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Abstract(s)
O escoamento sanguíneo é um dos temas de grande interesse para a comunidade científica.
Assim, a busca de fluidos que sejam análogos ao sangue bem como o estudo do
seu escoamento em microcanais, tal como acontece com o sangue nos capilares, continua
a ser alvo de investigação.
Numa primeira fase deste trabalho, procedeu-se ao desenvolvimento de um modelo
inovador para produzir glóbulos vermelhos artificiais, constituído por Vesículas Unilamelares
Gigantes, vulgarmente designadas Giant Unilamellar Vesicles (GUVs), com três
concentrações diferentes. Pretende-se que estas vesículas tenham um comportamento reológico
idêntico ao escoamento dos glóbulos vermelhos (GVs) em microcanais, permitindo
assim proceder a vários estudos hemodinâmicos. No desenvolvimento destas vesículas,
foi verificado que as mais adequadas são constituídas por uma mistura natural de
lípidos e lecitina de soja. Foi realizado um estudo relativamente à sua concentração, onde
se verificou que, com o aumento da quantidade da lecitina de soja nas soluções, a concentração
de GUVs tende a aumentar. Foi também realizado um estudo relativo aos diâmetros
dos GUVs para verificar se estes se aproximavam em termos de tamanho dos GVs,
onde foi verificado que a maioria dos GUVs possuem diâmetros com dimensões entre os
5 e 7 μm, tal como os GVs. Foi ainda verificado que a solução com a menor concentração
de lecitina de soja possui uma maior quantidade de GUVs com diâmetros entre os 5 e 7
μm.
Na segunda fase, foi estudado experimentalmente o escoamento das três soluções de
GUVs em microcanais hiperbólicos, com três caudais diferentes, com o objetivo de visualizar
a Camada Livre de Células (CLC), determinar a deformação e estudar as velocidades
destes. Foi verificado que existe a formação de CLC em todas as concentrações e que
aumenta com o aumento do caudal. Relativamente à deformação, esta é bastante mais
evidente na contração do microcanal onde a taxa deformação é máxima. Para o caso da
velocidade, foi observado um aumento bastante significativo e linear da velocidade na
região da contração do microcanal hiperbólico e uma velocidade baixa e aproximadamente
constante a montante e jusante da contração.
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Por fim, foi também realizado o estudo reológico dos GUVs, de forma a investigar se
estes têm uma viscosidade próxima do sangue. Foi verificado que os GUVs apresentam
uma viscosidade inferior à do sangue total e que existe um ligeiro aumento da viscosidade
dos GUVs com o aumento da sua concentração. Por último, também foi efetuada uma
comparação da viscosidade da solução de GUVs com uma solução de 5% de Hematócrito
(Hct) em soro fisiológico, onde foi verificado que ambas as viscosidades são muito próximas.
The blood flow is one of the major topics for the scientific community. The finding of fluids which are similar to the human blood and the study of their flow in microchannels, as it happens in blood vessels, is still under research. Firstly, it was developed an innovative model to replace red blood cells (RBCs), made by Giant Unilamellar Vesicles (GUVs), with three different concentrations. It was expected that these vesicles had a behavior identical to the flow of RBCs, allowing the possibility to make more studies. During the development of these vesicles, it was observed that the better ones are the ones made of a blend of natural lipids and soy lecithin. In addition, a study to investigate the concentration of GUVs was made and we have observed that the concentration increases as the quantity of soy lecithin increase in the solution. Another study was made to compare the GUVs diameters with the size of the human RBCs. In this latter study it was shown that GUVs have diameters between 5 to 7μm, like the majority of the human RBCs and with a lower quantity of soy lecithin, the solution has a higher concentration of GUVs with the previous diameters. Secondly, it was conducted an experimental study of the flow of three GUVs solutions in microchannels, with three different volumes with the objective of observing the existence of the Cell Free Layer (CFL), the existence of deformation and to study the GUVs velocities. It has been observed the existence of CFL for all the tested concentrations. However, the CFL increases as the volume increases. Regarding the deformation, it is higher at the contraction region of the hyperbolic microchannel. As for the velocity, it has been observed a major linear increase at the hyperbolic contraction region and a nearly constant velocity at the upstream and downstream of the microchannel. Lastly, another study was made concerning the rheology behavior of the GUVs. It was shown that they have low viscosity and viscosity tends to increase as the concentration increases. Moreover, it was made a comparison between the GUVs solution viscosity and a saline solution with low Hematocrit (Hct). The results have shown that both viscosities were in close agreement.
The blood flow is one of the major topics for the scientific community. The finding of fluids which are similar to the human blood and the study of their flow in microchannels, as it happens in blood vessels, is still under research. Firstly, it was developed an innovative model to replace red blood cells (RBCs), made by Giant Unilamellar Vesicles (GUVs), with three different concentrations. It was expected that these vesicles had a behavior identical to the flow of RBCs, allowing the possibility to make more studies. During the development of these vesicles, it was observed that the better ones are the ones made of a blend of natural lipids and soy lecithin. In addition, a study to investigate the concentration of GUVs was made and we have observed that the concentration increases as the quantity of soy lecithin increase in the solution. Another study was made to compare the GUVs diameters with the size of the human RBCs. In this latter study it was shown that GUVs have diameters between 5 to 7μm, like the majority of the human RBCs and with a lower quantity of soy lecithin, the solution has a higher concentration of GUVs with the previous diameters. Secondly, it was conducted an experimental study of the flow of three GUVs solutions in microchannels, with three different volumes with the objective of observing the existence of the Cell Free Layer (CFL), the existence of deformation and to study the GUVs velocities. It has been observed the existence of CFL for all the tested concentrations. However, the CFL increases as the volume increases. Regarding the deformation, it is higher at the contraction region of the hyperbolic microchannel. As for the velocity, it has been observed a major linear increase at the hyperbolic contraction region and a nearly constant velocity at the upstream and downstream of the microchannel. Lastly, another study was made concerning the rheology behavior of the GUVs. It was shown that they have low viscosity and viscosity tends to increase as the concentration increases. Moreover, it was made a comparison between the GUVs solution viscosity and a saline solution with low Hematocrit (Hct). The results have shown that both viscosities were in close agreement.
Description
Keywords
Fluidos bifásicos Vesículas unilamelares gigantes Escoamento em microcanais Deformação de células Camada livre de células Microcirculação