Browsing by Author "Faustino, Vera"
Now showing 1 - 10 of 25
Results Per Page
Sort Options
- Assessment of the deformability and velocity of healthy and artificially impaired red blood cells in narrow polydimethylsiloxane (PDMS) microchannelsPublication . Vilas Boas, Liliana; Faustino, Vera; Lima, Rui A.; Miranda, João; Minas, Graça; Fernandes, Carla S.; Catarino, SusanaMalaria is one of the leading causes of death in underdeveloped regions. Thus, the development of rapid, efficient, and competitive diagnostic techniques is essential. This work reports a study of the deformability and velocity assessment of healthy and artificially impaired red blood cells (RBCs), with the purpose of potentially mimicking malaria effects, in narrow polydimethylsiloxane microchannels. To obtain impaired RBCs, their properties were modified by adding, to the RBCs, different concentrations of glucose, glutaraldehyde, or diamide, in order to increase the cells' rigidity. The effects of the RBCs' artificial stiffening were evaluated by combining image analysis techniques with microchannels with a contraction width of 8 µm, making it possible to measure the cells' deformability and velocity of both healthy and modified RBCs. The results showed that healthy RBCs naturally deform when they cross the contractions and rapidly recover their original shape. In contrast, for the modified samples with high concentration of chemicals, the same did not occur. Additionally, for all the tested modification methods, the results have shown a decrease in the RBCs' deformability and velocity as the cells' rigidity increases, when compared to the behavior of healthy RBCs samples. These results show the ability of the image analysis tools combined with microchannel contractions to obtain crucial information on the pathological blood phenomena in microcirculation. Particularly, it was possible to measure the deformability of the RBCs and their velocity, resulting in a velocity/deformability relation in the microchannel. This correlation shows great potential to relate the RBCs' behavior with the various stages of malaria, helping to establish the development of new diagnostic systems towards point-of-care devices.
- Biomedical microfluidic devices by using low-cost fabrication techniques: a reviewPublication . Faustino, Vera; Catarino, Susana; Lima, Rui A.; Minas, GraçaOne of the most popular methods to fabricate biomedical microfluidic devices is by using a soft-lithography technique. However, the fabrication of the moulds to produce microfluidic devices, such as SU-8 moulds, usually requires a cleanroom environment that can be quite costly. Therefore, many efforts have been made to develop low-cost alternatives for the fabrication of microstructures, avoiding the use of cleanroom facilities. Recently, low-cost techniques without cleanroom facilities that feature aspect ratios more than 20, for fabricating those SU-8 moulds have been gaining popularity among biomedical research community. In those techniques, Ultraviolet (UV) exposure equipment, commonly used in the Printed Circuit Board (PCB) industry, replaces the more expensive and less available Mask Aligner that has been used in the last 15 years for SU-8 patterning. Alternatively, non-lithographic low-cost techniques, due to their ability for large-scale production, have increased the interest of the industrial and research community to develop simple, rapid and low-cost microfluidic structures. These alternative techniques include Print and Peel methods (PAP), laserjet, solid ink, cutting plotters or micromilling, that use equipment available in almost all laboratories and offices. An example is the xurography technique that uses a cutting plotter machine and adhesive vinyl films to generate the master moulds to fabricate microfluidic channels. In this review, we present a selection of the most recent lithographic and non-lithographic low-cost techniques to fabricate microfluidic structures, focused on the features and limitations of each technique. Only microfabrication methods that do not require the use of cleanrooms are considered. Additionally, potential applications of these microfluidic devices in biomedical engineering are presented with some illustrative examples.
- 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.
- Cell-free layer analysis in a polydimethysiloxane microchannel: A global approachPublication . Pinto, Elmano; Faustino, Vera; Pinho, Diana; Rodrigues, Raquel Oliveira; Lima, Rui A.; Pereira, Ana I.The cell-free layer (CFL) is a hemodynamic phenomenon that has an important contribution to the rheological properti es of blood flowing in microvessels. The present work aims to find the closest function describing RBCs flowing around the cell depleted layer in a polydimethysiloxane (PDMS) microchannel with a diverging and a converging bifurcation. The flow behaviour of the CFL was investigated by using a high-speed video microscopy system where special attention was devoted to its behaviour before the bifurcation and after the confluence of the microchannel. The numerical data was first obtained by using a manual tracking plugin and then analysed using the genetic algorithm approach. The results show that for the majority of the cases the function that more closely resembles the CFL boundary is the sum of trigonometric functions.
- A comparative study of image processing methods for the assessment of the red blood cells deformability in a microfluidic devicePublication . Faustino, Vera; Catarino, Susana; Pinho, Diana; Minas, Graça; Lima, Rui A.Red blood cells (RBCs) deformability is a high relevant mechanical property, whose variations are associated with some diseases, such as diabetes and malaria. Therefore, the present study aims to compare different image processing methods for assessing the RBCs deformability in a continuous flow, measured in a polydimethylsiloxane (PDMS) microchannel composed by 15 μm spacing inner pillars. The images were acquired with a high speed camera and analyzed with ImageJ software for tracking and measuring the RBCs deformation index (DI). Additionally, to understand the performance of the software, it was performed a comparison between different image processing tools provided by ImageJ and the best methods for the deformation measurements were selected, considering the measured RBCs number and their DIs. The results show that those image methods significantly affect the number of measured RBCs and their DIs and, therefore, the studies focused on the deformability measurements need to take into account the effect of the image processing methods for avoiding loss of relevant information in the images.
- Deformation of red blood cells, air bubbles and droplets in microfluidic devices: flow visualizations and measurementsPublication . Bento, David; Rodrigues, Raquel Oliveira; Faustino, Vera; Pinho, Diana; Fernandes, Carla S.; Pereira, Ana I.; Garcia, Valdemar; Miranda, João Mário; Lima, Rui A.Techniques, such as micropipette aspiration and optical tweezers, are widely used to measure cell mechanical properties, but are generally labor-intensive and time-consuming, typically involving a difficult process of manipulation. In the past two decades, a large number of microfluidic devices have been developed due to the advantages they offer over other techniques, including transparency for direct optical access,lower cost, reduced space and labor, precise control, and easy manipulation of a small volume of blood samples. This review presents recent advances in the development of microfluidic devices to evaluate the mechanical response of individual red blood cells (RBCs) and microbubbles flowing in constriction microchannels.Visualizations and measurements of the deformation of RBCs flowing through hyperbolic,smooth,and sudden-contraction microchannels were evaluated and compared. In particular, we show the potential of using hyperbolic-shaped microchannels to precisely control and assess small changes in RBC deformability in both physiological and pathological situations. Moreover, deformations of air microbubbles and droplets flowing through a microfluidic constriction were also compared with RBCs deformability.
- Erythrocyte deformability in a hyperbolic microchannelPublication . Faustino, Vera; Yaginuma, Tomoko; Pinho, Diana; Calhelha, Ricardo C.; Ferreira, Isabel C.F.R.; Lima, Rui A.Serious diseases such as diabetes and malaria are deeply related to microcirculation disorders caused by abnormal erythrocytes deformability [1]. Therefore, various studies on red blood cells (RBCs) deformation have been carried out but those studies rather focus on shear ow or extensional ow [2-6]. In this study, a relatively low aspect ratio (AR) hyperbolic microchannel was used in order to create an extensional ow combined with a shear ow, where AR= h w , h means the depth and w means the width of the microchannel. The objective of the study is to investigate the degree of RBC deformation throughout the microchannel at the centerline (y = 0). The blood samples were RBCs diluted with the Hank's Balanced Salt Solution (HBSS) with the hematocrit (Hct) level set to be 2%. A polydimethylsiloxane (PDMS) microchannel, having a hyperbolic contraction region followed by an abrupt expansion shape, was fabricated by a soft-lithography technique. The dimensions of the microchannel: width of the inlet (w), length of contraction region (l), width of the exit of contraction (wc) and depth (h) were 400 m, 580 m, 20 m and 14 m, respectively. Hence, the AR was 0:035. The experimental equipment consisted of an inverted microscope (Diaphot 300, Nikon), a high-speed camera (FASTCAM SA3, Photron) connected to a computer and a 1mL syringe (TERUMO R SYRING) controlled by a syringe pump (PHD ULTRA). The manufactured PDMS microchannel was placed on the stage of the microscope where the ow rate Q of the working uids was kept constant at 0:5 L=min. The owing RBCs were recorded by a high speed camera at a frame rate of 7500 frames/s and analyzed. The DI was obtained by DI= a b a + b where a refers to the major axis and b refers to the minor axis of the ellipse best tted to RBCs. High DI values in the contraction region were observed. It is possible to say that the RBCs highly elongate with both extensional and shear dominated ows achieved by a hyperbolic microchannel with a relatively low aspect ratio AR.
- Extensional flow-based microfluidic device: deformability assessment of red blood cells in contact with tumor cellsPublication . Faustino, Vera; Pinho, Diana; Yaginuma, Tomoko; Calhelha, Ricardo C.; Ferreira, Isabel C.F.R.; Lima, Rui A.Red blood cell (RBC) deformability has become one of the important factors to assess blood and cardiovascular diseases. The interest on blood studies have promoted a development of various microfluidic devices that treat and analyse blood cells. Recent years, besides the RBC deformability assessment, these devices are often applied to cancer cell detection and isolation from the whole blood. The devices for cancer cell isolation rely mainly on size and deformability of the cells. However, the examination of deformability of the RBCs mixed with cancer cells is lacking. This study aims at determining the deformation index (DI) of the RBCs in contact with cancer cells using a hyperbolic microchannel which generates a strong extensional flow. The DIs of human healthy RBCs and human RBCs in contact with a tumor cell line (HCT-15, colon carcinoma) were compared by analyzing the flowing RBCs images captured by a high speed camera. The results reveal that the RBCs that were in contact with HCT-15 cells have lower deformability than the normal RBCs.
- Flow of red blood cells in microchannel networks: in vitro studiesPublication . Cidre, Diana; Rodrigues, Raquel Oliveira; Faustino, Vera; Pinto, Elmano; Pinho, Diana; Bento, David; Fernandes, Carla S.; Dias, Ricardo P.; Lima, Rui A.Blood exhibits unique flow characteristics on micro-scale level, due to the complex biochemical structure of Red Blood Cells (RBCs) and their response to both shear and extensional flow, which influence the rheological properties and flow behavior of blood [1,2]. In the past years, several in vitro studies where made and have revealed some physiologically significant phenomena, such as Fahraeus and Fahraeus-Lindqvist effect, that played a key role in recent developments of lab-onchip devices for blood sampling, analysis and cell culturing. However, the blood flow in microvascular networks phenomena it remains incompletely understood. Thus, it is important to investigate in detail the behavior of RBCs flow occurring at a microchannel network, such as with divergent and convergent bifurcations. Previews in vitro studies in microchannels with a simple divergent and convergent bifurcation, have shown a pronounced cell depleted zone immediately downstream of the apex of the convergent bifurcation. In the present work, by using a highspeed video microscopy system, we investigated the cell depleted zone in a microchannel network. The working fluid used in this study was dextran 40 (Dx40) containing about 10% of haematocrit level (10 Hct) of ovine red blood cells. The high-speed video microscopy system used in our experiments consists of an inverted microscope (IX71, Olympus, Japan) combined with a highspeed camera (i-SPEED LT, Olympus). A syringe pump Apparatus (PHD ULTRATM) with 1 ml syringe (Terumo) was used to push the working fluids through the microchannel network. Additionally, we investigated the effect of the flow rate on the formation of the cell free layer.
- Flow of red blood cells in microchannel networks: in vitro studiesPublication . Cidre, Diana; Rodrigues, Raquel Oliveira; Faustino, Vera; Pinto, Elmano; Pinho, Diana; Bento, David; Correia, Teresa Montenegro; Fernandes, Carla S.; Dias, Ricardo P.; Lima, Rui A.Blood exhibits unique flow characteristics on micro-scale level, due to the complex biochemical structure of Red Blood Cells (RBCs) and their response to both shear and extensional flow, which influence the rheological properties and flow behavior of blood [1,2]. In the past years, several in vitro studies where made and have revealed some physiologically significant phenomena, such as Fahraeus and Fahraeus-Lindqvist effect, that played a key role in recent developments of lab-onchip devices for blood sampling, analysis and cell culturing. However, the blood flow in microvascular networks phenomena it remains incompletely understood. Thus, it is important to investigate in detail the behavior of RBCs flow occurring at a microchannel network, such as with divergent and convergent bifurcations. Previews in vitro studies in microchannels with a simple divergent and convergent bifurcation, have shown a pronounced cell depleted zone immediately downstream of the apex of the convergent bifurcation. In the present work, by using a highspeed video microscopy system, we investigated the cell depleted zone in a microchannel network. The working fluid used in this study was dextran 40 (Dx40) containing about 10% of haematocrit level (10 Hct) of ovine red blood cells. The high-speed video microscopy system used in our experiments consists of an inverted microscope (IX71, Olympus, Japan) combined with a highspeed camera (i-SPEED LT, Olympus). A syringe pump Apparatus (PHD ULTRATM) with 1 ml syringe (Terumo) was used to push the working fluids through the microchannel network. Additionally, we investigated the effect of the flow rate on the formation of the cell free layer.
- «
- 1 (current)
- 2
- 3
- »