Browsing by Author "Bento, David"
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- An in vitro experimental evaluation of the displacement field in an intracranial aneurysm modelPublication . Pinho, Diana; Bento, David; Ribeiro, J.E.; Lima, Rui A.; Vaz, M.A.P.The purpose of this paper is to develop a system able to study experimentally the displace-ment field of an in vitro intracranial aneurysm. Origin and growth of aneurysms is the result of a complex interaction between biological processes in the arterial wall and the involved hemo-dynamic phenomena’s. Once the aneurysm forms, the repetitive pressure and shear stresses exerted by the blood flow on the debilitated arterial wall can cause a gradual expansion. One promising method to evaluate and measure this expansion is to use optical field experimental techniques, such as interferometry. In this work the Electronic Speckle Pattern Interferometry was used to evaluate the deformation occurred on an intracranial aneurysm model fabricated in polydimensiloxane (PDMS) by using a 3D printer combined with a soft lithography tech-nique.
- Auditory system rehabilitation - available technologiesPublication . Bento, David; Ferreira, Stéphanie; Magalhães, B.F.T.; Rocha, Daniela; Teixeira, João PauloIn this article some of the different technologies and its functioning as well as some technological aids for people with partial or total auditory deficiency will be presented. The objective of the auditory rehabilitation is to develop the capacity of auditory perception to the individual carrying auditory deficiency, with aid of devices that can amplify the sound. Between these devices, we cite: the Baha auditory prostheses, vibrant sound-bridge, the cochlear implantations, the auditory brainstem implants, the hearing prosthesis, the bone conduction prostheses and the intra-channels hearing. Some technological aiding devices not used in the ear are also presented such as the signal amplifier to phone, amplifier magnetic field to TV, sign language translator, phone with handset and light bell for home.
- Blood flow in a bifurcation and confluence microchannel: effect of the cell-free layer in velocity profilesPublication . Pinho, Diana; Bento, David; Rodrigues, Raquel Oliveira; Fernandes, Carla S.; Garcia, Valdemar; Lima, Rui A.A few detailed studies have been performed in complex in vitro microvascular networks composed by bifurcations and confluences. The main purpose of the present work is to numerically simulate the flow of two distinct fluids through bifurcation and confluence geometries, i. e red blood cells (RBCs)suspended in Dextran40 with about 14% of heamatocrit and pure water. The simulations of pure water and RBCs flows were performed resorting to the commercial finite volume software package FLUENT. A well known hemodynamic phenomenon, known as Fahraeus-Lindqvist effect, observed in both in vivo and in vitro studies, results in the formation of a marginal cell-free layer (CFL) at regions adjacent to the wall. Recently, studies have shown that the formation of the CFL is affected by the geometry of the microchannel and for the case of the confluences a CFL tend to appear in the middle of the microchannel after the apex of the confluence. By using the CFL experimental data, the main objective of this work is to implement a CFL in the numerical simulations in order to obtain a better understanding of the effect of this layer on the velocity profiles.
- Blood flow in a bifurcation and confluence microchannel: the effect of the cell-free layer in the velocity profilesPublication . Pinho, Diana; Bento, David; Rodrigues, Raquel Oliveira; Fernandes, Carla S.; Garcia, Valdemar; Lima, Rui A.A few detailed studies have been performed in complex in vitro microvascular networks composed by bifurcations and confluences. The main purpose of the present work is to numerically simulate the flow of two distinct fluids through bifurcation and confluence geometries, i. e red blood cells (RBCs) suspended in Dextran40 with about 14% of heamatocrit and pure water. The simulations of pure water and RBCs flows were performed resorting to the commercial finite volume software package FLUENT. A well known hemodynamic phenomenon, known as Fahraeus-Lindqvist effect [1, 2], observed in both in vivo and in vitro studies, results in the formation of a marginal cell-free layer (CFL) at regions adjacent to the wall [3]. Recently, studies have shown that the formation of the CFL is affected by the geometry of the microchannel and for the case of the confluences a CFL tend to appear in the middle of the microchannel after the apex of the confluence [4, 5]. By using the CFL experimental data, the main objective of this work is to implement a CFL in the numerical simulations in order to obtain a better understanding of the effect of this layer on the velocity profiles.
- Blood flow of bubbles moving in microchannels with bifurcationsPublication . Bento, David; Lopes, Sara Helena Carvalho; Maia, Inês; Pereira, Ana I.; Fernandes, Carla S.; Miranda, João Mário; Lima, Rui A.The gas embolism is a well-known phenomenon. Previous studies have been performed to understand the formation, the behavior and the influence of air bubbles in microcirculation. This study aims to investigate the flow of bubbles in a microchannel network with bifurcations. For that purpose, a microchannel network was fabricated by soft lithography. The working fluids used were composed by sheep red blood cells (RBCs) suspended in dextran 40 and two different hematocrits were studied, 5% and 10%. The in vitro blood flow was analyzed for a flow rate of lO ~-tllmin, by using an inverted microscope and a high-speed camera. It was possible to visualize the formation of the bubbles and their behavior along the network. The results show that the passage of air bubbles influences the cells local concentration, since a higher concentration of cells was seen upstream to the bubble and lower concentrations downstream to the bubble.
- Cell-free layer (CFL) analysis in a glass capillary: comparison between a manual and automatic methodPublication . Bento, David; Pinho, Diana; Pereira, Ana I.; Lima, Rui A.In this study, in vitro blood flowing through a 100 m glass capillary was studied. The images were captured using a confocal system and post-processed using Image J and MatLab. The aim of the present work, was to measure the trajectories of the cell-free layer (CFL) by using two different methods, i. e., a manual method (MM) and an automatic method (AM). For theMM we have used amanual tracking plugin (MTrackJ) from Image J to track labeled red blood cells (RBCs) flowing around the boundary of the RBCs core. For the AM we have used a MatLab scripts to measure automatically the CFL trajectories. The preliminary numerical results suggest that the CFL trajectories follow a polynomial function for both methods.
- Cell-free layer (CFL) measurements in complex geometries: contractions and bifurcationsPublication . Novais, Susana; Pinho, Diana; Bento, David; Pinto, Elmano; Yaginuma, Tomoko; Fernandes, Carla S.; Garcia, Valdemar; Pereira, Ana I.; Lima, José; Mujika, Maite; Oliveira, Mónica S.N.; Dias, Ricardo P.; Arana, Sergio; Lima, Rui A.In this chapter we discuss the cell-free layer (CFL) developed adjacent to the wall of microgeometries containing complex features representative of the microcirculation, such as contractions, expansions, bifurcations and confluences. The microchannels with the different geometries were made of polydimethylsiloxane (PDMS) and we use optical techniques to evaluate the cell-free layer for red blood cells (RBC) suspensions with different hematocrit (Hct). The images are captured using a high-speed video microscopy system and the thickness of the cell free layer was measured using both manual and automatic image analysis techniques. The results show that in in vitro microcirculation, the hematocrit and the geometrical configuration have a major impact on the CFL thickness. In particular, the thickness of the cell-free layer increases as the fluid flows through a contraction-expansion sequence and that this increase is enhanced for lower hematocrit. In contrast, the flow rates tested in this studies did not show a clear influence on the CFL thickness.
- Cell-free layer measurements in a bifurcation microchannel : comparison between a manual and automatic methodsPublication . Bento, David; Pinho, Diana; Pinto, Elmano; Yaginuma, Tomoko; Correia, Teresa Montenegro; Lima, José; Pereira, Ana I.; Lima, Rui A.In the present work, in vitro blood flowing through a bifurcation microchannel was studied. The aim was to measure the Trajectories of the cell-free layer (CFL) by using different methods, i. e., a manual and two automatic methods.
- Cell-free layer measurements in a bifurcation microchannel : comparison between a manual and automatic methodsPublication . Bento, David; Pinho, Diana; Pinto, Elmano; Yaginuma, Tomoko; Correia, Teresa Montenegro; Lima, José; Pereira, Ana I.; Fernandes, Carla S.; Dias, Ricardo P.; Lima, Rui A.In the present work, in vitro blood flowing through a bifurcation microchannel was studied. The aim was to measure the Trajectories of the cell-free layer (CFL) by using different methods, i. e., a manual and two automatic methods.
- Cell-free layer measurements in a network with bifurcating microchannels using a global approachPublication . Bento, David; Pinho, Diana; Pereira, Ana I.; Lima, Rui A.One of the most interesting hemodynamic phenomenon observed in microchannels is the existence of a marginal cell-free layer (CFL) at regions adjacent to the wall. This is a well known phenomenon that occurs in simple glass capillaries and in vivo microvessels, but has never been investigated in detail in biomedical microdevices containing complex geometries. In the present chapter, in vitro blood flowing through bifurcating microchannels was studied, with the aim of characterizing the cell-free layer (CFL). For that three different videos with different hematocrit and flow rates were considered. All images were obtained by means of a high-speed video microscopy system and then processed in MatLab using the Image Processing toolbox. The numerical data was obtained automatically and analyzed by optimization techniques using the genetic algorithm approach. The results suggest that the CFL were formed in a similar way at the upper and lower regions in all bifurcations.