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Shrinkage and colour in the production of micro-sized PDMS particles for microfluidic applications

Publication . Anes, Cláudia Filipa; Pinho, Diana; Muñoz-Sánchez, Beatriz N.; Vega, E.J.; Lima, Rui A.

Polydimethylsiloxane (PDMS), due to its remarkable properties, is a suitable polymer for the production of microparticles with industrial and medical applications. The micro-sized PDMS liquid droplets suffer a pronounced shrinkage while curing to turn into solid particles. In this article, we report the calibration of the shrinkage phenomenon in the production of PDMS microparticles. Our results show that this shrinkage does not depend on the amount of curing agent in the PDMS precursor or on the addition of micro/nanoparticles to the mixture, but on the surface effects due to the relatively large droplet surface-to-volume ratio. Moreover, we have also investigated the addition of colour to the particles to improve their visualization/detection. The addition of colour by using pigments enhances the visualization of the contours of the PDMS microparticles, and reveals the capability of this technique to microencapsulate micro/nanoparticles in PDMS spheres with diameters below 10 μm. We demonstrate that the technique used in this work is able to work with a wide range of viscosities obtaining an acceptable degree of monodispersity.

2018Journal article

Open access

Prediction models for rail temperatures validated with experimental measurements

Publication . Frigeri, Ary Vinicius Nervis; Minhoto, Manuel; Piloto, P.A.G.; Pereira, Ana I.

Rail temperatures play an important role when understanding and predicting rail track instabilities. A rail temperature energy balance model was used, validated with FEA analysis, and compared with field-collected data. Both solution methods are in good agreement. Compared with the collected data, the model reaches an R² of 0.83. Boundary conditions improvements may be required.

2020Conference object

Open access

In vitro particulate analogue fluids for experimental studies of rheological and hemorheological behavior of glucose-rich RBC suspensions

Publication . Pinho, Diana; Campo-Deaño, Laura; Lima, Rui A.; Pinho, Fernando T.

Suspensions of healthy and pathological red blood cells (RBC) flowing in microfluidic devices are frequently used to perform in vitro blood experiments for a better understanding of human microcirculation hemodynamic phenomena. This work reports the development of particulate viscoelastic analogue fluids able to mimic the rheological and hemorheological behavior of pathological RBC suspensions flowing in microfluidic systems. The pathological RBCs were obtained by an incubation of healthy RBCs at a high concentration of glucose, representing the pathological stage of hyperglycaemia in diabetic complications, and analyses of their deformability and aggregation were carried out. Overall, the developed in vitro analogue fluids were composed of a suspension of semi-rigid microbeads in a carrier viscoelastic fluid made of dextran 40 and xanthan gum. All suspensions of healthy and pathological RBCs, as well as their particulate analogue fluids, were extensively characterized in steady shear flow, as well as in small and large amplitude oscillatory shear flow. In addition, the well-known cell-free layer (CFL) phenomenon occurring in microchannels was investigated in detail to provide comparisons between healthy and pathological in vitro RBC suspensions and their corresponding analogue fluids at different volume concentrations (5% and 20%). The experimental results have shown a similar rheological behavior between the samples containing a suspension of pathological RBCs and the proposed analogue fluids. Moreover, this work shows that the particulate in vitro analogue fluids used have the ability to mimic well the CFL phenomenon occurring downstream of a microchannel contraction for pathological RBC suspensions. The proposed particulate fluids provide a more realistic behavior of the flow properties of suspended RBCs when compared with existing non-particulate blood analogues, and consequently, they are advantageous for detailed investigations of microcirculation.

2017Journal article

Open access

Environmental performance assessment of the transport sector in the European Union

Publication . Gruetzmacher, Sarah; Vaz, Clara B.; Ferreira, Ângela P.

Reducing the European Union (EU) transport sector’s pressure on the environment is critical to achieve long-term sustainability. This study evaluates the environmental performance of the transport sector in 28 EU countries, from 2015 to 2017, towards a more sustainable mobility by using composite indicators (CI). The assessment was made through the aggregation of 7 sub-indicators into a CI using a DEA approach. The results indicate that the EU countries had almost no variation on their transport environmental performance in these 3 years analyzed.

2020Conference object

Open access

O design na valorização de territórios de montanha plataforma digital: ROOTURE residência artística: artes na montanha

Publication . Cá, Cândido; Costa, Carlos Casimiro da; Costa, Jacinta Casimiro da

A presente investigação foi desenvolvida no programa de formação em I&D Residência Artística Artes na Montanha. Teve como finalidade investigar a importância do Design na valorização da cultura e identidade de territórios de Montanha através do levantamento e análise de projetos no espaço europeu. Como resultado pretendia-se criar uma plataforma digital para arquivo destes trabalhos.

2020Conference object

Open access