A rapid and low-cost nonlithographic method to fabricate biomedical microdevices for blood flow analysis

Microfluidic devices are electrical/mechanical systems that offer the ability to work with minimal sample volumes, short reactions times, and have the possibility to perform massive parallel operations. An important application of microfluidics is blood rheology in microdevices, which has played a key role in recent developments of lab-on-chip devices for blood sampling and analysis. The most popular and traditional method to fabricate these types of devices is the polydimethylsiloxane (PDMS) soft lithography technique, which requires molds, usually produced by photolithography. Although the research results are extremely encouraging, the high costs and time involved in the production of molds by photolithography is currently slowing down the development cycle of these types of devices. Here we present a simple, rapid, and low-cost nonlithographic technique to create microfluidic systems for biomedical applications. The results demonstrate the ability of the proposed method to perform cell free layer (CFL) measurements and the formation of microbubbles in continuous blood flow.The authors acknowledge the financial support provided by PTDC/SAU-BEB/105650/2008, PTDC/SAU-ENB/116929/2010, EXPL/EMS-SIS/2215/2013 and scholarship SFRH/BD/89077/2012 and SFRH/BD/97658/2013 from FCT (Science and Technology Foundation), COMPETE, QREN and European Union (FEDER).info:eu-repo/semantics/publishedVersio

Low cost microfluidic device for partial cell separation: micromilling approach

Several studies have already demonstrated that it is possible to perform blood flow studies in microfluidic systems fabricated by using low-cost techniques. However, most of these techniques do not produce microchannels smaller than 100 microns and as a result they have several limitations related to blood cell separation. Recently, manufacturers have been able to produce milling tools smaller than 100 microns, which consequently have promoted the ability of micromilling machines to fabricate microfluidic devices able to perform separation of red blood cells (RBCs) from plasma. In this work, we show the ability of a micromilling machine to manufacture microchannels with dimensions down to 30 microns. Additionally, we show for the first time the ability of the proposed microfluidic device to enhance the cell-free layer close to the walls, leading to perform partial separation of RBCs from plasma.The authors acknowledge the financial support provided by PTDC/SAU-ENB/116929/2010 and EXPL/EMSSIS/2215/2013 from FCT (Science and Technology Foundation), COMPETE, QREN and European Union (FEDER). RR and DP acknowledge, respectively, the PhD scholarships SFRH/BD/97658/2013 and SFRH/BD/89077/2012 attributed by FCT.info:eu-repo/semantics/publishedVersio

Low cost microfluidic device for partial cell separation: micromilling approach

Several studies have already demonstrated that it is possible to perform blood flow studies in microfluidic systems fabricated by using low-cost techniques. However, most of these techniques do not produce microchannels smaller than 100 microns and as a result they have several limitations related to blood cell separation. Recently, manufacturers have been able to produce milling tools smaller than 100 microns, which consequently have promoted the ability of micromilling machines to fabricate microfluidic devices able to perform separation of red blood cells (RBCs) from plasma. In this work, we show the ability of a micromilling machine to manufacture microchannels with dimensions down to 30 microns. Additionally, we show for the first time the ability of the proposed microfluidic device to enhance the cell-free layer close to the walls, leading to perform partial separation of RBCs from plasma.The authors acknowledge the financial support provided by PTDC/SAU-ENB/116929/2010 and EXPL/EMSSIS/ 2215/2013 from FCT (Science and Technology Foundation), COMPETE, QREN and European Union (FEDER). RR and DP acknowledge, respectively, the PhD scholarships SFRH/BD/97658/2013 and SFRH/BD/89077/2012 attributed by FCT

Blood flow visualization and measurements in microfluidic devices fabricated by a micromilling technique

The most common and used technique to produce microfluidic devices for biomedical applications is the soft-lithography. However, this is a high cost and time-consuming technique. Recently, manufacturers were able to produce milling tools smaller than 100 m and consequently have promoted the ability of the micromilling machines to fabricate microfluidic devices capable of performing cell separation. In this work, we show the ability of a micromilling machine to manufacture microchannels down to 30 m and also the ability of a microfluidic device to perform partial separation of red blood cells from plasma. Flow visualization and measurements were performed by using a high-speed video microscopy system. Advantages and limitations of the micromilling fabrication process are also presented.The authors acknowledge the financial support provided by PTDC/SAU-ENB/116929/2010 and EXPL/EMS-SIS/ 2215/2013 from FCT (Science and Technology Foundation), COMPETE, QREN and European Union (FEDER). DP acknowledge the PhD scholarship SFRH/BD/89077/2012, and P.C. Sousa acknowledges the fellowship SFRH/BPD/75258/ 2010, all attributed by FCT.info:eu-repo/semantics/publishedVersio

Curvature Effects and Flow Uniformity Optimization of a Blood Microchannel

An important field of study in microfluidics is in the realm of blood rheology in microdevices. Many types of geometries have been developed for different lab-on-chip applications for sampling and analysis. The majority of experimental and numerical studies have revolved around straight blood vessel geometries, but in recent years there have been more complex profiles analyzed, such as microbifurcations. Some devices are developed to study blood flow similar to the microvascular network, such as diverging and converging bifurcations to study arterioles, which form a closed network. Cell adhesion studies of microchannels are also common, where symmetric bifurcation and confluence has been examined. Since sharp turns as well as bifurcation and confluence are common, the hemodynamics should be examined for many different shapes and the effects of channel geometry to the adhesion phenomena should be looked at. Different devices have different goals, such as isolating circulating tumor cells from blood, separating leukocytes from blood and isolating circulating tumor cells from peripheral blood. Studies have been targeted in breast cancer, cervical cancer and smooth muscle cell applications. Some studies provide result as to the role that the hemodynamic forces have on the recruitment of the metastatic cancer cells to endothelial cells, but the effects of device geometry on adhesion isn’t typically discussed formally. It has been shown that more complex geometries exhibit more non-uniform cell adhesion, adding to the confusion in the results and that an improvement in the velocity uniformity has been shown to improve the uniformity of the cell adhesion in sharp turn devices

Polymer microfluidic devices: an overview of fabrication methods

The 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

Cell-free layer analysis in a polydimethysiloxane microchannel: A global approach

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.The authors acknowledge the financial support provided by PTDC/SAU-ENB/116929/ 2010 and EXPL/EMS-SIS/2215/2013 from FCT (Science and Technology Foundation), COMPETE, QREN and European Union (FEDER). R.O. Rodrigues, D. Pinho and V. Faustino acknowledge respectively, the PhD scholarships SFRH/BD/97658/2013, SFRH/BD/89077/2012 and SFRH/BD/99696/2014 granted by FCT.info:eu-repo/semantics/publishedVersio

In vitro blood flow and cell-free layer in hyperbolic microchannels: visualizations and measurments

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.The authors acknowledge the financial support provided by PTDC/SAU-ENB/116929/2010 and EXPL/EMS-SIS/2215/2013 from FCT (Fundação para a Ciência e a Tecnologia), COMPETE, QREN and European Union (FEDER). R.O. Rodrigues, D. Pinho and P. C. Sousa acknowledge the scholarships SFRH/BD/97658/2013, SFRH/BD/89077/2012 and SFRH/BPD/75258/2010, respectively, all attributed by FCT

Microfluidic deformability study of an innovative blood analogue fluid based on giant unilamellar vesicles

Blood analogues have long been a topic of interest in biofluid mechanics due to the safety and ethical issues involved in the collection and handling of blood samples. Although the current blood analogue fluids can adequately mimic the rheological properties of blood from a macroscopic point of view, at the microscopic level blood analogues need further development and improvement. In this work, an innovative blood analogue containing giant unilamellar vesicles (GUVs) was developed to mimic the flow behavior of red blood cells (RBCs). A natural lipid mixture, soybean lecithin, was used for the GUVs preparation, and three different lipid concentrations were tested (1 × 10−3 M, 2 × 10−3 M and 4 × 10−3 M). GUV solutions were prepared by thin film hydration with a buffer, followed by extrusion. It was found that GUVs present diameters between 5 and 7 µm which are close to the size of human RBCs. Experimental flow studies of three different GUV solutions were performed in a hyperbolic-shaped microchannel in order to measure the GUVs deformability when subjected to a homogeneous extensional flow. The result of the deformation index (DI) of the GUVs was about 0.5, which is in good agreement with the human RBC’s DI. Hence, the GUVs developed in this study are a promising way to mimic the mechanical properties of the RBCs and to further develop particulate blood analogues with flow properties closer to those of real blood.COMPETE2020, NORTE2020, PORTUGAL2020, FEDER; FCT Project PTDC/QEQ-FTT/4287/2014 (POCI-01-0145-FEDER-016861); FCT Project PTDC/EMD-EMD/29394/2017 (NORTE-01-0145-FEDER-029394); FCT Project PTDC/EME-SIS/30171/2017 (NORTE-01-0145-FEDER-000032); FCT Project PTDC/QUI-QFI/28020/2017 (POCI-01-0145-FEDER-028020); SFRH/BD/99696/2014 PhD Grant;info:eu-repo/semantics/publishedVersio