Publications
157 results found
Villette C, Phillips A, 2024, Influence of a change in activity regime on femoral bone architecture and failure behaviour, PLoS One, ISSN: 1932-6203
Caillet AH, Phillips ATM, Farina D, et al., 2023, Motoneuron-driven computational muscle modelling with motor unit resolution and subject-specific musculoskeletal anatomy., PLoS Comput Biol, Vol: 19
The computational simulation of human voluntary muscle contraction is possible with EMG-driven Hill-type models of whole muscles. Despite impactful applications in numerous fields, the neuromechanical information and the physiological accuracy such models provide remain limited because of multiscale simplifications that limit comprehensive description of muscle internal dynamics during contraction. We addressed this limitation by developing a novel motoneuron-driven neuromuscular model, that describes the force-generating dynamics of a population of individual motor units, each of which was described with a Hill-type actuator and controlled by a dedicated experimentally derived motoneuronal control. In forward simulation of human voluntary muscle contraction, the model transforms a vector of motoneuron spike trains decoded from high-density EMG signals into a vector of motor unit forces that sum into the predicted whole muscle force. The motoneuronal control provides comprehensive and separate descriptions of the dynamics of motor unit recruitment and discharge and decodes the subject's intention. The neuromuscular model is subject-specific, muscle-specific, includes an advanced and physiological description of motor unit activation dynamics, and is validated against an experimental muscle force. Accurate force predictions were obtained when the vector of experimental neural controls was representative of the discharge activity of the complete motor unit pool. This was achieved with large and dense grids of EMG electrodes during medium-force contractions or with computational methods that physiologically estimate the discharge activity of the motor units that were not identified experimentally. This neuromuscular model advances the state-of-the-art of neuromuscular modelling, bringing together the fields of motor control and musculoskeletal modelling, and finding applications in neuromuscular control and human-machine interfacing research.
McMenemy L, Behan FP, Kaufmann J, et al., 2023, Association between combat-related traumatic injury and skeletal health: bone mineral density loss is localized and correlates with altered loading in amputees: the Armed Services Trauma Rehabilitation Outcome (ADVANCE) Study, Journal of Bone and Mineral Research, Vol: 38, Pages: 1227-1233, ISSN: 0884-0431
The association between combat-related traumatic injury (CRTI) and bone health is uncertain. A disproportionate number of lower limb amputees from the Iraq and Afghanistan conflicts are diagnosed with osteopenia/osteoporosis, increasing lifetime risk of fragility fracture and challenging traditional osteoporosis treatment paradigms. The aim of this study is to test the hypotheses that CRTI results in a systemic reduction in bone mineral density (BMD) and that active traumatic lower limb amputees have localized BMD reduction, which is more prominent with higher level amputations. This is a cross-sectional analysis of the first phase of a cohort study comprising 575 male adult UK military personnel with CRTI (UK-Afghanistan War 2003 to 2014; including 153 lower limb amputees) who were frequency-matched to 562 uninjured men by age, service, rank, regiment, deployment period, and role-in-theatre. BMD was assessed using dual-energy X-ray absorptiometry (DXA) scanning of the hips and lumbar spine. Femoral neck BMD was lower in the CRTI than the uninjured group (T-score -0.08 versus -0.42 p = .000). Subgroup analysis revealed this reduction was significant only at the femoral neck of the amputated limb of amputees (p = 0.000), where the reduction was greater for above knee amputees than below knee amputees (p < 0.001). There were no differences in spine BMD or activity levels between amputees and controls. Changes in bone health in CRTI appear to be mechanically driven rather than systemic and are only evident in those with lower limb amputation. This may arise from altered joint and muscle loading creating a reduced mechanical stimulus to the femur resulting in localized unloading osteopenia. This suggests that interventions to stimulate bone may provide an effective management strategy. © 2023 Crown copyright and The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Soci
Caillet AH, Avrillon S, Kundu A, et al., 2023, Larger and denser: an optimal design for surface grids of EMG electrodes to identify greater and more representative samples of motor units, eNeuro, Vol: 10, ISSN: 2373-2822
The spinal motor neurons are the only neural cells whose individual activity can be non-invasively identified. This is usually done using grids of surface electromyographic (EMG) electrodes and source separation algorithms; an approach called EMG decomposition. In this study, we combined computational and experimental analyses to assess how the design parameters of grids of electrodes influence the number and the properties of the identified motor units. We first computed the percentage of motor units that could be theoretically discriminated within a pool of 200 simulated motor units when decomposing EMG signals recorded with grids of various sizes and interelectrode distances (IED). Increasing the density, the number of electrodes, and the size of the grids, increased the number of motor units that our decomposition algorithm could theoretically discriminate, i.e., up to 83.5% of the simulated pool (range across conditions: 30.5-83.5%). We then identified motor units from experimental EMG signals recorded in six participants with grids of various sizes (range: 2-36 cm2) and IED (range: 4-16 mm). The configuration with the largest number of electrodes and the shortest IED maximized the number of identified motor units (56±14; range: 39-79) and the percentage of early recruited motor units within these samples (29±14%). Finally, the number of identified motor units further increased with a prototyped grid of 256 electrodes and an IED of 2 mm. Taken together, our results showed that larger and denser surface grids of electrodes allow to identify a more representative pool of motor units than currently reported in experimental studies.Significance StatementThe application of source separation methods to multi-channel EMG signals recorded with grids of electrodes enables users to accurately identify the activity of individual motor units. However, the design parameters of these grids have never been discussed. They are usually arbitrarily fixed, often bas
Bekele A, Wadee MA, Phillips ATM, 2023, Enhancing energy absorption through sequential instabilities in mechanical metamaterials, Royal Society Open Science, Vol: 10, Pages: 1-19, ISSN: 2054-5703
Structural components designed to absorb energy and shield a more valuable structure ideally require mechanical properties that combine a relatively high load-carrying capacity followed by a practically zero stiffness. This ensures that a specified energy quantity may be absorbed within a limited displacement and that any stress transfer to the valuable structure is minimized. Material damage has been historically mobilized to provide such properties but this obviously renders such components to be single-use. In contrast, mobilization of elastic instability can also provide the desired combination of properties but without necessarily damaging the material. This reveals an intriguing possibility of such components being potentially repairable and theoretically reusable with no significant loss in performance. A series of analytical, finite element and experimental studies are presented for a bespoke mechanical metamaterial arrangement that is designed to buckle sequentially and behave with the desired ‘high strength–low stiffness’ characteristic. It is found that the various axial and rotational stiffnesses associated with the geometric arrangement and its constituent connections may be tuned to provide the desired mechanical behaviour within the elastic range and delay the onset of significant damage thereby rendering the concept of harnessing instability to be feasible.
Altai Z, Boukhennoufa I, Zhai X, et al., 2023, Performance of multiple neural networks in predicting lower limb joint moments using wearable sensors, Frontiers in Bioengineering and Biotechnology, Vol: 11, Pages: 1-12, ISSN: 2296-4185
Joint moment measurements represent an objective biomechemical parameter in joint health assessment. Inverse dynamics based on 3D motion capture data is the current 'gold standard’ to estimate joint moments. Recently, machine learning combined with data measured by wearable technologies such electromyography (EMG), inertial measurement units (IMU), and electrogoniometers (GON) has been used to enable fast, easy, and low-cost measurements of joint moments. This study investigates the ability of various deep neural networks to predict lower limb joint moments merely from IMU sensors. The performance of five different deep neural networks (InceptionTimePlus, eXplainable convolutional neural network (XCM), XCMplus, Recurrent neural network (RNNplus), and Time Series Transformer (TSTPlus)) were tested to predict hip, knee, ankle, and subtalar moments using acceleration and gyroscope measurements of four IMU sensors at the trunk, thigh, shank, and foot. Multiple locomotion modes were considered including level-ground walking, treadmill walking, stair ascent, stair descent, ramp ascent, and ramp descent. We show that XCM can accurately predict lower limb joint moments using data of only four IMUs with RMSE of 0.046 ± 0.013 Nm/kg compared to 0.064 ± 0.003 Nm/kg on average for the other architectures. We found that hip, knee, and ankle joint moments predictions had a comparable RMSE with an average of 0.069 Nm/kg, while subtalar joint moments had the lowest RMSE of 0.033 Nm/kg. The real-time feedback that can be derived from the proposed method can be highly valuable for sports scientists and physiotherapists to gain insights into biomechanics, technique, and form to develop personalized training and rehabilitation programs.
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.
Kaufmann JJ, McMenemy L, Phillips ATM, et al., 2023, Bone Health in Lower-Limb Amputees, Blast Injury Science and Engineering A Guide for Clinicians and Researchers: Second Edition, Pages: 479-488, ISBN: 9783031103544
Bone mineral density (BMD) loss in lower-limb amputees has in the past been referred to as either osteopenia or osteoporosis. However, evidence and hypotheses in emerging literature are beginning to challenge this, suggesting that the use of these terms could be inappropriate due to key differences in the aetiology and mechanisms underpinning the bone loss in the younger amputee population. Computational and clinical analysis carried out within the Centre for Blast Injury Studies at Imperial College London and the ADVANCE Study has provided strong evidence to support this stance. Investigating BMD discordance in the spine and femur of 153 lower-limb amputees and a frequency-matched control population has shown that bone loss in amputees is localised to the amputated limb rather than systemic (as it manifests in age-related osteoporosis). Combined musculoskeletal and finite element modelling goes some way to explaining the cause of this. Weight bearing through a prosthetic socket offloads the distal femur, and consequently large areas of the femoral shaft and neck experience significantly reduced levels of stimulation when compared to weight bearing on a healthy limb. The long-term result of this is a phenomenon that we refer to as unloading osteopenia.
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
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- Citations: 6
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, Carty C, et al., 2022, Hill-type computational models of muscle-tendon actuators: a systematic review
<jats:title>Abstract</jats:title><jats:p>Backed by a century of research and development, Hill-type muscle-tendon models are extensively used for countless applications. Lacking recent reviews, the field of Hill-type modelling is however dense and hard-to-explore, with detrimental consequences on knowledge transmission, inter-study consistency, and innovation. Here we present the first systematic review of the field of Hill-type muscle-tendon modelling. It aims to clarify the literature by detailing its contents and proposing updated terminology and definitions, and discussing the state-of-the-art by identifying the latest advances, current gaps, and potential improvements in modelling muscle properties. To achieve this aim, fifty-five criteria-abiding studies were extracted using a systematic search and their Hill-type models assessed according to a completeness evaluation, which identified the modelled muscle-tendon properties, and a modelling evaluation, which considered the level of validation and reusability of the model, and attention given to its modelling strategy and calibration. It is concluded that most models (1) do not significantly advance the dated gold standards in muscle modelling and do not build upon more recent advances, (2) overlook the importance of parameter identification and tuning, (3) are not strongly validated, and (4) are not reusable in other studies. Besides providing a convenient tool supported by extensive supplementary material for understanding the literature, the results of this review open a discussion on the necessity for global recommendations in Hill-type modelling and more frequent reviews to optimize inter-study consistency, knowledge transmission and model reusability.</jats:p>
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 COMPUTATIONAL BIOLOGY, Vol: 18, ISSN: 1553-734X
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- Citations: 5
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, 9th World Congress of Biomechanics
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
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- Citations: 2
Deane J, Lim A, Phillips A, et al., 2022, Symptomatic individuals with lumbar disc degeneration use different anticipatory and compensatory kinematic strategies to asymptomatic controls in response to postural perturbation, Gait and Posture, Vol: 94, Pages: 222-229, ISSN: 0966-6362
Background:Lumbar Disc Degeneration (LDD) is associated with recurrent low back pain (LBP) (symptomatic). However, in some instances of LDD, people do not experience LBP (asymptomatic).Research question:As a step towards understanding why some people with LDD experience LBP and others do not, the primary aim of this study was to examine differences in anticipatory (APA) and compensatory postural adjustments (CPA), between symptomatic LDD patients (LDD pain) and asymptomatic LDD controls (LDD no pain) during postural perturbation. The secondary aim was to determine simultaneous differences in mental health, disability and quality of life status.Methods:3 T MRI was used to acquire T2 weighted images (L1-S1) from LDD no pain (n = 34) and LDD pain groups (n = 34). In this observational study, responses to predicted and unpredicted forward perturbations were examined using three dimensional motion capture. A Mann Whitney U test was conducted to examine group differences in sagittal spine and lower limb kinematics (integrated angular displacements during four established APA and CPA time intervals), anxiety, depression, disability and quality of life.Results:The LDD pain group exhibited lower hip and knee displacements (p = 0.049−0.040) than the LDD no pain group during predicted and unpredicted perturbation. The LDD pain group also exhibited higher compensatory lumbar displacement than the LDD no pain group (p = 0.040−0.005) in the predicted condition but there was no difference observed in the unpredicted condition. The LDD pain group experienced higher levels of depression, anxiety and disability (p < 0.0001) and lower quality of life (p = 0.0001) than LDD controls.Significance:Symptomatic LDD patients are different from LDD controls; they exhibit different kinematic strategies, levels of disability, anxiety, depression and quality of life. Effective care may benefit from evaluating and targeting these differences.
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
<jats:title>Abstract</jats:title><jats:p>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.</jats:p><jats:sec><jats:title>Author Summary</jats:title>&
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 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
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
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