ABSTRACT
Biological soft tissues exhibit a strongly nonlinear viscoelastic behaviour. Among parenchymous tissues, kidney and liver remain less studied than brain, and a first goal of this study is to report additional material properties of kidney and liver tissues in oscillatory shear and constant shear rate tests. Results show that the liver tissue is more compliant but more strain hardening than kidney. A wealth of multi-parameter mathematical models has been proposed for describing the mechanical behaviour of soft tissues. A second purpose of this work is to develop a new constitutive law capable of predicting our experimental data in the both linear and nonlinear viscoelastic regime with as few parameters as possible. We propose a nonlinear strain-hardening fractional derivative model in which six parameters allow fitting the viscoelastic behaviour of kidney and liver tissues for strains ranging from 0.01 to 1 and strain rates from 0.0151 s(-1) to 0.7s(-1).
Subject(s)
Kidney/physiology , Liver/physiology , Models, Biological , Animals , Computer Simulation , Elastic Modulus/physiology , Hardness/physiology , Nonlinear Dynamics , Stress, Mechanical , Swine , ViscosityABSTRACT
Tests were conducted on four rib cages to characterize their 3D deformation and the kinematics of the costovertebral joints. The influence of the structural properties, i.e. geometry and initial rib slopes, and of the costo-vertebral joints on the deformation capacity of the rib cage during a dynamic loading was studied. Each rib cage was loaded four times by increasing, up to 40% of the initial thickness, the mid-sternum deflection. The spine was rigidly fixed without constraining the costo-vertebral joints and the rib motions were computed from 3D video analysis. In addition, numerical simulations were performed with subject-specific models obtained from the rib cage geometry and a method for model personalization. The objective was to numerically evaluate the sensitivity to solely changes in geometry. The rib rotations were determined from the motion of 3D-markers close to the costo-vertebral joints and the 3D rib deformations were assessed from the motion of markers along the ribs. The rib rotations varied with the costal level (mean value 5.8 degrees [max. 7.9 degrees, min. 3.5 degrees], 2.9 degrees [4.8 degrees, 1.0 degree], 2.5 degrees [4.8 degrees, 1.1 degrees] and 2.2 degrees [3.5 degrees, 0.8 degree] for rib 2, 4, 6 and 8 respectively) and among the subjects (mean variation from 3.3 degrees to 7.1 degrees). The rib deformations were mainly in the sagittal plane for the upper ribs and in the rib plane for the lower. Although, no statistically significant correlations were found with different morphometrics parameters, a link (R2>0.4) was found between the initial rib slope and the amount of rotation and deformations, according to the assumption described by Kent et al (2005). The costovertebral joint was described by a functional rotation axis (i.e. helical axis) that does not correspond to the physiological axis of rotation. The orientation and the position of this helical axis changed with the level of deflection and varied with the costal level.
Subject(s)
Acceleration , Models, Biological , Physical Stimulation/methods , Ribs/anatomy & histology , Ribs/physiology , Weight-Bearing/physiology , Aged, 80 and over , Cadaver , Compressive Strength/physiology , Computer Simulation , Elastic Modulus/physiology , Female , Humans , Male , Movement/physiologyABSTRACT
An in-depth study was conducted through the analysis of medical reports and crash data from real world accidents. The objective was to investigate the abdominal injury patterns among car occupants in frontal crashes. The influence of the type of restraint system, the occupant seat, the age and the crash severity was investigated. The results indicate that the risk of abdominal AIS 3+ injuries increased with crash severity and decreased with the introduction of belt retractors. Rear belted passengers were observed to be more likely injured than front belted occupants. The organs injured in frontal crashes for belted occupants were mainly hollow organs especially jejunum, ileum and mesentery.
Subject(s)
Abdominal Injuries/physiopathology , Accidents, Traffic , Acceleration , Adult , Databases as Topic , Humans , Injury Severity Score , Logistic Models , Seat Belts/statistics & numerical data , United StatesABSTRACT
Six European laboratories have evaluated the biomechanical response of the new advanced frontal impact dummy THOR-alpha with respect to the European impact response requirements. The results indicated that for many of the body regions (e.g. shoulder, spine, thorax, femur/knee) the THOR-alpha response was close to the human response. In addition, the durability, repeatability and sensitivity for some dummy regions have been evaluated. Based on the tests performed, it was found that the THOR-alpha is not durable enough. The lack in robustness of the THOR-alpha caused a problem in completing the full test program and in evaluating the repeatability of the dummy. The results have demonstrated that the assessment of frontal impact protection can be greatly improved with a more advanced frontal impact dummy. Regarding biofidelity and injury assessment capabilities, the THOR-alpha is a good candidate however it needs to be brought up to standard in other areas. Based on the results obtained recommendations were defined for the improvement of the THOR-alpha dummy.
