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Percorrer CDRsp - Artigos em revistas internacionais por Domínios Científicos e Tecnológicos (FOS) "Ciências Naturais::Ciências da Computação e da Informação"
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- Analysis of manufacturing parameters on the shear strength of aluminium adhesive single-lap jointsPublication . Pereira, A. M.; Ferreira, J. M.; Antunes, F. V.; Bártolo, P. J.An experimental and numerical investigation into the shear strength behaviour of aluminium alloy adhesive lap joints was carried out in order to understand the effect of geometrical and manufacturing parameters on the strength of adhesive bonding joints, with the aim of optimizing shear strength. The adherend material used for the experimental tests was an aluminium alloy in the form of thin sheets, and the adhesive used was a high strength epoxy. Five surface treatments were studied. The surface treatments process using sodium dichromate-sulphuric acid etch (CSA) and abrasive polishing (AP) resulted in improved joint shear strength when compared to acetone cleaning (SW), caustic etch (CE), and Tucker's reagent etch (TR). The decrease in surface roughness was found to increase the shear strength of single-lap joints. An increase in adherend thickness and overlap length was found to increase shear strength which means that an increase in joint rigidity increases its strength. A numerical analysis was developed to explain the effect of the geometrical parameters on rotation angle, stress and strain fields, and failure load. An increase in adherend thickness and overlap length decreases the joint rotation angle, reducing the plastic strain peak and therefore increasing the failure load.
- Biomanufacturing for tissue engineering: Present and future trendsPublication . Bartolo, Paulo; Chua, C. K.; Almeida, Henrique de Amorim; Chou, S. M.; Lim, A. S. C.Tissue engineering, often referred to as regenerative medicine and reparative medicine, is an interdisciplinary field that necessitates 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. It has emerged as a rapidly expanding approach to address the organ shortage problem and comprises tissue regeneration and organ substitution. Cells placed on/or within constructs is the most common strategy in tissue engineering. Successful cell seeding depends on fast attachment of cell to scaffolds, high cell survival and uniform cell distribution. The seeding time is strongly dependent on the scaffold material and architecture. Scaffolds provide an initial biochemical substrate for the novel tissue until cells can produce their own extra-cellular matrix (ECM). Thus scaffolds not only define the 3D space for the formation of new tissues, but also serve to provide tissues with appropriate functions. These scaffolds are often critical, both in vivo (within the body) or in vitro (outside the body) mimicking in vivo conditions. Additive fabrication processes represent a new group of non-conventional fabrication techniques recently introduced in the biomedical engineering field. In tissue engineering, additive fabrication processes have been used to produce scaffolds with customised external shape and predefined internal morphology, allowing good control of pore size and pore distribution. This article provides a comprehensive state-of-the-art review of the application of biomanufacturing additive processes in the field of tissue engineering. New and moving trends in biomanufacturing technologies and the concept of direct cell-printing technologies are also discussed.
- EditorialPublication . Bártolo, Paulo; Chua, C. K.In this issue, we invited five winners of the ‘Best Paper Awards’ at the 4th International Conference on Advanced Research in Virtual and Rapid Prototyping, Leiria, Portugal, 6-10 October 2009, to enhance their conference papers to the standard of an international journal. One paper each from ‘Materials’ track, ‘Biomanufacturing’ track and ‘Virtual Environment & Simulation’ track and two papers from ‘Advanced Rapid Prototyping Technologies and Nanofabrication’ track.
- EditorialPublication . Bartolo, Paulo; Chua, C. K.Welcome to a brand new year of 2010! In this editorial, we bring you the latest update concerning rapid prototyping technologies,which of coursemany of you are aware, include many terminologies such as layer manufacturing and solid freeform fabrication, amongst others. The longstanding need to standardize the terminologies within the rapid prototyping andmanufacturing industry has nowbeenmetwith a new ASTMInternational standard, ASTMF2792, Terminology for Additive Manufacturing Technologies. The new document is the first approved standard under the jurisdiction of ASTM Committee F42 on Additive Manufacturing Technologies, which was formed in 2009.
- Evaluation of in vitro degradation of PCL scaffolds fabricated via BioExtrusion. Part 1: Influence of the degradation environmentPublication . Domingos, M.; Chiellini, F.; Cometa, S.; De Giglio, E.; Grillo-Fernandes, E.; Bártolo, P.; Chiellini, E.One of the most promising approaches in tissue engineering (TE) comprises the development of 3D porous scaffolds which are able to promote tissue regeneration. Biocompatible and biodegradable poly(e-caprolactone) (PCL) structures are increasingly used as temporary extra-cellular matrices for bone tissue engineering. To ensure an appropriate bone restoration over the long term, the selected material must have a degradation rate that match the in-growth of new bone. The in vivo process, by which the scaffold degrades and is resorbed transferring the load and function back to the host tissue, is complex. Consequently, an appropriate preliminary in vitro study is required. A novel extrusion-based technology called BioExtruder was used to produce PCL porous scaffolds made with layers of directionally aligned microfilaments. The in vitro degradation behaviour in both simulated body fluid (SBF) and phosphate buffer solution (PBS) were investigated over 6 months. The characterization of the degradation behaviour of the structures was performed at specific times by evaluating changes in the average molecular weight, the weight loss and its thermal properties. Morphological and surface chemical analyses were also performed using a Scanning Electron Microscopy (SEM) and an X-ray Photoelectron Spectroscopy (XPS), respectively.
- Experimental assessment of hybrid mould performancePublication . Pontes, Antonio J.; Queirós, Miguel P.; Martinho, Pedro G.; Bártolo, Paulo J.; Pouzada, António S.Hybrid moulds are a novel approach for rapid tooling of injection moulds that combines conventional machining for the mould structure and rapid prototyping techniques for the moulding blocks (core and cavity). In this study, two routes were used for producing the moulding blocks: selective laser sintering of stainless steel-based powder (hard tool) and epoxy resin vacuum casting (soft tool). The experimental work was based on a complex tridimensional commercial part. The mouldings were made in polypropylene, and the processing performance was monitored online in terms of pressure and temperature at the impression. The performance of the moulding blocks was analysed in terms of thermal and cycle performance and structural integrity. The epoxy tooling route is more adequate for fine detailing than selective laser sintering but is not adequate for parts with extensive ribs or deep bosses. The structural integrity of the less costly epoxy composite can be compromised during ejection, this suggesting the need to evaluate the stress field by simulation at the design stage of the mould.
- Layer manufacturing of magnesium and its alloy structures for future applicationsPublication . Ng, C. C.; Savalani, M. M.; Man, H. C.; Gibson, I.This research aims to develop a rapid layer manufacturing technique to provide magnesium bone substitute for future applications in the medical fields. Selective laser melting (SLM), which is a laser based additive layer manufacturing technique and capable of producing required geometries directly from CAD data, is selected to build magnesium structures. Magnesium has several intrinsic properties including its excellent biocompat-ibility, biodegradable, bioresorbabiltity and proper mechanical properties which would make it suitable for orthopaedic applications. This paper will discuss the status quo of this material and its future implications. A miniature SLM system was built to achieve better control of the atmospheric conditions in which the magnesium would melt. The results revealed that the SLM is a promising technique to fabricate magnesium substitute for various orthopaedic applications.