Accepted Manuscripts

Technical Brief  
Seyed mohammad javid Mahmoudzadeh Akherat, Kevin Cassel, Michael Boghosian, Promila Dhar and Mary Hammes
J Biomech Eng   doi: 10.1115/1.4035915
Given the current emphasis on accurate Computational Fluid Dynamics (CFD) modeling of cardiovascular flows, which encompasses realistic geometries and cardiac waveforms, it is necessary to revisit the conventional wisdom regarding the influences of non-Newtonian effects. In this study, patient-specific reconstructed 3D geometries, viscosity data, and venous pulses post dialysis access surgery are used as the basis for the hemodynamic simulations. Rheological analysis of the viscometry data initially suggested that the correct choice of constitutive relations to capture the non-Newtonian behavior of blood is important because the End Stage Renal Disease (ESRD) patient cohort under observation experience drastic alteration in whole blood viscosity throughout the hemodialysis treatment. Various constitutive relations have been tested for this purpose, namely Quemada and Casson. Because of the specific interest in the onset of Neointimal Hyperplasia (NH) and stenosis in this study, particular attention is placed on differences in Wall Shear Stress (WSS) as that drives the adaptation process that leads to geometric modifications over time. The results exhibit no major differences in the flow field and general flow characteristics between a non-Newtonian simulation compared to a corresponding identical Newtonian simulation. It is found that geometric features of patient-specific geometries have greater influence on the WSS distribution within the numerical domain.
TOPICS: Simulation, Hemodynamics, Flow (Dynamics), Computational fluid dynamics, Constitutive equations, Modeling, Surgery, Cardiovascular system, Diseases, Viscosity, Rheology, Blood, Hemorheology, Kidney, Hemodialysis, Shear stress
Design Innovation Paper  
John C Cagle, Per G. Reinhall, Brian J Hafner and Joan E Sanders
J Biomech Eng   doi: 10.1115/1.4035917
A set of protocols was created to characterize prosthetic liners across six clinically relevant material properties. Properties included compressive elasticity, shear elasticity, tensile elasticity, volumetric elasticity, coefficient of friction, and thermal conductivity. Eighteen prosthetic liners representing the diverse range of commercial products were evaluated to create test procedures that maximized repeatability, minimized error, and provided clinically meaningful results. Shear and tensile elasticity test designs were augmented with finite element analysis to optimize specimen geometries. Results showed that because of the wide range of available liner products, the compressive elasticity and tensile elasticity tests required two test maxima; samples were tested until they met either a strain-based or a stress-based maximum, whichever was reached first. The shear and tensile elasticity tests required that no cyclic conditioning be conducted because of limited endurance of the mounting adhesive with some liner materials. The coefficient of friction test was based on dynamic coefficient of friction, as it proved to be a more reliable measurement than static coefficient of friction. The volumetric elasticity test required that air be released beneath samples in the test chamber before testing. The thermal conductivity test best reflected the clinical environment when thermal grease was omitted and when liner samples were placed under pressure consistent with load bearing conditions. The developed procedures provide a standardized approach for evaluating liner products in the prosthetics industry. Test results can be used to improve clinical selection of liners for individual patients and guide development of new liner products.
TOPICS: Materials testing, Artificial limbs, Elasticity, Friction, Shear (Mechanics), Stress, Thermal conductivity, Bearings, Finite element analysis, Testing, Adhesives, Materials properties, Errors, Pressure
Rupak K. Banerjee, Gavin A. D'Souza, Anup K Paul and Ashish Das
J Biomech Eng   doi: 10.1115/1.4035916
Factors that affect the arterial wall compliance ('c') are the tissue properties, the in-vivo pulsatile pressure, and the prestressed condition of the artery. It is necessary to obtain the load-free geometry for determining the physiological prestress in the wall. The previously developed optimization-based inverse algorithm was improved to obtain the load-free geometry and the wall prestress of an idealized tapered femoral artery of a dog under varying arterial wall properties. The 'c' was also evaluated over a range of systemic pressures (72.5-140.7 mmHg), associated blood flows, and wall properties using the prestressed geometry. Results showed that the computed load-free outer diameter at the inlet of the artery was 6.7%, 9.0%, and 12% smaller than the corresponding in-vivo diameter for the 25% softer, baseline, and 25% stiffer wall properties, respectively. Conversely, variations in the prestressed geometry and circumferential wall prestress were less than 2% for variable wall properties. The 'c' at the inlet of the prestressed artery for the baseline wall property was 0.34, 0.19 and 0.13 % diameter change/mmHg for time-averaged pressures of 72.5, 104.1, and 140.7 mmHg, respectively. However, variations in 'c' due to the change in wall property were less than 6%. The load-free and prestressed geometries were accurately (within 1.2% of the in-vivo geometry) computed under variable wall properties. The 'c' was influenced significantly by the change in average pressure, but not due to wall property.
TOPICS: Optimization, Geometry, Stress, Algorithms, Pressure, Biological tissues, Physiology, Blood flow
Technical Brief  
Giulia Mantovani and Mario Lamontagne
J Biomech Eng   doi: 10.1115/1.4034708
The choice of marker set is a source of variability in motion analysis. Studies exist that assess the performance of marker sets when direct kinematics is used, but these results cannot be extrapolated to the inverse kinematic framework. Therefore, the purpose of this study was to examine the sensitivity of kinematic outcomes to inter-marker set variability in an inverse kinematic framework. The compared marker sets were Plug-in-Gait, University of Ottawa Motion Analysis Model and a 3-marker-cluster marker set. Walking trials of twelve participants were processed in OpenSim. The coefficient of multiple correlations was very good for sagittal (>0.99) and transverse (>0.92) plane angles, but worsened for the transverse plane (0.72). Absolute reliability indices are also provided for comparison among studies: minimum detectable change values ranged from the 3° for the hip sagittal range of motion, to the 16.6° of the hip transverse range of motion. Ranges of motion of hip and knee abduction/adduction angles, and hip and ankle rotations were significantly different among the three marker configurations (P<0.001), with Plug-in-Gait producing larger ranges of motion. Although the same model was used for all marker sets, the resulting minimum detectable changes were high and clinically relevant, which warns for caution when comparing studies that use different marker configurations, especially if they differ in the joint-defining markers.
TOPICS: Kinematics, Reliability, Performance, Knee
Technical Brief  
Nachiket M. kharalkar, Steven C. Bauserman and Jonathan W. Valvano
J Biomech Eng   doi: 10.1115/1.4026559
Effect of formalin fixation on thermal conductivity of the biological tissues is presented. A self-heated thermistor probe was used to measure the tissue thermal conductivity. The thermal conductivity of muscle and fatty tissue samples was measured before the formalin fixation and then 27 hours after formalin fixation. The results indicate that the formalin fixation does not cause a significant change in the tissue thermal conductivity of muscle and fatty tissues. In the clinical setting, tissues removed surgically are often fixed in formalin for subsequent pathological analysis. These results suggest that, in terms of thermal properties, it is equally appropriate to perform in vitro studies in either fresh tissue or formalin-fixed tissue.
TOPICS: Thermal conductivity, Biological tissues, Muscle, Probes, Surgery, Thermal properties

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