Repositório IC-Online
Repositório Científico da Instituição
Entradas recentes
Layer Thickness Evaluation Between Medical Imaging and Additive Manufacturing
Publication . Almeida, Henrique A.; Vasco, Joel; Correia, Mário Simões; Ruben, Rui; Ruben, Rui
Additive manufacturing (AM) applied to the orthopaedic and surgical domains provided access to newer solutions for customised implants, customised scaffolds or even organ printing. These solutions are based on imagological data, gathered from CT-scans and/or MRI-scans. The compromise between patient’s radiation exposition and resolution along the focus direction plays an important role for the successful production of biological products. Scan detail can be increased with a thinner scanning thickness to obtain the required biological features for replication. On the other hand, a thinner scan thickness requires more scanning slices and therefore, higher exposition time to radiation. Literature shows that a maximum amount of radiation is admissible for humans, requiring an optimized approach concerning the acquisition of internal details of the human body tissues. State-of-the-art scans offer focus resolution in the range of 100 to 200 µm, although such resolution is not used for the patient’s protection. In fact, in clinical practice distance between slices are in the range of 1 to 6 mm. Concerning the AM processes that are able to use biocompatible materials, different layer thicknesses are available upon the final application in spite of the digital layer thickness that was applied during the medical imaging exam. The layer thickness during production also details the mechanical properties of the implant, with an additional aspect that the geometric data is based on information of a different layer thickness. This study intends to discuss the layer thickness used in medical imaging, the layer thickness used in AM systems providing public awareness of the operating gap between medical imaging systems and AM systems. A brief description of the accumulated errors is also presented.
Thermal Stability of PCL/PLA Blends Produced by Physical Blending Process
Publication . Patrício, Tatiana; Bártolo, Paulo
The poly ɛ-caprolactone (PCL) and poly lactid acid (PLA) were used for prepared blends with different percentage. PCL/PLA blends (70/30 wt% and 50/50 wt%) were prepared by physical blending process, called solvent casting. These blends were analysed by morphological, thermal and rheological tests in order to evaluate the miscibility and thermal stability of the polymers and their blends, important characteristics to apply in scaffold fabrication. The Simultaneous Thermal Analyser (STA) demonstrated two separated melting peaks in the blends, which show the immiscible polymers. The blends surface were analysed through Scanning Electron Microscope (SEM) and the results shows the presence of droplets in the blends surface, characteristic of an immiscible polymer. The results of rheological measurements present a good thermal stability of the polymers and their blends.
Design of Pyrolysis System to Convert Waste Plastic to Fuels
Publication . Oliveira, Nelson S.; Pardo, Michael; Capela, Carlos; Gaspar, Marcelo; Vasco, Joel; Heleno, Lizete
The conventional recycling technology to process waste plastic, mechanical recycling, is not suitable to recycle waste thermoplastic with high content of contamination. Pyrolysis is a promising technology since it can convert into valuable products, such as fuels and monomers. This study focused on the design of the pyrolysis equipment for waste plastic based on polyolefins. The feeder of waste plastic is a worm screw conveyor that will be in a pre-heating system. The batch reactor has support for catalyzer and can operate between 300 up to 600 ºC with attached induction system for heating. The output flows into condenser in series to separate two liquid phases and gases, depending on its boiling point. The 3D model was done with SolidWorks, control system modelled in CADe SIMU and particle simulation with FloXpress.
Polyoxovanadate inhibition of Escherichia coli growth shows a reverse correlation with Ca2+-ATPase inhibition
Publication . Marques-da-Silva, Dorinda; Fraqueza, Gil; Lagoa, Ricardo; Vannathan, Anjana Anandan; Mal, Sib Sankar; Aureliano, Manuel
Recently, a global analysis of the structure–activity-relationship of a series of polyoxometalates (POMs) revealed that the most active POMs were ascribed to be polyoxovanadates (POVs), especially decavanadate (V10), which was very active against certain bacteria (Bijelic et al., Chem. Commun., 2018). The present study explores this observation and compares the effects of three POVs namely MnV11, MnV13 and V10 against Escherichia coli growth. It was observed that MnV11 presents the lowest growth inhibition (GI50) value for Escherichia coli followed by the MnV13 compound, being about 2 times lower than that of V10; respectively, the values obtained were 0.21, 0.27 and 0.58 mM. All three compounds were more effective than vanadate alone (GI50 = 1.1 mM) and also than decaniobate, Nb10 (GI50 > 10 mM), an isostructural POM of V10. However, the POVs exhibiting the highest antibacterial activity (MnV11) were shown to have the lowest Ca2+-ATPase inhibitor capacity (IC50 = 58 μM) whereas decavanadate, which was also very active against this membranar ATPase (IC50 = 15 μM), was less active against bacterial growth, suggesting that POV inhibition of ion pumps might not be associated with the inhibition of Escherichia coli growth.
Influence of Hydroxyapatite on Extruded 3D Scaffolds
Publication . Rodriguez, Geraldine; Dias, Juliana; d’Ávila, Marcos Akira; Bártolo, Paulo
Ideal scaffolds for tissue engineering must mimic the complex characteristics of natural tissues and their mechanical performance. In this work, Polycaprolactone (PCL) and composite Polycaprolactone/Hydroxyapatite (PCL/HA) (75/25) scaffolds were produced by using an extrusion-based process called BioExtruder. The structures were characterized regarding the chemical, thermal, morphological and mechanical properties, in order to investigate the effect of HA addition in the polymeric scaffolds. Results show that the incorporation of HA in the 3D structures improve both the thermal and mechanical properties.