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- Micro-flow visualization of in vitro blood through a microchannel with a bifurcation and confluencePublication . Cidre, Diana; Lima, Rui A.; Fernandes, Carla S.; Dias, Ricardo P.; Ishikawa, Takuji; Imai, Yohsuke; Yamaguchi, TakamiMicro-visualization techniques have been used to investigate the in vitro blood flow through straight glass capillaries. Although the glass microchannels present certain similarities to in vivo microcirculation, it is also clear that these kind of in vitro experiments differ from microvessels in several respects, such as: elasticity of microvessels, effect of the endothelial surface layer and microvascular networks composed with short irregular vessel segments which are linked by numerous bifurcations and convergences. Thus it was not surprising that several studies on blood flow in glass microtubes and in microvessels have yielded conflicting results with respect to blood viscosity and flow resistance. The main purpose of this work is to improve our understanding about the effect of a bifurcation and convergence on the rheological properties of in vitro blood. The microchannel containing a bifurcation and confluence will be fabricated in PDMS by using a soft lithography technique. The flow behaviour of both pure water (PW) and dextran 40 (Dx40) containing about 14% (14Hct) of human red blood cells (RBCs) will be investigated by means of a confocal micro-PTV system. Additionally, the experimental measurements obtained with PW will be also compared numerically by using the commercial finite element software package POLYFLOW®.
- Blood flow in microchannels manufactured by a low cost technique: xurographyPublication . Pinto, Elmano; Taboada, Bruna Rafaela Pereira; Faustino, Vera; Cidre, Diana; Rodrigues, Raquel Oliveira; Miranda, João Mário; Garcia, Valdemar; Dias, Ricardo P.; Lima, Rui A.The xurography is a technique that has been used to make molds to produce microchannels. In contrast to soft lithography [1, 2], xurography uses equipments and materials commonly used in the printing industry, such as cutting plotters, vinyl and other materials. The main advantage of this technique is to fabricate microchannels at a reduced cost [3, 4]. The Fahraeus-Lindqvist effect is a well know phenomenon that happens in microcirculation, where red blood cells (RBCs) have tendency to migrate toward the centre of the microtube resulting in a marginal cell-free layer (CFL) at regions adjacent to the wall [5]. Recently several studies showed strong evidence that the formation of the CFL is affected by the geometry of the microchannel [1, 6, 7] and the physiological conditions of the working fluid, such as the hematocrit (Hct) [2, 8]. The main objective of the present work is to fabricate polydimethysiloxane (PDMS) microchannels by using a soft xurography technique in order perform blood flow studies. Additionally, a high-speed video microscopy system is used to measure the CFL thickness in two different geometries, i. e., bifurcations and confluences.
- Pressão nos aneurismasPublication . Órfão, Eládio César Gonçalves; Ribeiro, J.E.; Lima, Rui A.Um aneurisma é uma área frágil na parede de um vaso sanguíneo que faz com que o vaso forme uma protuberância ou aumente de tamanho. Em situações limites, este enfraquecimento pode levar ao rompimento do vaso. O principal objetivo deste trabalho é o de compreender como ocorre a deformação do aneurisma quando sujeito a uma pressão interna semelhante à pressão sanguínea. O estado de deformação do aneurisma, permitirá definir quais as regiões é que estão sujeitas a deformações mais elevadas e que podem dar uma indicação de potencial rotura. Para realizar este estudo realizaram-se duas aproximações distintas, uma numérica e outra experimental. Para o estudo numérico utilizou-se o programa comercial de elementos finitos Ansys®. Neste caso, fez uma simulação considerando que material de que são constituídos os vasos sanguíneos têm um compartimento hiper-elástico e aplicou-se uma pressão interna constante. Para a fazer a análise experimental, foi desenvolvido um modelo in-vitro do aneurisma, para realização desse modelo recorreu-se a um sistema de prototipagem rápida utilizando uma impressora 3D, Solidoodle®. O material que foi utilizado para a criação do modelo tem um comportamento elástico próximo das paredes arteriais e designa- se por polidimetilsiloxano. Da análise dos resultados obtidos verificou-se que região em que ocorre uma deformação mais elevada encontra-se no topo do aneurisma, permitindo concluir-se que há uma forte probabilidade de ser nessa região que ocorra a rotura do aneurisma.
- Haemocompatibility of iron oxide nanoparticles synthesized for theranostic applications: a high-sensitivity microfluidic toolPublication . Rodrigues, Raquel Oliveira; Bañobre-López, Manuel; Gallo, Juan; Tavares, Pedro B.; Silva, Adrián; Lima, Rui A.; Gomes, HelderThe poor heating efficiency of the most reported magnetic nanoparticles (MNPs), allied to the lack of comprehensive biocompatibility and haemodynamic studies, hampers the spread of multifunctional nanoparticles as the next generation of therapeutic bio-agents in medicine. The present work reports the synthesis and characterization, with special focus on biological/toxicological compatibility, of superparamagnetic nanoparticles with diameter around 18 nm, suitable for theranostic applications (i.e. simultaneous diagnosis and therapy of cancer). Envisioning more insights into the complex nanoparticle-red blood cells (RBCs) membrane interaction, the deformability of the human RBCs in contact with magnetic nanoparticles (MNPs) was assessed for the first time with a microfluidic extensional approach, and used as an indicator of haematological disorders in comparison with a conventional haematological test, i.e. the haemolysis analysis. Microfluidic results highlight the potential of this microfluidic tool over traditional haemolysis analysis, by detecting small increments in the rigidity of the blood cells, when traditional haemotoxicology analysis showed no significant alteration (haemolysis rates lower than 2 %). The detected rigidity has been predicted to be due to the wrapping of small MNPs by the bilayer membrane of the RBCs, which is directly related to MNPs size, shape and composition. The proposed microfluidic tool adds a new dimension into the field of nanomedicine, allowing to be applied as a highsensitivity technique capable of bringing a better understanding of the biological impact of nanoparticles developed for clinical applications.
- Polymer microfluidic devices: an overview of fabrication methodsPublication . Rodrigues, Raquel Oliveira; Lima, Rui A.; Gomes, Helder; Silva, AdriánThe amount of applications associated with microfluidic devices is increasing since the introduction of Lab-on-a-chip devices in the 1990s, especially regarding biomedical and clinical fields. However, in order for this technology to leave the fundamental research and become a day-life technology (e.g., as point-of-care testing), it needs to be disposable and reasonably less expensive. Polymers, due to their several advantages, such as easier microfabrication and low-cost, fill these needs. Several methods are reported regarding microfabrication and, thus, the main aim of the present work is to provide an overview of the most relevant microfabrication techniques found in literature employing polymers, clarifying also the main advantages and disadvantages of each technique and especially considering their cost and time-consumption. Moreover, a future outlook of low-cost microfabrication techniques and standard methods is provided.
- In vitro blood flow behaviour in microchannels with simple and complex geometriesPublication . Garcia, Valdemar; Dias, Ricardo P.; Lima, Rui A.Over the years, various experimental methods have been applied in an effort to understand the blood flow behaviour in microcirculation. The development of optical experimental techniques has contributed to obtain possible explanations on the way the blood flows through microvessels. In recent years, due to advances in computers, optics, and digital image processing techniques, it has become possible to combine a conventional particle image velocimetry (PIV) system with an inverted microscope and consequently improve both spatial and temporal resolution. The present review outlines our most relevant studies on the flow properties of blood at a microscale level by using current micro-PIV and confocal micro-PIV techniques. In this chapter, our recent studies about in vitro blood flow behaviour in microchannels both in straight and with complex geometries are presented. In straight microchannels we present some phenomena such as Fahraeus effect and Fahraeus-Lindqvist effect, the flow of particles and red blood cells (RBCs) in diluted suspensions, the flow of RBCs in concentrated suspensions, the cell-free layer and sedimentations effects. The most recent studies in blood flow through complex geometries such as bifurcations, confluences and stenosis are also reviewed. By using a chromatographic method, the flow of RBC s through a network of microcapillaries is presented.
- A microfluidic device for partial cell separation and deformability assessmentPublication . Pinho, Diana; Yaginuma, Tomoko; Lima, Rui A.Blood flow in microcirculation shows several interesting phenomena that can be used to develop microfluidic devices for blood separation and analysis in continuous flow. In this study we present a novel continuous microfluidic device for partial extraction of red blood cells (RBCs) and subsequent measurement of RBC deformability. For this purpose, we use polydimethylsiloxane (PDMS) microchannels having different constrictions (25%, 50% and 75%) to investigate their effect on the cell-free layer (CFL) thickness and separation efficiency. By using a combination of image analysis techniques we are able to automatically measure the CFL width before and after an artificial constriction. The results suggest that the CFL width increases with enhancement of the constriction and contributes to partial cell separation. The subsequent measurements of RBCs deformation index reveal that the degree of deformation depends on the constriction geometries and hematocrit after the cell separation module. The proposed microfluidic device can be easily transformed into a simple, inexpensive and convenient clinical tool able to perform both RBC separation and deformability analysis in one single device. This would eliminate the need for external sample handling and thus reducing associated labor costs and potential human errors.
- Flow of red blood cells suspensions through hyperbolic microcontractionsPublication . Faustino, Vera; Pinho, Diana; Yaginuma, Tomoko; Calhelha, Ricardo C.; Kim, Geyong; Arana, Sergio; Ferreira, Isabel C.F.R.; Oliveira, Mónica S.N.; Lima, Rui A.The present study uses a hyperbolic microchannel with a low aspect ratio (AR) to investigate how the red blood cells (RBCs) deform under conditions of both extensional and shear induced flows. The deformability is presented by the degree of the deformation index (DI) of the flowing RBCs throughout the microchannel at its centerline. A suitable image analysis technique is used for semi-automatic measurements of average DIs, velocity and strain rate of the RBCs travelling in the regions of interest. The results reveal a strong deformation of RBCs under both extensional and shear stress dominated flow conditions.
- In vitro blood flow and cell-free layer in hyperbolic microchannels: visualizations and measurmentsPublication . Rodrigues, Raquel Oliveira; Lopes, Raquel; Pinho, Diana; Pereira, Ana I.; Garcia, Valdemar; Gassmann, Stefan; Sousa, Patrícia C.; Lima, Rui A.Red blood cells (RBCs) in microchannels has tendency to undergo axial migration due to the parabolic velocity profile, which results in a high shear stress around wall that forces the RBC to move towards the centre induced by the tank treading motion of the RBC membrane. As a result there is a formation of a cell free layer (CFL) with extremely low concentration of cells. Based on this phenomenon, several works have proposed microfluidic designs to separate the suspending physiological fluid from whole in vitro blood. This study aims to characterize the CFL in hyperbolic-shaped microchannels to separate RBCs from plasma. For this purpose, we have investigated the effect of hyperbolic contractions on the CFL by using not only different Hencky strains but also varying the series of contractions. The results show that the hyperbolic contractions with a Hencky strain of 3 and higher, substantially increase the CFL downstream of the contraction region in contrast with the microchannels with a Hencky strain of 2, where the effect is insignificant. Although, the highest CFL thickness occur at microchannels with a Hencky strain of 3.6 and 4.2 the experiments have also shown that cells blockage are more likely to occur at this kind of microchannels. Hence, the most appropriate hyperbolic-shaped microchannels to separate RBCs from plasma is the one with a Hencky strain of 3.
- Erythrocytes tracking through a microchannel using an automatic method of image analysisPublication . Taboada, Bruna Rafaela Pereira; Monteiro, Fernando C.; Lima, Rui A.In this study, an image processing and analyzing method has been developed in the MATLAB environment, to characterize the motion of RBCs flowing through a microchannel with a smooth contraction shape.