149 results found
Wadee MA, Bekele A, Phillips ATM, 2023, Harnessing instabilities within metamaterial structures, Pages: 653-659
Advances in additive manufacturing are increasingly allowing bespoke, carefully designed, metamaterial lattice structures to be constructed for enhanced mechanical performance. For instance, in structural elements that are designed to absorb energy and shield a more valuable structure, the properties combining a high initial stiffness followed by a practically zero underlying stiffness, ensure that a desired energy quantity may be absorbed within a limited displacement and that any stress transfer to the valuable structure is minimized. Presently, a lattice structure is studied that is deliberately designed to switch locally under compression between conventional material behaviour to that exhibiting auxetic (negative Poisson’s ratio) behavior through a sequence of snap-through instabilities within layers of individual lattice cells. The sequence of buckling instabilities can potentially be controlled to maintain the loading level alongside the low structural stiffness while the required energy quantity is absorbed, without necessarily damaging the material in the process. This departs from the usual paradigm where such structures are presently designed to be sacrificial and opens up the intriguing possibility of introducing such structural elements that are repairable and therefore reusable.
Bicer M, Phillips ATM, Melis A, et al., 2022, Generative deep learning applied to biomechanics: A new augmentation technique for motion capture datasets, JOURNAL OF BIOMECHANICS, Vol: 144, ISSN: 0021-9290
Caillet A, Phillips ATM, Farina D, et al., 2022, Mathematical relationships between spinal motoneuron properties, eLife, Vol: 11, ISSN: 2050-084X
Our understanding of the behaviour of spinal alpha-motoneurons (MNs) in mammals partly relies on our knowledge of the relationships between MN membrane properties, such as MN size, resistance, rheobase, capacitance, time constant, axonal conduction velocity and afterhyperpolarization period. We reprocessed the data from 40 experimental studies in adult cat, rat and mouse MN preparations, to empirically derive a set of quantitative mathematical relationships between these MN electrophysiological and anatomical properties. This validated mathematical framework, which supports past findings that the MN membrane properties are all related to each other and clarifies the nature of their associations, is besides consistent with the Henneman’s size principle and Rall’s cable theory. The derived mathematical relationships provide a convenient tool for neuroscientists and experimenters to complete experimental datasets, to explore relationships between pairs of MN properties never concurrently observed in previous experiments, or to investigate inter-mammalian-species variations in MN membrane properties. Using this mathematical framework, modelers can build profiles of inter-consistent MN-specific properties to scale pools of MN models, with consequences on the accuracy and the interpretability of the simulations.
Caillet AH, Phillips ATM, Farina D, et al., 2022, Estimation of the firing behaviour of a complete motoneuron pool by combining electromyography signal decomposition and realistic motoneuron modelling., PLoS Comput Biol, Vol: 18
Our understanding of the firing behaviour of motoneuron (MN) pools during human voluntary muscle contractions is currently limited to electrophysiological findings from animal experiments extrapolated to humans, mathematical models of MN pools not validated for human data, and experimental results obtained from decomposition of electromyographical (EMG) signals. These approaches are limited in accuracy or provide information on only small partitions of the MN population. Here, we propose a method based on the combination of high-density EMG (HDEMG) data and realistic modelling for predicting the behaviour of entire pools of motoneurons in humans. The method builds on a physiologically realistic model of a MN pool which predicts, from the experimental spike trains of a smaller number of individual MNs identified from decomposed HDEMG signals, the unknown recruitment and firing activity of the remaining unidentified MNs in the complete MN pool. The MN pool model is described as a cohort of single-compartment leaky fire-and-integrate (LIF) models of MNs scaled by a physiologically realistic distribution of MN electrophysiological properties and driven by a spinal synaptic input, both derived from decomposed HDEMG data. The MN spike trains and effective neural drive to muscle, predicted with this method, have been successfully validated experimentally. A representative application of the method in MN-driven neuromuscular modelling is also presented. The proposed approach provides a validated tool for neuroscientists, experimentalists, and modelers to infer the firing activity of MNs that cannot be observed experimentally, investigate the neuromechanics of human MN pools, support future experimental investigations, and advance neuromuscular modelling for investigating the neural strategies controlling human voluntary contractions.
Bicer M, Phillips A, Modenese L, 2022, Generative deep learning applied to biomechanics: creating an infinite number of realistic walking data for modelling and data augmentation purposes
Our work using generative deep learning models to generate synthetic human movement data to augment existing datasets was presented at the 9th World Congress of Biomechanics.
Bicer M, Phillips ATM, Modenese L, 2022, Altering the strength of the muscles crossing the lower limb joints only affects knee joint reaction forces, GAIT & POSTURE, Vol: 95, Pages: 210-216, ISSN: 0966-6362
Caillet A, Phillips ATM, Farina D, et al., 2022, Prediction of the firing behaviour of the motoneuron population for motoneuron-driven muscle modelling, 9th World Congress of Biomechanics
Modenese L, Caillet A, Phillips A, et al., 2022, A novel neuromechanical model for predicting muscle force from motoneuron spike trains, 27th Congress of the European Society of Biomechanics
Caillet AHD, Phillips ATM, Farina D, et al., 2021, Mathematical Relationships between Spinal Motoneuron Properties, Publisher: Cold Spring Harbor Laboratory
<jats:p>Our understanding of the behaviour of alpha-motoneurons (MNs) in mammals partly relies on our knowledge of the relationships between MN membrane properties, such as MN size, resistance, rheobase, capacitance, time constant, axonal conduction velocity and afterhyperpolarization period. Based on scattered but converging evidence, current experimental studies and review papers qualitatively assumed that some of these MN properties are related. In this systematic meta-analysis, we reprocessed the data from 40 experimental studies in adult cat, rat and mouse MN preparations in vivo to empirically derive mathematical relations between experimentally measured MN electrophysiological and anatomical properties. These mathematical relationships provide the first validated framework of MN-specific morphometric and electrophysiological properties that reproduce published experimental mammal data in vivo. These relationships moreover support the classic description of a MN as a membrane equivalent electrical circuit and describe for the first time the association between MN size and MN membrane capacitance and time constant. The obtained relationships finally indicate that motor units are recruited in order of increasing MN size, muscle unit size, MN rheobase, unit force recruitment thresholds and tetanic forces, but underlines that MN size and recruitment order may not be related to motor unit type.</jats:p>
Caillet A, Phillips ATM, Farina D, et al., 2021, Development of a high-density EMG-driven Hill-type muscle model, XXVII Congress of the International Society of Biomechanics, Publisher: International Society of Biomechanics
Bicer M, Phillips ATM, Modenese L, 2021, Changing the strength of muscles crossing single lower limb joints only affects knee joint reaction forces, ESBiomech 2021
Our work investigating effects of muscle strenghts on joint reaction force estimations was presented at the 26th Congress of the European Society of Biomechanics.
Favier C, McGregor A, Phillips A, 2021, Maintaining bone health in the lumbar spine: routine activities alone are not enough, Frontiers in Bioengineering and Biotechnology, Vol: 9, ISSN: 2296-4185
Public health organisations typically recommend a minimum amount of moderate intensity activities such as walking or cycling for two and a half hours a week, combined with some more demanding physical activity on at least 2 days a week to maintain a healthy musculoskeletal condition. For populations at risk of bone loss in the lumbar spine, these guidelines are particularly relevant. However, an understanding of how these different activities are influential in maintaining vertebral bone health is lacking. A predictive structural finite element modelling approach using a strain-driven algorithm was developed to study mechanical stimulus and bone adaptation in the lumbar spine under various physiological loading conditions. These loading conditions were obtained with a previously developed full-body musculoskeletal model for a range of daily living activities representative of a healthy lifestyle. Activities of interest for the simulations include moderate intensity activities involving limited spine movements in all directions such as, walking, stair ascent and descent, sitting down and standing up, and more demanding activities with large spine movements during reaching and lifting tasks. For a combination of moderate and more demanding activities, the finite element model predicted a trabecular and cortical bone architecture representative of a healthy vertebra. When more demanding activities were removed from the simulations, areas at risk of bone degradation were observed at all lumbar levels in the anterior part of the vertebral body, the transverse processes and the spinous process. Moderate intensity activities alone were found to be insufficient in providing a mechanical stimulus to prevent bone degradation. More demanding physical activities are essential to maintain bone health in the lumbar spine.
Favier C, Finnegan M, Quest R, et al., 2021, An open-source musculoskeletal model of the lumbar spine and lower limbs: a validation for movements of the lumbar spine, Computer Methods in Biomechanics and Biomedical Engineering, Vol: 24, Pages: 1310-1325, ISSN: 1025-5842
Musculoskeletal models of the lumbar spine have been developed with varying level of detail for a wide range of clinical applications. Providing consistency is ensured throughout the modelling approach, these models can be combined with other computational models and be used in predictive modelling studies to investigate bone health deterioration and the associated fracture risk. To provide precise physiological loading conditions for such predictive modelling studies, a new full-body musculoskeletal model including a detailed and consistent representation of the lower limbs and the lumbar spine was developed. The model was assessed against in-vivo measurements from the literature for a range of spine movements representative of daily living activities. Comparison between model estimations and electromyography recordings was also made for a range of lifting tasks. This new musculoskeletal model will provide a comprehensive physiological mechanical environment for future predictive finite element modelling studies on bone structural adaptation. It will be made freely available on https://simtk.org/projects/llsm/.
Deane JA, Papi E, Phillips A, et al., 2020, Reliability and minimal detectable change of the ‘Imperial Spine’ marker set for the evaluation of spinal and lower limb kinematics in adults, BMC Research Notes, Vol: 13, ISSN: 1756-0500
ObjectivesAs a step towards the comprehensive evaluation of movement in patients with low back pain, the aim of this study is to design a marker set (three rigid segment spine, pelvic and lower limb model) and evaluate the reliability and minimal detectable change (MDC) of this marker set in healthy adults during gait and sit to stand (STS) tasks using three dimensional motion capture.ResultsThe ‘Imperial Spine’ marker set was used to assess relative peak angles during gait and STS tasks using the minimum recommended sample size (n = 10) for reliability studies with minimum Intraclass Correlation Coefficient (ICC) of 0.70, optimum ICC 0.90 and 9 trials replicated per subject per task. Intra- and inter-tester reliability between an experienced and inexperienced user was examined. ICC, mean, standard error (SEM), Bland Altman 95% limits of agreement (LOA) and MDC were computed.ICC values demonstrated excellent intra- and inter-tester reliability in both tasks, particularly in the sagittal plane (majority ICCs > 0.80). SEM measurements were lower in gait (0.8–5.5°) than STS tasks (1°-12.6°) as were MDC values. LOA demonstrated good agreement. The ‘Imperial Spine’ marker set is reliable for use in healthy adults during functional tasks. Future evaluation in patients is required.
Villette C, Zhang J, Phillips A, 2020, Influence of femoral external shape on internal architecture and fracture risk, Biomechanics and Modeling in Mechanobiology, Vol: 19, Pages: 1251-1261, ISSN: 1617-7940
The internal architecture of the femur and its fracture behaviour vary greatly between subjects. Femoral architecture and subsequent fracture risk are strongly influenced by load distribution during physical activities of daily living. The objective of this work is to evaluate the impact of outer cortical surface shape as a key affector of load distribution driving femoral structure and fracture behaviour. Different femur cortical shapes are generated using a statistical shape model. Their mesoscale internal architecture is predicted for the same activity regime using a structural optimisation approach previously reported by the authors and fracture under longitudinal compression is simulated. The resulting total volume of bone is similar in all geometries although substantial differences are observed in distribution between trabecular and cortical tissue. Greater neck-shaft and anteversion angles show a protective effect in longitudinal compression while a thinner shaft increases fracture risk.
Wadee MA, Phillips ATM, Bekele A, 2020, Effects of disruptive inclusions in sandwich core lattices to enhance energy absorbency and structural isolation performance, Frontiers in Materials, Vol: 7, ISSN: 2296-8016
The energy absorption and structural isolation performance of axially-compressed sandwich structures constructed with stiff face plates separated with an auxetic lattice core metamaterial is studied. Advances in additive manufacturing increasingly allow bespoke, carefully designed, structures to be included within the core lattice to enhance mechanical performance. Currently, the internal structure of the lattice core is deliberately disrupted geometrically to engineer suitable post-buckling behaviour under quasi-static loading. The desirable properties of a high fundamental stiffness and a practically zero underlying stiffness in the post-buckling range ensure that energy may be absorbed within a limited displacement and that any transfer of strain to an attached structure is minimized as far as is feasible. It is demonstrated that such disruptions can be arranged to enhance the panel performance. The concept may be extended to promote cellular buckling where the internal lattice buckles with densification occurring at defined locations and in sequence to absorb energy while maintaining a low underlying mechanical stiffness.
Favier C, Deane J, McGregor A, et al., 2019, Design and preliminary testing of a low-cost balance perturbation system for the evaluation of real life postural adjustment on public transport, Journal of Medical Engineering and Technology, Vol: 43, Pages: 356-362, ISSN: 0309-1902
Balance recovery mechanisms are of paramount importance in situations like public transport where sudden loss of equilibrium can occur. These mechanisms can be altered by aging or pathological disorders. However it is almost impossible to investigate these phenomena in real-life conditions, and the safe environment of a laboratory is needed. This paper investigates how jerk perturbations in the transverse plane similar to those experienced on public transport can be simulated in a controlled manner. A platform capable of producing horizontal perturbations with a person standing on it was developed. Accuracy, repeatability, and load sensitivity of the system were assessed with repeated trials in all four directions of movement. Comparison between the destabilising effect experienced on public transport and the postural response to perturbations from the platform was also made by tracking acceleration of the centre of mass of four subjects in these two situations. Results show that balance perturbations representative of real-life situations, such as standing on public transport, can accurately and repeatedly be produced in a safe and controlled environment with a low-cost and low-maintenance system. Coupled to motion capture technology, the system can be used for pathology assessment and rehabilitation treatments.
Zaharie D, Phillips A, 2019, A comparative study of continuum and structural modelling approaches to simulate bone adaptation in the pelvic construct, Applied Sciences, Vol: 9, Pages: 1-18, ISSN: 2076-3417
This study presents the development of a number of finite element (FE) models of the pelvis using different continuum and structural modelling approaches. Four FE models were developed using different modelling approaches: continuum isotropic, continuum orthotropic, hybrid isotropic and hybrid orthotropic. The models were subjected to an iterative adaptation process based on the Mechanostat principle. Each model was adapted to a number of common daily living activities (walking, stair ascent, stair descent, sit-to-stand and stand-to-sit) by applying onto it joint and muscle loads derived using a musculoskeletal modelling framework. The resulting models, along with a structural model previously developed by the authors, were compared visually in terms of bone architecture, and their response to a single load case was compared to a continuum FE model derived from computed tomography (CT) imaging data. The main findings of this study were that the continuum orthotropic model was the closest to the CT derived model in terms of load response albeit having less total bone volume, suggesting that the role of material directionality in influencing the maximum orthotropic Young’s modulus should be included in continuum bone adaptation models. In addition, the hybrid models, where trabecular and cortical bone were distinguished, had similar outcomes, suggesting that the approach to modelling trabecular bone is less influential when the cortex is modelled separately.
Phillips A, 2019, Structural modelling of trabecular bone adaptation using a Voronoi network, International Society of Biomechanics
Favier C, McGregor A, Phillips A, 2019, Subject specific multiscale modelling for the study of lumbar pathologies, 17th International symposium on computer simulation in biomechanics, Publisher: International Society of Biomechanics
Phillips A, 2019, Structural modelling of trabecular bone adaptation using a Voronoi network, ISB TGCS Symposium on Computational Simulation in Biomechanics, Publisher: International Society of Biomechanics
Phillips A, 2019, Modelling Trabecular Bone as a Voronoi Structure, Bone Research Society / British Orthopaedic Research Society combined meeting 2019
Structural finite element models of trabecular boneadaptation within the femur(1) and pelvis(2) usedrandomized networks of truss elements with straindue to axial force used as a driver for adaptation oftrabeculae cross-sectional areas. At the macro-scalethe adapted models successfully highlightedtrabecular trajectories and were used to predictfracture initiation and progression, in the femoralneck(3). The use of a truss network requires a highnodal connectivity (NC) defined as the number ofstructural elements representing trabeculaeconnecting to each node, in order to maintainstructural and computational stability. A minimumNC of 6 results from the orthotropic nature of theprincipal stress directions that bone is believed toform trajectories along, while higher NCs are requiredto resist multiple load cases that introduce sheardue to off axis loading compared to the principalstress directions obtained when adaptation is carriedout for a single load case.Recent micro-CT studies characterising the structuralarchitecture of trabecular bone(4) contradict thetrajectory hypothesis indicating frequent NC valuesof 3 and 4 with nodes having common structuralarrangements or motifs. A Voronoi network is astructural form that provides an abundance of nodeswith a NC of 4. The Voronoi method of partitioningspace around control points is implemented inRhino using the Grasshopper parametric designtool to create a network as a collection of node andelement definitions. The Abaqus finite elementsolver is used to analyse this network using beamelements with strains developed due to axial force,biaxial bending and torsion moments. An extendedbone adaptation approach is used to adapt thecross-sectional properties at multiple points alongthe length of each trabeculae.Initial results suggest using a Voronoi network is apromising approach to model trabecular boneadaptation and fatigue micro-fracture. Ongoingwork will investigate the iterative placement of thecontrol points used to construct
Favier C, McGregor A, Phillips A, 2019, Full body subject specific musculoskeletal model for complex spine movements, XXVII Congress of the International Society of Biomechanics
Kaufmann J, Phillips A, McGregor A, 2019, Investigating bone health in lower-limb amputees, 2019 Blast Injury Conference
Kaufmann J, Phillips A, McGregor A, 2019, Investigating bone health in lower-limb amputees, TGCS 2019 - 17th International Symposium on Computer Simulation in Biomechanics
Kaufmann J, Phillips A, McGregor A, 2019, Investigating bone health in lower-limb amputees, ISB/ASB 2019
Sperry MM, Phillips ATM, McGregor AH, 2019, Lower back pain and healthy subjects exhibit distinct lower limb perturbation response strategies: a preliminary study, Journal of Back and Musculoskeletal Rehabilitation, Vol: 32, Pages: 27-35, ISSN: 1053-8127
BACKGROUND: It is hypothesized that inherent differences in movement strategies exist between control subjects and those with a history of lower back pain (LBP). Previous motion analysis studies focus primarily on tracking spinal movements, neglecting the connection between the lower limbs and spinal function. Lack of knowledge surrounding the functional implications of LBP may explain the diversity in success from general treatments currently offered to LBP patients. OBJECTIVE: This pilot study evaluated the response of healthy controls and individuals with a history of LBP (hLBP) to a postural disturbance. METHODS: Volunteers (n= 26) were asked to maintain standing balance in response to repeated balance disturbances delivered via a perturbation platform while both kinematic and electromyographic data were recorded from the trunk, pelvis, and lower limb. RESULTS: The healthy cohort utilized an upper body-focused strategy for balance control, with substantial activation of the external oblique muscles. The hLBP cohort implemented a lower limb-focused strategy, relying on activation of the semitendinosus and soleus muscles. No significant differences in joint range of motion were identified. CONCLUSIONS: These findings suggest that particular reactive movement patterns may indicate muscular deficits in subjects with hLBP. Identification of these deficits may aid in developing specific rehabilitation programs to prevent future LBP recurrence.
Wadee MA, Phillips ATM, Bekele A, 2019, From buckliphobes to buckliphiles: Recent developments in exploiting positive virtues of instability, 7th International Conference on Structural Engineering, Mechanics and Computation (SEMC), Publisher: CRC PRESS-BALKEMA, Pages: 455-461
Villette CC, Phillips ATM, 2018, Rate and age-dependent damage elasticity formulation for efficient hip fracture simulations, Medical Engineering and Physics, Vol: 61, Pages: 1-12, ISSN: 1350-4533
Prediction of bone failure is beneficial in a range of clinical situations from screening of osteoporotic patients with high fracture risk to assessment of protective equipment against trauma. Computational efficiency is an important feature to consider when developing failure models for iterative applications, such as patient-specific diagnosis or design of orthopaedic devices. The authors previously developed a methodology to generate efficient mesoscale structural full bone models. The aim of this study was to implement a damage elasticity formulation representative of an elasto-plastic material model with age and strain rate dependencies compatible with these structural models. This material model was assessed in the prediction of femoral fractures in longitudinal compression and side fall scenarios. The simulations predicted failure loads and fracture patterns in good agreement with reported results from experimental studies. The observed influence of strain rate on failure load was consistent with literature. The superiority of a simplified elasto-plastic formulation over an elasto-brittle bone material model was assessed. This computationally efficient damage elasticity formulation was capable of capturing fracture development after onset.
Kaufmann J, Phillips A, McGregor A, 2018, Investigating bone health in lower-limb amputees, 2018 Blast Injury Conference
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