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- Topological Shear Stress Optimisation of Micro-CT Based ScaffoldsPublication . Almeida, Henrique A.; Bártolo, Paulo J.Additive manufacturing technologies are being used to fabricate scaffolds with controlled architecture for tissue engineering applications. These technologies combined with computer-aided design systems enable to produce three-dimensional structures layer-by-layer in a multitude of materials. Actual prediction of the effective mechanical properties of scaffolds produced by Additive manufacturing systems, is very important for tissue engineering applications. One of the existing computer based techniques for scaffold design is topological optimisation. The goal of topological optimisation is to find the best use of material for a body that is subjected to either a single load or a multiple load distribution. This paper proposes a topological optimisation scheme based on existing micro-CT data in order to obtain the ideal topological architectures of scaffolds, maximising its mechanical behaviour under shear stress solicitations. This approach is based on micro-CT data of real biological tissues to create the loading (shear stress) and constraint surfaces of the scaffold during the topological optimisation process. This particular topological optimisation scheme uses the surface boundaries to produce novel models with different characteristics, which are different from the initial micro-CT models. This approach enables to produce valid biomimetic scaffold topologies for tissue engineering applications.
- Effects of Scaffold Electrical Properties on Electric Field Delivery in BioreactorsPublication . Meneses, João; Fernandes, Sofia R.; Alves, Nuno; Pascoal-Faria, Paula; Miranda, Pedro CavaleiroIn tissue engineering, cell culture scaffolds have been widely used in combination with electrical stimulation to promote multiple cellular outcomes, like differentiation and proliferation. Nevertheless, the influence of scaffolds on the electric field delivered inside a bioreactor is often ignored and requires a deeper study. By performing numerical analysis in a capacitively coupled setup, this work aimed to predict the effects of the scaffold presence on the electric field, considering multiple combinations of scaffold and culture medium electrical properties. We concluded that the effect of the scaffold on the electric field in the surrounding culture medium was determined by the difference in electrical conductivity of these two materials. The numerical simulations pointed to significant variations in local electric field patterns, which could lead to different cellular outcomes and confound the interpretation of the experimental results.
- Role of Anisotropy in Tissue EngineeringPublication . Mitchell, Geoffrey R.; Tojeira, AnaTissue engineering is a highly interdisciplinary field that requires the integrated expertise of clinicians, cell biologists, engineers and material scientists, to make progress in the development and deployment of biological substitutes that restore, maintain, or improve tissue function. The purpose is to provide the opportunities for tissue regeneration and organ replacement. Key advances in biological materials especially in the area of stem cells; growth and differentiation factors generate realistic opportunities to create tissues in the laboratory using an engineered extracellular matrix or scaffold and biologically active molecules. The scaffold acts as an artificial extracellular matrix and it needs to mimic the chemical composition and physical architecture of natural extracellular matrix to facilitate cell adhesion, proliferation, differentiation and new tissue formation. In this contribution we review the role of the scaffold system in promoting cell adhesion, proliferation and differentiation with respect to the anisotropic nature of the scaffold system. We address both the anisotropy which may exist at a microscopic or mesoscopic scale, for example the shape of pores as well as the molecular level interactions which may arise in a scaffold containing a molecular organization with a preferred orientation which may have been induced during the processing procedures used to prepare the scaffold. Of course some approaches to the preparation of scaffolds systems are inherently anisotropic, for example the wide-spread utilization of meshes prepared by electrospinning. In other words although the overall scaffold is isotropic, the basic elements in terms of an electrospun fibre is highly anisotropic in terms of its external form and possibly in terms of its internal structure. By reviewing the possible advantages of the inclusion of anisotropic elements in the scaffold we add to the knowledge base which allows scaffolds design to be optimised for specific tissue growth.
- SANS/WANS Time-resolving Neutron Scattering Studiesof Polymer Phase Transitions Using NIMRODPublication . Mitchell, Geoffrey Robert; Bowron, Daniel; Mateus, Artur; Bártolo, Paulo; Gkourmpis, Thomas; Phomphrai, Khamphee; Lopez, Daniel; Davis, FredABSTRACT We use new neutron scattering instrumentation to follow in a single quantitative time-resolving experiment, the three key scales of structural development which accompany the crystallisation of synthetic polymers. These length scales span 3 orders of magnitude of the scattering vector. The study of polymer crystallisation dates back to the pioneering experiments of Keller and others who discovered the chain-folded nature of the thin lamellae crystals which are normally found in synthetic polymers. The inherent connectivity of polymers makes their crystallisation a multiscale transformation. Much understanding has developed over the intervening fifty years but the process has remained something of a mystery. There are three key length scales. The chain folded lamellar thickness is ∼ 10nm, the crystal unit cell is ∼ 1nm and the detail of the chain conformation is ∼ 0.1nm. In previous work these length scales have been addressed using different instrumention or were coupled using compromised geometries. More recently researchers have attempted to exploit coupled time-resolved small-angle and wide-angle x-ray experiments. These turned out to be challenging experiments much related to the challenge of placing the scattering intensity on an absolute scale. However, they did stimulate the possibility of new phenomena in the very early stages of crystallisation. Although there is now considerable doubt on such experiments, they drew attention to the basic question as to the process of crystallisation in long chain molecules. We have used NIMROD on the second target station at ISIS to follow all three length scales in a time-resolving manner for poly(e-caprolactone). The technique can provide a single set of data from 0.01 to 100Å-1 on the same vertical scale. We present the results using a multiple scale model of the crystallisation process in polymers to analyse the results.
- Assessment of existing rc precast industrial buildings according with eurocode 8 - part 3Publication . Batalha, Nádia; Rodrigues, Hugo; Sousa, Romain; Varum, Humberto; Fernandes, PauloPrecast reinforced concrete (PRC) buildings are common in the Portuguese industrial park, as well as throughout Europe. In past earthquakes, namely in Italy and Turkey, this typology of buildings showed a poor performance, namely at structural level. One of the major concerns at structural level regards the connection between the beams and columns. In recent surveys at the Portuguese industrial buildings, it was observed that the buildings built before 1980 present, most of the times, only friction connections between beam and columns. This type of connection is pointed as one of the weakest structural system in this typology of structures and consequently led to serious local and global damage when subjected to seismic loads. Regarding this issue, it was considered appropriate and necessary the study of existing Portuguese buildings with this type of beam-to-column connection and compare it with the use of mechanical connections (dowels), which is a more common solution in the recent buildings. The seismic behaviour of two PRC buildings built with these two solutions was analysed considering nonlinear static and dynamic analyses addressing both global and local (connections) response parameters. When analysed in view of the seismic regulation for existing buildings (Eurocode 8 –Part 3), the results obtained show that, overall, this typology of buildings present an acceptable structural performance. Nonetheless, unsatisfactory performance was observed at the beam-to-column connection in one of the buildings built without steel dowels. The results presented in this study highlight the need to consider adequate models to simulate these connections in order to accurately represent the seismic behaviour on the structure and identify possible limitations in the use of nonlinear static procedures to assess the seismic performance of this typology of buildings. In general, the buildings in study, located in a region of moderate seismicity, exhibited a satisfactory behaviour. However particular attention should be paid to beam-to-column connections, especially in the case of friction connections. In this regard it is important to accurately represent in the model the mechanisms involved in the connections, particularly in buildings located in moderate to high seismic zones.
- Analysis of the influence of cladding panels in the seismic behaviour of a prc industrial buildingPublication . Ostetto, Liana; Sousa, Romain; Rodrigues, Hugo; Fernandes, PauloRecent reports on the latest earthquakes in Italy and Turkey have highlighted some critical problems in the connections of cladding panels on industrial precast reinforced concrete (PRC) structures. The panel connections did not perform as expected, causing non-structural damages and, in most cases, leading to the panels overturning. The damage and collapse of these elements may result in significant losses of human lives and large socio-economic impacts due to business interruption. Despite being demonstrated that cladding panels can have a significant contribution on seismic response, these elements are often considered as non-structural, ignoring the interaction with the RC frame, and considering that they do not influence the seismic behaviour. Making use of a simplified macro element, this study assesses the seismic capacity of commonly employed claddings-to-structure connections, as well as the interaction of the cladding panels with the PRC industrial buildings. The analyses were carried out considering a PRC building representative of the Portuguese industrial park, studied with and without cladding panels. The seismic behaviour of the structure are assess considering both non-linear static and dynamic procedures.
- Evaluating the Properties of an Alginate Wound Dressing for Skin RepairPublication . Pereira, Rúben F.; Mendes, Ausenda; Bártolo, Paulo J.The treatment of skin lesions is a costly and complex process, for which different strategies are currently available. In this study, we investigated the properties of novel films composed of alginate and aloe vera gel for application as wound dressing material. The films combine the occlusive and haemostatic properties of calcium alginate gels with the therapeutic properties of aloe vera. We expect that these films may improve the healing process through the release of aloe vera compounds directly into the wound bed and could be an alternative to the administration of synthetic drugs to infected wounds. The films exhibited high transparency in both dry and wet state, as well as adequate mechanical properties for skin use. The results indicated that the films present great potential to be explored as wound dressing material.
- PCL and PCL/PLA Scaffolds for Bone Tissue RegenerationPublication . Patrício, Tatiana; Gloria, Antonio; Bártolo, Paulo J.This paper investigates the use of PCL and PCL/PLA scaffolds, produced using a novel additive biomanufacturing system called BioCell Printing, for bone tissue engineering applications. Results show that the BioCell Printing system produces scaffolds with regular and reproducible architecture, presenting no toxicity and enhancing cell attachment and proliferation. It was also possible to observe that the addition of PLA to PCL scaffolds strongly improves the biomechanical performance of the constructs.
- OPTIMALMOULD | Cooling System Influence in Injection Moulding Cycle Time OptimizationPublication . Ramos, Carina; Carreira, Pedro; Bártolo, Paulo J.; Alves, NunoMost works undertaken on injection moulding cooling time optimization aimed at reducing the time required to produce plastic parts, this way minimizing industrial costs. An optimal cooling system is proposed to improve the injection moulding design. A multi-objective genetic algorithm called NSGA-II is used, to obtain the optimal parameters in the optimal-mould design. This new design method is an efficient tool to get optimal parameters for injection moulding design. A real case study was carried out to test the optimization platform.
- Levodopa Incorporation in Alginate Membranes for Drug Delivery StudiesPublication . Franco, Margarida Rosa; Viana, Tânia Filipa; Biscaia, Sara; Bártolo, PauloParkinsons Disease (PD) is the second most common progressive neurodegenerative disorder and is referred as a leading cause of neurologic disability. The symptoms and signs of PD result from a decrease of dopamines level in the basal ganglia. Accordingly to this, exogenous substitution with dopamine agonists like levodopa, is used to correct the mechanical disorders at the early stages of the disease. Levodopa is referred as a standard in the treatment of PD. The modern studies of PD drug development and experimental therapeutics focuses on the concept of slowing and targeting the release of levodopa to prolong the therapeutic effect and reduce the number of administrations. The transdermal route was thought to be the best route for providing a progressive supply of levodopa to the systemic circulation. Alginate was chosen as a drug carrier because of its biocompatible and biodegradable properties and also because it has been widely used in drug delivery systems (DDS). The aim of this research work was to produce alginate membranes with and without levodopa. A solvent casting based methodology was used. Calcium chloride was assayed as crosslinking agent. Membranes were characterized using Differential Scanning Calorimetry (DSC) techniques. Drug release was evaluated using UV Spectrophotometry.