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Isogeometric collocation for locking-free large deflection analysis of geometrically exact beams with intrinsic formulation
No full textThis paper presents an isogeometric collocation method for the large deflection analysis of geometrically exact beams using a fully intrinsic formulation. The intrinsic formulation is free from displacement or rotation variables and exhibits a low order of nonlinearity (quadratic at most), offering significant computational advantages over displacement-based formulations with higher-order nonlinearities. For the first time, we introduce the isogeometric collocation method to solve the strong form of the static intrinsic governing equations of geometrically exact beams in the present work. One of the key features of the proposed formulation is its ability to handle both conservative and follower loads within a unified framework. Through a series of benchmark problems, we demonstrate the accuracy of the proposed approach against analytical and finite element solutions and show that it is locking-free. We further demonstrate that statically indeterminate configurations can be effectively handled within the intrinsic formulation using an iterative shooting approach, without introducing displacement or rotation variables into the governing equations. Together, these features provide a reliable and efficient tool for analyzing arbitrarily large deflections of beam-like structures.peer-reviewe
A computational investigation of biomimetic and functionally graded lattice structures for orthopaedic applications
No full textThis thesis developed computational lattice-based structures, inspired by trabecular bone microarchitectures, and mechanically evaluated and characterised them. A suite of computational tools that enable the efficient generation of biomimetic lattice-based structures, were developed. The computational tools used alongside a novel computational optimisation framework, enabled the efficient design of functionally graded biomimetic lattice structures for orthopaedic medical implant applications.
In the first study, a computational investigation of the performance of three algorithms, as biomimetic models of trabecular bone architecture, was conducted through systematic evaluation of morphometric, topological, and mechanical properties. The studied structures were the gyroid lattice structure, the recently developed spinodoid structure, and a Voronoi-like lattice was introduced as the dual-lattice structure. While all computational models were calibrated to recreate the trabecular tissue volume, it was found that both the gyroid- and spinodoid-based structures showed substantial differences in many other morphometric and topological parameters and, in turn, showed lower effective mechanical properties compared to trabecular bone when their mechanical response was simulated using finite element analysis. The newly developed dual-lattice structures better captured both morphometric parameters and mechanical properties, despite certain differences being evident in their topological configuration compared to trabecular bone.
The second study evaluated the mechanical properties and energy absorption characteristics of as biomimetic lattices, through finite element analysis and experimental characterization. Computational models were calibrated to the observed experimental data, from mechanically tested 3D printed samples of low volume fractions of gyroid and dual-lattice structures, and the response of higher volume fractions were simulated. Energy absorption parameters were calculated and analysed. The results of the study showed that the dual-lattice was capable of absorbing more energy at each volume fraction cohort. However, gyroid structures showed to be a better candidate for energy absorption applications, with higher energy absorption efficiency and the onset of densification at higher strains.
In third study a new open-source MATALB toolbox “LatticeWorks” was developed, and the underlying theory was described. This toolbox enabled efficient design and generation of functionally graded, non-uniform, and multi-morphology lattice structures, in different configurations, such as cylindrical and spherical boundary shapes and boundary transitions. The LatticeWorks toolbox provided the necessary tools for mapping spatially varying lattices
on optimised mechanical or structural properties, besides volume infill using lattice structures.
The final study presented a computational optimisation framework of a hip implant through the development of a functionally graded biomimetic lattice structure, whose design was structurally optimised to limit stress shielding. The optimisation technique was inspired by the inverse of the bone remodelling algorithm, promoting an even stress distribution throughout the design region, by reducing the density and consequently the stiffness, in regions where strain energy was higher than the reference level. The result of the optimisation technique was a non-uniform graded density distribution field, that showed lower density on the sides of the implant stem, and higher material density around the medial axis. The performance of the porous implant design was evaluated through implementation of bone remodelling algorithm and comparing the bone response with a fully solid implanted bone. The results of the analysis showed improved bone formation on the bone-implant interface, and enhanced stress transmission to the surrounding bone from the implant
Development, production, and prediction of fibroin-based degradable implants
No full textSilk fibroin is a protein extracted from silk that exhibits excellent biocompatibility, high mechanical properties, while also being bioabsorbable, which makes it an excellent candidate as a sustainable constituent material of biomedical devices. However, the use of silk fibroin as an implantable material remains limited due to distinct challenges that are encountered during its processing phase, particularly in industrial setting where reproducibility remains an issue and
it can be difficult to produce complex structures. Indeed, several methods have been proposed to fabricate silk fibroin components, among which dip-coating is particularly promising given its versatility and scalability. Using a dip-coating process, there is potential to develop new techniques to obtain stand-alone silk fibroin structures, which could be applied for different scopes in the biomedical field. However, there is a general lack of understanding of the adhesion
mechanisms of silk fibroin during dip-coating and distinct challenges during post-processing steps when trying to isolate the material from the underlying substrate, which usually is performed with the use of additional surfactants possibly impacting the mechanical properties of the structures obtained. The objective of this thesis is to investigate dip-coating techniques as a scalable process for the production of silk fibroin coatings and stand-alone devices, in the form
of tubular structures that have potential application in endoluminal settings. Furthermore, a computational model able to describe the phenomenon of enzymatic degradation is developed to aid in the design process.
In this thesis, a dip-coating layer-by-layer deposition technique is used firstly to investigate the adhesion properties of aqueous silk fibroin to different metallic substrates. The dip-coating process is then optimised and several technical strategies are established to coat irregular medical implants specimens on both hard and soft substrates for dentistry and hernia applications, respectively. The silk-fibroin dip-coating process is then further exploited to enable the production of stand-alone tubular structures for endoluminal applications. This technique involves a multi-layer deposition process on Teflon mandrels and uses an innovative removal process based on water vapor annealing, which offers the possibility of combining the dip-coated layer to other processing techniques or to additional materials. The process is upscaled and applied to applications in the fields of biliary and oesophageal stenting, and the process is further optimised to produce vascular grafts with higher mechanical compliance by the combination of silk fibroin and elastin-like recombinamers (ELRs). Finally, a computational finite-element model was implemented to describe the different steps that characterise the enzymatic degradation of silk fibroin in a scaffold structure. The results showed that dip-coating achieved tightly adhered silk fibroin coatings on both magnesium and titanium substrates and highlighted that the coating adhesion strength was not only dependent on the roughness of the substrate, but also on other material properties such as hydrophilicity and electrode potential. The dip-coating technique also proved effective in coating several medical devices, with the process achieving a barrier layer or an open-porous structure depending on the requirements of the specific application. By applying the technique to Teflon substrates, reproducible and homogeneous tubular structures were obtained for endoluminal applications. In this work, it was shown that by the combination with an electrospun layer the silk fibroin devices were promising for biliary stenting applications, while the integration with a magnesium braided stent allowed to achieve a fully resorbable oesophageal stent. The dip-coating technique was also successful in obtaining, in a single-step, a double network between silk fibroin and ELRs. This enabled, for the first time, the production of silk-fibroin and ELR structures through dip-coating, with extensive mechanical testing demonstrating that this device fulfilled the requirements of mechanical stability and compliance, needed by small-diameter vascular
grafts. Finally, the computational model considering the enzymatic degradation correctly predicted the mass loss of silk fibroin scaffolds both in vitro and in vivo, revealing important considerations for the device design. Overall, this thesis provides significant technical advances and enhances the scientific understanding of the mechanical behaviour of dip-coated silk fibroin-based devices, which could see their more widespread implementation and further research in this area
Investigating the feasibility of vehicular communications with modern wireless access technologies
No full textVehicle-to-Everything (V2X) communications is a technology intended to facilitate information exchange among connected vehicles, targeting improved road safety and traffic efficiency. The wireless access segment of V2X communications is responsible for providing this connectivity to vehicles. Of the portfolio of wireless communication technologies currently in use today, Dedicated Short-Range Communication (DSRC) and Cellular Vehicle-to-Everything Communications (C-V2X) are the primary candidates to enable wireless access for V2X communications. Despite its potential benefits, V2X communications has not been widely adopted to date, indicating lingering technical challenges and thus motivating the primary research objective of this thesis: to investigate and characterise the wireless access challenges facing V2X communications as an industry vertical. Firstly, a review of the state-of-the-art in wireless access technologies for V2X communications is provided, beginning with an overview of V2X communications, its history, and standardisation. This is followed by a description of the two primary wireless access technologies, DSRC and C-V2X, and the presentation of a comprehensive review of the literature surrounding their candidacy. Results indicate that C-V2X is likely to be the most appropriate candidate wireless access technology due to its wider application support and potential for growth. Finally, active research areas that have the potential to address the challenges identified in the literature review are discussed. Secondly, a novel dataset is generated to evaluate and characterise the capabilities of early 5G New Radio (NR) cellular deployments, thus characterising the potential challenges towards the large-scale adoption of V2X communications. Results demonstrate that new 5G NR deployments can indeed outperform the existing 4G Long Term Evolution (LTE) cellular system in ideal conditions. However, results also indicate that the new 5G NR deployments are subject to a significant degree of variability and are much less reliable than the existing 4G LTE system. In particular, handovers were found to be a significant source of unreliability in V2X scenarios, with the inter-RAT (Radio Access Technology) handover type emerging as the primary contributor due to demanding control signalling and radio management requirements. Lastly, given the challenges associated with large-scale deployment of V2X communications, a small-scale Vehicle-to-Infrastructure (V2I) application intended for safety-critical use cases is proposed as a potential solution. The feasibility of the network architectures of the proposed V2I system is evaluated with particular consideration of the trade-offs associated with implementation constraints, i.e. cost, performance and security. Results show that the system is indeed feasible, however, several open questions about the system performance requirements of such safety-critical use cases remain. In summary, this thesis indicates that while non-safety-critical V2X applications are feasible with current wireless access technologies, significant advancements will be required to support safety-critical applications at scale. To this end, a number of potential solutions are proposed to bolster the capabilities and capacity of current networks and thus provide a path towards the large-scale adoption of V2X communications technology.This work has been produced by the Connaught Automotive Research (CAR) group at the University of Galway and was supported, in part, by Science Foundation Ireland grant 13/RC/2094 P2 and co-funded under the European Regional Development Fund through the Southern & Eastern Regional Operational Programme to Lero - the Science Foundation Ireland Research Centre for Software (www.lero.ie)
Actuation-mediated compression of a mechanoresponsive hydrogel by soft robotics to control release of therapeutic proteins
No full textTherapeutic proteins, the fastest growing class of pharmaceuticals, are subject to rapid proteolytic degradation in vivo, rendering them inactive. Sophisticated drug delivery systems that maintain protein stability, prolong therapeutic effects, and reduce administration frequency are urgently required. Herein, a mechanoresponsive hydrogel is developed contained within a soft robotic drug delivery (SRDD) device. In a step-change from previously reported systems, pneumatic actuation of this system releases the cationic therapeutic protein Vascular Endothelial Growth Factor (VEGF) in a bioactive form which is required for therapeutic angiogenesis, the growth of new blood vessels, in numerous clinical conditions. The ability of the SRDD device to release bioactive VEGF in a spatiotemporal manner from the hydrogel is tested in diabetic rats – a model in which angiogenesis is difficult to stimulate. Daily actuation of the SRDD device in the diabetic rat model significantly increased cluster of differentiation 31+ (CD31+) blood vessel number (p = 0.0335) and the diameter of alpha-smooth muscle actin+ (α-SMA+) blood vessels (p = 0.0025) compared to passive release of VEGF from non-actuated devices. The SRDD device combined with the mechanoresponsive hydrogel offers the potential to deliver an array of bioactive therapeutics in a spatiotemporal manner to mimic their natural release in vivo.The authors acknowledge the support of the Centre of Microscopy and Imaging at University of Galway and Explora-Bioscience Srl for imaging expertise. The authors also thank M. Canney for technical support and J. Reynolds and A. Manning for research assistance at the University of Galway. The authors would also like to acknowledge the support of the Centro Ricerche Sperimentali (Cen.Ri.S.) staff at Università Cattolica del Sacro Cuore (Rome, Italy) for the care and postsurgical monitoring of animals. E.J.W., E.B.D., L.P.B., G.B., S.S., F.C., G.C. and G.P.D. acknowledge funding from the DELIVER project which has received funding from the European Union's Horizon 2020 framework program under grant agreement number 812865. J.O.D acknowledges funding from Irish Research Council Government of Ireland Postdoctoral Fellowship GOIPD/2020/157. T.M. acknowledges funding from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement number 713690. T.M. acknowledges funding from the Science Foundation Ireland and the European Regional Development Fund Grant number 13/RC/2073.peer-reviewe
The return of the tortured ghost in Harkaitz Cano’s novel Twist (2011)
No full textThis article investigates the issue of political torture and forced disappearances within the context of the Basque political conflict as represented in the novel Twist by Harkaitz Cano. Although all violence is traumatic, the violence implicit in the systematic infliction of pain and humiliation on the state’s political ‘enemies’ by members of its security forces and, in some cases, their enforced disappearance translates into a traumatic memory that afflicts not only the victims, but the society represented by that state. Unresolved traumatic memory installs itself in the collective consciousness and generates ghosts that haunt the living and the future generations. One way they may be exorcised is by the cultural transmission of the events that caused the trauma through literary fiction.peer-reviewe
Green public procurement in construction: A systematic review
No full textGreen Public Procurement (GPP) is an increasingly important environmental policy being incorporated with national action plans (NAP) across the European Union (EU). The aim of this paper is to look at related literature in the construction industry with a goal of identifying any gaps in literature. In addition, the review defines different facilitator and barriers to implementing GPP in the construction field. The paper employs a relatively unique approach using a theoretical framework to explore a wider set of variables within the GPP field. All papers from year 2000 onwards in English were considered for the review. The review finds a lack of emphasis on systems modelling within the reviewed paper set and a need for more diverse economic evaluation metrics that incorporate social and environmental costs. Furthermore, the paper discusses broad range of subjects varying from behaviour to tendering procedure, highlighting potential avenues of future research.The authors are grateful for funding received for the Opps4GPP project (Project Ref: 2021-GCE-1039) under the EPA Research Programme 2021–2030, co-funded by the Department of Agriculture, Food, and the Marine. The EPA Research Programme is a Government of Ireland initiative funded by the Department of the Environment, Climate and Communications.peer-reviewe
Probing sub-resolution tissue structural and mechanical properties with optical coherence tomography
No full textThe structural and mechanical properties of biological tissues are intimately coupled with adequate organ function and tissue health. Optical coherence tomography (OCT) is extensively used in the study of human tissues, such as the cornea, skin and tympanic membrane, owing to its impressive resolution and depth range. However, diseases often manifest as tissue alterations below the resolution limit, and therefore, conventional intensity-based OCT is of limited use for early-stage detection or diagnosis. The aim of this work is to harness the sub-resolution signals from OCT to understand, detect and diagnose tissues. Vibrometric, nanosensitive and synthetic Fourier domain extensions of OCT were used to access sub-resolution signals related to the static and dynamic, structural and mechanical properties of tissue. Demonstration examples include corneal tissue, skin and stem cell spheroids.
The vibrational resonance frequency modes of six corneal phantoms and two ex vivo rabbit corneas were successfully measured with the co-axial, acoustic optical coherence vibrometry probe. The resonance frequencies of the corneal phantoms showed sensitivity to the thickness, Young’s modulus and intraocular pressure of the phantoms. The resonance frequencies of the ex vivo rabbit corneas were observed to increase with increased intraocular pressure.
The mean spatial period of mesenchymal stem cell pellets undergoing chondrogenic differentiation, measured with nanosensitive OCT, increased between days 1 and 4 and subsequently decreased between day 4 and 21. There was a net decrease in the mean spatial periodicity of the chondrogenic mesenchymal stem cell pellets of all three donors over the 21-day period of differentiation, in contrast to undifferentiated cells.
Synthetic Fourier domain OCT intensity images of reference samples resolved the harmonic refractive index variations within small regions of the samples. Images of different regions of human skin tissue were imaged, and a difference of the structural spatial periodicity profiles within smaller regions was observed. A comparison between a nanosensitive OCT image and synthetic Fourier domain OCT colour map of a potato slice showed that the spatial resolution of the synthetic Fourier domain OCT colour map was approximately 10 times superior.
The research detailed in this thesis demonstrates that the raw OCT interference signal manifests rich sub-resolution details which can be extracted for discovery and diagnosis of diseases and their mechanisms
Envisioning security for a more-than-human world
No full textThis paper considers a key securitization challenge that the world faces in the aftermath of the COVID-19 pandemic. It is a challenge that centres on discursively envisioning the kind of security required in tackling a wider set of human-environmental crises unfolding on the planet. In seeking to reimagine, reframe and re-resource strategies of security, the paper conceptualizes a conjoined sense of human-environmental security, which extends the human security concept to address more holistically the overlapping precarities of our human and non-human worlds. The paper sets out the task of moving beyond a concern for 'human precarity' to a concern for a broader sense of 'planetary precarity', which in turn prompts the need to strategize for a 'more-than-human' sense of security for the future of the planet.peer-reviewe