Browsing by Author "Vega, E.J."
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- Flexible PDMS microparticles to mimic RBCs in blood particulate analogue fluidsPublication . Pinho, Diana; Muñoz-Sánchez, Beatriz N.; Anes, Cláudia Filipa; Vega, E.J.; Lima, Rui A.Polydimethylsiloxane (PDMS) has a wide variety of commercial and industrial applications due to its mechanical and rheological properties in a range similar to the living tissues. In this study, we demonstrate that PDMS can be used to produce deformable microparticles to be integrated in the development of particulate blood analogue fluids. The difficulties associated with the use of in vitro blood make it necessary to perform in vitro experiments of blood flow with blood analogue fluids. However, an ideal analogue must match the rheology of blood at several points, and for that, blood analogue fluids should be a suspension of microparticles with similar properties (size, shape and flexibility) to blood cells, in particular to the red blood cells (RBCs). The microparticles used in this study were produced from a transparent PDMS with crosslinking ratios of 10:1, 8:2 and 6:4; from a black PDMS with a ratio of 1:1 and from a red-pigmented PDMS. Each PDMS microparticles sample was suspended in Dextran 40 to perform deformability assays and cell-free layer analysis in a hyperbolic-shaped microchannel and steady shear viscosity measurements in a rheometer. The proposed microparticles suspensions show a great potential to mimic the structural and rheological properties of RBC suspensions and consequently to develop blood analogue fluids with rheological properties similar to real blood.
- Flow focusing technique to produce PDMS microparticles for blood analogue fluidsPublication . Silva, S.F.; Vega, E.J.; Pinho, Diana; Garcia, Valdemar; Lima, Rui A.; Montanero, J.M.The study of the blood flow behaviour through microchannels is crucial to improve our understanding about blood flow phenomena happening in the human microcirculatory system. However, the difficulties associated with the use of in vitro blood, such as coagulation and sample storage, have promoted the increasing interest to develop fluids with rheological properties similar to real blood [1]. Polydimethysiloxane (PDMS), due its remarkable properties such as good optical transparency, biocompatibility and permeability to gases, is widely used to fabricate microfluidic devices for in vitro blood experiments [2]. Recently, this inert elastomer has been used to produce monodisperse PDMS microbeads through a microfluidic approach [3]. Jiang et. al. have proposed a flow-focusing technique where a PDMS precursor was dispersed into microdroplets within an aqueous continuous phase [3]. By using this method they were able to produce PDMS microbeads with an average dimension of 80 microns. However, to develop blood analogue fluids it is essential to have PDMS microparticles with dimensions more close to the blood cells, i. e., the microparticles should have dimensions smaller than 20 microns. Hence, in this study a novel flow focusing technique was used to produce PDMS microparticles with dimensions more close to real blood cells. This technique was recently proposed to produce jets, droplets, and emulsions with sizes ranging from tens of microns down to the submicrometer scale [4]. This procedure is also based on the flow focusing principle which the above mentioned method relies on. Nevertheless, our technique makes use of the breakage of a steady jet to form the microparticles, which can lead to much higher production rates. In our technique, liquid is injected at a constant flow rate through a hypodermic needle to form a film over the needle’s outer surface. This film flows toward the needle tip until a liquid ligament is steadily ejected. Both the film motion and the liquid ejection are driven by the viscous and pressure forces exerted by a coflowing fluid stream. The outcome is a capillary jet which breaks up into droplets.
- Generation of micro-sized PDMS particles by a flow focusing technique for biomicrofluidics applicationsPublication . Muñoz-Sánchez, Beatriz N.; Silva, Filipa Silva; Pinho, Diana; Vega, E.J.; Lima, Rui A.Polydimethylsiloxane (PDMS), due to its remarkable properties, is one of the most widely used polymers in many industrial and medical applications. In this work, a technique based on a flow focusing technique is used to produce PDMS spherical particles with sizes of a few microns. PDMS precursor is injected through a hypodermic needle to form a film/reservoir over the needle's outer surface. This film flows towards the needle tip until a liquid ligament is steadily ejected thanks to the action of a coflowing viscous liquid stream. The outcome is a capillary jet which breaks up into PDMS precursor droplets due to the growth of capillary waves producing a micrometer emulsion. The PDMS liquid droplets in the solution are thermally cured into solid microparticles. The size distribution of the particles is analyzed before and after curing, showing an acceptable degree of monodispersity. The PDMS liquid droplets suffer shrinkage while curing. These microparticles can be used in very varied technological fields, such as biomedicine, biotechnology, pharmacy, and industrial engineering.
- Shrinkage and colour in the production of micro-sized PDMS particles for microfluidic applicationsPublication . 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.