CDRsp - Comunicações em conferências internacionais
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Percorrer CDRsp - Comunicações em conferências internacionais por Domínios Científicos e Tecnológicos (FOS) "Engenharia e Tecnologia::Engenharia dos Materiais"
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- Characterisation of PCL and PCL/PLA Scaffolds for Tissue EngineeringPublication . Patrício, T.; Domingos, M.; A. Gloria; Bártolo, P.This paper investigates the use of PCL and PCL/PLA scaffolds produced using a novel additive biomanufacturing system called BioCell Printing. PCL/PLA blends were prepared using melt blend and solvent casting techniques. Scaffolds with 0/90° architecture and 350 μm of pore size were morphologically evaluated using scanning electron microscopy and atomic force microscopy. Biological tests, using osteosarcoma cell line G-63, were performed using the Alamar Blue Assay and Alkaline Phosphatase Activity. 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.
- Computational technologies in tissue engineeringPublication . Almeida, H. A.; Bártolo, P. J.In last decades, many advances have been made in order to aid the medical community. Numerous computational technologies have been developed and improved the efficiency in diagnostic and treatment of many diseases. Many of the technologies were developed with the main goal of aiding in the research of genetic and viral diseases. Tissue engineering is a multidisciplinary field that requires the combined effort of cell biologists, engineers, material scientists, mathematicians, geneticists, and clinicians toward the development of biological substitutes that restore, maintain, or improve tissue function. The success of this emerging medical domain relies on the current technological advances. This paper presents an overview of the existing computational technologies that have been implemented in tissue engineering and the design of scaffolds for tissue engineering applications. These computational technologies contemplate medical imaging processing, numerical calculations (structural, vascular and topological) and biofabrication techniques necessary for the scaffolds optimum design and production.
- Cyclic plastic behaviour of 7075 aluminium alloyPublication . Nogueira, F.; Cunha, J.; Mateus, A.; Malça, C.; Costa, J. D.; Branco, R.This paper aims at studying the cyclic plastic behaviour of the 7075-T651 aluminium alloy under fully-reversed strain-controlled conditions. Tests are conducted under strain-control mode, at room temperature, in a conventional servo-hydraulic machine, from smooth samples, using the single step method, with strain amplitudes (∆ε/2) in the range ±0.5 to ±2.75%. This material has exhibited a mixed behaviour, i.e. cyclic strain-hardens at higher strain amplitudes (∆ε/2/>1.1%) and cyclic strain-softens at lower strain amplitudes (∆ε/2<1.1%). A linear relationship between the degree of cyclic strain-hardening and the strain amplitude has been established for higher strain amplitudes. Fatigue-ductility and fatigue-strength properties agree with those found in the open literature for the same loading conditions.
- Degradation Behavior of Biopolymer-based Membranes for Skin Tissue RegenerationPublication . Pereira, Rúben F.; Bártolo, Paulo J.This research work investigates the long term in vitro degradation behavior of alginate-aloe vera composite membranes for skin regeneration. The membranes were prepared through a two-step procedure, which involves the synthesis of thin membranes and the crosslinking reaction. Degradation tests were performed through the immersion of the membranes into simulated body fluid solution at pH 7.4 and physiological temperature, during 6 months. Alginate-aloe vera membranes are resistant to the hydrolytic degradation and exhibit weight loss values in a range of 20.37-26.32%. Results show that an increase in the aloe vera content leads to a slight increase in the weight loss during the degradation process. Preliminary drug release studies, using nitrofurazone as a model drug, suggest the ability of the developed membranes to be used as a drug delivery system.
- Mechanical and Biological Behaviour of PCL and PCL/PLA Scaffolds for Tissue Engineering ApplicationsPublication . Patrício, Tatiana; Glória, António; Bártolo, PauloA new biomanufacturing system allowing to produce three-dimensional matrices (scaffolds) with well defined internal geometries, uniform pore distribution and good adhesion among different adjacent layers. Polymers selected are Poly ε-caprolactone (PCL) and Poly Lactic Acid (PLA), both these polymers are used in medical applications. These two polymers are interesting biomaterials because they are complementary on their physical properties and biodegradability. This work aims to assess the temperature evaluation during the extrusion process and the influences of the temperatures on the PCL and PCL/PLA scaffolds with lay down pattern 90º and pore size 350μm. The results demonstrated that extrusion process not modified the thermal properties of the scaffolds and these structures are able to sustain MG-63cells.
- Morphological Characteristics of Electrospun PCL Meshes – The Influence of Solvent Type and ConcentrationPublication . Dias, J.; Bártolo, P.Fibrous scaffolds, with fiber dimensions on the nanometer scale, are ideal for tissue engineering applications as they can mimic the physical structure of natural extracellular matrix. This paper investigates the effect of the solvent type and the solvent concentration on the morphological and hydrophobic characteristics of Polycaprolactone (PCL) meshes. Acetone and acetic acid with triethylamine (TEA) were used as solvents with different concentrations of PCL. Results show that its use allows the formation of meshes with high surface roughness, less surface friction and less hydrophobicity.
- Multiscale modeling of polymers closely coupled to Broad Q neutron scattering from NIMRODPublication . Gkourmpis, Thomas; Lopez, Daniel; Mitchell, Geoffrey R.We use data over an extended Q range from 0.01 to 100Å-1 from the recently commissioned NIMROD instrument at the ISIS pulsed neutron source to develop a multi-scale inverse modeling procedure which will provide insight in to the phase transformations of polymer systems. The first level of our procedure is atomistic and we use internal coordinates (bond length, bond angles and torsion angles) to define the polymer chain in full atomistic detail. Values were assigned to each internal coordinate within the chain using a stochastic Monte Carlo method in which the probabilities were drawn from distributions representing the possible range of values. Using this approach, random chain configurations could be rapidly built and the intrachain structure factor calculated utilizing a small set of parameters and compared with the experimental function. Parameters representing the probability distribution functions were systematically varied using a grid search to find the values which gave the best fit to the structure factor for Q > 3Å-1 in order to determine the details of the chain conformation in the molten phase. This process was repeated for data over the same extended Q range obtained at lower temperatures where the polymer was expected to crystallize. Polymers crystallize via chain-folded thin lamellae crystals. Such crystals give rise to an intense peak at Q ∼ 0.03Å-1. This scattering can be calculated using a lamellar stack model, coarse-grained from the single chain structure. We describe this approach using data obtained on the crystallization from the melt phase of perdeuterated polymers. The objective here is to follow the three key length scales; the chain folded lamellar thickness of ∼ 10nm, the crystal unit cell ∼ 1nm and the detail of the chain conformation is ∼ 0.1nm.
- Optimalmould - part II: Global optimization of the injection moulding cycle timePublication . Ramos, Carina; Carreira, Pedro; Bartolo, Paulo; Alves, NunoThe time required to produce a plastic part is a key issue in injection moulding process as it strongly determine the cost per part. Several approaches have been proposed to address this problem. However they do not cover all aspects related to the complete cycle time of the injection moulding process, only focusing on steps such as filling time, cooling time and packing time. This paper presents a global optimisation strategy for the injection moulding cycle time, covering all time steps related to the injection moulding process, including a novel mathematical model to predict the ejection time. An industrial case study was considered to validate the proposed approach. The obtained results are very close to the experimental ones. © 2012 American Institute of Physics.
- Optimalmould-part I: Multi-objective optimization to moulds design for injection of polymersPublication . Ramos, Carina; Carreira, P.; Bártolo, Paulo; Alves, NunoThe problem of mould design optimisation for polymer injection is a key issue for both mouldmaking and polymer injection industries. Several computational tools have proposed to address this problem. However they do not cover all aspects related to both mould design and injection moulding process, usually requiring the geometrical configuration of the initial mould solution. This paper presents a novel multi-objective optimisation tool, integrating CAD and CAE tools to optimise mould design parameters and injection moulding process parameters. No initial geometric definition of the mould is required. An industrial case study was considered to validate the proposed approach and the performance of several optimisation algorithms evaluated.
- Polycaprolactone-based scaffold plus BMP-2 in a sheep thoracic spine fusion modelPublication . Yong, M.; Melchels, F.; Vaquette, C.; Hutmacher, D.; Adam, C.; Domingos, M.; Bártolo, P.We report the application of a novel scaffold design in a sheep thoracic spine model for spine deformity correction. The combination of the calcium-phosphate coated polycaprolactone scaffolds with recombinant human bone morphogenic protein-2 are intended as a future bone graft substitute in ensuring the stability of bony intervertebral fusion. A solid free-form fabrication process based on melt extrusion has been utilized in the manufacturing of these scaffolds.