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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

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

A comparative study of image processing methods for the assessment of the red blood cells deformability in a microfluidic device

Publication . 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.

2018Conference 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