15 results found
Newell N, Carpanen D, Grigoriadis G, et al., 2019, Material properties of human lumbar intervertebral discs across strain rates, Spine Journal, Vol: 19, Pages: 2013-2024, ISSN: 1529-9430
Background context:The use of finite-element (FE) methods to study the biomechanics of the intervertebral disc (IVD) has increased over recent decades due to their ability to quantify internal stresses and strains throughout the tissue. Their accuracy is dependent upon realistic, strain-rate dependent material properties, which are challenging to acquire. Purpose:The aim of this study was to use the inverse FE technique to characterize the material properties of human lumbar IVDs across strain rates.Study Design:A human cadaveric experimental study coupled with an inverse finite element study.Methods:To predict the structural response of the IVD accurately, the material response of the constituent structures was required. Therefore, compressive experiments were conducted on 16 lumbar IVDs (39 ± 19 years) to obtain the structural response. An FE model of each of these experiments was developed and then run through an inverse FE algorithm to obtain subject-specific constituent material properties, such that the structural response was accurate.Results:Experimentally, a log-linear relationship between IVD stiffness and strain rate was observed. The material properties obtained through the subject-specific inverse FE optimization of the anulus fibrosus (AF) fiber and AF fiber ground matrix allowed a good match between the experimental and FE response. This resulted in a Young’s Modulus of AF fibers (YMAF - MPa) to strain rate (ε ̇ - /s) relationship of YMAF=31.5ln(ε ̇ )+435.5, and the C10 parameter of the Neo-Hookean material model of the AF ground matrix was found to be strain-rate independent with an average value of 0.68 MPa.Conclusions:These material properties can be used to improve the accuracy, and therefore predictive ability of FE models of the spine that are used in a wide range of research areas and clinical applications.Clinical SignificanceFinite element models can be used for many applications including investigating low-back p
Injuries sustained due to attacks from explosive weapons are multiple in number, complex in nature, and not well characterised. Blast may cause damage to the human body by the direct effect of overpressure, penetration by highly energised fragments, and blunt trauma by violent displacements of the body. The ability to reproduce the injuries of such insults in a well-controlled fashion is essential in order to understand fully the unique mechanism by which they occur, and design better treatment and protection strategies to alleviate the resulting poor long-term outcomes. This paper reports a range of experimental platforms that have been developed for different blast injury models, their working mechanism, and main applications. These platforms include the shock tube, split-Hopkinson bars, the gas gun, drop towers and bespoke underbody blast simulators.
Grigoriadis G, Carpanen D, Webster CE, et al., 2019, Lower limb posture affects the mechanism of injury in under-body blast, Annals of Biomedical Engineering, Vol: 47, Pages: 306-316, ISSN: 0090-6964
Over 80% of wounded Service Members sustain at least one extremity injury. The 'deck-slap' foot, a product of the vehicle's floor rising rapidly when attacked by a mine to injure the limb, has been a signature injury in recent conflicts. Given the frequency and severity of these combat-related extremity injuries, they require the greatest utilisation of resources for treatment, and have caused the greatest number of disabled soldiers during recent conflicts. Most research efforts focus on occupants seated with both tibia-to-femur and tibia-to-foot angles set at 90°; it is unknown whether results obtained from these tests are applicable when alternative seated postures are adopted. To investigate this, lower limbs from anthropometric testing devices (ATDs) and post mortem human subjects (PMHSs) were loaded in three different seated postures using an under-body blast injury simulator. Using metrics that are commonly used for assessing injury, such as the axial force and the revised tibia index, the lower limb of ATDs were found to be insensitive to posture variations while the injuries sustained by the PMHS lower limbs differed in type and severity between postures. This suggests that the mechanism of injury depends on the posture and that this cannot be captured by the current injury criteria. Therefore, great care should be taken when interpreting and extrapolating results, especially in vehicle qualification tests, when postures other than the 90°-90° are of interest.
Grigoriadis G, Carpanen D, Webster C, et al., 2018, The posture of the lower limb alters the mechanism of injury in under-body blast, International Research Council on the Biomechanics of Injury, IRCOBI, Pages: 758-759, ISSN: 2235-3151
Klemt C, Nolte D, Grigoriadis G, et al., 2017, The contribution of the glenoid labrum to glenohumeral stability under physiological joint loading using finite element analysis, Computer Methods in Biomechanics and Biomedical Engineering, Vol: 20, Pages: 1613-1622, ISSN: 1025-5842
Christou A, Grigoriadis G, Carpanen D, et al., 2017, Biomechanics of a lumbar functional unit using the finite element method, 2017 IRCOBI Conference, Pages: 668-669, ISSN: 2235-3151
Newell N, Carpanen D, Christou A, et al., 2017, Strain rate dependence of internal pressure and external bulge in human intervertebral discs during axial compression, 2017 IRCOBI Conference, Pages: 670-671, ISSN: 2235-3151
Grigoriadis G, Carpanen D, Webster C, et al., 2017, The effect of the posture of the lower limb in anti-vehicular explosions, 2017 IRCOBI Conference, Pages: 709-710, ISSN: 2235-3151
Newell N, Grigoriadis G, Christou A, et al., 2017, Material properties of bovine intervertebral discs across strain rates, Journal of The Mechanical Behavior of Biomedical Materials, Vol: 65, Pages: 824-830, ISSN: 1751-6161
The intervertebral disc (IVD) is a complex structure responsible for distributing compressive loading to adjacent vertebrae and allowing the vertebral column to bend and twist. To study the mechanical behaviour of individual components of the IVD, it is common for specimens to be dissected away from their surrounding tissues for mechanical testing. However, disrupting the continuity of the IVD to obtain material properties of each component separately may result in erroneous values. In this study, an inverse finite element (FE) modelling optimisation algorithm has been used to obtain material properties of the IVD across strain rates, therefore bypassing the need to harvest individual samples of each component. Uniaxial compression was applied to ten fresh-frozen bovine intervertebral discs at strain rates of 10-3–1/s. The experimental data were fed into the inverse FE optimisation algorithm and each experiment was simulated using the subject specific FE model of the respective specimen. A sensitivity analysis revealed that the IVD's response was most dependent upon the Young's modulus (YM) of the fibre bundles and therefore this was chosen to be the parameter to optimise. Based on the obtained YM values for each test corresponding to a different strain rate (View the MathML source), the following relationship was derived:View the MathML source. These properties can be used in finite element models of the IVD that aim to simulate spinal biomechanics across loading rates.
Ramasamy A, masouros S, grigoriadis, 2017, The lower extremities: Computational Modelling Attempts to Predict Injury, Military Injury Biomechanics The Cause and Prevention of Impact Injuries, Publisher: CRC Press, ISBN: 9781498742825
An international team of experts have been brought together to examine and review the topics. The book is intended for researchers, postgraduate students and others working or studying defence and impact injuries.
Grigoriadis G, Carpanen D, Bull AMJ, et al., 2016, A finite element model of the foot and ankle for prediction of injury in under-body blast, International Research Council on the Biomechanics of Injury, Publisher: IRCOBI, Pages: 457-458, ISSN: 2235-3151
Grigoriadis G, Newell N, Carpanen D, et al., 2016, Material properties of the heel fat pad across strain rates, Journal of the Mechanical Behavior of Biomedical Materials, Vol: 65, Pages: 398-407, ISSN: 1751-6161
The complex structural and material behaviour of the human heel fat pad determines the transmission of plantar loading to the lower limb across a wide range of loading scenarios; from locomotion to injurious incidents. The aim of this study was to quantify the hyper-viscoelastic material properties of the human heel fat pad across strains and strain rates. An inverse finite element (FE) optimisation algorithm was developed and used, in conjunction with quasi-static and dynamic tests performed to five cadaveric heel specimens, to derive specimen-specific and mean hyper-viscoelastic material models able to predict accurately the response of the tissue at compressive loading of strain rates up to 150 s−1. The mean behaviour was expressed by the quasi-linear viscoelastic (QLV) material formulation, combining the Yeoh material model (C10=0.1MPa, C30=7MPa, K=2GPa) and Prony׳s terms (A1=0.06, A2=0.77, A3=0.02 for τ1=1ms, τ2=10ms, τ3=10s). These new data help to understand better the functional anatomy and pathophysiology of the foot and ankle, develop biomimetic materials for tissue reconstruction, design of shoe, insole, and foot and ankle orthoses, and improve the predictive ability of computational models of the foot and ankle used to simulate daily activities or predict injuries at high rate injurious incidents such as road traffic accidents and underbody blast.
Newell N, Grigoriadis G, Christou A, et al., 2016, Mechanical characterisation of bovine intervertebral discs at a range of strain rates, Ircobi, Pages: 158-159
Christou AK, Spurrier E, Grigoriadis G, et al., 2015, Human cadaveric bi-segment impact experiments at different postures, Pages: 742-743
Grigoriadis G, Newell N, Masouros SD, et al., 2014, The material properties of the human heel fat pad across strain-rates: An inverse finite element approach, Pages: 478-479
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