Publications
157 results found
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
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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
Favier C, McGregor A, Phillips A, 2018, Subject specific multiscale modelling of the lumbar spine, 14th Annual Bath Biomechanics Symposium
Verbruggen S, Kainz B, Shelmerdine SC, et al., 2018, Altered biomechanical stimulation of the developing hip joint in presence of hip dysplasia risk factors, Journal of Biomechanics, Vol: 78, Pages: 1-9, ISSN: 0021-9290
Fetal kicking and movements generate biomechanical stimulation in the fetal skeleton, which is important for prenatal musculoskeletal development, particularly joint shape. Developmental dysplasia of the hip (DDH) is the most common joint shape abnormality at birth, with many risk factors for the condition being associated with restricted fetal movement. In this study, we investigate the biomechanics of fetal movements in such situations, namely fetal breech position, oligohydramnios and primiparity (firstborn pregnancy). We also investigate twin pregnancies, which are not at greater risk of DDH incidence, despite the more restricted intra-uterine environment. We track fetal movements for each of these situations using cine-MRI technology, quantify the kick and muscle forces, and characterise the resulting stress and strain in the hip joint, testing the hypothesis that altered biomechanical stimuli may explain the link between certain intra-uterine conditions and risk of DDH. Kick force, stress and strain were found to be significantly lower in cases of breech position and oligohydramnios. Similarly, firstborn fetuses were found to generate significantly lower kick forces than non-firstborns. Interestingly, no significant difference was observed in twins compared to singletons. This research represents the first evidence of a link between the biomechanics of fetal movements and the risk of DDH, potentially informing the development of future preventative measures and enhanced diagnosis. Our results emphasise the importance of ultrasound screening for breech position and oligohydramnios, particularly later in pregnancy, and suggest that earlier intervention to correct breech position through external cephalic version could reduce the risk of hip dysplasia.
Zaharie DZ, Phillips ATM, 2018, Pelvic construct prediction of trabecular and cortical bone structural architecture, Journal of Biomechanical Engineering, Vol: 140, Pages: 1-11, ISSN: 0148-0731
The pelvic construct is an important part of the body as it facilitates the transfer of upper body weight to the lower limbs and protects a number of organs and vessels in the lower abdomen. In addition, the importance of the pelvis is highlighted by the high mortality rates associated with pelvic trauma. This study presents a mesoscale structural model of the pelvic construct and the joints and ligaments associated with it. Shell elements were used to model cortical bone, while truss elements were used to model trabecular bone and the ligaments and joints. The finite element (FE) model was subjected to an iterative optimization process based on a strain-driven bone adaptation algorithm. The bone 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 modeling framework. The cortical thickness distribution and the trabecular architecture of the adapted model were compared qualitatively with computed tomography (CT) scans and models developed in previous studies, showing good agreement. The sensitivity of the model to changes in material properties of the ligaments and joint cartilage and changes in parameters related to the adaptation algorithm was assessed. Changes to the target strain had the largest effect on predicted total bone volumes. The model showed low sensitivity to changes in all other parameters. The minimum and maximum principal strains predicted by the structural model compared to a continuum CT-derived model in response to a common test loading scenario showed good agreement with correlation coefficients of 0.813 and 0.809, respectively. The developed structural model enables a number of applications such as fracture modeling, design, and additive manufacturing of frangible surrogates.
Kaufmann J, Phillips A, McGregor A, 2018, Investigating bone health in lower-limb amputees, 14th Bath Biomechanics Symposium
Favier C, McGregor A, Phillips A, 2018, Combined musculoskeletal and structural finite element modelling of the lumbar spine, 8th World Congress of Biomechanics
Kaufmann J, Phillips A, McGregor A, 2018, Investigating bone health in lower-limb amputees, Virtual Physiological Human 2018 Congress
Gillie M, Phillips A, 2018, Teaching creative structural design - Seminar, IABSE Conference Bath 2017 - Creativity and Collaboration, Pages: 33-34
This seminar will examine how teaching structural design to encourage creativity is best approached. It will consist of four short presentations from different perspectives, followed by a facilitated discussion aimed at provoking debate.
Bellamy L, Phillips A, Ward J, 2018, Optimisation of structural form based on multiple sustainability factors, IABSE Conference Bath 2017, Pages: 119-120
Structural design and analysis is dependent on optimisation approaches. However, such optimisation is mostly performed for the permanent structure and constructability is rarely considered at the design stages. The goal of the research presented here is to develop a digital design process that encompasses constructability and sustainability factors. The initial process uses common methods for cross-sectional, structural arrangement and structural form optimisation in an automated fashion and facilitates software packages to work together. Further development will enable the process to optimise the structure across construction stages.
Verbruggen S, Kainz B, Shelmerdine S, et al., 2018, Stresses and strains on the human fetal skeleton during development, Journal of the Royal Society Interface, Vol: 15, Pages: 1-11, ISSN: 1742-5662
Mechanical forces generated by fetal kicks and movements result in stimulation of the fetal skeleton in the form of stress and strain. This stimulation is known to be critical for prenatal musculoskeletal development; indeed, abnormal or absent movements have been implicated in multiple congenital disorders. However, the mechanical stress and strain experienced by the developing human skeleton in utero have never before been characterized. Here, we quantify the biomechanics of fetal movements during the second half of gestation by modelling fetal movements captured using novel cine-magnetic resonance imaging technology. By tracking these movements, quantifying fetal kick and muscle forces, and applying them to three-dimensional geometries of the fetal skeleton, we test the hypothesis that stress and strain change over ontogeny. We find that fetal kick force increases significantly from 20 to 30 weeks' gestation, before decreasing towards term. However, stress and strain in the fetal skeleton rises significantly over the latter half of gestation. This increasing trend with gestational age is important because changes in fetal movement patterns in late pregnancy have been linked to poor fetal outcomes and musculoskeletal malformations. This research represents the first quantification of kick force and mechanical stress and strain due to fetal movements in the human skeleton in utero, thus advancing our understanding of the biomechanical environment of the uterus. Further, by revealing a potential link between fetal biomechanics and skeletal malformations, our work will stimulate future research in tissue engineering and mechanobiology.
Villette CC, Castilho M, Malda J, et al., 2017, Heterogeneous design optimisation of tissue engineering scaffolds: in-vitro assessment of a digital design framework, 15th International Symposium on Computer Methods in Biomechanics and Biomedical Engineering, Publisher: Taylor & Francis, ISSN: 1025-5842
Phillips A, 2017, Engineering design, research and education: Breaking in and out of liminal space, IABSE Conference, Bath 2017: Creativity and Collaboration, Pages: 286-287
Engineering educators, researchers and designers are all stakeholders in the development of undergraduate engineering degrees, which seek to equip graduates with the knowledge and understanding, skills, attitudes and experience required in the profession. These stakeholders are often in conflict when considering the desired learning outcomes for graduate engineers. Breaking in and out of liminal space is presented as the core skill which we wish to pass on to engineering graduates. It provides a focus for constructive discussions on curriculum, activities and assessment on engineering degree courses.
Favier C, McGregor A, Phillips A, 2017, Development of a combined MSK and FEA model of the lower back, 13th Annual Bath Biomechanics Symposium
Villette CC, Phillips ATM, 2017, Microscale poroelastic metamodel for efficient mesoscale bone remodelling simulations., Biomechanics and Modeling in Mechanobiology, Vol: 16, Pages: 2077-2091, ISSN: 1617-7940
Bone functional tissue adaptation is a multiaspect physiological process driven by interrelated mechanical and biological stimuli which requires the combined activity of osteoclasts and osteoblasts. In previous work, the authors developed a phenomenological mesoscale structural modelling approach capable of predicting internal structure of the femur based on daily activity loading, which relied on the iterative update of the cross-sectional areas of truss and shell elements representative of trabecular and cortical bones, respectively. The objective of this study was to introduce trabecular reorientation in the phenomenological model at limited computational cost. To this aim, a metamodel derived from poroelastic microscale continuum simulations was used to predict the functional adaptation of a simplified proximal structural femur model. Clear smooth trabecular tracts are predicted to form in the regions corresponding to the main trabecular groups identified in literature, at minimal computational cost.
Favier C, Phillips A, 2017, Musculoskeletal model of lumbar spine and lower limb, XXVI Congress of the International Society of Biomechanics, Publisher: International Society of Biomechanics
Verbruggen SVW, Oyen M, Phillips A, et al., 2017, Function and failure of the fetal membrane: Modelling the mechanics of the chorion and amnion, PLOS One, Vol: 12, ISSN: 1932-6203
The fetal membrane surrounds the fetus during pregnancy and is a thin tissue composed of two layers, the chorion and the amnion. While rupture of this membrane normallyoccurs at term, preterm rupture can resultin increased risk of fetal mortality and morbidity, as well as danger of infection in the mother. Although structural changes have been observed in the membrane in such cases, the mechanical behaviour of the human fetal membrane in vivoremains poorly understoodand is challenging to investigate experimentally.Therefore,the objectiveof this study wasto developsimplifiedfinite element models toinvestigatethe mechanical behaviourand ruptureof the fetal membrane, particularlyits constituent layers,under variousphysiological conditions.It was found that modelling the chorion and amnion as a single layer predicts remarkably different behaviourcompared with a more anatomically-accurate bilayer, significantly underestimating stress in the amnion and under-predicting the risk ofmembrane rupture. Additionally,reductions in chorion-amnion interface lubrication and chorion thickness (reported in cases of preterm rupture)both resultedin increasedmembrane stress. Interestingly, the inclusion of a weak zone in the fetal membrane that has been observed to develop overlying the cervix would likelycause it to fail atterm,during labour. Finally, these findings support the theory that the amnion is the dominant structural component of the fetal membrane and is required to maintain its integrity. The results provide a novel insight into the mechanical effect of structural changes in the chorion and amnion, in cases of bothnormal andpreterm rupture.
Phillips ATM, 2017, Engineering education, research and design: breaking in and out of liminal space, Journal of Professional Issues in Engineering Education and Practice, Vol: 143, ISSN: 1943-5541
Liminality is presented as a concept familiar to engineering educators, researchers anddesigners, as a state of challenge and discomfort that we must fluxin and out of in orderto advance our respective aims. Common areas for discussion in familiarising engineeringlearners with liminality are sought. Threshold concepts, divergent-convergent thinking, andthe concept of design, research and education as iterative processes associated with breakingin and out of liminal space are explored. The duality of learning is discussed through theacquisition and participation metaphors. The use of design coursesin leading learners into and out of liminal space, and in particular the Group Design Projects on the ImperialCivil Engineering MEng degree are discussed. In closing the informedcreative, as opposedto routine design process, viewed from an engineering and a psychology perspective is brieflycharacterised, along with the skills and experiences that the engineering community wouldwish engineering graduates to have.
Geraldes DM, Modenese L, Phillips ATM, 2015, Consideration of multiple load cases is critical in modelling orthotropic bone adaptation in the femur, Biomechanics and Modeling in Mechanobiology, Vol: 15, Pages: 1029-1042, ISSN: 1617-7959
Functional adaptation of the femur has beeninvestigated in several studies by embedding bone remodellingalgorithms in finite element (FE) models, with simpli-fications often made to the representation of bone’s materialsymmetry and mechanical environment. An orthotropicstrain-driven adaptation algorithm is proposed in order topredict the femur’s volumetric material property distributionand directionality of its internal structures within a continuum.The algorithm was applied to a FE model of the femur,with muscles, ligaments and joints included explicitly. Multipleload cases representing distinct frames of two activitiesof daily living (walking and stair climbing) were considered.It is hypothesised that low shear moduli occur in areasof bone that are simply loaded and high shear moduli inareas subjected to complex loading conditions. In addition,it is investigated whether material properties of differentfemoral regions are stimulated by different activities. The loading and boundary conditions were considered to providea physiological mechanical environment. The resultingvolumetric material property distribution and directionalitiesagreed with ex vivo imaging data for the whole femur.Regions where non-orthogonal trabecular crossing has beendocumented coincided with higher values of predicted shearmoduli. The topological influence of the different activitiesmodelled was analysed. The influence of stair climbing onthe properties of the femoral neck region is highlighted. It isrecommended that multiple load cases should be consideredwhen modelling bone adaptation. The orthotropic model ofthe complete femur is released with this study.
Villette CC, Phillips ATM, 2015, Informing phenomenological structural bone remodelling with a mechanistic poroelastic model, Biomechanics and Modeling in Mechanobiology, Vol: 15, Pages: 69-82, ISSN: 1617-7959
t Studies suggest that fluid motion in the extracellularspace may be involved in the cellular mechanosensitivityat play in the bone tissue adaptation process. Previously,the authors developed a mesoscale predictive structuralmodel of the femur using truss elements to represent trabecularbone, relying on a phenomenological strain-basedbone adaptation algorithm. In order to introduce a responseto bending and shear, the authors considered the use of beamelements, requiring a new formulation of the bone adaptationdrivers. The primary goal of the study presented herewas to isolate phenomenological drivers based on the resultsof a mechanistic approach to be used with a beam elementrepresentation of trabecular bone in mesoscale structuralmodelling. A single-beam model and a microscale poroelasticmodel of a single trabecula were developed. A mechanisticiterative adaptation algorithm was implemented based onfluid motion velocity through the bone matrix pores to predictthe remodelled geometries of the poroelastic trabeculaunder 42 different loading scenarios. Regression analyseswere used to correlate the changes in poroelastic trabeculathickness and orientation to the initial strain outputsof the beam model. Linear (R2 > 0.998) and third-orderpolynomial (R2 > 0.98) relationships were found betweenchange in cross section and axial strain at the central axis,and between beam reorientation and ratio of bending strainto axial strain, respectively. Implementing these relationships into the phenomenological predictive algorithm for themesoscale structural femur has the potential to produce amodel combining biofidelic structure and mechanical behaviourwith computational efficiency.
Verbruggen SW, Loo JHW, Hayat TTA, et al., 2015, Modeling the biomechanics of fetal movements, Biomechanics and Modeling in Mechanobiology, Vol: 15, Pages: 995-1004, ISSN: 1617-7959
Fetal movements in the uterus are a natural part of development, and are known to play an important role in normal musculoskeletal development. However, very little is known about the biomechanical stimuli that arise during movements in utero, despite these stimuli being crucial to normal bone and joint formation. Therefore the objective of this study is to create a series of computational steps by which the forces generated during a kick in utero could be predicted from clinically observed fetal movements using novel cine-MRI data of three fetuses, aged 20-22 weeks. A custom tracking software was designed to characterise the movements of joints in utero, and average uterus deflection of 6.95 ± 0.41 mm due to kicking was calculated. These observed displacements provided boundary conditions for a finite element model of the uterine environment, predicting an average reaction force of 0.52 ± 0.15 N generated by a kick against the uterine wall. Finally, these data were applied as inputs for a musculoskeletal model of a fetal kick, resulting in predicted maximum forces in the muscles surrounding the hip joint of approximately 8 N, while higher maximum forces of approximately 21 N were predicted for the muscles surrounding the knee joint. This study provides a novel insight into the closed mechanical environment of the uterus, with an innovative method allowing elucidation of the biomechanical interaction of the developing fetus with its surroundings.
Geraldes D, Phillips A, 2015, The influence of different load cases in orthotropic bone adaptation in the femur, International Society of Biomechanics 2015
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