Browsing by Author "Gueiral, Nuno"
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- Acoustic Emission Studies in Hip Arthroplasty – Peak Stress Impact In Vitro Cemented ProsthesisPublication . Gueiral, Nuno; Nogueira, ElisabeteEngineering has a very important role in the development of non-destructive monitoring of orthopaedical systems allowing the evaluation of its integrity. Sir John Charnley revolutionized the field of joint arthroplasty in the 1960s with the development of the total hip replacement. He replaced the diseased hip joint with a steel femoral component and a plastic acetabular socket cup combination, both fixed into the bone using a self-curing acrylic cement, polymethylmethacrylate (PMMA) (Browne et al, 2005). That way, he has restored some of the most problematic joints in the human body. The placement of the metal implant in the channel open in the femoral bone without using cement or by mechanical attack, called a non cemented arthroplasty, came into use in an effort to solve the problem.
- Analyzing Total Hip Arthroplasty: Straight Stem vs Anatomical Stem with Different Materials and ActivitiesPublication . Queirós, Pedro; Gueiral, Nuno; González-Gómez, Carlos David; Gueiral, Nuno[Introduction] Total Hip Arthroplasty involves replacing damaged parts of the hip joint with a prosthetic comprised of an artificial acetabular cup and femoral head. These components, made of durable, low-friction materials, aim to restore mobility, and alleviate pain in patients with hip joint degeneration, such as osteoarthritis or fractures. Utilizing computational mathematical models, such as the finite element method (FEM), it is possible to predict the behavior of materials under simulated loads from common daily activities [1], thereby anticipating potential failures in the femoral stem or the material itself.
- Avaliação on-line em contexto de pandemia: Experiência pedagógica no ensino superiorPublication . Coelho, Maria Fátima; Guimarães, Pedro; Queirós, Ângela; Gueiral, Nuno; Iglesias, Teresa P.Pretende-se descrever a prática educativa usada na realização do exame online de Física Experimental, UC do 1.º ano de Engenharia Civil, com recurso às plataformas Moodle e Zoom. Os resultados obtidos na avaliação são comparados aos resultados obtidos em anos anteriores e permitem verificar taxas de aprovação idênticas o que contraria as evidências mostradas por alguns autores.
- Glucose diffusion in colorectal mucosa—a comparative study between normal and cancer tissuesPublication . Carvalho, Sónia; Gueiral, Nuno; Nogueira, Elisabete; Henrique, Rui; Oliveira, Luís; Tuchin, ValeryColorectal carcinoma is a major health concern worldwide and its high incidence and mortality require accurate screening methods. Following endoscopic examination, polyps must be removed for histopathological characterization. Aiming to contribute to the improvement of current endoscopy methods of colorectal carcinoma screening or even for future development of laser treatment procedures, we studied the diffusion properties of glucose and water in colorectal healthy and pathological mucosa. These parameters characterize the tissue dehydration and the refractive index matching mechanisms of optical clearing (OC). We used ex vivo tissues to measure the collimated transmittance spectra and thickness during treatments with OC solutions containing glucose in different concentrations. These time dependencies allowed for estimating the diffusion time and diffusion coefficient values of glucose and water in both types of tissues. The measured diffusion times for glucose in healthy and pathological mucosa samples were 299.2+/-4.7 s and 320.6+/-10.6 s for 40% and 35% glucose concentrations, respectively. Such a difference indicates a slower glucose diffusion in cancer tissues, which originate from their ability to trap far more glucose than healthy tissues. We have also found a higher free water content in cancerous tissue that is estimated as 64.4% instead of 59.4% for healthy mucosa.
- O impacto da pandemia COVID-19 na aprendizagem de estudantes de Engenharia: Taxa de aprovação em 6 anos consecutivos: Pré e pós pandemiaPublication . Gueiral, Nuno; Nogueira, Elisabete; Coelho, FátimaEste artigo analisa o impacto da pandemia COVID-19 nos estudantes que terminaram o ensino secundário (onde a frequência foi maioritariamente online) e ingressaram em cursos de engenharia presencial no ensino superior. Os resultados deste estudo poderão ser úteis para entender como a pandemia afetou o desempenho académico dos estudantes de engenharia e identificar estratégias para melhorar o ensino em ambientes STEM (Science, Technology, Engineering and Mathematics) nos pós pandemia.
- Total Hip Arthroplasty modelling and load simulation in COMSOL multiphysicsPublication . Gueiral, Nuno; Nogueira, ElisabeteIn total hip arthroplasty (THA), has been over time, an exponential growth of studies with Finite Element Method (FEM) computational simulation in order to obtain the prosthesis with a longer life duration, however just a few in COMSOL Multiphysics software. The main goal of this study was to perform stress and strain studies under different load conditions for the titanium and cobalt-chromium alloys in cementless prostheses. In software COMSOL Multiphysics, 3D models of a femur and a Lubinus SPII implant with two different alloys, were tested. Two COMSOL studies were carried out, one stationary and the other dynamic (time-dependent) for both material’s prostheses. In a stationary study for walking activity, the titanium alloy implant showed an equivalent von Mises stress maximum level of 0.9 × 108 Pa at the contact between the implant and the bone, having been found a similar value by other investigators ( Prasad, Karthika, et al. “Metallic biomaterials: current challenges and opportunities.“ Materials 10.8 (2017): 884.). In the Co-Cr alloy prosthesis, the equivalent von Mises stress for walking activity was like titanium alloy. The shear stress and normal stress of the two prostheses were compared. In the dynamic study for climbing stair activity the equivalent von Mises stress was greater 7.5 times than in walking activity for Co-Cr alloy implant. The maximum stress (stationary and dynamic) of the titanium alloy implant is slightly higher than the Co-Cr alloy implant, which indicates that Co-Cr prostheses react better when subjected to loads.
- Wavelength dependence of the refractive index of human colorectal tissues: comparison between healthy mucosa and cancerPublication . Carvalho, Sónia; Henrique, Rui; Gueiral, Nuno; Nogueira, Elisabete; Oliveira, Luís; Tuchin, ValeryBiological tissues have individual optical properties that may be used as an identity card. The refractive index in particular, which can be measured directly, is very significant for the improvement or development of optical technologies in clinical practice. With the objective of verifying if healthy and pathological tissues can be discriminated from refractive index measurements, we have studied human colorectal mucosa. By using the total internal reflection method to measure the refractive index from healthy and pathological colorectal mucosa tissues at different wavelengths, it was possible to calculate the dispersion curves for both types of tissues. It was observed a decaying refractive index with wavelength, both for healthy and pathological tissues, which were fitted with curves described by Cornu’s equation for wavelengths between ultraviolet and near-infrared range. Experimental results show higher refractive index values for the pathological mucosa for all wavelengths. By performing measurements at wavelengths near 850 nm, we have detected non-monotonic behavior for the refractive index of both healthy and pathological tissues. Such abnormal wavelength dependence is evidence of lipids in both tissues. The acquired experimental data demonstrated that it is possible to discriminate between healthy and pathological tissues from refractive index measurements. Similar studies can be made for different biological tissues. By using lasers with different wavelengths it might be possible to identify other tissue components.