Unidade de Investigação - CDRsp – Centro para o Desenvolvimento Rápido e Sustentado de Produto
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- 316L stainless steel mechanical and tribological behavior—A comparison between selective laser melting, hot pressing and conventional castingPublication . Bartolomeu, F.; Buciumeanu, M.; Pinto, E.; Alves, Nuno; Carvalho, O.; Silva, F: S.; Miranda, G.This work presents a comprehensive study on the influence of three different processing technologies (Selective Laser Melting, Hot Pressing and conventional casting) on the microstructure, mechanical and wear behavior of an austenitic 316L Stainless Steel.Acorrelation between the processing technologies,the obtained microstructure and the mechanical and wear behavior was achieved. The results showed that the highest mechanical properties and tribological performance were obtained for 316L SS specimens produced by Selective Laser Melting, when compared to Hot Pressing and conventional casting. The high wear and mechanical performance of 316L Stainless Steel fabricated by Selective Laser Melting are mainly due to the finer microstructure, induced by the process. In this sense, Selective Laser Melting seems a promising method to fabricate customized 316L SS implants with improved mechanical and wear performance
- 3D Photo-Fabrication for Tissue Engineering and Drug DeliveryPublication . Brás Pereira, Rúben Filipe; Bartolo, PauloThe most promising strategies in tissue engineering involve the integration of a triad of biomaterials, living cells, and biologically active molecules to engineer synthetic environments that closely mimic the healing milieu present in human tissues, and that stimulate tissue repair and regeneration. To be clinically effective, these environments must replicate, as closely as possible, the main characteristics of the native extracellular matrix (ECM) on a cellular and subcellular scale. Photo-fabrication techniques have already been used to generate 3D environments with precise architectures and heterogeneous composition, through a multi-layer procedure involving the selective photocrosslinking reaction of a light-sensitive prepolymer. Cells and therapeutic molecules can be included in the initial hydrogel precursor solution, and processed into 3D constructs. Recently, photo-fabrication has also been explored to dynamically modulate hydrogel features in real time, providing enhanced control of cell fate and delivery of bioactive compounds. This paper focuses on the use of 3D photo-fabrication techniques to produce advanced constructs for tissue regeneration and drug delivery applications. State-of-the-art photo-fabrication techniques are described, with emphasis on the operating principles and biofabrication strategies to create spatially controlled patterns of cells and bioactive factors. Considering its fast processing, spatiotemporal control, high resolution, and accuracy, photo-fabrication is assuming a critical role in the design of sophisticated 3D constructs. This technology is capable of providing appropriate environments for tissue regeneration, and regulating the spatiotemporal delivery of therapeutics.
- 3D printing of new biobased unsaturated polyesters by microstereo-thermal-lithographyPublication . Gonçalves, Filipa A. M. M.; Costa, Cátia S. M. F.; Fabela, Inês G. P.; Farinha, Dina; Faneca, Henrique; Simões, Pedro N.; Serra, Arménio C.; Bártolo, Paulo J.; Coelho, Jorge F. J.New micro three-dimensional (3D) scaffolds using biobased unsaturated polyesters (UPs) were prepared by microstereo-thermal-lithography (μSTLG). This advanced processing technique offers indubitable advantages over traditional printing methods. The accuracy and roughness of the 3D structures were evaluated by scanning electron microscopy and infinite focus microscopy, revealing a suitable roughness for cell attachment. UPs were synthesized by bulk polycondensation between biobased aliphatic diacids (succinic, adipic and sebacic acid) and two different glycols (propylene glycol and diethylene glycol) using fumaric acid as the source of double bonds. The chemical structures of the new oligomers were confirmed by proton nuclear magnetic resonance spectra, attenuated total reflectance Fourier transform infrared spectroscopy and matrix assisted laser desorption/ionization-time of flight mass spectrometry. The thermal and mechanical properties of the UPs were evaluated to determine the influence of the diacid/glycol ratio and the type of diacid in the polyester's properties. In addition an extensive thermal characterization of the polyesters is reported. The data presented in this work opens the possibility for the use of biobased polyesters in additive manufacturing technologies as a route to prepare biodegradable tailor made scaffolds that have potential applications in a tissue engineering area.
- 3D shape prior active contours for an automatic segmentation of a patient specific femur from a CT scanPublication . Almeida, D.; Folgado, J.; Fernandes, P.R.; Ruben, RuiThe following paper describes a novel approach to a medical image segmentation problem. The fully automated computational procedure receives as input images from CT scan exams of the human femur and returns a three dimensional representation of the bone. This patient specific iterative approach is based in 3D active contours without edges, implemented over a level set framework, on which the evolution of the contour depends on local image parameters which can easily be defined by the user but also on a priori information about the volume to segment. This joint approach will lead to an optimal solution convergence of the iterative method. The resulting point cloud can be an excellent starting point for a Finite Element mesh generation and analysis or the basis for a stereolitography for example.
- 3D-printed multisampling holder for microcomputed tomography applied to life and materials science researchPublication . Vasconcelos, Isabel; Franco, Margarida; Pereira, Mário; Duarte, Isabel; Ginjeira, António; Alves, NunoThe aim of this work was to design, fabricate, test and validate a 3D-printed multisampling holder for multi-analysis by microcomputed tomography. Different raw materials were scanned by microcomputed tomography. The raw material chosen was used to fabricate the holder by 3D printing. To validate the multisampling holder, five teeth were filled with a high density-material and scanned in two ways: a single and a multisampling scan mode. For each tooth, the root canal filling volume, porosity volume, closed pore volume, and open pore volume were calculated and compared when the same tooth was scanned in the two sampling scan mode. ABSplus P430™ allowed a high transmission value (84.3 %), and then it was the polymeric material selected to fabricate the holder. In a single sampling scan mode, the scan duration for scanning five teeth was 87.42 min, contrasting with 21.51 min for a multisampling scan mode, which scanned five teeth at the same time. The scan duration time and the cost using a multisampling holder represented a reduction of 75 % and the data volume generated represented a reduction of 60 %. Comparing the two scan modes, the results also showed that the difference of root canal filling volume, porosity volume, closed pore volume, and open pore volume was not statistically significant (p > .05). The multisampling holder was validated to do multi-analysis by microcomputed tomography without significant loss of quantitative accuracy data, allowing a reduction in scan duration time, imaging cost, and data storage.
- Additive manufactured porous biomaterials targeting orthopedic implants: A suitable combination of mechanical, physical and topological propertiesPublication . Bartolomeu, F.; Dourado, N.; Pereira, F.; Alves, N.; Miranda, G.; Silva, F. S.Orthopedic implants are under incessant advancement to improve their interactions with surrounding bone tissue aiming to ensure successful outcomes for patients. A successful biological interaction between implant and surrounding bone depends on the combination of mechanical, physical and topological properties. Hence, Ti6Al4V cellular structures appear as very promising solutions towards the improvement of conventional orthopedic implants. This work addresses a set of fundamental tools that allow improving the design of Ti6Al4V cellular structures produced by Selective Laser Melting (SLM). Three-point bending tests were carried out to estimate the elastic modulus of the produced structures. Morphological analysis allowed to evaluate the dimensional differences that were noticed between the model CAD and the SLM structures. Finite element models (adjusted CAD) were constructed with the experimentally obtained dimensions to replicate the mechanical response of the SLM structures. Linear correlations were systematically found for the dimensions of the SLM structures as a function of the designed model CAD dimensions. This has also been observed for the measured porosities as a function of the designed CAD models. This data can be used in further FE analyses as design guidelines to help engineers fabricating near-net-shape SLM Ti6Al4V cellular structures. Besides, polished and sandblasted surface treatments performed on the Ti6Al4V cellular structures allowed to obtain suitable properties regarding roughness and wettability when compared to as-produced surfaces. The capillarity tests showed that all the analyzed Ti6Al4V structures are able to transport fluid along its structure. The cell viability tests demonstrate Ti6Al4V cellular structures SLM produced did not release toxic substances to the medium, indicating that these structures can assure a suitable environment for cells to proliferate and attach. This study proposes a design methodology for Ti6Al4V cellular structures, that owe suitable mechanical properties but also provide a proper combination of porosity, roughness, wettability, capillarity and cell viability, all of them relevant for orthopedic applications. A Ti6Al4V cellular structured hip implant prototype gathering the suitable features addressed in this study was successfully SLM-produced.
- Additive manufacturing of tissues and organsPublication . Melchels, Ferry P.W.; Domingos, Marco; Klein, Travis J.; Malda, Jos; Bártolo, Paulo J.; Hutmacher, Dietmar W.Additive manufacturing techniques offer the potential to fabricate organized tissue constructs to repair or replace damaged or diseased human tissues and organs. Using these techniques, spatial variations of cells along multiple axes with high geometric complexity in combination with different biomaterials can be generated. The level of control offered by these computer-controlled technologies to design and fabricate tissues will accelerate our understanding of the governing factors of tissue formation and function. Moreover, it will provide a valuable tool to study the effect of anatomy on graft performance. In this review, we discuss the rationale for engineering tissues and organs by combining computer-aided design with additive manufacturing technologies that encompass the simultaneous deposition of cells and materials. Current strategies are presented, particularly with respect to limitations due to the lack of suitable polymers, and requirements to move the current concepts to practical application.
- An Additive Manufacturing Solution to Produce Big Green Parts from Tires and Recycled PlasticsPublication . Domingues, J.; Marques, T.; Mateus, A.; Carreira, P.; Malça, C.Recycling is crucial for the conservation and improvement of the environment. The reduction of natural resource exploration and recovery of waste are examples of actions to contribute to a sustainable development. Waste from end-of-life tires and undifferentiated plastics represents an environmental problem due to the very high number of tons of used tires and plastics produced, but with a high economic potential because their incorporation into high value-added products is an issue of utmost importance. The manufacturing technologies oriented to the increase in quality levels, functional advantages, structural and financial gains of the produced products are currently a hot topic in industry. Similarly, the use of additive manufacturing technologies, instead of conventional techniques, e.g. moulding to process materials obtained from waste recovery, is a great industrial challenge. In order to promote greater environmental responsibility and to present innovative solutions for the management and sustainable destination of used waste recovery from tires and undifferentiated plastics, a composite made from the blend of 60% of tire waste granulate and 40% of polypropylene (PP) recycled was tested with the final purpose of generating components with added value. Both waste recovery materials were used in the micronized state. The thermal and mechanical behaviours of the synthesized composite were studied through DSC/TGA analysis and tensile testing. The implementation of additive manufacturing methodologies to process the blends between used tires granulated with a high incorporation of wastes from undifferentiated plastics was also explored in this work in order to produce big green parts without mould needed, such as urban furniture.
- Advances in electrospun skin substitutesPublication . J.R. Dias; Granja, P.L.; Bártolo, P.J.In recent years, nanotechnology has received much attention in regenerative medicine, partly owing to the production of nanoscale structures that mimic the collagen fibrils of the native extracellular matrix. Electrospinning is a widely used technique to produce micro-nanofibers due its versatility, low cost and easy use that has been assuming an increasingly prominent position in the tissue engineering field. Electrospun systems have been especially investigated for wound dressings in skin regeneration given the intrinsic suitability of fibrous structures for that purpose. Several efforts have been made to combine distinct design strategies, synthetic and/or natural materials, fiber orientations and incorporation of substances (e.g. drugs, peptides, growth factors or other biomolecules) to develop an optimized electrospun wound dressing mimicking the native skin. This paper presents a comprehensive review on current and advanced electrospinning strategies for skin regeneration. Recent advances have been mainly focused on the materials used rather than on sophisticated fabrication strategies to generate biomimetic and complex constructs that resemble the mechanical and structural properties of the skin. The technological limitations of conventional strategies, such as random, aligned and core-shell technologies, and their poor mimicking of the native tissue are discussed. Advanced strategies, such as hybrid structures, cell and in situ electrospinning, are highlighted in the way they may contribute to circumvent the limitations of conventional strategies, through the combination of different technologies and approaches. The main research challenges and future trends of electrospinning for skin regeneration are discussed in the light of in vitro but mainly in vivo evidence.
- Analysis of friction in the ejection of thermoplastic mouldingsPublication . Correia, Mário Simões; Miranda, Antonio Sousa; Oliveira, Marta Cristina; Capela, Carlos Alexandre; Pouzada, Antonio SergioThe ejection force of injection-moulded thermoplastics depends on the contact conditions at the moment of ejection. Replication of the polymer part surface occurs onto the mould surface during injection of the melt. Ejection takes place in a very short time, hence the static coefficient of friction must be considered for modelling the ejection process. To understand the contribution of the mechanisms involved in the friction during the ejection stage, a mixed approach was followed: analytical simulation of the ploughing, numerical simulation of the deformation, and experimental inference of the adhesion. The relevance of roughness, temperature and contact pressure in the coefficient of friction was evidenced.