure PPF (p<0.0001). Compressive stiffness of all cages also increased with the addition of HA. HA increased the failure load of the porous cages significantly (p=0.0018) compared with nonporous cages. PPF:HA wt:wt ratio of 80:20 proved to be significantly stiffer and stronger than pure PPF. The current results suggest that this polymeric composite can be a suitable candidate material for intervertebral body cages.
TOPICS: Materials testing, Biomaterials, Stress, Polymer composites, Bulk solids, Mechanical properties, ASTM standards, Bone, Testing, Compression, Elastic moduli, Failure, Nanocomposites, Porosity, Stiffness, Tension, Biocompatibility
Nir Emuna, David Durban and Shmuel Osovski
J Biomech Eng   doi: 10.1115/1.4040400
Despite major advances made in modeling vascular tissue biomechanics, the predictive power of constitutive models is still limited by uncertainty of the input data. Specifically, key measurements, like the geometry of the stress-free (SF) state, involve a definite, sometimes non-negligible, degree of uncertainty. Here, we introduce a new approach for sensitivity analysis of vascular hyperelastic constitutive models to uncertainty in SF measurements. We have considered two vascular hyperelastic models: the phenomenological Fung model, and the structure-motivated Holzapfel-Gasser-Ogden model. Our results indicate up to 160% errors in the identified constitutive parameters for a 5% measurement uncertainty in the SF data. Relative margins of errors of up to 30% in the luminal pressure, 36% in the axial force, and over 200% in the stress predictions, were recorded for 10% uncertainties. These findings are relevant to the large body of studies involving experimentally based modeling and analysis of vascular tissues. The impact of uncertainties on calibrated constitutive parameters is significant in context of studies that use constitutive parameters to draw conclusions about the underlying microstructure of vascular tissues, their growth and remodeling processes, aging and disease states. The propagation of uncertainties into the predictions of biophysical parameters e.g. force, luminal pressure, and wall stresses, is of practical importance in the design and execution of clinical devices and interventions. Furthermore, insights provided by the present findings may lead to more robust parameters identification techniques, and serve as selection criteria in the trade-off between model complexity and sensitivity.
TOPICS: Stress, Uncertainty, Biological tissues, Constitutive equations, Modeling, Errors, Pressure, Measurement uncertainty, Tradeoffs, Geometry, Sensitivity analysis, Diseases, Design, Biomechanics
Mohammadreza Khani, Lucas Sass, Tao Xing, M. Keith Sharp, Olivier Balédent and Bryn Martin
J Biomech Eng   doi: 10.1115/1.4040401
Cerebrospinal fluid (CSF) dynamics are thought to play a vital role in central nervous system (CNS) physiology. The objective of the present study was to investigate the impact of spinal cord nerve roots (NR) on CSF dynamics. A subject-specific computational fluid dynamics (CFD) model of the complete spinal subarachnoid space (SSS) with and without anatomically realistic NR and non-uniform moving dura wall deformation was constructed. This CFD model allowed detailed investigation of the impact of NR on CSF velocities that is not possible in vivo using MRI or other non-invasive imaging methods. Results showed that NR altered CSF dynamics in terms of velocity field, steady-streaming and vortical structures. Vortices occurred in the cervical spine around NR during CSF flow reversal. The magnitude of steady-streaming CSF flow increased with NR, in particular within the cervical spine. This increase was located axially upstream and downstream of NR due to the interface of adjacent vortices that formed around NR.
TOPICS: Dynamics (Mechanics), Spinal cord, Cerebrospinal fluid, Computational fluid dynamics, Vortices, Cervical spine, Flow (Dynamics), Deformation, Magnetic resonance imaging, Imaging, Physiology, Nervous system
Rotem Halevi, Ashraf Hamdan, Gil Marom, Karin Lavon, Sagit Ben Zekry, Ehud Raanani and Rami Haj-Ali
J Biomech Eng   doi: 10.1115/1.4040338
Calcific aortic valve disease (CAVD) is a progressive disease in which minerals accumulate in the tissue of the aortic valve cusps, stiffening them and preventing valve opening and closing. The process of valve calcification was found to be similar to that of bone formation including cell differentiation to osteoblast-like cells. Studies have shown the contribution of high strains to calcification initiation and growth process acceleration. In this paper, a new calcification growth mechano-biology model is proposed. The model aims to explain the unique shape of the calcification and other disease characteristics. The calcification process was divided into two stages: Calcification initiation and calcification growth. The initiation locations were based on previously published findings and a reverse calcification technique (RCT), which uses computed tomography (CT) scans of patients to reveal the calcification initiation point. The calcification growth process was simulated by a finite element model (FEM) of one aortic valve cusp loaded with cyclic loading. Similar to Wolff's law, describing bone response to stress, our model uses strains to drive calcification formation. The simulation grows calcification from its initiation point to its full typical stenotic shape. Study results showed that the model was able to reproduce the typical calcification growth pattern and shape, suggesting that strain is the main driving force behind calcification progression. The simulation also sheds light on other disease characteristics, such as calcification growth acceleration as the disease progresses, as well as sensitivity to hypertension.
TOPICS: Valves, Biology, Diseases, Shapes, Finite element model, Simulation, Bone, Minerals, Stress, Biological tissues, Computerized tomography, Osteoblasts
Paola Tasso, Anastasios Raptis, Miltiadis Matsagkas, Maurizio Lodi Rizzini, Diego Gallo, Michalis Xenos and Umberto Morbiducci
J Biomech Eng   doi: 10.1115/1.4040337
Endovascular aneurysm repair (EVAR) has disseminated rapidly as an alternative to open surgical repair for the treatment of abdominal aortic aneurysms (AAAs), because of its reduced invasiveness, low mortality and morbidity rate. The effectiveness of the endovascular devices used in EVAR is always at question as postoperative adverse events can lead to re-intervention or to a possible fatal scenario for the circulatory system. Motivated by the assessment of the risks related to thrombus formation, here the impact of two different commercial endovascular grafts on local hemodynamics is explored through 20 image-based computational hemodynamic models of EVAR-treated patients (N=10 per each endograft model). Hemodynamic features, susceptible to promote thrombus formation, such as flow separation and recirculation, are quantitatively assessed and compared with the local hemodynamics established in image-based infrarenal abdominal aortic models of healthy subjects (N=10). The hemodynamic analysis is complemented by a geometrical characterization of the EVAR-induced reshaping of the infrarenal abdominal aortic vascular region. The findings of this study indicate that: (1) the clinically observed propensity to thrombus formation in devices used in EVAR strategies can be explained in terms of local hemodynamics by means of image-based computational hemodynamics approach; (2) reportedly pro-thrombotic hemodynamic structures are strongly correlated with the geometry of the aortoiliac tract postoperatively. In perspective, our study suggests that future clinical follow up studies could include a geometric analysis of the region of the implant, monitoring shape variations that can lead to hemodynamic disturbances of clinical significance.
TOPICS: Maintenance, Computational fluid dynamics, Hemodynamics, Aneurysms, Thrombosis, Shapes, Surgery, Cardiovascular system, Flow separation, Geometry
Jessica Buice, Amanda Esquivel and Christopher Andrecovich
J Biomech Eng   doi: 10.1115/1.4040311
Mild traumatic brain injuries (mTBIs), or concussions, can result from head acceleration during sports. Wearable sensors like the GForceTrackerTM (GFT) can monitor an athlete's head acceleration during play. The purpose of this study was to evaluate the accuracy of the GFT for use in boys' and girls' lacrosse. The GFT was mounted to either lacrosse goggles or a helmet. The assembly was fit to a Hybrid III headform instrumented with sensors and impacted multiple times at different velocities and locations. Measurements of peak linear acceleration and angular velocity were obtained from both systems and compared. It was found that a large percent error between the GFT and headform system existed for linear acceleration (29% for goggles and 123% for helmet) and angular velocity (48% for goggles and 17% for helmet). This error was substantially reduced when correction equations were applied based on impact location (3-14% for goggles and 3-11% for helmet). Our study has shown that the GFT does not accurately calculate linear acceleration or angular velocity at the CG of the head; however, reasonable error can be achieved by correcting data based on impact location.
TOPICS: Sensors, Eye protection, Errors, Sports, Traumatic brain injury, Manufacturing
Maziar Aghvami, John Brunski, Ustun Serdar Tulu, Chih-Hao Chen and Jill Helms
J Biomech Eng   doi: 10.1115/1.4040312
With the introduction of high-speed cutting tools, clinicians have recognized the potential for thermal damage to the material being cut. Here, we developed a mathematical model of heat transfer caused by drilling bones of different densities, and validated it with respect to experimentally measured temperatures in bone. We then coupled these computational results with a biological assessment of cell death following osteotomy site preparation. Parameters under clinical control, e.g., drill diameter, rotational speed, and irrigation, along with patient-specific variables such as bone density were evaluated in order to understand their contributions to thermal damage. Predictions from our models provide insights into temperatures and thresholds that cause osteocyte death and that can ultimately compromise stability of an implant.
TOPICS: Drilling, Bone, Damage, Temperature, Heat transfer, Irrigation (Agriculture), Drills (Tools), Cutting tools, Site preparation (Construction), Density, Stability
Alireza Noamani, Albert Vette, Richard Preuss, Milos R. Popovic and Hossein Rouhani
J Biomech Eng   doi: 10.1115/1.4040247
Kinetics assessment of the human head-arms-trunk (HAT) complex using a multi-segment model is required for clinical evaluation of several pathological conditions. Inaccuracies in body segment parameters (BSPs) is a major source of uncertainty in the estimation of the joint moments associated with the multi-segment HAT. Given the large inter-subject variability, there is currently no comprehensive database for the estimation of BSPs for the HAT. We propose a nonlinear, multi-step, optimization-based, non-invasive method for estimating individual-specific BSPs and calculating joint moments in a multi-segment HAT model. Eleven non-disabled individuals participated in a trunk-bending experiment, and their body motion was recorded using cameras and a force plate. A seven-segment model of the HAT was reconstructed for each participant. An initial guess of the BSPs was obtained by individual-specific scaling of the BSPs calculated from the Male Visible Human images. The inter-segmental moments were calculated using both bottom-up and top-down inverse dynamics approaches. Our proposed method adjusted the scaled BSPs and centre of pressure offsets to estimate optimal individual-specific BSPs that minimize the difference between the moments obtained by top-down and bottom-up inverse dynamics approaches. Our results indicate that the proposed method reduced the error in the net joint moment estimation by 77.59% (average among participants). Our proposed method enables accurate estimation of individual-specific BSPs and, consequently, accurate assessment of the three-dimensional kinetics of a multi-segment HAT model.
TOPICS: Dynamics (Mechanics), Pressure, Optimization, Databases, Errors, Uncertainty
Jorge Barrios-Muriel, Francisco Romero, F.J. Alonso and D.R. Salgado
J Biomech Eng   doi: 10.1115/1.4040250
Nowadays, both usability and comfort play a key role in the development of medical and wearable products. When designing any device that is in contact with the human body, the mechanical behaviour of the embraced soft tissue must be known. The unavoidable displacement of the soft tissue during motion may lead to discomfort adn, thus, the withdrawal of the wearable product. This work presents a new methodology to design and test a wearable device based on the measurement of the dynamic skin strain field. Furthermore, from this field, the anatomical lines with minimum strain (Lines of non extension, LoNEs) are calculated to design the structural parts of the wearable device. Whith this new criteria, the resulting product is not only optimized to reduce the friction in skin-device interface, but fully personalized to the patient's morphology and motion. The methodology is applied to the design of an ankle-foot wearable orthosis for subjects with ankle dorsiflexors muscles weakness due to nervous system disorders. The results confirm that the use of LoNEs may benefit the design of products with a high interaction with the skin.
TOPICS: Design, Skin, Soft tissues, Biomedicine, Nervous system, Mechanical behavior, Displacement, Muscle, Orthotics, Friction
Subhomoy Chatterjee, Sabine Kobylinski and Bikramjit Basu
J Biomech Eng   doi: 10.1115/1.4040249
Innovated acetabular shell designs of total hip replacement have been found to be better than the conventional hemispherical design in terms of component stability. In this study, the impact of shell design (conventional, finned, spiked and combined design) and liner material on the biomechanical response of periprosthetic bone has been analysed through finite element method. Two different liner materials: HDPE-20%HA-20%Al2O3 and highly cross linked ultrahigh molecular weight polyethylene (HC-UHMWPE) were used. The subject parameters included bone condition and bodyweight. Physiologically relevant load cases of a gait cycle were considered. The deviation of mechanical condition of the periprosthetic bone due to implantation was least for the finned shell design. No significant deviation was observed at the bone region adjacent to the spikes and the fins. This study recommends the use of the finned design, particularly for weaker bone conditions. For stronger bones, the combined design may also be recommended for higher stability. The use of HC-UHMWPE liner was found to be better for convensional shell design. However, closer biomechanical environment was found for both the liner materials in case of other shell designs. Overall, the study establishes the biomechanical response of pre-clinically tested liner materials together with new shell design for different subject conditions.
TOPICS: Biomechanics, Bone, Design, Finite element analysis, Modeling, Shells, Stability, Stress, Finite element methods, Cycles, Fins, Molecular weight, Hip joint prostheses
Ravi Patel, Andriy Noshchenko, R. Dana Carpenter, Todd Baldini, Carl Frick, Vikas V. Patel and Christopher Yakacki
J Biomech Eng   doi: 10.1115/1.4040252
Current implant materials and designs used in spinal fusion show high rates of subsidence. There is currently a need for a method to predict the mechanical properties of the endplate using clinically available tools. The purpose of this study was to develop a predictive model of the mechanical properties of the vertebral endplate at a scale relevant to the evaluation of current medical implant designs and materials. Twenty vertebrae (10 L1 and 10 L2) from 10 cadavers were studied using dual-energy x-ray absorptiometry (DEXA) to define bone status (normal, osteopenic, or osteoporotic) and CT to study endplate thickness (µm), density (mg/mm3), and mineral density of underlying trabecular bone (mg/mm3) at discrete sites. Apparent Oliver-Pharr modulus, stiffness, maximum tolerable pressure, and Brinell hardness were measured at each site using a 3mm spherical indenter. Predictive models were built for each measured property using various measures obtained from CT and demographic data. Stiffness showed a strong correlation between the predictive model and experimental values (r=.85), a polynomial model for Brinell Hardness had a stronger predictive ability compared to the linear model (r=.82), and the modulus model showed weak predictive ability (r=.44), likely due the low indentation depth and the inability to image the endplate at that depth (~0.15mm). Osteoporosis and osteopenia were found to be the largest confounders of the measured properties, decreasing them by approximately 50%. It was confirmed that vertebral endplate mechanical properties could be predicted using CT and demographic indices.
TOPICS: Mechanical properties, Computerized tomography, Lumbar spine, Stiffness, Osteoporosis, Bone, Density, Pressure, X-rays, Biomedicine, Polynomials, Spinal fusion, Minerals
Yogesh Deepak Bansod, Takeo Matsumoto, Kazuaki Nagayama and Jiri Bursa
J Biomech Eng   doi: 10.1115/1.4040246
Mechanical interaction of cell with extracellular environment affects its function. The mechanisms by which mechanical stimuli are sensed and transduced into biochemical responses are still not well understood. Considering this, two finite element (FE) bendo-tensegrity models of a cell in different states are proposed with the aim to characterize cell deformation under different mechanical loading conditions: a suspended cell model elucidating the global response of cell in tensile test simulation and an adherent cell model explicating its local response in atomic force microscopy (AFM) indentation simulation. The force-elongation curve obtained from tensile test simulation lies within the range of experimentally obtained characteristics of smooth muscle cells (SMCs) and illustrates a non-linear increase in reaction force with cell stretching. The force-indentation curves obtained from indentation simulations lie within the range of experimentally obtained curves of embryonic stem cells (ESCs) and exhibit the influence of indentation site on the overall reaction force of cell. Simulation results have demonstrated that actin filaments (AFs) and microtubules (MTs) play a crucial role in the cell stiffness during stretching, whereas actin cortex (AC) along with actin bundles (ABs) and MTs are essential for the cell rigidity during indentation. The proposed models quantify the mechanical contribution of individual cytoskeletal components to cell mechanics and the deformation of nucleus under different mechanical loading conditions. These results can aid in better understanding of structure-function relationships in living cells.
TOPICS: Finite element analysis, Tensegrity, Simulation, Deformation, Atomic force microscopy, Stiffness, Surface mount components, Stem cells, Antilock braking systems, Cellular mechanics, Elongation, Biological cells, Muscle, Simulation results
Technical Brief  
Fatemeh Farhadi, Muhammad Faraz, Marabelle Heng and Shane Johnson
J Biomech Eng   doi: 10.1115/1.4040248
Osteoarthritis sufferers commonly have first metatarsophalangeal joint problems in which articular surfaces are changed permanently due to fatigue. Therefore, medical devices for early diagnosis would increase the opportunity for prevention of disease progression. In previous studies on stiffness of the 1st MTPJ many details, although functionally of great importance, have not been fully considered including: design and size of the device, tribology consideration and errors from device. Therefore, the motivation of our research was to enhance the device design by reducing the size of the device, and device design was enhanced by minimizing measurement errors through development of a new ergonomic left and right foot instrument located medial to the 1st MTPJ (instead of beneath the foot). The 1st MTPJ stiffness (N.mm/ kg. radian) measurement was taken on 28 subjects with two replicates per subject by the same tester. The 1st MTPJ stiffness ranged from 3.49 to 14.42 N.mm/ kg. radian with the mean (SD) value of 8.28 (3.15) N.mm/ kg. radian for the left feet and 3.91 to 11.90 N.mm/ kg. radian with the mean (SD) value of 7.65 (2.07) N.mm/ kg. radian for the right feet. Reliability evaluation was measured using Intraclass Correlation Coefficient and described an excellent reliability between two tests.
TOPICS: Testing, Stiffness, Design, Reliability, Errors, Diseases, Instrumentation, Medical devices, Fatigue, Tribology, Osteoarthritis
Deva Chan, Andrew K. Knutsen, Yuan-Chiao Lu, Sarah H Yang, Elizabeth Magrath, Wen-Tung Wang, Philip V Bayly, John A. Butman and Dzung L. Pham
J Biomech Eng   doi: 10.1115/1.4040230
Understanding of in vivo brain biomechanical behavior is critical in the study of traumatic brain injury (TBI) mechanisms and prevention. Using tagged magnetic resonance imaging, we measured spatiotemporal brain deformations in 34 healthy human volunteers under mild angular accelerations of the head. Two-dimensional Lagrangian strains were examined throughout the brain in each subject. Strain metrics peaked shortly after contact with a padded stop, corresponding to the inertial response of the brain after head deceleration. Maximum shear strain of at least 3% was experienced at peak deformation by an area fraction (median ± standard error) of 23.5% ± 1.8% of cortical gray matter, 15.9% ± 1.4% of white matter, and 4.0% ± 1.5% of deep gray matter. Cortical gray matter strains were greater in the temporal cortex on the side of the initial contact with the padded stop and also in the contralateral temporal, frontal, and parietal cortex. These tissue-level deformations from a population of healthy volunteers provide the first in vivo measurements of full-volume brain deformation in response to known kinematics. Although strains differed in different tissue type and cortical lobes, no significant differences between male and female head accelerations or strain metrics were found. These cumulative results highlight important kinematic features of the brain's mechanical response and can be used to facilitate the evaluation of computational simulations of TBI.
TOPICS: Deformation, Magnetic resonance imaging, Brain, Matter, Biological tissues, Kinematics, Engineering simulation, Simulation, Biomechanics, Shear (Mechanics), Errors, Spatiotemporal phenomena, Traumatic brain injury
Carmen Ridao-Fernández, Joaquin Ojeda and Gema Chamorro-Moriana
J Biomech Eng   doi: 10.1115/1.4040020
The main objective was to analyze the changes in the spatial and temporal step parameters during a dual-task: walking with a forearm crutch to partially unload the body weight of the subject. The secondary objective was to determine the influence of the use of the crutch with the dominant or non-dominant hand in the essential gait parameters. Seven healthy subjects performed gait without crutches (GWC) and unilateral assisted gait (UAG) with the crutch carried out by dominant hand (DC) and non-dominant hand (NDC). Gait was recorded using a Vicon System; the GCH System 2.0 and the GCH Control Software 1.0 controlled the loads. The variables were: step length, step period, velocity, step width and step angle. The Wilcoxon signed-rank test compared GWC and UAG while also analyzing the parameters measured for both legs with DC and NDC in general and in each subject. Wilcoxon test only found significant differences in 1 of the 15 general comparisons between both legs. In the analysis by subject, step length, step period and velocity showed significant differences between GWC and UAG. These parameters obtained less differences in DC. The effect of a forearm crutch on UAG caused a reduction in step length and velocity, and an increase in step period. However, it did not entail changes in step angle and step width. UAG was more effective when the dominant hand carried the crutch. The unloading of 10% body weight produced an assisted gait which closely matched GWC.
TOPICS: Weight (Mass), Stress, Computer software

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