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Flow visualizations in a PDMS cerebral aneurysm biomodel
Publication . Souza, Andrews Victor Almeida; Souza, Maria Sabrina; Ferrera, Conrado; Puga, Hélder; Lima, Rui A.; Ribeiro, J.E.
Cerebral aneurysm is an abnormal dilatation of the blood vessel which
affects a high percentage of the worldwide population. One way to investigate
this pathology is using in vivo techniques, but these types of experiments have a
high cost and low reproducibility. Thus, to understand the local hemodynamics
of brain aneurysms, it is imperative to manufacture in vitro models that simulate
real brain aneurysms. These biomodels are suitable for experimental testing, as
well as for evaluating and validating computational models. In this work, was
manufactured a biomodel of a cerebral aneurysm made by polydimethylsiloxane
(PDMS), combining rapid prototyping technology with a PDMS gravity casting
process. Experimental flow visualizations were performed at different flow rates.
The flow visualizations results have shown that there is a transition from laminar
to turbulent flow for a flow rate near 6 ml/min. The proposed PDMS biomodels
have shown the ability to perform flow visualizations and have the potential to
help the development and validation of computational models.
Experimental and numerical analyses of the hemodynamics impact on real intracranial aneurysms: A particle tracking approach
Publication . Souza, Andrews; Lopes, Diogo; Souza, Sérgio; Ribeiro, J.E.; Ferrera, Conrado; Lima, Rui A.
This study investigates the impact of hemodynamics on real intracranial aneurysms (IAs) using experiments and
computational fluid dynamics (CFD) simulations. A particle tracking velocimetry (PTV) approach was used to
study the vortical structures inside a real aneurysm and validate numerical simulations performed at a steady
regime for different flow rates. Moreover, this and two additional patient-specific cases have been numerically
analyzed, focusing on flow patterns, wall shear stress (WSS), relative residence time (RRT), and oscillatory shear
index (OSI) for transient studies. For the transient simulations, vorticity profiles indicated significant rotation of
fluid particles in the neck and outlet arteries. TAWSS analysis revealed high WSS values in the bifurcation zone,
neck, and middle cerebral artery (MCA), with variations among the patients. OSI and RRT plots provided insights
into disturbed flow patterns, low or oscillatory WSS areas, and regions with prolonged residence time. This study
shows great potential for combining PTV and CFD to obtain detailed insights into flow structures in aneurysms,
which are crucial to developing effective treatments and interventions for IA management.
Recent developments on the thermal properties, stability and applications of nanofluids in machining, solar energy and biomedicine
Publication . Nobrega, Glauco Tapijara Vallicelli; Souza, Reinaldo Rodrigues de; Gonçalves, Inês M.; Moita, Ana S.; Ribeiro, J.E.; Lima, Rui A.
In this review work, the recent progress made in the use of nanofluids (NFs) applied in
three specific areas will be presented: machining, solar energy, and biomedical engineering. Within
this context, the discussions will be guided by emphasizing the thermal and stability properties of
these fluids. In machining, NFs play a prominent role in the processes of turning, milling, drilling,
and grinding, being responsible for their optimization as well as improving the useful life of the tools
and reducing costs. In the solar energy field, NFs have been used in the thermal management of the
panels, controlling and homogenizing the operating temperature of these systems. In the biomedical
area, the advantages of using NFs come from the treatment of cancer cells, the development of
vaccines before the improvement of diagnostic imaging, and many others. In all lines of research
mentioned in this study, the main parameters that have limited or encouraged the use of these fluids
are also identified and debated. Finally, the discussions presented in this review will inspire and
guide researchers in developing new techniques to improve the applications of NFs in several fields.
Low-cost multifunctional vacuum chamber for manufacturing PDMS based composites
Publication . Ariati, Ronaldo; Sales, Flaminio C.P.; Noronha, Verônica Teixeira; Lima, Rui A.; Ribeiro, J.E.
Polydimethylsiloxane (PDMS) is one of the best known elastomers and has been used in
several areas of activity, due to its excellent characteristics and properties, such as biocompatibility,
flexibility, optical transparency and chemical stability. Furthermore, PDMS modified with other
materials promotes the desired changes to broaden its range of applications in various fields of
science. However, the heating, mixing and degassing steps of the manufacturing process have
not received much attention in recent years when it comes to blending with solid materials. For
instance, PDMS has been extensively studied in combination with waxes, which are frequently in
a solid state at room temperature and as a result the interaction and manufacturing process are
extremely complex and can compromise the desired material. Thus, in this work it is proposed a
multifunctional vacuum chamber (MVC) with the aim to improve and accelerate the manufacturing
process of PDMS composites combined with additives, blends and different kinds of solid materials.
The MVC developed in this work allows to control the mixing speed parameters, temperature control
and internal pressure. In addition, it is a low cost equipment and can be used for other possible
modifications with different materials and processes with the ability to control those parameters. As
a result, samples fabricated by using the MVC can achieve a time improvement over 133% at the
heating and mixing step and approximately 200% at the last degassing step. Regarding the complete
manufacturing process, it is possible to achieve an improvement over 150%, when compared with
the conventional manufacturing process. When compared to maximum tensile strength, specimens
manufactured using the MVC have shown a 39% and 65% improvement in maximum strain. The
samples have also shown a 9% improvement in transparency at room temperature and 12% at
a temperature of about 75 C. It should be noted that the proposed MVC can be used for other
blends and manufacturing processes where it is desirable to control the temperature, agitation speed
and pressure.
Fluid flow and structural numerical analysis of a cerebral aneurysm model
Publication . Souza, Maria Sabrina; Souza, Andrews Victor Almeida; Carvalho, Violeta Meneses; Teixeira, Senhorinha F.C.F.; Fernandes, Carla S.; Lima, Rui A.; Ribeiro, J.E.
Intracranial aneurysms (IA) are dilations of the cerebral arteries and, in most cases, have no
symptoms. However, it is a very serious pathology, with a high mortality rate after rupture. Several
studies have been focused only on the hemodynamics of the flow within the IA. However, besides
the effect of the flow, the development and rupture of the IA are also associated with a combination
of other factors such as the wall mechanical behavior. Thus, the objective of this work was to
analyze, in addition to the flow behavior, the biomechanical behavior of the aneurysm wall. For
this, CFD simulations were performed for different Reynolds numbers (1, 100, 500 and 1000) and
for two different rheological models (Newtonian and Carreau). Subsequently, the pressure values of
the fluid simulations were exported to the structural simulations in order to qualitatively observe
the deformations, strains, normal stresses and shear stress generated in the channel wall. For the
structural simulations, a hyperelastic constitutive model (5-parameter Mooney–Rivlin) was used. The
results show that with the increase in the Reynolds number (Re), the recirculation phenomenon is
more pronounced, which is not seen for Re = 1. The higher the Re, the higher the strain, displacement,
normal and shear stresses values.
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Funding agency
Fundação para a Ciência e a Tecnologia
Funding programme
3599-PPCDT
Funding Award Number
EXPL/EME-EME/0732/2021