Untitled

Funder

Organizational Unit

Publications

Visualization and measurement of red blood cells flowing in microfluidic devices

Publication . Rodrigues, Raquel Oliveira; Pinho, Diana; Faustino, Vera; Yaginuma, Tomoko; Bento, David; Fernandes, Carla S.; Garcia, Valdemar; Lima, Rui A.

Several experimental techniques were performed in the past years using in vitro environments, in an attempt to not only understand the blood flow behaviour in microcirculation but also develop microfluidic devices as an alternative clinical methodology to detect blood diseases. Hence, the visualization and measurement of red blood cells (RBCs) flowing in a microfluidic device are important to provide not only essential information about hydrodynamic characteristics of the blood but also vital information to diagnose the initial symptoms of diseases during clinical investigations. For instance, RBC rigidity has been correlated with myocardial infarction, diabetes mellitus, hypertension, and also other haematological disorders and diseases that affect RBC deformation more directly, such as, hereditary spherocytosis, sickle cell anaemia and malaria. Regarding a better understanding of the RBCs deformation and motion, we present in this paper a compilation of studies made in our research group, using several microfluidic devices with different microchannel geometries and fabrication techniques (i.e., soft-lithography, xurography and hybrids) that focus in the shear and extensional flow behaviour, either in healthy or chemically stiffed RBCs.

2014Conference object

Open access

Visualization and measurement of the cell-free layer (CFL) in a microchannel network

Publication . Bento, David; Fernandes, Carla S.; Pereira, Ana I.; Miranda, João Mário; Lima, Rui A.

In the past years, in vitro blood studies have revealed several significant hemodynamic phenomena that have played a key role in recent developments of biomedical microdevices for cells separation, sorting and analysis. However, the blood flow phenomena happening in complex geometries, such as microchannel networks, have not been fully understood. Thus, it is important to investigate in detail the blood flow behavior occurring at microchannel networks. In the present study, by using a high-speed video microscopy system, we have used two working fluids with different haematocrit (1% Hct and 15% Hct) and we have investigated the cell-free layer (CFL) in a microchannel network composed by asymmetric bifurcations. By using the Z Project method from the image analysis software ImageJ, it was possible to conclude that the successive bifurcations and confluences influence the formation of the CFL not only along the upper and lower wall of the microchannel but also at the region immediately downstream of the confluence apex.

2018Conference object

Open access

Wall expansion assessment of an intracranial aneurysm model by a 3D digital image correlation system measurement

Publication . Rodrigues, Raquel Oliveira; Pinho, Diana; Bento, David; Lima, Rui A.; Ribeiro, J.E.

Intracranial aneurysm is a local dilatation of an intracranial artery with high risk of rupture and death. Although it is generally accepted that the weakening of the arterial wall is the main cause for the rupture of an aneurysm, it still no consensus about the reasons for its creation, expansion and rupture. In particular, what is the role played by the blood flow in these phenomena. In this way, the aim of this work is the in vitro mechanical assessment of the wall expansion, namely the displacements, deformations and strains occurring in a saccular intracranial aneurysm model, when subjected to different flow rates. To obtain new insights into the mechanisms involved in the aneurysm rupture, a 3D-VicTM Digital Image Correlation System was used and validated with a finite element analysis. The wall expansion results have revealed that the displacements, deformations and principal strains are directly related to the internal pressure caused by the fluid on the wall of the aneurism. These findings were especially observed in the weakened areas of the aneurysm model, where the wall was thinner. Furthermore, the technique used in this study has shown to be a potential method to validate numerical simulations of aneurysms, allowing the future performance of more complex and realistic haemodynamic studies.

2016Journal article

Restricted access

In vitro blood flow visualizations and cell-free layer (CFL) measurements in a microchannel network

Publication . Bento, David; Fernandes, Carla S.; Miranda, João Mário; Lima, Rui A.

Microvascular networks are not simple straight microchannels but rather complex geometries composed by successive asymmetric divergent and convergent bifurcations. Despite the extensive research work in this field, still lack of knowledge about the blood flow behavior in microvascular networks. The current study applies the most current advanced visualization and microfabrication techniques to provide further insights into to the blood flow in network geometries. Hence, by using a high-speed video microscopy system, blood flow measurements and visualizations of the cell-free layer (CFL) were performed along a microchannel network composed by several divergent and convergent bifurcations. The inlet flow rate was kept constant whereas the hematocrit (Hct) and the depth of the geometry was changed in order to evaluate their effects into the CFL thickness. The results, show clearly that the Hct has a significant impact on the CFL thickness whereas the effect of reducing the depth did not contribute to a noticeable change on the CFL. In addition, the in vitro blood flow results reported here provide for the first time that in microfluidic devices having several asymmetric confluences it is likely to have the formation of several CFLs not only around the walls but also in middle of the main channels just downstream of the last confluence apex. Although, to best of our knowledge there is no evidence that this kind of flow phenomenon also happens in vivo, we believe that for microvascular networks with similar geometries and under similar flow conditions tested in this work, this kind of phenomenon may also happen in vivo. Furthermore, the results from this study could be extremely helpful to validate current numerical microvascular network models and to develop more realistic multiphase numerical models of blood flow in microcirculation.

2019Journal article

Open access

Manual and automatic image analysis segmentation methods for blood flow studies in microchannels

Publication . Carvalho, Violeta Meneses; Gonçalves, Inês M.; Souza, Andrews Victor Almeida; Souza, Maria Sabrina; Bento, David; Ribeiro, J.E.; Lima, Rui A.; Pinho, Diana

In blood flow studies, image analysis plays an extremely important role to examine raw data obtained by high-speed video microscopy systems. This work shows different ways to process the images which contain various blood phenomena happening in microfluidic devices and in microcirculation. For this purpose, the current methods used for tracking red blood cells (RBCs) flowing through a glass capillary and techniques to measure the cell-free layer thickness in different kinds of microchannels will be presented. Most of the past blood flow experimental data have been collected and analysed by means of manual methods, that can be extremely reliable, but they are highly time-consuming, user-intensive, repetitive, and the results can be subjective to user-induced errors. For this reason, it is crucial to develop image analysis methods able to obtain the data automatically. Concerning automatic image analysis methods for individual RBCs tracking and to measure the well know microfluidic phenomena cell-free layer thickness, two developed methods are present and discuss in order to demonstrate their feasibility for accurate data acquisition in such studies Additionally, a comparison analysis between manual and automatic methods was performed.

2021Journal article

Open access