Browsing by Author "Souza, Andrews Victor Almeida"
Now showing 1 - 6 of 6
Results Per Page
Sort Options
- 3D manufacturing of intracranial aneurysm biomodels for flow visualizations: low cost fabrication processesPublication . Souza, Andrews Victor Almeida; Souza, Mauren S.; Pinho, Diana; Agujetas, Rafael; Ferrera, Conrado; Lima, Rui A.; Puga, Hélder Fernandes; Ribeiro, J.E.There is a continuous search for better and more complete in vitro models with mechanical properties closer to in vivo conditions. In this work a manufacturing process, based on a lost core casting technique, is herein reported to produce aneurysm biomodels to perform experimental hemodynamic studies. By us- ing real artery images combined with a lost core casting technique, three materials were tested: paraffin, beeswax and glycerin-based soap. All in vitro biomodels were compared according to their transparency and final structure. Additionally, comparisons between experimental and numerical flow studies were also performed. The results have shown that the biomodels produced with beeswax and glycerine-based soap were the most suitable in vitro models to perform direct flow visualizations of particulate blood analogue fluids. The biomodels proposed in this works, have the potential to provide further insights into the complex blood flow phenomena happening at different kinds of pathologies and answer to important hemodynamics questions that otherwise cannot be tackled with the existing in vitro models.
- Flow visualizations in a PDMS cerebral aneurysm biomodelPublication . Souza, Andrews Victor Almeida; Ferrera, Conrado; Puga, Hélder; Lima, Rui A.; Ribeiro, J.E.; Souza, Maria SabrinaCerebral 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.
- Fluid flow and structural numerical analysis of a cerebral aneurysm modelPublication . 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.
- Manual and automatic image analysis segmentation methods for blood flow studies in microchannelsPublication . Carvalho, Violeta Meneses; Gonçalves, Inês M.; Souza, Andrews Victor Almeida; Souza, Maria Sabrina; Bento, David; Ribeiro, J.E.; Lima, Rui A.; Pinho, DianaIn blood flow studies, image analysis plays an extremely important role to examine raw data obtained by high-speed video microscopy systems. This work shows different ways to process the images which contain various blood phenomena happening in microfluidic devices and in microcirculation. For this purpose, the current methods used for tracking red blood cells (RBCs) flowing through a glass capillary and techniques to measure the cell-free layer thickness in different kinds of microchannels will be presented. Most of the past blood flow experimental data have been collected and analysed by means of manual methods, that can be extremely reliable, but they are highly time-consuming, user-intensive, repetitive, and the results can be subjective to user-induced errors. For this reason, it is crucial to develop image analysis methods able to obtain the data automatically. Concerning automatic image analysis methods for individual RBCs tracking and to measure the well know microfluidic phenomena cell-free layer thickness, two developed methods are present and discuss in order to demonstrate their feasibility for accurate data acquisition in such studies Additionally, a comparison analysis between manual and automatic methods was performed.
- Polydimethylsiloxane composites characterization and its applications: a reviewPublication . Ariati, Ronaldo; Sales, Flaminio; Souza, Andrews Victor Almeida; Lima, Rui A.; Ribeiro, J.E.Polydimethylsiloxane (PDMS) is one of the most promising elastomers due its remarkable pro-prieties such as good thermal stability, biocompatibility corrosion resistance, flexibility, low cost, ease of use, chemically inertia, hyperplastic characteristics, and gas permeability. Thus, it can be used in areas like microfluidic systems, biomedical devices, electronic components, membranes for filtering and pervaporation, sensors and coatings. Although pure PDMS has low mechanical properties, such as low modulus of elasticity and strength, it can be improved by mixing the PDMS with other polymers and by adding particles or reinforcements. Fiber-reinforced PDMS has proved to be a good alternative to manufacture flexible displays, batteries, wearable devices, tac-tile sensors, and energy harvesting systems. PDMS and particulates are often used in the sepa-ration of liquids from wastewater by means of porosity followed by hydrophobicity. Waxes as beeswax and paraffin have proved to be materials capable of improving properties such as hy-drophobic, corrosion resistance, thermal and optical properties of PDMS. Finally, blended with polymers such as poly (vinyl chloride-co-vinyl acetate), PDMS became a highly efficient alterna-tive for separation membrane applications. However, to the best of our knowledge there are few works dedicated to the review and comparison of different PDMS composites. Hence, this review will be focused in PDMS composites, their respective applications, and properties. Generally, it will be discussed the combination of elastomer with fibers, particles, waxes, polymers, and others; aiming to be a review able to demonstrate the wide applications of this material and how tailored characteristics can be reached for custom applications.
- Properties and applications of PDMS for biomedical engineering: a reviewPublication . Miranda, Inês; Souza, Andrews Victor Almeida; Sousa, Paulo; Ribeiro, J.E.; Castanheira, Elisabete M.S.; Lima, Rui A.; Minas, GraçaPolydimethylsiloxane (PDMS) is an elastomer with excellent optical, electrical and mechanical properties, which makes it well-suitable for several applications such as microfluidic and pho-tonics in several areas. Due to its biocompatible feature, PDMS is widely used for biomedical purposes. This widespread led also to the massification of the soft-lithography technique, intro-duced for facilitating the rapid prototyping of micro and nanostructures using elastomeric ma-terials, most notably PDMS. This technique allowed advances on microfluidic, electronic and biomedical fields. In this review an overview of the PDMS properties and some of its commonly used treatments, aiming the suitability to those fields’ needs, are presented. Applications such as microchips in biomedical field, replication of cardiovascular flow and medical implants are also reviewed.