Percorrer por autor "Souza, Andrews"
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- Applications and properties of PDMS: From biomicrofluidics to transparent face masksPublication . Lima, Rui A.; Maia, Renata; Souza, Andrews; Barbosa, Filipe; Carvalho, Denise; Carvalho, Violeta; Neves, Lucas B.; Faria, Carlos; Miranda, Inês; Sousa, Paulo; Zille, Andrea; Teixeira, Senhorinha; Minas, Graça; Machado, Lúcio; Ribeiro, J.E.Polydimethylsiloxane (PDMS) is a versatile silicone elastomer widely used in biomedical engineering due to its exceptional properties, including flexibility, chemical stability, optical transparency, biocompatibility, and ease of manufacturing. This chapter explores the unique characteristics of PDMS and its applications in biomicrofluidics and sustainable product development. PDMS is a hyperelastic material with excellent optical transparency, thermal stability, and gas permeability, making it ideal for various applications such as microfluidics, biomodels, blood analogues, implants, and organs-on-chip platforms. Its biocompatibility minimizes adverse tissue reactions, making it suitable for medical implants and skin treatments. However, its hydrophobic nature can limit certain applications, particularly in bioflow transport phenomena. To address this, surface modification techniques, such as oxygen plasma treatment, have been developed to enhance its wettability and expand its usability. In biomicrofluidics, PDMS is extensively used to create microfluidic devices that study blood cell deformability, aiding in the diagnosis of diseases like cancer, diabetes, and malaria. These devices, featuring contractions and bifurcations, provide valuable insights into microscale blood rheology and flow phenomena, improving our understanding of blood flow behavior and validating numerical simulations. The chapter also highlights the innovative use of PDMS in the production of sustainable transparent face masks. By incorporating recycled PDMS and textile fabrics, these masks feature a transparent window that allows visibility of the user’s lips, making them ideal for individuals who rely on lip-reading. The masks meet European Directive EN 14683:2019 standards, achieving level 2 certification for general public use. They offer excellent breathability, bacterial filtration efficiency, and optical transparency, while also promoting sustainability by reusing PDMS at the end of its life cycle. In conclusion, PDMS is a highly adaptable material with significant potential in biomedical applications and sustainable product development. Despite its hydrophobic nature, advancements in surface modification techniques continue to enhance its functionality, making it a valuable resource for innovative solutions in healthcare and beyond.
- Characterization of shear strain on PDMS: numerical and experimental approachesPublication . Souza, Andrews; Marques, Eduardo do Carmo; Balsa, Carlos; Ribeiro, J.E.Polydimethylsiloxane (PDMS) is one of the most popular elastomers and has been used in di erent fields, especially in biomechanics research. Among the many interesting features of this material, its hyperelastic behavior stands out, which allows the use of PDMS in various applications, like the ones that mimic soft tissues. However, the hyperelastic behavior is not linear and needs detailed analysis, especially the characterization of shear strain. In this work, two approaches, numerical and experimental, were proposed to characterize the e ect of shear strain on PDMS. The experimental method was implemented as a simple shear testing associated with 3D digital image correlation and was made using two specimens with two thicknesses of PDMS (2 and 4 mm). A finite element software was used to implement the numerical simulations, in which four di erent simulations using the Mooney–Rivlin, Yeoh, Gent, and polynomial hyperelastic constitutive models were performed. These approaches showed that the maximum value of shear strain occurred in the central region of the PDMS, and higher values emerged for the 2 mm PDMS thickness. Qualitatively, in the central area of the specimen, the numerical and experimental results have similar behaviors and the values of shear strain are close. For higher values of displacement and thicknesses, the numerical simulation results move further away from experimental values.
- Composite material of PDMS with interchangeable transmittance: study of optical, mechanical properties and wettabilityPublication . Sales, Flaminio; Souza, Andrews; Ariati, Ronaldo; Noronha, Verônica Teixeira; Giovanetti, Elder Gulick; Lima, Rui A.; Ribeiro, J.E.Polydimethylsiloxane (PDMS) is a polymer that has attracted the attention of researchers due to its unique properties such as transparency, biocompatibility, high flexibility, and physical and chemical stability. In addition, PDMS modification and combination with other materials can expand its range of applications. For instance, the ability to perform superhydrophobic coating allows for the manufacture of lenses. However, many of these processes are complex and expensive. One of the most promising modifications, which consists of the development of an interchangeable coating, capable of changing its optical characteristics according to some stimuli, has been underexplored. Thus, we report an experimental study of the mechanical and optical properties and wettability of pure PDMS and of two PDMS composites with the addition of 1% paraffin or beeswax using a gravity casting process. The composites’ tensile strength and hardness were lower when compared with pure PDMS. However, the contact angle was increased, reaching the highest values when using the paraffin additive. Additionally, these composites have shown interesting results for the spectrophotometry tests, i.e., the material changed its optical characteristics when heated, going from opaque at room temperature to transparent, with transmittance around 75%, at 70 °C. As a result, these materials have great potential for use in smart devices, such as sensors, due to its ability to change its transparency at high temperatures.
- Coolant flow in structured grinding wheels: CFD validation via high-speed imaging and particle trackingPublication . Costa, Sharlane; Souza, Andrews; Neves, Lucas B.; Ribeiro, J.E.; Pereira, Mário; Soares, DelfimEfficient coolant delivery is essential in grinding to control heat generation, minimize tool wear, and preserve workpiece integrity. However, Computational Fluid Dynamics (CFD) models commonly used for coolant system design remain rarely validated due to the extreme speeds and complex multiphase flows involved. This work addresses this gap by combining CFD simulations with targeted experiments to evaluate heat removal effectiveness in internally cooled grinding wheels with three channel inclinations: positive, straight, and negative. Transparent resin prototypes enabled high-speed imaging and particle tracking for flow field validation, while grinding tests measured temperature rise and mechanical loads. Results demonstrate that channel inclination strongly affects fluid acceleration, jet coherence, and penetration into the grinding zone, with the positive inclination producing the highest outlet velocities and reducing temperature rise by up to 67%. Particle tracking confirmed CFD predictions within 16% deviation, validating the model’s reliability. By establishing a direct correlation between coolant jet dynamics, heat dissipation, and process performance, this study demonstrates a methodology for the thermal optimization of internal cooling systems in rotating tools. The approach provides a pathway for improving energy efficiency, extending tool life, and reducing coolant consumption in industrial machining processes.
- Experimental and numerical analyses of the hemodynamics impact on real intracranial aneurysms: A particle tracking approachPublication . 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.
- Flow visualizations in polydimethylsiloxane cerebral aneurysm biomodelsPublication . Souza, Andrews; Nobrega, Glauco; Ferrera, Conrado; Puga, Helder; Lima, Rui A.; Ribeiro, J.E.This chapter focuses on the study of intracranial aneurysms (IAs), which are localized dilations of arteries within the skull caused by weakened blood vessel walls. IAs pose a significant risk of rupture, leading to strokes with high mortality and dependency rates. The chapter emphasizes the importance of understanding the hemodynamics and geometry of blood vessels to prevent aneurysm rupture. The authors present an innovative technique for manufacturing intracranial aneurysm biomodels using Polysmooth as a sacrificial material and polydimethylsiloxane (PDMS) for the final model. PDMS is chosen for its transparency, flexibility, and ease of manufacturing, which facilitates flow visualization tests. The biomodels are designed with different geometric configurations (60° and 180° angles between inlet and outlet channels) to analyze the effects of channel geometry on blood flow patterns. The experimental setup includes high-speed video equipment, an inverted microscope, and a syringe pump to simulate blood flow using a glycerol-water solution with suspended particles. The flow visualization tests reveal differences in recirculation areas within the aneurysm based on the channel geometry, highlighting the impact of arterial structure on hemodynamics. The study concludes that the presented manufacturing technique is effective for creating realistic biomodels, enabling detailed analysis of blood flow behavior in aneurysms. This research provides valuable insights for developing numerical models and strategies to prevent aneurysm rupture
- Hemodynamic study in a real intracranial aneurysm: an in vitro and in silico approachPublication . Souza, Andrews; Ribeiro, J.E.; Araújo, Fernando da Silva
- In vitro biomodels in stenotic arteries to perform blood analogues flow visualizations and measurements: a reviewPublication . Carvalho, Violeta Meneses; Maia, Inês; Souza, Andrews; Ribeiro, J.E.; Costa, Pedro; Puga, Hélder Fernandes; Teixeira, Senhorinha F.C.F.; Lima, Rui A.Cardiovascular diseases are one of the leading causes of death globally and the most common pathological process is atherosclerosis. Over the years, these cardiovascular complications have been extensively studied by applying in vivo, in vitro and numerical methods (in silico). In vivo studies represent more accurately the physiological conditions and provide the most realistic data. Nevertheless, these approaches are expensive, and it is complex to control several physiological variables. Hence, the continuous effort to find reliable alternative methods has been growing. In the last decades, numerical simulations have been widely used to assess the blood flow behavior in stenotic arteries and, consequently, providing insights into the cardiovascular disease condition, its progression and therapeutic optimization. However, it is necessary to ensure its accuracy and reliability by comparing the numerical simulations with clinical and experimental data. For this reason, with the progress of the in vitro flow measurement techniques and rapid prototyping, experimental investigation of hemodynamics has gained widespread attention. The present work reviews state-of-the-art in vitro macro-scale arterial stenotic biomodels for flow measurements, summarizing the different fabrication methods, blood analogues and highlighting advantages and limitations of the most used techniques.
- Manufacturing process of a brain aneurysm biomodel in PDMS using rapid prototypingPublication . Souza, Andrews; Ribeiro, J.E.; Lima, Rui A.Cerebral aneurysm is an abnormal dilatation of the blood vessel into a saccular form. They can originate in congenital defects, weakening of the arterial wall with increasing age, atherosclerotic changes, trauma and infectious emboli. The in vivo experiments are an effective way of investigating the appearance, validating new practices and techniques, but beyond ethical issues, these types of experiments are expensive and have low reproducibility. Thus, to better understand the pathophysiological and geometric aspects of an aneurysm, it is important to fabricate in vitro models capable of improving existing endovascular treatments, developing and validating theoretical and computational models. Another difficulty is in the preoperative period of the non-ruptured cerebral aneurysm, known for the success of the skilled acts because there is an anatomical structure of the aneurysm as its current position. Although there are technologies that facilitate three-dimensional video visualization in the case of aneurysms with complex geometries the operative planning is still complicated, so the development of the real three-dimensional physical model becomes advantageous. In this work, the entire process of manufacturing an aneurysm biomodel using polydimethylsiloxane (PDMS) is disassembled by rapid prototyping technology. The manufactured biomodels are able to perform different hemodynamic studies, validate theoretical data, numerical simulations and assist in the preoperative planning.
- Mechanical and optical properties assessment of an innovative PDMS/beeswax composite for a wide range of applicationsPublication . Ariati, Ronaldo; Souza, Andrews; Souza, Maria S.; Zille, Andrea; Soares, Delfim; Lima, Rui A.; Ribeiro, J.E.Polydimethylsiloxane (PDMS) is an elastomer that has received primary attention from researchers due to its excellent physical, chemical, and thermal properties, together with biocompatibility and high flexibility properties. Another material that has been receiving attention is beeswax because it is a natural raw material, extremely ductile, and biodegradable, with peculiar hydrophobic properties. These materials are applied in hydrophobic coatings, clear films for foods, and films with controllable transparency. However, there is no study with a wide range of mechanical, optical, and wettability tests, and with various proportions of beeswax reported to date. Thus, we report an experimental study of these properties of pure PDMS with the addition of beeswax and manufactured in a multifunctional vacuum chamber. In this study, we report in a tensile test a 37% increase in deformation of a sample containing 1% beeswax (BW1%) when compared to pure PDMS (BW0%). The Shore A hardness test revealed a 27% increase in the BW8% sample compared to BW0%. In the optical test, the samples were subjected to a temperature of 80 ◦C and the BW1% sample increased 30% in transmittance when compared to room temperature making it as transparent as BW0% in the visible region. The thermogravimetric analysis showed thermal stability of the BW8% composite up to a temperature of 200 ◦C. The dynamic mechanical analysis test revealed a 100% increase in the storage modulus of the BW8% composite. Finally, in the wettability test, the composite BW8% presented a contact angle with water of 145◦. As a result of this wide range of tests, it is possible to increase the hydrophobic properties of PDMS with beeswax and the composite has great potential for application in smart devices, food and medicines packaging films, and films with controllable transparency, water-repellent surfaces, and anti-corrosive coatings.